高能核碰撞中带电多重数快度与能量和中心度的关系

用强子–弦级联模型JPCIAE及相应的Monte Carlo事例产生器研究相对论性核–核碰撞中带电粒子多重数的赝快度密度对能量和中心度的依赖关系.无需另调任何模型参数的条件下,此模型可以同时较好地描述相对论性pp实验数据及PHOBOS和PHENIX实验组的Au+Au实验数据.本文指出:因〈N_part〉并非严格定义的物理量,致使实验上和理论上确定〈N_part〉有一定任意性,从而使得每参加者核子对的带电粒子赝快度密度随着〈N_part〉的增加可能逐渐增大,也可能逐渐减小,因此用它来区分粒子产生机制是欠妥的.     

Inhibition by protease inhibitors of binding of adrenal and sex steroid hormones.

Binding of steroid hormones is inhibited by protease inhibitors and substrates. The protease inhibitors phenylmethyl sulphonylfluoride, tosyl-lysine chloromethyl ketone, and tosylamide-phenylethyl-chloromethyl ketone and the protease substrates tosyl arginine methyl ester and tryptophan methyl ester eliminate specific binding of aldosterone, dexamethasone, dihydrotestosterone, estrogen, and progesterone to their respective receptors. These protease inhibitors and substrates also inhibit binding of progesterone to the 20,000 molecular weight mero-receptor formed from the progesterone receptor in chick oviduct. The binding of estradiol to rat alpha-fetoprotein is inhibited by the protease inhibitors and substrates but not by tryptophan or tryptophan amide, indicating the importance of an ester structure in the inhibition of steroid binding. Our results suggest that all steroid hormone receptors have a site with both common structural features and a role in the regulation of steroid hormone binding.     

Preparation, separation and degradation of oligouronides produced by the polygalacturonic acid transeliminase of Bacillus pumilus.

Production of the end products of polygalacturonic acid degradation on a large scale was done by reacting free galacturonic acid with Bacillus pumilus polygalacturonic acid transeliminase (PATE, EC 4.2.2.2) to obtain a mixture of the barium salts of several oligouronides. Small amounts of the unsaturated oligouronides were separated by paper chromatography. Large quantities of unsaturated oligouronides were separated on a AG-1-X8 (formate) column by applying a sample of mixed oligouronides and stepwise elution was carried out with sodium formate buffer (pH 4.7). The unsaturated oligouronides were identified on the basis of chromatographic mobilities, Sephadex gel filtration data, COOH/CHO ratio, thiobarbituric acid-reacting material, bromine uptake, and chemical and enzymatic degradation data as unsaturated tri-, tetra-, and hexagalacturonic acids. The chemical degradation of these unsaturated oligouronides, done with 6 N HCl by heating at 100 degrees for 30 min, gave qualitatively identical products of hydrolysis. These products compared with authentic standards, were identified as galacturonic acid, formic acid, 5-formyl-2-furancarboxylic acid, and 2-furancarboxylic acid. Analysis of the enzymatic breakdown products of the higher unsaturated uronides showed that a minimum of four galacturonic acid units was required for the action of purified endo-PATE from B. pumilus. The unsaturated trimer was not attacked, thus accounting for its accumulation as the major end product of polygalacturonate degradation by this enzyme.     

A comparative investigation of the fatty acid compositions of the seeds of a number of lines of a genetic collection of Gossypium hirsutum

A comparative analysis has been made of the amounts of lipids and their fatty-acid compositions in the seeds of the lines of agenetic collection of cotton plants of the speciesGossypium hirsutum and their hybrids and the variety Tashkent-1. The results obtained on the fatty-acid compositions of some hybrids make it possible to recommend the use of individual lines of cotton plants as donors for improving the food-value indices of cottonseed oil.Institute of Chemsitry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. V. I. Lenin Tashkent State University. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 173–176, March–April, 1991.     

Surface tension effect on transmembrane channel stability in a model membrane

The effect of surface tension on the lipid bilayer membrane is a question that has drawn considerable research effort. This interest has been driven both by the desire to determine the surface tension effects on the lipid bilayer and from the suggestion that adding finite surface tension to a small membrane system may provide more realistic lipid properties in molecular dynamics simulations. Here, the effect of surface tension on a palmitololelylphosphatidylcholine (POPC) bilayer membrane containing a four-helix transmembrane alamethicin peptide bundle is investigated. Simulations of 10 ns were undertaken for two different ensembles, NPT and NP(z)gammaT with a surface tension, gamma, of 20 mN m(-1) per interface, which is near the pore-forming region. The significance of differences between the tension-free and surface tension simulations was determined using nonparametric statistical analysis on replicate simulations with different initial conditions. The results suggest that, when the membrane is under surface tension, the peptide helical structure is perturbed from that in the tension-free state but that the bundle conformation is more stable than that in the tension-free state, with hydrogen bonding playing an important stabilizing role. Surface tension counteracts the influence of the transmembrane helix bundle on nearby lipid order, making the lipid order more uniform throughout the membrane in the tension state. Conversely, the lipid mobility was less uniform in the tension state, with lipids far from the bundle being significantly more mobile than those near the bundle. One general implication of the results is that surface tension can affect the membrane nonuniformly, in that the properties of lipids near the peptide are different from those further away.     

Wavelength-modulated,continuum-source excited atomic fluorescence spectrometric system for wear metals in jet engine lubricating oils using electrothermal atomization

A system for measuring atomic fluorescence of atoms produced via an electrically-heated graphite filament in a flame (acetylene/air or acetylene/nitrous oxide) and excited with a 300-W Eimac xenon are lamp is described. The experimental system also included wavelength modulation for background emission/fluorescence/scatter correction and an optically-triggered electronic integrator for efficient monitoring of the analyte fluorescence signal. Copper, aluminum and molybdenum were determined in jet engine lubricating oil samples (1 μl) with no pretreatment. The determinations are evaluated with respect to the accuracy and repeatability criteria of the U.S. Joint Oil Analysis Program.     

Plutonium(IV) mononitrate and dinitrate complex formation in acid solutions as a function of ionic strength

Titrations of Pu(IV) with HNO₃ in a series of aqueous HClO₄ solutions ranging in ionic strength from 2 to 19 molal were followed using visible and near-infrared absorption spectrophotometry. The Pu 5f-5f spectra in the visible and near IR range change with complex formation. At each ionic strength, a series of spectra were obtained by varying nitrate concentration. Each series was deconvoluted into spectra of Pu⁴⁺ (aq), Pu(NO₃)³⁻ and Pu(NO₃)₂ ²⁺ complexes, and simultaneously their formation constants were determined. When corrected for the incomplete dissociation of nitric acid, the ionic strength dependence of each formation constant can be described by two parameters, β⁰ and Δε using the formulae of specific ion interaction theory.     

Quark loop model of vector meson mixing and radiative meson decays

We consider the one quark loop contributions to ω-φ mixing and radiative meson decays. With three triplets of colored quarks, we obtain a number of relations (some old and some new) which are in excellent accord with experiment.     

Synthesis and Crystal Structure of an Organic-Polyoxometalate (POM) Hybrid Compound Containing a Keggin Type Mo–Si Polyanion

Abstract  

Complex (1), which is comprised of a typical Keggin type anion, four protonated 3-amino-1,2,4-triazole (AmTAZ) ligands, one nitrate anion and an area of disordered unidentifiable species was synthesized via hydrothermal methods followed by slow evaporation. The structure is held together through a web of hydrogen bonding and crystallizes in the monoclinic space group P2₁/c with unit cell dimensions of a = 13.789(3) b = 15.551(3) c = 24.401(7) ?, β = 93.898(8)°, V = 5220(2) ?³ Z = 4, D = 2.896 Mg/m³.