Can severely fragmented patches of riparian vegetation still be important for arid-land bird diversity?     

C.L. Seymour  R.E. Simmons 《Journal of Arid Environments》2008,72(12):2275-2281

The vegetation of riparian habitats is often distinct from that of the surrounding landscape, thus representing unique habitat for a variety of biota. Although highly mobile, birds often exhibit distinct species assemblages associated with habitat. Therefore, degradation or removal of riparian habitat, particularly in arid environments, may threaten bird diversity. Along the Vaal River, South Africa, mining and agriculture have reduced natural riparian habitat to ca. 9% of its former extent in the Northern Cape Province. We surveyed bird assemblages within intact riparian, savanna and bush-thickened habitats along the Vaal River to ascertain their importance to bird diversity. Avian abundance and species richness did not differ between the three habitats. Species composition of riparian bird assemblages was significantly different to that of savanna and bush-thickened habitats, however, which were not significantly different from each other, and more species were characteristic of riparian habitat (17 species) than bush-thickened (seven species) or savanna (one species) habitats. Of three species reaching the south-western limit of their African distribution, all occurred in riparian habitat. Thus, despite its fragmented nature, the riparian vegetation on the Vaal still supports an important component of avian diversity, and a landscape-level approach is required to manage this relatively rich, arid-land, river.  相似文献   

The equation of state of CaSiO₃ perovskite to 108 GPa at 300 K     

Sang-Heon Shim  Thomas S. Duffy  Guoyin Shen 《Physics of the Earth and Planetary Interiors》2000,120(4):327-338

Pressure–volume measurements have been performed for CaSiO₃ perovskite to 108 GPa at 300 K using NaCl and argon pressure-transmitting media, and energy dispersive X-ray diffraction (EDXD) in a diamond-anvil cell (DAC). By determining a parameter that is the product of the elastic anisotropy, S, and the uniaxial stress component, t, for each data point, we define the stress condition of the sample. For different points at the same pressure in a temperature-quenched sample, the St value can differ by as much as a factor of 5, indicating heterogeneity in the stress condition. This may be responsible for the large scatter of earlier P–V measurements in the DAC which in general used a large diameter X-ray beam. Also, the St value provides insight into the elastic anisotropy, S, of CaSiO₃ perovskite and platinum. The sign of S (positive) for CaSiO₃ perovskite agrees with first principles calculations but the magnitude may be inconsistent. A new compression curve at 300 K was obtained for CaSiO₃ perovskite by using those data points which represent the most nearly hydrostatic conditions. It is observed that the data points with high St values yield larger volumes than the points with small St values at a given pressure. By selecting the data points having low St values (St≤0.005), combining with lower pressure large volume press (LVP) measurements and fitting to third order Birch–Murnaghan equation of state (EOS), we find that CaSiO₃ perovskite is more compressible (V₀=45.58±0.05 ų, K_T0=236±4 GPa, and K_T0′=3.9±0.2 GPa) than suggested by previous studies. The density and bulk modulus of CaSiO₃ perovskite at lower mantle pressures and 300 K are 1–3% greater and 5–15% smaller, respectively, than found in previous studies. This study demonstrates that defining the stress state of the sample is crucial to obtain an accurate 300 K compression curve for unquenchable high-pressure phases.  相似文献   

ENVIRONMENTALISM AND EUROCENTRISM     

JAMES M. BLAUT 《Geographical review》1999,89(3):391-408

ABSTRACT. Environmental determinism has served to validate a Eurocentric world history for several centuries, and it continues to do so today. This essay looks briefly at the historical marriage between environmental determinism and Eurocentric history, then develops a detailed critique of the environmental determinism put forward in two recent world-history books: Jared Diamond's Guns, Germs, and Steel (1997) and David Landes's The Wealth and Poverty of Nations (1998).  相似文献   

金刚石微粉质量的评定     

谈耀麟 《矿产与地质》1999,13(3):191-193

从用户和生产厂家的观点阐述如何评定金刚石微粉的质量。着重论述根据金刚石微粉的粒度、颗粒形状、锐利性、抗磨耗性和强度来评定金刚石微粉的质量  相似文献   

Discovery and exploration of the Gosowong epithermal gold deposit, Halmahera, Indonesia   总被引：1，自引：0，他引：1  

J. C. Carlile  G. R. Davey  I. Kadir  R. P. Langmead  W. J. Rafferty 《Journal of Geochemical Exploration》1998,60(3):207-227

The Gosowong epithermal gold deposit, on the island of Halmahera in eastern Indonesia, is located in an area of primary tropical rain forest with no previous history of gold mining or record of gold mineralisation. The deposit occurs in a newly recognised mineral district which contains a number of epithermal vein systems and at least two centres of low-grade porphyry style Cu–Au mineralisation. Several zones of argillic and advanced argillic alteration have been noted which may be related to additional centres of mineralisation. Gosowong is classified as a low-sulphidation epithermal quartz vein. Bonanza-grade gold–silver mineralisation is developed in shoots over a 400-m strike section of the vein system. Three types of veining are recognized; quartz–adularia veins and breccias; quartz–chlorite–illite veins and breccias; and crystalline or chalcedonic quartz vein stockworks. The area was targetted using a simple geological concept and the deposit was discovered and tested using basic exploration techniques commonly applied in the rugged tropical terrains of Indonesia. Sequential exploration methods comprised reconnaissance drainage sampling of stream sediment, BLEG and float media, ridge and spur soil sampling, prospect scale grid soil sampling, hand trenching and diamond drilling. Lapse time from identification of the initial reconnaissance anomaly to an inferred resource estimate of almost 1 million ounces of gold was less than 3.5 years. This case history illustrates that very detailed exploration is necessary to locate high-grade vein-type gold deposits in a tropical environment, but demonstrates that such resources still remain to be discovered in the relatively under-explored Neogene magmatic arcs of Indonesia.  相似文献   

New measurement of melting and thermal conductivity of iron close to outer core conditions     

Abhisek Basu  Matthew RField  Dougal GMcCulloch  Reinhard Boehler 《地学前缘(英文版)》2020,(2):565-568

The amount of literature on both melting and thermal conductivity of iron at Earth’s core conditions is overwhelming and the discrepancies are very large.There is a broad range of experimental techniques each of which is flawed to a certain degree,which may explain the discrepancy.In this report,we present new data using a different method for determining the phase behavior and resistivity of iron in the laser-heated diamond cell by measuring the electrical resistance of both solid and liquid iron wires.The experiment avoids some of the major flaws of previous experiments,the most important of which is the detection of the onset of melting.These measurements confirm a shallow melting curve found earlier and the resistivity data imply a trend towards low thermal conductivity in the liquid outer core.  相似文献   

我国海洋产业数字化水平测度与时空演化分析          下载免费PDF全文

邵业  宁凌  欧春尧  曹阳春 《海洋开发与管理》2024,41(1):3-14

文章在厘清海洋产业数字化相关概念的前提下,基于钻石模型构建了海洋产业数字化水平测度指标体系并采用投影寻踪模型测度2014—2020年我国沿海11个省(自治区、直辖市)的海洋产业数字化水平;在此基础上运用多种空间计量模型对我国海洋产业数字化水平的时空演化规律进行深入分析。研究发现：我国海洋产业数字化水平总体上呈现快速增长趋势,但不同区域沿海省(自治区、直辖市)之间存在一定差异;区域内差异是研究期内我国海洋产业数字化水平地区差异的主导因素,其中北部沿海地区内部差异最大,东部沿海地区内部差异最小,南部沿海地区内部差异居中;三大海洋经济圈内海洋产业数字化集聚形式各具特征：北部海洋经济圈内沿海省(自治区、直辖市)形成“高-低”集聚型,南部海洋经济圈内沿海省(自治区、直辖市)形成“低-高”集聚型,东部海洋经济圈内沿海省(自治区、直辖市)则形成“高-高”集聚型。  相似文献