通用连锁药店管理信息系统的设计与实现

本文结合实例阐述了基于PSTN的通用连锁药店管理信息系统的设计实现，并介绍了该系统的网络拓扑结构．功能模块设计和数据存储模式等。     

时分式平面—立体电视图像转换器

时分式平面－立体电视图像转换器是由视频图像信号处理电路、控制信号产生电路和液晶眼镜驱动电路三部分构成，根据其构成和工作原理，可采用多种具体电路来实现。     

TEMPERATURE EFFECT ON OXIDATION PROTECTION LIFE OF MULTI-LAYER COATING FOR C/C COMPOSITES

Carbon-carboncomposites(C/C)exhibitexcellentstructuralpropertiesabove165OC,andareconsideredasthemostpromisingcandidatematerialsforthehighthrust-weightratioturbineengines.Asakeytechnologyforthehigh-temperaturestructuralapplicationsofC/C,oxidationprotectionispaidmoreandmoreattentionrecently.TheoxidationprotectionllfeofacoatedC/Cisdeterminedbyenvironmenta1temperature,becauseitnotonlydecidesthether-mochemicalconditionsofinterfacesinacoating,butalsocontrolsthedynamicprocessofoxy-gendiffusion.The…     

Pro／ENGINEER在模具设计中的使用技巧

分析了Pro／ENGINEER进行模具设计的使用技巧，阐明了并行工程技术与Pro／ENGINEER软件相结合的重要性。     

平板上钝缘舵在超声速绕流中的三维分离特性研究

对于平板上的直立钝缘舵在M_∞=1.79、2.04和2.50的条件下,研究了该平板干扰区中的三维分离特性。着重讨论了钝缘直径、舵面迎角和来流马赫数对主分离线位置和形状的影响。分析了该类三维分离在性态上更强地依赖于无粘流动特性。此外,还对分离区内的二次分离发展过程和形态进行了初步讨论。     

宽带无线接入技术

介绍了两种宽带无线接入技术：本地多点分配业务(LMDS)和自由空间光通信(FSOC)。它们各具特色。前者将新兴的LMDS技术引入无线接入网,而后者是实现无线宽带接入的另一种途径。     

基于压电纤维复合材料的航天器动力学建模与振动抑制

压电纤维复合材料(MFC)在柔性航天器的振动主动抑制中具有很好的应用前景。利用哈密顿原理和压电驱动的载荷比拟方法,建立了带MFC压电驱动的离散形式的刚柔耦合动力学方程,采用线性二次型最优控制(LQR)算法进行主动控制。结果表明：在航天器的柔性体受到脉冲载荷激励条件下,使用MFC驱动器可以实现航天器挠性振动的快速抑制,并且同时保持中心刚体姿态的稳定性,即能够实现挠性振动与姿态运动的协同控制。基于MFC的主动控制方法对于高频响应也具有较好的控制效果。对于柔性占优的航天器,采用MFC的主动控制优于被动控制。本文方法在处理具有复杂柔性体的航天器时更具优势,更适合于工程应用。     

SiC/CVD SiC复合涂层的抗氧化及抗热震性能研究

为了提高C/SiC复合材料耐高温性能,采用泥浆浸渍裂解与真空化学气相沉积(CVD)在材料表面制备了SiC/CVD SiC复合涂层,通过XRD、SEM分析了涂层组成与结构;研究了复合涂层的高温抗氧化(700～1 500℃)和抗热震性能。结果表明,泥浆浸渍法制备的SiC涂层具有一定的封孔效果,可使材料开孔率下降,但高温抗氧化效果并不佳,1 200℃氧化10 min后材料弯曲强度保留率下降明显仅有86%。CVD SiC涂层结构致密,与SiC封孔涂层结合较好,在700～1 500℃具有较好的抗氧化效果,随着氧化温度的升高,氧化后涂层完好,表面O元素逐渐增加,材料失重率缓慢增加但不大于0.5%,且材料性能并未下降。涂层材料在1 200℃-10 min短时热震5次后材料弯曲强度保留率仍有95%以上,且未出现开裂、剥落等热震损伤。在1 200℃-30 min长时热震10次后,涂层材料基本被完全氧化,材料失去保护作用,弯曲强度下降至90%左右。     

Methane pyrolysis in preparation of pyrolytic carbon: Thermodynamic and kinetic analysis by density functional theory

The density functional theory has been successfully applied in analyzing pyrolytic carbon deposition by methane pyrolysis from the view of thermodynamics and kinetics based on a total number of 39 elementary reactions. M06-2X/def2-TZVP level was employed to optimize species structures and locate the transition states. The enthalpy changes and Gibbs free energy changes of all the reactions in the temperature range of 298.15–1800 K were derived with optimized species. Results show that the reacting temperature should be above 1200 K based on the equilibrium constant analysis, which is consistent with the typical reaction temperature adopted in experiments. Potential energy surface profiles report that radical attacking reactions have lower energy barriers than those direct decomposition reactions, especially hydrogen radical attacking reactions. The energy barriers of the first steps, dehydrogenations of methane and ethylene, are 272.4 kJ·mol⁻¹ and 288.9 kJ·mol⁻¹ at 1200 K, which are very close to the experimental activation energy for methane pyrolysis. The most favorable decomposition reaction path is the path of hydrogen radical attacking reactions. The highest energy barrier of the path at 1200 K is 185.7 kJ·mol⁻¹ presented by the C–H bond breaking in ethynyl attacked by hydrogen radical.     

Cutting path-dependent machinability of SiCp/Al composite under multi-step ultra-precision diamond cutting

Particle-tool interactions, which govern the synergetic deformation of SiC particle reinforced Al matrix composites under mechanical machining, strongly depend on the geometry of particle position residing on cutting path. In the present work, we investigate the influence of cutting path on the machinability of a SiCp/Al composite in multi-step ultra-precision diamond cutting by combining finite element simulations with experimental observations and characterization. Be consistent with experimentally characterized microstructures, the simulated SiCp/Al composite is considered to be composed of randomly distributed polygonally-shaped SiC particles with a volume fraction of 25vol%. A multi-step cutting strategy with depths of cut ranging from 2 to 10 μm is adopted to achieve an ultimate depth of cut of 10 μm. Intrinsic material parameters and extrinsic cutting conditions utilized in finite element simulations of SiCp/Al cutting are consistent with those used in corresponding experiments. Simulation results reveal different particle-tool interactions and failure modes of SiC particles, as well as their correlations with machining force evolution, residual stress distribution and machined surface topography. A detailed comparison between numerical simulation results and experimental data of multi-step diamond cutting of SiCp/Al composite reveals a substantial impact of the number of cutting steps on particle-tool interactions and machined surface quality. These findings provide guidelines for achieving high surface finish of SiCp/Al composites by ultra-precision diamond cutting.