Ultraviolet-background-induced bifurcation of galactic morphology     

Hajime Susa  Masayuki Umemura 《Monthly notices of the Royal Astronomical Society》2000,316(2):L17-L20

Based upon a novel paradigm of galaxy formation under the influence of an ultraviolet background, the evolutionary bifurcation of pre-galactic clouds is compared with observations of elliptical and spiral galaxies. The theory predicts that the dichotomy between dissipational and dissipationless galaxy formation stems from the degree of self-shielding from the ultraviolet background radiation. This is demonstrated on a bifurcation diagram of collapse epochs versus masses of pre-galactic clouds. Using the observed properties, the collapse epochs and mass are assessed for each type of galaxy . By direct comparison of the theory with observations, it turns out that the theoretical bifurcation branch successfully discriminates between elliptical and spiral galaxies. This suggests that the ultraviolet background radiation could play a profound role in the differentiation of galactic morphology into the Hubble sequence.  相似文献   

Experimental Study and Simulation Principles of An Oil-Gas Multiphase Transportation System   总被引：3，自引：0，他引：3  

WU Yingxiang 《中国海洋工程》2000,14(1):33-44

—Presented is an experimental study on the performance of an oil-gas multiphase transporta-tion system,especially on the multiphase flow patterns,multiphase pumping and multiphase metering ofthe system.A dynamic simulation analysis is conducted to deduce simulation parameters of the systemand similarity criteria under simplified conditions are obtained.The reliability and feasibility of two-phaseflow experiment with oil and natural gas simulated by water and air are discussed by using the similaritycriteria.  相似文献   

LiH formation by radiative association in Li⁺+H⁻ collisions     

A. S. Dickinson †  F. X. Gadéa 《Monthly notices of the Royal Astronomical Society》2000,318(4):1227-1231

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K-shell photoionization cross-sections of N v and O vi     

E. Charro  K. L. Bell  I. Martin  A. Hibbert 《Monthly notices of the Royal Astronomical Society》2000,313(2):247-251

An 11-state R -matrix calculation is performed to obtain cross-sections for the photoionization of the 1s²2s ²S ground states of N  v and O  vi . For both ions at low photon energies, corresponding solely to the 2s photoionization cross-section, excellent agreement is found with previous calculations. For higher photon energies, permitting inner-shell photoionization of the 1s electron, excellent accord is found with the recent calculation of Nahar for O  vi , whilst for N  v resonance structure is found which previous calculations omitted.  相似文献   

Lambert冰川流域东西两侧气候环境变化特征     

张明军  效存德  任贾文  LI Zhongqin  QIN Dahe 《地理学报(英文版)》2004,14(3):282-288

During the 1992-1993 joint Australian-Chinese over-snow traverse of the western Lambert Glacier Basin (LGB), two firn cores were drilled respectively at MGA and LGB16. During the 1996-1997 and 1997-1998 austral summers, two firn cores were drilled respectively at DT001 and DT085 on the eastern LGB. Based on the measurements made during the expeditions, the climatic and environmental features on both sides of the LGB have been studied. Results show that during the past 50 years, the trends of both air temperature and accumulation rate show a slight increase on the east side of the LGB, in contrast to the west side of the LGB. The spatial trends of the accumulation rate measured by accumulation canes at 2 km intervals along the nearly 500 km of the traverse lines on both sides of the LGB are different. Moreover, correlations of δ^18O vs T10 along the two sides of the LGB are also different. In addition, the variations of sea salt ion concentrations show different trends in the past 50 years. All the evidence shows that the Lambert Glacier is a dividing region for the different climatic regimes over the East Antarctic ice sheet, which may be due to different moisture resources resulting from special local circumfluence such as cyclone activities, local terrain influences.  相似文献   

交通廊道对城市社会空间的侵入作用——以北京市德外大街改造工程为例   总被引：7，自引：1，他引：6  

周尚意  王海宁  范砾瑶 《地理研究》2003,22(1):96-104

城市社会空间是城市规划和城市地理学的重要研究内容。城市实体结构是城市社会空间的重要影响因子,而城市交通廊道又是最活跃的一种城市实体要素。交通廊道对城市社会空间的作用有侵入、隔离、接替等。本文以北京市德外大街改造工程为例,分析交通廊道对所经过的社会空间的影响。就其理论意义而言,从一个侧面挖掘了美国地理学家莫迪“城市社会空间结构模型”中城市实体层面对社会空间层面的作用机制,即交通廊道是通过切断社会空间关联来影响所经社会空间的。就其实践意义而言,提出在城市大型交通廊道建设中,应该注意保持城市居民生活基本空间单元的完整性。同时指出城市社会空间是一个有机体,不同类型的城市社会空间单元在适应实体空间变化上存在差异性。帕森斯的AGIL理论可以解释德外社区为什么可以积极地适应交通廊道的侵入。  相似文献   

青藏高原臭氧的准两年振荡   总被引：2，自引：2，他引：2  

季崇萍  邹捍  周立波 《气候与环境研究》2001,6(4):416-424

通过对臭氧卫星观测资料及大气环流资料的分析,研究了青藏高原上空臭氧的季节和年际变化.通过分析青藏高原地区臭氧准两年振荡(QBO),并与同纬度无山区及赤道地区臭氧QBO进行比较,指出:青藏高原臭氧QBO的平均周期为29个月,平均振幅为8DU.青藏高原臭氧QBO变化位相与热带平流层纬向风场QBO相反,即热带平流层纬向西风时,青藏高原上空臭氧总量偏小,东风时臭氧总量偏大.还讨论了与青藏高原臭氧QBO相关的大气环流物质输送理论.  相似文献   

海洋工程设计风速与波高的联合分布     

董胜  郝小丽  樊敦秋 《海洋学报》2005,27(3):85-89

选取我国渤海某处21a的风暴过程后报资料,考虑风暴发生频次的影响,提出泊松二维逻辑分布,并且将其用于海洋石油工程设计中极值风速与波高的联合概率计算,给出了计算海域的风浪设计参数,并与传统的设计标准进行了比较.计算结果表明,新的统计模式适用于受风暴影响海区的海洋工程结构设计,特别是边际油田的开发建设.  相似文献   

Simulating saturation‐excess surface run‐off in a semi‐distributed hydrological model          下载免费PDF全文

Denis Arthur Hughes  Sbongiseni Mazibuko 《水文研究》2018,32(17):2685-2694

The level of complexity, and the number of parameters, to include in a hydrological model is a relatively contentious issue in hydrological modelling. However, it can be argued that explicitly representing important run‐off generation processes can improve the practical value of a model's outputs. This paper explores the benefits of including a new function into an existing semi‐distributed hydrological model (the Pitman model) that is widely used in the sub‐Saharan Africa region. The new function was designed to represent saturation‐excess surface run‐off processes at subcatchment scales and was motivated by the evidence of dambo (low topography riparian areas) type features in many sub‐Saharan river basins. The results for uncertainty versions of the model, with and without the new function, were compared for 25 catchments, which were divided up into those where evidence of dambos exists and those where there is no such evidence. The results suggest that the new function certainly improves the model results for the catchments where dambos exist, but not in situations where saturation‐excess surface run‐off is not expected to occur. The overall conclusion is therefore that the addition of the new function is justified.  相似文献   

Till kinematics in the Stargard drumlin field,NW Poland constrained by microstructural proxies     

Piotr Hermanowski  Jan A. Piotrowski  Piotr Duda 《第四纪科学杂志》2020,35(7):920-934

Deciphering the relationships between streamlined subglacial landforms and deposits therein helps to constrain the dynamics of past ice sheets. Here we present microstructural analyses of till from the largest drumlin field in the North European Lowland generated by a major palaeo-ice stream of the Scandinavian Ice Sheet. Data derived from thin sections and X-ray microtomography (μCT) reveal multiple microstructures including microshears, circular structures, grain stacks and crushed grains. Long axes of micro-clasts measured in thin sections are directionally clustered and have low, down-ice-oriented dip angles. Some samples reveal subordinate clustering oriented at high angles to the main direction. The μCT data show low clustering strengths of clasts and no systematic fabric pattern in the entire set of samples. There is no correspondence between the clast orientations and the directions of drumlin long axes, suggesting that the till is antecedent in relation to the drumlin-shaping process. The observations indicate spatially and temporally variable, shallow-seated brittle and ductile deformation controlled by porewater pressure fluctuations and generated time-transgressively parallel to till accretion. Consistently with previous studies, the data suggest that the Stargard drumlins are erosional remnants of a pre-existing terrain shaped by material removal from the inter-drumlin areas.  相似文献