太阳风等离子体输出流量的全日面二维结构

本文根据1983年十个 Carrington 周(1733—1742)期间的 K-日冕亮度、行星际闪烁(IPS)观测和光球磁场观测,首次探讨了太阳风等离子体质量、动量和能量输出流量 F_M,F_P 和 F_E 的全日面二维平均结构及其与光球磁场结构的关系.     

锂离子电池硅基负极材料的研究进展

硅基材料是新一代高容量锂离子蓄电池负极材料的典型代表,近年来已成为理论研究和应用研究的热点.本文介绍了锂离子电池硅基负极材料的制备方法、电化学性能及其研究现状,分析了硅材料作为锂离子电池负极材料存在的问题;讨论了硅材料作为锂离子电池负极材料的研究前景.并指出若能克服目前存在问题,将有望成为新一代锂离子电池负极材料.     

Suppressed ion chromatography for monitoring chemical impurities in steam for geothermal power plants

A suppressed ion chromatography (IC) technique has been evaluated as a chemical monitoring tool for detecting major anions (F-, Cl-, NO3- and SO4(2-)) of condensed steam in geothermal power plants. It is shown that the suppressed IC technique provides a suitable means for preventing possible damage to generating equipment in the geothermal industry. An electrical conductivity detector (0.1 microS sensitivity) with an anion-exchange column (IonPac AS4A-SC), a micro-membrane suppressor (AMMS II), and an isocratic high-pressure pump system were successfully used for detecting low concentrations of inorganic anions. Method detection limits for the anions of interest were <0.184 mg/L. Details of the IC methodology as well as some experimental results obtained during its application for the chemical monitoring of geothermal steam pipes are also described.     

Amplitude squared squeezed states in the Fock–Bargmann space

Squeezed states are normally studied in configuration space or using the Glauber formalism for the coherent states. Here we show that the use of the Fock–Bargmann space can lead to more general solutions, especially in the case of squeezed states associated with the square of field amplitude. The relations that we obtain are completely general and several well-known, approximate results can be obtained as the limit cases of our approach.© 1993 John Wiley & Sons, Inc.     

Fallout of uranium isotopes from the 1980 eruption of Mount St. Helens

A marked increase in the concentration of²³⁸U in rain was observed at Fayetteville (36 °N, 94 °W), Arkansas, after the 18 May 1980 eruption of Mount St. Helens. The fallout of natural uranium observed during the summer months of 1980 can be attributed to the 18 May 1980 events, which ejected an amount of ash material on the order of 4 km³ or about 8·10¹⁵ grams into the atmosphere.²³⁴U and²³⁵U were found to be highly enriched relative to²³⁸U in several rain samples collected at Fayetteville, Arkansas, prior to the volcanic eruption. The anomalous uranium seems to have originated from the Soviet satellite Cosmos-954, which fell over Canada, on 24 January 1978. The effect of the 25th Chinese nuclear test, which occurred on 16 October 1980, on the concentrations of uranium isotopes in rain appears to have been insignificant.     

Lipase from Carica papaya latex presents high enantioselectivity toward the resolution of prodrug (R,S)-2-bromophenylacetic acid octyl ester

Besides the well-known papain, lipolytic activity is another interesting enzymatic activity present in latex from Carica papaya. This lipolytic activity is strongly attached to the latex solid phase, resulting in a naturally immobilized biocatalyst. In this work we describe the kinetic resolution of (R,S)-2-bromophenylacetic acid octyl ester by Carica papaya crude latex and two partially purified latex fractions. Several parameters, such as substrate concentration and solvent effects were studied. The best results were obtained using decane as solvent with 50 mM of substrate and 50 mg/mL enzyme/reaction medium; under these conditions, a high enantioselectivity (E >200) was obtained with crude latex. A twofold increase of the initial rate maintaining E >200 was obtained using purified fractions without protease and without esterase. Lipase from Carica papaya latex is the most enantioselective wild-type enzyme ever described for the studied reaction.     

Enhanced Thermal Oxidation Stability of Reduced Graphene Oxide by Nitrogen Doping

Nitrogen‐doped reduced graphene oxide (N‐doped RGO) samples with a high level of doping, up to 13 wt. %, have been prepared by annealing graphene oxide under a flow of pure ammonia. The presence of nitrogen within the structure of RGO induces a remarkable increase in the thermal stability against oxidation by air. The thermal stability is closely related with the temperature of synthesis and the nitrogen content. The combustion reaction of nitrogen in different coordination environments (pyridinic, pyrrolic, and graphitic) is analyzed against a graphene fragment (undoped) from a thermodynamic point of view. In agreement with the experimental observations, the combustion of undoped graphene turns out to be more spontaneous than when nitrogen atoms are present.     

New oleanan-type triterpene and cincholic acid glycosides from Peruvian "Uña de Gato" (Uncaria tomentosa)

A new oleanan-type triterpene and three new cincholic acid glycosides were isolated from Peruvian "Una de Gato" (Cat's claw, plant of origin: Uncaria tomentosa), a traditional herbal medicine in Peru. Their structures were determined by spectroscopic analysis.