Mean first passage time approach to the problem of optimal barrier subdivision for Kramer's escape rate

We consider the effect of subdividing the potential barrier along the reaction coordinate on Kramer's escape rate for a model potential, Using the known supersymmetric potential approach, we show the existence of an optimal number of subdivisions that maximizes the rate, We cast the problem as a mean first passage time problem of a biased random walker and obtain equivalent results, We briefly summarize the results of our investigation on the increase in the escape rate by placing a blow-torch in the unstable part of one of the potential wells. (C) 1999 Elsevier Science B.V. All rights reserved.

Thermal barrier coating application of zircon sand

Naturally occurring zircon sand was plasma spray coated on steel substrates previously coated with NiCrAlY bond coat. The coatings were characterized for their microstructure, chemical composition, thermal shock resistance, and the nature of structural phases present, The as-sprayed coatings consisted of t-ZrO2 (major phase), m-ZrO2, ZrSiO4 (minor phases), and amorphous SiO2. These coatings, when annealed at 1200 degrees C/1.44 x 10(4) s yielded a ZrSiO4 phase as a result of the reaction between ZrO2 and SiO2, Dramatic changes occurred in the characteristics of the coatings when a mixture of zircon sand and Y2O3 was plasma spray coated and annealed at 1400 degrees C/1.44 x 10(4) s, The t-ZrO2 phase was completely stabilized, and these coatings were found to have considerable potential for thermal barrier applications.

Dielectric barrier discharge plasma interaction with the airflow over an airfoil

The effect of various parameters on the velocity of the induced jet produced by a dielectric barrier discharge (DBD) plasma was studied experimentally. The glow discharge was created at atmospheric conditions by using a high voltage RF power supply. Flow visualization and photographic studies of the plasma were performed. The parametric investigation of the characteristics of the plasma show that the width of the plasma in the uniform glow discharge regime was an indication of the velocity induced under stagnant conditions. It was observed that the spanwise overlap of the two electrodes, dielectric thickness, voltage and frequency of the applied voltage are the major parameters that govern the velocity and the extent of plasma in the streamwise direction.

Stability of fluid flow past a membrane

The stability of fluid flow past a membrane of infinitesimal thickness is analysed in the limit of zero Reynolds number using linear and weakly nonlinear analyses. The system consists of two Newtonian fluids of thickness R* and H R*, separated by an infinitesimally thick membrane, which is flat in the unperturbed state. The dynamics of the membrane is described by its normal displacement from the flat state, as well as a surface displacement field which provides the displacement of material points from their steady-state positions due to the tangential stress exerted by the fluid flow. The surface stress in the membrane (force per unit length) contains an elastic component proportional to the strain along the surface of the membrane, and a viscous component proportional to the strain rate. The linear analysis reveals that the fluctuations become unstable in the long-wave (alpha --> 0) limit when the non-dimensional strain rate in the fluid exceeds a critical value Lambda(t), and this critical value increases proportional to alpha(2) in this limit. Here, alpha is the dimensionless wavenumber of the perturbations scaled by the inverse of the fluid thickness R*(-1), and the dimensionless strain rate is given by Lambda(t) = ((gamma) over dot* R*eta*/Gamma*), where eta* is the fluid viscosity, Gamma* is the tension of the membrane and (gamma) over dot* is the strain rate in the fluid. The weakly nonlinear stability analysis shows that perturbations are supercritically stable in the alpha --> 0 limit.

Transformation in heterokaryons of Neurospora crassa is nuclear rather than cellular phenomenon

In Neurospora crassa, multinucleate macroconidia are used for genetic transformation. The barrier for such a transformation can be either at the cell membrane level or at the nuclear membrane level. For assessment of these possibilities, a forced heterokaryon (containing two genetically marked nuclei and auxotrophic for histidine) of Neurospora crassa was transformed with a plasmid containing his-3(+) gene. The transformants, which could grow without histidine supplementation, were then resolved into component homokaryons to determine into which nucleus or nuclei the plasmid had entered. Our results suggest that the barrier for transformation in Neurospora crassa is at the nuclear level, not at the cell membrane level. In a heterokaryon containing two genetically distinct nuclei, plasmid DNA integrated into only one of the nuclear types at any instance, but never into both nuclear types. Thus, in Neurospora crassa, the competent nucleus is essential for the transformation event to take place, and at a given time only one type of nucleus is competent to take up the exogenous DNA. Genomic Southern analysis showed that the transformants harbor both ectopic and homologous integrations of the plasmid DNA. The type and number of integrations were reflected at the post-translational level, since the specific activity of histidinol dehydrogenase (the translation product of his-3+ gene) was variable among several transformants and always less than the level of the wild type.

Amino acid interaction preferences in helical membrane proteins

Membrane proteins are involved in a number of important biological functions. Yet, they are poorly understood from the structure and folding point of view. The external environment being drastically different from that of globular proteins, the intra-protein interactions in membrane proteins are also expected to be different. Hence, statistical potentials representing the features of inter-residue interactions based exclusively on the structures of membrane proteins are much needed. Currently, a reasonable number of structures are available, making it possible to undertake such an analysis on membrane proteins. In this study we have examined the inter-residue interaction propensities of amino acids in the membrane spanning regions of the alpha-helical membrane (HM) proteins. Recently we have shown that valuable information can be obtained on globular proteins by the evaluation of the pair-wise interactions of amino acids by classifying them into different structural environments, based on factors such as the secondary structure or the number of contacts that a residue can make. Here we have explored the possible ways of classifying the intra-protein environment of HM proteins and have developed scoring functions based on different classification schemes. On evaluation of different schemes, we find that the scheme which classifies amino acids to different intra-contact environment is the most promising one. Based on this classification scheme, we also redefine the hydrophobicity scale of amino acids in HM proteins.

Epitaxial LaNiO3 thin films: A normal metal barrier for SNS junction

Epitaxial LaNiO3 thin films have been grown on SrTiO3 and several other substrates by pulsed laser deposition. The films are observed to be metallic down to 15 K, and the temperature dependence of resistivity is similar to that of bulk LaNiO3. Epitaxial, c-axis oriented YBa2Cu3O7-x films with good superconducting properties have been grown on the LaNiO3 (100) films. I-V characteristics of the YBa2Cu3O7-x-LaNiO3 junction are linear, indicating ohmic contact between them.

Temperature effect on hydrocarbon-enhanced nitric oxide conversion using a dielectric barrier discharge reactor

Experimental investigations into the effect of temperature on conversion of NO in the presence of hydrocarbons (ethylene, acetylene and n-hexane) are presented. An AC energized dielectric barrier discharge reactor was used as the plasma reactor. The experiments were carried out at different temperatures up to 200 degreesC. The discharge powers were measured at all the temperatures. The discharge power was found to increase with temperature. NO conversion in the presence of ethylene and n-hexane was better than that of acetylene at all temperatures. The addition of acetylene at room temperature showed no better conversion of NO compared to no additive case. While at higher temperatures, it could enhance the conversion of NO. A slight enhancement in NO and NOx removal was observed in the presence of water vapor. (C) 2003 Elsevier Science B.V. All rights reserved.

Barrier height inhomogeneities in InN/GaN heterostructure based Schottky junctions

The electrical transport properties of InN/GaN heterostructure based Schottky junctions were studied over a wide temperature range of 200-500 K. The barrier height and the ideality factor were calculated from current-voltage (I-V) characteristics based on thermionic emission (TE), and found to be temperature dependent. The barrier height was found to increase and the ideality factor to decrease with increasing temperature. The observed temperature dependence of the barrier height indicates that the Schottky barrier height is inhomogeneous in nature at the heterostructure interface. Such inhomogeneous behavior was modeled by assuming the existence of a Gaussian distribution of barrier heights at the heterostructure interface. (C) 2011 Elsevier Ltd. All rights reserved.

Bio-Composite Membrane Electrolytes for Direct Methanol Fuel Cells

A new class of bio-composite polymer electrolyte membranes comprising chitosan (CS) and certain biomolecules in particular, plant hormones such as 3-indole acetic acid (IAA), 4-chlorophenoxy acetic acid (CAA) and 1-naphthalene acetic acid (NAA) are explored to realize proton-conducting bio-composite membranes for application in direct methanol fuel cells (DMFCs). The sorption capability, proton conductivity and ion-exchange capacity of the membranes are characterized in conjunction with their thermal and mechanical behaviour. A novel approach to measure the permeability of the membranes to both water and methanol is also reported, employing NMR imaging and volume localized NMR spectroscopy, using a two compartment permeability cell. A DMFC using CS-IAA composite membrane, operating with 2M aqueous methanol and air at 70 degrees C delivers a peak power density of 25 mW/cm(2) at a load current density of 150 mA/cm(2). The study opens up the use of bio-compatible membranes in polymer-electrolyte-membrane fuel cells. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.030111jes] All rights reserved.