Mars exploration.

An international flotilla of spacecraft are to be sent to Mars over the next decade in an effort to understand the planet's geology and climate history, and to determine whether some form of life ever started there. At least two spacecraft will be sent at each launch opportunity, and at times up to four spacecraft may be operating simultaneously at the planet.     

A piezoelectric tracked vehicle with potential application to planetary exploration

A piezoelectric driving method for rover vehicles is proposed in this paper. Employing this method, a tracked vehicle driven by friction forces from a frame mounted with piezoelectric elements was developed. The vehicle is designed with no driver sprocket, no idler-wheel and no supporting bogie wheels, and the vehicle thus requires no lubrication and has potential application in planetary exploration. The frame consists of a pair of piezoelectric transducers. Each transducer comprises four annular parts jointed by beams adhered with piezoelectric ceramics. The tracks are set to the outer surface of the annular parts by means of track tension. Traveling rotating waves are generated by piezoelectric transducers in the annular parts, which generate microscopic elliptical motions at the interface of the tracks. The microscopic elliptical motions from the piezoelectric transducers drive the track vehicle to move. Finite elements analysis was carried out to verify the operation principle using commercial software ANSYS. Piezoelectric transducers were fabricated, assembled and tested to validate the concepts of the proposed rover vehicle and confirm the simulation results. A prototype vehicle with mass of 0.57 kg moves at a speed of 4.3 mm/s at a driving voltage of 250 V and operating frequency of 65.53 kHz.     

Hf-W-Th evidence for rapid growth of Mars and its status as a planetary embryo

Terrestrial planets are thought to have formed through collisions between large planetary embryos of diameter ～1,000-5,000?km. For Earth, the last of these collisions involved an impact by a Mars-size embryo that formed the Moon 50-150?million years (Myr) after the birth of the Solar System. Although model simulations of the growth of terrestrial planets can reproduce the mass and dynamical parameters of the Earth and Venus, they fall short of explaining the small size of Mars. One possibility is that Mars was a planetary embryo that escaped collision and merging with other embryos. To assess this idea, it is crucial to know Mars' accretion timescale, which can be investigated using the (182)Hf-(182)W decay system in shergottite-nakhlite-chassignite meteorites. Nevertheless, this timescale remains poorly constrained owing to a large uncertainty associated with the Hf/W ratio of the Martian mantle and as a result, contradicting timescales have been reported that range between 0 and 15?Myr (refs 6-10). Here we show that Mars accreted very rapidly and reached about half of its present size in only 1.8(+0.9)(-1.0) Myr or less, which is consistent with a stranded planetary embryo origin. We have found a well-defined correlation between the Th/Hf and (176)Hf/(177)Hf ratios in chondrites that reflects remobilization of Lu and Th during parent-body processes. Using this relationship, we estimate the Hf/W ratio in Mars' mantle to be 3.51?±?0.45. This value is much more precise than previous estimates, which ranged between 2.6 and 5.0 (ref. 6), and lifts the large uncertainty that plagued previous estimates of the age of Mars. Our results also demonstrate that Mars grew before dissipation of the nebular gas when ～100-km planetesimals, such as the parent bodies of chondrites, were still being formed. Mars' accretion occurred early enough to allow establishment of a magma ocean powered by decay of (26)Al.     

Water-maser emission from a planetary nebula with a magnetized torus.

A star like the Sun becomes a planetary nebula towards the end of its life, when the envelope ejected during the earlier giant phase becomes photoionized as the surface of the remnant star reaches a temperature of approximately 30,000 K. The spherical symmetry of the giant phase is lost in the transition to a planetary nebula, when non-spherical shells and powerful jets develop. Molecules that were present in the giant envelope are progressively destroyed by the radiation. The water-vapour masers that are typical of the giant envelopes therefore are not expected to persist in planetary nebulae. Here we report the detection of water-maser emission from the planetary nebula K3-35. The masers are in a magnetized torus with a radius of about 85 astronomical units and are also found at the surprisingly large distance of about 5,000 astronomical units from the star, in the tips of bipolar lobes of gas. The precessing jets from K3-35 are probably involved in the excitation of the distant masers, although their existence is nevertheless puzzling. We infer that K3-35 is being observed at the very moment of its transformation from a giant star to a planetary nebula.     

民治是建设海南公民社会的主要途径

民治即公民治理,是人民参与国家治理和社会管理.公民社会是独立于国家但又受到法律保护的社会生活领域及与之相关联的一系列社会价值或原则.在公民社会中,公民依靠自己与生俱来的权利而成为国家政治生活的主体,而不盲从于任何既定权威的安排.     

深水探井钻前含可信度的地层孔隙压力确立方法

针对深水探井钻井可参考信息有限的特点,提出改进的计算上覆岩层压力梯度和建立时深关系的方法.利用概率统计理论,研究Eaton法中各个参数对最终结果的影响规律和相互关系,提出基于层速度的有效应力法与Eaton法联合预测地层孔隙压力的方法,建立了含有可信度的地层孔隙压力剖面,使其不再是一条单一的曲线,而是具有可信度信息的区间.可信度越大,得出的地层孔隙压力梯度区间越大,其不确定范围越大;反之,虽然压力梯度的不确定范围缩小,但其可信程度也随之降低;地层孔隙压力的异常高压程度越剧烈,其压力区间也越大.西非深水区域一口探井计算结果与实测压力值具有较好的一致性.     

论如何构建人地和谐的和谐社会

构建人地和谐的和谐社会，首先在于认识人地关系，以及其不以人的意志为转移的客观规律．阐述了人地关系的概念及其内涵，分析了人地矛盾及其表现，论述了构建人地和谐的和谐社会应注重建立可持续发展的理念和系统发展观、树立生态伦理和环境道德观念、加强立法工作以保护生态环境和加强国民生态文明教育等几个方面的对策和措施．依照人地和谐的规律行事，构建民主法治、公平正义、诚信友爱、充满活力、安定有序、人与自然和谐相处的和谐社会．     

绿色班级创建的价值探求

创建绿色班级的目的是将让环保理念融入到大学生的学习、生活和工作中, 为经济社会可持续发展培养出有环境科学知识和生态伦理道德的高级人才. 提高环境意识的意义在于它是经济社会可持续发展的基础;是提高国民素质的重要内容. 提高环境意识要从环境价值观教育、环境责任感教育和自觉参与环保教育几个方面进行. 本文对高校创建绿色班级的价值进行了探讨. 广泛开展绿色班级创建活动, 能够使专业性环境教育转向素质型环境教育, 使高校成为培养绿色高级人才的摇篮和走向绿色文明的先导.     

太空探索新期待：“火星之旅”试演

虽然美国与欧洲公布的人类火星登陆计划均在2030年之后,但各国科学家显然并不局限于此,而是未雨绸缪,努力将此时间表加速提前.5月18日,俄罗斯科学院生物医学研究所在莫斯科宣布,人类首次模拟火星载人航天飞行试验"火星-500"将于6月3日在该所正式实施密闭,一场激动人心的"火星之旅"即将面对全世界试演(5月19日<人民日报>).     

现实必须正视规律不可抗拒--当代发达资本主义国家正处在向社会主义社会和平过渡之中

当代发达资本主义国家的现实是一个客观存在，对这个客观存在却有着不同的认识。发达而又发达的、不断否定着自身的资本主义还是原来的资本主义吗?本文认为，历史规律不可抗拒，社会进步势在必然，当代发达资本主义国家正处在向马克思主义经典作家所设想的、由社会历史规律所决定的本来意义上的社会主义社会和平过渡之中——这是马克思主义的胜利。