Radar glory from buried craters on icy moons

Three ice-covered moons of Jupiter, in comparison with rocky planets and Earth's moon, produce radar echoes of astounding strengths and bizarre polarizations. Scattering from buried craters can explain these and other anomalous properties of the echoes. The role of such craters is analogous to that of the water droplets that create the apparition known as "the glory," the optically bright region surrounding an observer's shadow on a cloud. Both situations involve the electromagnetic phenomenon of total internal reflection at a dielectric interface, operating in a geometry that strongly favors exact backscattering. Dim surface craters are transformed into bright glory holes by being buried under somewhat denser material, thereby increasing the intensity of their echoes by factors of hundreds. The dielectric interface thus formed at the crater walls nicely accounts for the unusual polarizations of the echoes.     

The dust halo of Saturn's largest icy moon, Rhea

Saturn's moon Rhea had been considered massive enough to retain a thin, externally generated atmosphere capable of locally affecting Saturn's magnetosphere. The Cassini spacecraft's in situ observations reveal that energetic electrons are depleted in the moon's vicinity. The absence of a substantial exosphere implies that Rhea's magnetospheric interaction region, rather than being exclusively induced by sputtered gas and its products, likely contains solid material that can absorb magnetospheric particles. Combined observations from several instruments suggest that this material is in the form of grains and boulders up to several decimetres in size and orbits Rhea as an equatorial debris disk. Within this disk may reside denser, discrete rings or arcs of material.     

Cassini finds an oxygen-carbon dioxide atmosphere at Saturn's icy moon Rhea

The flyby measurements of the Cassini spacecraft at Saturn's moon Rhea reveal a tenuous oxygen (O(2))-carbon dioxide (CO(2)) atmosphere. The atmosphere appears to be sustained by chemical decomposition of the surface water ice under irradiation from Saturn's magnetospheric plasma. This in situ detection of an oxidizing atmosphere is consistent with remote observations of other icy bodies, such as Jupiter's moons Europa and Ganymede, and suggestive of a reservoir of radiolytic O(2) locked within Rhea's ice. The presence of CO(2) suggests radiolysis reactions between surface oxidants and organics or sputtering and/or outgassing of CO(2) endogenic to Rhea's ice. Observations of outflowing positive and negative ions give evidence for pickup ionization as a major atmospheric loss mechanism.     

论有限合伙

有限合伙集有限责任与无限责任于一身,具有普通合伙与公司法人所不能同时具有的特殊优势。有限合伙是如今现有的所有企业组织形式中最有利于高风险投资的组织形式。应允许所有企业法人参与有限合伙,且不应限制有限合伙人的人数。     

Academe and industry debate partnership

Over 400 academic and corporate leaders attended a gathering, "Partners in the Research Enterprise: A National Conference on University-Corporate Relations in Science and Technology," held 14-16 Dec 1982 at the University of Pennsylvania. Problems explored included the protection of academic freedom and values in collaborative research, the sums of money involved, faculty roles, and patents. Representative Albert Gore, previewing his House subcommittee's report, called for a national guideline-writing conference. Both the universities and industry, however, prefer to draw up pluralistic guidelines based on individual circumstances.     

冰冻雪灾后茶叶病虫害发生趋热势分析及其防控对策

冰冻雪灾对茶叶造成巨大损害,分析了2008年冰冻雪灾后茶叶主要病虫害发生趋势,提出了搞好农业防治,控制病虫基数,恶化病虫发生条件;利用天敌资源,积极推广生物防治;适时药剂防治等针对性防治措施及重要防控对策.