Structure of ultra-thin confined alkane films from Monte Carlo simulations

Grand canonical Monte Carlo simulations are reported of thin films of n-alkane confined fluids (1,4, 10 carbons) and i-decane under thermodynamic conditions away from the freezing line. All simulated solvation pressure profiles exhibit damped oscillations with a main period of oscillation equal roughly to the size of a methane, methyl or methylene bead (4-4.5 Å). This reflects an arrangement of the beads in layers parallel with the confining walls, which causes an oscillation of the local density across the film. However, the alkane molecules themselves are not arranged in perfect layers. The oscillations do not vanish for long chain and/or branched molecules: they are only attenuated. Also n-decane films have been simulated under thermodynamic conditions closer to surface force apparatus experiments. In contrast with an earlier molecular dynamics study, an overall continuous variation in the average number of decane molecules with the walls separation was found, consistent with the smooth transition towards slower relaxation and increasing rigidity with decreasing film thickness observed in some experiments. The possible origin of the discrepancy between the different simulation findings is discussed.     

镧助剂对模拟生物沼气重整制备合成气中Ni/SBA-15催化剂结构和性能的影响

以介孔分子筛SBA-15为载体, 采用浸渍法制备了镍质量分数(w)为12.5%, 并且分别添加质量分数(w)为2.5%的镧、铈、镁、钙、锶等助剂的系列Ni基催化剂. 以CH4/CO2体积比为2:1的模拟生物沼气和适量氧气作为原料气, 在常压固定床反应器上评价了催化剂对模拟生物沼气重整制合成气的反应性能. 采用X射线粉末衍射(XRD)、N2吸附/脱附、透射电子显微镜(TEM)、X射线光电子能谱(XPS)及H2程序升温还原(H2-TPR)等对催化剂的结构进行了表征. 催化活性评价显示, 添加镧助剂的2.5%La/12.5%Ni/SBA-15催化剂比添加铈、镁、钙、锶等助剂的催化剂具有更高的催化活性, 并且具有很好的稳定性. 因此, 文中着重研究了镧助剂对催化剂结构和模拟生物沼气重整制合成气的反应性能的影响. 结果表明, 镧能明显提高Ni/SBA-15催化剂的表面镍含量, 同时还具有很好的抗积炭作用, 在850 ℃的温度下反应820 h没有发现积炭生成, 这些可能是提高催化剂性能和稳定性的重要因素.     

Fixed and Minimal Order Compensators

Given a time-invariant linear plant, the authors consider aminimal (or fixed) order compensator such that the (unity feedback)closed loop is stable with respect to a given region in thecomplex plane. The so-called critical constraint is used tofind points in the (parameter space) stability region. Thisenables some practical constraints to be added in the compensatordesign.     

Root-Clustering Criteria (I): The Composite-Matrix Approach

In a series of articles we investigate different approachesto root clustering criteria. In particular, given A C^nxn andan algebraic region A C, we are looking for a criterion (asingle set of inequalities) ensuring the inclusion (A) A. Here,in the first article, we collect previous ideas on transformableregions and composite matrices, state new results, and correctand refine others.     

Entropy driven demixing in binary mixtures of hard convex bodies: influence of molecular geometry

The recently introduced approach (Bosetti, H., and Perera, A., 2001, Phys. Rev. E, 63, 021206) for studying entropy driven demixing in binary mixtures of hard convex bodies is applied here to analyse the influence of molecular geometrical factors such as shape and size ratio on isotropic fluid-fluid phase separation. The theory is shown to be self-consistent, in the sense that it allows the calculation of both the binodal and the spinodal of the demixing, and both curves merge at the same lower consolute point. In the case of 3-dimensional fluids, demixing is usually allowed for sufficiently thick solutes, provided no orientational ordering destabilizes the mixture. Fluid—fluid demixing is explicitly forbidden in cases of equal breadth of the solute and the solvent molecules, regardless of the aspect ratio of both particles. In particular, mixtures of prolate and oblate particles will demix more easily. The influence of shape is more importantly seen at moderate elongations. Finally, within the present approximation, demixing is forbidden for binary mixtures of 2-dimensional fluids, irrespective of the shape of the bidimensional molecules.