采用光纤拉曼放大改善1550 nm外调制有线电视系统的组合二阶失真指标

为克服长距离光纤有线电视（CATV）系统中采用高增益掺铒光纤放大器（EDFA）所带来的非线性损伤．对在残留边带调幅（AM—VSB）外调制光纤有线电视系统中采用光纤分布拉曼放大时的组合二阶失真（CSO）进行了,理论研究。根据拉曼放大对信号光强的增益作用。导出了分布拉曼放大条件下的薛定谔方程。并采用微扰法解出了存在拉曼分布放大时,残留边带调幅外调制有线电视系统中．自相位调制（SPM）导致的组合二阶失真的解析表达式。相应数值计算结果表明．相对于采用掺铒光纤放大器功放．采用相同放大倍数的分布托曼放大可使长距离系统中自相位调制导致的组合二阶失真性能改善10dB以上。因此可以得出结论：在长距离残留边带调幅凋制的有线电视系统中,采用分布式光纤拉曼放大可以较好地改善由自相位调制导致的组合二阶失真恶化。     

Characterization and Antimicrobial Evaluation of Dilution-Stable Microemulsions Against Stenotrophomonas maltrophilia

The purpose of this study is to load glycerol monolaurate (GML) in a microemulsion system for the inactivation of Stenotrophomonas maltophilia. The influence of ethanol, propylene glycol (PG) and sodium benzoate (Na-Bz) on oil solubilization of GML microemulsions is clearly reflected in the phase behavior of these systems. One dilution-stable microemulsion formulation was determined and stable by the examination of the physical stability. Results showed that the microemulsion at 100 ppm, comparable to 3 mg/L ceftazidime, had much higher antimicrobial activities against S. maltophilia, with a major contribution of GML, and Na-Bz enhanced the antimicrobial activities as a hydrotrope.     

GLOBAL STABILITY OF SIVS MODEL WITH SATURATION INCIDENCE, INFECTION AGE AND IMPULSIVE VACCINATED RATE

In this paper, an impulsive vaccinated strategy to eradicate SIVS epidemic model is studied. Since infection age is an important factor of epidemic progression, we incorporate the infection age into the model. In this model, we analyze the dynamic behaviors of this model and obtain that there exists an infection-free periodic solution which is globally asymptotically stable under a sufficient condition. Our results indicate that a short period of pulse or a large pulse vaccination rate is the sufficient con...     

用电热方法测定海水的比热容

该文运用电热学方法来测定海水的比热容,用电来加热海水,从而计算出升温所吸收的热量,利用测量液体升高温度所吸收的热量,来计算海水的比热容。通过计算和总结,得出测量液体比热容的普遍方法。     

The up-conversion properties of Yb and Er doped Y4Al2O9 phosphors

Er³⁺ doped and Yb³⁺/Er³⁺ co-doped Y₄Al₂O₉ phosphors are prepared by the sol-gel method. The effect of dopant concentration on the structure and up-conversion properties is investigated by X-ray diffraction (XRD) and photoluminescence, respectively. XRD pattern indicates that the sample structure belongs to monoclinic. Under 980 nm excitation, the green and red up-conversion emissions are observed and the emission intensities depended on the Yb³⁺ ion concentration. The green up-conversion emissions decrease with the increase of Yb³⁺ concentration, while red emission increases as Yb³⁺ concentration increases from 0 to 8 at% and then decreases at high Yb³⁺ concentration. The mechanisms of the up-conversion emissions are discussed and results shows that in Er³⁺ and Yb³⁺/Er³⁺ co-doped system, cross-relaxation (CR) and energy transfer (ET) processes play an important role for the green and red up-conversion emissions.     

Preparation and fluorescence properties of Yb3+ and Er3+ co-doped GdAlO3 phosphors

Yb³⁺ and Er³⁺ co-doped GdAlO₃ phosphors are prepared by the sol–gel method. The effect of doping concentration on the structure and fluorescence properties is investigated by X-ray diffraction (XRD) and photoluminescence, respectively. XRD pattern indicates that the sample structure belongs to orthorhombic. The photoluminescence results show that both green and red fluorescence emission and upconversion emission intensities decrease with an increase in Yb³⁺ concentration due to the cross-relaxation process between Yb³⁺ and Er³⁺ ions. Based on the emission spectra, the mechanism of the upconversion emission is discussed, and we concluded that the upconversion emission is a two-photon process.     

NONLINEAR BOUNDARY VALUE PROBLEMS FOR FIRST ORDER DIFFERENTIAL EQUATIONS WITH PIECEWISE CONSTANT ARGUMENTS

The authors employ the method of upper and lower solutions coupled with the monotone iterative technique to obtain some results of existence and un-iqueness for nonlinear boundary value problem of differential equations with piecewise constant arguments.     

Global exponential stability of nonautonomous neural networks with time-varying delays and reaction-diffusion terms

A class of nonautonomous neural networks with time-varying delays and reaction-diffusion terms is considered. By means of Lyapunov functionals and differential inequality techniques, criteria on global exponential stability of this model with the Neumann boundary conditions and the Dirichlet boundary conditions are derived, respectively. The results of this paper are new and they improve and generalize previously known results.