The dynamic effect of a piled-foundation building on an incident vibration field from an underground railway tunnel

This paper presents a three-dimensional comprehensive model for the calculation of vibration in a building based on pile-foundation due to moving trains in a nearby underground tunnel. The model calculates the Power Spectral Density (PSD) of the building's responses due to trains moving on floating-slab tracks with random roughness. The tunnel and its surrounding soil are modelled as a cylindrical shell embedded in half-space using the well-known PiP model. The building and its piles are modelled as a 2D frame using the dynamic stiffness matrix. Coupling between the foundation and the ground is performed using the theory of joining subsystems in the frequency domain. The latter requires calculations of transfer functions of a half-space model. A convenient choice based on the thin-layer method is selected in this work for the calculations of responses in a half-space due to circular strip loadings. The coupling considers the influence of the building's dynamics on the incident wave field from the tunnel, but ignores any reflections of building's waves from the tunnel. The derivation made in the paper shows that the incident vibration field at the building's foundation gets modified by a term reflecting the coupling and the dynamics of the building and its foundation. The comparisons presented in the paper show that the dynamics of the building and its foundation significantly change the incident vibration field from the tunnel and they can lead to loss of accuracy of predictions if not considered in the calculation.

Nonlinear optical properties of semiconductor quantum wells under intense terahertz radiation

The nonlinear optical properties of semiconductor quantum wells driven by intense in-plane terahertz electric fields are investigated theoretically by employing the extended semiconductor Bloch equations. The dynamical Franz-Keldysh effect of the optical absorption near the band edge is analyzed with Coulomb correlation among the carriers included. The in-plane terahertz field induces a variety of behavior in the absorption spectra, including terahertz replicas of the (dark) 2p exciton and terahertz sidebands of the 1s exciton. The dependence of these interesting features on the intensity, frequency, and phase of the terahertz field is explored in detail.

Experimental study on polarization holographic storage in genetic mutant BR-D96N film

Recording with both parallel and orthogonal linearly polarized lights, polarization holographic storage in genetic mutant BR-D96N film is reported with both transmission type geometry and reflection type geometry. Polarization properties of diffraction light and scattering light are discussed for two different cases, parallel polarization recording and orthogonal polarization recording. It shows that, compared with recording with parallel polarization lights, orthogonal polarization holography can separate the diffraction light from the scattering noise, therefore improving the signal-to-noise ratio. It also shows that, compared with reconstruction with reference light, reconstruction with phase conjugated wave of the reference light can improve the signal-to-noise ratio of the reconstructed diffraction image, and also the wave-front aberration of the object light introduced by irregular phase object in the optical pass-way can also be corrected effectively, which ensures that the reconstructed diffraction image has a better fidelity. The preliminary angle-multiplexed volume holographic storage multiplexed by transmission type geometry and reflection type geometry is demonstrated in the BR-D96N film. Experiment shows that there is no cross-talk between the two pages of images except for some scattering noises.

Intersubband optical absorption in a step asymmetric semiconductor quantum well driven by a terahertz field

The nonlinear optical absorption in a three-subband step asymmetric semiconductor quantum well driven by a strong terahertz (THz) field is investigated theoretically by employing the intersubband semiconductor-Bloch equations. We show that the optical absorption spectrum strongly depends on the intensity, frequency, and phase of the pump THz wave. The strong THz field induces THz sidebands and Autler-Townes splitting in the probe absorption spectrum. Varying the pump frequency can bring not only the new absorption peaks but also the changing of the energy separation of the two higher-energy levels. The dependence of the absorption spectrum on the phase of the pump THz wave is also very remarkable.

TDR和FDR测定黄绵土土壤含水量的标定

时域反射仪(TDR)与频率反射仪(FDR)是目前最为先进,并且最具有发展前途的土壤含水量测量仪器。有便利、快捷、准确的优点。介绍了6种基于TDR或FDR原理的仪器对黄绵土含水量进行试验标定的方法与结果。标定结果表明:仪器的测量值与烘干法的测量值之间有一定的差异,CS616和Trime-T3烘干法测定结果接近,但是其余的4种仪器测定值均高于烘干法测定值,在应用这些仪器测定土壤含水量时需要进行标定。

Applicatioo of Pade Approximation in Simulating Photonic Crystals

To save finite-difference time-domain(FDTD) computing time, several methods are proposed to convert the time domain FDTD output into frequency domain. The Padé approximation with Baker's algorithm and the program are introduced to simulate photonic crystal structures. For a simple pole system with frequency 160THz and quality factor of 5000,the intensity spectrum obtained by the Padé approximation from a 28-item sequence output is more exact than that obtained by fast Fourier transformation from a 220-item sequence output. The mode frequencies and quality factors are calculated at different wave vectors for the photonic crystal slab from a much shorter FDTD output than that required by the FFT method,and then the band diagrams are obatined. In addition,mode frequencies and Q-factors are calculated for photonic crystal microcavity.

PERFORMANCE OF DOUBLE SIDEBAND MODULATED PROBE WAVE IN BOTDA DISTRIBUTED FIBER SENSOR

We report on the performance of double sideband (DSB) modulated probe wave in Brillouin optical time domain analysis (BOTDA) distributed fiber sensor. Compared to single sideband (SSB)modulation, along the sensing fiber the pump depletion of DSB modulation is remarkably suppressed in time domain and also has a relatively narrower Brillouin gain spectrum in frequency domain. Both the theoretical simulation and the experimental results demonstrate that the DSB modulation provides potentially longer sensing distance and higher accuracy in measurement than the SSB modulation in the BOTDA distributed fiber sensor system.

Self-organized Criticality Model for Ocean Internal Waves

In this paper, we present a simple spring-block model for ocean internal waves based on the self-organized criticality (SOC). The oscillations of the water blocks in the model display power-law behavior with an exponent of -2 in the frequency domain, which is similar to the current and sea water temperature spectra in the actual ocean and the universal Garrett and Munk deep ocean internal wave model [Geophysical Fluid Dynamics 2(1972) 225; J. Geophys. REs. 80 (1975) 291]. The influence of the ratio of the driving force to the spring coefficient to SOC behaviors in the model is also discussed.

基于多种群遗传算法的波能装置的优化设计及分析

作为可再生能源,波浪能的吸收和利用一直是国内外热点研究内容之一。本文提出一种新的基于惯性摆结构的波浪能吸收转换方法,对这种结构在波浪力作用下的频域响应进行了分析,建立了其最优化能量获取模型,提出采用多种群遗传算法对其结构进行优化设计,并针对系统所受波浪力(矩)随载体半径改变而改变,且求取困难的问题,采用最小二乘法对波浪力(矩)与载体半径变化的关系进行了拟和。通过优化结果找出影响结构获取波浪能量的因素,仿真结果表明了方法的先进性,为进一步的应用研究和频域波能获取研究奠定了基础。

一种轮式移动机器人实时速度估计方法

环境和机器人自身的不确定性影响轮式移动机器人的轨迹跟踪控制性能,此时仅仅使用里程计往往不能正确表达机器人的状态信息。在无速度传感器的情况下,讨论了使用加速度传感器和位置传感器的输出实时估计轮式移动机器人的速度。首先使用滑模观测器进行里程计信号处理,然后对车体加速度信号进行带通滤波提取车体扰动信息,通过频域融合信号表达轮式移动机器人的速度,并针对正交轮式全方位移动机器人进行了轨迹跟踪控制研究。试验结果表明采用融合数据可以更准确提供机器人的状态信息并得到更好的控制性能。

改进叠前深度偏移的计算效率＆叠前高分辨率成像

An high-resolution prestack imaging technique of seismic data is developed in this thesis. By using this technique, the reflected coefficients of sheet sands can be gained in order to understand and identify thin oil reservoirs. One-way wave equation based migration methods can more accurately model seismic wave propagation effect such as multi-arrivals and obtain almost correct reflected energy in the presence of complex inhomogeneous media, and therefore, achieve more superiorities in imaging complex structure. So it is a good choice to apply the proposed high-resolution imaging to the presatck depth migration gathers. But one of the main shorting of one-way wave equation based migration methods is the low computational efficiency, thus the improvement on computational efficiency is first carried out. The method to improve the computational efficiency of prestack depth migration is first presented in this thesis, that is frequency-dependent varying-step depth exploration scheme plus a table-driven, one-point wavefield interpolation technology for wave equation based migration methods; The frequency-dependent varying-step depth exploration scheme reduces the computational cost of wavefield depth extrapolation, and the a table-driven, one-point wavefield interpolation technology reconstructs the extrapolated wavefield with an equal, desired vertical step with high computational efficiency. The proposed varying-step depth extrapolation plus one-point interpolation scheme results in 2/3 reduction in computational cost when compared to the equal-step depth extrapolation of wavefield, but gives the almost same imaging. The frequency-dependent varying-step depth exploration scheme is presented in theory by using the optimum split-step Fourier. But the proposed scheme can also be used by other wave equation based migration methods of the frequency domain. The proposed method is demonstrated by using impulse response, 2-D Marmousi dataset, 3-D salt dataset and the 3-D field dataset. A method of high-resolution prestack imaging is presented in the 2nd part of this thesis. The seismic interference method to solve the relative reflected coefficients is presented. The high-resolution imaging is obtained by introducing a sparseness- constrained least-square inversion into the reflected coefficient imaging. Gaussian regularization is first imposed and a smoothed solution is obtained by solving equation derived from the least-square inversion. Then the Cauchy regularization is introducing to the least-square inversion , the sparse solution of relative reflected coefficients can be obtained, that is high-resolution solution. The proposed scheme can be used together with other prestack imaging if the higher resolution is needed in a target zone. The seismic interference method in theory and the solution to sparseness-constrained least-square inversion are presented. The proposed method is demonstrated by synthetic examples and filed data.

黄海海域前新生代残留盆地综合地质地球物理研究

China’s annual oil import volume has been increasing in recent years, but the oil price in the international market fluctuates and poses a severe threat to China’s economic development and national security. Therefore, it is of great importance to study the gas and oil exploration of Pre-Cenozoic Residual Basins in Yellow Sea. Yellow Sea has widespread and thick Mesozoic and Paleozoic strata that contain multilayer source rock. Hence, Yellow Sea Mesozoic and Paleozoic strata have good conditions of forming Pre-Cenozoic hydrocarbon reservoirs. Pre-Cenozoic Residual Basins are usually buried deep and then transformed many times in its long evolutional history. These characteristics make it difficult to apply a single method in exploring Pre-Cenozoic Residual Basins. On the other hand, it is highly effective to solve key problems of gas and oil exploration of Pre-Cenozoic Residual Basins in Yellow Sea by using integrated geological and geophysical methods which make full use of the advantages of various exploring techniques. Based on the principle of “the region controls the local; the deep restricts the shallow,” this study focuses on Pre-Cenozoic Residual Basins in Yellow Sea to describe the structure frame of its distribution, with gravity, magnetic, seismic, drill-hole and geological data and previous research findings. In addition, the distribution characteristics of Pre-Cenozoic Residual Basins in Yellow Sea are also analyzed. This paper explores the characteristics of error between gravity forward with constant density and gravity forward with variable density through the study on 2-D and 3-D gravity forward in frequency domain. The result shows that there is a linear relationship between error and depth of 2-D geological model but there is a nonlinear relationship between error and depth of 3-D geological model. The error can be removed according to its linear characteristics or statistical nature of nonlinear characteristics. There is also error between gravity inversion with constant density and gravity inversion with variable density due to variable density and edge-effect. Since there are not noticeable rules between the error and the two causes as variable density and edge-effect, this study adopts gravity inversion with variable density and methods to eliminate the edge-effect in basement inversion to improve inversion accuracy. Based on the study on the rock physical properties and strata distribution of Yellow Sea and adjacent regions, this study finds that there is a big density contrast between Cretaceous-Jurassic strata and their substratum. The magnetic basement of south Yellow Sea is regarded as top of Archeozoic-Proterozoic early strata, and there are double magnetic basements in north Yellow Sea. Gravity and magnetic data are used to inverse the gravity basement and magnetic basement of Yellow Sea, with seismic and drill-hole data as constrains. According to data of gravity and magnetic basement distribution, the depth of Cenozoic strata and previous research findings, this paper calculates the thickness of the Mesozoic and Pre-Mesozoic Residual Basins, draws the distribution outline of Pre-Cenozoic Residual Basins in Yellow Sea, and analyzes its macro-distribution characteristics. Gravity inversion is applied on a typical geological profile in Yellow Sea to analyze the characteristics of its fractures and magnetic basements. The characteristics of Pre-Cenozoic Residual Basins distribution outline in Yellow Sea and the fractures and magnetic basements of its typical profile shown by profile inversion provides new geophysical evidence for these structure views such as “the South Yellow Sea and the North Yellow Sea belong to different structural units” and “Sino-Korea and Yangtze blocks combine along Yellow Sea East Fractured Zone in Yellow Sea”.

有源电磁扩散场克希霍夫积分偏移

As active electromagnetic method, field data of CSAMT method follow the equation of diffusion. Propagting in solid earth media, diffusion EM signal has strong attenuation and dispersion, otherwise seismic wave shows weak attenuation and dispersion, therefore the resolution power of CSAMT method is not better than seismic reflection method. However, there is consistence and similarity between EM signal and seismic wave in wave equation, we can apply Kirchhoff integral migration technique, a proven one in seismic method in time domain, to carry out seduo-seismic processing for CSAMT signal in frequency domain so that the attenuation and dispersion could be made compensated in some extent, and the resolution power and interpretation precision of active EM wave could be improved. Satisfying passive homogeneous Helmholtz quation, we proceed with Green theorem and combine the active inhomogenous Helmholtz quation, the Kirchhoff integral formula could be derived. Given practical problems, if we only consider the surface integral value, and assume that the intergral value in other interface is zero, combined with Green theorem in uniform half space, the expression could be simplified, and we can obtain frequency-domain Kirchhoff integral formula in surface, which is also called downward continuation of EM field in frequency domain. With image conditions and energy compensation considered, in order to get image conditions in time domain Fourier inverse transformation in frequency domain can be performed, so we can formulate the active Kirchhoff integral migration expression. At first, we construct relative stratified model, with different frequency series taken into account, then we change the distances between transmitter and reciever, the EM response can be obtained. Analyzing the EM properties, we can clarify near and far zone that can instruct us to carry out transmitter layout in practical application. Combined with field data surveyed in far zone, We perform Kirchhoff integral migration and compare the results with model to interpret. Secondly, with far field EM data, we apply TM mode to get EM response of given 2D model, then apply Kirchhoff integral migration on modelling data and interpret the results.

基于广义Lippmann-Schwinger方程的地震波场模拟算法与应用

In the last several decades, due to the fast development of computer, numerical simulation has been an indispensable tool in scientific research. Numerical simulation methods which based on partial difference operators such as Finite Difference Method (FDM) and Finite Element Method (FEM) have been widely used. However, in the realm of seismology and seismic prospecting, one usually meets with geological models which have piece-wise heterogeneous structures as well as volume heterogeneities between layers, the continuity of displacement and stress across the irregular layers and seismic wave scattering induced by the perturbation of the volume usually bring in error when using conventional methods based on difference operators. The method discussed in this paper is based on elastic theory and integral theory. Seismic wave equation in the frequency domain is transformed into a generalized Lippmann-Schwinger equation, in which the seismic wavefield contributed by the background is expressed by the boundary integral equation and the scattering by the volume heterogeneities is considered. Boundary element-volume integral method based on this equation has advantages of Boundary Element Method (BEM), such as reducing one dimension of the model, explicit use the displacement and stress continuity across irregular interfaces, high precision, satisfying the boundary at infinite, etc. Also, this method could accurately simulate the seismic scattering by the volume heterogeneities. In this paper, the concrete Lippmann-Schwinger equation is specifically given according to the real geological models. Also, the complete coefficients of the non-smooth point for the integral equation are introduced. Because Boundary Element-Volume integral equation method uses fundamental solutions which are singular when the source point and the field are very close，both in the two dimensional and the three dimensional case, the treatment of the singular kernel affects the precision of this method. The method based on integral transform and integration by parts could treat the points on the boundary and inside the domain. It could transform the singular integral into an analytical one both in two dimensional and in three dimensional cases and thus it could eliminate the singularity. In order to analyze the elastic seismic wave scattering due to regional irregular topographies, the analytical solution for problems of this type is discussed and the analytical solution of P waves by multiple canyons is given. For the boundary reflection, the method used here is infinite boundary element absorbing boundary developed by a pervious researcher. The comparison between the analytical solutions and concrete numerical examples validate the efficiency of this method. We thoroughly discussed the sampling frequency in elastic wave simulation and find that, for a general case, three elements per wavelength is sufficient, however, when the problem is too complex, more elements per wavelength are necessary. Also, the seismic response in the frequency domain of the canyons with different types of random heterogeneities is illustrated. We analyzed the model of the random media, the horizontal and vertical correlation length, the standard deviation, and the dimensionless frequency how to affect the seismic wave amplification on the ground, and thus provide a basis for the choice of the parameter of random media during numerical simulation.