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Heterogeneity
Kinds of Heterogeneity Terms modified by Heterogeneity Selected AbstractsINVESTIGATING EVOLUTIONARY TRADE-OFFS IN WILD POPULATIONS OF ATLANTIC SALMON (SALMO SALAR): INCORPORATING DETECTION PROBABILITIES AND INDIVIDUAL HETEROGENEITYEVOLUTION, Issue 9 2010Mathieu Buoro Evolutionary trade-offs among demographic parameters are important determinants of life-history evolution. Investigating such trade-offs under natural conditions has been limited by inappropriate analytical methods that fail to address the bias in demographic estimates that can result when issues of detection (uncertain detection of individual) are ignored. We propose a new statistical approach to quantify evolutionary trade-offs in wild populations. Our method is based on a state-space modeling framework that focuses on both the demographic process of interest as well as the observation process. As a case study, we used individual mark,recapture data for stream-dwelling Atlantic salmon juveniles in the Scorff River (Southern Brittany, France). In freshwater, juveniles face two life-history choices: migration to the ocean and sexual maturation (for males). Trade-offs may appear with these life-history choices and survival, because all are energy dependent. We found a cost of reproduction on survival for fish staying in freshwater and a survival advantage associated with the "decision" to migrate. Our modeling framework opens up promising prospects for the study of evolutionary trade-offs when some life-history traits are not, or only partially, observable. [source] EFFECTS OF ENVIRONMENTAL HETEROGENEITY ON VICTIM,EXPLOITER COEVOLUTIONEVOLUTION, Issue 12 2008Sergey Gavrilets We study victim,exploiter coevolution in a spatially heterogeneous island model. In each species, fitness consequences of between-species interactions are controlled by a single haploid diallelic locus. Our emphasis is on the conditions for the maintenance of genetic variation, the dynamic patterns observed, the extent of local adaptation and genetic differentiation between different demes, and on how different parameters (such as the strength and heterogeneity in selection, migration rates, and the number of sites) affect the dynamic and static behavior of the system. We show that under spatially homogeneous selection the maintenance of genetic variation is possible through asynchronous nonlinear dynamics where the allele frequencies in a majority of demes quickly synchronize but the rest do not. Spatially heterogeneous selection can maintain genetic variation even if migration rates are maximal. This happens in an oscillatory way. Genetic variation is most likely to be maintained at high levels if the heterogeneity in selection is large. If there are some restrictions on migration, genetic variation can be maintained at a stable equilibrium. This behavior is most likely at intermediate migration rates. In this case, the system can exhibit high spatial subdivision as measured by FST values but relatively low local adaptation. [source] LOOKING AT THE "POPULATION PROBLEM" THROUGH THE PRISM OF HETEROGENEITY: WELFARE AND POLICY ANALYSES,INTERNATIONAL ECONOMIC REVIEW, Issue 3 2008C. Simon Fan Upon introducing heterogeneity and dynamics into a model of the demand for children, a problem of optimal population is defined and analyzed. It is shown that from the perspective of social welfare, better-educated individuals produce too few children while less-educated individuals produce too many children and all individuals invest too little in the education of their children. The impact of several policy tools geared at addressing the "population problem" is investigated, in particular how child allowances and other tax-subsidy policies can be harnessed to enhance welfare, and how and why early childhood education programs can mitigate the "population problem." [source] HETEROGENEITY OF THE CYANOBACTERIAL GENUS SYNECHOCYSTIS AND DESCRIPTION OF A NEW GENUS, GEMINOCYSTIS,JOURNAL OF PHYCOLOGY, Issue 4 2009Jana Korelusová The study and revision of the unicellular cyanobacterial genus Synechocystis was based on the type species S. aquatilis Sauv. and strain PCC 6803, a reference strain for this species. Uniformity in rRNA gene sequence, morphology, and ultrastructure was observed in all available Synechocystis strains, with the exception of the strain PCC 6308, which has been considered by some to be a model strain for Synechocystis. This strain differs substantially from the typical Synechocystis cluster according to both molecular (<90% of similarity, differences in 16S,23S rRNA internal transcribed spacer [ITS] secondary structure) and phenotypic criteria (different ultrastructure of cells). This strain is herein classified into the new genus Geminocystis gen. nov., as a sister taxon to the genus Cyanobacterium. Geminocystis differs from Cyanobacterium by genetic position (<94.4% of similarity) and more importantly by its different type of cell division. Because strain PCC 6308 was designated as a reference strain of the Synechocystis cluster 1 in Bergey's Manual, the members of this genetic cluster have to be revised and reclassified into Geminocystis gen. nov. Only the members of the Synechocystis cluster 2 allied with PCC 6803 correspond both genetically and phenotypically to the type species of the genus Synechocystis (S. aquatilis). [source] PREFERENCE HETEROGENEITY AND ECONOMIC GEOGRAPHY,JOURNAL OF REGIONAL SCIENCE, Issue 1 2009Antonella Nocco ABSTRACT We investigate the effect of preference heterogeneity between skilled and unskilled workers on agglomeration, and we identify a new source of dependence of equilibrium prices on the demand properties shaped by the inter-regional distribution of workers. We find a new preference effect, and we show that when the intensity of skilled workers' preference for the modern good and its variety is strong enough, prices charged by firms may even increase when the mass of local firms increases, therefore acting as a new dispersion force when trade costs are low or as a new agglomeration force when trade costs are high. [source] PHOTOGRAPHIC IDENTIFICATION OF NORTHERN BOTTLENOSE WHALES (HYPEROODON AMPULLATUS): SOURCES OF HETEROGENEITY FROM NATURAL MARKSMARINE MAMMAL SCIENCE, Issue 1 2001Shannon Gowans Abstract The use of natural marks in capture-recapture studies can lead to unequal capture probabilities. This paper examined a catalog of northern bottlenose whale (Hyperoodon ampullatus) photographs from the Gully, Nova Scotia, to identify potential sources of heterogeneity. This information can be used to select appropriate individuals and photographs to include in analyses. Individual northern bottlenose whales were sufficiently marked to uniquely identify individuals (x,= 14.5 marks/individual; range 1-67), but not all mark types persisted over time. Reliable marks were defined as mark types that were not lost over the nine-yeat study period (notches, back indentation, and mottled patches). Individuals were considered reliably marked if they possessed at least one back indentation or mottled patch (located within one dorsal fin width, at the base of the dorsal fin) or a notch on the dorsal fin. Sixty-six percent (SE = 5%) of the population were reliably marked. Longterm analyses (months to years) should use only reliably marked individuals, and the results scaled to account for the rest of the population. Our results also showed that photographic quality affected an observer's ability to identify individuals. For this catalog, quantitative analysis indicated only photographs of Q , 4 (on a 6-point scale with 6 representing the highest quality) should be included in mark-recapture analyses sensitive to heterogeneity. [source] DISTANCE, BANK HETEROGENEITY AND ENTRY IN LOCAL BANKING MARKETS,THE JOURNAL OF INDUSTRIAL ECONOMICS, Issue 3 2008ROBERTO FELICI We examine the determinants of entry into Italian local banking markets during the period 1991,2002 and build a simple model in which the probability of branching in a new market depends on the features of both the local market and the potential entrant. Econometric findings show that banks are more likely to expand into those markets that are closest to their pre-entry locations. Large banks are also more able to cope with distance-related entry costs than small banks. Finally, banks have become increasingly able to open branches in distant markets, due to the advent of information and communication technologies. [source] Random Copolymer Films with Molecular-Scale Compositional Heterogeneities that Interfere with Protein AdsorptionADVANCED FUNCTIONAL MATERIALS, Issue 21 2009Salmaan H. Baxamusa Abstract Smooth surfaces with compositional heterogeneities at a molecular-length scale are presented with the goal of disrupting surface,protein interactions. These surfaces are synthesized by utilizing photoinitiated chemical vapor deposition (piCVD) to deposit thin films of random copolymers consisting of highly hydrophilic and highly hydrophobic comonomers. Swellability, wettability, and surface roughness could be systematically controlled by tuning the copolymer composition. The surface composition was dynamic, and the surface reconstructed based on the hydration state of the film. Proteins adsorbed to the copolymer films less readily than to either of the respective homopolymers, indicating a synergistic effect resulting from the random copolymer presenting molecular-scale compositional heterogeneity. These results provide direct evidence that protein adsorption can be disrupted by such surfaces and a simple analytical model suggests that the heterogeneities occur over areas encompassing 4,5 repeat units of the polymer. The synthetic method used to create these films can be used to coat arbitrary geometries, enabling practical utility in a number of applications. [source] Influence of Small-Scale Heterogeneities on Contaminant Transport in Fractured Crystalline RockGROUND WATER, Issue 5 2006Ralph Mettier We present a sequence of purely advective transport models that demonstrate the influence of small-scale geometric inhomogeneities on contaminant transport in fractured crystalline rock. Special weight is placed on the role of statistically generated variable fracture apertures. The fracture network geometry and the aperture distribution are based on information from an in situ radionuclide retardation experiment performed at Grimsel test site (Swiss Alps). The obtained breakthrough curves are fitted with the advection dispersion equation and continuous-time random walks (CTRW). CTRW is found to provide superior fits to the late-arrival tailing and is also found to show a good correlation with the velocity distributions obtained from the hydraulic models. The impact of small-scale heterogeneities, both in fracture geometry and aperture, on transport is shown to be considerable. [source] Freud's Oedipus and Kristeva's Narcissus: Three HeterogeneitiesHYPATIA, Issue 1 2005SARA BEARDSWORTH The paper shows that three heterogeneities in Freud and Kristeva (unconscious/conscious, semiotic/symbolic, and imaginary/symbolic) expose the historical emergence, significance, and demise of psychic structures that present obstacles to our progressive political thinking. The oedipal and narcissistic structures of subjectivity represent the persistence of two past, bad forms of authority: paternal law and maternal authority. Contemporary psychoanalysis reveals a humankind going through the loss of this past in a process that opens up a different future of sexual difference in Western cultures. [source] Cross-disciplinary demands of multihost pathogensJOURNAL OF ANIMAL ECOLOGY, Issue 6 2008DANIEL T. HAYDON The dynamics of infectious disease spread depend on host population contact structure. Heterogeneities in this contact structure can arise from various forms of demographic and spatial phenomena. Craft et al. (this issue) have constructed an exploratory simulation model of the spread of canine distemper virus through a multispecies carnivore community. Each species in this community is modelled with a contact structure reflecting host social organization, ranging behaviour, and likely interspecific contact patterns. The results are used to infer the possible roles of different species in determining the observed spatio-temporal incidence of canine distemper virus in Serengeti lions during an outbreak in 1993,94. [source] Contribution of a haplotype in the HLA region to anti,cyclic citrullinated peptide antibody positivity in rheumatoid arthritis, independently of HLA,DRB1ARTHRITIS & RHEUMATISM, Issue 12 2009Yukinori Okada Objective To examine the risk of anti,cyclic citrullinated peptide (anti-CCP) antibody positivity in rheumatoid arthritis (RA) patients carrying certain haplotypes in the HLA region. Methods A total of 1,389 Japanese patients with RA were genotyped for 30 single-nucleotide polymorphisms (SNPs) in the HLA region using commercial oligonucleotide arrays (from Perlegen or Affymetrix) as well as for HLA,DRB1 alleles using a sequence-specific polymerase chain reaction method. Stepwise logistic regression was used to select from among the 30 SNPs the ones that represented a risk of anti-CCP antibody positivity. Haplotypes of the selected SNPs were inferred using an expectation-maximization algorithm. Associations of individual SNPs were evaluated with the Cochran-Armitage test for trend. DRB1 alleles and haplotypes were evaluated with the chi-square test. Heterogeneities of risks among the shared epitope (SE) and non-SE HLA,DRB1 alleles were examined using the exact test. Haplotype associations that were independent of individual HLA,DRB1 alleles were evaluated using the likelihood ratio test. Results Significant associations were found for 9 SNPs (smallest P value being 2.4 × 10,8) and in 4 HLA,DRB1 alleles (smallest P value being 2.0 × 10,10 in DRB1*0405). Stepwise logistic regression selected 4 SNPs (rs9262638, rs7775228, rs4713580, and rs9277359). Among the 16 inferred haplotypes of these 4 SNPs, 6 indicated significant associations (smallest P value being 1.9 × 10,11). Risks among SE and non-SE alleles were significantly heterogeneous (P = 0.0095 and P = 9.8 × 10,9, respectively), indicating the importance of stratification with individual DRB1 alleles rather than SE alleles. Conditional analysis of the risk associated with individual DRB1 alleles identified a risk haplotype that was independent of DRB1 (odds ratio 2.00 [95% confidence interval 1.44,2.79], P = 2.6 × 10,5). Conclusion Heterogeneous risks of anti-CCP antibody positivity were confirmed among SE and non-SE alleles in our patient population. A risk haplotype in the HLA region that is independent of HLA,DRB1 was confirmed. [source] Interdisciplinary Heterogeneity as a Catalyst for Product Innovativeness of Entrepreneurial TeamsCREATIVITY AND INNOVATION MANAGEMENT, Issue 2 2007Daniel Henneke Although more and more ventures are successfully founded by entrepreneurial teams, the specific benefits of the team-based founding approach have received little attention in extant empirical studies. This study explores the relationship between the level of interdisciplinary heterogeneity in entrepreneurial teams and the level of product innovativeness in high-tech ventures. It is proposed that an interdisciplinary new venture team composition impacts the quality of the strategic planning process (scanning activities, planning openness) and thereby indirectly shapes product innovativeness. The hypotheses are investigated using data from a sample of Canadian high-tech ventures. The findings provide support for the proposed relationship between team heterogeneity, strategic planning and product innovativeness. Venture capitalists, university faculty and incubator institutions are therefore well advised to direct their attention towards fostering a heterogeneous composition of founding teams. [source] Heterogeneity, Group Size and Collective Action: The Role of Institutions in Forest ManagementDEVELOPMENT AND CHANGE, Issue 3 2004Amy R. Poteete Collective action for sustainable management among resource-dependent populations has important policy implications. Despite considerable progress in identifying factors that affect the prospects for collective action, no consensus exists about the role played by heterogeneity and size of group. The debate continues in part because of a lack of uniform conceptualization of these factors, the existence of non-linear relationships, and the mediating role played by institutions. This article draws on research by scholars in the International Forestry Resources and Institutions (IFRI) research network which demonstrates that some forms of heterogeneity do not negatively affect some forms of collective action. More importantly, IFRI research draws out the interrelations among group size, heterogeneity, and institutions. Institutions can affect the level of heterogeneity or compensate for it. Group size appears to have a non-linear relationship to at least some forms of collective action. Moreover, group size may be as much an indicator of institutional success as a precondition for such success. [source] A systematic review of studies validating the Edinburgh Postnatal Depression Scale in antepartum and postpartum womenACTA PSYCHIATRICA SCANDINAVICA, Issue 5 2009J. Gibson Objective:, The Edinburgh Postnatal Depression Scale (EPDS) is the most widely used screening tool for postpartum depression (PPD). We systematically reviewed the published evidence on its validity in detecting PPD and antepartum depression (APD) up to July 2008. Method:, Systematic review of validation studies of the EPDS included 1987,2008. Cut-off points of 9/10 for possible PPD, 12/13 for probable PPD and 14/15 for APD were used. Results:, Thirty-seven studies met the inclusion criteria. Sensitivity and specificity of cut-off points showed marked heterogeneity between different studies. Sensitivity results ranged from 34 to 100% and specificity from 44 to 100%. Positive likelihood ratios ranged from 1.61 to 78. Conclusion:, Heterogeneity among study findings may be due to differences in study methodology, language and diagnostic interview/criteria used. Therefore, the results of different studies may not be directly comparable and the EPDS may not be an equally valid screening tool across all settings and contexts. [source] Heterogeneity of non-insulin-dependent diabetes expressed as variability in insulin sensitivity, ,-cell function and cardiovascular risk profileDIABETIC MEDICINE, Issue 1 2003K. I. Birkeland Abstract Aims The present study investigated the variability in insulin sensitivity and ,-cell function and their relationship to anti-glutamic acid decarboxylase (GAD) positivity and the metabolic syndrome in a group of patients with non-insulin-dependent diabetes mellitus (NIDDM). Methods Fifty-four subjects aged 59.5 ± 6.1 (mean ± sd) years with NIDDM for 7.9 ± 3.9 years referred to hospital due to poor glycaemic control, were investigated. Insulin sensitivity was determined by the euglycaemic hyperinsulinaemic glucose clamp technique as the glucose disposal rate relative to the insulin level obtained (GDRI), and also estimated with the homeostasis model assessment (HOMA-S). ,-cell function was measured by assaying the fasting and glucagon-stimulated C-peptide levels and with the HOMA-B. Results The insulin sensitivity varied 18-fold between subjects when estimated with the clamp and six-fold when estimated with HOMA-S, and was lower the more criteria for the metabolic syndrome present (P = 0.0001 by anova). The ,-cell function varied four-fold when measured as stimulated C-peptide, and eight-fold when estimated with the HOMA-B. The levels of fasting C-peptide and HOMA-B values tended to be lower in anti-GAD+ (n = 11) than in anti-GAD,subjects (P = 0.06 and P = 0.08, respectively). From previously published coronary risk charts, we estimated the 10-year risk of a coronary heart disease (CHD) event to be > 20% in 17 of 39 patients free from cardiovascular disease at the time of study, 16 of whom qualified for a diagnosis of the metabolic syndrome. Conclusions The wide variations in insulin sensitivity and ,-cell function found among subjects with NIDDM support the notion that the disorder is highly heterogeneous. Reduced insulin sensitivity was clearly related to the metabolic syndrome and an increased risk for CHD. [source] Heterogeneity in young adult onset diabetes: aetiology alters clinical characteristicsDIABETIC MEDICINE, Issue 9 2002K. R. Owen Abstract Aims To describe the characteristics of hepatocyte nuclear factor (HNF) 1, mutation carriers diagnosed with diabetes after 25 years and compare them with young-onset Type 2 diabetic patients (YT2D) diagnosed at the same age. Subjects and methods We studied 44 (21 male, 23 female) patients with HNF-1, mutations diagnosed with diabetes at ages 25,45 years and 44 YT2D subjects matched for sex and age of diagnosis. Results Median age of onset of diabetes was 35 years in both groups. The HNF-1, group demonstrated: lower body mass index (25.1 vs. 30.7 kg/m2; P < 0.001) and lower fasting triglycerides (1.37 vs. 2.96 mmol/l; P = 0.001) with similar fasting cholesterol level. They had lower glycated haemoglobin A1c (7.3 vs. 8.5%; P = 0.015) despite greater duration of diabetes (24 vs. 16 years; P = 0.02) and less frequent treatment with insulin (21% vs. 55%; P = 0.002). They were less likely to be treated for hypertension (13.3% vs. 56.3%; P = 0.009). Importantly, no difference was observed in reported parental history of diabetes between the two groups (65.9% vs. 63.6%; P = 0.92). Logistic regression showed that triglyceride levels and presence of anti-hypertensive treatment were the most important independent variables. Conclusions Patients with HNF-1, mutations may present with diabetes as young adults between the ages of 25,45 years. In this age range a wide differential diagnosis of diabetes is observed. Conventional criteria of age of onset and family history will not differentiate HNF-1, mutation carriers from YT2D subjects in this age range, but features of the metabolic syndrome, in particular fasting triglycerides and hypertension, are helpful. In patients diagnosed before 45 years without features of insulin resistance the diagnosis of HNF-1, should be considered. [source] Effectiveness of Corticosteroid Treatment in Acute Pharyngitis: A Systematic Review of the LiteratureACADEMIC EMERGENCY MEDICINE, Issue 5 2010Andrew Wing Abstract Objectives:, The objective was to examine the effectiveness of corticosteroid treatment for the relief of pain associated with acute pharyngitis potentially caused by group A beta-hemolytic Streptococcus (GABHS). Methods:, This was a systematic review of the literature. Data sources used were electronic databases (Cochrane Library, MEDLINE, EMBASE, Biosis Previews, Scopus, and Web of Science), controlled trial registration websites, conference proceedings, study references, experts in the field, and correspondence with authors. Selection criteria consisted of randomized controlled trials (RCTs) in which corticosteroids, alone or in combination with antibiotics, were compared to placebo or any other standard therapy for treatment of acute pharyngitis in adult patients, pediatric patients, or both. Two reviewers independently assessed for relevance, inclusion, and study quality. Weighted mean differences (WMDs) were calculated and are reported with corresponding 95% confidence intervals (CIs). Results:, From 272 potentially relevant citations, 10 studies met the inclusion criteria. When compared to placebo, corticosteroids reduced the time to clinically meaningful pain relief (WMD = ,4.54 hours; 95% CI = ,7.19 to ,1.89); however, they provided only a small reduction in pain scores at 24 hours (WMD = ,0.90 on a 0,10 visual analog scale; 95% CI = ,1.5 to ,0.3). Heterogeneity among pooled studies was identified for both outcomes (I2 = 81 and 74%, respectively); however, the GABHS-positive subgroup receiving corticosteroid treatment did have a significant mean reduction in time to clinically meaningful pain relief of 5.22 hours (95% CI = ,7.02 to ,3.42; I2 = 0%). Short-term side effect profiles between corticosteroids and placebo groups were similar. Conclusions:, Corticosteroid administration for acute pharyngitis was associated with a relatively small effect in time to clinically meaningful pain relief (4.5-hour reduction) and in pain relief at 24 hours (0.9-point reduction), with significant heterogeneity in the pooled results. Decision-making should be individualized to determine the risks and benefits; however, corticosteroids should not be used as routine treatment for acute pharyngitis. ACADEMIC EMERGENCY MEDICINE 2010; 17:476,483 © 2010 by the Society for Academic Emergency Medicine [source] Heterogeneity, speciation/extinction history and climate: explaining regional plant diversity patterns in the Cape Floristic RegionDIVERSITY AND DISTRIBUTIONS, Issue 3 2002R. M. Cowling Abstract. This paper investigates the role of heterogeneity and speciation/extinction history in explaining variation in regional scale (c. 0.1,3000 km2) plant diversity in the Cape Floristic Region of south-western Africa, a species- and endemic-rich biogeographical region. We used species-area analysis and analysis of covariance to investigate geographical (east vs. west) and topographic (lowland vs. montane) patterns of diversity. We used community diversity as a surrogate for biological heterogeneity, and the diversity of naturally rare species in quarter degree squares as an indicator of differences in speciation/extinction histories across the study region. We then used standard statistical methods to analyse geographical and topographic patterns of these two measures. There was a clear geographical diversity pattern (richer in the west), while a topographic pattern (richer in mountains) was evident only in the west. The geographical boundary coincided with a transition from the reliable winter-rainfall zone (west) to the less reliable non-seasonal rainfall zone (east). Community diversity, or biological heterogeneity, showed no significant variation in relation to geography and topography. Diversity patterns of rare species mirrored the diversity pattern for all species. We hypothesize that regional diversity patterns are the product of different speciation and extinction histories, leading to different steady-state diversities. Greater Pleistocene climatic stability in the west would have resulted in higher rates of speciation and lower rates of extinction than in the east, where for the most, Pleistocene climates would not have favoured Cape lineages. A more parsimonious hypothesis is that the more predictable seasonal rainfall of the west would have favoured non-sprouting plants and that this, in turn, resulted in higher speciation and lower extinction rates. Both hypotheses are consistent with the higher incidence of rare species in the west, and higher levels of beta and gamma diversity there, associated with the turnover of species along environmental and geographical gradients, respectively. These rare species do not contribute to community patterns; hence, biological heterogeneity is uniform across the region. The weak topography pattern of diversity in the west arises from higher speciation rates and lower extinction rates in the topographically complex mountains, rather than from the influence of environmental heterogeneity on diversity. [source] Spatial variability of soil and nutrient characteristics of semi-arid grasslands and shrublands, Jornada Basin, New MexicoECOHYDROLOGY, Issue 1 2008Eva Nora Mueller Abstract Heterogeneity of vegetation and soil properties is characteristic of semi-arid and arid environments. The potential underlying causes of the dynamics that create this spatial variability, with consequent impacts on landscape connectivity and thus ecological and ecohydrological processes, are not clearly understood. An investigation was carried out into the spatial variability of ponded infiltration rate, soil moisture, soil-aggregate stability, vegetation cover, random roughness and nutrient content in the soil (ammonium, nitrate and phosphorus) at grassland and shrubland sites for two spatial scales in the Jornada Basin, in the northern part of the Chihuahua desert. At the plant-interplant scale, statistically significant differences exist between vegetated and non-vegetated sites for soil moisture and infiltration rate within both shrublands and grasslands. The spatial distributions of all other parameters follow a more complex scheme at this scale. At the landscape scale, distinct differences exist for most parameters between the grasslands and the shrubland sites. Geostatistical analysis revealed that the autocorrelation lengths are not simply a function of average shrub sizes, but may be caused by a more complex pattern probably related to the spatial layout of rill and inter-rill areas and other localized transfers of soil resources through the redistribution of water and wind. These results demonstrate the importance of understanding spatial linkages of processes within the landscape in understanding dryland ecosystem dynamics. Copyright © 2007 John Wiley & Sons, Ltd. [source] Consequences for a host,parasitoid interaction of host-plant aggregation, isolation, and phenologyECOLOGICAL ENTOMOLOGY, Issue 4 2007ADAM J. VANBERGEN Abstract 1.,Spatial habitat structure can influence the likelihood of patch colonisation by dispersing individuals, and this likelihood may differ according to trophic position, potentially leading to a refuge from parasitism for hosts. 2.,Whether habitat patch size, isolation, and host-plant heterogeneity differentially affected host and parasitoid abundance, and parasitism rates was tested using a tri-trophic thistle,herbivore,parasitoid system. 3.,Cirsium palustre thistles (n= 240) were transplanted in 24 blocks replicated in two sites, creating a range of habitat patch sizes at increasing distance from a pre-existing source population. Plant architecture and phenological stage were measured for each plant and the numbers of the herbivore Tephritis conura and parasitoid Pteromalus elevatus recorded. 4.,Mean herbivore numbers per plant increased with host-plant density per patch, but parasitoid numbers and parasitism rates were unaffected. Patch distance from the source population did not influence insect abundance or parasitism rates. Parasitoid abundance was positively correlated with host insect number, and parasitism rates were negatively density dependent. Host-plant phenological stage was positively correlated with herbivore and parasitoid abundance, and parasitism rates at both patch and host-plant scales. 5.,The differential response between herbivore and parasitoid to host-plant density did not lead to a spatial refuge but may have contributed to the observed parasitism rates being negatively density dependent. Heterogeneity in patch quality, mediated by variation in host-plant phenology, was more important than spatial habitat structure for both the herbivore and parasitoid populations, and for parasitism rates. [source] Noncontractible Heterogeneity in Directed SearchECONOMETRICA, Issue 4 2010Michael Peters This paper provides a directed search model designed to explain the residual part of wage variation left over after the impact of education and other observable worker characteristics have been removed. Workers have private information about their characteristics at the time they apply for jobs. Firms value these characteristics differently and can observe them once workers apply. They hire the worker they most prefer. However, the characteristics are not contractible, so firms cannot condition their wages on them. This paper shows how to extend arguments from directed search to handle this, allowing for arbitrary distributions of worker and firm types. The model is used to provide a functional relationship that ties together the wage distribution and the wage,duration function. This relationship provides a testable implication of the model. This relationship suggests a common property of wage distributions that guarantees that workers who leave unemployment at the highest wages also have the shortest unemployment duration. This is in strict contrast to the usual (and somewhat implausible) directed search story in which high wages are always accompanied by higher probability of unemployment. [source] Income Variance Dynamics and HeterogeneityECONOMETRICA, Issue 1 2004Costas Meghir Recent theoretical work has shown the importance of measuring microeconomic uncertainty for models of both general and partial equilibrium under imperfect insurance. In this paper the assumption of i.i.d. income innovations used in previous empirical studies is removed and the focus of the analysis is placed on models for the conditional variance of income shocks, which is related to the measure of risk emphasized by the theory. We first discriminate amongst various models of earnings determination that separate income shocks into idiosyncratic transitory and permanent components. We allow for education- and time-specific differences in the stochastic process for earnings and for measurement error. The conditional variance of the income shocks is modelled as a parsimonious ARCH process with both observable and unobserved heterogeneity. The empirical analysis is conducted on data drawn from the 1967,1992 Panel Study of Income Dynamics. We find strong evidence of sizeable ARCH effects as well as evidence of unobserved heterogeneity in the variances. [source] Mortgage Terminations, Heterogeneity and the Exercise of Mortgage OptionsECONOMETRICA, Issue 2 2000Yongheng Deng As applied to the behavior of homeowners with mortgages, option theory predicts that mortgage prepayment or default will be exercised if the call or put option is ,in the money' by some specific amount. Our analysis: tests the extent to which the option approach can explain default and prepayment behavior; evaluates the practical importance of modeling both options simultaneously; and models the unobserved heterogeneity of borrowers in the home mortgage market. The paper presents a unified model of the competing risks of mortgage termination by prepayment and default, considering the two hazards as dependent competing risks that are estimated jointly. It also accounts for the unobserved heterogeneity among borrowers, and estimates the unobserved heterogeneity simultaneously with the parameters and baseline hazards associated with prepayment and default functions. Our results show that the option model, in its most straightforward version, does a good job of explaining default and prepayment, but it is not enough by itself. The simultaneity of the options is very important empirically in explaining behavior. The results also show that there exists significant heterogeneity among mortgage borrowers. Ignoring this heterogeneity results in serious errors in estimating the prepayment behavior of homeowners. [source] Recombinant clotting factor VIII concentrates: Heterogeneity and high-purity evaluationELECTROPHORESIS, Issue 16 2010Gian Maria D'Amici Abstract Factor VIII is an important glycoprotein involved in hemostasis. Insertion of expression vectors containing either the full-length cDNA sequence of human factor VIII (FLrFVIII) or B-domain deleted (BDDrFVIII) into mammalian cell lines results in the production of recombinant factor VIII (rFVIII) for therapeutic usage. Three commercially available rFVIII concentrates (Advate®, Helixate NexGen® and Refacto®), either FLrFVIII or BDDrFVIII, were investigated by 1- and 2-DE and MS. The objective of this study was to compare the heterogeneity and the high purity of both rFVIII preparations before and after thrombin digestion. In particular, the 2-D gel was optimized to better highlight the presence of contaminants and many unexpected proteins. Recombinant strategies consisting of insertion of expression vectors containing BDDrFVIII and FLrFVIII resulted in homogeneous and heterogeneous protein products, respectively, the latter consisting in a heterogeneous mixture of various B-domain-truncated forms of the molecule. Thrombin digestion of all the three rFVIII gave similar final products, plus one unexpected fragment of A2 domain missing 11 amino acids. Regarding the contaminants, Helixate NexGen® showed the presence of impurities, such as Hsp70,kDa, haptoglobin and proapolipoprotein; Refacto® showed glutathione S -transferase and ,-lactamase, whereas Advate® apparently did not contain any contaminants. The proteomic approach will contribute to improving the quality assurance and manufacturing processes of rFVIII concentrates. In this view, the 2-DE is mandatory for revealing the presence of contaminants. [source] The Influence of Top Management Team Heterogeneity on the Capital Raised through an Initial Public OfferingENTREPRENEURSHIP THEORY AND PRACTICE, Issue 3 2008Monica A. Zimmerman A significant body of research exists on the top management teams (TMTs) of established firms and specifically on the heterogeneity of TMTs of established firms. Little research exists, however, on the heterogeneity of TMTs of firms in the early stages of their existence. In this study, I examine the relationship among TMT heterogeneity and the capital raised by the firm through its initial public offering (IPO). I argue that TMT heterogeneity provides a signal to potential investors about the quality of the IPO and hence is associated with greater capital accumulations. My findings suggest that heterogeneity in the TMT's functional background and educational background is associated with greater capital raised through an IPO. [source] Entrepreneurial Founder Teams: Factors Associated with Member Entry and ExitENTREPRENEURSHIP THEORY AND PRACTICE, Issue 2 2003Deniz Ucbasaran This exploratory study provides a review of the neglected area of entrepreneurial founder team turnover. A novel distinction is made between entrepreneurial founder team member entry and team member exit. Ninety owner-managed ventures were monitored between 1990 and 2000. Presented hypotheses relating to a team's human capital were explored using multivariate logistic regression analysis. Variables associated with entry were found not to be the same as those associated with exit. The size of the founding team was significantly negatively associated with subsequent team member entry. The link between team turnover and entrepreneurial team heterogeneity was mixed. Functional heterogeneity was weakly significantly positively associated with team member entry. Heterogeneity of prior entrepreneurial experience was significantly positively associated with team member exit. In addition, family firms were significantly negatively associated with team member exit. The average age of the team was not significantly associated with team member entry or exit. Additional insights in future research may be gathered if a broader definition of team turnover (i.e., considering team member entry and exit) is considered. Practitioner awareness of the different factors associated with team member entry and exit may encourage them to provide assistance, which facilitates the team building process over time in developing firms. Promising areas for additional research are highlighted. [source] Impact of Kerogen Heterogeneity on Sorption of Organic Pollutants.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2009Abstract The overall goal of the present study was to establish correlations between organic pollutant sorption and physicochemical properties of kerogen materials. Three coal samples, each representing a typical kerogen type, were used as the starting materials. A thermal technique was employed to treat the kerogen materials under seven different temperatures ranging from 200 to 500C to simulate different diagenetic history. These samples were systematically characterized for their chemical compositions, functionalities, physical rigidity, and optical properties. The results showed that the chemical, spectroscopic, and optical microscopic properties of each kerogen series changed consistently as a function of treatment temperature or kerogen maturation. The oxygen-to-carbon atomic ratio decreased from 0.29, 0.12, and 0.07 for the original lignite (XF0), fusinite (HZ0), and lopinite (LP0) samples, respectively, to 0.07, 0.06, and 0.04 for XF7, HZ7, and LP7, respectively, that underwent the highest temperature treatment. The hydrogen-to-carbon atomic ratio exhibited similar reducing trend, which is consistent with the aromaticity increasing from 45 to 58% of the original samples to 76 to 81% of highly mature samples. Under the fluorescence microscope, the organic matrix changed from yellow (original lignite sample) and red-brown (original lopinite sample) to colorless for the samples of higher maturation. The measured reflecting index increased from the original samples to the highly mature samples. Moreover, the original and the slightly matured samples exhibited very different chemical compositions and structural units among the three types due to the difference in their source materials. As the kerogen maturation increased, such differences decreased, indicating highly mature kerogen became homogenized regardless of the source material. [source] Post-ictal fever: a rare symptom of partial seizuresEUROPEAN JOURNAL OF NEUROLOGY, Issue 5 2007A. O. Rossetti Although fever may induce seizures, especially in children, its occurrence following epileptic spells has been rarely described, except from generalized convulsive status epilepticus. We present two patients suffering from focal seizures accompanied by episodes of post-ictal fever, and review similar reports in the literature of the last 40 years. Temperature changes following non-convulsive seizures might be induced by gene upregulation occurring in the hypothalamus, the nucleus tractus solitarius, or in other brain regions, producing a local inflammatory response. Direct propagation of electrical discharges seems less consistent with the timing of development of this symptom. Heterogeneity of reported clinical features argues against the assumption of a definite localizing or lateralizing value for post-ictal fever. [source] Heterogeneity of V2-derived interneurons in the adult mouse spinal cordEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2007A. Al-Mosawie Abstract Spinal neurons and networks that generate rhythmic locomotor activity remain incompletely defined, prompting the use of molecular biological strategies to label populations of neurons in the postnatal mouse. During spinal cord development, expression of Lhx3 in the absence of Isl1 specifies a V2 interneuronal fate. In this study, postnatal V2-derived interneurons were identified by yellow fluorescent protein (YFP) expression in the double-transgenic offspring of Lhx3Cre/+ × thy1-loxP-stop-loxP-YFP mice. While some motoneurons were labelled, several populations of interneurons predominantly located in lamina VII could also be distinguished. Small interneurons were located throughout the spinal cord whereas larger interneurons were concentrated in the lumbar enlargement. Some V2-derived interneurons were propriospinal, with axons that bifurcated in the lateral funiculus. V2-derived interneurons gave rise to populations of both excitatory and inhibitory interneurons in approximately equal proportions, as demonstrated by in situ hybridization with VGLUT2 mRNA. Immunohistochemical studies revealed YFP+ boutons throughout the spinal cord. Both glutamatergic and glycinergic YFP+ boutons were observed in lamina IX where many apposed motoneuron somata. GABAergic YFP+ boutons were also observed in lamina IX, and they did not form P-boutons. At P0, more than half of the YFP+ interneurons expressed Chx10 and thus were derived from the V2a subclass. In adult mice, there was an increase in Fos expression in V2-derived interneurons following locomotion, indicating that these neurons are active during this behaviour. The heterogeneity of V2-derived interneurons in adult mice indicates that physiologically distinct subpopulations, including last-order interneurons, arise from these embryonically defined neurons. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||