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121.
N. Satyavani Kalachand Sain Malcolm Lall B. J. P. Kumar 《Marine Geophysical Researches》2008,29(3):167-175
Seismic data from the Andaman offshore region has been examined to investigate for the presence of gas hydrates. The seismic
data displays reflection characteristics such as blanking, enhanced reflection patterns, shadows in instantaneous frequency,
and increase in amplitude with the offset, which are indicative of gas hydrates and underlying free gas. A prominent bottom-simulating
reflection, BSR, coupled with reverse polarity is observed around 650–700 ms. Seismic attributes such as the reflection strength
and instantaneous frequency are computed along this reflector in order to probe for the presence of gas hydrates or free gas
in this region. The reflection plot shows a strong reflector paralleling the seafloor. In addition, attenuation of the high
frequency signal is noticed, indicating the presence of free gas below the BSR. 相似文献
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PM2.5是威胁人体健康的主要大气污染物之一.大量研究关注近地面PM2.5浓度的监测及其时空分布,但目前针对PM2.5排放及其与近地面浓度之间的关联研究较为缺乏.本文通过2000-2014年近地面PM2.5浓度格网数据和PM2.5排放格网数据,采用长时间序列分析法对PM2.5浓度和PM2.5排放从定性和定量两个角度进行... 相似文献
124.
横过西昆仑-塔里木结合地带的深地震反射剖面,首次揭露出新疆地学断面南部山盆结合部位地壳与上地幔顶部的精细结构,发现了塔里木岩石圈下部南倾,西昆仑山岩石圈下部北倾的强反射特征,它们相向倾斜,相互交织,构成了塔里木岩石圈挤入到西昆仑北带之下,与青藏高原西北缘岩石圈相碰撞的地震证据。深地震反射剖面还揭示出西昆仑山与塔里木盆地在岩石圈尺度呈“V”型的盆山耦合关系,这种“V”型的耦合关系代表了陆内陆-陆碰撞变形过程的一种样式。 相似文献
125.
采用综合指数评价、基尼系数、标准差椭圆等方法分析了2004~2014年长江三角洲地区门户功能的空间格局及其演化过程。结果表明:① 长江三角洲地区城市门户功能上升趋势明显,空间上由“一极三强”的格局演变为“一极四强”;② 各类门户功能的空间差异整体上呈缩小趋势,其中国际门户功能的差异明显大于综合和国内门户功能,而组间差异是导致门户功能差异的主要原因;③ 所有门户功能均由南-北方向分布向东-西方向分布转型。长三角地区门户功能的演化是由多重因素驱动形成的,国内和国际门户功能的驱动机理存在明显差异。 相似文献
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A numerical model is developed by combining a porous flow model and a two-phase flow model to simulate wave transformation in porous structure and hydraulic performances of a composite type low-crest seawall. The structure consists of a wide submerged reef, a porous terrace at the top and an impermeable rear wall. The porous flow model is based on the extended Navier-Stokes equations for wave motion in porous media and k−ε turbulence equations. The two-phase flow model combines the water domain with the air zone of finite thickness above water surface. A unique solution domain is established by satisfying kinematic boundary condition at the interface of air and water. The free surface advection of water wave is modeled by the volume of fluid method with newly developed fluid advection algorithm. Comparison of computed and measured wave properties shows reasonably good agreement. The influence of terrace width and structure porosity is investigated based on numerical results. It is concluded that there exist optimum value of terrace width and porosity that can maximize hydraulic performances. The velocity distributions inside and in front of the structure are also investigated. 相似文献
128.
The hydrodynamic performance of vertical and sloped plane, dentated and serrated seawalls were investigated using physical model studies. Regular and random waves of wide range of heights and periods were used. Tests were carried out for different inclinations of the seawall (i.e. θ=30, 40, 50, 60 and 90°) and for a constant water depth of 0.7 m. The wave reflection was measured to assess the dissipation character of the seawalls. It was observed that the serrated seawall was superior to the plane and dentated seawall in reducing the wave reflection. Even for the vertical case, the coefficient of reflection due to regular waves for dentated seawall ranged from 0.6–0.99 and for the vertical serrated seawall it was 0.45–0.98, whereas for the vertical plane wall, it was almost 1.0. It was found that the characteristic dimension of the seawall (i.e. L/W) and the relative water depth (i.e. d/L) were better influencing parameters compared to the conventionally used surf similarity parameter ‘ξ’ (ξ=tan θ/(Hi/L)0.5) in predicting the reflection from the dentated and serrated seawall, where L is the local wave length, W the width of the dent along the length of the seawall slope, d the water depth at the toe and Hi is the incident wave height. A similar trend was observed for the random waves too. The reduction in the wave reflection due to random waves for the dentated seawall as compared to the plane seawall was about 18% and for the serrated seawall, it was 20%. It was observed that the reflection due to random waves was lesser for all the three different walls than the regular waves, due to the mutual interaction of random waves. Multiple regression analysis on the measured data points was carried out and predictive equations for the reflection coefficient were obtained for both regular and random waves. This study will be useful in the design of energy dissipating type vertical quay walls in ports and harbours, sloped seawalls for shore protection from erosion and sloped caisson as breakwaters. Comparison of predictive formulae with the experimental results revealed that the prediction methods were good enough for practical purposes. 相似文献
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130.
中国区域发展时空格局变化分析及其预测 总被引:5,自引:1,他引:4
基于1997~2010年的全国省级、地级市和县级多尺度社会经济发展数据库,采用GIS与空间统计学相结合方法,揭示了中国经济发展的空间格局及其动态演变特征及时空格局的尺度依赖性,并对未来经济发展空间格局进行合理预测。结果表明:① 1997~2010年中国经济的空间中心位于河南省境内,并呈现出西北移动的趋势,出现沿海-大陆共生的经济空间格局并逐步均衡化。② 经济发展空间格局具有较为显著的尺度效应,其分布重心、形状和方位在不同尺度上发生变化;总体而言,空间尺度越小,其经济重心越偏向西南方向,其空间分布形状越接近于正圆,主轴方位越偏东。③ 预测结果表明未来10~20 a中国经济重心会继续向北移动,略微偏向东部地区,京津冀、长三角等沿海城市群仍是未来中国经济发展的主要增长引擎。研究结果可以为各级政府制定区域发展政策提供科学的理论依据。 相似文献