Ultrasonic Tomographic Imaging of an Encased, Highly Attenuating Solid Medium

Ultrasonic tomographic imaging has been performed on a highly attenuating, filled, hydroxyl-terminated polybutadiene, cast into a steel case. The detection of defects and the characterization of solid rocket propellant were thus possible. Extremely low signal levels due to the attenuation and scattering properties of the polymer were present. In addition, a nonideal tomographic reconstruction geometry was present, because of a cylindrical air-filled cavity in the center of the polymer. Complications also arose from high-amplitude guided waves within the steel case, which tended to mask directly transmitted signals through the propellant. These problems were solved using specially designed transducers and pulse-compression signal processing techniques. Modifications to the filtered back-projection reconstruction procedure were made to account for the discontinuity caused by the hole. Images are presented showing the detection of an artificial defect to demonstrate the technique.     

The Tomographic Ionized-Carbon Mapping Experiment (TIME) CII Imaging Spectrometer

The Tomographic Ionized-Carbon Mapping Experiment (TIME) and TIME-Pilot are proposed imaging spectrometers to measure reionization and large scale structure at redshifts 5–9. We seek to exploit the 158  \({\upmu } \mathrm{m}\) restframe emission of [CII], which becomes measurable at 200–300  GHz at reionization redshifts. Here we describe the scientific motivation, give an overview of the proposed instrument, and highlight key technological developments underway to enable these measurements.     

Ultrasonic Tomographic Imaging of an Encased,Highly Attenuating Solid Medium

Abstract

Ultrasonic tomographic imaging has been performed on a highly attenuating, filled, hydroxyl-terminated polybutadiene, cast into a steel case. The detection of defects and the characterization of solid rocket propellant were thus possible. Extremely low signal levels due to the attenuation and scattering properties of the polymer were present. In addition, a nonideal tomographic reconstruction geometry was present, because of a cylindrical air-filled cavity in the center of the polymer. Complications also arose from high-amplitude guided waves within the steel case, which tended to mask directly transmitted signals through the propellant. These problems were solved using specially designed transducers and pulse-compression signal processing techniques. Modifications to the filtered back-projection reconstruction procedure were made to account for the discontinuity caused by the hole. Images are presented showing the detection of an artificial defect to demonstrate the technique.     

A Microwave Tomographic Imaging Approach for Multibistatic Configuration: The Choice of the Frequency Step

This paper deals with the application of a frequency-domain microwave-tomography-imaging algorithm to a multibistatic configuration in ground-penetrating-radar applications. First, the authors formulate the inverse problem as a linear one by exploiting the Born approximation. Then, the reconstruction capabilities of the solution algorithm are investigated, and an optimal frequency step to be adopted for the reconstruction is discussed and determined. Finally, inversion results are presented with synthetic data obtained from time-domain simulations and then Fourier transformed in frequency domain     

Superconductivity with Local, Short-Range Attraction

The approaches to short coherence length superconductors based on theconcepts of local electron pairing are discussed. The properties of systemswith intersite pairing, the nature of the BCS-Bose superconductivitycrossover as well as a two-component model of local pairs and fermions areanalyzed. The question of a pseudogap and a possible scenario of crossoversin high temperature superconductors are briefly examined.     

Pairing and Short-Range Correlations in Nuclear Systems

The structure and density dependence of the pairing gap in infinite matter is relevant for astrophysical phenomena and provides a starting point for the discussion of pairing properties in nuclear structure. Short-range correlations can significantly deplete the available single-particle strength around the Fermi surface and thus provide a reduction mechanism of the pairing gap. Here, we study this effect in the singlet and triplet channels of both neutron matter and symmetric nuclear matter. Our calculations use phase-shift equivalent interactions and chiral two-body and three-body interactions as a starting point. We find an unambiguous reduction of the gap in all channels with very small dependence on the NN force in the singlet neutron matter and the triplet nuclear matter channel. In the latter channel, SRC alone provide a 50% reduction of the pairing gap.     

超近程拦截系统中信号处理单元的研究

为了提高超近程系统拦截空中目标的有效性,采用线性切割器作为毁伤元,根据线性切割器的原理及特点,针对雷达系统后端数据处理的计算时间要求,在地面坐标系中建立雷达参数模型,研究一种雷达信号处理单元,该单元具有能够对超长信号做出高速实时处理的能力,且精度高,对提高超近程反导命中概率具有一定的实用价值.     

Tomographic extreme-ultraviolet spectrographs: TESS

We describe the system of Tomographic Extreme Ultraviolet (EUV) SpectrographS (TESS) that are the primary instruments for the Tomographic Experiment using Radiative Recombinative Ionospheric EUV and Radio Sources (TERRIERS) satellite. The spectrographs were designed to make high-sensitivity {80 counts/s)/Rayleigh [one Rayleigh is equivalent to 10(6) photons/(4pi str cm(2) s)}, line-of-sight measurements of the oi 135.6- and 91.1-nm emissions suitable for tomographic inversion. The system consists of five spectrographs, four identical nightglow instruments (for redundancy and added sensitivity), and one instrument with a smaller aperture to reduce sensitivity and increase spectral resolution for daytime operation. Each instrument has a bandpass of 80-140 nm with approximately 2- and 1-nm resolution for the night and day instruments, respectively. They utilize microchannel-plate-based two-dimensional imaging detectors with wedge-and-strip anode readouts. The instruments were designed, fabricated, and calibrated at Boston University, and the TERRIERS satellite was launched on 18 May 1999 from Vandenberg Air Force Base, California.     

Tomographic imaging of particulate systems

The review illustrates selected applications of tomographic analysis applied to dry and wet particulate systems. The examples show the use of the method to gain information at different levels of inspection, such as the detailed structure of individual particles, structured particulate assemblies, and on the concentration and velocity of solids in a moving mixture. The utilization of the unique spatial information derived from tomography for the purpose of model validation, and, in some cases, for the monitoring and control of processes is discussed. Emerging applications show that utilization of tomographic methods can facilitate the creation of new and sophisticated models for particulate systems.     

Tomographic imaging with polarized light

We report three-dimensional tomographic reconstruction of optical parameters for the mesoscopic light scattering regime from experimentally obtained datasets by using polarized light. We present a numerically inexpensive approximation to the radiative transfer equation governing the polarized light transport. This approximation is employed in the reconstruction algorithm, which computes two optical parameters by using parallel and perpendicular polarizations of transmitted light. Datasets were obtained by imaging a scattering phantom embedding highly absorbing inclusions. Reconstruction results are presented and discussed.     

Tomographic imaging in hydrocarbon reservoirs

Clastic reservoirs saturated with heavy oils have been observed to exhibit a marked relationship between velocity of propagation of acoustic waves and changes introduced by certain kinds of enhanced oil recovery procedures, including heating of the reservoir. This observation forms the basis for a method of monitoring the changes which occur in the reservoir when these enhanced oil recovery (EOR) procedures are used. New developments in diffraction tomographic imaging allow accurate, high-resolution images to be obtained in hydrocarbon reservoirs, clearly delineating the zones affected by these enhanced oil recovery procedures. When both compressional and shear wave data can be obtained, additional physical parameters such as Poissons ratio can be reconstructed.     

Changes in the Short-Range Order of Chalcogenide Glasses upon Crystallization

The crystallization of the chalcogenide glass formers Se, As₂Se₃, and As₂S₃ is studied by x-ray fluorescence analysis (measurements of the relative integrated intensity of the last x-ray emission line). The results demonstrate that the integral parameter R describing the short-range order is larger in the glasses compared to the corresponding crystals. This finding correlates with earlier reports that glass crystallization is accompanied by a decrease in coordination number and also with the assumption that chalcogenide glasses contain hypervalent configurations.     

Tomographic reconstruction of stratified fluid flow

A method for imaging a moving fluid is proposed and evaluated by numerical simulation. A cross-section of a three-dimensional fluid is probed by high-frequency acoustic waves from several different directions. Assuming straight-ray geometric acoustics, the time of flight depends on both the scaler sound speed and the vector fluid velocity. By appropriately combining travel times, projections of both the sound speed and the velocity are isolated. The sound speed is reconstructed using the standard filtered backprojection algorithm. Though complete inversion of velocity is not possible, sufficient information is available to recover the component of fluid vorticity transverse to the plane of insonification. A new filtered backprojection algorithm for vorticity is developed and implemented. To demonstrate the inversion procedure, a 3-D stratified fluid is simulated and travel time data are calculated by path integration. These data are then inverted to recover both the scaler sound speed and the vorticity of the evolving flow.     

Tomographic reconstruction technique for pulsed-echo imaging

This article proposes a tomographic reconstruction technique using divergent ultrasonic waves of a circular arc wavefront which are formed by one-dimensional thin-phased array. The projection data which are obtained by phasing of transmitting and receiving signals are applied to the filtered back projection algorithm so that the image at the spherical surface is reconstructed. The experiments using a small steel sphere and a layer phantom of agar gel are performed using a commercially available phased-array system. The divergent waves are formed by the slit in the front of the array. As a result, images with a space-invariant, high-resolution unlike conventional B-scan image are obtained. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 432–437, 1997     

Short-Range Order and Structural Transformations in Al–Si Melts

The density of Al–Si melts containing 0.2–1.2 wt % Si was measured as a function of temperature. The results were used to construct the liquid microinhomogeneity diagram of the Al–Si system. The structural transformations in Al–Si melts were shown to be associated with microinhomogeneities resulting from the charge transfer from Al to Si.     

Multipatches multilayered UWB microstrip antennas

The authors present multipatches multilayered ultra-wideband (UWB) microstrip antennas. The antenna comprises a driven patch radiator with five parasitic patch radiators. Two antennas with different dielectric substrate combinations are studied. The antenna with low-high-low dielectric constant substrate combination (Antenna no. 1) has an improved performance in terms of impedance bandwidth, gain, overall antenna size and beam-squinting over the antenna with low-low-low dielectric constant substrate combination (Antenna no. 2). The low-high-low dielectric constant combination consisting of three dielectric substrates, namely low dielectric constant (ϵr = 3.38) for both bottom and upper substrate but, high dielectric constant (ϵr = 6.15) for middle substrate. Five parasitic patches and multi-dielectric layers are used for wide impedance bandwidth and less boresight gain variation with frequency. A measured 10 dB return loss bandwidth of 48% with boresight gain .5.0 dBi is achieved. Antenna no. 1 can have 8% wider impedance bandwidth, 40% overall area reduction and less beam-squinting compared with Antenna no. 2.     

Measurement of Density and Structural Short-Range Order of Levitated Liquid Metals

The determination of thermophysical properties and structure of undercooled metallic melts must be accomplished by contactless methods due to the high reactivity of the material. It has been shown that electromagnetic levitation provides high-purity conditions to allow deep undercooling. The density and thermal expansion of a levitated drop can be derived from volume measurements using a charge-coupled device (CCD) camera and a digital image processing system. Combining levitation with extended x-ray absorption fine structure (EXAFS) spectroscopy leads to the possibility of studying the local structure of the liquid in a wide temperature range including the deeply undercooled regime.     

Tomographic Spectrometer for Spectral Analysis of Images

A new type or imaging spectrometer is proposed, in which tomographic transformation of a two-dimensional image into a one-dimensional image is performed instead of scanning of the original image using the inlet slit. The optical circuits of the device and an experiment at spectral analysis of an image of the Earth's surface is performed. __________ Translated from Izmeritel'naya Tekhnika, No. 9, pp. 48–52, September, 2005.