微制造技术与仿生壁虎腿

壁虎甚至在真空中都可以在垂直光滑的玻璃墙壁上纹丝不动和爬行,显然,这不可能是摩擦力和真空吸力所致,它不分泌任何液体,也不可能是通常的粘合剂作用。对壁虎脚足刚毛吸力的精确测定表明,壁虎腿与物体表面的吸力完全是范德华力相互作用。本文详细介绍了有关壁虎腿仿生研究的最新进展和可能的制备壁虎胶带的微制造方法。     

聚合物流体的范德华凝聚行为

研究了由聚合物的范德华作用导致的凝聚行为. 研究发现, 尽管聚合物同小分子的相行为的形成原因不同(聚合物体系的相行为是由动能、构象熵项和范德华作用能三项相互竞争的结果, 而小分子的相行为是由动能和范德华作用能相互竞争的结果), 但是它们表现出了极为相似的相行为.     

Analysis of humidity-dependent adhesion between a probe tip and a surface

Adhesive forces commonly exhibit a monotonic increase or a maximum with increasing relative humidity. However, anomalous behavior has been reported. Here, a numerical model of adhesive forces, comprised mainly of capillary and van der Waals forces, between a tip and a surface is established. It is described by a power law that considers the geometry, the liquid bridge wetting radius, the contact angle, and the separation distance. Capillary forces (sum of surface tension and Laplace pressure) and van der Waals forces are calculated. The latter cannot be neglected in the adhesion even at high humidity. Decrease in adhesion with increasing relative humidity can be attributed to a blunt tip shape, which is validated by experimental data. Specifically, the decrease in adhesion is attributed primarily to a transition from a rounded to a blunt tip shape. Structuring objects at the micro- or nanoscale can either increase or decrease adhesion as a function of relative humidity. This has a wide range of applications in robotic manipulation and can provide a better understanding of adhesion mechanisms in atomic force microscopy in ambient air.     

Information Geometry in Roegenian Economics

We characterise the geometry of the statistical Roegenian manifold that arises from the equilibrium distribution of an income of noninteracting identical economic actors. The main results for ideal income are included in three subsections: partition function in distribution, scalar curvature, and geodesics. Although this system displays no phase transition, its analysis provides an enlightening contrast with the results of Van der Waals Income in Roegenian Economics, where we shall examine the geometry of the economic Van der Waals income, which does exhibit a “monetary policy as liquidity—income” transition. Here we focus on three subsections: canonical partition function, economic limit, and information geometry of the economic Van der Waals manifold.     

DEM simulation of soil-tool interaction under extraterrestrial environmental effects

In contrast to terrestrial environment, the harsh lunar environment conditions include lower gravity acceleration, ultra-high vacuum and high (low) temperature in the daytime (night-time). This paper focuses on the effects of those mentioned features on soil cutting tests, a simplified excavation test, to reduce the risk of lunar excavation missions. Soil behavior and blade performance were analyzed under different environmental conditions. The results show that: (1) the cutting resistance and the energy consumption increase linearly with the gravity. The bending moment has a bigger increasing rate in low gravity fields due to a decreasing moment arm; (2) the cutting resistance, energy consumption and bending moment increase significantly because of the raised soil strength on the lunar environment, especially in low gravity fields. Under the lunar environment, the proportions of cutting resistance, bending moment and energy consumption due to the effect of the van der Waals forces are significant. Thus, they should be taken into consideration when planning excavations on the Moon. Therefore, considering that the maximum frictional force between the excavator and the lunar surface is proportional to the gravity acceleration, the same excavator that works efficiently on the Earth may not be able to work properly on the Moon.     

La_(2-x)Sr_xCuO_4准二维体系的反常同位素效应

本文针对La_(2-x)Sr_xCuO_4的Cu-O面准二维体系给出了一个简单的物理掺杂模型。利用BCS理论弱耦合框架下的Van Hove奇点模型进行了掺杂量x与同位素效应指数α之间关系的计算,发现能与实验基本一致。     

二维体系的超导转变温度

如何解释氧化物超导体的高 T_c,是目前高温超导研究的主要任务之一。由于所发现的氧化物超导体具有二维的结构特征,态密度的 Van Hove 奇异性的作用又重新引起注意。本文较为严格地求解了决定 T_c 的积分方程,结果表明态密度的 Van Hove奇异性虽然可以提高 T_c,但并不如人们所估计的那么显著。     

The mass transfer kinetics in columns packed with Halo-ES shell particles

The average mesopore size of the new Halo-ES-Peptide shell particles is 160 ?, markedly larger than that of the classical Halo shell particles (90 ?). We found that this change causes a considerable decrease of the film mass transfer resistance measured for columns packed with these particles. We analyze data obtained by systematic measurements of the C term of the van Deemter equation for the peptide β-lipotropin (MW = 769 Da), the protein insulin (MW = 5800 Da), and a series of non-retained polystyrene standards (MW = 6400 and 13,200). The improvement in column performance is explained by an increase of the fraction of the external surface area of the shell that allows the entrance of the sample molecules inside the particle. The fraction of the shell surface accessible to a probe controls the rate of its external film mass transfer, i.e. its rate of transfer between the interstitial and the stagnant eluent. Although measurable, the increase in sample diffusivity through the porous shells does not account for the better performance of Halo-ES-peptide columns. Furthermore, the analysis of the HETPs data of small molecules (uracil, acetophenone, toluene, and naphthalene, MW< 150) reveals that the eddy diffusion (A) term of these new columns is 25% lower than that of the classical Halo columns. This result is consistent with the impact of intra-particle diffusivity on the eddy diffusion mechanism in packed columns. As shell diffusivity increases, so does the rate of transfer of sample molecules between the eluent stream-paths flowing through the packed particles and across the column diameter. Dispersion through short-range inter-channel and trans-column eddies is reduced.     

A Van Kampen theorem for π2

If the path connected topological space X has a countable open cover $\text{U}$ with path connected elements, then π₂(X,1) is computed as a colimit determined by the second homotopy groups of the intersection of elements of $\text{U}$ and the indices of the fundamental group injections of these intersections into the fundamental group of X. Aside from assuming that the inclusions induce such monomorphisms, certain other inclusions are also required to induce monomorphisms of fundamental groups and restrictions are placed on the arrangement of the elements of $\text{U}$.