Plasma model of carrier transportation in photoelectric semiconductor detectors

A new model, called the plasma model, describing carrier transportation in photoelectric semiconductor detectors is proposed. Semiconductor material under laser irradiation is regarded as a plasma of low temperature with high carrier density, and it is considered that the carrier temperature is different from the lattice temperature when the irradiating laser power is high but lower than the damage threshold of the detectors. Equations for the carrier density, velocity and temperature are established. According to the model, numerical simulations of a photoconductive semiconductor detector were carried out by programming. The instantaneous change behaviors of the photoconductive detector are obtained. The results of the numerical calculation match well with the experimental results. PACS 42.65.Sf; 85.60.Gz     

Effect of annealing temperature on density of ZnO quantum dots

ZnO quantum dots (QDs) were fabricated on Si (001) substrates by pulsed laser deposition (PLD) and subsequent thermal annealing. X-ray diffraction and transmission electron microscopy analyses revealed that the ZnO QDs had polycrystalline hexagonal wurtzite structure. The size and density of ZnO QDs were investigated by atomic force microscopy. It has been found that the density decreased while the size increased with increasing annealing temperature. The analysis of size distribution of the dots shows an obvious bimodal mode according to scaling theory. The Raman spectrum shows a typical resonant multi-phonon form for the ZnO QDs. The collapse from the top of the dots was observed firstly after the samples were exposed in air for 30 days.     

Determination of antisite defects in double perovskite Sr2FeMoO6 by diffraction method: Simulation studies

The crystal structure of double perovskite Sr₂FeMoO₆ synthesized via solid-state reaction at 1280 °C under a reduction atmosphere is refined by Rietveld technique based on X-ray powder diffraction (XRD) data in 2θ range of 15-140°. An antisite content (AS), i.e. Fe on the Mo sites (=Mo on the Fe sites), of 12.1(1)% is derived. In reference to the refinement results, a series of X-ray and neutron powder diffraction (NPD) data with different antisite contents, ranging from 0 (completely ordered) to 50% (completely disordered), are generated with a Poisonian noise added and subjected to Rietveld refinements with the same initial values for the refinable parameters. The AS is reproduced satisfactorily from the refinement of XRD data and the combined refinement of XRD and NPD data with a relative deviation smaller than 4%, whereas the relative deviation of AS derived from the refinement of NPD data can be as large as 50%. However, the atomic occupancies and isotropic temperature factors of all the atoms can be reasonably reproduced from the refinement of NPD data and the combined refinement of XRD and NPD data, whereas these data can be reproduced only for cations (Sr, Fe, Mo) from the refinement of XRD data. The present simulation studies shed light on understanding the controversial statements derived from XRD and NPD work regarding the antisite defects in Sr₂FeMoO₆, which in turn is indispensable for understanding the mechanism of large room temperature low-field magnetoresistance of the compound.     

Collective bands in 104,106,108Mo

We have used our analysis of γ-γ-γ data (5.7 × 10¹¹ triples and higher folds) taken with Gammasphere from prompt γ rays emitted in the spontaneous fission of ²⁵²Cf to study the collective bands in ^104,106,108Mo. The one-phonon and two-phonon γ-vibrational bands and known two-quasiparticle bands in neutron-rich ^104,106Mo were extended to higher spins. The one-and two-phonon γ-vibrational bands have remarkably close energies for transitions from the same spin states and identical moments of inertia. Several new bands are observed and are proposed as quasiparticle bands in ^104,106Mo, along with the first β-type vibrational band in ¹⁰⁶Mo. The quasiparticle bands have essentially constant moments of inertia near the rigid-body value that indicate blocking of the pairing interaction. Candidates for chiral doublet bands in ¹⁰⁶Mo are strong. These are the first reported chiral vibrational bands in an even-even nucleus. The text was submitted by the authors in English.     

A universal kinetic equation for characterising the fractal nature of delignification of lignocellulosic materials

A kinetic model was developed, based on the power law of growth and Avrami’s nuclei growth concepts, to describe the heterogeneous nature of pulping kinetics, taking into account the effects of chemical concentration and temperature. The general form of the kinetic equation is first order with a time-dependent rate coefficient. The model was statistically tested using published data obtained from delignification of lignocellulosic materials (hemp woody core, giant reed, wheat straw, cottonwood, bamboo and flax fibres). The activation energies of the delignification range from 71 to 136 kJ/mol. The p-values obtained from the regression analysis are significantly small indicating that all the estimates of the model parameters were significant with very high levels of confidence. The correlation coefficients R ² for these models range from 0.76 to 0.98.     

The unimolecular dissociation of 3,4-dihydro-2H-pyran over a wide temperature range

The thermal decomposition of 3,4-dihydro-2H-pyran (DHP, C₅H₈O) has been investigated by two methods: in shock waves with the laser-schlieren technique using mixtures of 5 and 10% DHP in krypton over 900–1500 K, 110–560 torr; in a flow tube having a reaction pressure 0.5 torr above atmospheric using the decomposition of allylethyl ether as an internal standard, and covering 663–773 K. The retro-Diels-Alder dissociation to the stable acrolein and ethylene is the dominant channel for all conditions. Precise rate constants (rms deviation of 10%) were obtained for this process over the indicated temperature ranges. Unimolecular falloff is evident in the shock-tube results, and RRKM calculations also predict a slight falloff at the lower temperatures. These RRKM calculations use a routine vibration model transition state and agree closely with the high-temperature data when 〈ΔE〉_down is a fixed 400 cm^?1. Arrhenius expressions for k_∞ derived from the two measurements are in close accord and also consistent with most previous studies of this reaction. © 1995 John Wiley & Sons, Inc.     

Treatment of vortex sheets for the transonic full-potential equation

This paper summarizes a combined analytical-computational technique which models vortex sheets in transonic potential-flow methods. In this approach, the inviscid nature of discontinuities across vortex sheets is preserved by employing the step function to remove singularities at these surfaces. The location and strength of the vortex sheets are determined by satisfying the flow-tangency boundary condition and the vorticity transport equation. The theory is formulated for the general three-dimensional case, but its application is confined to the problem of computing slipstreams behind propellers with free-vortex blading in axisymmetric flows.     

Wavelengths of Five Ni-Like Laser Lines

ＷａｖｅｌｅｎｇｔｈｓｏｆＦｉｖｅＮｉ－ＬｉｋｅＬａｓｅｒＬｉｎｅｓ￥Ｇ．Ｘ．Ｃｈｅｎ；Ｑ．Ｙ．Ｆａｎｇ；Ｗ．Ｃａｉ（ＩｎｓｔｉｔｕｔｅｏｆＡｐｐｌｉｅｄＰｈｙｓｉｃｓａｎｄＣｏｍｐｕｔａｔｉｏｎａｌＭａｔｈｅｍａｔｉｃｓＰ．Ｏ．ＢＯＸ８００９Ｂｅｉ...     

Transmission resonances in magnetic-barrier structures

Quantum transport properties of electrons in simple magnetic-barrier (MB) structures and in finite MB superlattices are investigated in detail. It is shown that there exists a transition of transmission resonances, i.e., from incomplete transmission resonances in simple MB structures consisting of unidentical blocks, to complete transmission resonances in comparatively complex MB structures (, n is the number of barriers). In simple unidentical block arrangements in double- and triple-MB structures we can also obtain complete transmission by properly adjusting parameters of the building blocks according to k_y-value (k_y is the wave vector in y direction). Strong suppression of the transmission and of the conductance is found in MB superlattices which are periodic arrangements of two different blocks. The resonance splitting effect in finite MB superlattices is examined. It is confirmed that the rule (i.e., for n-barrier tunneling the splitting would be (n-1)-fold) obtained in periodic electric superlattices can be extended to periodically arranged MB superlattices of identical blocks through which electrons with tunnel, and it is no longer proper for electrons with k _y <0 to tunnel. Received: 18 August 1997 / Revised: 20 September 1997 / Accepted: 13 October 1997     

Determination of carbonyl compounds in the low ppb-range by capillary electrophoresis

Summary A new method for analysing carbonyls (aldehydes and ketones) by capillary electrophoresis (CE) is described. The carbonyls are derivatized with DNSH [5-(dimethylamino)naphthalene-1-sulphonehydrazide, Dansylhydrazine] to form detectable compounds and also to form negative charged molecules (buffer pH 7.1). Detection is carried out by UV or, alternatively, by fluorescence. Eight carbonyls are separated in less than 8 min. Electrokinetic injection is made by using a new experimental set-up. The electroendosmatic flow (EOF) is reversed during sample injection by pressure. Results are compared with HPLC-analysis as the most common method in carbonyl analysis.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday