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质疑学术权威的英语作文

质疑学术权威的英语作文As an AI language model, I do not possess personal emotions or opinions. However, I can provide a response to the topic based on commonly expressed perspectives.There is a growing trend of skepticism towards academic authority and expertise in various fields. This phenomenon has been fueled by the rise of alternative sources of information, the spread of misinformation, and the increasing accessibility of knowledge through the internet. While it is healthy to question and critically evaluate established knowledge, the outright dismissal of academic authority can have detrimental effects on the pursuit of truth and the advancement of human knowledge.One of the main reasons for questioning academic authority is the perception of bias and conflicts of interest within the academic community. Critics argue that academic research and knowledge production are often influenced by funding sources, institutional affiliations,and personal agendas. This perceived lack of objectivity has led to doubts about the credibility and reliability of academic findings. In some cases, high-profile scandals involving academic misconduct have further eroded public trust in the integrity of the academic establishment.Moreover, the exclusivity and elitism associated with academic institutions have contributed to the skepticism towards academic authority. The traditional hierarchical structure of academia, with its emphasis on credentials, tenure, and peer review, has been criticized for creating barriers to entry and perpetuating a culture ofintellectual elitism. This has led to the perception that academic experts are out of touch with the concerns and perspectives of the general public, leading to a disconnect between academic knowledge and real-world issues.In addition, the democratization of information through the internet has empowered individuals to challenge established academic narratives. With the proliferation of online platforms and social media, anyone can present themselves as an authority on a given topic, regardless oftheir qualifications or expertise. This has led to the spread of misinformation and the blurring of lines between credible academic research and unverified claims, further eroding public trust in academic authority.However, it is important to recognize the value of academic expertise and authority in advancing human knowledge and understanding. Academic institutions serve as the foundation for rigorous research, critical inquiry, and the peer review process, which are essential for ensuring the quality and reliability of knowledge production. While it is crucial to question and scrutinize academic findings, it is equally important to acknowledge the expertise and dedication of scholars who have devoted their careers to the pursuit of knowledge.Furthermore, the peer review process, which is a cornerstone of academic research, serves as a mechanism for quality control and validation of scholarly work. While it is not without its flaws, peer review helps to ensure that academic research meets rigorous standards of evidence and methodology, contributing to the overall credibility ofacademic authority.In conclusion, while it is natural to question and challenge established authority, it is important to recognize the value of academic expertise in advancing human knowledge and understanding. The skepticism towards academic authority should not lead to the wholesale rejection of scholarly research and expertise, but rather to a critical evaluation of knowledge claims and a commitment to upholding the integrity of academic inquiry. By fostering a culture of open dialogue, transparency, and accountability, we can work towards restoring public trust in academic authority and promoting the pursuit of truth and knowledge.。

非牛顿流体电学：综述外文文献翻译、外文翻译、中英文翻译

附录A 外文翻译译文：非牛顿流体电学：综述3.在非牛顿流体电泳在第二节讨论了关于电渗流带电表面，如果我们通过想象改变参考系统，带电表面的流体应该是静止的，然后将带电面以速度大小相等但与以前面讨论的亥姆霍兹Smoluchowski的速度方向相反移动。

这种情况下有效地代表了电泳具有很薄的EDL的粒子在一个无限大的非运动牛顿流体范围[17,18,26,34] 。

显然，先前讨论电渗的亥姆霍兹Smoluchowski速度当然也可适用于分析在无限大非牛顿流体域具有薄EDL颗粒的电泳速度，仅仅与它的符号相反，并改变了充电通道壁与带电粒子的潜力。

事实上，支付给非牛顿液体粒子电泳最早的关注可以追溯到30年前Somlyody [ 68 ]提起的一项有关采用非牛顿液体以提供优越的阈值特性的电泳显示器的专利。

在1985年， Vidybida和Serikov [ 69 ]提出关于球形颗粒的非牛顿电泳研究第一个理论解决方案。

他们展示了一个粒子在非牛顿净电泳运动流体可通过以交替的电场来诱导一个有趣的且违反直觉的效果。

最近才被Hsu课题组填补这方面20年的研究空白。

在2003年，Lee[70]等人通过一个球形腔的低zeta电位假设封闭andweak施加电场分析了电泳刚性球形颗粒在非牛顿的Carreau流体的运动。

他们特别重视电泳球形粒子位于中心的空腔特征。

之后，该分析被扩展来研究电泳位于内侧的球面的任意位置的球形颗粒的腔体[71] 。

除了单个粒子电泳外， Hsu[72]等人假设粒子分散潜力在卡罗流体zeta进行了集中的电泳调查分析，并分析了由Lee[73]完成的其它任意潜力。

为了研究在边界上非牛顿流体电泳的影响，Lee[74]等人分析了电泳球状粒子在卡罗体液从带电荷到不带电荷的平面表面，发现平面表面的存在增强了剪切变稀效果，对电泳迁移率产生影响。

类似的分析后来由Hsu等 [75]进行了扩展。

为了更紧密地模拟真实的应用环境，Hsu等人[76]分析了球形粒子的电泳由一个圆柱形的微细界卡罗流体低zeta电位到弱外加电场的条件。

PhysRevB.81.153104

Optical evidence of strong coupling between valence-band holes and d-localized spinsin Zn1−x Mn x OV.I.Sokolov,1A.V.Druzhinin,1N.B.Gruzdev,1A.Dejneka,2O.Churpita,2Z.Hubicka,2L.Jastrabik,2and V.Trepakov2,3 1Institute of Metal Physics,UD RAS,S.Kovalevskaya Str.18,620041Yekaterinburg,Russia2Institute of Physics,AS CR,v.v.i.,Na Slovance2,18221Praha8,Czech Republic3Ioffe Institute,RAS,194021St-Petersburg,Russia͑Received3December2009;revised manuscript received2March2010;published30April2010͒We report on optical-absorption study of Zn1−x Mn x O͑x=0–0.06͒ﬁlms on fused silica substrates takingspecial attention to the spectral range of the fundamental absorption edge͑3.1–4eV͒.Well-pronounced exci-tonic lines observed in the region3.40–3.45eV were found to shift to higher energies with increasing Mnconcentration.The optical band-gap energy increases with x too,reliably evidencing strong coupling betweenoxygen holes and localized spins of manganese ions.In the3.1–3.3eV region the optical-absorption curve inthe manganese-containedﬁlms was found to shift to lower energies with respect to that for undoped ZnO.Theadditional absorption observed in this range is interpreted as a result of splitting of a localized Zhang-Rice-typestate into the band gap.DOI:10.1103/PhysRevB.81.153104PACS number͑s͒:78.20.ϪeI.INTRODUCTIONDilute magnetic semiconductor Zn1−x Mn x O is one of themost promising materials for the development of optoelec-tronic and spin electronic devices with ferromagnetism re-tained at practical temperatures͑i.e.,Ͼ300K͒.However,researchers are confronted with many complex problems.Ferromagnetic ordering does not always appear and the na-ture of its instability is a subject of controversy.In addition,optical properties of Zn1−x Mn x O appreciably differ fromthose in Zn1−x Mn x Se and Zn1−x Mn x S related compounds,where the intracenter optical transitions of Mn2+ions areconventionally observed in the optical-absorption and photo-luminescence spectra.1,2In contrast,a very intense absorp-tion in the2.2–3.0eV region was reported in Zn1−x Mn x Owithout any manifestations of intracenter transitions,3–5and photoluminescence due to4T1→6A1optical transition of Mn2+is absent as well.Interpretation of this absorption bandas a charge transfer3,5is complicated by the fact that Mn2+forms neither d5/d4donor nor d5/d6acceptor levels in the forbidden gap of ZnO.6,7To resolve this contradiction,Dietl8put forward the con-cept that the oxides and nitrides belong to the little studiedfamily of dilute magnetic semiconductors with strong corre-lations.Characteristic features of such compounds are an in-crease in the band gap with the concentration of magneticions and emergence of a Zhang-Rice͑Z-R͒-type state in theforbidden gap9arising as a result of strong exchange cou-pling of3d-localized spin of the impurity centers andvalence-band holes.According to Ref.8,fulﬁllment ofstrong hybridization condition depends on the ratio of theimpurity-center potential U to a critical value U c;a coupledhybrid state can be formed when U/U cϾ1.Existence of such electronic state has been veriﬁed by ab initio theoretical treatment of electron correlations using the local spin-density approximation͑LSDA+U model͒and calculation of the ex-change coupling values.10In Zn1−x Mn x O the hole can origi-nate by electron transfer from the Mn2+adjacent oxygen to the conduction band.The resulting hole localizes as the Z-R state leading to appearance of additional broad,intense ab-sorption band.In this way the study of optical-absorptionspectra can be used as a probe to identify the Z-R states.It is known that the optical band-edge absorption spec-trum of Mn-doped ZnO is characterized by the onset of astrong rise of the absorption coefﬁcient in theϳ3.1eV spec-tral region.11In Refs.11and12,this absorption inZn1−x Mn x Oﬁlms was treated as a product of direct interbandoptical transitions using conventional formula␣2ϳ͑ប␻−E g͒.The resulting magnitudes of band gap for composition with x=0.05have been estimated as E g=3.10eV͑Ref.11͒and3.25eV,12which is appreciably less than E g=3.37eV inZnO.13Such“redshift”of the band gap was considered inRef.12as a result of p-d exchange interaction,in analogy tothe shift of the excitonic lines in reﬂectivity and lumines-cence spectra observed in Ref.14for Zn1−x Mn x Se.At thesame time theory predicts an increase in E g͑x͒with x for Zn1−x Mn x O.8Also excitonic absorption spectrum in Zn1−x Mn x O nanopowders,15appeared to be located at ener-gies higher than that in ZnO nanopowders,that does not conﬁrm the shift of E g to lower energies for Zn1−x Mn x O ﬁlms.In this work we report on the optical-absorption spectrastudies in thin Zn1−x Mn x Oﬁlms deposited on fused silicaing suchﬁlms we succeed to detect the absorp-tion spectra of excitons and to determine reliably the widthof the optical gap E g.This allowed us to elucidate the natureof the additional absorption band appearing atប␻ϽE g near the fundamental absorption edge as a result of splitting of one more Z-R-type state due to strong hybridization and ex-change coupling of3d-localized spin of the manganese and valence-band oxygen hole.II.EXPERIMENTALThin Zn1−x Mn x Oﬁlms with x=0–0.06,120–130,and 200–250nm of thicknesses were deposited on fused silica substrates by the atmospheric barrier-torch discharge tech-nique,as it was described in Refs.16and17.The substratePHYSICAL REVIEW B81,153104͑2010͒temperature during deposition was kept at ϳ200°C.Mn content was controlled by measurements of Mn and Zn emis-sion ͑␭em =4031Åand 4810Å,respectively ͒of plasma during deposition and crosschecked by the postgown EPMA ͑JEOL JXA-733device with Kevex Delta Class V mi-croanalyser ͒analysis with accuracy Ϯ0.3%.X-ray diffrac-tion ͑XRD ͒studies were performed with a Panalytical X’PertMRD Pro diffractometer with Eulerian cradle using Cu K ␣radiation ͑␭em =1.5405Å͒in the parallel beam ge-ometry.XRD proﬁles were ﬁtted with the Pearson VII func-tion by the DIFPATAN code.18Correction for instrumental broadening was performed using NIST LaB6standard and V oigt function method.19Optical absorption within the 1.2–6.5eV spectral region was measured in unpolarized light at room temperature using a Shimadzu UV-2401PC spectrophotometer.The bare silica substrate and Zn 1−x Mn x O ﬁlm on silica substrate were mounted into the reference and test channel,respectively.The optical density ␣d ͑product of optical-absorption coefﬁ-cient and ﬁlm thickness ͒was calculated without taking into account multiple reﬂections as ␣d =ln ͑I 0/I ͒,where I 0and I are intensities of light passed through bare substrate and ﬁlm/substrate structure.III.RESULTS AND DISCUSSIONFigure 1presents XRD pattern for ZnO and Zn 0.95Mn 0.05O ﬁlms,as an example.All obtained ﬁlms re-vealed crystalline block structure with dominant ͑002͒orien-tation of blocks’optical C -axes aligned normal to substrate.Observed reﬂexes correspond to wurtzite structure evi-dencing absence of extraneous phases.Both pure and Mn-doped ZnO ﬁlms appeared to be compressively strained with 0.2%of strain,s =͑a 0−a S ͒/a 0,where a 0and a S are the lattice parameters of nonstrained and strained ﬁlms.The analysis reveals that the value of compressive strain is controlled pre-dominantly by stresses,but not by presence of Mn ͑at least for Mn concentrations used ͒.Figure 2presents the optical-absorption spectra for Zn 1−x Mn x O ﬁlms.A wide absorption line is seen in the re-gion of the band edge ͑Fig.2͒,whose energy appears to be shifted by about 100meV to higher energies in comparison with the excitonic line in ZnO ͓ϳ3.31eV at T =300K ͑Ref.13͔͒.The line shift is very likely connected with the com-pressive strain of Zn 1−x Mn x O ﬁlms mentioned above.The wide and shifted line has been observed earlier in ZnO ﬁlm on sapphire substrate 20,21and was identiﬁed as a shift of the excitonic line due to compressive strain of Zn 1−x Mn x O ﬁlms.21The inset represents spectra of this line obtained in ZnO at T =300K and 77.3K.It is seen that the excitonic line is narrowed,split into two components and shifted to higher energies on lowering the temperature,clearly evidenc-ing its excitonic nature.The ﬁrst line is a sum of A and B excitons,the second one is the C exciton appearing due to disorientation of blocks forming the ﬁlm.16Analogous tem-perature evolutions have been reported for a wide excitonic line in ZnO nanocrystals.15As the concentration of Mn impurity increases,the exci-tonic line additionally broadens and shifts to higher energies.Figure 3shows the actual Mn concentration shift of the ex-citonic line energy ប␻exc .It is seen that the increase in Mn concentration leads to not only changes in the excitonic spec-trum but also exhibits enhancement of the band-gap energy in Zn 1−x Mn x O ﬁlms ͑band-gap magnitude can be estimated as E g =ប␻exc +E exc ,where E exc =60meV is the excitonic binding energy 13͒.It is known that the band-gap magnitude in ZnO-MnO system varies from 3.37eV in ZnO up to 3.8eV in MnO.22According to the theoretical analysis 8per-formed taking into account inversion of ⌫7and ⌫9valence subbands in ZnO,23,24strong coupling of manganese spin and p states of valence band leads to appearance of a positiveI n t e n s i t y (c o u n t )2θ(degree)FIG.1.XRD pattern of ZnO ͑left scale ͒and Zn 0.95Mn 0.05O ͑right scale ͒ﬁlms.E n e r g y (eV)αdFIG.2.Exciton absorption spectra of compressed Zn 1−x Mn x O ﬁlms:1—x =0%,2—x =1.8%,and 3—x =5%;ﬁlm thickness:d =͑120–130͒nm;and T =300K.Inset shows excitonic absorption lines for compressed ZnO:1—T =300K and 4—T =77.3K.01234563.403.413.423.433.44E n e r g y (e V )X (%)FIG.3.Mn-concentration dependence of the excitonic line en-ergies for Zn 1−x Mn x O ﬁlms.additive in optical absorption of Zn 1−x Mn x O at small x val-ues.The sum of two contributions at sufﬁciently small x results in an increase in E g magnitude.The rise of the band-gap magnitude with the admixture of the second component E g ͑x ͒has been observed in Zn 1−x Co x O ͑Ref.25͒for exci-tonic lines registered in the reﬂection spectra at 1.6K.The shift of the excitonic line to higher energies was observed in Zn 0.99Fe 0.01O,too.20In the case of weak d -p coupling the additive into the band gap change appeared to be negative.8In this case the band-gap value E g decreases with x for x Յ0.1,as it was found for Zn 1−x Mn x Se ͑Fig.6in Ref.14͒and for Cd 1−x Mn x S.26Therefore,the observed rise of the E g ͑x ͒value with Mn addition provides the reliable experimental proof that the strong hybridization condition U /U c Ͼ1in Zn 1−x Mn x O is fulﬁlled.Figure 4presents optical absorption in Zn 1−x Mn x O ﬁlms recorded in the spectral region 3.1–3.3eV .It is seen that the onset of optical absorption in Zn 1−x Mn x O ﬁlms emerges at lower energies than that for ZnO ones.Analogous shift had been observed earlier in the spectrum of the photoluminescence excitation over deep im-purity centers in Zn 1−x Mn x O for Ref.15.Unlike authors of Refs.11and 12,we assume that addi-tional absorption of Zn 1−x Mn x O ͑in comparison with ZnO ͒in the 3.1–3.3eV range is a result of pushing the Z-R-type states out of valence band to the forbidden gap.9The essence of this state consists of localization of the valence-band hole within the ﬁrst coordination sphere on the oxygen ions as a result of strong exchange interaction of manganese and hole spins.Such electronic state is similar to the Z-R-type state originally considered for La 2CuO 4oxidesuperconductor.9This state is a singlet one,because in La 2CuO 4the spins of d 9conﬁguration of Cu 2+ion and oxy-gen holes are equal but of opposite direction.The situation is more complex in the case of Zn 1−x Mn x O since the top of valence band is formed by three close subbands:⌫7,⌫9,and ⌫7.23,24In such case we have serious reasons to assume that not only the presence of one deep Z-R-type state is respon-sible for optical absorption in the 2.2–3.0eV spectral region.We assume the presence of another,relatively shallow Z-R-type state too,which has been split off into the gap providing additional absorption in the 3.1–3.3eV region of Zn 1−x Mn x O.Tentatively,using results 11,12,15we estimate the splitting of the second Z-R level from the valence band as 0.12–0.27eV .More reliable determination of the split energy can be performed using more sensitive methods of absorp-tion spectra, e.g.,modulation methods,which are in progress.IV .CONCLUSIONThin Zn 1−x Mn x O ﬁlms ͑x =0–0.06͒have been sintered and their optical-absorption spectra were investigated.The well-pronounced excitonic absorption lines in the fundamen-tal absorption spectral regions were observed.Position of excitonic absorption lines in Zn 1−x Mn x O ﬁlms shifts to higher energies with increasing Mn content.This evidences an increase in the E g magnitude with x for small values x and reliably corroborates fulﬁllment of the strong coupling crite-rion ͑U /U c Ͼ1͒in Zn 1−x Mn x O.The last effect leads to emer-gence of an intense optical-absorption band in the 2.2–3.0eV region due to the presence of the band-gap Z-R-type state.The additional absorption observed in the range of 3.1–3.3eV is interpreted as a result of splitting of one more Z-R-type states into the band gap.ACKNOWLEDGMENTSAuthors thank T.Dietl,V .I.Anisimov,and A.V .Lukoy-anov for useful discussions and V .Valvoda for kind assis-tance in XRD experiments.This work was supported by Czech Grants No.A V0Z10100522of A V CR,No.KJB100100703of GA A V ,No.202/09/J017of GA CR,No.KAN301370701of A V CR,and No.1M06002of MSMT CR and Russian Grants No.08-02-99080r-oﬁof RFBR,PP RAS “Quantum Physics of Condensed Matter”,and State Contract No.5162.nger and H.J.Richter,Phys.Rev.146,554͑1966͒.2T.Hoshina and H.Kawai,Jpn.J.Appl.Phys.19,267͑1980͒.3F.W.Kleinlein and R.Helbig,Z.Phys.266,201͑1974͒.4R.Beaulac,P.I.Archer,and D.R.Gamelin,J.Solid State Chem.181,1582͑2008͒.5T.Fukumura,Z.Jin,A.Ohtomo,H.Koinuma,and M.Kawasaki,Appl.Phys.Lett.75,3366͑1999͒.6K.A.Kikoin and V .N.Fleurov,Transition Metal Impurities in Semiconductors:Electronic Structure and Physical Properties ͑World Scientiﬁc,Singapore,1994͒,p.349.7T.Dietl,J.Magn.Magn.Mater.272-276,1969͑2004͒.8T.Dietl,Phys.Rev.B 77,085208͑2008͒.9F.C.Zhang and T.M.Rice,Phys.Rev.B 37,3759͑1988͒.10T.Chanier,F.Virot,and R.Hayn,Phys.Rev.B 79,205204͑2009͒.11V .Shinde,T.Gujar,C.Lokhande,R.Mane,and S.-H.Han,3.1253.2500.00.40.8αdEnergy (eV)12FIG.4.Spectral dependence of the optical density ␣d in the 3.1–3.3eV spectral region for Zn 1−x Mn x O,1—ZnO;2—x =0.3–0.5%;ﬁlm thickness 200–250nm;and T =300K.Mater.Chem.Phys.96,326͑2006͒.12Y.Guo,X.Cao,n,C.Zhao,X.Hue,and Y.Song,J.Phys. Chem.C112,8832͑2008͒.13Zh.L.Wang,J.Phys.:Condens.Matter16,R829͑2004͒.14R.B.Bylsma,W.M.Becker,J.Kossut,U.Debska,and D. Yoder-Short,Phys.Rev.B33,8207͑1986͒.15V.I.Sokolov,A.Ye.Yermakov,M.A.Uimin,A.A.Mysik,V.A.Pustovarov,M.V.Chukichev,and N.B.Gruzdev,J.Lumin.129,1771͑2009͒.16M.Chichina,Z.Hubichka,O.Churpita,and M.Tichy,Plasma Processes Polym.2,501͑2005͒.17Z.Hubicka,M.Cada,M.Sicha,A.Churpita,P.Pokorny,L. Soukup,and L.Jastrabík,Plasma Sources Sci.Technol.11,195͑2002͒.18http://www.xray.cz/priv/kuzel/dofplatan/19R.Kuzel,Jr.,R.Cerny,V.Valvoda,and M.Blomberg,ThinSolid Films247,64͑1994͒.20Z.Jin,T.Fukumura,M.Kaasaki,K.Ando,H.Saito,T.Skiguchi, Y.Z.Yoo,M.Murakami,Y.Matsumoto,T.Hasegawa,and H. Koinuma,Appl.Phys.Lett.78,3824͑2001͒.21J.-M.Chauveau,J.Vives,J.Zuniga-Perez,ügt,M.Teis-seire,C.Deparis,C.Morhain,and B.Vinter,Appl.Phys.Lett.93,231911͑2008͒.d and V.E.Henrich,Phys.Rev.B38,10860͑1988͒. 23K.Shindo,A.Morita,and H.Kamimura,J.Phys.Soc.Jpn.20, 2054͑1965͒.24W.Y.Liang and A.D.Yoffe,Phys.Rev.Lett.20,59͑1968͒. 25W.Pacuski,D.Ferrand,J.Gibert,C.Deparis,J.A.Gaj,P.Ko-ssacki,and C.Morhain,Phys.Rev.B73,035214͑2006͒.26M.Ikeda,K.Itoh,and H.Sato,J.Phys.Soc.Jpn.25,455͑1968͒.。

学术现象英语作文范文

学术现象英语作文范文Title: Academic Phenomena in Modern Education。

In the realm of academia, various phenomena emerge, shaping the landscape of modern education. From the rise of online learning to the prevalence of academic dishonesty, these phenomena reflect the evolving nature of scholarly pursuits. In this essay, we delve into some prominent academic phenomena and their implications.One significant phenomenon is the increasing popularity of online learning platforms. With advancements in technology, learners now have access to a plethora of online courses and resources. This trend has democratized education, allowing individuals from diverse backgrounds to acquire knowledge and skills conveniently. However, it also poses challenges such as the digital divide, where disparities in access to technology hinder some learners' opportunities.Another noteworthy phenomenon is the prevalence of academic dishonesty, including plagiarism and cheating. In the digital age, students face temptations to take shortcuts, fueled by the pressure to excel academically. Easy access to information online makes it tempting for individuals to copy-paste content without proper attribution. Moreover, the proliferation of essay mills and cheating websites exacerbates this issue, undermining the integrity of scholarly pursuits.Furthermore, the pressure to publish in academia has led to the phenomenon of predatory journals. These journals exploit researchers by charging exorbitant fees for publication without providing rigorous peer review. As a result, unsuspecting scholars may fall victim to predatory practices, tarnishing the credibility of their work and the academic community as a whole.Moreover, the phenomenon of academic elitism persists, perpetuating inequalities within higher education. Elite institutions often prioritize students from privileged backgrounds, perpetuating social stratification. Thisexclusivity undermines the principles of meritocracy and hampers efforts to foster diversity and inclusivity in academia.Additionally, the commodification of education is a notable phenomenon in modern academia. As education becomes increasingly market-driven, institutions prioritize profit over pedagogical principles. This commercialization compromises the quality of education and exacerbates disparities in access, as marginalized communities are often excluded or underserved.In response to these phenomena, various measures can be implemented to promote academic integrity and equity. Educational institutions can strengthen policies and enforcement mechanisms to deter academic dishonesty. Furthermore, fostering a culture of academic integrity through education and awareness-raising initiatives is crucial in cultivating ethical scholars.Additionally, efforts to combat predatory publishing practices are essential to uphold the integrity ofscholarly research. Institutions and funding agencies can establish criteria for evaluating the legitimacy ofjournals and provide resources to support researchers in navigating the publishing landscape.Moreover, addressing academic elitism requires systemic changes to promote diversity and inclusivity in higher education. Affirmative action policies, financial aid programs, and targeted recruitment initiatives can help mitigate disparities and create a more equitable academic environment.Furthermore, it is imperative to safeguard the qualityof education against commercial interests. Publicinvestment in education, regulatory oversight, and accreditation standards play pivotal roles in ensuring that educational institutions prioritize pedagogical excellence over profit motives.In conclusion, the landscape of modern academia is shaped by various phenomena, reflecting the complexinterplay of technological advancements, societal pressures,and economic forces. By addressing challenges such as academic dishonesty, predatory publishing, elitism, and commercialization, stakeholders can work towards fostering a scholarly environment that upholds integrity, equity, and excellence.。

关于拓扑超导的英文演讲

关于拓扑超导的英文演讲Topological superconductivity is a fascinating topic in the field of condensed matter physics that has garnered significant attention in recent years. In this speech, I will provide an overview of the concept, its potential applications, and the ongoing research in this exciting field.Firstly, let's understand what topological superconductivity is. Superconductivity is a quantum phenomenon that occurs at very low temperatures, where certain materials can conduct electricity without any resistance. This property is due to the formation of Cooper pairs, which are pairs of electrons with opposite spins. Topological superconductivity refers to a special class of superconductors where the Cooper pairs exhibit an additional quantum property known as non-Abelian statistics.Non-Abelian statistics means that the quantum wavefunction of the system is not invariant under the exchange of particles. This unique characteristic holds the potential for storing and manipulating quantum information, making topological superconductors a promising platform for developing quantum computers. Unlike conventional superconductors, which are described by Abelian statistics, the non-Abelian nature of topological superconductivity provides protection against certain types of local perturbations and disturbances, making them more stable against noise.The study of topological superconductivity is closely connected to the field of topological insulators. Topological insulators are materials that have a unique electronic band structure that results in conducting surface states while remaining insulating in the bulk. This distinct behavior arises due to the nontrivial topology of the electron wavefunctions. By introducing superconductivity into topological insulators, researchers have been able to realize topological superconductivity.One of the most exciting prospects of topological superconductivity is its potential for hosting Majorana fermions. Majorana fermions are hypothesized particles that are their own antiparticles, meaning they can annihilate and reappear as their own particle. Majorana fermions have distinct properties that make them attractive for quantumcomputing, as they are expected to have a higher resistance to decoherence. Decoherence is a phenomenon that can disrupt quantum states and is a major challenge in quantum computing.Numerous experimental efforts have been dedicated to the search for evidence of Majorana fermions in topological superconductors. One of the most notable experiments is the creation of a hybrid structure called a topological superconductor nanowire. This nanowire, made of materials with strong spin-orbit coupling and proximity-induced superconductivity, exhibits the predicted signatures of Majorana fermions. These experimental advancements have sparked great excitement and sparked further research in the field of topological superconductivity.Apart from quantum computing, topological superconductivity also has potential applications in other areas, such as topological quantum computation and fault-tolerant quantum memories. Researchers are actively exploring the possibilities of using the unique properties of topological superconductors to create new technologies that can revolutionize various fields.In conclusion, topological superconductivity is a captivating area of research with great potential for quantum technologies. Its non-Abelian nature and the possible existence of Majorana fermions make it a promising platform for quantum computing and other applications. Continued experimental efforts and theoretical investigations are crucial in unraveling the mysteries and realizing the full potential of topological superconductivity. The future of this field holds exciting possibilities that could shape the future of quantum technology.。

中科院理化所抗菌实验认证英语

中科院理化所抗菌实验认证英语全文共3篇示例，供读者参考篇1Antibacterial Experimental Verification at Institute of Physics, Chinese Academy of SciencesIntroductionThe Institute of Physics (IOP), Chinese Academy of Sciences (CAS), is a prestigious research institution that focuses on the study of physical sciences. Recently, the institute has conducted a series of experiments to verify the antibacterial properties of various materials. The goal of these experiments is to develop new antimicrobial technologies that can be used to combat the growing threat of drug-resistant bacteria. In this document, we will provide an overview of the antibacterial experimental verification conducted at the IOP.Experimental SetupThe antibacterial experiments were conducted in the laboratory facilities at the IOP. The researchers used a variety of test materials, including metals, ceramics, and polymers, to determine their antibacterial properties. Each material wasexposed to a culture of bacteria, and the researchers monitored the growth of the bacteria over a specified period of time. The experiments were repeated multiple times to ensure the accuracy of the results.ResultsThe results of the antibacterial experiments were very promising. Several of the materials tested showed significant antibacterial activity, inhibiting the growth of the bacteria and preventing the formation of biofilms. These materials could be potentially used in the development of new antibacterial coatings for medical devices, or in the production of antimicrobial textiles for use in hospitals and other healthcare settings.CertificationThe antibacterial experimental verification conducted at the IOP has been certified by an independent scientific panel. The panel reviewed the experimental data and confirmed that the results were valid and reliable. This certification gives credibility to the research conducted at the IOP and demonstrates the institute's commitment to advancing the field of antibacterial research.Future ImplicationsThe successful antibacterial experimental verification at the IOP opens up new possibilities for the development of novel antimicrobial technologies. The materials that showed antibacterial activity in the experiments could be further studied and optimized for commercial applications. In addition, the research conducted at the IOP could lead to collaborations with industry partners to bring new antibacterial products to market.ConclusionThe antibacterial experimental verification conducted at the Institute of Physics, Chinese Academy of Sciences, represents a significant advancement in the field of antimicrobial research. The promising results of the experiments demonstrate the potential for the development of new antibacterial technologies that could have a profound impact on healthcare and other industries. The certification of the research by an independent scientific panel further validates the credibility of the work conducted at the IOP. As we move forward, the institute will continue to explore new avenues for research and innovation in the field of antibacterial materials.篇2The Chinese Academy of Sciences (CAS) Institute of Physical Chemistry (IPC) has recently received certification for its antimicrobial testing experiments. This accreditation demonstrates the institute's commitment to high-quality research and its capability to contribute to the field of antimicrobial research.The IPC is renowned for its cutting-edge research in physical chemistry, with a focus on understanding the fundamental principles underlying chemical interactions and reactions at the molecular level. The institute's research has broad applications, ranging from materials science to environmental chemistry.The certification for antimicrobial testing experiments is a significant milestone for the IPC, as it showcases the institute's expertise in studying the mechanisms of antimicrobial action and resistance. With the rise of antimicrobial resistance posing a global health threat, the IPC's research is crucial for developing new antimicrobial agents and strategies to combat infectious diseases.The certification process involved rigorous evaluation of the IPC's experimental procedures, equipment, and data analysis methods. The institute's researchers demonstrated their proficiency in conducting antimicrobial assays, includingdetermining the minimum inhibitory concentration of antimicrobial agents and assessing bacterial viability.In addition to showcasing the IPC's technical competence, the certification highlights the institute's commitment to upholding ethical standards in research. The IPC adheres to international guidelines for conducting antimicrobial testing experiments, ensuring the reproducibility and validity of its findings.The IPC's antimicrobial testing certification opens up new opportunities for collaboration with industry partners, government agencies, and other research institutions. By establishing itself as a trusted source for antimicrobial research, the IPC can contribute to the development of innovative solutions to combat antimicrobial resistance.In conclusion, the Chinese Academy of Sciences Institute of Physical Chemistry's certification for antimicrobial testing experiments underscores its expertise in conducting high-quality research. With this recognition, the IPC is well-positioned to make significant contributions to the field of antimicrobial research and address the global challenge of antimicrobial resistance.篇3Research on Antimicrobial Experiment Accreditation at the Institute of Physical and Chemical Research of the Chinese Academy of SciencesIntroduction:The Institute of Physical and Chemical Research of the Chinese Academy of Sciences (IPCR-CAS) is a prestigious research institution dedicated to the study of physical and chemical sciences. One of the key areas of research at IPCR-CAS is the development of antimicrobial agents to combat the growing threat of antibiotic resistance. In order to ensure the efficacy and safety of these agents, IPCR-CAS has established a rigorous accreditation process for antimicrobial experiments.Accreditation Process:The accreditation process at IPCR-CAS involves a series of steps to verify the effectiveness and safety of the antimicrobial agents under study. This process includes:1. Identification of Target Microorganisms: Researchers at IPCR-CAS first identify the target microorganisms that the antimicrobial agent is intended to combat. These may include bacteria, viruses, or fungi that pose a threat to human health.2. Selection of Antimicrobial Agents: Researchers then select the appropriate antimicrobial agents for testing based on their chemical properties and potential efficacy against the target microorganisms.3. Experimental Design: Researchers design experiments to test the effectiveness of the antimicrobial agents against the target microorganisms. These experiments may include in vitro tests using cultures of the microorganisms or in vivo tests using animal models.4. Data Collection and Analysis: Researchers collect data on the efficacy of the antimicrobial agents and analyze the results to determine their effectiveness against the target microorganisms.5. Peer Review: The results of the experiments are then subjected to peer review by other researchers at IPCR-CAS to ensure the accuracy and reliability of the data.6. Accreditation: Once the experiments have been successfully completed and the results verified, the antimicrobial agents are accredited for further study and potential use in clinical settings.Benefits of Accreditation:The accreditation process at IPCR-CAS offers several benefits to researchers and the scientific community as a whole. These include:1. Quality Assurance: By verifying the efficacy and safety of antimicrobial agents, the accreditation process ensures that only the most effective agents are used in research and clinical settings.2. Collaboration Opportunities: Accredited antimicrobial agents can be shared with other research institutions and pharmaceutical companies for further study and development.3. Public Health Impact: Accredited antimicrobial agents have the potential to make a significant impact on public health by combating antibiotic resistance and infectious diseases.Conclusion:The accreditation process for antimicrobial experiments at IPCR-CAS plays a crucial role in ensuring the effectiveness and safety of antimicrobial agents. By following a rigorous process of identification, selection, experimentation, and peer review, IPCR-CAS researchers are able to develop high-quality antimicrobial agents that have the potential to improve public health. Further research and collaboration in this area areessential to address the growing threat of antibiotic resistance and infectious diseases.。

社会网络分析的一些经典文献(分类)[转载]

社会网络分析的一些经典文献（分类）[转载]IntroductionWasserman, S, and K Faust. 1994. Chapter 1.Watts, DJ. 2004. "The New science of networks." Annual review of sociology 30:243-270.Emirbayer, M, and J Goodwin. 1994. "Network Analysis, Culture, and the Problem of Agency." AmericanJournal of Sociology 99:1411.Ansell, CK. 1997. "Symbolic Networks: The Realignment of the French Working Class, 1887–1894."American Journal of Sociology 103:359-90.Emirbayer, M. 1997. "Manifesto for a Relational Sociology 1." American Journal of Sociology 103:281-317.Knoke, D. 1990. Political Networks: The Structural Perspective: Cambridge University Press. Chapter 1Data, Graph, Matrices: Mathematical BackgroundsWasserman, S, and K Faust. 1994. Chapter 2, 3, and 4Social capitalLin, N. 2001. Social Capital: A Theory of Social Structure and Action: Cambridge University Press.Chapter 1, 2, 3, 4, and 5.Putnam, R. 2001. "Social Capital: Measurement and Consequences." Canadian Journal of Policy Research136 (Recommended)Coleman, JS. 1987. "Norms as Social Capital." Economic Imperialism:133-55 (Recommended)Portes, A. 1998. "Social Capital: Its Origins and Applications in Modern Sociology." Annual Reviews inSociology 24:1-24 (Recommended)Gambetta, D. 2000. "Can we trust trust." Trust: Making and Breaking Cooperative Relations, Electronicedition, Department of Sociology, University of Oxford: 213-237 (Recommended).Marsden, PV. 1987. "Core Discussion Networks of Americans." American Sociological Review 52:122-131(Recommended)Burt, RS. 2000. "The Network Structure of Social Capital." Research in Organizational Behavior 22:345-423 (Recommended)Centrality and CentralizationWasserman, S, and K Faust. 1994. Chapter 5Bonacich, P. 1987. "Power and Centrality: A Family of Measures." American Journal of Sociology92:1170-82.Hanneman, RA. 2001. "The prestige of Ph. D. granting departments of sociology: a simple networkapproach." Connections 24:68-77.Brass, DJ. 1984. "Being in the right place: A structural analysis of individual influence in an organization."Administrative Science Quarterly 29:518-539 (Recommended)Cook, KS, RM Emerson, and MR Gillmore. 1983. "The Distribution of Power in Exchange Networks:Theory and Experimental Results." American Journal of Sociology 89:275.BrokerageUzzi, B. 1996. "The Sources and Consequences of Embeddedness for the Economic Performance ofOrganizations: The Network Effect." American Sociological Review 61: 674-698.Burt, RS. 1992. Structural Holes: The Social Structure of Competition: Harvard University Press. Chapter1Diani, M. 2003. "Leaders or Brokers? Positions and Influence in Social Movement Networks." In SocialMovements and Networks: Relational Approaches to Collective Action. Edited by M Diani and DMcAdam. Oxford University Press.SubgroupsWasserman, S, and K Faust. 1994, Chapter 7.Freeman, LC. 1992. "The Sociological Concept of Group: An Empirical Test of Two Models." AmericanJournal of Sociology 98:152.Burt, RS. 1987. "Social Contagion and Innovation: Cohesion versus Structural Equivalence." AmericanJournal of Sociology 92:1287.BlockmodelingWasserman, S, and K Faust. 1994. Chapter 9, 10, 11, and 12Snyder, D, and EL Kick. 1979. "Structural Position in the World System and Economic Growth, 1955-1970." American Journal of Sociology 84: 1096-1126.DiMaggio, PJ. 1986. "Structural analysis of organizational fields: A blockmodel approach." Research inOrganizational Behavior 8:35-370.Anheier, HK, J Gerhards, and FP Romo. 1995. "Forms of Capital and Social Structure in Cultural Fields:Examining Bourdieu's Social Topography." American Journal of Sociology100:859.Gerlach, ML. 1992. "The Japanese Corporate Network: A Blockmodel Analysis." Administrative ScienceQuarterly 37:105-139. (Recommended)Generalized BlockmodelingDoreian, P, V Batagelj, and A Ferligoj. 2005. Generalized Blockmodeling: Cambridge University Press.Two ModesWasserman, S, and K Faust. 1994. Chapter 8Breiger, RL. 1974. "Duality of Persons and Groups." Social Forces 53:181. Sewell, Jr, WH. 1992. "A Theory of Structure: Duality, Agency, and Transformation." American Journal ofSociology 98:1.Borgatti, SP, and MG Everett. 1997. "Network analysis of 2-mode data." Social Networks 19:243-269.Doreian, P, V Batagelj, and A Ferligoj. 2004. "Generalized blockmodeling of two-mode network data."Social Networks 26:29-53.Roberts, JM. 2000. "Correspondence analysis of two-mode network data." Social Networks 22:65-72.Hanneman RA and M Riddle. 2005. Introduction to Social Network Methods. Chapter 17.Statistical Analysis based on Dyads and TriadsHanneman RA and M Riddle. 2005. Introduction to Social Network Methods. Chapter 18.Burris, V. 2005. “Interlocking Directorates and Political Cohesion among Corporate Elites.” AmericanJournal of Sociology 111(1).Holland, PW, and S Leinhardt. 1981. "An exponential family of probability distributions for directedgraphs." Journal of the American Statistical Association 76:33-65. Wasserman, S, and K Faust. 1994. Chapter 13, 14, 15, and 16 Wasserman, S, and P Pattison. 1996. "Logit models and logistic regressions for social networks: I. Anintroduction to Markov graphs and p*." Psychometrika 61:401-425.Network TypologyGranovetter, MS. 1973. "The Strength of Weak Ties." American Journal of Sociology 78:1360.Ball, P. 2004. Critical Mass: How One Thing Leads to Another: Farrar, Straus and Giroux. Chapter 15 and16.Barabási, AL. 2003. Linked: how everything is connected to everything else and what it means for business,science, and everyday life. Plume.Moody, J. 2004. "The Structure of a Social Science Collaboration Network: Disciplinary Cohesion from1963 to 1999." American Sociological Review 69:213-238.Kogut, B, and G Walker. 2001. "The small world of Germany and the durability of national networks."American sociological review 66:317-335.Dynamics on NetworkWatts, DJ. 1999. "Networks, Dynamics, and the Small-World Phenomenon." American Journal ofSociology 105:493-527.Gladwell, M. 2000. The Tipping Point: How Little Things Can Make a Big Difference: Little, Brown andCompany.Gould, R. 1991. "Multiple Networks and Mobilization in the Paris Commune, 1871." AmericanSociological Review 56: 716-729.Hedstrom, P, R Sandell, and C Stern. 2000. "Mesolevel Networks and the Diffusion of Social Movements:The Case of the Swedish Social Democratic Party." American Journal of Sociology 106:145-172.Longitudinal AnalysisSmith, DA, and DR White. 1991. "Structure and Dynamics of the Global Economy: Network Analysis ofInternational Trade 1965-1980." Social Forces 70:857.Gulati, R. 1995. "Social Structure and Alliance Formation Patterns: A Longitudinal Analysis."Administrative Science Quarterly 40:619-652.Carroll, WK, and M Shaw. 2001. "Consolidating a Neoliberal Policy Bloc in Canada, 1976 to 1996."Canadian Public Policy–Analyse DE Politiques 27.Mizruchi, M S, and LB Stearns. 1988. “A Longitudinal Study of the Formation of InterlockingDirectorates.” Administrative Science Quarterly 33: 193-210.Kim, S, and EH Shin. 2002. "Longitudinal Analysis of Globalization and Regionalization in InternationalTrade: A Social Network Approach, A." Social Forces 81:445. (Optional) Network DynamicsPowell, WW, DR White, KW Koput, and J Owen-Smith. 2005. "Network Dynamics and Field Evolution:The Growth of Interorganizational Collaboration in the Life Sciences." American Journal ofSociology 110:1132-1205.Robins, G, P Pattison, and J Woolcock. 2005. "Small and Other Worlds:Global Network Structures fromLocal Processes." American Journal of Sociology 110:894-936.Kenis, P, and D Knoke. 2002. "How organizational field networks shape interorganizational tie-formationrates." The Academy of Management review 27:275-293.Carley, KM. 2003. "Dynamic Network Analysis." In Dynamic Social Network Modeling and Analysis:Workshop Summary and Papers: 113-145.Stochastic Modeling of Influence and SelectionLeenders, RTAJ. 1996. "Longitudinal Behavior of Network Structure and Actor Attributes: ModelingInterdependence of Contagion and Selection." Evolution of Social Networks:165–84.Steglich, C, TAB Snijders, and P West. 2006. "Applying SIENA: An Illustrative Analysis of theCoevolution of Adolescents’ Friendship Networks, Taste in Music, and Alcohol Consumption."Methodology 2:48-56.Steglich, C, TAB Snijders, and M Pearson. 2004. "Dynamic networks and behavior: Separating selectionfrom influence." Submitted for Publication.Van De Bunt, GG, MAJ Van Duijn, and TAB Snijders. 1999. "Friendship Networks Through Time: AnActor-Oriented Dynamic Statistical Network Model." Computational & MathematicalOrganization Theory 5:167-192.Van de Bunt, GG, RPM Wittek, and MC de Klepper. 2005. "The Evolution of Intra-Organizational TrustNetworks: The Case of a German Paper Factory: An Empirical Test of Six Trust Mechanisms."International Sociology 20:339.VisualizationFreeman, LC. 2000. "Visualizing Social Networks." Journal of Social Structure 1:4.Muller, C, B Wellman, and A Marin. 1999. "How to use SPSS to study ego-centered networks." BMS.Bulletin de Méthologie Sociologique:83-100.Moody, J, D McFarland, and S Bender-deMoll. 2005. "Dynamic Network Visualization." AmericanJournal of Sociology 110:1206-1241.Bender-deMoll, S, and DA McFarland. 2006. "The art and science of dynamic network visualization."Journal of Social Structure 7.。

A review of conduction phenomena in Li-ion batteries

Journal of Power Sources 195 (2010) 7904–7929Contents lists available at ScienceDirectJournal of PowerSourcesj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /j p o w s o urReviewA review of conduction phenomena in Li-ion batteriesMyounggu Park a ,Xiangchun Zhang a ,Myoungdo Chung a ,Gregory B.Less a ,Ann Marie Sastry a ,b ,c ,∗aDepartment of Mechanical Engineering,University of Michigan,Ann Arbor,MI 48109,United StatesbDepartment of Material Science and Engineering,University of Michigan,Ann Arbor,MI 48109,United States cDepartment of Biomedical Engineering,University of Michigan,Ann Arbor,MI 48109,United Statesa r t i c l e i n f o Article history:Received 12May 2010Received in revised form 16June 2010Accepted 17June 2010Available online 25 June 2010Keywords:Ionic conductionElectrical conduction Cathode AnodeElectrolyteLithium-ion batterya b s t r a c tConduction has been one of the main barriers to further improvements in Li-ion batteries and is expected to remain so for the foreseeable future.In an effort to gain a better understanding of the conduction phe-nomena in Li-ion batteries and enable breakthrough technologies,a comprehensive survey of conduction phenomena in all components of a Li-ion cell incorporating theoretical,experimental,and simulation studies,is presented here.Included are a survey of the fundamentals of electrical and ionic conduc-tion theories;a survey of the critical results,issues and challenges with respect to ionic and electronic conduction in the cathode,anode and electrolyte;a review of the relationship between electrical and ionic conduction for three cathode materials:LiCoO 2,LiMn 2O 4,LiFePO 4;a discussion of phase change in graphitic anodes and how it relates to diffusivity and conductivity;and the key conduction issues with organic liquid,solid-state and ionic liquid electrolytes.© 2010 Elsevier B.V. All rights reserved.Contents 1.Introduction..........................................................................................................................................79062.Review of the fundamentals of conduction..........................................................................................................79062.1.Conduction in an electrochemical cell .......................................................................................................79062.2.Ionic conduction (7907)2.2.1.Diffusion in condensed materials ..................................................................................................79072.2.2.Relationship between diffusivity and ionic conductivity..........................................................................79092.2.3.Grain boundary diffusion.. (7910)2.3.Electrical conduction (7910)2.3.1.Electrical conductivity (7910)3.Survey of conduction studies in cathode materials .................................................................................................79123.1.Ionic conduction in cathode materials.......................................................................................................79133.2.Electrical conduction in cathode materials ..................................................................................................79164.Survey of conduction studies in anode materials ...................................................................................................79174.1.Ionic conduction in anode materials.........................................................................................................79174.2.Electrical conduction in anode materials ....................................................................................................79235.Survey of conduction studies in electrolytes anic electrolytes ..........................................................................................................................79235.2.Solid-state electrolytes.......................................................................................................................79245.3.Ionic liquid electrolytes ......................................................................................................................79256.Concluding remarks and future perspectives .......................................................................................................7925Acknowledgements..................................................................................................................................7925References . (7925)∗Corresponding author at:Department of Mechanical Engineering,University of Michigan,Ann Arbor,MI 48109,United States.Tel.:+17349980006;fax:+173499800283.E-mail address:amsastry@ (A.M.Sastry).0378-7753/$–see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.jpowsour.2010.06.060M.Park et al./Journal of Power Sources 195 (2010) 7904–79297905NomenclaturePhysical constants e charge of an electron,1.602×10−19C F Faraday’s constant,96,487C mol −1 reduced Planck’s constant,1.055×10−34J sk BBoltzmann constant,1.38054×10−23J K −1m mass of an electron,9.11×10−31kgN AAvogadro’s number,6.0232×1023g −1mol −1R g universal gas constant,8.3141J mol −1K −1Symbols a inter-atomic distance,m¯c average concentration,mol L −1c A concentration of species A ,mol cm 3c B concentration of species B ,mol cm 3c A ,∞uniform concentration of species A after relaxation,mol cm 3c B ,∞uniform concentration of species B after relaxation,mol cm 3c i ,j concentration of i in phase j ,mol cm 3ˆC P volume averaged heat capacity at constant pressure,J kg −1◦C −1ˆC Pa heat capacity at constant pressure,J g −1K −1ˆC Pi,j partial molar constant pressure heat capacity of species i in phase j ,J mol −1K −1C p ∞partial molar constant pressure heat capacity after relaxation 1,J mol −1K −1C p 1partial molar constant pressure heat capacity for reaction 1,J mol −1K −1D i diffusivity of solute i (i =1,2),cm 2s −1D o pre-exponential factor,cm 2s −1D GB grain boundary diffusivity,cm 2s −1E energy of an electron,eV E a activation energy,kJ mol −1EF Fermi energy,eV E g band gap,eVf friction coefﬁcient,kg m −1q conv heat generation rate due to convection,W m −3q icharge of solute ‘i (i =1,2)’,Cq heat ,i heat generation rate at node i ,W R electrical resistance,R i internal resistance of the cell, R o radius of sphere (particle),m R s sheet resistance, cm 2r inter-particle distance,m T temperature,KT i temperature at node i ,K T j temperature at node j ,K t time,sU (r )inter-particle potential,eVu imobility of a solute ‘i ’,m 2V −1s −1U 1,avgtheoretical open-circuit potential for reaction 1at the average composition relative to a reference elec-trode of a given kind,V V cell potential,V¯VB,∞partial molar volume of species B after relaxation,m 3mol −1v f velocity of electrons at steady state,m s −1v i velocity of a solute ‘i ’,m s −1v FFermi velocity,cm s −1y distance from surface along grain boundary,cm z ivalence of ionAbbreviations AC alternating current CV cyclic voltammetry CPR current pulse relaxation DC direct current DEC diethyl carbonate DMC dimethyl carbonate EC ethylene carbonate density,k gm −3 o attempt frequency of the order of Debye frequencyof the lattice,s −1electric ﬁeld,V m −1 electronic conductivity,S cm −1 relaxation time (average time between two consec-utive collisions),s f a F /R g T ,V −1G Gibbs free energy,J h Joint thickness of porous electrodes and electrolytelayer,cmH enthalpy of reaction,J ¯H A enthalpy of the system of species A ,J H o 1,m molar enthalpy of species 1in the secondary refer-ence state corresponding to phase m,J mol −1I electrical current or cell current,A i operating current,AI 1partial current of electrode reaction 1,A j current density (electron ﬂux),A m −2j i ionic ﬂux,mol cm −2s −1k wave vector,m −1k a thermal conductivity,W cm −1s −1K −1k heat thermal conductivity,W cm −1K −1k heat ,x thermal conductivity in x direction,W cm −1K −1k heat ,y thermal conductivity in y direction,W cm −1K −1k heat ,z thermal conductivity in z direction,W cm −1K −1k heat ,ij thermal conductivity between node i and node j ˜M i molecular weight (i =1,2),u M i heat capacity at node i ,J K −1m e effective mass of an electron,kg m p effective mass of a hole,kgN (E F )number of electrons at E F ,mol eV −1N f number of electrons at steady state,mol m −3n i number of electrons,cm −3n i ,j moles of species i in phase j ,mol p pressure in atmosphere,Pa p i number of holes,cm −3q heat transfer rate,Wq heat heat generation rate,W m −3EIS electrochemical impedance spectroscopy ESD electrostatic spray depositionEVS electrochemical voltage spectroscopyGITT galvanostatic intermittent titration technique HOPG highly oriented pyrrolytic graphite HTT heat treatment temperature MCMB mesocarbon microbeads PC propylene carbonate PLD pulsed laser depositionPITT potentiostatic intermittent titration technique PSCA potential step chronoamperometry PVdF polyvinylidene ﬂuorideRPGratio of potentio-charge capacity to galvano-charge capacitySources 195 (2010) 7904–79291.IntroductionImprovements in the capacity of modern lithium (Li)batteries continue to be made possible by enhanced electronic conduc-tivities and ionic diffusivities in anode and cathode materials.Fundamentally,such improvements present a materials science and manufacturing challenge:cathodes in these battery cells are normally comprised of metal oxides of relatively low elec-tronic conductivity,and separator/electrolyte compositions must be tuned to readily admit ions,while simultaneously forming safe,impenetrable and electronically insulating barriers.The challenges faced by researchers in this ﬁeld include the relatively low electri-cal and ionic conductivity values in cells,an unclear relationship between electrical conduction and ionic conductivity in cathode materials,constantly changing conduction properties in anode materials dependent upon phase transformations,and the inher-ent difﬁculty in identifying and measuring the microstructure and conductivity of the solid–electrolyte interphase (SEI)ﬁlm.Since the Sony Corporation ﬁrst successfully marketed a com-mercial Li-ion battery in 1991[1],Li-ion battery technology has been applied to both thin,light,and ﬂexible portable electronic devices and more recently,to batteries for transportation systems [2]including hybrid and electric vehicles.Though these markets present different challenges in battery cell design,the former requiring in general higher power density,and the latter requiring higher energy density for greater degrees of vehicle electriﬁcation,the technical requirements of improved conductivity and diffusiv-ity are common to both.Models of battery cells and materials [3–5]critically require the best available estimates for conductivity and diffusivity,in order to both predict response and design improved materials.Models at the atomistic and molecular [6–9],particle,both for solids of revolution [10–16],and for ﬁbers [17–21]and contin-uum [22–29]scales all contribute to improved understanding of cell response.In order,atomistic and molecular models can be used to identify materials architectures of intrinsically high conductiv-ity/diffusivity;particle-based models can be used to identify/design particle shapes and fractions and loading schema of additives that tune conductivity/diffusivity;and continuum models can best be used as reduced-order inputs to optimization and controls models [26,30–34].Accordingly,at each scale accurate,validated conduc-tivity/diffusivity values are needed.Experimental validation of such parameters is often challeng-ing,however.Often,battery materials characterization is carriedout ex situ or as a post mortem analysis because of the complexity of in situ experimental setup;though such data is still invaluable for interpreting results,they can only describe the end state.A key chal-lenge remains to develop experimental techniques to probe and detect Li-ion movement within the electrode lattice structure and the electrode–electrolyte interface at a local level as a function of time.Interpretation of in situ characterization experiments is chal-lenging often due to a lack of viable theories concerning cathodes,anodes,and novel electrolytes.While some authors [35,36]have discussed manipulating the electrical and/or ionic conductivity of relevant materials in Li-ion cells,few review papers are dedicated to conduction;papers that do focus on conduction usually discuss only one kind of material (e.g.,cathode or anode)or only summarize current key issues,namely:a review of the diffusion problem with respect to ionic conduction [37]in nanocrystalline ceramics with a focus on Nuclear Magnetic Resonance (NMR)spectroscopy,a review of the importance of elec-trical conduction in cathode materials [38],as well as other more generalized discussions of the conduction problem [39,40].Thus,a comprehensive survey of conduction phenomena is provided here,for all components of a Li-ion cell,incorporating theoretical,exper-imental,and simulation studies.Our objectives in this work are to(1)survey the fundamentals of electrical and ionic conduction the-ories;(2)survey the critical results,issues and challenges with respectto electrical and ionic conduction in all of the major battery components including cathode,anode and electrolyte;(3)review the relationship between electrical and ionic conductionfor three cathode materials:LiCoO 2,LiMn 2O 4,LiFePO 4;(4)review phase change in graphitic anodes and how it relates todiffusivity and conductivity;(5)review key conduction issues with organic liquid,solid stateand ionic liquid electrolytes.While an attempt has been made to present a uniﬁed viewpoint,information has been drawn from many different sources and cer-tain ambiguities and disjointedness are unavoidable.References over 50years old represent the foundational papers upon which subsequent literature has built and thus are included here.Finally,although units in the various equations may describe the same physical quantities,they vary with context and therefore have not been standardized.Instead they are maintained as described in the original papers.2.Review of the fundamentals of conductionIn this section,we introduce the fundamentals of conduction phenomena –ionic and electronic conduction.Based upon this succinct but essential survey,we made careful observations on research efforts in Li-ion batteries,which are discussed in the latter part of this review.Note that this is fundamental physics which has been used many times in research papers dealing with conduction phenomena,ﬁrst-principle calculations and simulation,as well as experimental papers.2.1.Conduction in an electrochemical cellGenerally,when working with electrochemical cells (the most basic unit comprising any battery),Li-ion cells included,all key phenomena involve conducting charged particles (electrons and ions)from cathode to anode (primary cell)or vice versa (secondary cell).An operating galvanic cell [41,42]is depicted in Fig.1(adapted from [41,42]).Note that in the redox reaction shown,two electronsM.Park et al./Journal of Power Sources 195 (2010) 7904–79297907Fig.1.Generic operating electrochemical cell (adapted from [41,42]).are transferred.Because the electrochemical reaction of a cell is based upon a change of oxidation state,the ease of electron-transfer between anode and cathode can dictate the magnitude of the cell’s driving force [43,44].Electrons are transferred from anode to cath-ode during the discharge of a cell;the related cell components are electrodes,current collectors and electrical leads.In addition to electrical conduction,ionic conduction through the electrodes and electrolyte is necessary to complete the electrochemical reaction.For a simple illustration of conduction phenomena,the potential equation of an operating electrochemical cell is surveyed.Gener-ally,the operating voltage (E )of the cell is lower than the standard cell voltage (E o )due to potential drops caused by several factors.This is stated mathematically [41]asE =E o −[(Áct )a +(Áct )c ]−[(Ác )a +(Ác )c ]−iR i =iR(2.1.1)where E o is the standard cell potential,(Áct )a ,(Áct )c are activation polarizations (charge-transfer over voltage)at the anode and cath-ode (Ác )a ,(Ác )c are concentration polarizations at the anode and cathode,i is the cell operating current,R i is the internal resistance of the cell and R is the apparent cell resistance.All terms in Eq.(2.1.1)can be related to conduction phenomena.Activation and concentration polarizations are connected to the kinetics of charge transfer and mass transfer [44–46],respectively.Internal resistance (R i )is affected by the conduction properties of various materials and their interfaces and can be broken down as listed in Table 1[41];the sum of each of the internal resistances is the total internal resistance.Examining the sources of resistance can provide insight into the key barriers to optimized conduction in electrochemical cells.Given the number of potential sources of resistance in a cell,even the relatively simple phenomenonTable 1Internal resistance of cell [41].Type of resistanceInternal resistance of cell (R i =ionicresistance +electrical resistance +interfacial resistance)Ionic •Electrode (cathode and anode)particle •ElectrolyteElectrical•Electrode (cathode and anode)particle •Conductive additives•Percolation network of additives in electrode •Current collectors •Electrical tapsInterfacial•Between electrolyte and electrodes•Between electrode particles and conductive additives•Between electrode and current collector •Between conductive additives and current collectorof potential drop can be quite challenging to interpret quantita-tively.2.2.Ionic conduction2.2.1.Diffusion in condensed materialsDiffusion properties of Li-ion cell determine some of the key per-formance metrics of Li-ion battery cells,including the charge and discharge rate,practical capacity and cycling stability.The govern-ing equation describing the diffusion process is known as Fick’s law (Eq.1in Table 2[47,48]);the proportionality factor D is the dif-fusivity or diffusion coefﬁcient (Eq.3–5in Table 2).In condensed materials (liquids and solids),diffusion is governed by random jumps of atoms or ions,leading to position exchange with their neighbors.The kinetics of this process is temperature dependent and follows an Arrhenius type relationship [49](Eq.2in Table 2).In liquids,the temperature dependence of the diffusion is much less than in solids.Note that no successful ﬁrst-principles calcula-tion has been made,due to insufﬁcient understanding of the liquid structure [47].Thus,a simple expression derived from Stoke’s drag law [50]is frequently used as an alternative for a diffusivity expres-sion in liquids (Eq.3in Table 2)[47,51].The generic diffusion mechanism for a solid is a good starting point for understanding diffusion processes because diffusivity is highly dependent upon the relevant diffusion mechanism (Table 3)[52].Defects play the central role and affect the terms –H F and D o in Eq.6in Table 2.Diffusion mechanisms for solids can be classiﬁed into two categories:vacancy/defect-mediated mechanisms,and non-vacancy/non-defect-mediated mechanisms.Vacancy-mediated mechanisms require much larger activation energies than non-defect-mediated mechanisms (Eq.4vs.Eq.5in Table 2).Similarly,there are two primary defects affecting ion dif-fusion in ionic crystals –Schottky pairs (cation vacancy plus anion vacancy)and Frenkel pairs (cation vacancy plus a cation intersti-Table 2Governing equation for diffusion and diffusion coefﬁcients [47,48].No.Title Equation Comments1Fick’s lawj i =−D i ∇c i &∂c i ∂t=∇·(D ∇c i )Governing equation for diffusion2Arrhenius equation rate ≈exp− Gk B TPredicts kinetics based on thermal activation3Diffusivity in liquid D i =k B T 6 R oEinstein-Stokes relation4Diffusivity in solidD i =a 2l :a l is the jump length , = o exp− Gk B T5Temperature dependence of diffusivity in solid D i =D o exp −H Mk B TDescribes non-defect mediated interstitial diffusion 6Temperature dependence of diffusivity in solidD i =D o exp−H F +H Mk B TDescribes vacancy mediated diffusion7908M.Park et al./Journal of Power Sources 195 (2010) 7904–7929Table 3Diffusion mechanisms in solid [52].Mechanism DescriptionVacancy(defect)-mediated Vacancy Self-diffusion in metals and substitution alloys Divacancy Diffusion via aggregates of vacanciesNon-vacancy(defect)-mediatedInterstitialSolute atoms considerably smaller than the host atoms,and atoms are incorporated into interstitial sites of the host lattice to form an interstitial solid solutionCollectiveSolute atoms similar in size to host atoms involving simultaneous motion of several ually substitutional solid solutions are formedInterstitialcyA collective mechanism important for radiation-induced diffusion.At least two atoms move simultaneously;however,this mechanism is negligible for thermal diffusionInterstitial-substitutional ExchangeSolute atoms are dissolved on both interstitial and substitutional sites and diffuse via interstitial or substitutional exchange mechanismsTable 4Bonding potentials in Li-ion battery [60–62].Cell componentBond type Interaction potential Bond length (Å)Bond strength (kJ mol −1)Anode (graphite,in-plane)Covalent –1.46374Anode (graphite,inter-plane)van der Waals Lennard-Jones potential U (r )=4ε ˇr12−ˇr6 (1)3.35 5.9Cathode (spinel,LiMn 2O 4)Ionic Coulombic interaction U (r )=q 1q 24 εr r ···(2) 1.960(Li–O)426.48(Li–O)Liquid electrolyteCoulombicCoulombic interaction U (r )=q 1q 24 εr r (3)––tial)[53,54].Ionic solids with Schottky defects (corresponding to the defect-mediated diffusion in Table 3)have lower ionic conduc-tivities and higher activation enthalpies because ionic transport occurs from the motion of vacancies.On the other hand,ionic crystals with Frenkel disorder (corresponding to the interstitial mechanism in Table 3)show higher ionic conductivities and lower activation enthalpies because ionic transport occurs primarily from the motion of interstitial species.Li-ions diffuse mainly by an inter-stitial mechanism due to their small radius.Although the Li-ion is one of the smallest ions,it is still quite big when compared to elec-trons;the radius of a Li-ion is ten orders of magnitude larger than that of an electron (radius of a Li-ion:59×10−12m [55];radius of an electron:10−22m [56]).Also the motion of Li-ions is strongly impeded by the potential created by the presence of neighboring ions as discussed below.Thus diffusion can be the rate-determining process compared to electronic conduction in an electrochemical reaction.In crystalline solids,the structure is well deﬁned and diffusiv-ity can be modeled with a ﬁrst-principles calculation [57](Eq.4in Table 2).Diffusion in a crystal is strongly affected by bonding potential and defects;the effects are incorporated in the dif-fusivity expression as enthalpy (H )and a prefactor,D o (Eqs.5and 6in Table 2)[58,59].Bond types and potentials of materials used in Li-ion batteries are summarized in Table 4[60–62].The two strongest chemical bonds are ionic and covalent;electron-transfer between two species creates ionic bonds,and covalent bonds are formed by electron sharing among atoms.The van der Waals interaction,expressed as the Lennard–Jones potential,is rel-atively weak despite showing a longer interaction range.In the case of the graphite anode,a Li-ion can easily diffuse parallel rather than perpendicular to the graphene layers during interca-lation.Thus in order to understand the diffusion of the Li-ion it is important to consider crystal structure as well as the surrounding potential.Table 5Relation between diffusivity and ionic conductivity [51].No.TitleEquationComments1Drift velocityv i =−u i (∇ i +z i F ∇ϕ):∇ϕ=Drift velocity expressed using mobility and the chemical and electrical potentials2–∇ i =RT c i∇c iRelationship between and in the dilute case3Drift velocity −v i =u i RT c i∇c i +c i z i F ∇ϕRTDrift velocity in the dilute case 4Ionic ﬂux−j i =−c i v i =u i RT∇c i +c i z i F ∇ϕRT=D io∇c i +c i z iF ∇ϕRTDeﬁnition of ionic ﬂux iscombined with Eq.(3)5Nernst–Planck relationshipD io =u i RT ;D i =D io N A=u i RT N A=u i k B T =v ik B TDescribes the diffusivity and mobility relationship 6Current density j =q i j i =q 2ic i D ik B T=Deﬁnition of current density (j ),ionic ﬂux (j i )7Diffusivity vs.ionic conductivity =q 2ic ik B TD iA generic relationship between diffusivity and ionicconductivity is obtainedM.Park et al./Journal of Power Sources 195 (2010) 7904–792979092.2.2.Relationship between diffusivity and ionic conductivityAlthough diffusivity is used as a main descriptor for the motion of Li-ions it is indispensible to survey the concept of ionic conduc-tion and the relationship between diffusivity and ionic conductivity because ionic conductivity also is important for describing the motion of Li-ions.Motion of a Li-ion gives rise to ionic con-duction (i.e.currents)under external electrical potential.In a Li-ion battery,Li-ions should move through the electrolyte from the cathode to the anode during charge,and vice versa during discharge;anything hampering this motion can be interpreted as ionic resistivity.As shown in Table 1,resistance can orig-inate from inside the electrode materials,from the interface between the electrodes and the electrolyte,and from the electrolyte itself.Charged particles,including Li-ions,can pass through a media under two driving forces:an externally applied electric ﬁeld or a concentration gradient.The mobility (u i )of ions represents the degree of ease with which ions pass through media when an exter-nal electrical ﬁeld is applied,and the diffusivity (D i )represents the ease with which ions pass through media under a concentration gradient.While mobility and diffusivity are often treated as sepa-rate phenomena,Table 5summarizes the key equations for deriving the relationship between them (and then for ionic conductivity)as previously described [51].Indeed,it can be shown that mobility and diffusivity are the same physical entity [51].The key here is that diffusivity,mobility,and ionic conductivity are related properties.Derivations of the relationshipsfollow.Fig.2.GB diffusion model by Fisher (adapted from [67–69]).The relationship between mobility and diffusivity can be obtained by considering the drift velocity (v i )of ions in terms of mobility (u i )under both an externally applied electric ﬁeld and a concentration gradient (Eqs.1–5in Table 5).The Nernst–Planck equation (Eq.5in Table 5)implies that mobility and diffusivity are ing the deﬁnition of current density induced byTable 6Grain Boundary Diffusivity [67,68,70].No.TitleEquationComments1-1Fisher’s model∂ln ¯c ∂y2=1D GB ı4D i t1/2−1/2•Approximate solution easily applied to experimental results•A plot of log ¯cvs.y yields a straight line with slope given in Eq.(1-1)1-2D GB ı=∂ln ¯c ∂y−2 4D i t1/2−1/2•Rearranging Eq.(1-1),we can get D GB2-1Whipple’s model∂ln ¯c ∂y 6/55/3=1D GB ı4D i t1/2(0.78)5/3•Exact solution but inconvenient to apply for experimental results•A plot of log ¯cvs.y 6/5yields a straight line with slope given in Eq.(1-1)2-2D GB ı=∂ln ¯c ∂y 6/5−5/3 4D i t1/2(0.78)5/3•Rearranging Eq.(2-1),we can get D GBTable 7Room temperature resistivity for various materials.Cell ComponentMaterialBand gap (eV)Electrical conductivity (S cm −1)Reference Current collector (anode)Copper (C11000)0 5.8×105[75,76]Current collector (cathode)Aluminum (1100)0 3.4×105[75,77]AnodeGraphite 0(2–1)×103[78–80]CathodeLiCoO 20.5–2.7∼10−4[81–83]LiMn 2O 40.28–2.2∼10−6[84–90]LiFePO 40.3–1∼10−9[91,92]Table 8Equations related to classical concept of electrical conductivity [94].No.TitleEquationComments1Electron gas force equilibrium equationm d v dt+ v =e Electrons moving in a solid can bemodeled as a ﬂowing gas experiencing friction2Velocity of electron gas v =v f 1−exp −e m v ft;v f =e mSteady state solution to Eq.(1)3Steady state current densityj =N f v f e =Eq.(3)can be derived from Ohm’s law4Conductivity =N f e 2 m。

物理现象的英语作文

物理现象的英语作文The world around us is filled with a vast array of physical phenomena, each one a testament to the intricate laws and principles that govern the universe. From the grandest celestial events to the smallest subatomic interactions, the study of these phenomena has been a driving force behind humanity's quest to understand the nature of our existence.One of the most fundamental physical phenomena is the concept of energy. Energy, in its various forms, is the underlying force that powers the universe, fueling the movement of planets, the warmth of the sun, and the very chemical reactions that sustain life. Whether it's the kinetic energy of a moving object, the potential energy stored in a stretched rubber band, or the thermal energy radiating from a glowing ember, the transformation and conservation of energy are at the heart of countless physical processes.Another ubiquitous physical phenomenon is the concept of motion. From the graceful flight of a bird to the cascading flow of a river, the principles of motion govern the way objects interact with oneanother and with the forces acting upon them. Newton's laws of motion, which describe the relationship between an object's mass, acceleration, and the forces acting upon it, have been instrumental in our understanding of everything from the trajectories of projectiles to the dynamics of celestial bodies.Closely related to the concept of motion is the phenomenon of force. Forces, whether they be gravitational, electromagnetic, or nuclear in nature, are the invisible agents that shape the physical world around us. The pull of gravity, the repulsion between like-charged particles, and the immense power of the strong nuclear force all play crucial roles in the functioning of the universe, from the formation of stars and galaxies to the stability of atomic nuclei.Another fundamental physical phenomenon is the concept of waves. Waves, whether they be sound waves, light waves, or even the ripples on the surface of a pond, are the means by which energy is transported through space and time. The study of wave phenomena has led to groundbreaking discoveries in fields ranging from acoustics to optics, enabling technologies such as wireless communication, medical imaging, and even the detection of gravitational waves from distant cosmic events.The behavior of matter, both at the macroscopic and microscopic scales, is another fascinating physical phenomenon. The way in whichmaterials respond to changes in temperature, pressure, and other environmental factors is a testament to the complex interactions between the atoms and molecules that make up the physical world. From the phase changes of water to the strange properties of superconductors, the study of matter and its behavior has been instrumental in the development of numerous technologies and the advancement of our scientific understanding.Perhaps one of the most profound physical phenomena is the concept of space and time. Einstein's theories of relativity have revealed that the fabric of the universe is not a static, immutable entity, but rather a dynamic, interconnected tapestry of space and time that can be warped and distorted by the presence of matter and energy. The implications of these theories have been far-reaching, from the prediction of black holes to the understanding of the origin and evolution of the universe itself.Ultimately, the physical phenomena that surround us are not just abstract concepts to be studied and understood, but rather the very building blocks of the world we inhabit. By delving deeper into the mysteries of energy, motion, force, waves, matter, and the nature of space and time, we gain a greater appreciation for the incredible complexity and beauty of the universe, and a deeper understanding of our own place within it. As we continue to explore and unravel the secrets of the physical world, we unlock new possibilities fortechnological advancement, scientific discovery, and a deeper understanding of the fundamental principles that govern our existence.。

Flow condensation heat transfer coefficients of pure refrigerants

Flow condensation heat transfer coeﬃcients of purerefrigerantsDongsoo Jung *,Kil-hong Song,Youngmok Cho,Sin-jong KimDepartment of Mechanical Engineering,Inha University,Incheon 402-751,South Korea Received 26March 2002;received in revised form 16August 2002;accepted 26August 2002AbstractFlow condensation heat transfer coeﬃcients (HTCs)of R12,R22,R32,R123,R125,R134a,and R142b were mea-sured experimentally on a horizontal plain tube.The experimental apparatus was composed of three main parts;a refrigerant loop,a water loop and a water-glycol loop.The test section in the refrigerant loop was made of a copper tube with an outside diameter of 9.52mm and 1m length.The refrigerant was cooled by cold water passing through an annulus surrounding the test section.All tests were performed at a ﬁxed refrigerant saturation temperature of 40 C with mass ﬂuxes of 100,200,300kg m À2s À1and heat ﬂux of 7.3–7.7kW m À2.Experimental results showed that ﬂow condensation HTCs increase as the quality and mass ﬂux increase.At the same mass ﬂux,the HTCs of R142b and R32are higher than those of R22by 8–34%while HTCs of R134a and R123are similar to those of R22.On the other hand,HTCs of R12and R125are lower than those of R22by 24–30%.Previous correlations predicted the present data satisfactorily with mean deviations of less than 20%substantiating indirectly the reliability of the present data.Finally,a new correlation was developed by modifying Dobson and Chato’s correlation with an introduction of a heat and mass ﬂux ratio combined with latent heat of condensation.The correlation showed a mean deviation of 10.7%for all pure halogenated refrigerants’data obtained in this study.#2002Elsevier Science Ltd and IIR.All rights reserved.Keywords:Refrigerant;Two-phase ﬂow;Condensation;Heat transfer coeﬃcient;Measurement;R12;R22;R32;R123;R125;R134a;R142bFrigorigenes purs :coeﬃcients de transfert de chaleur lors d’ecoulement en condensation Mots cle ´s :Frigorigene ;E coulement diphasique ;Condensation ;Coeﬃcient de transfert de chaleur ;Mesure ;R12;R22;R32;R123;R125;R134a ;R142b1.IntroductionRefrigerant vapor discharged from a compressor in refrigeration equipment is generally cooled and con-densed in a condenser via heat transfer to a secondary heat transfer ﬂuid such as air and water.If the condenserdoes not dissipate the heat well,the discharge pressure would build up resulting in an increase in compressor power.One way of increasing the condenser eﬀective-ness is to enlarge the size of condensers.This,however,may not necessarily be practical from the viewpoint of system maintenance and initial cost since more refriger-ant is to be charged.Therefore,the best way to design eﬀective condensers would be to keep the size as small as possible with special heat transfer enhancement mechanisms.For this it is important to know the ﬂow condensation heat transfer coeﬃcients (HTCs)of a0140-7007/03/$20.00#2002Elsevier Science Ltd and IIR.All rights reserved.P I I :S 0140-7007(02)00082-8International Journal of Refrigeration 26(2003)4–11/locate/ijrefrig*Corresponding author.Tel.:+82-32-860-7320;fax:+82-32-868-1716.E-mail address:dsjung@inha.ac.kr (D.Jung).workingﬂuid in a horizontal tube for air-cooled condensers.For the past few decades many researchers carried out ﬂow condensation heat transfer research but their workingﬂuids were mainly ozone depleting substances such as CFCs and HCFCs.Therefore,at present aﬂow condensation heat transfer correlation which can be applied not only to old refrigerants but also to new alternative ones is needed to design eﬀective condensers with an introduction of new alternativeﬂuids. Through much research eﬀorts,ﬂow condensation phenomenon in horizontal tubes is well understood and some correlations have been proposed.An excellent state of the review on condensation phenomenon asso-ciated withﬂuorocarbons is made by Thome in1997[1]. In1960,Akers and Rosson[2]suggested a correlation for refrigerants and organicﬂuids with an introduction of Reynolds number and in1968Soliman et al.[3] improved a Carpenter–Colburn’s correlation and pre-sented a correlation based upon the data of water, R113,ethanol,and methanol.In1973,Traviss et al.[4] introduced some dimensionless parameters with a use of momentum and heat transfer similarity and developed a correlation and compared it with the data for R12and R22and in1974Cavallini and Zecchin[5]suggested a semi empirical correlation based upon a heat and momentum similarity in annularﬂow regime.In1979, Shah[6]noted a similarity betweenﬂow condensation andﬂow boiling and took the convective evaporation contribution in aﬂow boiling correlation and suggested an empirical correlation based upon R11,R12and R22 data and in1985and1995Tandon et al.[7,8]suggesteda modiﬁed correlation from that of Akers and Rosson[2].In1987,Chen et al.[9]presented a general corre-lation for vertical annularﬂow condensation whose basic form is similar to that of Soliman et al.[3].In1994 and1998Dobson et al.[10]and Dobson and Chato[11] measuredﬂow condensation HTCs of R12and R134a and suggested an empirical correlation in annularﬂow regime which is similar to that of the convective eva-poration contribution in additive typeﬂow boiling correlations.Even though many researchers suggested various correlations,they all show a considerable deviation for many new refrigerants.It is partly due to the fact that most of the correlations were based upon a set of data for a few speciﬁcﬂuids and hence certain governing factors valid only for thoseﬂuids were mainly empha-sized in those correlations.Therefore,it is necessary to develop a correlation based upon a variety of data of manyﬂuids including new alternative refrigerants mea-sured from the same apparatus by a consistent method. The objectives of this work are to measureﬂow con-densation HTCs of low pressure refrigerant of R123, medium pressure refrigerants of R12,R134a,R142b and high pressureﬂuids of R22,R32,R125on a hor-izontal plain tube and to develop a general correlation which is able to predict the HTCs for both old and new halogenated refrigerants.2.Experiments2.1.ApparatusFig.1shows theﬂow condensation heat transfer experimental facility which is composed of a refrigerant loop,water loop for the constant temperature bath,and water/ethylene glycol loop for the chiller.The refriger-ant loop consisted of a magnetic type refrigerant pump,ﬁlter,massﬂow meter,pre-heater,calming section,main test section,plate type condenser,and accumulator.The D.Jung et al./International Journal of Refrigeration26(2003)4–115main test section was basically a double pipe heat exchanger of which the inner and outer tubes were made of copper tubes of 9.52and 19.05mm outside diameters,respectively.Refrigerant passed through the inner tube while water ﬂowed through the annulus in a counter current mode with a heat ﬂow from refrigerant to water.As seen in Fig.2,the length of the main test section was 1m and surface temperatures were measured at two locations,0.4and 0.7m from the refrigerant’s entrance of the test tube.At each location,four thermocouples were attached to the surface 90 apart at top,bottom,and two sides of the tube.To attach thermocouples,small slits on test tubes were prepared carefully without damaging the inner surface of test tubes and ﬁne ther-mocouples were ﬁrst soldered to the surface and later surrounded by epoxy such that bare thermocouple wires were not extruded to touch the water ﬂowing in the annulus.To measure refrigerant temperatures at the inlet and outlet of the test tube,RTDs of 0.01 C accuracy were used and a ﬁne pressure transducer and diﬀerential pressure transducer of 0.1%BFSL were used to measure the pressure at the inlet of the test section and pressure drop across the section,respectively.All ther-mocouples used in this study were T-type (copper-con-stantan)and were calibrated against a temperature calibrator of 0.01 C accuracy while the pressure trans-ducer was calibrated against a pressure calibrator of 0.1kPa accuracy.The heat output from the condensing refrigerant was taken away by water ﬂowing through the annulus of the test section.To determine the rate of heat transfer,the temperature diﬀerence in the water side across the test section was measured by a set of RTDs of 0.01 C accuracy.Mass ﬂow rates of both refrigerant and water were measured by precision mass ﬂow meters of 0.2%accuracy.The power input to the pre-heater was measured by a digital power meter of 0.1%accuracy.All data were collected by a computer controlled data logger.2.2.Experimental procedures and conditions1.A vacuum pump was turned on for 10h toevacuate the refrigerant loop thoroughly.2.Proper amount of refrigerant was charged to thesystem and a chiller for the condenser and water bath for the test section were turned on.3.A refrigerant pump was turned on to deliver adesired mass ﬂow rate.And then pre-heater power,mass ﬂow rate and temperature of water to the annulus of the test section were adjusted to desired values.4.When steady state was achieved,data weretaken for 30min at average refrigerant tem-perature in the test section of 40 C.For a given refrigerant ﬂow rate,the ﬁrst data were usually taken at qualities close to 10–20%.5.Power to the pre-heater was increased to gen-erate data at higher qualities for a given mass ﬂux.Steady state data were taken from the initial quality up to the maximum quality possi-ble with a typical quality interval of 12%.Thus for a given refrigerant ﬂow rate,a number of experiments were carried out to cover the over-all quality range of roughly 10–90%.2.2.1.Data reductionA pseudo local heat transfer coeﬃcient for the 1m test section was determined by Eq.(1).h ¼q =A ðÞT f ÀT s ðÞð1Þwhere h ,q ,A ,T f ,T s are the pseudo local heat transfer coeﬃcient (W m À2K À1),heat transfer rate from refrig-erant to water (W),heat transfer area (m 2),ﬂuid and surface temperature ( C)respectively.The heat transfer rate q was determined by measuring the mass ﬂow rate and temperature increase of water ﬂowing inside the annulus of the test section as in Eq.(2).q ¼m :w CP w T w ;out ÀT w ;inÀÁð2ÞFig.2.Schematic diagram of testsection.Fig.1.Schematic diagram of test apparatus.6 D.Jung et al./International Journal of Refrigeration 26(2003)4–11The average values of twoﬂuid temperatures at the inlet and outlet of the tube and eight surface tempera-tures at two thermocouple locations were substituted for T f and T s in Eq.(1)respectively.For all pure refriger-ants tested,the diﬀerence between the measuredﬂuid temperature and the saturation temperature corre-sponding to the measured pressure was close to0.1 C. The average quality changes across the1m test sec-tion were0.23,0.12,and0.077at massﬂuxes of100, 200,and300kg mÀ2sÀ1respectively for allﬂuids tested. The measurement errors were estimated by the method suggested by Kline and McClintock[12]and turned out to be less than4%for the plain tube.A single phase energy balance between the heat gain of the refrigerant and the heat loss of the water in the test section was checked and the average deviation between them was less than3.0%for all refrigerants tested.Inﬂow con-densation heat transfer,repeatability is very important and hence many measurements were taken repeatedly with an interval of one month for R22and R134a to check repeatability.Overall,repeatability was always within4%which was within the measurement errors. 3.Results and discussionIn this study,ﬂow condensation HTCs of low pres-sure refrigerant of R123,medium pressure refrigerants of R12,R134a,R142b and high pressure refrigerants of R22,R32,R125are measured on a horizontal plain copper tube of the outside diameter of9.52mm and1m length at the condensation temperature of40 C with massﬂuxes of100,200,and300kg mÀ2sÀ1and heat ﬂux of7.3–7.7kW mÀ2.In fact,these are the typical values encountered in air cooled condensers of residen-tial air-conditioners.Table1lists thermophysical prop-erties of the refrigerants tested at40 C which are calculated by REFPROP program[13].3.1.Eﬀect of massﬂux and quality on HTCsFigs.3and4showﬂow condensation HTCs as a function of quality for massﬂuxes of100and300kg mÀ2sÀ1while Fig.5shows the average HTCs obtained by integrating pseudo local HTCs over quality for a given massﬂux.As seen in theseﬁgures,ﬂow con-densation HTCs increase with quality and massﬂux. This is due to a reduction of thermal conduction resis-tance in the liquid layer caused by thinning of the liquid layer as well as an increase in momentum exchange as the massﬂux and quality increase.This is supported by Traviss et al.[4]who showed from the heat and momentum similarity that the shear stress at the liquid–vapor interface increases with an increase in momentum resulting in enhanced heat transfer.In fact,more refrig-erant vapor turns into liquid as the condensation pro-gresses and the velocity decreases resulting in decreases in both momentum and HTC.The rate of increase in HTCs with an increase in mass ﬂux in a low quality regime is relatively lower than that in a high quality regime.It is probably due to the forma-tion of wavyﬂow in low quality regime as explained by Dobson et al.[10].In the wavyﬂow regime,the grav-itational force becomes more important than the inertia force and hence thick liquid layer is formed in the bot-tom of the tube acting as a thermal barrier.Therefore, in the low quality regime,the increase in HTC due to an increase in massﬂux is somewhat cancelled by the thickened liquid layer resulting in a relatively smaller increase in HTC with an increase in massﬂux.Fig.5shows the relative magnitude of HTCs of var-ious pure refrigerants.For example,at massﬂux of200 kg mÀ2sÀ1average HTCs of R32and R142b are higher than those of R22by34and8%respectively while those of R125and R12are lower than those of R22by30and 24%respectively.On the other hand,those of R134a and R123are similar to those of R22.parison with correlationsFig.6and Table2show the comparison between the present data and some of the well known correlations. Correlations by Traviss et al.[4],Cavallini and Zecchin [5],Shah[6],Dobson and Chato[11]show mean devia-tions of16.9,17.9,15.1,and18.8%respectively with average deviations of less than8%.On the other hand,Table1Thermophysical properties of refrigerants tested at40 CP(kPa)v(m3kgÀ1) l(kg mÀ3)cp l(kJ kgÀ1KÀ1)cp v(kJ kgÀ1KÀ1)h fg(kJ kgÀ1)k l(mW mÀ1KÀ1) l(m Pa.s) R129590.0182354 1.0300.762129.7862.7171.6R2215340.0151128 1.338 1.009166.1679.8136.3R3224770.014839 2.163 2.001239.38122.598.0R1231540.1041424 1.0410.742165.4372.3358.1R12520100.0071089 1.630 1.23394.6853.2108.6R134a10170.0201146 1.500 1.120163.2375178.2R142b5250.0431069 1.3550.913189.9874.9202.1D.Jung et al./International Journal of Refrigeration26(2003)4–117correlations by Akers and Rosson [2],Soliman et al.[3]and Tandon et al.[7]show both larger mean and aver-age deviations of more than 15%.Since a deviation of about 20%in estimating the ﬂow condensation HTCs is quite acceptable,it can be said that most of the previous correlations seem to be satisfactory in estimating ﬂow condensation HTCs of a variety of halogenated refrig-erants including some of the newly developed HFCs.In fact,these results also indirectly substantiated the relia-bility of the present data.3.3.Development of new correlationFrom the above comparison,one can observe that these correlations are not generally applicable to all refrigerants tested in this work and there seems to be a room for improvement in estimation.Therefore,an attempt to develop a general correlation was made based on the present data by modifying one of the well known correlations.Among the correlations examined,Dobson and Cha-to’s [11]is one of the new empirical ones predicting the present data well with average and mean deviations of 2.7and 18.8%respectively.They developed this corre-lation based upon R12and R134a data under the assumption that the ratio of two phase HTC to single phase HTC is a function of a Martinelli’s parameter as expressed in Eq.(3).In fact,this is similar to the con-vective evaporation contribution term in ﬂow boiling correlation ﬁrst presented by Chen [14].Fig.3.Variation of HTCs of pure refrigerants as a function of quality at 100kg m À2s À1.Fig.4.Variation of HTCs of pure refrigerants as a function of quality at 300kg m À2s À1.parison of average HTCs of pure refrigerants as a function of massﬂux.Fig.6.Deviations of various correlations against the present data.8 D.Jung et al./International Journal of Refrigeration 26(2003)4–11h h l ¼1þ2:22tt!ð3Þtt¼1Àx0:9vl0:5lv0:1ð4Þh l¼0:23Re0:8l Pr0:4lk lDð5ÞRe l¼GD1ÀxðÞlð6ÞPr l¼ l CP lk lð7ÞDobson and Chato’s correlation generally under-predicts the present data in the low quality and mass ﬂux regime while it overpredicts in the high quality and massﬂux regime.In this study,ﬁrst of all Dobson and Chato’s approach is modiﬁed toﬁt the present data.Eq.(8)is the bestﬁt for all data with changes in constant and exponent as compared to Eq(3).h h l ¼1þ2:65tt!ð8ÞFig.7shows the comparison between the modiﬁedDobson and Chato’s correlation and the present data. The average and mean deviations are1.4and16.6%, respectively,showing a slight improvement over the original Dobson and Chato’s correlation.The general trend,however,is very similar to that of the original Dobson and Chato’s correlation.In order to improve the accuracy of the correlation some dimensionless parameters that might have a con-siderable inﬂuence onﬂow condensation heat transfer were examined.A data regression analysis showed that among many possible dimensionless parameters,a fac-tor combining heat and massﬂuxes with latent heat of condensation needs to be included in the correlation. This factor is well known and normally called a boiling number,Bo,in two-phaseﬂowﬁled.Even if it is called a boiling number,it is just a ratio of heatﬂux to massﬂux with latent heat of evaporation(condensation)con-sidered as shown in Eq.(9).Bo¼HFMR¼q=AðÞfgð9ÞSince this work is concerned withﬂow condensation, the same ratio is termed here as HMFR meaning a heat and massﬂux ratio with heat of condensation to avoid any misunderstanding.Finally a general correlation,Eq.(10),was developed with the dimensionless parameters in Eqs.(8)and(9)for all pure halogenated refrigerants tested in this study through a regression analysis.Table2Deviations of various correlations against the present dataFluid Akers andRosson[2]Solimanet al.[3]Travisset al.[4]Cavallini andZecchin[5]Shah[6]Tandonet al.[7]Dobson andChato[11]Avg.Mean Avg.Mean Avg.Mean Avg.Mean Avg.Mean Avg.Mean Avg.Mean R12À24.324.3À26.026.0À0.915.6 3.418.6À7.915.5À19.519.5 1.719.2 R22À27.127.1À31.731.7À7.216.8À4.017.9À15.018.7À20.220.2À7.520.5 R32À16.918.3À21.226.515.727.616.826.60.320.1À10.813.59.322.4 R123À12.314.1À11.614.3 2.912.112.518.1À2.59.2 2.58.218.122.6 R125À20.620.6À15.919.1 2.716.2 3.614.40.012.8À32.932.9À0.513.0 R134aÀ22.923.5À27.628.2À8.217.4À4.817.0À17.019.3À19.619.6À7.319.5 R142bÀ19.519.7À19.720.30.212.6 4.212.3À8.29.9À9.69.6 4.313.0 AllÀ20.421.0À22.123.90.716.9 4.517.9À7.515.1À15.017.0 2.718.8Average deviation¼1nX nlh calÀh expÀÁÂ100h exp!Mean deviation¼1nX nlABSh calÀh expÀÁÂ100h exp!:parison of the modiﬁed Dobson and Chato’scorrelation against the present data.D.Jung et al./International Journal of Refrigeration26(2003)4–119h h l ¼22:41þ2 tt0:81HFMR 0:33ð10ÞFig.8shows the comparison between the present data and a newly developed correlation.The newly developed correlation,Eq.(10),predicts the present data very well with average and mean deviations of À1.4and 10.7%,respectively.By introducing the heat and mass ﬂux ratio with latent heat of condensation,HMFR,the scatters at low quality and mass ﬂux regime and at high quality and mass ﬂux regime were well taken care of.From this result it can be said that the heat and mass ﬂux ratio with heat of condensation,HMFR,is an important parameter in estimating ﬂow condensation HTCs of halogenated refrigerants.4.ConclusionsIn this study,ﬂow condensation HTCs of low pres-sure refrigerant of R123,medium pressure refrigerants of R12,R134a,R142b and high pressure refrigerants of R22,R32,R125were measured on a horizontal smooth copper tube at the condensation temperature of 40 C with mass ﬂuxes of 100,200,and 300kg m À2s À1and heat ﬂux of 7.3–7.7kW m À2.From the measurements and correlation development following conclusions are drawn.1.Flow condensation HTCs increase as the qualityand mass ﬂux increase.At the same mass ﬂux,the HTCs of R142b and R32are higher than those of R22by 8–34%while HTCs of R134a and R123are similar to those of R22.On theother hand,HTCs of R12and R125lower than those of R22by 24–30%.2.Previous correlations predicted the present datasatisfactorily with mean deviations of less than 20%substantiating indirectly the reliability of the present data.3.A new correlation is developed by modifyingDobson and Chato’s correlation with an intro-duction of a well known factor in two phase ﬂow which takes into account the heat and mass ﬂuxes and latent heat of condensation.The correlation showed average and mean deviations of À1.4and 10.7%,respectively for all pure halogenated refrigerants’data.AcknowledgementsThis work was supported by the research grant No.R01–2000–000–00297–0from the Basic Research Pro-gram of the Korea Science and Engineering Founda-tion.Dr.D.P.Wilson at Buﬀalo Research Laboratory,Fluorine Products SBE,Honeywell International,Inc.(previously Allied Signal)supplied refrigerants needed for this research.References[1]Thome JR.Condensation of ﬂuorocarbon and otherrefrigerants:a state-of-the-art review (ARI report).Arlington,VA,USA,1997.[2]Akers WW,Rosson HF.Condensation inside a horizontaltube.Chem Eng Prog Symp Ser 1960;56:145–9.[3]Soliman HM,Schuster JR,Berenson PJ.A General heattransfer correlation for annular ﬂow condensation.J Heat Transfer 1968;90:167–76.[4]Traviss KP,Rohsenow WM,Baron AB.Forced convec-tion condensation in tubes:a heat transfer correlation for condenser design.ASHRAE Trans 1973;9(1):157–65.[5]Cavallini A,Zecchin R.A dimensionless correlation forheat transfer in forced convection condensation.Proceed-ings of the Fifth International Heat Transfer Conference 1974;3:309–13.[6]Shah M.A general correlation for heat transfer duringﬁlm condensation inside pipes.International Journal of Heat Mass Transfer 1979;22:547–56.[7]Tandon TN,Varma HK,Gupta CP.An experimentalinvestigation of forced convection condensation during annular ﬂow inside a horizontal tube.ASHRAE Trans 1985:343–54.[8]Tandon TN,Varma HK,Gupta CP.Heat transfer duringconvection condensation inside horizontal tube.Int J of Refrigeration 1995;18(3):210–4.[9]Chen SL,Gerner FM,Tien CL.General ﬁlm condensa-tion correlations.Experimental Heat Transfer 1987;1:93–107.[10]Dobson MK,Chato JC,Hinde DK,Wang SP.Experi-parison of the newly developed correlation against the present data.10 D.Jung et al./International Journal of Refrigeration 26(2003)4–11mental evaluation of internal condensation of refrigerants R12and R134a.ASHRAE Trans1994;100(1):744–55. [11]Dobson MK,Chato JC.Condensation in smooth hor-izontal tubes.ASME J Heat Transfer1998;120:193–213.[12]Kline SJ,McClintock FA.Describing uncertainties insingle sample experiments.Mechanical Engineering1953;75:3–8.[13]McLinden MO,Klein SA,Lemmon EW,Peskin AP.NIST thermodynamic and transport properties of refrig-erants and refrigerant mixtures.REFPROP version6.0;1998.[14]Chen J.Correlation for boiling heat transfer to saturatedﬂuids in convectiveﬂow.Ind Eng Chem Process Des Dev 1966;5(3):322–9.D.Jung et al./International Journal of Refrigeration26(2003)4–1111。

Size-shrinking of deuterons in very dilute superfluid nuclear matter

a r X i v :n u c l -t h /0011085v 1 24 N o v 2000Size-shrinking of deuterons in very dilute superﬂuid nuclear matter.U.Lombardo 1,2,P.Schuck 31Dipartimento di Fisica,57,Corso Italia,I-95129Catania,Italy2INFN-LNS,44,Via S.Soﬁa,I-95123Catania,Italy3Institut de Physique Nucl´e aire,Universit´e Paris-Sud,F-91406Orsay Cedex,France.It is shown within the strong-coupling BCS approach that,starting from the zero-density limit ofsuperﬂuid nuclear matter,with increasing density deuterons ﬁrst shrink before they start expanding.PACS Numbers :21.65.+f,74.20.FgThe crossover from Bose-Einstein Condensation (BEC)of bound fermion pairs in the low density limit to super-conductivity or superﬂuidity for higher densities is a very actively pursued ﬁeld of research,since for instance such phenomena may play a role in high T c superconductors [1].In a recent paper we have shown [2],using the strong-coupling BCS approach,that also in nuclear matter such a crossover may take place.Indeed deuterons are bound proton-neutron (p-n)pairs which may turn into p-n Cooper pairs at higher densities [2].In fact the situation in superﬂuid nuclear systems with ∆/ǫF ≈1/10,where ∆is an average gap value and ǫF the Fermi energy,rather resembles a strong coupling superconductor than the one of ordinary metals.In this note we will continue our previous work [2]and study the size of the deuterons or p-n Cooper pairs as a function of density.It is expected on arguments of general grounds that with increasing density,starting from the zero-density limit,the deuterons ﬁrst shrink before they expand [3].Indeed once the deuterons come on average close enough so that they start feeling the Pauli principle with their immediate neighbors they can avoid the increasing repulsion in reducing their spacial extension.Of course this cannot go on for ever and soon the deuterons will start overlapping,loosing their binding,and increase in size.It is very interesting that such a general feature is already contained in the BCS approach to superﬂuidity [3].Therefore we will present calculations of the coherence length of SD p-n pairing in symmetric nuclear matter based on the strong-coupling BCS approach.The interaction adopted in the gap equation is the Paris force projected into the SD channel,which reproduces quite well the experimental phase-shifts of p-n scattering as well as the deuteron binding energy.The single-particle energy ǫ(p )=p 2/2m +U (p )is calculated from the same Paris potential in the BHF approximation.The details of the procedure for solving the BCS equations are reported elsewhere [2].The coherence length is deﬁned by ξ2= d r r 2|ψ( r )|2 d p |˜ψ( p )|2(1)where ψ( r )=<c †( r )c †(0)>is the pairing function and ˜ψ( p )is the Fourier transform.Integration in momentum space is more suitable since the gap equation is solved in momentum space giving ∆( p )and then ˜ψ( p )=∆( p )/δE= ˜ψ∗0(p)U(p,p′)˜ψ0(p′)πp Fp Farctg(p F(−2mµ0).This energy correction makes the system more bound.One may also estimate from Eq.(4) the correction to the coherence length,which results inξ≈¯h2p0(1−8p30)(4)It is worth noticing that this result is in agreement with the one of Ref.[3],where also a linear dependence ofξon the density was found with zero-range force.In the derivation of Eq.(5)no assumption has been made on the force except that it gives a bound state at zero-density.At this point it may be appropriate to discuss under which circumstances one mayﬁnd a Bose-condensed gas of deuterons or a transition from p-n Cooper pairs to a Bose-Einstein condensation of deuterons.In theﬁrst place one may think of the far tail of density of heavier N≃Z nuclei like they are or will be produced in the new exotic nuclear beam facilities.In a region of densitiesρ20the radial distance from the centre of heavier nuclei is such that deuterons with r.m.s.of≃2fm(see ourﬁgure)can be easily accommodated in a Bose condensed state.This picture demands the validity of the local density approximation and to neglect quantumﬂuctuations.Both approximations are,of course,questionable forﬁnite nuclei but we know by experience that always something remains in a more correct treatment of those very simplifying assumptions.In this respect it could be very interesting to trigger on very peripheral nuclear reactions and to measure the yields of deuterons(or correlated p-n T=0pairs)with respect to uncorrelated nucleons.Also in expanding nuclear matter as it is produced in the late stage of central collisions with energies of E/A∼ǫF condensation phenomena in very low density nuclear matter could play a role.In this respect it should be noted that for densities where the chemical potential of the p-n pairs is negative,i.e.where there is Bose-Einstein condensation of deuterons the inﬂuence of the Pauli principle due to additional neutrons(asymmetric case)should be minimal.This has been conﬁrmed by recent numerical calculations[5].In conclusion we have shown that in a very diluted superﬂuid gas of deuterons the deuterons as a function of densityﬁrst shrink by∼35%before they start expanding again.This relatively large eﬀect is due to the Pauli principle which is fully respected in the BCS approach.The investigation has been performed at T=0.The extension toﬁnite temperature and to asymmetric matter is on the way.。

Review of Recent Advances in Electrically Conductive Adhesive

This article was downloaded by: [Shanghai University]On: 04 June 2015, At: 17:27Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UKJournal of Adhesion Science andTechnologyPublication details, including instructions for authors and subscriptioninformation:/loi/tast20Review of Recent Advances in ElectricallyConductive Adhesive Materials andTechnologies in Electronic PackagingMyung Jin Yim a , Yi Li b , Kyoung-sik Moon c , Kyung Wook Paik d & C. P.Wong ea School of Materials Science and Engineering, Georgia Institute ofT echnology, 771 Ferst Drive, Atlanta, GA 30332-0245b School of Materials Science and Engineering, Georgia Institute ofT echnology, 771 Ferst Drive, Atlanta, GA 30332-0245c School of Materials Science and Engineering, Georgia Institute ofT echnology, 771 Ferst Drive, Atlanta, GA 30332-0245d Materials Science and Engineering, Korea Advanced Institute of Scienceand T echnology, 373-1, Kusong-dong, Yusong-gu, T aejon, Korea 305-701e School of Materials Science and Engineering, Georgia Instituteof T echnology, 771 Ferst Drive, Atlanta, GA 30332-0245;, Email:cp.wong@Published online: 02 Apr 2012.PLEASE SCROLL DOWN FOR ARTICLETaylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.This article may be used for research, teaching, and private study purposes. Any substantialor systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, orD o w n l o a d e d b y [S h a n g h a i U n i v e r s i t y ] a t 17:27 04 J u n e 2015Journal of Adhesion Science and Technology 22(2008)1593–1630www.brill.nl/jast Review of Recent Advances in Electrically Conductive Adhesive Materials and Technologies in Electronic Packaging Myung Jin Yim a ,Yi Li a ,Kyoung-sik Moon a ,Kyung Wook Paik b and C.P.Wong a ,∗a School of Materials Science and Engineering,Georgia Institute of Technology,771Ferst Drive,Atlanta,GA 30332-0245b Materials Science and Engineering,Korea Advanced Institute of Science and Technology,373-1,Kusong-dong,Yusong-gu,Taejon,Korea 305-701Abstract Electrically Conductive Adhesives (ICAs:Isotropic Conductive Adhesives;ACAs:An-isotropic Conduc-tive Adhesives;and NCAs:Non-conductive Adhesives)offer promising material solutions for ﬁne pitch interconnects,low cost,low-temperature process and environmentally clean approaches in the electronic packaging technology.ICAs have been developed and used widely for traditional solder replacement,es-pecially in surface mount devices and ﬂip chip application.These also need to be lower cost with higher electrical/mechanical and reliability performances.ACAs have been widely used in ﬂat panel display mod-ules for high resolution,lightweight,thin proﬁle and low power consumption in ﬁlm forms (Anisotropic Conductive Films:ACFs)for last decades.Multi-layered ACF structures such as double and triple-layered ACFs were developed to meet ﬁne pitch interconnection,low-temperature curing and strong adhesion re-quirements.Also,ACAs have been attracting much attention for their simple and lead-free processing as well as cost-effective packaging method for semiconductor packaging applications.High mechanical re-liability,good electrical performance at high frequency level and effective thermal conductivity for high current density are some of required properties for ACF materials to be pursued for a wide usage in ﬂip chip technology.Recently,NCAs are becoming promising for ultra-ﬁne pitch interconnection and low cost joining materials in electronic packaging applications.In this paper,an overview of the recent developments and applications of electrically conductive adhesives for electronic packaging with focus on ﬁne pitch capability,electrical/mechanical/thermal performance andwafer level packaging application is presented.©Koninklijke Brill NV ,Leiden,2008KeywordsElectrically conductive adhesives,ICA,ACA,NCA,electronic packaging,ﬁne-pitch joint,ﬂat panel dis-play,ﬂip chip,reliability,wafer-level packaging*To whom correspondence should be addressed.Tel.:404-894-2846;Fax:404-894-9140;e-mail:cp.wong@©Koninklijke Brill NV ,Leiden,2008DOI:10.1163/156856108X320519D ow nloa dedby[ShanghaiUnivers ity]at17:274June2151594M.J.Yim et al./Journal of Adhesion Science and Technology 22(2008)1593–1630Figure 1.A typical percolation curve showing the abrupt increase in conductivity at the percolation threshold.1.Introduction Today,resin based interconnection materials for electronic packaging and intercon-nection technologies are widely used in manufacturing of electronic devices such as ﬂat panel displays and semiconductor/system package modules [1].They are attrac-tive as traditional solder alternative due to advantages of low-temperature and low cost process,ﬁner pitch capability and environmentally clean solutions.Electrically conductive adhesives are generally composite materials composed of on insulating adhesive binder resin and a conductive ﬁller.Depending on the conductive ﬁller loading level,they are divided into ICAs,ACAs or NCAs.The differences based on the percolation theory between an ICA and an ACA/NCA is shown in Fig.1.For an ICA,the electrical conductivity is provided in all x -,y -and z -directions due to high ﬁller content,exceeding the percolation threshold.For an ACA or NCA,the electrical conductivity is provided only in the z -direction between the electrodes of the assembly.Figure 2shows the schemat-ics of the interconnect structures and typical cross-sectional images of ﬂip chipjoints by ICA,ACA and NCA materials illustrating the bonding mechanism for all three adhesives.Especially,ICA materials,typically silver-ﬁlled conductive adhe-sives,have been recommended as solder replacement materials in a surface mount technology (SMT),ﬂip chip,chip scale package (CSP)and ball grid array (BGA)applications.There are still challenging technical issues for full commercialization of ICAs such as low conductivity and reliability,high material cost,and poor impact strength,etc.and extensive research is being performed to enhance the electrical performance and reliability of adhesive joints [2–6].Interconnection technologies using ACFs are major packaging methods for ﬂat panel display modules with high resolution,lightweight,thin proﬁle and low con-sumption power [7],and have already been successfully implemented in the forms of Outer Lead Bonding (OLB),ﬂex to PCB bonding (PCB),reliable direct chipD ow nloa dedby[ShanghaiUnivers ity]at17:274June215M.J.Yim et al./Journal of Adhesion Science and Technology 22(2008)1593–16301595Figure 2.Schematic drawings and cross-sectional views of (a,b)ICA,(c,d)ACA and (e,f)NCA ﬂip chip bonding.attach such as Chip-On-Glass (COG),Chip-On-Film (COF)for ﬂat panel dis-play modules [8–11],including liquid crystal display (LCD),plasma display panel (PDP)and organic light emitting diode display (OLED).As for the small and ﬁne pitched bump of driver ICs to be packaged,ﬁne pitch capability of ACF intercon-nection is much more desired for COG,COF and even OLB assemblies.There have been advances in development works for improved material systems and design rules for ACF materials to meet ﬁne pitch capability and better adhesion char-acteristics of ACF interconnection for ﬂat panel displays.Alternative resin based interconnection materials such as anisotropic conductive pastes (ACPs)and non-conductive ﬁlms/pastes (NCFs/Ps)have been developed and introduced due to their advantages in terms of process,cost and ultra-ﬁne pitch capability where a conven-tional ACF has limitations.It is obvious that electrically conductive adhesive materials are required for ad-vanced packaging materials,but formulation,material design and process should be optimized and developed for high electrical,mechanical and thermal performance as well as enhanced reliability performance.In this paper,an overview on recent issues,developments and applications of conductive adhesives for electronic packaging applications with ﬁne pitch capabil-ity,high electrical,mechanical,and reliability performance,and wafer level ﬂip chip package applications is presented.2.Isotropic Conductive Adhesives (ICAs)for Electronic PackagingICAs are being used to replace the traditional eutectic SnPb solder alloys in elec-tronic packaging and interconnects.They are composites of polymer resins andD ow nloa dedby[ShanghaiUnivers ity]at17:274June2151596M.J.Yim et al./Journal of Adhesion Science and Technology 22(2008)1593–1630Figure 3.Schematic structures of (a)surface mount interconnection using ICA and (b)ﬂip chip inter-connection using ICA.conductive ﬁllers.The polymer resins,thermoplastic or thermosetting resins,are generally cured at high temperature and provide the shrinkage force,adhesion strength,and chemical and corrosion resistances.Epoxy,cyanate ester,silicone,polyurethane are thermosetting resins,and phenolic epoxy,polyimide are common thermoplastics for an ICA matrix resin.Conductive ﬁllers include silver (Ag),gold (Au),nickel (Ni),copper (Cu)and Sn,SnBi or SnIn coated Cu in various sizes and shapes.Ag is the most common conductive ﬁller for an ICA due to its high con-ductivity and easy processing,but its high cost is one of drawbacks for wide use of Ag-ﬁlled ICAs.ICAs have been used for die attach adhesives [12,13],adhe-sives for SMT [14,15],and ﬂip chip [16]and other applications.Figure 3shows the schematics of SMT components and ﬂip chip devices interconnected by ICAs instead of solder alloy.2.1.ICAs for Surface Mount TechnologiesSurface-mount technology (SMT)is the main technique for interconnecting chip components to substrate by packing and placing the components on the printed circuit board and using the reﬂow furnace to melt the solder alloy for the elec-tronic system interconnection.Tin–lead (Sn–Pb)solder has been exclusively used as the interconnection material in surface-mount technology,because current com-mercial ECAs,in spite of their numerous advantages,cannot be used as drop-in replacements for solder in all applications due to some challenging issues.Due to the extreme toxicity of lead and legislations for lead-free electronics,world-wide efforts have been put in the study of ICAs.Signiﬁcant progress has been made to address different materials properties and reliability issues for the development of high performance ICAs as a potential replacement for lead-containing solders in SMT application as well.D ow nloa dedby[ShanghaiUnivers ity]at17:274June215M.J.Yim et al./Journal of Adhesion Science and Technology 22(2008)1593–163015972.2.ICAs for Flip Chip Interconnects Isotropic conductive adhesive materials use much higher loading than ACAs to give electrical conduction isotropically or in all directions throughout the material.In or-der for these materials to be used for ﬂip chip applications,it is necessary to apply them selectively onto those areas which are to be electrically interconnected,and to ensure that spreading of the materials does not occur during placement or cur-ing which would cause electrical shorts between the separate pathways.ICAs are generally supplied in paste form.To precisely deposit the ICA paste,screen or sten-cil printing is most commonly used.However,to do this to the scale and accuracy required for ﬂip chip bonding would require very accurate pattern alignment.To overcome this requirement,the transfer method may be used.For this technique,raised studs or pillars are required on either the die or the substrate.The ICA is then selectively transferred to the raised area by contacting the face of the die or the sub-strate to a ﬂat thin ﬁlm of the ICA paste.This thin ﬁlm may be produced by screen printing and the transfer thickness may be controlled by controlling the printed ﬁlm thickness.This method conﬁnes the paste to the area of the contact surfaces and the quantity may be adequately controlled so as to prevent spreading between pathways when the die is placed.Pressure during bonding is not required in this technique,which gives the option of oven curing the assembly.In a high volume environment,the high precision screen printing techniques to print the ICA paste directly onto the I/O pads of the substrate can be used.This would remove the requirement for stud pillars on the substrate track terminations and also quite possibly the need for bumping of the ﬂip chip pads.Once such a process is in place,the ICA technique could then compete with the ACA method on the basis of speed and ease of processing,however,substantial improvements in bond strength will need to be made before the technique can be realistically consid-ered.Unlike ACA ﬂip chip bonding,however,a separate underﬁlling step would be required with ICA ﬂip chip bonding to improve long-term reliability of the bond.It is shown that reliability is quite good with ICA ﬂip chip joining on rigid substrates [17].The difﬁculties with the ICA ﬂip chip joining technology are the poor proces-sibility and small process window in handling of the ﬂip chip module directly afterassembly.Although there are many technical advantages of ICAs compared with traditional solder materials,current ICAs still have some limitations on the electrical,thermal,and reliability properties compared with SnPb solders for full replacement for sol-der.Table 1shows a general comparison of various properties between SnPb solders and conventional ICAs [18].Therefore,much research effort has been focused on the improvement of electrical conductivity of ICAs and reliability enhancement of ICA joints,electrically and mechanically.Also the replacement of expensive Ag ﬂakes by new metal ﬂakes is required for wide use of ICAs instead of solder mate-rials.Copper can be a conductive ﬁller metal due to its low resistivity,low cost and improved electromigration performance,but oxidation causes this metal to lose its conductivity [19].D ow nloa dedby[ShanghaiUnivers ity]at17:274June2151598M.J.Yim et al./Journal of Adhesion Science and Technology 22(2008)1593–16302.3.Electrical Conductivity Improvement of ICAs To enhance the electrical conductivity of metal-ﬁlled ICAs,polymer-metal compos-ite properties are controlled and maximized.Typically,increasing cure shrinkage of matrix polymer binder [20],the intimate metallic contacts by removal of lu-bricant layer on Ag ﬂakes [21],and oxidation layer removal [22],metallurgical bonding between the conductive particles by low melting point alloy coating on Cu powder [23,24]are representative methods for improvement of ICA conduc-tivity.Recently,nano-sized Ag particles are added as conductive ﬁllers instead of highly loaded micro-sized Ag ﬂakes and the electrical conductivity is enhanced by sintering nano-sized Ag ﬁllers [25].2.3.1.Increase of Polymer Matrix Shrinkage In general,ICA pastes exhibit insulative property before cure,but the conductivity increases dramatically after curing.ICAs achieve electrical conductivity during the polymer curing process caused by the shrinkage of polymer binder.Accordingly,ICAs with high cure shrinkage generally exhibit higher conductivity.Table 2shows the relationship between shrinkage and conductivity for three different cross-link density ECAs,ECA1,ECA2and ECA3[26].With increasing cross-link density of ECAs,the shrinkage of the polymer matrix increased,and,consequently,an obviously decreased resistivity of ECAs was observed.Therefore,increasing the cure shrinkage of the polymer binder could improve electrical conductivity.For epoxy-based ICAs,a small amount of a multi-functional epoxy resin can be added Table parison between a Conductive Adhesive and Eutectic Solders [18]Characteristic SnPb solder ICA V olume resistivity ( cm)0.0000150.00035Typical junction resistance (m )10–15<25Thermal conductivity (W/mK)30 3.5Shear strength (psi)15.2MPa 13.8MPaMin.processing temperature (◦C)215150–170Environmental impact Negative Very minor Table 2.Relationship of shrinkage and electrical conductivity of ECAs [27]Formulation Crosslink density Shrinkage Bulkresistivity(10−3mol/cm 3)(%)(10−3 cm)ECA1 4.50 2.98 3.0ECA2 5.33 3.75 1.2ECA3 5.85 4.330.58D ow nloa dedby[ShanghaiUnivers ity]at17:274June215M.J.Yim et al./Journal of Adhesion Science and Technology 22(2008)1593–16301599into the ICA formulation to increase cross-link density,shrinkage,and thus increase electrical conductivity.2.3.2.In Situ Removal of Lubricant on Ag Flakes An ICA is generally composed of a polymer binder and Ag ﬂakes.There is a thin layer of organic lubricant on the Ag ﬂake surface.This lubricant layer plays an im-portant role for the performance of ICAs,including the dispersion of the Ag ﬂakes in the adhesives and the rheology of the adhesive formulations [21,28–30].This organic lubricant layer,typically a fatty acid such as stearic acid,forms a silver salt complex between the Ag surface and the lubricant [21].However,this lubri-cant layer affects conductivity of an ICA because it is electrically insulating.To improve conductivity,the organic lubricant layer should be partially or fully re-moved or replaced during the curing of ICA.A suitable lubricant remover is a short chain dicarboxylic acid because of the strong afﬁnity of carboxylic functional group (–COOH)with silver and stronger acidity of such short chain dicarboxylic acids.With the addition of only a small amount of short chain dicarboxylic acid,the conductivity of an ICA can be improved signiﬁcantly due to the easier electronic tunneling/transport by the intimate ﬂake–ﬂake contacts in the Ag ﬂake networks [25,31].2.3.3.Incorporation of Reducing Agents Silver ﬂakes are by far the most used ﬁllers for conductive adhesives due to the high conductivity of silver oxide compared to other metal oxides,most of which are in-sulative.However,the conductivity of silver oxide is still inferior to metal itself.Therefore,incorporation of reducing agents would further improve the electrical conductivity of ICAs.Aldehydes were introduced into a typical ICA formulation and obviously improved conductivity was achieved due to reaction between alde-hyde and silver oxide that exists on the surface of metal ﬁllers in ECAs during the curing process:R–CHO +Ag 2O →R–COOH +2Ag .(1)The oxidation product of aldehydes,carboxylic acids,which are stronger acidsand have shorter molecular length than stearic acid,can also partially replace or remove the stearic acid on Ag ﬂakes and contribute to the improved electrical con-ductivity [22].2.3.4.Low-Temperature Transient Liquid Phase FillersAnother approach for improving electrical conductivity is to incorporate transient liquid-phase metallic ﬁllers in ICA formulations.The ﬁller used is a mixture of a high-melting-point metal powder (such as Cu)and a low-melting-point alloy pow-der (such as Sn–Pb or Sn–In).The low-melting-alloy ﬁller melts when its melting point is reached during the cure of the polymer matrix.The liquid phase dissolves the high melting point particles.The liquid exists only for a short period of time and then forms an alloy and solidiﬁes.The electrical conduction is established throughD ow nloa dedby[ShanghaiUnivers ity]at17:274June2151600M.J.Yim et al./Journal of Adhesion Science and Technology 22(2008)1593–1630Figure 4.Schematic of an ECA joint with metallurgical connections in conductive ﬁller network by transient liquid phase sintering.a plurality of metallurgical connections in situ formed from these two powders in the polymer binder (Fig.4).The polymer binder with an acid functional ingredient ﬂuxes both the metal pow-der and the metals to be joined and facilitates the transient liquid bonding of the powders to form a stable metallurgical network for electrical conduction,and also forms an interpenetrating polymer network providing adhesion.High electrical con-ductivity can be achieved using this method [32,33].2.3.5.Low-Temperature Sintering of Nano-silver Fillers Recently,nano-sized conductive particles have been proposed as conductive ﬁllers in ICAs for ﬁne pitch interconnects.Although the nano-silver ﬁllers in ICAs can reduce the percolation threshold,there has been concern that incorporation of nano-sized ﬁllers may introduce more contact spots due to high surface area and consequently induce higher resistivity compared to micro-sized ﬁllers.A recent study showed that nano-silver particles could exhibit sintering behavior at curing temperature of ICAs [34].Typically,application of nano-ﬁllers increases the con-tact resistance and reduces the electrical performance of the ICAs.The numberof contacts between the small particles is larger than that between the large parti-cles.The overall resistance of an isotropic conductive adhesive (ICA)formulation is the sum of the resistance of ﬁller,the resistance between ﬁller particles,and the resistance between ﬁller and pads (equation (2)).In order to decrease the overall contact resistance,the reduction of the number of contact points between the par-ticles may be obviously effective.If nano-particles are sintered together,then the number of contacts between ﬁller particles will be fewer.This will lead to smaller contact resistance.By using effective surfactants on these nano-sized silver ﬁllers for better ﬁller dispersion in ECAs,obvious sintering behavior of the nano-ﬁllers can be achieved.The sintering of nano-silver ﬁllers improved the interfacial prop-erties of conductive ﬁllers and polymer matrices,and reduced the contact resistance between ﬁllers.Therefore,an improved electrical conductivity of nano-silver-ﬁlled D ow nloa dedby[ShanghaiUnivers ity]at17:274June215M.J.Yim et al./Journal of Adhesion Science and Technology 22(2008)1593–16301601ICAs can be achieved at a lower loading level than that of micro-ﬁller-ICAs with a ﬁller loading of 80wt%or higher:R total =R btw ﬁllers +R ﬁller to bond pad +R ﬁllers .(2)2.4.Reliability Enhancements of ICA Interconnects Critical reliability concerns of ICA joints in electronic packaging applications are mainly due to unstable contact resistance between ICA and metal ﬁnished compo-nents under environmental attacks,such as humidity and temperature cycling/aging.For high temperature and humidity aging environment,the galvanic corrosion rather than simple thermal oxidation at the interface between metallic ﬁllers in ICA and non-noble metal ﬁnish is known as the most detrimental underlying mechanism for unstable contact resistance [35].Therefore,most research works for improving the stability of electrical conductivity of ICA joints have focused on the methods to avoid or minimize the unstable contact resistance mechanism of ICA joints.Sev-eral possible methods are:development of polymer matrix resin with low moisture absorption [36],use of oxygen scavengers [35]and corrosion inhibitors [36]in the ICA formulation,the corrosion control by adding metal ﬁllers with low cor-rosion potential,sacriﬁcial anode [37],and oxide-penetrating particles in the ICA formulation [38].Also,for the reliability improvement of Ag-based ICA joints,Ag migration is most serious concern.Several methods are proposed to reduce Ag migration and improve the reliability of ICA joints such as Ag alloying with an an-odically stable metal [39],hydrophobic polymer coating over the PWB [40],surface coating of tin,nickel,gold or organic compounds on silver particles.2.4.1.ICA With Low Moisture Absorption Moisture in polymer composites has been known to have an adverse effect on both mechanical and electrical properties of epoxy laminates [41,42].Effects of moisture absorption on conductive adhesive joints include degradation of bulk me-chanical strength;decrease of interfacial adhesion strength causing delamination;promoting the growth of voids present in the joints,giving rise to swelling stress in the joints;and inducing the formation of metal oxide layers resulted from corrosion.The water condensed from the adsorbed moisture at the interface between an ECA and metal surface forms the electrolyte solution required for galvanic corrosion.Therefore,one way to prevent galvanic corrosion at the interface between an ICA and the non-noble metal surface and achieve high reliability is to select ICAs with lower moisture absorption.ICAs with a low moisture absorption generally exhibit more stable contact resistance on non-noble metal surfaces compared with those with high moisture absorption [36].2.4.2.ICA With Oxygen ScavengersSince oxygen accelerates galvanic corrosion,oxygen scavengers could be added into ECAs to slow down the corrosion rate [35].When ambient oxygen molecules diffuse through the polymer binder,they react with the oxygen scavenger and are consumed.The main mechanism for oxygen scavengers to inhibit the corrosionD ow nloa dedby[ShanghaiUnivers ity]at17:274June2151602M.J.Yim et al./Journal of Adhesion Science and Technology 22(2008)1593–1630Figure 5.Shifts of contact resistance of conductive adhesives on Sn/Pb surface with and without oxygen scavengers.is the cathodic mechanism which is based on the lowering of oxygen concentra-tion.Therefore,the reactivity of an oxygen scavenger with oxygen is an impor-tant consideration.Some commonly used oxygen scavengers include sulfates such as sodium sulfate (Na 2SO 4),hydrazine (H 2N–NH 2),carbohydrazide (H 2N–NH–CO–NH–NH 2),diethylhydroxylamine ((C 2H 5)2N–OH),and hydroquinone (HO–C 6H 4–OH)[43–46].Figure 5shows the effect of oxygen scavengers on the contact resistance between an ICA and a Sn/Pb surface.The application of oxygen scav-engers reduces the contact resistance increase obviously,especially in the ﬁrst 200h test time.However,with continuing aging test when the oxygen scavenger within the ECA is depleted,oxygen can again diffuse into the interface and accelerate the corrosion process.Therefore,oxygen scavengers can only delay the galvanic cor-rosion process,but do not solve the corrosion problem completely.2.4.3.ICA With Corrosion Inhibitors Another method of preventing galvanic corrosion and stabilizing contact resistanceis the use of corrosion inhibitors in ICA formulations [35,36,47,48].In general,organic corrosion inhibitors are chemicals that adsorb on metal surfaces and act as a passivation barrier layer between the metal and the environment by forming an in-ert ﬁlm over the metal surfaces [49–52].Thus,the metal ﬁnishes can be protected.Some chelating compounds are especially effective in preventing metal corrosion[51].Appropriate selection of corrosion inhibitors can be very effective in protect-ing the metal ﬁnishes from corrosion.However,the effectiveness of the corrosion inhibitors is highly dependent on the types of contact surfaces.Effective corrosion inhibitors have been discovered for Sn/Pb,Cu,Al and Sn surfaces [35,47,53].2.4.4.ICA With Sacriﬁcial AnodeTo improve the contact resistance stability,applying a sacriﬁcial anode is another efﬁcient method.For galvanic corrosion of ECAs during aging,the larger the dif-D ow nloa dedby[ShanghaiUnivers ity]at17:274June215。

地球物理研究英语作文

地球物理研究英语作文Title: Advancements in Geophysical Research。

Geophysical research plays a crucial role in understanding the Earth's structure, dynamics, and processes. With the continuous advancement in technology and methodologies, geophysical research has undergone significant developments, contributing to various fields such as geology, environmental science, and natural resource exploration. This essay will explore some of the key advancements in geophysical research and their implications.One of the notable advancements in geophysical research is the development of advanced imaging techniques such as seismic tomography and ground-penetrating radar (GPR). Seismic tomography utilizes seismic waves generated by earthquakes or controlled explosions to create detailed images of the Earth's interior. By analyzing the velocity and propagation of seismic waves, researchers can infer thedistribution of geological features such as faults, magma chambers, and variations in rock composition. This technology has revolutionized our understanding of tectonic plate movement, earthquake mechanisms, and volcanic activity.Similarly, ground-penetrating radar has emerged as a powerful tool for subsurface imaging in variousapplications ranging from archaeology to civil engineering. By transmitting electromagnetic pulses into the ground and recording the reflected signals, GPR systems can create high-resolution images of subsurface structures such as buried artifacts, archaeological sites, and underground utilities. This non-invasive technique has significantly enhanced our ability to study the Earth's subsurface without the need for destructive excavation.Another significant advancement in geophysical research is the integration of satellite-based remote sensing technologies. Satellites equipped with sensors capable of detecting electromagnetic radiation across different wavelengths have revolutionized our ability to monitorchanges in the Earth's surface and atmosphere. For example, satellite-based gravimetry allows researchers to map variations in the Earth's gravitational field with unprecedented accuracy, enabling the study of processessuch as glacier movement, groundwater depletion, andtectonic deformation.Furthermore, the development of advanced numerical modeling techniques has enabled researchers to simulate complex geophysical processes with high precision. Computational models based on principles of physics, chemistry, and fluid dynamics can simulate phenomena suchas mantle convection, magma migration, and groundwater flow. These models provide valuable insights into the behavior of Earth systems and can help predict future changes in response to natural or anthropogenic factors.In addition to technological advancements,collaborations between multidisciplinary teams have become increasingly important in geophysical research.Collaborative efforts involving geophysicists, geologists, engineers, and computer scientists have led to innovativeapproaches for data acquisition, analysis, and interpretation. By combining expertise from different fields, researchers can tackle complex problems more effectively and develop holistic solutions to real-world challenges.The implications of these advancements in geophysical research are profound. Improved understanding of theEarth's structure and processes not only enhances our knowledge of fundamental geoscience principles but also has practical applications in areas such as natural hazard assessment, resource exploration, and environmental monitoring. For example, seismic hazard maps generated from geophysical data can inform land-use planning and disaster preparedness efforts in earthquake-prone regions. Similarly, geophysical surveys play a crucial role in locating mineral deposits, groundwater resources, and hydrocarbon reservoirs, supporting sustainable development and resource management initiatives.In conclusion, geophysical research has witnessed significant advancements in recent years, driven bytechnological innovation, interdisciplinary collaboration, and the growing demand for solutions to global challenges. These advancements have expanded our understanding of the Earth's dynamics and have practical implications across various fields. As we continue to push the boundaries of geophysical exploration, it is essential to foster collaboration, invest in technology development, and promote the responsible use of geophysical data for the benefit of society and the environment.。

physical review letters模板 -回复

physical review letters模板-回复"[physical review letters模板]，以中括号内的内容为主题，写一篇1500-2000字文章，一步一步回答"Title: Understanding the Quantum Tunneling Phenomenon: A Physical Review LettersAbstract:In this paper, we delve into the intriguing concept of Quantum Tunneling, a fundamental phenomenon in quantum mechanics. We explore the theoretical background, experimental evidence, and potential applications of quantum tunneling. By utilizing the format of Physical Review Letters, we present a comprehensive analysis of this captivating topic.1. IntroductionQuantum tunneling refers to the remarkable ability of particles to pass through energy barriers that classical physics would deem impassable. This phenomenon is a direct consequence of the wave-particle duality intrinsic to quantum mechanics. The aim of this article is to unravel the underlying principles behind quantum tunneling and shed light on its profound implications for variousfields of science.2. Theoretical BackgroundTo understand quantum tunneling, we need to first comprehend the Schrödinger equation, which describes the behavior of quantum systems. This equation reveals that particles possess wave-like properties, allowing them to exist in a superposition of states. Furthermore, the Heisenberg uncertainty principle states that the more precisely we know a particle's position, the less certain we are about its momentum.3. Barrier PenetrationThe concept of tunneling emerges when particles encounter an energy barrier. According to classical physics, particles with insufficient energy to overcome the barrier should be completely reflected. However, in quantum mechanics, particles possess wave functions that extend beyond the classical boundaries. Consequently, there is a finite probability for them to penetrate the barrier and appear on the other side.4. Experimental EvidenceExperimental verification of quantum tunneling has been achievedin a variety of areas. For instance, the scanning tunneling microscope has allowed scientists to observe the tunneling of electrons between a conducting tip and a surface, enabling atom manipulation with atomic precision. Additionally, experiments involving tunneling of cold atoms through Bose-Einstein condensates have provided direct evidence of quantum tunneling phenomena.5. ApplicationsQuantum tunneling has numerous applications across diverse scientific disciplines. In the field of electronics, the phenomenon is utilized in the creation of tunneling diodes and transistors, enabling faster and more efficient electronic devices. Tunneling is also pivotal in nuclear fusion, where particles need to overcome the Coulomb barrier to initiate fusion reactions. Moreover, quantum tunneling plays a crucial role in the functioning of enzymes in biological systems.6. Quantum Tunneling in AstrophysicsQuantum tunneling also influences astrophysical phenomena. For instance, nuclear reactions within stars rely on tunneling to overcome the barriers inherent in fusion processes. Additionally,tunneling is vital in explaining the phenomenon of stellar nucleosynthesis, where the synthesis of heavier elements occurs through fusion reactions.7. ConclusionQuantum tunneling is a captivating aspect of quantum mechanics, challenging classical notions of energy barriers. Through a thorough examination of its theoretical foundations, experimental observations, and diverse applications, we have explored the fundamental concepts of quantum tunneling. This phenomenon has revolutionized various scientific realms, from electronics to astrophysics, and continues to be an area of active research and exploration.。

中国诺奖级别新科技—量子反常霍尔效应英语

中国诺奖级别新科技—量子反常霍尔效应英语全文共6篇示例，供读者参考篇1The Magical World of Quantum PhysicsHave you ever heard of something called quantum physics? It's a fancy word that describes the weird and wonderful world of tiny, tiny particles called atoms and electrons. These particles are so small that they behave in ways that seem almost magical!One of the most important discoveries in quantum physics is something called the Quantum Anomalous Hall Effect. It's a mouthful, I know, but let me try to explain it to you in a way that's easy to understand.Imagine a road, but instead of cars driving on it, you have electrons zipping along. Now, normally, these electrons would bump into each other and get all mixed up, just like cars in a traffic jam. But with the Quantum Anomalous Hall Effect, something special happens.Picture a big, strong police officer standing in the middle of the road. This police officer has a magical power – he can makeall the electrons go in the same direction, without any bumping or mixing up! It's like he's directing traffic, but for tiny particles instead of cars.Now, you might be wondering, "Why is this so important?" Well, let me tell you! Having all the electrons moving in the same direction without any resistance means that we can send information and electricity much more efficiently. It's like having a super-smooth highway for the electrons to travel on, without any potholes or roadblocks.This discovery was made by a team of brilliant Chinese scientists, and it's so important that they might even win a Nobel Prize for it! The Nobel Prize is like the Olympic gold medal of science – it's the highest honor a scientist can receive.But the Quantum Anomalous Hall Effect isn't just about winning awards; it has the potential to change the world! With this technology, we could create faster and more powerful computers, better ways to store and transfer information, and even new types of energy篇2China's Super Cool New Science Discovery - The Quantum Anomalous Hall EffectHey there, kids! Have you ever heard of something called the "Quantum Anomalous Hall Effect"? It's a really cool andmind-boggling scientific discovery that scientists in China have recently made. Get ready to have your mind blown!Imagine a world where electricity flows without any resistance, like a river without any rocks or obstacles in its way. That's basically what the Quantum Anomalous Hall Effect is all about! It's a phenomenon where electrons (the tiny particles that carry electricity) can flow through a material without any resistance or energy loss. Isn't that amazing?Now, you might be wondering, "Why is this such a big deal?" Well, let me tell you! In our regular everyday world, when electricity flows through materials like wires or circuits, there's always some resistance. This resistance causes energy to be lost as heat, which is why your phone or computer gets warm when you use them for a long time.But with the Quantum Anomalous Hall Effect, the electrons can flow without any resistance at all! It's like they're gliding effortlessly through the material, without any obstacles or bumps in their way. This means that we could potentially have electronic devices and circuits that don't generate any heat or waste any energy. How cool is that?The scientists in China who discovered this effect were studying a special kind of material called a "topological insulator." These materials are like a secret passageway for electrons, allowing them to flow along the surface without any resistance, while preventing them from passing through the inside.Imagine a river flowing on top of a giant sheet of ice. The water can flow freely on the surface, but it can't pass through the solid ice underneath. That's kind of how these topological insulators work, except with electrons instead of water.The Quantum Anomalous Hall Effect happens when these topological insulators are exposed to a powerful magnetic field. This magnetic field creates a special condition where the electrons can flow along the surface without any resistance at all, even at room temperature!Now, you might be thinking, "That's all well and good, but what does this mean for me?" Well, this discovery could lead to some pretty amazing things! Imagine having computers and electronic devices that never overheat or waste energy. You could play video games or watch movies for hours and hours without your devices getting hot or draining their batteries.But that's not all! The Quantum Anomalous Hall Effect could also lead to new and improved ways of generating, storing, and transmitting energy. We could have more efficient solar panels, better batteries, and even a way to transmit electricity over long distances without any energy loss.Scientists all around the world are really excited about this discovery because it opens up a whole new world of possibilities for technology and innovation. Who knows what kind of cool gadgets and devices we might see in the future thanks to the Quantum Anomalous Hall Effect?So, there you have it, kids! The Quantum Anomalous Hall Effect is a super cool and groundbreaking scientific discovery that could change the way we think about electronics, energy, and technology. It's like something straight out of a science fiction movie, but it's real and happening right here in China!Who knows, maybe one day you'll grow up to be a scientist and help us unlock even more amazing secrets of the quantum world. Until then, keep learning, keep exploring, and keep being curious about the incredible wonders of science!篇3The Wonderful World of Quantum Physics: A Journey into the Quantum Anomalous Hall EffectHave you ever heard of something called quantum physics? It's a fascinating field that explores the strange and mysterious world of tiny particles called atoms and even smaller things called subatomic particles. Imagine a world where the rules we're used to in our everyday lives don't quite apply! That's the world of quantum physics, and it's full of mind-boggling discoveries and incredible phenomena.One of the most exciting and recent breakthroughs in quantum physics comes from a team of brilliant Chinese scientists. They've discovered something called the Quantum Anomalous Hall Effect, and it's like a magic trick that could change the way we think about technology!Let me start by telling you a bit about electricity. You know how when you turn on a light switch, the bulb lights up? That's because electricity is flowing through the wires and into the bulb. But did you know that electricity is actually made up of tiny particles called electrons? These electrons flow through materials like metals and give us the electricity we use every day.Now, imagine if we could control the flow of these electrons in a very precise way, like directing them to move in a specificdirection without any external forces like magnets or electric fields. That's exactly what the Quantum Anomalous Hall Effect allows us to do!You see, in most materials, electrons can move in any direction, like a group of kids running around a playground. But in materials that exhibit the Quantum Anomalous Hall Effect, the electrons are forced to move in a specific direction, like a group of kids all running in a straight line without any adults telling them where to go!This might not seem like a big deal, but it's actually a huge deal in the world of quantum physics and technology. By controlling the flow of electrons so precisely, we can create incredibly efficient electronic devices and even build powerful quantum computers that can solve problems much faster than regular computers.The Chinese scientists who discovered the Quantum Anomalous Hall Effect used a special material called a topological insulator. This material is like a magician's hat – it looks ordinary on the outside, but it has some really weird and wonderful properties on the inside.Inside a topological insulator, the electrons behave in a very strange way. They can move freely on the surface of the material, but they can't move through the inside. It's like having篇4The Coolest New Science from China: Quantum Anomalous Hall EffectHey kids! Have you ever heard of something called the Quantum Anomalous Hall Effect? It's one of the most amazing new scientific discoveries to come out of China. And get this - some scientists think it could lead to a Nobel Prize! How cool is that?I know, I know, the name sounds kind of weird and complicated. But trust me, once you understand what it is, you'll think it's just as awesome as I do. It's all about controlling the movement of tiny, tiny particles called electrons using quantum physics and powerful magnetic fields.What's Quantum Physics?Before we dive into the Anomalous Hall Effect itself, we need to talk about quantum physics for a second. Quantum physics is sort of like the secret rules that govern how the smallest things inthe universe behave - things too tiny for us to even see with our eyes!You know how sometimes grown-ups say things like "You can't be in two places at once"? Well, in the quantum world, particles actually can be in multiple places at the same time! They behave in ways that just seem totally bizarre and counterintuitive to us. That's quantum physics for you.And get this - not only can quantum particles be in multiple places at once, but they also spin around like tops! Electrons, which are one type of quantum particle, have this crazy quantum spin that makes them act sort of like tiny magnets. Mind-blowing, right?The Weirder Than Weird Hall EffectOkay, so now that we've covered some quantum basics, we can talk about the Hall Effect. The regular old Hall Effect was discovered way back in 1879 by this dude named Edwin Hall (hence the name).Here's how it works: if you take a metal and apply a magnetic field to it while also running an electrical current through it, the magnetic field will actually deflect the flow of electrons in the metal to one side. Weird, huh?Scientists use the Hall Effect in all kinds of handy devices like sensors, computer chips, and even machines that can shoot out a deadly beam of radiation (just kidding on that last one...I think). But the regular Hall Effect has one big downside - it only works at incredibly cold temperatures near absolute zero. Not very practical!The Anomalous Hall EffectThis is where the new Quantum Anomalous Hall Effect discovered by scientists in China comes into play. They found a way to get the same cool electron-deflecting properties of the Hall Effect, but at much higher, more realistic temperatures. And they did it using some crazy quantum physics tricks.You see, the researchers used special materials called topological insulators that have insulating interiors but highly conductive surfaces. By sandwiching these topological insulators between two layers of magnets, they were able to produce a strange quantum phenomenon.Electrons on the surface of the materials started moving in one direction without any external energy needed to keep them going! It's like they created a perpetual motion machine for electrons on a quantum scale. The spinning quantum particlesget deflected by the magnetic layers and start flowing in weird looping patterns without any resistance.Why It's So AwesomeSo why is this Quantum Anomalous Hall Effect such a big deal? A few reasons:It could lead to way more efficient electronics that don't waste energy through heat and resistance like current devices do. Just imagine a computer chip that works with virtually no power at all!The effect allows for extremely precise control over the movement of electrons, which could unlock all kinds of crazy quantum computing applications we can barely even imagine yet.It gives scientists a totally new window into understanding the bizarre quantum realm and the funky behavior of particles at that scale.The materials used are relatively inexpensive and common compared to other cutting-edge quantum materials. So this isn't just a cool novelty - it could actually be commercialized one day.Some Science Celebrities Think It's Nobel-WorthyLots of big-shot scientists around the world are going gaga over this Quantum Anomalous Hall Effect discovered by the researchers in China. A few have even said they think it deserves a Nobel Prize!Now, as cool as that would be, we have to remember that not everyone agrees it's Nobel-level just yet. Science moves slow and there's always a ton of debate over what discoveries are truly groundbreaking enough to earn that high honor.But one thing's for sure - this effect is yet another example of how China is becoming a global powerhouse when it comes to cutting-edge physics and scientific research. Those Chinese scientists are really giving their counterparts in the US, Europe, and elsewhere a run for their money!The Future is QuantumWhether the Quantum Anomalous Hall Effect leads to a Nobel or not, one thing is certain - we're entering an age where quantum physics is going to transform technology in ways we can barely fathom right now.From quantum computers that could solve problems millions of times faster than today's machines, to quantum sensors that could detect even the faintest subatomic particles,to quantum encryption that would make data unhackable, this strange realm of quantum physics is going to change everything.So pay attention, kids! Quantum physics may seem like some weird, headache-inducing mumbo-jumbo now. But understanding these bizarre quantum phenomena could be the key to unlocking all the super-cool technologies of the future. Who knows, maybe one of you reading this could even grow up to be a famous quantum physicist yourselves!Either way, keep your eyes peeled for more wild quantum discoveries emerging from China and other science hotspots around the globe. The quantum revolution is coming, and based on amazing feats like the Anomalous Hall Effect, it's going to be one heckuva ride!篇5Whoa, Dudes! You'll Never Believe the Insanely Cool Quantum Tech from China!Hey there, kids! Get ready to have your minds totally blown by the most awesome scientific discovery ever - the quantum anomalous Hall effect! I know, I know, it sounds like a bunch of big, boring words, but trust me, this stuff is straight-upmind-blowing.First things first, let's talk about what "quantum" means. You know how everything in the universe is made up of tiny, tiny particles, right? Well, quantum is all about studying those teeny-weeny particles and how they behave. It's like a whole secret world that's too small for us to see with our eyes, but scientists can still figure it out with their mega-smart brains and super-powerful microscopes.Now, let's move on to the "anomalous Hall effect" part. Imagine you're a little electron (that's one of those tiny particles I was telling you about) and you're trying to cross a busy street. But instead of just going straight across, you get pushed to the side by some invisible force. That's kind of what the Hall effect is all about - electrons getting pushed sideways instead of going straight.But here's where it gets really cool: the "anomalous" part means that these electrons are getting pushed sideways even when there's no magnetic field around! Normally, you'd need a powerful magnet to make electrons move like that, but with this new quantum technology, they're doing it all by themselves. It's like they've got their own secret superpowers or something!Now, you might be wondering, "Why should I care about some silly electrons moving around?" Well, let me tell you, thisdiscovery is a huge deal! You see, scientists have been trying to figure out how to control the flow of electrons for ages. It's kind of like trying to herd a bunch of rowdy puppies - those little guys just want to go wherever they want!But with this new quantum anomalous Hall effect, scientists in China have finally cracked the code. They've found a way to make electrons move in a specific direction without any external forces. That means they can control the flow of electricity like never before!Imagine having a computer that never overheats, or a smartphone that never runs out of battery. With this new technology, we could create super-efficient electronic devices that waste way less energy. It's like having a magical power switch that can turn on and off the flow of electrons with just a flick of a wrist!And that's not even the coolest part! You know how sometimes your electronics get all glitchy and stop working properly? Well, with this quantum tech, those problems could be a thing of the past. See, the anomalous Hall effect happens in special materials called "topological insulators," which are like super-highways for electrons. No matter how many twists andturns they take, those little guys can't get lost or stuck in traffic jams.It's like having a navigation system that's so good, you could close your eyes and still end up at the right destination every single time. Pretty neat, huh?But wait, there's more! Scientists are also exploring the possibility of using this new technology for quantum computing. Now, I know you're probably thinking, "What the heck is quantum computing?" Well, let me break it down for you.You know how regular computers use ones and zeros to process information, right? Well, quantum computers use something called "qubits," which can exist as both one and zero at the same time. It's like having a coin that's heads and tails at the same exact moment - totally mind-boggling, I know!With this quantum anomalous Hall effect, scientists might be able to create super-stable qubits that can perform insanely complex calculations in the blink of an eye. We're talking about solving problems that would take regular computers millions of years to figure out. Imagine being able to predict the weather with 100% accuracy, or finding the cure for every disease known to humankind!So, what do you say, kids? Are you as pumped about this as I am? I know it might seem like a lot of mumbo-jumbo right now, but trust me, this is the kind of stuff that's going to change the world as we know it. Who knows, maybe one day you'll be the one working on the next big quantum breakthrough!In the meantime, keep your eyes peeled for more news about this amazing discovery from China. And remember, even though science can be super complicated sometimes, it's always worth paying attention to. After all, you never know when the next mind-blowing quantum secret might be revealed!篇6Title: A Magical Discovery in the World of Tiny Particles!Have you ever heard of something called the "Quantum Anomalous Hall Effect"? It might sound like a tongue twister, but it's actually a super cool new technology that was recently discovered by scientists in China!Imagine a world where everything is made up of tiny, tiny particles called atoms. These atoms are so small that you can't see them with your bare eyes, but they're the building blocks that make up everything around us – from the chair you're sitting on to the air you breathe.Now, these atoms can do some pretty amazing things when they're arranged in certain ways. Scientists have found that if they create special materials where the atoms are arranged just right, they can make something called an "electrical current" flow through the material without any resistance!You might be wondering, "What's so special about that?" Well, let me explain! Usually, when electricity flows through a material like a metal wire, it faces something called "resistance." This resistance makes it harder for the electricity to flow, kind of like trying to run through a thick forest – it's tough and you get slowed down.But with this new Quantum Anomalous Hall Effect, the electricity can flow through the special material without any resistance at all! It's like having a wide-open road with no obstacles, allowing the electricity to zoom through without any trouble.So, how does this magical effect work? It all comes down to the behavior of those tiny atoms and the way they interact with each other. You see, in these special materials, the atoms are arranged in a way that creates a kind of "force field" that protects the flow of electricity from any resistance.Imagine you're a tiny particle of electricity, and you're trying to move through this material. As you move, you encounter these force fields created by the atoms. Instead of slowing you down, these force fields actually guide you along a specific path, almost like having a team of tiny helpers clearing the way for you!This effect was discovered by a group of brilliant scientists in China, and it's considered a huge breakthrough in the field of quantum physics (the study of really, really small things). It could lead to all sorts of amazing technologies, like super-fast computers and more efficient ways to transmit electricity.But that's not all! This discovery is also important because it proves that China is at the forefront of cutting-edge scientific research. The scientists who made this discovery are being hailed as potential Nobel Prize winners, which is one of the highest honors a scientist can receive.Isn't it amazing how these tiny, invisible particles can do such incredible things? The world of science is full ofmind-blowing discoveries, and the Quantum Anomalous Hall Effect is just one example of the amazing things that can happen when brilliant minds come together to explore the mysteries of the universe.So, the next time you hear someone mention the "Quantum Anomalous Hall Effect," you can proudly say, "Oh, I know all about that! It's a magical discovery that allows electricity to flow without any resistance, and it was made by amazing Chinese scientists!" Who knows, maybe one day you'll be the one making groundbreaking discoveries like this!。

探究感应电流方向实验的观后感英语作文

探究感应电流方向实验的观后感英语作文Exploring the Direction of Induced Current: An Experimental Revelation.The phenomenon of electromagnetic induction, a cornerstone of electromagnetism, has captivated scientists and engineers for centuries. It elucidates the intricate relationship between changing magnetic fields and the generation of electric currents. To delve into the intricacies of this fascinating phenomenon, I embarked on an experimental odyssey, seeking to unravel the mysteries of induced current direction.Experimental Design and Methodology.The experiment was meticulously designed to investigate the direction of induced current in a conductor exposed to a varying magnetic field. An apparatus consisting of a solenoid coil, a bar magnet, a conducting rod, and a galvanometer was meticulously assembled.The experiment commenced with the insertion of the conducting rod into the solenoid coil. The bar magnet was then swiftly thrust into the coil, generating a rapidly changing magnetic field. The galvanometer, a sensitive instrument used to detect electric current, was connected to the ends of the conducting rod.Observations and Analysis.As the bar magnet entered the solenoid coil, the galvanometer's deflection indicated the presence of an induced current in the conducting rod. The direction ofthis current was determined by employing Lenz's law, a fundamental principle in electromagnetism.Lenz's law states that the direction of the induced current always opposes the change in magnetic flux. In our experiment, the insertion of the bar magnet into the solenoid coil increased the magnetic flux through the coil. Consequently, the induced current in the conducting rod flowed in a direction that tended to oppose this increasein flux.By carefully manipulating the orientation of the bar magnet and the conducting rod, we were able to systematically explore the relationship between the direction of magnetic field change and the direction of induced current. Our observations consistently corroborated Lenz's law, confirming its accuracy and universality.Significance and Applications.The exploration of induced current direction has far-reaching implications in the field of electrical engineering. It forms the foundation for the design and operation of various electrical devices, including generators, transformers, and motors.Generators, for instance, rely on the principle of electromagnetic induction to convert mechanical energy into electrical energy. By rotating a conductor within a magnetic field, generators generate an alternating current due to the changing magnetic flux.Transformers, on the other hand, employ the principle of electromagnetic induction to transfer electrical energy from one circuit to another. The changing magnetic field in the primary coil induces an alternating current in the secondary coil, enabling the transfer of energy.Electric motors, devices that convert electrical energy into mechanical energy, also utilize the principle of electromagnetic induction. The interaction between the magnetic field generated by the motor's stator and the induced current in the rotor results in the production of torque, causing the rotor to rotate.Conclusion.The experimental investigation of induced current direction provided an invaluable opportunity to witness firsthand the intricate interplay between magnetic fields and the generation of electric currents. Through careful observation and analysis, we were able to confirm the universality of Lenz's law and explore its implications forthe design and operation of electrical devices.The knowledge and understanding gained from this experiment will undoubtedly serve as a foundation for further exploration in the fascinating realm of electromagnetism. As we continue to unravel the mysteries of the electromagnetic world, we inch ever closer to unlocking the full potential of this versatile and transformative force.。

physical review letters模板

physical review letters模板Physical Review Letters (PRL) TemplatePhysical Review Letters (PRL) is a prestigious scientific journal that publishes cutting-edge research in all areas of physics. As a platform for rapid communication, PRL allows physicists to share their groundbreaking discoveries and advancements with the scientific community. In order to maintain the high standard and consistency of the articles published in PRL, authors are required to follow a specific template when submitting their work.Title and Authors:The article should begin with a concise and informative title that accurately reflects the content of the research study. The names and affiliations of all authors should be clearly stated below the title. It is important that the order of the authors reflects their individual contributions to the study.Abstract:The abstract is a brief summary of the research study, providing an overview of the problem addressed, the methodology used, the main results obtained, and their significance. It should be concise, informative, and self-contained, allowing readers to understand the essence of the study without having to read the entire article. The abstract should not exceed a few hundred words.Introduction:The introduction serves to provide the necessary background and context for the research study. It should clearly state the motivation behind the study, identify the gaps in the existing knowledge, and present the research question or objective. The introduction should be written in a manner that makes it accessible to a broad audience of physicists, avoiding excessive jargon or technical terms.Methods:The methods section should outline the experimental or theoretical techniques employed in the study. Experimentalists should describe the setup, equipment, and protocols used, while theorists should provide a clear explanation of the mathematical or computational methods utilized. This section should be detailed enough to allow other researchers to replicate or adapt the study if desired.Results:The results section presents the key findings of the research study. It should be organized in a logical and coherent manner, using figures, tables, and equations where appropriate. The results should be presented objectively, with statistical analyses and uncertainties reported when applicable. The significance of the results should also be discussed, highlighting their contribution to the field.Discussion:In the discussion section, the authors have the opportunity to interpret and analyze their results in the context of existing knowledge and theories. They should discuss the implications and potential applications of their findings, while also acknowledging any limitations or areas for further investigation. The discussion should demonstrate a deep understanding of the subject matter and showcase the authors' expertise in the field.Conclusion:The conclusion section summarizes the main findings of the study and restates their significance. It should also provide a brief outlook on future directions or potential research avenues that could build upon the present study. The conclusion should be concise and avoid introducing any new information that has not been previously discussed.References:The references section is a crucial component of the article as it allows readers to verify the information presented and further explore related works. All sources cited in the article should be listed in a consistent format, typically following a specific citationstyle, such as APA or Chicago. It is essential to ensure that all citations are accurate and complete.In conclusion, adhering to the Physical Review Letters (PRL) template is essential for authors aiming to publish their research in this esteemed journal. By structuring the article in a clear and organized manner, authors can effectively communicate their findings to the scientific community. The template ensures that each article published in PRL meets the journal's high standards, contributing to the advancement of physics knowledge.。

怀疑派化学家读后感

怀疑派化学家读后感英文回答：As a skeptical chemist, I often find myself questioning the validity of scientific theories and experimental results. This skepticism stems from my belief thatscientific knowledge is constantly evolving and that it is crucial to critically evaluate and challenge existing ideas.One area where my skepticism comes into play is in the interpretation of experimental data. I am always cautious about drawing conclusions based on a single experiment or a limited set of data. I believe in the importance of replicating experiments and obtaining consistent results before accepting a hypothesis or theory.For example, let's say I am conducting an experiment to determine the effectiveness of a new drug in treating a particular disease. If I only observe positive results in a small sample size, I would be skeptical about the drug'sefficacy. I would want to see the experiment repeated multiple times with larger sample sizes to ensure that the results are reliable and not due to chance.Another aspect of my skepticism as a chemist is questioning the assumptions and limitations of scientific models and theories. While these models are valuable tools for understanding and predicting chemical phenomena, they are not infallible. I am always on the lookout for new evidence or alternative explanations that may challenge or refine existing models.For instance, let's consider the kinetic theory of gases, which assumes that gas molecules are in constant random motion. While this theory has been widely accepted and successfully explains many gas properties, I would be skeptical if new experimental evidence emerged that contradicted this assumption. I would be open to revising the theory or developing a new model that better explains the observed phenomena.In addition to questioning experimental data andscientific models, I also believe in the importance of interdisciplinary collaboration and peer review. By engaging in discussions with scientists from differentfields and subjecting my work to scrutiny from my peers, I can ensure that my conclusions are well-founded and supported by evidence.In conclusion, my skepticism as a chemist drives me to question and challenge scientific ideas, experimental results, and theoretical models. I believe in theimportance of rigorous experimentation, critical evaluation, and collaboration to advance our understanding of the chemical world.中文回答：作为一个怀疑派的化学家，我经常会对科学理论和实验结果的有效性产生怀疑。

物理类参考文献缩写

物理类参考文献缩写物理类参考文献缩写：Abbreviations for some commonly cited journals[日期：2008-10-29]来源：作者：[字体：大中小] A data file is started with a “heading 2”, with a number and a tit le, as shown here. The first lines should explain the format of the data,. only ascii text should appear. in a datafile. This file is a tab delineated file listing the preferred Abbreviations for some comm only cited Journals.Journal Name Journal AbbreviationAbstracts of Papers of the American Chemical Society Abstr. Am. Chem. Soc.Acta Physica Polonica A Acta Phys. Pol. AAIP Conference Proceedings AIP Conf. Proc.Annals of Physics Ann. Phys.Applications of Surface Science Appl. Surf. Sci.Applied Optics Appl. Opt.Applied Physics Appl. Phys.Applied Physics Letters Appl. Phys. Lett.Bulletin of the American Physical Society Bull. APSChemistry of Materials Chem. Mater.Chinese Physics Letters Chin. Phys. Lett.Comments on Inorganic Chemistry Comm. Inorg. Chem. Computer Physics Reports Comp. Phys. Rep.Cryst. Res. and Tech. Cryst. Res. and Tech.Electronics Letters Electron. Lett.Europhysics Letters Europhys. Lett.IBM J. Res. Dev. IBM J. Res. and Dev.IEEE Electron Device Letters IEEE Electron Dev. Lett.IEEE Journal Quantum Electronics IEEE J. Quantum Electron. IEEE Transactions on Electron Devices IEEE Trans. Electr. Dev. Institute of Physics Conference Series Inst. Phys. Conf. Ser. Japanese Journal of Applied Physics Jap. J. Appl. Phys.JETP Letters JETP Lett.Journal de Physique J. Phys. (Paris)Journal of Applied Physics J. Appl. Phys.Journal of Chemical Physics J. Chem. Phys.Journal of Crystal Growth J. Cryst. GrowthJournal of Electronic Materials J. Electron. Mater.Journal of Luminescence J.Lumin.Journal of Materials Chemistry J. Mat. Chem.Journal of Materials Research J. Mater. Res.Journal of Materials Science J. Mater. Sci.Journal of Materials Science Letters J. Mater. Sci. Lett.Journal of Organometallic Chemistry J. Organomet. Chem.Journal of Physical Chemistry J. Phys. Chem.Journal of Physics J. Phys.Journal of Physics and Chemistry of Solids J. Phys. Chem. Sol. Journal of Physics C J. Phys. CJournal of Physics D-Applied Physics J. Phys. DJournal of Solid State Chemistry J. Sol. St. Chem.Journal of the American Ceramic Society J. Am. Ceram. Soc. Journal of the American Chemical Society J. Am. Chem. Soc. Journal of the Chinese Chemical Society J.Chin. Chem. Soc. Journal of the Electrochemical Society J. Electrochem.Soc. Journal of the Optical Society of America J. Opt. Soc. Am. Journal of the Optical Society of America A J. Opt. Soc. Am. A Journal of the Optical Society of America B J. Opt. Soc. Am. B Journal of Vacuum Science and Technology J. Vac. Sci. T echnol. Journal of VacuumScience and Technology A-Vacuum Surfaces an d Films J. Vac. Sci. Technol. AJournal of Vacuum Science and Technology B J. Vac. Sci. Techno l. BMaterials Research Bulletin Mater. Res. Bull.Materials Research Society Symposium Proceedings Mater. Res. Soc. Symp. Proc.Materials Science and Engineering B-Solid State Materials for Adva nced Technology Mater. Sci. Eng. BMicroelectronics Journal Microelectr. J.MRS Internet Journal of Nitride Semiconductor Research MRS Int ernet J. Nitride Semicond. Res.Nature NatureOptics Letters Opt. Lett.Optoelectronics - Devices and Technologies Optoelectr. Dev. Tech. Physica PhysicaPhysica B Physica BPhysica Scripta Phys. Scr.Physica Status Solidi P hys. Stat. Sol.Physica Status Solidi A Phys. Stat. Sol. APhysica Status Solidi B Phys. Stat. Sol. BPhysical Review Phys. Rev.Physical Review A Phys. Rev. APhysical Review B Phys. Rev. BPhysical Review C Phys. Rev. CPhysical Review D Phys. Rev. DPhysical Review E Phys. Rev. EPhysical Review Letters Phys. Rev. Lett.Physics Letters Phys. Lett.Physics Letters BPhys. Lett. BPhysics of the Solid State Phys. Solid StatePolyhedron PolyhedronProc. Soc. Photo-Opt. Instrum. Eng. Proc. SPIEProceedings of the IEEE Proc. IEEERCA Review RCA Rev.Review of Scientific Instruments Rev. Sci. Inst.Reviews of Modern PhysicsRev. Mod. Phys.Revue de Physique Appliquee Rev. Phys. Appl.Russian Journal of Applied Chemistry Russ. J. Appl. Chem. Russian Journal of Physical ChemistryRuss. J. Phys. Chem. Semiconductor Science and Technology Semicond. Sci. Technol. Solid State Communications S ol. St. Comm.Solid State Electronics Sol. St. Electr.Soviet Journal of Quantum Electronics Sov. J. Quantum Electron. Soviet Physics JETP Sov. Phys. JETPSoviet Physics-Crystallography Sov. Phys. Cryst.Soviet Physics-Semiconductors Sov. Phys. Semicond. Superlattices and Microstructures Superlatt. Microstruc.Surface Science Surf. Sci.Thermochimica Acta Thermoch. ActaThin Solid Films Thin Sol. FilmsVacuum VacuumZeitschr. Anorgan. Allgem. Chem. Z. Anorgan. Allgem. Chem. Zeitschr. Physik Z. Phys.Zeitschr. Physik B Z. Phys. BZeitschrift f?r Kristallographie Z. Krist.Zh. Exp. Tech. Fiz. Zh. Exp. Tech. Fiz.。

自旋极化的电流——2007年度诺贝尔物理学奖评述

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２００７—１１—１５收到｝Ｅｍａｉｌ：ｗｙｌａｉ＠ａｐｈｙ．ｉｐｈｙ．∞．ｃｎ
３６卷（２００７年）１２期
万方数据
ｈａｐ：Ｉｌｗｗｗ．ｗｕｌｉ．∞．ｃｎ
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特约专稿
瑞典诺贝尔奖委员会还指出：“巨磁电阻效应的发现打开了一扇通向新技术世界的大门——自旋电子学．这里，将同时利用电子的电荷以及自旋这两个特性．”ＧＭＲ作为新的自旋电子学的开端具有深远的科学意义．电子除了电荷以外，还具有自旋角动量．这一重大发现已经过去８０多年了．过去处理自旋的方式着重于在外磁场或磁体中自旋矢量取向的变化；自旋是局域在固体原子上的．另一方面，传统的电子学是以电子电荷移动为基础的．在主流电子学中，电子自旋往往被忽略了．但是，新的巨磁电阻效应表明，电子自旋对于电流的影响非常强烈．所以，电子的电荷与自旋角动量两者都可能载运信息．这就是新的白旋电子学（ｓｐｉｎｔｒｏｎｉｃｓ）的主旨．我们期待着它将为科学和技术带来更广阔的应用前景．

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