Showing papers by "University of Maryland, College Park published in 1971"
1,005 citations
TL;DR: Simple sets of parallel operations are described which can be used to detect texture edges, "spots," and "streaks" in digitized pictures and it is shown that a composite output is constructed in which edges between differently textured regions are detected, and isolated objects are also detected, but the objects composing the textures are ignored.
Abstract: Simple sets of parallel operations are described which can be used to detect texture edges, "spots," and "streaks" in digitized pictures. It is shown that, by comparing the outputs of the operations corresponding to (e.g.,) edges of different sizes, one can construct a composite output in which edges between differently textured regions are detected, and isolated objects are also detected, but the objects composing the textures are ignored. Relationships between this class of picture processing operations and the Gestalt psychologists' laws of pictorial pattern organization are also discussed.
811 citations
TL;DR: In this article, a set of intermediate-frequency long-wavelength waves were found to be unstable for any temperature ratio, and growth rates were on the order of the ion plasma (or lower hybrid) frequency, depending on the density and field strength.
Abstract: Electrons drifting relative to ions across a magnetic field are found to drive a set of intermediate-frequency long-wavelength waves (${\ensuremath{\omega}}_{\mathrm{ci}}l\ensuremath{\omega}l{\ensuremath{\omega}}_{\mathrm{ce}}$) unstable for any temperature ratio $\frac{{T}_{e}}{{T}_{i}}$ One instability is caused by the coupling of a drift wave in a nonuniform plasma to either the ion plasma oscillation or a lower hybrid oscillation, depending on density and field strength. Another instability is a form of the two-stream instability, shown here to exist even for drift speeds less than electron thermal speeds. Growth rates are on the order of the ion plasma (or lower hybrid) frequency, depending on the density and field strength.
359 citations
TL;DR: In this article, the authors assume that the asthenosphere is "soft" enough so that it does not transmit significant horizontal shear stress to the overlying lithosphere, and they show that any thermal mantle convection is likely to have its origin in cooling of the top layers of the oceanic mantle rather than being due to any heating that may arise farther down.
Abstract: The basis of this theoretical paper is the assumption that the asthenosphere is ‘soft’ enough so that it does not transmit significant horizontal shear stress to the overlying lithosphere. It is pointed out that any thermal mantle convection is likely to have its origin in the cooling of the top layers of the oceanic mantle rather than being due to any heating that may arise farther down. Next, there is geological evidence for the existence of regions that exhibit widespread horizontal tension, e.g., in East Africa. Submarine ridges can justifiably be considered as regions of horizontal tensile stress. In our model, the choice of mechanisms that can generate such stresses is severely limited; the one found to be satisfactory qualitatively and quantitatively arises through the disappearance of pieces of lithosphere, which slide down along the Gutenberg-Benioff fault zones. The lithosphere spreads to fill the gaps created. It is shown that this motion is likely to represent the surficial part of a thermally driven conveetive circulation in the mantle. The nature of the ‘return flow’ farther down is discussed.
312 citations
TL;DR: It is proved that several algorithms which perform a thinning transformation when applied to the picture in parallel do not change the connectivity properties of the picture.
Abstract: If a picture contains elongated objects of different thicknesses, one can make measurements on it which are thickness-invariant by first transforming it so that each object is thinned down to a \"medial line\" of constant thickness. Several algorithms are described which perform such a thinning transformation when applied to the picture in parallel. It is proved that these algorithms do not change the connectivity properties of the picture.
278 citations
TL;DR: Gas and thin layer chromatography and mass spectroscopy in particular, have been used to resolve some of the confusion concerning the sterol composition of algae.
Abstract: Available analytical techniques are now sufficient for the separation and identification of sterols from complex mixtures in plants. Gas and thin layer chromatography and mass spectroscopy in particular, have been used to resolve some of the confusion concerning the sterol composition of algae. Red algae (Rhodophyta) contain primarily cholesterol, although several species contain large amounts of desmosterol, and one species contains primarily 22-dehydrocholesterol. Only a few Rhodophyta contain traces of C-28 and C-29 sterols. Fucosterol is the dominant sterol of brown algae (Phaeophyta), apparently the major sterol of every species examined. Most Phaeophyta also contain traces of cholesterol and biosynthetic precursors of fucosterol. The sterols of green algae (Chlorophyta) are much more varied and complex than those of other groups of algae. Whereas the Phaeophyta and Rhodophyta contain one primary sterol, many of the Chlorophyta contain a complex mixture of sterols such as occurs in higher plants. The Chlorophyta contain such sterols as chondrillasterol, poriferasterol, 28-isofucosterol, ergosterol, cholesterol and others. Sterol composition may be of value in the systematics of plants such as the Chlorophyta. Recently (for the first time) complex mixtures of sterols have been isolated in very small amounts in the blue-green algae (Cyanophyta). Available data on the sterols of other groups of algae are insufficient for making useful comparisons.
253 citations
TL;DR: In this article, the problem of designing compensators, the dimensions of which are fixed a priori, for linear systems is considered, and two types of compensators are considered: static (gain only) compensators which operate directly upon the output signals to generate the controls, and dynamic compensators of fixed dimension.
Abstract: This paper considers the problem of designing compensators, the dimensions of which are fixed a priori, for linear systems. Two types of compensators are considered: first, static (gain only) compensators which operate directly upon the output signals to generate the controls, and second, dynamic compensators of fixed dimension. The equations that define the parameters of such compensators are developed.
194 citations
TL;DR: A spectrum of possibilities has been demonstrated, placing several apparently conflicting recent results in perspective.
186 citations
TL;DR: In this paper, a generalization of the results about short distance (xμ → 0) behaviour in quantum field theory is presented, where the authors show that the light cone behaviour is similar to the one described in this paper.
179 citations
TL;DR: The data for 3C 279, interpreted in terms of a symmetric double-source model and the accepted red-shift distance, indicate differential proper motion corresponding to an apparent speed about ten times that of light.
Abstract: Recent Goldstone-Haystack radio interferometric observations of the quasars 3C 279 and 3C 273 reveal rapid variations in their fine structure. Most notably, the data for 3C 279, interpreted in terms of a symmetric double-source model and the accepted red-shift distance, indicate differential proper motion corresponding to an apparent speed about ten times that of light. A number of possible mechanisms that might give rise to such an apparent speed are considered; although several may be plausible, no definitive choice can be made on the basis of present evidence. More interferometric observations of quasars are clearly needed to clarify their structure and internal kinematics.
175 citations
TL;DR: In this paper, the asymptotic time behavior of the velocity autocorrelation function and of the kinetic parts of the correlation functions for the shear viscosity and the heat conductivity is derived on the basis of a local equilibrium assumption and the linearized Navier-Stokes equations.
Abstract: The asymptotic time behavior ($\ensuremath{\sim}c{t}^{\ensuremath{-}\frac{d}{2}}$, where $d$ is the dimensionality of the system) of the velocity autocorrelation function and of the kinetic parts of the correlation functions for the shear viscosity and the heat conductivity is derived on the basis of a local equilibrium assumption and the linearized Navier-Stokes equations. The coefficients $c$ are expressed in terms of the transport coefficients and thermodynamic quantities. The physical mechanism responsible for the long-time tail is indicated, and the connections between the present work and investigations based on molecular dynamics and on kinetic theory are discussed.
TL;DR: In this paper, the electronic structure of binary alloys is discussed for a system in which both the atomic energy levels and the hopping integrals are random quantities, and three self-consistent equations are obtained that must be solved simultaneously; these replace the single CPA equation.
Abstract: The electronic structure of binary alloys is discussed for a system in which both the atomic energy levels and the hopping integrals are random quantities. This paper is a detailed study of the generalization of the coherent-potential approximation (CPA) introduced earlier by the present authors. We show that a locator description provides a particularly suitable formalism for setting up this generalized problem and how, with the aid of a simple device, configuration averaging may be performed by the use of established techniques. The approximation used is, as in the case of the usual CPA, a single-site one. Three self-consistent equations are obtained that must be solved simultaneously; these replace the single CPA equation. Numerical results are displayed for a series of alloys, and a discussion of certain aspects of the theory, such as its moment-preserving properties, is also included.
TL;DR: In this article, the authors describe a visual simulation technique by which fully computer-generated perspective views of three-dimensional objects may be produced, based on a relatively simple geometric modeling technique for the mathematical representa tion of the three elements essential to the picture-taking process.
Abstract: This paper describes a visual simulation technique by which fully computer-generated perspective views of three-dimensional objects may be produced. The method is based on a relatively simple geometric modeling technique for the mathematical representa tion of the three elements essential to the picture- taking process, namely, a camera, a light source, and the object or objects to be photographed. Once these three basic components have been defined, geometric ray tracing is employed to compute a "picture" of the object as it appears in the simu- Zated camera. In essence, individual light rays are traced from their source to the surface of the object. The reflected component of each ray is computed and traced to its point of intersection with the film plane. Thus, each reflected ray pro vides the intensity at a single point on the pic ture, and, when a sufficient number of points have been computed, the entire area of intensity data may be displayed on a cathode ray tube. Several examples of the pictorial...
TL;DR: A field experiment is described which uses the Delphi Process to assign subjective probabilities to the set of possible demand levels for a company's product.
Abstract: This article describes a field experiment which uses the Delphi Process to assign subjective probabilities to the set of possible demand levels for a company's product. The method is validated by t...
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TL;DR: In this paper, a method for the analysis of scattering from periodic structures based on the numerical solution of the integral equations is further developed using periodicity (Floquet's theorem), where the range of integral equations are reduced to a single period where the kernels are the Green's functions for periodic arrays.
Abstract: A method for the analysis of scattering from periodic structures based on the numerical solution of the integral equations is further developed. Using periodicity (Floquet's theorem), the range of the integral equations is reduced to a single period where the kernels are the Green's functions for periodic arrays. The numerical solution of the integral equations is obtained using the method of moments. Efficient numerical methods for the computation of the periodic Green's functions which allows their rapid evaluation with good accuracy are reported. A new treatment of the singularities which includes the effect of the surface curvature is given. Numerical results for the transverse electric scattering from a conducting surface with a sinusoidal height profile are presented, and several interesting physical phenomena are explored including Brewster angle effects and diffraction grating anomalies.
TL;DR: In this paper, a generalization of the Navier-Stokes equation, valid for wavelengths and times of a molecular order of magnitude, is discussed on the basis of viscoelastic behavior of simple classical liquids.
Abstract: A generalization of the Navier-Stokes equation, valid for wavelengths and times of a molecular order of magnitude, is discussed on the basis of viscoelastic behavior of simple classical liquids. In this theory, transport coefficients are replaced by appropriate viscoelastic memory functions. The theory is verified by analyzing the data on current-correlation functions obtained from computer experiments. Three different models for the time dependence of the viscoelastic memory are investigated, namely, a single-exponential decay, a modified-exponential decay, and a Gaussian decay. It is obsrved that the memory functions are approximately Gaussian, at least for times of the order of one or two relaxation times. This is in agreement with a conjecture of Forster, Martin, and Yip. The wave-number dependence of the half-width of the Gaussian decay, and of the longitudinal- and shear-viscosity coefficients, are found from computer experiments. The extrapolated values of these transport coefficients, in the limit $k\ensuremath{\rightarrow}0$, are in good agreement with experiments on liquid argon.
TL;DR: Although the specific site of action was not elucidated, BCM appears to interfere with DNA synthesis or some closely related process such as nuclear or cell division.
TL;DR: It is concluded that Plethodon c.
Abstract: Plethodon richmondi shenandoah occurs in at least three geographically isolated talus slopes in Shenandoah National Park, Virginia, USA, each surrounded by a continuous population of Plethodon c cinereus in the soil outside the talus Distributions are contiguous but largely non-overlapping The talus presents a much drier habitat than does the surrounding soil Four experiments were designed to test the responses of the two species to moisture and substrate Although shenandoah lives in a habitat generally drier than that of cinereus, both species choose the wet end of a moisture gradient and do not differ significantly in moisture preference When given choices between a substrate of rock or soil, the two species respond similarly: neither expresses a preference when both substrates are moist and both choose soil over rock as the substrates dry, showing that substrate preference is based on moisture content and not texture A third experiment demonstrates that cinereus suffers significantly greater mortality and loss of body water when subjected to a drying rock substrate than when subjected to a soil substrate, since the latter holds moisture longer Thus the talus most likely presents a greater stress of dehydration to salamanders than does the soil A fourth experiment shows that when forced to dehydrate, shenandoah survives longer, loses significantly less body water per hour, and withstands a greater loss of body water before death than does cinereusThe conclusions drawn are that cinereus inhabits areas of deep soil not due to a preference for that substrate but due to the requirement of a moist substrate, and it cannot enter the talus due to the dry conditions there P r shenandoah, on the other hand, neither prefers the rocky nor the dry conditions of the talus and is probably excluded from the soil by the presence of cinereus The survival of shenandoah in the talus is due, at least in part, to its ability to withstand the stress of dehydration for a longer period than can cinereus
TL;DR: In this paper, the viscosity of nitrogen, argon, and helium at 25°C was measured over a nominal range of pressures 1 −100 atm and at very closely spaced density intervals.
01 Jan 1971
TL;DR: In this article, the authors explore singularities in interface problems, where two interface curves cross, where an interface curve meets the boundary, or where a boundary has a discontinuous tangent (a corner).
Abstract: Publisher Summary This chapter explores singularities in interface problems. It presents the interface problem for second-order elliptic partial differential equations in two independent variables. The behavior of the solution is determined at the singular points of the problem: where two interface curves cross, where an interface curve meets the boundary, or where an interface or boundary has a discontinuous tangent (a corner). The chapter presents the application of these two dimensional results to analogous problems in three dimensions. The methods presented in the chapter are similar to those used by Birman and Skvorcov in studying the effect of a corner on the solution of an elliptic boundary value problem. The chapter also discusses a few results on higher dimensional corners. It presents a density theorem in two dimensions.
TL;DR: In this paper, an open semioroup of 3 is called an F-semigroup/f (i) a, b ~ 3 and ab = ba E ~ imply a ~ and b ~ ~, and (ii) there exists a closed ideal R such that ~ = q-1 (S), where S is an open semiigroup in ~B/R containin 9 G and havin 9 the property that S\G is also open.
Abstract: Definition 1. An open semioroup ~ of ~3 will be called an F-semigroup/f (i) a, b ~ ~3 and ab = ba E ~ imply a ~ ~ and b ~ ~, and (ii) there exists a closed ideal R such that ~ = q-1 (S), where S is an open semigroup in ~B/R containin 9 G and havin 9 the property that S\G is also open. It is clear that ~ contains the invertible elements of ~B, and that ~+-qc~. (1-1) If a ~ ~ and if~a is the (maximal connected open) component of~ containing a, then a + R C ~a.
TL;DR: The Hamiltonian for orbits near ℒ4 and mass ratios near μ1 was brought into a normal form by as discussed by the authors, who showed that two coefficients in this expansion predict the behavior of the periodic orbits.
Abstract: The Hamiltonian for orbits near ℒ4 and mass ratios near μ1 is brought into a normal form A theorem shows that two coefficients in this expansion predict the behavior of the periodic orbits
TL;DR: Elementary school boys, whom their teachers had selected as being among the three most hyperactive in their classes, were found to have significantly more minor physical anomalies than boys selected as not being hyperactive.
Abstract: Elementary school boys, whom their teachers had selected as being among the three most hyperactive in their classes, were found to have significantly more minor physical anomalies than boys selected as not being hyperactive.
TL;DR: In this paper, it was shown that the experimental data for the thermal conductivity of a gas becomes infinite at the critical point and that the values reported in the literature for the critical exponent of the Rayleigh linewidth should be revised downwards.
Abstract: The thermal conductivity of a gas becomes infinite at the critical point. It is shown that the experimental data for the thermal conductivity of C${\mathrm{O}}_{2}$ satisfy scaling-law relations very similar to those previously established for equilibrium properties near the critical point. The analysis also suggests that the values reported in the literature for the critical exponent of the Rayleigh linewidth should be revised downwards.
TL;DR: In this paper, the authors derived linear transport laws for the motion of the average position and velocity of an oscillator undergoing ordinary Brownian motion, and the resulting linear equations are valid for only small deviations of average values from thermal equilibrium.
Abstract: Starting with the Langevin equation for a nonlinear oscillator (the “Duffing oscillator”) undergoing ordinary Brownian motion, we derive linear transport laws for the motion of the average position and velocity of the oscillator. The resulting linear equations are valid for only small deviations of average values from thermal equilibrium. They contain a renormalized oscillator frequency and a renormalized and non-Markovian friction coefficient, both depending on the nonlinear part of the original equation of motion. Numerical computations of the position correlation function and its spectral density are presented. The spectral density compares favorably with experimental results obtained by Morton using an analog computer method.
TL;DR: The isolation of a new bovine herpesvirus is described and its effect on experimentally infected calves is described to study the pathogenicity of the agent.
TL;DR: It is hypothesized that the stereotypy of the Black-throated Green Warbler represents an adaptation to the extremely high density it experiences in large populations, which make up the major part of the gene pool.
Abstract: In this paper I attempt to answer the question, What (if any) differences occur in the foraging of isolated wood warblers (Parulidae) and ones in large multispecies populations? Parula (Parula americana), Myrtle (Dendroica coronata), and Black-throated Green (D. virens) Warblers were studied on seven small spruce-clad islands off the coast of Maine, each island supporting one pair of one to three of these species. Data obtained were compared with earlier studies of these species in large adjacent populations. Though seasonally isolated, all individuals belonged to the large gene pools of the appropriate species on the adjoining mainland. While the insular forests resemble those of the mainland, they are in general shorter and more open. When only one species was present, it was always the Parula Warbler; when two species were present, they were always the Parula and Myrtle. Black-throated Green Warblers only occurred in the presence of the latter two species. diversity increased as the size of forest and proportion of foliage in tree crowns grew. Parula and Myrtle Warblers experienced greater nesting success than Black-throated Green Warblers. Black-throated Green Warblers foraged much as they did in large populations; however, Myrtle and Parula Warblers demonstrated considerably more plasticity in foraging. When Black-throated Green Warblers were absent, the two other species tended to modify their foraging. On the one island studied in detail where only Parula Warblers occurred, they appeared to expand their foraging range farther than where Myrtle Warblers were present. Overlap in foraging usually decreased as species compositions became more depauperate. Though variability occurred among individuals of each species, variability of an individual in two different years appeared as great. Black-throated Green Warblers dominate the other two species socially, and the implications of this situation upon distributions in larger populations and on small islands are discussed. I hypothesize that the stereotypy of the Black-throated Green Warbler represents an adaptation to the extremely high density it experiences in large populations, which make up the major part of the gene pool. The higher degree of plasticity seen in Parula and Myrtle Warblers may be appropriate to their subordinate roles.