GMAT-Official Guide for GMAT Review 12 阅读翻译 20篇

pansy

1.A recent study has provided clues to predator-prey dynamics in the late Pleistocene era. Researchers compared the number of tooth fractures in carnivores that lived 36,000 to 10,000 years ago and that were preserved in the Rancho La Brea tar pits in Los Angeles. The breakage frequencies in the extinct species were strikingly higher than those in the present-day species.

In considering possible explanations for this finding, the researchers dismissed demographic bias because older individuals were not overrepresented in the fossil samples. They rejected preservational bias because a total absence of breakage in two extinct species demonstrated that the fractures were not the result of abrasion within the pits. They ruled out local bias because breakage data obtained from other Pleistocene sites were similar to the La Brea data. The explanation they consider most plausible is behavioral differences between extinct and present-day carnivores—in particular, more contact between the teeth of predators and the bones of prey due to more thorough consumption of carcasses by the extinct species. Such thorough carcass consumption implies to the researchers either that prey availability was low, at least seasonally, or that there was intense competition over kills and a high rate of carcass theft due to relatively high predator densities.

近期的一项研究为更新世后期食肉动物的捕食动态提供了线索。就食肉动物牙齿的磨损情况，研究者在现今食肉动物和生活在3600到10000年前的食肉动物（遗存于洛杉矶的拉布雷亚牧场沥青坑中）之间做了对比。这些已灭绝物种的牙齿破损发生率要明显高于现存物种。

在考虑对这一发现各种可能的解释时，研究者排除了统计偏差，因为年老个体没有过多占据化石样本总体。排除了可能因保存不当造成的偏差，因为两个完全没有破损的灭绝物种化石表明磨损不是由坑中的摩擦造成的。排除了地域性偏差，因为从其它更新世发掘地获得的数据与拉布雷亚的数据相近。而后研究者得出了他们认为最合理的解释——是因为灭绝物种和现存物种行为上的差异，尤其是由于已灭绝捕食者对猎物更彻底的啃食，使其牙齿与猎物骨头有更多的接触。研究者由这种彻底的啃食行为推断，不是猎物太少（至少是季节性的），就是捕食者太多，以致猎杀时有激烈的竞争和频繁的猎物盗取。

pansy

20．All the cells in a particular plant start out with the same complement of genes. How then can these cells differentiate and form structures as different as roots, stems, leaves, and fruits? The answer is that only a small subset of the genes in a particular kind of cell are expressed, or turned on, at a given time. This is accomplished by a complex system of chemical messengers that in plants include hormones and other regulatory molecules. Five major hormones have been identified: auxin, abscisic acid, cytokinin, ethylene, and gibberellin, studies of planrts have now identified a new class of regulatory molecules called oligosaccharins.
Unlike the oligosaccharins, the five well-known plant hormones are pleiotropic rather than specific; that is, each has more than one effect on the growth and development of plants. The five have so many simultaneous effects that they are not very useful in artificially controlling the growth of crops. Auxin, for instance, stimulates the rate of cell elongation, causes the plant to develop a vascular system, to form lateral roots, and to produce ethylene.
The pleiotropy of the five well-studied plant hormones is somewhat analogous to that of certain hormones in animals. For example, hormones from the hypothalamus in the brain stimulate the anterior lobe of the pituitary gland to synthesize and release many different hormones, one of which stimulates the release of hormones have specific effects on target organs all over the body. One hormone stimulates the thyroid gland, for example, another the ovarian follicle cells, and so forth. In other words, there is a hierarchy of hormones.
Such a hierarchy may also exist in plants. Oligosaccharins are fragments of the cell wall released by enzymes release different oligosaccharins. There are indications that pleiotropic plant hormones may actually function by activating the enzymes that release these other, more specific chemical messengers from the cell wall.


一棵植物中的所有细胞都开始于一套完整的基因。这些细胞是怎样分化成不同的细胞从而形成根、茎、叶和果实的呢？这是因为在特定时期一种细胞中只有一小部分基因在表达或表现。这是通过植物中激素及其它调控分子等复杂的化学信息系统实现的。已经被证实的有五大激素：生长素、脱落酸、细胞分裂素、乙烯和赤霉素。现代又发现了一种新的调控分子寡聚糖素。
与特效寡聚糖素不同，这五种熟知的植物激素是多效的，也就是说每一种都对植物的生长发展有多种影响。这五种激素有太多的同期影响以至于对人为控制作物生长不是非常有效。例如生长素，刺激细胞伸长，使枝干向上生长，根向下生长，阻碍侧枝生长。生长素还能促进植物维管束的形成，侧枝的生长和乙烯的产生。
这五种熟知的植物基因的多效性与与某种动物基因的多效性类似。例如，下丘脑分泌的激素能刺激垂体前叶合成并释放多种激素。其中一种又能刺激肾上腺皮质分泌激素。这些激素对全身各个器官有特定的作用。一种刺激甲状腺，另一种刺激卵泡细胞，等等。。。换句话说就是有一种激素层级。
这种层级也可能在植物中存在。寡聚糖素是酶分解的细胞壁碎片：不同的酶分解不同的寡聚糖素。有指征说明多效的植物激素可能通过激活从细胞壁释放其它化学信息的酶来起作用。

pansy

20．All the cells in a particular plant start out with the same complement of genes. How then can these cells differentiate and form structures as different as roots, stems, leaves, and fruits? The answer is that only a small subset of the genes in a particular kind of cell are expressed, or turned on, at a given time. This is accomplished by a complex system of chemical messengers that in plants include hormones and other regulatory molecules. Five major hormones have been identified: auxin, abscisic acid, cytokinin, ethylene, and gibberellin, studies of planrts have now identified a new class of regulatory molecules called oligosaccharins.
Unlike the oligosaccharins, the five well-known plant hormones are pleiotropic rather than specific; that is, each has more than one effect on the growth and development of plants. The five have so many simultaneous effects that they are not very useful in artificially controlling the growth of crops. Auxin, for instance, stimulates the rate of cell elongation, causes the plant to develop a vascular system, to form lateral roots, and to produce ethylene.
The pleiotropy of the five well-studied plant hormones is somewhat analogous to that of certain hormones in animals. For example, hormones from the hypothalamus in the brain stimulate the anterior lobe of the pituitary gland to synthesize and release many different hormones, one of which stimulates the release of hormones have specific effects on target organs all over the body. One hormone stimulates the thyroid gland, for example, another the ovarian follicle cells, and so forth. In other words, there is a hierarchy of hormones.
Such a hierarchy may also exist in plants. Oligosaccharins are fragments of the cell wall released by enzymes release different oligosaccharins. There are indications that pleiotropic plant hormones may actually function by activating the enzymes that release these other, more specific chemical messengers from the cell wall.


一棵植物中的所有细胞都开始于一套完整的基因。这些细胞是怎样分化成不同的细胞从而形成根、茎、叶和果实的呢？这是因为在特定时期一种细胞中只有一小部分基因在表达或表现。这是通过植物中激素及其它调控分子等复杂的化学信息系统实现的。已经被证实的有五大激素：生长素、脱落酸、细胞分裂素、乙烯和赤霉素。现代又发现了一种新的调控分子寡聚糖素。
与特效寡聚糖素不同，这五种熟知的植物激素是多效的，也就是说每一种都对植物的生长发展有多种影响。这五种激素有太多的同期影响以至于对人为控制作物生长不是非常有效。例如生长素，刺激细胞伸长，使枝干向上生长，根向下生长，阻碍侧枝生长。生长素还能促进植物维管束的形成，侧枝的生长和乙烯的产生。
这五种熟知的植物基因的多效性与与某种动物基因的多效性类似。例如，下丘脑分泌的激素能刺激垂体前叶合成并释放多种激素。其中一种又能刺激肾上腺皮质分泌激素。这些激素对全身各个器官有特定的作用。一种刺激甲状腺，另一种刺激卵泡细胞，等等。。。换句话说就是有一种激素层级。
这种层级也可能在植物中存在。寡聚糖素是酶分解的细胞壁碎片：不同的酶分解不同的寡聚糖素。有指征说明多效的植物激素可能通过激活从细胞壁释放其它化学信息的酶来起作用。

pansy

19．The majority of successful senior managers do not closely follow the classical model of first clarifying goals, estimating likelihoods of success, making a decision, and only then taking action to implement the decision. Rather, in their day-by-day tactical maneuvers, these senior executives rely on what is vaguely termed “intuition” to manage a network of interrelated problems that require them to deal with ambiguity, inconsistency, novelty, and surprise; and to integrate action into the process of thinking.
Generations of writers on management have recognized that some practicing managers rely heavily on intuition. In general, however, such writers display a poor grasp of what intuition is. Some see it as the opposite of rationality; others view it as an excuse for capriciousness.
Isenberg’s recent research on the cognitive processes of senior managers reveals that managers’ intuition is neither of these. Rather, senior managers use intuition in at least five distinct ways. First, they intuitively sense when a problem exists. Second, managers rely on intuition to perform well-learned behavior patterns rapidly. This intuition is not arbitrary or irrational, but is based on years of painstaking practice and hands-on experience that build skills. A third function of intuition is to synthesize isolated bits of data and practice into an integrated picture, often in an “Aha!” experience. Fourth, some managers use intuition as a check in the results of more rational analysis. Most senior executives are familiar with the formal decision analysis models and tools and those who use such systematic methods for reaching decisions are occasionally leery of solutions suggested by these methods which run counter to their sense of the correct course of action. Finally, managers can use intuition to bypass in-depth analysis and move rapidly to engender a almost instantaneous cognitive process in which a manager recognizes familiar patterns.
One of the implications of the intuitive style of executive management is that “thinking” is inseparable from acting. Since managers often “know” what is right before they can analyze and explain it, they frequently act first and explain later. Analysis is inextricably tied to action in thinking/acting cycles, in which managers develop thoughts about their companies and organizations not by analyzing a problematic situation and then acting, but by acting problematic situation and then acting and analyzing in close concert. Given the great uncertainty of many of the management issues that they face, senior managers often instigate a course of action simply to learn more about an issue. they then use the results of the action to develop a more complete understanding of the issue. One implication of thinking/acting cycles is that action is often part of defining the problem, not just of implementing the solution.

大部分成功的高级管理者做决策时，并不是按照传统的理性模式，即首先澄清目标、分析问题、构想可行方案、估计成功的可能性，然后再采取行动执行决议。实际上这些高级决策者在面对一天天的战略性决策时，是依靠“直觉”这个模糊词来解决一系列错综复杂的问题。 这要求他们能处理模棱两可、相互矛盾、新奇惊人的问题并且能在思考的过程中作出决策。
一批撰写管理方面书籍的作者认为一些积极的管理者在很大程度上依靠直觉做决策。总的来说这些作家显然没有领悟到直觉是什么。一些作家认为直觉是理智的反义词，还有一些作家把直觉看做决策变幻莫测的借口。
Isenberg 最近关于高级管理者认知过程的研究显示，管理者的直觉不属于以上任何一种。相反，高级管理者的直觉用于以下明确的五种情况：第一、他们能用直觉感受到问题的存在。第二、管理者能依靠直觉将他们熟知的行动方式迅速付诸实施。这种直觉不是武断或者不理智，而是基于多年的辛苦实践和增强技能的亲身经历。直觉的第三种功能是把相互孤立的数据和实际行动整合起来，随之而来的通常是“啊!”的一声惊叹。第四、一些管理者用直觉来检验相对理性的分析。大多数管理者熟知正规的决策分析方式和方法，并且使用这种程序性方法做决策的管理者有时会怀疑那些与他们感觉正确的方案相反的建议决策。最后一条，决策者会用直觉避开更深层的分析从而更快得出合理可行的决策。直觉运用于以上情境就是管理者再认熟知模式时的瞬间认知过程。这种依靠直觉的决策管理在一方面暗指“思考”和行动是不可分割的。因为管理者通常在分析和解释一个决策之前就“知道”它是对的，他们经常先采取行动再做解释。在思考-行动的循环中分析与行动是密不可分的，在这个循环中逐渐形成对公司和组织的看法。这种看法的形成不是通过分析一个产生问题的情况然后采取行动，而是通过采取行动而后再分析。面对管理问题中的许多不确定因素，高级管理者往往先采取一种处理方法以便对问题多一些了解，然后用这种处理方式所产生的结果来完善对问题的了解。一个完善的思考-行动循环即行动通常是阐明问题过程的一部分，而不是仅仅实施解决方案。

pansy

18．According to a recent theory, Archean-age gold-quartz veinsystens were formed more than two billion years ago from magmatic fluids that originated from molten granite-like bodies deep beneath the surface of the Earth. This theory is contrary to the widely held view that the systems were deposited from metamorphic fluids, that is, from fluids that formed during the dehydration of wet sedimentary tocks.
The recently developed theory has considerable practical importance. Most of the gold deposits discovered during the original gold rushes were exposed at the Earth’s surface and were found because they had shed trails of alluvial gold that were easily easily traced by simple prospecting methods. Although these same methods still lead to an occasional discovery, most deposits not yet discovered have gone undetected because they are buried and have no surface expression.
The challenge in exploration is therefore to unravel the subsurface geology of an area and pinpoint the position of buried minerals. Methods widely used today include analysis of aerial images that yield a broad geological overview; geophysical techniques that provide data on the magnetic, electrical, and mineralogical properties of the rocks being investigated; and sensitive chemical tests that are able to detect the subtle chemical halos that often envelop mineralization. However, none of these high-technology methods are of any value if the sites to which they are applied have never mineralized, and to maximize the chances of discovery the explorer must therefore pay particular attention to selecting the ground formations most likely to be mineralized. Such ground selection relies to varying degrees on conceptual models, which take into account theoretical studies of relevant factors.
These models are constructed primarily from empirical observations of known mineral deposits and from theories of ore-forming processes. The explorer uses the models to identify those geological features that are critical to the formation of the minerlization being modeled, and then tries to select areas for exploration that exhibit as many of the critical features as possible.

依据最新的理论，太古界时期的金石英脉形成于20亿年前由深入地球表面以下真石胚体熔化形成的岩浆流体。这一理论与广泛认为的由变质岩流体的沉积形成理论（也就是在潮湿泥沙盐的干燥过程中形成）相反。
这一最新形成的理论有重大实践意义。在最初淘金热时发现的金矿床大多显露在地球表面，通过简单的勘探就会发现冲积砂金留下的痕迹，尽管通过这种方法还会偶尔发现金矿，然而大多数没有被发现的金矿就探测不到了，因为这类金矿深埋在地下，在地球表面也没有什么表现。
因此勘探的挑战在于弄清一个地域地表以下的地质问题并为埋藏的矿藏明确定位。今天广泛使用的方法包括：分析航拍图像得出地质概况，运用地球物理技术获得所研究矿石的磁、电和矿物性能，通过敏感的化学实验来检测通常被不易察觉的化学晕所包围的矿化。但是，如果勘察的这些地点从来没有矿化，想要有所发现勘探者就要特别留意挑选最有矿化可能的底层。这样在这些高科技方法中，就没有一个有任何价值了。这种地层选择依赖于概念模型的程度变化，而概念模型要考虑相关因素的理论研究。
这些模型的建立，主要是依据对所知矿石的实验观察和成矿过程的理论。勘探者用这些模型来鉴别所模拟矿化形成的临界地质特征，然后试着挑选具有较多临界特征的勘探地域。

pansy

17．After evidence was obtained in 1920s that the university is expanding, it became reasonable to ask: will the universe expand indefinitely, or is there enough mass in it for the mutual attraction of its constituents to bring this expansion to a halt? It can be calculated that the critical density of matter needed to brake the expansion and “close” the universe is equivalent to there hydrogen atoms per cubic meter. But the density of the observable universe—luminous matter in the form of galaxies—comes to only a fraction of this. If the expansion of the universe is to stop there must be enough invisible matter in the universe to exceed the luminous matter in density by a factor of roughly 70.
  Our contribution to the search for this “missing matter” has been to study the rotational velocity of galaxies at various distances from their center of rotation. It has been known for some time that outside the bright nucleus of a typical spiral galaxy luminosity falls off rapidly with distance from the center. If luminosity were a true indicator of mass, most of the mass would be concentrated toward the center. Outside the nucleus the rotational velocity would decrease geometrically with distance from the center, in conformity with Kepler’s law. Instead we have found that the rotational velocity in spiral galaxies either remains constant with increasing distance from the center or increases slightly. This unexpected result indicates that the falloff in luminous mass with distance from the center is balanced by an increase in nonluminous mass.
  Our findings suggest that as much as 90 percent of the mass of the universe is not radiating at any wavelength with enough intensity to be detected on the Earth. Such dark matter could be in the form of extremely dim stars of low mass, of large planets like Jupiter, or of black holes, either small or massive. While it has not yet been determined whether this mass is sufficient to close the universe, some physicists consider it significant that estimates are converging on the critical value.

    十九世纪二十年代，人们证明宇宙是在不断扩大的，于是有人问：宇宙会继续无限地扩大下去，还是已经有足够大的质量来维系天体间的相互吸引使宇宙停止扩大。计算得出,使宇宙停止扩大所需要的临界密度等于三个氢原子/立方米。但是我们可以观测到的宇宙（星系中的可见物质）的密度小于该临界密度。如果要让宇宙停止扩大，那就必须要有超过可见物质密度约70倍的不可见物质存在。
为了寻找这些“丢失的物质”，我们研究了星系在据其环绕中心不同位置的环绕速度。我们曾经认为在典型螺旋星系的明亮中心以外，亮度随距中心距离的增加而急剧减弱。如果亮度标志着质量，那么大部分质量就应该集中在星系的中心。而根据开普勒定律，随着距中心距离的增加环绕速度应该呈几何递减。可是，我们发现螺旋星系中天体的环绕速度保持不变或是随距离增加稍稍变快。这个出乎意料的结果表明随距中心距离的增加，不可见物质质量的增加抵消了可见物质质量的减少。
我们的研究结果表明占宇宙质量90%的物质不能发出可从地球上观测到的光。这种暗物质可能是特别暗的质量轻的恒星，大的行星如木星或者是大、小黑洞。虽然还没有确定这些质量是否足以使宇宙停止扩大，一些物理学家认为这些推测正趋向接近临界值，这是意义重大的。

pansy

16．Frazier and Mosteller assert that medical research could be improved by a move toward larger, simpler clinical trials of medical treatments. Currently, researchers collect far more background information on patients than is strictly required for their trials—substantially more than hospitals collect—thereby escalating costs of data collection, storage, and analysis. Although limiting information collection could increase the risk, never entirely eliminable from research on entirely new treatments are new and unexpected variables likely to arise.
  Frazier and Mosteller propose not only that researchers limit data collection on individual patients but also that researchers enroll more patients in clinical trials, thereby obtaining a more representative sample of the total population with the disease under study. Often researchers restrict study participation to patients who have no ailments besides those being studied. A treatment judged successful under these ideal conditions can then be evaluated under normal conditions. Broadening the range of trial participants, Frazier and Mosteller suggest, would enable researchers to evaluate a treatment’s efficacy for diverse patients under various conditions and to evaluate its effectiveness for different patient subgroups. For example, the value of a treatment for a progressive disease may vary according to a patient’s stage of disease. Patients’ ages may also affect a treatment’s efficacy.
  
Frazier 和 Mosteller 声称可以通过进行更大规模，更简单易行的药物临床试验来改进医学研究。现在，研究者收集的病人资料远远超过了做实验所需要从医院收集的资料，这使得收集、保存和分析数据的花费都增加了。尽管所收集资料的局限性会增加研究者忽略相关研究因素的风险，但是Frazier 和 Mosteller 称这种风险不可能消除，只能在大多数研究中降到最低。只有在对新式疗法的研究中才有可能出现新的始料不及的变量。
   Frazier 和 Mosteller 不仅建议研究者将数据收集限制在个别病人身上，还建议研究者在临床试验中多加入一些病例，这样才能从病人的总体中获得更具代表性的样本。通常，研究者会把研究案例限制在除所研究病例外没有其它病情的病人中。如果治疗方案在这种理想的条件下被证明有效，将会被放在普通条件下再做评估。Frazier 和 Mosteller 认为扩大实验对象的范围便于研究者评估治疗方案在不同情况下对不同病人的疗效，以及对不同分组病人的有效性。例如，治疗方案的效果可能因病人所处病程的不同而变化。病人的年龄也可能影响疗效。

pansy

15．In1995 Maurice Duverger published The Political Role of Women, the first behaviotalist, multinational comparison of women’s electoral participation ever to use election data and survey data together. His study analyzed women’s patterns of voting, political candidacy, and political activism in four European countries during the first half of the twentieth century. Duverger’s research findings were that women voted somewhat less frequently than men (the difference narrowing the longer women had the vote) and were slightly more conservative.
Duverger’s work set an early standard for the sensitive analysis of women’s electoral activities. Moreover, to Duverger’s credit, he placed his findings in the context of many of the historical processes that had shaped these activities. However, since these contexts have changed over time, Duverger’s approach has proved more durable than his actual findings. In addition, Duverger’s discussion of his findings was hampered by his failure to consider certain specific factors important to women’s electoral participation at the time he collected his data: the influence of political regimes, the effects of political and social relations between women and men. Given this failure, Duverger’s study foreshadowed the enduring limitations of the behavioralist approach to the multinational study of women’s political participation.

1995，Maurice Duverger 出版了《女性的政治角色》，作为第一部行为主义著作，这部书中首次将选举数据和调查数据并用，对女性参与选举的情况进行了多国对比。Maurice Duverger 在研究中分析了20世纪上半叶欧洲四国女性的选举形势，候选资格和政治积极性。
研究结果表明，有时女性参加选举的频率低于男性（而女性参选时间越长，这一差别越小）并且比男性稍微保守些。
      Duverger的著作为细致分析女性选举行为创建了早期标准。此外，他将调查研究的背景置于影响女性选举活动发展的历史进程中，这也是值得称赞的。但是，因为这些背景是随时间变化的，所以Duverger的方法比他的研究结果更持久可靠。此外，Duverger对其研究结果的进一步讨论收到了阻碍，因为他在收集数据时没有考虑到对女性参与选举有重要影响的某些特殊因素，比如国家政体，经济因素，女性和男性间的政治社会关系。由此，Duverger的研究预示了行为主义者对女性参与政治的跨国研究所具有的局限将持续下去。

pansy

14．It was once believed that the brain was independent of metabolic processes occurring elsewhere in the body. In recent studies, however, we have discovered that the production and release in brain neurons of the neurotransmitter serotonin (neurotransmitters are compounds that neurons use to transmit signals to other cells) depend directly on the food that the body processes.
Our first studies sought to determine whether the increase in serotonin observed on rats given a large injection of the amino acid tryptophan might also occur after rats ate meals that change tryptophan levels in the blood. We found that, immediately after the rats began to eat, parallel elevations occurred in blood tryptophan, brain tryptophan, and brain serotonin levels. These findings suggested that the production and release of serotonin in brain neurons were normally coupled withblood-tryptophan increases. In later studies we found that injecting insulin into a rat’s blood and brain tryptophan levels. We then decided to see whether the secretion of the animal’s own insulin similarly affected serotonin production. We gave the rats a carbohydrate-containing meal that we knew would elicit insulin secretion. As we had hypothesized, the blood tryptophan level and the concentrations of tryptophan level and the concentrations of tryptophan and of serotonin in the brain increased after the meal.
Surprisingly, however, when we added a large amount of protein to the meal, brain tryptophan and serotonin levels fell. Since protein contains rtyptophan, why should it depress brain tryptophan levels? The answer lies in the mechanism that provides blood tryptophan to the brain cells. This same mechanism also provides the brain cells. This same mechanism also provides the brain cells with other amino acids found in protein, such as tyrosine and leucine. The consumption of protein increases blood concentration of the other amino acids much more, proportionately, than it does that of tryptophan. The more protein is in a meal, the lower is the ratio of the resulting blood-tryptophan concentration to the concentration of competing amino acids, and the more slowly is tryptophan provided of the brain. Thus the more protein in a meal, the less serotonin subsequently produced and released.
以前，我们认为大脑独立于身体其它部位进行新陈代谢。但是，最近研究发现大脑神经细胞递质血清素（递质是神经细胞间用来传递信息的化学物质）的产生和释放与身体消化的食物有直接关系。
我们的第一项研究是为了确定在给大鼠注射大量色氨酸后所观察到的递质增加是否同样会出现在给大鼠饲喂能引起血液色氨酸含量提高的食物后。我们发现大鼠刚开始进食，其血液中的色氨酸，大脑中的色氨酸和大脑中的血清素水平都相应提高。这些迹象表明大脑神经递质血清素的产生和释放通常是与血液色氨酸含量的增加紧密相关。随后的研究发现给大鼠注射胰岛素也会使其血液中色氨酸，大脑中色氨酸和大脑中递质血清素水平都相应提高。然后我们决定看看大鼠自己分泌的胰岛素是否会对递质血清素的产生有相似的影响。于是，我们给大鼠喂含糖的食物，知道这会引起胰岛素分泌。正如我们所推测的，血液中的色氨酸水平和大脑中色氨酸与递质血清素的浓度都在喂食后提高了。
然而，出人意料的是，当在大鼠的食物中加入大量蛋白质时，大脑中色氨酸和递质血清素的水平却降低了。既然蛋白质含有色氨酸，大脑中的色氨酸水平为什么会降低呢？原因在于由血液向脑细胞提供色氨酸的机制。这一机制还向脑细胞提供蛋白质中的其它氨基酸，如酪氨酸和亮氨酸。蛋白质的食入使血液中其它氨基酸的浓度相对色氨酸提高了许多。食入的蛋白质越多，血液中色氨酸相对其它氨基酸的浓度就越低，色氨酸向大脑的提供就越慢。所以食入的蛋白质越多，随之产生和释放的递质血清素就越少。

pansy

13.Two works published in 1984 demonstrate contrasting approaches to writing the history of United States women. Buel and Buel’s biography of Mary Fish (1736-1818) makes little effort to place her story in the context of recent historiography on women. Lebsock, meanwhile, attempts not only to write the history of women in one southern community, but also to redirect two decades of historiographical debate as to whether women gained or lost status on the nineteenth century as compared with the eighteenth century. Although both books offer the reader the opportunity to assess this controversy regarding women’s status, only Lebsock’s deals with it directly. She examines several different aspects of women’s status, helping to refine and resolve the issues. She concludes that while women gained autonomy in some areas, especially in the private sphere, they lost it in many aspects of the economic sphere. More importantly, she shows that the debate itself depends on frame of reference: in many respects, women lost power in relation to men, for example, as certain jobs (delivering babies, supervising schools) were taken over by men. Yet women also gained power in comparison with their previous status, owning a higher proportion of real estate, for example. In contrast, Buel and Buel’s biography provides ample raw material for questioning the myth, fostered by some historians, of a colonial golden age in the eighteenth century but does not give the reader much guidance in analyzing the controversy over women’s status.
1984年出版的两本书展现了描写美国女性历史所采用的两种截然不同的方式。在碧儿的自传《玛丽鱼》中，碧儿没有试图把自己的故事放在近来女性史学研究的背景下。相比之下，莱布斯克不仅描写了南部一地区的女性历史，还引述了关于女性在19世纪的地位与18世纪相比是提升了还是降低了这一历史学争论。尽管这两本书都向读者提供机会来了解关于女性地位的争议，但是只有莱布斯克直接涉及了这一争论。莱布斯克调查了女性在几个不同方面的地位问题，来帮助改善进而解决这一问题。并由调查得出，尽管女性在某些领域获得了自主权，尤其是在个人领域，但是在经济领域的许多方面女性却失去了自主权。更重要的是，她认为争论本身是建立在参照对比上的，例如， 在许多方面，女性相对于男性而言就失去了权利，某些工作（生孩子、看管学校）由男性接替。而女性与她们以前的地位相比获得了权利，例如，拥有不动产的比例提高了。与莱布斯克相比，碧儿在她的自传中引用了大量的原始资料来质疑一些历史学家提出的18世纪的殖民黄金时期，但是她没有引导读者分析关于女性地位的争议。