Classification of integral trees

A finite poset Q is called integral over a field k if there exists an ASL (algebra with straightening laws) domain on Q{–} over k. We classify all trees (rank one connected posets without cycles) which are integral over an infinite field.     

盐酸吡哆辛及其制剂的二阶导数差示脉冲极谱法定量研究

建立盐酸吡哆辛及其制剂的二阶导数差示脉冲极谱定量分析方法。盐酸吡哆辛在0.1mol/L氢氧化钠溶液-0.1moL/L磷酸二氢钾溶液-水(体积比为1.2:8.8:990)的混合溶液中,于-0.140V(vs·Ag/AgCl)处出现一良好的二阶导数差示脉冲极谱峰,盐酸吡哆辛浓度在3.6×10~(-4)～9.6×10~(-4)mol/L范围内与其峰幅值呈显著的线性关系(P<0.01),线性相关系数r=0.9997,检出限为9.0nmol/L。     

Isoperichoric focusing field-flow fractionation and thin layer isoperichoric focusing based on coupling of gradient generated by primary field with secondary field action: general principles and performances

The primary field forces can generate spatially oriented gradient of the effective property of a continuum or pseudo-continuum fluid (carrier liquid). When this gradient is coupled with the action of a secondary field of identical or different nature the isoperichoric focused zones of the dispersed species can appear. Consequently, they can be separated according to differences responding to the property gradient of the carrier liquid. This concept can be applied under static (non-flow) conditions in thin layer focusing as well as under dynamic conditions with the elution due to the carrier liquid flow in focusing field-flow fractionation. The gradient established by the action of the primary field and the concentration distribution of the isoperichoric focused zone formed by the coupled effect of the gradient and of the primary or secondary field are described theoretically. The rigorous relationship describing the shape of the focused zone is compared with the approximate solutions. The performances of the proposed principle were evaluated by model calculations. Potential experimental configurations considering the implementation of the static and dynamic conditions are discussed. The generalized isoperichoric focusing theory can be applied to describe the particular processes operating in analytical and preparative focusing separations of the particles of various, but especially of biological origin.     

基于非生物折叠体的分子识别

利用分子自组装的方法控制大分子量的线性有机分子的构象是物理有机化学一个富于挑战性的研究课题. 近年来, 化学家已经成功利用不同的分子内非共价键作用力如氢键和疏溶剂作用等诱导线性分子的折叠乃至螺旋构象的产生. 综述了近年来这种新的非生物二级结构形式在分子识别研究中的应用.     

Electrochemical reaction of lithium with nanosized vanadium antimonate

Nanometric vanadium antimonate, VSbO₄, was prepared by mechanical milling from Sb₂O₃ and V₂O₅ and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mossbaüer spectroscopy (MS) and X-ray photoelectron spectroscopy (XPS) techniques. Its reactivity towards lithium was examined by testing Li/VSbO₄ cells under galvanostatic and potentiostatic regimes. The amount of Li inserted was found to be consistent with a two-step process involving the reactions (i) VSbO₄+8 Li→Sb+V+4 Li₂O and (ii) Sb+3 Li→Li₃Sb, the former being virtually irreversible and the latter reversible as suggested by the shape of the anodic and cathodic curves. Ex situ XPS measurements of the discharged and charged electrode provided direct evidence of the formation of alloyed Sb and confirmed the results of the potentiostatic curves regarding the irreversible or reversible character of the previous reactions. The Li/VSbO₄ cell exhibited acceptable electrochemical performance, which surpassed that of other Sb-based compounds as the likely result of the formation of V and its associated enhanced electrode conductivity.     

水相锌二次电池正极材料V2O5/C的电化学性能研究

采用溶胶－凝胶法合成了一种V₂O₅/C复合材料.扫描电镜（SEM）和红外光谱（FTIR）分析表明,这是一种外层V₂O₅胶体包覆内层乙炔分子的多孔复合材料.以V₂O₅/C作正极,锌片为负极,Zn(ClO₄)₂溶液为电解质组成水相锌二次电池,采用循环伏安（CV）和电化学阻抗谱（EIS）等方法研究发现:V₂O₅:C质量比为1:1时电极具有最好的电化学性能,电池开路电压达1.64 V; Zn^2＋能分别在1.01 V和1.26 V处分步嵌入V₂O₅/C结构中A、B两种位置,其嵌入电流密度峰值最高可达70 mA•g^－1,并且具有较好的循环充放电性能;在一定放电深度下,V₂O₅/C电极反应速率受Zn^2＋的扩散过程控制.     

Structure and Electrochemical Behavior of Lithium-Manganese Spinels Doped with Chromium and Nickel

A series of compounds with the general formula LiMn_{2 - x - y} Cr _x Ni _y O₄, where x + y = 0.05, 0.5, or 1.0, is synthesized. It is shown that all these compounds are pure-phase spinels with parameter aequal to 0.8193-0.8236 nm. Doping a stoichiometric lithium-manganese spinel simultaneously with chromium and nickel makes the spinel structure stable. The initial specific capacity of a spinel depends on its doping degree. Doping LiMn₂O₄ with chromium and nickel simultaneously at an Mn : Cr : Ni ratio of 195 : 3 : 2 raises the spinel's specific capacity and reduces the cycling degradation. The change in the discharge capacity of LiMn_1.95Cr_0.03Ni_0.02O₄ electrodes cycled at 20, 0, and -14°C is determined.     

pH值和钙离子对尖吻蝮蛇抗血小板凝集素二级结构的影响

尖吻蝮蛇毒中抗血小板凝集素是凝血因子IX/凝血因子X结合蛋白，它具有抗凝血和抑制血小板凝集双重活性。用红外光谱、拉曼光谱和CD谱研究了抗血小板凝集素的二级结构以及pH值和钙离子对其二级结构的影响。用CD谱测得，在水溶液中，抗血小板凝集素的主要骨架构象为β-折叠(26.3%)和α-螺旋(19.6%)结构。拉曼光谱显示，在粉末状态，其α-螺旋含量显著降低。CD谱还表明，抗血小板凝集素在pH值3.0～11.0范围内保持稳定的天然结构，钙离子诱导的抗血小板凝集素结构变化是可逆的，钙离子在稳定抗血小板凝集素的天然结构中起重要作用。     

Electrochemical properties and synthesis of LiAl0.05Mn1.95O3.95F0.05 by a solution-based gel method for lithium secondary battery

The cathode materials, LiMn₂O₄, LiAl_0.05Mn_1.95O₄ and LiAl_0.05Mn_1.95O_3.95F_0.05 were firstly prepared by a simple solution-based gel method using the mixture of acetate and ethanol as the chelating agent. The synthesized samples were investigated by X-ray diffraction, scanning electronic microscope and differential and thermal analysis. The as-prepared powders were used as positive materials for lithium-ion battery, whose discharge capacity and cycle voltammogram properties were examined. The results revealed that LiAl_0.05Mn_1.95O_3.95F_0.05 synthesized by the solution-based gel method had higher initial capacity than LiAl_0.05Mn_1.95O₄ and better capacity retention rate (92%) than that of LiAl_0.05Mn_1.95O₄ and LiMn₂O₄, which revealed that Al and F dual-doped LiMn₂O₄ could gain better electrochemical properties of LiMn₂O₄ than only the Al-doped LiMn₂O₄.     

Addition of secondary phosphines to N-vinylpyrroles

Secondary phosphines 1-3 react readily with N-vinylpyrroles 4 and 5 under radical initiation to give regiospecifically anti-Markovnikov adducts, diorganyl-2-(1-pyrrolyl)ethylphosphines 6a-d, highly reactive building blocks for organic synthesis, in 88-91% yields.