准噶尔盆地中部III 区块原油中25-降藿烷分布特征与成因意义

通过对准噶尔盆地中部Ш区块原油或油砂抽提物的饱和烃气相色谱-质谱分析,研究了原油或油砂抽提物中25-降藿烷的分布规律.结果表明,不同井区或同一口井不同深度(层位)的原油25-降藿烷的相对含量存在比较明显的差别,表明其所遭受的生物降解程度有所差异,沿构造带从南到北,同一油层中原油的生物降解程度增强,比如位于构造北部(构造部位相对较高)的永1井、永3井侏罗系原油25-降藿烷丰度较高,表明生物降解比较明显,而位于南部(构造低部位)的永6井白垩系和侏罗系油层中的原油均无明显的生物降解现象;同一口井随深度增大生物降解作用将弱,如永2井浅部白垩系油层的原油降解较严重,而深部西山窑组的原油降解作用则不明显.根据原油生物降解的特征,结合车-莫古隆起调整对研究区油气成藏的影响,讨论了原油生物降解差异分布的成因机制.     

Climate changing characteristics of Zhangye City in Heihe River basin during 1968–2005

At present, researches on climate change of the Heihe River basin mainly focus on the relationship between basin climate change and regional water resources, regional desertification and dynamic climatic seasons of sandstorm, but less on climate change of oasis region, where there are more intense and frequent human activities. Based on data of precipitation, temperature, strong wind and dust events frequencies obtained from the six meteorological stations of Zhangye region in Heihe River basin, the features of climate change during 1968–2005 were carefully studied. Results show that the regional temperature rise rate exceeded the average level of China. The annual precipitation changed a little, but the precipitation had a slowly increasing trend in spring and winter. Frequencies of strong wind and sandstorm days show obviously descending trends, which had a close correlation with the regional temperature rise and the precipitation increase in spring and winter. Meanwhile, further human economic activities and exploitations to the oasis in the inland valley of arid regions also affected the climate change of this region, which has a sensitive and fragile eco-environment. __________ Translated from Journal of Desert Research, 2007, 27(6): 1048–1054 [译自: 中国沙漠]     

Impacts of growth in resource use and human population on the Nechako River: A major tributary of the Fraser River, British Columbia, Canada

Hydroelectric development, forest exploitation, agricultural land use and related human population numbers have increased rapidly during the last 40 years, in the basin of the Nechako River, a major tributary system of the Fraser River. The Kemano project of the Aluminum Company of Canada Ltd. begun in 1950, was the largest industrial scheme in the area. A key feature of the first stage of it was a dam which diverted about 40% of flow of the south branch of the Nechako River, through a tunnel in the mountains, to the Pacific Ocean. In 1987 an agreement for the Kemano Completion Project (KCP), which would have diverted 87% of the flow, was signed. This final phase of the project would have put important fisheries resources of the upper Fraser River at high risk. Mitigation for fisheries protection were inadequate or untested in the system at the time. Potential cumulative impacts of water abstraction, elevated pollution levels, increased water temperature and natural sediment were not addressed. In January 1995 KCP was cancelled but there remain at present no adequate measures to protect the fish and the river ecosystem. These measures are to be negotiated in the future. Future management of the whole Kemano development must provide biologically realistic flow and temperature regimes in the Nechako River, and must deal with cumulative impacts of population and industrial growth. To achieve sustainability of fisheries in the Nechako River and upper Fraser watershed the present approach to the Kemano development must be changed fundamentally. The future of the Kemano development must be set in the context of the whole future of the upper Fraser system. Continued growth and development, as has occurred in the upper Fraser and total basin, can not go on without inimical changes to ecosystem conditions and loss of fisheries resources.     

Photochemistry and Vertical Transport in Io's Atmosphere and Ionosphere

We present an updated model for the photochemistry of Io's atmosphere and ionosphere and use this model to investigate the sensitivity of the chemical structure to vertical transport rates. SO₂is assumed to be the dominant atmospheric gas, with minor molecular sodium species such as Na₂S or Na₂O released by sputtering or venting from the surface. Photochemical products include SO, O₂, S, O, Na, NaO, NaS, and Na₂. We consider both “thick” and “thin” SO₂atmospheres that encompass the range allowed by recent HST and millimeter-wave observations, and evaluate the possibility that O₂and/or SO may be significant minor dayside constituents and therefore likely dominant nightside gases. The fast reaction between S and O₂limits the column abundance of O₂to ∼10⁴less than that calculated by Kumar (J. Geophys. Res.87, 1677–1684, 1982; 89(A9), 7399–7406, 1984) for a pure sulfur/oxygen atmosphere. If a significant source of NaO₂or Na₂O were supplied by the surface and mixed rapidly upward, then oxygen liberated in the chemical reactions which also liberate free Na would provide an additional source of O₂. Fast eddy mixing will enhance the transport of molecular sodium species to the exobase, in addition to increasing the vertical transport rate of ions. Ions produced in the atmosphere will be accelerated by the reduced corotation electric field penetrating the atmosphere. These ions experience collisions with the neutral gas, leading to enhanced vertical ion diffusion. The dominant ion, Na⁺, is lost primarily by charge exchange with Na₂O and/or Na₂S in the lower atmosphere and by diffusion through the ionopause in the upper atmosphere. The atmospheric column abundance of SO, O₂, and the upper atmosphere escape rates of Na, S, O, and molecular sodium species are all strong functions of the eddy mixing rate. Most atmospheric escape, including that of molecular sodium species, probably occurs from the low density “background” SO₂atmosphere, while a localized high density “volcanic” SO₂atmosphere can yield an ionosphere consistent with that detected by the Pioneer 10 spacecraft.     

Coronal magnetic fields from microwave polarization observations

The solar active region (AR) 7530 was observed at 6 cm on July 3 and 4, 1993 with the Westerbork Synthesis Radio Telescope, using a multi-channel receiver with very narrow bandwidth. We compare the radio data with Yohkoh SXT observations and with the magnetic field extrapolated from the Marshall vector magnetograms in the force-free and current-free approximations. The comparison with soft X-rays shows that, although a general agreement exists between the shape of the radio intensity map and the X-ray loops, the brightness temperature, T _b, obtained using the parameters derived from the SXT is much lower than that observed. The comparison with the extrapolated photospheric fields shows instead that they account very well for the observed T _b above the main sunspots, if gyroresonance emission is assumed. In the observation of July 4 an inversion and strong suppression of the circular polarization was clearly present above different portions of the AR, which indicates that particular relationships exist between the electron density and the magnetic field in the region where the corresponding lines of sight cross the field quasi-perpendicularly. The extrapolated magnetic field at a much higher level ( 10¹⁰ cm), satisfies the constraints required by the wave propagation theory all over the AR. However, a rather low electron density is derived.     

The relationship between zooplankton,conductivity and lake-water ionic composition in 111 lakes from the Interior Plateau of British Columbia,Canada

Zooplankton collected from vertical net tows were related to the environmental variables from 98 lakes from the Interior Plateau of British Columbia. Canonical correspondence analysis showed that both salinity and ionic composition (pH and Mg) of the lake-water made major and significant contributions to the first two ordination axes (=0.42 and 0.11 respectively,P<0.05). BothArtemia franciscana andMoina hutchinsoni had their highest relative abundance in meso-hypersaline waters. However,Artemia franciscana preferred waters that were higher in Mg and Ca, whileMoina hutchinsoni was found in waters that were lower in Mg and Ca. Similarly, at intermediate salinities,Daphnia pulex and the calanoid copepods preferred waters slightly lower in Mg and Ca, whereasCeriodaphnia laticaudata andSimocephalus spp. were relatively more common in waters higher in Mg and Ca. Because the freshest lakes studied varied much less in ionic composition, the zooplankton in these lakes did not show a preference to ionic composition. As expected, multi-generic groups, such as the calanoid copepods, cyclopoid copepods and nauplii, had wider tolerances to conductivity than groups identified to lower taxonomic levels. Significant weighted-averaging regression and calibration models of conductivity were developed based on zooplankton species composition from the study lakes (r ²=0.56,P<0.05). Samples composed largely of multi-generic taxa yielded the worst estimates of salinity in the reconstruction model. This study suggests that zooplankton community composition may be developed into a useful proxy for paleosalinity reconstruction.     

Imaging coronal emission lines under high sky-background conditions

We have obtained images in solar coronal emission lines under high sky-background conditions by making precise differential measurements between the coronal emission line and the near-by continuum, which is primarily due to scattered light from the solar disk. Chopping between the two wavelengths was performed at 100 kHz to avoid artifacts from fast-flying dust particles and other aerosols, and also from seeing effects. The differential signal was detected with a novel CCD camera that demodulates signals up to 100 kHz. These preliminary observations show coronal emission at the 0.2% level of the scattered-light background and pave the way to efficient and precise imaging of coronal emission features under less than ideal coronal-sky conditions.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.     

About the specification of erosion flux for soft stratified cohesive sediments

The present paper deals with the specification of bed erosion flux that accounts for the effects of sediment-induced stratification in the water column. Owing to difficulties in measuring the bed shear stress _b and the erosive shear strength _s, we suggest a series of methods that combine laboratory and numerical experiments. A simplified turbulent transport model that includes these effects helps to quantify _b and _s. Focusing on soft stratified beds, the present study considers erosion rate formulas of the form =_f exp {[T_b-T_s]} where is a model constant (=1 for Gularte's (1978) formula and =1/2 for Parchure's (1984) formula). First, the bed erosive strength profile _s(Z) is adjusted by forcing the turbulent transport model with measured erosion rates. Second, three procedures are suggested to determine the erosion rate formula coefficients _f and : a global procedure and two different layer-by-layer procedures. Each procedure is applied to an erosion experiment conducted in a rotating annular flume by Villaret and Paulic (1986). The use of the layer-by-layer procedure based on a least squares fitting technique provides a closer fit than the global procedure. The present study points out the complementarity of experimental and numerical approaches and also suggests possible improvements in laboratory test procedures.