筑岛围堰在云龙湾大桥中的应用

桥梁施工时,通过筑岛围堰将水底复杂困难的施工条件转化为简单的陆地施工条件,优化了水中桩基和支架施工的条件,经济方便。结合天府新区云龙湾大桥工程施工实例,对筑岛围堰施工方案的制定与实施进行了分析,可为类似工程项目提供参考与借鉴。

A HISTORICAL EXAMINATION ON LAND DESERTIFICATION IN NORTH CHINA

Desertification control has been facing severe situations in the interlocking area between cultivated land and grazing land in North China since the Qing Dynasty because of unreasonable land utilization. The paper analyzes the policies of all the previous governments to open up land, and examines the historical and geographical background and process by means of historical records. We consider that causes of the area of land desertification to extend are increase of farming migrants, the change of life style of Mongol and weather and land conditions. In order to control the spread of land desertification, we suggest the level of the government to make policies should be improved, the number of farming migrants should be controlled, the Government′s general and specific polices should be actively publicized, and investment in agriculture should be increased.

Simulation of Solar Radiation Conditions in Coastal and Continental Areas by Using a New Algorithm

An algorithm developed at the University of Botswana is used to study solar radiation conditions in Namibia, South Africa, Mozambique and Botswana. The synoptic stations chosen for the study differ by meteorological conditions and location： some are in coastal areas and others are in continental locations. The simulation results reveal that daily direct beam solar radiation, Hbn, is usually higher in the continental area than in the coastal one. The same situation is observed with daily global solar radiation, Hg. The difference becomes even larger for partly cloudy weather, because in coastal areas sunshine hours are usually less than in continental areas. Furthermore, coastal areas have higher humidity and bigger air mass compared to continental locations. It is concluded that continental areas are more convenient for utilisation of solar energy using solar devices with concentrators （middle-temperature and high-temperature Rankine cycles）, while at coastal areas flat-plate collectors and PV-arrays are preferable. It is found out that the range of optimum slopes for SADC countries studied is from ＋30° to -62°.

Highly fractionated granites:Recognition and research

Granite is one of the most important components of the continental crust on our Earth; it thus has been an enduring studied subject in geology. According to present knowledge, granite shows a great deal of heterogeneity in terms of its texture,structure, mineral species and geochemical compositions at different scales from small dike to large batholith. However, the reasons for these variations are not well understood although numerous interpretations have been proposed. The key point of this debate is whether granitic magma can be effectively differentiated through fractional crystallization, and, if so, what kind of crystallization occurred during the magmatic evolution. Although granitic magma has high viscosity because of its elevated SiO2 content, we agree that fractional crystallization is effectively processed during its evolution based on the evidence from field investigation,mineral species and its chemical variations, and geochemical compositions. These data indicate that crystal settling by gravitation is not the only mechanism dominating granitic differentiation. On the contrary, flow segregation or dynamic sorting may be more important. Accordingly, granite can be divided into unfractionated, fractionated(including weakly fractionated and highly fractionated) and cumulated types, according to the differentiation degree. Highly fractionated granitic magmas are generally high in primary temperature or high with various volatiles during the later stage, which make the fractional crystallization much easier than the common granitic melts. In addition, effective magmatic differentiation can be also expected when the magma emplaced along a large scale of extensional structure. Highly fractionated granitic magma is easily contaminated by country rocks due to its relatively prolonged crystallization time. Thus, granites do not always reflect the characteristics of the source areas and the physical and chemical conditions of the primary magma. We proposed that highly fractionated granites are an important sign indicating compositional maturity of the continental crust, and they are also closely related to the rare-elemental(metal) mineralization of W,Sn, Nb, Ta, Li, Be, Rb, Cs, REEs, etc.

Advances in GDGT research in Chinese Marginal Seas: A review

Archaeal and bacterial glycerol dialkyl glycerol tetraethers(GDGTs) play a unique role in discerning the biogeochemical processes and climate change in terrestrial(e.g. soil, peat, stalagmites, lakes, rivers, hot springs) and marine environments. Organic proxies based on GDGTs(e.g. TEX_(86), MBT/CBT and BIT) have made impressive applications in the open ocean and terrestrial environments. However, the applicability of these proxies in marginal seas has not been thoroughly evaluated, which is necessary given the complexity and dynamics of these systems, such as organic matter(OM) flux, hydrodynamic conditions, and human impact. This review aims to summarize recent studies of GDGTs and GDGT-based proxies in the Chinese marginal seas(CMS), which are characterized by diverse gradient in terrigenous supplies and ocean productivity and hold rich information on climate and sea level changes, ocean current dynamics, sedimentary evolution and biogeochemical processes.