Molecular biology: CACA sequences — the ends and the means?
Molecular biology: CACA sequences — the ends and the means?
复制标题
分子生物学：CACA 序列——目的和手段？
作者：
J. Rogers
在最近一期的《物理评论快报》中，MT Yin和ML Cohen提出了钻石是否会在压力下转变的问题;他们的答案是，在23 Mbar左右，钻石将采用简单的立方体晶体结构。这一结果具有实际重要性，因为金刚石在用于产生高压的设备中广泛用作砧。金刚石非常坚固，并且可以以允许施加在相对大的面上的压力在较小面积的相对面上产生大得多的压力的形状获得。钻石对电磁辐射的光谱也是透明的，因此可以在砧座之间的压力下对材料进行许多实验。在过去的十年里，人们以这种方式获得了有关高压下物质行为的广泛重要结果2·目前，在高达500 kbar（-500，000 kg em· 2）的压力下进行测量非常普遍。在这类工作中最困难的任务之一是获得高压单元内的压力的精确值，但是压力标度现在已经合理地建立到500 kbar。向更高压力的进展涉及现有技术的稳定扩展，以及金刚石砧在压力下不会变形或失效的要求。货车Vechten在1971年根据锗和硅在压力下的行为进行了推断，预测金刚石的结构将在1.3 Mbar的压力下改变为β-锡结构（参考文献3）。然而，毛泽东和贝尔4随后声称已经达到了静压，
IN a recent issue of Physical Review Letters, MT Yin and ML Cohen'pose the question of whether diamonds will transform under pressure; their answer is that at around 23 Mbar diamond will adopt a crystallographic structure which is simply cubic. This result is of practical importance because of the widespread use of diamonds as anvils in equipment used to generate high pressures. Diamonds are very strong and are available in shapes which permit a pressure applied on a relaiively large face to produce a much greater pressure over an opposite face of smaller area. Diamonds are also transparent to a spectrum of electromagnetic radiation, so it is possible to carry out many experiments on materials confined under pressure between the anvils. During the past ten years a wide range of important results on the behaviour of matter at high pressure has been obtained in this way2•At present, measurements are being made quite commonly at pressures up to 500 kbar (-500,000 kg em· 2). One of the most difficult tasks in this type of work is to obtain accurate values for the pressure within the high-pressure cell, but pressure scales are now reasonably well established up to 500 kbar. Progress to higher pressures involves the steady extension of present techniques, and also the requirement that the diamond anvils will not transform or fail under pressure. Extrapolations from the behaviour of germanium and silicon under pressure made by Van Vechten in 1971 predicted that the structure of diamond would change to the (J-tin structure at a pressure of 1.3 Mbar (ref. 3). However, Mao and Bell4 subsequently claimed to have reached a static pressure of
酵母染色体末端是否有左手DNA？
影响因子：
64.8
作者：
Walmsley,RM;Szostak,JW;Petes,TD
通讯作者：
Petes,TD
细胞癌基因的转导：劳斯肉瘤病毒的起源。
DOI：
10.1073/pnas.80.9.2519
发表时间：
1983
影响因子：
11.1
作者：
Swanstrom,R;Parker,RC;Varmus,HE;Bishop,JM
通讯作者：
Bishop,JM
影响因子：
14.9
作者：
BEATON, AR;KRUG, RM
通讯作者：
KRUG, RM