Proton NMR studies of cytochrome c peroxidase mutant N82A: hyperfine resonance assignments, identification of two interconverting enzyme ofecies, quantitating the rate of interconversion, and determination of equilibrium constants

The cyanide-ligated form of the baker's yeast cytochrome c peroxidase mutant bearing the mutation Asn82-->Ala82 ([N82A]CcPCN) has been studied by proton NMR spectroscopy. This mutation alters an amino acid that forms a hydrogen bond to His52, the distal histidine residue that interacts in the heme pocket with heme-bound ligands. His52 is a residue critical to cytochrome c peroxidase's normal function. Proton hyperfine resonance assignments have been made for the cyanide-ligated form of the mutant by comparison with 1-D and NOESY spectra of the wild-type native enzyme. For [N82A]CcPCN, proton NMR spectra reveal two significant phenomena. First, similar to results published for the related mutant [N82D]CcPCN [Satterlee, J. D., et al. (1994) Eur. J. Biochem. 244, 81-87], for Ala82 mutation disrupts the hydrogen bond between His52 and the heme-ligated CN. Second, four of the 24 resolved hyperfine-shifted resonances are doubled in the mutant enzyme's proton spectrum, leading to the concept that the heme active site environment is dynamically microheterogeneous on a very localized scale. Two magnetically inequivalent enzyme forms are detected in a pure enzyme preparation. Varying temperature causes the two enzyme forms to interconvert. Magnetization transfer experiments further document this interconversion between enzyme forms and have been used to determine that the rate of interconversion is 250 (+/- 53) s-1. The equilibrium constant at 20 degrees C is 1.5. Equilibrium constants have been calculated at various temperatures between 5 and 29 degrees C leading to the following values: delta H = 60 kJ mol-1; delta S = 0.20 kJ K-1 mol-1.     

Studies of the positron lifetime and Doppler-broadened annihilation radiation of polypropylene-polystyrene alloys

Positron annihilation lifetime spectroscopy and Doppler-broadened annihilation radiation (DBAR) experiments were performed on polypropylene-polystyrene (PP-PS) alloys (0-100% styrene) prepared by in situ polymerisation of styrene in a PP host matrix. The mean size of free-volume holes estimated from the ortho-positronium lifetime τ₃ shows a continuous decrease from 0.119 nm³ in PP to 0.095 nm³ in PS. The intensity of the o-Ps component, I₃, the average positron lifetime τ_av, the curve-shape parameter S and the peak height H of the DBAR spectra increase linearly with the styrene concentration. This is attributed to a linear superposition of the Ps yields of PP and PS in the PP-PS alloys. The DBAR spectra were fitted by a sum of three Gaussians, the narrowest of them is attributed to self-annihilation of para-positronium confined within holes. After its subtraction, a ‘broad component’ is obtained which represents the momentum distribution of electrons bound to molecules. Its normalised peak height does not show any change with the composition which reflects the fact that both constituents of the PP-PS alloys contain only hydrogen and carbon atoms in their chemical units. Immersing of PP into styrene liquid leads to a very pronounced increases in the lifetime parameters which is attributed to the plasticisation of PP.     

Numerical study on thermal impacts of different void patterns on performance of chip-scale packaged power device

Chip scale package (CSP) technology offers promising solutions to package power device due to its relatively good thermal performance among other factors. Solder thermal interface materials (STIMs) are often employed at the die bond layer of a chip-scale packaged power device to enhance heat transfer from the chip to the heat spreader. Nonetheless, the presence of voids in the solder die-attach layer impedes heat flow and could lead to an increase in the peak temperature of the chip. Such voids which form easily in the solder joint during reflow soldering process at manufacturing stage are primarily occasioned by out-gassing phenomenon and defective metallisation. Apparently, the thermal consequences of voids have been extensively studied, but not much information exist on precise effects of different patterns of solder die-attach voids on the thermal performance of chip-level packaged power device. In this study, three-dimensional finite element analysis (FEA) is employed to investigate such effects. Numerical studies were carried out to characterise the thermal impacts of various voids configurations, voids depth and voids location on package thermal resistance and chip junction temperature. The results show that for equivalent voiding percentage, thermal resistance increases more for large coalesced void type in comparison to the small distributed voids configuration. In addition, the study suggests that void extending through the entire thickness of solder layer and voids formed very close to the heat generating area of the chip can significantly increase package thermal resistance and chip junction temperature. The findings of this study indicate that void configurations, void depth and void location are vital parameters in evaluating the thermal effects of voids.     

Effects of Silicon on Growth,Yield and Fruit Quality of Cantaloupe under Drought Stress

Silicon - Silicon (Si) plays an important role in mitigating adverse effects of various biotic and abiotic stresses including drought. Polyhouse experiment was conducted to evaluate the effects of...     

Evaluation of the surface photovoltage method of minority-carrier diffusion-length measurement

The surface photovoltage (SPV) method of semiconductor minority carrier diffusion length measurement is simulated numerically by solving the semiconductor equations under monochromatic illumination. It is shown that the extracted diffusion length is dependent on the SPV level and the initial surface potential. This dependence arises because of carrier generation in the surface space charge region. For the p-type silicon investigated, the extracted diffusion length is found to be within 10% of the actual value even when the assumption of low level injection is violated.     

Microstructural Characterization of Fried Potato Disks Using X‐Ray Micro Computed Tomography

Microstructural properties play a key role to affect oil uptake and product quality during frying of foods. The objective of this study was to observe the complex microstructural changes and mass transfer mechanisms in potato disks during frying. The potato disks of 1.65 mm thickness were fried at 190 °C for 0, 20, 40, 60, and 80 s. X‐ray micro‐computed tomography (CT) was used for 3‐dimensional (3D) imaging of microstructure of porous potato disks. Total porosity, pore size distribution, oil content, and air content of potato disks were calculated from resulting 3D data sets. Oil and air content measured by analysis of micro‐CT images followed trends similar to Soxtec and gas pycnometry methods, respectively. Image analysis showed a significant change in pore size distribution as a function of frying time. Frying time was also observed to have an effect on tortuosity, which is an important microstructural fluid transport property. Tortuosity was measured by path length ratio method from 3D data sets obtained from image analysis. A linear inverse relationship was observed between porosity and tortuosity where tortuosity decreased with the increase of porosity. It was also observed that during frying, oil content increased with the decrease of tortuosity. This phenomenon indicated that the lower tortuosity created a less complicated and sinuous path, thus resulting in less resistance to oil penetration. Micro‐CT technique can serve as an effective tool for elucidating microstructure of fried foods, and can provide complementary information to conventional lab techniques.     

Linear-Time Algorithms for Hole-free Rectilinear Proportional Contact Graph Representations

In a proportional contact representation of a planar graph, each vertex is represented by a simple polygon with area proportional to a given weight, and edges are represented by adjacencies between the corresponding pairs of polygons. In this paper we first study proportional contact representations that use rectilinear polygons without wasted areas (white space). In this setting, the best known algorithm for proportional contact representation of a maximal planar graph uses 12-sided rectilinear polygons and takes O(nlogn) time. We describe a new algorithm that guarantees 10-sided rectilinear polygons and runs in O(n) time. We also describe a linear-time algorithm for proportional contact representation of planar 3-trees with 8-sided rectilinear polygons and show that this is optimal, as there exist planar 3-trees that require 8-sided polygons. We then show that a maximal outer-planar graph admits a proportional contact representation using rectilinear polygons with 6 sides when the outer-boundary is a rectangle and with 4 sides otherwise. Finally we study maximal series-parallel graphs. Here we show that O(1)-sided rectilinear polygons are not possible unless we allow holes, but 6-sided polygons can be achieved with arbitrarily small holes.     

Optical pattern recognition using two-channel joint transform correlation

A new joint transform correlation (JTC) technique, named two-channel JTC (TJTC), is proposed in this paper for optical pattern recognition applications. The TJTC technique independently evaluates the autocorrelation and crosscorrelation values of the reference and the target images and employs a modified decision algorithm. In addition, optical threshold operation and fringe-adjusted filter are incorporated in the proposed technique to enhance the correlation output and to improve the discrimination performance. The proposed technique shows better recognition performance compared to existing JTC techniques. Computer simulation are presented to investigate the salient features of the proposed TJTC technique with noise-free as well as noisy input scenes. The text was submitted by the authors in English.     

The Effect of van der Waals and Viscous Forces on Aerosol Coagulation

An analysis is carried out to determine the combined effect of van der Waals and viscous fluid forces on coagulation of spherical aerosol particles in the free molecular, transition, and continuum regimes. The effect of viscous forces is taken into account by modifying the particle diffusion coefficient. An asymptotic solution is substituted for the classical formulation of viscous forces. The results of free molecular and continuum regimes are then extended to the transition size range by an interpolation formula.