A vertically integrated GaAs bipolar dynamic RAM cell with storagetimes of 4.5 h at room temperature

The storage times of FET-accessed GaAs dynamic RAM cells are limited to less than 1 min at room temperature by gate leakage in the access transistor. These transistor leakage mechanisms have been eliminated by designing a vertically integrated DRAM cell in which an n-p-n bipolar access transistor is merged with a p-n-p storage capacitor. Storage times of 4.5 h are obtained at room temperature, a 1000-fold increase over the best FET-accessed cells     

On the Hertzian fatigue cone crack propagation in ceramics

The Hertzian cone crack initiation and propagation in ceramics under cyclic fatigue loading with a spherical indenter is studied. Unlike the so-called quasi-static Hertzian cone crack, the fatigue Hertzian cone crack propagation eliminates the dynamic effect on unstable crack propagation. As such, the crack is found to propagate following the path of pure mode I type. We use an elasticity approach, a finite element analysis, and an empirical analysis to investigate the Hertzian cone crack in three stages: crack initiation, crack propagation, and crack kinking. The mechanism of the multiple concentric cone cracks is also explained. The purpose is to understand and predict the behavior of the formation of the Hertzian fatigue cone crack using available modeling tools.Zheng Chen is currently with Space Power Institute, Auburn University.     

An automated film reader for DNA sequencing based on homomorphicdeconvolution

An automated reader for electrophoresis based DNA sequencing methods is described that provides fast and accurate sequence determination. Digitized sequencing lanes are processed with homomorphic blind deconvolution in preparation for peak detection, interlane alignment, peak refinement and base calling. Initial reads from direct blot sequencing films have error rates of about 1% at the rate of 5 nucleotides/s. Typical read lengths are 500-600 nucleotides. The described reader is a significant improvement over existing readers and could be an essential component in the sequencing efforts of the Human Genome Project     

Use of the nuclear microprobe at the University of Arizona for the study of heavy metal deposition in rabbit renal tissue

Industrial wastes consigned to disposal sites frequently contain substantial amounts of heavy metals. We have successfully applied proton induced X-ray emission analysis (PIXE) in the conduct of heavy metal (Hg, Cd, Cr, As) toxicity studies using precision cut rabbit renal cortical slices. The large beam diameter (4000 μm) of the proton macroprobe at The University of Arizona Ion Beam Analysis facility allowed an overall concentration of the metal(s) of interest in the samples to be determined, but lacked the ability to resolve point concentrations in the tissue. The ability to locate these areas has now been made available to us with the addition of a rastering microprobe (μ-PIXE) to the facility. Studies now being conducted in our laboratory using this micro-technique include analysis of renal tissue taken from rabbits injected intraperitoneally with HgCl₂, K₂Cr₂O₇, and NaAsO₂. The small beam size (3 μm) and the ability to raster this beam over areas of up to 125 μm × 125 μm has allowed regional mapping of endogenous and non-endogenous metal concentrations and revealed trends in heavy metal deposition in in vivo treated renal tissue, significantly increasing the amount of information obtained from these animal studies using PIXE alone. The combination of small beam size, high resolution, and multi-element detection makes μ-PIXE a powerful tool for investigating the impact of non-endogenous metals on the kidney.     

Experimental determination of electron and hole mobilities in MOSaccumulation layers

This letter presents for the first time, the experimentally determined majority carrier mobilities in the accumulation layer of a MOSFET for both p-type and n-type channel doping for a wide range of doping concentrations. The measured carrier mobility is observed to follow a universal behavior at high transverse fields, similar to that observed for minority carriers in MOS inversion layers. At the higher doping levels, the effective mobility for majority carriers at low to moderate transverse fields is found to be very close to the bulk mobility. This is believed to be due to carrier screening of the ionized impurity scattering which dominates at the higher doping concentrations     

Analysis and measurement of mode polarizers in square waveguide

A general analysis approach for strip metallization structures enclosed in rectangular or square waveguide is presented. The technique involves the novel application of a commercially available 2.5-dimensional (2.5-D) method-of-moments-based (MoM) electromagnetic (EM) analysis tool to a three-dimensional (3-D) waveguide problem. Very good agreement is demonstrated between computed and measured results for several printed strip linear polarizers embedded within a square waveguide environment. This paper, to the authors' knowledge, represents the first such comparison of phase and magnitude between computed and measured data for strip grid polarizers in a waveguide environment. The developed approach involves construction of a theoretical waveguide “test fixture” and an associated theoretical de-embedding procedure. Computational advantages are expected over the alternative approach of using a finite-element-based fully 3-D analysis approach. The polarizer results have potential application to shielded versions of quasi-optic array components that have been demonstrated in open geometries, as well as to multimode antenna feeds, waveguide filters, and matching networks     

A time-frequency analysis method for radar scattering

A time-frequency analysis method to study electromagnetic scattering is presented and demonstrated using canonical objects. The time-frequency analysis method utilizes the Bargmann transform to formulate the signal representation in phase space. The use of the Bargmann transform leads to an attractive parametric signal representation in terms of complex polynomials, and elliptical filters can be constructed to crop or extract selected areas of the phase plane. The signal representation and filtering operations are demonstrated using scattering responses from spheres and thin wires, and the prominent scattering features are identified and extracted     

MMSE decision-feedback equalizers and coding. I. Equalizationresults

The minimum mean-squared-error decision-feedback equalizer (MMSE-DFE) has properties that suggest that it is a canonical equalization structure for systems that combine equalization with coded modulation. The structure and performance of the MMSE-DFE are succinctly derived using linear-estimation-theoretic principles in this first part of this two-part paper. The front-end of the MMSE-DFE, called the “mean-square whitened matched filter” (MS-WMF), is preferable in some ways to a matched filter or a whitened matched filter as a canonical receiver front end. In a coded system, the feedback filter of the MMSE-DFE may be implemented in the transmitter using precoding. The MMSE-DFE can perform significantly better than a zero-forcing decision-feedback equalizer, particularly at moderate-to-low SNR's and on severe-ISI channels. The MMSE-DFE is biased. The optimum unbiased MMSE-DFE is the MMSE-DFE with the bias removed. Removing bias improves error probability, but reduces the SNR to SNR_MMSE-DFE,U=SNR_MMSE-DFE-1. It is shown that this SNR relationship is a particular case of a very general result and that SNR_MMSE-DFE,U gives a more realistic estimate of SNR. The results are extended to partial response equalization and to equalization with correlated inputs in an appendix     

Calculation of secondary cable losses and ampacity in the presenceof harmonics

A simplified procedure for computing ohmic losses in secondary distribution cable systems by extending the Neher-McGrath model for 60 Hz losses is presented. Specifically, simplified formulae for evaluating ohmic losses due to harmonics are given. These results are subsequently used to compute the cable ampacity or the derating factor due to harmonics. The overall method is simple to follow and can be performed with a calculator. A typical example is given