荧光寿命的快速傅里叶变换拟合方法

介绍了一种利用快速傅里叶变换算法对稀土掺杂物质的荧光寿命进行数据拟合的方法。稀土掺杂物质可用来制备多种光学传感器,用于温度、pH值等多种参量测量领域。本方法利用快速傅里叶变换(FFT)结果作为基础,从非零项的相位角的正切值得出被测的荧光寿命,具有速度快、误差小、不受本底干扰等一系列优点。以掺铒光纤为例,通过数字仿真将本方法与其它几种传统的拟合方法进行了比较。快速傅里叶变换方法的测量偏差不到Prony方法的50％,为对数似合(log-fit)方法测量偏差的1／6。另外,快速傅里叶变换方法由于不受本底噪声影响,可以不必在信号处理时去掉本底噪声,因而可以明显缩短测量时间。     

Vibrational spectra of sodium gadolinium tungstate NaGd(WO4)2 single crystals: Observation of spatial dispersion

Room temperature polarized Raman scattering and infrared reflectance spectra of a NaGd(WO₄)₂ single crystal have been measured. The IR spectra interpretation was aided by a Kramers-Krönig analysis, and fitted to the independent oscillator model. All 13 theoretically expected Raman-active bands have been identified and assigned, as well as 7 out of 8 expected IR active bands. Splitting of bands in both Raman and IR clearly indicates a lowering of the crystal symmetry due to occupation disorder in the 4a site, that randomly accommodates either an Na⁺ or a Gd³⁺ ion. The reflectance IR spectra reveal a spatial dispersion, namely a dependence of the transverse optical (TO) polariton frequencies, on the propagation direction in the crystal. The crystal vibrational modes are correlated to the internal modes of the tungstate group WO₄^2?, and to the internal modes of the molecular skeleton. A detailed correlation map of the symmetry analysis is presented.     

Suppression of forced and convective flows of a stably stratified fluid in vertical channels

In order to improve certain technological processes, for example, single-crystal growing, it is desirable to be able to control the flow rate in order to influence the heat and mass transfer processes. For this purpose it is usual to employ rotation, an electromagnetic field or reduced gravity [1]. Here, with reference to simple solutions of the system of equations of free convection in infinite vertical channels, it is shown that the problem of reducing the intensity of the flow can be solved given a suitable relation between the degree of stable stratification (with respect to density) and the factors responsible for the flow. The possibility of using temperature stratification is considered, but all the conclusions are also fully applicable to concentration stratification.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 172–174, March–April, 1987.The authors wish to thank B. Ya. Martuzan for his useful comments and interest in the work.     

Transport Properties of Epoxy-Binary Filler Composites

This paper presents the results of changes in electrical resistivity and thermal conductivity of polymer composites (CMs) with two-component filler. It is shown that thermal conductivity of epoxy CMs strongly depends on structural and morphological characteristics of carbon fillers. The synergistic effect in electrical and thermal conductivities of the studied CMs is observed upon addition of boron nitride BN. The presence of a sufficiently large number of BN particles in CMs promotes a more efficient formation of chains of carbon filler and reduces thermal (electrical) contact resistance between the filler particles by decreasing the distance between particles of the filler.