Showing papers by "University of Maryland, College Park published in 1977"
TL;DR: A simplified scheduling problem involving identical processors and restricted task sets is shown to be P-complete, however, the LPT algorithm applied to this problem yields schedules which are near optimal for large n .
Abstract: The finishing time properties of several heuristic algorithms for scheduling n independent tasks on m nonidentical processors are studied. In particular, for m = 2 an n log n time-bounded algorithm is given which generates a schedule having a finishing time of at most (√5 + 1)/2 of the optimal finishing time. A simplified scheduling problem involving identical processors and restricted task sets is shown to be P-complete. However, the LPT algorithm applied to this problem yields schedules which are near optimal for large n.
815 citations
TL;DR: Finite input-output specifications are added to the syntax of programs so that they exercise the control and expression structure of a program as well as any tests can and can be verified at compile time.
Abstract: if finite input-output specifications are added to the syntax of programs, these specifications can be verified at compile time. Programs which carry adequate tests with them in this way should be resistant to maintenance errors. If the specifications are independent of program details they are easy to give, and unlikely to contain errors in common with the program. Furthermore, certain finite specifications are maximal in that they exercise the control and expression structure of a program as well as any tests can.
552 citations
TL;DR: A method for detecting sharp "corners" in a chain-coded plane curve is described and a measure for the prominence ("cornerity") of a corner is introduced.
Abstract: A method for detecting sharp "corners" in a chain-coded plane curve is described. A measure for the prominence ("cornerity") of a corner is introduced. The effectiveness of the method is illustrated by means of a number of examples.
531 citations
TL;DR: Examined the relationship between managerial locus of control (Rotter's Internal-External Control Scale), perceived stress (Subjective Stress Scale), coping behaviors (task- vs emotion-centered as defined in the R. L. Kahn et al 1964 typology), and performance (credit ratings).
Abstract: Examined the relationship between managerial locus of control (Rotter's Internal-External Control Scale), perceived stress (Subjective Stress Scale), coping behaviors (task- vs emotion-centered as defined in the R. L. Kahn et al 1964 typology), and performance (credit ratings). 90 small business own
429 citations
TL;DR: In this article, a number of simple and inexpensive enhancement techniques are suggested to make use of easily computed local context, features to aid in the reassignment of each point's gray level during histogram transfomation.
383 citations
TL;DR: The Vibrio cholerae strains isolated from Chesapeake Bay represent serotypes other than O-group I--that is, so-called nonagglutinable vibrios--and are not recognized as a serious epidemic threat, although they have caused cholera-like diarrhea sporadically.
Abstract: Vibrio cholerae was isolated at several locations in Chesapeake Bay in fall 1976 and spring 1977. Strains induced fluid accumulation in rabbit ileal loops and positive activity in Y-1 adrenal cells. Vibrio cholerae, Vibrio parahaemolyticus, and related vibrios show a spatial and temporal distribution characteristic of Vibrio species in an estuary. The Vibrio cholerae strains isolated from Chesapeake Bay represent serotypes other than O-group I--that is, so-called nonagglutinable vibrios--and are not recognized as a serious epidemic threat, although they have caused cholera-like diarrhea sporadically.
332 citations
TL;DR: This paper suggests that sex roles may be seen as the result of status processes and men are expected to be more competent than women and it is expected that competitive or dominating behavior is legitimate for men but not for women.
Abstract: In the past, sociologists have proposed that men and women approach situations in which they have to work with other people differently; that men are "task" or "instrumental" specialists, while women are "social" or "expressive" specialists. Subsequent advances in research on the social psychology of small groups, on families, and on personality has largely removed the theoretical and empirical supports for this proposition. On the other hand, researchers continue to observe sex differences in behavior in a variety of taskoriented situations. This paper suggests that sex roles may be seen as the result of status processes. Since men have higher status than women, men are expected to be more competent than women and it is expected that competitive or dominating behavior is legitimate for men but not for women. Empirical studies of sex roles as related to task appropriateness, group problem solving, conflict, dominating behavior and role expectations are reviewed in support of this theory.
329 citations
TL;DR: In this article, the local dispersion relation for the lower-hybrid-drift (LHD) instability is derived and analyzed, taking into account the finite-beta effects associated with transverse electromagnetic perturbations as well as with resonant and nonresonant electron-orbit modifications due to magnetic-field gradients.
Abstract: The local dispersion relation for the lower-hybrid-drift (LHD) instability is derived and analyzed, taking into account the finite-beta effects associated with transverse electromagnetic perturbations as well as with resonant and nonresonant electron-orbit modifications due to magnetic-field gradients The influence of finite-beta effects on the LHD instability is calculated in a fully self-consistent manner for arbitrary values of electron-ion temperature ratio, local beta, cross-field ExB velocity/ion thermal speed ratio, and other plasma parameters Stability properties are investigated analytically for the case of cold electrons, and the local dispersion relation is solved numerically in the parameter regime of most interest for high-density plasma pinches The results show that for all parameter regimes studied, the net effect of finite plasma beta is to reduce the maximum growth rate of the LHD instability, although the details can vary, depending on the plasma parameters Except in the limit where the electron/ion temperature ratio tends to zero, it is found that there is a critical value of plasma beta above which the LHD instability is completely stabilized
315 citations
TL;DR: In this paper, a fluctuating-local-band theory was proposed, which generalizes the old localized-itinerant complementarity, and the range of validity of the theory was shown to extend well above the Curie temperature.
Abstract: Itinerant ferromagnetism, particularly in iron, nickel, and cobalt, is described by a fluctuating-local-band theory, a new concept which generalizes the old band theory. In this description, the old unexplained localized-itinerant complementarity is resolved. It is noted that band structure itself is determined locally, on the scale of a few neighbors, and that the main coordinate which changes in space and time is $\stackrel{^}{M}$, the collective variable representing the magnetization direction. Because these changes are relatively slow, their effects on band structure can be calculated in a perturbation theory. It is stressed that the classical variable $\stackrel{^}{M}$ is appropriate, even though quantization is in some cases eventually necessary. In this paper a ferromagnetic-Fermi-liquid theory is set up and compared with previous versions which it generalizes. The range of validity of the theory is shown to extend well above ${T}_{C}$, the Curie temperature. Some estimates of ${T}_{C}$ on the basis of the new theory are obtained, which are encouraging. Agreement with a range of experiments is found. Papers II and III discuss nonlinear magnetization-fluctuation interactions, and their bearing on experiment.
259 citations
TL;DR: In this article, two related probabilistic models that can be used for making classification decisions with respect to mastery of specific concepts or skills are presented, and procedures for assessing the adequacy of the models, identifying optimal decision rules for mastery classification, and identifying minimally sufficient numbers of items necessary to obtain acceptable levels of misclassification.
Abstract: Descriptions are presented of two related probabilistic models that can be used for making classification decisions with respect to mastery of specific concepts or skills. Included are the development of procedures for: (a) assessing the adequacy of “fit” provided by the models; (b) identifying optimal decision rules for mastery classification; and (c) identifying minimally sufficient numbers of items necessary to obtain acceptable levels of misclassification.
254 citations
TL;DR: It is suggested that platelet MAO consists of essentially one distinguishable form of MAO which most closely resembles the MAO type B found in other tissues.
TL;DR: A relaxation process is described and is applied to the detection of smooth lines and curves in noisy, real world images, effective even for curves of low contrast, and even when many curves lie close to one another.
Abstract: A relaxation process is described and is applied to the detection of smooth lines and curves in noisy, real world images. There are nine labels associated with each image point, eight labels indicating line segments at various orientations and one indicating the no-line case. Attached to each label is a probability. In the relaxation process, interaction takes place among the probabilities at neighboring points. This permits line segments in compatible orientations to strengthen one another, and incompatible segments to weaken one another. Similarly, no-line labels are reinforced by neighboring no-line labels and weakened by appropriately oriented line labels. This process converges, in only a few iterations, to a condition in which points lying on long curves have achieved high line probabilities, while other points have high no-line probabilities, There is some tendency, under this process, for curves to thicken; however, a thinning procedure can be incorporated to counteract this. The process is effective even for curves of low contrast, and even when many curves lie close to one another.
TL;DR: No statistically significant difference between flowchart and nonflowchart groups has been shown, thereby calling into question the utility of detailed flowcharting.
Abstract: This paper describes previous research on flowcharts and a series of controlled experiments to test the utility of detailed flowcharts as an aid to program composition, comprehension, debugging, and modification. No statistically significant difference between flowchart and nonflowchart groups has been shown, thereby calling into question the utility of detailed flowcharting. A program of further research is suggested.
TL;DR: In this article, it was shown that filamentary plasma elements stretched out from the sun can penetrate impulsively and become engulfed into the magnetosphere, and the diamagnetic effects associated with these plasma inhomogeneities are observed in outer magnetospheres and magnetosheaths as dips or directional discontinuities in the magnetic field measurements.
TL;DR: The computational cost of template matching can be reduced by using only a subtemplate, and applying the rest of the template only when the subtemplate's degree of match exceeds a threshold.
Abstract: The computational cost of template matching can be reduced by using only a subtemplate, and applying the rest of the template only when the subtemplate's degree of match exceeds a threshold. A probabilistic analysis of this approach is given, with emphasis on the choice of subtemplate size to minimize the expected computational cost.
TL;DR: The Low Energy Charged Particle (LECP) experiment on the Voyager spacecraft is designed to provide comprehensive measurements of energetic particles in the Jovian, Saturnian, Uranian and interplanetary environments as mentioned in this paper.
Abstract: The Low Energy Charged Particle (LECP) experiment on the Voyager spacecraft is designed to provide comprehensive measurements of energetic particles in the Jovian, Saturnian, Uranian and interplanetary environments. These measurements will be used in establishing the morphology of the magnetospheres of Saturn and Uranus, including bow shock, magnetosheath, magnetotail, trapped radiation, and satellite-energetic particle interactions. The experiment consists of two subsystems, the Low Energy Magnetospheric Particle Analyzer (LEMPA) whose design is optimized for magnetospheric measurements, and the Low Energy Particle Telescope (LEPT) whose design is optimized for measurements in the distant magnetosphere and the interplanetary medium. The LEMPA covers the energy range from ∼10 keV to > 11 MeV for electrons and from ∼15 keV to ≳ 150 MeV for protons and heavier ions. The dynamic range is ∼0.1 to ≳ 1011 cm−2 sec−1 sr−1 overall, and extends to 1013 cm−2 sec−1 sr−1 in a current mode operation for some of the sensors. The LEPT covers the range ∼0.05 ≤ E ≳ 40 MeV/nucleon with good energy and species resolution, including separation of isotopes over a smaller energy range. Multi-dE/dx measurements extend the energy and species coverage to 300–500 MeV/nucleon but with reduced energy and species resolution. The LEPT employs a set of solid state detectors ranging in thickness from 2 to ∼2450 μ, and an arrangement of eight rectangular solid state detectors in an anticoincidence cup. Both subsystems are mounted on a stepping platform which rotates through eight angular sectors with rates ranging from 1 revolution per 48 min to 1 revolution per 48 sec. A ‘dome’ arrangement mounted on LEMPA allows acquisition of angular distribution data in the third dimension at low energies. The data system contains sixty-two 24-bit sealers accepting data from 88 separate channels with near 100% duty cycle, a redundant 256-channel pulse height analyzer (PHA), a priority system for selecting unique LEPT events for PHA analysis, a command and control system, and a fully redundant interface with the spacecraft. Other unique features of the LECP include logarithmic amplifiers, particle identifiers, fast (∼15 ns FWHM) pulse circuitry for some subsystems, inflight electronic and source calibration and several possible data modes.
TL;DR: In this article, a general theoretical formalism is presented which describes, in a self-consistent manner, the macroscopic transport produced by the (shortwave-length) turbulence associated with the microinstabilities enumerated above.
Abstract: The linear, non-linear, and anomalous transport properties associated with various microinstabilities driven by cross-field currents in high-temperature plasmas are reviewed. Particular emphasis is placed on instabilities pertinent to the implosion and post-implosion phases of theta-pinch plasmas, e.g. Buneman (electron-ion two-stream), ion acoustic, lower-hybrid-drift, electromagnetic ion cyclotron, and ion-ion cross-field instabilities. Analytic studies of the non-linear and quasi-linear evolution of these instabilities are presented, together with a detailed comparison with computer simulation experiments to test the validity of the various theoretical models and non-linear saturation mechanisms. A general theoretical formalism is presented which describes, in a self-consistent manner, the macroscopic transport produced by the (shortwave-length) turbulence associated with the microinstabilities enumerated above. The experimental evidence that such a self-consistent anomalous transport model is required for describing the implosion behaviour (characterized by diffuse current sheaths) in rapidly pulsed theta pinches is reviewed, together with the early attempts at modelling these implosions numerically with a one-fluid (MHD) model including artificial viscosity. It is shown that fluid-numerical simulations that include (at each space and time step) the effects of anomalous transport in a fully self-consistent manner, explain several features of the experimental observations. The relevance of reflected ions to sheath structure and implosion dynamics is also discussed, and state-of-the-art hybrid-numerical studies (Vlasov ions and fluid electrons) of pinch implosions are presented, which include reflected ion dynamics as well as the anomalous transport associated with cross-field instabilities. Finally, instability mechanisms for producing long-time interpenetration of plasma and magnetic field in post-implosion theta pinches are discussed, together with estimates of the anomalous resistivity.
TL;DR: In this paper, the effects of mixing various amounts of hydrogen-rich material into the intershell convective region of red giants undergoing helium shell flashes were examined, and it was shown that significant amounts of C-14 can be produced via the N-14(n, p)C-14 reaction.
Abstract: We have examined the effects of mixing various amounts of hydrogen-rich material into the intershell convective region of red giants undergoing helium shell flashes. We find that significant amounts of C-14 can be produced via the N-14(n, p)C-14 reaction. If substantial portions of this intershell region are mixed out into the envelopes of red giants, then C-14 may be detectable in evolved stars. We find a neutron flux many orders of magnitude above the flux required for the classical s-process, and thus an intermediate neutron process (i-process) may operate in evolved red giants. In all cases studied we find substantial enhancements of O-17. These mixing models offer a plausible explanation of the observations of enhanced O-17 in the carbon star IRC 10216. For certain physical conditions we find significant enhancements of N-15 in the intershell region.
TL;DR: The Glimm scheme for solving hyperbolic conservation laws has a stochastic feature; it depends on a random sequence, but this paper shows that the scheme converges for any equidistributed sequence, and thus the scheme becomes deterministic.
Abstract: The Glimm scheme for solving hyperbolic conservation laws has a stochastic feature; it depends on a random sequence. The purpose of this paper is to show that the scheme converges for any equidistributed sequence. Thus the scheme becomes deterministic.
01 Jun 1977
TL;DR: In this article, a method for computing stress intensity factors for cracks embedded in structural details is described, which consists of adding to accepted solutions for cracks in finite plates and bodies of uniform contour a geometry correction factor which accounts for the stress gradient produced by the geometric discontinuity of the detail.
Abstract: A method for computing stress intensity factors for cracks embedded in structural details is described. It consists of adding to accepted solutions for cracks in finite plates and bodies of uniform contour a geometry correction factor which accounts for the stress gradient produced by the geometric discontinuity of the detail. This correction factor is determined by integrating away the stresses normal to the line where the crack is to be inserted. The method is applied to the case of a crack emanating from a circular hole in a plate, and the results are found to be in good agreement with Bowie's numerical solution. Values of the stress intensity factor for cracks emanating from spherical weld porosities, and part-through cracks at stiffeners and cover plate ends are computed.
TL;DR: The theoretical consequences of assuming that a current flows along flaring arches consistent with a twist in the field lines of these arches are examined in this paper, and it is found that a sequence of magneto-hydrodynamic and resistive MHD instabilities driven by the assumed current (which they refer to as the toroidal current) can naturally explain most manifestations of a solar flare.
Abstract: The theoretical consequences of assuming that a current flows along flaring arches consistent with a twist in the field lines of these arches are examined. It is found that a sequence of magneto-hydrodynamic (MHD) and resistive MHD instabilities driven by the assumed current (which we refer to as the toroidal current) can naturally explain most manifestations of a solar flare.
TL;DR: Methods of detecting the angles and sides of a simple closed curve are developed that use approximations to the curve that have varying degrees of coarseness, and construct a hierarchy of angles and side that describes the curve at any desired level of detail.
Abstract: Methods of detecting the angles and sides of a simple closed curve are developed. These methods use approximations to the curve that have varying degrees of coarseness, and construct a hierarchy of angles and sides that describes the curve at any desired level of detail. The results can be used to obtain natural polygonal approximations to the curve.
01 Jul 1977-International Journal of Human-computer Studies \/ International Journal of Man-machine Studies
TL;DR: Experimental evidence is offered which supports the use of memorization/recall tasks as a further basis for judging program quality and programmer comprehension and a syntactic/semantic model of programmer behavior is presented.
Abstract: Judging the relative quality of computer programs and a programmer's comprehension of a given program has proven to be a difficult task. Ability to debug, modify, hand simulate execution or respond to questions about the program all have their weaknesses as comprehension metrics. This paper offers experimental evidence which supports the use of memorization/recall tasks as a further basis for judging program quality and programmer comprehension. A syntactic/semantic model of programmer behavior is presented to provide a basis for this hypothesis.
22 Aug 1977
TL;DR: Next, a procedure and framework for translating the declarative description of a mechanism into a population of associatively triggerable computation units is described, and the entire "Mechanisms Laboratory" is placed in the larger perspective of research into human problem solving.
Abstract: A theory of cause-effect representation is used to describe man-made mechanisms and natural laws. The representation, consisting of 10 link types that interconnect events into large declarative patterns, is illustrated on a relatively sophisticated device, the home gas forced air furnace, Next, a procedure and framework for translating the declarative description of a mechanism into a population of associatively triggerable computation units is described. The associative, of procedural, form can then be used to perform a discrete cause-effect simulation of the device. The declarative to procedural translation, including a simulation trace, is shown for the furnace. Topics of mechanism abstraction and mechanism invention are discussed, and the entire "Mechanisms Laboratory" is placed in the larger perspective of our research into human problem solving.
TL;DR: A new full-field technique for mapping lines of constant velocity in a fluid flow is demonstrated and is used with the established methods of speckle photography and interferometry to determine the velocity field.
Abstract: A new full-field technique for mapping lines of constant velocity in a fluid flow is demonstrated. The technique utilizes light scattered from scattering sites within a selected plane of interest of the flow field. The laser-speckle pattern thus formed is used with the established methods of speckle photography and interferometry to determine the velocity field. A double pulsed ruby laser is used to measure the velocity profile in a circular pipe. Turbulent flow fields will place a limitation on the technique; this limit is primarily a function of available equipment.
TL;DR: The results of the laboratory and field studies indicate that copepod can feed on ciliates and suggest that, in nature, ciliate may comprise an important source of food for copepods.
Abstract: Copepods of the genusEurytemora, isolated from the Patuxent River, a tributary of Chesapeake Bay, were fed suspensions of the ciliateUronema isolated from the Rhode River, a subestuary of Chesapeake Bay. Grazing by copepods was determined by the decrease in numbers of ciliates, which were monitored by both direct counting and particle size analysis. Results from both methods of analysis showed significant reduction in the numbers ofUronema in the suspension whenEurytemora was present. Survival of copepods with ciliates added as food source was significantly longer than without ciliates. Analysis of field samples collected in the fall showed that ciliates comprised approximately 20% of the total plankton biomass at selected sampling sites. The results of the laboratory and field studies indicate that copepods can feed on ciliates and suggest that, in nature, ciliates may comprise an important source of food for copepods.
TL;DR: The first optical absorption from excited states to autoionizing core-excited levels has been observed in lithium as discussed by the authors, where a 1MW dye laser tuned to the $1{s}^{2}2s\ensuremath{\rightarrow}1{ s}^{ 2}2p$ resonance produced a curve of the evolution from excited neutrals to 95% ions, and the significance of the Li observations for understanding the ionization mechanism was discussed.
Abstract: The first optical absorption from excited states to autoionizing core-excited levels has been observed in lithium. A 1-MW dye laser tuned to the $1{s}^{2}2s\ensuremath{\rightarrow}1{s}^{2}2p$ resonance produced \ensuremath{\sim}${10}^{16}$ excited atoms/${\mathrm{cm}}^{2}$ in a heat-pipe oven. Far-uv absorption spectra of ${\mathrm{Li}}^{*}(2p)$ and ${\mathrm{Li}}^{+}$ were obtained. A curve of the evolution from excited neutrals to \ensuremath{\sim}95% ions is presented, and the significance of the Li observations for understanding the ionization mechanism is discussed.