共查询到20条相似文献,搜索用时 15 毫秒
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Arnold G Kluge 《Cladistics : the international journal of the Willi Hennig Society》2002,18(6):585-593
The adequacy of a probabilistic interpretation must be judged according to the nature of the event, or thing, being inferred. For example, conditional (frequency) probability is not admissible in the inference of phylogeny, because basic statements of common ancestry do not fulfill the requirements of the relations specified by the probability calculus. The probabilities of the situation peculiar to the time and place of origin of species are unique. Moreover, according to evolutionary theory, an event of species diversification is necessarily unique, because species are parts of a replicator continuum—species arise from ancestral species. Also, these probabilities cannot be ascertained, because the relevant situation cannot be repeated—it is unique. Finally, the applicability of conditional (frequency) probability is denied, because events of common ancestry have already occurred—there is nothing to predict. However, hypotheses of species relationships can be identified objectively according to the degree to which they have survived simultaneous testing with critical evidence, not with generally confirming evidence. The most parsimonious hypothesis of species relationships represents the least disconfirmed, best supported, proposition among the alternatives being compared. That hypothesis does not, however, deserve any special epistemological status beyond serving as the focus of the next round of testing. 相似文献
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B Przybylska 《Zeitschrift für mikroskopisch-anatomische Forschung》1989,103(2):329-335
Both qualitative and quantitative comparative studies of "dark" and "light" pinealocytes of the porcine pineal gland have been carried out. These cells differ from each other in their electronic density of cytoplasm, shape of nucleus, the structure of membrane bound dense bodies and the number of microtubules and smooth endoplasmic reticulum. The membrane bound dense bodies--characteristic structures of pig pinealocytes as well dense core vesicles occur in both types of cells. The relative volume of the majority of the cells' organellae apart from the Golgi apparatus, also do not show any significant difference. The results obtained support a functional basis for pinealocyte differentiation in the porcine pineal gland. 相似文献
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Traditionally, the information content of the neural response is quantified using statistics of the responses relative to stimulus onset time with the assumption that the brain uses onset time to infer stimulus identity. However, stimulus onset time must also be estimated by the brain, making the utility of such an approach questionable. How can stimulus onset be estimated from the neural responses with sufficient accuracy to ensure reliable stimulus identification? We address this question using the framework of colour coding by the archer fish retinal ganglion cell. We found that stimulus identity, “what”, can be estimated from the responses of best single cells with an accuracy comparable to that of the animal''s psychophysical estimation. However, to extract this information, an accurate estimation of stimulus onset is essential. We show that stimulus onset time, “when”, can be estimated using a linear-nonlinear readout mechanism that requires the response of a population of 100 cells. Thus, stimulus onset time can be estimated using a relatively simple readout. However, large nerve cell populations are required to achieve sufficient accuracy.
Authors Summary
In our interaction with the environment we are flooded with a stream of numerous objects and events. Our brain needs to understand the nature of these complex and rich stimuli in order to react. Research has shown ways in which a ‘what’ stimulus was presented can be encoded by the neural responses. However, to understand ‘what was the nature of the stimulus’ the brain needs to know ‘when’ the stimulus was presented. Here, we investigated how the onset of visual stimulus can be signalled by the retina to higher brain regions. We used archer fish as a framework to test the notion that the answer to the question of ‘when’ something has been presented lies within the larger cell population, whereas the answer to the question of ‘what’ has been presented may be found at the single-neuron level. The utility of the archer fish as model animal stems from its remarkable ability to shoot down insects settling on the foliage above the water level, and its ability to distinguish between artificial targets. Thus, the archer fish can provide the fish equivalent of a monkey or a human that can report psychophysical decisions. 相似文献9.
野生生物、野生动植物和野生来源的定义及范畴 总被引:3,自引:0,他引:3
关于野生生物、野生动植物和野生来源的定义是科学研究、物种保护和政策管理工作 ,特别是野生动植物立法和执法方面经常遇到的问题。对见于各种法规和文献中的野生生物、野生动植物、野生来源、人工繁殖、人工培植、天然、人工合成等概念的定义进行了分类、比较与分析 ,讨论了这些概念的相对性和使用范畴 ,提出了野生动植物的简要定义 ,并指出了这些概念的定义需根据实际需要而发展调整。 相似文献
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A K Terman 《Fiziologicheski? zhurnal》1991,37(3):119-127
An attempt is made to consider disease and aging following from the concepts of the essence of life. The proposed definition of life represents a modified Engels' (1878) definition. Proceeding from the analysis of possible mechanisms of different disturbances in the life process leading to a decreased probability of the organism existence it is concluded that disease develops either as a result of hereditary changes in the genome or due-to disorders in its realization under certain unfavorable conditions. Aging is determined by the properties of the genome itself and develops in connection with age increase. 相似文献
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Carol A. Smith 《American anthropologist》1997,99(2):381-383
Articulating Hidden Histories: Exploring the Influence of Eric R. Wolf. Jane Schneider and Rayna Rapp. eds. Berkeley: University of California Press, 1995.400 pp.
Reconceptualizing the Peasantry: Anthropology in Global Perspective. Michael Kearney. Boulder, CO. Westview Press, 1996. 210 pp. 相似文献
Reconceptualizing the Peasantry: Anthropology in Global Perspective. Michael Kearney. Boulder, CO. Westview Press, 1996. 210 pp. 相似文献
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Half-site reactivity and the "induced-fit" hypothesis 总被引:1,自引:0,他引:1
Many subunit enzymes show the phenomenon of half-site reactivity, that is, the reaction with a substrate or substrate analogue shows a stoichiometry equal to one-half the number of “identical” subunits. One obvious potential explanation for this phenomenon is that reaction with one substrate molecule induces a change in an adjacent subunit, preventing a subsequent substrate molecule from reacting. Such an explanation has been proposed for the half-site reaction of the enzyme cytidine triphosphate synthetase with a substrate analogue (Levitzki et al., 1971). Analogous studies with glyceraldehyde-3-phosphate dehydrogenase reveal that the four active-site (Cys-149) sulfhydryl groups per tetrameric molecule react equivalently with iodoacetate whereas only two of the four sites undergo facile acylation with the substrate. The simple fact that the 2:1 stoichiometry ratio for the alkylation-acylation reactions is independent of the degree of prior alkylation rules out the ligand-induced asymmetry model as an explanation of the stoichiometries. Rather, it suggests that in muscle dehydrogenase there is a pre-existent non-equivalence among the subunits. On these bases we propose a procedure for distinguishing induced from pre-existent asymmetry in quaternary structure. 相似文献
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Natriuretic "hormone" and the renal prostaglandins 总被引:1,自引:0,他引:1
J B Lee 《Prostaglandins》1972,1(1):55-70
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Beyond "the State" and Failed Schemes 总被引:4,自引:2,他引:2
TANIA MURRAY LI 《American anthropologist》2005,107(3):383-394
In this article, I propose five ways to move beyond the analytical scheme of James Scott's Seeing Like a State (1998). I question the spatial optic that posits an "up there," all-seeing state operating as a preformed repository of power, spread progressively outward to "nonstate" spaces beyond its reach. I highlight the role of parties beyond "the state" that attempt to govern—social reformers, scientists, and the so-called nongovernmental agencies, among others. I look beyond authoritarian high modernism to the more general problematic of "improvement" emerging from a governmental rationality focused on the welfare of populations. I explore the recourse to mētis (contextualized, local knowledge and practice) situated beyond the purview of planning. Finally, I reframe the question posed by Scott—why have certain schemes designed to improve the human condition failed?—to examine the question posed so provocatively by James Ferguson: What do these schemes do? What are their messy, contradictory, conjunctural effects? 相似文献
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The distribution in the human genome of the largest family of mobile elements, the Alu sequences, has been investigated for the past 30 years, and the vast majority of Alu sequences were shown to have the highest density in GC-rich isochores. Ten years ago, it was discovered, however, that the small "youngest" (most recently transposed) Alu families had a strikingly different distribution compared with the "old" families. This raised the question as to how this change took place in evolution. We solved what was considered to be a "mystery" by 1) revisiting our previous results on the integration and stability of retroviral sequences, and 2) assessing the densities of acceptor sites TTTT/AA in isochore families. We could conclude 1) that the open state of chromatin structure plays a crucial role in allowing not only the initial integration of retroviral sequences but also that of the youngest Alu sequences, and 2) that the distribution of old Alus can be explained as due to Alu sequences being unstable in the GC-poor isochores but stable in the compositionally matching GC-rich isochores, again in line with what happens in the case of retroviral sequences. 相似文献
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Cell communication and the "bystander effect" 总被引:3,自引:0,他引:3
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Data on cytological peculiarities of dorsomedial nucleus neurones of the amygdala complex, one of the main zones of sexual dimorphism, in dynamics of estrous cycle are reported. We show that structural and functional characteristics of "dark" and "pale" cells may change depending on the concentrations of gonadal steroids in estrous and metaestrous stages. This specifies the previous hypothesis about mutual reorganization of these cells. 相似文献