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近十几年来,我国出现了前所未有的“申遗热”,这固然有利益驱动的因素,但遗产保护意识不断增强也是一个重要原因。被列入世界遗产名录能够提高一个国家、一个地区或一个城市在世界范围内的知名度,但更为重要的是,遗产保护事业在一定程度上还展示了一个国家文明进步的程度和教育科技文化发展的水平。需要指出的是, 相似文献
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苏小谦 《小哥白尼(野生动物画报)》2019,(3)
<正>许多在时空穿越中去过地球的长颈鹿都说,它们遇到了另一个自己。"那个名叫地球的星球在平行宇宙里,大气、密度、生命……都和咱们这里很像。我在那儿遇到了另一个我,它不仅外表和我一样,经历和思想几乎也和我一模一样。"一个小伙伴说。"我的另一个自己没我这么高大,不过它也很漂亮!"又一个小伙伴说。遇到另一个自己?小长颈鹿扎拉法想象不出那是 相似文献
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《小哥白尼(野生动物画报)》2014,(10)
<正>一个可爱的小公主在池塘边玩皮球,结果皮球掉进了水里,公主非常着急。这时候一只青蛙来到公主面前,对她说:"美丽的公主,我可以再给你一个球,但有一个要求——你必须和我做朋友。"公主思考了片刻,点点头。于是,青蛙把自己变成了一个球……注意,这不是冷笑话,而是一个科普故事。因为如果你认识了散疣短头蛙,《青蛙王子》的故事走向完全可以是这个样子…… 相似文献
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一个非常繁忙,在世界各地飞来飞去做生意的中国商人拥有很多的财富。一个深夜,在美国旧金山他突然发生难以忍受的腹部疼痛,到了医院后,急诊医生认真负责地接待了他,初步诊断是急腹症,需要上手术台剖腹探察。就在上手术台前,他用手机拨通了一个长途,手机很快转 相似文献
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以California大学Berkeley分校Sung-Hou Kim研究组为主发表的文章,被视作为癌基因作用研究上的一个里程碑。Kim及其同事报道了有关ras癌基因家族中的一个成员所编码的一种蛋白质的三维结构。“这是第一个被确定了结构的癌基因蛋白质”,Kim说,“由此提供了认识ras基因生物功能的结构基础”。 相似文献
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英国肯特郡有一个原不出名的斯旺斯考培(Swa-nscombe)小城镇。由于在50年前,牙科医生兼业余考古学家A.T.麦斯通,在这里一个采石场寻找石器时发现了人类化石,因而变得令人瞩目。斯旺斯考培古人的骨骼化石是50年前的一个周末发现的,50年后的一个周末举行了庆祝仪式,遗址揭匾开放。麦斯通挖出了两块头骨(枕骨和左顶骨),还有一块右顶骨是 相似文献
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Whitaker TB 《Molecular biotechnology》2003,23(1):61-71
It is difficult to obtain precise and accurate estimates of the true mycotoxin concentration of a bulk lot when using a mycotoxin-sampling
plan that measures the concentration in a small portion of the bulk lot. A mycotoxin-sampling plan is defined by a mycotoxin
test procedure and a defined accept/reject limit. A mycotoxin test procedure is a complicated process and generally consists
of several steps: (a) a sample is taken from the lot, (b) the sample is ground (comminuted) in a mill to reduce particle size,
(c) a subsample is removed from the comminuted sample, and (d) the mycotoxin is extracted from the comminuted subsample and
quantified. Even when using accepted test procedures, there is variability associated with each step of the mycotoxin test
procedure. Because of this variability, the true mycotoxin concentration in the lot cannot be determined with 100% certainty
by measuring the mycotoxin concentration in a sample taken from the lot. The variability for each step of the mycotoxin test
procedure, as measured by the variance statistic, is shown to increase with mycotoxin concentration. Sampling is usually the
largest source of variability associated with the mycotoxin test procedure. Sampling variability is large because a small
percentage of kernels are contaminated and the level of contamination on a single seed can be very large. Methods to reduce
sampling, sample preparation, and analytical variability are discussed. 相似文献
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Rob Lovering 《Bioethics》2020,34(3):242-251
Some people (e.g., Drs. Paul and Susan Lim) and, with them, organizations (e.g., the National Embryo Donation Center) believe that, morally speaking, the death of a frozen human embryo is a very bad thing. With such people and organizations in mind, the question to be addressed here is as follows: if one believes that the death of a frozen embryo is a very bad thing, ought, morally speaking, one prevent the death of at least one frozen embryo via embryo adoption? By way of a three-premise argument, one of which is a moral principle first introduced by Peter Singer, my answer to this question is: at least some of those who believe this ought to. (Just who the “some” are is identified in the paper.) If this is correct, then, for said people, preventing the death of a frozen embryo via embryo adoption is not a morally neutral matter; it is, instead, a morally laden one. Specifically, their intentional refusal to prevent the death of a frozen embryo via embryo adoption is, at a minimum, morally criticizable and, arguably, morally forbidden. Either way, it is, to one extent or another, a moral failing. 相似文献
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Lectin affinity electrophoresis is a powerful technique to investigate the interaction between a lectin and its ligand. Affinity
electrophoresis results from the reduced mobility of a charged species owing to its interaction with an immobile species.
In this protocol, a two-dimensional lectin affinity electrophoresis experiment is described that affords separation of oligosaccharides.
The first-dimension is composed of a weak, polyacrylamide, capillary tube gel containing a lectin. The example described involves
a mixture of fluorescently labeled disaccharides. The mobility of only the lectin-binding disaccharide is reduced affording
a separation in the first-dimension. The tube gel is then extruded and placed onto the second-dimension gradient polyacrylamide
gel and subjected to electrophoresis. Mobility in the second-dimension is dependent on molecular size and visualization is
by fluorescence under transillumination. This method is also applicable, with appropriate modifications, for the separation
and analysis of glycopeptides and glycoproteins. 相似文献
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This study examines the optimal seasonal timing of the life cycle for univoltine and bivoltine insects, assuming that resource
availability has a peak in the middle of a year and is symmetric around it. Results show that if the growth rate increases
in proporrion to the bodyweight, bivoltine life cannot be optimal. If the growth rate is a power function of the bodyweight
with a power smaller than unity, a symmetric bivoltine solution can be the optimal provided that the resource availability
has a plateau in the middle of the season. If the resource availability has a sharp peak, the optimal pattern is an asymmetric
bivoltine solution in which the larval periods of two generations differ in length. The bivoltine life cycle is more likely
to be superior to the univoltine one if: growth is fast, suitable growing season is long, biomass loss during nonlarval stages
is small, and egg size is small. 相似文献
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Summary The problem of determining the minimal phylogenetic tree is discussed in relation to graph theory. It is shown that this problem is an example of the Steiner problem in graphs which is to connect a set of points by a minimal length network where new points can be added. There is no reported method of solving realistically-sized Steiner problems in reasonable computing time. A heuristic method of approaching the phylogenetic problem is presented, together with a worked example with 7 mammalian cytochrome c sequences. It is shown in this case that the method develops a phylogenetic tree that has the smallest possible number of amino acid replacements. The potential and limitations of the method are discussed. It is stressed that objective methods must be used for comparing different trees. In particular it should be determined how close a given tree is to a mathematically determined lower bound. A theorem is proved which is used to establish a lower bound on the length of any tree and if a tree is found with a length equal to the lower bound, then no shorter tree can exist. 相似文献
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An SI epidemic model for a host with two viral infections circulating within the population is developed, analyzed, and numerically simulated. The model is a system of four differential equations which includes a state for susceptible individuals, two states for individuals infected with a single virus, one which is vertically transmitted and the other which is horizontally transmitted, and a fourth state for individuals infected with both viruses. A general growth function with density-dependent mortality is assumed. A special case of this model, where there is no coinfection and total cross immunity, is thoroughly analyzed. Several threshold values are defined which determine establishment of the disease and persistence at equilibrium for one or both of the infections within the host population. The model has applications to a hantavirus and an arenavirus that infect cotton rats. The hantavirus is transmitted horizontally whereas the arenavirus is transmitted vertically. It is shown through analysis and numerical simulations that both diseases can be maintained within a single host population, where individuals can be either infected with both viruses or with a single virus. 相似文献
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The control of balance is a primary objective in most human movements. In many cases, research or practice, it is essential to quantitatively know how good the balance is at a body posture or at every moment during a task. In this paper we suggest a new measure for postural upright stability which assigns a value to a body state based on the probability of avoiding a fall initiation from that state. The balance recovery problem is solved for a population sample using a strength database, and the probability of successfully maintaining the balance is found over the population and called the probability of recovery (PoR). It, therefore, describes an attribute of a body state: how possible the control of balance is, or how safe being at that state is. We also show the PoR calculated for a 3-link body model for all states on a plane, compare it to that found using a 2-link model, and compare it to a conventional metric: the margin of stability (MoS). It is shown, for example, that MoS may be very low at a state from which most of the people will be able to easily control their balance. 相似文献
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J H Relethford 《American journal of physical anthropology》1992,89(4):459-466
A model is developed that treats migration rates among populations as a function of the geographic distance between them and the size of both sources and recipient population. Specifically, mij/mjj = a(Ni/Nj)pe-bd, where mij/mjj is the relative migration rate into population j from population i, Ni is the size of the source population, Nj is the size of the recipient population, d is the geographic distance between populations i and j, p is a measure of differential density-dependence, b is a measure of distance decay, and a is an adjustment parameter with little demographic meaning. Methods of parameter estimation and hypothesis testing using maximum likelihood are outlined. These methods are applied to migration matrix data from 13 samples obtained from the literature representing a wide range of ecological settings. All samples show a significant effect of geographic distance on migration, and all but one show a significant effect of differential population size. All but one sample show an overall tendency for migration to be negative density-dependent; that is, the relative migration rate is greater from larger populations to smaller populations than the reverse. 相似文献
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The coalescent process in the human-chimpanzee ancestral population is investigated using a model, which incorporates a certain time period of gene flow during the speciation process. a is a parameter to represent the degree and time of gene flow, and the model is identical to the null model with an instantaneous species split when a=infinity. A maximum likelihood (ML) method is developed to estimate a, and its power and reliability is investigated by coalescent simulations. The ML method is applied to nucleotide divergence data between human and chimpanzee. It is found that the null model with an instantaneous species split explains the data best, and no strong evidence for gene flow is detected. The result is discussed in the view of the mode of speciation. Another ML method is developed to estimate the male-female ratio (alpha) of mutation rate, in which the coalescent process in the ancestral population is taken into account. 相似文献