Bradley Department of Electrical and Computer Engineering

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From pervasive computing, to smart power systems, Virginia Tech ECE faculty and students delve into all major areas of electrical and computer engineering. The main campus is in Blacksburg, and the department has additional research and teaching facilities in Arlington, Falls Church, and Hampton, Virginia.

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Survey of Approaches and Techniques for Security Verification of Computer Systems
Erata, Ferhat; Deng, Shuwen; Zaghloul, Faisal; Xiong, Wenjie; Demir, Onur; Szefer, Jakub (ACM)
This paper surveys the landscape of security verification approaches and techniques for computer systems at different levels: from a software-application level all the way to the physical hardware level. Different existing projects are compared, based on the tools used and security aspects being examined. Since many systems require both hardware and software components to work together to provide the system's promised security protections, it is not sufficient to verify just the software levels or just the hardware levels in a mutually exclusive fashion. This survey especially highlights system levels that are verified by the different existing projects and presents to the readers the state of the art in hardware and software system security verification. Few approaches come close to providing full-system verification, and there is still much room for improvement.
Stochastic wave-kinetic theory in the Liouville approximation
Besieris, Ioannis M.; Tappert, F. D. (AIP Publishing, 1976-05-01)
The behavior of scalar wave propagation in a wide class of asymptotically conservative, dispersive, weakly inhomogeneous and weakly nonstationary, anisotropic,random media is investigated on the basis of a stochastic, collisionless, Liouville_type equation governing the temporal evolution of a phase_space Wigner distribution density function. Within the framework of the first_order smoothing approximation, a general diffusion-convolution_type kinetic or transport equation is derived for the mean phase_space distribution function containing generalized (nonloral, with memory) diffusion,friction, and absorption operators in phase space. Various levels of simplification are achieved by introducing additional constraints. In the long_time, Markovian, diffusion approximation, a general set of Fokker-Planck equations is derived. Finally, special cases of these equations are examined for spatially homogeneous systems and isotropic media.
Closed 1st-Order And 2nd-Order Moment Equations For Stochastic Nonlinear Problems with Applications To Model Hydrodynamic And Vlasov-Plasma Turbulence
Besieris, Ioannis M.; Stasiak, W. B. (AIP Publishing, 1976-09-01)
Working along the lines of a procedure outlined by Keller, a technique is developed for deriving closed first_ and second_order moment equations for a general class of stochastic nonlinear equations by performing a renormalization at the level of the second moment. The work of Weinstock, as reformulated recently by Balescu and Misguich, is extended in order to obtain two equivalent representations for the second moment using an exact, nonperturbative, statistical approach. These general results, when specialized to the weak_coupling limit, lead to a complete set of closed equations for the first two moments within the framework of an approximation corresponding to Kraichnan's direct_interaction approximation. Additional restrictions result in a self_consistent set of equations for the first two moments in the stochastic quasilinear approximation. Finally, the technique is illustrated by considering its application to two specific physical problems: (1) modelhydrodynamicturbulence and (2) Vlasov_plasma turbulence in the presence of an external stochastic electric field.
Derivation Of an Exact Spectral Density Transport-Equation For A Nonstationary Scattering Medium
Besieris, Ioannis M. (AIP Publishing, 1976-09-01)
Within the framework of the quasioptical description and the pure Markovianrandom process approximation, an exact kinetic equation is derived for the spectral density function in the case of wave propagation in a nondispersive medium characterized by large_scale space-time fluctuations. Also, a quantity, called the degree of coherence function, is defined as a quantitative measure of the irreversible effects of randomness.
A Kinetic Formulation Of 3-Dimensional Quantum Mechanical Harmonic-Oscillator Under A Random Perturbation
Besieris, Ioannis M.; Stasiak, W. B.; Tappert, F. D. (AIP Publishing, 1978-02-01)
The behavior of a three_dimensional, nonrelativistic, quantum mechanical harmonic oscillator is investigated under the influence of three distinct types of randomly fluctuating potential fields. Specifically, kinetic (or transport) equations are derived for the corresponding stochastic Wigner equation (the exact equation of evolution of the phase_space Wigner distribution density function) and the stochastic Liouville equation (correspondence limit approximation) using two closely related statistical techniques, the first_order smoothing and the long_time Markovian approximations. Several physically important averaged observables are calculated in special cases. In the absence of a deterministic inhomogeneous potential field (randomly perturbed, freely propagating particle), the results reduce to those reported previously by Besieris and Tappert.
Beam Propagation in Focusing Media with Random Axis Misalignments: Second-Order And Higher-Order Moments
Besieris, Ioannis M. (AIP Publishing, 1978-12-01)
A novel statistical technique which allows the asymptotic evaluation of second_ and higher_order averaged observables related to the stochastic complex parabolic equation is applied to the problem of beam propagation in a focusing medium characterized by random_axis misalignments. Analytical and numerical results concerning on_ and off_axis statistics (e.g., the variance of intensity fluctuations, modal power transfer, the probability distribution density of the log_irradiance, etc.) are presented, and comparisons are made with previously reported findings.
Adhesive bondline interrogation using Stoneley wave methods
Claus, Richard O.; Kline, R. A. (American Institute of Physics, 1979)
In this work, a new technique for analyzing interfacial conditions in completed adhesive bonds is discussed. This method is based on the sensitivity of Stoneley waves, which propagate along the boundary between dissimilar solid media, to changes in the material properties of the interface region. Stoneley wave attenuation measured after processing was found to increase as a function of increasing surface roughness in specimens of borosilicate crown glass bonded with an aerobic cement to a substrate of 7740 Pyrex mirrorglass. Possible extensions of these results to high_strength structural adhesively bonded composites are discussed.
Single-thermal-source formation of Zn x Cd1-x S thin films
Burton, Larry C.; Hench, T. L.; Meakin, J. D. (American Institute of Physics, 1979)
Thermal sublimation of atomically homogeneous Zn x Cd1_x S powders from a single source results in films that are nonuniform in a direction normal to the substrate. This is attributed to initial preferential sublimation of Cd from the charge and is verified by energy dispersive x-ray analyses of film cross sections and of the charge residue. These results are related to the utility of this technique for forming Zn x Cd1_x S films for photovoltaic applications.
Composition Measurements related to the CU2S-ZNXCD1-XS Heterojunction
Burton, Larry C. (AIP Publishing, 1979)
Composition of zinc and cadmium have been measured for three key regions related to the formation of Cu2S on Zn x Cd1_x X by aqueous ion exchange. These are the ion_exchange solution, the resulting Cu2S, and the Zn x Cd1_x S near the Cu2S_Zn x Cd1_x interface. It is found that the participation of zinc in the ion_exchange reaction is incomplete. Zinc is thus retained in the p_n junction region, and is found mainly in the Zn x Cd1_x S just under the interface. This phenomenon helps to account for certain differences between electro_optical properties of Cu2S/CdS and Cu2S/Zn x Cd1_x S solar cells.
Nth-order multifrequency coherence functions: functional path integral approach
Rose, C. M.; Besieris, Ioannis M. (AIP Publishing, 1979-07-01)
A functional (or path) integral applicable to a broad class of randomly perturbed media is constructed for the nth_order multifrequency coherence function (a quantity intimately linked to nth_order pulse statistics). This path integral is subsequently carried out explicitly in the case of a nondispersive, deterministically homogeneous medium, with a simplified (quadratic) Kolmogorov spectrum, and a series of new results are derived. Special cases dealing with the two_frequency mutual coherence function for plane and beam pulsed waves are considered, and comparisons are made with previously reported findings.
Optical Transfer Function of an Acousto-Optic Heterodyning Image Processor
Poon, T. (1979-10)
Nth-order multifrequency coherence functions: A functional path integral approach. II.
Rose, C. M.; Besieris, Ioannis M. (AIP Publishing, 1980-08-01)
Nth_order multifrequency coherence functions arising in beam propagation through focusing media with random_axis misalignments and focusing media with additive statistical fluctuations are computed. The analysis is carried out by means of a simple formula which yields exact algorithmic solutions to a class of canonical path integrals.
On the uniqueness of solution of magnetostatic vector_potential problems by three-dimensional finite-element methods
Mohammed, O. A.; Davis, William A.; Popovic, Branko D.; Nehl, Thomas W.; Demerdash, Nabeel A. (American Institute of Physics, 1982)
In this paper, particular attention is paid to the impact of finite_element approximation on uniqueness and to approximations implicit in finite element formulations from the uniqueness requirements standpoint. It is also shown that the flux density is unique without qualifications. The theoretical and numerical uniqueness of the magnetic vector potential in three_dimensional problems is also given. This analysis is restricted to linear, isotropic media with Dirichlet Boundary conditions. As an interesting consequence of this analysis it is shown that, under usual conditions adopted in obtaining three_dimensional finite_element solutions, it is not necessary to specify div _ in order that _ be uniquely defined.
Cross diffusion of Cd and Zn in Cu2S formed on Zn x Cd1_x S thin films
Burton, Larry C.; Uppal, P. N.; Dwight, D. W. (American Institute of Physics, 1982)
Cadmium and zinc compositions in Cu 2S formed on Zn x Cd1_x S films (0
A transport-theoretic analysis of pulse propagation through ocean sediments
Besieris, Ioannis M.; Kohler, Werner E.; Freese, Herbert (Acoustical Society of America, 1982-09-01)
The reflection of pulsed acoustic plane waves from ocean sedimentary layers is studied using a stochastic transport theory originally introduced by Barabanenkov et. al. [Izv. Vyssh. Uchebn. Zaved., Radiofiz 15, 1852 (1972)]. The sediments are assumed to be a random medium in which the density and sound speed undergo small, highly laminated (pancakelike) fluctuations. Although the problem is formulated in a general context, the predictions of the theory are fully evaluated only in the special case of normal incidence and no refracting profile. However, even with these approximations, some reasonable qualitative agreement of theoretical predictions with measured data is achieved.
Compositional depth profiles of chemiplated Cu2S/(Zn,Cd)S heterojunction solar cells
Uppal, P. N.; Burton, Larry C.; Rivaud, Lydia; Greene, J. E. (American Institute of Physics, 1983)
Atomic absorption spectroscopy combined with controlled chemical etching and Auger electron spectroscopy profiling with ion beametching have been used to obtain composition versus depth analyses of Cu2S/(Zn,Cd)S heterojunctionsolar cells formed by an aqueous cation exchange, or chemiplating, process. The Cu2S films, ranging from 0.5 to 6 _m in thickness, were polycrystalline and exhibited a (001) preferred orientation on either textured polycrystalline or cleaved single crystal (Zn,Cd)S substrates. The profiling results showed that the interfacial regions were compositionally graded over very large distances ranging from tens to hundreds of nonometers depending on the Cu2S film thickness. This is much wider than observed for comparable Cu2S/CdS cells. Moreover, excess Zn in the form of both elemental Zn and ZnS was always found in the interfacial region and may be responsible for the short circuit current being lower than expected for these cells.
X-ray and XPS studies of evaporated cuxs thin-films
Uppal, P. N.; Burton, Larry C. (American Institute of Physics, 1983-04-01)
The structural changes in Cu x S films have been monitored by x_ray diffraction and correlated to the chemical changes taking place on the Cu x S surface, the latter monitored by XPS. The results show: evaporated Cu x S films contained chalcocite, free copper phases, and probably a third phase (of sulfur); resistivity is related to the amounts of free Cu and S in the film; air heat treatments converted chalcocite to Cu deficient phases and resulted in the disappearance of the sulfide and predominance of CuSO4_nH2O and CuO; argon heat treatment tended to react Cu and S to form Cu x S; Cd is detected on the surface of Cu x S deposited onto CdS and is significantly increased in amount by heat treatments. These results can be related to chemical processes occurring on Cu x S/CdS and Cu x S/(Zn,Cd)S solar cells. For the CdS cell, oxides and sulfates of Cu and Cd are found on the Cu x S surface and the sulfates are enhanced by the heat treatment in moist air. CuO and CuSO4 are formed in the absence of Cd, and dominate the Cu x S surface.
Incoherent Spatial-Filtering with A Scanning Heterodyne System
Indebetouw, Guy J.; Poon, Ting-Chung (Optical Society of America, 1984-01-01)
Imaging systems with two pupils in the receiving optics have been used to synthesize bipolar point spread functions in incoherent image processing. We describe a two-pupil system using a scanning illumination technique and compare its attributes with more conventional techniques. Experimental examples using two-pupil interaction and an acoustooptic frequency offset for the direct 2-D bandpass filtering of diffusely reflecting objects are presented.
Computer simulation of electron beams. I. Space charge algorithm for asymmetric beams
Dewolf, David A. (American Institute of Physics, 1985)
Longitudinal space_charge forces can be neglected in computer simulations of slowly curving quasilaminar electron beams. A particle mesh type algorithm for transverse space charge forces is developed, and great simplification in numerical calculation of asymmetric electron beams is demonstrated. Some typical examples for kinescope beams are discussed.
Computer simulation of electron beams. II. Low cost beam current reconstruction
Dewolf, David A. (American Institute of Physics, 1985)
Reconstruction of current density in electron beams is complicated by distortion of phase space which can require very fine discretization of the beam into trajectories. An efficient discretization of phase space is exploited, using conservation of charge and current in hypertriangle patches, to reconstruct the current density by fitting Gaussians through the distorted hypertriangles. Advantages and limitations are discussed.

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