Effect Of Local Environment Research Articles

The effects of fire, local environment and time on ant assemblages in fens and forests

ABSTRACTWe investigated the effects of the abiotic environment, plant community composition and disturbance by fire on ant assemblages in two distinct habitat types in the Siskiyou Mountains in northern California and southern Oregon, USA. Sampling over 2 years in burned and unburned Darlingtonia fens and their adjacent upland forests, we found that the effects of disturbance by fire depended on habitat type. In forests, fire intensity predicted richness in ant assemblages in both years after the fire, and plant community composition predicted richness 2 years after the fire. No factors were associated with richness in the species‐poor fen ant assemblages. Species‐specific responses to both habitat type and disturbance by fire were idiosyncratic. Assemblage composition depended on habitat type, but not disturbance by fire, and the composition of each assemblage between years was more dissimilar in burned than unburned sites.

Comparative tree growth efficiency in Sierra Nevada mixed-conifer forests

Tree growth efficiency, or volume growth increment per unit leaf area, was calculated in multiaged mixed-conifer stands in the Sierra Nevada, California. Five conifer species with a range of tolerance to shade were sampled over a wide range of canopy positions and ages to detect species-specific patterns of growth efficiency (GE). All species showed non-linear, sigmoidal trends of volume increment with increasing leaf area. This pattern indicates slow increase in GE in shaded understory conditions and a peak in GE at intermediate tree size in mid-canopy positions. Larger trees showed lower GE than intermediate size trees. Species with lower shade tolerance had greater GE than species with greater tolerance. To test the effect of local light environment on tree volume growth, we used a light model to calculate the growing season average of absorbed light for individual trees. Models of volume increment as a function of weighted leaf area showed increased GE for small trees, indicating that the slow increase in volume increment in smaller understory trees was an effect of limited light conditions. Patterns of growth efficiency in multiaged mixed-species stands can be used to predict growth patterns of sub-canopy trees and judge relative shade tolerance.

Systematic, multisite short-range-order corrections to the electronic structure of disordered alloys from first principles: The KKR nonlocal CPA from the dynamical cluster approximation

Although the Korringa-Kohn-Rostoker coherent-potential approximation (KKR-CPA) is used widely to configurationally average and get electronic structures and energies of disordered alloys, a single-site CPA misses local environment effects, including short-range order (SRO). A proposed nonlocal CPA (NLCPA) recovers translational invariance of the effective medium via $\mathbf{k}$-space coarse graining from the dynamical cluster approximation (DCA), where corrections are systematic as cluster size increases. We implement a first-principles KKR-NLCPA/DCA and show the effects of environment, including SRO, on the electronic structures of fcc CuAu and bcc NiAl.

Ab initiostudy of disorder broadening of core photoemission spectra in randomCu−PdandAg−Pdalloys

A first-principles study of the effect of local environment on the electronic structure of random face-centered cubic $\mathrm{Ag}\ensuremath{-}\mathrm{Pd}$ and $\mathrm{Cu}\ensuremath{-}\mathrm{Pd}$ alloys is presented. The core-level shift for each atom in the equiatomic alloys is calculated and compared to experimental data. It is shown how the initial-state and final-state distributions contribute to the total broadening. We find that the initial-state and the final-state contributions together increase the broadening for the investigated core levels in Cu and Ag, whereas they cancel each other to a large degree for Pd. We also demonstrated how local lattice relaxations influence the binding energy shift. We find that relaxation does not influence the average shift, though it is able to affect the broadening of the simulated x-ray photoelectron spectroscopy spectra.

Region‐ and age‐specific deficits in γ‐aminobutyric acidergic neuron development in the telencephalon of the uPAR–/– mouse

We have previously shown that in adult mice with a null mutation in the urokinase-type plasminogen activator receptor (uPAR) gene, maintained on a C57BL/6J/129Sv background, there is a selective loss of GABAergic interneurons in anterior cingulate and parietal cortex, with the parvalbumin-expressing subpopulation preferentially affected. Here, we performed a more detailed anatomical analysis of uPAR(-/-) mutation on the congenic C57BL/6J background. With glutamic acid decarboxylase-67 and gamma-aminobutyric acid (GABA) immunostaining, there is a similar region-selective loss of cortical interneurons in the congenic uPAR(-/-) mice from the earliest age examined (P21). In contrast, the loss of parvalbumin-immunoreactive cells is observed only in adult cortex, and the extent of this loss is less than in the mixed background. Moreover, earlier in development, although there are normal numbers of parvalbumin cells in the uPAR(-/-) cortex, fewer cells coexpress GABA, suggesting that the parvalbumin subpopulation migrates appropriately to the cortex, but does not differentiate normally. Among the other forebrain regions examined, only the adult hippocampus shows a loss of GABAergic interneurons, although the somatostatin, rather than the parvalbumin, subpopulation contributes to this loss. The data suggest that uPAR function is necessary for the normal development of a subpopulation of GABAergic neurons in the telencephalon. It is likely that the late-onset parvalbumin phenotype is due to the effects of an altered local environment on selectively vulnerable neurons and that the extent of this loss is strain dependent. Thus, an interplay between complex genetic factors and the environment may influence the phenotypic impact of the uPAR mutation both pre- and postnatally.

Structural and electronic properties of thein situimpurityAsHginHg0.5Cd0.5Te: First-principles study

The structural and electronic properties of the in situ impurity ${\mathrm{As}}_{\mathrm{Hg}}$ in ${\mathrm{Hg}}_{0.5}{\mathrm{Cd}}_{0.5}\mathrm{Te}$ (MCT) have been studied by using the density-functional theory within the full-potential linear augmented plane wave method. The supercell with 64 atoms has been considered in the calculations. The relaxation, local charge density, and density of states are shown to discuss the effects of local environment induced by impurity on the electronic structure. The in situ ${\mathrm{As}}_{\mathrm{Hg}}$ impurity in ${\mathrm{Hg}}_{0.5}{\mathrm{Cd}}_{0.5}\mathrm{Te}$ exhibits a single donor level to be close to the conduction-band minimum (CBM), and the donor level position is quantitatively determined to be 9 meV below the CBM, in agreement with the experimental results of the photoluminescence.

Crop Size and Fruit Neighborhood Effects on Bird Visitation to Fruiting Schefflera morototoni Trees in Puerto Rico1

ABSTRACTStudies of zoochorous seed dispersal systems often consider crop size, yet seldom consider the kinds and amounts of fruits surrounding parent plants (the fruit neighborhood) when attempting to explain among‐plant variation in fruit removal. We studied avian frugivory at 24 Schefflera morototoni trees from February to May 1998 in central Puerto Rico. The number of fruits removed by avian seed dispersers per visit was similar among focal trees (typically 2–4). In contrast, visitation rate was highly variable (range: 0–71 visits per 4 h). We used multiple regression analyses to evaluate the relative roles of crop size (focal tree ripe fruit abundance) and fruit neighborhood variables (measured within 30 m of focal trees) in affecting visitation to focal trees by avian frugivores. Visitation rate was positively related to crop size (although this variable was only significant in one of four regression models considered) and negatively related to the presence or abundance of conspecific fruits, suggesting that trees competed intraspecifically for dispersers. Relationships between visitation and heterospecific fruits were mixed—some kinds of fruits appeared to enhance visitation to focal trees, while others seemed to reduce visitation. In most regression models, neighborhood variables had larger effects on visitation than focal tree fruit crop size. Our results highlight the important effects of local fruiting environments on the ability of individual plants to attract seed dispersers.

Origin of magnetic frustrations inFe−NiInvar alloys

Pair exchange parameters ${J}_{ij}$ of the classical Heisenberg Hamiltonian for magnetic interactions in the archetypical Invar system, face centered cubic (fcc) $\mathrm{Fe}\ensuremath{-}\mathrm{Ni}$ alloys, are calculated from the first principles. The magnetic structure of $\mathrm{Fe}\ensuremath{-}\mathrm{Ni}$ alloys in the region of volumes and electron concentrations related to the Invar effect is highly frustrated. However, the origin of such a frustration in concentrated alloys and in the pure fcc Fe are different. While in Fe it is due to the long-range oscillating ${J}_{ij}$, in alloys with high Ni concentration it is mainly the consequence of a huge dispersion of the nearest-neighbor exchange parameters, caused by the local environment effects.

Electronic structure and magnetism of Fe3–xMnxAl alloys

AbstractThe electronic structure of Fe3–xMnxAl and the effect of local environment on formation of local magnetic moments are examined using self‐consistent spin‐polarised TB‐LMTO method. The electronic properties of the Fe3–xMnxAl compound have been calculated for the supercell structure with 32 atoms and in the range 0 ≤ x ≤ 0.5. The values and orientations of magnetic moments of the iron and the manganium atoms are presented. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Being high is better: effects of elevation and habitat on arctic ground squirrel demography

We investigated the effect of local environment on the demography and population dynamics of arctic ground squirrels (Spermophilus parryii plesius) by comparing reproduction, survival, and population trends of squirrels living in low elevation boreal forest and high elevation alpine tundra sites in southwestern Yukon Territory, Canada. Contrary to the trend for most birds and mammals, reproduction was significantly lower at the lower elevation and females living at higher elevation did not delay the age at which they first reproduced. Even though survival in the boreal forest was lower in summer than in the alpine, it was higher over winter so annual adult female survival was similar between sites.Sensitivity analysis of model parameters revealed that in the forest, population growth rate (λ) was most sensitive to small changes in adult active season survival whereas for the alpine population, λ was most sensitive to changes in juvenile winter survival. In their respective habitats, these parameters also showed high year to year variation and thus contributed greatly to the population trends observed. Even though ground squirrels persisted in the boreal forest, the measured demographic rates indicate the forest was sink habitat (λ<1) and may have relied on nearby grassy meadows for immigrants. In contrast, the alpine habitat maintained a ground squirrel population in the absence of immigration (λ=1).The variation in demographic rates between ground squirrels living at high and low elevation may arise from phenotypic responses of squirrels to different habitat structure. Arctic ground squirrels rely on sight to detect predators from a safe distance, and the boreal forest, with its lower visibility and higher predator density, appears to be suboptimal habitat.

Effect of Local Environment on Molecular Conduction: Isolated Molecule versus Self-Assembled Monolayer

Developing a fundamental understanding of molecular conduction in different device environments is essential to the advance of molecular electronics. We show through a quantitative comparison of two types of junctions with the same molecule - one based on an isolated individual molecule and the other on a self-assembled monolayer - that intrinsic differences in the conduction per molecule as large as several orders of magnitude can exist simply as a function of the presence or absence of neighboring molecules. This behavior can be understood on the basis of thermal and electrostatic effects that depend critically on the local molecular environment. These results will help to unify data obtained from disparate device structures and to provide an improved basis for designing future molecular electronic devices.

Control of Photochromism through Local Environment Effects Using Living Radical Polymerization (ATRP)

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTControl of Photochromism through Local Environment Effects Using Living Radical Polymerization (ATRP)Georgina K. Such, Richard A. Evans, and Thomas P. DavisView Author Information CSIRO Molecular Science, Bag 10, Clayton 3169 VIC, Australia; CRC for Polymers, 32 Business Park Drive, Notting Hill 3168 Vic, Australia; and Centre for Advanced Macromolecular Design (CAMD), School of Chemical Engineering and Industrial Chemistry, The University of New South Wales, Sydney, 2052 NSW, Australia Cite this: Macromolecules 2004, 37, 26, 9664–9666Publication Date (Web):November 25, 2004Publication History Received8 July 2004Revised13 October 2004Published online25 November 2004Published inissue 1 December 2004https://doi.org/10.1021/ma048627fCopyright © 2004 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views549Altmetric-Citations42LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (93 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Conjugate acid-base pairs,Dyes and pigments,Molecules,Polymers,Radical polymerization Get e-Alerts

Unusual Component Dynamics in Poly(ethylene oxide)/Poly(methyl methacrylate) Blends As Probed by Deuterium NMR

We analyze recent deuterium NMR data on blends of poly(ethylene oxide) (PEO) with poly(methyl methacrylate) (PMMA), using a model for the blend dynamics based on the coupling model. This model has previously been shown to describe the relaxation properties of blends whose component dynamics are strongly composition dependent. We show herein that the unusual feature of PEO/PMMA blends, an invariance of the PEO dynamics to composition, is a natural consequence of the high frequency and temperature of the NMR experiments. To wit, when the independent relaxation time of our model approaches the characteristic time for intermolecular cooperativity (∼2 ps), the effect of local environment on the component dynamics becomes negligible. A similar situation pertains for poly(vinyl methyl ether) mixed with polystyrene, at temperatures sufficiently high that the segmental relaxation times become small. On the other hand, for blends of 1,4-polyisoprene with poly(vinylethylene), the component dynamics retain their dependence on composition, even at high temperatures. The reason for the differing behavior is brought out by an analysis using our blend model.

The environmental dependence of galaxy properties in the local universe: effects of local and global environment

We investigate the environmental dependence of galaxy properties in the local universe based on the data of the Sloan Digital Sky Survey. We focus on how star formation and morphology of galaxies correlate with luminosity, local environment, and global environment. We find that galaxy properties abruptly change at a critical local density of . This fact suggests that environmental mechanisms that are effective only in rich clusters, such as ram-pressure stripping of cold gas and harassment, have not played a major role in suppressing galaxy star formation. Our results may suggest that evolution of bright galaxies is not strongly related to galaxy systems such as groups and clusters. On the other hand, evolution of faint galaxies may have a close connection.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

International compensation: learning from how managers respond to variations in local host contexts

Managers and researchers recognize that the tensions created by the interplay of globalization and national environments influence the behaviours of multinational enterprises (MNEs). We develop a model to help explain the effects of both global and local host environments on the design of managerial compensation systems in MNEs. We use a grounded theory-building process by integrating information we obtained from exploring the international compensation systems (ICS) of five MNEs. We extend two contemporary perspectives of IHRM – the national culture and strategic alignment models–and develop the idea that it is the relative degree of variation within and between local host contexts that is critical to understanding managers' ICS decisions. We present a different, pragmatic experimentation view of managers' ICS decision making, which we believe offers insights into how managers deal with the interplay between pressures to create aligned, integrated global systems and pressures to conform to local host contexts.

The moderating effect of local environment on a foreign affiliate's global IS strategy-effectiveness relationship

This study evaluates the moderating effects of local culture, local regulation, and local competition on a global information systems (GISs) strategy-effectiveness relationship. Cluster analyses and moderated regression analyses were used to test hypotheses in a sample of 312 foreign affiliates operating in Canada, Japan, the UK and the United States. Our findings suggested that GIS strategy was related to information systems (IS) effectiveness. This relationship was moderated by all three selected moderator variables. Our study also found that foreign affiliates that follow a globally integrative GIS strategy, but which operate in a more restrictive local environment, eventually achieve greater IS effectiveness. In addition, foreign affiliates that follow a locally responsive GIS strategy, but which operate in a more competitive and culturally different local environment, will also be able to run their IS more effectively.

Decoupling between rare-earth moment and transition metal moment in NdCo12−xVx compounds

Single-phase compounds NdCo12−xVx (x=2.2–2.6) crystallizing in the tetragonal ThMn12 structure with space group I4/mmm are synthesized. The lattice parameters a and c increase linearly with increasing V content. The Curie temperature of the compounds shows a linear decrease from 309 K for x=2.2 to 147 K for x=2.6. A domain-wall pinning phenomenon is observed in all of the compounds. It is intriguing that the Nd ions seem to make no contribution to the total moment of the compounds in an applied magnetic field up to 50 kOe. A further increase of the applied field induces a moment of a Nd sublattice that ferromagnetically couples with the moment of a Co sublattice. The instability of the Nd moment in NdCo12−xVx compounds can be well understood by the local environment effect.

Effect of alloying on the electronic structure and magnetic properties of Fe, Co and Ni with Au and Ag

We use the self-consistent, augmented space recursion technique to study the electronic structure and magnetic properties of alloys of the transition metals, Fe, Co and Ni with the noble metals, Ag and Au. We analyse the effect of local environment and the hybridization between the constituent bands on the electronic and magnetic properties.

Magnetism of Co nanocluster films

A cluster-beam technique is used to produce nearly monodispersed nanoclusters of Co while independently varying their size and concentration. The Co clusters are embedded in Cu and ${\mathrm{SiO}}_{2}$ to form films with cluster size varying from 300 to 9000 atoms and Co concentration varying from 10 to 50 vol %. The Co magnetization ${(M}_{s})$ increases with increasing cluster size and decreases with increasing Co concentration for a given cluster size but is always less than the bulk value. First-principles calculations are used to analyze the experimental data in terms of the local environment effects at the cluster-matrix interface and spin-glass-like behavior due to the strong ferro- and antiferromagnetic intercluster exchange interactions for small separations.

Screened Coulomb interactions in metallic alloys. II. Screening beyond the single-site and atomic-sphere approximations

A quantitative description of the configurational part of the total energy of metallic alloys with substantial atomic size difference cannot be achieved in the atomic-sphere approximation: It needs to be corrected at least for the multipole-moment interactions in the Madelung part of the one-electron potential and energy. In the case of a random alloy such interactions can be accounted for only by lifting the atomic-sphere and single-site approximations, in order to include the polarization due to local environment effects. Nevertheless, a simple parametrization of the screened Coulomb interactions for the ordinary single-site methods, including the generalized perturbation method, is still possible. We obtained such a parametrization for bulk and surface NiPt alloys, which allows one to obtain quantitatively accurate effective interactions in this system.