Copyright (c) 2009 University of Nebraska - Lincoln All rights reserved. http://digitalcommons.unl.edu/electricalengineeringfacpub Recent documents in Faculty Publications from the Department of Electrical Engineering en-us Sat, 01 Aug 2009 14:53:08 PDT 3600 http://digitalcommons.unl.edu/electricalengineeringfacpub/106 http://digitalcommons.unl.edu/electricalengineeringfacpub/106 Fri, 31 Jul 2009 09:03:03 PDT Previous attempts in producing light absorbing materials with bandgaps near the 1.37 eV efficiency optimum have included the partial substitution of gallium or aluminum for indium in the CIS system. The most efficient of these solar cells to date have had absorber layers with bandgaps < 1.2 eV. It is logical that an even smaller substitutional atom, boron, should lead to a wider bandgap with a smaller degree of atomic substitution. In this study, copper-indium-boron precursor films are sputtered onto molybdenum coated glass substrates and post-selenized. In the selenized films, although X-ray diffraction (XRD) measurements confirm that a CIS phase is present, Auger electron spectroscopy (AES) results indicate that boron is no longer homogeneously dispersed throughout the film as it was in the case of the unselenized precursor. C. A. Kamler http://digitalcommons.unl.edu/electricalengineeringfacpub/105 http://digitalcommons.unl.edu/electricalengineeringfacpub/105 Thu, 28 May 2009 08:38:59 PDT Lithium Niobate has a potential for applications in electronics and communication industries due to its unique electro-optical, piezoelectric and nonlinear properties. Femtosecond laser machining offers the best alternative to machine the mechanically fragile and optically delicate lithium niobate crystal. This paper reports a study of the effect of femtosecond laser machining on the surface integrity of lithium niobate. The transmission electron microscopy reveals a 100nm thin amorphous region and a void. The chemical analysis shows a loss of lithium and oxygen from the surface and sub-surface. Optical illumination facilitates the selective readout of the written spots of 2 microns size. A. Malshe http://digitalcommons.unl.edu/electricalengineeringfacpub/104 http://digitalcommons.unl.edu/electricalengineeringfacpub/104 Fri, 01 May 2009 10:15:53 PDT We report the results of a study of the electrostatic interaction between negatively charged particles in a plasma. The goal of the study was to investigate the possibility of an attractive interaction which would make possible the formation of "molecules" of particles. For all approximations relating the positive ion density to the local electrostatic potential that we examined, we find that the interaction is repulsive for all particle separations. M. E. Markes http://digitalcommons.unl.edu/electricalengineeringfacpub/103 http://digitalcommons.unl.edu/electricalengineeringfacpub/103 Wed, 29 Apr 2009 12:21:29 PDT Both differential pulse code modulation (DPCM) and adaptive predictive coding (APC) systems have been used somewhat successfully for low date rate digital voice transmission. A DPCM system has as its goal the removal of signal redundancy prior to transmission by a linear prediction of the incoming signal with a weighted combination of past signal estimates. The error in the prediction process is then quantized and transmitted to the receiver. An identical prediction loop is used at the receiver to reinsert the redundancy, and hence, to reconstruct the speech signal. Both the quantizer and predictor may or may not be adaptive. Jerry Gibson http://digitalcommons.unl.edu/electricalengineeringfacpub/102 http://digitalcommons.unl.edu/electricalengineeringfacpub/102 Wed, 29 Apr 2009 12:21:28 PDT Experiments have been conducted which reveal the existence of a detectable magnetic field associated with cardiac electrical activity. The relationship between the magnetic record and the electrocardiogram has been explored and it is shown that under certain conditions of axis orientation the voltage induced into a toroidal sensing element around the heart has the form of the first time derivative of the electrocardiogram. A formula based on Maxwell's equations has been developed to relate these two phenomona. R. A. Stratbucker http://digitalcommons.unl.edu/electricalengineeringfacpub/101 http://digitalcommons.unl.edu/electricalengineeringfacpub/101 Wed, 29 Apr 2009 12:21:26 PDT This article establishes a lower bound for the noise figure of two networks in cascade. This is illustrated by means of a passive low-level frequency converter which utilizes a back diode as a nonlinear conductance. Other investigators have analyzed the properties of low-level frequency converters. However, the greatest lower bound of a combination of the converter and intermediate frequency amplifier system was not considered previously and is the subject of this paper. Knowledge of this lower bound has practical significance because if a measured value of noise figure is less than this lower bound, it follows that the measurement is in error. For illustrative purposes a lower bound is established on one of the highest quality systems available, employing a special General Electric diode as a frequency converter for the first network, and a 60 MHz IF amplifier for the second network. This resulted in a noise figure lower bound of 3.86 db for the overall system. This paper shows how this lower bound was obtained. Also the controversial right angle diode characteristic is found to be undesirable from an impedance viewpoint. Grant Myers http://digitalcommons.unl.edu/electricalengineeringfacpub/100 http://digitalcommons.unl.edu/electricalengineeringfacpub/100 Wed, 29 Apr 2009 12:21:25 PDT Background: We propose a multiple sequence alignment (MSA) algorithm and compare the alignment-quality and execution-time of the proposed algorithm with that of existing algorithms. The proposed progressive alignment algorithm uses a grammar-based distance metric to determine the order in which biological sequences are to be pairwise aligned. The progressive alignment occurs via pairwise aligning new sequences with an ensemble of the sequences previously aligned. Results: The performance of the proposed algorithm is validated via comparison to popular progressive multiple alignment approaches, ClustalW and T-Coffee, and to the more recently developed algorithms MAFFT, MUSCLE, Kalign, and PSAlign using the BAliBASE 3.0 database of amino acid alignment files and a set of longer sequences generated by Rose software. The proposed algorithm has successfully built multiple alignments comparable to other programs with significant improvements in running time. The results are especially striking for large datasets. Conclusion: We introduce a computationally efficient progressive alignment algorithm using a grammar based sequence distance particularly useful in aligning large datasets. David Russell http://digitalcommons.unl.edu/electricalengineeringfacpub/99 http://digitalcommons.unl.edu/electricalengineeringfacpub/99 Wed, 29 Apr 2009 12:09:18 PDT Background: Occult organizational structures in DNA sequences may hold the key to understanding functional and evolutionary aspects of the DNA molecule. Such structures can also provide the means for identifying and discriminating organisms using genomic data. Species specific genomic signatures are useful in a variety of contexts such as evolutionary analysis, assembly and classification of genomic sequences from large uncultivated microbial communities and a rapid identification system in health hazard situations. Results: We have analyzed genomic sequences of eukaryotic and prokaryotic chromosomes as well as various subtypes of viruses using an information theoretic framework. We confirm the existence of a species specific average mutual information (AMI) profile. We use these profiles to define a very simple, computationally efficient, alignment free, distance measure that reflects the evolutionary relationships between genomic sequences. We use this distance measure to classify chromosomes according to species of origin, to separate and cluster subtypes of the HIV-1 virus, and classify DNA fragments to species of origin. Conclusion: AMI profiles of DNA sequences prove to be species specific and easy to compute. The structure of AMI profiles are conserved, even in short subsequences of a species' genome, rendering a pervasive signature. This signature can be used to classify relatively short DNA fragments to species of origin. Mark Bauer http://digitalcommons.unl.edu/electricalengineeringfacpub/98 http://digitalcommons.unl.edu/electricalengineeringfacpub/98 Mon, 08 Dec 2008 13:28:48 PST Diamond-like carbon (DLC) films were deposited on tungsten tips under KrF excimer laser irradiation in benzene solution. The deposition process was found to be highly dependent on tip sharpness. Tips with larger curvature radii and smaller aspect ratios could not be coated with DLC films under the same condition as that for sharp tips. Raman spectra showed that more sp3 tetrahedral structures were present in the DLC films on a tip with a smaller curvature radius. Simulation results showed that the tip sharpness dependent local optical enhancement played an important role in the DLC deposition process. An optical field gradient from apex to tip body was also found in the simulation. We suggest that there are two modes in the process of DLC deposition on nanotips under different laser fluences, i.e., local apex DLC deposition under low laser fluences and phase-graded DLC deposition under high laser fluences. J. Shi http://digitalcommons.unl.edu/electricalengineeringfacpub/97 http://digitalcommons.unl.edu/electricalengineeringfacpub/97 Mon, 08 Dec 2008 13:23:22 PST Diamond-like carbon sDLCd films were deposited on tungsten sWd tips under the KrF excimer laser in a laser chemical vapor deposition sLCVDd chamber. Raman spectroscopy showed that the deposited DLC films were phase-graded along the tips from the apexes. The DLC films were more diamondlike at or near the tip apexes. From numerical simulation, there is a strongly confined and enhanced optical field at the tip apexes. The simulation also indicates that there is an optical-field gradient from tip apexes to tip bodies. Therefore, the variations in the phases of deposited DLC films were attributed to the corresponding variations in local optical intensities along the tips. Hence, optical local near field was confirmed to be responsible to the DLC deposition. J. Shi