Synthesis and Characterization of Li‐containing Boron Carbide r‐Li~1B13C2

Transparent and nearly colorless single crystals of r‐LiB₁₃C₂ were obtained by reaction of boron with Li₂CO₃ in a Cu melt at 1250–1300 °C. The structure analysis [R3 m, a = 5.6535(1), c = 12.5320(2) Å, 421 independent reflections, 22 parameters, R₁ = 0.034, wR₂ = 0.093] revealed a crystal structure that can be described as a filling variant of rhombohedral B₁₃C₂. Li⁺ is located in a void above or below the linear CBC unit. The site occupation is close to 50 % resulting in an electron‐precise composition according to Wade's rules if a positive charge is given to the CBC entity: Li⁺(B₁₂)^2–(CBC)⁺. The displacement parameters of the CBC unit indicate disorder in the [001] direction, that relates to the short Li–C distance and the partial occupation of the Li⁺ site. The composition is confirmed by EELS measurements of single crystals. Band gap calculations give a value of 2.94 eV, which is in agreement to the crystals being colorless. The evaluation of the electron density by application of the QTAIM formalism as proposed by Bader modifies the assignment pictured above according to Wade's rules. In agreement to the electronegativities the carbon atoms carry a negative charge (–2.31/–2.42) and the effective charges are: Li^+0.81(B₁₂)^+2.02(CBC)^–2.83.     

用于合成纯硅分子筛 AST 和 LTA 的动态有机结构导向剂(英文)

Pure-silica-zeolite(PSZ) AST and LTA are synthesized successfully by using the same structure-directing agent(SDA) molecule,but at different concentrations.A dynamic organic SDA is proposed to discuss the mechanism of phase discrimination between AST and LTA.Data suggest that the SDA molecules can self-assemble into dimer or trimer complexes at different concentrations by π-π interactions,and these differences can be taken advantage of to selectively synthesize either PSZ AST or LTA.These deviations from the Liebau's rules indicate that small changes in SDA chemistry,structure,and order in solution can have a great impact on the structure selectivity of the zeolite synthesis.     

遵照国家法制规定大力开发强化食品

介绍了我国食品营养强化剂使用卫生标准,特别是对其中一些重要备注和规定进行了归纳和说明.     

High‐spin behavior of molecular crystals and extended π systems

The qualitative rules for the existence of high‐spin ground states in extended systems and molecular crystals are examined here on a firmer theoretical footing. Extended systems have been categorized into three groups, namely, type I, type II, and type III, depending on the type of bonding interactions. The general form of the spin Hamiltonian operators have been written down. The active spaces have been restricted to the minimum size for each of these three types of spin systems. The zeroth‐order state vectors and the Hartree–Fock ground‐state energies have been identified for unit species of each type. The extended system Hamiltonian operators are further truncated in such a way that only the nearest‐neighbor interactions are retained. Expressions have been derived for the energy gap from a molecular orbital approach. The relatively small effects of electron correlation on the energy gaps have been estimated for the type I systems, which belong to the systems of solid‐state physics. In particular, it has been shown that for the type I systems the singlet–triplet gap, and hence the ferromagnetic coupling constant, primarily depends upon the difference of one‐electron kinetic energies and not on the two‐electron exchange integrals. This result agrees with the concept of kinetic exchange that was introduced in the context of a resonating valence‐bond formalism. Type II systems are exemplified by extended systems that can be prepared from conjugated molecules while organic molecular crystals form examples of type III species. For these systems, however, the Coulomb exchange interaction has been shown to dominate the energy gap. A quick review of the Heisenberg spin Hamiltonian for the H₂ molecule is sufficient to point out that the sign of the calculated ferromagnetic coupling constant depends on the method of calculation, the nature of the basis set, and the bond length. This is amply supported by ab initio calculations on this species. Numerical data have also been obtained from computations on m‐phenylene‐coupled nitroxy radicals and stacks of α‐nitronyl nitroxide, but these calculations have been based on a semiempirical quantum chemical methodology (INDO) since some of the species involved are exceedingly large. Computed energy gaps are in good agreement with experimental and other theoretical (AM1, PM3) results. Nevertheless, for the dimer, trimer, tetramer, and pentamer of the type II specimen, the important π orbitals are far from being degenerate. The quantitative results clearly deviate from the criterion of degeneracy that was suggested from qualitative theories for the existence of a high‐spin ground state. Therefore, the criteria for the existence of high spins have been reformulated in terms of the monomer orbitals. © 2000 John Wiley & Sons, Inc. Int J Quant Chem 79: 308–324, 2000     

VA族元素对阳极铅(Ⅱ)氧化物膜半导体性质的影响(Ⅱ)

用光电化学电流法研究了铅、铅砷、铅锑和铅铋合金在4．5mol·L－1H2SO4溶液（22℃）中，以0．9V（vs．Hg／Hg2SO4）极化7h而形成的阳极膜中的氧化铅的半导体性质，合金添加剂砷、锑和铋对t－PbO（四方氧化铝）和o-PbO（斜方氧化铝）的禁带宽度没有影响，从量子效率和电位的关系可求Pb，Pb－lat％As（at％表示原子百分比，全文同），Pb-lat％Sb和Sb－lat％Bi上膜中t－Pbo的施主密度（ND）分别为9．3×1015，1．0×1016，3．1×1016和1．3×1017cm-3，平带位分别为-0．20，－0．22，－0．28和-0．08V（vs．Hg／Hg2SO4）．比较VA元素砷、锑和铋对上述膜中t－Pbo的ND（从而自由电子密度）和膜中t－Pbo的生长速率的影响，可认为法添加剂砷、锑和铋对阳极膜中t-Pbo的作用符合Hauffe规则．     

Dilatation transformation and sum rules for general potentials including self-consistent field potentials

The eigenfunctions and energies of general dilated Hamiltonians are expanded in powers of the dilatation parameter. These expansions, augmented by stationarity and stability conditions, are used to derive exact sum rules for bound and resonance states. Particular attention is paid to Hamiltonians with potentials which depend on external parameters, such as the nuclear coordinates in molecules, and to self-consistent potentials. The sum rules can be employed in practical computations to improve the quality of the results and may also serve in analyzing the results from approximate calculations.     

Influence of chain length and degree of branching of alcohol + chlorobenzene mixtures on determination and modelling of V by CEOS and CEOS/G mixing rules

The densities of binary mixtures of (1-propanol, or 1-butanol, or 2-butanol, or 1-pentanol + chlorobenzene) have been measured at temperatures 288.15, 293.15, 298.15, 303.15, 308.15 and 313.15 K and atmospheric pressure while for the system (2-methyl-2-propanol + chlorobenzene) measurements were performed at the same pressure and temperatures 303.15, 308.15, 313.15, 318.15 and 323.15 K. All measurements were performed by means of an Anton Paar DMA 5000 digital vibrating-tube densimeter. Excess molar volumes V^E were determined and fitted by the Redlich–Kister equation. It was observed that in all cases, V^E increase with rising of temperature. The values of limiting excess partial molar volumes have been calculated, as well. The obtained results have been analysed in terms of specific molecular interactions present in these mixtures taking into consideration effect of the chain length of alcohols, degree of branching in the chain, relative position of the alkyl and OH group in an alcohol and the effect of temperature on them. In addition, the correlation of V^E binary data was performed with the Peng–Robinson–Stryjek–Vera cubic equation of state (PRSV CEOS) coupled with the van der Waals (vdW1) and CEOS/G^E mixing rule introduced by Twu, Coon, Bluck and Tilton (TCBT). Also, the possibility of cross prediction between V^E and VLE by means of the NRTL parameters of G^E model available in literature and those incorporated in the TCBT model was tested.     

World-line approach to the Bern-Kosower formalism in two-loop Yang-Mills theory

Based on the world-line formalism with a sewing method, we derive the Yang-Mills effective action in a form useful to generate the Bern-Kosower-type master formulae for gluon scattering amplitudes at the two-loop level. It is shown that four-gluon (φ⁴ type sewing) contributions can be encapsulated in the action with three-gluon (φ³ type) vertices only, the total action thus becoming a simple expression. We then derive a general formula for a two-loop Euler-Heisenberg type action in a pseudo-abelian su(2) also studied.     

取代吡啶衍生物的13C NMR谱研究

本文测试了三十三个α、β、γ单取代吡啶和二、三取代吡啶衍生物的¹³C NMR谱,归属了全部¹³C NMR谱线。由其¹³C NMR谱线变化规律,研究和总结出各类碳数大于2的烷基取代基对α、β、γ单取代吡啶环碳化学位移的经验取代参数和吡啶环作为一个官能团对烷烃衍生物的取代效应,讨论了单烷基和多烷基吡啶的取代基加和规律。     

Sequential stopping rules for the multistart algorithm in global optimisation

In this paper a sequential stopping rule is developed for the Multistart algorithm. A statistical model for the values of the observed local maxima of an objective function is introduced in the framework of Bayesian non-parametric statistics. A suitablea-priori distribution is proposed which is general enough and which leads to computationally manageable expressions for thea-posteriori distribution. Sequential stopping rules of thek-step look-ahead kind are then explicitly derived, and their numerical effectiveness compared.