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Different Phenomena (different + phenomenon)
Selected AbstractsA diversity of beta diversities: straightening up a concept gone awry.ECOGRAPHY, Issue 1 2010Part 1. The term beta diversity has been used to refer to a wide variety of phenomena. Although all of these encompass some kind of compositional heterogeneity between places, many are not related to each other in any predictable way. The present two-part review aims to put the different phenomena that have been called a beta component of diversity into a common conceptual framework, and to explain what each of them measures. In this first part, the focus is on defining beta diversity. This involves deciding what diversity is and how the observed total or gamma diversity (,) is partitioned into alpha (,) and beta (,) components. Several different definitions of "beta diversity" that result from these decisions have been used in the ecological literature. True beta diversity is obtained when the total effective number of species in a dataset (true gamma diversity,) is multiplicatively partitioned into the effective number of species per compositionally distinct virtual sampling unit (true alpha diversity,d) and the effective number of such compositional units (,Md=,/,d). All true diversities quantify the effective number of types of entities. Because the other variants of "beta diversity" that have been used by ecologists quantify other phenomena, an alternative nomenclature is proposed here for the seven most popular beta components: regional-to-local diversity ratio, two-way diversity ratio, absolute effective species turnover (=regional diversity excess), Whittaker's effective species turnover, proportional effective species turnover, regional entropy excess and regional variance excess. In the second part of the review, the focus will be on how to quantify these phenomena in practice. This involves deciding how the sampling units that contribute to total diversity are selected, and whether the entity that is quantified is all of "beta diversity", a specific part of "beta diversity", the rate of change in "beta diversity" in relation to a given external factor, or something else. [source] REVIEW: Reward sensitivity: issues of measurement, and achieving consilience between human and animal phenotypesADDICTION BIOLOGY, Issue 2 2010David N. Stephens ABSTRACT Reward is a concept fundamental to discussions of drug abuse and addiction. The idea that altered sensitivity to either drug,reward, or to rewards in general, contributes to, or results from, drug-taking is a common theme in several theories of addiction. However, the concept of reward is problematic in that it is used to refer to apparently different behavioural phenomena, and even to diverse neurobiological processes (reward pathways). Whether these different phenomena are different behavioural expressions of a common underlying process is not established, and much research suggests that there may be only loose relationships among different aspects of reward. Measures of rewarding effects of drugs in humans often depend upon subjective reports. In animal studies, such insights are not available, and behavioural measures must be relied upon to infer rewarding effects of drugs or other events. In such animal studies, but also in many human methods established to objectify measures of reward, many other factors contribute to the behaviour being studied. For that reason, studying the biological (including genetic) bases of performance of tasks that ostensibly measure reward cannot provide unequivocal answers. The current overview outlines the strengths and weaknesses of current approaches that hinder the conciliation of cross-species studies of the genetics of reward sensitivity and the dysregulation of reward processes by drugs of abuse. Some suggestions are made as to how human and animal studies may be made to address more closely homologous behaviours, even if those processes are only partly able to isolate ,reward' from other factors contributing to behavioural output. [source] A review of reliable numerical models for three-dimensional linear parabolic problemsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2007I. Faragó Abstract The preservation of characteristic qualitative properties of different phenomena is a more and more important requirement in the construction of reliable numerical models. For phenomena that can be mathematically described by linear partial differential equations of parabolic type (such as the heat conduction, the diffusion, the pricing of options, etc.), the most important qualitative properties are: the maximum,minimum principle, the non-negativity preservation and the maximum norm contractivity. In this paper, we analyse the discrete analogues of the above properties for finite difference and finite element models, and we give a systematic overview of conditions that guarantee the required properties a priori. We have chosen the heat conduction process to illustrate the main concepts, but engineers and scientists involved in scientific computing can easily reformulate the results for other problems too. Copyright © 2006 John Wiley & Sons, Ltd. [source] Isolating the root cause of propagated oscillations in process plantsINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 4 2005Xiaoyun Zang Abstract Oscillations are a common type of propagated disturbance, whose sources might be attributable to a number of different phenomena such as poor controller tuning or actuator nonlinearity. A number of data-driven methods have already been proposed to isolate the source loop of nonlinearity induced plant-wide oscillations. Amongst these the bi-amplitude ratio index, correlation dimension, maximal Lyapunov exponent, nonlinearity index and spectral ICA show promise. The propagation of oscillations is first examined in order to gain an understanding of how this might affect the performances of the various techniques. The various methods are then described and their performance on a set of simulation generated data and two industrial case studies are compared. Copyright © 2004 John Wiley & Sons, Ltd. [source] Latitudinal and bathymetric trends in egg size variation: a new look at Thorson's and Rass's rulesMARINE ECOLOGY, Issue 1 2006Vladimir Laptikhovsky Abstract The inverse relationship between egg size in marine animals and water temperature was simultaneously described by two outstanding marine scientists: G. Thorson and T.S. Rass. This rule consists of two different phenomena. Thorson's rule describes ecological processes related to changes in larval biology and morphology that are caused by a selective pressure of natural selection on the different types of larval development. It belongs to the realm of macro-evolution. Rass's rule describes physiological processes within populations and species, and between closely related species. This is not related to changes in reproductive strategy, and therefore belongs to the realm of micro-evolution and to the early stages of macro-evolution. Populations begin to produce larger eggs in colder environments because of phenotypic plasticity. Thorson's rule describes temperature-dependent changes in the relative abundance of small- and large-egged species, whereas Rass's rule describes a temperature-dependent relative position of both groups within an adaptive range of reproductive strategies. [source] Influence of inter-fiber spacing and interfacial adhesion on failure of multi-fiber model composites: Experiment and numerical analysisPOLYMER COMPOSITES, Issue 9 2008Hongzhou Li The uniaxial tension experiments on glass-fiber-reinforced epoxy matrix composites reveal that the fragmentations of fibers display vertically aligned fracture, clustered fracture, coordinated fracture, and random fracture with the increase of inter-fiber spacing. The finite element analysis indicates that the fragmentations of fibers displaying different phenomena are due to the stress concentration as well as the inherent randomness of fiber defects, which is the dominant factor. The experimental results show that matrices adjacent to the fiber breakpoints all exhibit birefringent-whitening patterns for the composites with different interfacial adhesion strengths. The larger the extent of the interfacial debonding, the less the domain of the birefringent-whitening patterns. The numerical analysis indicates that the orientation of the matrix adjacent to a fiber breakpoint is caused by the interfacial shear stress, resulting in the birefringent-whitening patterns. The area of shear stress concentrations decides on the domain of the birefringent-whitening patterns. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers [source] | |||||||||||||