Computerized indoor radio channel estimation using ray tracing

This paper describes a computer tool for site specific indoor radio channel characterization. The behavior of the electromagnetic fields associated with a base station and a portable radio unit is simulated by combining approximate geometric optics and ray tracing techniques. Given a building plan and the transmitter/receiver locations, the set of all[attenuation / time delay /phase] vectors, each representing an electromagnetic propagation path between transmitter and receiver, is computed using ray shooting techniques to generate the channel wideband impulse response. The model takes into account specular reflection and transmission. Linear polarization and various antenna patterns can be simulated as well. The simulated results are shown to correlate well with experimental data. The computer tool can be used to provide estimates of the coverage of a base station and of the channel quality.     

Impurity ‘Hot Spots’ in MBE HgCdTe/CdZnTe

In this work, impurity ‘hot spot’ macro-defects—high impurity level macro-defect contaminates were examined. ‘Hot spots’ have very high localized concentrations of: K, Mg, Ni, Cr, Mn, Ca, Al, Na, Fe, and Cu. For example, these ‘hot spot’ macro-defects can have Cu concentrations >?1?×?10¹⁸ cm^?3. Focused ion beam scanning transmission electron microscopy analysis of four ‘hot spots’ was performed. The origin of ‘hot spot’ defects is unresolved—however, our analysis has shown ‘hot spots’ can arise due to molecular beam epitaxy spit defects and CdZnTe substrate defects. The estimated ‘hot spot’ density is ～?30 cm^?2. The presence of impurity ‘hot spot’ macro-defects in HgCdTe/CdZnTe is confirming evidence for the occurrence of L. Bubulac’s impurity ‘pipe’ mechanism.     

金属沾污对超薄栅氧(2. 5nm)特性的影响

采用可控的金属沾污程序 ,最大金属表面浓度控制在 10 1 2 cm- 2数量级 ,来模拟清洗工艺最大可能金属沾污表面浓度 .利用斜坡电流应力和栅注入方式测量本征电荷击穿来评估超薄栅氧特性和金属沾污效应 .研究了金属锆和钽沾污对超薄栅氧完整性的影响 .实验结果表明金属锆沾污对超薄栅氧完整性具有最严重危害 ;金属钽沾污的栅氧发生早期击穿现象 ,而金属铝沾污对超薄栅氧完整性没有明显影响 .     

Two-dimensional singular vector elements for finite-elementanalysis

The finite-element method (FEM) exhibits a reduced convergence rate when used for the analysis of geometries containing sharp edges where the electromagnetic field is singular. The convergence of the method can be-improved by introducing singular elements that model analytically predicted singular behavior. A number of authors have developed singular elements that are compatible with the scalar FEM. In this paper, we propose a new singular element that is compatible with edge-based vector finite elements and can cope with any order of singularity while preserving the sparsity of the FEM equations. Edge-based singular elements more correctly model singular fields and thus require fewer unknowns, while avoiding the introduction of spurious modes in the numerical solution. Numerical results verify that the convergence of the FEM is significantly improved     

A fully pipelined RLS-based array for channel equalization

It is shown that several recursive least squares (RLS) type equalization algorithms such as, e.g., decisiondirected schemes and orthogonalized constant modulus algorithms, possess a common algorithmic structure and are therefore rather straightforwardly implemented on an triangular array (filter structure) for RLS estimation with inverse updating. While the computational complexity for such algorithms isO(N ²), whereN is the problem size, the throughput rate for the array implementation isO(1), i.e., independent of the problem size. Such a throughput rate cannot be achieved with standard (Gentleman-Kung-type) RLS/QR-updating arrays because of feedback loops in the computational schemes.     

Higher-order vector finite elements for tetrahedral cells

Edge-based vector finite elements are widely used for two-dimensional (2-D) and three-dimensional (3-D) electromagnetic modeling. This paper seeks to extend these low-order elements to higher orders to improve the accuracy of numerical solutions. These elements have relaxed normal-component continuity to prohibit spurious modes, and also satisfy Nedelec's constraints to eliminate unnecessary degrees of freedom while remaining entirely local in character. Element matrix derivations are given for the first two vector finite element sets. Also, results of the application of these basis functions to cavity resonators demonstrate the superiority of the higher-order elements     

A stochastic continuation approach to piecewise constant reconstruction.

We address the problem of reconstructing a piecewise constant 3-D object from a few noisy 2-D line-integral projections. More generally, the theory developed here readily applies to the recovery of an ideal n-D signal (n > or =1) from indirect measurements corrupted by noise. Stabilization of this ill-conditioned inverse problem is achieved with the Potts prior model, which leads to a challenging optimization task. To overcome this difficulty, we introduce a new class of hybrid algorithms that combines simulated annealing with deterministic continuation. We call this class of algorithms stochastic continuation (SC). We first prove that, under mild assumptions, SC inherits the finite-time convergence properties of generalized simulated annealing. Then, we show that SC can be successfully applied to our reconstruction problem. In addition, we look into the concave distortion acceleration method introduced for standard simulated annealing and we derive an explicit formula for choosing the free parameter of the cost function. Numerical experiments using both synthetic data and real radiographic testing data show that SC outperforms standard simulated annealing.     

Probing stress effects in HfO2 gate stacks with time dependent measurements

Effects of constant voltage stress (CVS) on gate stacks consisting of an ALD HfO₂ dielectric with various interfacial layers were studied with time dependent sensing measurements: DC I–V, pulse I–V, and charge pumping (CP) at different frequencies. The process of injected electron trapping/de-trapping on pre-existing defects in the bulk of the high-κ film was found to constitute the major contribution to the time dependence of the threshold voltage (V_t) shift during stress. The trap generation observed with the low frequency CP measurements is suggested to occur within the interfacial oxide layer or the interfacial layer/high-κ interface, with only a minor effect on V_t.     

PET imaging-based evaluation of aerosol drugs and their delivery devices: nasal and pulmonary studies

Three-dimensional (3-D) positron emission tomography (PET) imaging of inhaled radiolabeled aerosol in the nasal or pulmonary regions provides an in vivo measurement of drug distribution using the drug itself as the tracer. Repeated or dynamic PET scans over the time after inhalation provides us with further information about the fate of the deposited drug. These quantitative measurements are sufficient to describe the performance of a drug or device and they are obtained in a noninvasive fashion, which cannot be achieved by using any other methods. Using this PET-imaging paradigm, we conducted a sequence of drug studies to evaluate the performance of aerosol drugs and delivery devices; to compare the performance of similar drugs from different manufacturers; to assess the similarity between different formulations and propellants for the same drug; to appraise delivery devices such as spacers and nebulizers, etc. This paper reviews only the imaging and data analysis techniques developed for the above-mentioned studies that include multi-modality image registration, region definition and region-based data analysis, and nonregion-based data analysis. We separated the techniques into nasal and pulmonary studies because of the uniqueness of each group. Specific drugs or devices are not identified and no result about drug performance is given because the imaging and data analysis methodology, which is the focus of this paper, applies to all these studies regardless of the drugs or their delivery devices. The quantitative data are used as the scientific basis for evaluation although we also developed visualization techniques to enhance the results drawn from the data.