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Constant Thickness (constant + thickness)
Selected AbstractsGeochronological evidence for pervasive Miocene weathering, Minas Gerais, BrazilEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2004Isabela de O. Carmo Abstract 40Ar/39Ar laser incremental-heating analyses of 22 individual grains of supergene cryptomelane from three weathering pro,les, up to 400 km apart, in the Rio Doce valley and Barbacena regions at Minas Gerais, Brazil, show that the formation of weathering pro,les in these regions is contemporaneous, suggesting a strong weathering event in the Middle to Late Miocene (10,8 Ma). The preservation of these Miocene samples at or near the present surface suggests that either erosion rates have been very low in the region since the Miocene or that a much thicker weathering mantle was present in the region originally. Assuming a constant thickness of weathering pro,les in the region throughout the Tertiary, we may calculate weathering front propagation rates of 4,8 m Myr,1 during the past 10 Ma. Copyright © 2004 John Wiley & Sons, Ltd. [source] Investigation of electrical conduction mechanism in double-layered polymeric systemJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2009Prashant Shukla Abstract The electrical conduction in solution-grown polymethylmethacrylate (PMMA), polyvinylidenefluoride (PVDF) and PMMA-PVDF double-layered samples in the sandwich configuration (metal-polymer-metal) was investigated at different fields in the range 100,120 kV/cm as a function of temperature in the range 293,423 K for samples of constant thickness of about 50 ,m. Certain effects which lead to a large burst of current immediately after the application of field were observed in double-layered samples. An attempt was made to identify the nature of the current by comparing the observed dependence on electric field, electrode material and temperature with the respective characteristic features of the existing theories on electrical conduction. The observed linear I-V characteristics show that the electrical conduction follows Pool-Frenkel mechanism in PMMA and PVDF samples. Whereas, the non-linear behavior of current-voltage measurements in PMMA-PVDF double-layered samples have been interpreted on the basis of space charge limited conduction (SCLC) mechanism. The conductivity of the polymer films increased on formation of their double-layer laminates. The polymer-polymer interface act as charge carrier trapping centres and provides links between the polymer molecules in the amorphous region. The interfacial phenomenon in polymer-polymer heterogeneous system has been interpreted in terms of Maxwell-Wagner model. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] Water Vapor Transmission Rates and Sorption Behavior of Chitosan FilmsJOURNAL OF FOOD SCIENCE, Issue 7 2000J.L. Wiles ABSTRACT: This study measured the water vapor transmission rates (WVTR) and moisture sorption of chitosan films over a range of water vapor pressures at 25 °C. Films of a constant thickness were made using chitosan with 3 levels of deacetylation. Films were tested at test relative humidity (RH) difference between RH values of 84%, 75%, 69%, 53%, 43%, 33%, 23%, 11%, and 0 at 25 °C using ASTM F1249-90 or ASTM E 96-80. The equilibrium moisture content in the films ranged from 3.7% to 31.8% (dry basis) corresponding to 11% to 84% RH. WVTRs of films increased with increase in water vapor pressure. The mean WVTR ranged from 6.7 to 1146 (g/m2/d) over the range of water vapor pressure from 2.68 (11% RH) to 19.9 mmHg (84% RH). The percentage of deacetylation of chitosan films and the viscosity of the cast solution did not have an effect on the WVTR properties of chitosan films. [source] Oxidation and Volatilization of Silica Formers in Water VaporJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2003Elizabeth J. Opila At high temperatures, SiC and Si3N4 react with water vapor to form a SiO2 scale. SiO2 scales also react with water vapor to form a volatile Si(OH)4 species. These simultaneous reactions, one forming SiO2 and the other removing SiO2, are described by paralinear kinetics. A steady state, in which these reactions occur at the same rate, is eventually achieved. After steady state is achieved, the oxide found on the surface is a constant thickness, and recession of the underlying material occurs at a linear rate. The steady-state oxide thickness, the time to achieve steady state, and the steady-state recession rate can be described in terms of the rate constants for the oxidation and volatilization reactions. In addition, the oxide thickness, the time to achieve steady state, and the recession rate also can be determined from parameters that describe a water-vapor-containing environment. Accordingly, maps have been developed to show these steady-state conditions as a function of reaction rate constants, pressure, and gas velocity. These maps can be used to predict the behavior of SiO2 formers in water-vapor-containing environments, such as combustion environments. Finally, these maps are used to explore the limits of the paralinear oxidation model for SiC and Si3N4. [source] Approximate transmission conditions through a weakly oscillating thin layerMATHEMATICAL METHODS IN THE APPLIED SCIENCES, Issue 4 2009Clair Poignard Abstract We study the behavior of the electro-quasistatic voltage potentials in a material composed by a bidimensional medium surrounded by a weakly oscillating thin layer and embedded in an ambient medium. We build approximate transmission conditions in order to replace the layer by these conditions on the boundary of the interior material. We deal with a weakly oscillating thin layer: the period of the oscillations is greater than the square root of the thinness. Our approach is essentially geometric and based on a suitable change of variable in the layer. This paper extends previous works (Méthodes asymptotiques pour le calcul de champs électromagnétiques dans des milieux à couche mince. Application aux cellules biologiques. Thesis, Université Lyon 1, France, November 2006; IEEE Trans. Magn. 2007. http://hal.archives-ouvertes.fr/hal-00165049/fr.) of the former author, in which the layer had constant thickness. Copyright © 2008 John Wiley & Sons, Ltd. [source] Exploring the interactions of gliadins with model membranes: Effect of confined geometry and interfacesBIOPOLYMERS, Issue 8 2009Amélie Banc Abstract Mechanisms leading to the assembly of wheat storage proteins into proteins bodies within the endoplasmic reticulum (ER) of endosperm cells are unresolved today. In this work, physical chemistry parameters which could be involved in these processes were explored. To model the confined environment of proteins within the ER, the dynamic behavior of ,-gliadins inserted inside lyotropic lamellar phases was studied using FRAP experiments. The evolution of the diffusion coefficient as a function of the lamellar periodicity enabled to propose the hypothesis of an interaction between ,-gliadins and membranes. This interaction was further studied with the help of phospholipid Langmuir monolayers. ,- and ,-gliadins were injected under DMPC and DMPG monolayers and the two-dimensional (2D) systems were studied by Brewster angle microscopy (BAM), polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and surface tension measurements. Results showed that both gliadins adsorbed under phospholipid monolayers, considered as biological membrane models, and formed micrometer-sized domains at equilibrium. However, their thicknesses, probed by reflectance measurements, were different: ,-gliadins aggregates displayed a constant thickness, consistent with a monolayer, while the thickness of ,-gliadins aggregates increased with the quantity of protein injected. These different behaviors could find some explanations in the difference of aminoacid sequence distribution: an alternate repeated - unrepeated domain within ,-gliadin sequence, while one unique repeated domain was present within ,-gliadin sequence. All these findings enabled to propose a model of gliadins self-assembly via a membrane interface and to highlight the predominant role of wheat prolamin repeated domain in the membrane interaction. In the biological context, these results would mean that the repeated domain could be considered as an anchor for the interaction with the ER membrane and a nucleus point for the formation and growth of protein bodies within endosperm cells. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 610,622, 2009. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] The Structure-Controlling Solventless Synthesis and Optical Properties of Uniform Cu2S NanodisksCHEMISTRY - A EUROPEAN JOURNAL, Issue 35 2008Yu-Biao Chen Dr. Abstract Uniform Cu2S nanodisks have been synthesized from a well-characterized layered copper thiolate precursor by structure-controlling solventless thermolysis at 200,220,°C under a N2 atmosphere. The development from small Cu2S nanoparticles (diameter ,3,nm) to nanodisks (diameter 8.3,nm) and then to faceted nanodisks (diameter 27.5,nm, thickness 12.7,nm) is accompanied by a continuous phase transition from metastable orthorhombic to monoclinic Cu2S, the ripening of small particles by aggregation, and finally the crystallization process. The growth of the nanoproduct is constrained by the crystal structure of the precursor and the in situ-generated thiol molecules. Such controlled anisotropic growth leads to a nearly constant thickness of faceted nanodisks with different diameters, which has been confirmed by TEM observations and optical absorption measurements. [source] | |||||||||||||