PS-InSAR技术在北京平原区地面沉降监测中的应用研究

北京市近60年长期超量开采地下水已经引起了严重的地下水水位下降和大范围地面沉降,截止到2009年最大累计沉降量达到1 096 mm,并以30~60 mm·y-1速率扩展,严重威胁城市规划建设和人民交通安全。相对于传统的水准测量、分层标等地面沉降监测手段,永久散射体干涉测量技术(PS-InSAR)可以快速获取高分辨率的地表形变细节信息。利用PS-InSAR技术和2003年12月—2009年3月Envisat卫星29景ASAR影像监测北京平原区地面沉降发展情况,发现北京平原区沉降漏斗已连成一片,沉降梯度变化较大地区主要分布在北京第四系凹陷区,覆盖面涉及朝阳、昌平、顺义、通州等区县,并有东移外扩趋势,平谷县境内出现新的沉降中心。沉降分布受前门—良乡—顺义、黄庄—高丽营、南口—孙河等主要断层控制,地面沉降与地下水水位变化具有明显相关性,呈现季节性下降(3月—6月)与回弹(11月—3月)趋势,并受弱透水层应力应变本构关系(弹性-塑性-黏弹性)影响。     

Dynamic and mass transfer characteristics of the flow issued from a bent chimney around buildings

The present work consists in an experimental investigation of the flow issuing from a bent chimney over a downstream obstacle. Our purpose is to explore the resulting flow field and its different characterizing features. These features were captured by means of the Particle Image Velocimetry technique. A numerical simulation of the problem has also been carried out and validated after comparison of the corresponding results to the experimental data. A good level of agreement was achieved between the experiments and the calculations. Then, we tried to upgrade our model by adopting large (real) scale dimensions. Our purpose consisted mainly in the observation and evaluation of the behavior of the incoming flow in presence of a double tandem obstacle. In a second step, we proposed to increase the number of the placed obstacles to four. The results given by the three-dimensional model are likely to highlight the dynamic features of the established field as well as the resulting mass transfer. Finally, we tried to evaluate the effect of further parameters on the characterizing features of the resulting flow filed such as the velocity ratio, the obstacles’ gap, the arrangement of the obstacles and the obstacles’ geometry.     

CS-MRI 中评价随机欠采样矩阵的新方法

在压缩感知-磁共振成像(CS-MRI)中,随机欠采样矩阵与重建图像质量密切相关．而选取随机欠采样矩阵一般是通过计算点扩散函数(PSF),以可能产生的伪影的最大值为评价参数,评估欠采样对图像重建的影响,然而最大值只反应了伪影的最坏情况．该文引入了两种新的统计学评价参数平均值(MV)和标准差(SD),其中平均值评估了伪影的平均大小,标准差可以反映伪影的波动情况．该文分别使用这3种参数对小鼠和人体脑部MRI数据以不同的采样比率进行CS图像重建,实验结果表明,当采样比率不低于4倍稀疏度时,使用平均值获得了质量更优的重建图像．因此,通过稀疏度先验知识指导合理选取采样比率,并以平均值为评价参数选取随机欠采样矩阵,能够获得更优的CS-MRI重建图像．
     

Investigation of a turbulent wall jet in forced convection issuing into a directed coflow stream

In the present paper, we have studied numerically the directed coflow stream effects on mean and turbulent flow properties of a turbulent plane wall jet in forced convection emerging into a directed coflow stream. The system of equations governing the studied configuration is solved with a finite difference scheme using a staggered grid for numerical stability, not uniform in the two directions of the flow. The modified version of the first-order low Reynolds number k–? turbulence model is used and compared to existing experimental findings. It is found that predicted results are in satisfactory agreement with the experimental data and that the wall jet fluid decays faster in presence of a directed coflow stream. Results show also that the increase of coflow deviation angles causes an increase of the growth rates of the dynamic and thermal half-width of the jet and enhances the turbulent mixing. It is found that the longitudinal development of normalised forms of the jet characteristics parameters at different directed coflow velocity ratios can be reasonably well collapsed onto universal trends through the use of momentum length scale.     

膀胱癌病人尿液中的特征物质研究

采用顶空气相色谱/质谱联用法分析膀胱癌病人的尿液,寻找尿液中的挥发性特征物质,以期作为尿液检查诊断膀胱癌的一种方式。选取一组膀胱癌患者,对其尿液进行定性定量分析,并将分析结果与健康人尿液进行比较。进样口温度280℃,进样量100μL;起始柱温45℃,保留3min,以16℃/min的速率程序升温到280℃。结果表明:膀胱癌病人尿液中含有两种特征物质4-庚酮和二甲基硫醚。膀胱癌患者尿液中4-庚酮的浓度范围为0.14～1.32μL/L;二甲基硫醚的浓度范围为0.009～0.73μL/L。推测4-庚酮可能来源于增塑剂邻苯二甲酸二异辛酯(di(2-ethylhexyl)phthalate,DEHP)在人体内的降解;二甲基硫醚来源于含硫化合物在人体内的合成与降解。尿液中4-庚酮和二甲基硫醚的含量与膀胱癌具有相关性。     

Information theoretical statistical discrimination measures for electronic densities

Journal of Mathematical Chemistry - Information theoretical measures are examined as methodologies for optimizing linear and non-linear parameters to obtain the best densities for particular...     

Monovalent Cation–Phenolic Crystals with pH-Driven Reversible Crystal Transformation

The conversion of renewable plant polyphenol to advanced materials with tailorable properties and various functions is desirable and challenging. In this work, monovalent cation-phenolic crystals contained K⁺ or Na⁺ ions were synthesized by using plant polyphenol as an organic source in alkaline solution. The crystal structure was resolved, showing a laminar crystal structure with M⁺ as connecting nodes. The morphologies (e.g., rod-like and spindle-shaped) and chemical compositions of crystals could be tuned by changing the cations. Interestingly, these polymer crystals exhibited a pH-driven reversible crystal transformation. They transformed into their protonated crystalline form under acidic conditions (e.g., pH 2) and went back to the cation-bound crystalline form in alkaline solutions. Furthermore, the crystals proved excellent antioxidants and heavy metal ion adsorbents.     

Symbolic research of the periodic solutions of the nonintegrable Hamiltonian system of Ollongren

The main aim of this work is to look for the periodic solutions of the nonintegrable Hamiltonian system of Ollongren in the neighborhood of the origin. We apply a functional algorithm derived from the method of Lindstedt-Poincaré. We first show that the system admits six main periodic families and then, by means of the computer algebra system “Mathematica”, compute the series corresponding to these families up to O(ε¹⁴A²⁹) as well as to their periods up to O(ε¹⁵A³⁰), where A is the zeroth-order amplitude and έ is a perturbative parameter. Reducing the system to one degree of freedom we also prove that the period of the two “oblique” periodic families is rigorously equal to a Gauss hypergeometric series. Moreover, we study numerically the convergence of the L-P series and test the validity of these series using a numerical integration technique. Finally, we compare our results with those of a geometrical method and a Lie series method. This revised version was published online in June 2006 with corrections to the Cover Date.     

Conduction Studies on Bismuth Selenide Thin Films

Thin films of Bi₂Se₃ have been prepared by vacuum deposition technique onto well cleaned glass and freshly cleaved KBr substrates. The film thicknesses are measured by Tolansky technique. The capacitance and dielectric constant have been measured from 303 K to 383 K in the frequency range of 10 kHz to 10 MHz. The a.c. conductivity s is calculated at different frequencies for various temperatures. The relation s μ wn fits well and the value of n is found to be greater than 1.5 and above at high frequencies suggests that the conduction mechanism in Bi₂Se₃ thin film is hopping. The d.c. conduction studies revealed the non-ohmic type of conduction( Log I versus Log V plot). From the Log I versus F1/2 plot, the field lowering coefficient b is evaluated.     

Comparative study of the forward and backward methods for calculating jet properties in pp collisions at s~(1/2)=7 TeV

We propose a forward method based on PYTHIA6.4 to study the jet properties in ultra-relativistic pp collisions.In the forward method,the partonic initial states are first generated with PYTHIA6.4 and then hadronized in the Lund string fragmentation model,and finally the hadronic jets are constructed from the created hadrons.Jet properties calculated with the forward method for pp collisions at √s=7 TeV are comparable to those calculated with the usual anti-kt algorithm(backward method)in PYTHIA6.4.The comparison between the backward and forward methods may contribute to the understanding of the partonic origin of jets in the backward method.