Evolution of Residual Stress in Sprayed Yttria Stabilised Zirconia Thermal barrier coating

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发展生物能源确保粮食安全

1050 ISSN1000-3061 CN11-1998/Q Chin J Biotech June 25, 2008 Vol.24 No.6(2) 低浓度H 2O 2连续胁迫控制策略在7 L 发酵罐上得到应用。

最终GSH 产量为922 mg/L, 胞内GSH 含量为1.64%, 比对照分别提高7%和35%。

说明此策略可行有效。

(3) H 2O 2对细胞产生一定的胁迫作用, 进而影响了细胞的生长和GSH 的合成。

较适宜的H 2O 2添加模式将进一步提高GSH 的胞内含量和GSH 的产量。

根据微生物细胞的生理特性设计的胁迫发酵策略, 能够促进GSH 的合成, 这一结论对研究胁迫条件下C . utilis 合成GSH 的生理学机制具有一定的借鉴意义, 同时为基于微生物细胞生理学特性以提高工业发酵产品效率的发酵策略研究提供了新的思路。

REFERENCES[1] Meister A, Anderson ME. Glutathione. Annual ReviewBiochemistry , 1983, 52: 711−760.[2] Sies H. Glutathione and its role in cellular functions. FreeRadical Biology & Medicine , 1999, 27: 916−921.[3] Mehdi K, Penninckx M. A short review on the role ofGlutathione in the response of yeast to nutritional, environmental, and oxidative stresses. Enzyme Microbial Technology , 2000, 26(9-10): 737−742.[4] Mehdi K, Penninckx M. An important role for glutathioneand glutamyl transpeptidase in the supply of growth requirements during nitrogen starvation of the yeast Saccharomyces cerevisiae . Microbiology , 1997, 143: 1885−1889. [5] Izawa S, Inoue Y, Kimura A. Oxidative stress response inyeast: effect of glutathione on adaptation to hydrogen peroxide stress in Saccharomyces cerevisiae . FEBS Letters , 1995, 368: 73−76.[6] Nie W, Wei GY, Du GC, et al . Enhanced intracellularglutathione synthesis and excretion capability of Candida utilis by using a low pH-stress strategy. Letters in Applied Microbiology , 2005, 40(5): 378−384.[7] Riccillo P, Muglia C, de Bruijn FJ, et al . Glutathione isinvoloved in envirnonmental stress responses in Rhizobium tropici , including acid tolerance. Journal of Bacteriology , 2000, 182(6): 1748−1753.[8] Duwat P, Cesselin B, Sourice S, et al . Lactococcus lactis ,a bacterial model for stress responses and survial. International Journal of Food Microbiology , 2000, 55: 83−86.[9] May MJ, Leaver CJ. Oxidative stimulation of glutathionesynthesis in Arabidopsis thaliana suspension cultures. Journal of Plant Physiology , 1993, 103, 621−627.[10] Pinkus R, Weiner LM, Daniel V. Role of quinone-mediated generation of hydroxyl radicals in the induction of glutathione-S-transferase. Gene Expression Biochemistry , 1995, 34: 81−88.[11] Alfafara CG, Kanda A, Shioi T, et al . Effect of amino acids onglutathione production by Saccharomyces cerevisiae . Applied Microbiology and Biotechnology , 1992, 36(4): 538−540.[12] Wei GY, Li Y, Du GC, et al . Application of a two-stagetemperature control strategy for enhanced glutathione production in the batch fermentation by Candida utilis. Biotechnology Letters , 2003, 25(11): 887−890.[13] Tietze F. Enzymic method for quantitative determinationof nanogram amounts of total and oxidized glutathione: application to mammalian blood and other tissues. Analytical Biochemistry , 1969, 27: 502−522.GFGFGFGFGFGFGFGFGFGFGFGFGFGFGFGFGFGFGFGFGFGF发展生物能源确保粮食安全以粮食为原料发酵生产生物燃料如醇类燃料等仅是生物能源开发源的一个方面。

如何解决疲劳效应英语作文

如何解决疲劳效应英语作文Title: Strategies to Combat Fatigue Effect。

Fatigue effect, the depletion of mental and physical energy over time, poses a significant challenge to individuals in various aspects of life, be it academic, professional, or personal. Addressing this issue requires a multifaceted approach encompassing lifestyle adjustments, cognitive strategies, and self-care practices. In this essay, we will delve into effective methods to tackle fatigue effect and enhance overall well-being.Firstly, establishing a balanced lifestyle is paramount in combating fatigue. Adequate sleep is fundamental for replenishing energy levels and sustaining cognitive function. Research suggests that adults should aim for 7-9 hours of sleep per night for optimal health. Additionally, maintaining a consistent sleep schedule, even on weekends, helps regulate the body's internal clock, promoting better sleep quality and reducing daytime fatigue.Moreover, incorporating regular physical activity into one's routine is beneficial for combating fatigue. Exercise stimulates the release of endorphins, neurotransmittersthat elevate mood and energy levels. Engaging in activities such as jogging, yoga, or swimming not only enhances physical fitness but also boosts mental clarity and alertness. Even short bouts of exercise throughout the day can mitigate feelings of fatigue and improve overall productivity.In conjunction with lifestyle modifications, adopting cognitive strategies can mitigate the impact of fatigue on cognitive function. Time management techniques, such as the Pomodoro Technique, involve breaking tasks into manageable intervals separated by short breaks. This method prevents burnout and enhances focus by capitalizing on the brain's natural rhythm of attention.Furthermore, implementing mindfulness practices can counteract the cognitive effects of fatigue. Mindfulness meditation, characterized by non-judgmental awareness ofthe present moment, promotes mental clarity and resilience to stress. Studies have shown that regular meditation reduces fatigue and enhances cognitive flexibility, enabling individuals to navigate challenges with greater ease.In addition to lifestyle and cognitive interventions, self-care practices play a crucial role in combatingfatigue effect. Nutrition plays a pivotal role in sustaining energy levels throughout the day. Consuming a balanced diet rich in whole grains, lean proteins, fruits, and vegetables provides essential nutrients that support optimal brain function and mitigate fatigue.Moreover, practicing self-compassion and setting realistic expectations are vital components of self-care. Perfectionism and excessive self-criticism can contribute to burnout and exacerbate feelings of fatigue. Cultivating self-compassion involves treating oneself with kindness and understanding, particularly during periods of heightened stress or fatigue.Furthermore, establishing boundaries and prioritizing self-care activities is essential for preventing burnout. Carving out time for leisure activities, social connections, and relaxation fosters resilience and replenishes depleted energy stores. Whether it's reading a book, spending time with loved ones, or engaging in hobbies, prioritizing activities that bring joy and fulfillment is essential for maintaining well-being.In conclusion, addressing fatigue effect necessitates a comprehensive approach encompassing lifestyle adjustments, cognitive strategies, and self-care practices. Byprioritizing sleep, exercise, mindfulness, nutrition, and self-compassion, individuals can mitigate the impact of fatigue and cultivate resilience in the face of challenges. Empowering oneself with effective coping mechanisms is keyto sustaining energy levels and optimizing overall well-being.。

伊士曼Tritan材料介绍

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雅思作文c14t3

雅思作文c14t3英文回答：In the contemporary era of rapid technological advancements, the question of whether individuals should embrace or resist technological progress has sparked a heated debate. Advocates of technological progress contend that it offers a myriad of benefits that can enhance human lives and drive societal evolution. On the other hand, detractors express concern over the potential adverse consequences, such as job displacement, social isolation, and the erosion of privacy.Proponents of technological progress argue that it leads to innumerable innovations and discoveries that can profoundly improve living standards. For instance, advancements in medicine have enabled the development of life-saving treatments and extended human lifespans. Technological innovations have also revolutionized industries, leading to increased productivity, efficiency,and convenience. Smartphones, computers, and the internet have connected people across vast distances, facilitating global communication and access to information.However, the opponents of technological progress raise valid concerns about its potential negative effects. The automation of tasks and the rise of artificial intelligence have led to job displacement in certain sectors,potentially exacerbating unemployment and economic inequality. Excessive reliance on technology can also contribute to social isolation, as individuals spend more time engaging with devices rather than interacting with others in person. Furthermore, the increasing collection and sharing of personal data through technological platforms raise concerns about privacy and surveillance.Ultimately, the decision of whether to embrace orresist technological progress is a complex one that requires a careful consideration of both the potential benefits and risks. It is essential to recognize the transformative power of technology while acknowledging its potential drawbacks. By striking a balance betweeninnovation and responsible use, societies can harness the benefits of technological progress while mitigating its negative consequences.中文回答：科技的快速发展在当代引发了激烈的争论，争论的核心是人们是对科技进步持拥抱还是抵制态度。

Nature of Soil–Water Characteristic Curve for Plastic Soils

Nature of Soil–Water Characteristic Curve for Plastic SoilsFernando A.M.Marinho 1Abstract:Determinations of unsaturated soil parameters using experimental procedures are time consuming and difﬁcult.In recent years,the soil–water characteristic curve ͑SWCC ͒has become an important tool in the interpretation of the engineering behavior of unsaturated soils.Difﬁculties associated with determining such parameters have justiﬁed the use of indirect determination.This paper presents the general behavior of the SWCC for plastic soils,in terms of gravimetric water content versus soil suction,according to the soil type,and also the stress history of the soil.In order to investigate possible relationships between the liquid limit ͑w 1͒,suction capacity and SWCC,data from the literature were collected and analyzed.The present study examined 49SWCCs from 18soils.The objectives of the paper were twofold:to contribute to the interpretation and use of the SWCC and to present a simple method for inferring the SWCC for plastic soils,taking into account the stress history of the soil.DOI:10.1061/͑ASCE ͒1090-0241͑2005͒131:5͑654͒CE Database subject headings:Unsaturated soils;Soil water storage;Soil suction;Liquid limit;Stress history .IntroductionThe soil-water characteristic curve ͑SWCC ͒has been used as a tool for predicting the mechanical and hydraulic properties of unsaturated soils.The indirect determination of these parameters may be justiﬁed not only by the difﬁculties involved in such tests but also by the costs associated with determinations of these pa-rameters ͑e.g.,Fredlund 1998͒.The proliferation of SWCC use for indirect determination of unsaturated soil properties is un-avoidable and in some cases desirable.The volume change with increased suction will depend on the initial void ratio and/or the stress history.The shape of the SWCC reﬂects the inﬂuence of stress history on the soil.For this reason,models used for pre-dicting unsaturated soil parameters should consider the inﬂuence of the stress history of the soil via the SWCC.An understanding of the phenomena involved in the relationship between water con-tent and suction is paramount for adequate interpretation of the SWCC.One of the objectives of this paper was to contribute to the interpretation and use of the SWCC,which in turn would help in understanding the engineering behavior of unsaturated soils.The SWCC was analyzed in terms of gravimetric water content versus soil suction,according to the soil type and taking into account the stress history of the soil.A further objective was to present a simple method for deducing the SWCC for plastic soils using one water content/suction determination and the liquid limit of the soil.Background to Soil–Water Characteristic Curve The shape of the SWCC depends on the pore size distribution and compressibility of the soil in relation to suction.These two char-acteristics of porous materials are affected by the initial water content,soil structure,mineralogy,and the stress history ͑e.g.,Lapierre et al.1990;Vanapalli et al.1999;Simms and Yanful 2000͒.Most SWCCs are S shaped and the curve shapes are a response to the pore size distribution of the material.For a rigid porous material of single pore size ͑i.e.,uniform pore size distri-bution ͒,whether it is a soil or not,the SWCC should be similar to curve ͑a ͒shown in Fig.1.However,complete water loss with suction increasing beyond the air entry value is not usual.In other words,it is difﬁcult to remove all the water from a porous mate-rial by means of a small increase in suction.Even in a porous material with uniform pore size distribution,some water would still be present in the material due to surface phenomena.The SWCC shape for a material of single pore size could be more appropriately represented by curve ͑b ͒in Fig.1.Nevertheless,for this material even after air entry suction,some water still remains in the soil and for the removal of the residual water higher energy are required.Curve ͑c ͒in Fig.1represents an example of material with two pore sizes.Each of the sizes is associated with one suction value via the capillary phenomenon ͑e.g.,Fredlund and Rahardjo 1993͒.Material with great numbers of pore sizes should present a more gradual reduction in water content with an in-crease in suction,as shown in curve ͑d ͒in Fig.1.By applying the capillary model,the equivalent pore size for the material can be deduced ͑i.e.,from 0.0146to 0.0000146mm ͒.Clay soils typically have nonuniform grain size and pore size distributions ͑e.g.,Delage and Lefebvre 1983͒.As a consequence,linear and less steeply sloping SWCCs ͑using a semilog plot ͒are normally obtained for clays.Clays may experience shrinkage that reduces pore size.Fine-grained soils with a liquid limit greater than 25%typically exhibit signiﬁcant shrinkage characteristics when dried.This can be observed in Fig.2,in which the liquid limit and shrinkage limit for some soils are presented.This ﬁgure also illustrates that the shrinkage limit by itself is not a sufﬁcient parameter for identifying soil behavior.Shrinkage phenomena in1Associate Professor,Dept.of Foundation and Engineering.,Univ.of São Paulo,CED 04318-002Sao Paulo,Brazil.E-mail:fmarinho@usp.br Note.Discussion open until October 1,2005.Separate discussions must be submitted for individual papers.To extend the closing date by one month,a written request must be ﬁled with the ASCE Managing Editor.The manuscript for this paper was submitted for review and pos-sible publication on May 31,2000;approved on September 23,2004.This paper is part of the Journal of Geotechnical and Geoenvironmental Engineering ,V ol.131,No.5,May 1,2005.©ASCE,ISSN 1090-0241/2005/5-654–661/$25.00.654/JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ©ASCE /MAY 2005D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .clays due to increased suction can play an important role in shap-ing the SWCC.During shrinkage the emptying of pores is accom-panied by reduction in pore size,which keeps the spaces ﬁlled with water and increases the air entry value.A reduction in pore size in clays may also occur due to me-chanical overconsolidation.In this case,the air entry value is higher than for the normally consolidated soil,and the SWCC shape for this type of material is relatively ﬂat.Various methods are commonly used when deﬁning the SWCC for a soil from lower to higher suction levels ͑e.g.,McQueen and Miller 1974;Blight and Roussev 1995;Barbour 1998͒.The reason for this is that not all methods used to measure suction can cover all suction ranges.Depending on the method used,total or matric suction is obtained.When a combination of methods is used without paying attention to the type of suction that is being measured,the SWCC shape may be affected if the value of osmotic suction is signiﬁcant.For suctions up to 30kPa,the pressure plate method with the hanging column is usually convenient.For suctions between 30and 1,500kPa,the pressure plate ͑i.e.,axis-translation technique ͒or ﬁlter paper methods can be used.In most high suction range ͑i.e.,greater than 1,500kPa ͒the suction measured is the total suction,regardless of the method used for measurement.Marinho and Chandler ͑1993͒drew attention to the fact that the ﬁlter paper,even when in con-tact with the soil,may not have adequate contact with the soil–water and hence this method may measure a combination of total and matric suction.Effect of Soil Plasticity on Soil–Water Characteristic CurveThe inﬂuence of soil plasticity on the SWCC has been demon-strated in the literature ͑e.g.,Black 1962;Mitchell and Avalle 1984;Fleureau et al.1990,among others ͒.Results obtained by Marinho and Chandler ͑1993͒showed a relationship between liq-uid limit and suction capacity ͑C ͒for compacted soils.Suction capacity is deﬁned as the reduction in water content ͑expressed in percent ͒over one logarithmic cycle.It has also been suggested that soils prepared from slurries should represent the upper limit of suction capacity for a given soil.There is a unique relationship between soil suction and water content normalized by the suction capacity C ͑i.e.w /C ͒,for dynamically compacted soils.The value of C could be reduced in accordance with the stress history.Har-rison and Blight ͑2000͒emphasized the relationship between C and some soil properties such as plasticity index,clay fraction and linear shrinkage.Harrison and Bligh ͑2000͒observed that,for residual soils,the relationship did not present good correlation.The effect of soil plasticity on the SWCC is displayed sche-matically in Fig.3͑a ͒,showing that the slope of the SWCC changes with the liquid limit when a log scale is used for repre-senting suction.This effect can be compared to the relationship between void ratio and effective overburden pressure for saturated soils presented by Skempton ͑1970͒.The general behavior of clay samples with different stress histories or different preparation pro-cedures is schematically shown in Fig.3͑b ͒.The behavior ob-served is also in agreement with data presented by Croney and Coleman ͑1954͒and Toll ͑1988͒.The SWCC for most soils with a liquid limit of more than 25%can be assumed to be a straight line between suctions of 100and 10,000kPa,on a semilog plot,regardless of the suction method used ͑McQueen and Miller 1974;Marinho and Chandler 1993͒.Some soils,such as residual soils,may present some predomi-nance of void size that induces a change in suction capacity at suction levels within the interval mentioned above.The soil state at the liquid limit has been used for relating soil properties.Burland ͑1990͒introduced the concept of intrinsic properties for saturated clays,which was based on the voidratioFig.1.General shape of soil–water characteristic curve according to pore sizedistributionFig.2.Relation between liquid limit and shrinkage limit for some soils ͓Holtz ͑1959͒;Fleureau et al.͑1993͒;Tuncer ͑1988͔͒Fig.3.Plasticity chartJOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ©ASCE /MAY 2005/655D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .of samples prepared between the liquid limit ͑w L ͒and 1.5w L .The relationship between water content and stress during isotropic consolidation can be obtained provided the speciﬁc gravity of the soil is known.The results obtained from drying saturated clay are equivalent to the isotropic consolidation,provided the soil re-mains saturated ͑e.g.,Blight 1965͒.Reddi and Poduri ͑1997͒pre-sented a study in which the void ratio at the liquid limit was used to obtain the water retention properties of the soil at other states.Marinho and Pinto ͑1997͒,in discussing the work presented by Reddi and Poduri ͑1997͒,presented data showing the relationship between w L and the pore size distribution index ͑␭͒,based on the Brooks and Corey ͑1966͒model for undisturbed soils and soils prepared at the w L .Effect of Stress History on Soil–Water Characteristic CurveCroney and Coleman ͑1954͒were among the ﬁrst investigators to study the effect of the stress history of the sample on the SWCC.It is clear from the ﬁndings of this study that,for the same water content,overconsolidation induces a reduction in suction and as a consequence in suction capacity.The degree of saturation of an overconsolidated sample is always higher than that of a normally consolidated soil,provided the suction is higher than the air entry value of the normally consolidated sample.Toll ͑1988͒performed a series of tests and described the soil behavior during desatura-tion,presenting a framework for examining the relationship be-tween water content and volume change with suction.Toll ͑1988͒also presented the concept of a virgin desaturation line ͑VDL ͒,which is the line where,for some value of suction,the relation-ship between water content and logarithm of suction is unique ͓see Fig.3͑b ͔͒.The point at which soils in different initial states reach the VDL is associated with the air entry value.Delage and Lefebvre ͑1983͒used mercury intrusion porosimetry to show the effect of the stress history on the air entry value of plastic soils.Tests were performed on St.Marcel clay,consolidated at different stress levels,including dried samples.The results clearly indi-cated that the air entry value increases with the consolidationpressure and is even higher for samples previously dried.It should be pointed out that the air entry value increases with the overconsolidation of the soil but,as for saturated soils,the stress required to reach the same water content is lower.Vanapalli et al.͑1999͒performed a series of tests using a sandy clay till ͑Indian Head till ͒to deduce the effect of soil struc-ture and stress history on the SWCC.The samples were statically compacted,placed in an oedometer cell,soaked under constant volume,and mechanically loaded to different values of net nor-mal stress.After the required stress was reached,the samples were unloaded under drained conditions.The loading and unload-ing of the sample induced additional overconsolidation in the sample.The samples were then removed from the oedometer cell and the SWCC was obtained from a pressure plate.No correction for volume change was made when the degree of saturation was used to represent the SWCC.A negligible volume change of the soil during drying was observed.Vanapalli et al.͑1999͒observed a signiﬁcant difference in the SWCC ͑represented as degree of saturation versus suction ͒,particularly at the beginning of the curve ͑low suctions ͒,thus reﬂecting the macrostructure of the soil.The results also suggested that the increase in stress after compaction reduced the differences observed in the SWCC at low suctions.Relationship between Suction Capacity and Liquid LimitThere seems to be an upper limit for the suction capacity C ,and this is related to the samples prepared and tested from slurry.The upper limit for C also agrees well with the data for saturated clays presented by Burland ͑1990͒and shown by Marinho and Chan-dler ͑1993͒in terms of suction capacity.There also seems to be a lower limit for the suction capacity related to overconsolidated clays.The stress history of the sample plays an important role in its suction capacity.Hence,a compacted soil may be near the upper limit or near the lower limit for the C value.It depends on the level of stress to which the sample was subjected.For differentTable 1.Soils Analyzed Soil w 1͑%͒w p ͑%͒I p ͑%͒Reference1London clay 78.026.052Croney and Coleman ͑1954͒2Silty clay41.520.521Croney and Coleman ͑1954͒3Red clay from Kenya 95.035.060Coleman et al.͑1964͒4London clay70.024.046Marinho ͑1994͒5Taplow Terrace Brickearth 36.019.017Dumbleton and West ͑1968͒6Kaolinite 61.030.031Biarez et al.͑1987͒7Yellow clay 40.020.020Fleureau et al.͑1990͒8Residual soil48.029.019Marinho and Stuermer ͑1998͒9Residual of gneiss ͑from 1.6m depth ͒50.031.01910Residual of gneiss ͑from 3.0m depth ͒50.034.01611Residual of gneiss ͑from 4.4m depth ͒53.033.02012Residual of gneiss ͑from 6.0m depth ͒51.039.01213London clay77.029.048Marinho ͑1994͒1490%London clay/10%sand 69.024.045Marinho ͑1994͒1570%London clay/30%sand 54.019.035Marinho ͑1994͒1650%London clay/50%sand 40.017.023Marinho ͑1994͒1730%London clay/70%sand 24.018.06Marinho ͑1994͒18Carsington63.031.032Marinho ͑1994͒656/JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ©ASCE /MAY 2005D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .samples of a soil compacted with the same energy but different water contents,little difference is observed in the suction capacity ͑e.g.,Marinho and Stuermer 2000͒.The SWCC determined by Marinho and Stuermer ͑2000͒started from the compaction water content,thus implying that only the micropores are controlling behavior.Simms and Yanful ͑2000͒observed that the pore size distributions of the micropores are similar,regardless of the com-paction water content.Even for nonplastic materials,such as the till tested by Watabe et al.͑2000͒,the effect of the compaction water content can be detected.Watabe et al.͑2000͒tested samples compacted at differ-ent initial water contents.The samples were dynamically com-pacted and saturated using backpressure.The results showed that the higher the degree of saturation after compaction,the higher the suction at the air entry value is.The SWCC shape obtained differed signiﬁcantly up to 300kPa,thereby showing the effect of the compaction water content on the initial portion ͑i.e.,macropores ͒of the SWCC.The effect of the stress history from a particular initial structure on the SWCC was not investigated by Watabe et al.͑2000͒.It should be pointed out that,although the till tested by Watabe et al.͑2000͒was a nonplastic material,it was a well-graded soil with clay content ͑%Ͻ2␮m ͒of 7%,silt con-tent of approximately 36%,and ﬁne sand content of about 30%.The clay content and grain size distribution of the nonplastic por-tion may be an important factor in the observed behavior.Normalization of Using Suction CapacityMarinho and Chandler ͑1993͒proposed the normalization of water content on the SWCC.It was found that the normalization of the SWCC applied to dynamically compacted soils gives a unique relationship for the soils analyzed.Models for Predicting Soil–Water Characteristic CurvesThere are several models available in the literature for predicting the SWCC using a limited quantity of data ͑e.g.,Black 1962;McQueen and Miller 1974;Gupta and Larson 1979͒.None of the suggested methods take into account the stress history of the soil.In order to obtain the complete SWCC,most of the available models divide the SWCC into segments.The geometrical and mathematical aspects of the ﬁtting method may justify the proce-dure of dividing the SWCC into segments.The models are also aimed at characterizing the physical meaning of the holding forces that are present at different levels of suction.McQueen and Miller ͑1974͒presented a procedure for deﬁning the SWCC based on one suction/water content measurement.A straight line on a semilog plot can,according to McQueen and Miller ͑1974͒,rep-resent the SWCC in the range between 30kPa and 10Mpa.It should be pointed out that this suction range can still be associ-ated with capillary water provided the pore sizes are equivalent to the suction.McQueen and Miller’s ͑1974͒method makes no ref-erence to the history of the soil specimen.Black ͑1962͒presented a method that correlates the plasticity index,water content and soil suction.The method was to be used for remolded soils and was based on results obtained using British clays.All data analyzed by Black ͑1962͒were above the A line on the plasticity chart and the relationship between soil suction and water content presented a well-deﬁned correlation with the plas-ticity index.In order to investigate possible relationships between theliq-Fig. 4.Schematic representation of relationship between water content and suction for:͑a ͒different soils in similar states and ͑b ͒same soil in differentstatesFig. 5.Soil–water characteristic curves for soil starting drying process fromslurry Fig.6.Soil–water characteristic curves for stiff soils upondryingFig.7.Soil–water characteristic curves for dynamically compacted samples upon dryingD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .uid limit,suction capacity and SWCC,previously reported data were collected and analyzed.The results presented in this paper show a consistent relation-ship between the slope of the SWCC ͑with suction in log scale ͒and the rigidity of the soil in relation to suction increase.This peculiar behavior suggests the possibility of adopting a simple model for deducing the SWCC.Soils Considered in AnalysisData from 42SWCCs from 18soils were analyzed.The Atterberg limits and the reference sources for the soils analyzed are shown in Table 1.Fig.4presents soils analyzed in this paper on a plas-ticity chart.It can be seen that most of the soils are located above the “A line.”Only the residual soils ͑8,9,10,11,and 12͒lie below the A line.Figs.5–8present the relationship between water content and soil suction for samples at initial state ranging from slurry to stiff material,including dynamically compacted and statically com-pacted,respectively.Even for the same type of sample ͑prepared from slurry,with dynamic compaction,etc.͒,the behavior can vary widely according to the soil type.In some cases slurry samples have low water content values,thereby indicating a low value for suction capacity,particularly at low suction levels.This behavior is associated with the storage capacity of the soil,and in this case it is more directly associated with soil mineralogy.This paper shows that the liquid limit can adequately reﬂect the rela-tionship between storage capacity and the stress history of the soil.The soil state that represents the association between water content and suction at failure conditions is called the “continu-ously disturbed state”͑e.g.,Croney and Coleman 1954;Brady 1988͒.After each suction measurement the sample is deliberately mixed or disturbed,to simulate a failure condition.The continu-ously disturbed state can also be identiﬁed as a critical state line for the SWCC ͑e.g.,Croney and Coleman 1954;Brady 1988͒.Fig.9presents the SWCC for continuously disturbed samples obtained from results presented by Croney and Coleman ͑1954͒,Dumbleton and West ͑1968͒,and Marinho ͑1994͒.Fig.10presents the relationship between suction capacity and liquid limit obtained from tests with samples at four different initial conditions.In addition to the data related to the soils pre-sented in Table 1,Fig.10also presents some data from the litera-ture,in which it was not possible to obtain the SWCC,but the suction capacity could be deduced ͑e.g.,Holmes 1955;Blight 1961;Matyas,1963;Olson and Langfelder 1965;Cepeda-Diaz 1987;Jucá1990;Ho et al.1992;Ridley 1995;Clarke and Neves,Jr.1996͒.From the analysis of the data collected from the literature,it was observed that the normalization with the suction capacitywasFig.8.Soil–water characteristic curves for statically compacted samples upondryingFig.9.Soil–water characteristic curves for continuously disturbedsamples Fig.10.Relationship between suction capacity and liquid limit for different samplehistoriesFig.11.Soil–water characteristic curve normalization using the suction capacityD o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .not universal.The suction capacity alone cannot represent the SWCC of the soils.Some discrepancies were observed in the data used.The differences in the position of the SWCC can be ob-served in Fig.11,where the normalized water content is plotted against soil suction on a logarithmic scale.One important observation related to Fig.11is that most of the normalized data lay along parallel lines.This empirical behavior can be used to indirectly estimate the SWCC for plastic soils using only one suction/water content measurement and the soil–liquid limit,and using the empirical relation between the liquid limit and suction capacity ͑Fig.10͒.Deducing Soil–Water Characteristic Curve Using One Set of Data and Liquid LimitThe steps to be followed for obtaining the SWCC for soils with a liquid limit of more than 25%are described as follows:The At-terberg limits for the soil must be determined in order to certify that the soil lies above the A line on the plasticity ing the liquid limit and observing the soil state,the suction capacity can be determined using Fig.10.At least one value of water content ͑w i ͒and suction ͑suction i ͒needs to be obtained.Any method for suction measured can be used for determining the necessary suc-tion ing the ﬁlter paper method at least 7days is neces-sary for equilibrium.If a high capacity tensiometer ͑e.g.,Marinho and Pinto 1997͒is used,just few minutes are necessary.With the water content ͑w i ͒of the sample,Fig.12can be used to estimate the line related to the suction capacity obtained ing the interception point as a reference,a horizontal line is then traced.A vertical line is drawn at the value of the suction mea-sured ͑suction i ͒that is associated with the water content ͑w i ͒.The intersection between that vertical line and the horizontal traced line is a point on the line that relates the normalized water content͑w /C ͒and the soil suction.In order to convert the relationship between the normalized water content ͑w /C ͒and suction into the SWCC,the suction capacity ͑C ͒previously obtained is used.Applying MethodThree examples of the use of the method are presented using data from Bao and Ng ͑2000͒,Ridley ͑1995͒,and Vaunat and Romero ͑2000͒.However,experimental results obtained by Vaunat and Romero were not included in the data used for the development of the method.The data taken from the above references were the liquid limit and one suction/water content measurement,as shown in Table 2.Table 2also presents the parameters obtained from the method.A guide to the use of the method is presented for the soil shown by Bao and Ng ͑2000͒:1.The liquid limit of the soil is 63.5%and its plastic limit is27.3%͑Ng,personal communication,May 2001͒.2.The soil is above the A line in the plasticity chart.3.Since the soil is an undisturbed expansive soil,it is assumedthat the soil is heavily overconsolidated.From Fig.10,the suction capacity ͑C ͒is 5%.4.The values of water content and suction were obtained di-rectly from the reference,as shown in Table 2͑Bao and Ng 2000͒.5.By entering the water content in Fig.12,the intercept withthe dotted line corresponding to the C value is obtained in Fig.10.6.The interception point corresponds to a normalized watercontent ͑w /C ͒of 5.9.ing the suction value from Table 2,the line showing therelationship between normalized water content and suction is obtained.8.Assuming that C =5%,the value of the water content can beobtained for some points.Considering this is a graphical method,the linear relationship may not be accurately obtained.Fig.13presents the experimental data from Bao and Ng ͑2000͒,Ridley ͑1995͒,and Vaunat and Romero ͑2000͒,and a line representing the results obtained using the method.The results obtained when using the method for the soils presented by Bao and Ng ͑2000͒and Ridley ͑1995͒was reasonably good.The SWCC prediction for the soil presented by Vaunat and Romero ͑2000͒was also reasonable,although a small discrepancy was observed.This discrepancy obtained may be as-sociated with the interpretation of the stress history of the soil.ConclusionsFrom the analysis of data from 42SWCCs from 18soils obtained from the literature,it was possible to classify the behavior of the soil according to its nature ͑associated parameter w 1͒and its stress history ͑associated parameter C ͒.It was observed that soilsTable 2.Data from Literature and Parameters of Method ReferenceSample type w 1͑%͒Water content ͑%͒Suction ͑kPa ͒C ͑%͒w /C Bao and Ng ͑2000͒Undisturbed 63.5281005 5.9Ridley ͑1995͒Compacted643057012 2.5Vaunat and Romero ͑2000͒Compacted high density562245054.5Fig.12.Diagram for soil–water characteristic curve approximation using one data set and liquid limitJOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ©ASCE /MAY 2005/659D o w n l o a d e d f r o m a s c e l i b r a r y .o r g b y H a r b i n I n s t i t u t e o f T e c h n o l o g y o n 11/17/13. C o p y r i g h t A S CE .F o r p e r s o n a l u s e o n l y ; a l l r i g h t s r e s e r v e d .。

c12t8大作文范文

c12t8大作文范文英文回答：In the realm of synthetic biology, the advent of CRISPR-Cas systems has revolutionized the field by providing scientists with an unprecedented level of precision and control over genome editing. The implications of this technology extend far beyond the laboratory, potentially shaping the future of medicine, agriculture, and even human evolution.One of the most significant applications of CRISPR-Cas is in gene therapy. By precisely targeting and editing specific genes, scientists can potentially correct genetic defects that cause diseases such as sickle cell anemia and cystic fibrosis. This holds immense promise for improving the health and well-being of millions of people worldwide.Another transformative application of CRISPR-Cas lies in agriculture. By manipulating the genomes of crops,scientists can enhance their nutritional value, resistance to pests and diseases, and yield potential. This has the potential to address global food security challenges and promote sustainable farming practices.Moreover, CRISPR-Cas systems have opened up new possibilities for studying gene regulation and understanding the genetic basis of complex traits. By precisely disrupting or activating specific genes, researchers can uncover their functions and interactions, leading to a deeper understanding of biology at the molecular level.While the potential of CRISPR-Cas technology is vast, it is essential to approach its use with caution and ethical considerations. The ability to manipulate the genomes of living organisms carries significant implications for society, and decisions must be made regarding the responsible use of this powerful tool.中文回答：CRISPR-Cas系统对合成生物学的影响。

脊髓损伤修复是否应遵循进化论原则

NEURAL REGENERATION RESEARCH Volume 7, Issue 11, April 2012Cite this article as: Neural Regen Res. 2012;7(11):849-852.849Zhicheng Zhang ☆, Studying for doctorate, Attending physician, PLA Institute of Orthopedics, Beijing Army General Hospital, Beijing 100700, ChinaCorresponding author: Tiansheng Sun, Master, Professor, PLA Institute of Orthopedics, Beijing Army General Hospital, Beijing 100700, Chinasuntiansheng-@Received: 2011-11-29 Accepted: 2012-02-11 (NY20111121002/H)Zhang ZC, Li F, Sun TS. Does repair of spinal cord injury follow the evolutionary theory? Neural Regen Res. 2012;7(11):849-852.doi:10.3969/j.issn.1673-5374.2012.11.009Does repair of spinal cord injury follow the evolutionary theory?*☆Zhicheng Zhang, Fang Li, Tiansheng SunPLA Institute of Orthopedics, Beijing Army General Hospital, Beijing 100700, ChinaAbstractLower vertebrates, such as fish and amphibians, and higher vertebrates in embryonic development can acquire complete regeneration of complex body structures, including the spinal cord, an important part of the central nervous system. However, with species evolution and development, this regenerative capacity gradually weakens and even disappears, but the cellular and molecular mechanisms remain poorly understood. We explored the differences in mechanisms of spinal cord regeneration capability between lower and higher vertebrates, investigated differences in theircellular and molecular mechanisms and between the spinal cord structures of lower vertebrates and mammals, such as rat and monkey, to search for theoretical evidence and therapeutic targets for nerve regeneration in human spinal cord.Key Words: spinal cord injury; evolutionary theory; lower vertebrates; higher vertebrates; mammals; cell transplantationAbbreviations: SCI, spinal cord injury; OEG, olfactory ensheathing gliaINTRODUCTIONSome clinical and basic problems arising from spinal cord injury (SCI) have not been explained fully. Why can the spinal cord in lower vertebrates completely regenerate after injury, while in higher vertebrates it does not? Why can SCI in the rat get satisfactory functional recovery, including motion, using various integrated intervention strategies, but is not successful in humans? Why is the self-repair capability of neural structures at lower evolutionary level superior to that at the higher evolutionary level following SCI? Does SCI repair follow the principles of evolutionism? Early in the 1970s, Dobzhansky pointed out that“Nothing in biology makes sense except in the light of evolution” [1]. Maybe answers to these questions will lead to a revolution in the repair and treatment of SCI.EVOLUTIONARY THEORY IN SCI REPAIRThe primary successful application of stem cell transplantation was for Parkinson's disease treatment suggesting that stem cell transplantation could be used to treat other neurological diseases, including SCI [2-3]. This idea seems logical, but it neglects a fundamental and important fact. Thepathological basis of P arkinson’s disease is the primitive ganglion cell, but that of SCI isthe highly developed and advanced Betz ’s motor neuron. The nervous system has evolved through the following process: no nerve (protozoa) → primitive nervous system (sponges) → reticular nervous system (coelenterates) → ladder nervous system (p latyhelminthes) → chain nervous system (annelid and arthropods - ganglion cells ) → tubular nervous system(vertebrates - Betz's cells)[4]. There is an interval of millions of years in evolutionary pedigree between mature Betz ’s cells and ganglion cells. The two kinds of nerve cells are vastly different and not comparable. Lower vertebrates, such as fish andamphibians, and higher vertebrates during embryonic development can acquire complete regeneration of complex body structures, including the spinal cord, an important part of the central nervoussystem [5]. For example, some kinds of tailed amphibians, newts and salamanders, can regenerate their spinal cord, retina, and even part of the telencephalon. However, tailless amphibians, such as frogs, may regenerate neural structures in larvae but such capability decreases as theydevelop [6-7]. A high regenerative capacityduring development is not unique to anurans, and it has been well reported in highervertebrates, such as birds and marsupials (a subclass of Mammalia)[8]. Their embryos are easily accessible for manipulation andanalysis unlike those whose entire gestation is intrauterine. There are evidences of spinalcord regeneration in rodent embryos but not in sheep[9]. However, with species evolution and development, this regenerative capacity gradually lessens or even disappears. From the most common animal model, the rat, to the rarer model of macaque[10], many animal models have been established for studies of SCI repair. Clinical trials are limited to assessing nerve regeneration using electrophysiological or functional measures since pathological changes cannot be observed directly in SCI patients. Regeneration of the spinal cord may be detected using histological methods in animal models, but not in humans. Several previous experimental studies on SCI showed that rats can recover more sensory and motor function than humans following various treatments especially after complete SCI. In clinical practices, a little spontaneous recovery of motor function was seen in a longitudinal study of patients with complete SCI[11]. In animals it has been possible to visualize, using special histological methods, axonal regeneration over a collagen nanofiber scaffold after complete transection of the spinal cord[12]. Akhtar et al[13] explored the reasons for different responses to multiple neuroprotective agents between the promising animal studies and disappointing clinical trials and concluded that the differences betweenlaboratory-induced SCI and clinical SCI, difficulties in interpreting functional outcome in animals, andinter-species differences in pathophysiology of SCI could be responsible. The differences in neural plasticity between animal models and human SCI have been discussed in relation to the severity of injury, the effect of locomotor training, the localization of neural plasticity, and the implications for interpreting the translatability of animal model data to human study and clinical practice[14]. The evolutionary differences among species may have a direct role on their regenerative capacity and we explored this neglected area of investigation.It remains poorly understood why this regeneration potential is lost with evolution and development and becomes very limited in adult mammals. Regenerative capacity changes are most likely due to a combination of several factors, such as cellular and molecular changes during evolution, environmental difference between embryonic and adult spinal cord, and the decrease in number of neural progenitors[15], or the capacity to recruit them in vivo in the adult spinal cord of higher vertebrates[16]. We should study the mechanism of spinal cord regeneration and the difference in the capability between lower vertebrates and higher vertebrates. We could also explore differences in their intercellular, cellular and molecular mechanisms and the spinal cord structures in animals from different evolutionary levels, e.g. fish, chick, rats and monkeys, to search for a theoretical basis, the guiding principles and therapeutic targets. INVESTIGATION AND VERIFICATION OF THE EVOLUTIONARY THEORY IN SCI REPAIR First, the mechanisms of spinal cord self-regeneration and self-repair capabilities in various species from different evolutionary levels can be explored[17].In the high evolutionary mammals, SCI has been considered unable to regenerate and repair. However, research on various integrated intervention strategies following rat spinal cord contusion injury has resulted in satisfactory functional recovery including motor function[18].Cell transplantations may bridge disrupted axons, support axonal regeneration, secrete various growth factors to promote nerve regeneration, and may replace damaged neurons. Each of these procedures may involve an aspect of SCI repair. The basis of stem cell application in SCI repair is the plasticity of stem cells to differentiate into the mature cell type. The lesser the maturity of stem cells, the stronger capability they have to repair the injury, however, there is a greater risk of malignant transformation. A large number of studies have reported that different stem cells, including embryonic and adult stem cells, have been transplanted into animal models of SCI via different administration paths. Fortunately, in many cases, stem cells transplantations have resulted in modest sensory and motor recovery[19]. However, it is important to confirm that the stem cell transplantation could maintain a long lifespan and to determine whether or not tumors will eventually form. In addition, it is necessary to confirm whether oriented differentiation and long-term survival of stem cells are required for functional recovery, and which type of progenitor cells and quantity are optimal[20].If the spinal cord progenitor or stem cells are not available, then the cells of more primitive evolutionary structures in human central nervous system evolution, olfactory system, limbic system or reticular formation[21], could be used to repair SCI. Recent studies have shown that the olfactory system has a better repair capability than the limbic system or the reticular formation. Cells from the olfactory system can be obtained readily from the nasal mucosa epithelial tissue of the olfactory bulb and the lateral ventricles system. Indeed, the olfactory system has a wide range of cells, far more than the olfactory ensheathing glia (OEG). When the OEG were transplanted into rat corticospinal tract of SCI, fairly satisfactory functional recovery including motor function was observed[22].On the other hand, patients who received OEG transplantation treatment using the same target corticospinal tract injection only gained slight functional improvement[23].Clinical studies of cell transplantation include a study of more than 400 SCI patients who have been treated with OEG transplantation[24]. Some functional recovery of lower evolutionary level spinal cord structures, such as skin temperature and color recovery, bladder and bowel function improvement (autonomic nerve function), muscle tonus decrease (spinocerebellar tract), was detected in the majority of these patients. However, these functions were not easily measured in most clinics or were often ignored. Some patients also had significant sensory function improvement (touch and pain) and the850sensory level dropped 3 to 10 spinal segments and the American Spinal Injury Association sensory scores increased significantly. Several patients experienced motor function recoveries of the injured spinal cord level with increased strength of an injured level key muscle. However, no motor recovery was found below the injured level that resulted in any obvious motor score increase. Our clinical study of 11 SCI patients treated with OEG transplantation obtained similar results[23].On the contrary, SCI animals that received OEG transplantation obtained fairly satisfactory functional recovery, including motor function[22]. Hierarchical order of the extent of functional recovery and the possibility of recovery from high to low was skin nutrition, spasms, bladder and bowel function, superficial sensation (up to 10 levels), and motor function. Coincidentally, this is entirely consistent with the theory of evolution. The lower evolutionary level structures have higher repair capability and these low-level functions were restored first[25]. Although OEG transplantation can result in some repair of SCI, it is far from complete. Due to the complexity of spinal cord and SCI, any single therapeutic intervention cannot be expected to solve all the problems. Transplanted cells play some roles in SCI repair, providing means of bridging, supporting, secreting growth factors and replacing damaged cells, evidence has shown that several intervention strategies need to be integrated to optimize recovery[18].Different results were obtained in clinical and animal experimental studies using the same transplantation strategy. This fact may reflect the evolutionary differences between the nervous systems of the human (mammals, primates, human subjects) and the rat (mammals, rodents, murine). First, we could analyze the anatomical differences to ascertain any differences in response to the same treatment strategy. Second, the mechanism of differences among self-repair andself-regeneration capability of neural structures with different evolutionary level should be explored. The modern human central nervous system is the most complex and develops biological system. Archeological studies have identified the oldest structures of the modern central nervous system are the olfactory system, limbic system and reticular formation[21]. These systems exist in early vertebrate fossils, but other systems exist only in later evolutionary species and their fossils.The repair possibility of different neural structures seems to follow the order of evolution. That is, the more ancient structure, the larger possibility of repair and regeneration. Newer structures have less capacity[26]. The order of the development of nervous system, relevant to the spinal cord, from the ancient to today is the reticular formation, cerebellum system, sensory thalamic system and forebrain systems, followed by the motor system[3] (Figure 1).The spinal cord has structures connecting to the brain and peripheral nervous system, so it covers a broad range of neural structures from the earliest evolutionary structure (reticular formation) to the most developed neurons (Betz’s cells) and their axons (pyramidal tract).Current basic research results showed that the sequence of spinal cord structure repair capacity is reticular formation, cerebellum tract, rubrospinal tract, spinothalamic tract, and corticospinal tract[25]. Furthermore, the reticular formation is also involved in the repair of injured spinal cord. These results were entirely consistent with the theory of evolution which has important significance in the law of nerve tissue repair. However, not only regeneration capacity and plasticity difference but also the role in repair of the spinal cord among neural structures of different evolutionary levels remains poorly understood. In clinical practice, the neurological function recovery sequence may also follow the evolutionary principles. Current assessment systems of functional recovery have some deficiencies in that most attention has been paid to the recovery of motor function. The functions at the low evolutionary level, including skin nutrition, bladder function, gastrointestinal function and sensory functions, are also significant. These should be included in a broader assessment system for future clinical studies.PROSPECTSThe differences in capability and mechanisms to repair SCI among different evolutionary species and neural structures should be explored at the genetic, molecular, cellular, organ and systems’ levels in the body with possible approaches of developmental biology, comparative biology, pathology, and cellular biology and molecular biology. The potential molecular mechanisms may include the change and evolution of polymers, e.g. DNA, large proteins (receptors), small proteins (growth factors) or small molecules, e.g. ligands or changes in the systems at the molecular level, e.g. signaling. It will provide an evolutionary theory basis for transition from basic research to clinical applications. According to the Figure 1 Phylogenetic order of development of thecentral nervous system[3].851differences of evolution in genes, molecules, cells, and organs, several interventions should be performed to find new therapeutic targets to improve the regeneration of human SCI.Acknowledgments: We thank Dajue Wang from the National Spinal Injuries Centre, Stoke Mandeville Hospital UK for giving us inspiration, some useful ideas and information.Funding: This work was supported by the National Natural Science Foundation of China, No. 30872604.Author contributions: Zhicheng Zhang reviewed the references, extracted the data, and wrote the manuscript. Fang Li contributed to the paper revision and study instruction. Tiansheng Sun designed this study.Conflicts of interest: None declared.REFERENCES[1] Dobzhansky T. Nothing in biology makes sense except in the lightof evolution. Am Biol Teach. 1973;35:125-129.[2] Bjorklund LM, Sánchez-Pernaute R, Chung S, et al. Embryonicstem cells develop into functional dopaminergic neurons aftertransplantation in a Parkinson rat model. Proc Natl Acad Sci U S A.2002;99(4):2344-2349.[3] Kim JH, Auerbach JM, Rodríguez-Gómez JA, et al. Dopamineneurons derived from embryonic stem cells function in an animalmodel of Parkinson’s disease. Nature. 2002;418:50-56.[4] Northcutt RG. Evolution of the vertebrate central nervous system:patterns and processes. Amer Zool. 1984;24:701-716.[5] Clarke JDW, Ferretti P. CNS regeneration in lower vertebrates. In:Ferretti P, Ge’raudie J, eds. Cellular and Molecular Basis ofRegeneration: from Invertebrates to Humans. Chichester,England: John Wiley and Sons, Ltd. 1998.[6] Holder N, Clarke JD. Is there a correlation between continuousneurogenesis and directed axon regeneration in the vertebratenervous system? Trends Neurosci. 1988;11:94-99.[7] Filoni S. Experimental aspects of regeneration of central nervoussystem of the anuran amphibians. In: Benedetti I, Bertolini B,Capanna E, eds. Neurology Today. Modena: Mucchi. 1992.[8] Ferretti P, Whalley K. Successful neural regeneration in amniotes:the developing chick spinal cord. Cell Mol Life Sci. 2008;65:45-53.[9] Yingling CD, Meuli-Simmen C, Meuli M, et al. Experimental fetalneurosurgery: effects of in-utero manipulations on somatosensory evoked potentials. Pediatr Surg Int. 1999;15:535-539.[10] Jia L, Yu Z, Hui L, et al. Fas and FasL expression in the spinalcord following cord hemisection in the monkey. Neurochem Res.2011;36:419-425. [11] Steeves JD, Kramer JK, Fawcett JW, et al. Extent of spontaneousmotor recovery after traumatic cervical sensorimotor completespinal cord injury. Spinal Cord. 2011;49:257-265.[12] Hurtado A, Cregg JM, Wang HB, et al. Robust CNS regenerationafter complete spinal cord transection using aligned poly-L-lacticacid microfibers. Biomaterials. 2011;32:6068-6079.[13] Akhtar AZ, Pippin JJ, Sandusky CB. Animal models in spinal cordinjury: a review. Rev Neurosci. 2008;19:47-60.[14] Tansey KE. Neural plasticity and locomotor recovery after spinalcord injury. PM R. 2010;2:S220-226.[15] Whalley K, Gögel S, Lange S, et al. Changes in progenitorpopulations and ongoing neurogenesis in the regenerating chickspinal cord. Dev Biol. 2009;332:234-245.[16] Dubois-Dalcq M, Williams A, Stadelmann C, et al. From fish toman: understanding endogenous remyelination in central nervous system demyelinating diseases. Brain. 2008;131:1686-1700. [17] Muramatsu R, Ueno M, Yamashita T. Intrinsic regenerativemechanisms of central nervous system neurons. Biosci Trends.2009;3:179-183.[18] Bunge MB. Novel combination strategies to repair the injuredmammalian spinal cord. J Spinal Cord Med. 2008;31:262-269. [19] Louro J, Pearse DD. Stem and progenitor cell therapies: recentprogress for spinal cord injury repair. Neurol Res. 2008;30:5-16.[20] Thomas KE, Moon LD. Will stem cell therapies be safe andeffective for treating spinal cord injuries? 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Epigenetic regulation of stress responses in plants-2009

Available online at Epigenetic regulation of stress responses in plants Viswanathan Chinnusamy1and Jian-Kang Zhu2Gene expression driven by developmental and stress cues often depends on nucleosome histone post-translationalmodiﬁcations and sometimes on DNA methylation.A number of studies have shown that these DNA and histone modiﬁcations play a key role in gene expression and plant development under stress.Most of these stress-induced modiﬁcations are reset to the basal level once the stress is relieved,while some of the modiﬁcations may be stable,that is,may be carried forward as ‘stress memory’and may be inherited across mitotic or even meiotic cell divisions.Epigenetic stress memory may help plants more effectively cope with subsequent stresses. Comparative studies on stress-responsive epigenomes and transcriptomes will enhance our understanding of stress adaptation of plants.Addresses1Water Technology Centre,Indian Agricultural Research Institute,New Delhi110012,India2Department of Botany and Plant Sciences,Institute for Integrative Genome Biology,University of California,Riverside,CA92521,USACorresponding author:Zhu,Jian-Kang(jian-kang.zhu@)Current Opinion in Plant Biology2009,12:133–139This review comes from a themed issue onGenome studies and molecular geneticsEdited by Masahiro Yano and Roberto TuberosaAvailable online27th January20091369-5266/$–see front matter#2008Elsevier Ltd.All rights reserved.DOI10.1016/j.pbi.2008.12.006IntroductionInformation content of the genome(DNA sequence)and its expression in response to stress are crucial for the adaptability of a genotype.Expression of the genome is inﬂuenced by chromatin structure,which is governed by processes often associated with epigenetic regulation, namely histone variants,histone post-translational modi-ﬁcations,and DNA methylation.Developmental and environmental signals can induce epigenetic modiﬁ-cations in the genome,and thus,the single genome in a plant cell gives rise to multiple epigenomes in response to developmental and environmental cues[1].Under-standing stress-induced epigenetic processes in stress tolerance of plants requires answers to the following questions:How much of the stress-induced gene expres-sion changes are associated with alterations in DNA methylation and histone modiﬁcation marks?Are stress-induced DNA and histone modiﬁcations during acclimation or during theﬁrst experience of stress mem-orized and inherited mitotically and meiotically?What are the adaptive values of epigenetic stress memory?This review brieﬂy describes epigenetic processes,and then focuses on recent data on the epigenetic regulation of stress responses and its heritability in plants. Epigenetic regulation of stress responses Retention of stress memory for short durations is well known in plants,as evident from acclimation responses [2,3].The stress memory can be retained for only short durations if the memory depends on the half-life of stress-induced proteins,RNAs,and metabolites,while the memory can last longer if it involves reprogramming in phenology and morphology of plants.Epigenetic processes,that is,stable or heritable DNA methylation and histone modiﬁcations,can also be a choice of retaining stress memory for longer times.Methods to decipher epigenetic changes are brieﬂy described in Box1.Histone modiﬁcationsN-terminal regions of nucleosome core complex histones undergo various post-translational modiﬁcations.In addition,each histone has variants encoded by different genes.The combinations of histone variants and post-translational modiﬁcations can be considered a‘histone code’,which plays a key role in chromatin structure and thus determines the transcriptional state and expression level of genes.Some histone modiﬁcations,namely acety-lation,and certain phosphorylation and ubiquitination [4,5],enhance transcription,while biotinylation and sumoylation repress gene expression[6,7].Trimethyla-tion of H3K4activates transcription,while dimethylation of H3K9and H3K27represses transcription[5].Because several of the histone modiﬁcations are associated with changes in gene transcription in general,it is not surpris-ing that stress-induced gene regulation is associated with histone modiﬁcations in all cases that have been inves-tigated.Changes in histone variants,histone modiﬁ-cations as well as DNA methylation are often referred to as epigenetic regulation.However,such changes may or may not be truly epigenetic in nature because common epigenetics deﬁnition requires mitotic or meiotic herit-ability.Drought induced the linker histone variant H1-S in tomato.H1-S appears to be involved in the negative regulation of stomatal conductance,because stomatal con-ductance and transpiration rates were higher in antisense transgenic H1-S tomato plants than in wild type(WT) plants[8].In rice seedlings,submergence induced histone H3K4 trimethylation and H3acetylation in alcohol dehydrogen-ase1(ADH1)and pyruvate decarboxylase1(PDC1) genes.These histone modiﬁcations were correlated with enhanced expression of ADH1and PDC1under stress. The modiﬁcations,however,were dynamic and were restored to the basal level after stress was relieved by reaeration[9 ].Environmental and endogenous signals can repress the target genes through reduction in histone acetylation levels.The REDUCED POTASSIUM DEPEN-DENCY3(RPD3)family histone deacetylases(HDACs), namely HDA6and HDA19,mediate histone deacetyla-tion in response to biotic and abiotic stresses in Arabi-dopsis.HDA6is induced by jasmonic acid(JA)and ethylene[10].HDA6is involved in transcriptional gene silencing(TGS)[11]and RNA-directed DNA methyl-ation(RdDM)in Arabidopsis[12].Wounding,infection by Alternaria brassicicola,and plant hormones(JA and ethyl-ene)induced the expression of the HDA19/HD1/ AtRPD3A gene.Overexpression of HDA19in transgenic plants reduced histone acetylation levels and increased the expression levels of ETHYLENE RESPONSE FAC-TOR-1(ERF1)and PATHOGENESIS-RELATED(PR)genes.In contrast,RPD3A-RNAi plants exhibited higher histone acetylation,which was accompanied by down-regulation of ERF1and PR genes in Arabidopsis[10]. Enhanced HDA6and HDA19expression caused by stress and hormonal signals thus might affect chromatin modi-ﬁcations at several loci.ABA downregulated the expression of AtHD2C(a mem-ber of plant-speciﬁc HD2family of HDACs).Transgenic Arabidopsis plants overexpressing AtHD2C exhibited enhanced expression of ABA-responsive genes and greater salt and drought tolerance than the WT plants [13 ].In rice,expression of different members of the HDAC families is also differentially regulated by abiotic factors such as cold,osmotic and salt stress,and hormones such as ABA,JA,and salicylic acid[14].Besides the HDACs,the WD-40repeat protein TBL1 (T ransducin B eta-L ike protein-1)is associated with histone deacetylation in humans.The Arabidopsis hos15 (high expression of osmotic stress responsive genes15)mutant was hypersensitive to freezing stress,and was hypersen-sitive,in terms of germination,to ABA or NaCl.HOS15 encodes a protein similar to TBL1,which interacts with histone H4.HOS15is probably involved in H4deacety-lation because acetylated H4was higher in hos15mutants than in WT plants,and thus regulates stress tolerance through chromatin remodeling in Arabidopsis[15 ]. Drought-induced expression of stress-responsive genes is associated with an increase in H3K4trimethylation and H3K9acetylation in Arabidopsis[16 ].In Drosophila,H3 Ser-10phosphorylation activates transcription during heat shock responses[17].In Arabidopsis also,high sal-inity,cold stress,and ABA triggered rapid and transient upregulation of histone H3Ser-10phosphorylation,H3 phosphoacetylation,and H4acetylation followed by stress-type-speciﬁc gene expression[18 ].Histone acetyltransferases(HATs)interact with tran-scription factors and are involved in activating stress-responsive genes.GCN5is the catalytic subunit of the Spt-Ada-Gcn5acetyltransferase(SAGA)and transcrip-tional adaptor(ADA).Like ADA2and GCN5in the response of yeast to extreme temperature stress,in Ara-bidopsis as well,GCN5and ADA regulate cold tolerance by interacting with C-repeat B inding F actor-1(CBF1). CBF1activates transcription of its downstream cold-responsive genes probably through the recruitment of ADA/SAGA-like complexes that may mediate chromatin remodeling in target genes[19].DNA methylationDNA cytosine methylation,both asymmetric(m CpHpH)-methylation and symmetric(m CpG and m CpHpG)-meth-ylation,is associated with repressive chromatin in gene promoters and with repression of gene transcription.De134Genome studies and molecular geneticsBox1Deciphering epigenetic changesHistone modifications:Chromatin immunoprecipitation(ChiP)—histones bound to the DNA in vivo are covalently crosslinked to DNA in situ by vacuum infiltration of plant tissue with formaldehyde.Then chromatin is isolated as part of cell extract,fragmented,and protein–DNA complexes are immunoprecipitated with antibodies specific against modified histone,for example,acetylated or dimethylated H3K9. DNA is isolated from the immunoprecipitate and analyzed by PCR [4,9 ,15 ,16 ,18 ,51].ChiP-Seq—this method combines ChiP with next-generation sequencing technology such as Solexa sequencing to analyze gen-ome-wide-speciﬁc histone modiﬁcations[52].DNA methylation:Methylation-sensitive restriction endonucleases—the classical method of cytosine methylation analysis is the restriction analysis of template DNA with methylation-sensitive restriction enzymes.Re-stricted DNA is then ligated to restriction site specific adaptor and analyzed by PCR or restricted genomic DNA is analyzed by Southern blotting[22,27 ,49 ,50 ].Bisulﬁte method—sodium bisulﬁte converts cytosines,but not50-methylcytosines,into uracil,under denaturing conditions.PCR ampliﬁcation of bisulﬁte-treated DNA results in conversion of uracil to thymine.Bisulﬁte-treated DNA is analyzed by PCR or DNA sequen-cing[4,23 ,33 ,49 ,50 ]Methylated-DNA immunoprecipitation(MeDIP)—genomic DNA is fragmented and precipitated with5-methylcytosine-speciﬁc anti-body.The precipitated DNA is then analyzed by PCR or whole-genome tiling microarrays[53,54].Shotgun bisulﬁte-sequencing—this combines bisulﬁte treatment of genomic DNA with next generation sequencing technology such as Solexa sequencing.The converted sequences are mapped to the reference genome sequence to identify methyl-cytosines[21,55].novo methyltransferases DRM1(DOMAINS REARRANGED METHYLASE1)and DRM2catalyze new cytosine methylation,while the maintenance of symmetric CG and CHG methylation is mediated by the DNMT1-like enzyme MET1and the plant-speciﬁc enzyme Chromomethylase3(CMT3),respectively[20]. Recent studies suggested that MET1and CMT3may also catalyze de novo methylation,while DRM1and DRM2are also important for the maintenance of sym-metric methylation[1,21].Stresses can induce changes in gene expression through hypomethylation or hypermethylation of DNA.In maize roots,cold stress-induced expression of ZmMI1was cor-related with a reduction in methylation in the DNA of the nucleosome core.Even after seven days of recovery,cold-induced hypomethylation was not restored to the basal level[22].In tobacco,aluminum,paraquat,salt,and cold stresses induced-DNA demethylation in the coding sequence of the NtGPDL(a glycerophosphodiesterase-like protein)gene correlated with NtGDPL gene expres-sion[23 ].Osmotic stresses induced transient DNA hypermethyla-tion in two heterochromatic loci in tobacco cell-suspen-sion culture[24].DNA hypermethylation was also induced by drought stress in pea[25].In the facultative halophyte Mesembryanthemum crystallinum L.,drought and salt stresses-induced a switch in photosynthesis mode from C3to CAM.This metabolic change was associated with stress-induced-speciﬁc CpHpG-hypermethylation of satellite DNA[26].Transposons constitute a signiﬁcant portion of plant genomes and are maintained in a repressed state by DNA methylation.Environmental factors may activate transposons through DNA demethylation.In Antirrhinum majus,cold stress induced hypomethylation,and transpo-sition of the Tam-3transposon[27 ].Stress-induced histone modiﬁcations can also inﬂuence DNA methylation.Knockout mutants and RNAi lines of stress-inducible HDA6of Arabidopsis and HDA101of maize showed an increase in histone acetylation accom-panied by changes in histone methylation pattern and derepression of silenced genes[28,29].Speciﬁc histone modiﬁcation-dependent pathways appear to mediate methylation of about two-thirds of the methylated loci in the Arabidopsis genome[1].Thus,dynamic histone modiﬁcation marks could be converted into DNA meth-ylation marks,which are often more stable.RNA-directed DNA methylationGenetic analysis using Arabidopsis mutants impaired in genes for siRNA biogenesis or action revealed the invol-vement of small interfering RNAs(siRNAs)in RdDM [20,30].Integration of the Arabidopsisﬂoral epigenome with theﬂoral transcriptome and small RNA proﬁles revealed a direct correlation between the ability of geno-mic sequences to produce small RNAs and DNA meth-ylation[21].In fact,siRNAs are involved in the methylation of at least one-third of methylated loci [21].Studies on the repressor of silencing1(ros1)mutant of Arabidopsis revealed that the DNA glycosylase ROS1 actively demethylates DNA by a base excision repair mechanism and can counteract RdDM[31,32].ROS3, a RNA recognition motif-containing protein,binds to small RNAs and may direct sequence-speciﬁc demethyl-ation by ROS1and related DNA demethylases[33 ]. Gene silencing processes can be sensitive to temperature. Temperature and other abiotic stresses can also regulate speciﬁc small RNAs.Low temperature promoted virus-induced gene silencing,while high temperature delayed it[34].Endogenous siRNAs that are regulated by abiotic stress have been identiﬁed in Arabidopsis[35].In Arabi-dopsis,24-nt SRO5-P5CDH nat-siRNA downregulates the expression of P5CDH mRNAs through mRNA clea-vage,leading to decreased proline degradation,and enhanced proline accumulation and salt stress tolerance [36].This and other stress-regulated siRNAs conceivably could also lead to changes in histone modiﬁcations and DNA methylation.Microarray data showed that abiotic stresses and ABA inﬂuence the expression of many of the genes implicated in RdDM pathways in Arabidopsis(our unpublished data).Further studies are clearly needed to unravel the roles of RdDM pathway under stress. Plant development under stress Reprogramming of cell differentiation in response to environmental stress leads to phenological and develop-mental plasticity,which are important mechanisms of stress resistance.Phenotypic plasticity helps adjust the durations of various phenological phases in plants,and thus allows plants to avoid exposure of critical growth phases,and especially reproductive development,to stress.Further,adjustment of growth and development is critical for effective use of resources under stress. Germination and vegetative growthOsmotic stress reduces the uniformity of seed germina-tion and seedling establishment.Several HDACs are induced by ABA in Arabidopsis[13 ]and rice[14].Arabi-dopsis HDA19/HD1interacts with a global corepressor of transcription,AtSIN3,which in turn interacts with AtERF7(APETALA2/EREBP-type transcription fac-tor).Suppression of AtERF7and AtSIN3in plants caused hypersensitivity to ABA during germination and seedling growth[37].Arabidopsis HDA6/HDA19double repression lines showed growth arrest after germination and for-mation of embryo-like structures on true leaves[38]. These results suggest that ABA accumulation leads to change in expression or activity of HDACs,which in turn regulate growth under stress.Epigenetics of stress tolerance Chinnusamy and Zhu135Transgenic Arabidopsis overexpressing a SNF2/ BRAHMA-type chromatin remodeling gene AtCHR12 exhibited growth arrest of primary buds and growth reduction of the primary stem.These responses were more pronounced under drought and heat stress than under nonstress conditions.Conversely,the growth arrest response under stress was less in the AtCHR12-knockout mutant than in the WT plants[39 ].Reproductive developmentFlowering and seed development are crucial for plant reproduction.Hence,plants have evolved mechanisms toﬂower when environmental conditions are appropriate. In Arabidopsis,low temperatures during vernalization induce epigenetic mechanisms which repress the FLOW-ERING LOCUS C(FLC,a MADS-box protein)gene,and the repressed FLC chromatin is maintained till transition toﬂowering.The mechanisms of mitotic inheritance of the repressed epigenetic state of FLC chromatin and resetting during reproduction are not fully understood [40].Because the low temperatures that induce vernali-zation also induce cold acclimation,some of the gene expression programs could be under common epigenetic control.Mutations in some of the genes involved in stress-related epigenetic processes cause changes inﬂowering time. The hos15,a freezing sensitive mutant of Arabidopsis, was lateﬂowering owing to downregulation ofﬂower-ing-regulatory genes SOC and FT[15 ].Plant hormone and stress-regulated HDA6and HDA19may act as a link between stress and developmental cues that controlﬂow-ering and plant development.Reduction in HDA19 expression in antisense transgenic plants/T-DNA mutants resulted in developmental abnormalities in-cluding delayedﬂowering[41,42].HDA6-RNAi lines and axe1-5/hda6mutants showed hyperacetylation of histone H3globally,downregulation of JA-responsive genes,upregulation of FLC,and delayedﬂowering[43 ]. In Arabidopsis,FCA and FPA proteins form an autonom-ousﬂowering pathway by downregulatingﬂowering repressor FLC.Both FCA and FPA are RNA-binding proteins that can regulate DNA methylation[44].ABA and drought stress induced the expression of chromatin remodeling gene PsSNF5(Pisum sativum SNF5). PsSNF5interacts with Arabidopsis SWI3-like proteins (SWI3A and SWI3B),which in turn interact with FCA [45,46].ABA-induced SNF5and FCA may regulate ﬂowering time and stress responses through chromatin remodeling.Because stresses reduce crop yield and quality,and ABA regulates seed development partly through epigenetic processes[47],effects of stress on ABA accumulation or epigenetic processes therefore may affect seed/fruit development under stress.SenescenceAbiotic stresses induce premature leaf senescence,which leads to reduced photosynthesis and thus less biomass accumulation.JA–and ethylene-responsive-HDACs, HDA6and HAD19,appear to modulate leaf senescence. Arabidopsis HDA6-RNAi lines and axe1-5(hda6)mutants exhibited downregulation of JA-responsive genes and senescence-associated genes,and delayed senescence as indicated by higher chlorophyll content and PSII activity as compared to WT plants[43 ].In contrast, HDA19antisense transgenic plants/T-DNA mutants showed early senescence[41].Stress memoryUV-C radiation orﬂagellin(an elicitor of plant defense) induced a high frequency of somatic homologous recom-bination,and the hyper-recombination state was trans-mitted as a dominant trait to untreated progenies of stress-treated parents[48 ].Similarly,tobacco mosaic virus(TMV)infection resulted in a high frequency of somatic and meiotic recombination rates in tobacco.The progeny of TMV-infected plants exhibited hypomethyla-tion in several leucine-rich repeat(LRR)-containing loci and a higher frequency of recombination in hypomethyl-ated LRR-containing TMV(N-gene)resistant gene [49 ].The adaptive value of stress-induced epigenetic plasticity was studied in hypomethylation progenies of5-aza-deox-ycytidine(inhibitor of DNA cytosine methylation)-trea-ted rice seeds.In one of the progenies,methylation was completely erased in Xa21G,a Xa21-like protein gene. The erasure of promoter methylation and inheritance of this epigenetic state resulted in constitutive expression of Xa21G in the progeny line and enhanced resistance to the pathogen Xanthomonas oryzae pv.oryzae,race PR2[50 ]. ConclusionsStress-induced changes in histone variants,histone N-tail modiﬁcations,and DNA methylation have been shown to regulate stress-responsive gene expression and plant de-velopment under stress.Transient chromatin modiﬁ-cations mediate acclimation response.Heritable, epigenetic modiﬁcations may provide within-generation and transgenerational stress memory(Figure1).It is unclear how much of the stress-induced histone and DNA modiﬁcation changes that have been observed to date may be epigenetic in nature because little is known about their mitotic or meiotic heritability.Abiotic stress-induced epigenetic changes might have an adaptive advantage.However,stress memory could have a nega-tive impact on crop yield by preventing the plant from growing to its full potential.Thus,stress memory has implications for the use of seeds from stressed crop to raise ensuing crops by the farmers,breeding for stress environments and in situ conservation of plant species. Recent progress in understanding DNA methylation and136Genome studies and molecular geneticsdemethylation,histone modiﬁcations,small RNAs and in developing powerful and versatile tools to study these epigenetic processes makes it possible to critically ana-lyze epigenetic stress memory and harness it for crop management and improvement.Conﬂict of interestThere is no conﬂict of interest relating to this article.AcknowledgementsThe work in J-KZ lab was supported by National Institutes of Health grants R01GM070795and R01GM059138.References and recommended readingPapers of particular interest,published within the period of review,have been highlighted as:of special interestof outstanding interest1.Zhu JK:Epigenome sequencing comes of age .Cell 2008,133:395-397.2.Thomashow MF:Plant cold acclimation:freezing tolerance genes and regulatory mechanisms .Annu Rev Plant Physiol Plant Mol Biol 1999,50:571-599.3.Iba K:Acclimative response to temperature stress in higher plants:approaches of gene engineering for temperature tolerance .Annu Rev Plant Biol 2002,53:225-245.4.Sridhar VV,Kapoor A,Zhang K,Zhu J,Zhou T,Hasegawa PM,Bressan RA,Zhu JK:Control of DNA methylation andheterochromatic silencing by histone H2B deubiquitination .Nature 2007,447:735-738.5.Zhang K,Sridhar VV,Zhu J,Kapoor A,Zhu JK:Distinctive core histone post-translational modiﬁcation patterns in Arabidopsis thaliana .PLoS ONE 2007,11:e1210.6.Nathan D,Ingvarsdottir K,Sterner DE,Bylebyl GR,Dokmanovic M,Dorsey JA,Whelan KA,Krsmanovic M,Lane WS,Meluh PB et al.:Histone sumoylation is a negative regulator in Saccharomyces cerevisiae and shows dynamic interplay with positive-acting histone modiﬁcations .Genes Dev 2006,20:966-976.7.Camporeale G,Oommen AM,Grifﬁn JB,Sarath G,Zempleni J:K12-biotinylated histone H4marks heterochromatin in human lymphoblastoma cells .J Nutr Biochem 2007,18:760-768.8.Scippa GS,Di Michele M,Onelli E,Patrignani G,Chiatante D,Bray EA:The histone-like protein H1-S and the response of tomato leaves to water deﬁcit .J Exp Bot 2004,55:99-109.9.Tsuji H,Saika H,Tsutsumi N,Hirai A,Nakazono M:Dynamic and reversible changes in histone H3-Lys4methylation and H3acetylation occurring at submergence-inducible genes in rice .Plant Cell Physiol 2006,47:995-1003.Epigenetics of stress tolerance Chinnusamy and Zhu 137Figure1Epigenetic regulation of stress tolerance.Primary and secondary stress signals induce changes in the expression and/or activity of epigenetic regulators namely,small RNAs,RdDM components,histone variants,histone modification enzymes,and chromatin remodeling factors.Theseepigenetic regulators modify histone variants,histone modifications,and DNA methylation.Some of these are heritable epigenetic modifications,while others are transient changes.Transient chromatin modifications mediate acclimation response.Heritable epigenetic modifications provide within-generation and transgenerational stress memory.This study showed that submergence stress-induced histone H3K4 trimethylation and H3acetylation in alcohol dehydrogenase1and pyr-uvate decarboxylase1genes are correlated with enhanced expression of ADH1and PDC1.These histone modiﬁcations were restored to the basal level after the stress was relieved.10.Zhou C,Zhang L,Duan J,Miki B,Wu K:HISTONEDEACETYLASE19is involved in jasmonic acid and ethylenesignaling of pathogen response in Arabidopsis.Plant Cell2005, 17:1196-1204.11.Probst AV,Fagard M,Proux F,Mourrain P,Boutet S,Earley K,Lawrence RJ,Pikaard CS,Murfett J,Furner I et al.:Arabidopsis histone deacetylase HDA6is required for maintenance oftranscriptional gene silencing and determines nuclearorganization of rDNA repeats.Plant Cell2004,16:1021-1034. 12.Aufsatz W,Mette MF,Van Der Winden J,Matzke M,Matzke AJ:HDA6,a putative histone deacetylase needed to enhance DNA methylation induced by double-stranded RNA.EMBO J2002, 21:6832-6841.13. 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Zhu J,Jeong J,Zhu Y,Sokolchik I,Miyazaki S,Zhu JK, Hasegawa PM,Bohnert HJ,Shi H,Yun DJ et al.:Involvement of Arabidopsis HOS15in histone deacetylation and cold tolerance.Proc Natl Acad Sci U S A2007,105:4945-4950.This study showed that Arabidopsis HOS15,a WD-40repeat proteint ransducin b eta-l ike protein-1(TBL1),interacts with histone H4and is important for H4deacetylation.Further,H4deacetylation mediated byHOS15regulates stress-responsive andﬂowering genes,and thus mod-ulates stress tolerance andﬂowering time.16. Kim JM,To TK,Ishida J,Morosawa T,Kawashima M,Matsui A, Toyoda T,Kimura H,Shinozaki K,Seki M:Alterations of lysine modiﬁcations on histone H3N-tail under drought stress conditions in Arabidopsis thaliana.Plant Cell Physiol2008, 49:1580-1588.This study showed that drought-induced expression of stress-responsive genes is associated with an increase in H3K4trimethylation and H3K9 acetylation on the promoter region and H3K23and H3K27acetylation on the coding regions.17.Nowak SJ,Corces VG:Phosphorylation of histone H3correlates with transcriptionally active loci.Genes Dev2000,14:3003-3013.18. Sokol A,Kwiatkowska A,Jerzmanowski A,Prymakowska-Bosak M:Up-regulation of stress-inducible genes in tobacco and Arabidopsis cells in response to abiotic stresses and ABA treatment correlates with dynamic changes in histone H3and H4modiﬁcations.Planta2007,227:245-254.This study showed correlation between stress-type-speciﬁc gene expression and stress-induced upregulation of histone H3Ser-10phos-phorylation,H3phosphoacetylation,and H4acetylation.19.Stockinger EJ,Mao Y,Regier MK,Triezenberg SJ,Thomashow MF:Transcriptional adaptor and histoneacetyltransferase proteins in Arabidopsis and theirinteractions with CBF1,a transcriptional activator involved in cold regulated gene expression.Nucleic Acids Res2001,29:1524-1533.20.Henderson IR,Jacobsen SE:Epigenetic inheritance in plants.Nature2007,447:418-424.21.Lister R,O’Malley RC,Tonti-Filippini J,Gregory BD,Berry CC,Millar AH,Ecker JR:Highly integrated single-base resolutionmaps of the epigenome in Arabidopsis.Cell2008,133:523-536.22.Steward N,Ito M,Yamaguchi Y,Koizumi N,Sano H:Periodic DNAmethylation in maize nucleosomes and demethylation byenvironmental stress.J Biol Chem2002,277:37741-37746.23.Choi CS,Sano H:Abiotic-stress induces demethylation andtranscriptional activation of a gene encoding aglycerophosphodiesterase-like protein in tobacco plants.Mol Genet Genome2007,277:589-600.This study showed that aluminium,salt,cold,and oxidative stresses induced DNA demethylation in the coding sequence of the NtGPDL gene within one hour in leaves,and this demethylation correlated with NtGDPL gene expression.24.Kovarik A,Koukalova B,Bezdek M,Opatrn Z:Hypermethylationof tobacco heterochromatic loci in response to osmoticstress.Theor Appl Genet1997,95:301-306.bra M,Ghiani A,Citterio S,Sgorbati S,Sala F,Vannini C,Rufﬁni-Castiglione M,Bracale M:Analysis of cytosine methylationpattern in response to water deﬁcit in pea root tips.Plant Biol (Stuttgart)2002,4:694-699.26.Dyachenko OV,Zakharchenko NS,Shevchuk TV,Bohnert HJ,Cushman JC,Buryanov YI:Effect of hypermethylation ofCCWGG sequences in DNA of Mesembryanthemumcrystallinum plants on their adaptation to salt stress.Biochemistry(Moscow)2006,71:461-465.27.Hashida SN,Uchiyama T,Martin C,Kishima Y,Sano Y,Mikami T: The temperature-dependent change in methylation of theAntirrhinum transposon Tam3is controlled by the activity of its transposase.Plant Cell2006,18:104-118.Authors showed that low temperature decreases DNA methylation and promotes Tam3transposase binding in demethylated cytosine motif and thus enhances tranposition of Tam3.28.Earley K,Lawrence RJ,Pontes O,Reuther R,Enciso AJ,Silva M,Neves N,Gross M,Viegas W,Pikaard CS:Erasure of histoneacetylation by Arabidopsis HDA6mediates large-scalegene silencing in nucleolar dominance.Genes Dev2006,20:1283-1293.29.Rossi V,Locatelli S,Varotto S,Donn G,Pirona R,Henderson DA,Hartings H,Motto M:Maize histone deacetylase hda101isinvolved in plant development,gene transcription,andsequence-speciﬁc modulation of histone modiﬁcation ofgenes and repeats.Plant Cell2007,19:1145-1162.30.Pontes O,Li CF,Nunes PC,Haag J,Ream T,Vitins A,Jacobsen SE,Pikaard CS:The Arabidopsis chromatin-modifying nuclear siRNA pathway involves a nucleolar RNAprocessing center.Cell2006,126:79-92.31.Gong Z,Morales-Ruiz T,Ariza RR,Roldan-Arjona T,David L,Zhu JK:ROS1,a repressor of transcriptional gene silencing in Arabidopsis,encodes a DNA glycosylase/lyase.Cell2002,111:803-814.32.Agius F,Kapoor A,Zhu JK:Role of the Arabidopsis DNAglycosylase/lyase ROS1in active DNA demethylation.ProcNatl Acad Sci U S A2006,103:11796-11801.33.Zheng X,Pontes O,Zhu J,Miki D,Zhang F,Li WX,Iida K,Kapoor A, Pikaard CS,Zhu JK:ROS3is an RNA-binding protein required for DNA demethylation in Arabidopsis.Nature2008,455:1259-1262. This study showed that a small RNA-binding protein,ROS3,facilitates sequence-speciﬁc demethylation by the DNA glycosylase ROS1.34.Tuttle JR,Idris AM,Brown JK,Haigler CH,Robertson D:Geminivirus-mediated gene silencing from cotton leafcrumple virus is enhanced by low temperature in cotton.Plant Physiol2008,148:41-50.35.Sunkar R,Zhu JK:Novel and stress-regulated microRNAsand other small RNAs from Arabidopsis.Plant Cell2004,16:2001-2019.36.Borsani O,Zhu J,Verslues PE,Sunkar R,Zhu JK:EndogenoussiRNAs derived from a pair of natural cis-antisense transcripts regulate salt tolerance in Arabidopsis.Cell2005,123:1279-1291.37.Song CP,Agarwal M,Ohta M,Guo Y,Halfter U,Wang P,Zhu JK:Role of an Arabidopsis AP2/EREBP-type transcriptionalrepressor in abscisic acid and drought stress responses.Plant Cell2005,17:2384-2396.38.Tanaka M,Kikuchi A,Kamada H:The Arabidopsis histonedeacetylases HDA6and HDA19contribute to the repression of embryonic properties after germination.Plant Physiol2008,146:149-161.138Genome studies and molecular genetics。

The Vogel-Fulcher-Tamman law in the elastic theory of glass transition

a r X i v :0704.2975v 2 [c o n d -m a t .d i s -n n ] 23 J u l 2008The Vogel-Fulcher-Tammann law in the elastic theory of glass transitionKostya TrachenkoDepartment of Earth Sciences,University of Cambridge,Downing Street,Cambridge,CB23EQ,UK We propose that the origin of the Vogel-Fulcher-Tammann law is the increase of the range of elastic interaction between local relaxation events in a liquid.In this picture,we discuss the origin of cooperativity of relaxation,the absence of divergence of relaxation time at a ﬁnite temperature and the crossover to a more Arrhenius behaviour at low temperature.The transition of a liquid into a glass on lowering the temperature may appear conceptually simple,yet this phenomenon has turned out to be one of the most diﬃcult and controversial problems in condensed matter physics,the problem of the glass transition [1,2].At high tem-perature,relaxation time τof a liquid follows Arrhenius dependence.On lowering the temperature,τalmost uni-versally deviates from Arrhenius dependence,and follows the Vogel-Fulcher-Tammann (VFT)law:τ=τ0expA2dFIG.2:Illustration of the elastic interaction between local re-laxation events.This interaction takes place within the range d el from the central relaxing regions.Shaded and open circles represent local relaxing regions inside and outside,respec-tively,of the interaction sphere.centre.A remote shear LRE,similar to the one shown in Figure1,creates elastic shear waves,which include waves of high frequency.This is because the deformation,asso-ciated with a LRE,creates a wave with a length compa-rable to interatomic separations(see Figure1),and hence with a frequency on the order of the Debye frequency.At high frequencyω>1/τ,a liquid supports propagating shear waves[8],which propagate stress and its variations from remote LREs to the central point.Ifτis macro-scopically deﬁned as the time of decay of shear stress in a liquid[8,9],d el=cτgives the length of this decay, where c is the speed of sound.Here,d el gives an estima-tion of the maximal range over which shear stress decays in a liquid.At the microscopic level,the relevance of d el=cτis as follows.A high-frequency shear wave origi-nating from a LRE propagates stress until a remote LRE takes place at the front of the wave,at which point the wave front is absorbed by the remote LRE.Suppose this happens at distance d el from the original LRE.d el can be calculated from the condition of equality of the wave travel time,d el/c,and the time at which the remote LRE takes place at point d el.The latter time is given byτ, because microscopically,τis deﬁned as the average time between two consecutive LREs at one point in space[8], and we obtain d el=cτas before.Therefore,d el deﬁnes the maximal distance over which the central LRE is aﬀected by elastic shear stresses due to other LREs in a liquid(see Figure2).For this reason, d el can be called the liquid elasticity length.Note that relaxation of the central event is aﬀected by all those stresses that have enough time to propagate to the centre. Because it takes timeτfor the central event to relax, its relaxation is aﬀected by the stresses from all LREs located distance cτaway.After timeτ,the central event relaxes,and the process repeats.Therefore,the deﬁnition d el=cτis self-consistent.Because c is on the order of a/τ0,where a is the in-teratomic separation of about1˚A andτ0the oscillation period,or inverse of Debye frequency(τ0≈0.1ps),d el=cτ=aτ3LRE is accompanied by a strain in the direction agreeing with the applied external stress,and reduces the local stress and energy (see Figure 1).In order to counter-balance this decrease,other local regions in asystem sup-port more stress [15].Goldstein applied the same argu-ment to a viscous liquid under external stress [16].Con-sider that this stress is counterbalanced by stresses sup-ported by local regions.Because a local region supports less stress after a concordant LRE than before,other lo-cal regions in the liquid should support more stress after that event than before in order to counter-balance [16].Lets consider a liquid perturbed by a pulse of an ex-ternal ﬁeld.At time zero,shear stresses supported by local regions counterbalance external shear stress.As re-laxation proceeds,each concordant shear LRE reduces stress locally,until the external stress is relaxed by a cer-tain number of LREs N .When this process is complete,the liquid relaxes to equilibrium.At times smaller than L/c ,where L is the system size,the external stress can be considered constant,and the stress redistribution ar-gument of Orowan-Goldstein applies.Alternatively,we can consider an external stress constantly compensating for the decreases of local stresses.In the resulting steady ﬂow,τis the time needed to relax an increment of exter-nal perturbation,and can be viewed as the time of the liquid’s retardation behind the external ﬁeld.Let n be the current number of LREs,such that n →N .If ∆p is the increase of shear stress on the liquid around a current local region that arises from the need to counter-balance the decreases of stresses due to previous remote concor-dant LREs,∆p increases with n .The increase of ∆p consistently increases the elastic strain in the direction of external shear stress,increasing the background shear energy of the liquid around the current local region.As discussed above,V for the current LRE increases as a result.The increase of V ,∆V ,due to ∆p is the work∆p d q .If q a is the activation volume [14],∆V =∆pq a ,and V =V 0+q a ∆p ,where V 0is the high-temperature activation barrier.Because ∆p increases with n ,V also increases with n .This gives the elastic feed-forward in-teraction mechanism for LREs,which sets SER [10].To calculate V as a function of d el ,lets consider the last LRE that relaxes an increment of external shear stress to be in the centre of a sphere of radius d el (see Figure 2).As relaxation proceeds,the shear stress on the central re-gion increases in order to counterbalance stress decreases due to previous remote concordant LREs.Importantly,because this mechanism operates in the range set by d el and because d el increases on lowering the temperature (see Eq.(2)),stresses from an increasing number of re-mote LREs need to be counterbalanced by the central re-gion.It is also important to note that all stresses within a distance d el =cτhave enough time to propagate to the centre and aﬀect relaxation of the central event (recall self-consistency in deﬁnition of d el ).Let ∆p i (0)be the reduction of local stress due to a re-mote concordant LRE i .∆p i decays with distance,hence we denote ∆p i (r )as its value at the centre in Figure 2.The increase of stress on the central rearranging region,∆p ,can be calculated as∆p =ρd eld 0/24πr 2∆p i (r )d r(3)where ρis the density of local rearranging regions andd 0is on the order of the size of a relaxing region (in Figure 1,d 0≥3a ).Note that in Eq.(3),d el is the upper integration limit.In what follows,we assume,for simplicity,that ∆p i (0)are constant,∆p i (0)=∆p 0.In an elastic medium,stresses decay as ∆p (r )∝1/r 3[9].Because ∆p (r )=∆p 0at d 0/2,∆p (r )=∆p 0(d 0/2r )3.Integration of Eq.(3),together with V =V 0+q a ∆p from the discussion above,givesV =V 0+π/2ρq a ∆p 0d 30ln(2d el /d 0)(4)Using τ=τ0exp(V/kT )in Eq.(2),we obtaind el =a expVT −T 0(6)where A =V 0+π/2ρq a ∆p 0d 30ln(2a/d 0)and kT 0=π/2ρq a ∆p 0d 30.From Eq.(6),the VFT law follows:τ=τ0expAT −T 0(8)4When T approaches T0,d el diverges,and quickly exceeds anyﬁnite size of the system L.When d el≥L,all LREs in the system elastically interact,and there is no room for the increase of V by way of increasing d el.The upper limit of integral(3)becomes d el=L,giving temperature-independent V∝ln(L)(see Eq.(4)).Further decrease of temperature has a weaker eﬀect on V,and can be due to,e.g.,density increase,but not to the increase of d el (the density-related contribution to V does not depend on d el or L).As a result,the behaviour ofτtends to Arrhenius,pushing the divergence to zero temperature.d el exceeds the experimental value of L above T g:if τ(T g)=103sec,d el(T g)=103km,according to Eq.(2). Hence our theory predicts the crossover from the VFT law to a more Arrhenius behaviour at low temperature, as is seen in the experiments[3].According to Eq.(2),τat the crossover isτ=τ0L/a.If a typical value of L is 1mm,τat the crossover is10−6sec,consistent with the experimental results[17].We note here that d el vastly exceeds the size of“co-operatively rearranging regions”(CRR),which is several nm at T g(for review,see,e.g.,Ref.[6]).The physical picture of CRR is not clear[2].It is possible that the observed nm scale of CRR is set by the distance beyond which the elastic strains from LREs decay to the values undistinguishable from thermalﬂuctuations.d el gives an insight into the origin of liquid fragility[18].According to Eq.(4),as long as at high temper-ature d el<L,lowering the temperature increases V, resulting in a fragile behaviour.If,on the other hand, d el≥L at high temperature already,further decrease of temperature has a weaker eﬀect on V,giving weak super-Arrhenius behaviour.Experimentally,for many systems the studied range of temperatures varies from about2T g and T g[12],hence we consider the increase of d el from high temperature T h=2T g to T g.Take,for example,two systems on the stronger side of fragility plots,BeF2and SiO2.From the experimental values of V h/kT g(V h is the activation barrier at the highest measured temperature), weﬁnd V h/kT h=24and19.6for BeF2and SiO2,re-spectively[19].According to Eq.(5),this gives d el=2.6 m and33mm at T h for the two systems.Because a typ-ical experimental value of L is on the order of1mm,our theory correctly predicts that these systems should be on the strong end of fragility plots.For two fragile sys-tems,toluene and propylene carbonate,V h/kT h=3.34 and5.75,giving d el=28and314˚A at T h,respectively. This is much smaller than L,hence our theory predicts that these systems should be fragile,as is seen experi-mentally.An interesting prediction from this picture is that strong systems will show increased fragility at high temperature when d el<L(note that strong systems have been measured at relatively low temperature only[18]). Before concluding,we note that we discussed a typical experimental setup,in which a liquid is perturbed and τis measured as the time of return to equilibrium.All above results remain the same in the equilibrium case as well,when thermallyﬂuctuating LREs interact via induced elastic stresses in the range set by d el[20].In summary,we proposed that the origin of the Vogel-Fulcher-Tammann law is the increase of the range of elas-tic interaction between local relaxation events in a liquid. In this picture,we discussed the origin of cooperativity of relaxation,the absence of divergence of relaxation time at aﬁnite temperature and the crossover to an Arrhenius behaviour at low temperature.We suggest that the proposed theory is applicable to other systems,in which local rearrangements interact via theﬁelds they induce.This includes a wide range of phenomena,for example,relaxation in spin glasses. Here,the same universal relaxation eﬀects as in struc-tural glasses are observed,including the VFT law,coop-erativity,SER and other phenomena.I am grateful to V.V.Brazhkin, A.Kehagia,R. Casalini and C.M.Roland for discussions,and to EPSRC for support.[1]nger,Physics Today60,(Feb.2007)8.[2]J.C.Dyre,Rev.Mod.Phys.78(2006)953.[3]F.Stickel,E.W.Fischer and R.Richert,J.Chem.Phys.104(1996)2043.[4]G.Adam and J.H.Gibbs,J.Chem.Phys.43(1965)139.[5]K.L.Ngai,J.Non-Cryst.Sol.353(2007)709.[6]O.Yamamuro et al,J.Phys.Chem.B102(1998)1605.[7]A.S.Argon,Acta Metall.27(1979)47.[8]J.Frenkel,Kinetic Theory of Liquids(ed.R.H.Fowler,P.Kapitza,N.F.Mott,Oxford University Press,1947).[9]ndau and E.M.Lifshitz,Theory of Elasticity(Pergamon Press,1986).[10]K.Trachenko,Phys.Rev.B.75(2007)212201.[11]J.Colmenero,A.Arbe and A.Alegria,Phys.Rev.Lett.71(1993)2603;R.Zorn et al,Phys.Rev.E52(1995)781;C.M.Roland,K.L.Ngai and L.J.Lewis,J.Chem.Phys.103(1995)4632;K.L.Ngai,C.M.Roland and G.N.Greaves,J.Non-Cryst.Sol.182(1995)172;J.Colmenero et al,Phys.Rev.Lett.78(1997)1928.[12]R.Casalini,K.L.Ngai and C.M.Roland,Phys.Rev.B68(2003)014201.[13]S.V.Nemilov,J.Non-Cryst.Sol.352(2006)2715.[14]J.C.Dyre,N.B.Olsen and T.Christensen,Phys.Rev.B53(1996)2171.[15]E.Orowan,Proceedings of the First National Congressof Applied Mechanics(American Society of Mechanical Engineers,New York),453(1952).[16]M.Goldstein,J.Chem.Phys.51(1969)3728.[17]A.Sch¨o nhals,Europhys.Lett.56,(2001)815;V.N.Novikov and A.P.Sokolov,Phys.Rev.E67(2003) 031507.[18]C.A.Angell,Science267(1995)1924.[19]See supplementary information in V.N.Novikov and A.P.Sokolov,Nature431(2004)961.[20]K.Trachenko and V.V.Brazhkin(unpublished).。

2021版《三维设计》高考英语(人教版)大一轮复习跟踪检测：必修五 Module 2

必修五Module 2“阅读＋七选五＋完形”组合练——练题型(限时：35分钟)Ⅰ.阅读理解(2022·江西赣州高三摸底考试)It is a familiar scene these days: employees taking newly laid-off (下岗)co-workers out for a drink for comfort. But which side deserves sympathy more, the jobless or the still employed? On March 6, researchers at a conference at the University of Cambridge heard data suggesting it's the latter.Brendan Burchell, a Cambridge sociologist, presented his analysis based on various surveys conducted across Europe. The data suggest that employed people who feel insecure in their jobs show similar levels of anxiety and depression as those who are unemployed. Although a newly jobless person's mental health may “bottom out” after about six months, and then even begin to improve，the mental state of people who are continuously worried about losing their job “just continues to get worse and worse，” Burchell says.Evolutionary psychologists support this theory by arguing that human beings feel more stress during times of insecurity because they sense an immediate but invisible threat. Patients have been known to experience higher levels of anxiety, for example, while waiting for examination results than knowing what they are suffering from — even if the result is cancer. It's better to get the bad news and start doing something about it rather than wait with anxiety. When the uncertainty continues, people stay in a nonstop “fight or flight” response, which leads to damaging stress.But not every employee in insecure industries has such a discouraging view, Burchell says. In general, women get on better. While reporting higher levels of anxiety than men when directly questioned, women scored lower in stress on the GHQ 12, even when they had a job they felt insecure about losing. As Burchell explains, “For women, most studies show that any job — it doesn't matter whether it is secure or insecure —gives psychological improvement over unemployment.” Burchell supposes that the difference in men is that they tend to feel pressure not only to be employed, but also to be the primary breadwinner, and that more of a man's self-worth depends on his job.语篇解读：本文是一篇说明文。

三维设计高考英语外研大一轮复习教师用书：必修五含答案

Module 1British and American EnglishⅠ.单词—在语境中默写，在联想中积累[写得准][用得活][积得多] 1.accent n．口音2.structure n. 结构；体系3.present v t. 陈述；提出(观点、计划等)adj. 目前的；到场的；出席的4.attempt n．& v. 尝试；努力bination n．结合→combine v t.结合6.confusing adj.令人困惑的；难懂的→confuse v t.使困惑→confused adj.感到困惑的pare v t.比较→comparison n．比较；比喻8.variety n．种类→variation n．变化→vary v．改变；使变化→various adj.各种各样的9.differ v i.不同，有区别→difference n．不同；区别→different adj.不同的，有区别的用所给词的适当形式填空1.The confused look on her faceshowed she was confused by theconfusing question.(confuse)2. From the appearance, we cannot tell the differences betweenthe twins, though they alwayshave some different ideas. As forthis phenomenon, ideas differamong many people.(differ)3.He made simple remarks onher remarkableachievements.(remark)4.After he was criticised by thecritic,_he realized that criticismwas very important.(criticise)5.The book explains grammarsimply and clearly, because theauthor used simple examplesentences to simplify abstractconcepts.(simple)bine反义词集锦①separate v t.使分离；使分开②divide v. 分开③divorce v. (使)离婚/分离④isolate v. 隔离；孤立⑤split v t. 分离；使分离2.-ify结尾动词清单①simplify 简化②identify 确定；鉴定；识别③electrify 使电气化；使充电④horrify 使恐惧⑤classify 分类；分等⑥modify 修改，修饰；更改Ⅲ.句式—在解读中学懂，在仿写中学通[背原句][记句式][会仿用] 1.Americans use a flashlight, while forthe British, it's a torch.美国人把手电筒称为flashlight，而英国人叫它torch。

机械制造技术英文PPT25

（3） Arrange the process of eliminating internal stress.
One is to the blank or in the large workpiece rough processing, let the workpiece stay under natural conditions for a period of time to process, using the natural change of temperature to make it many times hot expansion and cold contraction, natural aging. The second is through artificial aging heat treatment process, such as casting, forging, welding parts for annealing or tempering; Parts are tempered after quenching; For high precision parts, such as bed, screw, or precision spindle box, making low temperature tempering after rough machining, even for screw cold processing, precision spindle after finishing, etc. Third, some casting, forging, welding parts in the form of vibration will be added to the mechanical energy on the workpiece, vibration aging treatment, causing the internal lattice creep of the workpiece, so that the metal internal structure stability, the elimination of internal stress.

神经生长因子在慢性阻塞性肺疾病大鼠血、肺组织、支气管灌洗液中的表达

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合医院ꎻ３江苏省中医药研究院)
〔摘要〕目的建立单纯香烟刺激诱导的慢性阻塞性肺疾病( ＣＯＰＤ) 大鼠模型ꎬ并观察神经生长因子( ＮＧＦ) 在香烟刺
激ＣＯＰＤ大鼠、戒烟１个月ＣＯＰＤ大鼠中血、肺组织、支气管灌洗液中的表达变化ꎮ 方法２４只雄性ＳＤ大鼠ꎬ随机分为正常
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１８ＹａｎｇＰꎬＳｕｎＭꎬＬｉＬꎬｅｔａｌ. ８￣ｈｙｄｒｏｘｙ￣ｄｉｐｒｏｐｙｌａｍｉｎｏｔｅｔｒａｌｉｎｐｒｏｍｏｔｅｓ
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(５) :１１１６￣３２
１６ＧａｍａＳｏｓａＭＡꎬ ＤｅＧａｓｐｅｒｉＲꎬ ＰｅｒｅｚＧａｒｃｉａＧＳꎬ ｅｔａｌ. Ｌｏｗ￣ｌｅｖｅｌ

植物逆境生理生态英文作文

植物逆境生理生态英文作文Title: Plant Responses to Abiotic Stress: An Unfettered Journey into Adaptation。

1. Embracing the Wild: The Unyielding Nature of Plants。

In the realm of plant biology, adversity is not a stranger, but a constant companion. When faced with harsh conditions, like drought, cold, or pollution, our resilient botanical friends exhibit remarkable resilience. They are,in essence, "plants in the wild," defying the odds withtheir unspoken resilience.2. The Art of Adaptation: Water Scarcity。

The dance of water in plants during drought is a symphony of survival. They develop mechanisms to conserve moisture, like deep root systems that dig deep for life-giving H2O. Their leaves may even shed to minimize water loss, a testament to their 'survival of the fittest'strategy.3. Cold Comfort: Frosty Trials and Thawing Triumphs。

当有科研压力时英语作文

当有科研压力时英语作文Coping with the Pressures of Scientific Research.Scientific research, by its nature, is a highly pressurized endeavor. It demands rigorous thinking, continuous learning, innovation, and the ability to withstand repeated failures. The pressure can be immense, especially when dealing with tight deadlines, competitive funding environments, and the expectation to produce groundbreaking results. However, it is essential to learn healthy coping mechanisms to manage this pressure and ensure that it does not overtake one's well-being.1. Understanding the Source of Pressure.The first step in coping with pressure is to identify its sources. In scientific research, this pressure often stems from the need to publish in high-impact journals, secure funding for projects, meet research targets, and compete with peers for recognition and advancement.Understanding these sources helps researchers gain perspective and identify strategies to manage the pressure.2. Prioritizing Work and Personal Life.It is crucial to maintain a healthy work-life balance. This involves setting clear boundaries between work and personal time, taking regular breaks, and ensuringsufficient rest. By prioritizing personal well-being, researchers can avoid burnout and maintain a positive mindset, which is essential for creative thinking and problem-solving.3. Developing Coping Skills.Coping skills such as time management, prioritization, and stress management techniques can help researchers effectively handle pressure. Time management tools like to-do lists, calendars, and reminders can help keep track of tasks and ensure that important work is completed on time. Prioritization skills allow researchers to focus on the most critical tasks first, ensuring that limited resourcesand time are used effectively. Stress management techniques like meditation, yoga, or simple breathing exercises can help reduce stress levels and improve mental clarity.4. Seeking Support.Support from colleagues, mentors, and peers is crucial in coping with research pressure. Researchers should feel free to ask for help when needed and share their challenges and successes. Collaborating with others can provide valuable insights, ideas, and emotional support. Additionally, professional organizations and counseling services can provide resources and guidance to help researchers manage stress and pressure.5. Staying Motivated.Maintaining motivation is key to staying resilient in the face of research pressure. Researchers should remind themselves of their long-term goals and the impact their work can have on society. Celebrating small successes and milestones can help keep motivation high. Additionally,finding work that is personally fulfilling and aligned with one's values can provide a sense of purpose and drive.6. Caring for One's Mental Health.Caring for one's mental health is essential in coping with research pressure. Researchers should be aware of the signs of stress and burnout, such as decreased motivation, anxiety, and sleep disturbances. If these symptoms persist, it is important to seek professional help. Additionally, maintaining a healthy lifestyle with regular exercise, a balanced diet, and sufficient sleep can help improve mental well-being.In conclusion, coping with the pressures of scientific research requires a multifaceted approach. By understanding the sources of pressure, prioritizing work and personal life, developing coping skills, seeking support, staying motivated, and caring for one's mental health, researchers can manage the pressure effectively and continue to make valuable contributions to the field of science.。

在增压与减压中成长英语作文

在增压与减压中成长英语作文英文回答：Growing up under pressure and decompression is a common experience for many young people today. The pressure to succeed academically, socially, and financially can be overwhelming, and it can lead to feelings of anxiety, depression, and burnout. On the other hand, decompression activities, such as spending time with friends and family, exercising, and pursuing hobbies, can help to relieve stress and promote well-being.There is no one-size-fits-all answer to the question of how to balance pressure and decompression. However, there are some general principles that can help. First, it is important to identify the sources of pressure in your life. Once you know what is causing you stress, you can start to develop strategies for managing it. Second, it is important to make time for decompression activities on a regular basis. These activities should be things that you enjoy andthat help you to relax and de-stress. Finally, it is important to be kind to yourself. Everyone makes mistakes, and it is okay to take breaks when you need them.Here are some specific tips for managing pressure and decompression:Identify your sources of pressure. What is causing you stress? Is it school, work, relationships, finances, or something else?Develop coping mechanisms for dealing with pressure. Once you know what is causing you stress, you can start to develop strategies for managing it. Some helpful coping mechanisms include exercise, relaxation techniques, and talking to a friend or family member.Make time for decompression activities. Decompression activities are activities that you enjoy and that help you to relax and de-stress. Some examples of decompression activities include spending time with friends and family, exercising, pursuing hobbies, and reading.Be kind to yourself. Everyone makes mistakes, and itis okay to take breaks when you need them. Don't put too much pressure on yourself to be perfect.Growing up under pressure and decompression can be challenging, but it is possible to find a balance thatworks for you. By following these tips, you can manage stress, promote well-being, and achieve your goals.中文回答：在压力与减压的成长环境中长大是当今许多年轻人普遍的经历。

有关解压与增压的英语作文

有关解压与增压的英语作文1. Decompression: 。

Decompression is like a breath of fresh air after being trapped in a stuffy room. It's that feeling of relief when you finally let go of all the stress and tension that has been building up. It's like taking off a heavy backpackthat has been weighing you down. Decompression is necessary to recharge and rejuvenate, to let go of all the negative energy that has been accumulating. It's about finding that moment of peace and tranquility amidst the chaos of everyday life. 。

2. Pressure release: 。

Pressure release is like a burst of energy, a sudden rush that propels you forward. It's that feeling of exhilaration when you finally let go of all the constraints and limitations that have been holding you back. It's like breaking free from the chains that have been binding you.Pressure release is necessary to unleash your true potential, to push yourself beyond your limits. It's about finding that moment of empowerment and liberation amidst the challenges and obstacles. 。

neural regeneration research分区

Neural Regeneration ResearchIntroductionNeural regeneration research is a field of study aimed at understanding and developing strategies to repair or replace damaged or lost neural tissue. The central nervous system (CNS), which includes the brain and spinal cord, has limited regenerative capabilities compared to other tissues in the body. However, recent advancements in neuroscience and regenerative medicine have provided new insights and potential therapeutic approaches for promoting neural regeneration.Importance of Neural RegenerationNeural damage or degeneration can occur as a result of various conditions, such as stroke, traumatic brain injury, neurodegenerative diseases (e.g., Alzheimer’s and Parkinson’s), and spinal cord injury. These conditions can lead to significant functional impairments and disabilities. The ability to regenerate damaged neural tissue could potentially restore lost functions and improve the quality of life for affected individuals.Neural Regeneration MechanismsNeural regeneration involves complex cellular and molecular processes that aim to repair or replace damaged neurons and their connections. Several mechanisms contribute to neural regeneration:1.Neuroplasticity: The brain’s ability to reorganize and form newconnections to compensate for damaged or lost neurons. Thisprocess involves changes in synaptic strength and the growth ofnew dendritic spines.2.Axonal sprouting: Neurons can extend new branches (axonal sprouts)to form connections with nearby neurons. This process allows forthe rewiring of neural circuits and the formation of newfunctional connections.3.Neurogenesis: The generation of new neurons from neural stem cellsor progenitor cells. Neurogenesis primarily occurs in specificregions of the brain, such as the hippocampus, and plays a crucial role in learning, memory, and mood regulation.4.Glial scar modulation: After neural injury, glial cells form ascar tissue that can impede regeneration. Modulating the formation and composition of the glial scar can promote axonal growth andfunctional recovery.Current Research and TechniquesScientists and researchers are actively investigating various approaches to enhance neural regeneration. Some of the prominent areas of research include:1.Stem cell therapy: The transplantation of neural stem cells orinduced pluripotent stem cells (iPSCs) to replace damaged neurons or promote endogenous repair processes. Stem cells have thepotential to differentiate into various neural cell types andprovide structural and functional support to the damaged tissue. 2.Gene therapy: The use of gene editing tools, such as CRISPR-Cas9,to modify genes involved in neural regeneration. Gene therapy can enhance neuroplasticity, promote axonal growth, and regulate theimmune response to facilitate neural repair.3.Biomaterial scaffolds: The development of biocompatible scaffoldsthat can provide structural support and guidance for regenerating axons. These scaffolds can be combined with growth factors ortherapeutic molecules to enhance the regeneration process.4.Electrical stimulation: The application of electrical currents ormagnetic fields to stimulate neural activity and promote axonalsprouting. Electrical stimulation techniques, such as transcranial magnetic stimulation (TMS) and deep brain stimulation (DBS), have shown promise in promoting neural regeneration and functionalrecovery.Challenges and Future DirectionsDespite significant progress in neural regeneration research, several challenges still need to be addressed:1.Limited regeneration capacity: The CNS has inherent limitations inits regenerative capabilities. Understanding the factors thatrestrict neural regeneration and developing strategies to overcome these limitations is crucial.2.Integration of regenerated tissue: Ensuring proper integration ofregenerated neurons into existing neural circuits is essential for functional recovery. Further research is needed to optimize theconnectivity and functionality of regenerated tissue.3.Safety and efficacy: Developing safe and effective therapies forneural regeneration is of utmost importance. Extensive preclinical and clinical studies are necessary to evaluate the long-termeffects and potential risks associated with different regenerative approaches.In the future, advancements in technologies such as tissue engineering, 3D printing, and biofabrication hold great promise for enhancing neural regeneration. Furthermore, a better understanding of the cellular and molecular mechanisms underlying neural regeneration will enable the development of targeted therapies and interventions.ConclusionNeural regeneration research is an exciting and rapidly evolving field with the potential to revolutionize the treatment of neural injuries and degenerative diseases. Understanding the mechanisms of neural regeneration and developing innovative strategies to enhance this process are essential for improving patient outcomes and restoring lost functions. Continued research efforts and interdisciplinary collaborations will pave the way for groundbreaking discoveries and the development of effective regenerative therapies.。

提高心理阈值英语作文

提高心理阈值英语作文Title: Enhancing Psychological Resilience。

In today's fast-paced and often unpredictable world, cultivating psychological resilience has becomeincreasingly important. Psychological resilience refers to the ability to bounce back from adversity, adapt to change, and thrive despite challenges. Building a strong psychological threshold is essential for maintaining mental well-being and navigating life's ups and downs effectively. In this essay, we will explore various strategies to enhance psychological resilience.First and foremost, fostering a positive mindset is crucial in bolstering psychological resilience. Positive thinking helps individuals reframe setbacks as temporary and surmountable rather than insurmountable obstacles. This involves practicing gratitude, focusing on strengths rather than weaknesses, and maintaining optimism even in the face of adversity.Moreover, developing effective coping mechanisms is essential for building resilience. These mechanisms may include problem-solving skills, seeking social support, engaging in relaxation techniques such as meditation or deep breathing exercises, and maintaining a healthylifestyle encompassing regular exercise, nutritious diet, and adequate sleep. By adopting these coping strategies, individuals can better manage stress and bounce back from setbacks more quickly.Furthermore, cultivating self-awareness and emotional intelligence contributes significantly to psychological resilience. Being aware of one's thoughts, feelings, and reactions allows individuals to better understand their own behavior and develop healthier ways of coping with stressors. Emotional intelligence enables individuals to regulate their emotions, empathize with others, and maintain positive relationships, all of which are essential components of resilience.Another key aspect of enhancing psychologicalresilience is fostering a strong support network. Having supportive relationships with friends, family members, colleagues, or mentors provides a crucial buffer against life's challenges. These individuals can offer emotional support, practical assistance, and valuable perspective during difficult times, helping individuals to navigate adversity more effectively.In addition to interpersonal support, fostering a sense of purpose and meaning in life can significantly enhance resilience. When individuals have a clear sense of their values, goals, and priorities, they are better able to persevere in the face of obstacles and setbacks.Cultivating a sense of purpose can provide motivation, direction, and resilience in times of adversity.Moreover, building resilience involves cultivating adaptability and flexibility in response to change. In today's rapidly evolving world, the ability to adapt to new circumstances, learn from experiences, and embrace uncertainty is essential for thriving in the face of adversity. By developing a growth mindset and embracingchallenges as opportunities for growth and learning, individuals can build resilience and thrive in the face of adversity.Finally, practicing self-care and prioritizing mental health is fundamental to building psychological resilience. This includes setting boundaries, managing stress effectively, and seeking professional help when needed. Taking care of one's physical, emotional, and psychological well-being ensures that individuals have the resources and resilience to cope with life's challenges effectively.In conclusion, enhancing psychological resilience is essential for thriving in today's complex and uncertain world. By fostering a positive mindset, developingeffective coping mechanisms, cultivating self-awareness and emotional intelligence, building a strong support network, fostering a sense of purpose and meaning, embracing adaptability and flexibility, and prioritizing self-care, individuals can build the resilience needed to navigatelife's challenges and thrive in the face of adversity.。

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Please cite this article as: Lixia Yang, Fan Yang, Ying Long, Yang Zhao, Xiang Xiong, Xiaofeng Zhao, Ping Xiao, Evolution of Residual Stress in Air Plasma Sprayed Yttria Stabilised Zirconia Thermal Barrier Coatings after Isothermal Treatment, Surface & Coatings Technology (2014), doi: 10.1016/j.surfcoat.2014.04.009
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Evolution of Residual Stress in Air Plasma Sprayed Yttria Stabilised Zirconia Thermal Barrier Coatings after Isothermal Treatment Lixia Yang, Fan Yang, Ying Long, Yang Zhao, Xiang Xiong, Xiaofeng Zhao, Ping Xiao PII: DOI: Reference: To appear in: Received date: Revised date: Accepted date: S0257-8972(14)00323-5 doi: 10.1016/j.surfcoat.2014.04.009 SCT 19329 Surface & Coatings Technology 5 November 2013 25 February 2014 4 April 2014
Manchester M1 7HS, UK
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School of Powder Metallurgy Research Institute, Central South University, Changsha
*Corresponding author
Phone: +86-021-54742561 Fax: +86-021-54742561
1. Introduction Air plasma-sprayed (APS) yttria stabilised zirconia (YSZ) thermal barrier coatings (TBCs) have been widely used in the hot-section of gas turbine to increase the inlet temperature and to protect the engine components. Failure of TBCs under isothermal treatment typically occurs within the YSZ layer, i.e., several micrometers above the thermally grown oxide (TGO) [1]. The failure driven by the residual stress in the YSZ layer, developed during cooling after high-temperature treatment [2], through a sequence of crack nucleation, propagation and coalescence process [3]. Therefore, determination of the residual stresses in the YSZ layer is of great importance to understand the failure mechanisms of APS TBCs. Due to the complicated microstructures and various thermal treatment conditions, the stress values of the APS YSZ coatings from different researchers/techniques show a significant scatter, For example, Teixeira and Andritschky [2, 4] reported there is a compressive stress of about -70 to -300 MPa of the APS YSZ layer after thermal cycling. Portinha et al. [5] reported a compressive stress of -404 MPa measured by X-ray diffraction (XRD), -22 MPa investigated by XRD-sin2Ψ method and -594 MPa by Raman spectroscopy for the APS YSZ layer after isothermal treatment. To date, there has been no systematic research to study the evolution of the residual stresses. Thus, it is necessary to know the stress state evolution in YSZ layer due to isothermal treatment, which is important for understanding the degradation and failure of TBCs. Various methods have been employed to study the residual stresses in TBCs, such as neutron
Keywords: Thermal barrier coatings (TBCs); Stress; Air plasma spray; Raman spectrascopy; Phase transformation
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Evolution of Residual Stress in Air Plasma Sprayed Yttria Stabilised Zirconia Thermal Barrier Coatings after Isothermal Treatment Lixia Yanga, Fan Yangb, Ying Longc, Yang Zhaob, Xiang Xiongc, Xiaofeng Zhaoa,* and Ping Xiaoa.b
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Abstract
The evolution of residual stresses in yttria stablised zirconia (YSZ) thermal barrier coatings (TBCs) produced by air plasma-spray technique after thermal treatments at 1150˚C was investigated. The residual stresses in YSZ layer were measured using the Raman spectroscopy and curvature method, respectively. Generally, the YSZ layer was under compressive stress in as-deposited condition, but changed to tensile after thermal treatment for 30 hours partly due to the monoclinic to tetragonal phase transformation in YSZ layer. With prolonged thermal treatment, the residual stress gradually transformed from tensile to compressive, which can be attributed to the sintering in the YSZ layer. In addition, the β-NiAl to γ/γ′-Ni3Al phase transformation in the bond coat also plays an important role on the stress in the YSZ layer.
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diffraction [6, 7], XRD [8], luminescence spectroscopy [9-11], curvature measurement [12, 13] and Raman spectroscopy [4, 14-16]. The limitation of neutron diffraction is the large depth of penetration which will not reveal the stresses within the YSZ layer. XRD has a small penetration depth which limits the stress measurement close to the surface of the YSZ layer. Luminescence spectroscopy, on the other hand, has been used for measuring the residual stresses in the TGO, but not applicable to the YSZ layer. Among those, Raman spectroscopy is an easy and non-destructive technique to study the stresses in YSZ layer. It is able to provide localized information of the residual stresses for its high spatial resolution (of the order of 1 μm). Meanwhile, curvature method is considered as one of the simplest and easiest methods. This method can obtain the overall stress information in the TBCs. To understand the crack nucleation behavior, the local stress should be known, while the failure of TBCs is related to the overall stress. Therefore, Raman spectroscopy and curvature method are both applied to obtain local and overall information. The aim of this study is to investigated the evolution of residual stresses in the APS YSZ layer with isothermal treatment time at 1150˚C by Raman spectroscopy and curvature method. These are related to SEM, XRD and micro-indentation to study the effect of the microstructure, phase transformation and mechanical properties aspects on the stress in the YSZ layer. Then the results from Raman spectroscopy and curvature method were compared and their limitations discussed.