奇异星壳层塌缩的数值研究

当奇异星表面的电场不足以支撑整个壳层的时候,壳层就有可能全部落入奇异核中.对这一过程的研究,可以为观测上证认奇异星提供一些可能的理论线索.数值计算表明,底部密度为-8.3×1010gcm-3,亦即质量为-3 4×10-6M(?)的壳层在约5.4×10-3s时间内塌缩到奇异核中,可导致一次持续约0.15s的爆发事件.在过程中平均每个重子释放约6.3 MeV的能量,总辐射能则可高达-1046-1047ergs.这可以用来解释宇宙中一些爆发现象.     

High-energy particle acceleration and production of ultra-high-energy cosmic rays in the giant lobes of Centaurus A

The nearby radio galaxy Centaurus A is poorly studied at high frequencies with conventional radio telescopes because of its very large angular size, but is one of a very few extragalactic objects to be detected and resolved by the Wilkinson Microwave Anisotropy Probe ( WMAP ). We have used the five-year WMAP data for Cen A to constrain the high-frequency radio spectra of the 10° giant lobes and to search for spectral changes as a function of position along the lobes. We show that the high-frequency radio spectra of the northern and southern giant lobes are significantly different: the spectrum of the southern lobe steepens monotonically (and is steeper further from the active nucleus) whereas the spectrum of the northern lobe remains consistent with a power law. The inferred differences in the northern and southern giant lobes may be the result of real differences in their high-energy particle acceleration histories, perhaps due to the influence of the northern middle lobe, an intermediate-scale feature which has no detectable southern counterpart. In light of these results, we discuss the prospects for Fermi Gamma-ray Space Telescope detections of inverse-Compton emission from the giant lobes and the lobes' possible role in the production of the ultra-high-energy cosmic rays (UHECR) detected by the Pierre Auger Observatory. We show that the possibility of a Fermi detection depends sensitively on the physical conditions in the giant lobes, with the northern lobe more likely to be detected, and that any emission observed by Fermi is likely to be dominated by photons at the soft end of the Fermi energy band. On the other hand, we argue that the estimated conditions in the giant lobes imply that UHECRs can be accelerated there, with a potentially detectable γ-ray signature at TeV energies.     

Predicted interplanetary shocks/particles at Mars compared with in-situ observations: An overview

The biological and technological consequences of long-duration, solar-related, energetic particle radiation for manned/unmanned spacecraft warrant that consideration be given to providing reliable space weather predictions for future space missions to planet Mars. An account is, herein, provided of how the HAFv.2 numerical model was applied to predict the arrivals of four, flare-related, shocks at Mars generated during a >20-day active period on the Sun in March 1989, and of the arrival of another composite shock produced in association with a 10-day period of solar activity in December 2006. These predictions are compared with in-situ measurements of shock signatures at Mars recorded, in the former case, by the solar-low-energy-detector (SLED) and by the low-energy-telescope (LET) aboard the Phobos-2 spacecraft and, in the latter case, in data recorded by the ASPERA-3/IMA instrument aboard Mars Express. The success of the predictions is discussed and the requirement for further validation of the modeling technique using a large statistical sample pointed out. In-situ measurements made aboard Mars Express by the ASPERA-3/IMA experiment during the rising phase of Solar Cycle 24 can provide data relevant to such validation. The successful application of a SOLar Particle ENgineering COde (SOLPENCO), that estimates solar energetic particle (SEP) fluxes and fluences at the Earth, to the case of an energetic particle event at Mars (6 March 1989) is discussed. Measurements of SEP events recorded by the Solar TErrestrial RElations Observatory (STEREO) supplemented by Mars Express measurements can potentially allow the predictions of SOLPENCO to be further studied downstream using a large statistical sample. However, we are presently only at the beginning of our understanding of the complex Sun-Earth-Mars scenarios that give rise to shock/particle events in the close Martian environment.     

海水中碳酸根与固体粒子的相互作用

本文研究了海水中碳酸根在固体粒子上的吸附。碳酸根在各种因素颗粒物上的吸附程度上大小顺序为：赤铁矿〉δ－ＭｎＯ２〉水锰矿〉ＳｉＯ２,最大吸附量可达到约２ｍｇＣ／ｇ吸附剂,且最大吸附值均在天然海水ｐＨ（ｐＨ８）左右。在低ＰＨ时,碳酸根对ＮａＣｌ介质中砷酸根的吸附没有影响,在高ｐＨ时,则降低了砷酸根在固体颗粒物上的吸附量,因此碳酸根的存在对其他阴离子的吸附会产生竞争作用。     

透明胞外聚合颗粒物碳输运新途径

目前大家普遍认为,透明胞外聚合颗粒物(Transparent Exopolymer Particles,TEP)因其独特的凝聚效应导致碳通量向海底输出。但是,近几年的研究表明TEP不仅影响了碳沉降途径,其本身能够悬浮甚至向海水表层迁移,导致其在海洋微表层(Surface Micro-layer, SML)积累,最终显著影响海洋表层碳通量。TEP和其他颗粒物聚集形成凝聚物后,其运动趋势则由凝聚物中TEP的含量占比,即最终颗粒物密度所决定。一个新的值得注意的现象是,密度低的TEP通过与其他微粒聚合形成表面活性物质(Surface-active Substances, SAS),会在海洋–大气界面形成薄膜,显著影响海–气CO₂交换通量,甚至对全球气候变化造成影响。     

Storm-driven shelf-to-canyon suspended sediment transport at the southwestern Gulf of Lions

Shelf-to-canyon suspended sediment transport during major storms was studied at the southwestern end of the Gulf of Lions. Waves, near-bottom currents, temperature and water turbidity were measured on the inner shelf at 28-m water depth and in the Cap de Creus submarine canyon head at 300 m depth from November 2003 to March 2004. Two major storm events producing waves H_s>6 m coming from the E–SE sector took place, the first on 3–4 December 2003 (max H_s: 8.4 m) and the second on 20–22 February 2004 (max H_s: 7 m). During these events, shelf water flowed downcanyon producing strong near-bottom currents on the canyon head due to storm-induced downwelling, which was enhanced by dense shelf water cascading in February 2004. These processes generated different pulses of downcanyon suspended sediment transport. During the peak of both storms, the highest waves and the increasing near-bottom currents resuspended sediment on the canyon head and the adjacent outer shelf causing the first downcanyon sediment transport pulses. The December event ended just after these first pulses, when the induced downwelling finished suddenly due to restoration of shelf water stratification. This event was too short to allow the sediment resuspended on the shallow shelf to reach the canyon head. In contrast, the February event, reinforced by dense shelf water cascading, was long enough to transfer resuspended sediment from shallow shelf areas to the canyon head in two different pulses at the end of the event. The downcanyon transport during these last two pulses was one order of magnitude higher than those during the December event and during the first pulses of the February event and accounted for more than half of the total downcanyon sediment transport during the fall 2003 and winter 2004 period. Major storm events, especially during winter vertical mixing periods, produce major episodes of shelf-to-canyon sediment transport at the southwestern end of the Gulf of Lions. Hydrographic structure and storm duration are important factors controlling off-shelf sediment transport during these events.     

EXPERIMENTAL STUDY ON FALL VELOCITY OF NON-UNIFORM SEDIMENT IN FLOWING WATER

I INTRODUCTIONThe settlement of particles in fluid has been studied in many fields such as hydraulics, metallurgy andchemistry since the middle of 19 century because of its great importance. Although the settlement ofsingle particle and group settling velocity of uniform particles in still water are relatively well-studied, yetthe settlement of non-uniform particles in flowing water lacks understanding. For instance, Cunningham(1910), Richardson (1954) and Batchelor (1972), have obtained…