Contribution of galaxies to the background hydrogen-ionizing flux

We estimate the evolution of the contribution of galaxies to the cosmic background flux at 912 Å by means of a semi-analytic model of galaxy formation and evolution. Such modelling has been quite successful in reproducing the optical properties of galaxies. We assume that high-redshift damped Lyman α systems are the progenitors of present-day galaxies, and we design a series of models that are consistent with the evolution of cosmic comoving emissivities in the available near-infrared, optical, ultraviolet and far-infrared bands along with the evolution of the neutral hydrogen content and average metallicity of damped Lyman α systems. We use these models to compute the galactic contribution to the Lyman-limit emissivity and background flux for 0 ≃  z  ≤ 4. We take into account the absorption of Lyman-limit photons by H  I and dust in the interstellar medium of the galaxies. We find that the background Lyman-limit flux due to galaxies might dominate (or be comparable to) the contribution from quasars at almost all redshifts if the absorption by H  I in the interstellar medium is neglected. Such H  I absorption would result in a severe diminishing of this flux — by almost three orders of magnitude at high redshifts and by one to two orders at z  ≃ 0. Though the resulting galaxy flux is completely negligible at high redshifts, it is comparable to the quasar flux at z  ≃ 0.     

Meteorology and haze structure during AGASP-II,Part 2: Canadian Arctic flights, 13–16 April 1986

In April 1986, a well-instrumented NOAA WP-3D research aircraft conducted three flights in the Canadian Arctic tied to the Canadian Atmospheric Environment Service baseline station in Alert, Northwest Territories. Two of the flights were coordinated with the National Aeronautical Establishment of Canada Twin Otter and the University of Washington C-131 research aircraft. The haze observed in the Canadian Arctic was well-aged and mixed throughout the troposphere in concentrations well below those observed during the previous weeks in the Alaskan Arctic. Over the ice, beneath the surface temperature inversion, ozone was generally depleted to near zero. Over the coast at Alert, there is evidence that topography and downslope winds reduce the strength of the inversion, thus allowing lower tropospheric gases and aerosols to mix down to the surface. At the top of the troposphere, an aerosol-depleted region was observed. In the lower stratosphere, aerosol concentrations were elevated above those observed in the troposphere.     

偏光镜下宝石消光异常的解析

对宝石在偏光镜检测中经常出现的消光异常现象做了总结和解析，以帮助检测者更淮确地判断宝石光性。     

Biotic recovery from the Late Devonian F-F mass extinction event in China

The Frasnian-Famennian (F-F) mass extinction is one of the five great extinctions of marine life during the Phanerozoic. The F-F event killed most of the Devonian reefs, the characteristic Devonian corals, stromatoporoids, bryozoans, nearly all tentaculites, a few superfamilies of brachiopods, such as Atrypacea and Pentameracea and some important elements of goniatites, such as Manticoceras. The end-Frasnian was a phase of mass extinction. A large number of shelly benthos were killed by the F-F event. Early and middle Famennian was the survival interval. The marine faunas were very rare at that time. The late Famennian was the recovery interval. There appeared to have many new taxa in the Strunian stage. It lacked a radiation interval in Late Devonian Famennian because another event (the D-C mass extinction) happened at the Devonian-Carboniferous boundary. Several causes for the F-F mass extinction have been proposed by some geologists, which have been grouped into two broad types, terrestrial and extraterrestrial. The former is related to sea level changes, climate changes and anoxic water event. The latter is linked with some forms of meteorite impact. A large-scale eustatic change of sea level and black shales representing an anoxic environment has been invoked to explain one of the causes for the F-F mass extinction.     

Aerosol concentration measurement with multiple light scattering system and laser aerosol spectrometer

The performance of two different optical concentration-measuring techniques was investigated over a concentration range starting with about 10² cm⁻³ and extending over more than four decades. Both instruments are capable of real-time counting, however due to their particular design-single particle counter and ensemble particle-measuring system—they operate in overlapping, but different concentration ranges. The upper, coincidence-free counting limit for the single particle counter used in this study was established to be in the order of 10⁴ cm⁻³. The ensemble technique was found to be functional and stable for concentrations of about 10³ cm⁻³ and limited by the onset of multiple scattering at concentrations nearby 2×10⁶ cm⁻³. Within the determined boundaries, both techniques proved to provide reliable aerosol concentration data.     

Lower Triassic Inorganic Carbon Isotope Excursion in Chaohu, Anhui Province, China

This paper reports a Lower Triassic carbon isotope profile from the North Pingdingshan Section in Chaohu, Anhui Province, China, which was stituated in a deep part of the Lower Yangtze carbonate rapm. The δ(^13C) excursion shows two periods from the Permian-Triassic boundary to the lower Spathian substage, corresponding to the ecosystem undergoing evolution and recovery after the end-Permian mass extinction and related events.The first period starts at the δ(^13C) depletion caused by the mass extinction and evolves with a gradual δ(^13C) increase resulting from the development of some disaster taxa during the Induan. The strong Smithian δ(^13C) depletion in the second period might be formed by the collapse of the disaster ecosystem and the biotic recovery occurred with the explosive increase of bioproductivity in the Spathian. Thus the δ(^13C) excursion in the Lower Triassic expresses patterns of biotic evolution and recovery during the eratic ecosystem that followed the great end-Permian mass extinction.     

Geochemistry of Late Permian to Early Triassic pelagic cherts from southwest Japan: implications for an oceanic redox change

Major, trace, and rare earth element abundances were determined for the southwestern Japanese pelagic chert sequence from the early Late Permian to early Early Triassic to investigate a redox change in deep-sea pelagic environments before and at the Permo-Triassic boundary (PTB) (251 Ma). The sequence was primarily deposited in the deep-sea of the superocean Panthalassa, and then was accreted to Japan in the Middle Jurassic. A remarkable lithostratigraphic change from red chert to siliceous∼carbonaceous claystone through gray chert is observed in this sequence. Constituent elements for these sedimentary rocks are essentially derived from two sources: (1) an ancient seawater via biogenic (mainly radiolarian), hydrothermal, and authigenic materials and (2) an average shale-like terrigenous material. The present measurement demonstrates significant stratigraphic changes of the Ce/Ce_non-ter* value (estimated Ce anomaly value of non-terrigenous component, recalculated by subtraction of terrigenous REEs from bulk REEs) and the (Mn/TE)_sample/(Mn/TE)_PAAS value (excess Mn component other than terrigenous one; TE=terrigenous elements including Ti, Al, Nb, Hf, Th; PAAS=Post-Archean Average Australian Shale) in the Permian chert. The Ce/Ce_non-ter* values increase from <0.2 to 1 and the (Mn/TE)_sample/(Mn/TE)_PAAS values decrease up-section, suggesting that the redox condition of deep-sea open-ocean changed from oxic to suboxic in an interval of approximately 10 Myr. The (∑Fe/TE)_sample/(∑Fe/TE)_PAAS and (Mn/TE)_sample/(Mn/TE)_PAAS values of carbonaceous claystone near or at the PTB are less than unity, suggesting that reductive dissolution of iron and manganese occurred under an anoxic condition. This supports the idea of the PTB oceanic anoxia in the superocean Panthalassa. The present data suggest that the anoxic condition prevailed in the deep-sea pelagic regions for an extremely long period, much more than 10 Myr, from the middle Late Permian to early Early Triassic. This long-term development of widespread oceanic anoxia may have been linked to the greatest mass extinction of the Phanerozoic.     

历史上新疆白鹳的地理分布区域考证

经过实地考察和访问，以及结合中国古籍和近代的鸟类学文献，对曾经分布于我国新疆的中亚白鹳（Ciconia ciconia asiatica)种群的过去和现在有了比较清楚的认识。据Scully(1876)和Ludlow and Kinnear(1933-34)等记载，一百年前，这是一个比较常见的种类，曾广泛分布于新疆南部的莎车和喀什等地区。根据笔者自1985－2001年对新疆各地的调查和访问，中亚白鹳在新疆（或者说在全中国）消失的年代大约为1980年前后。其原因归结为人为因素和自然因素，如绿洲人口的增加、农业开垦、栖息环境（湿地）的破坏和丧失、种间竞争（自然因素）以及不应有的滥捕乱猎行为等。白鹳比较喜欢亲近人类（有“送子鸟”之美誉），这也是其遭受厄运的原因之一。目前，新疆还有十几种鸟类（如鹈鹕、琵鹭、黑鹳、鸿雁、疣鼻天鹅、云石斑鸭、白肩雕、马雕、猎隼、黄爪率、白鹤、斑胸田鸡、长脚秧鸡、大鸨、小鸨、波斑鸨、遗鸥、小鸥、中亚鸽等）亦正面临相同的命运。