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Exponential Decrease (exponential + decrease)
Selected AbstractsEffect of substrate temperature on the properties of vacuum evaporated indium selenide thin filmsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2005C. Viswanathan Abstract Thin films of InSe were obtained by thermal evaporation techniques on glass substrates maintained at various temperatures (Tsb = 30°, 400°C). X-ray diffraction analysis showed the occurrence of amorphous to polycrystalline transformation in the films deposited at higher substrate temperature (400°C). The polycrystalline films were found to have a hexagonal lattice. Compositions of these films have been characterized by EDAX and the surface analysis by scanning electron microscopy. Optical properties of the films, investigated by using spectrophotometer transmittance spectra in the wavelength range (300 , 1100 nm), were explained in terms of substrate temperatures. Films formed at room temperature showed an optical band gap (Egopt) 1.56 eV; where as the films formed at 400°C were found to have a Egopt of 1.92 eV. The increase in the value of Egopt with Tsb treatment is interpreted in terms of the density of states model as proposed by Mott and Davis. The analysis of current -Voltage characteristics, based on space charge limited currents (SCLC) measurements, confirms the exponential decrease of density of states from the conduction band edge towards the Fermi level for both the amorphous and polycrystalline films. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The importance of plant root characteristics in controlling concentrated flow erosion ratesEARTH SURFACE PROCESSES AND LANDFORMS, Issue 4 2003G. Gyssels Abstract While it has been demonstrated in numerous studies that the aboveground characteristics of the vegetation are of particular importance with respect to soil erosion control, this study argues the importance of separating the influence of vegetation on soil erosion rates into two parts: the impact of leaves and stems (aboveground biomass) and the influence of roots (belowground biomass). Although both plant parameters form inseparable constituents of the total plant organism, most studies attribute the impact of vegetation on soil erosion rates mainly to the characteristics of the aboveground biomass. This triggers the question whether the belowground biomass is of no or negligible importance with respect to soil erosion by concentrated flow. This study tried to answer this question by comparing cross-sectional areas of concentrated flow channels (rills and ephemeral gullies) in the Belgian Loess Belt for different cereal and grass plant densities. The results of these measurements highlighted the fact that both an increase in shoot density as well as an increase in root density resulted in an exponential decrease of concentrated flow erosion rates. Since protection of the soil surface in the early plant growth stages is crucial with respect to the reduction of water erosion rates, increasing the plant root density in the topsoil could be a viable erosion control strategy. Copyright © 2003 John Wiley & Sons, Ltd. [source] Characterisation of microbial community composition of a Siberian tundra soil by fluorescence in situ hybridisationFEMS MICROBIOLOGY ECOLOGY, Issue 1 2004Svenja Kobabe Abstract The bacterial community composition of the active layer (0,45 cm) of a permafrost-affected tundra soil was analysed by fluorescence in situ hybridisation (FISH). Arctic tundra soils contain large amounts of organic carbon, accumulated in thick soil layers and are known as a major sink of atmospheric CO2. These soils are totally frozen throughout the year and only a thin active layer is unfrozen and shows biological activity during the short summer. To improve the understanding of how the carbon fluxes in the active layer are controlled, detailed analysis of composition, functionality and interaction of soil microorganisms was done. The FISH analyses of the active layer showed large variations in absolute cell numbers and in the composition of the active microbial community between the different horizons, which is caused by the different environmental conditions (e.g., soil temperature, amount of organic matter, aeration) in this vertically structured ecosystem. Universal protein stain 5-(4,6-dichlorotriazin-2-yl)aminofluorescein (DTAF) showed an exponential decrease of total cell counts from the top to the bottom of the active layer (2.3 × 109,1.2 × 108 cells per gram dry soil). Using FISH, up to 59% of the DTAF-detected cells could be detected in the surface horizon, and up to 84% of these FISH-detected cells could be affiliated to a known phylogenetic group. The amount of FISH-detectable cells decreased with increasing depth and so did the diversity of ascertained phylogenetic groups. [source] Length-dependence of electron transfer coupling matrix in polyene wires: Ab initio molecular orbital theory study,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 6 2009Govind Mallick Abstract The electron transfer (ET) properties of ,-electron conjugated quasi-one-dimensional molecular wires, consisting of polyene, [>CC<]n (n = 1,11), including ,-carotene, is investigated using ab initio molecular orbital theory within Koopmans theorem (KT) approach. The ET coupling matrix element, VDA, for 1,3- trans -butadiene molecule calculated with the KT approach shows excellent agreement with the corresponding results obtained with two-state model. The calculated values of VDA for the polyene oligomers exhibit exponential decrease in magnitude with increasing length of the wire. However, the decay curve exhibits three different regimes. The magnitude of the decay constant, ,, decreases with the increase in length of the wire. A highly delocalized ,-electron cloud in the polyene chain appears to facilitate retention of the electronic coupling at large separations between the donor and acceptor centers. Published 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] Seasonal abundance, spatial distribution and sampling indices of thrip populations on cotton; a 4-year survey from central GreeceJOURNAL OF APPLIED ENTOMOLOGY, Issue 7-8 2002P. N. Deligeorgidis Thus, in a cotton field (1.1 ha) in central Greece, 45 leaves were collected (one leaf per cotton plant) at 10-day intervals from May to September, for four consecutive growing seasons (1995,98). Five species of thrips were found: Frankliniella intonsa was the most abundant species followed by Thrips angusticeps, Thrips tabaci, Frankliniella occidentalis and Aeolothrips intermedius. Although considerable differences were observed in the population fluctuations among species, the highest population densities, for all species found, were recorded in July and August. As indicated by Taylor's power law estimates, all species presented aggregated distribution among sampling units. As this type of spatial pattern indicates, the accuracy obtained in estimating mean population density increased with the increase of the mean. Furthermore, the increase of the mean caused an exponential decrease in sample size. However, the precision level is acceptable only in high mean values, while at the same time the benefit from an increase in sample size is of no practical value. [source] Effect of solute lipophilicity on penetration through canine skinAUSTRALIAN VETERINARY JOURNAL, Issue 12 2003PC MILLS Objective To investigate the effect of lipophilicity on the percutaneous penetration of a homologous series of alcohols through canine skin Design Skin harvested from Greyhound thorax was placed in Franz-type diffusion cells and the in vitro passage of radio-labelled (14C) alcohols (ethanol, butanol, hexanol and octanol (Log P 0.19 - 3.0)) through separate skin sections was measured in replicates of five. Permeability coefficient (kP, cm/h), maximum flux (Jmax, mol/cm2/h) and residue remaining within the skin were determined. Results The kP increased with increasing lipophilicity (6.2 times 10 -4± 1.6 times 10 -4 cm/h for ethanol to 1.8 times 10 -2± 3.6 times 10 -3 cm/h for octanol). Alcohol residues remaining within each skin sample followed a similar pattern. An exponential decrease in Jmax with increasing lipophilicity was observed. Conclusion Changes in canine skin permeability occur with increasing alcohol lipophilicity. This finding has practical consequences for the design of topical formulations and optimisation of drug delivery through animal skin. [source] | ||||||||||