磁星发现之旅

1979年3月5日,两艘苏联宇宙飞船(金星11和金星12号)正沿着椭圆轨道在内太阳系的太空中遨游。飞船上携带仪器的辐射读数在预期值———每秒100次———附近上下稳定地跳动着。23时51分,异变突起,一束神秘的伽玛射线脉冲骤然袭来,在一毫秒的若干分之一的时间内,辐射强度值陡升至每秒20万次单位以上,仪器量程饱和至无法统计。11秒后,此束伽玛射线横扫美国航空航天局(NASA)的“太阳神2号”空间飞船,它当时也在环绕太阳的轨道上运行,并很快抵达了金星,使金星轨道飞行器上的探测器量程达到饱和。接下来几秒钟,伽玛射线就光临地球,淹没了美国国防…     

The differential impact of academic self-regulatory methods on academic achievement among university students with and without learning disabilities

Although research on academic self-regulation has proliferated in recent years, no studies have investigated the question of whether the perceived usefulness and the use of standard self-regulated learning strategies and compensation strategies provide a differential prediction of academic achievement for university students with and without learning disabilities (LD). We developed and tested a model explaining interrelationships among self-regulatory variables and grade point average (GPA) using structural equation modeling and multiple group analysis for students with LD (n = 53) and without LD (n = 421). Data were gathered using a new instrument, the Learning Strategies and Study Skills survey. The results of this study indicate that students with LD differed significantly from students without LD in the relationships between their motivation for and use of standard self-regulated learning strategies and compensation strategies, which in turn provided a differential explanation of academic achievement for students with and without LD. These paths of influence and idiosyncrasies of academic self-regulation among students with LD were interpreted in terms of social cognitive theory, metacognitive theory, and research conducted in the LD field.     

费马定理卷土重来

费马定理卷土重来郭凯声，郭敏物理学家兼诗人皮特·海因说过：“值得人们研究的问题常常会反扑过来从而证明其价值。”费马最后定理正好就是这种情况。它在去年夏天看来已被击倒之后却又从拳击垫上跳起来以进行新一轮较量。这一表面上十分简单的定理是说，当指数Ｎ大于２...     

土星华章

土星是继火星之后又一个令人瞩目的焦点。它所展现给世人的奇妙景观可能比今年两个孪生火星车所捕获的火星盐海的沉积物和数块千疮百孔的火山岩更加蔚为壮观。耗资33亿美元的卡西尼轨道环绕器和它所搭载的惠更斯号探测器在历经7年的漫长旅途后即将于7月初飞抵环土星轨道。届时,环绕着巨大光环和一群卫星的整个土星系统的真实面目将被彻底摸清。“卡西尼—惠更斯号”探测器是人类迄今为止建造的规模最大、复杂程度最高的行星探测器。科学家特别希望运用“卡西尼“上强大的仪器组对年轻的、充满活力的土星环系统进行深入的探索。奔赴土星一波…     

Secretary's advisory committee on genetic testing: its emerging role in public policy deliberation on genetic tests

The Secretary's Advisory Committee on Genetic Testing (SACGT) was established by the U.S. Secretary of Health and Human Services, Donna E. Shalala, to provide a public forum for the formulation of policy advice in the complex and growing area of genetic testing. After a careful nomination and selection process, the Secretary announced the appointment of thirteen advisors to the SACGT in June 1999. The first meeting of the SACGT was held June 30, 1999. This article describes the purpose, formation, and function of the SACGT. Before addressing these questions about the role of the SACGT, we first will explain what genetic testing is, how it is currently used, and what new uses it may be put to in the future.     

Screening the active constituents of Chinese medicinal herbs as potent inhibitors of Cdc25 tyrosine phosphatase, an activator of the mitosis-inducing p34cdc2 kinase

Objective: To screen and evaluate the active constituents of Chinese medicinal herbs as potent inhibitors of Cdc25 phosphatase. Methods: The affinity chromatography purified glutashione-S-transferase/Cdc25A phosphatase fusion protein and Cdc2/cyclin B from the extracts of starfish M phase oocytes are used as the cell cycle-specific targets for screening the antimitotic constituents. We tested 9 extracts isolated from the Chinese medicinal herbs and vegetables including the agents currently used in cancer treatment by measuring the inhibition of Cdc25A phosphatase and Cdc2 kinase activity. The antitumor activity of the extracts was also evaluated by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and flow cytometry. Results: Cdc25A inhibitory activity and antitumor activity are detected in the extracts isolated from three Chinese medicinal herbs Agrimona pilosa; Herba solani lyrati; Galla chinesis. Conclusion: We found three extracts isolated from Chinese medicinal herbs have potential inhibitory activity of Cdc25 phosphatase using a highly specific mechanism-based screen assay for antimitotic drug discovery.     

烧钱的太空

虽然美国航空航天局（NASA）的预算在过去两年中增加了7％，但它的责任却以更快的速度在加码。首先，它必须重新启动航天飞机的飞行，而且确保安全（自2003年哥伦比亚号失事以后，航天飞机的飞行就中止了）。其次，它计划继续组装国际空间站，这座部分完工的轨道据点目前有两名宇航员长驻，并由俄罗斯飞船运送补给品。第三，布什总统去年命令它研制“载人探索飞船”（Crew Exploration Vehicle，CEV），设计这种新型飞行器，旨在把宇航员重新送上月球，并最终实现人类登陆火星。     

恐龙为什么长得快?

大多数人都可以悠闲地站在做成标本的霸王龙（Tyrannosaurus rex）的颌线下面，或者是在腕龙（Brachiosaurus）的肋骨骨架下面自由行走，而不必担心撞到自己的头。霸王龙的个头跟最大的非洲象相当，而腕龙则与其他的大型蜥脚类亚目动物相仿，远远大于现今地球上生存的任何一种陆地动物。我们对恐龙那令人望而生畏的巨大个头早就习队为常，以至于几乎忘了想一想恐龙究竟是如何长得加此庞大的。恐龙长到这样大要花多长时间，而它们的寿命又有多长呢？恐龙的生长方式是否有助于我们了解其机体的运作机制呢？     

不速之客:年轻球状星团

传统观点认为，球状星团是宇宙中一群古怪的“老家伙”，但实际上存在许多年轻的球状星团，并不断有更新的产生。