Hauling Australia into the twenty‐first century: geographical perspectives on transport reform     

Michael Taylor 《The Australian geographer》1991,22(2):120-123

  相似文献   

环境剪应力值τ0的稳定性和预测效能分析   总被引：1，自引：1，他引：0  

杨马陵  叶秀薇 《地震》2005,25(3):56-62

利用峰值加速度αp、峰值速度νp和峰值位移dp,计算了广东省河源地区64个地震的环境剪应力值τ0。结果表明,同一地震的τ0α、τ0v、τ0d可相差很大,τ0v、τ0d的误差主要来自地震矩M0。因此,如果不能从震源谱计算M0,则以峰值加速度方法计算τ0误差最小。剪应力值为使用震级序列分析地震趋势提供了明确的物理基础。即高震级地震多发说明应力场处于高强度背景,有发生更大地震的可能;反之则为低应力场背景,发生更大地震的可能性不大。公式分析和实际数据拟合得到lg（τ0）与ML有很好的线性相关,因此震级序列与剪应力值序列的地震预测效能是基本相同的。但与震级序列相比,τ0的计算显然要复杂,且误差也较大。  相似文献   

Improving the ecological efficiency of the bottom trawl fishery in the Western Mediterranean: It's about time!     

《Marine Policy》2017

The improvement of fishing technology has been detrimental to the sustainability of fisheries, which is particularly clear for the bottom trawl fishery. Reducing its environmental impact is a key point for the development of a more sustainable fishery. The present work analyzed different possibilities to mitigate the impact of gears on the seabed and to increase the efficiency of the bottom trawl fishery of the Western Mediterranean. The analysis of three experiments showed that innovative technical and regulation measures can lead to benefits such as the reduction of fishing effort, the improvement of the cost-benefit relation and the reduction of the direct impact on the seabed and the indirect effect on the ecosystems through reduce discards and the emission of CO₂ into the atmosphere. After years of studies focused on improving the sustainability of this fishery, it's about time to turn this improvement into reality.  相似文献   

Numerical study of the bearing capacity for two interfering strip footings on sands     

A. Mabrouki  D. Benmeddour  R. Frank  M. Mellas 《Computers and Geotechnics》2010

Current studies of bearing capacity for shallow foundations tend to rely on the hypothesis of an isolated footing. In practice a footing is never isolated; it is mostly in interaction with other footings. This paper focuses on a numerical study using the finite-difference code Fast Lagrangian Analysis of Continua (FLAC), to evaluate the bearing capacity for two interfering strip footings, subjected to centered vertical loads with smooth and rough interfaces. The soil is modeled by an elasto-plastic model with a Mohr–Coulomb yield criterion and associative flow rule. The interference effect is estimated by efficiency factors, defined as the ratio of the bearing capacity for a single footing in the presence of the other footing to that of the single isolated footing. The efficiency factors have been computed individually to estimate the effects of cohesion, surcharge, and soil weight using Terzaghi’s equation, both in a frictional soil with surcharge pressures and in a cohesive-frictional soil with surcharge pressures. The results have been compared with those available in the literature.  相似文献   

The 1996 eruption at Gjálp,Vatnajökull ice cap,Iceland: efficiency of heat transfer,ice deformation and subglacial water pressure   总被引：1，自引：1，他引：0  

Magnús?T.?GudmundssonEmail author  Freysteinn?Sigmundsson  Helgi?Bj?rnsson  Thórdís?H?gnadóttir 《Bulletin of Volcanology》2004,66(1):46-65

The 13-day-long Gjálp eruption within the Vatnajökull ice cap in October 1996 provided important data on ice–volcano interaction in a thick temperate glacier. The eruption produced 0.8 km³ of mainly volcanic glass with a basaltic icelandite composition (equivalent to 0.45 km³ of magma). Ice thickness above the 6-km-long volcanic fissure was initially 550–750 m. The eruption was mainly subglacial forming a 150–500 m high ridge; only 2–4% of the volcanic material was erupted subaerially. Monitoring of the formation of ice cauldrons above the vents provided data on ice melting, heat flux and indirectly on eruption rate. The heat flux was 5–6×10⁵ W m^-2 in the first 4 days. This high heat flux can only be explained by fragmentation of magma into volcanic glass. The pattern of ice melting during and after the eruption indicates that the efficiency of instantaneous heat exchange between magma and ice at the eruption site was 50–60%. If this is characteristic for magma fragmentation in subglacial eruptions, volcanic material and meltwater will in most cases take up more space than the ice melted in the eruption. Water accumulation would therefore cause buildup of basal water pressure and lead to rapid release of the meltwater. Continuous drainage of meltwater is therefore the most likely scenario in subglacial eruptions under temperate glaciers. Deformation and fracturing of ice played a significant role in the eruption and modified the subglacial water pressure. It is found that water pressure at a vent under a subsiding cauldron is substantially less than it would be during static loading by the overlying ice, since the load is partly compensated for by shear forces in the rapidly deforming ice. In addition to intensive crevassing due to subsidence at Gjálp, a long and straight crevasse formed over the southernmost part of the volcanic fissure on the first day of the eruption. It is suggested that the feeder dyke may have overshot the bedrock–ice interface, caused high deformation rates and fractured the ice up to the surface. The crevasse later modified the flow of meltwater, explaining surface flow of water past the highest part of the edifice. The dominance of magma fragmentation in the Gjálp eruption suggests that initial ice thickness greater than 600–700 m is required if effusive eruption of pillow lava is to be the main style of activity, at least in similar eruptions of high initial magma discharge.Editorial responsibility: J. Donnelly-Nolan  相似文献   

1:1万地形图高程注记点采集方法研究     

袁桂生  羌树华  曹泉根 《现代测绘》2006,29(5):19-21

通过时水准仪散点法、GPS-RTK高程和内业全数字摄影测量工作站三种高程注记点的采集方法进行系统的研究，力求找到既保证满足成图精度要求，又减少劳动强度，提高工作效率，并符合现实情况的一种准确、高效、经济的采集方法，为我省新一轮基础测绘顺利完成提供科学依据。  相似文献   

GPS"射线打靶”模式的并行计算   总被引：3，自引：0，他引：3  

Li Shuyong  Wang Bin  Zhang Xin 《大气科学进展》2001,18(6):1185-1191

全球定位系统（ＧＰＳ）“射线打靶”模式是ＧＰＳ／ＭＥＴ（气象）资料变分同化中联系ＧＰＳ原始观测与大气状况的一种自成一体的观测算子，但因其计算量非常巨大而一直没能得到实用。为了克服这一困难，我们建立一个并行版本的 ＧＰＳ“射线打靶”模式，并在国家重点基础研究发展规划项目“大规模科学计算研究”资助下研制的微机机群系统（ＬＳＳＣ）上成功地实现了并行计算，取得了理想的加速比和并行效率，而且具有良好的可扩展性，为该观测算子达到实用迈出了实质性的一步。  相似文献   

论期货市场风险监管体系的目标     

王里青 《成都信息工程学院学报》1998,(2)

期货市场风险监管体系的三大目标是安全性,公平性和效率性。监管的最终目的是实现这三大目标的平衡。三大目标的平衡是监管当局最高的追求。在期货市场的不同发展阶段,监管者目标的侧重点也不一样。我国期货市场由于正处于刚发展阶段,现阶段监管当局的目标应是安全性,具体的监管措施应建立在对安全性的考虑上。  相似文献   

Characteristics of energy dissipation in hyperconcentrated flows   总被引：1，自引：0，他引：1  

An-ping SHU  Qing-quan LIU  Yu-jun YI  Zhi-dong ZHANG 《国际泥沙研究》2008,23(4):387-397

An equilibrium equation for the turbulence energy in of solid-liquid two-phase flow theory. The equation sediment-laden flows was derived on the basis was simplified for two-dimensional, uniform, steady and fully developed turbulent hyperconcentrated flows. An energy efficiency coefficient of suspended-load motion was obtained from the turbulence energy equation, which is defined as the ratio of the sediment suspension energy to the turbulence energy of the sediment-laden flows. Laboratory experiments were conducted to investigate the characteristics of energy dissipation in hyperconcentrated flows. A total of 115 experimental runs were carried out, comprising 70 runs with natural sediments and 45 runs with cinder powder. Effects of sediment concentration on sediment suspension energy and flow resistance were analyzed and the relation between the energy efficiency coefficient of suspended-load motion and sediment concentration was established on the basis of experimental data. Furthermore, the characteristics of energy dissipation in hyperconcentrated flows were identified and described. It was found that the high sediment concentration does not increase the energy dissipation; on the contrary, it decreases flow resistance.  相似文献   

On the efficiency and predictability of strain energy for the evaluation of liquefaction potential: A numerical study     

Y. Jafarian  A. Sadeghi Abdollahi  R. Vakili  M.H. Baziar  A. Noorzad 《Computers and Geotechnics》2011

Strain energy concept has been employed by the researchers for the assessment of liquefaction phenomenon which is a disastrous type of earthquake-induced failure in saturated soils. The efficiency and predictability conditions of strain energy concept for liquefaction potential assessment are investigated herein using effective stress numerical analyses. Several earthquake ground motions were introduced to the base of a calibrated numerical model using an advanced fully coupled constitutive model. Results of the numerical analyses indicate that earthquake-induced excess pore pressure is more rigorously proportional to strain energy compared with the other examined intensity measures. Subsequently, a simple relationship was derived using the results of dynamic analyses to predict cumulative strain energy density in terms of magnitude, source to site distance, and effective overburden pressure. This relationship, which tries to guarantee the predictability condition of strain energy demand, has demonstrated a successful capability in discrimination between the liquefied and non-liquefied case histories recorded after several well-known earthquakes. This study has provided a practical linkage between numerical analysis and field observations. Finally, it is concluded that although strain energy approach possesses a great conceptual efficiency in liquefaction potential assessment, its precise prediction in actual field conditions involves some difficulties.  相似文献