DNA molecular configurations in flows near adsorbing and nonadsorbing surfaces

We investigate experimentally -phage and T2-coliphage DNA molecules near both non-adsorbing glass and adsorbing 3-aminopropyltriethoxysilane (APTES)-coated glass surfaces in a simple steady shearing flow generated by a torsional flow cell. The DNA molecular deformations near the surface are found to be considerably weaker than in bulk flow at the same shear rate. This affects the DNA molecules deposition and stretching on the adsorbing surface. Surprisingly, for a simple shearing flow in the torsional shearing device, the observed stretch, for molecules both near (<10 µm) the surface and adsorbed to it, is much less than predicted by simulations.     

拉压性能不同材料全量型本构关系及厚壁筒的应力分析

将经典全量理论作了推广，考虑了应力状态及塑性体积变形对拉压性能不同材料的塑性行为的影响。应用该本构模型分别计算了厚壁筒在内压和外压作用下的应力分布。给出了径向应力、环向应力和轴向应力沿壁厚的分布图。将本文的计算解与拉压性能相同(不考虑体积变形、强化曲线唯一)的幂函数强化材料的厚壁筒的理论解进行了比较。结果表明，材料的拉压性能不同对厚壁筒的环向应力和轴向应力影响较大。因此，对于拉压性能不同材料，考虑到其对应力状态及塑性体积变形敏感时，是不能将其简化成拉压性能相同、体积不可压缩、强化曲线唯一的理想材料。     

Three-dimensional micromechanical modeling of voided polymeric materials

A three-dimensional micromechanical unit cell model for particle-filled materials is presented. The cell model is based on a Voronoi tessellation of particles arranged on a body-centered cubic (BCC) array. The three-dimensionality of the present cell model enables the study of several deformation modes, including uniaxial, plane strain and simple shear deformations, as well as arbitrary principal stress states.The unit cell model is applied to studies on the micromechanical and macromechanical behavior of rubber-toughened polycarbonate. Different load cases are examined, including plane strain deformation, simple shear deformation and principal stress states. For a constant macroscopic strain rate, the different load cases show that the macroscopic flow strength of the blend decreases with an increase in void volume fraction, as expected. The main mechanism for plastic deformation is broad shear banding across inter-particle ligaments. The distributed nature of plastic straining acts to reduce the amount of macroscopic strain softening in the blend as the initial void volume fraction is increased. In the case of plane strain deformation, the plastic flow is observed to initiate across inter-particle ligaments in the direction of constraint. This particular mode of deformation could not have been captured using a two-dimensional, plane strain idealization of cylindrical voids in a matrix.The potential for localized crazing and/or cavitation in the matrix is addressed. It is observed that the introduction of voids acts to relieve hydrostatic stress in the matrix material, compared to the homopolymer. It is also seen that the predicted peak hydrostatic stress in the matrix is higher under plane strain deformation than under triaxial tension (with equal lateral stresses), for the same macroscopic stress triaxiality.The effect of void volume fraction on the macroscopic uniaxial tension behavior of the different blends is examined using a Considère construction for dilatant materials. The natural draw ratio was predicted to decrease with an increase in void volume fraction.     

4106航空润滑油拖动特性研究

采用高速球-盘式拖动力试验装置测定了4106航空润滑油在不同载荷、滚动速度、入口油温及滑滚比下的拖动系数,分析了润滑油的拖动特性,建立了拖动系数的简单计算公式.结果表明:4106航空润滑油的拖动系数随着载荷变化出现转折;在高速和高压条件下,4106航空润滑油呈现非牛顿特性;当入口油温较低时润滑油的热效应较显著;随着载荷增大,入口油温和滚动速度对拖动系数的影响减小;理论计算结果同实测值吻合良好.     

On the functional form of non-local elasticity kernels

The functional form of non-local elasticity kernels is studied within the context of the integral formalism. The study is limited to linear isotropic elasticity. The kernels are derived analytically based on the discrete structure of the material at the atomic scale. Atomistic simulations are used to validate the results. Materials in which the interatomic interactions are represented by pair, as well as embedded atom-type potentials are considered. The derived kernels have a range which extends up to the cut-off radius of the interatomic potential, are positive at the origin, and become negative approximately one atomic distance away, thus departing from the commonly assumed Gaussian functional form. The functional form of the potential and the radial distribution function of interacting neighbors about a representative atom fully define their shape. This new continuum model involves two material length scales that are both derived from atomistics for a Morse solid and for Al. Two applications are considered in closure. It is shown that in strained superlattices, the non-local model predicts maximum stresses that are much larger than those obtained within the local theory. This observation has implications for defect nucleation in these structures. Furthermore, the new non-local model improves upon the Gaussian one by predicting a more realistic wave dispersion relationship, with essentially zero group velocity at the boundary of the Brillouin zone.     

阳极结构调整对稀土电解槽的影响

以目前使用的6 k A稀土电解槽为研究对象,采用实验验证与数值模拟计算相结合的方式对采用不同阳极结构的稀土电解槽进行了全面分析讨论。使用斜角切割阳极片可以在维持电解槽槽电压、氧化物利用率、产品合格率等技术指标不变的情况下,克服传统正交切割阳极片在使用过程中随着阳极片反应消耗造成电流效率降低及缩短石墨坩埚使用寿命的现象。其可作为稀土电解槽工艺改造的一个发展方向。     

搅拌速率对β-PbO_2-CeO_2-ZrO_2复合电极材料电化学性能的影响

为了提高三价铬镀铬工艺中阳极材料的性能,采用阳极氧化法制备了掺杂纳米颗粒的β-Pb O2-Ce O2-Zr O2复合电极材料。通过扫描电化学显微镜和析氧极化曲线的测量,考察了不同搅拌速率条件下制备的复合电极材料在硫酸盐体系三价铬镀液中的电催化活性,利用塔菲尔曲线考察了复合电极材料的耐蚀性,并辅以扫描电镜表征了电极材料的微观形貌。结果表明:当施镀搅拌速率为350 r·min-1时,所制备的复合电极材料具有结构致密、电催化活性高、耐蚀性强等特点。