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Theoretical Expectations (theoretical + expectation)
Selected AbstractsElite Consensus as a Determinant of Alliance Cohesion: Why Public Opinion Hardly Matters for NATO-led Operations in AfghanistanFOREIGN POLICY ANALYSIS, Issue 3 2010Sarah Kreps Despite the increasing popularity of fighting wars through multilateral coalitions, scholars have largely been silent on the question of how public opinion in member states affects alliance cohesion. This article assesses public opinion data for states contributing to operations in Afghanistan. It finds that despite the unpopularity of the war, leaders have largely bucked public opinion and neither reduced nor withdrawn troops from NATO-led operations in Afghanistan. Theoretical expectations about international cooperation and evidence from case studies point to elite consensus as the reason why leaders are not running for the exits in Afghanistan when their publics would prefer that they do. As the article shows, operating through a formal institution such as NATO creates systemic incentives for sustained international cooperation. The result is that elite consensus inoculates leaders from electoral punishment and gives states' commitments to Afghanistan a "stickiness" that defies negative public opinion. A formal alliance such as NATO may therefore create more policy constraints than an ad hoc coalition but also increase the costs of defection and confer a degree of staying power that is unexpected given the adverse public opinion environment. [source] Male body size predicts sperm number in the mandarinfishJOURNAL OF ZOOLOGY, Issue 3 2010M. B. Rasotto Abstract Theory predicts that, in species with non-resource-based mating systems, female preference for male sexual traits might be selected to ensure higher levels of fertility. Accordingly, secondary sexual traits used by females to assess males are expected to covary with ejaculate size and/or quality transferred during copulation, and female fecundity should be directly linked to mating with more attractive males. To date, direct tests of this hypothesis have been performed on internal fertilizing species, where several factors, such as for instance sperm competition, cryptic female choice, male parasite load, may affect ejaculate characteristics and female fecundity. Here, we used as a model the mandarinfish Synchiropus splendidus a small pelagic spawner where males only provide females with ejaculates and sperm competition does not occur. Males are significantly larger than females and we experimentally demonstrated that females prefer larger males. In addition, by collecting gametes from 67 natural spawning events, we attained a measure of the number of eggs and sperm released in each spawning event and the fertilization rates. The mean number of gametes produced positively correlates with body size in both sexes. Males do not regulate sperm number according to egg number and/or female body size. Fertilization success is significantly related to the mean number of sperm released but not directly to male body size. These findings, despite not fully accomplishing theoretical expectation, suggest that larger and more fecund females may suffer sperm limitation in mating with smaller males. In addition, our results have possible implications for the aquarium fishery of this species, which targets large males. [source] galics, V: Low- and high-order clustering in mock Sloan Digital Sky SurveysMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006Jérémy Blaizot ABSTRACT We use the galics hybrid model of galaxy formation to explore the nature of galaxy clustering in the local Universe. We bring the theoretical predictions of our model into the observational plane using the momaf software to build mock catalogues which mimic Sloan Digital Sky Survey (SDSS) observations. We measure low- and high-order angular clustering statistic from these mock catalogues, after selecting galaxies the same way as for observations, and compare them directly to estimates from the SDSS data. Note that we also present the first measurements of high-order statistics on the SDSS DR1. We find that our model is in general good agreement with observations in the scale/luminosity range where we can trust the predictions. This range is found to be limited (i) by the size of the dark matter simulation used , which introduces finite volume effects at large scales , and by the mass resolution of this simulation , which introduces incompleteness at apparent magnitudes fainter than r, 20. We then focus on the small-scale clustering properties of galaxies and investigate the behaviour of three different prescriptions for positioning galaxies within haloes of dark matter. We show that galaxies are poor tracers of either DM particles or DM substructures, within groups and clusters. Instead, SDSS data tells us that the distribution of galaxies lies somewhat in between these two populations. This confirms the general theoretical expectation from numerical simulations and semi-analytic modelling. [source] Exercise test mode dependency for ventilatory efficiency in women but not menCLINICAL PHYSIOLOGY AND FUNCTIONAL IMAGING, Issue 2 2006James A. Davis Summary Ventilatory efficiency is commonly defined as the level of ventilation V,E at a given carbon dioxide output (V,CO2). The slope of the V,E versus V,CO2 relationship and the lowest V,E/V,CO2 are two ventilatory efficiency indices that can be measured during cardiopulmonary exercise testing (CPET). A possible CPET mode dependency for these indices was evaluated in healthy men and women. Also evaluated was the relationship between these two indices as, in theory, V,E/V,CO2 falls hyperbolically towards an asymptote that numerically equals the V,E versus V,CO2 slope at exercise levels below the ones that cause respiratory compensation for metabolic acidosis. Twenty-eight healthy subjects (14 men) underwent treadmill and cycle ergometer CPET on different days. Ventilation and the gas fractions for oxygen and CO2 were measured with a vacumed metabolic cart. In men, paired t -test analysis failed to find a mode difference for either ventilatory efficiency index but the opposite was true in the women as each woman had higher values for both indices on the treadmill. For men, the lowest V,E/V,CO2 was larger than the V,E versus V,CO2 slope by 1·3 on the treadmill and 0·8 on the cycle ergometer. The corresponding values for women were 1·7 and 1·4. We conclude that in healthy subjects, women, but not men, demonstrate a mode dependency for the two ventilatory efficiency indices investigated in this study. Furthermore, our results are consistent with the theoretical expectation that the lowest V,E/V,CO2 has a numerical value just above the asymptote of the V,E/V,CO2 versus V,CO2 relationship. [source] Alternative models of issue voting: The case of the 1991 and 1995 elections in BelgiumEUROPEAN JOURNAL OF POLITICAL RESEARCH, Issue 3 2001BART MADDENS Previous research has indicated that the success of the directional model of issue voting depends on levels of political sophistication and how party position is measured. Using 1991 and 1995 Belgian Election Surveys, the predictive power of proximity and directional measures are compared controlling for both variables. It is shown that when one uses overall mean placements, instead of mean placements by level of political sophistication, the proximity effect declines most among the highly sophisticated voters. The article also compares the performance of the proximity and directional measures across party systems. Contrary to theoretical expectations, party,system differences between Flanders and Wallonia do not affect the explanatory power of either of these measures. It is only in the cases of the liberal, socialist and extreme right parties that the directional measure is clearly superior. A closer analysis of this result indicates that the relative success of the directional measure is due to the limited number of issues from which those parties draw support. [source] VIRULENCE AND COMPETITIVENESS: TESTING THE RELATIONSHIP DURING INTER- AND INTRASPECIFIC MIXED INFECTIONSEVOLUTION, Issue 9 2010Peter A. Staves Understanding the reasons why different parasites cause different degrees of harm to their hosts is an important objective in evolutionary biology. One group of models predicts that if hosts are infected with more than one strain or species of parasite, then competition between the parasites will select for higher virulence. While this idea makes intuitive sense, empirical data to support it are rare and equivocal. We investigated the relationship between fitness and virulence during both inter- and intraspecific competition for a fungal parasite of insects, Metarhizium anisopliae. Contrary to theoretical expectations, competition favored parasite strains with either a lower or a higher virulence depending on the competitor: when in interspecific competition with an entomopathogenic nematode, Steinernema feltiae, less virulent strains of the fungus were more successful, but when competing against conspecific fungi, more virulent strains were better competitors. We suggest that the nature of competition (direct via toxin production when competing against the nematode, indirect via exploitation of the host when competing against conspecific fungal strains) determines the relationship between virulence and competitive ability. [source] ADAPTIVE POPULATION DIFFERENTIATION IN PHENOLOGY ACROSS A LATITUDINAL GRADIENT IN EUROPEAN ASPEN (POPULUS TREMULA, L.): A COMPARISON OF NEUTRAL MARKERS, CANDIDATE GENES AND PHENOTYPIC TRAITSEVOLUTION, Issue 12 2007David Hall A correct timing of growth cessation and dormancy induction represents a critical ecological and evolutionary trade-off between survival and growth in most forest trees (Rehfeldt et al. 1999; Horvath et al. 2003; Howe et al. 2003). We have studied the deciduous tree European Aspen (Populus tremula) across a latitudinal gradient and compared genetic differentiation in phenology traits with molecular markers. Trees from 12 different areas covering 10 latitudinal degrees were cloned and planted in two common gardens. Several phenology traits showed strong genetic differentiation and clinal variation across the latitudinal gradient, with QST values generally exceeding 0.5. This is in stark contrast to genetic differentiation at several classes of genetic markers (18 neutral SSRs, 7 SSRs located close to phenology candidate genes and 50 SNPs from five phenology candidate genes) that all showed FST values around 0.015. We thus find strong evidence for adaptive divergence in phenology traits across the latitudinal gradient. However, the strong population structure seen at the quantitative traits is not reflected in underlying candidate genes. This result fit theoretical expectations that suggest that genetic differentiation at candidate loci is better described by FST at neutral loci rather than by QST at the quantitative traits themselves. [source] Iterative resolution estimation in least-squares Kirchhoff migrationGEOPHYSICAL PROSPECTING, Issue 6 2002Sergey Fomel ABSTRACT We apply iterative resolution estimation to least-squares Kirchhoff migration. Reviewing the theory of iterative optimization uncovers the common origin of different optimization methods. This allows us to reformulate the pseudo-inverse, model resolution and data resolution operators in terms of effective iterative estimates. When applied to Kirchhoff migration, plots of the diagonal of the model resolution matrix reveal low illumination areas on seismic images and provide information about image uncertainties. Synthetic and real data examples illustrate the proposed technique and confirm the theoretical expectations. [source] The Cost-Effectiveness of Independent Housing for the Chronically Mentally Ill: Do Housing and Neighborhood Features Matter?HEALTH SERVICES RESEARCH, Issue 5 2004Joseph Harkness Objective. To determine the effects of housing and neighborhood features on residential instability and the costs of mental health services for individuals with chronic mental illness (CMI). Data Sources. Medicaid and service provider data on the mental health service utilization of 670 individuals with CMI between 1988 and 1993 were combined with primary data on housing attributes and costs, as well as census data on neighborhood characteristics. Study participants were living in independent housing units developed under the Robert Wood Johnson Foundation Program on Chronic Mental Illness in four of nine demonstration cities between 1988 and 1993. Study Design. Participants were assigned on a first-come, first-served basis to housing units as they became available for occupancy after renovation by the housing providers. Multivariate statistical models are used to examine the relationship between features of the residential environment and three outcomes that were measured during the participant's occupancy in a study property: residential instability, community-based service costs, and hospital-based service costs. To assess cost-effectiveness, the mental health care cost savings associated with some residential features are compared with the cost of providing housing with these features. Data Collection/Extraction Methods. Health service utilization data were obtained from Medicaid and from state and local departments of mental health. Non-mental-health services, substance abuse services, and pharmaceuticals were screened out. Principal Findings. Study participants living in newer and properly maintained buildings had lower mental health care costs and residential instability. Buildings with a richer set of amenity features, neighborhoods with no outward signs of physical deterioration, and neighborhoods with newer housing stock were also associated with reduced mental health care costs. Study participants were more residentially stable in buildings with fewer units and where a greater proportion of tenants were other individuals with CMI. Mental health care costs and residential instability tend to be reduced in neighborhoods with many nonresidential land uses and a higher proportion of renters. Mixed-race neighborhoods are associated with reduced probability of mental health hospitalization, but they also are associated with much higher hospitalization costs if hospitalized. The degree of income mixing in the neighborhood has no effect. Conclusions. Several of the key findings are consistent with theoretical expectations that higher-quality housing and neighborhoods lead to better mental health outcomes among individuals with CMI. The mental health care cost savings associated with these favorable features far outweigh the costs of developing and operating properties with them. Support for the hypothesis that "diverse-disorganized" neighborhoods are more accepting of individuals with CMI and, hence, associated with better mental health outcomes, is mixed. [source] Hybrid finite-volume finite-difference scheme for the solution of Boussinesq equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2005K. S. Erduran Abstract A hybrid scheme composed of finite-volume and finite-difference methods is introduced for the solution of the Boussinesq equations. While the finite-volume method with a Riemann solver is applied to the conservative part of the equations, the higher-order Boussinesq terms are discretized using the finite-difference scheme. Fourth-order accuracy in space for the finite-volume solution is achieved using the MUSCL-TVD scheme. Within this, four limiters have been tested, of which van-Leer limiter is found to be the most suitable. The Adams,Basforth third-order predictor and Adams,Moulton fourth-order corrector methods are used to obtain fourth-order accuracy in time. A recently introduced surface gradient technique is employed for the treatment of the bottom slope. A new model ,HYWAVE', based on this hybrid solution, has been applied to a number of wave propagation examples, most of which are taken from previous studies. Examples include sinusoidal waves and bi-chromatic wave propagation in deep water, sinusoidal wave propagation in shallow water and sinusoidal wave propagation from deep to shallow water demonstrating the linear shoaling properties of the model. Finally, sinusoidal wave propagation over a bar is simulated. The results are in good agreement with the theoretical expectations and published experimental results. Copyright © 2005 John Wiley & Sons, Ltd. [source] On the relation between temporal variability and persistence time in animal populationsJOURNAL OF ANIMAL ECOLOGY, Issue 6 2003Pablo Inchausti Summary 1The relationship between temporal variability, spectral redness and population persistence for a large number of long-term time series was investigated. Although both intuition and theory suggest that more variability in population abundance would mean greater probability of extinction, previous empirical support for this view has not been conclusive. Possible reasons are the shortage of long-term data and the difficulties of adequately characterizing temporal variability, two issues that are explicitly addressed in this paper. 2We examined the relationship between population variability and quasi-extinction time (measured as the time required to observe a 90% decline of population abundance) for a large set of data comprising 554 populations for 123 species that were censused for more than 30 years. Two aspects of temporal variability were considered in relation with the quasi-extinction time: a baseline value (coefficient of variation over a fixed, 30-year, time scale), and a measure of the rate of increase of the population variability over time (spectral exponent). 3The results show that the quasi-extinction time was shorter for populations having higher temporal variability and redder dynamics. The relation between persistence time and population variability was compared for different taxa, trophic levels, habitat type (aquatic and terrestrial) and body sizes and compared with theoretical expectations. [source] Contrasting approaches to statistical regression in ecology and economicsJOURNAL OF APPLIED ECOLOGY, Issue 2 2009P. R. Armsworth Summary 1Conservation and natural resource management challenges are as much social problems as biological ones. In recognition of this fact, ecologists and economists work increasingly closely together. We discuss one barrier to effective integration of the two disciplines: put simply, many ecologists and economists approach statistical regression differently. 2Regression techniques provide the most commonly used approach for empirical analyses of land management decisions. Researchers from each discipline attribute differing importance to a range of possibly conflicting design criteria when formulating regression analyses. 3Ecologists commonly attribute greater importance to spatial autocorrelation and parsimony than do economists when designing regressions. Economists often attribute greater importance than ecologists to concerns about endogeneity and conformance with a priori theoretical expectations. 4Synthesis and applications. The differing importance attributed to different design characteristics may reflect a process of cultural drift within each discipline. Greater interdisciplinary collaboration can counteract this process by stimulating the flow of ideas and techniques across disciplinary boundaries. [source] Male choice generates stabilizing sexual selection on a female fecundity correlateJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2007S. F. CHENOWETH Abstract We know very little about male mating preferences and how they influence the evolution of female traits. Theory predicts that males may benefit from choosing females on the basis of traits that indicate their fecundity. Here, we explore sexual selection generated by male choice on two components of female body size (wing length and body mass) in Drosophila serrata. Using a dietary manipulation to alter female size and 828 male mate choice trials, we analysed linear and nonlinear sexual selection gradients on female mass and wing length. In contrast to theoretical expectations and prevailing empirical data, males exerted stabilizing rather than directional sexual selection on female body mass, a correlate of fecundity. Sexual selection was detected only among females with access to standard resource levels as an adult, with no evidence for sexual selection among resource-depleted females. Thus the mating success of females with the same body mass differed depending upon their access to resources as an adult. This suggests that males in this species may rely on signal traits to assess body mass rather than assessing it directly. Stabilizing rather than directional sexual selection on body mass together with recent evidence for stabilizing sexual selection on candidate signal traits in this species suggests that females may trade-off resources allocated to reproduction and sexual signalling. [source] The burgeoning field of statistical phylogeographyJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2004L. L. Knowles Abstract In the newly emerging field of statistical phylogeography, consideration of the stochastic nature of genetic processes and explicit reference to theoretical expectations under various models has dramatically transformed how historical processes are studied. Rather than being restricted to ad hoc explanations for observed patterns of genetic variation, assessments about the underlying evolutionary processes are now based on statistical tests of various hypotheses, as well as estimates of the parameters specified by the models. A wide range of demographical and biogeographical processes can be accommodated by these new analytical approaches, providing biologically more realistic models. Because of these advances, statistical phylogeography can provide unprecedented insights about a species' history, including decisive information about the factors that shape patterns of genetic variation, species distributions, and speciation. However, to improve our understanding of such processes, a critical examination and appreciation of the inherent difficulties of historical inference and challenges specific to testing phylogeographical hypotheses are essential. As the field of statistical phylogeography continues to take shape many difficulties have been resolved. Nonetheless, careful attention to the complexities of testing historical hypotheses and further theoretical developments are essential to improving the accuracy of our conclusions about a species' history. [source] The effects of carotenoid and food intake on caudal fin regeneration in male guppiesJOURNAL OF FISH BIOLOGY, Issue 4 2006G. R. Kolluru The trade-offs involved in allocating carotenoid pigments and food to healing and regrowing damaged caudal fin tissue v. other functions were examined in guppies Poecilia reticulata, a species in which females prefer males that display larger amounts of carotenoids in their skin. The guppies were derived from four natural populations in Trinidad that differed in resource availability but not predation intensity. Carotenoids, food and site of origin did not affect either absolute or relative fin regrowth, which suggested that fin regeneration in guppies was not constrained by carotenoid availability. It is possible that carotenoid intake influences fin regeneration in the presence of natural stressors such as predators. There was a significant negative interaction between food level in the laboratory and resource availability in the field: males from low-resource-availability sites regrew more fin tissue when raised on the high food level, and males from high-resource-availability sites regrew more fin tissue when raised on the low food level. The direction of this interaction runs counter to theoretical expectations. [source] Plot shape effects on plant species diversity measurementsJOURNAL OF VEGETATION SCIENCE, Issue 2 2005Jon E. Keeley Abstract. Question: Do rectangular sample plots record more plant species than square plots as suggested by both empirical and theoretical studies? Location: Grasslands, shrublands and forests in the Mediterranean-climate region of California, USA. Methods: We compared three 0.1-ha sampling designs that differed in the shape and dispersion of 1-m2 and 100-m2 nested subplots. We duplicated an earlier study that compared the Whittaker sample design, which had square clustered subplots, with the modified Whittaker design, which had dispersed rectangular subplots. To sort out effects of dispersion from shape we used a third design that overlaid square subplots on the modified Whittaker design. Also, using data from published studies we extracted species richness values for 400-m2 subplots that were either square or 1:4 rectangles partially overlaid on each other from desert scrub in high and low rainfall years, chaparral, sage scrub, oak savanna and coniferous forests with and without fire. Results: We found that earlier empirical reports of more than 30% greater richness with rectangles were due to the confusion of shape effects with spatial effects, coupled with the use of cumulative number of species as the metric for comparison. Average species richness was not significantly different between square and 1:4 rectangular sample plots at either 1- or 100-m2. Pairwise comparisons showed no significant difference between square and rectangular samples in all but one vegetation type, and that one exhibited significantly greater richness with squares. Our three intensive study sites appear to exhibit some level of self-similarity at the scale of 400 m2, but, contrary to theoretical expectations, we could not detect plot shape effects on species richness at this scale. Conclusions: At the 0.1-ha scale or lower there is no evidence that plot shape has predictable effects on number of species recorded from sample plots. We hypothesize that for the mediterranean-climate vegetation types studied here, the primary reason that 1:4 rectangles do not sample greater species richness than squares is because species turnover varies along complex environmental gradients that are both parallel and perpendicular to the long axis of rectangular plots. Reports in the literature of much greater species richness recorded for highly elongated rectangular strips than for squares of the same area are not likely to be fair comparisons because of the dramatically different periphery/area ratio, which includes a much greater proportion of species that are using both above and below-ground niche space outside the sample area. [source] Heterogeneous agglutinitic glass and the fusion of the finest fraction (F3) modelMETEORITICS & PLANETARY SCIENCE, Issue 12 2002Abhijit Basu They include (1) theoretical expectations that shock pulses should engulf and melt smaller grains more efficiently than larger grains, (2) experimental results of impact shock, albeit at lower than presumed hypervelocity impacts of micrometeorites on the lunar regolith, and (3) new analyses confirming previous results that average compositions of agglutinitic glass are biased towards that of the finest fraction of lunar soils from which they had formed. We add another reason in support of the F3 model. Finer grains of lunar soils are also much more abundant. Hence, electrostatic forces associated with the rotating terminator region bring the finest grains that are obviously much lighter than courser grains to the surface of the Moon. This further contributes to the preferential melting of the finest fraction upon micrometeoritic impacts. New backscattered electron imaging shows that agglutinitic glass is inhomogeneous at submicron scale. Composition ranges of agglutinitic glass are extreme and deviate from that of the finest fraction, even by more than an order of magnitude for some components. Additionally, we show how an ilmenite grain upon impact would produce TiO2 -rich agglutinitic glass in complete disregard to the requirements of fusion of the finest fraction. We propose an addition to the F3 model to accommodate these observations (i.e., that micrometeorite impacts indiscriminately melt the immediate target regardless of grain size or grain composition). We, therefore, suggest that (1) agglutinitic glass is the sum of (a) the melt produced by the fusion of the finest fraction of lunar soils and (b) the microvolume of the indiscriminate target, which melts at high-shock pressures from micrometeoritic impacts, and that (2) because of the small volume of the melt and incorporating cold soil grains, the melt quenched so rapidly that it did not mix and homogenize to represent any preferential composition, for example, that of the finest fraction. [source] Isotopic compositions of different presolar silicon carbide size fractions from the Murchison meteoriteMETEORITICS & PLANETARY SCIENCE, Issue 5 2000Sachiko AMARI Ratios of 12C/13C range from 37 to 42 and 14N/15N ratios from 370 to 520, within the range of single-grain measurements on coarser samples and in agreement with an asymptotic giant branch (AGB) star origin of most of the grains. Variations among size fractions do not show any simple trend and can be explained by varying contamination with isotopically normal material. Silicon isotopic ratios vary only little and, with one exception, lie to the right of the singlegrain mainstream correlation line. This might indicate a higher percentage of the minor populations Y and Z among finer grain-size fractions. All bulk samples have large 26Mg excesses attributed to the presence of short-lived 26Al at the time of grain formation. Inferred 26Al/27Al ratios are much larger than those measured in single larger mainstream grains. This is probably because of the presence of SiC grains of type X; we obtain an estimate of 0.4 for their 26Al/27Al ratio. Our Ca-isotopic measurements, the first made on presolar SiC grains, show excesses in 42Ca and 43Ca, which is in general agreement with theoretical expectations for AGB stars. Calcium-44 excesses are much larger than expected and are probably because of X grains, which have high44Ca excesses because of the decay of short-lived 44Ti produced in supernova explosions. We arrive at an estimate of 0.014 for the initial 44Ti/48Ti ratio of the X grains, within the range obtained from previous single X grain measurements. The Ti-isotopic ratios of the bulk samples show a V-shaped pattern with excesses of all isotopes relative to 48Ti. Isotopes 46Ti, 47Ti, and 50Ti show excesses relative to the correlation between Ti and Si ratios for single grains and are in general agreement with theoretical models of s-process nucleosynthesis in AGB stars. In contrast, 49Ti does not show any excess relative to the singlegrain data; it also fails to agree with theory, which predicts much larger excesses than observed. Measured 53Cr/52Cr and 57Fe/56Fe ratios are normal within errors. The first result is expected even for Cr in AGB star envelopes, but the second result suggests that most of the Fe analyzed originates from contamination. We have found no simple trends in isotopic composition with respect to grain size that can be interpreted in terms of nucleosynthetic origin, unlike the results for Kr, Xe, Ba, and Sr. [source] Spatial distribution of luminous X-ray binaries in spiral galaxiesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008Zhao-yu Zuo ABSTRACT We have modelled the spatial distribution of luminous X-ray binaries (XRBs) in spiral galaxies that are like the Milky Way using an evolutionary population synthesis code. In agreement with previous theoretical expectations and observations, we find that both high- and low-mass XRBs show clear concentrations towards the galactic plane and bulge. We also compare XRB distributions under the galactic potential with a dark matter halo and the modified Newtonian dynamics potential, and we suggest that the difference may serve as potential evidence to discriminate between these two types of model. [source] The effects of thermal conduction on the intracluster medium of the Virgo clusterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2005Edward C. D. Pope ABSTRACT Thermal conduction has been suggested as a possible mechanism by which sufficient energy is supplied to the central regions of galaxy clusters to balance the effect of radiative cooling. Recent high-resolution observations of the nearby Virgo cluster make it an ideal subject for an attempt to reproduce the properties of the cluster by numerical simulations, because most of the defining parameters are comparatively well known. Here, we present the results of a simulated high-resolution, 3D Virgo cluster for different values of thermal conductivity ( times the full Spitzer value). Starting from an initially isothermal cluster atmosphere, we allow the cluster to evolve freely over time-scales of roughly 1.3,4.7 × 109 yr. Our results show that thermal conductivity at the Spitzer value can increase the central intracluster medium (ICM) radiative cooling time by a factor of roughly 3.6. In addition, for larger values of thermal conductivity, the simulated temperature and density profiles match the observations significantly better than for the lower values. However, no physically meaningful value of thermal conductivity was able to postpone the cooling catastrophe (characterized by a rapid increase in the central density) for longer than a fraction of the Hubble time nor explain the absence of a strong cooling flow in the Virgo cluster today. We also calculate the effective adiabatic index of the cluster gas for both simulation and observational data and compare the values with theoretical expectations. Using this method, it appears that the Virgo cluster is being heated in the cluster centre by a mechanism other than thermal conductivity. Based on this and our simulations, it is also likely that the thermal conductivity is suppressed by a factor of at least 10 and probably more. Thus, we suggest that thermal conductivity, if present at all, has the effect of slowing down the evolution of the ICM, by radiative cooling, but only by a factor of a few. [source] Thin discs, thick dwarfs and the effects of stellar feedbackMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010R. Sánchez-Janssen ABSTRACT We investigate the role of stellar mass in shaping the intrinsic thickness of galaxy discs by determining the probability distribution of apparent axial ratios (b/a) for two different samples that probe the faint end of the galaxy luminosity function. We find that the b/a distribution has a characteristic ,U-shape' and identify a limiting mass M*, 2 × 109 M, below which low-mass galaxies start to be systematically thicker. This tendency holds for very faint (MB,,8) dwarfs in the local volume, which are essentially spheroidal systems. We argue that galaxy shape is the result of the complex interplay between mass, specific angular momentum and stellar feedback effects. Thus, the increasing importance of turbulent motions in lower mass galaxies leads to the formation of thicker systems, a result supported by the latest hydrodynamical simulations of dwarf galaxy formation and other theoretical expectations. We discuss several implications of this finding, including the formation of bars in faint galaxies, the deprojection of H i line profiles and simulations of environmental effects on the dwarf galaxy population. [source] On the solution of an initial-boundary value problem that combines Neumann and integral condition for the wave equation,NUMERICAL METHODS FOR PARTIAL DIFFERENTIAL EQUATIONS, Issue 1 2005Mehdi Dehghan Abstract Numerical solution of hyperbolic partial differential equation with an integral condition continues to be a major research area with widespread applications in modern physics and technology. Many physical phenomena are modeled by nonclassical hyperbolic boundary value problems with nonlocal boundary conditions. In place of the classical specification of boundary data, we impose a nonlocal boundary condition. Partial differential equations with nonlocal boundary specifications have received much attention in last 20 years. However, most of the articles were directed to the second-order parabolic equation, particularly to heat conduction equation. We will deal here with new type of nonlocal boundary value problem that is the solution of hyperbolic partial differential equations with nonlocal boundary specifications. These nonlocal conditions arise mainly when the data on the boundary can not be measured directly. Several finite difference methods have been proposed for the numerical solution of this one-dimensional nonclassic boundary value problem. These computational techniques are compared using the largest error terms in the resulting modified equivalent partial differential equation. Numerical results supporting theoretical expectations are given. Restrictions on using higher order computational techniques for the studied problem are discussed. Suitable references on various physical applications and the theoretical aspects of solutions are introduced at the end of this article. © 2004 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2005 [source] Stomatal sensitivity to vapour pressure difference over a subambient to elevated CO2 gradient in a C3/C4 grasslandPLANT CELL & ENVIRONMENT, Issue 8 2003H. MAHERALI ABSTRACT In the present study the response of stomatal conductance (gs) to increasing leaf-to-air vapour pressure difference (D) in early season C3 (Bromus japonicus) and late season C4 (Bothriochloa ischaemum) grasses grown in the field across a range of CO2 (200,550 µmol mol,1) was examined. Stomatal sensitivity to D was calculated as the slope of the response of gs to the natural log of externally manipulated D (dgs/dlnD). Increasing D and CO2 significantly reduced gs in both species. Increasing CO2 caused a significant decrease in stomatal sensitivity to D in Br. japonicus, but not in Bo. ischaemum. The decrease in stomatal sensitivity to D at high CO2 for Br. japonicus fit theoretical expectations of a hydraulic model of stomatal regulation, in which gs varies to maintain constant transpiration and leaf water potential. The weaker stomatal sensitivity to D in Bo. ischaemum suggested that stomatal regulation of leaf water potential was poor in this species, or that non-hydraulic signals influenced guard cell behaviour. Photosynthesis (A) declined with increasing D in both species, but analyses of the ratio of intercellular to atmospheric CO2 (Ci/Ca) suggested that stomatal limitation of A occurred only in Br. japonicus. Rising CO2 had the greatest effect on gs and A in Br. japonicus at low D. In contrast, the strength of stomatal and photosynthetic responses to CO2 were not affected by D in Bo. ischaemum. Carbon and water dynamics in this grassland are dominated by a seasonal transition from C3 to C4 photosynthesis. Interspecific variation in the response of gs to D therefore has implications for predicting seasonal ecosystem responses to CO2. [source] Source Cues, Partisan Identities, and Political Value ExpressionAMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 4 2009Paul Goren This article examines the conditions under which partisan identities shape the positions people express on four political values: equal opportunity, self-reliance, moral traditionalism, and moral tolerance. The theoretical framework posits that (1) party source cues activate latent partisan biases in the minds of citizens, which in turn affect the degree to which individuals express support for these values; (2) out-party cues are more powerful motivators of value expression than in-party cues; (3) value shifts are more pronounced when liberal-conservative identities reinforce partisan sentiments; and (4) partisan cues promote horizontal constraint among these values. These hypotheses are tested using data from a set of experiments appearing on a novel national survey. The empirical results generally support these theoretical expectations. [source] Agency Problems, the 17th Amendment, and Representation in the SenateAMERICAN JOURNAL OF POLITICAL SCIENCE, Issue 2 2009Sean Gailmard A prominent change in American electoral institutions occurred when the 17th Amendment to the Constitution established direct election of U.S. Senators as of 1914. How did this change the political agency relationship between the mass electorate and U.S. Senators? We develop theoretical expectations about the representational effects of direct election by a relatively inexpert mass electorate and indirect election by a relatively expert political intermediary, based on principal-agent theory. The chief predictions are that the representative will be more responsive to the mass electorate under direct election, but will also have more discretion to pursue his or her own ends. We use the 17th Amendment as a quasi-experiment to test the predictions of the theory. Statistical models show strong support for both predictions. Moreover, the 17th Amendment is not associated with similar changes in the U.S. House of Representatives,as expected, since the amendment did not change House electoral institutions. [source] Sex-specific sibling interactions and offspring fitness in vertebrates: patterns and implications for maternal sex ratiosBIOLOGICAL REVIEWS, Issue 2 2006Tobias Uller ABSTRACT Vertebrate sex ratios are notorious for their lack of fit to theoretical models, both with respect to the direction and the magnitude of the sex ratio adjustment. The reasons for this are likely to be linked to simplifying assumptions regarding vertebrate life histories. More specifically, if the sex ratio adjustment itself influences offspring fitness, due to sex-specific interactions among offspring, this could affect optimal sex ratios. A review of the literature suggests that sex-specific sibling interactions in vertebrates result from three major causes: (i) sex asymmetries in competitive ability, for example due to sexual dimorphism, (ii) sex-specific cooperation or helping, and (iii) sex asymmetries in non-competitive interactions, for example steroid leakage between fetuses. Incorporating sex-specific sibling interactions into a sex ratio model shows that they will affect maternal sex ratio strategies and, under some conditions, can repress other selection pressures for sex ratio adjustment. Furthermore, sex-specific interactions could also explain patterns of within-brood sex ratio (e.g. in relation to laying order). Failure to take sex-specific sibling interactions into account could partly explain the lack of sex ratio adjustment in accordance with theoretical expectations in vertebrates, and differences among taxa in sex-specific sibling interactions generate predictions for comparative and experimental studies. [source] Short-term versus Long-term Impact of Managers: Evidence from the Football IndustryBRITISH JOURNAL OF MANAGEMENT, Issue 2 2010Mathew Hughes Studies into the impact of top manager change on organization performance have revealed inconsistent findings. Using longitudinal data over a 12-year period on football organizations, we test for the short-term and long-term effects of manager change in comparison to the tenures of incumbent top managers. We find that long incumbent tenures are associated with performance far above the average. But when looking at change events, contrary to theoretical expectations, we find that change in the short term leads to a brief reprieve in poor performance only for performance to deteriorate in the long term as underlying weaknesses once again take hold. Our findings reveal the illusion of a short-term reprieve and the long-term consequences of this illusion. We map several implications for research and practice from our work. [source] Explaining the impact of ISO 14001 on emission performance: a dynamic capabilities perspective on process and learningBUSINESS STRATEGY AND THE ENVIRONMENT, Issue 5 2009Michael V. Russo Abstract I draw upon the dynamic capability model to explore how new process standards influence the ability of manufacturing facilities to improve environmental performance by reducing toxic emissions. The process standards studied are the ISO 14001 environmental management standards, in use since 1996. Hypotheses are developed to account for how early adoption of ISO 14001 and experience with the standards influence emission levels. These hypotheses are tested using a large sample of electronics manufacturing facilities and data from 1996 through 2001. Consistent with theoretical expectations, analyses show that being one of the first facilities to adopt ISO 14001 was associated with lower emissions. Further, a separate effect is due to experience: the longer a facility operated under ISO 14001, the lower its emissions. The paper discusses the implications of these results for theory and policy development. Copyright © 2007 John Wiley & Sons, Ltd and ERP Environment. [source] Electronic Structure, Spectra, and Magnetic Circular Dichroism of Cyclohexa-, Cyclohepta-, and CyclooctapyrroleCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2005Alexander Gorski Abstract Three recently obtained expanded porphyrins represent nice examples of compounds for which the electronic and spectral properties can be predicted from symmetry considerations alone. Perimeter-model-based theoretical analysis of the electronic structure of doubly protonated cyclo[6], cyclo[7], and cyclo[8]pyrrole leads to the anticipation of qualitatively the same electronic absorption and magnetic circular dichroism patterns for all three compounds. These predictions are fully confirmed by experiments, as well as DFT and INDO/S calculations. Due to a characteristic pattern of frontier molecular orbitals, a degenerate HOMO and a strongly split LUMO pair, the three cyclopyrroles show comparable absorption intensity in the Q and Soret regions. Magnetic circular dichroism spectra reveal both A and B Faraday terms, of which the signs and magnitudes are in remarkably good agreement with theoretical expectations. The values of the magnetic moments of the two lowest degenerate excited states have also been obtained. [source] | |||||||||||||||||||||||||