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91.
A large system of N strains of parasite and a single host is analyzed as a function of the degree of virulence in the strains when there is super-infection
between hosts (more virulent strains can infect hosts that are already infected) and within-host transition between strains
that is neutral. When this small amount of local switching is allowed, steady-state solutions converge to a continuous distribution
as the number of strains increases. The resulting nonlinear-nonautonomous integro-differential equation is reduced to a fourth
order boundary value problem (BVP) and the existence of positive solutions is proven. The methods here and associated BVP
allow for a thorough exploration of parameter space for this class of models.
相似文献
92.
The future role of bio-ontologies for developing a general data standard in biology: chance and challenge for zoo-morphology 总被引:1,自引:1,他引:0
Lars Vogt 《Zoomorphology》2009,128(3):201-217
Due to lack of common data standards, the communicability and comparability of biological data across various levels of organization
and taxonomic groups is continuously decreasing. However, the interdependence between molecular and higher levels of organization
is of growing interest and calls for co-operations between biologists from different methodological and theoretical backgrounds.
A general data standard in biology would greatly facilitate such co-operations. This article examines the role that defined
and formalized vocabularies (i.e., ontologies) could have in developing such a data standard. I suggest basic criteria for
developing data standards on grounds of distinguishing content, concept, nomenclatural, and format standards and discuss the
role of data bases and their use of bio-ontologies in current activities for data standardization in biology. General principles
of ontology development are introduced, including foundational ontology properties (e.g. class–subclass, parthood), and how
concepts are defined. After addressing problems that are specific to morphological data, the notion of a general structure
concept for morphology is introduced and why it is required for developing a morphological ontology. The necessity for a general
morphological ontology to be taxon-independent and free of homology assumptions is discussed and how it can solve the problems
of morphology. The article concludes with an outlook on how the use of ontologies will likely establish some sort of general
data standard in biology and why the development of a set of commonly used foundational ontology properties and the use of
globally unique identifiers for all classes defined in ontologies is crucial for its success. 相似文献
93.
Dip listening refers to our ability to catch brief "acoustic glimpses" of speech and other sounds when fluctuating background noise levels momentarily decrease. Exploiting dips in natural fluctuations of noise contributes to our ability to overcome the "cocktail party problem" of understanding speech in multi-talker social environments. We presently know little about how nonhuman animals solve analogous communication problems. Here, we asked whether female grey treefrogs (Hyla chrysoscelis) might benefit from dip listening in selecting a mate in the noisy social setting of a breeding chorus. Consistent with a dip listening hypothesis, subjects recognized conspecific calls at lower thresholds when the dips in a chorus-like noise masker were long enough to allow glimpses of nine or more consecutive pulses. No benefits of dip listening were observed when dips were shorter and included five or fewer pulses. Recognition thresholds were higher when the noise fluctuated at a rate similar to the pulse rate of the call. In a second experiment, advertisement calls comprising six to nine pulses were necessary to elicit responses under quiet conditions. Together, these results suggest that in frogs, the benefits of dip listening are constrained by neural mechanisms underlying temporal pattern recognition. These constraints have important implications for the evolution of male signalling strategies in noisy social environments. 相似文献
94.
高质量发展战略对中国生态经济系统的运行提出了更高要求。当前对高质量发展的研究侧重经济子系统,对生态子系统和社会子系统的分析相对薄弱,且缺乏省级以下中微观尺度的分析。从经济质量、创新潜力、环境质量、生态安全、人民生活和城乡协调六个维度解析了高质量发展内涵,搜集了全国306个地级区域2018年的数据资料,构建地级区域高质量发展综合评价指标体系,定量测算了地级区域高质量发展指数,揭示了区域格局,考察了影响因素,识别了问题区域,并提出了发展质量提升策略。研究表明:(1)高质量发展指数存在明显的区域差异,东部地区和长江流域发展水平相对较高,东北地区和黄河流域发展水平相对较低。(2)经济质量、创新潜力和人民生活指数的均值相对较低,是高质量发展的薄弱环节。(3)高质量发展水平受到自然环境适宜性、城市等级和人口集聚、投资水平、交通区位、数字经济等因素的综合影响,且具有较强的空间溢出效应。(4)识别出8大类174个高质量发展的问题地市,分布在26个省区,在黄河流域和东北地区相对集中。最后,从制度建设、全国层面和具体区域层面探讨了高质量发展水平提升路径,可为制定区域发展战略和区域政策提供科学参考。 相似文献
95.
老工矿区污染生态问题与今后研究展望 总被引:6,自引:0,他引:6
老工矿区的环境污染及其引发的生态问题,已成为当今制约经济与社会可持续发展的世界性技术难题.对老工矿区这一概念的基本定义与范畴仍有争议,本文首先对这一概念从理论上进行了探讨;然后从剖析我国老工矿区现状尤其是其环境污染现实问题的复杂性入手,对老工矿区的区域二次污染这一科学前沿给予了重点关注;在深入阐述老工矿区环境污染问题复杂性与其特点的基础上,建议今后从国家层面上开展老工矿区二次污染发生机理与控制的系统研究,以及从分子生态毒理学角度系统开展有关新型疾病对环境污染响应的研究,是21世纪初环境科学和生态学研究的两大关键科学问题,这无疑是今后我国环境保护战略的重要组成部分. 相似文献
96.
97.
Hong Qian 《Molecular & cellular biomechanics : MCB》2004,1(4):267-278
In recent single-particle tracking (SPT) measurements on Listeria monocytogenes motility in cells [Kuo and McGrath (2000)], the actin-based stochastic dynamics of the bacterium movement has been analyzed statistically in terms of the mean-square displacement (MSD) of the trajectory. We present a stochastic analysis of a simplified polymerization Brownian ratchet (BR) model in which motions are limited by the bacterium movement. Analytical results are obtained and statistical data analyses are investigated. It is shown that the MSD of the stochastic bacterium movement is a monotonic quadratic function while the MSD for detrended trajectories is linear. Both the short-time relaxation and the long-time kinetics in terms the mean velocity and effective diffusion constant of the propelled bacterium are obtained from the MSD analysis. The MSD of the gap between actin tip and the bacterium exhibits an oscillatory behavior when there is a large resistant force from the bacterium. For comparison, a continuous diffusion formalism of the BR model with great analytical simplicity is also studied. 相似文献
98.
Dynamic AngioThermography (DATG) is a contact-plate technique capable of producing a digital representation of breast vascularity. The inception and growth of a tumor are associated with neoangenesis, which may result in a demonstrable alteration in the regional blood flow, while in normal health conditions the vascularity remains unchanged throughout life. DATG, if included in the clinical evaluation for breast cancer, could potentially improve the accuracy of the diagnosis of this disease.Conventional DATG is limited, however, in that it is a projection (i.e. two-dimensional) imaging technique that does not provide any information on the depth and its effect on the pattern of the perfusion revealed by this technique. In fact, the blood pattern is detected by projecting temperature signals on the plate, thus acquiring a digital two-dimensional image.In this article we propose a new approach for extracting information on depth through the inversion of the Fourier heat equation. The idea is to extract the information along the third axis while acquiring and analyzing the temporal sequence during the process of image formation. The method implemented has been tested on a dedicated “electric phantom” and in one in vivo experiment.In spite of the limits of these preliminary tests, the experimental results have shown that this method makes it possible to obtain a 3D representation of the vascularity. Although it appears to be promising, further validation and characterization of our technique are required. 相似文献
99.
100.
《Current biology : CB》2020,30(15):3057-3061.e2