A Closed-Form Formulation for the Build-Up Factor and Absorbed Energy for Photons and Electrons in the Compton Energy Range in Cartesian Geometry

In this work, we report on a closed-form formulation for the build-up factor and absorbed energy, in one and two di- mensional Cartesian geometry for photons and electrons, in the Compton energy range. For the one-dimensional case we use the LTSN method, assuming the Klein-Nishina scattering kernel for the determination of the angular radiation intensity for photons. We apply the two-dimensional LTSN nodal solution for the averaged angular radiation evaluation for the two-dimensional case, using the Klein-Nishina kernel for photons and the Compton kernel for electrons. From the angular radiation intensity we construct a closed-form solution for the build-up factor and evaluate the absorbed energy. We present numerical simulations and comparisons against results from the literature.

基于Geometry因子计算校正的下行TD-LTE调度优化研究

由于无线频谱资源日益短缺,多层次组网、高复用方式频繁应用造成同频干扰现象时有发生,导致网络传输不畅。为得到较好改善,首先从3GPP已有协议出发,采用两种方案推导获取关键参数Geometry因子;其次针对网络有效性、规避潜在风险性,通过分析对比及实验室验证,确定RSRP作为其计算模式;最后将该因子应用于已有系统,以减小资源碰撞为目的,调整调度时序以协调资源分配。仿真以两种网络标准拓扑进行,并依据网络实际探测能力进行限制,结果表明,可以达到提升系统吞吐量的目的,且密集组网场景下增益提升更明显。

Analysis of acquisition parameters and geometry quality

High-quality seismic geometry is the key to obtain high-quality seismic data, and can affect the accuracy of data processing and imaging. Based on the analysis of the relationship between the quality of the geometry and the four acquisition parameters(the number of traces, shot line spacing, and the space and number of receiver lines), a quality evaluation method of the geometry based on comprehensive quality factor(CQF) is proposed, and the relationship between the geometry quality and the four parameters is given. We use field data collected in an oil field in Western China with complex geology: First we use a wide azimuth geometry. Then, we calculate the relationship curve between geometry and data quality by varying each parameter while keeping the rest fixed. and the analysis results are given by using the CQF evaluation method. The results show that the shot-line spacing has the greatest effect on the quality of the geometry, and the increase of the receiver line spacing can appropriately improve the quality of the geometry, and the increase of the number of receiving traces can improve the geometry quality. The different acquisition parameters have different effects on the imaging quality of shallow and deep events. The model forward and prestack depth migration are used to generate prestack depth migration profiles with different acquisition parameters. The imaging results are consistent with the above calculated results. According to the depth of the target layer, the quality factor evaluation method is applied to guide the design of the geometry and optimize the acquisition parameters to improve the imaging accuracy of seismic data.

Spatio-temporal Characteristics of Area Coverage and Observation Geometry of the MISR Land-surface BRF Product: A Case Study of the Central Part of Northeast Asia

The Multi-angle imaging spectroradiometer(MISR) land-surface(LS) bidirectional reflectance factor(BRF) product(MILS_BRF) has unique semi-simultaneous multi-angle sampling and global coverage. However, unlike on-satellite observations, the spatio-temporal characteristics of MILS_BRF data have rarely been explicitly and comprehensively analysed. Results from 5-yr(2011–2015) of MILS_BRF dataset from a typical region in central Northeast Asia as the study area showed that the monthly area coverage as well as MILS_BRF data quantity varies significantly, from the highest in October(99.05%) through median in June/July(78.09%/75.21%) to lowest in January(18.97%), and a large data-vacant area exists in the study area during four consecutive winter months(December through March). The data-vacant area is mainly composed of crop lands and cropland/natural vegetation mosaic. The amount of data within the principal plane(PP)±30°(nPP) or cross PP ±30°(nCP), varies intra-annually with significant differences from different view zeniths or forward/backward scattering directions. For example, multiple off-nadir cameras have nPP but no nCP data for up to six months(September through February), with the opposite occurring in June and July. This study provides explicit and comprehensive information about the spatio-temporal characteristics of product coverage and observation geometry of MILS_BRF in the study area. Results provide required user reference information for MILS_BRF to evaluate performance of BRDF models or to compare with other satellite-derived BRF or albedo products. Comparing this final product to on-satellite observations, what was found here reveals a new perspective on product spatial coverage and observation geometry for multi-angle remote sensing.

On the Build-Up Factor from the Multi-Group Neutron Diffusion Equation with Cylindrical Symmetry

We consider the time dependent neutron diffusion equation for one energy group in cylinder coordinates, assuming translational symmetry along the cylinder axis. This problem for a specific energy group is solved analytically applying the Hankel transform in the radial coordinate r. Our special interest rests in the build-up factor for a time dependent linear neutron source aligned with the cylinder axis, which in the limit of zero decay constant reproduces also the static case. The new approach to solve the diffusion equation by integral transform technique is presented and results for several parameter sets and truncation in the solution for the flux and build-up factor are shown and found to be compatible to those of literature [1,2].

Geometric Study of Two-Dimension Stellated Reentrant Auxetic Structures to Transformable Architecture

Transformable architecture is totally linked to the study and knowledge of geometry.There are some materials in nature,whose geometric invariants establish equivalent structural behavior regarding the scalar transformations,developing different spatial typologies according to dimensional variation.Auxetic materials are characterized by their negative Poisson’s ratio.They can change their geometric configuration from a line to a surface,and from a surface to a volume or spatial framework.This paper is based on establishing and comparing those stellated reentrant auxetic geometries to be able to build new spaces defined by their capacity for architectural transformation,studying analytically geometric properties of stellated reentrant auxetic structures that,from the molecular to the macroscopic level,can be part of the architecture construction.In this investigation,a comparative study by means of CAD of stellated reentrant auxetic patterns has been realized.A Computer-Aided Design study of stellated reentrant auxetic structures will be realized to use them in architecture.The geometric behavior of the different stellated reentrant auxetic patterns is analyzed from the developed study to generate a systematic comparison,evaluating properties of these forms,such as their maximum achievable area reductions in relation to the total length of bars of the structure,in order to obtain a growth factor.

基于辛几何方法测定Ⅰ型应力强度因子

为得到高精度的Ⅰ型应力强度因子,提出了一种基于辛几何方法测定裂纹尖端Ⅰ型应力强度因子的方法。通过在裂纹尖端构建扇形区域,分离辛几何方法下裂纹尖端的全状态向量,结合裂纹尖端的位移场,计算出裂纹的应力强度因子。利用Ⅰ型裂纹尖端位移场的理论解,研究了扇形区域的特征点个数、圆心角大小以及半径长度对应力强度因子精确度的影响。研究结果表明:特征点个数对该方法求解Ⅰ型应力强度因子的精度的影响较大,特征点个数大于37时,相对误差稳定趋向于0;扇形圆心角对应力强度因子的精度影响较小,但是相同精度要求下,不同的扇形圆心角需要的特征点个数不同;扇形半径过小时,由于断裂过程中裂纹尖端塑性区域的影响,应力强度因子的解不稳定且相对误差较大。对比相对误差可以发现该方法计算得到的Ⅰ型应力强度因子的精度较高,且该方法只需得到裂纹尖端的位移场就可以精确得到应力强度因子,解决了以往求解体系在复杂应力等情况下求解步骤复杂,导致无法精确得到Ⅰ型应力强度因子的难题。

对接接头缺口应力集中系数不确定性分析

[目的]以典型对接接头为研究对象进行参数化建模,建立焊缝几何形状存在不确定性的有限元模型,来研究焊缝几何存在不确定性的对接接头焊趾处缺口应力集中系数K_(t),并统计分析其分布规律。[方法]首先,对以往采用的网格尺寸和单元类型进行改进,通过有限元网格敏感性分析,研究不同类型的单元以及网格尺寸对K_(t)的影响;其次,沿对接接头焊缝法向提取节点应力,通过绘制应力分布图,确定焊趾处最大应力集中所在部位;然后,通过引入控制点描述对接焊缝几何形状的变化来真实反映焊缝几何形状的不确定性,结合实际测量的焊缝形状数据的分布规律,随机抽样得到大量的焊缝几何参数数据;最后,基于缺口应力法计算K_(t),并对其进行统计分析,探究对接接头在焊缝几何参数存在不确定性时K_(t)的分布规律。[结果]结果表明,K_(t)的分布满足正态分布。[结论]通过探究焊趾处的应力分布,对于分析疲劳强度和提高疲劳寿命预测精度具有重要意义。

一种基于平行因子分解的电磁矢量传感器MIMO雷达测向算法

现有的电磁矢量传感器?多输入多输出(Electromagnetic vector sensor multiple?input multiple?output, EMVS?MIMO)雷达大多限制收发阵元以半波长约束分布,极大限制了雷达测向的分辨率。针对此问题,本文提出了一种基于平行因子(Parallel factor, PARAFAC)分解方法对目标进行二维角度估计的算法,该算法适用于所有任意发射阵列几何以及任意稀疏的接收阵列几何。首先,对接收阵列的匹配滤波后的信号构造三阶平行因子张量模型。然后,利用PARAFAC分解,得到发射方向、接收方向以及复合因子矩阵的估计值。最后,联合旋转不变法、矢量叉积法和最小二乘法,得到目标的高分辨率、无模糊特性二维角度估计的闭式解。本文所提出的算法具有精度高、计算复杂度低的特点,计算机仿真验证了基于张量分解的算法在任意双基地EMVS?MIMO雷达模型上的应用,该算法能够准确地估计出多个目标的二维角度参数,证明了所提算法的有效性和优越性。

Infrared thermography for prediction of spontaneous combustion of sulfide ores

The method of infrared thermography to predict the temperature of the sulfide ores has a large error. To solve this problem, the temperature of the sulfide ores is measured by thermal infrared imager and recording thermometric instrument contrastively. The main factors, including emissivity, distance, angle and dust concentration that affect the temperature measurement precision, are analyzed. The regression equations about the individual factors and comprehensive factors are obtained by analyzing test data. The application of the regression equations improves the precision of the thermal infrared imager. The geometric information lost in traditional infrared thermometry is determined by visualization grid method and interpolation method, the relationship between the infrared imager and geometry information is established. The geometry location can be measured exactly.

观测系统综合质量因子分析

观测系统的优劣决定地震采集数据的质量。目前用于地震勘探观测系统评价的大多是仅能反映观测系统某一方面特征的单一属性。为此,基于前人研究成果,综合观测系统中的覆盖次数、炮检距和方位角分布特征、炮检距非均匀性系数等几种属性,推出观测系统综合质量因子评价方法;通过对四种常用观测系统和四种不同接收线距的OBC观测系统实例做分析,探究综合质量因子的影响因素及其变化特征。结果证实本文方法可定量地评价观测系统质量,从而建立起观测系统定量评价与分析的新方法和新思路。

煤层压裂裂缝延伸及影响因素分析

为提高煤层压裂效果,采用拟三维裂缝延伸模型,系统全面分析了岩石物性参数(弹性模量、泊松比、断裂韧性)、地应力差、产层厚度、施工条件(排量、黏度、压裂液滤失性)等对裂缝几何形态的影响。结果表明:应力差、排量、产层厚度等与缝长、缝宽成正相关;弹性模量、泊松比、断裂韧性、排量、黏度等与缝高成正相关;滤失与缝高、缝长、缝宽三者成负相关。此研究结果对获取理想的裂缝几何形态有重要的理论指导意义。

不同截面微通道中流动阻力特性

实验研究了微通道内去离子水的流动阻力特性,微通道当量直径范围De=0.210～1.069mm,雷诺数范围Re=102～104,截面形状分为矩形、半圆形及三角形.通过测量微通道沿程压降及出、入口局部压降随流量变化关系,获得了沿程阻力系数及局部阻力系数.结果表明:当截面形状相同时,摩擦阻力系数随着当量直径的减小而降低;当量直径接近,截面形状不同时,其摩擦阻力系数也不相同;进、出口局部阻力系数变化趋势一致,且入口局部阻力系数要比出口的大;流型发生转变的临界雷诺数Rec=600～1 000.

一种加权计算基础矩阵的高精度算法

分析了图像匹配点对基础矩阵的不同影响,引入具有明显几何意义的匹配点到对极线的距离作为匹配点的加权因子,将匹配点集合看作随机变量并将加权因子作为匹配点的概率分布。在此基础上对原始图像数据进行归一化处理,利用8点算法得到基础矩阵。大量的试验结果表明,该方法明显降低了计算余差,提高了基础矩阵的计算精度。

基于随机表面微面元理论的二向反射分布函数几何衰减因子修正

现有几何光学方法的二向反射分布函数BRDF(bidirectional reflection distribution function)模型在计算阴影遮蔽效应时普遍应用Blinn几何衰减效应假设,其等倾角V形槽近似得出的分段折线形式的几何衰减因子导致BRDF曲线存在较大的误差.基于倾斜角随机高斯分布的微面元理论提出了一种新的几何衰减模型,得出了积分形式的几何衰减因子表达式,数值模拟比较了Blinn几何衰减因子与修正后的积分型衰减因子以及对应的BRDF模型曲线.结果表明:提出的几何衰减因子在物理合理性以及模拟精度方面都有明显提升,使BRDF模型曲线与已有BRDF数据之间的标准误差由0.0636减小到0.0084.

基于最大整体包容度约束非负矩阵分解的高光谱遥感图像混合像元分析算法

针对高光谱遥感图像中存在高度混合无纯像元的现象,提出了端元整体包容度约束,并将其加入非负矩阵分解的目标函数.在满足端元非负性与和为一约束的同时,利用数据在特征空间的几何特性,要求端元构成的单形体所容纳的像元尽可能多.该算法不需对原始数据降维,不损害数据的物理意义,在迭代过程中使用乘性规则,避免了传统梯度优化过程中常见的整体步长难以控制现象.对模拟图像和真实图像进行实验评测并比较了提取端元精准度、鲁棒性以及执行效率,结果表明,本文算法可有效分析高光谱遥感图像混合像元.

水力压裂垂直裂缝几何形态数值模拟及影响因素分析

建立了均质地层上下地应力为非对称的、适用于一般裂缝几何形态的水力压裂拟三维数学模型，分析了各种因素对裂缝延伸的影响。杨氏模量增大使缝宽下降，而注入流量和压裂液粘度的增加均使缝宽增大，压裂液粘度和杨氏模量增加使缝高增加，地应力差增加使缝高下降。讨论了利用人为因素控制裂缝延伸的方法。用实际施工的一口井资料进行验证，裂缝闭合后的井壁缝高与测井曲线的高度基本一致，其相对误差为５．３％。

击距系数的实验研究与理论分析

针对经典电气几何模型认为雷电先导对导线、避雷线、大地三者之间击距相等的不合理问题,提出了用击距系数来描述雷电先导对导线与大地击穿强度的差别;依据长间隙放电与雷击放电的相似性,开展了棒-板间隙实验以得到击中目的物概率为50%时雷电先导与地面、导线之间的位置关系。实验结果显示击距系数随线路高度的增加而减小,实验结果修正之后得到击距系数与线路高度之间的关系,并依据电磁场理论的知识推得雷电先导击中地面的临界场强为500kV/m;导线的临界击穿强度随线路高度变化满足一定关系时,计算分析所得的击距系数与实验所得的非常接近。实验所得的击距系数公式可用于线路绕击防雷计算中。

低匹配对接接头应力集中系数计算及回归分析

针对高强钢低匹配的横向对接接头形状设计,以最大限度提高接头静载承载能力和疲劳强度为目标,采用有限元计算的方法,考察了焊缝余高、焊趾过渡圆弧半径、盖面焊道宽度、板厚等几何参数对焊趾和焊根处应力集中的影响,回归分析得出的焊趾和焊根处的应力集中系数的经验方程式,对高强钢低匹配对接接头设计具有指导意义。

基于二维ISAR图像序列的雷达目标三维重建方法

该文基于刚体目标3维运动过程中的几何不变性,将因子分解法引入ISAR图像处理领域,成功实现了雷达目标从2维到3维的重建。文中基于卡尔曼滤波和最邻近数据关联准则完成不同姿态下2维散射中心的关联,应用因子分解法进行目标结构的分层重建,最后给出评判准则检验重建性能。仿真实验证明,该文方法简单易行,能够有效实现单天线ISAR 3维成像。