基于矩阵扩展方法的多速率线性离散码设计

在采用空时码的无线通信系统中,收发2端较差的路径会降低系统的性能.提出了多速率线性离散码(LDC),并对其进行了分析,给出了一种基于矩阵扩展方法的设计算法.多速率LDC是传统LDC和LDC-TAS的BER性能的折中.进而提出了一种性能优于传统LDC-A-TAS算法的多速率LDC自适应发送天线选择(A-TAS)算法.     

一种新的径向导热界面参数插值格式

以变系数径向导热问题为研究对象,由傅里叶导热定律提出了较之文献更为合理的热导计算方法.根据流的相容性原理分别推导得出极坐标、柱坐标和球坐标系下新的界面半径和界面导热系数插值格式.通过几个变系数和非线性导热问题对插值格式进行考核,并与文献中的插值格式进行对比.结果表明,推导的格式充分考虑了变截面和变物性的综合影响,对于非线性和变系数导热问题能得到更精确的结果.     

复格拉斯曼流形G(2,5)中的调和2-球面

运用调和序列和活动标架研究复格拉斯曼流形G(2,5)中的调和2-球面.通过S²上全纯微分形式的构造, 简化G(2,5)中沿调和2-球面的活动标架,并且给出高斯曲率的上界估计.     

倾斜界面绕射波时距曲线特征及其应用

根据几何地震学原理推导了倾斜界面情况下的绕射波时距曲线方程,采用2种方法证明倾斜界面反射波与绕射波交点位置解的存在性及其唯一性.理论分析表明,倾斜界面绕射波时距曲线仍具有双曲线特征,且最小旅行时点的位置始终在绕射点正上方,与地层倾角等因素无关,是水平界面情况的一般形式.定性和定量研究了交点坐标趋向于无穷大时的临界参数计算公式,数值实例验证了这一结论.采用实际地震资料指出了常规地震容易导致的解释误区.     

线性和非线性双重视角下煤炭价格波动对中国经济增长的影响

基于线性和非线性双重假设,以1993年1月-2014年12月的时间序列数据为样本,采用邹氏检验、Granger因果关系检验和脉冲响应函数等多种方法,定量分析了煤炭价格波动对中国经济增长的影响。线性假设下的研究结果表明:从2002年开始煤炭价格波动对中国经济增长的影响由不显著转变为显著;在2002年1月至2014年12月这个区间内,煤炭价格波动在期初对中国经济增长造成负向影响后,随后转变为正向影响,且这种影响效力随着时间的推移逐渐消失。非线性假设下的研究结果表明:同样在此区间内,煤炭价格波动对中国经济增长的影响存在非对称性,即与煤炭价格上涨相比,煤炭价格下跌对中国经济增长的影响更为显著,具体表现为煤炭价格下跌在期初会促进经济增长,但随后会对经济增长起阻碍作用,这可能是受国内外煤炭价差及煤炭净进口量变化的影响。最后,就上述研究结论,从推进煤炭价格的市场化、完善煤炭市场的宏观调控以及优化能源消费结构三个方面提出了政策建议。     

对鲁棒线性规划保守性的进一步讨论

保守性是衡量鲁棒优化模型好坏的重要指标,也是研究鲁棒优化方法的一个关键问题.在先前关于鲁棒线性优化保守性的研究中,我们发现,线性规划最优解中非零分量的数目k是刻画鲁棒线性规划模型保守性的一个重要参数.本文通过分析基解是鲁棒线性规划问题最优解的概率,给出了参数k的概率分布和数学期望.     

基于压缩感知的SAR图像压缩算法

研究基于压缩感知的合成孔径雷达(SAR)图像压缩算法.根据压缩感知理论,在信号降维方面,提出一种更优化的观测矩阵构造方法;在信号重构方面,提出一种基于微分熵和迭代加权最小二乘的改进重构算法.通过对SAR图像进行压缩和性能比较,得出结论:本文提出的改进算法优于传统的压缩感知算法.     

重庆市钢铁存量估算及驱动力分析

钢铁存量的准确估算可为预测钢铁需求量、理论报废量、制定资源环境管理政策提供科学依据。本文以重庆市全行政区面积为研究边界,采用自下而上的方法估算了1985—2014年重庆市钢铁存量及其行业分布。研究结果表明,重庆市的钢铁总存量及人均存量在过去30年间分别增长了10倍和12倍,于2014年分别达到0.59亿t和1748kg/人;在钢铁存量的行业分布结构上,建筑钢铁存量的历年占比均达到50%以上,该结果与邯郸市、美国纽黑文市的钢铁存量行业分布模式相似。基于钢铁存量的估算结果,本文利用IPAT模型对重庆市钢铁存量的变化进行了驱动力分析,研究发现,经济发展与人口增长是重庆市钢铁存量增长的主要驱动因素,其中经济发展始终是最强劲的驱动力,而技术的负向作用表明,重庆市未来对钢铁的需求将降低。     

Reliability of power and velocity variables collected during the traditional and ballistic bench press exercise

This study aimed to examine the reliability of different power and velocity variables during the Smith machine bench press (BP) and bench press throw (BPT) exercises. Twenty-two healthy men conducted four testing sessions after a preliminary BP one-repetition maximum (1RM) test. In a counterbalanced order, participants performed two sessions of BP in one week and two sessions of BPT in another week. Mean propulsive power, peak power, mean propulsive velocity, and peak velocity at each tenth percentile (20–70% of 1RM) were recorded by a linear transducer. The within-participants coefficient of variation (CV) was higher for the load–power relationship compared to the load–velocity relationship in both the BP (5.3% vs. 4.1%; CV ratio = 1.29) and BPT (4.7% vs. 3.4%; CV ratio = 1.38). Mean propulsive variables showed lower reliability than peak variables in both the BP (5.4% vs. 4.0%, CV ratio = 1.35) and BPT (4.8% vs. 3.3%, CV ratio = 1.45). All variables were deemed reliable, with the peak velocity demonstrating the lowest within-participants CV. Based upon these findings, the peak velocity should be chosen for the accurate assessment of BP and BPT performance.     

Which tier? Effects of linear assessment and student characteristics on GCSE entry decisions

In England, students obtain General Certificate of Secondary Education (GCSE) qualifications, typically at age 16. Certain GCSEs are tiered; students take either higher‐level (higher tier) or lower‐level (foundation tier) exams, which may have different educational, career and psychological consequences. In particular, foundation tier entry, if inappropriate, risks capping students' achievement because of the restricted range of attainable grades and reduced learning that may occur. Tiering decisions may be affected by other aspects of the education system in which they take place, such as by the timing of assessment. The move to linear assessment in 2012 provided a unique opportunity to compare tiering decisions for the same GCSE specifications when taken in a linear system, where students are exclusively assessed at the end of the course, with tiering decisions in a modular system, where students are assessed at different time points. Multilevel logistic regression was used to examine students' likelihood of being entered for the foundation tiers of GCSEs in science, language and mathematics in two exam sessions: June 2013, which allowed modular assessment, and June 2014, which required linear assessment. The analyses also investigated whether these effects depended on student characteristics. Results showed that foundation tier entry was less likely in the linear than modular system for GCSEs in science and languages, but more likely for one mathematics GCSE. This pattern contrasts with concerns that linear assessment may encourage general risk‐aversion, and instead indicates that effects on tiering decisions are more complicated, varying by subject and student factors.