一种基于波束-频域处理的自适应波束形成方法

在天波超视距雷达中 ,通道之间的频响不一致影响了自适应波束形成的性能。去斜处理使得不同距离对应于不同频率 ,故不同距离单元的幅相不一致性与不同的频率相对应。经距离维FFT处理后 ,各路之间的通道不一致性得到降低 ,带内起伏趋于固定。基于上述特性 ,本文提出一种波束 频域处理方法 ,该方法不仅有效对消干扰 ,同时不会恶化天线方向图。更重要的是该方法降低了处理维数 ,减少了计算的复杂度。     

平砧拔长矩形截面毛坯的理论

从理论上分析与论证了平砧拔长矩形截面毛坯只有砧宽比(W/H)一个工艺参数是不足的,认为应增加,个工艺参数料宽比(B/H),才能正确描述拔长毛坯中心区域的应力状态与有效控制锻件质量。该理论已被实验验证。     

Variable trends of chain-folding in separate stages of strain-induced crystallization of bulk polymers

We performed dynamic Monte Carlo simulations of isothermal crystallization of bulk polymers at a high temperature, which was induced by a homogeneous stretching with a constant strain rate over a wide range of strains. We observed that the crystallites exhibit variable trends of chain folding in three sequential regions of strains, revealing hierarchical mechanisms of strain-induced polymer crystallization: in the first region, sporadic stretched segments initiate intermolecular crystal nucleation with less chain folding at higher strains; in the second region, massive less-stretched segments perform crystal growth with more chain folding at higher strains; in the third region, those folded chains extend via a melting-recrystallization process, again with less chain folding at higher strains. Different trends of chain-folding between crystal nucleation and growth appear intrinsic and ultimately lead to shish-kebab crystals. Our observations provided a molecular-level rationale to understand various experimental phenomena upon the processing for oriented semi-crystalline polymers.     

Biomechanical comparison of carpet-stretching devices

Peak impact forces, measured from seven male carpetlayers using a knee-kicker over 39 trials were 2933?N (SD 397), taking 9·5?ms (SD ± 1·1) to reach peak. The knee-kicking cycle involved high knee decelerations of 880?m.s^?2 (SD ±271). Angles at peak force for the knee (63° SD ± 10°) and hip (80° SD ± 35°) showed considerable variation between individuals. Kneeling forces on the non-kicking leg during the kick cycle were 894?N: comparative forces were 368?N and 476?N measured during use of the power stretcher and crab re-stretcher, respectively. Under dynamic conditions the effective mechanical advantage of the knee-kicker was less than 1·0. In comparison, the mechanical advantage of the power stretcher was approximately 14 times greater over the stretch action. When tested with a crab re-stretcher, the breaking strength of the smooth-edge to which the carpet attaches averaged 2384?N (SD ± 245). Design guidelines for an improved carpet stretching device are provided.     

拉伸流动场诱导PVDF/BaTiO3流延膜结晶行为研究

利用挤出流延过程中的拉伸应力场对聚偏氟乙烯/钛酸钡(PVDF/BaTiO3)复合材料进行原位非等温拉伸试验,研究了拉伸比及BaTiO3用量对PVDF/BaTiO3流延膜结晶结构和介电性能的影响。广角X射线衍射结果表明,PVDF/BaTiO3复合膜的取向程度明显大于纯PVDF。X射线小角衍射结果显示:对于纯PVDF,第二个散射峰的强度随拉伸的进行而不断提高,在拉伸比为1.5时,其强度明显超过第一个散射峰;加入BaTiO3后,第一个散射峰的强度比纯PVDF明显提高,而第二个散射峰的强度也随拉伸比的提高而增强。复合膜的组成相同时,其介电常数随拉伸比的提高而减小,而介电损耗随拉伸比的提高而增大。     

Boundary layer equations and stretching sheet solutions for the modified second grade fluid

A modified second grade non-Newtonian fluid model is considered. The model is a combination of power-law and second grade fluids in which the fluid may exhibit normal stresses, shear thinning or shear thickening behaviors. The equations of motion are derived for two dimensional incompressible flows. The boundary layer equations are derived from the equations. Symmetries of the boundary layer equations are calculated using Lie Group theory. For a special power law index of m = −1, the principal Lie algebra extends. Using one of the symmetries, the partial differential system is transferred to an ordinary differential system. The ordinary differential equations are numerically integrated for the stretching sheet boundary conditions. Effects of power-law index and second grade coefficient on the boundary layers are shown and solutions are contrasted with the usual second grade fluid solutions. The shear stress on the boundary is also calculated.     

扁丝及其编织品的几个工艺及设计问题探讨

本文讨论了扁丝生产几个工艺参数对扁丝性能的影响，并提出了扁丝及编织物的八个经验公式。     

MHD boundary-layer flow due to a moving extensible surface

The flow due to a moving extensible sheet that obeys a more general stretching law is considered. The sheet occupies the negative x-axis and is moving continually in the positive x-direction, in an incompressible viscous and electrically conducting fluid. The sheet somehow disappears in a sink that is located at (x, y) = (0, 0). The governing system of partial differential equations is first transformed into a system of ordinary differential equations, and the transformed equations are solved numerically using a finite-difference scheme, namely the Keller-box method. The features of the flow and heat-transfer characteristics for different values of the governing parameters are analyzed and discussed. It is found that dual solutions exist for the flow near x = 0, where the velocity profiles show a reversed flow.     

国产细纱机纺CJ 4.3 tex纱技术要点

为了在国产细纱机上顺利生产特细号纱,保证成纱质量,通过纺纱实践,总结出原料选配、设备状态及工艺配置方面的技术要求.指出纺制特细号纱要注意原料的选配,保证细纱机粗纱喂入部分、罗拉牵伸部分、牵伸轮系部分及锭子卷绕部分机械状态良好,细纱工序要合理配置罗拉隔距、钳口隔距、罗拉加压等工艺,加强牵伸过程中对纤维的控制,合理调整纺纱张力,减少断头.     

宽幅高速低雾度BOPP高收缩烟膜工艺研究

研究了宽幅高速双拉设备制取的BOPP高收缩烟膜在生产及储存过程中雾度的变化情况。对比分析拉伸倍率、拉伸温度、定型温度、横拉出口冷却温度对BOPP收缩膜雾度变化的影响,结果表明:在相同的配方条件下,采用低拉伸温度、高拉伸倍率、低定型温度、低冷却温度,可制得低雾度BOPP高收缩烟膜,且雾度不会随着时间推移而明显的增大。