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Effective Density (effective + density)
Selected AbstractsDensity-dependent growth of young-of-the-year Atlantic salmon Salmo salar in Catamaran Brook, New BrunswickJOURNAL OF ANIMAL ECOLOGY, Issue 3 2005I. IMRE Summary 1While density-dependent mortality and emigration have been widely reported in stream salmonid populations, density-dependent growth is less frequently detected. A recent study suggests that density-dependent growth in stream salmonids occurs at low densities, whereas density-dependent mortality and emigration occur at high densities. 2To test the hypothesis that density-dependent growth occurs primarily at low rather than at high densities, we examined the relationship between average fork length and population density of young-of-the-year (YOY) Atlantic salmon at the end of the growing season using a 10-year data set collected on Catamaran Brook, New Brunswick. We tested whether (1) average body size decreases with increasing density; (2) the effect of density on average body size is greatest at low densities; (3) growth rate will decrease most rapidly at low effective densities [,(fork length)2]; (4) density-dependent growth is weaker over space than over time; and (5) the strength of density-dependent growth increases with the size of the habitat unit (i.e. spatial scale) when compared within years, but not between years. 3There was a strong negative relationship between the average body size and population density of YOY Atlantic salmon in the autumn, which was best described by a negative power curve. Similarly, a negative power curve provided the best fit to the relationship between average body size and effective density. Most of the variation in average body size was explained by YOY density, with year, location and the density of 1+ and 2+ salmon accounting for a minor proportion of the variation. 4The strength of density-dependent growth did not differ significantly between comparisons over space vs. time. Consistent with the last prediction, the strength of density-dependent growth increased with increasing spatial scale in the within-year, but not in the between-year comparisons. 5The effect of density on growth was strongest at low population densities, too low to expect interference competition. Stream salmonid populations may be regulated by two mechanisms: density-dependent growth via exploitative competition at low densities, perhaps mediated by predator-induced reductions in drift rate, and density-dependent mortality and emigration via interference competition at high densities. [source] Fabrication and analysis of polymer field-effect transistorsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2004S. Scheinert Abstract Parameters of organic field-effect transistors (OFET) achieved in recent years are promising enough for R & D activities towards a commercial low-cost polymer electronics. In spite of the fast progress, preparations dominated by trial and error are concentrated essentially on higher mobility polymers and shorter channel patterning, and the analysis of measured data is based on oversimplified models. Here ways to professionalize the research on polymer field-effect transistors are discussed exploiting experience accumulated in microelectronics. First of all, designing the devices before fabricating and subsequently analyzing them requires appropriate modelling. Almost independently from the nature of the transport process, the device physics is basically described by the drift-diffusion model, combined with non-degenerate carrier statistics. Therefore, with a modified interpretation of the so-called effective density of states, existing simulation tools can be applied, except for special cases which are discussed. Analytical estimates are helpful already in designing devices, and applied to experimental data they yield input parameters for the numerical simulations. Preparations of OFET's and capacitors with poly(3-ocylthiophene) (P3OT), poly(3-dodecylthiophene) P3HT, Arylamino-poly-(phenylene-vinylene) (PPV), poly(2-methoxy, 5 ethyl (2, hexyloxy) paraphenylenevinylene) MEH-PPV, and pentacene from a soluble precursor are described, with silicon dioxide (SiO2) or poly(4-vinylphenol) (P4VP) as gate insulator, and with rather different channel length. We demonstrate the advantage of combining all steps from design/fabrication to analysis of the experimental data with analytical estimates and numerical simulation. Of special importance is the connection between mobility, transistor channel length, cut-off frequency and operation voltage, which was the starting point for the development of a low-cost fabrication of high-performance submicrometer OFET's by an underetching technique. Finally results of simulation studies are presented concerning the formation of inversion layers, the influence of a trap distribution (as in the a-Si model) and of different types of source/drain contacts on top and bottom contact OFET's, and short-channel effects in submicrometer devices. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ionic and electronic defects in a-BaTiO3 thin films studied by transient and steady state conductivity measurementsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2007F. El Kamel Abstract Conduction mechanisms in BaTiO3 films deposited at low temperatures on Cu-electrodes have been investigated in transient and steady regimes as a function of temperatures and electric field. This work aims to identify possible defects which govern the leakage current. Electrical measurements reveal that Space Charge Limited Current (SCLC) constitutes the main leakage mechanism in both the transient and the steady regimes. Based on the theory of SCLC, two types of defects can be detected. At higher temperatures, oxygen vacancies constitute the main defects which migrate across the film to generate an ionic leakage current. Diffusion of these defects is thermally activated with an activation energy around 1 eV. Moreover, at lower temperatures the J - E measurements reveals the presence of a discrete set of shallow traps at 0.45 eV below the conduction band with an effective density of 4 × 1022 m,3. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||