Selective use and spatial distribution of native and non‐native fish in wetland habitats

Wetland habitats are crucial for many fish species as spawning, feeding or nursery areas, but the major factors that govern their use by fish are poorly identified. In the present study, we aim to investigate the selective use and the spatial distribution of native and non‐native fish species in different types of wetland habitats (grasslands and reed beds) in a large freshwater marsh (North Western France). The selective use was measured by comparing the community that uses wetland habitats to the total community of the marsh (sampled in the permanent aquatic habitats (canals) during the low water period). The spatial distribution was studied by analyzing the presence probability of fish in wetland habitats as a function of the distance from adjacent canals. All sampled wetland habitats were occupied by fish, and the fish community in wetland habitats was dominated by three native (Abramis brama, Scardinius erythrophthalmus and Anguilla anguilla) and three non‐native (Ameiurus melas, Gambusia holbrooki and Lepomis gibbosus) species. Species richness and total fish abundance differed between canals and wetland habitats as a consequence of a variable propensity to use wetland habitats by native (avoidance and preference) and non‐native (no preference) species. Non‐native species were also more abundant in reed beds than in grassland while no differences were observed for native species. Universally, the presence probability of fish always decreased in wetland habitats as the distance from the canals increased and only a narrow area, close to canals (50–80 m), was well used by fish. However, non‐native fish species used over greater distances in reed beds than in grasslands while no differences were observed for native species. Variable interpretations related to species tolerance, reproductive guilds or diet are proposed to understand the mechanisms that might explain the widespread success of non‐native species in this spatially varying environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Using the copper selenide as hole injector electrode in MeH-PPV polymer light emitting diodes

This work addresses the electrical characterization of the junction copper selenide (Cu_2?xSe) and poly-[2-metoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MeH-PPV). The Cu_2?xSe film was produced on copper (Cu) substrate using the chemical bath deposition technique. The polymer light emitting diodes were processed using the following layers: Cu/Cu_2?xSe or ITO (indium tin oxide), MeH-PPV and aluminum (Al). The barrier height (?) of Cu/Cu_2?xSe/MeH-PPV was estimated using the Fowler–Nordheim field-emission tunneling theory. We observed that ? decreases from 180 meV, for conventional ITO/MeH-PPV/Al device, to 10 meV for Cu/Cu_2?xSe/MeH-PPV/al diode.     

Oriented vertex and arc colorings of outerplanar graphs

A homomorphism from an oriented graph G to an oriented graph H is an arc-preserving mapping φ from V(G) to V(H), that is φ(x)φ(y) is an arc in H whenever xy is an arc in G. The oriented chromatic number of G is the minimum order of an oriented graph H such that G has a homomorphism to H. The oriented chromatic index of G is the minimum order of an oriented graph H such that the line-digraph of G has a homomorphism to H.In this paper, we determine for every k?3 the oriented chromatic number and the oriented chromatic index of the class of oriented outerplanar graphs with girth at least k.     

Immune phenotype of chronic liver disease

Immune disorders in chronic liver disease may reflect common host propensities or disease-specific factors. Our aim was to determine the principal bases for these expressions. Four hundred fifty-one patients with various chronic liver diseases were assessed prospectively for concurrent immune disorders. Individuals with immune diseases were more frequently women (73% vs 60%, P = 0.02) and they had HLA DR4 more often than counterparts with other HLA (46% vs 23%, P = 0.000008). The association between HLA DR4 and immune disease was apparent within individual liver diseases and within different categories of liver disease. Women with HLA DR4 had a higher frequency of immune disease than women without HLA DR4 (52% vs 22%, P < or = 0.000001), and they also had immune diseases more commonly than DR4-positive men (52% vs 31%, P = 0.03). DR4-positive men, however, had higher frequencies of immune disease than DR4-negative men, especially in the nonimmune types of liver disease (26% vs 4%, P = 0.002). We conclude that HLA DR4 and female gender constitute an immune phenotype that is an important basis for autoimmune expression in chronic liver disease.     

Modelling nonlinear count time series with local mixtures of Poisson autoregressions

A novel class of nonlinear models is studied based on local mixtures of autoregressive Poisson time series. The proposed model has the following construction: at any given time period, there exist a certain number of Poisson regression models, denoted as experts, where the vector of covariates may include lags of the dependent variable. Additionally, the existence of a latent multinomial variable is assumed, whose distribution depends on the same covariates as the experts. The latent variable determines which Poisson regression is observed. This structure is a special case of the mixtures-of-experts class of models, which is considerably flexible in modelling the conditional mean function. A formal treatment of conditions to guarantee the asymptotic normality of the maximum likelihood estimator is presented, under stationarity and nonstationarity. The performance of common model selection criteria in selecting the number of experts is explored via Monte Carlo simulations. Finally, an application to a real data set is presented, in order to illustrate the ability of the proposed structure to flexibly model the conditional distribution function.     

3D numerical model of snow deformation without failure and its application to cold room mechanical tests

A three-dimensional model developed for the slow deformation, without macroscopic failure, of a stratified snow cover has been used to simulate laboratory mechanical tests performed on sieved snow. The model is based on a non-linear visco-elastic constitutive law for snow whose parameters depend on the snow temperature and density. Snow densification is derived from the bulk viscous strain. The model has been implemented in the Flac3D finite-difference code. The experimental device is a convergent channel in which snow is forced at a constant velocity in the range 1–100 μm s^− 1. Although snow is compressed under plane strain conditions, the channel geometry allows obtaining a multi-axial stress-state. Since the testing conditions involve ranges of variation of both the snow density and the strain-rate wider than those encountered for a natural snowpack, the constitutive relations of the model had to be modified. In this paper we present the constitutive model for snow, some details about its implementation into the Flac3D code, and its application to the numerical simulation of the mechanical tests. The comparison of the model and experimental results shows a relatively good agreement, although snow microstructure is accounted for only through its density. However, the treatment of the non-linearity of the viscosity must be improved. This 3D numerical model can be regarded as an interesting tool for assessing a constitutive law for snow on the basis of cold-room experiments, as well as for studying natural snow covers.     

XAFS and CEMS study of dilute magneto-optical semiconductor, Fe doped TiO2 films

TiO₂ films doped with 6% Fe were prepared by pulsed laser deposition (PLD) under different oxygen pressures, and characterized by X-ray absorption fine spectra (XAFS) and conversion electron Mössbauer spectra (CEMS). The edge energy and spectrum profiles of Fe- and Ti K X-ray absorption showed only Fe³⁺ and Ti⁴⁺ states for rutile TiO₂ films prepared under 10^− 1 Torr, the metallic Fe and Ti⁴⁺ for rutile TiO₂ films prepared in 10^− 6 Torr, and the metallic Fe and the average valance of less than “4+” for Ti in Ti_nO_2n−x films prepared by the PLD under 10^− 8 Torr. The metallic Fe clusters are also found in the TEM images of Ti_nO_2n−x film. Magnetic property of Fe doped TiO₂ films prepared by PLD at high vacuum (10^− 6 and 10^− 8 Torr) is considered to originate mainly from the magnetic metal iron clusters.     

Hydrogen permeation through internally oxidized Pd alloys

Hydrogen diffusivity and solubility were determined by electrochemical hydrogen permeation tests in samples of Pd_0.97 Al_0.03 and Pd_0.97 Ce_0.03 in the as received and internally oxidized conditions. Internal oxidization caused the appearance of nanosized oxide precipitates in the Pd matrix. The shape and size of precipitates and also the coherence between the precipitates and the matrix were observed by transmission electron microscopy (TEM). Electrochemical hydrogen permeation tests revealed that the presence of oxides increases the apparent hydrogen solubility, S _app, but decreases the hydrogen diffusivity, D _app. The values of D _app were 2.0 × 10⁻¹¹ m² s⁻¹ for vacuum heat treated Pd_0.97 Al_0.03 alloy and 4.0 × 10⁻¹² m² s⁻¹ for internally oxidized Pd_0.97 Al_0.03 alloy. However, the concentration of trapped hydrogen was 49 mol H.m⁻³ for the Pd_0.97 Al_0.03 alloy in the vacuum heat treated condition and 403 mol H.m⁻³ for the Pd_0.97 Al_0.03 alloy in the internally oxidized condition. Both heat treatments were performed at 1073 K for 24 h. The influence of the nature, size and distribution of the precipitates on the hydrogen permeation parameters are discussed in this paper.     

Effects of hydrogen on the mechanical properties of a 2 1/4Cr–1Mo steel

This paper explores the effects of hydrogen on the mechanical properties of a 2 1/4Cr–1Mo steel. The results for both microstructural conditions, as received and aged, indicated a loss of ductility after hydrogen charging treatment, but the yield strength and ultimate tensile strength remained unaltered. The fractograph analysis revealed that the fracture mode was modified by the hydrogen. The steel in the as-received condition showed craters and fisheyes on the fracture surface. The aged steel showed a brittle appearance associated with cleavage facets and small portion of areas with dimples. The hydrogen diffusivity and solubility were investigated using electrochemical permeation technique. It was observed that the hydrogen diffusivity decreased from 2.3 ± 0.4 × 10⁻¹⁰ m² s⁻¹ in the as-received condition to 5.7 ± 0.1 × 10⁻¹¹ m² s⁻¹ in the aged condition. The hydrogen solubility showed an increase for the aged condition in comparison to the as received sample. Both phenomena can be attributed to carbide evolution during aging, resulting in an increase of the carbide/matrix interfacial area.     

Higher-order statistics of input ensembles and the response of simple model neurons

Pairwise correlations among spike trains recorded in vivo have been frequently reported. It has been argued that correlated activity could play an important role in the brain, because it efficiently modulates the response of a postsynaptic neuron. We show here that a neuron's output firing rate critically depends on the higher-order statistics of the input ensemble. We constructed two statistical models of populations of spiking neurons that fired with the same rates and had identical pairwise correlations, but differed with regard to the higher-order interactions within the population. The first ensemble was characterized by clusters of spikes synchronized over the whole population. In the second ensemble, the size of spike clusters was, on average, proportional to the pairwise correlation. For both input models, we assessed the role of the size of the population, the firing rate, and the pairwise correlation on the output rate of two simple model neurons: a continuous firing-rate model and a conductance-based leaky integrate-and-fire neuron. An approximation to the mean output rate of the firing-rate neuron could be derived analytically with the help of shot noise theory. Interestingly, the essential features of the mean response of the two neuron models were similar. For both neuron models, the three input parameters played radically different roles with respect to the postsynaptic firing rate, depending on the interaction structure of the input. For instance, in the case of an ensemble with small and distributed spike clusters, the output firing rate was efficiently controlled by the size of the input population. In addition to the interaction structure, the ratio of inhibition to excitation was found to strongly modulate the effect of correlation on the postsynaptic firing rate.