Discovery of Jupiter's 'gossamer' ring

Jupiter's ring system has previously been described as being composed of a 'bright' narrow ring and an interior, vertically-extended halo. The one image which reveals this morphology most clearly is Voyager 2's parting shot of the Jupiter system, a wide-angle (WA) view of the ring ansa in forward-scattered light (FDS 20693.02). The bright ring is plainly visible, and the halo appears after slight contrast enhancement. By further enhancement of this image we have discovered an additional ring, which is far fainter than either of the (already faint) components previously identified, extending to a radius of 210,000 km.     

椭圆齿旋流口平带传热管内自动清洗及其传热强化

介绍了一种特殊结构的旋流口椭圆齿平带的研制。平带上的每个椭圆齿都是使平带自转的流体动力结构元素,平带两侧的旋流口结构能够使管内的部分液体形成螺旋线流,因而具有近似斜齿纽带那样能够在较低流速下自转实现管内污垢在线自动清洗的宝贵性能。由于椭圆齿后的大量涡流、管内部分液体流线转变为螺旋线流股以及螺旋线流股与轴向流股分合交错这样3方面的作用,管内的对流传热强化的幅度由此远远高于光滑纽带。试验结果表明,这种平带不仅容易制造,并且综合性能好,在管内流速0.5m/s左右就可运行;管内侧的传热系数提高170%,流体阻力在一般工程许可的范围内,因此具有较高的工程应用价值。     

Chondrule formation in particle-rich nebular regions at least hundreds of kilometres across

Chondrules are millimetre-sized spherules (mostly silicate) that dominate the texture of primitive meteorites. Their formation mechanism is debated, but their sheer abundance suggests that the mechanism was both energetic and ubiquitous in the early inner Solar System. The processes suggested--such as shock waves, solar flares or nebula lightning--operate on different length scales that have been hard to relate directly to chondrule properties. Chondrules are depleted in volatile elements, but surprisingly they show little evidence for the associated loss of lighter isotopes one would expect. Here we report a model in which molten chondrules come to equilibrium with the gas that was evaporated from other chondrules, and which explains the observations in a natural way. The regions within which the chondrules formed must have been larger than 150-6,000 km in radius, and must have had a precursor number density of at least 10 m(-3). These constraints probably exclude nebula lightning, and also make formation far from the nebula midplane problematic. The wide range of chondrule compositions may be the result of different combinations of the local concentrations of precursors and the local abundance of water ice or vapour.