英文文献+翻译
Characterization of production of Paclitaxel and related Taxanes in Taxus Cuspidata Densiformis suspension cultures by LC,
LC/MS, and LC/MS/MS
CHAPTER THERE
PLANT TISSUE CULTURE
Ⅰ. Potential of Plant cell Culture for Taxane Production
Several alternative sources of paclitaxel have been identified and are currently the subjects of considerable investigation worldwide. These include the total synthesis and biosynthesis of paclitaxel, the agriculture supply of taxoids from needles of Taxus species, hemisynthesis (the attachment of a side chain to biogenetic precursors of paclitaxel such as baccatin Ⅲ or 10-deacetylbaccatin Ⅲ), fungus production, and the production of taxoids by cell and tissue culture. This reciew will concentrate only on the latter possibility.
Plant tissue culture is one approach under investigation to provide large amounts and a stable supply of this compound exhibiting antineoplastic activity. A process to produce paclitaxel or paclitaxel-like compounds in cell culture has already been parented. The development of fast growing cell lines capable of producing paclitaxel would not only solve the limitations in paclitaxel supplies presently needed for clinical use, but would also help conserve the large number of trees that need to be harvested in order to isolate it. Currently, scientists and researchers have been successful in initiating fast plant growth but with limited paclitaxel production or vice versa. Therefore, it is the objective of researchers to find a method that will promote fast plant growth and also produce a large amount of paclitaxel at the same time.
Ⅱ. Factors Influencing Growth Paclitaxel Content
A.Choice of Media for Growth
Gamborg's (B5) and Murashige & Skoog's (MS) media seem to be superior for callus growth compared to White's (WP) medium. The major difference between these two media is that the MS medium contains 40 mM nitrate and 20mM ammonium, compared to 25mM nitrate and 2mM ammonium. Many researchers have selected the B5 medium over the MS medium for all subsequent studies, although they achieve similar results.
Gamborg's B5 media was used throughout our experiments for initiation of callus cultures and suspension cultures due to successful published results. It was supplemented with 2% sucrose, 2 g/L casein hydrolysate, 2.4 mg/L picloram, and 1.8 mg/L α-naphthalene acetic acid. Agar (8 g/L) was used for solid cultures.
B. Initiation of Callus Cultures
Previous work indicated that bark explants seem to be the most useful for establishing callus. The age of the tree did not appear to affect the ability to initiate callus when comparing both young and old tree materials grown on Gamborg's B5 medium supplemented with 1-2 mg/L of 2,4-dichlorophenoxyacetic acid. Callus cultures initiated and maintained in total darkness were generally pale-yellow to light brown in color. This resulted in sufficient masses of friable callus necessary for subculture within 3-4 weeks. However, the growth rate can decline substantially following the initial subculture and result in very slow-growing, brown-colored clumps of callus. It has been presumed that these brown-colored exudates are phenolic in nature and can eventually lead to cell death. This common phenomenon is totally random and unpredictable. Once this phenomenon has been triggered, the cells could not be saved by placing them in fresh media. However, adding polyvinylpyrrolidone to the culture media can help keep the cells alive and growing. Our experience with callus initiation
was similar to those studies.
Our studies have found that callus which initiated early (usually within 2 weeks ) frequently did not proliferate when subcultured and turned brown and necrotic. In contrast, calli which developed from 4 weeks to 4 months after explants were fist placed on initiation media were able to be continuously subcultured when transferred at 1-2 month intervals. The presence of the survival of callus after subsequent subculturing. The relationship between paclitaxel concentration and callus initiation, however, has not been clarified.
C. Effect of Sugar
Sucrose is the preferred carbon source for growth in plant cell cultures, although the presence of more rapidly metabolized sugar such as glucose favors fast growth. Other sugars such as lactose, galactose, glucose, and fructose also support cell growth to some extent. On the other hand, sugar alcohols such as mannitol and sorbital which are generally used to raise the sugars added play a major role in the production of paclitaxel. In general, raising the initial sugar levels lead to an increase of secondary metabolite production. High initial levels of sugar increase the osmotic potential, although the role of osmotic pressure on the synthesis of secondary metabolites is not cleat. Kim and colleagues have shown that the highest level of paclitaxel was obtained with fructosel. The optimum concentration of each sugar for paclitaxel production was found to be the same at 6% in all cases. Wickremesinhe and Arteca have provided additional support that fructose is the most effective for paclitaxel production. However, other combinations of sugars such as sucrose combined with glucose also increased paclitaxel production.
The presence of extracellular invertase activity and rapid extracellular sucrose hydrolysis has been observed in many cell cultures. These reports suggest that cells secrete or possess on their surface excess amounts of invertase, which result in the hydrolysis of sucrose at a much faster rate. The hydrolysis of sucrose coupled with the rapid utilization of fructose in the medium during the latter period of cell growth. This period of increased fructose availability coincided with the faster growth phase of the cells.
D. Effect of Picloram and Methyl Jasmonate
Picloram (4-amino-3.5.6-trichloropicolinic acid) increases growth rate while methyl jasmonate has been reported to be an effective elicitor in the production of paclitaxel and other taxanes. However, little is known about the mechanisms or pathways that stimulate these secondary metabolites.
Picloram had been used by Furmanowa and co-workers and Ketchum and Gibson but no details on the effect of picloram on growth rates were given. Furmanowa and hid colleagues observed growth of callus both in the presence and absence of light. The callus grew best in the dark showing a 9.3 fold increase, whereas there was only a 2-4 fold increase in the presence of light. Without picloram, callus growth was 0.9 fold. Unfortunately,this auxin had no effect on taxane production and the high callus growth rate was very unstable.
Jasmonates exhibit various morphological and physiological activities when applied exogenously to plants. They induce transcriptional activation of genes involved in the formation of secondary metabolites. Methyl jasmonate was shown to stimulate paclitaxel and cephalomannine (taxane derivative) production in callus and suspension cultures. However, taxane production was best with White's medium compared to Gamborg's B5 medium. This may be due to the reduced concentration of potassium nitrate and a lack of ammonium sulfate with White's medium.
E. Effect of Copper Sulfate and Mercuric Chloride
Metal ions have shown to play significant roles in altering the expression of secondary metabolic pathways in plant cell culture. Secondary metabolites,such as furano-terpenes, have been production by treatment of sweet potato root tissue with mercuric chloride. The results for copper sulfate, however, have not been reported. F. Growth Kinetics and Paclitaxel Production
Low yields of paclitaxel may be attributed to the kinetics of taxane production that is not fully understood. Many reports stated inconclusive results on the kinetics of taxane production. More studies are needed in order to quantitate the taxane production. According to Nett-Fetto, the maximum instantaneous rate of paclitaxel production occurred at the third week upon further incubation. The paclitaxel level either declined or was not expected to increase upon further incubation. Paclitaxel production was very sensitive to slight variations in culture conditions. Due to this sensitivity, cell maintenance conditions, especially initial cell density, length of subculture interval, and temperature must be maintained as possible.
Recently, Byun and co-workers have made a very detailed study on the kinetics of cell growth and taxane production. In their investigation, it was observed that the highest cell weight occurred at day 7 after inoculation. Similarly, the maximum concentration for 10-deacetyl baccatin Ⅲ and baccatin Ⅲ were detected at days 5 and 7, respectively. This result indicated that they are metabolic intermediates of paclitaxel. However, paclitaxel's maximum concentration was detected at day 22 but gradually declined. Byun and his colleagues suggested that paxlitaxel could be a metabolic intermediate like 10-deacetyl baccatin Ⅲ and baccatin Ⅲ or that pacliltaxel could be decomposed due to cellular morphological changes or DNA degradation characteristic of cell death.
Pedtchanker's group also studied the kinetics of paclitaxel production by comparing the suspension cultures in shake flasks and Wilson-type reactors where bubbled air provided agitation and mixing. It was concluded that these cultures of Taxus cuspidata produced high levels of paclitaxel within three weeks (1.1 mg/L per day ). It was also determined that both cultures of the shake flask and Wilson-type reactor produced similar paclitaxel content. However, the Wilson-type reactor had a more rapid uptake of the nutrients (i.e. sugars, phosphate, calcium, and nitrate). This was probably due to the presence of the growth ring in the Wilson reactor. Therefor, the growth rate for the cultures from the Wilson reactor was only 135 mg./L while the shake flasks grew to 310 mg/L in three weeks.
In retrospect, strictly controlled culture conditions are essential to consistent production and yield. Slight alterations in media formulations can have significant effects upon the physiology of cells, thereby affecting growth and product formation. All of the manipulations that affect growth and production of plant cells must be carefully integrated and controlled in order to maintain cell viability and stability.
利用LC,LC/MS和LC/MS/MS悬浮培养生产紫杉醇及邓西佛米斯红
豆杉中相关紫杉醇类的特征描述
第三章
植物组织培养
Ⅰ.利用植物细胞培养生产紫杉的可能性
紫杉醇的几个备选的来源已被确定，而且目前是全球大量调查的主题。这些来源包括人工合成紫杉醇，农业提供针头红豆杉紫杉，半合成体（紫杉醇生物前体的一条侧链的附属物，例如浆果赤霉素Ⅲ或10-去乙酰浆果赤霉素Ⅲ），
真菌生产，以及通过细胞和组织培养生产紫杉。这次审查将只集中在后者的可能性上。
植物组织培养是调查中用以提供大量稳定数量的这种具有抗肿瘤活性化合物的一种方法。用细胞培养生产紫杉醇或者紫杉醇样化合物的方法已获得专利。能够生产紫杉醇的的快速增长的细胞系的发展不仅能解决现在在临床应用上紫杉醇供应受限的问题，而且将有助于保护大量为了使之隔离需要收获的树。然而，植物组织培养技术生产紫杉醇的速度不能满足需求。目前，科学家和研究员已成功地启用了植物快速生长的方法，但这种方法紫杉醇的生产有限，反之亦然。因此，研究者的目标是找到一种能促进植物快速生长同时也能生产大量紫杉醇的方法。
Ⅱ影响植物生长和紫杉醇含量的因素
A 生长培养基的选择
B5和MS培养基与WP培养基相比似乎更有利于愈伤组织生长。这两种培养基的主要区别在于MS培养基包含40mM硝酸盐和20mM铵，B5培养基中包含25mM硝酸盐和2mM铵。相比之下，WP培养基包含10mM硝酸盐和5mM 铵.一些研究者在所有随后的研究中选择B5培养基的数量超过MS培养基，尽管他们获得的结果相似。
由于成功的公布的结果，B5培养基在开始愈伤组织培养和悬浮培养的整个实验中使用。它增补了2℅的蔗糖，2g/L干酪素水解物，2.4mg/L毒莠定和1.8mg/L 萘乙酸。琼脂（8g/L）用于固体培养。
B.愈伤组织培养的开始
以往的工作表明树皮外植体似乎是对建立愈伤组织最有用的。当我们比较生长在补充了1-2mg/L 2，4-二氯苯氧乙酸的B5培养基中年轻的和老的树材料时，我们发现树龄并不影响创造愈伤组织的能力。完全在黑暗中培养的愈伤组织一般都是淡黄色至浅棕色。这充分保证了在3-4周内次培养所需要的易碎愈伤组织。然而，随着次培养的开始，愈伤组织的生长速度会大幅度下降并且会导致愈伤组织生长缓慢并成棕色团块。据推测，这些棕色的渗出物是酚醛树脂性质，最终能导致细胞死亡。这个普遍的现象完全是随机的，不可预测的。一旦这个现象被触发，把细胞被转移到新的培养基也无法挽救。然而，通过给培养基添加聚乙烯吡咯烷酮有助于保持细胞活力和生长。我们在愈伤组织培养上的经历与那些研究相似。
我们的研究发现那些早期（通常在2个星期内）开始培养的愈伤组织在次培养时不会增生，会变成棕色并且坏死。相比之下，在外植体第一次被放置到培养基上后培养4个星期到4个月的愈伤组织能够继续进行次培养，如果每间隔1-2个月进行转移的的话。外植体中紫杉醇的存在似乎不会影响次培养后愈伤组织的存活比例。紫杉醇浓度与愈伤组织培养之间的关系还不是很清楚。
C.糖的作用
蔗糖是植物细胞培养中植物生长首选的碳源，尽管像葡萄糖这种代谢更加迅速的糖的存在利于快速增长。其他的糖，例如乳糖，半乳糖，果糖也能在一定程度上促进细胞生长。另一方面，糖醇，比如甘露醇和山梨(糖)醇，一般用于提高
培养基的渗透力，一点也不能促进生长。所添加的糖的浓度对紫杉醇的生产发挥重要作用。一般来说，提高初始糖的浓度会导致次生代谢产物的生产增加。高浓度的糖会增加培养基的渗透能力，尽管渗透力对次生代谢的作用还不清楚。基姆以及他的同事证明最高级别的紫杉醇获得果糖。生产紫杉醇的每种糖的最高浓度在所有情况下都是6﹪。Wickremesinhe和Arteca提供了额外的证明支持果糖对紫杉醇生产的作用最大。然而，糖的其他结合，如蔗糖与葡萄糖的结合也能增加紫杉醇生产。
细胞转化和快速的外蔗糖水解的存在已在许多细胞培养中观察到。这些报告表明细胞表面的细胞分泌物超过转化量会使蔗糖水解的速度更快。在细胞早期生长阶段蔗糖的水解加上葡萄糖的快速利用增进了细胞后期生长过程中培养基中果糖的可利用性。增加果糖利用的这个时期与细胞的快速生长阶段一致。
D. 毒莠定和茉莉酸甲酯的作用
毒莠定能提高生长速度，而据报道茉莉酸甲酯在紫杉醇和其他紫杉烷的生产中是一种有效的刺激素。然而，我们对它刺激这些次生代谢产物的机制或途径知之甚少。
毒莠定被Furmanowa 及其同事，Ketchum 以及Gibson所使用，但他们没有给出毒莠定对生长速度的影响的细节。Furmanowa 及其同事在有光和无光的条件下观察了愈伤组织的生长。在黑暗中生长状况最佳的愈伤组织显示了9.3倍的增长，而在有光的条件下仅增长了2-4倍。在不加毒莠定的条件下，愈伤组织增长0.9倍。不幸的是，这种生长素对紫杉烷的生产没有影响，并且愈伤组织快速增长速度很不稳定。
当给植物运用外部刺激时，茉莉呈现出不同的形态和生理活动。他们诱导参与形成次生代谢产物的基因的转录激活。茉莉酸甲酯被证明能促进愈伤组织和悬浮培养中紫杉醇和西双版纳粗榧碱的生产。然而，与B5培养基相比，紫杉烷生产选择用WP培养基是最好的。这可能是由于WP培养基硝酸钾的浓度低以及缺少硫酸盐的缘故。
E. 硫酸铜和氯化亚汞的作用
在植物细胞培养中，金属离子被证明对改变次生代谢产物的运输途径有很大的影响。次生代谢产物，如萜烯类物质，由含有氯化亚汞的甘薯根组织产生。然而硫酸铜的影响尚未报导出来。
F.生长动力学和紫杉醇生产
紫杉醇的低产量可能归因于尚未被完全了解的紫杉烷生产动力学。一些报导陈述了紫杉烷生产动力学的不确定的结果。为了测定紫杉烷生产的数量，我们需要进行更多的研究。据Nett-Fetto所说，紫杉醇生产的最大瞬时速率发生在细胞繁殖的第三个星期。紫杉醇产量不是下降就是没期望进一步培育增长。紫杉醇生产对培养基条件的轻微变化都很敏感。由于这种敏感性，细胞维持的条件，尤其是起始的细胞密度，次培养的间隔时间长度和温度必须尽可能保持准确。
最近，Byun及其同事针对细胞生长动力学和紫杉烷生产进行了一次很详细的研究。在他们的调查中，据观察细胞最重的时候是繁殖后的第七天。类似的，10-双乙酰浆果赤霉素Ⅲ和浆果赤霉素Ⅲ浓度最高的时候据检测分别是在第5天和第7天。这个结果表明他们是紫杉醇的代谢中间体。然而，紫杉醇的最高浓度据检测是在第22天但会逐渐减少。Byun及其同事表明紫杉醇可能是像10-双乙
酰浆果赤霉素Ⅲ和浆果赤霉素这样的代谢中间体，或者是由于细胞形态的变化或细胞死亡的DNA降解特性使紫杉醇进行了分解。
Pestchanker的团队通过比较在摇瓶中的悬浮培养和对空气进行搅拌和混合的威尔逊型反应堆中的悬浮培养对紫杉醇生产动力学进行了研究。这个研究得出的结论是这些东北红豆杉的培养能在3周内产生大量紫杉醇（每天1.1mg/L）。它也表明摇瓶悬浮培养和威尔逊型反应堆悬浮培养都能生产同样的紫杉醇量。然而，威尔逊型反应堆悬浮培养能更快地吸收营养（例如糖，磷酸盐，钙和硝酸盐）。这很可能是由于威尔逊型反应堆中生长环的存在。因此，通过威尔逊型反应堆悬浮培养的生长速度只有135 mg/L，而摇瓶悬浮培养在3周内增长到了310 mg/L。
检讨过去，我们知道严格控制培养条件对紫杉醇的连续生产是必要的。培养基成分的轻微改变就会对细胞的生理状况产生重大影响，从而影响产品的增长和形成。为了保持细胞活力和稳定性，所有影响植物细胞生长和生产的操作必须谨慎地加以综合控制。
英文文献翻译
外文文献原稿和译文 原稿 Sodium Polyacrylate: Also known as super-absorbent or “SAP”(super absorbent polymer), Kimberly Clark used to call it SAM (super absorbent material). It is typically used in fine granular form (like table salt). It helps improve capacity for better retention in a disposable diaper, allowing the product to be thinner with improved performance and less usage of pine fluff pulp. The molecular structure of the polyacrylate has sodium carboxylate groups hanging off the main chain. When it comes in contact with water, the sodium detaches itself, leaving only carboxylions. Being negatively charged, these ions repel one another so that the polymer also has cross-links, which effectively leads to a three-dimensional structure. It has hige molecular weight of more than a million; thus, instead of getting dissolved, it solidifies into a gel. The Hydrogen in the water (H-O-H) is trapped by the acrylate due to the atomic bonds associated with the polarity forces between the atoms. Electrolytes in the liquid, such as salt minerals (urine contains 0.9% of minerals), reduce polarity, thereby affecting superabsorbent properties, especially with regard to the superabsorbent capacity for liquid retention. This is the main reason why diapers containing SAP should never be tested with plain water. Linear molecular configurations have less total capacity than non-linear molecules but, on the other hand, retention of liquid in a linear molecule is higher than in a non-linear molecule, due to improved polarity. For a list of SAP suppliers, please use this link: SAP, the superabsorbent can be designed to absorb higher amounts of liquids (with less retention) or very high retentions (but lower capacity). In addition, a surface cross linker can be added to the superabsorbent particle to help it move liquids while it is saturated. This helps avoid formation of "gel blocks", the phenomenon that describes the impossibility of moving liquids once a SAP particle gets saturated. History of Super Absorbent Polymer Chemistry
英文文献+翻译
Characterization of production of Paclitaxel and related Taxanes in Taxus Cuspidata Densiformis suspension cultures by LC, LC/MS, and LC/MS/MS CHAPTER THERE PLANT TISSUE CULTURE Ⅰ. Potential of Plant cell Culture for Taxane Production Several alternative sources of paclitaxel have been identified and are currently the subjects of considerable investigation worldwide. These include the total synthesis and biosynthesis of paclitaxel, the agriculture supply of taxoids from needles of Taxus species, hemisynthesis (the attachment of a side chain to biogenetic precursors of paclitaxel such as baccatin Ⅲ or 10-deacetylbaccatin Ⅲ), fungus production, and the production of taxoids by cell and tissue culture. This reciew will concentrate only on the latter possibility. Plant tissue culture is one approach under investigation to provide large amounts and a stable supply of this compound exhibiting antineoplastic activity. A process to produce paclitaxel or paclitaxel-like compounds in cell culture has already been parented. The development of fast growing cell lines capable of producing paclitaxel would not only solve the limitations in paclitaxel supplies presently needed for clinical use, but would also help conserve the large number of trees that need to be harvested in order to isolate it. Currently, scientists and researchers have been successful in initiating fast plant growth but with limited paclitaxel production or vice versa. Therefore, it is the objective of researchers to find a method that will promote fast plant growth and also produce a large amount of paclitaxel at the same time. Ⅱ. Factors Influencing Growth Paclitaxel Content A.Choice of Media for Growth Gamborg's (B5) and Murashige & Skoog's (MS) media seem to be superior for callus growth compared to White's (WP) medium. The major difference between these two media is that the MS medium contains 40 mM nitrate and 20mM ammonium, compared to 25mM nitrate and 2mM ammonium. Many researchers have selected the B5 medium over the MS medium for all subsequent studies, although they achieve similar results. Gamborg's B5 media was used throughout our experiments for initiation of callus cultures and suspension cultures due to successful published results. It was supplemented with 2% sucrose, 2 g/L casein hydrolysate, 2.4 mg/L picloram, and 1.8 mg/L α-naphthalene acetic acid. Agar (8 g/L) was used for solid cultures. B. Initiation of Callus Cultures Previous work indicated that bark explants seem to be the most useful for establishing callus. The age of the tree did not appear to affect the ability to initiate callus when comparing both young and old tree materials grown on Gamborg's B5 medium supplemented with 1-2 mg/L of 2,4-dichlorophenoxyacetic acid. Callus cultures initiated and maintained in total darkness were generally pale-yellow to light brown in color. This resulted in sufficient masses of friable callus necessary for subculture within 3-4 weeks. However, the growth rate can decline substantially following the initial subculture and result in very slow-growing, brown-colored clumps of callus. It has been presumed that these brown-colored exudates are phenolic in nature and can eventually lead to cell death. This common phenomenon is totally random and unpredictable. Once this phenomenon has been triggered, the cells could not be saved by placing them in fresh media. However, adding polyvinylpyrrolidone to the culture media can help keep the cells alive and growing. Our experience with callus initiation
英文文献及翻译
Geotextile reinforced by soft soil 1. Introduction Geotextile known, it has high tensile strength, durability, corrosion resistance, texture, flexibility, combined with good sand, to form reinforced composite foundation, effectively increase the shear strength , tensile properties, and enhance the integrity and continuity of soil. Strengthening mechanism for the early 60's in the 20th century, Henri Vidal on the use of triaxial tests found a small amount of fiber in the sand, the soil shear strength can improve the image of more than 4 times in recent years, China's rock Laboratory workers also proved in the reinforced sand can effectively improve the soil's bearing capacity, reduce the vertical ground settlement, effectively overcome the poor soil and continuity of overall poor performance. As with the above properties of reinforced soil and the characteristics of its low price, so the project has broad application prospects. 2.1 Project Overview The proposed retaining wall using rubble retaining wall of gravity, the wall is 6 meters high, the bearing capacity of foundation soil required to 250kPa, while the basement geology from the top down as follows: ①clay to a thickness of 0.7 to 2 meters saturated, soft plastic; ② muddy soil, about 22 - 24 meters thick, saturated, mainly plastic flow, local soft plastic; ③ sand layer to a thickness of 5 to 10 meters, containing silty soil and organic matter, saturated, slightly wet; ④ gravel layer, the thickness of the uneven distribution points, about 0 to 2.2 meters, slightly dense; ⑤ weathered sandstone. Including clay and silty soil bearing capacity is 70kPa, obviously do foundation reinforcement. 2.2 Enhanced Treatment of reinforced foundation cushion Reinforcement replacement method can be used for sand and gravel used for
英文文献翻译
Path Dependence and The Validation of Agent-based Spatial Models of Land Use DANIEL G. BROWN, SCOTT PAGE, RICK RIOLO, MOIRA ZELLNER and WILLIAM RAND In this paper, we identify two distinct notions of accuracy of land-use models and highlight a tension between them. A model can have predictive accuracy: its predicted land-use pattern can be highly correlated with the actual land-use pattern. A model can also have process accuracy: the process by which locations or land-use patterns are determined can be consistent with real world processes.To balance these two potentially conflicting motivations, we introduce the concept of the invariant region, i.e., the area where land-use type is almost certain,and thus path independent; and the variant region, i.e., the area where land use depends on a particular series of events, and is thus path dependent. We demonstrate our methods using an agent-based land-use model and using multi-temporal land-use data collected for Wash tenaw County, Michigan, USA. The results indicate that, using the methods we describe, researchers can improve their ability to communicate how well their model performs, the situations or instances in which it does not perform well, and the cases in which it is relatively unlikely to predict well because of either path dependence or stochastic un certainty. Keywords: Agent-based modeling; Land-use change; Urban sprawl; Model validation; Complex systems 1.Introduction The rise of models that represent the functioning of complex adaptive systems has led to an increased awareness of the possibility for path dependency and multiple equilibria in economic and ecological systems in general and spatial land-use systems in particular (Atkinson and Oelson 1996, Wilson 2000,Balmann 2001). Path dependence arises from negative and positive feedbacks.Negative feedbacks in the form of spatial dis-amenities rule out some patterns of development and positive feedbacks from roads and other infrastructure and from service centers reinforce existing paths (Arthur 1988, Arthur 1989). Thus, a small random component in location decisions can lead to large deviations in settlement patterns which could not result were those feedbacks not present (Atkinson and Oleson 1996). Concurrent with this awareness of the unpredictability of settlement patterns has been an increased availability of spatial data within geographic information systems (GIS). This has led to greater emphasis on the validation of spatial land-use models (Costanza 1989, Pontius 2000, 2002, Kok et al. 2001). These two scientific advances, one theoretical and one empirical, have lead to two contradictory impulses in land-use modeling: the desire for increased accuracy of prediction and the recognition of unpredictability in the process. This paper addresses the balance between these two impulses: the desire for accuracy of prediction and accuracy of process. Accuracy of prediction refers to the resemblance of model output to data about the
(完整word版)英文文献及翻译：计算机程序
姓名：刘峻霖班级：通信143班学号：2014101108 Computer Language and Programming I. Introduction Programming languages, in computer science, are the artificial languages used to write a sequence of instructions (a computer program) that can be run by a computer. Simi lar to natural languages, such as English, programming languages have a vocabulary, grammar, and syntax. However, natural languages are not suited for programming computers because they are ambiguous, meaning that their vocabulary and grammatical structure may be interpreted in multiple ways. The languages used to program computers must have simple logical structures, and the rules for their grammar, spelling, and punctuation must be precise. Programming languages vary greatly in their sophistication and in their degree of versatility. Some programming languages are written to address a particular kind of computing problem or for use on a particular model of computer system. For instance, programming languages such as FORTRAN and COBOL were written to solve certain general types of programming problems—FORTRAN for scientific applications, and COBOL for business applications. Although these languages were designed to address specific categories of computer problems, they are highly portable, meaning that the y may be used to program many types of computers. Other languages, such as machine languages, are designed to be used by one specific model of computer system, or even by one specific computer in certain research applications. The most commonly used progra mming languages are highly portable and can be used to effectively solve diverse types of computing problems. Languages like C, PASCAL and BASIC fall into this category. II. Language Types Programming languages can be classified as either low-level languages or high-level languages. Low-level programming languages, or machine languages, are the most basic type of programming languages and can be understood directly by a computer. Machine languages differ depending on the manufacturer and model of computer. High-level languages are programming languages that must first be translated into a machine language before they can be understood and processed by a computer. Examples of high-level
3000字英文参考文献及其翻译范例
3000字英文参考文献及其翻译 【注意：选用的英文一定要与自己的论文题目相关。 如果文章太长，可以节选（用省略号省略一些段略）。如果字数不够，可以选2至3篇，但要逐一注明详细出处。英文集中在一起放前面，对应的中文翻译放后面。中文翻译也要将出处翻译，除非是网页。 对文献的翻译一定要认真！对英文文献及其翻译的排版也要和论文正文一样！ 特别注意：英文文献应该放在你的参考文献中。】 TOY RECALLS——IS CHINA THE PROBLEM？ Hari. Bapuji Paul W. Beamish China exports about 20 billion toys per year and they are the second most commonly imported item by U.S. and Canada. It is estimated that about 10,000 factories in China manufacture toys for export. Considering this mutual dependence, it is important that the problems resulting in recalls are addressed carefully. Although the largest portion of recalls by Mattel involved design flaws, the CEO of Mattel blamed the Chinese manufacturers by saying that the problem resulted ‘in this case （because）one of our manufacturers did not follow the rules’. Several analysts too blamed the Chinese manufacturers. By placing blame where it did not belong, there is a danger of losing the opportunity to learn from the errors that have occurred. The first step to learn from errors is to know why and where the error occurred. Further, the most critical step in preventing the recurrence of errors is to find out what and who can prevent it. …… From:https://www.360docs.net/doc/4d19215408.html,/loadpage.aspx?Page=ShowDoc&Category Alias=zonghe/ggmflm_zh&BlockAlias=sjhwsd&filename=/doc/sjhwsd/2 00709281954.xml, Sep. 2007
英文文献及翻译(计算机专业)
英文文献及翻译(计算机专业) The increasing complexity of design resources in a net-based collaborative XXX common systems。design resources can be organized in n with design activities。A task is formed by a set of activities and resources linked by logical ns。XXX management of all design resources and activities via a Task Management System (TMS)。which is designed to break down tasks and assign resources to task nodes。This XXX。 2 Task Management System (TMS) TMS is a system designed to manage the tasks and resources involved in a design project。It poses tasks into smaller subtasks。XXX management of all design resources and activities。TMS assigns resources to task nodes。XXX。 3 Collaborative Design
Collaborative design is a process that XXX a common goal。In a net-based collaborative design environment。n XXX n for all design resources and activities。 4 Task n XXX is the process of XXX for better management of resources and activities。as well as more XXX of the task as a whole。TMS XXX for effective management of all design resources and activities。 5 n Management System An n management system is a system that manages the storage and retrieval of n。In a net-based collaborative design environment。an n management system is essential for managing the diverse and complex design resources。TMS serves as an n management system by XXX。
收藏知乎网友总结的23种英文文献翻译软件,助力文献阅读
01 搜狗翻译 搜狗翻译的文档翻译功能有三个优点： 第一，可以直接上传文档，流程操作简单化，这才是一键翻译哇，我之前只能说是很多键……； 第二，在线阅读翻译结果时，系统可实时提供原文与译文的双屏对照，方便对比查看； 第三，译文可直接免费下载，方便进一步研读或分享。 02 Google Chrome浏览器 假设一个情景，你想在PubMed上找到以清华大学为第一单位的施一公教授的文章，那么，可以在Chrome浏览器上，登上PubMed，搜索格式为Yigong Shi Tsinghua University，即可找到其发表的文章。 接着，看上一篇蛮不错的，点击进去看看，然后，还是全英文。这时候，你可以试下Chrome自带的网页翻译，真的可以秒翻译，将英文翻译为中文，而且还可以快速转换中/英界面。
03 Adobe Acrobat 笔者在这里给大伙介绍另一款秒翻译PDF文档的神器（笔者使用的Adobe Acrobat Pro DC，至于具体的下载和安装方式，读者可自行百度）。但是，需要注意一点，这是Adobe Acrobat，而不是Adobe Reader。
在这里，请应许笔者介绍下开发出Adobe Acrobat的公司——Adobe。Adobe，在软件界绝对是巨头中巨头的存在。打个比方，我们常用的PS、PR、AE、In、LR等，无一例外都是领域中的顶尖水平，而且都是Adobe家的。其中，Adobe家中就有一款几位出色的PDF编辑及处理软件——Adobe Acrobat。（据说PDF作为国际通用的文件存储格式，也是依它而起） OK，进入主题，Adobe Acrobat是长这个样子的。它可能干嘛呢？PDF 转word、图片合拼为PDF、编辑PDF等等，可以说，与PDF相关的，它都可以搞定。 那如何使用它来帮助我们翻译文献PDF呢？ 第一步，用它打开文献PDF文件；
3英文文献及翻译格式示例
哈尔滨工业大学毕业设计（论文） 英文原文（原文也可以直接将PDF版打印） ASSESSING CREDIT OR DETERMINING QUANTITY? THE EVOLVING ROLE OF RATING AGENCIES Lynnette D. Purda* This version: April 21, 2011 Abstract Over the past ten years, credit rating agencies have come under intense criticism from both practitioners and academics, first for their failure to identify problems resulting in bankruptcies at Enron and Worldcom and second for providing overly optimistic ratings for structured finance products. While many investors question the value of rating agencies in light of these criticisms, they have proven remarkably resilient. This paper provides a brief background on how rating agencies secured competitive advantages in evaluating credit quality. It then reviews the empirical evidence on the information content of ratings given these advantages. I argue that the information content of ratings stems from two intertwined sources: 1) information related to credit quality and 2) information related to the firm’s ability to access debt. Based on this evidence, I suggest that the dominant role for ratings today is as a benchmark for financial contracting. In this way, ratings remain influential in establishing the supply and demand of debt securities. 译文 评级机构的发展的作用评估信用还是决定数量？ 本文：2011.4.21 摘要 在过去的十年，信用评级机构一直处于来自实践者和学者的激烈的批评中，首先他们未能发现问题，导致安然和世通破产；其次对结构性金融产品提供过于乐观的评级。虽然许多投资者因为这些批评对评级机构的价值提出了质疑，但他们仍然被证明是相当有活力的。这篇文章首先在评估机构如何在信用评级质量中获得竞争优势提供一个简单地背景介绍，然后考虑到这些优势回顾了一些信息内容方面的评级经验证据。个人认为信息内容的评级来自两种交织在一起（错综复杂）的来源：1）和信贷质量相关的信息；2)和公司获取债务资本能力相关的信息。以此为据，我建议当前评级的主导作用是作为基准的金融收缩。以这种方式，在建立债券的供应和需求方面评级仍然是有效的。 - -1
文献的英文名称
文献的英文名称 科学出版社2019年8月出版的《图书馆·情报与文献学名词》（以下简称“《名词》”）在定义文献时列出了两个英文词“literature”“document”，都可译为中文的“文献”。关于文献的英文名称，南京大学杰出校友、化学家、文献学家、中科院院士、中国科技情报事业创始人之一袁翰青先生在55年前就有过详细的分析。他说，在英文中，与中文“文献”对应的有两个词，一是literature, 另一个是document。二者都可以译成文献，这是共性，但在具体用法上有微小区别。前者“是集合名词，无单数和复数之分。科学技术论文的文末，常附有供参考用的文献目录”，即用此词。如Subject Index to Polarographic Literature（极谱学文献主题索引）。Literature一般只指书刊资料。后者“就历史性强的文件而言，既用单数，也用复数，分别指一篇或几篇文献，恒用于社会科学的著作中”。Document还可以包括印刷品以外的文字记录，如碑文、古币图文等。这两个词的微小区别，在将中文翻译成英文时就需要特别注意，尤其是在翻译人文社会科学文献时应格外留心。如《民族政策文献汇编》一书，书名中的文献一词，可译成英文documents，也可译成archives，但绝不能译为literature。 还有一个词documentation，周文骏先生主编的词典翻译成“文献学”，袁翰青先生翻译成“文献工作”，并下定义说，文献工作“是组织知识的工作。更明确一点可以说，文献工作是将分散记录起来的知识，特别是文献中新发现的知识单元，经过学术分析与抽出之后，用一定的方法组织起来，对使用者提供最大的便利，能随时被检索到并参考利用”。袁老在50多年前就提出了“知识单元”的概念，并认为将“新发现的知识单元”标引出来和排序起来，以利于检索和利用，是文献工