Showing papers by "University of Maryland, College Park published in 1981"

Goal setting and task performance: 1969–1980.

Abstract: : A review of both laboratory and field studies on the effect of setting goals when learning or performing a task found that specific, challenging goals led more often to higher performance than easy goals, 'do your best' goals or no goals. This is one of the most robust and replicable findings in the psychological literature, with 90% of the studies showing positive or partially positive results. The main mechanisms by which goals affect performance are by directing attention, mobilizing effort, increasing persistence, and motivating strategy development. Goal setting is most likely to improve task performance when the goals are specific and sufficiently challenging, when the subjects have sufficient ability (and ability differences are controlled), when feedback is provided to show progress in relation to the goal, when rewards such as money are given for goal attainment, when the exerimenter manager is supportive, and when the assigned goals are actually accepted by the individual. No reliable individual differences have emerged in goal setting studies, probably because goals were typically assigned rather than self-set. Need for achievement and self esteem may be the most promising individual difference variables. (Author)

Neutrino Masses and Mixings in Gauge Models with Spontaneous Parity Violation

Abstract: Unified electroweak gauge theories based on the gauge group $\mathrm{SU}{(2)}_{L}\ifmmode\times\else\texttimes\fi{}\mathrm{SU}{(2)}_{R}\ifmmode\times\else\texttimes\fi{}\mathrm{U}{(1)}_{B\ensuremath{-}L}$, in which the breakdown of parity invariance is spontaneous, lead most naturally to a massive neutrino. Assuming the neutrino to be a Majorana particle, we show that smallness of its mass can be understood as a result of the observed maximality of parity violation in low-energy weak interactions. This result is shown to be independent of the number of generations and unaffected by renormalization effects. Phenomenological consequences of this model at low energies are studied. Observation of neutrinoless double-$\ensuremath{\beta}$ decay will provide a crucial test of this class of models. Implications for rare decays such as $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\gamma}$, $\ensuremath{\mu}\ensuremath{\rightarrow}\mathrm{ee}\overline{e}$, etc. are also noted. It is pointed out that in the realm of neutral-current phenomena, departure from the predictions of the standard model for polarized-electron-hadron scattering, forward-backward asymmetry in ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$, and neutrino interactions has a universal character and may be therefore used as a test of the model.

The Architectural Organization of a Mobile Radio Network via a Distributed Algorithm

Abstract: In this paper we consider the problem of organizing a set of mobile, radio-equipped nodes into a connected network. We require that a reliable structure be acquired and maintained in the face of arbitrary topological changes due to node motion and/or failure. We also require that such a structure be achieved without the use of a central controller. We propose and develop a self-starting, distributed algorithm that establishes and maintains such a connected architecture. This algorithm is especially suited to the needs of the HF Intra-Task Force (ITF) communication network, which is discussed in the paper.

An optimal algorithm for mutual exclusion in computer networks

Abstract: An algorithm is proposed that creates mutual exclusion in a computer network whose nodes communicate only by messages and do not share memory. The algorithm sends only 2*(N - 1) messages, where N is the number of nodes in the network per critical section invocation. This number of messages is at a minimum if parallel, distributed, symmetric control is used; hence, the algorithm is optimal in this respect. The time needed to achieve mutual exclusion is also minimal under some general assumptions. As in Lamport's "bakery algorithm," unbounded sequence numbers are used to provide first-come firstserved priority into the critical section. It is shown that the number can be contained in a fixed amount of memory by storing it as the residue of a modulus. The number of messages required to implement the exclusion can be reduced by using sequential node-by-node processing, by using broadcast message techniques, or by sending information through timing channels. The "readers and writers" problem is solved by a simple modification of the algorithm and the modifications necessary to make the algorithm robust are described.

Role Conflict and Role Ambiguity: Integration of the Literature and Directions for Future Research

Abstract: Although research on role conflict and ambiguity has been extensive, there has been only moderate consistency in the focus and results of the research, while several areas of role conflict and ambiguity research are still relatively unexamined. This paper suggests that a framework for organizing the recent research may assist in consolidating the field and providing an understanding of where we are, what is left to be done and, therefore, direction for future role conflict and ambiguity research.

Program slicing

Abstract: Program slicing is a method used by experienced computer programmers for abstracting from programs. Starting from a subset of a program's behavior, slicing reduces that program to a minimal form which still produces that behavior. The reduced program, called a “slice”, is an independent program guaranteed to faithfully represent the original program within the domain of the specified subset of behavior.Finding a slice is in general unsolvable. A dataflow algorithm is presented for approximating slices when the behavior subset is specified as the values of a set of variables at a statement. Experimental evidence is presented that these slices are used by programmers during debugging. Experience with two automatic slicing tools is summarized. New measures of program complexity are suggested based on the organization of a program's slices.

Capacitated arc routing problems

Abstract: A capacitated node routing problem, known as the vehicle routing or dispatch problem, has been the focus of much research attention On the other hand, capacitated arc routing problems have been comparatively neglected Both classes of problems are extremely rich in theory and applications Our intent in this paper is to define a capacitated arc routing problem, to provide mathematical programming formulations, to perform a computational complexity analysis, and to present an approximate solution strategy for this class of problems In addition, we identify several related routing problems and develop tight lower bounds on the optimal solution

Strange attractors and chaotic motions of dynamical systems

Abstract: A review is presented of recent work related to strange attractors and chaotic motions of dynamical systems. First, simple systems capable of displaying chaotic behavior are discussed. In order of increasing dimensionality of the system, they are one-dimensional noninvertible maps, two-dimensional invertible maps, and autonomous systems of three coupled ordinary differential equations. The concept of fractional dimension of the strange attractor is stressed. Several physical examples well be reviewed, along with the possible relevance to turbulence in systems, such as fluids or plasmas, that are described by partial differential equations.

Regional geochemistry of trace elements in Chesapeake Bay sediments

Abstract: The concentrations of Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb in 177 surface sediment samples from throughout Chesapeake Bay are reported. Analyses were made of both unfractionated samples and the <63 μm fractions. Analytical uncertainty, always less than ±10%, controlled reproducibility in analyses of the <63 μm fractions, but sampling variance controlled reproducibility in the unfractionated samples, especially when coarse-grained sediments were being analyzed. Sediments in the northernmost part of the bay are enriched relative to average continental crust in all elements except Cr. This reflects the composition of dissolved and suspended material being delivered to that region by the Susquehanna River. The enriched sediments appear not to be transported south of Baltimore in significant quantily. Zinc, cadmium, and lead are enriched relative to average crust throughout the bay and in most other estuaries in the eastern United States.

Cosmic ray drift, shock wave acceleration, and the anomalous component of cosmic rays

Abstract: A model of the anomalous component of the quiet-time cosmic ray flux is presented in which ex-interstellar neutral particles are accelerated continuously in the polar regions of the solar-wind termination shock, and then drift into the equatorial regions of the inner heliosphere. The observed solar-cycle variations, radial gradient, and apparent latitude gradient of the anomalous component are a natural consequence of this model.

The semistate description of nonlinear time-variable circuits

Abstract: It is shown that, by the possible use of circuit equivalences, circuits satisfying rather light assumptions possess the semistate description {\cal Q} \dot{x} + \cal B(x, t)= \cal D u y ={\cal F} x where u = input, y = output, x = semistate, and {\cal Q}, {\cal D} ,{\cal F} are constant operators. The semistate can be chosen as tree branch voltages and link branch currents; a determination of consistent initial semistates is given which stems from a forward stepping solution equation. An appropriate reduction with attendant signal-flow graph for design is obtained in the linear time-invariant case.

Measuring the Cost of Time in Recreation Demand Analysis: An Application to Sportfishing

Abstract: Since the work of Cesario and Knetsch, economists have recognized that the opportunity cost of time plays an important role in determining the demand for outdoor recreation. The opportunities one has for spare time are more significant for consumption of time-intensive outdoor recreation activities than for other commodities, especially nondurables. Bishop and Heberlein illustrate "the overwhelming importance of time costs to final [recreational] values. . . . Total consumer surplus is nearly four times as large . . . [when] time costs are added at half the income rate . . . [as when] time costs were set at zero" (p. 21). Despite the recognition, economists have neither successfully integrated the costs of time with the methods of recreational demand analysis nor reached a consensus on how it should be measured. Brown, Charbonneau, and Hay state, "Finally, the apparently crucial importance of how opportunity cost of time is handled needs further work. While we are convinced it is an appropriate concept, . . . exactly how it should be included and measured S. . remains to be determined" (p. 24). Several approaches have been taken to include it in the travel cost method. One approach (Brown and Nawas, Gum and Martin) suggests that time in transit be considered as a separate independent variable. Another approach (Bishop and Heberlein; Brown, Charbonneau, Hay; Nicols, Bowes, Dwyer; Cesario and Knetsch) measures the cost of time and adds it to other costs. Several approaches have been suggested to measure time costs. One approach is simply to choose an hourly wage, e.g., $2.00 per hour, or perhaps the minimum wage rate. A more flexible but still ad hoc approach is to use some proportion of the individual's wage rate as the opportunity cost of time (Nichols, Bowes, Dwyer). The proportion is usually taken from independent studies and used to value the travel time. This approach is better than using a constant opportunity cost of time because it allows variation across individuals. It suffers because the choice of the percentage of the wage rate is arbitrary, independent of the sampled population. Cesario has discussed the consequences of ignoring time costs and the differences in values arising from alternative measurement approaches. In this paper, we argue that the opportunity cost of time is some proportion of the individual's market wage rate or income per hour and that this proportion can be determined from sample data. This method permits the proportion to vary from one study to another, rather than imposing either an arbitrary estimate or one from a sample different from the study's sample.'

Stochastic models for closed boundary analysis: Representation and reconstruction

Abstract: The analysis of closed boundaries of arbitrary shapes on a plane is discussed. Specifically, the problems of representation and reconstruction are considered. A one-to-one correspondence between the given closed boundary and a univariate or multivariate sequence of real numbers is set up. Univariate or multivariate circular autoregressive models are suggested for the representation of the sequence of numbers derived from the closed boundary. The stochastic model representing the closed boundary is invariant to transformations like sealing, translation, choice of starting point, and rotation over angles that are multiples of 2\pi/N , where N is the number of observations. Methods for estimating the unknown parameters of the model are given and a decision rule for choosing the appropriate number of coefficients is included. Constraints on the estimates are derived so that the estimates are invariant to the transformations of the boundaries. The stochastic model enables the reconstruction of a dosed boundary using FFT algorithms. Results of simulations are included and the application to contour coding is discussed.

Quantized Hall resistance and the measurement of the fine-structure constant

Abstract: An elementary, exact calculation of two-dimensional electrons in crossed electric and magnetic fields with a $\ensuremath{\delta}$-function impurity is carried out in the quantum limit. A state localized on the impurity exists and carries no current. However, the remaining mobile electrons passing near the impurity carry an extra dissipationless Hall current exactly compensating the loss of current by the localized electron. The Hall resistance should thus be precisely $\frac{h}{{e}^{2}}$, as found experimentally by Klitzing et al. Other possible sources of deviation from this result are briefly examined.

Mate choice in the wood frog, rana sylvatica.

Abstract: Since Darwin's (1871) introduction of the theory of sexual selection, studies of mating associations have emphasized three patterns: (1) male-male competition (intrasexual selection) for control of females (Parker, 1970; Le Boeuf, 1974; Davies and Halliday, 1979; Wells, 1979), (2) male control of resources favored by females (Thornhill, 1976; Wells, 1977a; Howard, 1978), and (3) non-random mate choice by females (intersexual selection). Later refinements of Darwin's theory have focused on the differential investment of males and females in reproduction (Bateman, 1948), individual behaviors which maximize reproductive success (Trivers, 1972), and the ecological factors influencing patterns of mate choice (Orians, 1969; Borgia, 1979). Trivers (1972) and others (Bateman, 1948; Fisher, 1958; Williams, 1975) concluded that females generally have a much greater investment in reproduction and a higher certainty of parenthood than males and would be expected to be more discriminating in their choice of potential mates. Male reproductive success is generally limited by access to females and the number of female gametes fertilized. While natural selection in both sexes favors increased genetic representation in future generations (Williams, 1975), males are expected to maximize their reproductive success by increasing the number of matings, whereas females should choose higher quality mates. The major mechanism hypothesized that underlies patterns of sexual selection is that discriminating females control the reproduction of indiscriminate males. A fourth pattern of mating associations is non-random mate choice by males. Discussions of male choice are usually restricted to monogamous mating systems where males contribute an amount of parental effort that equals or exceeds that of females (Wilson, 1975) and in cases where sex role reversal occurs (Hohn, 1967; Smith, 1976). Otherwise males are assumed to lose little in indiscriminate matings (Bateman, 1948; Trivers, 1972; Williams, 1975). Few studies have examined the role of male choice in mating systems. This paper reports the importance of both male-male competition and male discrimination in the mating pattern of the wood frog, Rana sylvatica. Results of field observations and experiments performed with natural populations in woodland ponds, and of laboratory mate-choice experiments using males and females of varying ages, body sizes and geographic origins are presented. Experiments were designed to assess (1) relative importance of male and female choice, (2) effects of age and size on male reproductive success and (3) presence of non-random, assortative mating.

Differential Treatment of Females and Males in Mathematics Classes

Abstract: Mathematics courses in high school continue to attract fewer women than men. Recent data gathered concerning the background of first-year students at the University of Maryland (Sells, Note 1) show that 53% of white men had at least 4 years of mathematics in high school; only 20% of white women had the same preparation. For black men and women, the figures were 22% and 10%, respectively. As Sells (Note 2) has suggested, mathematics acts as a critical filter that keeps many women out of a variety of careers because they lack the necessary mathematics background. Why do so many women elect not to study mathematics when given the choice? Numerous studies (Fennema & Sherman, 1977, 1978; Fox, 1976; Jacobs, 1974; Casserly, Note 3; Fennema, Note 4) have suggested that sociocultural factors are involved in the achievement in, and the study of, mathematics by young women; however, few data have been available that tell us what is happening in the mathematics classroom that might contribute to the lack of persistence of women in the study of mathematics. Fennema and Sherman (1978) encourage research into the factors within a school milieu that might have an impact on the attrition rate of females in mathematics.

Data Abstraction, Implementation, Specification, and Testing

Abstract: A compiler-based system DAISTS that combines a data-abstraction implementation language (derived from the SIMULA class) with specification by algebraic axioms is described. The compiler, presented with two independent syntactic objects in the axioms and implementing code, compiles a \"program\" that consists of the former as test driver for the latter. Data points, in the form of expressions using the abstract functions and constant values, are fed to this program to determine if the implementation and axioms agree. Along the way, structural testing measures can be applied to both code and axioms to evaluate the test data. Although a successful test does not conclusively demonstrate the consistency of axioms and code, in practice the tests are seldom successful, revealing errors. The advantage over conventional programming systems is threefold:

Aeromonas hydrophila: ecology and toxigenicity of isolates from an estuary.

Abstract: A microbiological survey of Aeromonas hydrophila in Chesapeake Bay and its tributaries showed that this species is ubiquitous, occurring in numbers ranging from <0.3/l to 5 × 103/ml in the water column and ca. 4.6 × 102/g in sediment. It was recovered from water samples collected at several locations in Chesapeake Bay representing various salinity regimes, but the numbers of A. hydrophila in higher salinity water, i.e. 15O/OO, were low. Results of stepwise multiple linear regression analysis showed that concentrations of A. hydrophila were correlated with total, aerobic, viable, heterotrophic, bacterial counts, and, in addition, were inversely related to salinity and to concentration of dissolved oxygen. Seasonal occurrence was recorded, with fewer strains of A. hydrophila encountered during the winter months. The potential pathogenicity of A. hydrophila strains isolated from Chesapeake Bay was estimated by testing selected isolates for toxigenicity, using the Y-1 adrenal cell assay. Of 116 isolates tested, 83 (71%) produced a cytotoxic response, a characteristic found to be correlated with the lysine decarboxylase and Voges-Proskauer reactions. Eight of 11 strains tested, which elicited fluid accumulation in the rabbit ligated ileal loop assay, also provoked a cytotoxic reaction in the Y-l adrenal cell assay. Results of the study indicate that large numbers of toxigenic A. hydrophila can be found in an estuary and such strains may be pathogenic for man and/or animals.

Characteristics of hot plasma in the Jovian magnetosphere: Results from the Voyager spacecraft

Abstract: Measurements of the intensities, energy spectra, angular variations, and composition characteristics of the low-energy ion populations (approximately 30 keV to 4 MeV) obtained by both Voyager spacecraft in the outer (more than about 10 Jupiter radii) Jovian magnetosphere are reported and interpreted. Also shown are some of the energetic electron measurements. Using the spectral and angular ion measurements, density and pressure profiles in the magnetosphere are constructed and then compared with results reported by the plasma wave and plasma science investigations (density) and the magnetic field investigation (pressure).

Connected Component Labeling Using Quadtrees

Abstract: : An algorithm is presented for labeling the connected components of an image represented by a quadtree. The algorithm proceeds by exploring all possible adjacencies for each node once and only once. Once this is done, any equivalences generated by the adjacency labeling phase are propagated. Analysis of the algorithm reveals that its worst case average execution time is bounded by a quantity proportional to the product of the log of the region's diameter and the number of blocks comprising the area connected by the components.

First-principles electronic structure of Si, Ge, GaP, GaAs, ZnS, and ZnSe. I. Self-consistent energy bands, charge densities, and effective masses

Abstract: The self-consistent electronic structures of Si, Ge, and zinc-blende GaP, GaAs, ZnS, and ZnSe have been determined using the linear combination of Gaussian orbitals method with a local-density form of the exchange-correlation functional. A completely general form of the spatial dependence of the potential has been used to describe accurately the bonding character in the tetrahedral environment. Results are presented for the valence- and conduction-band energies, densities of states, effective masses, and charge densities. Comparisons are made with previous calculations and with photoemission measurements. A striking result is that the local-density theory underestimates the optical band gaps by approximately 30% or more, although the general conduction-band topology is good. The theoretical valence-band energies, charge densities, and electron and hole effective masses are also in good agreement with experiment. The energies and wave functions presented here are used to determine the optical properties of these materials in the following paper.

Simulation of a perpendicular bow shock

Abstract: Simulations of a high Mach number shock with parameters typical of the earth's bow shock have been performed using a hybrid (particle ions, fluid electrons) code. The simulations reproduce the observed ion reflection and overshoots in the magnetic field and density. These features are shown to be closely associated with ion gyration.

Monitoring and Resolving Comprehension Obstacles: An Investigation of Spontaneous Text Lookbacks among Upper-Grade Good and Poor Comprehenders.

Abstract: THE RESEARCH REPORTED here was designed to answer questions about spontaneous use of text lookbacks to resolve comprehension obstacles. Nineteen good comprehenders and 19 poor comprehenders were presented with a narrative passage divided into three segments. Interspersed in the text were six non-lookback questions and four lookback questions (i.e., questions presented in one segment but demanding retrieval of information presented in an earlier segment for correct responses). Subjects were seen individually by two investigators who alternated in the roles of directiongiver and intra-experiment observer. Analysis of correct responses to lookback questions and of lookback behaviors noted by the observers yielded evidence of reading proficiency and age/experience effects on use of lookbacks. Converging evidence from the question response and observational notation analyses supported the pronounced good comprehender-poor comprehender monitoring differences found in earlier research.