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筹２章磁究舞戆、内容、秀法和检测撵搽翻２．３固相萃取（ＳＰＥ）系统蜜物图图２．４圄褐萃取暖酣桂实物瞬３．有机物分离步骤凄簪涛洗手净瓣麓爨，连接袋濯２５掰琴溅程晔习，瘩襻遁过吸黠援翡滚速控锩《在１．５～２．５ｍ１．／ｍｉｎ，洗脱时的流速控制覆ｏ．５～１．０ｍｌｊｍｉｎｌ４ｓ！。
Ｗｌ—Ｗｊ串性亲承谯有枧物极性亲承性有枫物匿２．５有机物将｛耋分离流程匿０．４５芦ｍ过滤后的试验水样，用５ＭＨＣＩ将ｐＨ调至２．０，通过ＤＡＸ－８树脂１８纂２孝麟究嚣静、内容、方法露检测攒嚣吸附柱，吸附在ＤＡＸ－８树脂的溶解性有机物是强疏水性有机物，主要缎成是溶解淼腐殖酣５２１．吸附在ＤＡＸ－８树脂有机物用０．１ＭＮａＯＨ洗脱。
而通道ＤＡＸ－８秘爨骧瓣桂戆试验承榉，秀遴避ＸＡＤ－４拷戆吸瓣拄，吸辫在ＸＡＤ－４誊唾耱豹溶麟髓有机物，主黉弱疏水佳膏概物潮．吸附猩ＸＡＤ－４树脂上的溶解住有机物同样用０．１ＭＮａＯＨ洗脱。
此时，试验水样中的溶解性有机物被分为亲水性有机物秘疏水性有机物【５３】。
丽亲水饺有机物主要是菲胡敏酸缀分，如蛋白成、氮基酸秘辕承纯台麓。
耨逶遘ＸＡＤ－４耱嚣蔽戮鼗垂骞试验承群螂诿至蘩８．０，矮ＩＲＡ－９５８树脂吸附柱进行吸附，被ＩＲＡ－９５８Ｉ驳附的有机物怒极性亲水憔有机物，主舞是氨基酸，小分子量的烷糕羧酸、胺，以及烷基二羧酸。
最后，用１ＭＮａＯＨ羁１ＭＮａＣｌ混会渡将承Ａ．９５８爨耱洗瓣。
遴ｊ霪ＩＲＡ－９５８楗驻疆辫控豹残分主要是中性亲水溶解饿有机物，童黉是多糖，小分子量的烷纂簿、醛、酮ｆ５射。
分离样品时滞作吸收组份阐收，且回收攀达到８０％以上，方可使用。
样品分离詹需将ｐＨ调肇至７．０左蠢后，才可以遴行ＤＯＣ、ｕｖ鹚粒分子量分布等的涌定。
２．３检测指标本磅究圭簧捻测指标魏下；１．溶解性有机炭（ＤｉｓｓｏｌｖｅｄＯｒｇａｎｉｃＣａｌ如ｏｌｌ，ＤＯＣ）值：水样通过０．４５ｐｍ滤Ｊ摸过滤后，测褥的总有机炭（ＴＩＤｃ）即为溶解性有机炭，称之为ＤＯＣ。
带来影响的英文作文1. The pandemic has brought about a significant impact on the global economy, leading to widespread job losses and financial instability for many individuals and businesses.2. The rapid spread of misinformation on social media platforms has had a detrimental effect on public health, causing confusion and distrust in scientific information and guidelines.3. The closure of schools and universities has disrupted the education of millions of students, creating challenges for both teachers and learners in adapting to remote learning environments.4. The restrictions on travel and social gatherings have resulted in feelings of isolation and loneliness for many people, affecting their mental health and well-being.5. The increased demand for online shopping anddelivery services has put a strain on supply chains and logistics, leading to delays and shortages of essential goods.6. The rise of remote work has changed the way companies operate, with many businesses opting to continue with virtual work arrangements even after the pandemic is over.7. The emphasis on hygiene and sanitation practices has become more prevalent in everyday life, with individuals and businesses implementing stricter measures to prevent the spread of infectious diseases.8. The shift towards digital entertainment and streaming services has transformed the way people consume media, with traditional forms of entertainment such as movie theaters and live events facing challenges in attracting audiences.。
生物分离工程的英语Biological Separation Engineering is a specialized field that focuses on the isolation and purification of biological products. It plays a crucial role in the pharmaceutical, food, and biotechnology industries, where the extraction ofbioactive compounds from natural sources is essential.The process typically begins with the selection of an appropriate feedstock, which could be anything from plant material to microorganisms. Once the feedstock is identified, it undergoes a series of steps to separate the desired components. These steps may include:1. Pre-treatment: This involves breaking down the complex structure of the feedstock to release the target molecules. Techniques such as mechanical disruption, enzymatic digestion, or chemical treatment may be used.2. Extraction: The target molecules are then extractedfrom the pre-treated material. This can be done using solvent extraction, where a solvent is used to dissolve the desired compounds, or by using methods like supercritical fluid extraction, which employs high-pressure gases to extract the compounds.3. Concentration: After extraction, the solution is often diluted and needs to be concentrated to increase the concentration of the target molecules. This can be achievedthrough evaporation, membrane filtration, or centrifugation.4. Purification: The concentrated solution may still contain impurities, so further purification is necessary. Chromatography is a common technique used at this stage, which separates molecules based on their affinity to the stationary phase.5. Polishing: The final step is to polish the purified product to ensure it meets the required specifications. This may involve additional rounds of purification or the use of specific techniques to remove any remaining impurities.Biological separation engineering is a complex process that requires a deep understanding of both the properties of the target molecules and the various separation techniques available. Advances in this field are continually improving the efficiency and selectivity of these processes, making it possible to produce high-quality biological products for a wide range of applications.。
参与抗生素生物合成的FADH_2依赖型卤化酶研究进展李航;朱丽;陈代杰【摘要】从发现第一个天然卤化物到现在已有100多年了.在已发现的约4500个天然卤化物中有很多在医药等领域应用广泛,其中包括许多重要的抗生素.直到19世纪90年代中期,人们一直认为生物卤化反应主要由卤过氧化物酶负责催化.近期在许多关于抗生素生物合成基冈簇的研究中发现FADH_2依赖型卤化酶催化的卤化反应殖是许多微生物及其它生物中的主要卤化机制.本文综述了参与抗生素生物合成的FADH_2依赖型卤化酶的发现,催化机制及各种来源的该类卤化酶研究进展,并介绍了该类酶在组合生物合成及寻找天然卤化物等方面的应用.【期刊名称】《中国抗生素杂志》【年(卷),期】2010(035)001【总页数】6页(P1-6)【关键词】FADH_2依赖型卤化酶;抗生素;卤化物【作者】李航;朱丽;陈代杰【作者单位】上海医药工业研究院,上海,200040;上海来益生物药物研发中心,上海,201203;上海医药工业研究院,上海,200040【正文语种】中文【中图分类】TQ465从发现第一个天然卤化代谢物到现在已有100多年了，很长一段时间内该类化合物被认为是很特殊的一类化合物[1]。
直到1960年，被发现的天然卤化物才共有29个[2]。
随着该类化合物广泛的应用于医药，杀虫剂等领域，人们对该类化合物越来越感兴趣，目前为止共发现天然卤化物约4500个[3]。
该类化合物由许多不同的生物产生，且其中很多有较强的生物活性，例如：由土壤细菌产生的万古霉素[4]，由哺乳动物甲状腺产生的甲状腺素[5]，由藻青菌产生的抗肿瘤物质自念珠藻环肽A等[6]。
在这些卤化物中，陆地环境中发现的主要为氯化物，而海洋生物中发现的主要为溴化物。
天然氟化物则较稀少，仅在一些植物和细菌代谢物中被发现[7]。
随着越来越多的卤化物被发现，人们对相关的卤化酶及其作用机制的研究也越来越感兴趣。
从1966年在Caldariomyces fumago中发现第一个卤化酶[8]以来，目前为止共有4大类的卤化酶被发现，分别为：卤过氧化物酶(haloperoxidase)[9]，非血红素Fe2+α-酮戊二酸及O2依赖型卤化酶(non-heme FeII αketoglutarate- and O2-dependent halogenase)[10]，S-腺苷甲硫氨酸依赖型氯化酶(S-adenosyl-L-methionine dependent chlorinase)[11]和FADH2依赖型卤化酶(FADH2-dependent halogenase)。
物种概念及其界定龚佐山;买买提明·苏来曼【摘要】半世纪以来,物种概念的定义备受关注,不同研究方向的生物学家提出24种不同或至少有分歧的物种概念,根据其不同的物种概念,物种的界定和物种的数量会出现很大的差异.人们普遍认同:物种是进化分离的微居群谱系,但把谱系分离过程中获得的特征如生殖隔离、可鉴定性、单系统发生等视为鉴定物种次级特征却有不同的声音.该文提出统一的物种概念,把谱系进化分离作为物种界定的唯一而又必要的特征,把谱系分离过程中获得的次级特征作为界定谱系分离的证据.鉴于此,物种概念间的分歧就会化解.其一,物种概念化与物种界定明显分开,不再混淆;其二,谱系的次级特征只与物种界定有关,在某种程度上为谱系分离提供证据;第三,若能把合理解释的任何一个特征作为某物种客观存在的证据,这样更多的特征更能确定谱系分离;最后最重要的是,统一物种概念使我们解放思想,扬弃传统的物种界定标准,探求物种界定的新思路.%From the half century to now,the issue of species delimitation has long been confused by species conceptu alization, according to controversy species concepts,the boundaries and numbers of species could be great difference. Alternative species concepts agree in treating existence as a separately evolving metapopulation lineage as the primary defining property of the species category, but adopting different properties acquired by lineages during the course of divergence(e. G. Intrinsic reproductive isolation,diagnosability,monophyly)as secondary species criteria causes differ ent sounds. The paper gave a unified species concept treating a separately evolving metapopulation lineage as the only necessary property of species,and secondary species criteria as differentlines of evidence relevant to assessing lineage separation. This unified concept of species had several consequences for species delimitation as follows: first,the is sues of species conceptualization and species delimitation were clearly separated; the secondary species criteria were no longer considered relevant to species conceptualization but only to species delimitation. Second,all of the properties formerly treated as secondary species criteria were relevant to species delimitation to the extent that they provide evi dence of lineage separation. Third,if possible,the presence of any one of the properties was evidence for the existence of aspecies,though more properties and thus more lines of evidence are associated with a higher degree of corrobora tion;Lastly,the unified species made ones liberate minds from the traditional species criteria,not tied to those properties,and develop new methods of species delimitation.【期刊名称】《广西植物》【年(卷),期】2012(032)002【总页数】6页(P274-279)【关键词】物种概念;物种界定;统一【作者】龚佐山;买买提明·苏来曼【作者单位】新疆大学,生命科学与技术学院,乌鲁木齐市,830046;安徽省霍邱县第一中学,安徽,六安市,237400;新疆大学,生命科学与技术学院,乌鲁木齐市,830046【正文语种】中文【中图分类】Q111.21物种是生物学功能单位之一，尤其在系统生物学上，与基因、细胞、器官等各级结构和功能单位同等重要（de Queiroz，2005）。
胡壮麟《语言学教程》（修订版）测试题——第二章：语音您所查看的帖子来源于考研加油站考研论坛() Chapter 2 Speech SoundsI. Choose the best answer. (20%)1. Pitch variation is known as __________ when its patterns are imposed on sentences.A. intonationB. toneC. pronunciationD. voice2. Conventionally a __________ is put in slashes (/ /).A. allophoneB. phoneC. phonemeD. morpheme3. An aspirated p, an unaspirated p and an unreleased p are __________ of the p phoneme.A. analoguesB. tagmemesC. morphemesD. allophones4. The opening between the vocal cords is sometimes referred to as __________.A. glottisB. vocal cavityC. pharynxD. uvula5. The diphthongs that are made with a movement of the tongue towards the center are known as __________ diphthongs.A. wideB. closingC. narrowD. centering6. A phoneme is a group of similar sounds called __________.A. minimal pairsB. allomorphsC. phonesD. allophones7. Which branch of phonetics concerns the production of speech sounds?A. Acoustic phoneticsB. Articulatory phoneticsC. Auditory phoneticsD. None of the above8. Which one is different from the others according to places of articulation?A. [n]B. [m]C. [ b ]D. [p]9. Which vowel is different from the others according to the characteristics of vowels?A. [i:]B. [ u ]C. [e]D. [ i ]10. What kind of sounds can we make when the vocal cords are vibrating?A. VoicelessB. V oicedC. Glottal stopD. ConsonantII. Decide whether the following statements are true or false. (10%)11. Suprasegmental phonology refers to the study of phonological properties of units larger than the segment-phoneme, such as syllable, word and sentence.12. The air stream provided by the lungs has to undergo a number of modification to acquire the quality of a speech sound.13. Two sounds are in free variation when they occur in the same environment and do not contrast, namely, the substitution of one for the other does not produce a different word, but merely a different pronunciation.14. [p] is a voiced bilabial stop.15. Acoustic phonetics is concerned with the perception of speech sounds.16. All syllables must have a nucleus but not all syllables contain an onset and a coda.17. When pure vowels or monophthongs are pronounced, no vowel glides take place.18. According to the length or tenseness of the pronunciation, vowels can be divided into tense vs. lax or long vs. short.19. Received Pronunciation is the pronunciation accepted by most people.20. The maximal onset principle states that when there is a choice as to where to place a consonant, it is put into the coda rather than the onset.III. Fill in the blanks. (20%)21. Consonant sounds can be either __________ or __________, while all vowel sounds are __________.22. Consonant sounds can also be made when two organs of speech in the mouth are brought close together so that the air is pushed out between them, causing __________.23. The qualities of vowels depend upon the position of the __________ and the lips.24. One element in the description of vowels is the part of the tongue which is at the highest point in the mouth. A second element is the __________ to which that part of the tongue is raised.25. Consonants differ from vowels in that the latter are produced without __________.26. In phonological analysis the words fail / veil are distinguishable simply because of the two phonemes /f/ - /v/. This is an example for illustrating __________.27. In English there are a number of __________, which are produced by moving from one vowel position to another through intervening positions.28. __________ refers to the phenomenon of sounds continually show the influence of their neighbors.29. __________ is the smallest linguistic unit.30. Speech takes place when the organs of speech move to produce patterns of sound. These movements have an effect on the __________ coming from the lungs.IV. Explain the following terms, using examples. (20%)31. Sound assimilation32. Suprasegmental feature33. Complementary distribution34. Distinctive featuresV. Answer the following questions. (20%)35. What is acoustic phonetics?（中国人民大学，2003）36. What are the differences between voiced sounds and voiceless sounds in terms of articulation?（南开大学，2004）VI. Analyze the following situation. (20%)37. Write the symbol that corresponds to each of the following phonetic descriptions; then give an English word that contains this sound. Example: voiced alveolar stop [d] dog. （青岛海洋大学，1999）(1) voiceless bilabial unaspirated stop(2) low front vowel(3) lateral liquid(4) velar nasal(5) voiced interdental fricative以下内容跟帖回复才能看到==============================Key:I.1~5 ACDAA 6~10 DBABBII.11~15 TTTFF 16~20 TTTFFIII.21. voiced, voiceless, voiced 22. friction23. tongue 24. height25. obstruction 26. minimal pairs27. diphthongs 28. Co-articulation29. Phonemes 30. air streamIV.31. Sound assimilation: Speech sounds seldom occur in isolation. In connected speech, under the influence of their neighbors, are replaced by other sounds. Sometimes two neighboring sounds influence each other and are replaced by a third sound which is different from both original sounds. This process is called sound assimilation.32. Suprasegmental feature: The phonetic features that occur above the level of the segments are called suprasegmental features; these are the phonological properties of such units as the syllable, the word, and the sentence. The main suprasegmental ones includes stress, intonation, and tone.33. Complementary distribution: The different allophones of the same phoneme neveroccur in the same phonetic context. When two or more allophones of one phoneme never occur in the same linguistic environment they are said to be in complementary distribution.34. Distinctive features: It refers to the features that can distinguish one phoneme from another. If we can group the phonemes into two categories: one with this feature and the other without, this feature is called a distinctive feature.V.35.Acoustic phonetics deals with the transmission of speech sounds through the air. When a speech sound is produced it causes minor air disturbances (sound waves). Various instruments are used to measure the characteristics of these sound waves.36.When the vocal cords are spread apart, the air from the lungs passes between them unimpeded. Sounds produced in this way are described as voiceless; consonants [p, s, t] are produced in this way. But when the vocal cords are drawn together, the air from the lungs repeatedly pushes them apart as it passes through, creating a vibration effect. Sounds produced in this way are described as voiced. [b, z, d] are voiced consonants.VI.37.Omit.。
1Master of Global ManagementExam of Economic AnalysisThe History and Influence of Fluctuation of ChineseCurrency’s Exchange RateKaiyue ZhaoDoreen Sharleena KarimMonday, January 20, 2014Executive SummaryThis report offers a reflection on the history and influence of Chinese currency exchange rate. We provide a brief introduction of currency and exchange rate regimes. Then we provide a brief historical evolution of exchange rate regime over the last century. We also provide the factors that influences exchange rate fluctuations. Based on this foundation, we then looked at the Chinese currency and review the Chinese strategy on this. In last part, we briefly discussed about the influence that current situation of the exchange rate of RMB brought2Directory1.Introduction (1)1.1 What is Exchange Rate (1)1.1.1Floating Currency Exchange Rate: (1)1.1.2Pegged Currency Exchange Rate: (2)2.History (2)2.1The evolution of global exchange system (2)2.2The history of Chinese exchange rate regime (the choice china made) (4)2.2.1The Planned Economy Period （1949-1978） (4)2.2.2Economic Transition Period (1979-1993) (4)2.2.3The Socialist Market Economy Period (1994-now) (5)3.Analysis of current situation (7)3.1The continuous appreciation of external value (8)3.2The devaluation of intrinsic value (8)4.Influence of the change of nominal exchange rate (8)4.1 The impact on the domestic economy (9)4.1.1 The impact on purchase of consumer (9)4.1.2 The impact on employment (9)4.1.3 The impact on domestic financial market (10)4.1.4The impact on export trade (11)4.2 The impact on world economy (11)3Reference (13)41.IntroductionIn the simplest form, currency means money. We buy things that we want and need in our daily life by money. Our employers paid us for in the form of money, with which we buy foods, cloths, pay bills, live in a house etc. We sometimes put some money in the bank as savings for our future needs. Historically, currency was defined as a unit of purchasing power. It was a medium of exchange, a substitute for goods or services. Besides, currency (or money) is also the foundation of wealth.Over the last 3,000 years or so, the form of currency has evolved significantly, for example Commodity, Coins, Paper Money and Electronic Currency are all represent different forms of currency. In addition, world does not depend on one type of currency, albeit the forms are similar. Different countries have different currencies. As such, when we travel or go to different countries we are required to use the currency of that specific country. For example, US dollar cannot be used in Japan. To buy something in Japan, one first has to go to a bank and exchange the US dollar into Japanese Yen. This leads us to the question on how this exchange happens, under what rate and who determines that. In the next subsection we discuss this.1.1 What is Exchange RateCurrency Exchange Rate is the rate at which one currency may be converted into another, i.e., the exchange rate is used when simply converting one currency to another (such as for the purposes of travel to another country).There are a wide variety of factors, which influence the exchange rate, such as interest rates, inflation, and the state of politics and the economy in each country. Each country, through varying mechanisms, manages the value of its currency. As part of this function, it determines the exchange rate regime that will apply to its currency. For example, the currency may be free-floating, pegged or fixed, or a hybrid.1.1.1Floating Currency Exchange Rate:The market determines a floating exchange rate. In other word currency is worth whatever buyers are willing to pay. If a currency is free-floating, its exchange rate is allowed to vary against that of other currencies and is determined by the market forces of supply and demand.1Exchange rates for such currencies are likely to change almost constantly as quoted on financial markets, mainly by banks, around the world.1.1.2Pegged Currency Exchange Rate:A movable or adjustablepeg system is a system of fixed exchange rates, but with a provision for the revaluation (usually devaluation) of a currency. This rate will not change or fluctuate from day to day. The government has to work to keep the exchange rate stable. For example, between 1994 and 2005, the Chinese RMB was pegged to the United States dollar at RMB 8.2768 to $1. China was not the only country to do this; from the end of World War II until 1967, Western European countries all maintained fixed exchange rates with the US dollar based. But that system had to be abandoned in favor of floating, market-based regimes due to market pressures and speculations in the 1970s.2.History2.1The evolution of global exchange systemFor many years, the currencies of the world were backed by gold. That is, a piece of paper currency issued by any world government represented a real amount of gold held in a vault by that government. This monetary system is known as “Gold Standard” in whi ch the standard economic unit of account is based on a fixed quantity of gold. However, this “Gold Standard” collapsed entirely during the great depression of the 1930’s. Some economists explained this collapse by saying that the adherence to the gold standard had prevented monetary authorities from expanding the money supply rapidly enough to revive economic activity.To revive the world economy, representatives of most of the world's leading nations met at Bretton Woods, New Hampshire, USA in 1944 to create a new international monetary system. Because the United States at the time accounted for over half of the world's manufacturing capacity and held most of the world's gold, the leaders decided to tie world currencies to the U.S. dollar, which, in turn, they agreed should be convertible into gold at $35 per ounce. This monetary system is known as “Bretton Woods” system. Other countries followed this system and based the value of their currencies on the U.S. dollar. Since everyone knew how much gold a U.S. dollar was worth, then the value of any other currency against the dollar could be based on its value in gold. A currency worth twice as much gold as a U.S dollar was, therefore, also2worth two U.S. dollars.Under the Bretton Woods system, central banks of countries other than the United States were given the task of maintaining fixed exchange rates between their currencies and the dollar. They did this by intervening in foreign exchange markets. If a country's currency was too high relative to the dollar, its central bank would sell its currency in exchange for dollars, driving down the value of its currency. Conversely, if the value of a country's money was too low, the country would buy its own currency, thereby driving up the price.Unfortunately, the real world of economics outpaced this system. In late 1960, the U.S. dollar suffered from inflation (its value relative to the goods it could purchase decreased), while other currencies became more valuable and more stable. Americans urged Germany and Japan, both of which had favorable payments balances, to appreciate their currencies. But those nations were reluctant to take that step, since raising the value of their currencies would increases prices for their goods and hurt their exports. Eventually, the U.S. could no longer pretend that the dollar was worth as much as it had been, so the value was officially reduced so that 1 ounce of gold was now worth $70. The dollar's value was cut in half. Finally, the United States abandoned the fixed value of the dollar and allowed it to "float" (as mentioned in the earlier section as Floating Exchange Rate) that is, to fluctuate against other currencies. The dollar promptly fell. World leaders sought to revive the Bretton Woods system with the so-called Smithsonian Agreement in 1971, but the effort failed. By 1973, the United States and other nations agreed to allow exchange rates to float.Today, the U.S. dollar still dominates many financial markets. In fact, exchange rates are often expressed in terms of U.S. dollars. Currently, the U.S. dollar and the euro account for approximately 50 percent of all currency exchange transactions in the world. Adding British pounds, Canadian dollars, Australian dollars, and Japanese yen to the list accounts for over 80 percent of currency exchanges altogether.32.2The history of Chinese exchange rate regime(the choice china made)2.2.1The Planned Economy Period （1949-1978）On January 8, 1949, the people's bank of China began to publish the exchange rates of currency to public. Under the unified management of the central, Shanghai and guangzhou used tianjin exchange rate as the standard, took the local price situation into consideration, published their own exchange rate. In volatile financial background, to avoid a recession and maintain the stability of exchange rate with some long-term trade partners, RMB exchange rate, after a long historical period of a fixed exchange rate in planned economy period, now has been pegged to a basket of currencies. Dollar, yen, pound sterling, the deutsche mark, Swiss franc always play an2.2.2Economic Transition Period (1979-1993)In this period, China had a dual exchange rate system characterized by two parallel exchange rates: the market swap rate and the official rate. The official rate was much lower than the market swap rate. In 1981-1984, official RMB exchange rate has a trade internal settlement price and non-trade dual exchange rate system of open quotation. On January 1, 1985 the4central bank of China canceled internal settlement price, in order to eliminateexchange rateovervalued and to make the change in exchange rate suits the change in price of commodities , central bank adjust the official price several times. In 1988, foreign trade systemhas undergone majorreforms. The system for contracted responsibility was introduced to China. In 1991, foreign trade system turn to self-financing instead of subsidy mechanism. With the deepening of reform, exchange ratebecamethe primary means ofregulatingthe import and2.2.3The Socialist Market Economy Period (1994-now)In 1994, China unified these two rates into one single exchange rate based on the market swap rate. China began to peg its currency to the US dollar at 8.3 RMB per dollar since 1996. At the same time, China’s central bank, the People’s Bank of China (PBOC) enlarged the amount of foreign exchange for foreign firms in China. Meanwhile China also officially declared the convertibility of the RMB under current account at the end of 1996. At the end of 1998, China’s foreign exchange swap markets were abolished and China Foreign Exchange Trading Center (CFETC) began to buy and sell foreign exchange, with only three foreign currencies traded: the US dollar, the Hong Kong dollar (HKD), and the Japanese Yen (JPY). The foreign exchange rate market is intervened by the People’s Bank of China. And designatedforeign bank have to sell the foreign exchanges in the market when they exceed the margin limits assigned by the PBOC. At that time, there are 60% of foreign exchanges purchased by Chinese banks and 28% purchased by the PBOC. And the designated foreign banks can purchase only 12% of foreign exchanges. The demand and supply of foreign exchanges are not determined by the market but 。
《The Dangers of Isolation》高考优秀英语作文The Dangers of IsolationIn today’s world, isolation can have serious consequences for individuals and society. We are now more connected globally than ever before, yet despite this, some people still lead very isolated lifestyles.On a personal level, self-imposed isolation can have severe mental and physical health impacts. Social relationships play an important role in human wellbeing, providing support and the opportunity to cultivate meaningful connections. Without these interpersonal bonds, people can suffer from loneliness and depression, as well as physical health issues due to lack of exercise and poor diet.From a societal perspective, isolation can lead to exclusion, inequality and prejudice. Those who are isolated can be left feeling out of touch with the world around them, lose interest in the greater community, and become vulnerable to exploitation. This can lead to further segregation, entrenching social divisions and putting certain groups at a disadvantage.To strive for a healthier and more equitable society, we must work to reduce isolation and ensure everyone has access to social networks and resources. This can include providing public or virtual spaces for people to meet, access to free or low-cost services, and education about the dangers of isolation. Ultimately, it is important to remember that we all have aresponsibility to look out for each other and create a more inclusive world where everyone feels safe and connected.。
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ORIGINAL PAPERInfluence of In-Isolation Properties of Geogrids on Their Pullout Performance in a Dense Graded AggregateKianoosh Hatami •Tahsina Mahmood •Rouzbeh Ghabchi •Musharraf ZamanReceived:4February 2013/Accepted:22April 2013/Published online:8May 2013ÓIndian Geotechnical Society 2013Abstract A series of in-isolation and pullout tests was carried out on selected extruded (EGG)and non-extruded (NEGG)geogrid products that are available for base rein-forcement and subgrade stabilization applications.The objective of the study was to examine the influence of selected geogrids index properties on their in-aggregate performance in roadway applications.The pullout tests were carried out in Oklahoma Department of Transporta-tion (ODOT)Type-A aggregate,which is a dense-graded aggregate most commonly used in ODOT projects.Pullout tests provide useful information on the in-aggregate per-formance of geogrids outside the stress bulb directly beneath the tire pressure.The in-isolation properties stud-ied included the geogrids low-strain (i.e.2and 5%strain)rib strength,and ultimate rib strength and junction strength in both machine and cross-machine directions.Results of the study indicated that for both EGG and NEGG catego-ries of geogrids examined,greater rib and junction strength properties overall resulted in greater pullout resistance.Geogrids junction strength and low-strain rib strength showed a reasonably strong correlation with their pulloutperformance regardless of the geogrid category examined.The rib strength at 2%strain showed a stronger correlation than the 5%-strain strength with the geogrid pullout per-formance.However,ultimate rib strength of geogrid showed convincing correlations with their pullout perfor-mance only when they were examined in separate catego-ries with respect to their manufacturing technique (i.e.when the EGG and NEGG geogrids were examined as separate categories).The findings of this study are expected to be beneficial in relating the in-isolation properties of geogrids to their in-aggregate performance.Keywords Geogrids ÁPullout resistance ÁIn-isolation properties ÁRib strength ÁJunction strength ÁAggregate baseIntroductionAdequate mechanical properties (e.g.rib and junction strength)are essential for biaxial geogrids in order to transfer and distribute the traffic load in their longitudinal and transverse ribs effectively and thereby provide ade-quate confining effects on the aggregates in base rein-forcement and subgrade stabilization applications.A few recent studies have been aimed at developing correlations between index properties of geogrids and their in-aggregate performance [3,4,8,10,13,15,19–23].These studies involved laboratory tests and/or large-scale field tests on geogrid-reinforced pavements to examine the interaction between the geogrids and the surrounding (i.e.base and subgrade)materials.Results of these studies indicated that geogrid reinforcement reduces pavement deformation and distress and hence results in a more durable and econom-ical pavement in the long run.K.Hatami (&)ÁT.Mahmood ÁR.GhabchiSchool of Civil Engineering and Environmental Science (CEES),University of Oklahoma,202W.Boyd St.,Room 334,Norman,OK 73019,USAe-mail:kianoosh@ T.Mahmoode-mail:tahsina@ R.Ghabchie-mail:ghabchi@M.ZamanCollege of Engineering,University of Oklahoma,202W.Boyd St.,Room 334,Norman,OK 73019,USA e-mail:zaman@Indian Geotech J (October–December 2013)43(4):303–320DOI 10.1007/s40098-013-0060-8Perkins et al.[20]developed numerical models and test methods to determine input parameters for geogrid rein-forcement and its interaction with the aggregate and sub-grade materials.Their test methods included tensile tests to determine direction-dependent,non-linear elastic constants for the reinforcement,and cyclic pullout tests to determine stress-dependent values for the resilient shear modulus of the geogrid-aggregate interface.Perkins et al.[20]carried out wide-width tensile tests according to ASTM D4595[2] with a cyclic loading protocol on three geosynthetic rein-forcement products.They studied the influences of the geogrids elastic tensile modulus,equivalent isotropic modulus and Poisson’s ratio on the elastic response of reinforced pavement models.They also carried out cyclic pullout tests on selected geogrids in an asphalt concrete mixture aggregate which showed that the interface shear modulus was dependent on the magnitudes of normal and shear stresses at the interface.Chehab et al.[3]studied the effects of aperture size, tensile strength at2%strain,ultimate tensile strength, junction strength andflexural rigidity of geogrids on rutting performance of small-scale roadway models.They per-formed accelerated pavement tests(APTs)in a2.2m-wide by3.7m-long test pit.The pit was originally4.3m deep but was backfilled with a Type-2A aggregate base con-forming to the PennDOT specifications.The densely-compacted aggregate layer served as a bedrock-like sup-port.The top400mm was considered as the pavement section.A silty-sandy soil typical of central Pennsylvania was used as the subgrade,and Type-2A aggregate according to PennDOT specifications was used as the base layer in their model.An asphalt slab was constructed on the top of the base layer.Chehab et al.[3]proposed a series of correlations between the geogrid index properties and the rutting performance of their reinforced models.They concluded that adequate ultimate junction strength is essential for the geogrid to develop high pullout resistance. Overall,good correlations were found between the geogr-ids rib and junction strength properties and their interface shear and pullout performance.Christopher et al.[4]suggested that rib strength at2% strain is a suitable serviceability design value for geogrids in base reinforcement applications.They proposed that junction strength at2%strain should therefore be used as an appropriate value to achieve a consistent design.Tang et al.[22]examined the correlations between index properties such as the aperture size,wide-width tensile strength and junction strength of four geogrid products and their bench-scale interface test and pullout test results.They found that junction and tensile strength properties of geogrids at small strains showed strong cor-relations with their in-aggregate performance.They observed that the pullout coefficients of interaction of the geogrids tested increased with their junction strength and rib tensile strength at2%strain.Cuelho and Perkins[5]constructedfield test sections to evaluate the performance of several geosynthetics for sub-grade stabilization applications.A sandy clay soil was pre-pared as a weak roadbed material at a CBR value of approximately1.8,and a200mm thick aggregate layer was compacted over the geosynthetic reinforcement.They examined the effects of the tensile strength at2%strain,5% strain and the ultimate tensile strength on the rutting per-formance of geogrid-reinforced roadway test sections. Cuelho and Perkins[5]acknowledged that a number of geosynthetic properties may be working together to stabilize a subgrade.However,they attributed a major portion of the stabilization benefit to the geosynthetics ability to support loads in a direction transverse to the applied load,i.e.their cross-machine direction(XD).They made a direct compar-ison between the rib tensile strength in the XD direction at2 and5%strain and the number of traffic passes to produce75 and100mm of rut depth in theirfield-scale model.Cuelho and Perkins[5]concluded that increasing the geogrid2%-strain and(to a lesser extent)5%-strain tensile strength values in the XD direction could reduce the amount of rutting and hence improve the performance of the pavement.Kwon and Tutumluer[15]developed a mechanistic model for the analysis of geogrid-reinforcedflexible pavements based on thefinite element method(FEM). They modeled a stiffer layer near the geogrid reinforce-ment due to aggregate interlock resulting from compaction-induced residual stresses as the initial condition in their FEM analysis.They carried out dynamic cone penetration (DCP)tests on geogrid-reinforced base pavement sections in California and observed increased strength and stiffness properties in the base course.They also simulated several pullout tests using the discrete element method(DEM) which indicated that a stiffened zone within10–15cm above and below the geogrid retained higher contact forces after unloading following aggregate compaction.The above studies have revealed the significance of geo-grid mechanical properties on their in-aggregate perfor-mance.However,the influence of individual index properties of geogrids on their in-aggregate performance is still not well understood and requires further study.Cur-rently,there is a lack of:(1)a universally accepted design methodology that would incorporate in-isolation material properties of geogrids for base aggregate reinforcement and subgrade stabilization applications,and(2)agreement as to which geogrid properties are most relevant to their in-aggregate performance in order to develop consistent materials specifications for departments of transportation and similar agencies in charge of construction and mainte-nance of roads and highways.This is particularly important as new geogrids and manufacturing processes are introducedin the market on a continuous basis.Realizing the need for further research in this area,the authors have carried out a series of in-isolation and large-scale in-aggregate(i.e.pull-out and cyclic plate load)tests on selected geogrid products as part of a long-term study.The results of the in-isolation and pullout tests are presented and discussed in this paper.In this study,mechanical tests carried out on geogrids in the absence of other materials such as soils and aggregates are referred to in-isolation tests(e.g.rib and junction strength tests).In contrast,the tests carried out on the geogrids when placed in aggregate and subjected to factors such as over-burden pressure that simulatefield conditions are called in-aggregate tests(e.g.plate load and pullout tests).The primary objective of this study was to investigate the influence of selected in-isolation properties of geogrids on their pullout performance.The focus of the study was on the rib and junction strength properties of geogrids.More specifically,the ultimate junction strength,ultimate rib strength and small-strain rib strength values(i.e.those at 2%strain and5%strain)were investigated in machine direction(MD)and XD directions.The geogrids investi-gated in the study were classified in two basic categories of extruded(EGG)and non-extruded(NEGG)geogrids.The latter category primarily included the woven(WGG)and knitted(KGG)geogrid products.MaterialsGeogridsA comprehensive survey was carried out on commercially available geogrids and those(or equivalent properties)recommended by the departments of transportation across the United States.Following an analysis of geogrid prop-erties from this survey eight geogrid products were selected for a more detailed study(Table1).The geogrids investi-gated were classified into EGG and NEGG categories.All geogrid products,with the exception of the EGG2geogrid, were tested in their as-supplied condition.The EGG2ge-ogrids are supplied by the manufacturer in the form of two layers that are stitched together using polyester ties in an offset arrangement.In practice,EGG2is used as a double-layer geogrid.However,the mechanical properties of this product are determined for single-layer samples as rec-ommended by the manufacturer company.Also,in order to widen the range of material properties in our parametric study,the EGG2geogrid was separated and tested as a single layer.Therefore,the EB2results reported in this study are for single-layer geogrid specimens. AggregateA series of LA abrasion tests were carried out on the ODOT Type-A aggregate as per the ASTM C131-06test standard to determine its durability.This test has been widely used as an indicator of the relative quality of vari-ous sources of aggregate having similar mineral composi-tions.It is also used to measure the degradation of aggregate minerals due to loading over a project service life.The average loss for the aggregate was found to be 20.5%,which is less than the50%maximum acceptable loss for base aggregates according to ODOT guidelines [18].Optimum moisture content values for the upper(UL) and lower limit(LL)gradations of ODOT Type-A are6.2Table1General information on geogrid products used in this studyGeogrid name Designation inthis study FabricationcategoryManufacturer Aperture size(mm)PolymerMD XDBX1200EGG1EGG Tensar2533PPEB2(single layer)a EGG2Maccaferri4250TX140EGG3b Tensar40c40dTX160EGG4b Tensar40c40dBXG11WGG1NEGG TenCate-Mirafi25.425.4PET;PVC coatingBXG12WGG2TenCate-Mirafi25.425.4SF11WGG3Synteen2525SG150KGG1Strata25.424.1PET;a proprietary UV stabilized coatingBX biaxial,TX triaxial,PP polypropylene,PET polyester,PVC polyvinyl chloride,UV ultra violeta EB2geogrid was separated as a single layer in order to widen the range of the parametric study.However,it was originally supplied by the manufacturer as a double-layer productb Triangular aperture geometryc Longitudinal ribd Diagonal riband 5.0%,respectively.The corresponding values of maximum dry unit weight for the UL and LL gradations are 22.9and 22.6kN/m 3,respectively [9].The gradation of the aggregate is shown in Fig.1.Junction Strength TestsJunction strength tests were performed in both MD and XD following the GRI-GG2guidelines [7].A minimum of five replicate samples of each product were prepared and tested.In these tests,a junction clamp firmly gripped the trans-verse ribs on each side of the junction and the specimen was subjected to a monotonic tensile load until the junction failed.Junctions were marked and a non-contact digitalFig.2Clamping systems used for rib strength tests a extruded geogrids,b non-extruded geogridsFig.3The pullout test system used in this studyFig.4Geogrid specimens prepared for pullout tests a Biaxial,b Triaxial Fig.5Junction strength testresults of geogrids used in thisstudyimagery technique[12,13,24]was used to measure junction deformations and the strain in EGG geogrids.Due to the manufacturing technique and comparatively low junction strength of the NEGG geogrids,their strain mag-nitudes were too low to yield meaningful data.Therefore,it was decided to measure and report only the ultimate junction strength of the NEGG products.Rib Strength TestsRib tensile strength tests were carried out according to the ASTM D6637[2]standard.The rib deformation was tracked using the same digital imagery system used in junction tests. The EGG ribs were tested using a clamping system made of 102mm9102mm96mm steel plates that werelined Fig.5continuedwith two layers of sandpapers on the inside (Fig.2a).However,the same setup was found to be unsuited to test NEGG geogrids because the polyester yarns were pulled out of the PVC coating leaving a piece of the coating in the clamp.Therefore,a different clamping technique (involving Capstan-type roller clamps)was used to test the NEGG products (Fig.2b).Pullout TestsGeogrids used in aggregate base reinforcement applica-tions can be subjected to significant compaction-induced stresses during the construction stage.Pullout tests can provide a methodic means to study geogrid-aggregate interactions at different stress levels undercontrolledFig.6Rib tensile strength test results for the geogrids examined in this studyconditions.In addition,pullout tests can help to isolate the tensile performance of geogrids in the anchorage zone outside the pressure bulb of the tire from its out-of-plane membrane behavior when the geogrid is subjected to the vertical load of traffic[12].Pullout tests were carried out in MD in ODOT Type-A aggregate as per the ASTM D6706test protocol[1,16,17].A picture of the pullout test equipment used in this study is shown in Fig.3.The tests were carried out at95%of the aggregate maximum dry unit weight subjected to3.3,6.6 and11.5kPa overburden pressures.These overburden pressures on the geogrid-aggregate interface were primar-ily due to the weight of a compacted aggregate layer with different heights on the top of the geogrid in thepullout Fig.6continuedbox.These pressure levels resemble field conditions (out-side the tire pressure bulb)where pullout (as opposed to geogrid rupture)would be the likely failure mechanism.Pullout tests on biaxial and triaxial geogrid specimens (Fig.4)were carried out in the MD.However,due to the distinctive geometry of triaxial products (i.e.EGG3and EGG4),the MD geogrid ribs are actually at 30°angles diagonally from the MD on both sides (Fig.4b).In-Isolation Testing Results of Selected Geogrids The MD and XD junction strength test results for all eight geogrids tested in this study are summarized in Fig.5.Results are shown for three nominally identical specimens for each geogrid in each direction.The horizontal line in Fig.5indicates the minimum required ultimate junction strength (111°N)as per the FHWA recommendations [6,7,14]based on earlier construction survivability studies.Results shown in Fig.5indicate that the ultimate junction strength values of EGG geogrids are significantly greater than those of the NEGG geogrids in both MD and XD.Figure 6shows a summary of rib strength test results in MD and XD.The in-isolation properties of geogrids tested in this study are presented in Table 2.Figure 7shows a classification of the geogrid products used in this study with respect to their rib and junction strength values [11].It should be noted that the pullout tests in this study were meant to isolate the geogrid junction strength in one direction to examine its influence on the pullout capacity of the reinforcement in that same direction.For this purpose,the geogrids are classified according to their rib and junc-tion strength values in MD.Pullout Response of Selected GeogridsAccording to ASTM D6706,the maximum pullout resis-tance measured during the test should be reported toindicate the pullout resistance of a geosynthetic rein-forcement material.However,obtaining consistent pullout test data and getting a well-defined peak for geogrids in aggregates is challenging due to significant interlocking that develops between these materials.In the pullout test data presented in this paper,the ultimate pullout resistance,P r ,for each test case had to be determined by inspection.In several cases,this value was determined as the first peak in the pullout response curve that preceded a plateau,fol-lowed by subsequent peaks or a monotonic increase in the pullout load.These strain-hardening features at larger displacements were attributed to the likely influence of the front boundary condition and were therefore dismissed.This was done even though the test box included a pair of 200mm-long sleeves and geofoam blocks on the inside of its front wall to minimize the influence of an otherwise rigid front boundary on the test results.The magnitude ofTable 2Properties of geogrid products tested in this study Geogrid typeRib strength (kN/m)Ultimate junction strength (N)At 2%strain At 5%strain Ultimate MDXD MD XD MD XD MD XD EGG113.022.022.034.026.038.0601671EGG2(single layer value) 2.6 2.5 5.4 4.9 6.89.7363418EGG3 5.3 6.511.512.815.016.0212207EGG4 5.88.111.814.018.015.5253293WGG18.99.717.721.964.032.115489WGG212.08.727.028.836.439.8125105WGG39.211.715.715.944.059.67349KGG16.75.59.07.631.728.36130Fig.7Classification of geogrid products used in this studyFig.8Comparison of pullout responses of geogrids at different confining pressuresthe peak pullout resistance,P r ,in Fig.8through 14is presented in terms of the load per unit reinforcement width.Figure 8compares pullout response results of all eight geogrid products (i.e.four EGG and four NEGG products)tested in ODOT Type-A aggregate.It is observed that peak pullout resistances of the EGG1geogrid for the range of overburden pressure values tested are reached at front displacements between 20and 35mm as shown in the figure using solid markers.The front displacement reported for each test is a calculated value for the point on the geogrid where it leaves the aggregate at the front of the test box toward the actuator.This displacement value was calculated using the measured data from the front wireline potentiometer (WP1)and the actuator displacement,taking into account the extension of a short in-air portion of the geogrid specimen linking the actuator roller clamp to the in-aggregate portion of the specimen.Results in Fig.8indicate that with the exception of EGG1,EGG geogrids reached their peak pullout resistance at significantly lower displacements (i.e.3–8mm)as compared to the NEGG geogrids (17–38mm).It should be noted that in two test cases (i.e.EGG3subjected to 4.95kPa overburden pressure and EGG4subjected to 6.6kPa overburden pressure),the peak value of the pullout force recorded was due to premature rupture of the geogrid inside the aggregate.The pullout response data for all geogrids in Figs.8and 9overall show reasonable trends with respect to the overburden pressure in that a greater overburden pressure resulted in a greater pullout resistance.Furthermore,inspection of geogrid properties given in Table 2and the results shown in Figs.8and 9indicate that geogrids with greater rib and junction strength values usually developed greater values of pullout resistance.However,it should be noted that EGG3and EGG4are ‘triaxial’type geogrids with triangular apertures which are different from the biaxial-type,EGG1and EGG2geogrids.Therefore,pullout behavior of these two groups of geogrids is expected to be different,especially at higher overburden pressures.Due to their triangular aperture geometry,the load distribution in the ribs and junctions in EGG3and EGG4are different (and more complex)than that in the EGG1and EGG2specimens.Post-test excavations of these pullout specimens revealed that the geogrids with com-paratively low rib strength but strong junction (i.e.EGG2,EGG3and EGG4—see Table 2)experienced more bending and breaking of their ribs than stretching as compared to the performance of geogrid products with stronger ribs.As a result,geogrid rupture was the failure mode for EGG2,EGG3and EGG4at higher overburden pressureswhereasFig.9Peak pullout resistance of geogrids tested in this study as a function of overburden pressureTable 3Statistical data for the results shown in Fig.9Geogrid Linear regression equationR 2-value Slope (m)CommentEGG1P r =0.82r n ?8.660.840.82EGG2P r =0.76r n ?3.160.790.76EGG3P r =0.98r n ?5.07 1.000.98EGG4P r =2.47r n -1.990.96 2.47Largest gradient WGG1P r =0.96r n -4.110.960.96WGG2P r =0.54r n -4.74 1.000.54WGG3P r =0.74r n -3.760.860.74KGG1P r =0.42r n -2.070.990.42Smallest gradientpullout was the dominant failure mode for the other products.Therefore,the pullout responses of EGG2,EGG3and EGG4geogrids shown in Fig.8at higher overburden pressures are ‘‘brittle’’.It is therefore concluded that brittle behavior (i.e.sudden failure)would be expected from ge-ogrids which fall in (or border)the ‘weak rib category’according to the classification table given in Fig.7.Finally,it should be noted that regardless of the failure mode observed in each test case reported in this study,the lesser of the geogrid rupture or the pullout load was used as the pullout resistance of the geogrid specimen according to the FHWA guidelines (2009).Results in Fig.9indicate that the EGG1geogrid with the largest 2%-strain rib strength and junction strength values resulted in the largest pullout resistance among all geogrids tested.The triaxial geogrid (EGG4)with com-paratively large ultimate junction strength values resulted in a significant pullout resistance and showed the largest increase in its pullout resistance with overburden pressure among all the geogrids examined.These results confirm that the combined influence of large junction strength and low-strain rib strength results in effective confinement and interlocking in the aggregate (e.g.[15]).The measured value of EGG4pullout resistance at 3.3kPa overburden pressure in Fig.9is believed to underestimate its expected value.This is because the EGG4rib and junction strength values are greater than those for EGG3(Table 2)but the EGG4P r value at 3.3kPa is lower than that for EGG3.Another indication is that this low P r value has resulted in a negative offset value for the EGG4regression line in Table 2.However,even if the data point for the EGG4at 3.3kPa is adjusted upward with respect to the results for EGG3,the trend of pullout resistance data for EGG4still indicates a more significant dependence on the overburden pressure when compared to other geogrids shown in the figure.This observation and the compara-tively strong pullout performance of EGG3,considering that the rib strength values of EGG3and EGG4are among the lowest in Table 2,suggest that geogrids with a trian-gular aperture geometry could be more effective than those with conventional rectangular apertures to confine and interlock with the aggregatetested.Fig.10Correlations between pullout force and rib tensile strengths in MD at a 2%strain,b 5%stain and c Ultimate rib strengths and d Ultimate junction strengths of geogrids examined in this study (EGG:represented by solid markers,NEGG:represented by hollow markers)Comparing the rib strength properties and pullout per-formances of the biaxial EGG1and triaxial EGG4geogrids (Fig.9)also indicates that the triangular aperture config-uration could be more effective than a rectangular shape in providing interlocking and confinement.This is because significantly lower rib and junction strength properties of the EGG4geogrid as compared to those of EGG1did not result in proportionally smaller EGG4pullout strength. However,it should be noted that both EGG3and EGG4 specimens were found to have been significantly ripped or otherwise damaged when tested at higher overburden pressure of 6.6kPa.Even though the ultimate pullout strength is not likely to be mobilized infield applications, these observations indicate that strengthening the ribs of triaxial geogrids could further enhance theirfield performance.A comparison of the pullout test results for EGG1and EGG2specimens reveals the significance of low-strain rib strength in in-aggregate performance of geogrids.Even though the junction strength values of EGG2geogrids are the second largest among all geogrids listed in Table2,their pullout resistance was among the lowest due to their low rib strength.On the other hand,KGG1and WGG3 geogrids with rib strength values comparable or larger than those of EGG3and EGG4showed the weakest pullout characteristics due to their low junction strength. In fact,the junction strength values of these geogrids did not meet the minimum required value of111°N according to the FHWA guidelines(2009).Basic statistical infor-mation related to the results shown in Fig.9is given in Table3.Figure10shows the correlations between the measured pullout resistance and index strength properties in the MD for the geogrids tested.Results shown in Fig.10a,b indi-cate that the in-aggregate performances of the geogrids examined show a reasonable correlation with their rib strength at2and5%strain within the range of overburden pressures examined(i.e. 3.3–11.5kPa).However,rib strength at2%-strain appears to be more influential than rib strength at5%-strain and ultimate rib strength because the slopes of the corresponding regression lines are the greatest(1.09for11.5kPa,0.41for6.6kPa and0.43for Fig.11Correlation between pullout force and rib tensile strengths in XD at a2%strain,b5%stain and c Ultimate rib strengths and d Ultimate junction strengths of geogrids examined in this study(EGG:represented by solid markers,NEGG:represented by hollow markers)。
