A novel approach to the acoustic characterisation of porous road surfaces

Porous road surfaces offer an effective means of reducing the generation and propagation of noise from road traffic. However, the porosity of these surfaces can deteriorate over time, leading to a reduction in their noise reducing properties. Efficient methods are therefore required for monitoring this performance. Existing techniques for performing in-situ measurements of acoustic absorption are unsuitable for use within the traffic stream. Static measurements using time domain Maximum Length Sequence (MLS) based techniques have been demonstrated to offer advantages over traditional techniques, presenting the opportunity for measurements under dynamic conditions. This paper describes the design of a system for carrying out dynamic MLS-based measurements. Results are presented which demonstrate that stable dynamic measurements can be carried out at speeds of up to 30 km/h.     

Characterization of defects in real surfaces by ellipsometry

It is shown that ellipsometry can be used for nondestructive characterization of defects in surface layers of both single crystal and amorphous materials. Results of ellipsometric measurements on surfaces of materials such as silicon, potassium chloride and glasses, with widely varying preparatory histories are presented and discussed.     

3D reconstruction of road surfaces using an integrated multi-sensory approach

In this paper, we present our experience in building a mobile imaging system that incorporates multi-modality sensors for road surface mapping and inspection applications. Our proposed system leverages 3D laser-range sensors, video cameras, global positioning systems (GPS) and inertial measurement units (IMU) towards the generation of photo-realistic, geometrically accurate, geo-referenced 3D models of road surfaces. Based on our summary of the state-of-the-art systems for a road distress survey, we identify several challenges in the real-time deployment, integration and visualization of the multi-sensor data. Then, we present our data acquisition and processing algorithms as a novel two-stage automation procedure that can meet the accuracy requirements with real-time performance. We provide algorithms for 3D surface reconstruction to process the raw data and deliver detail preserving 3D models that possess accurate depth information for characterization and visualization of cracks as a significant improvement over contemporary commercial video-based vision systems.     

等效道路线声源位置优化研究

计算道路交通噪声时,一般将每个车道等效为1个线声源。有时,为了简化计算,将道路等效为1个线声源,等效线声源位置为道路中轴;或等效为2个线声源,等效线声源位置为道路两侧中心线或两侧最外车道中心线。推导不同等效方法下观测点噪声的计算公式,并探讨不同等效方法引起的误差。研究结果表明,将道路等效为2个线声源,等效线声源位置为道路两侧中心线的简化方法引起的误差最小。     

Minimum measurement time interval to estimate a reliable sound pressure level of road traffic noise using two types of dynamic statistics

A new method to determine the minimum measurement time interval needed to obtain the equivalent continuous A-weighted sound pressure level with a designated reliability is presented. This method considers variations in the noise emission from passing vehicles. To verify the validity and availability, simulation experiments based on our dynamic model are examined under various traffic conditions. A statistic quantity, the mean time interval between two maximum sound pressure levels consecutively observed during the reference measurement time interval, is introduced in the experimental analysis. Additionally, the theoretical analysis includes another statistic quantity corresponding to the mean time interval, the mean recurrence time of the maximum sound pressure level, when the transition probability, rate of heavy vehicles, and probability distribution of vehicles passing the observation point during the reference measurement time interval are known.     

Integral geometry on families of surfaces in the space

A complex {B_ξ} of submanifolds is called admissible in the sense of integral geometry if there are such densities μ_ξ on B_ξ, that the integral transformation

has a local inversion formula. We prove that compact smooth surfaces of an admissible complex in P³ has degree 3 and obtain complete classification of admissible complexes of quadrics. Several general theorems and conjectures about admissible complex of k-dimensional submanifolds are stated.     

微型化频率选择表面的设计研究

利用容性表面与感性表面之间的耦合机理能够制备微型化频率选择表面(MEFSS),周期单元尺寸将不受工作波长限制.为了提高MEFSS角度与极化的稳定性,展宽MEFSS的-3 dB带宽,文章结合传统频率选择表面"Y"形单元,利用"Y"图形构造容性表面的贴片单元与感性表面的网栅单元且以正三角形栅格拓展周期单元,采用矢量模匹配法对MEFSS栅格排布及其他结构参数变化进行精确计算.通过镀膜与光刻技术在0.15 mm厚聚酰亚胺膜两侧制备容性表面、感性表面并利用自由空间法测试.计算与实验结果均表明,采用正三角形栅格排布的MEFSS,-3 dB带宽达到7.6 GHz,不同极化下60°扫描时中心频点稳定在f₀,为MEFSS应用于曲面天线罩时提供理论与实验参考依据. 关键词： 天线罩 微型化频率选择表面 容性表面 感性表面     

基于DSP+FPGA的实时信号采集系统设计与实现

为了提高对实时信号采集的准确性和无偏性,提出一种基于DSP+FPGA的实时信号采集系统设计方案。系统采用4个换能器基阵并联组成信号采集阵列单元,对采集的原始信号通过模拟信号预处理机进行放大滤波处理,采用TMS32010DSP芯片作为信号处理器核心芯片实现实时信号采集和处理,包括信号频谱分析和目标信息模拟,由DSP控制D/A转换器进行数/模转换,通过FPGA实现数据存储,在PC机上实时显示采样数据和DSP处理结果。通过仿真实验进行性能测试,结果表明,该信号采集系统能有效实现实时信号采集和处理,抗干扰能力较强。     

Robust pre-specified time synchronization of chaotic systems by employing time-varying switching surfaces in the sliding mode control scheme

In the conventional chaos synchronization methods, the time at which two chaotic systems are synchronized, is usually unknown and depends on initial conditions. In this work based on Lyapunov stability theory a sliding mode controller with time-varying switching surfaces is proposed to achieve chaos synchronization at a pre-specified time for the first time. The proposed controller is able to synchronize chaotic systems precisely at any time when we want. Moreover, by choosing the time-varying switching surfaces in a way that the reaching phase is eliminated, the synchronization becomes robust to uncertainties and exogenous disturbances. Simulation results are presented to show the effectiveness of the proposed method of stabilizing and synchronizing chaotic systems with complete robustness to uncertainty and disturbances exactly at a pre-specified time.     

Eigenvalue system for the scattering from rough surfaces - Saving in computation time by a physical approach

The curvilinear coordinate method is an efficient theoretical tool for analysing rough surfaces. It consists on solving Maxwell’s equations written in a nonorthogonal coordinate system. The C method leads to eigenvalue systems and the scattered fields can be expanded as a linear combination of eigensolutions. The boundary conditions allow the combination coefficients to be determined. The dominant computational cost for the C method is the eigenvalue problem solution which is of order of N³ where N is the size of eigenvalue systems. In this paper, we propose a new approach based on the association of the C method with the beam simulation method (BSM) in order to reduce the computational time. The BSM is based on decomposing a large incident beam into narrower subbeams and then synthesizing the large beam by coherent superposition. The adopted procedure consists of two stages. First, the surface fields are obtained by the C method associated with each elementary beam illuminating smaller surfaces. Second, the total surface field is deduced from a coherent superposition of elementary surface current densities. The far-field and the scattering coefficients are derived from the Huygens principle applied to the total surface fields. We confirm the efficiency and the validity of the approach and show that the BSM applied with the C method allows a significant saving in computation time.     

The calculation of the surface energy of high-index surfaces in metals at zero temperature

We used the molecular dynamics simulation with interatomic potentials of the embedded atom method to calculate the high-index surface energies of the surfaces containing the 〈0 0 1〉 axis or 〈−1 1 0〉 axis in f.c.c. metal Al, Cu and Ni at zero temperature. We generalized an empirical formula based on structural unit model for high-index surfaces and present some new formulas that can be used to estimate the surface energy and structural feature of high-index surfaces very well. The results show that the closest surfaces have the lowest surface energy and the surface energies of the closest (1 1 1) surface and the next closest (1 1 0), (1 0 0) surfaces are the extremum on the curve of surface energy versus orientation angle. We also calculated the b.c.c. metal Fe and obtained a similar result. The difference is that in the b.c.c. metal the surface energies of the closest (1 1 0) surface and the next closest (1 0 0), (1 1 2) surfaces are the extremum on the curve of surface energy versus orientation angle. The results of theoretical simulation and the empirical formula consist well with the experiment data.     

等势面族的条件及例子

介绍静电场中等势面的条件以及几个例子.     

稳定In/Si表面的LEED研究

利用LEED图形拟合的方法对大量不同取向In/Si表面的稳定性和小面化进行了研究，新发现了In覆盖度在1/2单层原子以下的三个稳定表面：Si(214)-In，Si(317)-In和Si(436)-In，以及In覆盖度在1单层原子左右的两个稳定表面Si(101)-In和Si(313)-In.此外还确定了In覆盖度在1单层原子左右的6个稳定In/Si表面的家族领地以及In覆盖度在1/2单层原子以下的4个稳定In/Si表面的家族领地.特别值得注意的是 Si(103)-In的家族领地相当大，甚至比最稳定的Si(1 关键词： 硅表面 铟 稳定表面 家族领地     

Elastic wave surfaces for the (111) plane of cubic crystals

The nature of inverse velocity surfaces as well as energy surfaces for elastic wave propagation in the (111) plane have been studied for a number of cubic crystals. The sections of inverse velocity surfaces by the (111) plane exhibit six-fold symmetry in all cases. Cuspidal edges are exhibited with a six-fold symmetry by both the slow transverse and fast transverse shear modes in the (111) plane, unlike the case of the (100) and (110) planes for which only the slow transverse shear mode exhibits cuspidal edges. The slow transverse mode energy surface exhibits cuspidal edges along direction or an equivalent symmetry direction. The inverse velocity surfaces of the A-15 compounds exhibit unusually large inflexions for the slow transverse mode, whereas their energy surfaces have large cuspidal edges which intersect each other resulting in common regions of cusps.     

Manipulation of oxide surfaces

Metal oxides have considerable potential as insulating supports for nanoscale electronic devices. One of the key attributes of metal oxide surfaces is their capacity to be modified by electron beams and scanning probe tips. Such modifications can involve the creation of O vacancies or an area of a different reconstruction, which in principle can act as anchoring points or templates for molecules or metal interconnects. In this Prospective we describe previous attempts at well-defined modification in order to illustrate this potential.     

On the properties of real cadmium telluride surfaces

Optical and electrical properties of lapped, mechanically polished, and etched cadmium telluride surfaces have been studied by ellipsometry, infrared transmission, reflectivity, and sheet resistance measurements. They have been related to the characteristics of Schottky barriers realized by deposition of gold on these surfaces. These experiments indicate that the electrical behaviour of devices made of cadmium telluride critically depends on the surface damages produced during the sample preparation: while good diodes can be made when bromine in methanol etching is used, lapping and polishing produce a disturbed layer of poor electrical and optical properties whose thickness is related to the size of the abrasive powder used during the preparation.     

High order numerical approximation of minimal surfaces

We present an algorithm for finding high order numerical approximations of minimal surfaces with a fixed boundary. The algorithm employs parametrization by high order polynomials and a linearization of the weak formulation of the Laplace–Beltrami operator to arrive at an iterative procedure to evolve from a given initial surface to the final minimal surface. For the steady state solution we measure the approximation error in a few cases where the exact solution is known. In the framework of parametric interpolation, the choice of interpolation points (mesh nodes) is directly affecting the approximation error, and we discuss how to best update the mesh on the evolutionary surface such that the parametrization remains smooth. In our test cases we may achieve exponential convergence in the approximation of the minimal surface as the polynomial degree increases, but the rate of convergence greatly differs with different choices of mesh update algorithms. The present work is also of relevance to high order numerical approximation of fluid flow problems involving free surfaces.     

An extension of a result of Grannan and Swindle on the poisoning of catalytic surfaces

Grannan and Swindle considered a model in which molecules of several types of reactant land on a catalytic surface. When two different reactants find themselves adjacent, they diffuse from the surface and leave the sites vacant. They showed that if the rate of bonding onto the surface of one reactant is sufficiently close to one, then the surface becomes poisoned by that type. In this paper we show that a sufficient condition for poisoning is that one reactant should bond at rate greater than that of the other reactants combined.     

Monitoring road surfaces by close proximity noise of the tire/road interaction

Applied acoustics is becoming an important field for civil infrastructure and environmental assessment, and road maintenance or rehabilitation strategies. In this research LA(2)IC has developed a GPS-based measurement techniques and apparatus on a test vehicle, for monitoring the acoustical properties of different road pavement surfaces with a reference tire. A field test on PA-12 Spanish porous pavement found in Ciudad Real is developed. The test procedure, a modification based upon the close-proximity method (CPX), relies on the use of three standard microphones situated very close to the tire/road contact patch. This procedure allows the simultaneous measurement of the sound emission synchronized to a GPS receiver, which permits tracking of the position of the sound emission. Geo-referenced sound spectra for every 10 m during individual passes of the test vehicle are analyzed to determine the tire/road noise emissions from tire/PA-12 pavement interaction. Noise levels of around 102 dB(A), with a variability of approximately 0.6 dB(A), are found at a reference vehicle speed of 85 kmh. The frequency spectrum analysis over the test section shows noticeable differences for frequencies above 1 kHz, where the tire/road noise generation mechanisms are dominated by air pumping.     

Hot electron plasmas trapped in helical magnetic surfaces

Experimental studies on nonneutral (pure electron) plasmas of finite temperature, trapped in helical closed magnetic surfaces have been conducted. The helical electron plasmas are produced with thermal electrons launched from the outside of the last closed flux surface (LCFS). About 150 μs after the electron injection, the plasmas reach equilibrium state. Around the LCFS, a steep gradient of plasma space potential φ _s is formed. The corresponding radial electric field is about 2.5 kV/m. On the other hand, around the magnetic axis of helical magnetic surfaces, φ _s is almost constant, indicating that there are little electrons there. The volume-averaged electron density is on the order of 10¹³ m^–3, smaller than the Brillouin density limit. The confinement time seems to be limited by a disruptive instability, and is so far about 1.5 ms.