Bragg-grating-enhanced polarization instabilities

Experiments demonstrate a dramatic decrease in polarization-instability threshold as an optical pulse is tuned near the short-wavelength edge of the photonic bandgap formed by a fiber Bragg grating. These enhanced nonlinear interactions and birefringent effects are modeled with coupled-mode numerical simulations. Nonlinearities are shown to increase much more rapidly than the effective birefringence as the pulse wavelength approaches the bandgap edge.     

Gravitational energy-momentum density in teleparallel gravity

In the context of a gauge theory for the translation group, a conserved energy-momentum gauge current for the gravitational field is obtained. It is a true spacetime and gauge tensor, and transforms covariantly under global Lorentz transformations. By rewriting the gauge gravitational field equation in a purely spacetime form, it becomes the teleparallel equivalent of Einstein's equation, and the gauge current reduces to the Moller's canonical energy-momentum density of the gravitational field.     

Production of heavy neutron-rich nuclei “south" of lead

The production of heavy neutron-rich nuclei is investigated using cold-fragmentation reactions. More than 25 new heavy neutron-rich nuclei were produced in the fragmentation of ²⁰⁸Pb projectiles at 1 A GeV impinging a beryllium target. The precise measurement of their production cross sections enables to benchmark the predictive power of different model calculations and make reliable predictions of the production rates expected in future radioactive beam facilities.     

Effects of temperature on the relaxation to equilibrium and stationary nonequilibrium states of some Langevin systems

We investigate the effects of temperature on the properties of the time relaxation to equilibrium and nonequilibrium steady states of correlation functions of some Langevin harmonic systems. We consider commonly used dissipative and conservative Langevin dynamics, and show that the time relaxation rate depends on the temperature in the case of thermal reservoirs at different temperatures connected to the system, but it does not happen in the case of relaxation to equilibrium, i.e., if all the heat bath are at the same temperature. Our formalism maps the initial stochastic problem on a noncanonical quantum field theory, and the calculations of the relaxation rates are based on a perturbative analysis. We argue to show the reliability of the perturbative computation.     

土壤的光谱特征及氮含量的预测研究

应用近红外光谱分析技术(NIR)测定土壤参数具有快速、方便的特点.文章分析了不同含水率、不同颗粒大小的土壤样本在不同测试角、不同测试高度对土壤光谱的影响,并得到了不同含水率和不同粒径土壤的含氮量预测模型.研究了这些因素对含氮率测量的影响,分析了NIR技术在田间实地应用预测的可能性.研究表明,光谱仪在距土壤高度为100 mm,测试角为45°时,具有最大的吸光度.土壤粒径和含水率这2个参数明显影响,当粒径在0.5～5 mm变化时,含氮量预测相关系数r为0.81左右,当土壤粒径在＜0.25和＞5 mm模型的预测能力变差.当土壤样品呈天然潮湿状态时,氮的预测结果较差.而样品干燥以后,预测相关系数较高.为土壤原位光谱测试提供了依据.     

Operator Splitting Multiscale Finite Volume Element Method for Two-Phase Flow with Capillary Pressure

A numerical method used for solving a two-phase flow problem as found in typical oil recovery is investigated in the setting of physics-based two-level operator splitting. The governing equations involve an elliptic differential equation coupled with a parabolic convection-dominated equation which poses a severe restriction for obtaining fully implicit numerical solutions. Furthermore, strong heterogeneity of the porous medium over many length scales adds to the complications for effectively solving the system. One viable approach is to split the system into three sub-systems: the elliptic, the hyperbolic, and the parabolic equation, respectively. In doing so, we allow for the use of appropriate numerical discretization for each type of equation and the careful exchange of information between them. We propose to use the multiscale finite volume element method (MsFVEM) for the elliptic and parabolic equations, and a nonoscillatory difference scheme for the hyperbolic equation. Performance of this procedure is confirmed through several numerical experiments.     

Cu-Ni alloys in electrochemical oxygen analysis

Cu-rich Cu-Ni alloys (containing 70–90% Cu) are shown to be excellent indicator electrode materials for voltammetric measurements at cathodic potentials. These electrodes have been characterised using a variety of methods: rotating disk voltammetry, amperometric measurements and sono-ring-disk voltammetry. The mechanism of electrochemical oxygen reduction at the Ni-30Cu alloy has been established. The results are compared with the surface study results. Received: 2 December 1999 / Revised: 17 February 2000 / Accepted: 25 February 2000     

Braided reinforced composite rods for the internal reinforcement of concrete

This paper reports on the development of braided reinforced composite rods as a substitute for the steel reinforcement in concrete. The research work aims at understanding the mechanical behaviour of core-reinforced braided fabrics and braided reinforced composite rods, namely concerning the influence of the braiding angle, the type of core reinforcement fibre, and preloading and postloading conditions. The core-reinforced braided fabrics were made from polyester fibres for producing braided structures, and E-glass, carbon, HT polyethylene, and sisal fibres were used for the core reinforcement. The braided reinforced composite rods were obtained by impregnating the core-reinforced braided fabric with a vinyl ester resin. The preloading of the core-reinforced braided fabrics and the postloading of the braided reinforced composite rods were performed in three and two stages, respectively. The results of tensile tests carried out on different samples of core-reinforced braided fabrics are presented and discussed. The tensile and bending properties of the braided reinforced composite rods have been evaluated, and the results obtained are presented, discussed, and compared with those of conventional materials, such as steel. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 44, No. 4, pp. 327–338, May–June, 2008.