考虑冷变形加工硬化的翻边力理论计算

在分析现有计算公式存在不足的基础上,根据翻边变形区材料的应力应变特点,考虑了冷变形加工硬化(取幂函数硬化规律)和变形区材料厚度变化(翻边为变薄)两个因素的影响,利用金属塑性成形问题求解理论中的主应力法,推导和提出了圆孔翻边力计算的一个新公式.通过用钢板(SPCC)和铜板(T1)进行了翻边工艺试验的验证,并与经验公式和现有理论公式的计算结果进行了比较,表明新公式计算结果能接近于实际,且原理上更为科学合理.     

Synchronization and channel estimation for MIMO OFDM wireless LAN systems

A new preamble structure is designed for wireless LAN based on MIMO OFDM systems, which can be used for both synchronization and channel estimation. Modulatable orthogonal polyphase sequence is utilized in training symbol design regarding its correlation properties. The time synchronization and channel estimation are achieved by measuring the correlation between the received training sequence and the locally generated training sequence. Repeated training symbols are used to get carrier frequency offset (CFO) estimation. It is shown from the analysis that the accuracy of frequency synchronization is close to the Cramér-Rao lower bound. The training sequences are optimal for channel estimation based on the minimum mean square error (MMSE).     

Prevention and forecasting of rock burst hazards in coal mines

Rock bursts signify extreme behavior in coal mine strata and severely threaten the safety of the lives of miners, as well as the effectiveness and productivity of miners. In our study, an elastic-plastic-brittle model for the deformation and failure of coal/rock was established through theoretical analyses, laboratory experiments and field testing, simulation and other means, which perfectly predict sudden and delayed rock bursts. Based on electromagnetic emission (EME), acoustic emission (AE) and microseism (MS) effects in the process from deformation until impact rupture of coal-rock combination samples, a multi-parameter identification of premonitory technology was formed, largely depending on these three forms of emission. Thus a system of classification for forecasting rock bursts in space and time was established. We have presented the intensity weakening theory for rock bursts and a strong-soft-strong (3S) structural model for controlling the impact on rock surrounding roadways, with the objective of laying a theoretical foundation and establishing references for parameters for the weakening control of rock bursts. For the purpose of prevention, key technical parameters of directional hydraulic fracturing are revealed. Based on these results, as well as those from deep-hole controlled blasting in coal seams and rock, integrated control techniques were established and anti-impact hydraulic props, suitable for roadways subject to hazards from rockbursts have also been developed. These technologies have been widely used in most coal mines in China, subject to these hazards and have achieved remarkable economic and social benefits.     

Prevention of rockburst by guide holes based on numerical simulations

We studied variations in the stress field around guide holes drilled during tunnel excavation to understand the mechanical mechanism by which these holes help prevent rockburst. The study used elasto-plastic analysis of a circular chamber under non-axisymmetrical loads. The results showed that the unloading of in-situ stresses, and the forming of a secondary stress field, leads to a severe change in the stress field around the guide holes. This causes the formation of an X-shaped area of plastic deformation, which prevents the rockburst. Adopting a sub-model finite dement technique, we analyzed the factors that influence the distribution of the plastic area, such as the guide hole distribution and the in-situ stress state. The calculations showed that higher initial stresses result in greater adjustment to the stress field. When the stress concentration is greater the size of the plastic area surrounding the guide hole is larger. A multi-row distribution of the guide holes shaped like a quincunX can increase the interconnectivity of the plastic areas and allow the plastic area to extend from the tunnel wall deep into the surrounding rock. An optimized design was put forward based on the distribution of the plastic area around guide holes and the factors that influence it.     

蜂窝陶瓷型La0．8Sr0.2MnO3催化剂VOCs催化燃烧反应活性

以堇青石(CH)为第一载体,六铝酸盐(HA)为第二载体(washcoat),La0.8Sr0.2MnO3(LSM)为活性物种,制备了LSM/HA/CH催化剂.XRD表征发现,LSM具有完善的钙钛矿晶型.SEM观察表明,活性物种在涂层表面分散均匀.通过对苯、甲苯、二甲苯、乙酸乙酯、丙酮和乙醇六种有机物的性能测试,发现LSM/HA/CH对上述六种有机物均具有很好的催化活性,特别是对乙酸乙酯等含氧有机物表现出更好的燃烧性能,在10000 h-1空速下,反应温度为240℃时即可将含氧有机物完全燃烧.     

南宋初期山水画生态环境之考察

中国绘画史上许多重要风格的产生常常与其所处的政治、经济、文化环境的某些变化产生紧密联系,即艺术风格的转变不仅仅是其内心自律性的产物,更与具体的社会历史情境有关。南宋由政治巨变带来的社会动荡,在社会生活的方方面面均有反映。本文通过对宋室南渡后南宋社会生态环境的考察,了解南宋山水画赖以存在和发展的土壤,说明南宋山水画之清远雅洁、雅俗通融的特征与画家们的生存环境、相关赞助群体以及地域、文化变迁之间有着不可分割的密切关系。     

掺灰膨胀土的膨胀特性试验研究

通过生石灰对膨胀土的改性作用,在相同初始含水率的条件下,比较改性前后膨胀力、膨胀率的变化趋势,寻求最佳掺灰率;分析了膨胀力与初始含水率,膨胀率与初始含水率以及终止吸水量与初始含水率等关系.     

淮水北调输水管道关键技术研究与应用

介绍了输水主管道的设计制造关键技术问题,通过比较备选管材特性,研究了选用的PCCP管道设计制作技术、空气阀布置设计和管道基座安装技术,对管道铺设方案、煤矿塌陷区的地基变形进行了分析。     

广西老堡铅锌矿褶皱形成机制及其控矿规律

老堡铅锌矿床主要赋存在陡山沱组白云岩或老堡组硅质岩中,顺层产出,受地层与褶皱的双重控制。矿区主干褶皱为一复式向斜,由2个次级向斜和1个次级背斜组成。从构造几何学、运动学角度,运用现代测试技术,对矿区的小构造、显微构造和组构进行构造分析后揭示,老堡褶皱构造的形成机制是以弯滑作用为主、兼具弯流作用的纵弯褶皱作用的产物。铅锌矿体主要赋存在褶皱的转折端虚脱部位及两翼滑移量较大的层间滑动破碎带中。     

基于BER性能约束的MIMO系统码本设计优化算法

提出了一种基于误码率（BER）性能约束的码本优化设计算法。在提出的算法中,采用了联合预编码和功率控制的发射方案,并基于容量准则进行码本设计。仿真结果表明,与已有的码本设计算法相比,所提出的码本设计算法可以达到更高的容量,并能保证期望的BER性能。