Showing papers by "Virginia Tech published in 1979"

Statistical and structural approaches to texture

Abstract: In this survey we review the image processing literature on the various approaches and models investigators have used for texture. These include statistical approaches of autocorrelation function, optical transforms, digital transforms, textural edgeness, structural element, gray tone cooccurrence, run lengths, and autoregressive models. We discuss and generalize some structural approaches to texture based on more complex primitives than gray tone. We conclude with some structural-statistical generalizations which apply the statistical techniques to the structural primitives.

Systematics of the spinel structure type

Abstract: Systematic trends in the geometry of 149 oxide and 80 sulfide binary and ternary spinels have been examined from the standpoint of ionic radius and electronegativity. The mean ionic radii of the octahedral and tetrahedral cations, taken together, account for 96.9 and 90.5% of the variation in the unit cell parameter, a, of the oxides and sulfides, respectively, with the octahedral cation exerting by far the dominant influence in sulfides. The mean electronegativity of the octahedral cation exerts an additional, but small, influence on the cell edge of the sulfides. The equation a=(8/3√d)d tet+(8/3)d oct, where d tet and d oct are the tetrahedral and octahedral bond lengths obained from the sum of the ionic radii, accounts for 96.7 and 83.2% of the variation in a in the oxides and sulfides, respectively, again testifying to the applicability of the hard-sphere ionic model in the case of the spinel structure. Comparison of observed and calculated u values for 94 spinels indicates that up to 40% of the experimentally measured anion coordinates may be significantly in error. In addition to these compounds, u values are given for 52 spinels for which no data have previously been determined. Diagrams are presented for the rapid interpretation of the internal consistency of published data and the prediction of the structural parameters of hypothetical or partially studied spinels.

The Consistent Labeling Problem: Part II

Abstract: In this second part of a two-part paper, we explore the power and complexity of the g=fKP and g=vKP class of look-ahead operators which can be used to speed up the tree search in the consistent labeling problem. For a specified K and P we show that the fixedpoint power of g=fKP and g=vKP is the same, that g=fKP+1 is at least as powerful as g=fKP, and that g=vK+1p is at least as powerful at g=fKP. Finally, we define a minimal compatibility relation and show how the standard tree search procedure for finding all the consistent labelings is quicker for a minimal relation. This leads to the concept of grading the complexity of compatibility relations according to how much look-ahead work it requires to reduce them to minimal relations and suggests that the reason look-ahead operators, such as Waltz filtering, work so well is that the compatibility relations used in practice are not very complex and are reducible to minimal or near minimal relations by a g=fKP or g=vKP look-ahead operator with small value for parameter P.

An economic theory of mutually advantageous issue linkages in international negotiations

Abstract: There has been considerable interest in recent years in the question of issue linkages in international negotiations. What is significant about discussions of linkages in the present era is the stress put on making trade-offs explicit among issues. Most of the highly publicized cases of proposed issue linkages appear to have been motivated by attempts of individual countries or groups of countries to extend their dominant bargaining or veto power in one particular issue area into other areas so as to achieve maximum advantage from their whole array of international interactions. The existence of an additional rationale for linkage that relies upon mutual interest has important implications. Drawing on the economic theory of exchange, the use of issue linkages to facilitate the completion of a greater number of mutually beneficial agreements among nations is considered.

Modeling and Estimation for Tracking Maneuvering Targets

Abstract: A new approach to the three-dimensional airborne maneuvering target tracking problem is presented. The method, which combines the correlated acceleration target model of Singer [3] with the adaptive semi-Markov maneuver model of Gholson and Moose [8], leads to a practical real-time tracking algorithm that can be easily implemented on a modern fire-control computer. Preliminary testing with actual radar measurements indicates both improved tracking accuracy and increased filter stability in response to rapid target accelerations in elevation, bearing, and range.

Stability of three-dimensional boundary layers

Abstract: A theory is presented for the three-dimensional stability of boundary layers. Equations are derived for the evolution of a disturbance having a given frequency and originating at a given curve. These equations are used to determine the rays along which the disturbance energy propagates. It is shown that the results can be obtained by using the saddle-point method, or kinematic wave theory, or the method of multiple scales. Extension of the theory to the case of a wave packet is also presented.

Elastic moduli of transversely isotropic graphite fibers and their composites

Abstract: This paper demonstrates that it is possible to calculate the complete set of elastic mechanical properties for graphite-epoxy fiber-reinforced materials at any fiber-volume fraction by modifying equations previously developed to include transversely isotropic graphite-fiber properties. Experimental verification of the modified equations is demonstrated by using these equations to curve fit elastic-property data obtained ultrasonically over a range of fiber-volume fractions. Material systems under consideration are T300/5208, AS-3501 and Modomor II/LY558 graphite epoxy. Using the modified equations it is possible to extrapolate for fiber properties. From Modomor II/LY558 ultrasonic data, it is shown that five out of seven extrapolated graphite-fiber properties are consistent with the assumption that graphite fibers are transversely isotropic. Elastic properties for T300/5208 and AS-3501 are ultrasonically evaluated by propagating stress waves through six individual specimens but at various angles from a block of unidirectional material. Particular attention is devoted to specimen dimensions. To demonstrate the need for accurately calculating or experimentally measuring all lamina elastic properties, a brief discussion is included on the effect that variations in lamina elastic properties have on calculating interlaminar stresses.

Decomposition of Two-Dimensional Shapes by Graph-Theoretic Clustering

Abstract: This paper describes a technique for transforming a twodimensional shape into a binary relation whose clusters represent the intuitively pleasing simple parts of the shape. The binary relation can be defined on the set of boundary points of the shape or on the set of line segments of a piecewise linear approximation to the boundary. The relation includes all pairs of vertices (or segments) such that the line segment joining the pair lies entirely interior to the boundary of the shape. The graph-theoretic clustering method first determines dense regions, which are local regions of high compactness, and then forms clusters by merging together those dense regions having high enough overlap. Using this procedure on handdrawn colon shapes copied from an X-ray and on handprinted characters, the parts determined by the clustering often correspond well to decompositions that a human might make.

An extrapolation procedure for band-limited signals

Abstract: In this paper, the task of extrapolating a time-truncated version of a band-limited signal shall be considered. It will be shown that the basic extrapolation operation is feasible for only a particular subset of the class of band-limited signals (i.e., the operation is well-posed mathematically). An efficient algorithmic method for achieving the desired extrapolation on this subset is then presented. This algorithm is structured so that all necessary signal manipulations involve signals which are everywhere zero except possibly on a finite "observation time" set. As a consequence, its implementation is straightforward and can be carried out in real time. This is to be contrasted with many existing extrapolation algorithms which theoretically involve operations on signals that are nonzero for almost all values of time. Their numerical implementation thereby necessitates an error producing time-truncation and a resultant deleterious effect on the corresponding extrapolation. Using straightforward algebraic operations, a convenient one-step extrapolation procedure is next developed. This is noteworthy in that this procedure thereby enables one to effectively circumvent any potentially slow convergence rate difficulties which typically characterize extrapolation algorithms. The effectiveness of this one-step procedure is demonstrated by means of two examples.

Studies in the History of Probability and Statistics. XXXVII A. M. Turing's statistical work in World War II

Abstract: SUMMARY An account is given of A. M. Turing's unpublished contributions to statistics during 1941 or 1940.

Generalized Computer-Aided Discrete Time-Domain Modeling and Analysis of DC-DC Converters

Abstract: A generalized discrete time-domain modeling and analysis technique is presented for all types of switching regulators using any type of duty-cycle controller and operating in both continuous and discontinuous inductor currents. State-space techniques are employed to derive an equivalent nonlinear discrete time model that describes the converter exactly. The system is linearized about its equilibrium state to obtain a linear discrete time model for small signal performance evaluations, such as stability, audiosusceptibility, and transient response. The analysis makes extensive use of the digital computer as an analytical tool. It is universal, exact, and easy to use.

A Nonparametric Procedure for Process Control Based on Within-Group Ranking

Abstract: A nonparametric procedure is developed for the problem of quickly detecting any shift in the mean of a sequence of observations from a specified control value. The proposed procedure is based on Wilcoxon signed-rank statistics where ranking is within groups. A cumulative sum control chart type stopping rule is used with the Wilcoxon statistics. Using a Markov chain approach, the average run length of the procedure can be computed exactly for any distribution for which the distribution of the Wilcoxon signed-rank statistic is known. The procedure has the same average run length for any continuous distribution which is symmetric about the control value.

Behavioral Measures of Aircrew Mental Workload

Abstract: Behavioral research literature pertaining to the measurement of aircrew workload was classified into general categories of subjective opinion, spare mental capacity, and primary task metrics Fourt

Collaborative Evaluation of a Proposed Reference Dilution Method of Susceptibility Testing of Anaerobic Bacteria

Abstract: An agar dilution method for susceptibility testing of anaerobic bacteria was evaluated to determine whether results obtained would be consistent enough to recommend it as a reference method. The study was conducted in 10 laboratories where the minimum inhibitory concentrations of six antibiotics (carbenicillin, cefoxitin, chloramphenicol, clindamycin, penicillin G, and tetracycline) were determined against 10 bacterial strains on Wilkins-Chalgren agar prepared by three manufacturers. Minimum inhibitory concentrations falling on the modes varied from 57 to 80% of all determinations and on the mode or within +/-1 log(2) dilution of the mode from 87 to 100% within each laboratory. When data from all laboratories were pooled, minimum inhibitory concentrations from each laboratory agreed with the overall mode 48 to 71% of the time, with an overall agreement at +/-1 log(2) dilution of 96%. This degree of reproducibility allows for recommendation of the procedure as a reference method. Results with three of the test strains were very consistent, and these strains are recommended as control strains: Clostridium perfringens ATCC 13124, Bacteroides fragilis ATCC 25285 and Bacteroides thetaiotaomicron ATCC 29741. The minimum inhibitory concentrations for these strains were on the mode or within +/-1 log(2) dilution of the mode 98, 99, and 99% of the time, respectively. The remaining anaerobic bacteria are recommended as reference strains.

Comparison of five mental workload assessment procedures in a moving-base driving simulator

Abstract: Five methods of measuring mental workload (secondary task performance, visual occlusion, cardiac arrhythmia, subjective opinion rating scales, and primary task performance) were compared for sensitivity to changes in operator loading. Each was used to differentiate among low, medium and high levels of workload defined in terms of the application point of crosswind gusts in a driving task. The driving task was produced using an automobile driving simulator with a six-degree of freedom computer generated display, a four-degree of freedom physical motions system, and a four-channel sound system. Gusts at the front of the vehicle represented high workload levels, and gusts toward the center of the vehicle represented progressively lower levels of workload. The results showed significant differences among workload levels for subjective opinion scales and primary performance measures of lateral deviation, yaw deviation, and steering reversals. A relative sensitivity estimate of these would be, from highest to lowest sensitivity, steering reversals and yaw deviation, rating scales, and lateral deviation. The techniques of occlusion, cardiac arrhythmia, and secondary task performance yielded no significant workload effect.

Physiological measures of aircrew mental workload.

Abstract: Physiological measures of aircrew mental workload were divided into fourteen specific classes. Each class was then summarized in terms of background, applications, and implications for research and...

Increasing tree search efficiency for constraint satisfaction problems

Abstract: In this paper we explore the number of consistency checks made by a tree search in order to solve binary constraint satisfaction problems. We show analytically and experimentally that the two principles of first trying the places most likely to fail and remembering what has been done to avoid repeating the same mistake twice improve the standard backtracking search. We experimentally show that a lookahead procedure called forward checking (to remember the future) which employs the most likely to fail principle performs better than standard backtracking, Ullman's, Waltz's, Mackworth's, and Haralick's discrete relaxation in all cases tested, and better than Gaschnigs backmarking in the larger problems.

Estimating the hazard of chemical substances to aquatic life

Abstract: The assessment of the hazard associated with the introduction of chemical substances into the environment is receiving considerable attention in current ecological, political, and public forums. The purpose of this paper is to identify and evaluate the basic concepts involved in assessing the hazard of chemical substances to aquatic life. A conceptual framework for conducting a hazard assessment is elaborated. In addition, several proposed procedures for conducting aquatic hazard assessment are compared and contrasted. A discussion of the decision criteria currently utilized in hazard assessment procedures is included. The use of safety factors or ‘uncertainty factors’ as a central concept in a sequential testing approach is presented. An assessment of the ‘state-of-the-art’ in aquatic hazard assessment and recommendations for suceeding stpes in the development of procedures constitute the conclusion of the paper.

Spatial variability of soils

Abstract: Place-to-place variation within soil units influences the study and use of soil, but is seldom formally acknowledged in soil maps and descriptions. Research on soil variation could be improved by increased coordination of experimental designs and by application of statistical methods suitable for analysis of place-to-place variation, including statistical functions such as spatial autocorrelation. Eventually it may be possible to estimate spatial variation in unstudied soils by means of easily observable landscape characteristics used as surrogates for soil variability.

A convergence proof for a hyperstable adaptive recursive filter (Corresp.)

Abstract: Hyperstability, a concept from nonlinear stability theory, is used to develop a real-time adaptive recursive filter useful in a nonstationary environment.

Mutagens in the feces of 3 South-African populations at different levels of risk for colon cancer.

Abstract: The incidence of mutagens in the feces of 3 South-African populations at different risk levels for colon cancer has been determined Lyophilized fecal samples were extracted with ether and the mutagenicity of the extracts determined using the Salmonella/mammalian microsome mutagenicity test 19% of the samples from urban white South-Africans, a population at a high risk for colon cancer, were mutagenic using Salmonella typhimurium strain TA100 This incidence was significantly greater (p less than 0001) than the incidence of mutagen excretion in the low-risk populations of urban blacks (2%) and rural blacks (0%) This pattern was also obtained using Salmonella typhimurium strain TA98 The incidence of mutagen excretion for urban whites was 10%, as compared to 5% and 2% for urban and rural blacks, respectively

Thermography — An NDI Method for Damage Detection

Abstract: Video-thermography, the time-resolved observation of infrared radiation, is a nondestructive inspection technique which offers many potential applications in the study of material behavior. The present work emphasizes detection of damage in both homogeneous and composite materials. This work differs from most others because the materials are subjected to some steady-state mechanical energy, such as fatigue loads or low-amplitude vibrations, that activates heat sources near the damaged regions. Experimental observations are discussed for a variety of materials, including boron/aluminum, boron/epoxy, graphite/epoxy, aluminum, and plastics. Thermography has been used to investigate initiation and progression of subsurface damage caused by fatigue; vibrothermography has been used to locate delaminations and similar damaged regions. Discussed are several analytical studies of the relation between evolution of heat and the stress field in the region of the damaged zone, and the expected surface heat pattern from a subsurface heat source in an anisotropic material.

The effect of Appalachian Mountain topography on seismic waves

Abstract: A field program was conducted during the summer of 1977 in the Appalachian Mountains to study some of the effects of topography on seismic-wave motions. The study areas included Powell Mountain (394 m of relief) in Lee County, Virginia, Bays and River Mountains (260 m of relief) in Sullivan County, Tennessee, and Gap and Brush Mountains (236 m of relief) in Montgomery County, Virginia. The majority of the data were recorded using 1 Hz horizontal seismometers aligned parallel to the long dimension of the northeast trending ridges. Some vertical (1 Hz) data were also collected. The signal sources were quarry and mine blasts located mostly to the west and northwest of the study areas. The Tennessee earthquake of July 27, 1977 [ m b (Lg) = 3.5] was recorded at Bays and River Mountains by both horizontal and vertical sensors. The basic data consist of maximum amplitudes and their associated periods measured from the Sg-Lg coda (some Rayleigh-wave and P -wave data were also obtained) at various sites on the ridges and in the valleys. In total, 137 events were considered from which 444 measurements of trace amplitude and wave period were made. These were cast in the form of 382 amplitude ratios between the individual sites. Four of the five ridges (Powell Mountain, Gap Mountain, Bays Mountain, and River Mountain) show amplification at the mountaintops with respect to the valleys. However, one ridge, with a less pronounced crest than the others (Brush Mountain), exhibited some wave-amplitude suppression. The vertical data obtained display a lesser degree of amplification than do the horizontal data as might be expected from other published observations. To reduce the scatter found in the individual amplitude ratios, average amplitude ratios between mountaintop and valley sites were determined. These average ratios showed that the seismic wave amplitudes at the mountaintops were amplified by factors from 1.7 to 3.4. Employing the theory for scattering of SH waves in a half-space with an irregular free surface, the predicted ground motions for each of the study areas were obtained. The comparison of the observed average ratios with these theoretical calculations indicates that a topographic effect is present but inadequately modeled by the theory.

On the relation between modified Mercalli intensity and body-wave magnitude

Abstract: This paper is concerned with estimating body-wave magnitude, mb , from the intensity distribution of an earthquake. Initially, it is assumed that modified Mercalli (MM) intensity values are directly related to the ( A/T ) z values of 1-Hz, Lg -wave ground motion. By comparison with the intensity values of a reference earthquake, magnitudes are calculated for 41 western and central United States earthquakes. Magnitudes of these earthquakes also are determined independently, in the conventional manner, using teleseismic P -wave amplitudes. Comparison of the two sets of magnitude values indicates that the assumed relation between 1-Hz, Lg -wave ( A/T ) z values and MM intensity does not hold exactly over the mb range of 4.0 to 6.2. An empirical equation is derived to adjust the mb values obtained from intensity data so that they agree with the teleseismic P -wave magnitudes. The method then is applied to estimate mb of some historical earthquakes which occurred prior to 1962. These include the set for which Kanamori and Jennings (1978) estimated ML from strong-motion accelerograms. Some noteworthy United States earthquakes also are considered. These include: the 1811 New Madrid earthquake for which mb is estimated to be 7.3; the 1886 Charleston, South Carolina earthquake, for which mb is estimated to be 6.6 to 6.9; the 1897 Giles County, Virginia earthquake, for which mb is estimated to be 5.8; the 1906 San Francisco, California earthquake, for which mb is estimated to be 6.8 to 7.1. The intensity-attenuation method cannot be used for estimating mb of all historical earthquakes because the intensity data are not always adequate. In some cases, however, the total felt area or the area enclosed by the Modified Mercalli IV isoseism can be determined. It was found that empirical equations relating mb to these areas, which were derived for central and northeastern United States earthquakes, also apply for events in the southeast. These empirical methods are used to estimate mb values for a set of historical Virginia earthquakes.

Heats of reaction and kinetics of a thermoset polyester

Abstract: The curing reaction of a thermoset polyester was investigated by using the isothermal and dynamic techniques of differential scanning calorimetry (DSC). The heats of reaction (at different curing temperatures) and a kinetic expression of the crosslinking reaction are presented and compared to the results of the previous studies. The proposed kinetic model can be utilized to obtain the rates of heat generation and the extent of cure at different cure temperatures and time. The overall activation energy of the curing reaction was calculated on the basis of experimental data as 17.0 kcal/mole and the overall reaction rate constant as 2.60 × 109 exp (−17,000/RT) min−1.