蜂窝小区内分层中继组播策略的信道容量分析

蜂窝网小区内,中继终端的移动性会引起协同中继信道的不稳定,进而造成组播码流的频繁中断. 为解决这一问题,提出了一种既能保持协同网络高带宽特性,又能改善组播服务连续性的分层中继组播策略. 利用抽象信道模型和非衰减无线信道模型,对满足该策略的分层多节点中继信道的容量进行了分析. 理论分析和仿真结果表明,同普通非分层中继网络相比,新策略虽然在信道容量上略有降低,但保证了组播服务的连续性.     

循环动载作用下层状介质长期沉降计算方法

针对循环动载作用下交通基础设施长期沉降,研究解决在移动条形荷载作用下层状介质动应力和循环加卸载条件下层状介质残余应力、永久应变与残余沉降计算2个基本问题.采用Fourier积分变换与递推矩阵方法,依据平面问题动力微分方程、边界条件与层间连续条件,推导得到移动条形荷载作用下的层状介质动应力解析解.考虑应力水平和应力路径的影响,提出新的永久应变经验公式,通过卸载条件下附加永久应变的弹性边值问题求解,获得循环动载作用下层状介质残余应力与长期沉降的表达式.针对3种不同路基半刚性基层沥青路面环道试验,研究路表残余长期沉降变化规律;通过实测值和预测值对比分析验证了本文方法的合理性和可靠性.     

一种数控机床学习机的设计

介绍了一种数控机床学习机的功能和特点,详细阐述了设计方案.该机采用了真实、分层、可视、人机一体化等独特的设计理念,集数控手工编程与操作学习、零部件造型和自动编程学习、数控PMC编程与调试学习、数控结构与原理学习、数控连接与调试学习、数控电气控制学习等多种功能于一身,具有真实再现、功能丰富、可视清晰、人机合理、操作方便、安全可靠等特点,有利于学习者快速掌握数控技术.     

层状岩体受压力学特征结构面效应数值分析

煤层底板岩体是沉积岩,具有显著的层状结构特点。为研究层状岩体压缩强度的结构面效应,通过FLAC3D数值软件,结合改进的遍布节理本构模型,建立层状岩体压缩数值模型,分析单轴、三轴压缩情况下的应力应变响应以及强度特征。研究结果表明：层状岩体压缩强度具有显著的结构面倾角效应。随着倾角的增大,层状岩体的压缩强度呈现先减小后增大的趋势。当结构面倾角为40＆#176;～80＆#176;时,岩体强度整体较低,破裂面主要沿结构面展开。数值试验和理论分析反映的岩体强度随结构面倾角变化规律一致。层状岩体弹性模量沿平行于结构面方向最大,而垂直于结构面方向最小,并随结构面与水平面之间夹角的增加而增大。     

Electromagnetic wave absorbing properties of Cr2AlB2 powders and the effect of high-temperature oxidation

The electromagnetic (EM) wave absorbing properties of Cr₂AlB₂ powders and those after high-temperature oxidation were investigated. Coupling of magnetic and dielectric loss enables Cr₂AlB₂ with good absorption properties. The minimum reflection loss (RL) value is −44.9 dB at 8.5 GHz with a thickness of 2.7 mm, and the optimized effective absorption bandwidth (E_AB) is 4.4 GHz (13.0-17.4 GHz) with a thickness of 1.6 mm. After oxidation at 750, 900, and 1000°C for 2 h, the minimum RL values, respectively, are −23.9 dB (17.5 GHz, 1.5 mm), −41.4 dB (16.5 GHz, 1.5 mm), and −39.5 dB (8.0 GHz, 3.0 mm); and the corresponding E_AB values, respectively, are 3.8 GHz (13.6-17.4 GHz, 1.7 mm), 4.1 GHz (13.5-17.6 GHz, 1.6 mm), and 4.4 GHz (13.0-17.4 GHz, 1.7 mm). With an absorber thickness of 1.5-4.0 mm, the E_AB with a RL value of less than −10 dB can be tuned in a broad-frequency range 5.0-18.0 GHz, which basically covers C (4-8 GHz), X (8-12 GHz), and Ku (12-18 GHz) bands. These results demonstrate that Cr₂AlB₂, as a high-efficient and oxidation-resistant absorber, is a promising candidate for microwave absorption applications and can retain good EM wave absorbing properties after high-temperature oxidation.     

Polydimethylsiloxane based polyurethane and its composite with layered double hydroxide: Synthesis and its thermal properties

This investigation reports the synthesis of a new class of polyurethane (PU) based on bis(hydroxyalkyl) polydimethylsiloxane (PDMS) as diol and isophorone diisocyanate as diisocyanate followed by the preparation of PU/layered double hydroxide (PU/LDH) nanocomposite via ex-situ technique. Nuclear magnetic resonance and Fourier-transform infrared spectroscopy studies confirm the formation of PU and incorporation of PDMS into the PU backbone. Thermogravimetry analysis revealed that thermal stability of the composite improves significantly with incorporation of LDH into the PU matrix. This may be accredited to the barrier effect rendered by the LDH layers. Differential scanning calorimetry study reveals that with the incorporation of LDH, glass transition temperature (T_g) of the composite increases for an optimum level of loading beyond which it remains constant.     

Synthesis and electrochemical characterization of layered Li[Ni1/3CO1/3 Mn1/3]O2 cathode material for Li-ion batteries

1 INTRODUCTIONDue to the high cost of LiCoO2,a commonlyused cathode material in commercial rechargeablelithium-ion batteries , much efforts have been madeto develop cheaper cathode materials than LiCoO2,Li Ni O2and Li MnO2have been studied extensivelyas possible alternatives to LiCoO2[1 4 ]. Stoichio-metric Li Ni O2is knownto be difficult to synthesizeandits multi-phase reaction during electrochemicalcyclingleads to structural degradation,andlayeredLi MnO2has a significant drawback…     

Q235B 热轧H型钢拉伸试验分层断口的显微分析

Q2 35B热轧H型钢拉伸试验后出现分层断口。用扫描电镜进行了显微观察 ,发现分层现象与试样中超长的带状组织密切相关。用能谱仪对断口分层处和超长铁素体带上的夹杂物进行了成分分析 ,证实都是硫化物。试样拉伸时在铁素体带上密集分布的硫化物处产生大量微裂纹 ,同时超长铁素体带的变形又受到阻碍 ,导致该处在试样拉断之前裂纹已经贯通 ,最终在断口上形成分层。因此 ,拉伸试验断口出现分层的原因是试样中存在密集分布的硫化物和超长的带状组织。     

混凝土成层结构的流激振动特性

泄流激励引起水工建筑物振动的现象时有发生且形式多样,严重的还可能引起结构的破坏。对于混凝土成层结构而言,由振动引起破坏的案例不多,对其振动响应机制的研究也不够深入。以混凝土拱坝为例,通过数值计算及模型试验对比分析了整体与成层两种不同结构在相同泄流荷载作用下结构的振动响应,探讨了响应与结构自身的关系,并结合"拍"的概念,对混凝土成层结构振动响应特性与泄流荷载之间的关系进行了研究。结果表明,成层结构频率相近的前两阶振动是拍振形成的主要原因。此外,即使不满足拍振形成的条件,振动曲线同样可以表现为"拍"的形式,且振动量较受迫振动大幅增加,实质为"水力共振"现象。     

基于对称三层架构的Petri网仿真工具开发

设计了一种Petri网建模工具.针对该工具的特点定义了一种新的分层体系结构—对称三层架构,采用该架构设计了该工具的体系结构和核心类;对该工具进行了验证.结果表明:通过该工具,可以以图形化的方式建立、分析和仿真Petri网模型.