地震波非线性反演的某些数学问题

以地震波广义散射(包括透射、折射、反射、绕射等)为背景,以求解其反演问题为主线,在回顾反演理论发展的同时,着重对地震波逆散射问题研究过程中各种数学、物理的基本理论和基本假设如何被应用以及非线性偏微分方程的求解过程及其作用做理论分析,同时对地震波逆散射问题中相应数学方法的发展过程及在使用中尚存在的问题做简单介绍。在文末,指出了现在地球物理界在地质结构异常较强烈所造成的非弱散射的反演问题上所遇到的问题。进而就今后如何处理这类问题的数学研究方法和假设中应注重的问题提出了一些想法和展望。     

LAKE SHORE PROTECTION AGAINST WIND-GENERATED WAVES1

ABSTRACT: A method is reported for estimating the height of wind waves in any lake for a given wind condition. Maximum wind speeds from five climatological stations in and around Ilinois for the period of 1950–1972 were analyzed and the maximum wind speed for various durations and return periods were presented. Statistical analysis of wind wave data collected from Carlyle Lake indicated the Rayleigh distribution fitted the wave height distribution reasonably well and that the nondimensional energy spectra followed the (f/f_m)^-5 rule in the equilibrium range of frequencies. From a consideration of various forces and physical properties of riprap particles and water, a relationship was developed to estimate the stable weight of riprap particles. A practical design criteria is proposed to stabilize lake shores against wind waves.     

Modelling the motion of an internal solitary wave over a bottom ridge in a stratified fluid

A series of laboratory experiments has been carried out to investigate the passage of an internal solitary wave of depression over a bottom ridge, in a two-layer fluid system for which the upper and lower layer is linearly-stratified and homogeneous respectively. Density, velocity and vorticity fields induced by the wave propagation over the ridge have been measured simultaneously at three locations, namely upstream, downstream and over the ridge crest, for a wide range of model parameters. Results are presented to show that wave breaking may occur for a sufficiently large wave amplitude and a strong ridge blockage factor, with accompanying mixing and overturning. Density field data are presented (i) to illustrate the overturning and mixing processes that accompany the wave breaking and (ii) to quantify the degree of mixing in terms of the wave and ridge parameters. For weak encounters, good agreement is obtained between the laboratory experimental results (velocity and vorticity fields induced by the wave propagation) and the predictions of a recently-developed fully nonlinear theory. Discrepancies between theory and experiment are discussed for cases in which breaking and mixing occur.     

Surface waves and roughness in self-aerated supercritical flow

In high-velocity open channel flows, free-surface aeration is commonly observed. The effects of surface waves on the air–water flow properties are tested herein. The study simulates the air–water flow past a fixed-location phase-detection probe by introducing random fluctuations of the flow depth. The present model yields results that are close to experimental observations in terms of void fraction, bubble count rate and bubble/droplet chord size distributions. The results show that the surface waves have relatively little impact on the void fraction profiles, but that the bubble count rate profiles and the distributions of bubble and chord sizes are affected by the presence of surface waves.     

The extraordinary events of the major,sudden stratospheric warming,the diminutive antarctic ozone hole,and its split in 2002

GOAL, SCOPE AND BACKGROUND: Great interest in the unprecedented events of the major, sudden stratospheric warming and the ozone hole split over Antarctica in September 25, 2002 motivates a necessity to analyze the current understanding on the dynamics, chemistry and climate impacts that are associated with both events. METHODS: Significant progress in the analysis of the observational data obtained, as well as successful development and application of dynamical modeling, which have been achieved very recently, create a basis for the first survey on the role of the major, sudden stratospheric warming observed in the southern hemisphere and its relationship to the diminutive Antarctic ozone hole and its break up into two parts. RESULTS AND DISCUSSION: Special attention has been paid to assessments of the causes of the major warming event and the future expectations concerning the stratospheric ozone depletion effect. Among the principal results is the fact that, as the polar vortex elongated, it became hydrodynamically unstable, and this insta-, bility affected the upper troposphere and stratosphere. During the major, sudden stratospheric warming, the middle stratospheric vortex split into two pieces; one piece rapidly mixed with extra vortex air, while the other returned to the pole as a much weaker and smaller vortex. The polar night jet was considerably weaker than normal, and was displaced more poleward than has been observed in previous winters, resulting from a series of wave events (propagated from the troposphere) that took place over the course of the winter. Finally, the relative ozone decrease (increase) in the eastern Antarctic is tightly associated with westerly (easterly) zonal wind anomalies near the southern tip of South America, and the unusual behavior of the ozone hole in 2002 therefore appears to be caused by great easterlies in this region. CONCLUSIONS: The main conclusion is that the southern polar vortex and the diminutive ozone hole split into two parts in September 2002, due to the prevalence of very strong planetary waves, led to the appearance of a major, sudden stratospheric warming. Although there is evidence that sea surface temperature anomalies contributed to the excitation of the quite strong planetary waves over Antarctica in 2002, there is not yet a widely approved mechanism supporting that. RECOMMENDATIONS AND OUTLOOK:The appearance of the near-record size of the 2003 ozone hole confirmed that the 'no-ozone-hole' episode observed in the year 2002 does not denote a recovery of the ozone layer. Despite the current successful attempts to get a sufficient understanding for the genesis of both extraordinary events, more observations and further modeling efforts are necessary to more reliably assess the contribution of various dynamic mechanisms to the recently observed tropo-stratospheric surprises.     

Upstream Channel Changes Following Dam Construction and Removal Using a GIS/Remote Sensing Approach1

Abstract: This study used an innovative GIS/remote sensing approach to study historical river channel changes in the Huron River, a wandering gravel‐bedded river in northern Ohio. Eight sets of historical aerial photographs (1958‐2003) span the construction of a low‐head dam (1969), removal of the spillway (1994), and removal of the dam itself (2002). Construction of the dam modified stream gradients >4 km upstream of the small impounded reservoir. This study tracked changes in the polygon size, shape, and centroid position of 12 sand‐gravel bars through a study reach 0.2‐4.1 km upstream of the dam. These bars were highly responsive, tending to migrate obliquely downstream and toward the outer bank at rates up to 9 m/year. Historical changes in the size and position of the bars can be interpreted as the downstream translation of one or more sediment waves. Prior to dam construction, a sediment wave moved downstream through the study reach. Following construction of the dam, this sediment wave became stationary and degraded in situ by dispersion. The growth of bars throughout the study reach during this time interval resulted in a progressive increase in channel sinuosity. Removal of the spillway rejuvenated downstream translation of a sediment wave through the study reach and was followed by a reduction in channel sinuosity. These results illustrate that important geomorphologic changes can occur upstream of low‐head dams. This may be a neglected area of research about the effects of dams and dam removals.     

超声技术在污泥生物产氢中的应用研究

污泥中含有丰富的有机质,为了加速其厌氧消化进程,增加沼气产量,本试验在pH=11.0、P=2.2×105Pa、T=130℃的条件下,对污泥进行30min热消解和30min的超声波预处理,试验结果表明,污泥中的菌胶团结构遭到破坏,固氮酶、脱氢酶、α-淀粉酶等酶的活性得到增强,菌胶团吸附的有机质被释放至溶液中,迅速成为厌氧微生物的营养物被消耗。与对照组相比,可溶解性化学需氧量(SCOD)增加了4.5倍,溶出率提高了350.00%;COD降解率提高了12%,是自然降解率的1.19倍,产氢周期缩短至6.5d,最大产氢率为67.91mL/g(VS),平均产氢率提高到21.6mL/g(VS),是对照组的3.9倍,效果较好。     

从内波SAR图像中提取跃层深度和内波振幅的非线性方法

针对SAR图像进行内波参数提取方法的不足:非线性方法将跃层深度作为已知量,将跃层深度作为未知量却用了线性方法.本文将根据非线性内波KdV方程的频散关系,结合半日潮假定并利用从SAR图像上得到的半波宽度,提出了非线性框架下同时从内波SAR图像反演内波振幅及跃层深度的方法.然后利用实测数据和内波SAR图像数据对此方法进行了分析,所得结果较理想.最后根据倾斜底地形内波波包的周期验证了文中所用半日潮假定的正确性.