Hall effect in the normal state of high Tc cuprates

合集下载

熊海虹主编《高等学校研究生英语综合教程-上》Unit7-Unit10课文翻译及课后练习答案

熊海虹主编《高等学校研究生英语综合教程-上》Unit7-Unit10课文翻译及课后练习答案Unit SevenON HUMAN NATURE Frank and Lydia Hammer 我对人类的了解越多，对他们的期望就越低。

和以前相比，我现在常常以较宽松的标准把一个人叫做好人。

——塞缪尔·约翰逊博士论人性弗兰克，莉迪亚·汉默尔1 Human nature is the basis of character, the temperament and disposition; it is that indestructible matrix upon which the character is built, and whose shape it must take and keep throughout life. This we call a person's nature.1人性是性格、气质和性情的基础，性格正是基于这种牢不可破的基质之上的，它必须以这种基质的形式存在，并将它保留终生，这种基质，我们称之为一个人的本性。

2 The basic nature of human beings does not and cannot change. It is only the surfacethat is capable of alteration, improvement and refinement; we can alter only people's customs, manners, dress and habits. A study of history reveals that the people who walked thisearth in antiquity were moved by the same fundamental forces, were swayed by the same passions, and had the same aspirations as the men and women of today. The pursuit of happiness still engrosses mankind the world over.2人类的本性不会也不能改变，只有一些表面特征才会变化、改善和进一步提升；我们可以改变人们的风格、举止、衣着和习惯。

In-plane Hall effect in c-axis-oriented MgB2 thin films

a r X i v :c o n d -m a t /0105024v 2 [c o n d -m a t .s u p r -c o n ] 16 J a n 2002Hall eﬀect in c-axis-oriented MgB 2thin ﬁlmsW.N.Kang,∗Hyeong-Jin Kim,Eun-Mi Choi,Heon Jung Kim,Kijoon H.P.Kim,H.S.Lee,and Sung-Ik LeeNational Creative Research Initiative Center for Superconductivity and Department of Physics,Pohang University of Scienceand Technology,Pohang 790-784,Republic of KoreaWe have measured the longitudinal resistivity and the Hall resistivity in the ab-plane of highly c-axis-oriented MgB 2thin ﬁlms.In the normal state,the Hall coeﬃcient (R H )behaves as R H ∼T with increasing temperature (T )up to 130K and then deviates from that linear T -dependence at higher temperatures.The T 2dependence of the cotangent of the Hall angle is only observed above 130K.The mixed-state Hall eﬀect reveals no sign anomaly over a wide range of current densities from 102to 104A/cm 2and for magnetic ﬁelds up to 5T.I.INTRODUCTIONThe recent discovery of superconductivity in MgB 2,with a transition temperature (T c )of about 39K [1],has attracted extensive scientiﬁc interest in the ﬁelds of basic research and applications.Already,several physi-cal properties,such as the Hall eﬀect,the thermoelectric power,the magnetization,and the magnetoresistance,have been investigated using polycrystalline samples [2–6].However,many experimental results still remain controversial because of the relatively high anisotropic nature of this compound.Based on measurements of the upper critical ﬁeld for diﬀerent crystal planes of MgB 2single crystals [7,8]and of highly c-axis-oriented thin ﬁlms [9],they have conﬁrmed the anisotropic nature of MgB 2superconductor.These results strongly suggest that the physical properties of MgB 2should be investi-gated by either using single crystals or high-quality thin ﬁlms having preferred orientations.For the Hall measure-ments,since sizable single crystals are not available and the Hall signal is very small due to its metallic charac-ter,the thin-ﬁlm form is the best candidate for achieving accurate experimental results.In our earlier work on polycrystalline samples [2],we conﬁrmed that the majority charge carriers were holelike,which was consistent with theoretical estimates [10];sub-sequently,similar results were also reported for polycrys-talline MgB 2thin ﬁlms [11].To the best of our knowl-edge,the in-plane Hall eﬀect for MgB 2has not been pre-viously studied;thus,measurement of the ab-plane Hall eﬀect for c-axis-oriented MgB 2thin ﬁlms should provide signiﬁcant input for future investigations of its electronic transport properties and vortex dynamics.For high-T c cuprate superconductors (HTS),a univer-sal T 2dependence of the cotangent of the Hall angle (cotΘH )has been extensively discussed.Anderson [12]has proposed that this behavior can be explained if two diﬀerent scattering rates,a transport scattering time and a Hall (transverse)scattering time,are considered,where the longitudinal resistivity (ρxx )is determined by the for-mer and the Hall resistivity (ρxy )is determined by both.Most experimental results for HTS have supported this theory [13–15],and it is generally accepted that,in thenormal state,a cotΘH ∼T 2law is universal over a wide temperature range.Similar behavior has also been re-ported for polycrystalline MgB 2superconductors [2,11].Another interesting feature concerning the mixed-state Hall eﬀect as a probe of superconductivity is the anoma-lous sign change near T c as a function of the T and the magnetic ﬁeld,and its origin has remained an unsolved subject for over 30years.The sign anomaly has been ob-served in some conventional superconductors [16],as well as in most HTS [16–18].However,in clean superconduc-tors,such as pure Nb,V,and 2H -NbSe2,no sign anomaly has been found [16].Our Hall data for MgB 2are more similar to the behavior seen in Nb,V,and 2H -NbSe2,suggesting that MgB 2might be a clean-limit supercon-ductor [19].In this paper,we report the ﬁrst measurement of the in-plane Hall eﬀect of MgB 2.The measurement was car-ried out using highly c-axis-oriented thin ﬁlms,and we found that the sign of the R H was positive like those of HTS.Also,the R H appeared to follow a linear behavior for the T region from 30to 130K,which is diﬀerent from the behaviors of polycrystalline MgB 2and of HTS.The Hall eﬀect in the mixed state showed no sign anomaly over a wide range of current densities from 102to 104A/cm 2and for magnetic ﬁeld up to 5T,which is con-trast to the observations in most HTS and polycrystalline MgB 2thin ﬁlms.II.EXPERIMENTThe MgB 2thin ﬁlms were grown on Al 2O 3(1¯102)single crystals under a high-vacuum condition of ∼10−7Torr by using the pulsed laser deposition and the postan-nealing techniques reported in an earlier paper [20].Typ-ical samples were 10mm in length,10mm in width,and 0.4µm in thickness.The ﬁlm thickness was measured us-ing scanning electron microscopy.Standard photolitho-graphic techniques were used to produce thin-ﬁlm Hall bar patterns,which consisted of a rectangular strip (1mm in width and 3mm in length)of MgB 2with three pairs of sidearms (the upper inset of Fig.2).The nar-row sidearm width of 0.1mm was patterned so that thesidearms would have an insigniﬁcant eﬀect on the ing this6-probe conﬁguration,we were able to measure simultaneously theρxx andρxy at the same T; thus the cotΘH was obtained very precisely.To achieve good ohmic contacts(<1Ω),we coated Auﬁlm on the contact pads after cleaning the sample surface by using Ar-ion milling.After installing a low-noise preampliﬁer prior to the nanovoltmeter,we achieved a voltage res-olution of below1nV.The magneticﬁeld was applied perpendicular to the sample surface by using a supercon-ducting magnet system,and the applied current densities were102−104A/cm2.The Hall voltage was found to be linear in both the current and the magneticﬁeld.III.RESULTS AND DISCUSSIONThe structural analysis was carried using X-ray diﬀrac-tometry,and the results are shown in Fig.1(a).The MgB2thinﬁlm showed a highly c-axis-oriented crystal structure,and the sample purity exceeded99%and had only a minor{101}oriented phase.Figure1(b)shows the low-ﬁeld magnetization at H=4Oe for both the zero-ﬁeld-cooled(ZFC)andﬁeld-cooled(FC)states of an MgB2ﬁlm.A very sharp diamagnetic transition is observed.Even at a high T of37K and under self-ﬁeld conditions,the critical current density determined by di-rect current vs voltage measurements was observed to be on the order of105A/cm2[21].These results indicate that the MgB2ﬁlms used in the present study were ho-mogeneous and of very high quality.Figure2shows the T dependence ofρxx for a MgB2ﬁlm at H=0and5T.The upper inset shows the6-probe Hall-bar pattern.Pads3-4and5-6were used to measureρxy andρxx,respectively,while the current was applied between1and2.The lower inset shows a magniﬁed view near the superconducting transition.The onset T c was39.2K and had a narrow transition width of∼0.15K,as judged from the10to90%supercon-ducting transition.At40K,ρxx was3.4µΩcm,giving a residual resistivity ratio[RRR=ρxx(300K)/ρxx(40K)] of3,which was smaller than the value observed for MgB2 single crystals[7,8].A very small(less than0.5%)mag-netoresistance was observed in the normal state at5T. The T dependence of the R H at5T is shown in Fig.3. The oﬀset voltage due to the misaligned Hall electrodes was eliminated by reversing theﬁeld from-5T to5T (inset of Fig.3),and the Hall voltage was taken as the average value,V xy=(V+H-V−H)/2,for all data points. The oﬀset voltage at H=0T was very small compared to V xy at5T,indicating excellent alignment of the Hall electrodes.The value of V xy was about2orders of mag-nitude larger than that of polycrystalline bulk samples [2].Due to our high-resolution measurements,we were able to interpret our Hall data rigorously.The value of R H was positive over the entire T range,which is consis-tent with the result of band calculations[10].Although the charge carrier density cannot be determined simply within the context of the Boltzmann theory because of the anisotropic band structure and the complex Fermi surface of MgB2,such a calculation would be meaningful for comparison with other superconductors.At100K, the R H was3×10−11m3/C,and the hole carrier den-sity,calculated from1/eR H,was∼2×1023holes/cm3. The absolute value of the hole density was two orders of magnitude larger than that YBa2Cu3O7[22],indicating that MgB2has a metallic superconductor.The average value of the R H was consistent with theoretical estimates [10].As the T was increased from the T c,the R H decreased linearly up to130K(T∗)and then deviated from that linear behavior at higher T,suggesting that the electronic transport mechanism changes at around130K.The T∗was observed to be independent of magneticﬁelds up to 5T.This feature is somewhat diﬀerent from previous results for polycrystalline bulk[2]and thin-ﬁlm samples [11]for which the R H exhibited the same T dependence over the entire T range from the T c to300K.These re-sults suggest that MgB2might have diﬀerent transport mechanisms in the in-plane and the out-of-plane direc-tions.A similar distinct T-dependence around150K was also observed in the thermoelectric power measure-ments[3,4];the thermoelectric power increased linearly with increasing T up to around150and then showed a downward deviation from linearity.This behavior is be-lieved to be due to the diﬀerent T dependences of the multi-band contributions to the transport properties;at low T(below150K),charge transport is governed mainly by hole carriers whereas at higher T,the contribution of electron carriers must be considered[3].In Fig.4,we show the T dependence of cotθH at5 T.A good linearﬁt to AT2+B is observed for the T range from130to300K;clear deviation from a T2de-pendence is seen below130K.According to the Ander-son theory[12],which is based on charge-spin separa-tion,charge transport is governed by two separate scat-tering times with diﬀerent T dependences.The longitu-dinal conductivity(σxx)is proportional to the transport scattering time(τtr)whereas the Hall conductivity(σxy) is determined byτHτtr where the Hall relaxation time (τH)is proportional to1/T2.TheτH is mainly governed by spinon-spinon interactions;thus,its T dependence is not aﬀected by impurities.As a result,the cotθH(=σxx/σxy)should follow a T2law.Such a universal tem-perature dependence has been observed in most HTS[13], and the T2law has been conﬁrmed not to depend on im-purities[14,15].Above130K,our experimental data are also in good agreement with a T2law as observed in most HTS.However,our data cannot be interpreted within the Anderson theory because MgB2does not have active spins.We also observe a distinct T2dependenceof cotθH at around130K.Finally,we address the transport properties in the su-perconducting state.In Fig.5(a),we show the T de-pendence of theρxx for magneticﬁelds of2and5T and at current densities of102to104A/cm2.A broad su-perconducting transition is observed,which implies the existence of a relatively wide vortex-liquid phase in this compound.This result is quite similar to those for HTS. In a separate paper[23],we reported that this vortex phase could be interpreted well by using two distinct re-gions;a thermalﬂuctuation region at high T near T c and a vortex-glass region at low T.Moreover,we found a very narrow thermally activatedﬂux-ﬂow region,which was diﬀerent from the case of HTS.The correspondingρxy data are plotted in Fig.5(b). No sign reversal was detected in the Hall data measured for magneticﬁelds from1to5T and over two orders of magnitude of the current density.A puzzling sign rever-sal has been observed in the mixed-state Hall eﬀect for most HTS[18]and even for polycrystalline MgB2ﬁlms [11].In conventional superconductors,this sign change occurs mostly in moderately clean superconductors,but is not seen in either clean-limit superconductors,such as V,Nb,and NbSe2,or dirty-limit superconductors,such as superconducting alloys[16].Therefore,the absence of the Hall sign anomaly suggests that MgB2should be categorized as a clean-limit superconductor.Indeed,a short superconducting coherence length(∼50˚A)and a relatively large mean free path(250−600˚A)have been reported for this compound[19,24].An interesting microscopic approach based on the time-dependent Ginzburg-Landau theory has been pro-posed in a number of papers[25–27].According to this model,the mixed-state Hall conductivity in type II su-perconductors is determined by the quasiparticle contri-bution and the hydrodynamic contribution of the vor-tex cores.Since the hydrodynamic contribution is deter-mined by the energy derivative of the density of states [26,27],if that term is negative and dominates over the quasiparticle contribution,a sign anomaly can appear. This theory is consistent with experimental data for HTS [28].For the mixed-state Hall eﬀect in MgB2compound, since no sign anomaly was detected,we may suggest that the hydrodynamic contribution is very small or negligible in this superconductor.IV.SUMMARYUsing high quality c-axis-oriented MgB2thinﬁlms,we studied the in-plane Hall eﬀect as a function of the mag-neticﬁeld over a wide range of current densities.The normal-state R H increased linearly with increasing T up to130K and then showed a downward deviation from its linear dependence at higher T,which is probably due to the distinct T dependences of the electronic states of the MgB2compound.Our Hall data were also in good agree-ment with a cotθH∼T2law above130K.The mixed-state Hall eﬀect revealed no sign anomaly for magneticﬁelds from1to5T over two orders of magnitude of the current density.ACKNOWLEDGMENTS:We thank J.Crayhold foruseful discussions.This work is supported by the Min-istry of Science and Technology of Korea through the Creative Research Initiative Program.[17]W.N.Kang,D.H.Kim,S.Y.Shim,J.H.Park,T.S.Hahn,S.S.Choi,W.C.Lee,J.D.Hettinger,K.E.Gray, and B.Glagola,Phys.Rev.Lett.76,2993(1996). [18]W.N.Kang,B.W.Kang,Q.Y.Chen,J.Z.Wu,Y.Bai,W.K.Chu,D.K.Christen,R.Kerchner,and Sung-Ik Lee,Phys.Rev.B61,722(2000),and references therein.[19]P.C.Canﬁeld,D.K.Finnemore,S.L.Bud’ko,J.E.Os-tenson,pertot,C.E.Cunningham,and C.Petrovic, Phys.Rev.Lett.86,2423(2001).[20]W.N.Kang,Hyeong-Jin Kim,Eun-Mi Choi,C.U.Jung,and Sung-Ik Lee,Science252,1521(2001);(10.1126/sci-ence1060822).[21]Hyeong-Jin Kim,W.N.Kang,Eun-Mi Choi,Mun-SeogKim,Kijoon H.P.Kim,and Sung-Ik Lee,Phys.Rev.Lett.87,087002(2001).[22]J.M.Harris,Y.F.Yan,and N.P.Ong,Phys.Rev.B46,14293(1992).[23]Heon-Jung Kim,W.N.Kang,Hyeong-Jin Kim,Eun-MiChoi,Kijoon H.P.Kim,H.S.Lee,and Sung-Ik Lee (unpublished).[24]F.Manzano,A.Carrington,N.E.Hussey,S.Lee,and A.Yamamoto,cond-mat/0110109(2001).[25]A.T.Dorsey,Phys.Rev.B46,8376(1992).[26]N.B.Kopnin,B.I.Ivlev,and V.A.Kalatsky,J.LowTemp.Phys.90,1(1993);N. B.Kopnin and A.V.Lopatin,Phys.Rev.B51,15291(1995);N.B.Kopnin, Phys.Rev.B54,9475(1996)..[27]A.van Otterlo,M.Feigel’man,V.Geshkenbein,and G.Blatter,Phys.Rev.Lett.75,3736(1995).[28]D.M.Ginsberg and J.T.Manson,Phys.Rev.B51,515(1995); C.C.Almasan,S.H.Han,K.Yoshiara, M.Buchgeister,D.A.Gajewski,L.M.Paulius,J.Her-rmann,M.B.Maple,A.P.Paulikas,Chun Gu,and B.W.Veal,ibid.51,3981(1995);J.T.Kim,J.Giapintzakis, and D.M.Ginsberg,ibid.53,5922(1996).FIG.1.(a)X-ray diﬀraction patterns of MgB2thinﬁlms.A highly c-axis-oriented crystal structure normal to the sub-strate surfaces was observed.S denotes the substrate peaks.(b)Magnetization at H=4Oe in the ZFC and FC states.FIG.2.Temperature dependence of the resistivity of MgB2 thinﬁlms for H=0and5T.The lower inset shows a mag-niﬁed view near the T c.A sharp transition,with a narrow transition width of∼0.15K,was observed.The upper inset is a schematic diagram of the Hall bar pattern.FIG.3.R H vs Temperature of MgB2thinﬁlms at5T. Distinct temperature dependences of the R H are evident be-low and above130K.The data were measured by reversing the magneticﬁeld from-5T to5T at aﬁxed temperature, as shown in the inset.FIG.4.Temperature dependence of cotθH at5T.A clear T2law was observed above130K.FIG.5.Mixed-state(a)ρxx and(b)ρxy measured at ap-plied current densities of102,103,and104A/cm2and for H =2and5T.No sign change was observed,which is diﬀerent from the case of HTS.10203040-1.0-0.50.0(b)H = 4 O eZFCFCM (a .u .)T (K)2030405060M gB 2 / Al 2O 3SS(a)(002)(001)(101)2θ (degrees)203040500245 T0 T501001502002503000246810Fig. 2. Kang et al.ρx x (µΩ c m )T (K)050100150200250300204060Fig. 3. Kang et al.T*J = 104A/cm 2H = 5 TR H (10-12m 3/C )T (K)012345-20-1001020T = 40 KV x y (µV )IH (T)I02468100.00.51.01.5H = 5 T J = 104A/cm2T*Fig. 4. Kang et alc o t Θ (103)T (104K 2)1520253035400.000.010.02(b)2 T5 Tρx y (µΩ c m )T (K)01234102 A/cm 2103A/cm 2104 A/cm2(a)2 T5 Tρx x (µΩ c m )。

peoplesquare人民广场英文介绍

Brief：People's Square is the biggest public square in Shanghai. It is an awesome area to visit while in Sh anghai and it’s a great place to go and see how the people of Shanghai are.It is the city’s center of politics, economy, culture and art with a group of magnificent buildings lik e museum, the exhibition hall, and the grand theater.The crystal-like theater is especially beautiful at night with lights on.History:In concession days, together with People’s Park next door, it was a racecourse.After liberation in 1949, the northern part of the racecourse was built into today’s People Park an d the southern part, into the People’s Square.Location：Located in downtown Shanghai, the People Square is the largest public square.Transportation:Under the Square is a large central Metro station where the No.1 . 2and 8 metro lines meet. Within the station itself are two modern marketplaces: one features popular stores from the Hon g Kong, and the other is the Dimei underground market.FountainIn the center of the square is a 320 sq. meter fountain，named the “Light of the Huangpu River”. It is the first giant music-synchronized "dancing" foun tain in the country. Red, blue and yellow sculptures in the fountain portray a beautiful, glowing di splay, creating a grand sight for those who visit the area.There are two small squares beside the central square. The east square is called the Rising Sun Sq uare; the west is called the Bright Moon Square.Transportation:Under the Square is a large central Metro station where the No.1 . 2 and 8 metro lines meet. Within the station itself are two modern marketplaces: one features popular stores from the Hon g Kong, and the other is the Dimei underground market.PigeonsSouthwest of the square is a beautiful blue and white home for pigeons! Thousands of pigeons fly from their house to the Square's lawn to meet tourists each day. Their coming promotes a feelin g of peace and serenity to all that visit the area.Spots brief:To the north of the Square stands a grand building, the City Hall (the Municipal Government Build ing of Shanghai).The Shanghai Museum is located south of the Square and directly faces the City Hall. The beautif ul Shanghai Grand Theatre is situated in the northwest part of the Square, and is close to the Government Building.To the northeast of the Square is the Shanghai Urban Planning Exhibition Hall.Shanghai Gallery.Shanghai Museum Brief:Shanghai Museum is a must-see for foreign visitors to Shanghai.Shanghai Museum is especially famous for its treasures of bronzes, ceramics, Chinese calligraphy and traditional paintings.Location:The Shanghai Museum is situated in the heart of People’s Square. Opposite to the City Hall and is surrounded by the moon and sun Corridor.History:It was built in the 1930s, formerly occupied by Zhong Hui Bank owned by a Shanghai celebrity Yu esheng Du. In 1952, it was converted into a museum. The new museum building was erected in September 1994 and most of the facilities were installed in 1995. It was entirely opened on October 12 in 1996. The five big gilt characters on the lintel were written by Yi Chen, the first mayor of Shanghai after the founding of new China. With a collection of over 120,000 pieces of cultural relics in 12 categories, including bronze, ceramics (pottery and porcelain ware), calligraphy, paintings, jade and ivory ware, numismatics, furniture, seal carvings, sculptures, arts and crafts and costumes of Chinese minorities, Shanghai Museum is especially famous for its collection of bronzes, ceramics, paintings and calligraphy. And there is also a special gallery of donated relics and three temporary exhibition halls. With a collection of over 120,000 pieces of cultural relics in 12 categories, including bronze, ceramics (pottery and porcelain ware), calligraphy, paintings, jade and ivory ware, numismatics, furniture, seal carvings, sculptures, arts and crafts and costumes of Chinese minorities, Shanghai Museum is especially famous for its collection of bronzes, ceramics, paintings and calligraphy. And there is also a special gallery of donated relics and three temporary exhibition halls.AppearanceAs you view Shanghai Museum from a distance in People’s Square, you wi ll find that the building itself is a work of art, featuring multiple orientations, multi-visual angles and many distinctive characteristics. The elegant construction perfectly combines traditional cultural themes with modern technological innovation. The building uses a round top section to symbolize heaven and a square base representing the earth, implying the Chinese traditional expression of “a round heaven and a square earth”. It is 24 meters high with sever floors, two are underground and five above, covering a total area of 38,000 sqm.Shanghai Museum has installed advanced security and fire alarm systems, educational services, a computerized library and an automation system. Besides this, Shanghai Museum has facilities for multimedia guide, an information center, a High Definition Graphics system, an audio tour, the lecture room equipped with a system of spontaneous interpretation. You can check out a device that allows you to hear a description of an item after punching in the item number. The aud io tour is available in eight languages. The library in the museum has 200,000 volumes of books in collection.Shanghai Grand TheatreLocation:Shanghai Grand Theatre is located to the west of the City Hall in the People’s Square, the city's he art. The Shanghai Grand Theatre occupies an area of 2.1 hectares, facing the People's Boulevard i n the south. With its unique style and beautiful outlook, the theatre has become a representative building in Shanghai.History and brief intro:It is opened to the public on August 27, 1998.The Shanghai Grand Theatre has successfully staged such shows and evenings as operas, musicals, ballets, symphonies, chamber music concerts, spo ken drama and the Chinese operas. It has a high reputation both at home and abroad as many hig h officials and VIPs, both domestic and international, gave the highest praises of the theatre for it s perfect combination of art and architecture.Appearance:With a total construction area of 62,803 square meters and a total height of 41 meters, the Shang hai Grand Theatre has 10 storeys, 2 for underground, 6 for above ground and 2 top floors. The ne w style architecture combines the Eastern and Western flavor together. The theatre represents a f ine integration of new technology, new craft and new material. It looks like a crystal palace in the light at night.The lobby of Shanghai Grand Theatre is approximate 2000 square meters with the white as its ma in tone, which signifies elegant and pure. The floor is made of a rare marble called "Greece Crysta l White".Function:The Shanghai Grand Theatre has three theatres, a 1,800 seats main theatre for ballet, opera and s ymphony performances, this lyric theatre is divided into the auditorium, the 2nd-floor, the 3rd-flo or and six balconies. The drama theatre has 750 seats and the studio theatre has 300 seats.In addition to performances, the Shanghai Grand Theatre has a restaurant for tourists with an are a of 1,600 square meters and a shopping center for audio-video products with an area of 2,500 sq uare meters. Also there are VIP lounge, which is for government officials to meet world-famous a rtists and performing groups.Now it has become an important window of cultural exchange between China and the world and a bridge of artistic ommunication.Shanghai Urban Planning Exhibition HallLocation:It is located in the east of the City Hall.Shanghai Urban Planning Exhibition Hall has a total floor space of 19 thousand square meters. It f ully displays the achievements of Shanghai in city planning and construction and embodies the th eme of “city, man, environment, and development”. The Exhibition Hall adopts modern exhibition technology and uses high-tech to achieve an integration of professionalism, knowledge, interest, and art, giving stress to the exhibition of the future of the city. Citizens and tourists can see the ch anges of the leased territory, the vicissitudes of the Bund, the achievements of Shanghai in urbanplanning and construction ever since the reform and opening-up of the country, in particular, sin ce the 1990s, and the rapid changes of the Pudong New Area. Above all, they can see the bright f uture of Shanghai there. The main model of urban planning, which is in the proportion of 1:2000, exhibits the urban geography and scenery in an extent of a hundred and more square meters wit hin the inner elevated ring road. It is the world’s biggest model of urban planning.This amazing building contains an incredibly accurate model of the city in a couple of decades, co mplete with every tiny little detail and every single building! The model is huge and incredible. Th ere is also a super-cool rotating statue of Shanghai's modern buildings in the lobby.。

霍尔传感器 hall effect sensors

&KDSWHU+DOO (IIHFW 6HQVRUVIntroductionThe Hall effect was discovered by Dr. Edwin Hall in 1879 while he was a doctoral candidate at Johns Hopkins University in Baltimore. Hall was attempting to verify the theory of electron flow proposed by Kelvin some 30 years earlier. Dr. Hall found when a magnet was placed so that its field was perpendicular to one face of a thin rectangle of gold through which current was flowing, a difference in potential appeared at the opposite edges. He found that this voltage was proportional to the current flowing through the conductor, and the flux density or magnetic induction perpendicular to the conductor. A l-though Hall’s experiments were successful and well received at the time, no applications outside of the realm of theoretical physics were found for over 70 years.With the advent of semiconducting materials in the 1950s, the Hall effect found its first applications. However, these were severely limited by cost. In 1965, Everett Vorthmann and Joe Maupin, MICRO SWITCH Sensing and Control senior d e-velopment engineers, teamed up to find a practical, low-cost solid state sensor. Many different concepts were examined, but they chose the Hall effect for one basic reason: it could be entirely integrated on a single silicon chip. This breakthrough resulted in the first low-cost, high-volume application of the Hall effect, truly solid state keyboards. MICRO SWITCH Sensing and Control has produced and delivered nearly a billion Hall effect devices in keyboards and sensor products.Theory of the Hall EffectWhen a current-carrying conductor is placed into a magnetic field, a voltage will be generated perpendicular to both the current and the field. This principle is known as the Hall effect.Figure 2-1 illustrates the basic principle of the Hall effect. It shows a thin sheet of semicon-ducting material (Hall element) through which a current is passed. The output connections are perpendicular to the direction of current. When no magnetic field is present (Figure 2-1), current distribution is uniform and no potential difference is seen across the output.When a perpendicular magnetic field is present,as shown in Figure 2-2, a Lorentz force is exerted on the current. This force disturbs the currentdistribution, resulting in a potential difference (voltage) across theoutput. This voltage is the Hall voltage (V H ). The interaction of the magnetic field and the current is shown in equation form as equ a-tion 2-1.Hall effect sensors can be applied in many types of sensing devices. If the quantity (parameter) to be sensed incorporates or can incorporate a magnetic field, a Hall sensor will perform the task.V H ∝ I × BFormula (2-1)Figure 2-4 Basic Hall effect sensorA differential amplifier with these characteristics can be readily integrated with the Hall element using standard bipolar transistor technology. Temperature compensation is also easily i n tegrated.As was shown by equation 2-1, the Hall voltage is a function of the input current. The purpose of the regulator in Figure 2-4 is to hold this current constant so that the output of the sensor only reflects the intensity of the magnetic field. As many systems have a regulated supply available, some Hall effect sensors may not include an internal regul a tor.Figure 2-12 NPN (Current sinking) . . . Digital output sensor。

hall effect

霍尔元件在汽车工业中的的应用
• 车速、转速检测
通常汽车的转速检测中，使用磁电式检测系统测量转速，但是它存在检测速度阈值的问题，在低速行驶中无法准确的检测，这是磁电式传感器的固有特性，然而低速数据也是至关重要的。由霍尔效应原理可以得知，霍尔传感器的输出电压VH与被测量导体的速度无关。它是将速度转换为脉冲测量，所以即使速度是 0 或者理论上速度极限快，其均可以满足速度的测量，也因此现代汽车车速测量传感器开始大规模使用霍尔式传感器。
开关型霍尔集成元件
霍尔效应简介
霍尔集成电路
霍尔元件在汽车工业中的应用
结束语
霍尔元件在汽车工业中的的应用
汽车电气与电子是汽车的灵魂，它不但保证了汽车安全性、可靠性和舒适性，而且使汽车更有灵气。现代技术的汽车配有很多传感器，而其中霍尔传感器就是作为汽车感觉器官的传感器将各种输入参量转换为电信号。这些电信号是为调节和控制发动机管理系统、安全系统和舒适系统所必需的。
霍尔元件在汽车工业中的的应用
方式二磁钢测速与电子打火
磁钢用来提供霍尔能感应的磁场，当霍尔元件以切割磁力线的方式相对磁钢运动时，在霍尔输出端口就会有电压输出，所以霍尔传感器和磁钢需要配对使用。霍尔传感器检测转速示意图如下。在非磁材料的圆盘边上粘贴一块磁钢，霍尔传感器固定在圆盘外缘附近。圆盘每转动一圈，霍尔传感器便输出一个脉冲。通过单片机测量产生脉冲的频率，就可以得出圆盘的转速。同样道理，根据圆盘(车轮)的转速，再结合圆盘的周长就是计算出物体的位移。如果要增加测量位移的精度，可以在圆盘(车轮)上多增加几个磁钢。同时此原理也可用于点火电路，每当磁钢转到霍尔器件时，输出一个脉冲，经放大升压后送人点火线圈。
由于齿轮的转动，使得通过霍尔器件的磁件将输出一准正弦波电压，然后此信号经过整形电路如施密特电路使信号转换为脉冲电压。由于差分霍尔传感器使用两个霍尔器件，且它们的霍尔电压相位相差180 °再经过差分放大后，其灵敏度是普通霍尔传感器（单霍尔器件）的两倍。

信息工程专业术语（16）

hacker 计算机迷 half adder 半加器 half byte 半字节 half current 半选电流 half duplex 半双向的 half duplex channel 半双向通道 half duplex circuit 半双⼯电路 half duplex line 半双⼯线路 half duplex operation 半双通信 half duplex transmission 半双⼯传输 half select 半选 half subtractor 半减器 half title 副标题 half tone 半⾳ half toning 半⾊导术 half word 半字 half word boundary 半字界 half word buffer 半字缓冲器 half write pulse 半写脉冲 hall device 霍⽿掐 hall effect 霍⽿效应 hall element 霍⽿掐 hall transducer 霍⽿传感器 halt 停⽌ halt address 停⽌地址 halt instruction 断点指令 halt key 停⽌键 halt point 断点 halt signal 停⽌信号 hamilton's function 哈密尔顿函数 hammer 印字锤 hamming code 汉秒 hamming distance 汉娩距 hand feed ⼿⼯馈送 hand feed punch ⼿⼯馈送穿孔机 hand held calculator ⼿提式计算器 hand held computer ⼿提式计算机 hand operation ⼿⼯操作⼈⼯操作 handler 处理程序 handling specification 操祖程 handshake 信号交换 handshaking 建⽴同步交换 handshaking protocol 信号交换协议 handshaking signal 认可信号 hang up 暂停 hard copy 硬拷贝 hard copy terminal 硬拷贝终端 hard disk 固定磁盘 hard error 硬错误 hard failure 硬失效 hard image 对⽐图象 hard sectored disk 硬扇⾯盘 hard stop 硬件停机 hardcore 核⼼硬件 hardware 硬件 hardware algorithm 硬件算法 hardware architecture 硬件总体结构 hardware check 硬件检验 hardware check point 硬件检验点 hardware compatibility 硬件兼容性 hardware component 硬件成分 hardware configuration 硬件配置 hardware costs 硬件费⽤ hardware design 硬件设计 hardware device 硬件部件 hardware division 硬件除法 hardware engineer 硬件⼯程师 hardware environment 硬件环境 hardware error 硬件错误 hardware failure 硬件故障 hardware independence 硬件独⽴性 hardware interrupt 硬件中断 hardware maintenance 硬件维修 hardware module 硬件模块 hardware multiplication 硬件乘法 hardware program 硬件程序 hardware redundancy 硬件冗余法 hardware reliability 硬设备可靠性 hardware representation 硬件表⽰ hardware restriction 硬件限制 hardware sprite 硬件⼦画⾯ hardware stack 硬件栈 hardware subprogram 硬件辅程序 hardware support 硬件⽀持 hardware system 硬件系统 hardwared automation 硬的⾃动化 hardwired knowledge 硬连线知识 hardwired logic 硬连线逻辑 hardwired subprogram 硬连线辅程序 harmonic analysis 谐波分析 harmonic analyzer 谐波分析仪 harmonic distortion 谐波失真 harmonic frequency 谐频 harmonic response characteristic 谐波响应特性 hartley 哈特利 hash ⽆⽤数据 hash addressing 散列寻址 hash chain 散列链 hash function 散列函数 hash table 散列表 hash total ⽆⽤数据总和 hashing 散列法 hashing function 散列函数 hazard rate 故障率 hdb ⾼密度双极编码 hdtv ⾼清晰度电视 hdx 半双向的 head 头 head crash 磁头碰撞 head gap 磁头缝隙 head per track disk 固定头磁盘 head processor 枝理机 head stack 磁头组 header 头部 header card 标题卡⽚ header label ⽂件始标 header line 标题⾏ header record 标题记录 header segment 标题段 header table 标题表 heading 头部 heap 堆 heap manager 堆管理 heat conduction 热传导 heat dissipation 热耗散 heat exchanger 热交换器 heat sensitive paper 热敏纸 heating coil 加热线圈 heavy duty software 重负载软件 heavy line 粗线 height balanced tree ⾼度平衡树 help 帮助 help information 求助信息 help library 求助库 help line 求助⾏ help menu 求助菜单 help mode 求助⽅式 help request 求助请求 help screen 帮助屏幕 hesitation 暂停 heuristic algorithm 启发式算法 heuristic approach 试探法 heuristic program 试探程序 heuristic programming 试探编程 heuristic routing 试探选路 heuristics 试探 hexadecimal constant ⼗六进制常数 hexadecimal digit ⼗六进制数字 hexadecimal format ⼗六进制格式 hexadecimal keyboard ⼗六进制键盘 hexadecimal notation ⼗六进制记数法 hexadecimal number ⼗六进制数 hexadecimal number system ⼗六进制记数制 hexadecimal system ⼗六进制 hf bus ⾼频母线 hidden fault 隐故障 hidden file 隐式⽂件 hidden line elimination 隐线消除 hidden line removal 隐线消除 hidden surface 隐⾯ hierarchical access method 分层存取法 hierarchical addressing 分层寻址 hierarchical database 分层数据库 hierarchical direct access method 分层直接存取法 hierarchical indexed direct access method 分层她直接存取法 hierarchical indexed sequential access method 分层她顺序存取法 hierarchical memory 分层存储器 hierarchical multicomputer system 分级多计算机系统 hierarchical network 层次络 hierarchical organization 分层结构 hierarchical sequential access method 分层顺序存取法 hierarchical structure 分层结构 hierarchy 分级 hierarchy chart 层次图 hierarchy memory 分层存储器 high bound 上界 high byte ⾼位字节 high definition television ⾼清晰度电视 high density bipolar coding ⾼密度双极编码 high density recording ⾼密度记录 high end computer ⾼级计算机 high level compiler ⾼级编译程序 high level computer ⾼级语⾔计算机 high level data link control ⾼级数据链路控制程序 high level goal ⾼级⽬标 high level language ⾼级语⾔ high level language computer ⾼级语⾔计算机 high level programming ⾼级程序设计 high level programming language ⾼级编程序语⾔ high level protocol ⾼级协议 high level signal ⾼电平信号 high order ⾼位 high order digit ⾼数位 high order language ⾼级语⾔ high order position ⾼位 high order zero ⾼位零 high performance computer ⾼性能计算机 high performance equipment ⾼性能设备 high performance mos ⾼性能⾦属氧化物半导体 high priority user ⾼优先⽤户 high resistance paper ⾼电阻纸 high resolution ⾼分辨率 high resolution graphics ⾼分辨率图 high resolution mode ⾼分辨率⽅式 high resolution timer ⾼分辨率计时器 high speed bus 快速总线 high speed carry ⾼速进位 high speed circuit ⾼速电路 high speed computer ⾼速计算机 high speed data network ⾼速数据络 high speed memory ⾼速存储器 high speed multiplication ⾼速乘法 high speed printer ⾼速打印机 high speed reader ⾼速输⼊机 high threshold logic ⾼阈值逻辑 high value resistor ⾼值电阻 high voltage level ⾼压电平 higher level language ⾼级语⾔ higher level module ⾼级模块 highest byte 字节 highest order 位 highway 局内线路 histogram 直⽅图 history 档案 history file 存档⽂件 hit 命中 hit on the fly printer 飞唤打印机 hit rate 命中率 hldlc ⾼级数据链路控制程序 hll ⾼级语⾔ hmos ⾼性能⾦属氧化物半导体 hold mode 保持状态 holding area 保存区 holding circuit 保持电路 holding register 保持寄存器存储寄存器 holding time 保持时间 hole 空⽳ hole conduction 空⽳导电 hole pattern 孔模 hollerith card 霍勒内斯卡⽚ hollerith code 霍勒内斯码 hollerith constant 霍勒内斯常数 hollerith machine 霍勒内斯计算机 hologram 全息照相 holographic memory 全息照相存储器 holographic retrieval 全息检索 home 出发点 home address 内部地址 home block 起始块 home channel 市内线路 home computer 家⽤计算机 home exchange 本地交换局 home key 起始键 home location 起始单元 home loop 本地回路 home position 原位 home record 起始记录 homography 同形异义性 homophone 同⾳字母 hook 钩 hop 转移 hopper 送卡箱 horizontal cursor 横向光标 horizontal feed ⽔平馈送 horizontal line ⽔平线 horizontal microinstruction 横向微指令 horizontal microprogramming 横向微程序设计 horizontal parity 横向奇偶 horizontal pointer 横向指⽰符 horizontal polarization ⽔平极化 horizontal processor 横向处理机 horizontal redundance check 横向冗余校验 horizontal tabulation 横向制表 horizontal tabulation character 横向制表字符 horn clause 霍队句 host bus 周线 host communications 与助通信 host computer 制算机 host language 诛⾔ host language processor 诛⾔处理程序 host machine 助 host processor 枝理机 host system 值统 hot line 热线 hot loop 热线 hot spare 热备件 hot standby 热备件 hot zone ⾏续区 housekeeping 内务操作 housekeeping data 内务数据 housekeeping information 内务信息 housekeeping instruction 内务指令 housekeeping operation 内务操作 housekeeping routine 内务程序 housing 箱 hrt ⾼分辨率计时器 ht 横向制表 htl ⾼阈值逻辑 hub 磁盘套 hue ⾊调 hull 外壳 human computer interface ⼈机接⼝ human engineering ⼯效学 human factor ⼈员因素 human factor error ⼈错误 human failure ⼈为失效 human oriented language ⾯向⼈的语⾔ hunting 不规则振荡 hybrid circuit 混合电路 hybrid computer 混合计算机 hybrid database 混合数据库 hybrid integrated circuit 混合集成电路 hybrid microcircuit 混合微电路 hybrid network 混合络 hybrid packaging 混合组装 hybrid system 混合系统 hypercube 超⽴⽅ hypermedia 超媒体 hypertext 超级正⽂ hypervisor 超级监视者 hyphen 连字符 hyphenation 连字符连接 hypothetical reference circuit 假设基准电路 hypothetical world 假想世界 hysteresis 滞后现象 hysteresis curve recorder 滞后曲线记录器 hysteresis error 滞后特性误差 hysteresis loop 滞后回线 hysteresis loop recorder 滞后曲线记录器 hysteresis meter 滞后测定器 i/o 输⼊输出 i/o bound task 受输⼊输出限制的任务 i/o buffer 输⼊输出缓冲器 i/o bus 输⼊输出总线 i/o bus controller 输⼊输出总线控制器 i/o channel 输⼊输出通道 i/o control 输⼊输出控制 i/o control program 输⼊输出控制程序 i/o control system 输⼊输出控制系统 i/o conversion 输⼊输出数据型转换 i/o data 输⼊输出数据 i/o limited program 受输⼊输出限制的程序 i/o operation 输⼊输出操作 i/o port 输⼊输出⼝ ia 指令地址 ibm ibm ibm compatible computer ibm 兼容机 ic 集成电路 ic chip 集成电路⽚ ic computer 集成电路计算机 ic memory 集成电路存储器 ic socket 集成电路插孔 ic tester 集成电路测试机 icon 图标 iconic representation 图象表⽰ id 识别码 ideal value 理想值 idealized system 理想化系统 ident 识别 identical transformation 恒等变换 identification 识别 identification byte 标识字节 identification card 标识卡⽚ identification character 标识字符 identification code 识别码 identification division 识别部分 identifier 标识符 identify element 全同元件 identifying information 识别信息 identity 等同 identity gate 同门 identity operation 全同运算 identity unit 全同单元 idle channel 空闲通道 idle character ⽆效字符 idle mode 空闲状态 idle state 空闲状态 idle time 空闲时间 idn 综合数字 idp 集中数据处理 if statement 如果语句 if then operation 蕴含操作 ifip 国际信息处理联合会 il 等平⾯集成注⼊逻辑 il technology il 技术 illegal access ⾮法存取 illegal access protection ⾮法存取保护 illegal character ⾮法字符 illegal code ⾮法代码 illegal command check ⾮法命令校验 illegal instruction ⾮法指令 illegal operation ⾮法操作 illegal symbol ⾮法符号 image 图象 image copy 图象副本 image dissector 析像器图像传感器 image file 图象⽂件 image generation 图象⽣成 image graphics 图象图形 image memory 图象存储器 image processing 图象处理 image processor 图象处理机 image regeneration 再⽣ image restoration 图象复原 image sensor 图象传感器 image store 图象存储 image transmission 视频传输 image understanding 图象理解 imager 图象机 imaginary number 虚数 imaginary part 虚数部 immediate access ⽴即存取 immediate access memory ⽴即存取存储器 immediate access storage ⽴即存取存储器 immediate address ⽴即地址 immediate addressing ⽴即寻址 immediate answer ⽴即应答 immediate command ⽴即命令 immediate data 直接数据 immediate instruction ⽴即指令 immediate mode ⽴即⽅式 immediate operand ⽴即操 immediate predecessor relation 直接先秦系 immediate processing 直接处理 impact printer 或式打印机 impact printing 或式印刷 imparity check 奇数奇偶性较验 impedance 阻抗 imperative go to statement 强制go to语句 imperative language 强制性语⾔ imperative statement 强制语句 imperfect tape 缺陷带 implementation 执⾏ implementation specification 实现规格 implementator 实现者。

凤凰古城英语导游词精选

凤凰古城英语导游词精选凤凰古城，位于湖南省湘西土家族苗族自治州的西南部，土地总面积约10平方千米。

20xx年底约5万人口，由苗族、汉族、土家族等28个民族组成，为典型的少数民族聚居区。

以下是我为大家整理好的凤凰古城英语导游词，欢送大家参考学习哦!凤凰古城英语导游词Ladie.an.gentleme..welcom.t.fenghuang.th.plac.wher.wer.arrivin.i.on.o.th .tw.mos.beautifu.tow.i.china----th.ol.tow.o.fenghuang,It..ver.importan.poin.tha.connect.huaihu.huna.an.tongre.guizho.together .an.it.th.hometow.o.m.shengcongwen.ndscapes,it.ver.ho.fo.travellin.sinc.th.ol.t ime.eve..lo.o.teleplay.wer.produce.here.fenghuan.i.als..dradl.fo.famou.peopl.,shencongwe.an.xiongxilin.ar.bot.spen.thei.childhoo.here.Now.let.se.ou.t.enjo.thes.fantasti.goo.views.Th.forme.residenc.o.shencongwenThi.i.th.forme.residenc.o.shencongwen,.ver.famou.auther.archaeologis.a n.historia.i.china.Line.i.th.zhongyin.stree.i.th.sout.par.o.th.fenghuan.ol.town.th.residenc.i.. typica.spaciou.ancien.countryar.wit.specia.tectoni.styl.o.min.an.qin.dyna sty.wal.int.th.yard.yo.ca.fin.tha.ther.i..smal.pati.i.th.cente.o.th.countryard .whic.i.buil.wit.re.rock.aroun.th.pati..ther.ar.abou.1.room.whic.ar.smal.bu .decorate.b.specia.carve.woode.window..it.s.beautiful.Thi.countryar.i.buil.b.m.shen.grandfathe.i.186.o.dec.28,1902.shencongw e.wa.bor.i.th.ol.countyard.an.spen.hi.childhoo.here.i.1917,whe.h.wa.1.ye ar.old.m.she.lef.famil.an.joine.th.army.fro.191.t.1922.m.she.ha.live.wit.so ildiers.farmers.worker.an.som.otherCommo.people,an.kno.thei.tragi.lives.thi.specia.experienc.stunne.u.hi.en thusias.o.writhin..s.i.1919.m.she.wen.t.beijin.alone.an.bega.hi.har.writin. .afte.hi.serie.o.work.wes.o.huna.fring.tow.wer.punished.m.she.becam.na tio.-wid.wel.-known.a.tha.time.h.wa.evenA.famou.a.luxun.anothe.famou.authe.i.chies.literatur.area.it.sai.tha.shen congwe.i.th.on.wh.i.th.mos.possibl.t.wi.th.prize.M.she.devote.al.hi.lif.t.writing,hi.5-millio.wor.work.ar.thoug.a.th.preciou.l egac.t.th.worl.literature.meanwhile.thes.work.ar.als.ver.veluabl.dat.fo.res earchin.th.histor.o.huna.provinc.an.eve.china.Thi.101-years-ol.countyar.wa.renovate.i.11019.th.1s.roo.o.th.righ.han.i.f o.displayin.m.shen.photos.an.wha.displaye.i.th.2n.roo.ar.m.shen.handwr itingarticles.a.th.lef.side,yo.l.fin..lis.o.m.shen.wor.o.differen.additions.i.th .cente.o.th.middl.roo..ther.i..m.shen.lin.drawin.hangin.o.th.wall.th.lef.frin gl.roo.i.m.shen.bedroo.an.anothe.on.o.th.righ.i.ful.o.marbl.desk.an.chair凤凰古城英语导游词Phoeni.ancien.cit..nationa.historica.cultura.well-know.city.hav.bee.eas.A. L.b.Ne.Zealande.famou.write.roa.prais.fo.th.on.o.Chines.mos.beautifu.lit tl.city.ra.sprou.villag.her.wit.th.virtu.o.luck.head.obe.foreve.th.Buddhis.n e.mountai.o.fierc.hol.rive.an.Guizho.appearanc.neighbor.i.boso.mel..luck n.betwee.wil.g.throug.road.20.natio na.highwaie.wit.Xian.Qia.sav.roa.wea.for.fro.count.boundar.pas..coppe.b enevolen.bi.moo.airpor.distanc.count.onl.2.kilometers.traffi.convenient. phoeni.scener.beautiful.histor.long.sceni.spot.an.historica.site..lot.cit..an cien.gat.towe..settl.ancien.courtyar.elegan.appearanc.tomorro.still.ancie n.simpl.Tu.rive.quie.flo.quietl.she..suburba.hav.sout.Chin.mountai.nation a.fores.par.an.cit.tak.of.artisti.palac.od.bea.hole.buil.i.Tan.th.bridg.ancien .cit.o.yellowis.filamen.o.generation.attrac.worldwid.attentio.sout.th.Grea n.outstandin.perso.spirit.nam.abl.c rg.numbers.beautifu.littl.cit.phoeni.mountai.city.locat.i.Tu.rive.side.crow.mountai.surroun..(mountain)pas.mal.odd.th.rive.wate.o.dar.gree.tak.of.fro.ancien.cit. wal.curve.pas..fol.gree.sout.Chin.th.foo.o..mountai.fal.reflec.rive.heart.ri ve.i.th.severa.poin.o.fishin.vessel.mountai.betwee.dus.dru.mornin.cloc.cr .simultaneously.stee.clif.o.han.foo.buildin.ligh.smok.curlin.upwards.pie.si ng...phoeni.stin.jus.lik. .pai.o.thic.in.i.yo.shal ndscap.paintin..i.Chan.Yan.ancien.cit.buil.wit.ston.roc.boar .stree..th.ancien.buildin.o.bot.side.hol.physica.feature.each.ro.upo.row.p avilio.buildin.cabine.overlapping.flutte.a.hug.dragon.see.A.fis.sprea.th.wi ng..drizzl.soun.in.see.biograph.knoc.int.th.ox-hid.spike.shoe.o.fragran.pe rso.attac.stree.surface.sen.ou..sound.mak.on.produc.th.sens.tha.separat e.lifetim..She.Con.We.forme.residenc.locat.i.sout.i.battalio.street.i.th.sou t..o..typica.cas.joi.ancien.courtyard.ancien.courtyar.cente.hav.littl.courty ard.sprea.wit.re.ston.squar.slabstone.courtyar.fou.week.i.th.ancien.hous. o.bric.timbe.structure.straigh.hous.3.wing-roo.4.remai.1.between.hous.s hort.thoug.dra.phoeni.withou.vultur.dragon.bu.loo.smal.an.exquisit.nove l.antique.hav.especiall.th.woode.windo.o.carvin.Xian.wes.characteristic.e speciall.eye-catching.Phoeni.i.o.Decembe.28,190..She.Con.We.i.bor.i.her..h.childhoo.i.i.her.pas s.o.mor.tha.10.years.i.She.Con.We.grandfathe.She.Ho n.bu.o.ric.han..develo.becaus.o.history.fe.b.i.eas.God.fo.sho.fo.She.Con.We.th.respectfu.feeling.o.ol.person.stud.hi.stud.frequentl.fro.Li.har.pe.pl oug..fo.th.outstandin.contributio.o.nationa.literatur.caus.sel.stud.spirit.e ernmen.decid.bu.r etur.thi.house.renovat.again.tak.patter.g.t.capita.sen.She.Con.writin.appr ov..She.Con.We.tak.il.reception.pu.forwar.opinio.fo.pattern.sa..hous.i.meshe..repai..i.als.goo..bu.t.pu.u..repai..d.no.spen.man.money.i.i. poo.tha.hometow.i.returne..t.economiz.a.fa.a.possibl..endur.renovat..ma k.thi.di.ancien.courtyar.reappea.look.han.o.curren.doo.hav.She.Con.We.forme.residenc.horizonta.inscribe.board.righ..room.i.She.Con.We.th.photograp.o.lif.story ..room.i.She.Con.documen.draf.original.lef.wing-roo.displa.variou.edition .fro.writin.works.straigh.hous.centra.scrol.han.th.sketc.portrai.o.She.Con. Wen.lef.roo.i.bedroom.i.She.Con.We.i.bor.place.righ.roo.displa.th.des.etc .thin.o.marbl.to.o..table.Bea.hope.tha.ag.forme.residenc.locate.i..phoeni.ancien.littl.alle.i.cit.nort .writin.sta.stree.i.th.pas.easter.20.o.forme.residenc.metr.i.beautifu.Tu.riv er.forme.residenc.i.fo.quadrangl.th.woode.til.structur.o.sout.ancien.type. compar.shor.bu.th.ver.fin.extan.hous.o.forme.residenc..i.maintenanc.basi call.origina.look.hav.sprou.cla.sentimen.ver.much.i.count.ke.historica.reli. protectio.unit.th.Republi.o.chin..years.1917.summe.autum.durin.capita.saliv..tap.floo.serious.h.tak.th.responsibilit.D.d.floo.rive.wor.matter.concer nin.reconstruction.uphol.rais.mone..relie.victims.th.Republi.o.chin..years .1918)ernmen.agre..wil.fragran.mountai.quie.suitabl.garde.alte.b catio.i.hi.b..natura.calamit.wai.child.h.ha ndl.al.courtyar.affir.2.year.fo.mor.than.h.hav..poetr.writ.road.th.tre.han.o. .fo.seein.flower.chil. mont.an.coloure.al.length.pic.u.coloure.smile.Popla.th.domesti.beginnin.o.ancestra.hal.buil.i.roa.smoot.1.years.183.ye ars.th.abou.tw.floo.an.quadrangl.o.timbe.structure.cove.a.are.o.77.squar positio.o.ma i.hall.submi.rectangle.stag.res.fo.singl.eave.summit.ac.a.satisfactor.cu.arc .unde.eaves.1.hig.metres..colum.vulture.drago.carv.phoenix.stag.figh.typ .fo.wearing.mai.hal.i.lif.bea.type.entir.buildin.workmanshi.meticulous.ver .ric.nationa.characteristic.belon.t.count.ke.historica.reli.protectio.unit.po pla.domesti.ancestra.hal.repos.i.th.ancien.sid.o.cit.wal.o.count.northeast .crow.princ.insur..frui.brav.marqui.an.tow.ro.tota.soldie.popla.les.virtu.co ntribut.mone.construc.i.settl.roa.smoot.1.years.183.year.).ancestra.hal.fr p osition.i.th.quadrangl.buildin.o.typica.case.cove.a.are.o.77.squar.metres. stag.res.fo.singl.eave.summit.wea.cu.typ.structure.1.hig.metre.an.surfac..ric.metres.ente..dee.metres.eave.pus..colum.vultur.drago.a.jad.cu.carv.p hoenix.mai.hal.construc.fo.liftin.bea.type.gabl.pus.fo.ca.th.back.divid.int. .Min.E.A.3.bot.side.matc.hav.wing-room.popla.th.domesti.desig.o.ancest ra.hal.exquisite.wor.meticulous.window.doo.an.eave.decoration.M.hollo w-ou.carving.overal.buildin.hav.brigh.nationa.characteristi.an.ver.hig.buil din.artisti.value.Chines.sout.th.Grea.Wal.locate.i.Xian.Qia.borde.area.o.fro.Guizho.coppe. kernel.insur.t.Huna.Jin.th.38.o.tota.lengt.remai.in.buil.i.Min.Cha.Wa.al.pr eviou.4.years.par.1615).fe.b.exten.repai.i.mor.rea.tha.Qin.Cha.Ji.Jin.finali z.th.desig.o..it.pillbo.wal.betwee.yea.i.2..metre.1..bas.wid.metres.to.wid. .metre.an.wal.bod.normall.hig.mostl.dra.materia.o.th.spo.wit.stone.shal. plicati e.i.statio .troop.th.floo.fortress.villag.car.an.sentr.pos.employe.b.th.empero.Taiwa partmen..clos.an.countles.buil.wit.ston.soldie. room.the.genera.garriso.arme.force.800.person.contro..no.som.plac.na me.a..L.Yin.an.da.sta.battalio..yello.jointl.operat..Wan.P.stor.u.battalio..tri itar.battalio.an.o.cu.battalio.etc.t ap.th.plac.o.battalio.wor.i.th.mai.point.o.garriso.troop.o.th.sid.o.th.Grea. Wall.导游词。

Hall Effect Aplication

Section 3 - Applications3Section 3 - ApplicationsIntroductionSolid-state switches have been available for many years. In various applications, Hall- Effect Sensors (Hall ICs) have replaced mechanical contact switches completely. In the mid 1980’s the ignition points in automobiles were replaced by Hall ICs. The automotive market now consumes more than 40 million Hall ICs per year. Melexis has been manufacturing high quality Hall-Effect Sensors and signal conditioning ASICs for nearly a decade, and has pioneered the next generation of programmable sensors and sensor interfaces.This section contains some fundamental information about Hall-Effect sensors, magnetics, and the added value of programmable sensors and sensor interfaces. It is intended to be useful for the novice as well as the expert. Design Kit MaterialsThis section refers to magnets and devices which are included in the Melexis Hall-Effect Sensor Design Kit or the MLX90308 demo kit. Contents of these kits are listed below. These items can be ordered directly from the factory by contacting Melexis at (603) 223-2362.Hall-Effect Sensor Design KitSquare Neodymium, sample magnet “A” (approximately 200mT)Cylindrical Neodymium, sample magnet “B” (approximately 380mT)Gauss meter circuit diagramMLX90215 linear Hall Effect sensor and calibration chartSamples of various Melexis Hall ICsSensor Interface Demo KitMLX90308 demo boardSerial interface cableMLX90308 programming software (31/2” Diskette)Note: Kit requires IBM compatible PC with a free COM portMelexis Reference MagnetsMelexis offers calibrated magnets for use as a reference magnetic field available in 3 ranges. These are for ref-erence only, and are not calibrated from a traceable source nor are they intended for calibration of any type of instrumentation. They are intended for programming MLX linear Hall ICs, and for general lab reference. SDAP-RM-10 10mT calibrated reference magnetSDAP-RM-50 50mT calibrated reference magnetSDAP-RM-100100mT calibrated reference magnetSection 3 - Applications3-1The Hall-EffectThe Hall-Effect principle is named for physicist Edwin Hall. In 1879 he discovered that when a conductor or semiconductor with current flowing in one direction was introduced perpendicular to a magnetic field a voltage could be measured at right angles to the current path.The Hall voltage can be calculated fromV Hall= σB where:V Hall=emf in voltsσ= sensitivity in Volts/GaussB = applied field in GaussI = bias currentswitch. (right)The continuing evolution of Hall transducers technology saw a progression from single element devices to dual orthogonally arranged elements. This was done to minimize offsets at the Hall voltage terminals. The next pro-gression brought on the quadratic of 4 element transducers. These used 4 elements orthogonally arranged in a bridge configuration. All of these silicon sensors were built from bipolar junction semiconductor processes. A switch to CMOS processes allowed the implementation of chopper stabilization to the amplifier portion of the circuit. This helped reduce errors by reducing the input offset errors at the op amp. All errors in the circuit non chopper stabilized circuit result in errors of switch point for the digital or offset and gain errors in the linear out-put sensors. The current generation of CMOS Hall sensors also include, a scheme that actively switched the direction of current through the Hall elements. This scheme eliminates the offset errors typical of semiconduc-tor Hall elements. It also actively compensates for temperature and strain induced offset errors. The overall effect of active plate switching and chopper stabilization yields Hall-Effect sensors with an order of magnitude improvement in drift of switch points or gain and offset errors.Melexis uses the CMOS process exclusively, for best performance and smallest chip size. The developments to Hall-Effect sensor technology can be credited mostly to the integration of sophisticated signal conditioning cir-cuits to the Hall IC. Recently Melexis introduced the world’s first programmable linear Hall IC, which offered a glimpse of future technology. Future sensors will programmable and have integrated microcontroller cores to make an even “smarter” sensor.How Does it Work?A Hall IC switch is OFF with no magnetic field and ON in the presence of a magnetic field, as seen in Figure1. The Earth’s field will not operate a Hall IC Switch, but a common refrigerator magnet will provide sufficient strength to actuate the sensor.Figure 1, How it WorksNo magnetic field = OFF South magnetic pole = ONBut How Much Do They Cost?The cost of a Hall IC depends on the application. Automotive Hall ICs may cost $0.35 to $1.50 or more, while Hall ICs for Industrial and Consumer applications, such as appliances, game machines, industrial manufactur-ing, instrumentation, telecom and computers, cost $0.20 or less.Automotive chip costs are higher because of the unique requirements for shorted loads, reverse battery, double battery voltage, load dump, 100% test at three temperatures and temperature operation up to 200o C. Devices that do not meet the stringent automotive specifications are more than adequate for other environments, such as in industrial and consumer products. Melexis products are created primarily to meet automotive specifications, with off-spec parts sold at a lower price. The cost directly reflects how well the part performs versus the sever-ity of the operating environment.Section 3 - Applications3-2Activation - Using Hall-Effect SwitchesA switch requires a Hall IC, a magnet and a means of moving the magnet or the magnetic field. Figures 2, 3 and 4 show several ways by which a magnet can control the Hall IC switch. The following examples are simi-lar in principle to most real applications. Slide-by, proximity and interrupt configurations represent the three basic mechanical configurations for moving the magnet in relation to the Hall IC.Slide-by SwitchIn the Slide-by configuration, the motion of the magnet changes the field from North to South within a small range of motion. This configuration provides a well defined position and switching relationship. The minimum required motion may be as little as 1 or 2 mm.Figure 2, Slide-by SwitchIn Figure 2A, the South magnetic pole is too far away, so the switch stays OFF. In Figure 2B, the South magnetic pole turns the switch ON.Section 3 - Applications3-3Proximity SwitchThe proximity configuration is the simplest, though it requires the greatest amount of physical movement. It is also less precise in terms of the position that results in turning the sensor ON and OFF. The magnetic field intensity is greatest when the magnet is against the branded face of the Hall IC and decreases exponentially as the magnet is moved away.Figure 3, Proximity SwitchIn Figure 3A, the South magnetic pole is close to the Hall IC, so the switch turns ON. In Figure 3B, the South magnetic pole has moved too far away, so the switch turns OFF.Section 3 - Applications3-4An invisible or sealed switch may be made with either configuration. The Hall IC may be inside a sealed container to shield it from oil or water, while the magnetic field penetrates or “sees” through the sealed enclosure. Refer to Figure 4.Figure 4, Sealed BoxThe Hall IC can be shielded from the elements and remain sensitive to magnetic fields.Interrupt SwitchWhen the Hall IC and magnet are fixed, the Hall IC can be activated using a ferrous vane. This system,composed of a Hall IC, magnet and ferrous vane is called an interrupt switch. In the interrupt switch the magnet is positioned so the South pole turns ON the switch while the Hall IC and magnet positions are fixed relative to each other. When a vane made of a ferrous material is placed between the magnet and Hall IC, the magnetic field is shunted or reduced to a very small fraction of the maximum field, turning the switch OFF. This vane is shown in Figure 5 as a notched interrupter. This switch is an effective way to sense position.Figure 5, Interrupt SwitchIn Figure 5A, the South magnetic pole is exposed to the Hall IC through the vane, so the switch turns ON. In figure 5B, the switch turns OFF because the magnetic field is blocked by ferrous material.Section 3 - Applications3-5Rotary Interrupt SwitchThe interrupt switch can be incorporated in applications of speed or position sensing, generally of rotat-ing objects. The Rotary Interrupt Switch, in Figure 6, uses a toothed ring to interrupt the magnetic field reaching the Hall IC. When a solid piece of steel (ferrous vane) blocks the magnetic field, the switch turns OFF. During the gaps, or spaces in the steel, the South magnetic pole turns ON the switch. This is the sys-tem commonly used for automotive ignition and many industrial applications, where accurate position is critical.Figure 6, Rotary Interrupt SwitchFigure 6 uses a notchedinterrupter on a rotatingshaft to activate the device.Section 3 - Applications3-6R otary Slide-by SwitchFigure 7, Rotary Slide-by SwitchThe Rotary Slide-by Switch in Figure 7 is generally used to measure rotary speed to synchronize switch-ing with position. The Hall IC is activated by a rotating magnet. When the South pole passes by the Hall IC, the IC is switched ON. As the North pole passes, the Hall IC is switched OFF. The solid circular mag-net, shown in Figure 7A, is called a Ring Magnet. A ring magnet has alternating North and South poles.Ring magnets may have from two poles to thirty-six or more, depending on size. Graph 1, below illus-trates the transition between North and South polarity at various air gaps. Notice the transition point is similar at the various gaps.Graph 1, Rotary Slide-by vs. Air gapSection 3 - Applications3-7Working With Magnetic FieldsHow Do They Work?magnetic field is described in terms of flux liTesla. The intensity of the magnetic field depends on many variables, such as cross-sectional area, length,shape, material and ambient temperature. Each one of these variables must be considered when designing the Hall Effect sensor integrated circuit and magnetic system for your application. The following section is intend-ed to explain some fundementals which are useful in Hall Sensor designs and applications.Figure 9, Magnetic SpectrumNS Figure 8, Flux PathsEvolution of MagneticsModern society would not exist in its present form if not for the development of permanent magnet technology. Many of the major advances in the last century can be traced to the development of yet better grades of magnet materials. The earliest magnets were naturally occurring iron ore chunks mostly originating in Magnesia hence the name magnes. We now know these materials to be Fe3O4, a form of magnetite. Their unique properties were considered to be supernatural. Compasses based on these magnes were called lodestones after the lodestar or guidestar. They were highly prized by the early sailing captains.The PioneersMore sophisticated magnets did not come into use until the 15th century when William Gilbert made scientific studies of magnets and published the results. He found that heating iron bars and allowing them to cool while aligned to the earth's field would create a stronger magnet than a naturally occurring lodestone. His magnet tech-nology however remained a curiosity until the 19th century when Hans Christian Oersted developed the idea that electricity and magnetism were related. He was the first to determine that magnetic fields surround a current carrying wire. It would require the development of atomic particle theories before scientific explanations of per-manent magnets made further advances. The practical applications for magnets continued throughout the 19th century.Magnetism in a solid object seems to defy rational explanation. The magnetism is developed in a manner simi-lar to electrons moving through a coil of wire, magnetic fields are created by electrons in motion around the atom-ic nucleus. This nuclear model of an atom with electrons spinning in orbit around a nucleus provides a source of charges in motion. In most materials however, the number of electrons moving in one direction equals that mov-ing oppositely and hence their magnet fields cancel. This results in no overall magnetic field for the material. It takes many electrons spinning in the same direction to generate a measurable field. Unfortunately there are kinet-ic forces at work causing atoms to constantly vibrate and rotate resulting in random alignment. The higher the temperature the more kinetic energy and the more difficult it is to maintain alignment. Fortunately soldsme mate-rials exhibit an electrostatic property known as exchange interaction which serves to maintain parallel alignment of groups of atoms. This force only works over short distances amounting to a few million billion atoms. This may sound like a large quantity but on an atomic scale it is a relatively small amount. These groups are known as dipoles and are the fundamental building blocks that determine the properties and behavior of permanent mag-net.Relative Magnetic PropertiesMagnets and magnetic materials are classified by many terms which describe many different properties, some of which are explained and used in this book. Perhaps the most commonly asked question about a magnet is “How strong is it?” Although this can lead to a complex explanation, Figure 9 is an excellent guide to the rela-tive strength of magnetic forces, from strongest magnetic forces known such as solar flares to the nearly unde-tectable magnetic signals passing through the neuro network of our bodies.The Hysteresis CurveA solid block of magnetic material is composed of multiple dipoles wherein the alignment of all of the dipoles results in a constant field of maximum value. This maximum field attainable is known as the saturation field. This condition is obtained by placing a sample of material in a sufficiently strong electromagnetic field and increas-ing the electric current through the magnetizing coil. As the samples dipoles begin to align a function for the rela-tionship between the magnetizing field and the field in the sample becomes apparent. In the low field levels the slope of the curve is very steep.This relates to the rapid alignment with the magnetizing field of a majority of dipoles. As current levels increaselinearly the number of dipoles aligning decreases. The result is a shallow slope to the function curve. At some point, related to the material properties, increases in current through the magnetizing coil will not increase the value of the field in the magnet. This is the saturation value for the material. When the external magnetizing field is removed the magnetic field value of the sample "relaxes" to a steady state known as the B r value, or resid-ual flux value.An analogy to charging a battery is appropriate. At some level the battery is fully charged and will not accept any more energy. It is an amazing thing however that the magnet will never lose its charge unless it is subjected to a larger field of opposite polarity, or if the temperature is raised above the point known as the Curie Temperature.This temperature varies depending on the material and is specified in all manufacturers data sheets.In summary we have discussed two of the three forces at work, one the magnetizing force measured in oersteds with cgs units or ampere turns/meter in the SI system. The second is the resultant or induced field in the sample, this is measured with gauss in cgs units and Teslas in the SI system (see Tables 1 and 2, below).Table 1, Magnetic Units ComparisonThe third is reluctance or its' reciprocal permeability, think of this as the magnetic resistance per unit volume of the sample being magnetized. Now that we have a magnetized magnet we can consider what occurs when forces act to de-magnetize it. If we reverse the direction of current flow in the magnetizing coil a negative field is cre-ated. As the negative current is increased the dipole alignment is reversed or undone. A curve results which is similar to the magnetizing curve but in mirror image form. When the samples' flux value is completely demag-netized the demagnetizing force at that instant is the coercive force -HC. This force is also measured like the magnetizing force in Oersteds. Increasing the negative current level in the magnetizing coil.A magnet in a closed high permeability magnetic circuit (an iron bar connecting the north to the south pole) will operate at or near the Br value. A magnet with no pole pieces will operate with a flux density down the demagnetization curve from the Br value, how far down is dependant on the aspect ratio or the ratio of the length to the diameter. Short wide magnets will generate lower flux than tall skinny magnets of the same vol-ume.The concept of the load line and the operating point on the demagnetization curve will influence many magnet-ic parameters. These include the flux density available to actuate a sensor and the reversible temperature coeffi-cient.Temperature EffectsGraphical representations are often used to determine the operating point on the demagnetization curve. Temperature effects on permanent magnets are dependent on the type of material considered. Manufacturers will specify various figures of merit to describe the temperature performance of magnet materials. Among these are the Reversible losses that are represented by Tc. The term refers to the losses in the Br and the Hc. A calcula-tion can show that for every incremental change in temperature the magnet will lose a proportion of its strength. This loss will be recovered completely so long as the temperature does not exceed the Tmax or maximum prac-tical operating temperature in air. The Tmax value is dependent on the magnets operating point on the demag-netization curve. A magnet operating closer to Br can have a higher Tmax. Irreversible losses are described as losses that can only be recovered by re-magnetizing the sample to saturation with an electromagnetic field. These losses occur when the operating point falls below the "knee" on the demagnetization curve. This can occur due to temperature and inefficient magnetic circuit design. An important feature of magnet materials is the Curie tem-perature, TCurie,. This is a temperature at which the metallurgical properties of the sample are adversely effect ed. In most applications the ambient temperature can never approach the Curie temperature without completely destroying the electronic components first.Losses Over TimeTime has minimal effect on the strength of permanent magnets. Long term studies in the industry have shown that at 100,000 hours the losses for Rare Earth Samarium Cobalt magnets were essentially zero and for Alnico 5 were less than 3%. In the case of Rare Earth Neodymium materials the losses are compounded by internal cor-rosion.Corrosion & CoatingsIt is often necessary to provide coatings to these materials to minimize the corrosion that results from the Iron content. We lay-people refer to this stuff as rust. The options for coatings include epoxies, zinc and nickel. The best of these is nickel however it is slightly magnetic and marginally reduces the available field. Coatings can also be useful with Rare Earth Samarium to minimize "spalling" or the fracture of tiny slivers from the corners of this brittle, hard material.In many sensor applications these characteristics are of little significance but as with all engineering tasks it is up to the design engineer to know what can safely be ignored and what must be consider for the projects suc-cess.Many texts are available to aid in a complete understanding of magnets. The Magnetic Material Producers Association is a trade group that establishes and maintains standards for basic grades and classes of materials. Their reference booklets are an excellent source for detailed technical data on the various generic classes of mate rials. Certain manufacturers also provide excellent databooks with helpful applications and design sections. These include Arnold Engineering Company, Magnet Sales & Manufacturing, Magnetfabrik Schramberg, Hitachi Metals; Magnetic Materials Division and Widia Magnettechnik.Rare-Earth MagnetsNeodymium Iron BoronAttributes of NeodymiumLow costVery high resistance to demagnetizationHigh energy for sizeGood in ambient temperatureMaterial is corrosive and should be coated for long-term maximum energy output Low working temperatureApplications of NeodymiumMagnetic separatorsLinear actuatorsServo motorsDC motors (automotive starters)Computer rigid disk drivesSamarium CobaltAttributes of SamariumHigh resistance to demagnetizationHigh energy (magnetic strength is strong for its sizGood temperature stabilityExpensive materialApplications of SamariumComputer disk drivesAutomotive high-temperature environmentsTraveling-wave tubesLinear actuatorsSatellite systemsSection 3 - Applications3-10Alnico MagnetsAttributes of Both Cast and Sintered Alnico (Large Magnets)Very stable, great for high temperature applicationsMaximum working temperature 5240C to 5490CMay be ground to sizeDoes not lend itself to conventional machining (hard & brittle)High residual induction and energy product, compared to ceramic materialLow coercive force, compared to ceramic and rare-earth materials (more subject to demagnetization) Most common grades of Alnico are 5 & 8Applications of Alnico MagnetsMagnetos Security systemsCoin acceptors Clutches and bearingsDistributors MicrophonesDC motorsCeramic MagnetsAttributes of Ceramic MagnetsHigh intrinsic coercive forceTooling is expensiveLeast expensive material, compared to Akbuci and rare-earth magnetsLimited to simple shapes, due to manufacturing processLower service temperature than Alnico,.greater than rare-earth magnetsFinishing requires diamond cutting or grinding wheelLower energy product than Alnico and rare-earth magnetsMost common grades of ceramic are 5 & 8 (1-8 possible)Grade 8 is the strongest ceramic material availableApplications of Ceramic MagnetsSpeaker magnetsDC brushless motorsMagnetic Resonance Imaging (MRI)Magnetos used on lawnmowers and outboard motorsDC permanent-magnet motors (used in cars)Separators (separate ferrous material from nonferrous)Used in magnetic assemblies designed for lifting, holding, retrieving and separatingSection 3 - Applications3-11Table 4, Magnetic CharacteristicsSection 3 - Applications3-12Magnetic DesignInput CharacteristicsDigital Hall-Effect Sensors have specific magnetic response characteristics that govern their actuation from OFF to ON. These characteristics are classified in terms of operate point, release point and differ-ential. The operate point, commonly referred to as BOP, is the point at which the magnetic flux density turns the Hall Sensor ON, allowing current to flow from the output to ground. Conversely, the release point, commonly referred to as BRP, is the point at which the magnetic flux density turns the Hall Sensor OFF. The absolute difference between BOP and BRP is referred to as Hysteresis, Bhys. The purpose of hysteresis is to eliminate false triggering, which can be caused by minor variations in input, electrical noise and mechanical vibration. There are three basic types of Digital Hall Sensors commonly used, as listed below:Switch - (unipolar) Operates with a single magnetic pole. Guaranteed not to latch ON in the absence ofa magnetic field. Opposing field has no effect. Generally used for mechanical switch replacement.Latch - (bipolar) responds to both magnetic poles. Turns on in the presence of North or south pole, and turns off only when the opposing field is sufficiently strong. Guaranteed to latch. Used primary ily in brushless DC motor applications.Bipolar Switch - (unipolar or bipolar) described as a device which responds to the zero-crossing from North to South polesThe Hall-Effect LatchThe latch is a type of Hall IC which remains in either state (output ON or Off) until an opposite pole mag-net is applied. A South magnetic pole turns the device ON (BOP). The device will stay ON until a North magnetic pole is applied and turns it OFF (BRP). Melexis manufactures two types of Hall Effect latches. designated for .2.2V to 18V operation. The US2880 series of Hall Effect Latches are designed for high sensitivity. For more information refer to the data sheet section of this manual.The Hall Effect SwitchThere are two types of Hall Effect Switches, unipolar. The unipolar switch is normally “OFF” in the absence of a magnetic field. The device turns ON(BOP) in the presence of a sufficiently strong South magnetic pole, and turns OFF BRP) in the presence of a weaker South magnetic pole. MELEXIS manu-factures the US5881UA and US5881SO Hall Effect Switches. For more information refer to the data sheet section of this manual.Magnetic Design ConsiderationsWhen designing a magnetic circuit, there are five considerations to be covered:1. Cost of Hall IC, Magnet and Assembly2. Temperature Range3. Position Tolerance of Assembled Parts4. Position Switching Accuracy5. Tolerance BuildupSection 3 - Applications3-28CostHall IC cost will vary depending on the temperature specifications of BOP, BRP and Bhys. A loosely specified device may easily be one half to one third the cost of a tightly specified device, yet perform the same job. By providing steep slopes of flux density vs. distance and using strong magnets, the Hall ICcost may be reduced.Temperature RangeHall Effect Sensors are categorized into different temperature ranges for the use in application-specific design. It is very important that the Hall IC you select complies with your system’s ambient temperature. Position ToleranceDepending on the application and how it is assembled, the position of components, such as the magnet,Hall IC and mechanical assembly, will determine the mechanical variations of the system. Some systemsare more tolerant of changes in air gap and lateral motion than others.Position Switching AccuracyThe requirement in angular (degree) or linear position ultimately governs the magnetic circuit and HallIC specifications. That is if switching must repeat +0.1250in. or +0.1mm then the Hall IC specificationwill be much tighter than if the specification is +1.00 or +1.0mm.Tolerance BuildupTolerance buildup is the sum of all the variables that determine the operate point and release point of aHall IC. These variables include position tolerance,temperature coefficient, wear and aging of the assem-bly and magnet variations.Total Effective Air GapAs mentioned previously, both Magnet A and Magnet B in the design Kit are composed of the same mate-rial. Although the two magnets have similar characteristics, due to the difference in size and shapetotal Effective Air Gap (TEAG) will have different effects on each magnets’ flux density vs. distance curve.TEAG is defined as the sum of active area depth and the distance between the Hall IC’s branded face tothe surface of the magnet. TEAG = Air Gap + Active Area Depth. Active area depth is simply the dis-tance from the branded face of the sensor to the actual Hall Cell within it. The TEAG should be as smallas the physical system will allow, after taking into consideration factors such as the change in air gap with temperature due to mounting, vane or interrupt thickness and wear on mounting brackets.Graph 2 is given to show the effects of air gap on the slope of a graph using a single-pole slide-by con-figuration with magnet A.Section 3 - Applications3-29。

HALL EFFECT SENSING AND APPLICATION 01

H ALL E FFECT S ENSING AND A PPLICATION MICRO SWITCH Sensing and Control7DEOH RI &RQWHQWVChapter 1 • Hall Effect SensingIntroduction (1)Hall Effect Sensors (1)Why use the Hall Effect (2)Using this Manual (2)Chapter 2 • Hall Effect SensorsIntroduction (3)Theory of the Hall Effect (3)Basic Hall effect sensors (4)Analog output sensors (5)Output vs. power supply characteristics (5)Transfer Function (6)Digital output sensors (7)Transfer Function (7)Power Supply Characteristics (8)Input Characteristics (8)Output Characteristics (8)Summary (8)Chapter 3 • Magnetic ConsiderationsMagnetic Fields (9)Magnetic materials and their specifications (9)Basic magnetic design considerations (10)Magnetic materials summary (11)Magnetic systems (11)Unipolar head-on mode (12)Unipolar slide-by mode (12)Bipolar slide-by mode (13)Bipolar slide by mode (ring magnet) (14)Systems with pole pieces (15)Systems with bias magnets (16)Magnetic systems comparison (17)Ratiometric Linear Hall effect sensors (18)Summary (18)For application help: call 1-800-537-6945 Honeywell • MICRO SWITCH Sensing and Control iTable of ContentsChapter 4 • Electrical ConsiderationsIntroduction (19)Digital output sensors (19)Electrical specifications (20)Specification definitions (20)Absolute Maximum Ratings (20)Rated Electrical Characteristics (21)Basic interfaces (21)Pull-up resistors (21)Logic gate interfaces (22)Transistor interfaces (22)Symbols for design calculations (24)Analog Output Sensors (29)Electrical specifications (30)Basic interfaces (30)Interfaces to common components (31)Summary (32)Chapter 5 • Hall-based Sensing DevicesIntroduction (33)Vane-operated position sensors (33)Principles of Operation (33)Sensor Specifications (35)Digital current sensors (36)Principles of Operation (37)Sensor Specifications (37)Linear current sensors (38)Principles of Operation (38)C.losed Loop Current Sensors (39)Principles of Operation (39)Mechanically operated solid state switches (41)Principles of Operation (41)Switch specifications (42)Gear Tooth Sensors (42)Principles of Operation (43)Target Design (43)Summary (44)Chapter 6 • Applying Hall-effect Sensing DevicesGeneral sensing device design (45)Design of Hall effect-based sensing devices (47)System definition (48)Concept definition...Discrete sensing devices. (48)Digital output Hall effect-based sensing devices (49)Design approach... Non-precision applications.. (49)Design Approach... Precision applications (51)Linear output Hall effect-based sensing devices (53)ii Honeywell • MICRO SWITCH Sensing and Control For application help: call 1-800-537-6945Table of Contents Design approach... Linear output sensors. (53)Design approach... Linear current sensors (55)Sensor packages (57)Design approach... Vane-operated sensors.. (58)Design approach... Digital output current sensor.. (59)Summary (60)Chapter 7 • Application ExamplesFlow rate sensor (digital) (63)Sequencing sensors (63)Proximity sensors (64)Office machine sensors (64)Adjustable current sensor (65)Linear feedback sensor (66)Multiple position sensor (66)Microprocessor controlled sensor (67)Anti-skid sensor (67)Door interlock and ignition sensor (67)Transmission mounted speed sensor (68)Crankshaft position or speed sensor (68)Distributor mounted ignition sensor (68)Level/tilt measurement sensor (69)Brushless DC motor sensors (69)RPM sensors (70)Remote conveyor sensing (70)Remote reading sensing (71)Current sensors (71)Flow rate sensor (linear output (72)Piston detection sensor (73)Temperature or pressure sensor (73)Magnetic card reader (74)Throttle angle sensor (75)Automotive sensors (76)Appendix A • Units and Conversion Factors (77)Appendix B • Magnet Application Data (79)Appendix C • Magnetic Curves (89)Appendix D • Use of Calibrated Hall Device (99)Glossary (103)For application help: call 1-800-537-6945 Honeywell • MICRO SWITCH Sensing and Control iiiTable of Contentsiv Honeywell • MICRO SWITCH Sensing and Control For application help: call 1-800-537-6945For application help: call 1-800-537-6945 Honeywell • MICRO SWITCH Sensing and Control 1&KDSWHU+DOO (IIHFW 6HQVLQJIntroductionThe Hall effect has been known for over one hundred years, but has only been put to noticeable use in the last three de c-ades. The first practical application (outside of laboratory experiments) was in the 1950s as a microwave power sensor.With the mass production of semiconductors, it became feasible to use the Hall effect in high volume products. MICRO SWITCH Sensing and Control revolutionized the keyboard industry in 1968 by introducing the first solid state keyboard using the Hall effect. For the first time, a Hall effect sensing element and its associated electronics were combined in a si n -gle integrated circuit. Today, Hall effect devices are included in many products, ranging from computers to sewing machines, automobiles to aircraft, and machine tools to medical equipment.Hall effect sensorsThe Hall effect is an ideal sensing technology. The Hall element is constructedfrom a thin sheet of conductive material with output connections perpendicular tothe direction of current flow. When subjected to a magnetic field, it responds withan output voltage proportional to the magnetic field strength. The voltage outputis very small (µV) and requires additional electronics to achieve useful voltagelevels. When the Hall element is combined with the associated electronics, itforms a Hall effect sensor. The heart of every MICRO SWITCH Hall effect d e-vice is the integrated circuit chip that contains the Hall element and the signalconditioning electronics.Although the Hall effect sensor is a magnetic field sensor, it can be used as theprinciple component in many other types of sensing devices (current, temperature,pressure, position, etc.).Hall effect sensors can be applied in many types of sensing devices. If the quantity(parameter) to be sensed incorporates or can incorporate a magnetic field, a Hallsensor will perform the task. Figure 1-1 shows a block diagram of a sensing d e-vice that uses the Hall effect.In this generalized sensing device, the Hall sensor senses the field produced bythe magnetic system. The magnetic system responds to the physical quantity to be sensed (temperature, pressure, position,etc.) through the input interface. The output interface converts the electrical signal from the Hall sensor to a signal that meets the requirements of the application. The four blocks contained within the sensing device (Figure 1-1) will be exa m-ined in detail in the following chapters.Figure 1-1 General sensor based on the Hall effectChapter 1 • Hall Effect SensingWhy use the Hall effect?The reasons for using a particular technology or sensor vary according to the application. Cost, performance and availabi l-ity are always considerations. The features and benefits of a given technology are factors that should be weighed along with the specific requirements of the application in making this decision.General features of Hall effect based sensing devices are:•True solid state•Long life (30 billion operations in a continuing keyboard module test program)•High speed operation - over 100 kHz possible•Operates with stationary input (zero speed)•No moving parts•Logic compatible input and output•Broad temperature range (-40 to +150°C)•Highly repeatable operationUsing this manualThis manual may be considered as two parts: Chapters 2 through 5 present the basic information needed to apply Hall effect devices. Chapter 6 brings this information together and relates it to the design and application of the Hall effect sensing systems.Chapter 2, Hall effect sensors. Introduces the theory of operation and relates it to the Hall effect sensors. Both digital and analog sensors are discussed and their characteristics are examined. This chapter describes what a Hall effect sensor is and how it is specified.Chapter 3, Magnetic considerations. Covers magnetism and magnets as they relate to the input of a Hall effect device. Various magnetic systems for actuating a sensor are e xamined in detail.Chapter 4, Electrical considerations. Discusses the output of a Hall effect device. Electrical specifications as well as various interface circuits are examined. These three chapters (2, 3, and 4) provide the nucleus for applying Hall effect tec h-nology.Chapter 5, Sensing devices based on the Hall effect. These devices combine both a magnetic system and a Hall effect sensor into a single package. The chapter includes vane operated position sensors, current sensors, gear tooth sensors and magnetically-operated solid state switches. The principles of operation and how these sensors are spec ified are examined. Chapter 6, Applying Hall effect sensors. This chapter presents procedures that take the designer from an objective (to sense some physical parameter) through detailed sensor design. This chapter brings together the Hall sensor (Chapter 2), its input (Chapter 3), and its output (Chapter 4).Chapter 7, Application concepts. This is an idea chapter. It presents a number of ways to use Hall effect sensors to pe r-form a sensing function. This chapter cannot by its nature be all inclusive, but should stimulate ideas on the many additional ways Hall effect technology can be applied.This manual may be used in a number of ways. For a complete background regarding the application of Hall effect sensors, start with Chapter 1 and read straight through. If a sensing application exists and to determine the applicability of the Hall effect, Chapter 7 might be a good place to start. If a concept exists and the designer is familiar with Hall effect sensors, start with Chapter 6 and refer back to various chapters as the need arises.2 Honeywell • MICRO SWITCH Sensing and Control For application help: call 1-800-537-6945。

大环多胺

New1H-Pyrazole-Containing Polyamine Receptors Able ToComplex L-Glutamate in Water at Physiological pH ValuesCarlos Miranda,†Francisco Escartı´,‡Laurent Lamarque,†Marı´a J.R.Yunta,§Pilar Navarro,*,†Enrique Garcı´a-Espan˜a,*,‡and M.Luisa Jimeno†Contribution from the Instituto de Quı´mica Me´dica,Centro de Quı´mica Orga´nica Manuel Lora Tamayo,CSIC,C/Juan de la Cier V a3,28006Madrid,Spain,Departamento de Quı´mica Inorga´nica,Facultad de Quı´mica,Uni V ersidad de Valencia,c/Doctor Moliner50, 46100Burjassot(Valencia),Spain,and Departamento de Quı´mica Orga´nica,Facultad deQuı´mica,Uni V ersidad Complutense de Madrid,A V plutense s/n,28040Madrid,SpainReceived April16,2003;E-mail:enrique.garcia-es@uv.esAbstract:The interaction of the pyrazole-containing macrocyclic receptors3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene1[L1],13,26-dibenzyl-3,6,9,12,13,16,-19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene2[L2],3,9,12,13,16,22,-25,26-octaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene3[L3],6,19-dibenzyl-3,6,9,12,13,-16,19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene4[L4],6,19-diphenethyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetraene5[L5],and 6,19-dioctyl-3,6,9,12,13,16,19,22,25,26-decaazatricyclo-[22.2.1.111,14]-octacosa-1(27),11,14(28),24-tetra-ene6[L6]with L-glutamate in aqueous solution has been studied by potentiometric techniques.The synthesis of receptors3-6[L3-L6]is described for the first time.The potentiometric results show that4[L4]containing benzyl groups in the central nitrogens of the polyamine side chains is the receptor displaying the larger interaction at pH7.4(K eff)2.04×104).The presence of phenethyl5[L5]or octyl groups6[L6]instead of benzyl groups4[L4]in the central nitrogens of the chains produces a drastic decrease in the stability[K eff )3.51×102(5),K eff)3.64×102(6)].The studies show the relevance of the central polyaminic nitrogen in the interaction with glutamate.1[L1]and2[L2]with secondary nitrogens in this position present significantly larger interactions than3[L3],which lacks an amino group in the center of the chains.The NMR and modeling studies suggest the important contribution of hydrogen bonding andπ-cation interaction to adduct formation.IntroductionThe search for the L-glutamate receptor field has been andcontinues to be in a state of almost explosive development.1 L-Glutamate(Glu)is thought to be the predominant excitatory transmitter in the central nervous system(CNS)acting at a rangeof excitatory amino acid receptors.It is well-known that it playsa vital role mediating a great part of the synaptic transmission.2However,there is an increasing amount of experimentalevidence that metabolic defects and glutamatergic abnormalitiescan exacerbate or induce glutamate-mediated excitotoxic damageand consequently neurological disorders.3,4Overactivation ofionotropic(NMDA,AMPA,and Kainate)receptors(iGluRs)by Glu yields an excessive Ca2+influx that produces irreversible loss of neurons of specific areas of the brain.5There is much evidence that these processes induce,at least in part,neuro-degenerative illnesses such as Parkinson,Alzheimer,Huntington, AIDS,dementia,and amyotrophic lateral sclerosis(ALS).6In particular,ALS is one of the neurodegenerative disorders for which there is more evidence that excitotoxicity due to an increase in Glu concentration may contribute to the pathology of the disease.7Memantine,a drug able to antagonize the pathological effects of sustained,but relatively small,increases in extracellular glutamate concentration,has been recently received for the treatment of Alzheimer disease.8However,there is not an effective treatment for ALS.Therefore,the preparation of adequately functionalized synthetic receptors for L-glutamate seems to be an important target in finding new routes for controlling abnormal excitatory processes.However,effective recognition in water of aminocarboxylic acids is not an easy task due to its zwitterionic character at physiological pH values and to the strong competition that it finds in its own solvent.9†Centro de Quı´mica Orga´nica Manuel Lora Tamayo.‡Universidad de Valencia.§Universidad Complutense de Madrid.(1)Jane,D.E.In Medicinal Chemistry into the Millenium;Campbell,M.M.,Blagbrough,I.S.,Eds.;Royal Society of Chemistry:Cambridge,2001;pp67-84.(2)(a)Standaert,D.G.;Young,A.B.In The Pharmacological Basis ofTherapeutics;Hardman,J.G.,Goodman Gilman,A.,Limbird,L.E.,Eds.;McGraw-Hill:New York,1996;Chapter22,p503.(b)Fletcher,E.J.;Loge,D.In An Introduction to Neurotransmission in Health and Disease;Riederer,P.,Kopp,N.,Pearson,J.,Eds.;Oxford University Press:New York,1990;Chapter7,p79.(3)Michaelis,E.K.Prog.Neurobiol.1998,54,369-415.(4)Olney,J.W.Science1969,164,719-721.(5)Green,J.G.;Greenamyre,J.T.Prog.Neurobiol.1996,48,613-63.(6)Bra¨un-Osborne,H.;Egebjerg,J.;Nielsen,E.O.;Madsen,U.;Krogsgaard-Larsen,P.J.Med.Chem.2000,43,2609-2645and references therein.(7)(a)Shaw,P.J.;Ince,P.G.J.Neurol.1997,244(Suppl2),S3-S14.(b)Plaitakis,A.;Fesdjian,C.O.;Shashidharan,S Drugs1996,5,437-456.(8)Frantz,A.;Smith,A.Nat.Re V.Drug Dico V ery2003,2,9.Published on Web12/30/200310.1021/ja035671m CCC:$27.50©2004American Chemical Society J.AM.CHEM.SOC.2004,126,823-8339823There are many types of receptors able to interact with carboxylic acids and amino acids in organic solvents,10-13yielding selective complexation in some instances.However,the number of reported receptors of glutamate in aqueous solution is very scarce.In this sense,one of the few reports concerns an optical sensor based on a Zn(II)complex of a 2,2′:6′,2′′-terpyridine derivative in which L -aspartate and L -glutamate were efficiently bound as axial ligands (K s )104-105M -1)in 50/50water/methanol mixtures.14Among the receptors employed for carboxylic acid recogni-tion,the polyamine macrocycles I -IV in Chart 1are of particular relevance to this work.In a seminal paper,Lehn et al.15showed that saturated polyamines I and II could exert chain-length discrimination between different R ,ω-dicarboxylic acids as a function of the number of methylene groups between the two triamine units of the receptor.Such compounds were also able to interact with a glutamic acid derivative which has the ammonium group protected with an acyl moiety.15,16Compounds III and IV reported by Gotor and Lehn interact in their protonated forms in aqueous solution with protected N -acetyl-L -glutamate and N -acetyl-D -glutamate,showing a higher stability for the interaction with the D -isomer.17In both reports,the interaction with protected N -acetyl-L -glutamate at physiological pH yields constants of ca.3logarithmic units.Recently,we have shown that 1H -pyrazole-containing mac-rocycles present desirable properties for the binding of dopam-ine.18These polyaza macrocycles,apart from having a highpositive charge at neutral pH values,can form hydrogen bonds not only through the ammonium or amine groups but also through the pyrazole nitrogens that can behave as hydrogen bond donors or acceptors.In fact,Elguero et al.19have recently shown the ability of the pyrazole rings to form hydrogen bonds with carboxylic and carboxylate functions.These features can be used to recognize the functionalities of glutamic acid,the carboxylic and/or carboxylate functions and the ammonium group.Apart from this,the introduction of aromatic donor groups appropriately arranged within the macrocyclic framework or appended to it through arms of adequate length may contribute to the recognition event through π-cation interactions with the ammonium group of L -glutamate.π-Cation interactions are a key feature in many enzymatic centers,a classical example being acetylcholine esterase.20The role of such an interaction in abiotic systems was very well illustrated several years ago in a seminal work carried out by Dougherty and Stauffer.21Since then,many other examples have been reported both in biotic and in abiotic systems.22Taking into account all of these considerations,here we report on the ability of receptors 1[L 1]-6[L 6](Chart 2)to interact with L -glutamic acid.These receptors display structures which differ from one another in only one feature,which helps to obtain clear-cut relations between structure and interaction(9)Rebek,J.,Jr.;Askew,B.;Nemeth,D.;Parris,K.J.Am.Chem.Soc.1987,109,2432-2434.(10)Seel,C.;de Mendoza,J.In Comprehensi V e Supramolecular Chemistry ;Vogtle,F.,Ed.;Elsevier Science:New York,1996;Vol.2,p 519.(11)(a)Sessler,J.L.;Sanson,P.I.;Andrievesky,A.;Kral,V.In SupramolecularChemistry of Anions ;Bianchi,A.,Bowman-James,K.,Garcı´a-Espan ˜a,E.,Eds.;John Wiley &Sons:New York,1997;Chapter 10,pp 369-375.(b)Sessler,J.L.;Andrievsky,A.;Kra ´l,V.;Lynch,V.J.Am.Chem.Soc.1997,119,9385-9392.(12)Fitzmaurice,R.J.;Kyne,G.M.;Douheret,D.;Kilburn,J.D.J.Chem.Soc.,Perkin Trans.12002,7,841-864and references therein.(13)Rossi,S.;Kyne,G.M.;Turner,D.L.;Wells,N.J.;Kilburn,J.D.Angew.Chem.,Int.Ed.2002,41,4233-4236.(14)Aı¨t-Haddou,H.;Wiskur,S.L.;Lynch,V.M.;Anslyn,E.V.J.Am.Chem.Soc.2001,123,11296-11297.(15)Hosseini,M.W.;Lehn,J.-M.J.Am.Chem.Soc.1982,104,3525-3527.(16)(a)Hosseini,M.W.;Lehn,J.-M.Hel V .Chim.Acta 1986,69,587-603.(b)Heyer,D.;Lehn,J.-M.Tetrahedron Lett.1986,27,5869-5872.(17)(a)Alfonso,I.;Dietrich,B.;Rebolledo,F.;Gotor,V.;Lehn,J.-M.Hel V .Chim.Acta 2001,84,280-295.(b)Alfonso,I.;Rebolledo,F.;Gotor,V.Chem.-Eur.J.2000,6,3331-3338.(18)Lamarque,L.;Navarro,P.;Miranda,C.;Ara ´n,V.J.;Ochoa,C.;Escartı´,F.;Garcı´a-Espan ˜a,E.;Latorre,J.;Luis,S.V.;Miravet,J.F.J.Am.Chem.Soc .2001,123,10560-10570.(19)Foces-Foces,C.;Echevarria,A.;Jagerovic,N.;Alkorta,I.;Elguero,J.;Langer,U.;Klein,O.;Minguet-Bonvehı´,H.-H.J.Am.Chem.Soc.2001,123,7898-7906.(20)Sussman,J.L.;Harel,M.;Frolow,F.;Oefner,C.;Goldman,A.;Toker,L.;Silman,I.Science 1991,253,872-879.(21)Dougherty,D.A.;Stauffer,D.A.Science 1990,250,1558-1560.(22)(a)Sutcliffe,M.J.;Smeeton,A.H.;Wo,Z.G.;Oswald,R.E.FaradayDiscuss.1998,111,259-272.(b)Kearney,P.C.;Mizoue,L.S.;Kumpf,R.A.;Forman,J.E.;McCurdy,A.;Dougherty,D.A.J.Am.Chem.Soc.1993,115,9907-9919.(c)Bra ¨uner-Osborne,H.;Egebjerg,J.;Nielsen,E.;Madsen,U.;Krogsgaard-Larsen,P.J.Med.Chem.2000,43,2609-2645.(d)Zacharias,N.;Dougherty,D.A.Trends Pharmacol.Sci.2002,23,281-287.(e)Hu,J.;Barbour,L.J.;Gokel,G.W.J.Am.Chem.Soc.2002,124,10940-10941.Chart 1.Some Receptors Employed for Dicarboxylic Acid and N -AcetylglutamateRecognitionChart 2.New 1H -Pyrazole-Containing Polyamine Receptors Able To Complex L -Glutamate inWaterA R T I C L E SMiranda et al.824J.AM.CHEM.SOC.9VOL.126,NO.3,2004strengths.1[L1]and2[L2]differ in the N-benzylation of the pyrazole moiety,and1[L1]and3[L3]differ in the presence in the center of the polyamine side chains of an amino group or of a methylene group.The receptors4[L4]and5[L5]present the central nitrogens of the chain N-functionalized with benzyl or phenethyl groups,and6[L6]has large hydrophobic octyl groups.Results and DiscussionSynthesis of3-6.Macrocycles3-6have been obtained following the procedure previously reported for the preparation of1and2.23The method includes a first dipodal(2+2) condensation of the1H-pyrazol-3,5-dicarbaldehyde7with the corresponding R,ω-diamine,followed by hydrogenation of the resulting Schiff base imine bonds.In the case of receptor3,the Schiff base formed by condensation with1,5-pentanediamine is a stable solid(8,mp208-210°C)which precipitated in68% yield from the reaction mixture.Further reduction with NaBH4 in absolute ethanol gave the expected tetraazamacrocycle3, which after crystallization from toluene was isolated as a pure compound(mp184-186°C).In the cases of receptors4-6, the precursor R,ω-diamines(11a-11c)(Scheme1B)were obtained,by using a procedure previously described for11a.24 This procedure is based on the previous protection of the primary amino groups of1,5-diamino-3-azapentane by treatment with phthalic anhydride,followed by alkylation of the secondary amino group of1,5-diphthalimido-3-azapentane9with benzyl, phenethyl,or octyl bromide.Finally,the phthalimido groups of the N-alkyl substituted intermediates10a-10c were removed by treatment with hydrazine to afford the desired amines11a-11c,which were obtained in moderate yield(54-63%).In contrast with the behavior previously observed in the synthesis of3,in the(2+2)dipodal condensations of7with 3-benzyl-,3-phenethyl-,and3-octyl-substituted3-aza-1,5-pentanediamine11a,11b,and11c,respectively,there was not precipitation of the expected Schiff bases(Scheme1A). Consequently,the reaction mixtures were directly reduced in situ with NaBH4to obtain the desired hexaamines4-6,which after being carefully purified by chromatography afforded purecolorless oils in51%,63%,and31%yield,respectively.The structures of all of these new cyclic polyamines have been established from the analytical and spectroscopic data(MS(ES+), 1H and13C NMR)of both the free ligands3-6and their corresponding hydrochloride salts[3‚4HCl,4‚6HCl,5‚6HCl, and6‚6HCl],which were obtained as stable solids following the same procedure previously reported18for1‚6HCl and2‚6HCl.As usually occurs for3,5-disubstituted1H-pyrazole deriva-tives,either the free ligands3-6or their hydrochlorides show very simple1H and13C NMR spectra,in which signals indicate that,because of the prototropic equilibrium of the pyrazole ring, all of these compounds present average4-fold symmetry on the NMR scale.The quaternary C3and C5carbons appear together,and the pairs of methylene carbons C6,C7,and C8are magnetically equivalent(see Experimental Section).In the13C NMR spectra registered in CDCl3solution, significant differences can be observed between ligand3,without an amino group in the center of the side chain,and the N-substituted ligands4-6.In3,the C3,5signal appears as a broad singlet.However,in4-6,it almost disappears within the baseline of the spectra,and the methylene carbon atoms C6and C8experience a significant broadening.Additionally,a remark-able line-broadening is also observed in the C1′carbon signals belonging to the phenethyl and octyl groups of L5and L6, respectively.All of these data suggest that as the N-substituents located in the middle of the side chains of4-6are larger,the dynamic exchange rate of the pyrazole prototropic equilibrium is gradually lower,probably due to a relation between proto-tropic and conformational equilibria.Acid-Base Behavior.To follow the complexation of L-glutamate(hereafter abbreviated as Glu2-)and its protonated forms(HGlu-,H2Glu,and H3Glu+)by the receptors L1-L6, the acid-base behavior of L-glutamate has to be revisited under the experimental conditions of this work,298K and0.15mol dm-3.The protonation constants obtained,included in the first column of Table1,agree with the literature25and show that the zwitterionic HGlu-species is the only species present in aqueous solution at physiological pH values(Scheme2and Figure S1of Supporting Information).Therefore,receptors for(23)Ara´n,V.J.;Kumar,M.;Molina,J.;Lamarque,L.;Navarro,P.;Garcı´a-Espan˜a,E.;Ramı´rez,J.A.;Luis,S.V.;Escuder,.Chem.1999, 64,6137-6146.(24)(a)Yuen Ng,C.;Motekaitis,R.J.;Martell,A.E.Inorg.Chem.1979,18,2982-2986.(b)Anelli,P.L.;Lunazzi,L.;Montanari,F.;Quici,.Chem.1984,49,4197-4203.Scheme1.Synthesis of the Pyrazole-Containing MacrocyclicReceptorsNew1H-Pyrazole-Containing Polyamine Receptors A R T I C L E SJ.AM.CHEM.SOC.9VOL.126,NO.3,2004825glutamate recognition able to address both the negative charges of the carboxylate groups and the positive charge of ammonium are highly relevant.The protonation constants of L 3-L 6are included in Table 1,together with those we have previously reported for receptors L 1and L 2.23A comparison of the constants of L 4-L 6with those of the nonfunctionalized receptor L 1shows a reduced basicity of the receptors L 4-L 6with tertiary nitrogens at the middle of the polyamine bridges.Such a reduction in basicity prevented the potentiometric detection of the last protonation for these ligands in aqueous solution.A similar reduction in basicity was previously reported for the macrocycle with the N -benzylated pyrazole spacers (L 2).23These diminished basicities are related to the lower probability of the tertiary nitrogens for stabilizing the positive charges through hydrogen bond formation either with adjacent nonprotonated amino groups of the molecule or with water molecules.Also,the increase in the hydrophobicity of these molecules will contribute to their lower basicity.The stepwise basicity constants are relatively high for the first four protonation steps,which is attributable to the fact that these protons can bind to the nitrogen atoms adjacent to the pyrazole groups leaving the central nitrogen free,the electrostatic repulsions between them being therefore of little significance.The remaining protonation steps will occur in the central nitrogen atom,which will produce an important increase in the electrostatic repulsion in the molecule and therefore a reduction in basicity.As stated above,the tertiary nitrogen atoms present in L 4-L 6will also contribute to this diminished basicity.To analyze the interaction with glutamic acid,it is important to know the protonation degree of the ligands at physiological pH values.In Table 2,we have calculated the percentages ofthe different protonated species existing in solution at pH 7.4for receptors L 1-L 6.As can be seen,except for the receptor with the pentamethylenic chains L 3in which the tetraprotonated species prevails,all of the other systems show that the di-and triprotonated species prevail,although to different extents.Interaction with Glutamate.The stepwise constants for the interaction of the receptors L 1-L 6with glutamate are shown in Table 3,and selected distribution diagrams are plotted in Figure 1A -C.All of the studied receptors interact with glutamate forming adduct species with protonation degrees (j )which vary between 8and 0depending on the system (see Table 3).The stepwise constants have been derived from the overall association constants (L +Glu 2-+j H +)H j LGlu (j -2)+,log j )provided by the fitting of the pH-metric titration curves.This takes into account the basicities of the receptors and glutamate (vide supra)and the pH range in which a given species prevails in solution.In this respect,except below pH ca.4and above pH 9,HGlu -can be chosen as the protonated form of glutamate involved in the formation of the different adducts.Below pH 4,the participation of H 2Glu in the equilibria has also to be considered (entries 9and 10in Table 3).For instance,the formation of the H 6LGlu 4+species can proceed through the equilibria HGlu -+H 5L 5+)H 6LGlu 4+(entry 8,Table 3),and H 2Glu +H 4L 4+)H 6LGlu 4(entry 9Table 3),with percentages of participation that depend on pH.One of the effects of the interaction is to render somewhat more basic the receptor,and somewhat more acidic glutamic acid,facilitating the attraction between op-positely charged partners.A first inspection of Table 3and of the diagrams A,B,and C in Figure 1shows that the interaction strengths differ markedly from one system to another depending on the structural features of the receptors involved.L 4is the receptor that presents the highest capacity for interacting with glutamate throughout all of the pH range explored.It must also be remarked that there are not clear-cut trends in the values of the stepwise constants as a function of the protonation degree of the receptors.This suggests that charge -charge attractions do not play the most(25)(a)Martell,E.;Smith,R.M.Critical Stability Constants ;Plenum:NewYork,1975.(b)Motekaitis,R.J.NIST Critically Selected Stability Constants of Metal Complexes Database ;NIST Standard Reference Database,version 4,1997.Table 1.Protonation Constants of Glutamic Acid and Receptors L 1-L 6Determined in NaCl 0.15mol dm -3at 298.1KreactionGluL 1aL 2aL 3bL 4L 5L 6L +H )L H c 9.574(2)d 9.74(2)8.90(3)9.56(1)9.25(3)9.49(4)9.34(5)L H +H )L H 2 4.165(3)8.86(2)8.27(2)8.939(7)8.38(3)8.11(5)8.13(5)L H 2+H )L H 3 2.18(2)7.96(2) 6.62(3)8.02(1) 6.89(5)7.17(6)7.46(7)L H 3+H )L H 4 6.83(2) 5.85(4)7.63(1) 6.32(5) 6.35(6) 5.97(8)L H 4+H )L H 5 4.57(3) 3.37(4) 2.72(8) 2.84(9) 3.23(9)L H 5+H )L H 6 3.18(3) 2.27(6)∑log K H n L41.135.334.233.634.034.1aTaken from ref 23.b These data were previously cited in a short communication (ref 26).c Charges omitted for clarity.d Values in parentheses are the standard deviations in the last significant figure.Scheme 2.L -Glutamate Acid -BaseBehaviorTable 2.Percentages of the Different Protonated Species at pH 7.4H 1L aH 2LH 3LH 4LL 11186417L 21077130L 3083458L 4083458L 51154323L 6842482aCharges omitted for clarity.A R T I C L E SMiranda et al.826J.AM.CHEM.SOC.9VOL.126,NO.3,2004outstanding role and that other forces contribute very importantly to these processes.26However,in systems such as these,which present overlapping equilibria,it is convenient to use conditional constants because they provide a clearer picture of the selectivity trends.27These constants are defined as the quotient between the overall amounts of complexed species and those of free receptor and substrate at a given pH[eq1].In Figure2are presented the logarithms of the effective constants versus pH for all of the studied systems.Receptors L1and L2with a nonfunctionalized secondary amino group in the side chains display opposite trend from all other receptors. While the stability of the L1and L2adducts tends to increase with pH,the other ligands show a decreasing interaction. Additionally,L1and L2present a close interaction over the entire pH range under study.The tetraaminic macrocycle L3is a better(26)Escartı´,F.;Miranda,C.;Lamarque,L.;Latorre,J.;Garcı´a-Espan˜a,E.;Kumar,M.;Ara´n,V.J.;Navarro,mun.2002,9,936-937.(27)(a)Bianchi,A.;Garcı´a-Espan˜a,c.1999,12,1725-1732.(b)Aguilar,J.A.;Celda,B.;Garcı´a-Espan˜a,E.;Luis,S.V.;Martı´nez,M.;Ramı´rez,J.A.;Soriano,C.;Tejero,B.J.Chem.Soc.,Perkin Trans.22000, 7,1323-1328.Table3.Stability Constants for the Interaction of L1-L6with the Different Protonated Forms of Glutamate(Glu) entry reaction a L1L2L3L4L5L6 1Glu+L)Glu L 3.30(2)b 4.11(1)2HGlu+L)HGlu L 3.65(2) 4.11(1) 3.68(2) 3.38(4) 3Glu+H L)HGlu L 3.89(2) 4.48(1) 3.96(2) 3.57(4) 4HGlu+H L)H2Glu L 3.49(2) 3.89(1) 2.37(4) 3.71(2)5HGlu+H2L)H3Glu L 3.44(2) 3.73(1) 2.34(3) 4.14(2) 2.46(4) 2.61(7) 6HGlu+H3L)H4Glu L 3.33(2) 3.56(2) 2.66(3) 4.65(2) 2.74(3) 2.55(7) 7HGlu+H4L)H5Glu L 3.02(2) 3.26(2) 2.58(3) 4.77(2) 2.87(3) 2.91(5) 8HGlu+H5L)H6Glu L 3.11(3) 3.54(2) 6.76(3) 4.96(3) 4.47(3) 9H2Glu+H4L)H6Glu L 2.54(3) 3.05(2) 3.88(2) 5.35(3) 3.66(4) 3.56(3) 10H2Glu+H5L)H7Glu L 2.61(6) 2.73(4) 5.51(3) 3.57(4) 3.22(8) 11H3Glu+H4L)H7Glu L 4.82(2) 4.12(9)a Charges omitted for clarity.b Values in parentheses are standard deviations in the last significantfigure.Figure1.Distribution diagrams for the systems(A)L1-glutamic acid, (B)L4-glutamic acid,and(C)L5-glutamicacid.Figure2.Representation of the variation of K cond(M-1)for the interaction of glutamic acid with(A)L1and L3,(B)L2,L4,L5,and L6.Initial concentrations of glutamate and receptors are10-3mol dm-3.Kcond)∑[(H i L)‚(H j Glu)]/{∑[H i L]∑[H j Glu]}(1)New1H-Pyrazole-Containing Polyamine Receptors A R T I C L E SJ.AM.CHEM.SOC.9VOL.126,NO.3,2004827receptor at acidic pH,but its interaction markedly decreases on raising the pH.These results strongly suggest the implication of the central nitrogens of the lateral polyamine chains in the stabilization of the adducts.Among the N-functionalized receptors,L4presents the largest interaction with glutamate.Interestingly enough,L5,which differs from L4only in having a phenethyl group instead of a benzyl one,presents much lower stability of its adducts.Since the basicity and thereby the protonation states that L4and L5 present with pH are very close,the reason for the larger stability of the L4adducts could reside on a better spatial disposition for formingπ-cation interactions with the ammonium group of the amino acid.In addition,as already pointed out,L4presents the highest affinity for glutamic acid in a wide pH range,being overcome only by L1and L2at pH values over9.This observation again supports the contribution ofπ-cation inter-actions in the system L4-glutamic because at these pH values the ammonium functionality will start to deprotonate(see Scheme2and Figure1B).Table4gathers the percentages of the species existing in equilibria at pH7.4together with the values of the conditional constant at this pH.In correspondence with Figure1A,1C and Figure S2(Supporting Information),it can be seen that for L1, L2,L5,and L6the prevailing species are[H2L‚HGlu]+and[H3L‚HGlu]2+(protonation degrees3and4,respectively),while for L3the main species are[H3L‚HGlu]+and[H4L‚HGlu]2+ (protonation degrees4and5,respectively).The most effective receptor at this pH would be L4which joins hydrogen bonding, charge-charge,andπ-cation contributions for the stabilization of the adducts.To check the selectivity of this receptor,we have also studied its interaction with L-aspartate,which is a competitor of L-glutamate in the biologic receptors.The conditional constant at pH7.4has a value of3.1logarithmic units for the system Asp-L4.Therefore,the selectivity of L4 for glutamate over aspartate(K cond(L4-glu)/K cond(L4-asp))will be of ca.15.It is interesting to remark that the affinity of L4 for zwiterionic L-glutamate at pH7.4is even larger than that displayed by receptors III and IV(Chart1)with the protected dianion N-acetyl-L-glutamate lacking the zwitterionic charac-teristics.Applying eq1and the stability constants reported in ref17,conditional constants at pH7.4of 3.24and 2.96 logarithmic units can be derived for the systems III-L-Glu and IV-L-Glu,respectively.Molecular Modeling Studies.Molecular mechanics-based methods involving docking studies have been used to study the binding orientations and affinities for the complexation of glutamate by L1-L6receptors.The quality of a computer simulation depends on two factors:accuracy of the force field that describes intra-and intermolecular interactions,and an adequate sampling of the conformational and configuration space of the system.28The additive AMBER force field is appropriate for describing the complexation processes of our compounds,as it is one of the best methods29in reproducing H-bonding and stacking stabiliza-tion energies.The experimental data show that at pH7.4,L1-L6exist in different protonation states.So,a theoretical study of the protonation of these ligands was done,including all of the species shown in5%or more abundance in the potentiometric measurements(Table4).In each case,the more favored positions of protons were calculated for mono-,di-,tri-,and tetraprotonated species.Molecular dynamics studies were performed to find the minimum energy conformations with simulated solvent effects.Molecular modeling studies were carried out using the AMBER30method implemented in the Hyperchem6.0pack-age,31modified by the inclusion of appropriate parameters. Where available,the parameters came from analogous ones used in the literature.32All others were developed following Koll-man33and Hopfinger34procedures.The equilibrium bond length and angle values came from experimental values of reasonable reference compounds.All of the compounds were constructed using standard geometry and standard bond lengths.To develop suitable parameters for NH‚‚‚N hydrogen bonding,ab initio calculations at the STO-3G level35were used to calculate atomic charges compatible with the AMBER force field charges,as they gave excellent results,and,at the same time,this method allows the study of aryl-amine interactions.In all cases,full geometry optimizations with the Polak-Ribiere algorithm were carried out,with no restraints.Ions are separated far away and well solvated in water due to the fact that water has a high dielectric constant and hydrogen bond network.Consequently,there is no need to use counteri-ons36in the modelization studies.In the absence of explicit solvent molecules,a distance-dependent dielectric factor quali-tatively simulates the presence of water,as it takes into account the fact that the intermolecular electrostatic interactions should vanish more rapidly with distance than in the gas phase.The same results can be obtained using a constant dielectric factor greater than1.We have chosen to use a distance-dependent dielectric constant( )4R ij)as this was the method used by Weiner et al.37to develop the AMBER force field.Table8 shows the theoretical differences in protonation energy(∆E p) of mono-,bi-,and triprotonated hexaamine ligands,for the (28)Urban,J.J.;Cronin,C.W.;Roberts,R.R.;Famini,G.R.J.Am.Chem.Soc.1997,119,12292-12299.(29)Hobza,P.;Kabelac,M.;Sponer,J.;Mejzlik,P.;Vondrasek,put.Chem.1997,18,1136-1150.(30)Cornell,W.D.;Cieplak,P.;Bayly,C.I.;Gould,I.R.;Merz,K.M.,Jr.;Ferguson,D.M.;Spelmeyer,D.C.;Fox,T.;Caldwell,J.W.;Kollman,P.A.J.Am.Chem.Soc.1995,117,5179-5197.(31)Hyperchem6.0(Hypercube Inc.).(32)(a)Fox,T.;Scanlan,T.S.;Kollman,P.A.J.Am.Chem.Soc.1997,119,11571-11577.(b)Grootenhuis,P.D.;Kollman,P.A.J.Am.Chem.Soc.1989,111,2152-2158.(c)Moyna,G.;Hernandez,G.;Williams,H.J.;Nachman,R.J.;Scott,put.Sci.1997,37,951-956.(d)Boden,C.D.J.;Patenden,put.-Aided Mol.Des.1999, 13,153-166.(33)/amber.(34)Hopfinger,A.J.;Pearlstein,put.Chem.1984,5,486-499.(35)Glennon,T.M.;Zheng,Y.-J.;Le Grand,S.M.;Shutzberg,B.A.;Merz,K.M.,put.Chem.1994,15,1019-1040.(36)Wang,J.;Kollman,P.A.J.Am.Chem.Soc.1998,120,11106-11114.Table4.Percentages of the Different Protonated Adducts[HGlu‚H j L](j-1)+,Overall Percentages of Complexation,andConditional Constants(K Cond)at pH7.4for the Interaction ofGlutamate(HGlu-)with Receptors L1-L6at Physiological pH[H n L‚HGlu]an)1n)2n)3n)4∑{[H n L‚HGlu]}K cond(M-1)L13272353 2.44×103L2947763 4.12×103L31101324 3.99×102L423737581 2.04×104L51010222 3.51×102L6121224 3.64×102a Charges omitted for clarity.A R T I C L E S Miranda et al. 828J.AM.CHEM.SOC.9VOL.126,NO.3,2004。

An Analysis of “Hawthorne Effect” in College English Teaching

一一一一一一一一学术思潮本栏目责任编辑：王力1What Is “Hawthorne Effect ”?The Hawthorne Effect is a type of reactivity in which individu⁃als modify or improve an aspect of their behavior in response to their awareness of being observed.In 1920s,the National Research Council of the United States organized psychologists group of Har⁃vard University to go to the Hawthorne Plant near Chicago,which belonged to Western Electric Company.The intention of the ex⁃perts was to study on the relationship between the change of produc⁃tion condition and worker ’s productivity by improving the surround⁃ing factors,such as working condition and environment,and in or⁃der to acquire the way to improve the labor productivity.In order to investigate the influences of various production conditions on work⁃ers ’productivity,they selected six female workers who assembled small electronic devices in the relay workshop as observers.During the process of lighting experiment,the experimenter changed the lighting intensity constantly to explore the relationship between the change of illumination intensity and the productivity change.Re⁃searchers found out that any changes in lighting intensity,includ⁃ing positive and negative changes,both improved the productivity of workers.As a result,the experts found out that any change in the intensity of the illumination (including positive or negative chang⁃es),both increased the productivity of the workers.Researchers in⁃terpreted it as the implementation of the study.As the research hap⁃pened in Hawthorne Plant,the situation which has caused the ris⁃ing of performance just because of additional attention was known as “Hawthorne Effect ”.The researchers wanted to find out the relationship between external factors such as lighting intensity and worker ’s behavioral efficiency.Researchers realized that workers are stimulated not on⁃ly by external factors,but also by their own subjective conscious⁃ness caused by external factors.The managers of the plants no lon⁃ger regard workers as appendages of machines,but rather treat them as producers with subjective initiation.In the Hawthorne plant,when the six women were pulled out of as a group,they are aware of their concern,and redouble our efforts,to prove that he is good,and is worth paying attention to promote their behavior to im⁃prove the efficiency of production rising.2The Necessity of “Hawthorne Effect ”in College English TeachingNowadays,higher education,especially college English teach⁃ing faces a series of problems,because of less functions and ap⁃proaches are applied to class teaching,education quality is much lower than before,college students also lack of learning motivation and effectiveness,so their comprehension ability is poorer,and nowadays,more and more after-class activities are being held,stu⁃dents are busy in engaging into these activities.Many scholars try to solve these problems by introducing different theories.Therefore,Hawthorne Effect has been quoted as it could create a good class⁃room atmosphere,improve teaching effect,enlighten students ’pas⁃sion in English learning;it is also been used to discuss how to deal with the problems in the management of college students,and how to improve the college English teaching effect and so on.In short,Hawthorne Effect is necessary to college English class,and it is critical to be used to increase English teaching effect.Both teach⁃ers and students lack of certain things,so in order to make college teaching,especially college English teaching more effective and more interesting to students,the deficiency must be taken into con⁃sideration and the necessity of making use of Hawthorne Effect must be done.2.1Lack of attention to studentsAs language learners,English learners should be positive and active in classes,while the English teachers,especially college English teachers must aim at the comprehensive language ability training rather than the knowledge teaching,that is because listen⁃ing,speaking,reading and writing are the four main factors or skills for all English learners or even language learners.Besides,the pur⁃pose of college English teaching is to cultivate students ’ability to communicate freely in English,train their ability to acquire English comprehensive knowledge as well as make use of what they have learnt to enhance the subjective initiative and creativity.Therefore,the class should be a freely talking while rigidly managed class,teachers should focus on students ’ability development,a good at⁃mosphere and more attention are important.Presently,the teaching of college English is still at the stage of teaching and learning,nei⁃收稿日期：2017-02-11修回日期：2016-03-12作者简介：孙冬妮，女，江苏泰州人，西南民族大学外国语学院旅英语专业本科生。

英语对话：Hawthorne Effect(霍桑效应)

Hawthorne Effect2019.5.30 A:Hi,B.Emmm,I think you look terrible.B:Yeah,I feel very anxious and tired these days.Sometimes I can’t even eat and sleep.A:Oh my god.I think you should go to the hospital.Is something bad happening?B:That’s what I’m going to do.After entering the university,I have been studying as hard as I did in high school.However,I generally found that my interest in learning was declining,and my study state was getting worse and worse.A:This is very strange.As far as I know,you are a person who loves learning very much.B:You know,after entering collage,I found there were so many excellent people.Not only do they do well in school,but they also win prizes in various activities they participate in.People like me who only learn will be ignored by others.A:This sounds familiar.Ah,I remember.Do you know Hawthorne Effect?B:Never heard of it.A:This is a theory of social psychology.You’re a philosophy students,maybe you don’t know much about it.B:Can you tell me in detail?A:In the 1920s and 1930s,psychologists at Harvard University were working in a factory called Hawthorne.The experiment initially looked at the relationship between working conditions and productivity, but found that people do better when they are noticed finally.B:What does this have to do with me?A:I think what you're saying has a lot to do with this case.In fact, you lose the motivation to learn because of the lack of attention from others.B:Yes,as you said.So what should I do?A:I think you should go to the hospital in time.Doctors can help you more.B:I’m going this weekend.A:Before that,I suggest you talk to someone you trust and find your right position.Talking to others and give yourself an accurate position is good for you to know yourself.B:Your suggestion sounds common.Is this related to the Hawthorne Effect?A:Yeah.Hawthorne Effect tells us that positive external stimuli can make us do better.When you have a correct understanding of yourself,you will not expect too much achievement.Of course,I know less about Hawthorne Effect.If you are interested,you can check the information yourself.B:Thank you for telling me so much.A:You’re welcome.。

the fractional quantum hall effect

$the fractional quantum hall effect$

The Fractional Quantum Hall EffectIntroductionThe fractional quantum Hall effect (FQHE) is a phenomenon that occurs in two-dimensional electron systems subjected to a strong magnetic field at low temperatures. It was first discovered by Daniel Tsui, Horst Störmer, and Robert Laughlin in 1982, for which they were awarded the Nobel Prize in Physics in 1998. The FQHE is a fascinating quantum mechanical effect that has revolutionized our understanding of condensed matter physics.Overview of the Quantum Hall EffectBefore delving into the fractional quantu m Hall effect, let’s briefly review the classical quantum Hall effect. When a two-dimensional electron gas (2DEG) is subjected to a perpendicular magnetic field, Landau quantization occurs. The energy levels of electrons become quantized into discrete Landau levels, forming a series of equally spaced energy bands. In the presence of impurities or disorder, these energy bands can be partially filled with electrons.Under normal circumstances, when all the energy bands are completely filled with electrons up to a certain level called the Fermi level, no current flows through the system as all available states are occupied. However, when an electric field is applied perpendicular to the current flow direction, a potential difference develops across the sample due to the Lorentz force acting on moving charges. This results in an electric field perpendicular to both the current and magnetic field directions.In response to this electric field, charges move along equipotential lines within the sample until they reach dissipationless edges where they can freely flow without scattering due to impurities. These edge states carry quantized currents proportional to their respective Landau level filling factors and are responsible for the observed quantization of Hall resistance.Discovery and Explanation of Fractional Quantum Hall EffectIn 1982, Tsui, Störmer, and Laughlin observed unexpected anomalies in their measurements while studying 2DEGs at very low temperatures and high magnetic fields. They discovered that the Hall resistance exhibitedplateaus at fractional values of h/e^2, where h is Planck’s constant and e is the elementary charge.This discovery challenged the prevailing understanding of the quantum Hall effect, which only accounted for quantized resistance at integer values of h/e^2. Laughlin proposed a groundbreaking theory to explain these fractional plateaus in terms of new quantum states of mattercalled fractional quantum Hall states (FQHS).According to Laughlin’s theory, the FQHS arises from strong ele ctron-electron interactions in a 2DEG. At low temperatures, when electrons are confined to their lowest Landau level due to strong magnetic fields, they form a strongly correlated electron liquid. This liquid can exhibit a variety of exotic collective behavior, including fractional charges and anyonic statistics.The FQHS can be understood using the concept of quasiparticles. In this context, an electron with its surrounding cloud of interacting electrons behaves as a composite particle carrying fractional charge andstatistics different from those of ordinary particles.Experimental ObservationsExperimental measurements have confirmed the existence of FQHS and provided evidence for Laughlin’s theory. By measuring not only Hall resistance but also longitudinal resistance and tunneling conductance, researchers have gained insights into the nature of these exotic states.One crucial experimental technique used in studying FQHE is called shot noise spectroscopy. Shot noise refers to fluctuations in current due to discrete arrival times of individual electrons. By measuring shot noise in FQHE samples, researchers can determine the charge carried by quasiparticles and their statistics.Another powerful technique is called edge state spectroscopy. By probing edge states using tunneling or scanning probe microscopy, researchers can directly observe excitations associated with different filling fractions.Applications and Future DirectionsThe fractional quantum Hall effect has not only deepened our understanding of condensed matter physics but also has promising applications. The FQHE has been proposed as a platform for realizingfault-tolerant quantum computation, where quasiparticles with non-Abelian statistics could serve as robust qubits.Furthermore, researchers continue to explore new FQHS with unconventional properties and fractional charges. Recent studies have focused on topological order, anyonic braiding, and the interplay between FQHE and other quantum phenomena such as high-temperature superconductivity.In conclusion, the fractional quantum Hall effect is a remarkable manifestation of strong electron-electron interactions in two-dimensional electron systems subjected to strong magnetic fields. It has opened up new avenues of research in condensed matter physics and holds promise for future technological advancements. Further exploration of FQHS could lead to breakthroughs in both fundamental physics and practical applications.Note: The content provided above is a brief overview of thefractional quantum Hall effect. To meet the word countrequirement, additional details, experimental techniques, andtheoretical concepts can be included. The content should beorganized in a coherent manner with proper headings andsubheadings to enhance readability.。

试验一霍尔效应HallEffect

將實驗器材架設好，磁場測試板置於指定位置(如上頁右下角圖)。
量測示意圖
利用壓克力墊片改變N極與半導體距離。
13
注意事項
當受測材料為N型半導體(主要載子電子)時，電荷
累積情形與上述情況相反，但計算公式仍然可用。
利用B-V關係圖去判斷材料的型態。高斯計與探針為昂貴器材，務必小心使用。
霍爾效應是電場和磁場在移動中的電荷上所施力的
結果 (勞倫茲力及靜電力) 。
3
應用
測定元件的主要載子濃度。
利用霍爾元件測量出磁場，可確定導線電流的大小
。利用這一原理可以設計制成霍爾電流傳感器。
霍爾元件具有對磁場敏感、結構簡單、體積小、頻
率響應寬、輸出電壓變化大和使用壽命長等優點，因此，在測量、自動化、計算機和信息技術等領域得到廣泛的應用。
歸零使用按鈕上方英文字所提示功能時，須先按住SHIFT鍵才可使用。
選取單位
數值擷取
範圍設定
11
實驗儀器
厚壓克力墊片磁場測試板
探針置入位置測試板放置處
探針
待測半導體材料
磁鐵架
12
如何量測磁場
先將高斯計執行
歸零程序。
依操作說明找出磁鐵N 、S極。
實驗
1
霍爾效應 (Hall Effect)
實驗目的
決定磁鐵在特定距離下所建立之磁場。
學習如何量測磁場大小。
決定半導體材料是P型或為N型。決定半導體材料之主要載體濃度。
2
何謂霍爾效應?
Edwin H. Hall 於1879年發現在帶電流的薄金屬片
上加磁場時會出現一反向電壓。

HANLE EFFECT

Physics 77 Experiment 7 September 2000HANLE EFFECTThis experiment is useful in several ways: (1) it provides precise measurements of atomic lifetimes; (2) the method of precessing a radiation pattern to measure the product of magnetic moment x magnetic field is also used in nuclear and high energy physics ("perturbed angular correlation"); and (3) the phenomenon can be interpreted either quantum mechanically or classically, such dual interpretations deepening our understanding of quantum mechanics. This experiment is a particular case of a more general method used in atomic physics called the "level crossing technique" for measuring the width (lifetime) of atomic states.THEORY:The principle of this experiment can be understood by reference to Figure 1. Light polarized in the OY direction is incident along the X-axis on a scattering atom at the origin. The light is of just the right wavelength to induce a transition in the target atom. The excited atom then re-radiates after a characteristic lifetime τ,θFigure 1. Geometry of the Hanle Effect experiment.in a classical dipole distribution proportional to sin2θ. If a B-field is applied in the OZ direction, the excited atomwill precess about the OZ axis with a Larmor frequency ωµL B J=/!, where µ is the magnetic moment of the excited state which has angular momentum J!. The radiation field distribution precesses with the excited atom. The likelihood that the atom will radiate in the OY direction during the interval (t, t + dt) will now be given by (e-t/τ) (sin2ωL t)dt where the first factor reflects the exponential decay of the excited state, and the second factor makes allowance for the precession of the atom about the vertical axis. The observed intensity is given by integrating the expression above to infinity.Radiation observed along 0Y;e tdt t L L −∞=+z /sin ()τωτωτ220214(1)A plot of the intensity observed along the OY axis, as a function of B, has its minimum value atB (or ωL ) = 0, with an increase to one-half of its asymptotic value at ωL t = 1/2 or:B g J 1202/=!µτ(2)where µ0 is the Bohr magneton and g J is the electronic g factor for the excited state. The mean life τ can be determined from B l/2 if µ is known (µ=g J µ0J). These measurements always detect the product µτ and one must have additional information to get individual values of τ and µ. We will calculate the value of µ on the assumption that the state is described approximately by ""L S • coupling, in which case:g S S L L J J J =++−++321121()()()(3)See the Optical Pumping writeup (Experiment 8) for the derivation. [The Lurio paper expression for I(τ) isincorrect. The correct expression is discussed by V. Leyva in the Hanle Effect Experiment Reference binder.]Figure 2. Term Diagram for Mercury (Hg).THE EXPERIMENTThe optical system consists of a source arm and an orthogonal detector arm. The source arm contains a low-pressure mercury discharge lamp, a quartz collimating lens, and a UV-transmitting polarizing filter. The absorption/scattering cell is located at the intersection of the optical axes of the two arms. The detector arm contains a second UV-polarizing filter, a quartz lens to focus scattered light onto a detector, an interference bandpass filter centered on 253.7 nm (15.0 nm FWHM), and a UV-sensitive photomultiplier. Polarizing filters that function efficiently at the short UV wavelengths are used (ordinary "Polaroid" filters are totally opaque at UV wavelengths.) in both the lamp and detector arms. The description above of the principle of the experiment leaves out details such as incident line shape, trapping, collision broadening, etc. The reprint by de Zafra describes these complications and the analysis of results. The Franken and Happer papers go further into the theory.Figure 3. Experimental setup for the Hanle Effect experiment.INSTRUMENTATION AND APPARATUSLAMP:The lamp consists of a pair of electrodes sealed into a synthetic quartz capillary that is folded into a hairpin shape. It is filled with natural abundance Hg at a low pressure (~1 atmosphere at operating temperature). An ideal light source would emit a spectrum that exhibits the natural width of the upper radiating 3P1 state. (See the term diagram Figure 2.) However, if there are unexcited Hg atoms in the 1S0 ground state, populating the hollow sheath surrounding the excited cylindrical core of the radiating source, these unexcited atoms will absorb some of the emitted radiation. If the absorbing atoms are cold, and the radiating atoms hot (the usual situation since the temperature will decrease from the centerline to the lamp wall), the spectral line emitted from the hot atoms is wider than the absorption line of the cooler atoms, and what escapes from the source has a dip in the middle. This phenomenon is called self-reversal. We can minimize this problem by running the source as cool as possible (by reducing the operating voltage). That action has the further benefit of reducing Doppler broadening by keeping the internal lamp pressure from rising excessively. Caution: The Hg lamp emits 95% of its energy in the 253.7 nm line. Don't look directly at the bare lamp for extended periods of time without eyeglasses. It also produces copious quantities of O3 (ozone) when operated in open air. It is mounted in a closed housing to completely shield the UV from the user and minimize the production of O3.ABSORPTION/SCATTERING CELL:The absorption cell, constructed from UV transmitting synthetic quartz, is known as a Wood's Horn. It is entirely covered with a black light-absorbing coating except for the entrance and exit windows. The shape, plus coating, insures a minimum of internal reflections so that incident light will encounter the resident Hg atoms only once before reflections alter its plane of polarization. Isotopically pure 198Hg has been used for the absorption/scattering material, unlike the lamp which is filled with natural-abundance Hg (10% 198Hg).DETECTOR:The detector (SSR Quantum Photometer) consists of a UV-sensitive photomultiplier (PMT), a high voltage power supply, and a count-rate meter/nano-ammeter. The operating voltage for the 1P28 PMT has been carefully adjusted to produce the maximum gain at minimum noise (i.e., the optimum signal-to-noise ratio), and is not altered by the user. The count-rate meter mode is used for very low intensities (<108 cps), while the nano-Ammeter (nA) mode (normally used) extends measurement capability to higher intensities. The nA mode allows selection of severalcompromise between low statistical uncertainty and realistic response time. An adjustable zero offset is also available that allows easy examination of a small percentage change in signal strength. The UV interference filter installed at the PMT entrance window passes only the wavelength of interest, substantially improving the signal-to-noise ratio of the system, while insuring that room lighting will neither damage the PMT photocathode nor seriously influence the intensity data.FIELD COMPENSATION COIL SETS 1 & 2:It is necessary to cancel out the ambient magnetic field at the Hg cell. This is accomplished with two pairs of rectangular coils (Sets 1 & 2), in the Helmholtz configuration, driven by two independently adjustable power supplies. Careful positioning of the plane of one pair normal to the horizontal component of the ambient field (rotating the entire experiment on the table), allows the use of only two pairs of coils instead of three. The two power supplies are operated in their Constant Voltage mode, since the current required is too small for sensitive current adjustment or regulation when the supply is in the Constant Current mode..MAGNETOMETER:An air-driven magnetometer is used for the adjustment of the currents through the field-canceling coils. This is a sphere of copper [Oxygen-Free High-Conductivity (OFHC) grade], supported on non-magnetic copper-beryllium ball bearings and rotated about its axis by two jets of air. A central hole has been drilled through the rotor at right angles to the axis of rotation. Two 10,000 turn coils, connected in series-aiding, closely surround the rotor. When the Cu sphere rotates, it is a single turn that cuts any magnetic field lines that may be present. Large eddy currents are induced in the low-resistance single turn which then induce a signal in the fixed coils. It is this signal that is displayed on the Oscilloscope (CRO). The ball bearings are not as hard or durable as ordinary hardened steel (magnetic) ball bearings, which limits the speed of rotation to <600 rps, i.e., a driving air pressure of less than 2-3 psi. The Tektronix 503 CRO is operated in the Differential Input mode to suppress rather large common-mode signals at line frequency and its harmonics.HELMHOLTZ COIL SET 3:A known magnetic field can be applied to the scattering cell by means of a third set of coils (Set 3), a circular pair, also in the Helmholtz configuration. A stable regulated power supply (in Constant-Current mode), a reversing switch, and a digital Ammeter complete this system. The field conversion factor for this pair is 1.87 Gauss/Ampere.DATA ANALYSIS:The laboratory PCs contain useful programs for analyzing the data from this experiment. Math CAD and FFIT are available, and Curvefit (Mathematica) and FFIT are quite capable of fitting a Lorentzian.PRELAB EXERCISE1. Read the de Zafra paper to understand the principles of the experiment.2. Estimate B l/2 for the 3P l state of Hg (τ = ~10-7 sec [See TASK 7.]) for the current geometry. How does this compare to the earth's magnetic field and any stray fields expected in the laboratory?EXPERIMENTAL TASKS:1. Replace the Hg cell with the Vantson magnetometer by rotating the support. A manual describing the magnetometer is available. In essence, it is a generator with output voltage:V peak to peak x B T V S Gauss ().,−−=−⋅286104c h (4)where T is the period of the AC output of the generator. Drive the magnetometer with compressed air at about 2-3psi pressure. Trigger the CRO from the 60 Hz LINE and "tweak" the rotor speed (air pressure) to obtain a stable display at a precise harmonic of 60 Hz. Adjust the currents in the horizontal and vertical bucking coils to minimize the output voltage when the magnetometer axis is oriented properly. The axis of rotation is perpendicular to the disk containing the air inlet and output connector. A small AC field will persist and cannot be canceled with the present arrangement. What is the source of this field? What is the minimum DC field you can produce at the absorption cell? What are the magnitudes of the two components of the ambient DC magnetic field? Record the voltage settings for the two bucking coils and keep them constant for the duration of the experiment.2. Familiarize yourself with the operation of the photometer. A separate manual on the SSR photometer is available.3. Turn on the Hg lamp, beginning with a Variac voltage of 100 V. If the lamp starts to flicker, increase the voltage slightly (1-2 V) until the flicker stops. Wait 15-20 minutes for equilibrium to be reached. The lamp should be run at a voltage that is low enough to produce narrow emission lines without flicker, but high enough (<105 V) to give a good signal-to-noise ratio.4. Adjust the magnetic field produced by the Helmholtz coils (Set #3) to find the minimum and maximum photometer readings. Set the magnetic field such that photometer reads halfway between minimum and maximumvalues and check the peak symmetry when the field is reversed. If asymmetry is more than a few percent, and if the earth's magnetic field has been properly minimized, the polarizer(s) probably needs adjustment. Ask instructor for help.5. Measure and plot the yield of photons scattered at 90° as a function of B (vertical) produced by the Set #3 Helmholtz coils. Repeat the measurements enough to make certain that lamp intensity and scattering cell temperature are not drifting rapidly with time. Even if you have evidence of a slow time dependence, you can make an accurate measure of the half-width of the current dip by measuring the depth of the dip and then setting the current quickly to give a signal at half the full magnitude. Reverse the current to see whether the dip is symmetrical about B vert = 0.6. Repeat step (5) when the tip of the cell is placed in cool water from a refrigerated water cooler. Ice water, or colder baths, will be too cold, reducing the Hg vapor pressure in the absorption cell to a level too low to produce a usable signal.7. Compute the lifetime of the 3P1 state of Hg. Explain the temperature dependence of your results. Compare with the accepted value of τ = 118 ns ±3% (Radzig & Smirnov). Mathematica 3.0, Math CAD and FFIT, on the PC's, are available for fitting Lorentzians.QUESTIONS:(1) How much of your B = 0 signal is due to dark current? How much to room lights? Where does the rest come from?(2) Why do you want the Hg lamp cool?(3) How will self reversal of the 253.7 nm line from the Hg lamp affect the shape of the light curve? How will it affect the determination of the 3P l lifetime?(4) How does the number of Hg vapor (atoms/cm3) vary with temperature? How does this affect the coherent-trapping process? How does this in turn influence the "lifetime" that you observe? Could you remove one of the polarizers and still get good data? Which one is most important? How would you correctly set the UV Polarizers when setting up an experiment for the first time?(5) Why was expensive isotopically pure 198Hg used to fill the scattering cell? How would the data be altered if natural abundance Hg were substituted?(6) Why is the scattering cell shaped, and coated, the way it is? Would satisfactory results be obtained if the simpler right-cylindrical geometry had been used?REFERENCES:1. P. A. Franken, "Interference Effects in the Resonance Fluorescence of "Crossed" Excited Atomic States," Phys. Rev. 121, 508 (1961).2. A. Lurio, R. L. deZafra, and R. J. Goshen, "Lifetime of the First 1P1 State of Zinc, Calcium, and Strontium," Phys. Rev.,A134, 1198 (1964).3. A. C. G. Mitchell and Zemansky, Resonance Radiation and Excited Atoms, (Cambridge University Press, 1971).4. A. A. Radzig & Smirnov, Reference Data on Atoms, Ions, & Molecules, (Springer-Verlag, 1985).5. W. Happer, Review article bound in Reference binder.6. R. L. deZafra and W. Kirk, "Measurement of Atomic Lifetimes by the Hanle Effect," Amer. J. Phys.35, 573 (1967).7. G. Moruzzi and F. Strumia, The Hanle Effect and Level - Crossing Spectroscopy, (Plenum Press, 1991).8. R. Ignace, K. H. Nordsieck, and J. P. Cassinelli, "The Hanle Effect as a Diagnostic of Magnetic Fields in Stellar Envelopes. I. Theoretical Results for Integrated Line Profiles," The Astrophysical Journal, 486, 550 (1997) and II, The Astrophysical Journal, 520, 335 (1999). These two papers are good examples of modern applications of the。

邓宁-克鲁格效应

邓宁-克鲁格效应在生活中，你可能遇到过这样的人：•他们刚入职不久，就觉得自己已经能把工作做得相当好，期望升职接受更大的挑战；•他们自己打球水平不高，却总是在论坛上对职业球员的球技、教练的战术安排指指点点；•他们看到一篇新闻报道，就觉得自己仿佛身在事发现场一般，洞悉全局；•在疫情中，他们本来毫无医学经验，却鼓吹一些具有“神奇疗效”的治疗或防控方法，甚至认为可以注射消毒剂……相反，你也可能遇到一些人，他们精通于某一领域，却始终清楚自己的不足，对别人的指摘虚心接受，并且认为他们能做到的，很多人也能做到。

在评价自己的能力时，能力差的人往往极度高估自己的能力，而能力最强的人却倾向于低估自己的能力，这一现象最早由美国康奈尔大学的两位心理学家邓宁和克鲁格通过研究发现，因此被称为“邓宁-克鲁格效应”(Dunning-Kruger effect)，简称达克效应（D-K effect）。

邓宁和克鲁格做这一项研究的缘起很有意思。

在20世纪90年代，已有大量心理学研究表明在人们的自我评价中存在普遍的“优于平均效应”，即在各项重要的品质、能力上，人们都会认为自己优于人群的平均值。

当然，根据平均值的定义，每个人都优于平均值是不可能的，显然，人们会高估自己。

但是，每个人高估自己的程度一样吗？1995年在美国匹兹堡发生了一起银行抢劫案，抢劫犯没有做任何伪装，甚至还在走出银行前对着摄像头微笑。

在逮捕抢劫犯并进行调查后，警方无语地发现，抢劫犯声称在自己身上涂了柠檬汁，以为柠檬汁能让他隐形，因为柠檬汁能作为隐形墨水，用柠檬汁写的字只有在遇热时才会显形。

这个抢劫犯没有任何精神问题，他只是搞错了柠檬汁“隐形”的用法……这件事引起了邓宁和克鲁格的注意，他们推测，能力越差的人，高估自己的程度也会越高。

[1]四个阶段在邓宁和克鲁格的研究中，他们比较的是客观能力不同的个体，在主观自我评价上的差异。

得到的结果显示，能力最差的1/4被试，却认为他们的能力比60%的人更强；而能力最强的1/4被试的自我评价则比客观能力略微偏低。

化工一厂大检修盲板标准化管理规定

盲板信息卡片包括盲板编号、负责人、管径、盲板厚度、管线名称、盲板状态及计划日期（具体形式可参照附件）。盲板信息卡片必须在交出检修前一周挂到盲板对应位置。 4、盲板标识牌
盲板标识牌内容包括盲板编号、负责人（具体形式可参照附件）。在实施盲板加装作业之后，立即根据盲板编号和位置对相应盲板挂盲板标识牌，并将盲板信息卡片取走，检修完毕拆除盲板时将对应的盲板标识牌一同回收，并将盲板标识牌上交调度室。 5、盲板检查确认
In or der to e nsur e normal tea chi ng or der, prote cting st ude nts ' healt hy growt h, ensuri ng that nati onal (pr operty) is not l ost, to prevent or minimize the occurrence of safety accide nts, foll ow the " prevent, res cue each ot her, e ns ure safety and reduce l os ses" pri nci ple, a ccor ding t o the l ocal conditi ons, make t he manageme nt system. 1, t he pri nci pal is t he res ponsi bility of s chool safety, s chool s ecur ity under the leader shi p of Presi dent security work lea ding gr oup. The hea d teacher to t he lea dershi p team is res ponsi ble for, impleme ntation of the accounta bility system. 2 , school mont hly student knowle dge about safety education, educati on s hould be diversified i n the form every safety educati on for st udents of class es per week s hould be targeted. To carry on emergency iss ues deali ng with e ducation in G eneral, self -help a nd mut ual res cue k nowledge. Emergency calls (s uch as 1 10, 119, 12 2, 120, and so on) use common sense in e ducation. 3, t he esta blis hment of major a ccide nt reporti ng system. School st ude nts re port maj or accide nt within a n hour of educati on; student r un a nd disa ppe arance s to re port ; report of the ac cide nt to a written re port i n tripli cate, a corre ctional centre, a police station, a tow ns hip people's Gover nment shall not concea l the a cci de nt. 4 w eek, tea chers are on duty system, esta blish and improve the le aders hip values ; strengt hen the e ducation, manageme nt of tea chi ng activitie s in schools to ensure normal tea chi ng or der; re spons ible for school safety lea dership alway s maintai ned close conta ct and di strict poli ce stations, canva ssing support from the police station on school safety a nd help. 5, strengthe ning teachers ' moral education, e stablis h a dedi cated l ove, impr oving e ducation quality, observe t he st ude nts ' psychologi cal cha nges at a ny time and take preventive meas ures, no corporal punis hment a nd covert cor poral punis hment on st udents, st ude nt out of the cla ssroom, s chools may not be. 6, units or de partments use student Street propaganda or participate i n the celebrati ons, as well a s partici pating i n other social work, without approval of the Corre ctional Ce ntre, school pri nci pals consent, without organi zation. Without the a ppr oval of relevant departments , may organize st ude nts to parti cipate i n fire fighting, di saster relief and so on. 7, school s shoul d educate st ude nts to obey the school rules a nd reg ulations, on time, on time home t o prevent a cci dent s. 8, s chool to school ins pe ctions on a regular basis, found hi dde n in time, a nd in severe ca ses, it is hard to elimi nate immediately cl ose d, and reported to the local pe ople' s Gover nment, education, and rule of law secti on. 9, the s chool shoul d always check t he inter nal walls , retaining wa lls, ponds, raili ngs, handrails, doors, Window s, stairca ses a nd a variety of s ports, extracurricular activitie s, facilitie s such as fire safety, i nfrastruct ure se curity, unsafe faci lity to immediately re pair and demoliti on to ens ure that teachers a nd st ude nts work , learn, live ve nue s and facilities are safe and reli able. Song Li n Xia ng Li u Jia ping e lementary s chool Mar ch 2 016 s ong Lin Xiang Liu Jia pi ng primary s chool fire safety systems to en hance fire safety, protecti on of publi c pr operty a nd the life and pr operty safety of teachers a nd st ude nts, s chool fire safety into day-to-day manageme nt, is developing the following fire safety system. 1, stre ngthe n fire safety educati on of the whole s chool. A ccording to t he requirements of the Fire Servi ces Act, so that every one has of keeping fire control safety, prote cting fire control facilitie s, fire preventi on, re ports of fire

1、下载文档前请自行甄别文档内容的完整性，平台不提供额外的编辑、内容补充、找答案等附加服务。
2、"仅部分预览"的文档,不可在线预览部分如存在完整性等问题,可反馈申请退款(可完整预览的文档不适用该条件!)。
3、如文档侵犯您的权益，请联系客服反馈,我们会尽快为您处理(人工客服工作时间：9:00-18:30)。

PREPRINT
Hall effect in the normal state of high Tc cuprates
J. Boka and J. Bouviera
a
Solid State Physics Laboratory - ESPCI. 10, rue Vauquelin. 75231 PARIS Cedex 05, FRANCE.
σxy =
2 e3 Al B h2
(4)
where Al is the area enclosed by C.E.C., in the (lx, ly) plane. There may be secondary loops in the l
r
curve. When the C.E.C. is non-convex, the l curve presents several parts where the circulation are opposite (see Ref 9 Fig. 2). Then the effective density of carriers that must be taken in computing σxy is n e = Γ n e for the electron-like orbits, with
' p h − b 2 ne V RH = e ( p h + b ( p h 0 − p h ))2
(2) (5)
where σxy and σxx are the components of the conductivity tensor. We follow the approach given by N. P. Ong [9] :
where b is the ratio of the average mobilities of the carriers on the electron and hole like orbits. That is the mean value of
σxy =
ቤተ መጻሕፍቲ ባይዱ
Emax
∂ f0 ∫ σ x y (E ) dE − ∂E E min
Abstract We propose a model for explaining the dependence in temperature of the Hall effect of high Tc cuprates in the normal state, in various materials (LSCO, YBCO, BSCCO, GdBCO). They all show common features: a decrease of the Hall coefficient RH with temperature and a universal law, when plotting RH(T)/RH(T0) versus T/T0 where T0 is defined from experimental results. This behaviour is explained by using the well known electronic band structure of a CuO2 plane, showing saddle points at the energies ES in the directions [0, ± π] and [± π, 0]. This is well confirmed by photoemission experiments. We remark that in a magnetic field, for energies E > ES the carrier orbits are hole-like and for E < ES they are electron-like, giving opposite contributions to RH. We are able to fit all experimental results for a wide range of hole doping (ph0) (0.09 < ph0 < 0.30), and to fit the universal curve. For us kBT0 is simply EF – ES, where EF is the Fermi level varying with the doping. PACS: 74.72.-h; 74.25.Fy; 73.50.Jt Keywords: High Tc cuprates, Hall effect, normal state
Εk = -2t(cosX + cosY) + 4t’ cosX cosY
+ EF - ES + 4t’ (1) where t is the transfer integral between the first nearest neighbours, t’ between the second nearest neighbours, a the lattice parameter, ES the energy of the saddle point (Van Hove singularity, VHS) and EF is the Fermi level, which varies with the doping [6]. These electronic structures have been
1.
Introduction
Many measurements of the Hall effect in various high Tc cuprates have been published [1-5]. The main results are the following : (i) at low temperature T, RH ≈ 1/ph0e, where ph0 is the hole doping, when T increases RH decreases, and for highly overdoped samples becomes even negative [1] (ii) these authors are also able to define a temperature T0 , where RH changes its temperature behaviour, and such RH(T)/RH(T0) versus T/T0 is a universal curve for a large doping domain (from ph0 = 0.10 to ph0 = 0.27). We show that we can explain these results by using the band structure for carriers in the CuO2 planes. In particular, the existence of hole-like and electronlike constant energy curves, which give contributions of opposite sign to the Hall coefficient
(3)
τ /m
, where τ is the relaxation
where f0 is the Fermi Dirac distribution function, Emin and Emax are the bottom and the top of the band, and σxy(E) is σxy computed on a constant energy surface. For metals, where kBT << EF, σxy is usually chosen as σxy = σxy (EF ), computed on the Fermi surface only, this is done by N. P. Ong [9]. In our case, kBT is not small compared to EF - ES , so when T increases the electron-like orbits as well as the hole-like orbits are populated. The electron-like orbits give a negative contribution to RH, so that RH decreases with temperature. This is our original approach to the problem. To compute RH, we use the following method: we compute first σxy(E) using the Ong approach. The idea is to draw the l curve swept by the vector l = v k
__________________________________________________ * To whom correspondence should be addressed: E-mail : julien.bok@espci.fr
RH. The transport properties explore a range of energy kBT around the Fermi level, when T is increased more and more carriers are on the electron like orbits, resulting in a decrease of RH. 2. Calculation of the Hall coefficient The constant energy surfaces of carriers in the CuO2 planes are well describe by the following formula: