Asymptotic Analysis of the Current-Voltage Curve of a pnpn Semiconductor Device

We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure.     

The Fermi to Gamow-Teller mixing ratio of theβ + decay of52Mn and time-reversal invariance

To date, ten experimental measurements of the asymmetry parameter have been made for the positron decay of⁵²Mn. The Fermi to Gamow-Teller mixing ratioy can be deduced from such measurements and this quantity is important because the time-reversal violating amplitude is proportional toy/(1+y²). Our theoretical calculation using the Collective Model yieldsy=? 3.5×10^?4 for the deformation parameterβ=0.1 andy=? 4.6×10^?4 forβ=0.2. Such small values ofy are consistent with time-reversal invarisance.     

Thermal analysis of Vectran® fibers and films

Vectra^® liquid crystalline polymers (LCP's) were introduced as commercial products in the mid-1980's. The first of these (Vectra A130) was a wholly aromatic thermotropic copolyester ofp-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid. Vectra A130 is a thermotropic LCP that can be melt spun into filaments that on heat treatment are characterized by high strength and high modulus. Vectra resin can also be extruded into films. In the fiber or film form this material is commercially known as Vectran^®. Heat treatment enhances the tensile strength of Vectran fiber variants. Because of this, the elucidation of the physical transformations taking place in the internal structure of the material during heating has always been an important subject. Several thermal techniques are used to indicate clearly that what is observed as a glass transition is unlike the conventional glass transition in typical semicrystalline polymers. There is also an indication of the presence of multiple states of mesophase aggregation that collapse into a single state when taken to high enough temperatures.     

Catastrophic phase inversion in region II of an ionomeric polymer-water system

Previous work has identified distinct regions, on a phase inversion map, for dispersions of polyurethane ionomer (PUI) and water. In this study, events that occur, before, during, and after catastrophic phase inversion (provoked by adding water to polyurethane ionomer (PUI) in the RII regions of the phase inversion map) have been studied in order to characterise the inversion mechanism. Before phase inversion, initial water addition leads to the hydration of ionic groups and eventually water drops start to form in the hydrophobic portions of the polymer matrix. At the phase inversion point, the PUI-water interface restructures and the ionomer disintegrates into a dispersion of spherical particles enclosed by a continuous aqueous phase. It is suggested that pseudo-drop structures are formed simultaneously during the production of the small polymer-in-water drops. After phase inversion, water addition dilutes the emulsion and destroys the apparent ionic-centre-rich environment surrounding any isolated ionic groups on a particle surface. The larger water-in-polymer drops are likely to have participated in the phase inversion and the smaller water drops form the primary water drops in the multiple emulsions. The resultant emulsions are stable over a period of a few months but very few multiple drops remain after 1(1/4) years.     

Determination of trace amounts of antimony by spectrofluorimetry in hydrobromic acid medium at liquid nitrogen temperature

Trace amounts of antimony(III) may be determined in 6M hydrobromic acid by measurement of the red fluorescence of its bromide complex at -196 degrees , the optimum wavelengths of excitation and emission (360 and 586 nm respectively) being used. Calibration graphs are linear between 0.01 and 0.25 ppm. The effect of the presence of 50-fold molar amounts of 55 foreign ions has been studied. Of the ions studied, only iron(III) and tellurium(IV) interfere, and these may be tolerated at the 50- and 20-fold levels respectively. A 1000-fold molar amount of arsenic(III) causes no interference.     

Optical Generation of mm-Wave Signal Through Optoelectronic Phase-Locked Loop

In this paper, we propose a scheme for the generation of low phase noise tunable mm-wave signal by beating two lightwaves in a photodiode. These two lightwaves are made phase coherent by an optoelectronic phase locked loop.Calculated mm-wave power at a frequency of 60 GHz is found to be -4 dBm.     

Machine-Shop Problems: An Operational Research Approach

Production planning and scheduling in a batch production environment presents management with many problems, ranging from long-term capital investment in machine tools to short-term batch sequencing. This paper, which is aimed at the production manager, introduces the general concept of model building and then discusses the more specific technique of computer simulation modelling. A simple example of the latter is used to illustrate the basic properties of such a model and then the actual model currently being used is described. The possible applications of such models are discussed and developed. Finally, a case study is presented which shows how the model has been employed in an actual production environment.     

Stage effects of negative emotion on spatial and verbal working memory

Background  

The effects of negative emotion on different processing periods in spatial and verbal working memory (WM) and the possible brain mechanism of the interaction between negative emotion and WM were explored using a high-time resolution event-related potential (ERP) technique and time-locked delayed matching-to-sample task (DMST).     

Inertial clustering of particles in high-Reynolds-number turbulence

We report experimental evidence of spatial clustering of dense particles in homogenous, isotropic turbulence at high Reynolds numbers. The dissipation-scale clustering becomes stronger as the Stokes number increases and is found to exhibit similarity with respect to the droplet Stokes number over a range of experimental conditions (particle diameter and turbulent energy dissipation rate). These findings are in qualitative agreement with recent theoretical and computational studies of inertial particle clustering in turbulence. Because of the large Reynolds numbers a broad scaling range of particle clustering due to turbulent mixing is present, and the inertial clustering can clearly be distinguished from that due to mixing of fluid particles.     

Crystal structure of an antiviral ankyrin targeting the HIV-1 capsid and molecular modeling of the ankyrin-capsid complex

Ankyrins are cellular repeat proteins, which can be genetically modified to randomize amino-acid residues located at defined positions in each repeat unit, and thus create a potential binding surface adaptable to macromolecular ligands. From a phage-display library of artificial ankyrins, we have isolated Ank^GAG1D4, a trimodular ankyrin which binds to the HIV-1 capsid protein N-terminal domain (NTD^CA) and has an antiviral effect at the late steps of the virus life cycle. In this study, the determinants of the Ank^GAG1D4-NTD^CA interaction were analyzed using peptide scanning in competition ELISA, capsid mutagenesis, ankyrin crystallography and molecular modeling. We determined the Ank^GAG1D4 structure at 2.2 Å resolution, and used the crystal structure in molecular docking with a homology model of HIV-1 capsid. Our results indicated that NTD^CA alpha-helices H1 and H7 could mediate the formation of the capsid-Ank^GAG1D4 binary complex, but the interaction involving H7 was predicted to be more stable than with H1. Arginine-18 (R18) in H1, and R132 and R143 in H7 were found to be the key players of the Ank^GAG1D4-NTD^CA interaction. This was confirmed by R-to-A mutagenesis of NTD^CA, and by sequence analysis of trimodular ankyrins negative for capsid binding. In Ank^GAG1D4, major interactors common to H1 and H7 were found to be S45, Y56, R89, K122 and K123. Collectively, our ankyrin-capsid binding analysis implied a significant degree of flexibility within the NTD^CA domain of the HIV-1 capsid protein, and provided some clues for the design of new antivirals targeting the capsid protein and viral assembly.