Levels Of Hierarchical Structure Research Articles

A Hierarchical Domain Decomposition Boundary Element Method Applied to the Multiregion Problems of Neutron Diffusion Equations

A technique is presented for solving neutron diffusion equations with the boundary element method (BEM) based on a hierarchical domain decomposition technique. In this method, the reactor domain is decomposed into homogeneous regions and the boundary condition on the common boundary of regions is initially assumed. The neutron diffusion equation is solved iteratively at two levels of hierarchical structure: First, BEM is applied to solve the neutron diffusion equation of each homogeneous region under the given assumed boundary conditions and an assumed multiplication factor. Then, these assumed values are modified to satisfy the continuity conditions for the neutron flux and neutron current.The proposed technique is useful for multiregion problems with a large number of regions of complex geometry, where the finite difference approximation cannot be applied properly.

Distribution and reproductive success of the Pied Flycatcher Ficedula hypoleuca in relation to forest patch size and vegetation characteristics; the effect of scale

We studied habitat choice, distribution and reproductive success in the Pied Flycatcher Ficedula hypoleuca in relation to the spatial structure of a fragmented forest area. Two hierarchical levels of forest habitat structure were used: (1) forest patch size (macrohabitat) and (2) vegetative structure within forest patches (microhabitat). In spring, both males and females settled preferentially in large and medium‐sized forest stands (>1 ha) where breeding density was also higher than in small stands (<1 ha). Stands <5 ha were occupied later, and the proportion of unpaired males was higher there than in large stands (>5 ha). The known age distributions of breeding birds and breeding success were independent of forest patch size. Nest predation rate was not associated with stand size or nest distance from the forest edge. The preference of breeding birds for large forest patches was presumably related to the higher amount of resources (nest sites, mates, food) a large patch can offer for reproduction compared with a small patch. At the microhabitat level, territories of old males were characterized by relatively more deciduous trees that contained more invertebrate food than coniferous tree‐dominated territories of yearling males. The reproductive success of old males, as measured by the number of fledged young per male, was higher than that of yearling males. This suggests that the larger body size and blacker plumage of old males possibly contributed to male dominance and that old males excluded younger males from preferred habitats through territorial behaviour. Our results suggest that habitat choice of the Pied Flycatcher was affected by both micro‐ and macrohabitat. On the basis of settlement pattern, density and reproductive success, the distribution of Pied Flycatchers across forest stands of different sizes followed the ideal‐free distribution model, whereas at the microhabitat level, age‐related unequal distribution of males followed the ideal‐despotic model of Fretwell and Lucas.

Testing a Second-Order Multidimensional Model of Negative Affectivity: A Cross-Validation Study

A number of conceptualizations and subsequent measures of Negative Affectivity (NA) have been presented in the literature. However, very few studies have attempted to establish the dimensionality of the NA construct prior to its use. The purpose of this preliminary investigation was to explore both the lower order and hierarchical conceptualizations of NA using Stokes and Levin's scale. The NA scale contains lower order factors of nervousness, pessimism, and dissatisfaction. Two samples were used to assess the hierarchical structure of the scale. The first sample consisted of management students (N = 356) of a large southeastern university. The second study consisted of managerial employees of a large automobile distributorship (N = 102) located in the southeastern United States. In each sample, the data indicated that the most satisfactory representation of the underlying structure of Stokes and Levin's NA scale was that of a higher order model. Following Watson and Clark, the authors recommend that researchers assess both levels of hierarchical structure of NA when using the Stokes and Levin scale, as well as other subsequent measures of the construct.

Hierarchical Levels of Spatial Structure and Their Consequences for the Evolution of Sex Allocation in Mites and Other Arthropods

Evolutionarily stable (ES) sex allocation strategies depend critically on how the population is structured with regard to competition for mates and resources. This structure is determined by spatial heterogeneity, dispersal, and colonization behavior. In mating groups lasting one generation where mating precedes female dispersal, female-biased sex ratios will be favored by mate competition, especially when the number of foundresses is small. When groups last several generations before dispersal takes place (haystack structure), relatedness among population members develops, and this can favor an extra female bias. However, when groups are permanent, with some dispersal in each generation (island structure), relatedness builds up without an effect on sex ratio bias because most competition takes place within groups. Current models of evolution under a haystack structure generally assume unlimited growth for a fixed number of generations (and hence no local density dependence), absence of substructure, and sex ratios that are inflexible over generations. These model limitations warrant scrutiny. Using extended versions of the haystack model, we show that, although local density depen- dence in the haystack population diminishes the sex ratio bias, strongly female-biased sex ratios are still possible if foundress numbers are low. It is also shown that substructure in the haystack by subdivision into one-generation mating groups promotes the female bias. Finally, it is shown that the ES sex ratio can change radically with generations within haystacks. When population growth is density dependent, the sex ratio of the last generation should be more female biased than in the preceding generations. In the case of haystacks subdivided into local mating groups, the sex ratio in the first generation should be less female biased than in the following generations. It is argued that a haystack structure is frequently found among small arthropods with a coloniz- ing lifestyle and that subdivision into one-generation mating groups may occur, for example, among plant-inhabiting mites. To illustrate these points, predatory mites of the family Phytoseii- dae are considered in more detail. Some species are found to exhibit a stronger female bias in their sex ratios than expected from local mating competition alone. This extra bias may well stem from selection in a haystack or subdivided haystack structure. Other phytoseiid species have a lifestyle that leads to more permanent subpopulations that have an island-like structure. As predicted, these species generally show less female-biased sex ratios.

A 1.2 mW video-rate 2-D color subband decoder

A 2-D subband decoder has been designed for real-time video decompression in low-power applications. The chip is capable of reconstructing four levels of hierarchical subband structures for images up to 256 pixels wide. The chip's maximum performance decodes 60 M pixels per second of color RGB video output with a 5 V supply and 120 MHz clock frequency. For portable applications with a resolution of 176 pixels wide, 240 lines, and 30 frames/s color video, the chip dissipates less than 1.2 mW with a 1 V supply. Besides the reduced supply voltage, the low power consumption is achieved through algorithmic innovations for energy conservation. Higher-resolution images can be decoded by cascading multiple chips in parallel each operating on a 256 pixel wide image slice.

Spatio-Temporal Dispersal Strategies and Annual Plant Species Coexistence in a Structured Landscape

Field observations and models have shown: (1) differences in dispersal and dormancy strategies could account for species coexistence in disturbed environments, (2) small scale disturbances contribute to species coexistence in plant communities, and (3) recolonization success may depend on the spatial pattern of suitable sites for establishment. A spatially explicit, two-species, simulation model was developed to examine the interaction between dispersal strategies, dormancy strategies and small-scale disturbances on the pattern of coexistence of two annual plant species in patchy landscapes. Patchy landscapes with three hierarchical levels of structure were randomly generated and the dynamics for species differing in mean dispersal distance and dormancy strategy was simulated. The results showed that when species differed only in mean dispersal distance, the species with the shorter range dispersal would always displace the other. When disturbances prevented reproduction and activated dormant seeds, then differences in dormancy strategy could result in coexistence of species with different dispersal capabilities. When species differed only in their dormancy rate (i.e., the proportion of dormant seeds produced per year), the range of disturbance intensities allowing coexistence was rather narrow, but differences in the response of species to disturbance (i.e., disturbance-broken seed dormancy versus gradual germination of dormant seeds) allowed coexistence under a wider range of disturbance intensities. These results suggest that differences in the ways species exploit the resources in space and time can mediate coexistence through storage effects. The patterns of coexistence obtained in the simulations were consistent with conclusions of a field study, in species-rich Mediterranean old-fields, about the role for coexistence of the interactions among dispersal and dormancy strategies, spatial heterogeneity, and small-scale disturbances. Coexistence patterns depended on the degree of suitability and the patchiness of the landscapes, mostly in relation to the interactions between landscape structure and mean dispersal distance, but also through complex interactions with dormancy characteristics. Therefore, disturbance regimes are not sufficient for predicting patterns of coexistence, and the unique spatial features of the landscapes need to be taken into account.

Spatial attention and cuing to global and local levels of hierarchical structure.

Spatial attention and cuing to global and local levels of hierarchical structure.

Spatial attention and cuing to global and local levels of hierarchical structure.

Five experiments investigated the role of attention in identifying global and local targets in hierarchically structured patterns. Hierarchical patterns were presented at a variable stimulus onset asynchrony (SOA) either after a cue (4 arrows or shaded boxes) or after no cue. Targets occurred at the cued level 80% of the time and at the uncued level 20%. On uncued trials, target level probability was .5. Global cues produced benefits for both global and local targets over SOA on cued trials. Local cues produced benefits only for local targets. For uncued trials, responses favored local targets overall when interspersed with locally cued trials but favored global targets when interspersed with globally cued trials. The role of an attentional window and discrete distribution of attention over global and local levels of hierarchical patterns are discussed.

Theoretical studies of protein conformation by means of energy computations

In this review we describe fundamental concepts and applications of conformational energy computations, with emphasis on some recent advances and problems being investigated. The formulation of potential energy functions is described, including the nature of the intramolecular force field, the representation of interactions with the solvent, and considerations of entropy contributions. Approaches to the search for the optimal potential energy are summarized. Examples cited among applications of conformational energy computations include refinement of X-ray crystallographic structures, the use of computations in conjunction with NMR data, prediction of the structures of proteins based on either homology or on other procedures that surmount the multiple-minima problem, the analysis of hierarchical levels of structure and assembly, and interactions in enzyme-substrate complexes.

Component mechanisms underlying the processing of hierarchically organized patterns: Inferences from patients with unilateral cortical lesions.

Subjects identified target letters that occurred randomly at the local or global level in a divided attention task. The visual angle of the stimuli was varied. Neurologically intact controls showed a reaction time advantage for local targets which increased as visual angle increased. Patients with lesions centered in the posterior superior temporal gyrus (STG) showed a larger local advantage than controls if the lesion was on the right and a global advantage if the lesion was on the left. STG patients were no more influenced by visual angle than were controls. Control subjects also showed the usual interference of global distractors on responding to local targets. STG patients showed little evidence of interference. Control patients with lesions centered in the rostral inferior parietal lobe performed normally. The findings suggest that several component mechanisms are involved in the processing of hierarchical levels of structure, each linked to specific anatomical regions.

Study of dispersed solid-phase ontogenesis using hierarchical structure data

Ontogenesis of the dispersed solid phase of BaCO3 has been studied under the conditions of fast reagent mixing. Crystallization was followed by high-resolution electron microscopy. It was found, on retarding the ageing process with EDTA, that the formation of the solid phase is stepwise: individual microcrystals to primary aggregates to secondary aggregates to pseudo-dendrites. Etching the pseudo-dendrites with EDTA shows the presence of the same levels of hierarchical structure. The experimentally determined crystal-size distribution agrees well with that previously reported. It is, therefore, possible to evaluate the ontogenesis of the solid phase from the morphology of the crystals at the end of crystallization.