Steroids from green alga Chaetomorpha basiretorsa Setchell     

史大永  范晓  孙杰  韩丽君  石建功 《中国海洋湖沼学报》2008,26(4)

Six steroids have been isolated from ethanolic extract of green alga Chaetomorpha basiretorsa Setehell by a combination of repeated normal phase silica gel and Sephadex LH-20 gel column chromatography as well as recrystallization. Using spectroscopic methods including MS and NMR, their structures were determined as β-lawsaritol (1), saringosterol (2), 24-hydroperoxy-24-vinyl-cholesterol (3), β-stigmasterol (4), stigmast-4-en-3α, 6β-diol (5), 29-hydroxystigmasta-5, 24 (28)-dien-3β-ol (6). All these compounds were obtained from this genus for the first time and they were inactive (IC5010 μg/ml) against KB, Bel-7402, PC-3M, Ketr 3 and MCF-7 cell lines.  相似文献   

宁静期间双峰电流片的观测研究          下载免费PDF全文

汤朝灵  路立  李中元 《地球物理学报》2007,50(4):979-985

2001年8月19日2011～2030UT,AE指数相对较小(40～130 nT),Cluster 卫星穿越磁尾电流片.利用Cluster 观测资料分析,发现宁静期间有双峰电流片存在,这期间没有明显的高速流,没有明显的电流片振荡. 同时,进一步分析双峰电流片中的离子特性发现:质子数密度Np在中性线（<Bx> = 0）附近相对较大,呈非对称性分布;质子温度分布比较均匀;在中性线两侧,质子y方向上的流速Vy方向相反. 最后讨论LHDI（低混杂漂移不稳定性）的非线性演化可能是形成宁静期间双峰电流片的主要机制. 这些对进一步完善电流片形成机制可能有很重要的意义.  相似文献   

Identification of low frequency waves in the vicinity of the terrestrial bow shock     

M.A. BalikhinO.A. Pokhotelov  S.N. Walker  M. Andre 《Planetary and Space Science》2003,51(11):693-702

In this paper, methods for the determination of the wave mode for low frequency waves based on observed differences in phase are reviewed. Examples, using measurements made in the terrestrial foreshock and magnetosheath, are used to illustrate the application of these methods. The use of advance methods such as NARMAX modelling or genetic algorithms to identify the plasma wave mode is also discussed.  相似文献   

Double-Pulse Laser-Driven Jets on OMEGA     

S. Sublett  J. P. Knauer  I. V. Igumenshchev  A. Frank  D. D. Meyerhofer 《Astrophysics and Space Science》2007,307(1-3):47-50

A double-pulse laser drive is used to create episodic supersonic plasma jets that propagate into a low density ambient medium. These are among the first laser experiments to generate pulsed outflow. The temporal laser-intensity profile consists of two 1-ns square pulses separated by 9.6 ns. The laser is focused on a truncated conical plug made of medium Z material inserted into a high-Z washer. Unloading material from the plug is collimated within the cylindrical washer hole, then propagates into the low-Z foam medium. The resulting jet is denser than the ambient medium. Double-pulse jet evolution is compared to that driven by a single laser pulse. The total drive energy is the same for both jets, as if a source with fixed energy generated a jet from either one or two bursts. Radiographs taken at 100 ns show that a single-pulse jet was broader than the double-pulse jet, as predicted by hydrodynamic simulations. Since the initial shock creating the jet is stronger when all the energy arrives in a single pulse, the jet material impacts the ambient medium with higher initial velocity. Detailed comparisons between single- and double-pulsed jet rheology and shock structure are presented. 2-D hydrodynamic simulations are compared to the experimental radiographs. PACS: 52.30.−q 41.75.Jv 42.62.−b 42.68.Sq 47.40.−x 47.56.+r  相似文献   

ICP—光量计测定地质样品中的Sc     

宁军  张立行  陈虹 《国土资源》1997,(3)

本方法是用ＩＣＰ—光量计测定地质样品中的Ｓｃ，用氢氟酸—盐酸溶解样品，对几个国家级标样进行测定，结果与推荐值一致。方法检出限为Ｓｃ：０．２２μｇ／ｇ，本方法简单、快速、准确  相似文献   

一株海绵共附生真菌Pleosporaceae sp.中甾体类化合物及其生物活性     

赵琨  孙雪萍  韩磊  郑彩娟  陈敏  邵长伦  佘志刚  王长云 《中国海洋大学学报(自然科学版)》2011,41(12):81-85

在生物活性测定指导下,综合运用硅胶柱层析、凝胶柱层析以及半制备HPLC等方法,从南海海绵Xestospongiatestudinaria来源的一株共附生真菌Pleosporaceae sp.发酵液的乙酸乙酯提取物中分离鉴定出5个甾体类化物,通过NMR,MS等波谱技术鉴定其结构分别为:(22E,24R)-5α,8α-epidioxy-ergosta-6,22-dien-3β-ol(1),(22E,24R)-5α,8α-epidioxy-ergosta-6,9,22-trien-3β-ol(2),(22E)-ergosta-5,7,22-trien-3β-ol(3),ergosta-6α-hydroxy-4,22-dien-3-one(4),(22E)-5α-cholesta-7,22-diene-3β,5α,6β-triol(5)。这些化合物均为首次从Pleosporaceae属真菌中分离获得。化合物1,4和5具有较强的卤虫Ar-temia salina致死活性,化合物1还显示强的抗藤壶Balanus amphitrite附着活性,其EC50为0.85μg/mL。  相似文献   

Electrostatic dust-cyclotron waves in plasmas with opposite polarity grains     

N. D'Angelo 《Planetary and Space Science》2002,50(4):375-378

The dispersion relation is derived for electrostatic dust-cyclotron (EDC) waves in a collisional plasma with dust grains having both positive and negative charges. The critical electric fields for excitation of two EDC modes in such a plasma are numerically calculated for a laboratory-type plasma.  相似文献   

Observational limits on intergalactic matter     

Bogdan Wszolek 《Astrophysics and Space Science》1995,227(1-2):151-155

Intergalactic gas and dust are very difficult to detect. Several methods to detect intergalactic gas have been developed. The results of these methods have provided qualitative arguments and quantitative limits on the amount of intergalactic matter in the intergalactic environment. We present here arguments as to why the density of intergalactic matter is higher than previously thought possible.  相似文献   

Bounding greybody and deflection angle of improved Schwarzschild black hole     

《New Astronomy》2022

In this paper, we study the weak deflection angle in the spacetime of improved Schwarzschild black hole using the method derived by Gibbons and Werner. To do so, we derive the optical curvature from the optical metric and calculate deflection angle in weak field limits by using the Gauss–Bonnet theorem. Moreover, we study the effect of the plasma medium on the weak gravitational lensing using the Gauss–Bonnet theorem. Furthermore, we also study the graphical analysis of the deflection angle in both the plasma and non-plasma mediums. Moreover, we obtain the bound on greybody for improved Schwarzschild black hole.  相似文献   

Dynamic non-null magnetic reconnection in three dimensions–II: composite solutions     

A.L. Wilmot-Smith  G. Hornig  E.R. Priest 《地球物理与天体物理流体动力学》2013,107(6):515-534

In this series of papers we examine magnetic reconnection in a domain where the magnetic field does not vanish and the non-ideal region is localised in space so that the reconnection is fully three dimensional. In a previous paper we presented a technique for obtaining analytical solutions to the full set of stationary resistive MHD equations and examined specific examples of non-ideal reconnective solutions. Here we further develop the model, noting that certain ideal solutions may be superimposed onto the fundamental non-ideal solutions. This provides the first analytical demonstration of a lack of coupling between reconnective and non-reconnective flows. We examine the effect of imposing various such ideal flows. Significant implications are found for the evolution of magnetic flux in the reconnection process so that several reconnection solutions may have the same reconnection rate, as defined by the integral of the parallel electric field along the reconnection line, but each appear quite different in terms of their global effect. It is shown that, in contrast to the two-dimensional case, in three dimensions there is a very wide variety of physically different steady reconnection solutions.  相似文献