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研究超声波经过两个烧结样品的行为.两个烧结样品为有序的面心立方结构,它们的结构几乎相同.研究表明:在两个有序的准均匀的介质中分别有一个禁带区域.就禁带区域而言,在两个样品中产生禁带的区域非常接近.同时在禁带出现的区域群速度为负值.我们的结果表明群速度的负值的确存在于有序介质中的禁带区域内. 相似文献
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Eusociality, which occurs among mammals only in two species of African mole-rat, is characterized by division of labour between morphologically distinct 'castes'. In Damaraland mole-rats (Cryptomys damarensis), colony labour is divided between 'infrequent worker' and 'frequent worker' castes. Frequent workers are active year-round and together perform more than 95% of the total work of the colony, whereas infrequent workers typically perform less than 5% of the total work. Anecdotal evidence suggests that infrequent workers may act as dispersers, with dispersal being limited to comparatively rare periods when the soil is softened by moisture. Here we show that infrequent workers and queens increase their daily energy expenditure after rainfall whereas frequent workers do not. Infrequent workers are also fatter than frequent workers. We suggest that infrequent workers constitute a physiologically distinct dispersing caste, the members of which, instead of contributing to the work of the colony and helping the queen to reproduce, build up their own body reserves in preparation for dispersal and reproduction when environmental conditions are suitable. 相似文献
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Jones C Roper VC Foucher I Qian D Banizs B Petit C Yoder BK Chen P 《Nature genetics》2008,40(1):69-77
Planar cell polarity (PCP) refers to coordinated polarization of cells within the plane of a cell sheet. A conserved signaling pathway is required for the establishment of PCP in epithelial tissues and for polarized cellular rearrangements known as convergent extension. During PCP signaling, core PCP proteins are sorted asymmetrically along the polarization axis; this sorting is thought to direct coordinated downstream morphogenetic changes across the entire tissue. Here, we show that a gene encoding a ciliary protein (a 'ciliary gene'), Ift88, also known as Polaris, is required for establishing epithelial PCP and for convergent extension of the cochlear duct of Mus musculus. We also show that the proper positioning of ciliary basal bodies and the formation of polarized cellular structures are disrupted in mice with mutant ciliary proteins ('ciliary mutants'), whereas core PCP proteins are partitioned normally along the polarization axis. Thus, our data uncover a distinct requirement for ciliary genes in basal body positioning and morphological polarization during PCP regulation. 相似文献
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Two FORTRAN IV computer programs were developed to facilitate reduction of meteorologic data from irrigated and nonirrigated plots at Provo, Utah. The first program compiles and tabulates daily, monthly, and yearly summaries of precipitation as rain and/or snow, snowfall, total snow cover, soil moisture, dew, relative humidity, potential evaporation, cloud cover, and wind. Temperature values are tabulated for measurements taken in a standard weather shelter. 5 cm beneath soil surface under grass cover, at soil surface under grass cover, and on bare ground. The second program enables complete computerized (Calcomp) construction, labeling, and graphing of 10 different meteorologic measurements and 3 calculated comparisons of temperature means. Advantages of the first computer program relate generally to that obviously noticeable with any computerized tabulation. Those of the second program relate more specifically to the greatly reduced cost of computerized graphs compared with those produced manually, as well as to the marked reduction of errors compared with the number frequently associated with the usual tedious and laborious plotting of voluminous weather data. Meteorologic data collected for the year demonstrated the beneficial effect of irrigation in the creation of microenvironments for living organisms. 相似文献
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Does strychnine block inhibition post-synaptically? 总被引:1,自引:0,他引:1
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Group decision-making in animals 总被引:8,自引:0,他引:8
Groups of animals often need to make communal decisions, for example about which activities to perform, when to perform them and which direction to travel in; however, little is known about how they do so. Here, we model the fitness consequences of two possible decision-making mechanisms: 'despotism' and 'democracy'. We show that under most conditions, the costs to subordinate group members, and to the group as a whole, are considerably higher for despotic than for democratic decisions. Even when the despot is the most experienced group member, it only pays other members to accept its decision when group size is small and the difference in information is large. Democratic decisions are more beneficial primarily because they tend to produce less extreme decisions, rather than because each individual has an influence on the decision per se. Our model suggests that democracy should be widespread and makes quantitative, testable predictions about group decision-making in non-humans. 相似文献
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