碳/环氧复合材料的冲击拉伸

该文研究了T300碳纤维单向增强的环氧复合材料,在应变率从10~(-3)/s到10~3/s范围内的冲击拉伸行为.通过对实验数据进行拟合,得出该范围内材料对应变率具有弱的敏感性,表现在破坏强度及破坏应变随应变率增加不显著变化,平均模量几乎不受应变率的影响.分析了试件的几何尺寸效应,讨论了应力波作用对破坏形态的影响以及实验中观察到的拔出现象.从应变率在10~2～10~3/s附近材料行为某些非确定性,指出在更宽范围内了解其性能的必要性.     

横向联邦学习中PCA差分隐私数据发布算法

为了让不同组织在保护本地敏感数据和降维后发布数据隐私的前提下,联合使用PCA进行降维和数据发布,提出横向联邦PCA差分隐私数据发布算法。引入随机种子联合协商方案,在各站点之间以较少通信代价生成相同随机噪声矩阵。提出本地噪声均分方案,将均分噪声加在本地协方差矩阵上。一方面,保护本地数据隐私;另一方面,减少了噪声添加量,并且达到与中心化差分隐私PCA算法相同的噪声水平。理论分析表明,该算法满足差分隐私,保证了本地数据和发布数据的隐私性,较同类算法噪声添加量降低。实验从隐私性和可用性角度评估该算法,证明该算法与同类算法相比具有更高的可用性。     

海域双排钢板桩围堰与明挖基坑变形特性分析

以深圳海滨大道一期Ａ段海底隧道工程为背景,针对海域环境双排钢板桩围堰与明挖基坑在施工过程中的变形控制难题,利用ＰＬＡＸＩＳ数值模拟软件建立有限元模型,通过建立有限元模型,系统的研究了海域双排钢板桩围堰与明挖基坑变形特性及相互影响规律,分析了围堰与基坑距离、基坑内支撑形式及基坑开挖步序等因素对钢板桩围堰变形的影响作用。研究结果表明:基坑开挖将造成围堰较大的水平位移;地连墙最大变形出现在墙体中下部;减小施工平台宽度和增大基坑内支撑刚度等方式可以有效减小钢板桩围堰变形。研究成果可以为类似工程的钢板桩围堰与明挖基坑设计提供参考依据。     

Finite-size effects in surface tension: Thermodynamics and the Gaussian interface model

It has been suggested by Kayser that finite-size effects associated with capillary waves might play a significant role in some surface tension measurements; for capillary rise between plates a distance D apart, an effect varying as 1/D and apparently observable in measurements, was proposed. In reconsidering this problem, one must analyze the thermodynamics of finite-size corrections to surface tension. In particular, one sees that capillary rise between plates does not measure the interfacial free energy density but, rather, a derivative of the interfacial free energy with respect to a system dimension. The quantity needed to draw definite conclusions, the finite-size residual free energy, can be calculated within the harmonic or Gaussian capillary wave model in d spatial dimensions with the aid of Poisson summation techniques and should yield the correct leading asymptotic behavior. For d=3 and experimentally relevant parameter values, the results are independent of the short-wavelength cutoff needed in the model and can be checked against the theory of conformai covariance at two-dimensional critical points. It is found that the finite-size effects in capillary-rise measurements of surface tension vary as 1/D ² (with a universal coefficient) but are too small to be seen in current experiments.Invited paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

A generalized equation for surface tension from the triple point to the critical point

A three-parameter generalized equation is proposed for surface tension from the triple point to the critical point. This equation not only fits the data well but also is good for interpolation between the normal boiling point and the critical point. This equation is also good for extrapolation to the triple point. This equation has been tested using the surface tension of water from the triple point to the critical point. The constants of this equation obtained using orthobaric surface tensions are given for a number of compounds. The isobaric surface tensions determined at a pressure of 1 atm do not differ significantly from the orthobaric surface tensions. Such data also have been used in obtaining equations from the triple to the critical point.Nomenclature T _c Critical temperature, K - T _t Triple point, K - T _m Melting point, K - T _r Reduced temperature, K - X (T _c-T)/T _c - Surface tension, dyne · cm^–1;10^–3N · m^–1 - _m Surface tension at the melting point - _f Surface tension at T _r=0.9 - _t Surface tension at the triple point - Relative deviation 100[ _obsd– _calcd]/ _obsd - Standard deviation [( _obsd– _calcd)²/(No. points—No. parameters)]^0.5     

A relation between interfacial and bulk properties along the saturation curve

A liquid-vapor interface in thermal equilibrium was considered, where the pressure tensor depends upon the density (z) and the position z. The surface tension coefficient results are parametrized with the bulk compressibility, liquid-vapor density difference, and interfacial width along the saturation curve. Previous results at the triple and critical points reported by other investigators are verified. Also included is a plot of the computed results using the parametric equation and experimental data for different substances.     

Thermophysical properties data on molten semiconductors

Thermophysical properties of molten semiconductors are reviewed. Published data for viscosity, thermal conductivity, surface tension, and other properties are presented. Several measurement methods often used for molten semiconductors are described. Recommended values of thermophysical properties are tabulated for Si, Ge, GaAs, InP, InSb, GaSb, and other compounds. This review shows that further measurements of thermophysical properties of GaAs and InP in the molten state are required. It is also indicated that a very limited amount of data on emissivity is available. Space experiments relating to thermophysical property measurements are described briefly.Nomenclature Density - C _p Specific heat - Kinematic viscosity - Dynamic viscosity= - Thermal diffusivity - Thermal conductivity=C_p - Volumetric thermal expansion coefficient - Surface tension - d/dT Temperature coefficient of surface tension - g Gravitational acceleration - T Temperature - T Temperature difference - L Characteristic dimension     

Surface and Biocidal Properties of Gemini Cationic Surfactants Based on Propoxylated 1,6-Diaminohexane and Alkyl Bromides

Two new classes of gemini cationic surfactants—hexanediyl-1,6-bis[(isopropylol) alkylammonium] dibromide {in the abbreviation form: C_nC₆C_n[iPr-OH] and C_nC₆C_n[iPr-OH]₂; alkyl: C_nH_{2n + 1} with n = 9, 10, 12 and 14}—have been synthesized by interaction of alkyl bromides with N,N′-di-(isopropylol)-1,6-diaminohexane and N,N,N′,N′-tetra-(isopropylol)-1,6-diaminohexane. The surface tension, electrical conductivity, and dynamic light scattering (DLS) techniques were used to investigate the aggregation properties of the gemini cationic surfactants in aqueous solution. The formation of critical aggregates at two concentrations in an aqueous solution from obtained gemini cationic surfactants were determined via the tensiometric method. Thus, these gemini cationic surfactants start to form aggregates at concentrations well below their critical micelle concentrations (CMC). The surface properties and the binding degree (β) of the opposite ion were tested against the length of the surfactant hydrocarbon chain and the number of the isopropylol groups in the head group. By applying the DLS technique, it was explored that how the number of isopropylol groups in gemini cationic surfactants with C₁₂H₂₅ chain affects the sizes of micelles at concentrations greater than CMC. It was discovered that the obtained gemini cationic surfactants have a biocidal character.     

Synthesis,Micellization, and Surface Activity of Novel Linear-Dendritic Carboxylate Surfactants

Two generations of novel linear-dendritic carboxylate surfactants C₁₈-G₁-(COONa)₂ and C₁₈-G₂-(COONa)₄ have been synthesized by the divergent method and their structures are characterized by ¹H Nuclear Magnetic Resonance and Infrared analysis. The electrical conductivity measurement is used to measure the Krafft temperatures of C₁₈-G₁-(COONa)₂ and C₁₈-G₂-(COONa)₄, which are much smaller than those of the corresponding conventional surfactant sodium stearate. The markedly enhanced solubility of two linear-dendritic surfactants is ascribed to the high hydrophilicity of surfactant headgroups induced by the carboxylate and ester groups. The critical micelle concentration (CMC) values obtained from both the electrical conductivity and surface tension measurements indicate that the micellizations of linear-dendritic surfactants become favorable with the increase in the number of the surfactant headgroup. However, the surface activity parameters including the surface tension at the CMC, maximum surface excess, and minimum surface area reveal that C₁₈-G₁-(COONa)₂ exhibits greater efficiency in absorbing at the air/water interface compared to C₁₈-G₂-(COONa)₄, owing to their different steric repulsions of the surfactant headgroups. In addition, C₁₈-G₁-(COONa)₂ and C₁₈-G₂-(COONa)₄ have higher emulsifying ability than the conventional surfactants sodium stearate and sodium octadecyl sulfate.     

有机涂层钢板生产线主要工艺

介绍了有机涂层钢板生产线上钢基板的预处理,全线张力控制,纠偏装置的布置,固化炉的选型.