Showing papers by "Worcester Polytechnic Institute published in 1984"

Signal Processing for Diffraction Tomography

Abstract: On distingue 2 problemes dans le traitement du signal; le premier concerne la reconstruction d'une image a partir de donnees mesurees transformees de facon appropriee qui echantillonnent le plan de frequences spatiale le long d'arcs circulaires; le second probleme est celui de desenroulement de phase des profils mesures

Current Harmonics, Voltage Distortion, and Powers Associated with Electric Vehicle Battery Chargers Distributed on the Residential Power System

Abstract: The harmonic performance of the networks of several types of electric vehicle (EV) battery chargers is documented. Cumulative effects at the substation level for random distributions of each of five different charger types are reported. Chargers with and without current- smoothing inductors and with and without controlled rectifiers for maintenance of constant current are included. Results are reported as magnitudes of expected harmonic current; active power; apparent, reactive, and distortive volt amperes; and power factor hour by hour over typical daily recharge cycles for the network of chargers. Results regarding comparisons among chargers demonstrate the desirability of including a current-smoothing inductor in the charging circuit and indicate that constant-current type chargers using controlled rectifiers generate significantly more harmonic current than the simple noncontrolled taper-current chargers. Typical third harmonic current values of 15 A per charger on the 120-V side and 20 A per phase on the 12.8-kV side for a network of chargers (at ten percent penetration of chargers into the residential distribution network) indicate the possibility for harmful effects to customer and utility equipment and for interference into communications circuits. The results reported here should be useful in both predicting harmful effects at various densities of EV chargers on the residential network and in designing chargers to minimize those effects. supported in part by the New England Electric System.

N2O Evolution by Green Algae

Abstract: Evidence is presented here that axenic cultures of Chlorella, Scenedesmus, Coelastrum, and Chlorococcum spp. evolve N2O when grown on NO2−, showing that the Chlorophyceae are a source of N2O in aquatic systems.

An operational strategy for unstable recombinant DNA cultures.

Abstract: A simple operational strategy is shown to offer a viable means of enhancing plasmid stability in chemostat systems where plasmid loss is a common problem. Feedback control can be used to stabilize coexistence states, which are naturally unstable in the system investigated, and thus gurantee retention of the plasmid-carrying strain. The strategy exploits the normally undesirable characteristics of substrate inhibited growth kinetics, and is illustrated with specific reference to methanolutilizing organisms. Since the methodology may be easily implemented in practice, it offers an alternative to costly environmental methods such as antibiotic addition.

Three methods for postoptimal analysis in integer linear programming

Abstract: Postoptimal analysis in LP is based on the existence of necessary and sufficient optimality conditions, for which complete information is contained in the optimal basic inverse. The same is not true for ILP. Optimality can only be proven through an algorithm. The possibility for postoptimal analysis is therefore dependent on the algorithm used to solve the ILP. In this paper we study methods for performing postoptimal analysis when the ILP has been solved by enumeration, branch-and-bound and cutting planes, respectively.

Kinetics of enzymatic starch liquefaction: Simulation of the high-molecular-weight product distribution.

Abstract: Enzymatic corn starch liquefaction with alpha-amylase was carried out. Molecular weight distributions of the resulting hydrolysates are presented using aqueous size exclusion chromatographic techniques. It is demonstrated that despite the fact that the enzyme employed reacts in a random endoacting manner, the product distributions are nonrandom. The results are explained in part by a multimerization process whereby the polymeric substrate molecules preferentially associate, forming intermolecular aggregates. These aggregates are either a consequence of the manner in which the material is deposited into the native granular structure of starch or due to intrinsic physical chemical properties of the polysaccharide. In the latter case, the results are shown to correspond to known multimerized amylose, although complete characterization of the polysaccharide is currently not available. The results presented are used to develop a simplified kinetic model of starch liquefaction and shown to simulate the product distributions accurately.

Noninvasive Transcutaneous Monitoring of Arterial Blood Gases

Abstract: Valuable clinical and physiological data concerning the function of the cardiopulmonary system can be obtained from continuous monitoring of hemoglobin oxygen saturation (SaO2), oxygen tension (PO2), and carbon dioxide tension (PCO2) in blood. While periodic blood sampling is still used clinically to determine arterial blood gases, it is becoming apparent that the recent introduction of continuous noninvasive monitoring of blood gases can offer many advantages. This paper discusses the historical development and significant accomplishments of various techniques available for transcutaneous blood gas monitoring. Four major areas are reviewed: electrochemistry, spectrophotometry, mass spectrometry, and gas chromatography. For each of these techniques, the theoretical basis, instrumentation, and clinical applications are discussed.

Fourier Domain Reconstruction Methods with Application to Diffraction Tomography

Abstract: Presented are algorithms for reconstructing two-dimensional functions from discrete and finite information available about their Fourier transform. The procedure is based upon an interpolation technique in the Fourier domain. The concept is applied to straight-path and diffraction tomography where Fourier domain information is available on a finite number of rotated contours. Finally, the resultant Fourier domain based methods are compared with their corresponding spatial domain based methods, i.e., filtered backprojection and backpropagation in terms of accuracy of reconstruction and computational efficiency.

Kinetics of a First-Order Phase Transition: Computer Simulations and Theory

Abstract: We make a quantitative comparison between the predictions of the Becker-Doring equations and computer simulations on a model of a quenched binary A-B alloy. The atoms are confined to the vertices of a simple cubic lattice, interact through attractive nearest neighbor interactions, and move by interchanges of nearest neighbor pairs (Kawasaki dynamics). We study in particular the time evolution of the number of clusters of A atoms of each size, at four different concentrations: ρA=0.035, 0.05, 0.075, and 0.1 atoms per lattice site. The temperature is 0.59 times the critical temperature. At this temperature the equilibrium concentration of A atoms in the B-rich phase is ρ A eq =0.0145 atoms/lattice site. The coefficients entering the Becker-Doring equations are obtained by extrapolation from previously published low-density calculations, leaving the time scale as the only adjustable parameter. We find good agreement at the three lower densities. At 10% density the agreement is, as might be expected, less satisfactory but still fairly good-indicating a quite wide range of utility for the Becker-Doring equations.

Tritium form factors at low q

Abstract: The elastic charge and magnetic form factors of $^{3}\mathrm{H}$ have been measured in the region $0.0477l{q}^{2}l2.96$ ${\mathrm{fm}}^{\ensuremath{-}2}$. Throughout this range, the charge form factor is found to be larger than previous measurements, whereas the magnetic form factor agrees with the earlier work. The change in the charge form factor slightly increases the discrepancy between the calculated and observed binding energy difference between $^{3}\mathrm{H}$ and $^{3}\mathrm{He}$.

Image reconstruction from frequency domain data on arbitrary contours

Abstract: This paper presents a new view of the problem of image reconstruction in the spatial Fourier domain based on the generalized projections of a two-dimensional image. The algorithms that are presented are derived from the exact continuous relations between the Fourier transforms of a spatially limited image and those of its generalized projections. A Fourier domain reconstruction formula is derived that is a natural consequence of these relations giving values of the two-dimensional transform on a regular grid useful for inverse FFT. This approach is contrasted with the more ad hoc methods of Fourier domain interpolation and with the spatial domain approaches such as the backprojection and backpropagation methods.

Computation of Upper and Lower Bounds on Reliability Indices for Bulk Power Systems

Abstract: Bulk power system reliability analysis includes the computation of probability of system failure. This quantity may be evaluated based on the probability of individual component outage events which are classified as resulting in system failure or nonfailure. The amount of computation required increases exponentially with the numdber of components in the system. Therefore, an exact calculation of system failure probability is not feasible for even moderately large systems.

P-groups with non-abelian automorphism groups and all automorphisms central

Abstract: For each odd prime p this paper gives an example of a non-abelian p-group with a non-abelian automorphism group in which each automorphism is central.

Scaling and Roundoff in Fixed-Point Implementation of Control Algorithms

Abstract: The analysis and design of digital controllers on microprocessors using fixed-point arithmetic have been considered. Three scaling techniques are applied to the design of digital controllers in such a way as to avoid overflow and to optimize the signal-to-roundoff noise ratio. Both the scaler and the multivariable cases are treated. Statistical estimates of the steady-state roundoff and quantization errors are derived.

Some remarks about the wave speed and travelling wave solutions of a nonlinear integral operator

Abstract: In this paper, we extend the existence of travelling wave solutions of a nonlinear operator in the inferior case to higher dimensions and establish the uniqueness of that solution. In addition we determine the sign of the wave speed in a special case.

On the Use of the General Partial Autocorrelation Function for Order Determination in ARMA(p, q) Processes

Abstract: We show that the General Partial Autocorrelation Function (GPAC), which has recently been suggested to be used as one of a set of convenient tools for order identification in ARMA models, has unstable behavior when applied to time series of moderate length. Its use in detecting the order of MA components in real series is very limited and can only be recommended as a means to confirm a pure AR fit to the data.

System development for aqueous gel permeation chromatography

Abstract: To devise an improved gel permeation chromatography system for the analysis of macromolecules, with a strongly alkaline solution as eluent, three Fractogel TSK gels were investigated. Because primary standards are usually unavailable, calibration was achieved by using Benoit's universal procedure and polystyrene sulfonates, polyethylene glycols, and dextrans as secondary calibrants. Continuous monitoring of intrinsic viscosity resulted from coupling a viscodetector with a classical differential refractometer. It was found that column efficiency and fractionation range could be extended well beyond those of previously studied systems on a reasonably short period of analysis.

Direct Current Generation in Single-Phase Residential Systems DC Effects and Permissible Levels

Abstract: This paper suggests the value of 50 mA direct current as an acceptable level of dc pollution in residential single-phase 120V/240V services. This conclusion is based on experimental measurements carried out on a typical single-phase distribution transformer and on an analytical model which considers the flux- magnetizing current characteristic of the transformer. The response to dc biasing of single-phase motors and transformers used in residential circuits was the key factor in establishing the permissible level of dc injection.

Object identification and orientation determination in 3-space with no point correspondence information

Abstract: The problem of identification of rigid planar-patch objects from images projected from random orientations in 3-D space is approached using tensor representation of image measures. This allows standardization of object orientation without knowledge of object identity, and hence permits a simple one-step comparison operation between the standardized unknown and each library image. Geometric transformations due to oblique viewing angles, as well as translation, rotation, and scale change are handled. Experimental results using a library of camera-acquired images demonstrate correct performance of the algorithm.