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Model Only (model + only)
Selected AbstractsCharacterizing sediment acid volatile sulfide concentrations in European streamsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2007G. Allen Burton Abstract Sediment acid volatile sulfide (AVS) concentrations were measured in wadeable streams of a wide variety of ecoregions of western Europe (84 sites in 10 countries and nine ecoregions) to better understand spatial distribution and ecoregion relationships. Acid volatile sulfide has been shown to be a major factor controlling the bioavailability and toxicity of many common trace metals, such as Cd, Cu, Ni, Pb, and Zn. Sediment characteristics varied widely. The ratio of the sum of the simultaneously extracted metals (SEM) to AVS ranged from 0.03 to 486.59. The ,SEM-AVS ranged from ,40.02 to 17.71 ,mol/g. On a regional scale, sediment characteristics such as dominant parent soil material showed significant trends in AVS distribution and variation by ecoregion. Total Fe and Mn were correlated weakly with SEM concentrations. Three AVS model approaches (i.e., the SEMAVS ratio, SEM-AVS difference, and carbon normalization) were compared at threshold exceedance levels of SEM/AVS > 9, SEM-AVS > 2, and SEM-AVS/foc > 150 ,mol/g organic carbon (OC). Only 4.76% of the sediments exceeded all three AVS thresholds; 22.6% of the sediments exceeded two models; and 13% of the sediments exceeded one model only. Using the SEM:AVS, SEM-AVS, and fraction of organic carbon models, and including site-specific data and regional soil characteristics, ecoregions 1 (Portugal), 3 (Italy), 4 (Switzerland), and 9 (Belgium/Germany) had the highest potential metals toxicity; ecoregions 13 and 8 (Belgium/France) showed the lowest potential toxicity. However, because AVS can vary widely spatially and temporally, these data should not be considered as representative of the sampled ecoregions. The general relationship between AVS levels and sediment characteristics provides some predictive capability for wadeable streams in the European ecoregions. [source] Species richness,standing crop relationship in stream bryophyte communities: patterns across multiple scalesJOURNAL OF ECOLOGY, Issue 1 2001Risto Virtanen Summary 1,We tested for a unimodal (,hump-backed') relationship between species richness and standing crop at various spatial scales in stream bryophyte communities. Bryophyte species and their biomasses were determined from 20 to 25 quadrats in eight river and six stream sites in northern Finland. 2,Regression analyses revealed a quadratic relationship between richness and biomass in only two of the river sites and a positive correlation in one other. A quadratic relationship was detected in three stream sites and richness increased linearly with biomass in another. 3,We also tested for the hump-shaped pattern across individual stream boulders, representing an elevational gradient from continuously submerged to permanently dry conditions, with an intermediate zone with fluctuating water level. 4,Species richness-standing crop relationship conformed to the hump-backed model only when samples from all three microhabitats were included in the analysis. A significant positive correlation occurred in the exposed low biomass end of the gradient which is characterized by semi-aquatic species, whereas the relationship tended to be negative in permanently submerged areas with high biomass of large canopy-forming species. Quadrats close to the water level had intermediate standing crop and highest species richness. 5,Species dominant at either end of the gradient appeared unable to monopolize space in the intermediate zone where disturbances (e.g. scouring by ice) detach mosses from the substratum, creating vacant gaps for colonization. The unimodal relationship between richness and biomass is likely to occur only in streams that contain large boulders protruding above the water line, thus providing scope for community diversification along very short vertical distances. [source] Populating dark matter haloes with galaxies: comparing the 2dFGRS with mock galaxy redshift surveysMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2004Xiaohu Yang ABSTRACT In two recent papers, we developed a powerful technique to link the distribution of galaxies to that of dark matter haloes by considering halo occupation numbers as a function of galaxy luminosity and type. In this paper we use these distribution functions to populate dark matter haloes in high-resolution N -body simulations of the standard ,CDM cosmology with ,m= 0.3, ,,= 0.7 and ,8= 0.9. Stacking simulation boxes of 100 h,1 Mpc and 300 h,1 Mpc with 5123 particles each we construct mock galaxy redshift surveys out to a redshift of z= 0.2 with a numerical resolution that guarantees completeness down to 0.01L*. We use these mock surveys to investigate various clustering statistics. The predicted two-dimensional correlation function ,(rp, ,) reveals clear signatures of redshift space distortions. The projected correlation functions for galaxies with different luminosities and types, derived from ,(rp, ,), match the observations well on scales larger than ,3 h,1 Mpc. On smaller scales, however, the model overpredicts the clustering power by about a factor two. Modelling the ,finger-of-God' effect on small scales reveals that the standard ,CDM model predicts pairwise velocity dispersions (PVD) that are ,400 km s,1 too high at projected pair separations of ,1 h,1 Mpc. A strong velocity bias in massive haloes, with bvel,,gal/,dm, 0.6 (where ,gal and ,dm are the velocity dispersions of galaxies and dark matter particles, respectively) can reduce the predicted PVD to the observed level, but does not help to resolve the overprediction of clustering power on small scales. Consistent results can be obtained within the standard ,CDM model only when the average mass-to-light ratio of clusters is of the order of 1000 (M/L), in the B -band. Alternatively, as we show by a simple approximation, a ,CDM model with ,8, 0.75 may also reproduce the observational results. We discuss our results in light of the recent WMAP results and the constraints on ,8 obtained independently from other observations. [source] Can non-Gaussian cosmological models explain the WMAP high optical depth for reionization?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2003Xuelei Chen ABSTRACT The first-year Wilkinson Microwave Anisotropy Probe data suggest a high optical depth for Thomson scattering of 0.17 ± 0.04, implying that the Universe was reionized at an earlier epoch than previously expected. Such early reionization is likely to be caused by ultraviolet (UV) photons from first stars, but it appears that the observed high optical depth can be reconciled within the standard structure formation model only if star formation in the early Universe was extremely efficient. With normal star formation efficiencies, cosmological models with non-Gaussian density fluctuations may circumvent this conflict as high density peaks collapse at an earlier epoch than in models with Gaussian fluctuations. We study cosmic reionization in non-Gaussian models and explore to what extent, within available constraints, non-Gaussianities affect the reionization history. For mild non-Gaussian fluctuations at redshifts of 30 to 50, the increase in optical depth remains at a level of a few per cent and appears unlikely to aid significantly in explaining the measured high optical depth. On the other hand, within available observational constraints, increasing the non-Gaussian nature of density fluctuations can easily reproduce the optical depth and may remain viable in underlying models of non-Gaussianity with a scale-dependence. [source] Fault-tolerant procedures for redundant computer systemsQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 1 2009Refik Samet Abstract Real-time computer systems deployed in life-critical control applications must be designed to meet stringent reliability specifications. The minimum acceptable degree of reliability for systems of this type is ,7 nines', which is not generally achieved. This paper aims at contributing to the achievement of that degree of reliability. To this end, this paper proposes a classification scheme of the fault-tolerant procedures for redundant computer systems (RCSs). The proposed classification scheme is developed on the basis of the number of counteracted fault types. Table I is created to relate the characteristics of the RCSs to the characteristics of the fault-tolerant procedures. A selection algorithm is proposed, which allows designers to select the optimal type of fault-tolerant procedures according to the system characteristics and capabilities. The fault-tolerant procedure, which is selected by this algorithm, provides the required degree of reliability for a given RCS. According to the proposed graphical model only a part of the fault-tolerant procedure is executed depending on the absence or presence (type and sort) of faults. The proposed methods allow designers to counteract Byzantine and non-Byzantine fault types during degradation of RCSs from N to 3, and only the non-Byzantine fault type during degradation from 3 to 1 with optimal checkpoint time period. Copyright © 2008 John Wiley & Sons, Ltd. [source] A Process Model of Attachment,Friend Linkages: Hostile Attribution Biases, Language Ability, and Mother,Child Affective Mutuality as Intervening MechanismsCHILD DEVELOPMENT, Issue 6 2008Nancy L. McElwain This study identified mechanisms through which child,mother attachment security at 36 months was associated with mother- and teacher-reported friendship quality at 3rd grade. Data from a subsample of 1,071 children (536 boys) participating in the National Institute of Child Health and Human Development Study of Early Child Care and Youth Development were used. Separate structural equation models were tested for mother and teacher reports of peer functioning. For both models, the total indirect effect between attachment security and friendship quality was significant. Tests of specific indirect effects indicated that attachment security was associated with friendship quality via greater mother,child affective mutuality and better language ability at 54 months and fewer hostile attributions (teacher model only) and greater peer competence at first grade. The findings highlight interpersonal and intrapersonal mechanisms of attachment,friend linkages. [source] Structural determinations by circular dichroism spectra analysis using coupled oscillator methods: An update of the applications of the DeVoe polarizability model,CHIRALITY, Issue 7 2004Stefano Superchi Abstract The exciton (coupled oscillator) model for optical activity is a very useful and powerful method which allows to analyze a circular dichroism (CD) spectrum in a nonempirical way, arriving at a safe assignment of the absolute configuration of organic and inorganic compounds. Usually in this model only the exciton coupling of two electrically allowed transitions (oscillators) is taken into account. This approach has the important advantage of an easy application but, sometimes, it may lead to wrong results. Thus, in this review article a more general treatment, which allows considering the simultaneous coupling of several oscillators, i.e., the DeVoe model, is presented and critically analyzed, discussing in detail the latest applications reported in the literature. In the authors opinion, since the DeVoe model joins generality and reliability requiring an almost negligible computational effort, it represents the method of choice for stereochemical assignments, even by nonspecialists. Chirality 16:422,451, 2004. © 2004 Wiley-Liss, Inc. [source] | ||||||||||