红外/毫米波双模共孔径光学系统

本文叙述一种折反式卡塞格伦光学系统,该系统通过一个公共孔径可以使红外成象器和毫米波雷达同时工作。采用适当的双色镀膜和基板材料,使红外和毫米波的焦点分开。对设计进行了评价,基本方法是建立一个模型,并在实验室里测试其性能。测量时要特别注意,以便隔离每一种模式由于另一种模式存在而受到的影响。给出了试验结果,并通过分析得出如下结论:此项设计是可行的,但在次镜设计和双色导电镀膜工艺方面都需要做些改进。对于次镜问题,提出了一种明确的解决办法;而关于导电镀膜问题,则论证了对这种镀膜的技术要求不久即可实现。     

美国空军加速推进B-2轰炸机的首次飞行

美国空军与Northrop公司研制的B-2先进技术轰炸机(ATB),如不出现大的设计问题或技术问题,预计会在1988年末进行首次飞行(原订于1987年)。这个飞翼式隐身ATB的首次公开展示和持续45分钟的首次飞行将在位于加州的Northrop Palmdale研究所和附近的爱德华空军基地的飞行试验中心进行。     

Large-scale complementary integrated circuits based on organic transistors

Thin-film transistors based on molecular and polymeric organic materials have been proposed for a number of applications, such as displays and radio-frequency identification tags. The main factors motivating investigations of organic transistors are their lower cost and simpler packaging, relative to conventional inorganic electronics, and their compatibility with flexible substrates. In most digital circuitry, minimal power dissipation and stability of performance against transistor parameter variations are crucial. In silicon-based microelectronics, these are achieved through the use of complementary logic-which incorporates both p- and n-type transistors-and it is therefore reasonable to suppose that adoption of such an approach with organic semiconductors will similarly result in reduced power dissipation, improved noise margins and greater operational stability. Complementary inverters and ring oscillators have already been reported. Here we show that such an approach can realize much larger scales of integration (in the present case, up to 864 transistors per circuit) and operation speeds of approximately 1 kHz in clocked sequential complementary circuits.     

关于相对性原理和等价原理在爱因斯坦引力論中的作用

引言本文目的是要分析建立引力论所依据的原理,換言之,是要分析这一理論的邏輯結构。今天看来,相对论和引力論都成了經典的东西了,但是直到目前为止,对于它們——尤其是对引力論——有时还有些不正确的观念,因而也形成了一些不正确的术语。反之,已经建立起来的不正确术语又使不正确的观念得以保存。因此,术語問题不是一个簡单的形式上的問题,而必須对它加以注意。从这观点出发,下面首先要考察“广义的相对性”和“广义相对論”这两个术語。后者一般是指爱因斯坦的引力論而言。这些术語是爱因斯坦本人引进的,它們反映着他对自己創立的理論的观点。下面簡单介紹一下这些观点。     

The breakdown of continuum models for mechanical contacts

Forces acting within the area of atomic contact between surfaces play a central role in friction and adhesion. Such forces are traditionally calculated using continuum contact mechanics, which is known to break down as the contact radius approaches atomic dimensions. Yet contact mechanics is being applied at ever smaller lengths, driven by interest in shrinking devices to nanometre scales, creating nanostructured materials with optimized mechanical properties, and understanding the molecular origins of macroscopic friction and adhesion. Here we use molecular simulations to test the limits of contact mechanics under ideal conditions. Our findings indicate that atomic discreteness within the bulk of the solids does not have a significant effect, but that the atomic-scale surface roughness that is always produced by discrete atoms leads to dramatic deviations from continuum theory. Contact areas and stresses may be changed by a factor of two, whereas friction and lateral contact stiffness change by an order of magnitude. These variations are likely to affect continuum predictions for many macroscopic rough surfaces, where studies show that the total contact area is broken up into many separate regions with very small mean radius.