Molecular dynamics simulation and energy minimization of O2 adsorbed on a graphite surface

Simulation studies of O₂ on graphite show that the quadrupole interaction strongly affects the orientational correlation between neighbouring molecules in the adsorbed solid. The energy minimization study shows two non-equivalent competing structures with nearest neighbours arranged parallel and at an angle of 60°. The precise value of the quadrupole moment stabilises one structure with respect to the other. For Θ = 0 the simulated structure agrees with experiment. For values of the quadrupole close to the experimental value there is a significant discrepancy between experiment and theory. This discrepancy can be understood in terms of the neglect of the magnetic forces arising from the exchange interaction. The best effective σ₀₀ is 5% higher than the value recommended by bulk solid studies. The minimum energy structure is incommensurate and molecules are aligned preferentially parallel to the surface at the coverage in this study.     

Inelastic electron tunneling spectroscopy of a model catalyst: CO on Rh/Al2O3

Using tunneling spectroscopy we have studied the preparation and behavior of dispersed rhodium model catalysts supported on alumina. Samples were prepared by vacuum evaporation from Rh metal or Rh₂O₃ sources onto an oxidized Al film and CO was adsorbed in-situ. The tunnel junctions were formed by adding a Pb top electrode and the vibrational spectra of the adsorbed species were measured. We observed qualitatively different spectra when the preparation procedure was varied. Special care was taken to monitor and control background gases. We obtained different results from Rh of Rh₂O₃ sources and the presence of oxygen or water affects the vibrational spectra of the adsorbed CO. We also study the effect of the Rh thickness on the spectral intensity. Other experiments were measurement of the superconducting tunneling spectra of the Pb and a TEM study of Rh particle size. Previously reported data from tunneling and IR measurements are compared with the present work. Based on these results, we conclude that there are two species present, either a linear Rh-CO or doubly (geminal) adsorbed Rh(CO)₂ depending upon the degree of dispersion and oxidation of the Rh. The evidence also indicates that in both instances a dispersed form of Rh, rather than relatively large Rh metal particles, is responsible for the observed spectra.     

不规则H形量子势垒增强AlGaN基深紫外发光二极管性能

针对AlGaN基多量子阱中有效的平衡载流子注入问题,研究了有源区势垒层中Al组分调制形成的非规则H形量子势垒对AlGaN基深紫外发光二极管(LED)器件性能的影响及载流子的输运行为。研究发现,与多量子阱中常用的单Al组分势垒相比,加入Al组分较高的双尖峰势垒可以有效地提高内量子效率和光输出功率。进一步研究表明,电子在有源区因凸起的尖峰势垒而得到了有效的阻挡,减少了电子的泄露,而空穴获得更多的动能从而穿过较高的势垒进入有源区。因此,采用非对称H形量子势垒的深紫外LED器件中载流子输运实现了较好的平衡,量子阱中的载流子复合速率远高于普通的深紫外发光二极管。     

Facile route to high-density, ordered ZnO nanowire arrays and their photoluminescence properties

A simple template-directed wet chemistry route based on traditional thermal decomposition technique has been developed for the preparation of high-density, ordered ZnO nanowire arrays. The fabrication was performed at relative low temperature without involving complex procedures, sophisticated equipment and rigorous experiment conditions, thereby providing a straightforward and mild method to produce metal/metal oxide ordered nanostructures. The nanowire array system was evaluated by SEM, XRD, TEM and PL. A stable luminescence at 425 nm was present.     

高效毛细管电泳法测定全天麻胶囊中天麻素的含量

建立了利用毛细管电泳技术测定全天麻胶囊中天麻素含量的新方法.所用熔融石英毛细管规格为50μm×60cm(有效长度为45cm),检测波长为220nm,分离电压为12kV,缓冲液为pH7.6的200mmol/L硼酸缓冲溶液.结果表明,天麻素在10-800μg/mL范围内线性关系良好(r=0.9995),加样回收率为98.5...     

Anisotropic charge transport in flavonoids as organic semiconductors

A quantum mechanical approach has been used to investigate on the potential for using two naturally occurring flavonoids: quercetin and luteolin as candidates for organic semiconductor. Selection of flavonoids enables to evaluate the effects of hydroxyl group structural features. The relationship between molecular packing and charge transport in flavonoids is presented. The calculated results indicate that quercetin should be an ideal candidate as high-performance p-type organic semiconductor material, while luteolin is predicted as n-type organic semiconductor material. The predicted maximum electron mobility value of quercetin is 0.075 cm² V^?1 s^?1, which appears at the orientation angle near 91°/271° of conducting channel on the reference planes b–c. Theoretical investigation of natural semiconductors is helpful for designing higher performance electronic materials used in biochemical and industrial field to replace expensive and rare organic materials.     

Risk estimation of infectious diseases determines the effectiveness of the control strategy

Usually, whether to take vaccination or not is a voluntary decision, which is determined by many factors, from societal factors (such as religious belief and human rights) to individual preferences (including psychology and altruism). Facing the outbreaks of infectious diseases, different people often have different estimations on the risk of infectious diseases. So, some persons are willing to vaccinate, but other persons are willing to take risks. In this paper, we establish two different risk assessment systems using the technique of dynamic programming, and then compare the effects of the two different systems on the prevention of diseases on complex networks. One is that the perceived probability of being infected for each individual is the same (uniform case). The other is that the perceived probability of being infected is positively correlated to individual degrees (preferential case). We show that these two risk assessment systems can yield completely different results, such as, the effectiveness of controlling diseases, the time evolution of the number of infections, and so on.     

盐酸硫胺催化合成乙酰苯胺的新工艺

盐酸硫胺俗称VB1在回流条件下催化乙酰苯胺的合成,反应收率高,副反应少,后处理简单,是一种绿色合成的新工艺.本文研究了该反应的影响因素,结果表明其最佳的反应条件是:苯胺和乙酸的物质的量比为1∶2,带水剂甲苯3mL,催化剂用量占反应物料总量的2 mol％,反应时间为2h,乙酰苯胺收率可达89％.