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。     

仿海豹胡须阵列检测水中运动目标尾流特征

为检测水中运动目标的尾流特征,获取运动目标运动轨迹方向、几何尺寸等参数信息,通过模仿海豹使用胡须探测猎物的机理,提出了一种仿海豹胡须的尾流探测方法。首先,用3D打印技术制作了与海豹胡须形态相似的胡须模型,并结合压阻元件等材料制作了可感知水中运动目标尾流的传感器阵列。其次,设计尾流检测实验方案,并对0.5、1.0、1.5 m/s的均匀来流及具有微小波动的非均匀流场情况进行仿真分析,获取不同流场情况下的尾流速度场分布,分析S₁₁的升力系数及频谱分布,并与理论计算得到的尾流漩涡脱落频率进行对比,验证实验方案的有效性。最后,在实验室条件下,采用该传感器阵列实现了对被测目标尾流特征的测量,并分析了仿海豹胡须夹角对尾流检测的影响。结果表明：在不同来流情况下,胡须模型升力系数波动较明显,经快速傅里叶变换获得的主频与尾流漩涡脱落频率理论值一致性较好;在尾流区内传感器探测尾流信号的平均电压值是非尾流区的3倍以上,由此可准确识别出尾流区和非尾流区。在此基础上,对平均电压值衰减的梯度方向进行分析,实现了对被测目标运动轨迹方向的估算。该传感器阵列测得尾流信号的最大响应频率接近数值仿真的主...     

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     

直径2.5×40米窑尾的改造

新疆新工建材有限责任公司1999年对原直径2.5×40米两级旋风三级偏心立筒预热器窑进行了改造,利用原有混凝土框架,加装了四级旋风预热器和分解炉,改造成为一种简易的预分解窑系统。其后又经多次改造,台时产量由原来的5.5吨/小时提高到19吨/小时,最高时达21吨/小时,窑的运转率达90%以上。主要技术参数　　为了减少投资,利用原砼框架,因而旋风筒和分解炉的尺寸将受到限制。其流程如图1所示:　　图1中各部分具体规格尺寸如下:　　回转窑:直径2.5×40米　有效内径2.15米　　回转窑电机功率:75千瓦　　分解炉:直径2.45×16.8米　　预热器:C1…