Variational inequality model for the simulation of gas transmission networks

The steady-state simulation of a gas transmission network involves the solution of a system of nonlinear algebraic equations subject to a set of inequality constraints. The purpose of this paper is to consider how the problem can be cast into a variational inequality framework using the dual extremum principles described by Noble and Sewell in 1972. The reliability of the model is tested on two networks supplied by the British Gas Corporation.     

基于首要教学原理的化学实验微课设计

基于首要教学原理,以聚焦问题为原则,展示了碘量法测定维生素C含量的微课中激活旧知—示证新知—尝试应用—融会贯通4个模块化的设计过程,并探讨了微课的教学评价及存在的问题。     

Interactions between hydrogenated diamond surface and adsorbates with different concentration of NO2 molecules: A first‐principles study

To elucidate the effects of NO₂ and H₂O molecules on the surface conductivity of hydrogenated diamond film, models of various adsorbates containing different molecular ratio of NO₂ and H₂O on hydrogenated diamond (100) surfaces were constructed. The adsorption energies, equilibrium geometries of adsorbates, density of states, and atomic Mulliken populations were studied by using first‐principles method. The results showed that H₂O molecule in the adsorbate could weaken the interactions between the adsorbates and hydrogenated diamond surface significantly. Compared with H₂O molecule, NO₂ molecule relaxes more dramatically when adsorbed on hydrogenated diamond surface. In addition, density of states for C(100):H–2NO₂, C(100):H–NO₂, and C(100):H–NO₂ + H₂O systems are very similar to each other, which indicates an obvious peak at valence band maximum level for all the three samples. It can be attributed to mainly single occupied molecule orbital of NO₂ molecule and slightly C–H bond of C(100):H substrate. When the adsorbates contain one NO₂ and two H₂O molecules, the peak shifts slightly into valence band, but its intensity increases significantly. All the samples exhibit p‐type surface conductivity when adsorbed with pure NO₂ molecules, and the surface conductivity remains as H₂O molecules added into the NO₂ adsorbate layer. However, for oxygenated diamond surface, very week interactions generate between diamond surface and various adsorbates. All the oxygenated diamond (100) surfaces with various adsorbates containing different NO₂ and H₂O molecules on it exhibit an insulating property.     

Water adsorption on the surface of Ni‐ and Co‐based layer‐structured cathode materials for lithium‐ion batteries

Ni‐based layer‐structured cathode materials are more vulnerable to moisture than conventional LiCoO₂ cathodes, adsorbing more water and easily forming LiOH on the surface. This study investigated the moisture adsorption mechanism on the surface of layer‐structured cathodes. The behavior of water molecules on LiCoO₂ and LiNiO₂ surfaces were simulated and the structural and chemical changes during the adsorption process were analyzed by first‐principles methods. It was found that the adsorption occurs via two types of mechanism: one involving ionic interactions between Li on the crystal surface and O in the adsorbate, and the other involving covalent bonding between the transition metal (TM) on the surface and O in the adsorbate, which restores the coordination of the TM by recovering its broken bonds. The difference between the water adsorption behaviors of Ni‐based and Co‐based layer‐structured cathodes was found to be mainly due to the ionic‐interaction‐driven adsorption on the (003) surface.     

Nonexistence and uniqueness of positive solutions of Yamabe type equations on nonpositively curved manifolds

We prove nonexistence and uniqueness of positive -solutions of the elliptic equation , , on a nonpositively curved, complete manifold .

     

Fuzzy Principles and Characterization of Trustworthiness

We show that (a) the basic principles of subdifferential calculus (various local and global fuzzy principles, multidirectional mean value theorem, extremal principle) which are shown to be equivalent for -subdifferentials are in fact equivalent for any subdifferential and (b) for -versions of -subdifferentials these principles turn out to be also equivalent to the properties of the space to be a trustworthy or a subdifferentiability space (with respect to a given subdifferential).     

Interface of ZnS single sheet and substrates: a first‐principles study

Two‐dimensional materials have aroused great interests because of their unique properties not seen in the bulk counterparts. The interface of the ZnS single sheet and substrates are studied in this paper. Different from isolated ZnS single sheet, here in this study, the ZnS single sheet has a remarkable corrugation feature because of the interaction between the ZnS single sheet and the substrate. The top‐site Zn means an attractive reaction with the substrate while the top‐site S means repulsive. For ZnS single sheet/Si(111) interface, the symmetry of the interface does not decrease after geometry optimization because the two layers have a good lattice matching. For ZnS single sheet/Ag(111) interface, an unbalanced interaction (attractive or repulsive) between the ZnS single sheet (Zn or S atom) and Ag surface leads to remarkable corrugation of the ZnS single sheet and the symmetry of the interface decreases. Copyright © 2017 John Wiley & Sons, Ltd.     

Chiral vectors-tunable electronic property of MoS2 nanotubes

It has been demonstrated that the mechanical and electronic properties of materials change significantly when the external dimension are confined to the nanoscale. Consequently, one-dimensional (1D) transition-metal dichalcogenide (TMDC) nanotubes (NTs), obtained from scrolling two-dimensional (2D) TMDC, have attracted much attentions because of their intriguing properties wherein the chirality of NTs plays a key role in affecting the electronic properties. Taking into the amount of speculations on the mechanism and the increasing needs for better device design and performance control, understanding the effect of chirality on the electronic properties is timely and relevant. Here, MoS₂ NTs are comprehensively studied by first-principles calculations. The results show that the armchair (6≤ch≤14) exhibits the indirect-band-gap and zigzag (10≤ch≤20) with direct-band-gap. Moreover, the carrier mobility is enhanced with the decrease of radial length, in accord with the smaller effective mass of hole and electron for both types NTs. Finally, the formation energy showed that the smaller the radial diameters is, the harder the NTs is to form. Moreover, the similarity of lattice parameters and formation energy implies a potential possibility of transition between two types of NTs with low index chiral vectors, such as ANT(6,6)/ZNT(10,0).     

浅谈高职院校图书采购质量问题

高职图书馆采用政府招标制度是市场经济条件下形成的一种高效、合理、方便、科学的图书采购方法,也是当前高职院校图书馆图书采购工作的主要形式。介绍了政府采购招标及高职院校图书馆图书采购中出现的问题,针对这些问题,提出了具体的有针对性的建议。     

大学生消费者海外代购意向影响因素研究——以安徽财经大学为例

随着电子商务的发展和居民消费水平的提高,海外代购市场飞速发展,并受到了大学生群体的青睐。为了对大学生群体的代购意向进行研究,借助合理行为模型考察大学生代购意向的影响因素,结果表明:主观规范、个体态度、原产国形象、群体一致对代购意向均有显著影响。这一结果对国内产品的推广和营销、调节供需平衡具有一定的借鉴作用。