光纤光栅弹簧管压力传感器的压力和温度特性

本文利用弹簧管对于压力的机械放大作用,将弹簧管与光纤光栅悬臂梁调谐技术相结合,研制了一种新颖的光纤光栅弹簧管压力传感器,大大提高了光纤布喇格光栅对压力测量的灵敏度,压力灵敏度系数可达-1.79×10^-4/MPa,比裸光栅提高了两个数量级,在0～12MPa的压力范围内,光纤布喇格光栅中心反射波长的改变与压力成良好的线性关系.同时由于悬臂梁热膨胀效应的影响,光纤光栅的温度灵敏度提高为裸光栅的7倍.     

Photoluminescence studies of vacancies and vacancy-impurity complexes in annealed GaAs

Photoluminescence measurements made at various depths below the surface of annealed GaAs single crystals are compared with vacancy distribution profiles obtained from electrical measurements. Results on undoped n-GaAs indicate that isolated Ga or As vacancies form non radiative centers. A broad-band emission at 1.20 eV, arising from V_Ga-donor complexes, is observed in spectra taken from n-type samples doped with Si, Sn or Te. The intensity of the 1.20eV band varies with depth and reaches its maximum value in the region where Ga vacancies are dominant. These results show the consistency between photoluminescence and electrical measurements. A band at 1.37eV has previously been assigned to V_As-acceptor complexes. This band was observed in this study only when the samples had been annealed in ampoules prepared from quartz containing traces of Cu. It is concluded that the 1.37eV band is due to Cu contamination rather than V_As-acceptor complexes.     

Structure of styrene–butadiene–styrene block copolymers by diffusion analysis

In this study, solvent sorption was used to investigate the morphology of a styrene–butadiene–styrene (SBS) triblock copolymer. The sorption process was found to deviate from the normal Fickian character, usually found in conventional elastomer–solvent systems, because of the presence of an interfacial region for both polybutadiene and polystyrene. This interphase absorbed solvent at a temperature below its glass transition and contributed to the resulting non-Fickian time-dependent diffusion process. The equilibrium diffusion coefficient was estimated to be 3.2 × 10^?7 cm²/sec regardless of the casting surface. Nevertheless, according to the sorption measurements, the casting surface did have an effect on the approach to equilibrium. The results indicated a denser packing of the molecules and hence a decreased diffusion coefficient for Teflon and glass cast films, because of internal stresses left within the films during casting.     

Gap effect on moiré patterns

Résumé Nous analysons les caractéristiques principles des lignes de moiré produitues par des réseaux, dont les deux plans ne coïncident pas, illuminés par la lumière diffuse et non cohérente.Nous étudions, les aspects physiques de la formation des lignes de moiré et obtenons des équations qui donnent les valeurs des déformations fictives produites par la non-coïncidence des plans du réseau témoin et du réseau déformé.Les résultats théoriques sont comparés avec les mesures expérimentales. L'écart constaté entre les deux valeurs correspond aux erreurs expérimentales.     

A modified Marton-type electron interferometer

It is shown that the original Marton-type electron interferometer is based on the Fresnel diffraction of two coherent beams by a crystal. The modified Marton-type electron interferometer presented here is based on the Fraunhofer diffraction. The advantages of the proposed interferometer are given in the text along with a simplified sketch of the major components.     

Quantitative analysis of a mixture of cresols by carbon-13 NMR spectroscopy

The suitability of ¹³C NMR as a technique for determining o-, m, and p-cresols in their mixtures was investigated. Spectra were determined in methanol, containing o-toluidine as an internal standard, without nuclear Overhauser suppression. Ratios of peak areas of each cresol isomer to o-toluidine were determined by means of the standard calibration method, and then mixtures of cresol isomers were prepared and quantified in varying concentrations from 8.30 to 66.84 mol% for each isomer, with an average absolute error of 0.78% for all isomers. The method described was convenient and the results were generally satisfactory.     

Magnetohydrodynamic flow in a rectangular duct with perfectly conducting electrodes

Zusammenfassung Grenzschichtverfahren werden benutzt, um das Problem der magnetohydrodynamischen Strömung einer leitenden Flüssigkeit durch einen unendlichen rechteckigen Kanal bei grosser Hartmannzahl zu lösen für den Fall, dass die Wände, die parallel zum angelegten Magnetfeld sind, perfekt leiten, während die anderen beiden Wände Isolatoren sind. Das Problem ist als Integralgleichung für die Stromdichte an der Elektrode formuliert. Diese Gleichung besitzt als Lösung eine einfache, geschlossene Form.

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Part of this work was done in partial fulfillment of the degree of Doctor of Philosophy at the University of Minnesota.