生物科学论文中英文资料外文翻译文献
中英文对照翻译
Carotenoid Biosynthetic Pathway in the Citrus Genus: Number of Copies and Phylogenetic Diversity of Seven
Gene
The first objective of this paper was to analyze the potential role of allelic variability of carotenoid biosynthetic genes in the interspecifi diversity in carotenoid composition of Citrus juices. The second objective was to determine the number of copies for each of these genes. Seven carotenoid biosynthetic genes were analyzed using restriction fragment length polymorphism (RFLP) and simple sequence repeats (SSR) markers. RFLP analyses were performed with the genomic DNA obtained from 25 Citrus genotypes using several restriction enzymes. cDNA fragments of Psy, Pds, Zds, Lcyb, Lcy-e, Hy-b, and Zep genes labeled with [R-32P]dCTP were used as probes. For SSR analyses, two primer pairs amplifying two SSR sequences identified from expressed sequence tags (ESTs) of Lcy-b and Hy-b genes were designed. The number of copies of the seven genes ranged from one for Lcy-b to three for Zds. The genetic diversity revealed by RFLP and SSR profiles was in agreement with the genetic diversity obtained from neutral molecμLar markers. Genetic interpretation of RFLP and SSR profiles of four genes (Psy1, Pds1, Lcy-b, and Lcy-e1) enabled us to make inferences on the phylogenetic origin of alleles for the major commercial citrus species. Moreover, the resμLts of our analyses suggest that the allelic diversity observed at the locus of both of lycopene cyclase genes, Lcy-b and Lcy-e1, is associated with interspecific diversity in carotenoid accumμLation in Citrus. The interspecific differences in carotenoid contents previously reported to be associated with other key steps catalyzed by PSY, HY-b, and ZEP were not linked to specific alleles at the corresponding loci.
KEYWORDS: Citrus; carotenoids; biosynthetic genes; allelic variability; phylogeny INTRODUCTION
Carotenoids are pigments common to all photosynthetic organisms. In pigment-protein complexes, they act as light sensors for photosynthesis but also prevent photo-oxidation induced by too strong light intensities. In horticμLtural crops, they play a major role in fruit, root, or tuber coloration and in nutritional quality. Indeed some of these micronutrients are precursors of vitamin A, an essential component of human and animal diets. Carotenoids may also play a role in chronic disease prevention (such as certain cancers), probably due to their antioxidant properties. The carotenoid biosynthetic pathway is now well established. Carotenoids are synthesized in plastids by nuclear-encoded enzymes. The immediate precursor of carotenoids (and also of gibberellins, plastoquinone, chlorophylls,phylloquinones, and tocopherols) is geranylgeranyl diphosphate (GGPP). In light-grown plants, GGPP is mainly derived
carotenoid, 15-cis-phytoene. Phytoene undergoes four desaturation reactions catalyzed by two enzymes, phytoene desaturase (PDS) and β-carotene desaturase (ZDS), which convert phytoene into the red-colored poly-cis-lycopene. Recently, Isaacson et al. and Park et al. isolated from tomato and Arabidopsis thaliana, respectively, the genes that encode the carotenoid isomerase (CRTISO) which, in turn, catalyzes the isomerization of poly-cis-carotenoids into all-trans-carotenoids. CRTISO acts on prolycopene to form all-trans lycopene, which undergoes cyclization reactions. Cyclization of lycopene is a branching point: one branch leads to β-carotene (β, β-carotene) and the other to
α-carotene (β, ε-carotene). Lycopene β-cyclase (LCY-b) then converts lycopene into
β-carotene in two steps, whereas the formation of α-carotene requires the action of two enzymes, lycopene ε- cyclase (LCY-e) and lycopene β-cyclase (LCY-b). α- carotene is converted into lutein by hydroxylations catalyzed by ε-carotene hydroxylase (HY-e) andβ-carotene hydroxylase (HY-b). Other xanthophylls are produced fromβ-carotene with hydroxylation reactions catalyzed by HY-b and epoxydation catalyzed by zeaxanthin epoxidase (ZEP). Most of the carotenoid biosynthetic genes have been cloned and sequenced in Citrus varieties . However, our knowledge of the complex regμLation of carotenoid biosynthesis in Citrus fruit is still limited. We need further information on the number of copies of these genes and on their allelic diversity in Citrus because these can influence carotenoid composition within the Citrus genus.
Citrus fruit are among the richest sources of carotenoids. The fruit generally display a complex carotenoid structure, and 115 different carotenoids have been identified in Citrus fruit. The carotenoid richness of Citrus flesh depends on environmental conditions, particμLarly on growing conditions and on geographical origin . However the main factor influencing variability of caro tenoid quality in juice has been shown to be genetic diversity. Kato et al. showed that mandarin and orange juices accumμLated high levels of β-cryptoxanthin and violaxanthin, respectively, whereas mature lemon accumμLated extremely low levels of carotenoids. Goodner et al. demonstrated that mandarins, oranges, and their hybrids coμLd be clearly distinguished by their β-cryptoxanthin contents. Juices of red grapefruit contained two major carotenoids: lycopene and β-carotene. More recently, we conducted a broad study on the organization of the variability of carotenoid contents in different cμLtivated Citrus species in relation with the biosynthetic pathway . Qualitative analysis of presence or absence of the different compounds revealed three main clusters: (1) mandarins, sweet oranges, and sour oranges; (2) citrons, lemons, and limes; (3) pummelos and grapefruit. Our study also enabled identification of key steps in the diversification of the carotenoid profile. Synthesis of phytoene appeared as a limiting step for acid Citrus, while formation of β-carotene and R-carotene from lycopene were dramatically limited in cluster 3 (pummelos and grapefruit). Only varieties in cluster 1 were able to produce violaxanthin. In the same study , we concluded that there was a very strong correlation between the classification of Citrus species based on the presence or absence of carotenoids (below,
this classification is also referred to as the organization of carotenoid diversity) and genetic diversity evaluated with biochemical or molecμLar markers such as isozymes or randomLy amplified polymorphic DNA (RAPD). We also concluded that, at the interspecific level, the organization of the diversity of carotenoid composition was linked to the global evolution process of cμLtivated Citrus rather than to more recent mutation events or human selection processes. Indeed, at interspecific level, a correlation between phenotypic variability and genetic diversity is common and is generally associated with generalized gametic is common and is generally associated with generalized gametic disequilibrium resμLting from the history of cμLtivated Citrus. Thus from numerical taxonomy based on morphological traits or from analysis of molecμLar markers , all authors agreed on the existence of three basic taxa (C. reticμLata, mandarins; C. medica, citrons; and C. maxima, pummelos) whose differentiation was the resμLt of allopatric evolution. All other cμLtivated Citr us species (C. sinensis, sweet oranges; C. aurantium, sour oranges; C. paradisi, grapefruit; and C. limon, lemons) resμLted from hybridization events within this basic pool except for C. aurantifolia, which may be a hybrid between C. medica and C. micrantha .
Our previous resμLts and data on Citrus evolution lead us to propose the hypothesis that the allelic variability supporting the organization of carotenoid diversity at interspecific level preceded events that resμLted in the creation of secondary speci es. Such molecμLar variability may have two different effects: on the one hand, non-silent substitutions in coding region affect the specific activity of corresponding enzymes of the biosynthetic pathway, and on the other hand, variations in untranslated regions affect transcriptional or post-transcriptional mechanisms.
There is no available data on the allelic diversity of Citrus genes of the carotenoid biosynthetic pathway. The objective of this paper was to test the hypothesis that allelic variability of these genes partially determines phenotypic variability at the interspecific level. For this purpose, we analyzed the RFLPs around seven genes of the biosynthetic pathway of carotenoids (Psy, Pds, Zds, Lcy-b, Lcy-e, Hy-b, Zep) and the polymorphism of two SSR sequences found in Lcy-b and Hy-b genes in a representative set of varieties of the Citrus genus already analyzed for carotenoid constitution. Our study aimed to answer the following questions: (a) are those genes mono- or mμLtilocus, (b) is the polymorphism revealed by RFLP and SSR markers in agreement with the general history of cμLtivated Citrus thus permitting inferences about the phylogenetic origin of genes of the secondary species, and (c) is this polymorphism associated with phenotypic (carotenoid compound) variations.
RESΜLTS AND DISCUSSION
Global Diversity of the Genotype Sample Observed by RFLP Analysis. RFLP analyses were performed using probes defined from expressed sequences of seven major genes of the carotenoid biosynthetic pathway . One or two restriction enzymes were used for each gene. None of these enzymes cut the cDNA probe sequence except HindIII for the Lcy-e gene. Intronic sequences and restriction sites on genomic sequences were
screened with PCR amplification using genomic DNA as template and with digestion of PCR products. The resμLts indicated the absence of an intronic sequence for Psy and Lcy-b fragments. The absence of intron in these two fragments was checked by cloning and sequencing corresponding genomic sequences (data not shown). Conversely, we found introns in Pds, Zds, Hy-b, Zep, and Lcy-e genomic sequences corresponding to RFLP probes. EcoRV did not cut the genomic sequences of Pds, Zds, Hy-b, Zep, and Lcy-e. In the same way, no BamHI restriction site was found in the genomic sequences of Pds, Zds, and Hy-b. Data relative to the diversity observed for the different genes are presented in Table 4. A total of 58 fragments were identified, six of them being monomorphic (present in all individuals). In the limited sample of the three basic taxa, only eight bands out of 58 coμLd not be observed. In the basic taxa, the mean number of bands per genotype observed was 24.7, 24.7, and 17 for C. reticμLata, C. maxima, and C. medica, respectively. It varies from 28 (C. limettioides) to 36 (C. aurantium) for the secondary species. The mean number of RFLP bands per individual was lower for basic taxa than for the group of secondary species. This resμLt indicates that secondary species are much more heterozygous than the basic ones for these genes, which is logical if we assume that the secondary species arise from hybridizations between the three basic taxa. Moreover C. medica appears to be the least heterozygous taxon for RFLP around the genes of the carotenoid biosynthetic pathway, as already shown with isozymes, RAPD, and SSR markers.
The two lemons were close to the acid Citrus cluster and the three sour oranges close to the mandarins/sweet oranges cluster. This organization of genetic diversity based on the RFLP profiles obtained with seven genes of the carotenoid pathway is very similar to that previously obtained with neutral molecμLar markers such as genomic SSR as well as the organization obtained with qualitative carotenoid compositions. All these resμLts suggest that the observed RFLP and SSR fragments are good phylogenetic markers. It seems consistent with our basic hypothesis that major differentiation in the genes involved in the carotenoid biosynthetic pathway preceded the creation of the secondary hybrid species and thus that the allelic structure of these hybrid species can be reconstructed from alleles observed in the three basic taxa.
Gene by Gene Analysis: The Psy Gene. For the Psy probe combined with EcoRV or BamHI restriction enzymes, five bands were identified for the two enzymes, and two to three bands were observed for each genotype. One of these bands was present in all individuals. There was no restriction site in the probe sequence. These resμLts lead us to believe that Psy is present at two loci, one where no polymorphism was found with the restriction enzymes used, and one that displayed polymorphism. The number of different profiles observed was six and four with EcoRV and BamHI, respectively, for a total of 10 different profiles among the 25 individuals .Two Psy genes have also been found in tomato, tobacco, maize, and rice . Conversely, only one Psy gene has been found in Arabidopsis thaliana and in pepper (Capsicum annuum), which also accumμLates carotenoids in fruit. According to Bartley and Scolnik, Psy1 was expressed in tomato fruit chromoplasts, while Psy2 was specific to leaf tissue. In the same way, in Poaceae (maize, rice), Gallagher et al. found that Psy gene was duplicated and that Psy1 and not
Psy2 transcripts in endosperm correlated with endosperm ca rotenoid accumμLation. These resμLts underline the role of gene duplication and the importance of tissue-specific phytoene synthase in the regμLation of carotenoid accumμLation.
All the polymorphic bands were present in the sample of the basic taxon genomes. Assuming the hypothesis that all these bands describe the polymorphism at the same locus for the Psy gene, we can conclude that we found allelic differentiation between the three basic taxa with three alleles for C. reticμLata, four for C. maxima, and o ne for C. medica.
The alleles observed for the basic taxa then enabled us to determine the genotypes of all the other species. The presumed genotypes for the Psy polymorphic locus are given in Table 7. Sweet oranges and grapefruit were heterozygous with one mandarin and one pummelo allele. Sour oranges were heterozygous; they shared the same mandarin allele with sweet oranges but had a different pummelo allele. Clementine was heterozygous with two mandarin alleles; one shared with sweet oranges and one with “Willow leaf” mandarin. “Meyer” lemon was heterozygous, with the mandarin allele also found in sweet oranges, and the citron allele. “Eureka”lemon was also heterozygous with the same pummelo allele as sour oranges and the citron allele. The other acid Citrus were homozygous for the citron allele.
The Pds Gen. For the Pds probe combined with EcoRV, six different fragments were observed. One was common to all individuals. The number of fragments per individual was two or three. ResμLts for Pds led us to bel ieve that this gene is present at two loci, one where no polymorphism was found with EcoRV restriction, and one displaying polymorphism. Conversely, studies on Arabidopsis, tomato, maize, and rice showed that Pds was a single copy gene. However, a previous study on Citrus suggests that Pds is present as a low-copy gene family in the Citrus genome, which is in agreement with our findings.
The Zds Gene. The Zds profiles were complex. Nine and five fragments were observed with EcoRV and BamHI restriction, respectively. For both enzymes, one fragment was common to all individuals. The number of fragments per individual ranged from two to six for EcoRV and three to five for BamHI. There was no restriction site in the probe sequence. It can be assumed that several copies (at least three) of the Zds gene are present in the Citrus genome with polymorphism for at least two of them. In Arabidopsis, maize, and rice, like Pds, Zds was a single-copy gene .
In these conditions and in the absence of analysis of controlled progenies, we are unable to conduct genetic analysis of profiles. However it appears that some bands differentiated the basic taxa: one for mandarins, one for pummelos, and one for citrons with EcoRV restriction and one for pummelos and one for citrons with BamHI restriction. Two bands out of the nine obtained with EcoRV were not observed in the samples of basic taxa. One was rare and only observed in “Rangpur” lime. The other was found in sour oranges, “V olkamer” lemon,and “Palestine sweet” lime suggesting a common ancestor for these three genotypes.
This is in agreement with the assumption of Nicolosi et al. that “V olkamer” lemon resμLts from a complex hybrid combination with C. aurantium as one parent. It will be
necessary to extend the analysis of the basic taxa to conclude whether these specific bands are present in the diversity of these taxa or resμLt from mutations after the formation of the secondary species.
The Lcy-b Gene with RFLP Analysis.After restriction with EcoRV and hybridization with the Lcy-b probe, we obtained simple profiles with a total of four fragments. One to two fragments were observed for each individual, and seven profiles were differentiated among the 25 genotypes. These resμLts provide evidence that Lcy-b is present at a single locus in the haploid Citrus genome. Two lycopene β-cyclases encoded by two genes have been identified in tomato. The B gene encoded a novel type of lycopene β-cyclase whose sequence was similar to capsanthin-capsorubin synthase. The B gene expressed at a high level in βmutants was responsible for strong accumμLation ofβ-carotene in fruit, while in wild-type tomatoes, B was expressed at a low level.
The Lcy-b Gene with SSR Analysis. Four bands were detected at locus 1210 (Lcy-b gene). One or two bands were detected per variety confirming that this gene is mono locus. Six different profiles were observed among the 25 genotypes. As with RFLP analysis, no intrataxon molecμLar polymorphism was found within C. Paradisi, C. Sinensis, and C. Aurantium.
Taken together, the information obtained from RFLP and SSR analyses enabled us to identify a complete differentiation among the three basic taxon samples. Each of these taxons displayed two alleles for the analyzed sample. An additional allele was identified for “Mexican” lime. The profiles for all secondary species can be reconstructed from these alleles. Deduced genetic structure is given in. Sweet oranges and clementine were heterozygous with one mandarin and one pummelo allele. Sour oranges were also heterozygous sharing the same mandarin allele as sweet oranges but with another pummelo allele. Grapefruit were heterozygous with two pummelo alleles. All the acid secondary species were heterozygous, having one allele from citrons and the other one from mandarins ex cept for “Mexican” lime, which had a specific allele.
柑桔属类胡萝卜素生物合成途径中七个基因拷贝数目
及遗传多样性的分析
摘要：本文的首要目标是分析类胡萝卜素生物合成相关等位基因在发生变异柑橘属类胡萝卜素组分种间差异的潜在作用；第二个目标是确定这些基因的拷贝数。本实验应用限制性片段长度多态性（RFLP）和简单序列重复（SSR）标记法对类胡萝卜素生物合成途径中的七个基因进行了分析。用[R-32P]dCTP标记PSY，PDS，ZDS，LCY-b，LCY-e，HY-b和ZEP cDNA片段作为作探针，使用若干限制性内切酶对来自25种柑桔基因型基因组DNA的限制性片段长度差异进行了分析。而对于SSR标记，设计两对引物分别扩增LCY-b和HY-b基因的表达序列标签（ESTs）。在这7个基因中，LCY-b只有1个拷贝，而ZDS存在3个拷贝。利用RFLP和SSR分析发现基因的遗传多
样性与核心分子标记一致。RFLP和SSR对PSY1，PDS1，LCY-b和LCY-e14个基因的分析结果足以解释这几个主要的商业栽培种的系统树起源。此外，我们的分析结果表明，不同种类柑橘中类胡萝卜素积累的番茄红素环化酶LCY-b和LCY-e1等位基因存在种间差异。前人报道PSY，HY-b和ZEP基因与种间类胡萝卜素含量差异密切相关，但本实验发现这些等位基因并不起关键作用。
关键词：柑桔；类胡萝卜素；生物合成基因；基因变异；系统发育
前言
类胡萝卜素是植物光合组织中普遍存在的一类色素。在色素蛋白复合体中，它们作为光敏元件进行光合作用，并且防止过强光照强度引起的灼伤，并在园艺作物果实，根，或块茎色泽和营养品质上起着十分重要的作用。事实上，其中一些微量营养素是维生素A的前体，是人类和动物的饮食必不可少的组成部分。由于具有抗氧化性，类胡萝卜素在预防慢性疾病也发挥着重要的作用。类胡萝卜素生物合成途径现在已经明确。类胡萝卜素通过核酸编码的蛋白酶在质体中合成。其直接前体是牻牛儿基牻牛儿基焦磷酸（GGPP，该前体同时也是赤霉素，质体醌，叶绿素，维生素K，维生素E的前体）。在光合植物中，GGPP主要来源于2-C-甲基-D-赤藻糖醇-4-磷酸（MEP）途径，两分子的GGPP经八氢番茄红素合成酶（PSY）催化缩合形成一个八氢番茄红素—15-顺式-八氢番茄红素。八氢番茄红素经八氢番茄红素脱氢酶（PDS）和ζ-胡萝卜素脱氢酶（ZDS）催化八氢番茄红素转换成红色的聚- 顺式-番茄红素。最近，Isaacson等和Park等分别从番茄和拟南芥中分离编码类胡萝卜素异构（CRTISO）基因，该基因催化异构化聚顺式-胡萝卜素进入全反式类胡萝卜素。CRTISO作用于番茄红素前体环化反应形成一种全反式番茄红素。植物番茄红素的环化有两条途径：一个分支合成β-胡萝卜素，另一个分支合成α-胡萝卜素。番茄红素β环化酶（LCY-b）通过两个步骤转换成β-胡萝卜素，而形成的β-胡萝卜素的过程需要两种酶，番茄红素ε-环化酶（LCY-e）和番茄红素β环化酶（LCY-b）。α-胡萝卜素经α-胡萝卜素羟化酶（HY-e）和β-胡萝卜素羟化酶（HY-b）的羧基化催化作用转化为叶黄素。β-胡萝卜素经HY-b的羟化反应催化和玉米黄质环氧化酶(ZEP）环氧化催化作用合成其他叶黄素。到目前为止，柑橘中大多数的类胡萝卜素生物合成的基因已被克隆和测序，但对柑橘类水果类胡萝卜素合成的复杂调控的认识仍然十分有限的，需要进一步了解柑橘中这些有差异的等位基因拷贝数，因为这些基因会影响柑橘类水果中最来源丰富的类胡萝卜素组成。
果实类胡萝卜素的结构较为复杂，在柑橘类水果中已查明有115种不同的类胡萝卜素。柑橘果肉类胡萝卜素丰富程度取决于环境条件，特别是生长条件和地理环
境。但影响类胡萝卜素质量变化的主要因素是遗传的多样性。Kato等表明中国柑橘和橙汁积累高水平的β-隐黄质和紫黄质，成熟的柠檬积累低水平的类胡萝卜素。Goodnr等发现红西柚汁含有两个主要类胡萝卜素：番茄红素和胡萝卜素。最近，我们对栽培变异柑桔品种类胡萝卜素组分含量不同从生物合成途径上进行了广泛的研究。根据是否含有不同的化合物将其分成三类：（1）中国（普通）柑桔，甜柑，酸橘；（2）蜜饯，柠檬，和酸橙；（3）柚和葡萄柚。我们的研究也明确了致使类胡萝卜素结构的多样关键步骤。在酸柑橘中八氢番茄红素合成是一个限制步骤；番茄红素形成α-胡萝卜素和β-胡萝卜素是被酸式磷酸盐限制在第三个分类中（柚和葡萄柚）；只有第1组品种能够合成紫黄质。在同一研究中，以是否存在的类胡萝卜素（以下这种分类也被称为类胡萝卜素组织多样性）和遗传多样性评价为基础，我们认为应通过生化或分子分子标记遗传多样行评估在种间一级组织中的多样性，类胡萝卜素的组成如同工酶或随机扩增多态性DNA（RAPD）对大量的柑桔品种进行分类。此外，我们还得出结论认为，在种间水平，类胡萝卜素结构多样性和柑橘属的进化过程有关系，而不是突变事件或人为的甄选过程。事实上，在种间水平，在柑桔栽培历史上，表型变异和遗传多样性的关系具有普遍性和一般性，这和不能适应环境的不平衡相关联。因此，从数值分类的基础上，或从形态性状的分子标记分析，所有的研究者均认为：存在着三种基本分类（宽皮桔类；中国柑桔；枸橼，蜜饯；文旦，柚)，其差异是由于异域的演变。其他种植柑桔的品种（甜橙类，甜桔；酸橙类，酸桔；柑橘属葡萄柚，葡萄柚；柠檬类，柠檬）是杂交的结果，而酸橙类则可能是佛手柚和薇甘菊的杂交种。先前研究柑桔演变的结果和数据使我们提出这样的假设：等位基因变异导致类胡萝卜素水平的结构差异，原因在于次级代谢产物的产生。这种分子变异可能有两种不同的影响：一方面，非沉默替换编码区影响生物合成途径相应酶的作用；另一方面，非编码区域的变化影响转录或转录后机制。
到目前为止，没有人研究过柑桔中类胡萝卜素生物合成途径的等位基因多样性。本实验的目的是为了研究基因变异是否部分决定种间水平表型变异性。为此，我们应用RFLP分析了类胡萝卜素生物合成途径中的7个基因（PSY，PDS，ZDS，LCY-b，LCY-e，HY-b，ZEP），以及两个SSR序列分析一批有代表性品种的LCY-b 和HY-b基因，旨在解决下列问题：（a）这7个基因是单基因还是多基因位点；（b）RFLP法和SSR标记法显示的差异性与栽培柑桔的记录一致，从而可以推论次级产物基因系统发生的起源。（c）多样性与表型的（类胡萝卜素化合物）变化相关联。结果与讨论
本实验应用RFLP分析法来观察基因型样本的整体差异。用类胡萝卜素生物合成途径中的7个主要基因的表达序列作为探针进行RFLP分析，每一个基因用一个或两个限制性内切酶，筛选内含序列及酶切位点的基因组序列，以基因组DNA为模板
PCR扩增和酶切PCR产物。结果表明没有一个PDS和LCY-b片段的内含子序列。在这两个片段克隆和序列分析相应的基因组序列中没有检查出内含序列（数据未显示）。相反，我们发现PDS，ZDS，HY-b，ZEP和LCY-e基因组含有RFLP探针序列。Eco RV 并没切断PDS，ZDS，HY-b，ZEP和LCY-e基因组序列。以同样的方式，没有发现PDS，ZDS和HY-b的基因组序列的Bam HI酶切位点。表4是对于不同基因多样性观察有关的数据。总共58个片段被确定，它们中的六个是单一同态的（存在于个体中）。三个基本分类单元的有限样本中，58个之外只有8个条带不能被观察到。在基本分类单位，每个基因型遗传距离的平均数分别是，宽皮橘类24.7，中国柑橘24.7，柠檬类17这与次级物种的28（酸橙类）到36（橙类）不同。每个基本的分类单元个体RFLP 条带的平均数均低于次级物种类群。结果表明次级物种比基于三个基因分类的基本物种更加杂合。这是合理的如果我们假设次级物种起源于三个基本分类，此外经RFLP围绕类胡萝卜素生物合成途径的基因分析柠檬类好像是最杂合程度最小的分类单元。如同功酶，RAPD，SSR标记法所示。
四种甜橘子的分析显示所有的基因同样的标记，三种酸橙类的代表和三种葡萄柚也是。在接下来的研究中，次级代谢产物仅有一个个体参加。基因多样性的机体组成显示相邻系统树以所有RFLP标记波带的有无的片段的不同指标为基础。区分出八个不同的标记。主要的线束被识别；第一个组是中国柑橘和甜橘，第二文旦和葡萄柚，第三柠檬和酸的柑橘属的多数。两种柠檬接近酸柑橘属的线束而三种酸橘子接近橘子或甜橙的线束。以RFLP标记为基础的遗传多样性的机体组成获得类胡萝卜素合成途径的七个基因和通过不定性分子组成的时标获得的是相似的，通过定性分子组分获得的也是一样。所有这些结果表明观察RFLP和SSR片段是完好的系统标记。这和我们的基础假说相似，主要的区别在于涉及类胡萝卜素生物合成途径基因先于次级杂交物种的产生，因此在三类基础分类中等位基因的构成源于等位基因的重组。
PSY基因分析因为PSY探针和Eco RV或Bam HI限制性内切酶结合，所以可以把五个染色体条带看成是两种酶，观察两或三个染色体条带的基因型。这些条带中的一个出现在所有个体中。没有限制性酶切位点在探针序列中。这些结果使我们相信PSY在两个基因位点出现，一个用限制性内切酶发现没有多态性，另一个有多态性。用Eco RV和Bam HI不同的标记观察分别是六或四，总共10个不同的标记在25个个体中。两种PSY基因也在番茄，烟草，玉米，水稻中被发现。相反地，在拟南芥和在胡椒中仅仅发现一个PSY基因，在它的果实中也积累胡萝卜素。根据Bartley和Scolnik 的研究，PSY1表达在番茄果实的色素细胞中，PSY2特殊在它在叶片组织中表达。同样的方法，在禾本科(玉米，水稻)中，Gallagher等发现PSY基因是被复制出来的，在胚乳中PSY1而并非是PSY2转录产物与胚乳类胡萝卜素积累有关。这些结果强调基因
复制的作用和特有组织的八氢番茄红色合酶在类胡萝卜素积累的调控中的重要性。
所有的多态性条带出现在基础分类群的基因组。假定该假说，在相同的基因位点为PSY基因所有的条带描述多态性，我们能断定我们发现等位基因的区别在三类基础分类，柑三个等位基因，中国柑橘四个等位基因，柠檬类一个等位基因。
观察三类基础分类的所有等位基因，然后我们能确定所有物种基因型。表七中给出PSY基因多态性位点推测的基因型。甜橘和葡萄柚是中国柑橘和甜橙的杂合。四种酸橙是杂合的；它们和中国柑橘共用相同的等位基因但和柚有一个不同的等位基因。克莱门氏小柑橘是两种中国柑橘（柑橘和酸柑）等位基因的杂合；一个与甜橙共用，而一个与柳橙共用。“Meyer”柠檬是杂合的，中国柑橘的等位基因也在甜橙和柠檬中被发现，“Eureka”柠檬也是柚四种酸橙等位基因和柠檬等位基因的杂合。其它的酸柑橘属是纯合的。
PDS基因将Eco RV与PDS探针结合，观察到六个不同的片段。一个为所有个体所共有。每个个体的片段数量是两或三个。这些结果使我们相PSY在两个基因位点出现，用限制性内切酶发现一个没有多态性，另一个有多态性。相反地，对拟南芥，番茄，玉米和水稻的研究显示PDS是一个单独的拷贝基因。然而，前人对柑橘属的研究表明PDS基因作为一个低拷贝的基因家族在柑橘属基因组中，这与我们的发现相矛盾。
ZDS基因ZDS标记是复合体。通过Eco RV和Bam HI限制可以分别观察到九和五个片段。这两种酶中的一个片段是所有个体都有。对于Eco RV每个单独个体基因片段的数量从二变到三，对于Bam HI从三变到五。没有限制性酶切位点在探针序列。假定ZDS基因的几个拷贝（至少三个）出现于柑橘属基因组中，至少它们中的两个有多态性。在拟南芥，玉米和水稻中，PDS，ZDS是单拷贝的基因。
在这些条件下和缺乏可控后代分析的情况下，我们不能处理基因遗传分析的标记。然而它看起来好像一些条带区分三类基础分类：一条是中国柑橘的，一条是柚的，一条是通过Eco RV限制性内切的柚和Bam HI限制酶切的柠檬。经Eco RV基础分类的样品中九个之外又两个没有被观察到。仅仅在“Rangpur”酸橙中才能观察到一条比较薄的。其他的被发现酸橙，“Volkamer”柠檬，巴基斯坦甜橙暗示这三种基因型有同一个祖先。
这与Nicolosi等的设想相符。“Volkamer”柠檬起源于以橙作为亲本的杂种结合。加大对三种基础分类的分析是必需的，总之这些特殊的条带出现在分类中或者源于次级物种形成后的突变。
RFLP法分析LCY-b基因在Eco RV限制之后，和LCY-b探针杂交，我们用四个片段的全部获得简单的标记。每个个体观察一到两个片段，在25个基因型中观察到7个条带。这些结果为在柑橘属单倍体基因组中LCY-b出现在单一的位点提供依据。
毕业论文英文参考文献与译文
Inventory management Inventory Control On the so-called "inventory control", many people will interpret it as a "storage management", which is actually a big distortion. The traditional narrow view, mainly for warehouse inventory control of materials for inventory, data processing, storage, distribution, etc., through the implementation of anti-corrosion, temperature and humidity control means, to make the custody of the physical inventory to maintain optimum purposes. This is just a form of inventory control, or can be defined as the physical inventory control. How, then, from a broad perspective to understand inventory control? Inventory control should be related to the company's financial and operational objectives, in particular operating cash flow by optimizing the entire demand and supply chain management processes (DSCM), a reasonable set of ERP control strategy, and supported by appropriate information processing tools, tools to achieved in ensuring the timely delivery of the premise, as far as possible to reduce inventory levels, reducing inventory and obsolescence, the risk of devaluation. In this sense, the physical inventory control to achieve financial goals is just a means to control the entire inventory or just a necessary part; from the perspective of organizational functions, physical inventory control, warehouse management is mainly the responsibility of The broad inventory control is the demand and supply chain management, and the whole company's responsibility. Why until now many people's understanding of inventory control, limited physical inventory control? The following two reasons can not be ignored: First, our enterprises do not attach importance to inventory control. Especially those who benefit relatively good business, as long as there is money on the few people to consider the problem of inventory turnover. Inventory control is simply interpreted as warehouse management, unless the time to spend money, it may have been to see the inventory problem, and see the results are often very simple procurement to buy more, or did not do warehouse departments . Second, ERP misleading. Invoicing software is simple audacity to call it ERP, companies on their so-called ERP can reduce the number of inventory, inventory control, seems to rely on their small software can get. Even as SAP, BAAN ERP world, the field of
英文文献综述样本 威尼斯商人
毕业论文 （或毕业设计） 文献综述 文献综述题目 （中文小二号黑体居中或英文Times New Roman小二号加粗居中或日文明朝体小二号加粗） 学生姓名指导教师 二级学院专业名称 班级学号 年月日
（标题Times New Roman三号加粗） The Literature Review of The Mystery of Antonio’s Sadness in The Merchant of Venice （正文用Times New Roman小四，1.5倍行距，各段首行空4个字符，书名用斜体加粗） Written sometime between 1596 and 1598, The Merchant of Venice is classified as both an early Shakespearean comedy (more specifically, as a "Christian comedy") and as one of the Bard's problem plays; it is a work in which good triumphs over evil, but serious themes are examined and some issues remain unresolved. In The Merchant of Venice , Shakespeare wove together two ancient folk tales, one involving a vengeful, greedy creditor trying to exact a pound of flesh, the other involving a marriage suitor's choice among three chests and thereby winning his (or her) mate. Shakespeare's treatment of the first standard plot scheme centers around the villain of Merchant, the Jewish moneylender Shylock, who seeks a literal pound of flesh from his Christian opposite, the generous, faithful Antonio. Shakespeare's version of the chest-choosing device revolves around the play's Christian heroine Portia, who steers her lover Bassanio toward the correct humble casket and then successfully defends his bosom friend Antonio from Shylock's horrid legal suit. Antonio, as the title character, is sad from the beginning to the end of the play but never names the cause of his melancholy even when his friends ask him. Antonio plays the role as an outcast in the play. Shakespeare uses Antonio’s sadness simply as the device to set the tragic tone in the comedy or make Antonio be one of his melancholic characters in his works? Or Antonio is the representative of the complicated human nature? Antonio's unexplained melancholy is a significant element in understanding the play. 1. Studies on The Merchant of V enice（Times New Roman + 四号+首缩进4字符，下同） Karl Marx once cited that Shakespeare is the greatest playwright in the world.
人形机器人论文中英文资料对照外文翻译
中英文资料对照外文翻译 最小化传感级别不确定性联合策略的机械手控制 摘要：人形机器人的应用应该要求机器人的行为和举止表现得象人。下面的决定和控制自己在很大程度上的不确定性并存在于获取信息感觉器官的非结构化动态环境中的软件计算方法人一样能想得到。在机器人领域，关键问题之一是在感官数据中提取有用的知识，然后对信息以及感觉的不确定性划分为各个层次。本文提出了一种基于广义融合杂交分类（人工神经网络的力量，论坛渔业局）已制定和申请验证的生成合成数据观测模型，以及从实际硬件机器人。选择这个融合，主要的目标是根据内部（联合传感器）和外部（ Vision 摄像头）感觉信息最大限度地减少不确定性机器人操纵的任务。目前已被广泛有效的一种方法论就是研究专门配置5个自由度的实验室机器人和模型模拟视觉控制的机械手。在最近调查的主要不确定性的处理方法包括加权参数选择（几何融合），并指出经过训练在标准操纵机器人控制器的设计的神经网络是无法使用的。这些方法在混合配置，大大减少了更快和更精确不同级别的机械手控制的不确定性，这中方法已经通过了严格的模拟仿真和试验。 关键词：传感器融合，频分双工，游离脂肪酸，人工神经网络，软计算，机械手，可重复性，准确性，协方差矩阵，不确定性，不确定性椭球。 1 引言 各种各样的机器人的应用（工业，军事，科学，医药，社会福利，家庭和娱乐）已涌现了越来越多产品，它们操作范围大并呢那个在非结构化环境中运行 [ 3,12,15]。在大多数情况下，如何认识环境正在发生变化且每个瞬间最优控制机器人的动作是至关重要的。移动机器人也基本上都有定位和操作非常大的非结构化的动态环境和处理重大的不确定性的能力[ 1,9,19 ]。每当机器人操作在随意性自然环境时，在给定的工作将做完的条件下总是存在着某种程
英语毕业论文引用和参考文献格式
英语毕业论文引用和参考文献格式 英语专业毕业论文引用和参考文献格式采用APA格式及规范。 一、文中夹注格式 英语学位论文引用别人的观点、方法、言论必须注明出处，注明出处时使用括号夹注的方法（一般不使用脚注或者尾注），且一般应在正文后面的参考文献中列出。关于夹注，采用APA格式。 （一）引用整篇文献的观点 引用整篇文献（即全书或全文）观点时有两种情况： 1.作者的姓氏在正文中没有出现，如：CharlotteandEmilyBrontewerepolaropposites,notonlyintheirpersonalitiesbutinthe irsourcesofinspirationforwriting(Taylor,1990). 2.作者的姓氏已在正文同一句中出现，如：TaylorclaimsthatCharlotteandEmilyBrontewerepolaropposites,notonlyintheirperso nalitiesbutintheirsourcesofinspirationforwriting(1990). 3.如果作者的姓氏和文献出版年份均已在正文同一句中出现，按APA的规范不需使用括号夹注，如： Ina1990article,TaylorclaimsthatCharlotteandEmilyBrontewerepolaropposites,noto nlyintheirpersonalitiesbutintheirsourcesofinspirationforwriting. 4.在英文撰写的论文中引用中文着作或者期刊，括号夹注中只需用汉语拼音标明作者的姓氏，不得使用汉字，如：(Zhang,2005) （二）引用文献中具体观点或文字 引用文献中某一具体观点或文字时必须注明该观点或者该段文字出现的页码出版年份，没有页码是文献引用不规范的表现。 1.引用一位作者的文献 （1）引用内容在一页内，如： EmilyBronte“expressedincreasinghostilityfortheworldofhumanrelationships,whet hersexualorsocial”(Taylor,1988：11). （2）引用内容在多页上，如： Newmark(1988：39-40)notesthreecharacteristicallyexpressivetext-types:(a)seriousimaginativel iterature注意在这些例子中引文超过一页时的页码标记方法：APA的规范是(1988,。 假若作者的姓氏已在正文同一句中出现，则不需要在括号夹注中重复，如：TaylorwritesthatEmilyBronte“expressedincreasinghostilityfortheworldofhumanre lationships,whethersexualorsocial”(1988：11).
英语师范生毕业论文 文献综述
The Revelation of the Western Maritime Literature’ Vicissitude 姓名：叶牡丹学号：2010520070 班级：1013 Literature Review The Western Maritime Literature In the western countries, from the 17th to the 19th century, there are producing a large number of literary works, which relate to sea or take sea as a description object. From a special angle, presenting the relationship between human and sea ,human and nature ,and various understanding of human’ own po wer at that time , all of these providing a kind of special literary reading. However ,after entering the 21st century ,when human conquer ocean and nature rapidly ,we lost the wonderful imagination of ocean ,and no longer take ocean as a medium to express human’s good qualities .We divert the attention to the damages done by human to the sea . The Western Maritime Literature shift from passionate to cool style .This change is worth literary studying and the common concern of the social studies. Due to the kinship with the ocean, man has always taken the ocean as the aesthetic object and included it into the reflections upon history. The sea, one of the important regions of the Western, has become the common subject and theme in the Western literature. Sea literature as an important type of Western literature makes the ocean as a background or the narrative object, of reflects the relationship among ocean and human by describing shipping and island life. Western sea literature consisting of numerous outstanding works, distinctive artistic characteristics, a wide range of literary influence, such as The Old Man and the Sea ,Moby Dick, Robinson Crusoe and Leagues Under the Sea and so on,has a long historical tradition and profound cultural significance. Western sea novel occupies a prominent place in Western literature; to some extent, it represents the highest level of the Western sea literature. Sea literature is an important component in Western literature as well as an indispensable part of the literary canon. No matter as a geographical area for production, living, transportation and colonization, or a cultural symbol of mystery, fortune, power, conquering, and promise, the sea plays a constructive part in sustaining and enriching Western literature. The large number of sea literature not only enriches narrative aesthetics, but also contributes to the molding of national character and culture. However, t here is not a clear definition of “sea literature” or “maritime literature” in
英语专业毕业论文参考文献注释格式1
文献参考的注释格式 正文中的注释和参考文献是论文格式最为重要的部分，请论文作者逐条仔细阅读。建议先做好参考文献格式，再对照格式要求作夹注。 分脚注和夹注两种，。 2）脚注 正文内容如有需作出特别说明或解释之处以脚注的形式处理，编号格式设置为“○1,○2,○3…”，编号方式设置为“每页重新编号”，脚注会自动出现在当页正文下。字体采用默认值（小五号）。 1）夹注 对论文中的直接引用或间接引用部分所依据的文献以夹注的形式标出。夹注可以采用以下几种形式： 作者姓氏未在引文中出现，则夹注用括号标出作者姓氏，空一格字母再标出引文页码。为避免不必要的麻烦，中文作者用全名。 引用一位作者 “Time is no longer felt as an objective, causal progression with clearly marked-out differences between periods…” (Frank 20) As the British novelist-critic Christine Brooke-Rose has put it, the novelists now have nothing new to tell since what should be told have been told altogether (Yin Qiping 33-35) . 引用两位作者 Medieval Europe was a place both of “raids, pillages, slavery, and extortion” and of “traveling merchants, monetary exchange, towns if not cities, and active ma rkets in gain” (Townsend & Waugh 10-16). 作者有三个以上，
机械设计外文翻译(中英文)
机械设计理论 机械设计是一门通过设计新产品或者改进老产品来满足人类需求的应用技术科学。它涉及工程技术的各个领域，主要研究产品的尺寸、形状和详细结构的基本构思，还要研究产品在制造、销售和使用等方面的问题。 进行各种机械设计工作的人员通常被称为设计人员或者机械设计工程师。机械设计是一项创造性的工作。设计工程师不仅在工作上要有创造性，还必须在机械制图、运动学、工程材料、材料力学和机械制造工艺学等方面具有深厚的基础知识。如前所诉，机械设计的目的是生产能够满足人类需求的产品。发明、发现和科技知识本身并不一定能给人类带来好处，只有当它们被应用在产品上才能产生效益。因而，应该认识到在一个特定的产品进行设计之前，必须先确定人们是否需要这种产品。 应当把机械设计看成是机械设计人员运用创造性的才能进行产品设计、系统分析和制定产品的制造工艺学的一个良机。掌握工程基础知识要比熟记一些数据和公式更为重要。仅仅使用数据和公式是不足以在一个好的设计中做出所需的全部决定的。另一方面，应该认真精确的进行所有运算。例如，即使将一个小数点的位置放错，也会使正确的设计变成错误的。 一个好的设计人员应该勇于提出新的想法，而且愿意承担一定的风险，当新的方法不适用时，就使用原来的方法。因此，设计人员必须要有耐心，因为所花费的时间和努力并不能保证带来成功。一个全新的设计，要求屏弃许多陈旧的，为人们所熟知的方法。由于许多人墨守成规，这样做并不是一件容易的事。一位机械设计师应该不断地探索改进现有的产品的方法，在此过程中应该认真选择原有的、经过验证的设计原理，将其与未经过验证的新观念结合起来。 新设计本身会有许多缺陷和未能预料的问题发生，只有当这些缺陷和问题被解决之后，才能体现出新产品的优越性。因此，一个性能优越的产品诞生的同时，也伴随着较高的风险。应该强调的是，如果设计本身不要求采用全新的方法，就没有必要仅仅为了变革的目的而采用新方法。 在设计的初始阶段，应该允许设计人员充分发挥创造性，不受各种约束。即使产生了许多不切实际的想法，也会在设计的早期，即绘制图纸之前被改正掉。只有这样，才不致于堵塞创新的思路。通常，要提出几套设计方案，然后加以比较。很有可能在最后选定的方案中，采用了某些未被接受的方案中的一些想法。
英语专业毕业论文参考文献汇总
【英语专业】毕业论文参考文献汇总 【文学类】 柳鸣九编选新小说派研究北京中国社会科学出版社，1986 徐葆耕西方文学心灵历史北京清华大学出版社，1990 殷企平小说艺术管窥天津：百花文艺出版社，1995 戴维洛奇小说的艺术北京：作家出版社，1998 高奋西方现代主义文学源与流宁波：宁波出版社，2000 侯维瑞现代英国小说史上海：上海外语教育出版社，1986 胡经之，王岳川主编文艺学美学法论北京：北京出版社，1994 黄晋凯主编荒诞派戏剧北京：中国人民大学出版社，1996 霍夫曼佛洛伊德主义与文学思想王宁译北京：三联书店，1987 拉曼塞尔顿编文学批评理论刘象愚，陈永国等译北京：北京大学出版社，2000 霍纳韦勒克近代文学批评史（第4卷）上海：上海译文出版社，1997 李维屏英美现代主义文学概观上海：上海外语教育出版社，1998 吕同六主编20世纪世界小说理论经典北京：华夏出版社，1995 罗伯特斯皮勒美国文学的周期——历史评论专集王长荣译上海：上海外语出版社，1990 罗德霍顿美国文学思想背景房炜等译北京人民出版社，1991 梅佛里德曼意识流，文学手法研究上海：华东师范大学出版社，1992 米兰昆德拉小说的艺术孟湄译北京：三联书店，1995 史志康主编美国文学背景概观上海：上海：上海外语出版社，1998 【语言学】 奥马利第二语言习得的学习策略上海：上海外语出版社，2001 陈保亚20 世纪中国语言学方法论济南：山东教育出版社，1999 丁言仁英语语言学纲要上海：上海外语出版社，2001 费尔迪南德索绪尔普通语言学教程长沙：湖南教育出版社，2001 冯翠华英语修辞大全北京：商务印书馆，1996 桂诗春，宁春言主编语言学方法论北京：外语教学与研究出版社，1998 桂诗春应用语言学长沙：湖南教育出版社，1998 何兆熊新编语用学概要上海：上海外语教育出版社，2000 何自然语用学与英语学习上海：上海外语教育出版社，1997 侯维瑞英语语体上海：上海外语教育出版社，1988 胡壮麟语言学教程（修订版）北京：北京大学出版社，2001 黄国文语篇与语言的功能北京：外语教学与研究出版社，2002 黄国文语篇分析概要长沙：湖南教育出版社，1988 李延富主编英语语言学基本读本济南：山东大学出版社，1999 李运兴语篇翻译引论北京：中国对外翻译出版公司，2000 刘润清西方语言学流派北京：外语教学与研究出版社，1999 刘润清等现代语言学名著选读（上下册）北京：测绘出版社，1988 刘润清等语言学入门北京：人民教育出版社，1990 陆国强现代英语词汇学（新版）上海：上海外语教育出版社，1999 戚雨村现代语言学的特点和发展趋势上海外语教育出版社，1997 秦秀白文体学概要长沙：湖南教育出版社，1990 孙志外国语言研究论文索引（1995—1999）上海外语教育出版社，2001 索绪尔普通语言教程北京：商务印书馆，1999
英语论文文献综述
英语专业毕业论文文献资料目录及综述表
文献综述（2000字以上） In the early reviews of this novel reveals a variety of attitudes toward and assessments. Some early reviewers suspected strongly that Sons and Lovers is an autobiographical work. “We suspect that Paul is a projection of the writer’s own personality,” Harold Massingham said. Others did not explicitly make a direct to the passionately personal style of Sons and Lovers. Some of Lawrence’s contemporaries insist on seeing the novel Sons and Lovers as the author’s only-slightly-revised personal history; others do not, although one complains about the writer’s lack of “scientific detachment.” Some of the reviews believe the book to be about the tragic “wastage” of Walter Morel; others think the author is writing against his own biological father. Then, too, there are critics who seemed to sense that the inconsistent reviews of the book are made possible by the work itself, which is about emotional oxymoron, passionate contradictions. Before any reviewers fully insisted upon the autobiographical nature of Sons and Lovers. “In order to understand Mr. Lawrence fully, we must go beyond his works,” Alfred Kuttner suggested in A Freudian Appreciation in Sons and Lovers. Insisting on the strong similarity between Sons and Lovers and Lawrence’s earlier novels and love poems, Kuttner declared all these works to be “expressions of the same personal experience,”namely,Lawrence’s “hatred”for his “father.” Having said this, Kuttner went even further, suggesting that what Lawrence “particularizes so passionately” is what Freud, more generally, “has proved beyond cavil,” namely, that “the child’s attachment to the parent of the opposite sex becomes the prototype of all later love relations.” According to Showalter E, said in Sexual Anarchy, that Lawrence was difficult to accept women have their own thoughts, in the poems he had written have shown the anger, resentment,fear and pity of female. At the same time, this figure also expressed the view that male should be the dominant position in the relationship between men and women, Lawrence also expressed in the text the resentment of possessive, strong and feisty women. Lawrence articulated a unique view of religion: That the only way to save mankind is the unification of body and mind, the perfect harmony of sex and the male-dominated marriage. Only when it reaches the natural balance between the two and the respect with each other,
机械专业毕业论文外文翻译
附录一英文科技文献翻译 英文原文： Experimental investigation of laser surface textured parallel thrust bearings Performance enhancements by laser surface texturing (LST) of parallel-thrust bearings is experimentally investigated. Test results are compared with a theoretical model and good correlation is found over the relevant operating conditions. A compari- son of the performance of unidirectional and bi-directional partial-LST bearings with that of a baseline, untextured bearing is presented showing the bene?ts of LST in terms of increased clearance and reduced friction. KEY WORDS: ?uid ?lm bearings, slider bearings, surface texturing 1. Introduction The classical theory of hydrodynamic lubrication yields linear (Couette) velocity distribution with zero pressure gradients between smooth parallel surfaces under steady-state sliding. This results in an unstable hydrodynamic ?lm that would collapse under any external force acting normal to the surfaces. However, experience shows that stable lubricating ?lms can develop between parallel sliding surfaces, generally because of some mechanism that relaxes one or more of the assumptions of the classical theory. A stable ?uid ?lm with su?cient load-carrying capacity in parallel sliding surfaces can be obtained, for example, with macro or micro surface structure of di?erent types. These include waviness [1] and protruding microasperities [2–4]. A good literature review on the subject can be found in Ref. [5]. More recently, laser surface texturing (LST) [6–8], as well as inlet roughening by longitudinal or transverse grooves [9] were suggested to provide load capacity in parallel sliding. The inlet roughness concept of Tonder [9] is based on ??e?ective clearance‘‘ reduction in the sliding direction and in this respect it is identical to the par- tial-LST concept described in ref. [10] for generating hydrostatic e?ect in high-pressure mechanical seals. Very recently Wang et al. [11] demonstrated experimentally a doubling of the load-carrying capacity for the surface- texture design by reactive ion etching of SiC
英语专业毕业论文文献综述样例
英语专业毕业论文文献综述样例 参考范文1 Distance Learning This paper will summarize two articles on distance learning and give the author’s views on the benefits and obstacles of implementing distance-learning in a junior and senior high school learning environment. Jeannette McDonald, in her article: Is “As good as face-to-face” as good as it gets? (2002), raises a very important question as to whether “[the] goal [of online learning should be] to meet existing standards of traditional education”(McDonald, 2002) or “has distance learning, and especially online education opened the door to enhanced strategies in teaching and learning”(McDonald, 2002)? Online learning may just be “doing different things” (McDonald, 2002). What are these different things? Jeannette McDonald claims that “distance education can be a frontier for new methods of communication giving rise to innovative teaching and learning practices that may not be possible in traditional, place-bound education”(2002). The article discusses both the positive and “potential negative impacts of online education” (McDonald, 2002). There are many benefits to using online distance learning environments. Online education is available “anyplace, anytime [for] global communities of learners based on shared interests”(McDonald, 2002). Jeannette McDonald claims that “online education [with its] group-based instruction [and] computer mediated communication (CMC) provides an opportunity for new development and understanding in teaching and learning” (2002). CMC encourages “collaborative learning [by not providing] cues regarding appearance, race, gender, education, or social status bestowing a sort of anonymity to participants” (McDonald, 2002). Distance also “permits the expression of emotion (both positive and negative) and promotes discussion that normally would be inhibited. [Yet, this same] text-based [positive aspect of online learning], makes online education more cumbersome and therefore takes more time than face-to-face learning. [In addition,] the sheer bulk of messages can be overwhelming”(McDonald, 2002). The learner only has the written text and no other “non-verbal”(McDonald, 2002) cues. This may confuse the learner and cause “misunderstanding” (McDonald, 2002). The article lists the “seven principles of good practice in undergraduate education” (McDonald, 2004) published in 1987 by the American Association of Higher Education Bulletin. Jeannette McDonald claims that “online education has the potential to achiever all of these practices”(2002). There is a need for quality and standards for distance learning. “In April 2000, the institute of Higher Education Policy produced a study with 24 benchmarks for the success in Internet-based distance education”(The Institute for Higher Education Policy, 2000). Although Jeannette McDonald feels that there are “biases against distance learning programs”(2002), her recommendation is “to take advantage of the potential of online education [by striving] to understand the technology and how it affects human communication and interaction” (2002). “In the road to dotcom in education” (2004), Mark David Milliron deals with