Multiple lines of stratigraphic, geochemical, and fossil data suggest that fresh-mesohaline paleolakes were widespread in the Tengger Desert of northwestern China and underwent major fluctuations during the late Pleistocene. The paleolakes started to develop at ca. 42,000 14C yr B.P. The lake levels were the highest between 35,000 and 22,000 14C yr B.P., during which Megalake Tengger dominated the landscape. The climatic conditions at this time were unique for this area and have no modern analogue. After an episode of decline between 22,000 and 20,000 14C yr B.P. and an episode of rebound between 20,000 and 18,600 14C yr B.P., the paleolakes started to desiccate and completely disappeared around 18,000 14C yr B.P. The environmental proxy data indicate that the Megalake Tengger formed under warm–humid climates. The reconstructed climatic variations appear to be correlative with the abrupt climatic events reconstructed for the North Atlantic.

Our pollen-based climate reconstruction shows that both temperature and moisture were low during the early Holocene from ˜1 0,000 to ˜8 000 cal. a BP and gradually climbed from ˜8 000 to ˜6 000 cal. a BP. The last ˜6 000 years have been generally warm and wet with high-amplitude fluctuations. The high-moisture conditions for the past ˜6 000 years are not only corroborated by high arboreal pollen/non-arboreal (AP/NAP; trees and shrubs over herbs) pollen ratio and high pollen concentration but also by high organic matter content and diatom data. We suggest that lower winter insolation and remaining ice covers in the early Holocene might have slowed down temperature rise in the continental interiors and that the resulted low temperature might have suppressed regional evaporation that was a major water vapor source for precipitation. At the same time, icemelt-water injection into the North Atlantic Ocean might have also suppressed water vapor supplies to the downwind areas, including the northern Mongolian Plateau. The increase in winter insolation and the final melting of ice sheets, together with the increased atmospheric CO 2 concentration and the associated increase in atmospheric water vapor, could be responsible for the higher temperature during the past ˜6 000 years. The icemelting and the associated rise of sea level during the past ˜6 000 years might be responsible for the weakening of the winter monsoon in the interior of Asian continent, thus alluring farther eastward penetration of the relatively warm and wet Atlantic air masses and consequently bringing more precipitation to the northern Mongolian Plateau.

No abstract

In order to investigate the effect of hyperbranched polymer modified on impact strength of epoxy resin at 77K. One modifier called H204 was employed to methyl nadic anhydride (MNA) cured diglycidyl ether of bisphenol A (DGEBA) epoxy resin system. The impact strength at 77 K was studied and the results indicated that introduction of modifier used in this study can enhance the impact strength at cryogenic temperature. The 58.57% increase was obtained by addition of 10 wt% H204 into the epoxy matrix. Furthermore, scanning electron microscopy (SEM) was used to investigate the fracture mechanism and strengthening effect.