生命:认知的延伸

“宇宙和生命”始终是人们关注并孜孜不倦进行探求的终极问题。我们认为，一切生物都是从低级进化到高级，再从高级到另一层次的低级；系统从简单到复杂，再从复杂到另一层次的简单，乃至无穷循环下去。我们的传统理论只是这条螺旋链条上的一段“从低级到高级，从简单到复...     

生物进化的第一动力

人们把"进化"一词定义为:"生物逐渐演变,由低级到高级,由简单到复杂,种类由少到多的发展过程"。这里的"由低级到高级"一般被理解为"由劣到优""、由落后到先进"。例如很多人就是这样认为:高级先进的优     

重演进化

在达尔文之前,西方学术界对生物界的看法是既静止又有序的,遵循亚里士多德的"自然界阶梯"观念:生物界存在着一个从低等生物到高等生物,从简单到复杂,从不完美到完美的"阶梯",位于这个"阶梯"最顶端的,是最高等、最复杂、最完善的人。拉马克的进化论只是把这个"阶梯"从静态的变成动态的:低等生物在内在驱动力的驱使下,不停地往上爬以变成高等的生物。只有达尔文的进化论,才彻底摆脱了这个"阶梯"的影响。19世纪20年代,拉斯克发现在鸟     

火星上有外星人的遗迹吗?--火星上金字塔之谜

火星上没有高级生命,这已是确定的事实,但许多人根据种种迹象提出,在那里可能有低级生命存在和过去的火星人或外星人留下的遗迹。 美国生物化学家吉·利文研制的一台进行生物实验的仪器,1976年7月20日由“海盗Ⅰ”号探测器带到火星表面。这台仪器把一种含有示踪元素的液态化学药品注入到火星表面九个地点的土壤中,然后检测土壤中有关生命的信息。结果,利文的仪器探测到了微生物的“打嗝”声。     

通向天庭的台阶(中)──古埃及金字塔揭谜

通向天庭的台阶（中）古埃及金字塔揭谜晨飞编译金字塔这个名称也许源于一个希腊语词，意思是“麦面饼”，可能是因为古希腊人和古埃及人所做的饼是这个形状的缘故。第一个这样的宏伟建筑就是撒哈拉的阶梯金字塔。这是第三王朝著名的大臣伊姆霍特普为“圣者”佐塞所修建的...     

生命的发源地

据外刊报道 ,美国和欧洲的一些天文学家目前正在讨论一个有趣的问题 :生命是否起源于火星而非地球？芬兰科学家毛利威尔托嫩最近在给美国天文学会的一份报告中指出 ,近几年的天文观察和实验结果 ,使得有关的科学家越来越相信 :我们地球人的祖先 ,很可能是来自火星的“火星人”！当前 ,大多数科学家都认为 ,生命起源于一个类似现代细菌那样的“先祖”细胞 ,这个细胞后来进化为植物、动物和人类等多种生命形式。传统的观点认为 ,地球上第一个这样的细胞出现在３８亿年～３５亿年之前。然而 ,一个由１０位来自欧美国家的天文学家组成的高级专家…     

网罟座

因为嗣罟座的形状成一个小小的菱形。像颗钻石。所以原先叫“钻石座”。后来，法国天文学家拉卡伊在南非开普敦观测南天星空时．在他的天文望远镜上使用了定位十字丝．提高了测定恒星位置的精确度。为了纪念这个新手段的应用．他就把这个星座改“网罟座”。所以“网罟”并不是渔网的意思。     

人类进化的缺失环节

人类从哪里来，将要到哪里去？这始终是我们追寻的问题。科技发展到今天，已经给我们带来了巨大的益处。曾几何时，我们宣布我们解决了一切问题，不再需要有新的科技、新的发现和新的理论。但随着时间的推移，我们不得不面对一个窘迫的局面：似乎已有的东西，不能使某些问题得到解决，还需要有更多的发现、更多的理论来解决。其中之一就是人类进化中“缺失的环节”。说起“缺失的环节”，不得不从１９世纪中期的一次考古发现谈起：１８５６年８月，在德国西北部的尼安德特河流域发现了一个残缺的头骨。这个头骨在当时引起了巨大的轰动，因为…     

拼版式的世界

看看世界地图就会清楚:如果各块大陆能象玩大型的拼板游戏那样移动,非洲大陆凸出的那部分恰好妥贴地嵌到美洲大陆上.早在1912年,两块大陆的轮廓互相吻合这一点,启发一位德国的气象学家阿·威格纳去探索一种令人瞠目的理论.他认为,地球上的七大洲原先是连着的,是一大整块陆地,他把这个超大洲取名为“潘加埃”,意思是“总大陆”.它在满布着地滞性岩块的海上漂浮,历经了几亿年才漂散开来.威格纳的理论对现存和已绝迹的很多类动植物的分布现象,提供了很有说服力的理由.例如,不少南美的淡水鱼种在非洲有极类似的近支,而它们是不可能远渡重洋,从一个大陆到另一个大陆的.同样,在南美洲和非洲发现的野生猴子,也不像是在两地分别进化的.     

人类能否收到外星人的信号

看过美国电影《外星人》的人们一定还记得这么一组镜头:小外星人躺在临时医院里奄奄一息,周围的人闹哄哄乱成一团,突然,一位科学家脸现喜色冲了进来,大声喊道:“他身上含有DNA!他身上含有DNA!”这里我们不禁要问:为什么要把这个外星人称为“他”呢?为什么要说“他”含有“DNA”呢?事实上,我们对于外星人生命的起源和进化方式一无所知.我们丝毫也不知道性是否是创造某一高级生命所必不可少的.我们还不能断定DNA或别的什么类似的复杂遗传物质是智力存在的必要条件.     

一种运载火箭用大功率电动伺服驱动器的散热设计

散热对电子设备的性能有着直接的影响,散热器广泛应用于电子产品的热设计用于改善其散热能力,因此散热器应作为关键部件进行设计。针对航天领域使用的大功率电动伺服驱动器的散热问题,提出了通过热力学理论计算指导散热器结构设计的方法。首先通过理论计算结果确定散热器的结构尺寸,然后通过PRO/E三维建模软件对散热器进行建模并利用ANYSY ICEPAK热仿真软件对所设计的散热器进行热仿真,最后搭建了伺服驱动器的热试验环境。仿真结果和试验数据均验证了该设计方法的正确性。     

灾难之最

自然界一旦发威,人类瞬间就会变得手无缚鸡之力,只能对其俯首称臣.龙卷风、海啸、地震和火山爆发都能在顷刻之间夺去成千上万的生命,而最终的死亡人数通常永远都不得而知.     

The exosat mission

Exosat, the European X-ray Observatory, was placed in orbit on 26 May 1983. The spacecraft, stabilized axes in three to a few arc second, carries four instruments, two one-metre focal length imaging telescopes, a large area proportional counter array and a gas scintillation proportional counter spectrometer. The salient features of the instrumentation, the sensitivities achieved in orbit and the status after the first year of orbital operation are described. Three specific observations, VO332+53, SCO X–1 and M.83 are discussed to demonstrate the power of the EXOSAT instrumentation and the operational flexibility of the spacecraft and ground system.     

The ROSAT mission

A primary scientific objective of the ROSAT mission is to perform the first all-sky survey with an imaging X-ray telescope leading to an improvement in sensitivity by several orders of magnitude compared with previous surveys. A large number of new sources (? 10⁵) will be discovered and located with an accuracy of 1 arcmin or better. These will comprise almost all astronomical objects from nearby normal stars to distant quasistellar objects. After completion of the survey which will take half a year the instrument will be used for detailed observations of selected sources with respect to spatial structure, spectra and time variability. In this mode which will be open for guest observers ROSAT will provide substantial improvement over the imaging instruments of the Einstein observatory.The main ROSAT telescope consists of a fourfold nested mirror system with 83 cm aperture having three focal plane instruments. Two of them will be imaging proportional counters (0.1 – 2 keV) providing a field of view of 2°, an angular resolution of ≈ 30″ in the pointing mode and a spectral resolution ^ΔE/E ≈ 45% FWHM at 1 keV. The third focal instrument will be a high resolution imager (≈ 3″). The main ROSAT telescope will be complemented by a parallel looking Wide Field camera which extend the spectral coverage into the XUV band.     

The SIGMA mission

SIGMA, a hard X-ray/medium energy gamma ray (30 keV-2 MeV) imaging experiment, is being designed and constructed to attain an angular resolution of the order of 1 arcminute, and a sensitivity of several milliCrabs. The instrument uses a position sensitive detector of the Anger camera variety, and a two dimensional coded mask. The results of the instrument definition study are presented; a flight model will be constructed for a late 1987 launch.     

The tenma mission

Tenma, the second X-ray astronomy satellite of Japan launched in February 1983, is outlined. The main instrument of Tenma is a large-area gas scintillation proportional counter array. Some of the highlights of the results thus far obtained are briefly discussed.     

The Magellan project

Magellan is one of the future space projects being studied by the European Space Agency. The aim is to provide high resolution (λ/Δλ ≥ 2.5 × 10⁴) spectra in the far and extreme UV (between 500 and 1550 Å) of faint galactic and extragalactic objects (V ≤ 16^m). The instrument consists of a mechanical collimator, a concave holographic grating and a bidimensional photon-counting detector. A low resolution mode (λ/Δλ ≥ 10³) will provide spectra of objects as faint as 18^m.5. Magellan is planned as an observatory, operated in real time, and allowing interaction with the observer.     

The Venus ionosphere

Physical properties of the Venus ionosphere obtained by experiments on the US Pioneer Venus and the Soviet Venera missions are presented in the form of models suitable for inclusion in the Venus International Reference Atmosphere. The models comprise electron density (from 120 km), electron and ion temperatures, and relative ion abundance in the altitude range from 150 km to 1000 km for solar zenith angles from 0° to 180°. In addition, information on ion transport velocities, ionopause altitudes, and magnetic field characteristics of the Venus ionosphere, are presented in tabular or graphical form. Also discussed is the solar control of the physical properties of the Venus ionosphere.     

The SAX mission

SAX denotes the X-Ray Astronomy Satellite selected by the Italian National Space Plan for inclusion in the Science Programme. The purpose of SAX is to perform spectroscopic, spectral and time variability studies of celestial X-Ray sources in the energy band from 1 to 200 KeV. It is intended to continue and expand upon previous observations of such sources. The instrumentation consists of four X-Ray imaging concentrators sensitive from 1 to 10 KeV (one of them extending down to 0.1 KeV), one Gas Scintillation Proportional Counter sensitive from 3 to 120 KeV, a Sodium Iodide Scintillator Crystal in Phoswich configuration operating from 15 KeV to 200 KeV; these detectors are coaligned to a common pointing axis. Three Wide Field Cameras (2–30 KeV) with axis at 90° to that of the narrow field instruments complete the payload.The Satellite launch is foreseen for 1988, in a low altitude (500 Km), low inclination (12°) orbit.The SAX scientific programme is carried out by a Consortium of Italian Institutes, in cooperation with Institutes from Holland; a partecipation of the Space Science Department of ESA is also foreseen.     

The SIRTF mission

This paper describes the status of NASA's Space Infrared Telescope Facility (SIRTF) program. SIRTF will be a cryogenically cooled observatory for infrared astronomy from space and is planned for launch early in the next decade. We discuss a newly modified baseline SIRTF mission and review the state of the detector technology which will provide the heart of SIRTF's scientific advances.