遥感与水动力模型相结合的宽大潮滩历史地形反演

潮滩作为陆海交互区,面积宽广,测量困难,历史地形资料缺失,已经严重影响到潮滩的开发利用。以辐射沙脊群潮滩为实验区,利用1987年前后的TM、MSS影像提取不同潮情下的系列水边线,运用Mike21水动力模型模拟遥感图像对应时刻下的瞬时海面高度,为水边线赋值,进而通过地形反复迭代得到数字高程模型。结果表明,在辐射沙脊群潮滩区,水边线法获取的地形结果与海图上测点的相关性较高,决定系数R~2达0.864,绝对平均误差0.37 m,均方根误差0.41 m,地形结果可用于进一步的潮滩地貌演变分析。     

基于滑移/非滑移异质界面的动压润滑性能优化

合理布置的滑移/非滑移异质界面可以提高流体动压润滑性能,但目前滑移区和非滑移区的组合方式大多采用单一的直线拼接法,没有针对流体润滑摩擦副的各类工况设计出相应的优化方案,为此本文建立了一组离散式二次方程来描述滑移区和非滑移区拼接轨迹,并引入计算域单元的宽长比作为优化变量,分别以液膜刚度和摩擦因数作为优化目标,通过MATLAB数值仿真求解不同宽长比条件下滑移区和非滑移区的最优拼接轨迹。结果表明,与直线拼接法相比,选取二次方程所描述的抛物线作为滑移区和非滑移区拼接轨迹的方法使流体润滑摩擦副在摩擦因数和液膜刚度等性能指标上都有所改善,而且根据不同的优化目标参数可以方便地绘制出最优拼接方案,验证了本文方法在改善动压润滑性能上的可行性和普适性。     

Effects of laser irradiation on optical properties of a-Se100−x Te x thin films

The effect of laser irradiation on the optical properties of thermally evaporated Se_100?x Te _x (x=8, 12, 16) chalcogenide thin films has been studied. The result shows that the irradiation causes a shift in the optical gap. The results have been analyzed on the basis of laser irradiation-induced defects in the film. The width of the tail of localized state in the band gap has been evaluated using the Urbach edge method. As the irradiation time increases, the values of the optical energy gap for all compositions decrease, while tail energy width increases. It is also observed that the optical energy gap decreases with increasing Te content in the alloy. These changes are a consequence of an increment in disorder produced by laser irradiation in the amorphous structure of thin film.     

Amplitude modulation control of escape from a potential well

We demonstrate the effectiveness of periodic amplitude modulations in controlling (suppressing and enhancing) escape from a potential well through the universal model of a damped Helmholtz oscillator subjected to an external periodic excitation (the escape-inducing excitation) whose amplitude is periodically modulated (the escape-controlling excitation). Analytical and numerical results show that this multiplicative control works reliably for different subharmonic resonances between the two periodic excitations involved, and that its effectiveness is comparable to those of different methods of additive control. Additionally, we demonstrate the robustness of the multiplicative control against the presence of low-intensity Gaussian noise.     

Like‐Charge Attraction: A Combined Electrostatic–Hydrodynamic Approach

Abstract

This article discusses the like‐charge attraction of colloidal spheres close to a charged plate and compares results produced by an electrostatic and a hydrodynamic model with experimental data. Hydrodynamic coupling is shown to be the dominating effect, while the electrostatic influence may often be neglected. Some observations, however, can be explained only by means of a combined electrostatic–hydrodynamic model, which is derived in this work. The combined model is able to predict not only the attractive force between particles of similar charge close to a charged plate but also the change to a purely repulsive force once the sphere‐plate distance is further reduced. This prediction matches qualitatively results of experiments reported in the literature.     

Nonlinear interaction mechanisms of disturbances in supersonic flat-plate boundary layers

Due to the complexity of compressible flows, nonlinear hydrodynamic stability theories in supersonic boundary layers are not sufficient. In order to reveal the nonlinear interaction mechanisms of the rapidly amplified 3-D disturbances in supersonic boundary layers at high Mach numbers, the nonlinear evolutions of different disturbances in flat-plate boundary layers at Mach number 4.5, 6 and 8 are analyzed by numerical simulations. It can be concluded that the 3-D disturbances are amplified rapidly when the amplitude of the 2-D disturbance reaches a certain level. The most rapidly amplified 3-D disturbances are Klebanoff type (K-type) disturbances which have the same frequency as the 2-D disturbance. Among these K-type 3-D disturbances, the disturbances located at the junction of upper branch and lower branch of the neutral curve are amplified higher. Through analyzing the relationship between the amplification rate and the spanwise wavenumber of the 3-D disturbances at different evolution stages, the mechanism of the spanwise wavenumber selectivity of K-type 3-D disturbances in the presence of a finite amplitude 2-D disturbance is explained.     

鄂尔多斯盆地NL油田延9流动单元研究

从国内外流动单元研究现状出发,结合研究区实际的岩心、地质、测井和生产动态资料,根据流动带指标和岩性-物性划分法划分流动单元.研究中遵循单井、剖面到平面的思路,开展了流动单元特征参数优选、取心井流动单元分析、非取心井的流动单元划分工作.运用动态资料验证流动单元划分的合理性,进行了流动单元剖面、平面特征研究及流动单元生产能力分析.研究表明,所选用的渗透率、孔隙度和流动层带指标IFZ3个参数可满足本区流动单元划分要求,研究区延9储层流动单元可划分为Ⅰ、Ⅱ、Ⅲ、Ⅳ类.     

Fields,particles and universality in two dimensions

We discuss the use of field theory for the exact determination of universal properties in two-dimensional statistical mechanics. After a compact derivation of critical exponents of main universality classes, we turn to the off-critical case, considering systems both on the whole plane and in presence of boundaries. The topics we discuss include magnetism, percolation, phase separation, interfaces, wetting.     

Pulsed-field separation of particles in a microfluidic device

We demonstrate the proof-of-principle of a new separation concept for micrometer-sized particles in a structured microfluidic device. Under the action of externally applied, periodic voltage-pulses two different species of like-charged polystyrene beads are observed to simultaneously migrate into opposite directions. Based on a theoretical model of the particle motion in the microdevice that shows good agreement with the experimental measurements, the underlying separation mechanism is identified and explained. Potential biophysical applications, such as cell sorting, are briefly addressed.     

Non-classical correlation of the two emission fields by a four-level atomic ensemble

The normalized second-order correlation of the emission fields from a driven four-level atomic ensemble is investigated theoretically by using the state vector method. The violation of Cauchy-Schwarz inequality, which indicates the establishment of non-classical correlation between two emission fields, has been found. The effects of various decays and time delay on the correlation are discussed in detail, which are helpful in finding the ways to obtain high non-classical correlation. This technique for the generation of non-classical light is operable based on the current experimental technology and will lead to some potential applications in quantum information science.