966 resultados para the east of Yunnan and the west of Guizhou
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An overview of the work of the Isotype Institute in the Western Region of Nigeria in the 1950s.
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This book provides a critical investigation into the discursive processes through which the North Atlantic Treaty Organisation (NATO)reproduced a geopolitical order after the end of the Cold War and the demise of its constitutive enemy, the Soviet Union.
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lsochronal layers in firn detected with ground-penetrating radar (GPR) and dated using results from ice-core analyses are used to calculate accumulation rates along a 100 km across-flow profile in West Antarctica. Accumulation rates are shown to be highly variable over short distances. Elevation measurements from global positioning system surveys show that accumulation rates derived from shallow horizons correlate well with surface undulations, which implies that wind redistribution of snow is the leading cause of this variability. Temporal changes in accumulation rate over 25-185 year intervals are smoothed to along-track length scales comparable to surface undulations in order to identify trends in accumulation that are likely related to changes in climate. Results show that accumulation rates along this profile have decreased in recent decades, which is consistent with core-derived time series of annual accumulation rates measured at the two ends of the radar profile. These results suggest that temporal variability observed in accumulation-rate records from ice cores and GPR profiles can be obscured by spatial influences, although it is possible to resolve temporal signals if the effects of local topography and ice flow are quantified and removed.
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Interior ice elevations of the West Antarctic Ice Sheet (WAIS) during the last glaciation, which can serve as benchmarks for ice-sheet models, are largely unconstrained. Here we report past ice elevation data from the Ohio Range, located near the WAIS divide and the onset region of the Mercer Ice Stream. Cosmogenic exposure ages of glacial erratics that record a WAIS highstand similar to 125 m above the present surface date to similar to 11.5 ka. The deglacial chronology prohibits an interior WAIS contribution to meltwater pulse 1A. Our observational data of ice elevation changes compare well with predictions of a thermomechanical ice-sheet model that incorporates very low basal shear stress downstream of the present day grounding line. We conclude that ice streams in the Ross Sea Embayment had thin, low-slope profiles during the last glaciation and interior WAIS ice elevations during this period were several hundred meters lower than previous reconstructions.
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The deeply eroded West Gondwana Orogen is a major continental collision zone that exposes numerous occurrences of deeply subducted rocks, such as eclogites. The position of these eclogites marks the suture zone between colliding cratons, and the age of metamorphism constrains the transition from subduction-dominated tectonics to continental collision and mountain building. Here we investigate the metamorphic conditions and age of high-pressure and ultrahigh-pressure eclogites from Mali, Togo and NE-Brazil and demonstrate that continental subduction occurred within 20 million years over at least a 2,500-km-long section of the orogen during the Ediacaran. We consider this to be the earliest evidence of large-scale deep-continental subduction and consequent appearance of Himalayan-scale mountains in the geological record. The rise and subsequent erosion of such mountains in the Late Ediacaran is perfectly timed to deliver sediments and nutrients that are thought to have been necessary for the subsequent evolution of sustainable life on Earth.
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Azerbaijan’s cooperation with the West, launched two decades ago, has helped it become a relatively strong and ambitious actor on the international stage. It has become a key country in the region from the Western (USA and the EU) and Turkish points of view, as well as an important partner in the energy sector. The strategic EU concept of the Southern Gas Corridor, also supported by the United States, is among the initiatives based on cooperation with Azerbaijan. Surprisingly, however, Azerbaijan’s increased ambition and importance have caused its policy to diverge ever farther from the expectations and plans formulated by the West. The changes in the balance of power in the South Caucasus, occurring in the context of the conflict in Ukraine, have forced Azerbaijan to revise its assessment of its position in the region. The main impetus for Azerbaijan’s actions is fear of Russia, as well as the weakness of the West which has become particularly apparent in the recent stages of the Ukrainian crisis. Azerbaijan’s actions so far have displayed its tendency to deepen its self-isolation in foreign affairs and consolidate its authoritarian system. This comes as a challenge to the West, whose ability to shape its relations with Azerbaijan has weakened considerably. This state of affairs poses the threat that in the current situation, the Southern Gas Corridor concept, which Azerbaijan amended in 2012 in its own favour, might become totally blocked.