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.     

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.     

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.     

Capacity of a class of relay channels with orthogonal components

The capacity of a class of discrete-memoryless relay channels with orthogonal channels from the sender to the relay receiver and from the sender and relay to the receiver is shown to be equal to the max-flow min-cut upper bound. The result is extended to additive white Gaussian noise (AWGN) relay channels where the channel from the sender to the relay uses a different frequency band from the channel from the sender and the relay to the receiver.     

High-Performance On-Chip Transformers With Partial Polysilicon Patterned Ground Shields (PGS)

In this brief, we propose the concept of "partial patterned ground shields (PGSs)" to improve the performances of RF passive devices, such as inductors and transformers. Partial PGS can be achieved after the redundant PGS of a traditional complete PGS, which is right below the spiral metal lines of an RF passive device, is removed for the purpose of reducing the large parasitic capacitance. A set of test transformers has been implemented to demonstrate the partial PGS. The results show that when the partial PGS was adopted, a 56.5% (from 6.12 to 9.58) and a 55.7% (from 5.55 to 8.64) increase in Q-factor, an 18.2% (from 0.67 to 0.79) and a 21.4% (from 0.66 to 0.8) increase in maximum available power gain (G_Amax), and an 18.4% (from 0.69 to 0.82) and a 21.2% (from 0.69 to 0.83) increase in magnetic-coupling factor (k_im) were achieved at 4.2 and 5.2 GHz, respectively, for a bifilar transformer with an overall dimension of 230times215 mum². Furthermore, compared with the transformer with traditional PGS, a 9.9% (from 10.1 to 11.1 GHz) increase in resonant frequency (f_SR), a 38% (from 6.94 to 9.58) increase in Q-factor at 4.2 GHz, and a 5.3% (from 0.75 to 0.79) increase in G_Amax at 4.2 GHz were obtained. These results demonstrate that the proposed partial PGS is very promising for high-performance RF-ICs applications     

Frequency dependence of amplitude scintillation

In the prediction models of tropospheric scintillation on Earth-satellite paths from Karasawa, Yamada, and Allnutt and ITU-R, the frequency dependence of scintillation is expressed as a power law with a different exponent for each model. This is verified using a collection of measurement results from different satellite links in Europe, the US, and Japan at frequencies from 4 to 50 GHz and elevation angles from 2.5 to 52°. It shows that the exponent of the power law varies widely among the results from the different sites. Possible explanations of this are: (1) the frequency dependence of scintillation due to cloudy turbulence is different from that due to clear-sky turbulence and this kind of scintillation may be present to different extents in the various databases due to climatic differences and different clear-sky selection procedures or (2) angle-of-arrival fluctuations due to turbulence have a different frequency dependence and this effect may have some impact on the measured scintillation at some of the sites     

A three-component scattering model for polarimetric SAR data

An approach has been developed that involves the fit of a combination of three simple scattering mechanisms to polarimetric SAR observations. The mechanisms are canopy scatter from a cloud of randomly oriented dipoles, evenor double-bounce scatter from a pair of orthogonal surfaces with different dielectric constants and Bragg scatter from a moderately rough surface. This composite scattering model is used to describe the polarimetric backscatter from naturally occurring scatterers. The model is shown to describe the behavior of polarimetric backscatter from tropical rain forests quite well by applying it to data from NASA/Jet Propulsion Laboratory's (JPLs) airborne polarimetric synthetic aperture radar (AIRSAR) system. The model fit allows clear discrimination between flooded and nonflooded forest and between forested and deforested areas, for example. The model is also shown to be usable as a predictive tool to estimate the effects of forest inundation and disturbance on the fully polarimetric radar signature. An advantage of this model fit approach is that the scattering contributions from the three basic scattering mechanisms can be estimated for clusters of pixels in polarimetric SAR images. Furthermore, it is shown that the contributions of the three scattering mechanisms to the HH, HV, and VV backscatter can be calculated from the model fit. Finally, this model fit approach is justified as a simplification of more complicated scattering models, which require many inputs to solve the forward scattering problem     

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。     

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.     

BRDF models to predict spectral reflectance and emissivity in thethermal infrared

This paper presents modifications to the linear kernel bidirectional reflectance distribution function (BRDF) models from Roujean et al. and from Wanner et al. that extend the spectral range into the thermal infrared (TIR). The present authors application is to synthesize the TIR optical properties of a scene pixel from laboratory component measurements. The angular reflectance and emissivity are needed to convert the radiance of a pixel as measured from space to land-surface temperature. The kernel models will be applied to develop a look-up table for the MODIS land-surface temperature algorithm to estimate the spectral, angular scene emissivity from land cover classification. A shrub scene and a dense canopy scene illustrate qualitative differences in angular emissivity that would not be evident without the kernel model modifications. They conclude that the modified models provide a simple and efficient way to estimate scene optical properties over a wide spectral range     

Analysis of CNR penalty of radio-over-fiber systems including the effects of phase noise from laser and RF oscillator

The effect of phase noises from a laser and an oscillator on radio-over-fiber (RoF) systems is analyzed and discussed with a power spectral density (PSD) function. A Mach-Zehnder modulator (MZM) and a phase shifter are employed to externally generate an optical single sideband (OSSB) signal since the OSSB signal is tolerable for power degradation due to a chromatic fiber-dispersion effect. It is shown that a carrier-to-noise ratio (CNR) penalty is deeply related to the bandwidth of a receiver filter and the phase noise from a radio frequency (RF) signal oscillator rather than that from a laser in a small differential-delay environment and a direct detection scheme. The CNR penalty due to the increment of the laser linewidth from 10 to 624 MHz is almost 1.1 dB, while the increase of the RF-oscillator linewidth from 1 to 100 Hz results in about a 20-dB penalty at a 30-GHz 10-km transmission in a standard single-mode fiber (SSMF) with a fiber chromatic dispersion of 17 ps/km/spl middot/nm.     

Dual dihedral angles for bidirectionally scattered electromagneticwaves

A spherical coordinate system is typically used to quantify the directional characteristics of doubly hemispherical scattering of bidirectional reflectance distribution function (BRDF) entailing an incident angle or cone angle from surface normal, and a heading or azimuthal angle from the incident plane. An alternate angular coordinate system is described entailing two dihedral angles. One component is a dihedral angle from the incident plane, simply out-of-plane, and the second component is a dihedral angle from the specular beam to the detector direction projected onto the incident plane, or simply degrees off specular. The suggested system is believed easier to convey scattering characteristics, and to compute the scattering from complex surfaces such as mountains with exposed rocks, or buildings. This communication presents an example of an experimental configuration to measure a doubly hemispherical BRDF, a mathematical formulation to relate the angular coordinate systems, and a computational example     

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     

Properties of contour codes

Objects within a binary image are efficiently encoded by traversing their outlines to produce a string of codes each of which defines a directed line to the next point on the outline. Most commonly four or eight codes are defined because these are all that are necessary to define a move from one pixel to an adjacent pixel on a square grid. Many features of the binary objects or blobs may be extracted directly from the code string which describes the outline or contour. The paper draws attention to the fundamental nature of the crack coding scheme, shows that the chain code and midcrack code may be derived from the crack code, and proves relationships between simple measures of perimeter and area as obtained from the different codes and from bit quads. An enclosing octagon is introduced     

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.     

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     

Content-based indexing and retrieval of visual information

The ease of capturing and encoding digital images has produced a massive amount of visual information online. As a consequence, grand challenges have emerged in the areas of storage, indexing, and retrieval of visual information in large archives. How does one find a photograph from a large archive that contains millions of pictures? How does a CNN video journalist find a specific clip from the myriad of video tapes, ranging from historical to contemporary, from sports to humanities? Efficient, real-time algorithms and systems are needed to address these needs of not only professionals but for users who want to find visual information online     

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     

Locating Intersections for Autonomous Vehicles: A Bayesian Network Approach

A novel idea is presented to locate intersections in a video sequence captured from a moving vehicle. More specifically, we propose a Bayesian network approach to combine evidence extracted from a video sequence and evidence from a database, maximizing evidence from various sensors in a systematic manner and locating intersections robustly.     

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.