月球勘测者"月球勘测轨道器"

美国计划在未来十年内重返月球,向月球发射机器人月球登陆器,并再次实现载人登月.为了给这一宏伟计划做准备,NASA将在2008年十月发射"月球勘测轨道器"(LRO).     

实现机队的最大价值

KealizingtheGreatestValuefromYourFleet编者按：经营性租赁对于中国航空界来说已不是什么新概念，中国南方航空公司就曾在国内率先采用经营性租赁并收到了良好的效果。但是，与传统的购买飞机的航空公司运营方式相比，经营性租赁所占的比例仍较低。本文从经济学的角度详细论述了这种租赁方式的优点，它能令航空公司拥有一文灵活的机队，而无需占用过多的资金，应该说这对于那些新成立的航空公司，或急于占领市场的承运人来说无疑具有十分重要的意义。目前，在经历了1998年亚洲金融危机后，亚太地区，尤其是中国的航空公司普遍面临着效益…     

Implications of subzero metabolic activity on long-term microbial survival in terrestrial and extraterrestrial permafrost

The survival of microorganisms over extended time frames in frozen subsurface environments may be limited by chemical (i.e., via hydrolysis and oxidation) and ionizing radiation-induced damage to chromosomal DNA. In an effort to improve estimates for the survival of bacteria in icy terrestrial and extraterrestrial environments, we determined rates of macromolecular synthesis at temperatures down to -15°C in bacteria isolated from Siberian permafrost (Psychrobacter cryohalolentis K5 and P. arcticus 273-4) and the sensitivity of P. cryohalolentis to ionizing radiation. Based on experiments conducted over ≈400 days at -15°C, the rates of protein and DNA synthesis in P. cryohalolentis were <1 to 16 proteins cell(-1) d(-1) and 83 to 150 base pairs (bp) cell(-1) d(-1), respectively; P. arcticus synthesized DNA at rates of 20 to 1625?bp cell(-1) d(-1) at -15°C under the conditions tested. The dose of ionizing radiation at which 37% of the cells survive (D(37)) of frozen suspensions of P. cryohalolentis was 136?Gy, which was ～2-fold higher (71?Gy) than identical samples exposed as liquid suspensions. Laboratory measurements of [(3)H]thymidine incorporation demonstrate the physiological potential for DNA metabolism at -15°C and suggest a sufficient activity is possible to offset chromosomal damage incurred in near-subsurface terrestrial and martian permafrost. Thus, our data imply that the longevity of microorganisms actively metabolizing within permafrost environments is not constrained by chromosomal DNA damage resulting from ionizing radiation or entropic degradation over geological time.