分层码率控制策略在机器人遥操作中的应用

为实现卫星自维护遥操作系统中稳定可靠的视频反馈目标,提出一种基于分层码率控制的视频传输策略.利用实时探测到的带宽选择不同码率的视频流分层,使得视频传输对于不同的网络带宽具有自适应性.试验结果表明,该策略能够在波动带宽下给予遥操作者稳定流畅的视频反馈,有效地提高了遥操作系统的视觉临场感性能.     

一种多元复合地基复合模量的计算方法

多元复合地基的沉降计算依赖于其复合模量的取值.目前多元复合地基复合模量计算均未考虑桩对桩间土的侧向挤密作用,因而其沉降计算结果与实际值相差较大.而考虑桩体与桩间土的侧向挤压作用,依据线弹性变形理论,推求的多元复合地基的复合模量公式应用于工程实例,结果表明,该方法是合理可行的,并且存在着参数易于确定、方法简便、机理清楚的特点.     

地质雷达和瑞雷波检测公路工程质量技术研究

地球物理方法的应用,使公路工程质量检测技术变得更加简捷、高效和经济,能够有效缓解当前路况检测和公路工程维护所面临的压力.在介绍了地质雷达和瑞雷波探测法的基本工作原理的基础上,将这2种探测技术应用在公路工程质量检测中,详细介绍了它们对公路厚度、压实度、抗压强度、弯沉值、含水量、脱空区段等检测的具体实施方法和步骤,并指出了相关注意事项.分析认为,随着技术的更新和设备的完善,地质雷达和瑞雷波技术能够有效地应用到公路工程的质量检测过程中,有着很好的应用前景和推广价值.     

Research on the friction and wear mechanism of Poly(vinyl alcohol)/hydroxylapatite composite hydrogel

Poly(vinyl alcohol)/Hydroxylapatite (PVA/HA) composite hydrogel was prepared with poly(vinyl alcohol) and hydroxylapatite as raw materials, using the method of repeated freezing and thawing. The morphologies of PVA/HA composite hydrogel were observed by means of high-accuracy 3D profiler and scanning electron microscope (SEM). The compressive elastic modulus and the stress relaxation characteristics of PVA/HA composite hydrogel were measured using the flat-head cylinder indenter. The friction and wear tests between PVA/HA composite hydrogel and bovine knee articular cartilage were performed on the micro-tribometer. The worn morphologies of PVA/HA composite hydrogel were observed with environmental scanning electron microscope (ESEM). The results showed that PVA/HA composite hydrogel has the cross-link network microstructure which is similar to that of the natural bovine knee articular cartilages. With the increase of freezing-thawing cycles and the HA content, the degree of cross-link and the crystallization of PVA/HA composite hydrogel both increase, the elastic modulus increases evidently, the rate of stress relaxation is improved and the value of balance stress decreases. The friction coefficient decreases with the increase of the freezing-thawing cycles and the HA content. The more the freezing-thawing cycles are, the earlier the friction coefficient reaches the stable balance value. The friction deformation depth between PVA/HA composite hydrogel and bovine knee articular cartilage is inversely proportional to freezing-thawing cycles and the HA content. The main wear mechanisms of PVA/HA composite hydrogel are plastic flowing and adhesive flaking. The wear severity degree decreases with the increase of freezing-thawing cycles and the HA content. Supported by Key Program of the National Natural Science Foundation of China (Grant No. 50535050), Program for New Century Excellent Talents in University (Grant No. NCET-06-0479) and Natural Science Foundation of Jiangsu Province (Grant No. BK2005403)     

无机纳米-聚酰亚胺复合薄膜介电性研究

测试了纳米Al2O3-聚酰亚胺(PI)复合薄膜和纳米SiO2-聚酰亚胺复合薄膜的介电常数、介质损耗角正切和电导电流特性.结果表明,随着无机物含量的增加,两种复合薄膜的相对介电常数和介质损耗角正切增大,电老化阈值减小;无机物含量相同时,Al2O3-聚酰亚胺复合薄膜的相对介电常数和介质损耗角正切比SiO2-聚酰亚胺复合薄膜大,电导电流大,电老化阈值小.     

聚丙烯/弹性体复合材料的性能研究

通过共混改性的方法制备了PP/EPDM复合材料。然后对复合材料的性能进行分析,研究了EPDM的含量对复合材料的拉伸强度、冲击强度、维卡软化温度以及流动性等方面的影响规律,并对此影响规律进行合理的解释。     

石油勘探电磁层析成像在复杂岩层的应用仿真

对石油岩层进行勘探时,是通过电磁波形成稳定图像,对石油岩层进行勘探.由于石油区域的岩层结构密集和稀松部分分布不均匀,电磁层析成像在分布不均匀的岩石结构中,电磁波回波过程发生不定衰减,导致电磁析图像发生局部变异.传统的石油勘探电磁层析成像技术在图像局部变异下,会严重影响后期的成像效果,成像信息失真明显.提出采用加权小波分析的石油勘探中电磁层析成像复杂结构声波过滤方法.用非线性方程描述所有的石油勘探中电磁层析成像结构声波,选取一组成像信号作为样本数据,计算成像信号的权重,获取所有成像信号在声波过滤过程中的重要程度.针对上述结果进行小波变换处理,完成成像信号的分解,将所有的因子进行重构,实现声波过滤.实验结果表明,利用改进算法进行石油勘探中电磁层析成像复杂结构声波过滤,能够极大的提高过滤准确性,得到清晰的成像信号.     

Milled fibre reinforced epoxy resin — an engineering polymer composite

A milled fibre reinforced epoxy resin composite (MFRE) has been developed for low temperature use. It is resistant to fracture at temperatures down to at least 77 K in direct contact with liquefied gases. It can be used as an adhesive, a gap-filling mastic or a moulding compound for difficult cryogenic applications. The characteristics of the material and some applications are described.     

On the oxidation kinetics and mechanisms of various SiC-coated carbon-carbon composites

SiC coatings on the surface of C-C were produced by either silicone resin impregnation/ pyrolysis or reaction sintering. Cycles of resin impregnation/pyrolysis produced an SiC coating, on the walls of fine open pores, which was effective in reducing the oxidation rate of C-C and in shifting the transition temperature to a higher value. Unless it is pre-coated with a pyrocarbon layer before sintering, plain reaction sintered SiC has oxidation behaviors similar to those of the above-mentioned SiC. The dense pyrocarbon film deposition on the surface of C-C could form a better SiC film than others. The carbon film homogenized the surface of C-C and a dense SiC film was established. The oxidation of the coated C-C can be modelled by a set of “oxidation resistors” in series and/or in parallel, with each resistor corresponding to an oxidation element. The controlling mechanism can be resolved from the activation energy. A combined resistant layer, consisting of resin impregnation, pyrocarbon film and reaction sintering SiC, showed the best oxidation resistance of any single-layer coated C-C composite.     

Thermal expansion of an SiC particle-reinforced aluminum composite

Using a push-rod dilatometer, we measured between 76 and 390 K the thermal expansion of a particle-reinforced-composite wrought plate obtained by powdermetallurgy methods. The particles, 30% by volume, consisted of monocrystals of -SiC with sizes near 10 m. The matrix consisted of a 6061 aluminum alloy with original particle sizes near 20 m. We found the perpendicular thermal expansivity, ₃, higher by 26% than the in-plane thermal expansivity, ₁-₂. These values differ from a rule-of-mixture prediction by –3 and –23%, respectively. All three _i, components lie outside the Rosen-Hashin bounds. Levin's isotropic model agrees within 10% with the ₁-₂-₃ average. Both the anisotropy and the bounds violation result from microstructural nonhomogeneity arising from processing. Rosen and Hashin's transverse-isotropicsymmetry relationships account approximately for these effects by introducing the anisotropic elastic constants. Using neutron diffraction, we determined that the SiC particles are textureless.Paper presented at the Tenth International Thermal Expansion Symposium, June 6–7, 1989, Boulder, Colorado, U.S.A.