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Showing papers by "University of Maryland, College Park published in 1992"


Journal ArticleDOI
TL;DR: The stability of a queueing network with interdependent servers is considered and a policy is obtained which is optimal in the sense that its Stability Region is a superset of the stability region of every other scheduling policy, and this stability region is characterized.
Abstract: The stability of a queueing network with interdependent servers is considered. The dependency among the servers is described by the definition of their subsets that can be activated simultaneously. Multihop radio networks provide a motivation for the consideration of this system. The problem of scheduling the server activation under the constraints imposed by the dependency among servers is studied. The performance criterion of a scheduling policy is its throughput that is characterized by its stability region, that is, the set of vectors of arrival and service rates for which the system is stable. A policy is obtained which is optimal in the sense that its stability region is a superset of the stability region of every other scheduling policy, and this stability region is characterized. The behavior of the network is studied for arrival rates that lie outside the stability region. Implications of the results in certain types of concurrent database and parallel processing systems are discussed. >

3,018 citations


Journal ArticleDOI
TL;DR: The authors measured the heterogeneity of establishment-level employment changes in the U.S. manufacturing sector over the 1972 to 1986 period and measured this heterogeneity in terms of the gross creation and destruction of jobs and the rate at which jobs are reallocated across plants.
Abstract: This study measures the heterogeneity of establishment-level employment changes in the U. S. manufacturing sector over the 1972 to 1986 period. We measure this heterogeneity in terms of the gross creation and destruction of jobs and the rate at which jobs are reallocated across plants. Our measurement efforts enable us to quantify the connection between job reallocation and worker reallocation, to evaluate theories of heterogeneity in plant-level employment dynamics, and to establish new results related to the cyclical behavior of the labor market.

1,835 citations


Journal ArticleDOI
TL;DR: In this article, the authors present a theoretical analysis of the nature and development of children's achievement task values and discuss different theoretical components of achievement values and present empirical evidence for these components.

1,690 citations


Book
01 Oct 1992
TL;DR: This book provides an introduction to the design and analysis of parallel algorithms, with the emphasis on the application of the PRAM model of parallel computation, with all its variants, to algorithm analysis.
Abstract: Written by an authority in the field, this book provides an introduction to the design and analysis of parallel algorithms. The emphasis is on the application of the PRAM (parallel random access machine) model of parallel computation, with all its variants, to algorithm analysis. Special attention is given to the selection of relevant data structures and to algorithm design principles that have proved to be useful. Features *Uses PRAM (parallel random access machine) as the model for parallel computation. *Covers all essential classes of parallel algorithms. *Rich exercise sets. *Written by a highly respected author within the field. 0201548569B04062001

1,577 citations


Journal ArticleDOI
TL;DR: This paper deals with a two-dimensional space-filling approach in which each node is a rectangle whose area is proportional to some attribute such as node size.
Abstract: The traditional approach to representing tree structures is as a rooted, directed graph with the root node at the top of the page and children nodes below the parent node with lines connecting them (Figure 1). Knuth (1968, p. 305-313) has a long discussion about this standard representation, especially why the root is at the top and he offers several alternatives including brief mention of a space-filling approach. However, the remainder of his presentation and most other discussions of trees focus on various node and edge representations. By contrast, this paper deals with a two-dimensional (2-d) space-filling approach in which each node is a rectangle whose area is proportional to some attribute such as node size.

1,573 citations


Journal ArticleDOI
TL;DR: In this paper, a minimum necessary condition for sustainability is the maintenance of the total natural capital stock at or above the current level, to be relaxed only when solid evidence can be offered that it is safe to do so.
Abstract: A minimum necessary condition for sustainability is the maintenance of the total natural capital stock at or above the current level. While a lower stock of natural capital may be sustainable, society can allow no further decline in natural capital given the large uncertainty and the dire consequences of guessing wrong. This “constancy of total natural capital” rule can thus be seen as a prudent minimum condition for assuring sustainability, to be relaxed only when solid evidence can be offered that it is safe to do so. We discuss methodological issues concerning the degree of substitutability of manufactured for natural capital, quantifying ecosystem services and natural capital, and the role of the discount rate in valuing natural capital. We differentiate the concepts of growth (material increase in size) and development (improvement in organization without size change). Given these definitions, growth cannot the sustainable indefinitely on a finite planet. Development may be sustainable, but even this aspect of change may have some limits. One problem is that current measures of economic well-being at the macro level (i.e., the Gross National Product) measure mainly growth, or at best conflate growth and development. This urgently requires revision. Finally, we suggest some principles of sustainable development and describe why maintaining natural capital stocks is a prudent and achievable policy for insuring sustainable development. There is disagreement between technological optimists (who see technical progress as eliminating all resource constraints to growth and development) and technological skeptics (who do not see as much scope for this approach and fear irreversible use of resources and damage to natural capital). By maintaining natural capital stocks (preferably by using a natural capital depletion tax), we can satisfy both the skeptics (since resources will be conserved for future generations) and the optimists (since this will raise the price of natural capital depletion and more rapidly induce the technical change they predict).

1,510 citations


Journal ArticleDOI
04 Sep 1992-Cell
TL;DR: It is concluded that rab5 is a rate-limiting component of the machinery regulating the kinetics of membrane traffic in the early endocytic pathway.

1,286 citations


Journal ArticleDOI
TL;DR: Drawing on cognitive adaptation theory, optimism, psychological control, and self-esteem were explored as longitudinal predictors of adjustment to college in a sample of 672 freshmen and indicated that self- esteem and control predicted greater motivation and higher grades, controlling for college entrance exam scores.
Abstract: Drawing on cognitive adaptation theory, optimism, psychological control, and self-esteem were explored as longitudinal predictors of adjustment to college in a sample of 672 freshmen. Although a direct effect of optimism on adjustment was found, most of the predicted effects were mediated by coping methods. Controlling for initial positive and negative mood, the beneficial effects of optimism, control, and self-esteem on adjustment were mediated by the nonuse of avoidance coping, greater use of active coping, and greater seeking of social support. Alternative models of the causal relations among these variables did not fit the data as well as the a priori mediational model. The results of a 2-year follow-up indicated that self-esteem and control predicted greater motivation and higher grades, controlling for college entrance exam scores. Implications for cognitive adaptation theory and for interventions with populations under stress are discussed.

1,056 citations



Journal ArticleDOI
TL;DR: MT induction or increased levels of MT-bound metals in individuals in metal-contaminated environments can be used to justify continued development and testing of diagnostics markers of metal exposure based on MT function.

839 citations


Journal ArticleDOI
TL;DR: In this article, the directional hemispherical spectral reflectance of a wide range of natural earth surface materials has been measured and is summarized and used to predict directional spectral emissivity from these data.

Journal ArticleDOI
TL;DR: The influence functional path-integral method is used to derive an exact master equation for the quantum Brownian motion of a particle linearly coupled to a general environment at arbitrary temperature and applies it to study certain aspects of the loss of quantum coherence.
Abstract: We use the influence functional path-integral method to derive an exact master equation for the quantum Brownian motion of a particle linearly coupled to a general environment (ohmic, subohmic, or supraohmic) at arbitrary temperature and apply it to study certain aspects of the loss of quantum coherence.

Journal ArticleDOI
TL;DR: In this paper, the possibility of an avalanche-type increase of the number of runaway electrons leading to a new type of electric breakdown of gases was considered, which could take place in the atmosphere during a thunderstorm stimulated by cosmic ray secondaries.

Journal ArticleDOI
TL;DR: In this article, a meta-analysis of 54 experiments investigated the influence of social expectations on memory for information that is congruent and incongruent with those expectations, and found that social expectations influence memory for congruence and contrast.
Abstract: A meta-analysis of 54 experiments investigated the influence of social expectations on memory for information that is congruent and incongruent with those expectations

Journal ArticleDOI
TL;DR: This article used a name-matching paradigm developed by Taylor et al. to investigate how people use the immediately apparent features of others as a basis of social categorization and found that people were more likely to categorize targets according to their sex than their race but also tended to categorise using a single subordinate category that represented sex and race simultaneously.
Abstract: Five experiments used a name-matching paradigm developed by Taylor et al (1978) to investigate how people use the immediately apparent features of others as a basis of social categorization. Ss were more likely to categorize targets according to their sex than their race but also tended to categorize using a single subordinate category that represented sex and race simultaneously.


Journal ArticleDOI
TL;DR: In this article, the authors survey and critically comment on some basic concepts and notions relevant to the methodology dealing with process capability indices (PCI's), focusing on distributional and inferential aspects.
Abstract: In this paper we survey and critically comment on some basic concepts and notions relevant to the methodology dealing with process capability indices (PCI's). The emphasis is on distributional and inferential aspects. The intent is to contribute to the ..

Journal ArticleDOI
TL;DR: An early version of a physical model was modified and expanded to derive surface solar irradiance from satellite observations as mentioned in this paper, which can produce both direct and diffuse spectral components in the 0.2-4.0-micron interval.
Abstract: An early version of a physical model was modified and expanded to derive surface solar irradiance from satellite observations. The model is based on radiative transfer theory, and can produce both direct and diffuse spectral components in the 0.2-4.0-micron interval. Attention is given to the absorption and scattering processes in the atmosphere and the interaction of radiation with the surface. The bidirectional nature of the exiting radiation at the top of the atmosphere is also accounted for. In this paper the emphasis will be on describing the current status of the model and its implementation on a global scale with the International Satellite Cloud Climatology Project C1 data.

Book ChapterDOI
TL;DR: There has been an explosion of research on marine microbial foodweb processes in the past decade as mentioned in this paper, and it is widely accepted that about 50% of the primary production in marine and fresh water is processed by bacteria each day.
Abstract: There has been an explosion of research on marine microbial foodweb processes in the past decade. Today it is widely accepted that about 50% of the primary production in marine and fresh water is processed by bacteria each day (Williams, 1981; Cole et al., 1988). This striking finding was stimulated, as others have noted, by the introduction of convenient methods for the estimation of microbial biomass and activities in natural waters. Hobbie et al. (1977) and Watson et al. (1977) demonstrated conclusively that bacterial populations in the sea were large. By 1980, in addition to the pioneering and prescient work by Sorokin (e.g., Sorokin, 1971, 1973), reports of bacterial production measurements had begun to emerge (Sieburth et al., 1977; Karl, 1979; Larsson and Hagstrom, 1979; Fuhrman and Azam, 1980). Brock (1971) and Sieburth (1977) wrote early reviews on the subject, and Pomeroy (1974) introduced the importance of marine microbial processes to a large audience. In this chapter we review recent research on bacterial production in the ocean. The emphasis is on the open sea, but we will also discuss other marine habitats, partly because there are still few comprehensive studies of oceanic bacterial production. There is an equally large and rapidly growing literature on bacterial production in fresh waters (Cole et al., 1988; Currie, 1990) which deserves a review of its own, as well as comparison with the marine findings (Hobbie, 1988). We will not review related work in sediments, nor for the most part, related work on bacteriovores.

Journal ArticleDOI
TL;DR: A fundamental analis step in an ad',nced optimizing compiler (as well as many other software tools) is data dependence analysis f o r arrays, which determines whether two references to an array can refer to the same e lement and under what conditions.
Abstract: ndamental analis step in an ad',nced optimizing compiler (as well as many other software tools) is data dependence analysis f o r arrays. This means deciding i f two references to an array can refer to the same e lement and i f so, under what conditions. This information is used to determine allowable program transformations and optimizations. For example, we can determine that in the fo l lowing code fragment , no location o f the array is both read and written. Once we also verify that no location is writ ten more than once, we know that the writes can be done in any order. for i = 1 to 100 do f o r j -i to 100 do A[i, j + 11 = A[100,j]

Journal ArticleDOI
TL;DR: The authors survey the major memory residence optimizations and briefly discuss some of the MMDBs that have been designed or implemented.
Abstract: Main memory database systems (MMDBs) store their data in main physical memory and provide very high-speed access Conventional database systems are optimized for the particular characteristics of disk storage mechanisms Memory resident systems, on the other hand, use different optimizations to structure and organize data, as well as to make it reliable The authors survey the major memory residence optimizations and briefly discuss some of the MMDBs that have been designed or implemented >

Proceedings ArticleDOI
01 Jun 1992
TL;DR: A new concept for direct manipulation of databases, called dynamic queries, that allows users to formulate queries with graphical widgets, such as sliders, is designed, implemented and evaluated.
Abstract: We designed, implemented and evaluated a new concept for direct manipulation of databases, called dynamic queries, that allows users to formulate queries with graphical widgets, such as sliders. By providing a graphical visualization of the database and search results, users can find trends and exceptions easily. Eighteen undergraduate chemistry students performed statistically significantly faster using a dynamic queries interface compared to two interfaces both providing form fill-in as input method, one with graphical visualization output and one with all-textual output. The interfaces were used to explore the periodic table of elements and search on their properties.

Journal ArticleDOI
TL;DR: For folding on a simple two-dimensional lattice it is found that the genetic algorithm is dramatically superior to conventional Monte Carlo methods.

Journal ArticleDOI
TL;DR: A model emphasizing the role of the parasympathetic nervous system and particularly the vagus nerve in mediating homeostasis and defining stress is proposed, which will allow the assessment of the stressful impact of various clinical treatments on the young infant and permit the identification of individuals with vulnerabilities to stress.
Abstract: Vagal tone is proposed as a novel index of stress vulnerability and reactivity with applications in all branches of medicine, and with particular value in pediatrics. The paper proposes a model emphasizing the role of the parasympathetic nervous system and particularly the vagus nerve in mediating homeostasis and defining stress. Measurement of cardiac vagal tone is proposed as a method to assess on an individual basis both the stress response and the vulnerability to stress. The method monitors the neural control of the heart via the vagus (ie, vagal tone) as an index of homeostasis. The method provides a standard instrument with statistical parameters that are comparable between patients and throughout the life span. This noninvasive method will allow the assessment of the stressful impact of various clinical treatments on the young infant and permit the identification of individuals with vulnerabilities to stress.

Journal ArticleDOI
TL;DR: High levels of registration are needed for reliable monitoring of global change in the absence of any actual changes to the land surface, using spatially degraded Landsat MSS images.
Abstract: The impact of misregistration on the detection of changes in land cover has been evaluated using spatially degraded Landsat MSS images, focusing on simulated images of the normalized difference vegetation index (NDVI) Single-date images from seven areas were misregistered against themselves, and the statistical properties of the differences were analyzed In the absence of any actual changes to the land surface, the consequences of misregistration were very marked even for subpixel misregistrations Pairs of images from different time periods were then misregistered For four densely covered areas, an error equivalent to greater than 50% of the actual differences in the NDVI, as measured by the semivariance, was induced by a misregistration of only one pixel To achieve an error of only 10%, registration accuracies of 02 pixels or less are required For three more sparsely vegetated areas with semiarid climates, a registration accuracy of between 05 and 10 pixel was sufficient to achieve an error of 10% or less The results indicate that high levels of registration are needed for reliable monitoring of global change >

Journal ArticleDOI
TL;DR: An improved and general approach to connected-component labeling of images is presented, and it is shown that when the algorithm is specialized to a pixel array scanned in raster order, the total processing time is linear in the number of pixels.
Abstract: An improved and general approach to connected-component labeling of images is presented. The algorithm presented in this paper processes images in predetermined order, which means that the processing order depends only on the image representation scheme and not on specific properties of the image. The algorithm handles a wide variety of image representation schemes (rasters, run lengths, quadrees, bintrees, etc.). How to adapt the standard UNION-FIND algorithm to permit reuse of temporary labels is shown. This is done using a technique called age balancing, in which, when two labels are merged, the older label becomes the father of the younger label. This technique can be made to coexist with the more conventional rule of weight balancing, in which the label with more descendants becomes the father of the label with fewer descendants. Various image scanning orders are examined and classified. It is also shown that when the algorithm is specialized to a pixel array scanned in raster order, the total processing time is linear in the number of pixels. The linear-time processing time follows from a special property of the UNION-FIND algorithm, which may be of independent interest. This property states that under certain restrictions on the input, UNION-FIND runs in time linear in the number of FIND and UNION operations. Under these restrictions, linear-time performance can be achieved without resorting to the more complicated Gabow-Tarjan algorithm for disjoint set union.

Journal ArticleDOI
TL;DR: An analytically tractable framework is presented to describe mechanical and neural processing in the early stages of the auditory system, and algorithms are developed to assess the integrity of the acoustic spectrum at all processing stages.
Abstract: An analytically tractable framework is presented to describe mechanical and neural processing in the early stages of the auditory system. Algorithms are developed to assess the integrity of the acoustic spectrum at all processing stages. The algorithms employ wavelet representations, multiresolution processing, and the method of convex projections to construct a close replica of the input stimulus. Reconstructions using natural speech sounds demonstrate minimal loss of information along the auditory pathway. Close inspection of the final auditory patterns reveals spectral enhancements and noise suppression that have close perceptual correlates. The functional significance of the various auditory processing stages is discussed in light of the model, together with their potential applications in automatic speech recognition and low bit-rate data compression. >

Journal ArticleDOI
TL;DR: It is proposed that this deviation arises due to short-range correlations between polar regions, and that these correlations at high temperatures are the precursor to a freezing of the polarization fluctuations into a glassy state.
Abstract: The deviation from Cure-Weiss behavior has been investigated in lead magnesium niobate relaxor ferroelectrics. At high temperatures, the susceptibility was found to follow the Curie-Weiss relationship. A Curie constant and temperature of 1.2\ifmmode\times\else\texttimes\fi{}${10}^{5}$ and 398 K, respectively, were obtained. With decreasing temperature the deviation was found to increase. It is proposed that this deviation arises due to short-range correlations between polar regions, and that these correlations at high temperatures are the precursor to a freezing of the polarization fluctuations into a glassy state. A local (glassy) order parameter was calculated from the susceptibility by analogy to spin glasses [D. Sherrington and S. Kirkpatrick, Phys. Rev. Lett. 35, 1972 (1975)]. These results are compared to the rms polarization [G. Burns and F. Dacol, Solid State Commun. 48, 853 (1983)] and to the measured remanent polarization. The frequency and field dependence has also been investigated.

Journal ArticleDOI
TL;DR: Transactional strategies instruction as mentioned in this paper is a form of instruction in which teachers provide support and guidance to students as they attempt to use strategies to learn regular elementary content in a group instruction setting.
Abstract: Comprehension strategies are being taught in schools, with important similarities across some schools that are teaching them well. Strategy teaching typically occurs daily in these schools as part of group instruction. It is long term and complex since students are taught to coordinate traditional memory and comprehension strategies with interpretive processes. Consistent with both reader response theories and psychological theories, we refer to this approach as transactional strategies instruction: Student and teacher transactions with text are the heart of this form of instruction, with classroom discourse consisting of teachers providing support and guidance to students as they attempt to use strategies to learn regular elementary content. The limited evidence available suggests that this approach is effective and deserves research. Longitudinal experiments and quasi experiments are required, as are detailed descriptive analyses. There are many potential effects of transactional strategies instruction ...

Journal ArticleDOI
TL;DR: Structural and biochemical changes probably contribute to the decreases in muscle mass, strength, and endurance often observed in healthy but sedentary older men and women.
Abstract: To examine the effects of aging on human skeletal muscle, 10 men and 10 women, 64 +/- 1 yr old (Mean +/- SE), and 10 men and 10 women, 24 +/- 1 yr old, were studied. All subjects were sedentary nonsmokers who were carefully screened for latent cardiovascular, metabolic, or musculoskeletal disease. Needle biopsy samples were obtained from the lateral gastrocnemius muscle and examined using histochemical and biochemical techniques. The percentage of Type I, Type IIa, and Type IIb fibers did not differ with age. However, Type I fibers occupied a larger percent of total muscle area in the older men and women (60.6 +/- 2.6 vs 53.6 +/- 2.0%; p less than .05), because Type IIa and Type IIb fibers were 13-31% smaller (p less than .001) in these subjects. Muscle capillarization and mitochondrial enzyme (i.e., succinate dehydrogenase, citrate synthase, and beta-hydroxyacyl-CoA dehydrogenase) activities were also approximately 25% lower (p less than .001-.05) in the old subjects. Although it is difficult to determine whether these differences are due to aging itself or are simply due to inactivity, these structural and biochemical changes probably contribute to the decreases in muscle mass, strength, and endurance often observed in healthy but sedentary older men and women.