半定规划的逆问题

本文提出了半定规划的逆问题,利用半定规划的最优性条件,分别给出了其在ｌ∞,ｌ１,ｌ２ 模意义下的数学模型,它们仍为半定规划问题．     

水分子辅助的一碳单元转移机理的密度泛函研究

The one-carbon unit transfer reaction catalysed by glycinamide ribonucleotide transformylase（GARTfase）is a key step in the de novo purine biosynthetic pathway. In order to give a theoretical research of the assumption from the experiments,the water-assisted mechanism in GAR Tfase catalysed one-carbon unit transfer reaction has been investigated by a Density Functional Theory method,B3LYP,at 6-31G* basis level. There are two possible reaction channels for the whole reaction,one is concerted（path a）and the other is stepwise（path b）. The water molecule serve as a bridge to connect the proton donor to the proton acceptor. All the transition states in both paths have a six-membered ring in their structures due to the joint of the water molecule. The calculations show that the latter is preferable to the former due to the lower energy barriers. The results have verified the presumption from experiments,and proved that the joint of a water molecule can relax the strong strain in the unstable system,so it is propitious to the whole reaction.     

Fabrication of liquid crystal Fe3O4 composites and their magnetorheological properties

Some supramolecular polyacrylate-based liquid crystal polymers (PLCPs) were prepared by polyacrylic acid, a liquid crystal monomer and 3,5-pyridinedicarboxylic acid. Series of magnetic liquid crystal particles (Fe₃O₄@PLCPs) with core-shell structure were prepared by modifying surface of magnetic nanoparticles Fe₃O₄ by the PLCPs. The Fe₃O₄@PLCPs showed a saturation magnetization strength above 51.17 emu/g, which is similar to pure magnetic Fe₃O₄, indicating good magnetism and magnetic field dependence. Series of magnetorheological fluids were fabricated by Fe₃O₄@PLCPs (using as dispersed phase) and silicone oil (using as carrier liquid). The effects of mesogen, magnetic particle, and the polymer matrix on magnetorheological performance and settling stability were investigated. The magnetorheological fluid based on 10% Fe₃O₄@PLCP-1 showed the best performance at an applied magnetic field of 100 mT in this study. Furthermore, the magnetorheological fluids showed excellent settling stability because the density of Fe₃O₄@PLCPs was lower than that of Fe₃O₄. The Fe₃O₄@PLCPs-based fluids presented certain application potential in the field of magnetic fluid due to the excellent magnetorheological effect and settling stability.     

聚甲基丙烯酸甲酯和聚碳酸酯各向异性光学性质理论研究

作为重要的光学薄膜材料,聚甲基丙烯酸甲酯(PMMA)和聚碳酸酯(PC)在诸多工业领域已得到广泛应用.本文利用密度泛函理论结合分子动力学方法深入系统地研究了这两种聚合物的各向异性光学性质,并对比分析了不同分子链长度和微观结构对其各向异性光学性质的影响.计算结果表明PMMA和PC都具有较高的本征双折射率,且分子链长度对本征折射率的影响显著.在可见光范围内,单体单元PMMA本征双折射率在10%以上,而三单元结构本征折射率则不到4%.对于体相结构多聚体,从立方结构拉伸到厚度仅有6?的过程中,PC不同方向折射率最大差异高达6%,而同样情况下PMMA不同方向折射率差异仅有1.3%.此项研究有助于理解PMMA和PC聚合物各向异性光学特征产生的原因和影响因素,从而进一步指导和促进其在更多领域的发展与应用.     

Mechanics of water pore formation in lipid membrane under electric field

Transmembrane water pores are crucial for sub-stance transport through cell membranes via membrane fusion, such as in neural communication. However, the molecular mechanism of water pore formation is not clear. In this study, we apply all-atom molecular dynamics and bias-exchange metadynamics simulations to study the pro-cess of water pore formation under an electric field. We show that water molecules can enter a membrane under an electric field and form a water pore of a few nanometers in diame-ter. These water molecules disturb the interactions between lipid head groups and the ordered arrangement of lipids. Fol-lowing the movement of water molecules, the lipid head groups are rotated and driven into the hydrophobic region of the membrane. The reorientated lipid head groups inside the membrane form a hydrophilic surface of the water pore. This study reveals the atomic details of how an electric field influences the movement of water molecules and lipid head groups, resulting in water pore formation.     

一种改进的旋转式微机械结构

给出了一种改进的旋转式微机械薄膜残余应变测试结构．与已有的普通微旋转结构相比,改进的微旋转结构执行梁的宽度都保持一致．改进的微旋转结构在旋转变形之后,整个执行梁都会发生弯曲变形,所以在变形之后结构的残余应力非常小且分布均匀,没有普通微旋转结构的高应力集中,因此测量精度高于传统微旋转结构,更适合于高残余应变薄膜的测试．文中详细推导了改进微旋转结构的力学模型,并用有限元软件进行了模拟分析,同时详细地给出了改进的微旋转结构与传统微旋转结构的性能对比,最后用实验对改进微旋转结构的理论模型进行了验证．     

A DFT Study on the Selective Extraction of Metallic Ions by 12-Crown-4

In order to predict the extraction ability of 12-crown-4 for different metallic ions, the complexes [M(12-crown-4)] and [M(H₂O)₄] (where M=Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺, Cu²⁺ and Zn²⁺) were investigated by the density functional theory without restrictions for their geometry. The metal binding capability was evaluated using the binding energy, and the effect of nature of the metal on the binding properties was also studied. The results of the calculations showed that the coordination ability of a donor molecule towards different metal ions increased in proportion to their ionization potential. In addition, based on the extraction distribution coefficient, we found that 12-crown-4 can selectively extract Cu²⁺ and Be²⁺ ions from aqueous solutions of mixed cations. Obviously, the stability of complexes and the extraction power of extractants depend greatly on the nature of the metal ions. Calculation results from our study could be used to predict the extraction power of this crown ether and could play a guiding role in planning experiments.     

Electrochemical noise analysis of the effects of a magnetic field on cathodic hydrogen evolution

The effect of a static magnetic field on the evolution of hydrogen gas from a small platinum electrode in an aqueous electrolyte has been studied by recording the noise spectrum of overpotential voltage fluctuations at a constant current density of ?50 mA mm^?2. A 1/f² variation of the power spectrum characteristic of droplet coalescence is found for frequencies >10 Hz. The overpotential for hydrogen evolution decreases with applied field. When the production of gas bubbles is quasiperiodic, there is a threshold field of 0.5 T beyond which the size of the bubbles released is approximately doubled. This is explained by enhanced coalescence of small bubbles swept across the electrode surface by forced convection due to the Lorentz force.     

A novel threefold‐interpenetrating primitive cubic network based on a dinuclear Zn2 node

In the mixed‐ligand metal–organic polymeric compound poly[[μ₂‐1,4‐bis(imidazol‐1‐yl)benzene](μ₂‐terephthalato)dizinc(II)], [Zn₂(C₈H₄O₄)₂(C₁₂H₁₀N₄)]_n or [Zn₂(bdc)₂(bib)]_n [H₂bdc is terephthalic acid and bib is 1,4‐bis(imidazol‐1‐yl)benzene], the asymmetric unit contains one Zn^II ion, with two half bdc anions and one half bib molecule lying around inversion centers. The Zn^II ion is in a slightly distorted tetrahedral environment, coordinated by three carboxylate O atoms from three different bdc anions and by one bib N atom. The crystal structure is constructed from the secondary building unit (SBU) [Zn₂(CO₂)₂N₂O₂], in which the two metal centers are held together by two bdc linkers with bis(syn,syn‐bridging bidentate) bonding modes. The SBU is connected by bdc bridges to form a two‐dimensional grid‐like (4,4)‐layer, which is further pillared by the bib ligand. Topologically, the dinuclear SBU can be considered to be a six‐connected node, and the extended structure exhibits an elongated primitive approximately cubic framework. The three‐dimensional framework possesses a large cavity with dimensions of approximately 10 × 13 × 17 Å in cross‐section. The potential porosity is filled with mutual interpenetration of two identical equivalent frameworks, generating a novel threefold interpenetrating network with an α‐polonium topology [Abrahams, Hoskins, Robson & Slizys (2002). CrystEngComm, 4 , 478–482].