寻常恒星的壮丽死亡

猫眼星云（NGC 6543）可谓星系中最奇特的行星状星云之一。它是一团多层次，多色彩的气体云，距太阳约3000光年。这类星云其实同行星毫不沾边。“行星状星云”不过是历史上遗留下来的一个术语，实际上这类星云是中等大小恒星缓慢走向死亡的过程中形成的。我们的太阳也将像这样结束自己的一生，哈勃太空望远镜1994年摄下了这张猫眼星云的照片，为了解释它的复杂“猫眼”结构，天文学家们绞尽了脑汗。     

第二次登月

对于研究月球的科学家来说，1969至1972年间进行的6次阿波罗登月飞行（共把12名宇航员送上月球）给他们留下了两大撼事。最大的遗憾当然是阿波罗计划突然结束，致使月球的许多东西来不及探索。还有一种遗憾就是，阿波罗计划的巨大成功使人们产生了一种流行的误解：由于宇航员已经访问过月球似乎没有必要了。     

黑暗中的烛光

用通俗语言宣传科学，使普通大众都能了解科技成果。自从伽利略开创了这个传统以来，科学界的“排外派”和“开放派”之争从来就没有停止过。排外派认为搞科研是专业人士的专利，把科学普及到广大群众有失学者的尊严。开放派则认为：不论哪个层次的科学，都需要明晰的表述，让公众理解科研过程与成果。     

A semester-long project for teaching basic techniques in molecular biology such as restriction fragment length polymorphism analysis to undergraduate and graduate students

Several reports on science education suggest that students at all levels learn better if they are immersed in a project that is long term, yielding results that require analysis and interpretation. I describe a 12-wk laboratory project suitable for upper-level undergraduates and first-year graduate students, in which the students molecularly locate and map a gene from Drosophila melanogaster called dusky and one of dusky's mutant alleles. The mapping strategy uses restriction fragment length polymorphism analysis; hence, students perform most of the basic techniques of molecular biology (DNA isolation, restriction enzyme digestion and mapping, plasmid vector subcloning, agarose and polyacrylamide gel electrophoresis, DNA labeling, and Southern hybridization) toward the single goal of characterizing dusky and the mutant allele dusky(73). Students work as individuals, pairs, or in groups of up to four students. Some exercises require multitasking and collaboration between groups. Finally, results from everyone in the class are required for the final analysis. Results of pre- and postquizzes and surveys indicate that student knowledge of appropriate topics and skills increased significantly, students felt more confident in the laboratory, and students found the laboratory project interesting and challenging. Former students report that the lab was useful in their careers.     

变化的风

去年的飓风季节，由于佛洛伊德飓风(Floyd)所产生的每小时155英里的风暴，增加了人们的恐惧：美国的墨西哥湾至大西洋沿岸地区已进入了一个活跃风暴增长的周期，安德鲁斯飓风留给人们的印象太深刻了。有关公共安全，特别是飓风是否将袭击一个主要城市中心等问题的提出越来越强烈。在一个表现世界末日的电影剧本里，     

时间反转声响效应

换能器阵列能再现声音并将其发射回声源，就宛如时间被反转一般。此声学过程可用于粉碎肾结石、材料探伤及与潜艇通信。     

大西洋森林的凤梨科植物

沿着巴西海岸，那曾一度繁茂的大片森林，如今只有8％残存下来，而这片幸存下来的森林却是多种多样的凤梨科植物的家园。生物学家们登岩攀树，正是为了采集这些珍奇的植物。     

Leucine125Valine (Leu125Val) Gene Polymorphism of Platelet Endothelial Cell Adhesion Molecule-1 (PECAM-1) and Myocardial Infarction in Indian Population

Platelet-endothelial cell adhesion molecule-1 (PECAM-1) has role in atherosclerotic plaque development as well as in thrombosis leading to myocardial infarction (MI). Present study was aimed to analyse the association of PECAM-1 Leu125Val gene polymorphism with MI in Indian population. Subjects included healthy individuals as control (N = 116) and MI patients (N = 100) divided into two groups; MI patients at presentation of the acute event (MI-Group-1, N = 46) and patients with recent event of MI stabilized with treatment 4.5 days from their symptoms (MI-Group-2, N = 54). The difference in the distribution of Leu125Val genotype frequencies of controls and patients did not reach statistical significance. However Leu allele frequency (0.57) was more associated with MI patients as compared to control (0.504). sPECAM-1 levels were significantly elevated in patients at acute event of MI (MI-Group-1) by 44.1% (P = 0.009) as compared to controls and by 95.2% (P = 0.001) as compared to stabilized MI patients (MI-Group-2).     

Errors in the estimation of hydration status from changes in body mass

Hydration status is not easily measured, but acute changes in hydration status are often estimated from body mass change. Changes in body mass are also often used as a proxy measure for sweat losses. There are, however, several sources of error that may give rise to misleading results, and our aim in this paper is to quantify these potential errors. Respiratory water losses can be substantial during hard work in dry environments. Mass loss also results from substrate oxidation, but this generates water of oxidation which is added to the body water pool, thus dissociating changes in body mass and hydration status: fat oxidation actually results in a net gain in body mass as the mass of carbon dioxide generated is less than the mass of oxygen consumed. Water stored with muscle glycogen is presumed to be made available as endogenous carbohydrate stores are oxidized. Fluid ingestion and sweat loss complicate the picture by altering body water distribution. Loss of hypotonic sweat results in increased osmolality of body fluids. Urine and faecal losses can be measured easily, but changes in the water content of the bladder and the gastrointestinal tract cannot. Body mass change is not always a reliable measure of changes in hydration status and substantial loss of mass may occur without an effective net negative fluid balance.