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.     

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.     

Dual-parameter radar rainfall measurement from space: a test resultfrom an aircraft experiment

An aircraft experiment has been conducted with a dual-frequency ( X/Ka-bands) radar to test various rainfall retrieval methods from space. The authors test a method to derive raindrop size distribution (DSD) parameters from the combination of a radar reflectivity profile and a path-integrated attenuation derived from the surface return, which may be available from most spaceborne radars. The test results indicate the feasibility of the dual-parameter radar measurement from space in achieving a better accuracy in quantitative rainfall remote measurements     

Image reconstruction and multidimensional field estimation from randomly scattered sensors.

Many important problems in statistical signal processing can be formulated as function estimation from randomly scattered sensors in a multidimensional space, e.g., image reconstruction from photon-limited images and field estimation from scattered sensors. We present a novel approach to the study of signal reconstruction from random samples in a multidimensional space. In particular, we study a classical iterative reconstruction method and demonstrate that it forms a sequence of unbiased estimates for band-limited signals, which converge to the true function in the mean-square sense. We subsequently rely on the iterative estimation method for multidimensional image reconstruction and field estimation from sensors scattered according to a multidimensional Poisson and uniform distribution. Computer simulation experiments are used to demonstrate the efficiency of the iterative estimation method in image reconstruction and field estimation from randomly scattered sensors.     

Electromagnetic interference from discharge phenomena of electriccontacts

The electromagnetic interference (EMI) from steady arc and showering arc electrical discharges was investigated. The experiment was carried out on Ag, Pd, and Ag-Pd alloy contacts under several circuit current conditions. Radiated noise levels were measured at frequencies up to 200 MHz. Experimental results show that the EMI levels from a steady arc, which is generally the phenomenon of the break of a noninductive circuit, are dependent on the composition of contact materials. The EMI levels from a showering arc, which is generally the phenomenon of the break of an inductive circuit, are independent of the composition of contact materials. The EMI from a steady arc is roughly inversely proportional to the frequency in the 0.1-10.0-MHz range, whereas in the 25-200-MHz range, the maximum level of EMI appears at about 70 MHz. The frequency characteristics of EMI from a showering arc are similar to those from a steady arc. The EMIs from these arcs exceed, in part, statutory limits     

基于微多普勒特征的空中目标识别

分析了直升机目标回波信号的微多普勒频谱，基于直升机目标和固定翼飞机目标多普勒频谱的差别，提出了两种微多普勒特征用于识别直升机目标和固定翼飞机目标，其中一种利用了直升机回波信号正负多普勒频谱能量的不对称性，另一种模式特征利用了机身回波信号能量与旋翼回波信号能量的对比，使用仿真数据和试验测试录制的数据的计算结果表明该方法具有很好的识别效果。     

MIMO系统中的迭代分组MAP检测算法

该文提出了在分组MAP检测器内部进行干扰信息更新和检测信息迭代反馈的检测算法。在MIMO系统基本的分组MAP检测算法基础上,利用先检测分组产生的后验信息替代先验信息提高干扰信号的估计精确度,进一步可以使用迭代反馈的方法在检测器内部进行反馈检测分组的后验信息,从而提高了检测信号的分集度。仿真结果表明在未编码系统中改进的分组检测方法能够显著地提高系统误码率性能,在编码系统中能够加快整个系统的收敛。     

Study of Area Scaling Effect on Integrated Circuit Reliability Based on Yield Models

Two models for the effect of area scaling on reliability are derived from two distinct yield models with different assumptions on defect distributions. One is derived from the Poisson yield model assuming a uniform random distribution of defects as in an early model. The other is based on the negative binomial yield model to account for deviation from a uniform random distribution of defects caused by clustering. Experimental data from backend test structures show that the model based on defect clustering explains observed data well while the model assuming a uniform random distribution shows a significant departure from it.     

Learning Color Names for Real-World Applications

Color names are required in real-world applications such as image retrieval and image annotation. Traditionally, they are learned from a collection of labeled color chips. These color chips are labeled with color names within a well-defined experimental setup by human test subjects. However, naming colors in real-world images differs significantly from this experimental setting. In this paper, we investigate how color names learned from color chips compare to color names learned from real-world images. To avoid hand labeling real-world images with color names, we use Google image to collect a data set. Due to the limitations of Google image, this data set contains a substantial quantity of wrongly labeled data. We propose several variants of the PLSA model to learn color names from this noisy data. Experimental results show that color names learned from real-world images significantly outperform color names learned from labeled color chips for both image retrieval and image annotation.     

Simulation of corrugated horns and exciters for circular corrugated waveguides

A method is proposed for simulating the problem of radiation from a finite-length corrugated horn joined with a regular corrugated waveguide. Obtained with the help of the factorization method, a solution to the problem of radiation from the open end of a circular waveguide is applied to formulate the conditions of radiation from the horn.     

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.     

An absorber tip diffraction coefficient

The UTD corner diffraction solution for a perfectly conducting corner is empirically modified for the case of a dielectric corner. The dielectric may be lossless or lossy, but is assumed to be homogeneous. This modified solution is used to calculate the bistatic scattering from the tip of a dielectric pyramid. Sample calculations display some features of the scattering from a single lossy dielectric pyramid. To verify the solution, calculations are compared with backscatter measurements of a single pyramid that is cut from a homogeneous lossless dielectric (polyethylene). Calculations are then compared with measurements for the more pertinent case of bistatic scattering from a wall of pyramidal radar absorbing material     

Transformation of continuous-time model of a linear multivariable system from its discrete-time model

The problem of identification of the state-space model of a multivariable continuous system from the samples of its input-output data is considered. Hence, a method is suggested for determining the continuous-time model of a system from its discrete-time model obtained from the samples of its input-output data.     

Design and measurement of a SAW three-phase unidirectional transducer reflector

A novel reflector made from the highly unidirectional structure of the three-phase interdigital transducer resulting in high reflection coefficients from extremely short transducer lengths is presented. Such a reflector only requires a single phasing component. The dependency of the reflection on the unidirectionality yields frequency tuning capabilities via the phasing component. Such a reflector was fabricated and measured to determine the reflection from a short transducer. Two independent methods for determining the reflection coefficient from the measurements are presented.<>     

Tooth segmentation of dental study models using range images

The accurate segmentation of the teeth from the digitized representation of a dental study model is an important component in computer-based algorithms for orthodontic feature detection and measurement and in the simulation of orthodontic procedures such as tooth rearrangement. This paper presents an automated method for tooth segmentation from the three-dimensional (3-D) digitized image captured by a laser scanner. We avoid the complexity of directly processing 3-D mesh data by proposing the innovative idea of detecting features on two range images computed from the 3-D image. The dental arch is first obtained from the plan-view range image. Using the arch as the reference, a panoramic range image of the dental model can be computed. The interstices between the teeth are detected separately in the two range images, and results from both views are combined for a determination of interstice locations and orientations. Finally, the teeth are separated from the gums by delineating the gum margin. The algorithm was tested on 34 dental models representing a variety of malocclusions and was found to be robust and accurate.     

1 W operation of singly ionized silver and copper lasers

We report a multiline output power of 1 W from the 800.4, 825.5, and 840.4 nm Ag II transitions and 350 mW from the 408.6 nm Ag II transition resulting from pulsed operation of a silver hollow cathode laser. Continuous output of 1 W was obtained in a copper hollow cathode from the 780.8 nm Cu II transition. Design considerations for continuous high-power operation of the hollow cathode discharge are also discussed.     

Evidence of thermally activated transfer of excited carriers between CdSe/ZnSe quantum dots

Temperature dependent photoluminescence and cathodoluminescence of selfassembled CdSe/ZnSe quantum dots grown by metalorganic vapor phase deposition were investigated. We found an unusual large red shift and a narrowing of the photoluminescence peak with temperature increases. Cathodoluminescence studies of a small number of quantum dots showed that the broad peak observed in the photoluminescence spectra is, in fact, made up of a series of narrower peaks, coming from quantum dots of different sizes. While the intensity of luminescence from small dots drops monotonously with temperature rises, that from the large dots displays a peculiar behavior. It actually increases within the temperature range of 140–170 K, the same range in which the photoluminescence peak shows narrowing. The simultaneous increase of luminescence from some quantum dots and decrease from others are believed to be responsible for the red shift and narrowing of the observed photoluminescence peak. A simple analytically solvable rate equation model was used to understand the spectral data. We suggest that the unusual behaviors observed can be understood as resulting from a transfer of thermally activated carriers from small to large quantum dots.     

Source and drain resistance determination for MOSFET's

A new method has been developed for determining the source and drain resistances of MOSFET's from 2-D process and device modeling. The method connects the current predicted from a standard drain current formula to an approximate current computed from the output of a 2-D device simulator. This approximate current is compared with the exact current calculated from the 2-D device simulator to locate the effective edges of the inversion channel. The source/drain resistance for use in the standard formula is then computed from the quasi-Fermi levels at these effective channel edges. Good agreement is obtained with source/drain resistances extracted from experimental ID-VG data.     

Evaluation of perfectly matched layer mesh terminations infinite-element bioelectromagnetic scattering computations

There has been considerable interest in and development of perfectly matched layer (PML) mesh terminations for electromagnetic scattering problems. For the most part, PML performance has been characterized on benchmarks which involve scattering from perfectly conducting objects. In this paper, we evaluate a recent PML implementation for node-based finite-element formulations using a prototype problem which is relevant to bioelectromagnetic computations. Variables under consideration include the layer material properties, layer thickness, and layer distance from the biological body. The results demonstrate that distance from the body is the strongest determinant of solution accuracy with increasing errors occurring with increasing frequency at a fixed distance, although average solution variations of less than 10% are observed in most cases where layers are located at a distance of at least 1.5 times the smallest body dimension. In addition, the PML need only consist of two to three layers in order to reduce solution variations resulting from layer thickness, and this thickness requirement is largely independent of layer distance from the body. This is in contrast to results from perfectly conducting scatterers where six to eight or more layers have been recommended. Further, the computed solutions are not a strong function of the layer material property and this parameter can easily be determined from a simple analytical decay formula without compromising PML performance. These findings are encouraging from a computational economy perspective and they suggest that the PML concept is an excellent choice for finite-element mesh truncation in bioelectromagnetic computations     

Synthesis of Resonator Filters With Arbitrary Topology Using Hybrid Method

This paper presents a new synthesis method for resonator filters of arbitrary topology using an evolutionary hybrid method. This method consists of a Levenberg-Marquardt algorithm for a local optimizer and genetic algorithm for a global optimizer, respectively. Unlike the conventional hybrid method in which the local optimization is performed after finding appropriate initial values from global optimization, the local optimizer in the proposed method is used as a genetic-algorithm operator to prevent trapping in local minima of the cost function. This method can provide fast convergence and good accuracy to find the final solution from initial population generated by a random number and the known value for the filters with stringent requirements. In addition, multiple coupling matrices to meet the given requirement can be obtained from the initial population based on a random number. Resonator filters with asymmetric eight-pole configurations for single and dual passbands are synthesized using the current method for validation. Excellent agreement between the response computed from characteristic polynomials and the response computed from couplings is obtained from the proposed method.