Showing papers by "University of Maryland, College Park published in 1979"

A theory of the terrestrial kilometric radiation

Abstract: During magnetospheric substorms, electrons with energies of about 1 keV are injected from the plasma-sheet region into the auroral region. A fraction of these energetic electrons can precipitate into the upper atmosphere, and the rest are reflected because of the mirror effect of the convergent geomagnetic field. It is found that these reflected electrons can result in the amplification of electromagnetic waves via a relativistic normal cyclotron resonance. This process may explain the recently discovered terrestrial kilometric radiation.

Integrability of Nonlinear Hamiltonian Systems by Inverse Scattering Method

Abstract: A simple and direct scheme is presented to test the integrability of nonlinear evolution equations by inverse scattering method. The time part of the Lax equation needed for inverse scattering transform is identified with the linearized equation of the original nonlinear Hamiltonian system, while the Lax spectral operator is identified with a recursion operator connecting polynomial solutions of the linearized equation. This spectral operator is obtained by using a perturbative linear mode coupling scheme. A simple example discovered to be integrable by our scheme is shown explicitly to illustrate the detail procedures.

Curriculum '78: recommendations for the undergraduate program in computer science— a report of the ACM curriculum committee on computer science

Abstract: Contained in this report are the recommendations for the undergraduate degree program in Computer Science of the Curriculum Committee on Computer Science (C3S) of the Association for Computing Machinery (ACM).The core curriculum common to all computer science undergraduate programs is presented in terms of elementary level topics and courses, and intermediate level courses. Elective courses, used to round out an undergraduate program, are then discussed, and the entire program including the computer science component and other material is presented. Issues related to undergraduate computer science education, such as service courses, supporting areas, continuing education, facilities, staff, and articulation are presented.

Syntactic/semantic interactions in programmer behavior: A model and experimental results

Abstract: This paper presents a cognitive framework for describing behaviors involved in program composition, comprehension, debugging, modification, and the acquisition of new programming concepts, skills, and knowledge. An information processing model is presented which includes a long-term store of semantic and syntactic knowledge, and a working memory in which problem solutions are constructed. New experimental evidence is presented to support the model of syntactic/semantic interaction.

Fuzzy digital topology

Abstract: Topological relationships among parts of a digital picture, such as connectedness and surroundedness, play an important role in picture analysis and description. This paper generalizes these concepts to fuzzy subsets, and develops some of their basic properties.

Countergradient selection in the green frog, rana clamitans.

Abstract: Variation in life history characteristics among different populations of a single species is commonly interpreted as a set of multiple evolutionary adaptations to differing environments. Studies on amphibians have shown that populations of a single species at several altitudes may differ markedly in their embryonic developmental rates (Ruibal, 1955), sizes at metamorphic climax (Licht, 1975; Pettus and Angleton, 1967), and conditions of age and size at first reproduction (Martof and Humphries, 1959; Tilley, 1973). Phenotypic variation in a character, however, whether it is ecological, physiological, or developmental could result from either of two factors: a) environmental induction or modification during development; or b) genuine genetic adaptation to local conditions. It is essential that the relative importance of these components be separated in order to interpret correctly the adaptive significance of the phenotypic variation. The importance of this distinction applies to ectotherms in general, since environmental temperature has been shown to be one important proximal factor controlling developmental and physiological processes (copepods: McLaren et al., 1969; insects: Howe, 1967; amphibians: Kollros, 1961; Smith-Gill and Berven, 1978). Temperature also has been invoked as a strong selective force leading to genetically based differences in anuran embryonic developmental rates (Moore, 1939) as well as temperature tolerance in adult anurans (Brattstrom, 1968; Miller and Packard, 1977; Snyder and Weathers, 1975). Because temperature varies systematically with altitude, one expects correlations of developmental patterns with temperature between high and low elevation populations for either genetic or induced reasons. Amphibian metamorphosis is a developmental process which is sensitive to ambient temperature and which can influence life history parameters in ecologically important ways. Length of the larval period and size at metamorphic climax have been used as predictors of future survival and reproductive success (Brockelman, 1969; Wilbur, 1972, 1977a; Collins, 1975; Smith-Gill and Gill, 1978). Either early maturation, large body size or both may have a significant selective advantage in certain environments (Hairston, Tinkle and Wilbur, 1970; Pianka, 1972). Thus, not only may ambient temperature influence life history patterns in montane and lowland populations directly, but it may also act as a selective factor generating genetic differences between local populations as well. The present investigation reports the results of natural history observations and an experimental investigation designed 1) to compare postembryonic rates of growth and development of montane and lowland populations of the green frog, Rana clamitans, and 2) to determine whether the observed populational differences in growth and development are induced ontogenetically by the ambient environment or controlled genetically.

Identification of gaseous SO2 and new upper limits for other gases on Io

Abstract: The identification of gaseous sulfur dioxide on Io by Voyager 1 is reported, and preliminary upper limits for other atmospheric gases are presented. Averaged spectra taken by the Voyager IRIS experiment in the range of 1,000 to 1,200/cm are interpreted as containing three fundamental sulfur dioxide bands, with intensities most nearly corresponding to an atmospheric model with a sulfur dioxide abundance of 0.2 cm atm. Upper limits for COS, CS2, SO3, H2S, CO2, O3, N2O, H2O, CH4, NH3 and HC1, not detected in the spectra, were calculated on the basis of the radiative transfer equation for temperatures of 130 and 250 K; a depletion of hydrogen, carbon and nitrogen is noted. It is suggested that a SO2 outgassing from a cooling sulfur extrusion is the major source of the observed atmospheric SO2.

Environmental Uncertainty and Buying Group Structure: An Empirical Investigation:

Abstract: This research presents both a conceptual and a methodological framework for examining organizational buying behavior from a multiperson level of analysis. Focusing on those organizational members w...

Preturbulence: A Regime Observed in a Fluid Flow Model of Lorenz*

Abstract: This paper studies a forced, dissipative system of three ordinary differential equations. The behavior of this system, first studied by Lorenz, has been interpreted as providing a mathematical mechanism for understanding turbulence. It is demonstrated that prior to the onset of chaotic behavior there exists a preturbulent state where turbulent orbits exist but represent a set of measure zero of initial conditions. The methodology of the paper is to postulate the short term behavior of the system, as observed numerically, to establish rigorously the behavior of particular orbits for all future time. Chaotic behavior first occurs when a parameter exceeds some critical value which is the first value for which the system possesses a homoclinic orbit. The arguments are similar to Smale's “horseshoe”.

Isis 1 observations at the source of auroral kilometric radiation

Abstract: Observations of auroral kilometric radiation (AKR) were made by Isis 1 in the source region. The radiation is found to be generated in the extraordinary mode just above the local cut-off frequency and to emanate nearly perpendicular to the magnetic field. It occurs within local depletions of electron density, where the ratio of plasma frequency to cyclotron frequency is less than 0.2. The density depletion is restricted to altitudes above about 2000 km, and the upper AKR frequency limit corresponds to the extraordinary cut-off frequency at this altitude. AKR is observed from Isis 1 above the nighttime auroral zone over a wider extent in longitude than in latitude with an intense source region observed most often near 2200 LMT and 70 deg invariant latitude. It is directly related to inverted V electron precipitation events with an electron-to-wave energy conversion efficiency of the order of 0.1 to 1%.

Infrared observations of the jovian system from voyager 1.

Abstract: The infrared spectroscopy and radiometry investigation has obtained spectra of Jupiter and its satellites between approximately 180 and 2500 kayser with a spectral resolution of 4.3 kayser. The Jupiter spectra show clear evidence of H2, CH4, C2H2, C2H6, CH3D, NH3, PH3, H2O, and GeH4. A helium concentration of 0.11 plus or minus 0.03 by volume is obtained. Meridional temperature cross sections show considerable structure. At high latitudes, the stratosphere is warmer in the north than in the south. The upper troposphere and lower stratosphere are locally cold over the Great Red Spot. Amalthea is warmer than expected. Considerable thermal structure is observed on Io, including a relatively hot region in the vicinity of a volcanic feature.

Metastable Chaos: The Transition to Sustained Chaotic Behavior in the Lorenz Model

Abstract: The system of equations introduced by Lorenz to model turbulent convective flow is studied here for Rayleigh numbersr somewhat smaller than the critical value required for sustained chaotic behavior. In this regime the system is found to exhibit transient chaotic behavior. Some statistical properties of this transient chaos are examined numerically. A mean decay time from chaos to steady flow is found and its dependence uponr is studied both numerically and (very close to the criticalr) analytically.

Direct and inverse error estimates for finite elements with mesh refinements

Abstract: The finite element method is used to solve a second order elliptic boundary value problem on a polygonal domain. Mesh refinements and weighted Besov spaces are used to obtain optimal error estimates and inverse theorems.

Professionalism as A Predictor of Organizational Commitment, Role Stress, and Turnover: A Multidimensional Approach

Abstract: The article investigates the relationship between the attitudinal dimensions that characterize professionalism and several organizational outcomes in the employment of professionals. The study exam...

Quasilinear hyperbolic systems

Abstract: We construct global solutions for quasilinear hyperbolic systems and study their asymptotic behaviors. The systems include models of gas flows in a variable area duct and flows with a moving source. Our analysis is based on a numerical scheme which generalizes the Glimm scheme for hyperbolic conservation laws.

A bound for the least prime ideal in the Chebotarev Density Theorem

Abstract: as x --, oc. In [7] two versions of the Chebotarev density theorem were proved, one unconditional and the other on the assumption of the Generalized Riemann Hypothesis (GRH), each of which expressed ~Zc(X ) as the sum of the main term ICI IC]_lGt Li(x) and an error term which is an effectively computable function of x, i-~-' and the associated field constants n K = [ K : Q ], h i = [L :Q] and dK,dz, (the absolute values of the discriminants of the two fields). Assuming the truth of the GRH for ~L(s), that paper also proved the existence of an effectively computable constant b (independent of K and L) such that for any conjugacy class C, there exists a prime

Some Correlates of Experienced Job Stress: A Boundary Role Study

Abstract: Bank branch employees and customers from 23 branches of a large commercial bank responded to questionnaires designed to assess issues regarding employee perceptions of management's orientation to s...

Approximation Algorithms for Some Postman Problems

Abstract: Approxtmatton algorithms for several NP-complete edge-covermg routing problems are presented and analyzed m terms of the worst-case ratio of the cost of the obtained solutmn to the cost of the opt imum solutton A worst-case bound of 2 is proved for the mixed postman algortthm of Edmonds and Johnson, and a related algorithm for the mixed postman problem is shown also to have a worst-case bound of 2 A mixed strategy approach ts used to obtain a bound of ~ for the mixed postman problem A second mixed strategy algorithm, for the mtxed postman on a planar graph, ~s shown to have a worst-case bound of

Infrared observations of the Saturnian system from Voyager 2

Abstract: During the passage of Voyager 2 through the Saturn system, infrared spectral and radiometric data were obtained for Saturn, Titan, Enceladus, Tethys, Iapetus, and the rings. Combined Voyager 1 and Voyager 2 observations of temperatures in the upper troposphere of Saturn indicate a seasonal asymmetry between the northern and southern hemispheres, with superposed small-scale meridional gradients. Comparison of high spatial resolution data from the two hemispheres poleward of 60 deg latitude suggests an approximate symmetry in the small-scale structure, consistent with the extension of a symmetric system of zonal jets into the polar regions. Longitudinal variations of 1 to 2 K are observed. Disk-averaged infrared spectra of Titan show little change over the 9-month interval between Voyager encounters. By combining Voyager 2 temperature measurements with ground-based geometric albedo determinations, phase integrals of 0.91 plus or minus 0.13 and 0.89 plus or minus 0.09 were derived for Tethys and Enceladus, respectively. The subsolar point temperature of dark material on Iapetus must exceed 110 K. Temperatures (and infrared optical depths) for the A and C rings and for the Cassini division are 69 plus or minus 1 K (0.40 plus or minus 0.05), 85 plus or minus 1 K (0.10 plus or minus 0.03), and 85 plus or minus 2 K (0.07 plus or minus 0.04), respectively.

Drinking, Homicide, and Rebellion in Colonial Mexican Villages

Abstract: This study analyzes the impact of Spanish rule on Indian peasant identity in the late colonial period by investigating three areas of social behavior. Based on the criminal trial records and related documents from the regions of central Mexico and Oaxaca, it attempts to discover how peasants conceived of their role under Spanish rule, how they behaved under various kinds of street, and how they felt about their Spanish overlords. In examining the character of village uprisings, typical relationships between killers and the people they killed, and the drinking patterns of the late colonial period, the author finds no warrant for the familiar picture of sullen depredation and despair. Landed peasants of colonial Mexico drank moderately on the whole, and mostly on ritual occasions; they killed for personal and not political reasons. Only when new Spanish encroachments threatened their lands and livelihoods did their grievances flare up in rebellion, and these occasions were numerous but brief. The author bolsters his conclusions with illuminating comparisons with other peasant societies.

Gravity effects in fluids near the gas--liquid critical point

Abstract: The presence of a gravitational field leads to both practical and fundamental limits of the resolution in critical phenomena experiments in fluids near the gas-liquid critical point. We present equations that yield estimates of the gravitational limitations in a variety of critical phenomena experiments for a large number of fluids and as a function of the magnitude of the gravitational field. Various strategies for improving the resolution of such experiments are discussed, including procedures that remove a fluid from thermodynamic equilibrium (e.g., stirring). A comparison is made between the gravitational limitations in earth-bound experiments and those at the microgravitational levels that may become accessible in an orbiting laboratory.

Bacteria associated with the surface and gut of marine copepods.

Abstract: Little is known about the nature of bacteria associated with the surface and gut of marine copepods, either in laboratory-reared animals or in the natural environment. Nor is it known whether such animals possess a gut flora. The present report deals with studies of microorganisms isolated from healthy, laboratory-reared copepods of the species Acartia tonsa Dana, from several species of wild copepods collected from a marine or estuarine environment, and from laboratory dishes containing moribund copepods. Evidence for a unique gut flora in laboratory-reared animals is presented; the predominant bacteria were represented by the genus Vibrio. Other organisms such as Pseudomonas and Cytophaga were found less abundantly associated with the copepods and not specifically associated with the gut. Images