Sound propagation and radiation through a vaneless diffuser

A simple analysis has been carried out to examine acoustic effects of attaching to the termination of an annular duct a vaneless diffuser through which incident plane waves propagate and radiate out circumferentially. The results are shown in the form of a reflection coefficient which expresses the ration of the incident and reflected waves at the diffuser inlet.     

Radiation and reflection acoustical fields of an annular phased array

The characteristics of the radiation and reflection acoustical fields of an annular phased array are investigated. The effects of the element number, element radius, interelement spacing, centre frequency, focus position, and other parameters on the radiation acoustical field of the annular phased array is theoretically studied. In experiment, an annular transducer with 8 equal-area elements is designed and fabricated, and a series of experimental measurements are conducted. The radiation acoustical field and its reflection on a liquid-solid interface are theoretically and experimentally studied. The experimental result is in good agreement with the theoretical one.     

Propagation and radiation of sound from flanged circular ducts with circumferentially varying wall admittances,I: Semi-infinite ducts

The propagation of acoustic waves in an infinite circular duct with a circumferentially varying wall admittance is theoretically considered. An exact solution is obtained and used to investigate the characteristics of wave dispersion, mode shapes and admittance. The scattering from a flanged termination of the circular duct is then analyzed with use of a rigorous solution in oblate spheroidal co-ordinates. The effects of the asymmetry of the duct wall admittance on the amplitude reflection coefficients, radiated power transmission losses and the far field radiation directivity patterns are examined.     

Evaluation of interface wave velocity, reflection coefficients and interfacial stiffnesses of contacting surfaces

The phase velocity of the antisymmetric-mode interface wave as well as the longitudinal and shear wave reflection coefficients have been measured for contacting poly(methyl methacrylate) (PMMA) surfaces subjected to different contact pressures. It has been found that while the reflection coefficients decrease as the contact pressure is increased, the phase velocity of the interface wave increases from that of the Rayleigh wave toward that of the bulk shear wave. From these measurements, the normal and tangential interfacial stiffnesses of the contacting PMMA surfaces have been evaluated as functions of the contact pressure. As a result, the two independent procedures to evaluate the tangential stiffness, namely, from the interface wave velocity and from the shear wave reflection measurements, have yielded mutually consistent results. Furthermore, it has been found that the tangential/normal stiffness ratio and the shear/longitudinal reflection ratio of the contact interface are consistent with the predictions of an existing theoretical model for kissing bond interfaces.     

Fast Neutron Albedo Calculations for a Concrete Shield with Different Curvatures

The O5R Monte Carlo neutron transport Code had been used to calculate the neutron albedo for neutrons reflected from plane and curved concrete shields. The present calculations were performed to investigate the fast-neutron albedo in case of ordinary concrete shield, in order to perform comparative studies with the case of neutron reflection against a flat wall. The calculations were performed for three different neutron source energies of 1 MeV, 5 MeV and 15 MeV and at neutron incident angles of 5°, 30°, 45°, 60° and 90° and for surfaces with different curvatures (flat, 100, 50, 20 and 5 cm). The results obtained reveal that there will be an appreciable error on using the flat wall albedo value in the case of duct penetration calculations. The error was assumed to be due to the neglection of the curvature effect as well as to the improper choice of the neutron incident angle.     

Boundary reflection from curved liquid surfaces and its application

A boundary light reflection from curved liquid surfaces was discovered. Due to the wetting effect, the liquid surface near the plate which was inserted into the liquid was deformed. When a collimated light beam vertically illumined the curved liquid surface, special reflective patterns of a strip-shape dark region in the center and the visibility interference fringes on both sides was observed for the up-curved liquid surface. The width of the dark region increases with the decreasing width of the incident beam. The relation of the dark region width and the incident beam width was derived theoretically. The slope and the height of curved liquid surface were obtained directly from measuring the dark central region width of the reflection pattern and the incident beam width. Furthermore, the analytic expression of the profile of the curved liquid surface was derived. As a result, it shows that an effective and practical technique for measuring the characterization of curved liquid surface was found.     

Comparison of ray-tracing methods for semitransparent slab with variable spatial refractive index

The ray-tracing technique has the main difficulty in solving radiative transfer in the medium with variable spatial refractive index. Recently, three methods have been developed for the application of the ray-tracing technique in those medium. To compare and discuss the numerical characteristics of those methods, a semitransparent slab with variable spatial refractive index is taken as an example, and the reflectivity and the transmissivity of the slab are computed by the curved ray-tracing method, the multi-layer approach, and the discrete curved ray-tracing method, respectively. As the result, it is shown that, the discrete curved ray-tracing method gives the result with good accuracy and convergence characteristics than the multi-layer approach. Due to accounting physically inexistent reflection on the interface between sublayers, the multi-layer approach converges slowly.     

Surface‐sensitive reflection‐mode EXAFS from layered sample systems: the influence of surface and interface roughness

The calculation of reflection‐mode grazing‐incidence X‐ray absorption spectra from single surfaces and (multi‐)layered systems is studied here. In particular, the influence of the surface and interface roughness was investigated in detail. Simulations of grazing‐incidence reflection‐mode EXAFS spectra using a simple Fresnel theory neglecting any effect of roughness are compared with the Névot–Croce model and the elaborated distorted‐wave Born approximation which both include surface and interface roughness. Data are presented for clean gold surfaces, where the strong influence of the surface roughness on the resulting spectra is demonstrated. Furthermore, in the case of layered systems, the influence of both the outer (air or vacuum side) surface roughness and the inner interface roughness on the reflection‐mode EXAFS spectra is evaluated. The practical consequences of the observed correlations are discussed, and a quantitative data analysis of a copper sample that was oxidized in ambient air for several months is shown, including the evaluation of specular reflectivity profiles at fixed energy.     

Transport of a cathodic arc plasma in a straight, magnetized duct

Measurements are presented of the transport of a supersonic, cathodic-arc plasma through a straight, magnetized duct. These measurements are compared to previous work on curved ducts, in order to illuminate the effect of duct curvature on the transport. The axial ion flux through the straight duct decays as ions are lost to the walls. This decay is exponential, with a scale length of seven duct radii; this is two to three times longer than in most experiments on curved ducts. The scale length is independent of the magnetic field strength for fields from 5-40 mT. (For this range of magnetic fields, the electron Larmor radius varies from 0.03-0.003 duct radii; while the ion Larmor radius varies from 4-0.5 duct radii.) This differs from previous experiments with curved ducts, where the attenuation length generally increases with magnetic field. Also in contrast to experiments on curved ducts, biasing the duct wall to positive voltages similar to the ion energy produces only a slight decrease in the ion losses to the wall. The observed scale length for ion loss and its independence from the magnetic field strength are in quantitative agreement with a plasma fluid simulation. Differences in plasma transport through straight and curved ducts are discussed     

Explicit results for wave scattering and transmission through a rough fluid-fluid interface

This paper describes an analysis of reflection and transmission of acoustic waves from an imperfectly reflecting, rough fluid-fluid interface within the Kirchhoff approximation. It presents the results of calculations of the coherent and diffuse field. This work is motivated by the fact that few explicit results of the characteristics of the scattered and transmitted wave field exist in the literature for this problem. For the problem of interest, the surface reflection coefficient depends at each point upon the local angle between the incident wave and the rough surface. For surfaces with statistically independent local surface position and gradient, coherent field calculations show that the correction to constant reflection coefficient analyses is simply a multiplicative factor that depends upon the statistical characteristics of the surface gradient, sound speed and density ratio across the surface. This multiplicative factor is interpreted as an average reflection or transmission coefficient, <R> and <T>, respectively. The principle differences between these results and constant reflection coefficient analyses occur when waves impinge upon regions with higher sound speeds, where total internal reflection may occur. While the wave characteristics of smooth or constant reflection coefficient surfaces change abruptly in the vicinity of the angle of total internal reflection, the average reflection coefficient exhibits a much smoother dependence upon angle of incidence or sound speed ratio for rough surfaces. It is also shown that the direction of maximum diffuse scattering moves relative to its value were the reflection coefficient constant.     

Real-time defect detection on highly reflective curved surfaces

This paper presents an automated defect detection system for coated plastic components for the automotive industry. This research activity came up as an evolution of a previous study which employed a non-flat mirror to illuminate and inspect high reflective curved surfaces. According to this method, the rays emitted from a light source are conveyed on the surface under investigation by means of a suitably curved mirror. After the reflection on the surface, the light rays are collected by a CCD camera, in which the coating defects appear as shadows of various shapes and dimensions. In this paper we present an evolution of the above-mentioned method, introducing a simplified mirror set-up in order to reduce the costs and the complexity of the defect detection system. In fact, a set of plane mirrors is employed instead of the curved one. Moreover, the inspection of multiple bend radius parts is investigated. A prototype of the machine vision system has been developed in order to test this simplified method. This device is made up of a light projector, a set of plane mirrors for light rays reflection, a conveyor belt for handling components, a CCD camera and a desktop PC which performs image acquisition and processing. Like in the previous system, the defects are identified as shadows inside a high brightness image. At the end of the paper, first experimental results are presented.     

Design and operation of a double-fiber scanning system for surface profiling

Design and operation of an opto-mechanical system for surface profiling are reported in this study. The reported system consists of a double-fiber optical design and an electro-mechanical scanning system. In this arrangement one fiber transmits the source light to the object surface and the second one transmits the light reflected off the surface to a photodetector. By scanning the double-fiber assembly in one-direction, reflection properties of different curved surfaces are investigated. Reflection signals for the cylindrical surfaces made with different curvatures and materials are reported. In order to see the effect of the surface material, for a fixed radius cylinder, the surface is covered with thin paper materials of different colors and results are compared. Our results show that the reported system can be used effectively to monitor the object surface profiles of metallic and non-metallic materials. In another study to investigate the precision and sensitivity of the reported system the reflection result of the structured surface is compared with that of a smooth surface. The reported system provides a simple and accurate means for the object shape study and determination of different surface macrostructures through the optical reflection monitoring. The novelty of the reported system is the fact that provides a great potential to analyze the small features such as the holes and grooves on a target surface. The obtained results clearly show such ability and make the reported opto-mechanical system a suitable tool for object surface analysis in spite of the simplicity and low cost.     

Holographic interferometric visualization of the Richtmyer-Meshkov instability induced by cylindrical shock waves

Results of quantitative holographic interferometric flow visualization of cylindrical interface instability induced by converging cylindrical shock waves are reported. Experiments were conducted in an annular vertical co-axial diaphragmless shock tube, in which cylindrical soap bubbles filled with He, Ne, Air, Ar, Kr, Xe and SF₆ were co-axially placed in its test section. Pressure histories at different radii during the shock wave implosion and reflection from the center were measured. Diagnostic method base on double exposure holographic interferometry was applied for the measurement of turbulent mixing zone at the interface. The observed cylindrical interfaces were found to have a higher growth rate of turbulent mixing zone than that of the plane shock / plane interface.     

Positive-negative birefraction phenomenon for TM polarization in annular photonic crystal

We propose a two-dimensional (2D) annular photonic crystal (APC) with dual equi-frequency contours (EFCs) in one band. The refractive behaviors of a Gaussian beam incident from air to the APC are analyzed by the EFC analysis and finite-diflerence time-domain (FDTD) method. The results show the positive-negative birefraction phenomenon for the transverse magnetic (TM) polarization in the same band occurs at the interface between air and the APC, and the surface termination of the APC has a large effect on the strength of the negatively refracted beam.     

Device Physics Modeling of Surfaces and Interfaces from an Induced Gap State Perspective

An overview of a device physics formulation of induced gap state (IGS) modeling is presented. IGS modeling attempts to explain the electronic properties of metal (M), semiconductor (S), or insulator (I) surfaces and interfaces in terms of intrinsic behavior associated with evanescent states arising from the termination of a bulk material at a surface or interface. Specifically, semiconductor and insulator surfaces as well as metal-semiconductor (MS), semiconductor-semiconductor (SS), insulator-insulator (II), insulator-semiconductor (IS), metal-metal (MM), metal-insulator-metal (MIM), and metal-insulator-semiconductor (MIS) interfaces are considered. Key aspects of this review involve the development of the electrostatic foundations of IGS modeling and the utilization of equivalent circuits and energy band diagrams to elucidate surface and interface electronic behavior.     

Negative Goos-Hänchen shift on a concave dielectric interface

We study the Goos-H?nchen shift (GHS) on a curved surface through numerical simulation by the boundary element method. A negative GHS is first discovered on a concave dielectric interface below the critical angle, accompanied by a large positive GHS on the convexity. The simulation shows that the GHS on a planar interface is the composition of the GHS from a concave and the corresponding convex interface. This work will enrich the study of the GHS for different curved surfaces, which will have potential applications in micro-optics and near-field optics.     

Three-dimensional matched interface and boundary (MIB) method for treating geometric singularities

This paper reports the three-dimensional (3D) generalization of our previous 2D higher-order matched interface and boundary (MIB) method for solving elliptic equations with discontinuous coefficients and non-smooth interfaces. New MIB algorithms that make use of two sets of interface jump conditions are proposed to remove the critical acute angle constraint of our earlier MIB scheme for treating interfaces with sharp geometric singularities, such as sharp edges, sharp wedges and sharp tips. The resulting 3D MIB schemes are of second-order accuracy for arbitrarily complex interfaces with sharp geometric singularities, of fourth-order accuracy for complex interfaces with moderate geometric singularities, and of sixth-order accuracy for curved smooth interfaces. A systematical procedure is introduced to make the MIB matrix optimally symmetric and banded by appropriately choosing auxiliary grid points. Consequently, the new MIB linear algebraic equations can be solved with fewer number of iterations. The proposed MIB method makes use of Cartesian grids, standard finite difference schemes, lowest order interface jump conditions and fictitious values. The interface jump conditions are enforced at each intersecting point of the interface and mesh lines to overcome the staircase phenomena in finite difference approximation. While a pair of fictitious values are determined along a mesh at a time, an iterative procedure is proposed to determine all the required fictitious values for higher-order schemes by repeatedly using the lowest order jump conditions. A variety of MIB techniques are developed to overcome geometric constraints. The essential strategy of the MIB method is to locally reduce a 2D or a 3D interface problem into 1D-like ones. The proposed MIB method is extensively validated in terms of the order of accuracy, the speed of convergence, the number of iterations and CPU time. Numerical experiments are carried out to complex interfaces, including the molecular surfaces of a protein, a missile interface, and van der Waals surfaces of intersecting spheres.     

Annular pancreas diagnosed by single-shot MR cholangiopancreatography

Magnetic resonance cholangiopancreatography (MRCP) has become widely used due to the rapid advances made as a non-invasive diagnostic method for the pancreatobiliary ducts. We report a case with annular pancreas in an adult in whom the pancreatic duct in the annular portion could be clearly visualized by magnetic resonance cholangiopancreatography, which was very useful for the definite diagnosis as annular pancreas.     

非镜面膜的椭偏研究

本文提出了SnO_2:F绒面膜的三层膜模型;从表示平面波传播性质的界面矩阵和膜层矩阵出发,导出了三层膜系统的散射矩阵和总反射系数,建立了反射式椭偏术的基本公式;利用反射式椭偏光谱法,测得SnO_2:F绒面膜的厚度和色散关系.     

Suppression of flow-acoustic coupling in sidebranch ducts by interface modification

The flow-acoustic coupling of shear layer instabilities with the acoustic resonances at the interface of a closed sidebranch and main duct can produce high-amplitude pure-tone noise, known as “whistle”. This study investigates experimentally the effect of various interface geometry modifications on whistles. The objective of the modifications is to suppress the noise by redirecting the shear layer at the main duct-sidebranch interface. Interchangeable suppressor blocks of varying shapes and sizes mounted upstream and downstream of the sidebranch opening are used to change the geometry. The block shapes include those with square edges, ramps, bevelled edges, and curved (radiused) edges. The experiments are conducted in a flow facility at conditions that include certain ranges of Strouhal numbers known to coincide with significant noise generation. The effectiveness of various suppressors in reducing the noise is assessed by analyzing the measured sound pressure levels.