Optimum and standard beam widths for numerical modeling of interface scattering problems

Author Posting. © Acoustical Society of America, 2000. This article is posted here by permission of Acoustical Society of America for personal use, not for redistribution. The definitive version was published in Journal of the Acoustical Society of America 107 (2000): 1095-1102, doi:10.1121/1.428399.Gaussian beams provide a useful insonifying field for surface or interface scattering problems such as encountered in electromagnetics, acoustics and seismology. Gaussian beams have these advantages: (i) They give a finite size for the scattering region on the interface. (ii) The incident energy is restricted to a small range of grazing angles. (iii) They do not have side lobes. (iv) They have a convenient mathematical expression. The major disadvantages are: (i) Insonification of an interface is nonuniform. The scattered field will depend on the location of the scatterers within the beam. (ii) The beams spread, so that propagation becomes an integral component of the scattering problem. A standard beam parameterization is proposed which keeps propagation effects uniform among various models so that the effects of scattering only can be compared. In continuous wave problems, for a given angle of incidence and incident amplitude threshold, there will be an optimum Gaussian beam which keeps the insonified area as small as possible. For numerical solutions of pulse beams, these standard parameters provide an estimate of the smallest truncated domain necessary for a physically meaningful result.This work was carried out under Office of Naval Research Grant Nos. N00014-90-I-1493, N00014-96-1-0460, and N00014-95-1-0506 and under a Mellon Independent Study Award from Woods Hole Oceanographic Institution

Linear-time haplotype inference on pedigrees without recombinations

In this paper, a linear-time algorithm, which is optimal, is presented to solve the haplotype inference problem for pedigree data when there are no recombinations and the pedigree has no mating loops. The approach is based on the use of graphs to capture SNP, Mendelian and parity constraints of the given pedigree. © Springer-Verlag Berlin Heidelberg 2006.link_to_subscribed_fulltex

Maxillary distraction for cleft lip and palate patients

Over the past 40 years the problem of nonspecular reflection of bounded beams from fluid-solid interfaces has been extensively studied. Early investigations by Schoch [1] and Bertoni and Tamir [2] have concentrated on planar structures, both halfspaces and plates. More recent studies on reflection of sound from cylinders have concentrated on far-field scattering with emphasis on azimuthal resonance phenomena [3, 4], and on specular interaction of well-collimated beams with fluid-solid cylindrical interfaces [5, 6]

Fast multipole method as an efficient solver for 2D elastic wave surface integral equations

The fast multipole method (FMM) is very efficient in solving integral equations. This paper applies the method to solve large solid-solid boundary integral equations for elastic waves in two dimensions. The scattering problem is first formulated with the boundary element method. FMM is then introduced to expedite the solution process. By using the FMM technique, the number of floating-point operations of the matrix-vector multiplication in a standard conjugate gradient algorithm is reduced from O(N2) to O(N1.5), where N is the number of unknowns. The matrix-filling time and the memory requirement are also of the order N1.5. The computational complexity of the algorithm is further reduced to 0(N4/3) by using a ray propagation technique. Numerical results are given to show the accuracy and efficiency of FMM compared to the boundary element method with dense matrix.link_to_subscribed_fulltex

Application of the FMM technique to elastic wave surface integral equations

The fast multipole method (FMM) and ray propagation fast multipole techniques were applied to boundary element method (BEM) for elastic wave modeling. The new techniques were used to solve two-dimensional solid-solid surface scattering problems where the solids are assumed to be bonded at the interfaces.link_to_subscribed_fulltex

Mechanistic insight into point mutations in sedlin that result in spondyloepiphyseal dysplasia tarda

Understanding and predicting the effects of surface roughness on ultrasonic pulse-echo measurements is important in a variety of applications. In particular, it is of interest for cased well evaluation in the oilfield industry where the measurement is used to investigate the cement seal placed between the casing and the formation wall (see Fig. 1(a)) [1]. Here, the acoustic transducer signal arises from multiple reflections taking place at the various interfaces of the layered (borehole fluid)-(steel casing)-cement-(rocky formation) structure. Previous numerical models, developed to account for this measurement, have been limited to canonical configurations where, in particular, the various interfaces are smooth [2]. Typically, the cement-formation interface is rough with widely varying rms height and correlation length. In order to predict the effect of roughness of arbitrary sizeon the reflection echo attributed to this interface, a frequency-domain hybrid analytical/numerical simulation model has been developed. The model has been preliminary implemented for a two-dimensional (2D) configuration where an acoustic transducer with a Gaussian profile interacts with the aforementioned structure in a planar geometry (see Fig. 1(b)). In this configuration, the transducer aperture has a finite size in the (x, z) and is infinite in the y direction. The fluid, steel layer, cement layer, and halfspace formation are assumed to be isotropic and homogeneous. The cement-formation interface, denoted by S 0, is in general irregular or rough and parameterized by the function z = h(x) describing the height of a particle on S 0 measured from the (mean) plane z = 0. A time-harmonic variation e iωt is assumed throughout

A knowledge-based online workflow scheudling system

Lamb waves have been widely used in ultrasonic NDE to characterize material properties or assess material quality [1], Of the previous work on materials using phase-matched fluid-loaded coupling, most has been performed in water-coupled testing [2]. With the development of efficient non-contacting ultrasonic air-coupled transducers [3], it has become feasible to apply air-coupled ultrasonic methods to NDE. Because of the low signal noise ratio resulting from the large impedance mismatch between the air and the solid object, most work of air-coupled (AC) ultrasound is qualitative, with defects in plates and C-scan imaging being the principal objectives. As demonstrated by Safaeinili, et al. [4], however, it is possible to characterize elastic plates, both isotropic and anisotropic, by using AC ultrasound, despite the signal-to-noise ratio (SNR) penalty

Ultrasonic Transducer Radiation through a Curved Fluid-Solid Interface

A number of typical ultrasonic immersion inspections require the transducer radiation to propagate through components with non-planar surfaces. As the complexity of the component’s surface increases in terms of shape and curvature, the effects of the part’s curvature on the transmitted wavefield become difficult, if not impossible, to predict by simple heuristic approaches. The development of accurate transducer beam models that can handle these types of fluid-solid interfaces, therefore, becomes essential

Identification of a potential auto-regulatory site upstream of the mouse Hoxb-3 gene

In prior studies of Gaussian beam reflection from immersed plates [1–5], it is shown that the reflected field or receiver voltage as a function of transducer position, at any incident angle, can be calculated or measured at constant frequency, and the 2-D calculated reflected field or receiver voltage in the incident plane is almost the same as a 3-D calculation, except for a scale factor as we show later in this paper. This is not the case, however, for the reflection and transmission frequency spectrum, which is widely used to infer the plate material parameters [6,7]. In this paper we extend the complex transducer point (CTP) to this widely used ultrasonic Lamb wave technology. We show that the reflection frequency spectrum requires a full 3-D voltage calculation to achieve the desired accuracy under all conditions. The 3-D receiver voltage frequency spectrum calculated here is compared to extensive experimental results on several materials and in different experimental configurations. The results show that the 3-D voltage spectrum calculation must be used under some conditions to make accurate deductions of material parameters

The role of Id1 in prostate carcinogenesis

Nonspecular reflection effects of a bounded ultrasonic beam incident from a liquid onto an elastic structure have been the subject of a great deal of interest during last decades for material characterization [1–10]. It refers to phenomena where the reflected beam has an intensity profile different from that of the incident beam, including a lateral beam displacement, one or several minimum intensity area and a trailing field (Fig. 1). This phenomena occurs when the incident beam is phase-matched to one of the leaky waves supported by the structure. Numerous theoretical studies, based on the calculation of the reflection coefficient, have successfully explained the nonspecular reflection profile of a bounded beam incident at a critical angle [1, 3, 6–10]. In this paper, we present a mode theory for analyzing these nonspecular reflection effects. This approach, which gives a good physical insight, has been recently used to study the excitation of Lamb waves by the a bounded beam [11]