上覆煤柱影响下工作面应力场分布变化规律

为了研究近距离煤层群下行开采过程中,下煤层工作面受到上覆煤柱影响形成高应力区后,导致顶板垮落、冲击地压、煤壁片帮、瓦斯爆炸等煤矿灾害的发生问题,本文运用FLAC~(3D)软件,分别对厚度为1m、2m、3m、5m的上覆煤柱作用下位煤层开采前及开采过程中顶板应力分布动态变化规律进行数值模拟与分析。研究表明:①在下煤层未开采前,上覆煤柱会使下煤层处于应力集中状态;当煤柱厚度增加时,下煤层顶板支承应力场峰值、应力集中系数和应力集中区域范围逐渐减小,支承应力场峰值始终处于煤柱中心线附近。②随着工作面推进距离的增加,采区前方应力集中区域范围逐渐减小,支承应力场峰值及集中系数先增大后减小;在工作面推进过程中,煤柱厚度越小,工作面前方顶板支承应力峰值、集中系数和集中范围越大,应力集中区域与工作面的距离越小,越应注意防止冒顶、顶板破碎等矿井灾害事故的发生。     

姜汁凝乳影响因素的研究

生姜经清洗、打浆榨汁后可制得姜汁,将姜汁以2%的比例添加到经杀菌和冷却处理的鲜乳中可制成具有凝乳状态的姜汁牛乳。为了探讨姜汁凝乳的影响因素,文中研究了温度、pH值、牛乳蛋白质和盐类等对姜汁凝乳的影响。结果表明,温度和pH值是影响姜汁凝乳的关键外部因素。牛乳蛋白质、CaCl2、NaCl是凝乳促进物。     

金刚石红外增透保护膜的研制及特性拟合

论述了在硅基板上用热灯丝法制备金刚石红外增透保护膜的工艺，通过多灯丝法、预打磨处理以及加偏压等方法得到了特性优良的金刚石薄膜，并利用对金刚石薄膜─硅板体系红外透射率的曲线拟合，推知了一系列不易直接测量的特性参数，如折射率，吸收系数，薄膜厚度等。     

A finite-difference time-domain method for the design and analysisof guided-wave optical structures

A CAD tool employing the finite-difference time-domain (FDTD) algorithm is developed for the design and analysis of optical waveguide structures. The basic formulation of the algorithm is given, and practical conditions for its application are briefly outlined. The accuracy of the numerical scheme is investigated through a study of a canonical parallel-slabs coupling structure. Both the coupling length and the field distribution are in good agreement with results in the literature. The use of the method is illustrated by an analysis of a directional coupler     

IMPINGEMENT CASTING PROCESS: TURBULENT MIXING IN AN IMPINGEMENT MIXER

Theoretical analysis for turbulent mixing in an isotropic turbulent field was carried out. Depending on the material properties and flow field, either viscous shear force or dynamic pressure force breaks-up the globules. From an order of magnitude analysis, generalized equations for predicting globule sizes were derived. Experimental work on turbulent impingement mixing of kerosene and water revealed that macromixing and micromixing vary dramatically depending on the mixing chamber geometry. Best mixing (fast macromixing and small globule sizes) was obtained in an arrow shaped mixing chamber where the incoming jets were opposite to each other and slanted upward toward the mixing head. The coefficients of the equation for predicting the maximum globule size of immiscible liquids were obtained from the experimental results of arrow-shaped impingement mixers.     

Analysis of T cell receptor Vbeta gene usage during the course of disease in patients with chronic hepatitis B

Polyvinyl siloxane impression materials have applications in a variety of indirect procedures in prosthodontics and restorative dentistry. Favourable handling properties, good patient acceptance and excellent physical properties have resulted in their popularity in today's practice. In this review, the chemistry and important physical properties of polyvinyl siloxanes are summarized, and recent clinical questions of improved hydrophilics, tray adhesives, disinfection, and glove-induced polymerization inhibition are addressed.     

Limitations in fibre Raman amplifiers imposed by Rayleighscattering of signals

A simple method of Rayleigh scattering noise calculation in fibre Raman amplifiers is proposed. Using the method, it is disclosed that the optimal Raman pump power is lower when the Rayleigh scattering of both signal and amplified spontaneous emission (ASE) are considered than when the Rayleigh scattering of ASE only is considered