A Unified Method of Broad-Band Echo Characterization for Diagnostic Ultrasound

Blood flow can be described by a scattering function, i.e., by the expected distribution of Doppler shifts and delays that are introduced by a collection of moving point scatterers. An equivalent representation is the echo autocovariance function, measured for a sequence of echoes from different transmitted pulses. Tissue structure can be characterized by the frequency dependence of acoustic reflectivity for echoes from large acoustic discontinuities (highlight echoes), and by the "texture" of the echo from a distributed reflector. Highlight structure and frequency dependence of tissue reflectivity can be obtained from the signal-echo cross-ambiguity function, and texture differences are related to differences in echo power spectra and auto-covariance functions.     

Extraction of left ventricular contours from left ventriculograms by means of a neural edge detector

We propose a method for extracting the left ventricular (LV) contours from left ventriculograms by means of a neural edge detector (NED) in order to extract the contours which accord with those traced by a cardiologist. The NED is a supervised edge detector based on a modified multilayer neural network, and is trained by use of a modified back-propagation algorithm. The NED can acquire the function of a desired edge detector through training with a set of input images and the desired edges obtained from the contours traced by a cardiologist. The proposed contour-extraction method consists of 1) detection of "subjective edges" by use of the NED; 2) extraction of rough contours by use of low-pass filtering and edge enhancement; and 3) a contour-tracing method based on the contour candidates synthesized from the edges detected by the NED and the rough contours. Through experiments, it was shown that the proposed method was able to extract the contours in agreement with those traced by an experienced cardiologist, i.e., we achieved an average contour error of 6.2% for left ventriculograms at end-diastole and an average difference between the ejection fractions obtained from the manually traced contours and those obtained from the computer-extracted contours of 4.1%.     

A comparison of deconvolution and windowed subtraction techniques for scatter compensation in SPECT

Three procedures for the removal of Compton-scattered data in SPECT by constrained deconvolution are presented. The first is a deconvolution of a 2-D measured PSRF containing scatter from a single reconstructed transaxial image; the second is a deconvolution of a 2-D measured point-source response function (PSRF) from each frame of projection data prior to reconstruction; the third involves deconvolution of a 3-D measured PSRF from a stack of reconstructed slices. Results of applying these procedures to data obtained from a phantom containing cold cylinders and to data from a cold spot-resolution phantom are presented and are shown to be superior to the results of correcting for scatter by scatter-window substraction. Both 3-D deconvolution from reconstructed images and 2-D deconvolution from projection data show major improvements in image contrast, resolution, and quantitation. Improvements are especially marked for small (1.0-3.0 cm) cold sources.     

干噪比估算新方法及被动跟踪精度问题研究

本文从空间干扰源及其散射体的概念出发,分析并指出主动雷达进行被动跟踪时,干扰源散射体的散射功率从旁瓣进入接收机,是影响跟踪精度的主要"噪声功率",分别给出了跟踪主瓣接收的干扰源干扰功率和跟踪旁瓣接收的干扰源散射体的散射功率计算公式,重点分析了干扰源若干空间以外搜索波束接收的干扰功率的特点,提出了一种用搜索波束接收的干扰功率代替不容易计算的跟踪旁瓣接收的散射功率来估算干噪比的新方法,分析和试验结果表明这种代替和估计是正确和合理的.     

Carrier transfer and capture into quantum wire arrays grown on V-groove substrates

The mechanisms of carrier transfer from barrier regions (superlattices, side-wall and vertical quantum wells) into arrays of quantum wires are investigated by time-resolved photoluminescence. The wires are grown by different techniques on V-groove substrates. The transfer times range from 25 to 900 ps, depending on the details of the whole structure. The fast carrier transfer is modeled by a diffusion equation which allows one to estimate the quantum mechanical capture time from a two-dimensional vertical QW into a one-dimensional QWR to be <2 ps.     

Aperture efficiency and line feed phase center of parabolic cylindrical reflector antenna

Formulas for calculation of the aperture efficiency of a parabolic cylindrical reflector antenna fed by a line feed along the focal line are presented. The efficiency is factorized into a number of subefficiencies which include contributions from line feed end diffraction, and from blockage and reflections from line feed supports and from diffraction by gaps in the reflector surface. One of the subefficiencies is used to define a phase center for the line feed as well as to obtain a formula for calculating it.     

Corner diffraction coefficients for the quarter plane

The current near a right-angled corner on a perfectly conducting flat scatterer illuminated by a plane wave is expressed as a sum of three currents. The first is the physical optics current, which describes the surface effect. The second is the fringe wave current, which is found from the half-plane solution and accounts for the distortion of the current caused by the edges. The third is the corner current, which is found from the numerical solution to the electric-field integral equation applied to the square plate, and accounts for the distortion of the current caused by the corner. It is found that the corner current for the right-angled corner, illuminated from a forward direction, consists mainly of two edge waves propagating along the edges forming the corner. Analytical expressions for these edge wave currents are constructed from the numerical results. A corner diffracted field is calculated by evaluating the asymptotic corner contributions to the radiation integral over the sum of the three currents. It is found that the corner contribution from the edge wave currents in some cases is of the same size as the corner contributions from the physical optics current and the fringe wave current     

H∞ approximation with point constraints applied to impedance estimation

This paper offers a flexible new approach to interpolating impedance data by bounded analytic functions. This approach is motivated by the conviction that any scheme for interpolating data from a physical system must incorporate knowledge of the system into the procedure. The classical Nehari's method is extended to include physical constraints from the system and point constraints from the data. An algorithm is developed and applied to estimating the impedance function of an antenna from a minimal data set.Funding provided by the Independent Research Program at NCCOSC and the Office of Naval Research.     

Diffraction ellipsometric measurement of step height on wafer surfaces

A diffraction-ellipsometry method is described for determining step height on a homogeneous material or an arbitrary multilayer. It consists in measuring ellipsometric parameters for individual beams reflected from the respective sides of a step and for a combined beam obtained from the two reflected beams, with the step height calculated from the measured data by a specially designed algorithm. With multilayers, the ellipsometric parameters are also to be measured with the specimen immersed in a suitable liquid. Beam combining is performed by a special device, which is also designed to change the amplitude and phase of each beam by specific amounts. Care is taken to make the respective wave fronts of the reflected beams parallel on the photodetector.Translated from Mikroelektronika, Vol. 34, No. 2, 2005, pp. 119–128.Original Russian Text Copyright © 2005 by Gornev, Lonskii.     

New test structure for nanometer-level overlay andfeature-placement metrology

A new electrical test structure for overlay measurement has been evaluated by replicating arrays of its complementary components from two different photomasks into a conducting film on a quartz substrate. The features resulting from images projected from the first mask were used as a reference grid which was calibrated by the NIST line-scale interferometer. A first subset of the relative placements of the images projected from the second mask, which were derived from the electrical overlay measurements and the reference grid, agreed to within 13 nm with corresponding measurements made directly by the line-scale interferometer over distances up to 13.5 mm. A second comparison made at another substrate location indicated that gradients of projected feature linewidths across the exposure site may need to be measured, and corrected for, in the electrical extraction of overlay     

Evaluation of graduate engineering education by television at Purdue university

The Schools of Engineering at Purdue University have an off-Lafayette campus graduate engineering education program in which televised instruction plays a major role. A Lafayette campus class is televised and distributed by a microwave network and/or by videotape to a variety of reception sites, including industrial locations and other campuses. Over fifteen hundred evaluations from sixty courses over eight semesters have been collected from Lafayette and off-Lafayette students. The evaluation data from all televised courses in a single semester are lumped together and then the data are sorted into Lafayette student responses and off-Lafayette student responses (referred to as all-TV student responses). The all-TV responses are then subdivided into TV-with-audio-talkback responses and TV-videotape responses. The data indicate that students do learn by televised instruction, that students prefer TV-with-audio-talkback over videotaped instruction, and that students prefer live instruction to either kind of televised instruction. Some TV reception classes were Staffed with persons paid by Lafayette to provide local class monitoring. The evaluation data from these classes were indistinguishable from the evaluation data from TV classes without paid class monitors.     

Radiation from a monopole excited cone

This paper considers radiation from a finite, right circular, perfectly conducting cone which is excited by a quarter-wave monopole protruding from the center of its base. The cone is assumed to be of a size which places it above the resonance region, making a solution by the geometrical theory of diffraction possible. A formula which allows determination of the tip radiated ray from a semi-infinite cone excited by a uniform, in-phase, magnetic ring current is first derived. This is then used in conjunction with certain other known canonical solutions to obtain a complete solution for the proposed excitation. Radiation patterns, computed on a digital machine from the formulas derived, are compared with measured results and good agreement demonstrated.     

Bounds on estimating the acoustic attenuation of small tissue regions from reflected ultrasound

The acoustic attenuation coefficient of most soft biological tissues has an approximately linear-with-frequency attenuation characteristic. The slope of the attenuation coefficient with frequency, denoted by β, has been observed to vary with the severity of liver disease. Two approaches for estimating the β value from reflected ultrasound signals are examined: the spectral-difference approach, which estimates β from the slope of the difference between log-spectra from two locations within the liver, and the spectral-shift approach, which estimates β from the downward shift experienced by the propagating pulse spectrum with penetration into the liver. This paper considers signals reflected from a small tissue region, defined by a cell measuring D by D centimeters in the plane of the sonogram, thus determining the feasibility of producing attenuation images. Lower bounds on the variance of the two β estimators are calculated by deriving maximum-likelihood estimators and by locating the tissue cell in the focal plane of the transducer. If W denotes the usable bandwidth in the reflected signals, the bounds are shown to be proportional to (WD)^-3for β estimates calculated from individual reflected signals, and (WD)^-4for estimates from all the signals reflected from the tissue region. With currently available technology, clinically useful results can be obtained for cell sizes measuring approximately 2.0 cm on a side.     

Estimating equivalent dipole polarizabilities for the inductive response of isolated conductive bodies

Away from a conductive body, secondary magnetic fields due to currents induced in the body by a time-varying external magnetic field are approximated by (equivalent) magnetic dipole fields. Approximating the external magnetic field by its value at the location of the equivalent magnetic dipoles, the equivalent magnetic dipoles' strengths are linearly proportional to the external magnetic field, for a given time dependence of external magnetic field, and are given by the equivalent dipole polarizability matrix. The polarizability matrix and its associated equivalent dipole location are estimated from magnetic field measurements made with at least three linearly independent polarizations of external magnetic fields at the body. Uncertainties in the polarizability matrix elements and its equivalent dipole location are obtained from analysis of a linearized inversion for polarizability and dipole location. Polarizability matrix uncertainties are independent of the scale of the polarizability matrix. Dipole location uncertainties scale inversely with the scale of the polarizability matrix. Uncertainties in principal polarizabilities and directions are obtained from the sensitivities of eigenvectors and eigenvalues to perturbations of a symmetric matrix. In application to synthetic data from a magnetic conducting sphere and to synthetic data from an axially symmetric elliptic conducting body, the estimated polarizability matrices, equivalent dipole locations, and principal polarizabilities and directions are consistent with their estimated uncertainties.     

A New Approach To Inference From Accelerated Life Tests

In a recent paper, the authors have proposed a new approach for making inferences from accelerated life tests. Their approach is appreciably different from those that have been considered in the past, and is motivated by what is actually done in practice. Prior information which is generally available to the engineer is incorporated by adopting a Bayesian point of view. The usual assumptions about the failure distributions and the acceleration functions, which are appealing from a statistical point of view, have been sacrificed to achieve greater reality. We apply this new approach to some real life data arising from an accelerated life test. In the process, we explain our new approach in a manner which makes it easy to understand and apply by the reliability practitioner. Because of the nonparametric nature of the approach, the statistical precision of the results is less than that which can be achieved by making parametric assumptions. On the other hand, the chance of selecting an incorrect model is diminished.     

本征掺杂环栅MOSFET器件连续表面势电压方程及其在从积累到反型区域的解析解

本文提出了本征掺杂的长沟环栅MOSFET器件的连续表面势方程并讨论了其物理解。这个 方程适用于器件从积累到强反型的工作区域。原始方程通过简化Poisson方程的精确解得到, 然后通过经验修正得到满足连续性条件的表面势电压方程,允许表面电势及其导数由 解析式表示,同时在积累到反型、线性到饱和区域精确连续。基于这个结果,我们对 表面电势和中心电势对器件尺寸的依赖关系进行了分析,并通过三维的器件模拟进行 了验证。     

Switching response of graded-base PN junction diodes

This paper extends the earlier analysis by Kingston of the switching response of a uniform-base diode to a graded-base diode. It concerns the time required to switch a diode from a forward-biased to a reverse-biased condition. The current transient can be separated into two phases: 1) the constant current phase during which the carrier density at the junction changes gradually from a forward-biased to a reverse-biased condition, and 2) the nonconstant current phase during which the injected carriers stored in the base region gradually disappear. In the present analysis, it is found that in a graded-base diode where the impurity concentration decreases from the emitter junction towards the base contact, the time for the constant current phase is greatly shortened because of favorable initial carrier distribution. The effect is already significant if the impurity concentration changes by a factor from 3 to 1 from the emitter junction to the base contact. To shorten the nonconstant current phase, however, a much larger change of impurity concentration, say of the order from 500 to 1, from the emitter junction to the base contact is needed.     

An efficient formulation to determine the scatteringcharacteristics of a conducting body with thin magnetic coatings

Two new and efficient surface integral equations, derived from corresponding volume integral equations, are developed to calculate the scattering of electromagnetic (EM) waveform from an arbitrarily shaped conducting body coated with thin lossy magnetic film. Their numerical solutions by the method of moments (MM) for two-dimensional structures with full or partial coatings are presented. It is shown that the radar cross-section of a conducting body can be significantly reduced by coating it with a lossy magnetic film. To verify the validity and accuracy of the proposed formulation, another method based on the expansion of cylindrical harmonic functions with real arguments is also developed to calculate the scattering of a plane EM wave from an electrically large coated circular cylinder. The same problem was also solved by the proposed formulation, and excellent agreement between the two approaches was achieved. In addition, numerical results of the scattering from a rectangular coated cylinder is shown to be consistent with that obtained by a modified finite-difference-time-domain (FDTD) method     

The use of visual search for knowledge gathering in image decision support

This paper presents a new method of knowledge gathering for decision support in image understanding based on information extracted from the dynamics of saccadic eye movements. The framework involves the construction of a generic image feature extraction library, from which the feature extractors that are most relevant to the visual assessment by domain experts are determined automatically through factor analysis. The dynamics of the visual search are analyzed by using the Markov model for providing training information to novices on how and where to look for image features. The validity of the framework has been evaluated in a clinical scenario whereby the pulmonary vascular distribution on Computed Tomography images was assessed by experienced radiologists as a potential indicator of heart failure. The performance of the system has been demonstrated by training four novices to follow the visual assessment behavior of two experienced observers. In all cases, the accuracy of the students improved from near random decision making (33%) to accuracies ranging from 50% to 68%.     

2020年春节期间芜湖市典型大气污染过程分析

2020年春节期间(1月24日-2月8日),受新冠肺炎疫情影响,芜湖市居民活动水平降到最低,但芜湖市却出现了三次不同程度的空气污染过程,为探索芜湖市大气污染成因提供了契机.利用地面气象要素监测数据、激光雷达监测数据以及HYSPLIT后向轨迹模型分析了这三次污染过程的污染特征和成因.结果表明:1月27日08:00-28日...