欧亚冰盖的消融     

D．R．Lindstrom王贵彬  龚建明 《海洋地质前沿》1994,(7):18-19

巴巴多斯和新几内亚的海平面变化表明：在过去的15000a中曾有过两次大规模的冰川融水流．同其它环境变化(如北大西洋深水环流)相比，这两次融水流形成的时间显然有助于我们进一步了解从未次冰期到问冰期的气候变迁及新仙女木事件．  相似文献   

中印度洋盆地中生物对铁锰微结核生长的影响     

Baner.  R 辛文锋 《海洋地质译丛》1991,(6):58-62

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Irish on the move     

King R  Mcgrath F  Shuttleworth I  Strachan A 《Geography review》1989,3(3):23-27

Trends in emigration from Ireland over time are reviewed. "During the eighteenth and nineteenth centuries overseas migration to the United States and seasonal harvest migration to Britain were the main types of movement, but over the past 100 years the Irish have developed a special affinity for settling in British towns. Although the outflow was halted for a time during the 1970s, when return migration took over, the 1980s have seen a renewal of the exodus. This time, however, the character of the flow has changed from predominantly low-skill construction and factory workers to embrace better-educated emigrants, including many graduates. This shift reflects Ireland's changing position in the international market for labour."  相似文献   

乙醇生产将导致2008年粮食价格继续升高     

Lester  R．Brown  兰月 《国土资源情报》2008,(8):55-56

我们正在经历人类历史上巨大灾难。美国降低对石油的依赖度转而用粮食提炼原料用于汽车燃油的错误决策,已经引起了前所未有的全球范围粮食危机。  相似文献   

印度板块和亚洲大陆在何时何地碰撞   总被引：1，自引：0，他引：1  

Jonathan C Aitchison  Jason R Ali  Aileen M Davis 《地质通报》2008,27(9)

印度板块和亚洲大陆的初始碰撞时间是所有相关的喜马拉雅-西藏造山体系演化模式的主控条件,并严重影响到对众多与青藏高原隆升和东亚大陆挤出相关的地质过程速率的解释,以及对新生代全球气候变化的理解。尽管印度板块和亚洲大陆汇聚的速率在55Ma突然减缓被广泛地认为是初始碰撞的标志,但这次碰撞所造成的主要构造效应直到20多个百万年以后才显现出来。对印度板块和亚洲大陆相对位置的重新估算,表明它们在55Ma时并没有达到可以彼此发生碰撞的距离。基于来自西藏新的野外证据和对已有数据的重新评估,认为初始碰撞发生在始新世—渐新世之交（约34Ma）,并对55Ma时发生的地质事件提出了另一种解释  相似文献   

Quantification of the effects of secondary matrix on the analysis of sandstone composition, and a petrographic-chemical technique for retrieving original framework grain modes of altered sandstones     

Cox R  Lowe DR 《Journal of sedimentary research. Section A, Sedimentary petrology and processes : an international journal of SEPM (Society for Sedimentary Geology)》1996,66(3):548-558

Most studies of sandstone provenance involve modal analysis of framework grains using techniques that exclude the fine-grained breakdown products of labile mineral grains and rock fragments, usually termed secondary matrix or pseudomatrix. However, the data presented here demonstrate that, when the proportion of pseudomatrix in a sandstone exceeds 10%, standard petrographic analysis can lead to incorrect provenance interpretation. Petrographic schemes for provenance analysis such as QFL and QFR should not therefore be applied to sandstones containing more than 10% secondary matrix. Pseudomatrix is commonly abundant in sandstones, and this is therefore a problem for provenance analysis. The difficulty can be alleviated by the use of whole-rock chemistry in addition to petrographic analysis. Combination of chemical and point-count data permits the construction of normative compositions that approximate original framework grain compositions. Provenance analysis is also complicated in many cases by fundamental compositional alteration during weathering and transport. Many sandstones, particularly shallow marine deposits, have undergone vigorous reworking, which may destroy unstable mineral grains and rock fragments. In such cases it may not be possible to retrieve provenance information by either petrographic or chemical means. Because of this, pseudomatrix-rich sandstones should be routinely included in chemical-petrological provenance analysis. Because of the many factors, both pre- and post-depositional, that operate to increase the compositional maturity of sandstones, petrologic studies must include a complete inventory of matrix proportions, grain size and sorting parameters, and an assessment of depositional setting.  相似文献   

Emigration,return, immigration: a review and evaluation of Greece's postwar experience of international migration     

Fakiolas R  King R 《International journal of population geography : IJPG》1996,2(2):171-190

"This paper offers a review and evaluation of the Greek experience of international migration.... The analysis is based partly on available published data, and partly on qualitative appraisals. Three major international migration phases are analysed--emigration, return migration and immigration--and the main socio-economic and cultural effects of these migration trends are discussed. The paper pays particular attention to the recent mass immigration movements, noting their heterogeneity...and describing their impact on the Greek labour market. The article concludes with some comments on the difficulties of formulating a Greek migration policy in the light of the country's location, open borders and internationalized economy."  相似文献   

Coupled atmosphere-ocean models of Titan's past     

McKay CP  Pollack JB  Lunine JI  Courtin R 《Icarus》1993,102(1):88-98

We have developed a coupled atmosphere and ocean model of Titan's surface. The atmospheric model is a 1-D spectrally-resolved radiative-convective model. The ocean thermodynamics are based upon solution theory. The ocean, initially composed of CH4, becomes progressively enriched in ethane over time. The partial pressures of N2 and CH4 in the atmosphere are dependent on the ocean temperature and composition. We find that the resulting system is stable against a runaway greenhouse. Accounting for the decreased solar luminosity, we find that Titan's surface temperature was about 20 K colder 4 Gyr ago. Without an ocean, but only small CH4 lakes, the temperature change is 12 K. In both cases we find that the surface of Titan may have been ice covered about 3 Gyr ago. In the lakes case condensation of N2 provides the ice, whereas in the ocean case the ocean freezes. The dominant factor influencing the evolution of Titan's surface temperature is the change in the solar constant--amplified, if an ocean is present, by the temperature dependence of the solubility of N2. Accretional heating can dramatically alter the surface temperature; a surface thermal flux of 500 erg cm-2 sec-1, representative of small levels of accretional heating, results in a approximately 20 K change in surface temperatures.  相似文献   

Numerical simulation of the general circulation of the atmosphere of Titan     

Hourdin F  Talagrand O  Sadourny R  Courtin R  Gautier D  McKay CP 《Icarus》1995,117(2):358-374

The atmospheric circulation of Titan is investigated with a general circulation model. The representation of the large-scale dynamics is based on a grid point model developed and used at Laboratoire de Météorologie Dynamique for climate studies. The code also includes an accurate representation of radiative heating and cooling by molecular gases and haze as well as a parametrization of the vertical turbulent mixing of momentum and potential temperature. Long-term simulations of the atmospheric circulation are presented. Starting from a state of rest, the model spontaneously produces a strong superrotation with prograde equatorial winds (i.e., in the same sense as the assumed rotation of the solid body) increasing from the surface to reach 100 m sec-1 near the 1-mbar pressure level. Those equatorial winds are in very good agreement with some indirect observations, especially those of the 1989 occultation of Star 28-Sgr by Titan. On the other hand, the model simulates latitudinal temperature contrasts in the stratosphere that are significantly weaker than those observed by Voyager 1 which, we suggest, may be partly due to the nonrepresentation of the spatial and temporal variations of the abundances of molecular species and haze. We present diagnostics of the simulated atmospheric circulation underlying the importance of the seasonal cycle and a tentative explanation for the creation and maintenance of the atmospheric superrotation based on a careful angular momentum budget.  相似文献   

Polarization reversal in the development of Brazilian metropolises? An analysis based on demographic indicators,using the example of Sao Paulo     

Bahr J  Wehrhahn R 《Erdkunde》1995,49(3):213-231

"Using the example of Sao Paulo, this paper addresses itself to the question of how far the decrease in growth rates one observes in large Brazilian metropolises can be interpreted as a process of polarization reversal. The analysis is carried out on the basis of demographic data from small area units, which include the results from the most recent 1991 census. Although it had already been possible in the 1970s to discern first indications of such a process setting in, in the decade 1981-91 indicators of population growth and migration balances agree in pointing to a polarization reversal." (SUMMARY IN ENG)  相似文献