Showing papers by "University of Maryland, College Park published in 1986"

Mathematical models of hysteresis

Abstract: A new approach to the scalar Preisach model of hysteresis, which emphasizes its phenomenological nature and mathematical generality, is described. The theorem, which gives the necessary and sufficient conditions for the representation of actual hysteresis nonlinearities by the scalar Preisach model, is reported. The significance of this theorem is that it establishes the limits of applicability of Preisach's model regardless of the physical nature of hysteresis. Then, the vector Preisach models are formulated and some basic properties of these models are briefly summarized. Numerical implementations of Preisach's models are discussed and some computational results are given.

A Simple Biosphere Model (SIB) for Use within General Circulation Models

Abstract: A simple realistic biosphere model for calculating the transfer of energy, mass and momentum between the atmosphere and the vegetated surface of the earth has been developed for use in atmospheric general circulation models. The vegetation in each terrestrial model grid is represented by an upper level, representing the perennial canopy of trees and shrubs, and a lower level, representing the annual cover of grasses and other heraceous species. The vegetation morphology and the physical and physiological properties of the vegetation layers determine such properties as: the reflection, transmission, absorption and emission of direct and diffuse radiation; the infiltration, drainage, and storage of the residual rainfall in the soil; and the control over the stomatal functioning. The model, with prescribed vegetation parameters and soil interactive soil moisture, can be used for prediction of the atmospheric circulation and precipitaion fields for short periods of up to a few weeks.

Neutrino mass and baryon-number nonconservation in superstring models

Abstract: We propose new mechanisms for understanding neutrino masses in superstring models that contain ${\mathrm{E}}_{6}$-singlet zero-mass fields after compactification. We show that the low-energy gauge group of these models can be phenomenologically acceptable. We then comment on \ensuremath{\Delta}B=1 and \ensuremath{\Delta}B=2 baryon-number-violating processes in these models.

Training in Organizations: Needs Assessment, Development, and Evaluation

Abstract: In this extensive revision of his best-selling text, Irwin Goldstein, a leader in the training field, teams up with Kevin Ford, well-known for his work in "the learning organization," to provide readers with a framework for examining and establishing viable training programs in education, business, and government. Capturing the excitement of training research and systems issues, the author discusses training as it occurs in real organizations. Part I focuses on societal training issues, how organizations conduct assessments to understand their training needs, and significant issues in learning and instruction. Part II focuses on the evaluation process, and Part III reviews training programs and procedures.

The Euler characteristic of the moduli space of curves

Abstract: Let Fg 1, g> 1, be the mapping class group consisting of all isotopy classes of base-point and orientation preserving homeomorphisms of a closed, oriented surface F of genus g. Let )~(~1) be its Euler characteristic in the sense of Wall, that is Z(F~I)= [Fgl: F] l z(E/F), where F is any torsion free subgroup of finite index in F~ 1 and E is a contractible space on which F acts freely and properly discontinuously. An example of such a space is the Teichmiiller space ~-~1, and g(F~ ~) can be interpreted as the orbifold Euler characteristic of ~-~'/F~I =JOin, the moduli space of curves of genus g with base point. The purpose of this paper is to prove the following formula for )~(F~I):

Review of galactic constants

Abstract: La commission 33 de l'UAI (Delhi, 21 novembre, 1985) a adopte les deux constantes R 0 =8,5 kpc et O 0 =220 kms −1

Mechanism for understanding small neutrino mass in superstring theories.

Abstract: We propose a new mechanism for understanding small neutrino masses in supersymmetric theories without unnatural fine tuning of parameters. This idea may be useful for superstring ${\mathrm{E}}_{6}$ models, where the conventional mechanism is not available for suppressing neutrino masses.

Experimentation in software engineering

Abstract: A framework is presented for analyzing most of the experimental work performed in software engineering over the past several years. The framework of experimentation consists of four categories corresponding to phases of the experimentation process: definition, planning, operation, and interpretation. A variety of experiments are described within the framework and their contribution to the software engineering discipline is discussed. Some recommendations for the application of the experimental process in software engineering are included.

Fracture dislocations of the tarsometatarsal joints: end results correlated with pathology and treatment.

Abstract: Seventy-two patients with 76 fracture-dislocations of the Lisfranc tarsometatarsal joint complex were evaluated. Fifty-eight (81%) were polytrauma patients and the remainder suffered isolated injuries. Sixty of the original 72 patients were available for long-term study. Eight of these had an amputation at or shortly after the original admission, leaving 52 patients with 55 Lisfranc injuries for analysis. The average length of follow-up was 4.2 years (range, 20 months to 11 years). According to the Painful Foot Center scoring system, 27 feet (49%) achieved an excellent or good result and 28 (51%), a fair or poor result. Direct crush injuries did poorly with only one of eight scoring good or excellent. Of the various treatment modalities, open reduction and internal fixation with Kirschner wires yielded the best results. The major determinant of unacceptable results was identified as the quality of the initial reduction. Tarsal instability and late degenerative joint disease caused most of the symptoms. Twenty-three of the 52 patients (44%) have had or should have further mid-foot surgery to improve function and comfort. Because our results were often poor, our present protocol includes closed or open reduction and Kirschner wire internal fixation. Displacement greater than 2 mm or a talometatarsal angle greater than 15 degrees on radiographs following a closed reduction mandates open reduction.

The virtual cohomological dimension of the mapping class group of an orientable surface

Abstract: Let F = F ~ r be the mapping class group of a surface F of genus g with s punctures and r boundary components. The purpose of this paper is to establish cohomology properties of F parallel to those of the arithmetic groups. If G is a linear algebraic group defined over Q, X is the symmetric space associated to G and A is an arithmetic subgroup of G, then A is virtually torsion free and acts properly discontinuously on X. The rational homology of A is the same as that of X/A. Furthermore there is a "bordification" of X ([BS]) to a manifold with corners 3~ and an extension of the action of A to a properly discontinuous action on Jf so that the quotient X / A is compact. The boundary of Jf is homotopy equivalent to a wedge of spheres, say of dimension d, and the virtual cohomological dimension of A is n d + 1, where n is the dimension of X. In the case of the mapping class group there is no analog for G, Ivanov (unpublished) has proven that F is not arithmetic. Nevertheless, F acts properly discontinuously on Teichmiiller space r which is homeomorphic to Euclidean space (of dimension 6 g 6 + 2 s ) ; 3"will play the role of the symmetric space. The quotient of .9by F is the moduli space of curves whose rational homology is then identified with that of E Harvey [Har] has constructed a Borel-Serre bordification J of 3-by analytic methods. In the case where F has punctures, we will build g by a different, combinatorial method. In addition, we will explicitly describe inside Y a cell complex Y of dimension 4 g 4 + s onto which J may be F-equivariantly retracted, thus establishing an analog of the constructions for SL n by Serre, Soul6 ([Sol) and Ash ([A]). This complex will be of the lowest possible dimension because we will use J= to prove our main result:

Analysis of the dynamics of African vegetation using the normalized difference vegetation index

Abstract: Images at a resolution of 8 km are currently being generated for the whole of Africa, displaying the normalized difference vegetation index (NDVI). These images have undergone a process of temporal compositing to reduce the effects of cloud cover and atmospheric variation. When the NDVI is plotted against time, different cover types are shown to have characteristic profiles corresponding closely with their phenology. The resultant pattern of NDVI values displayed on the images is analyzed in terms of the cover types present and local variations in rainfall. Comparison between images for 1983 and 1984 overall showed considerable similarities, but significant differences were observed in the northward extent of the greening wave in the Sahel, the greening up of the Kalahari Desert and East African communities. It is concluded that vegetation monitoring using NDVI images needs to be associated with scene stratification according to cover type.

Multiresolution path planning for mobile robots

Abstract: The problem of automatic collision-free path planning is central to mobile robot applications. An approach to automatic path planning based on a quadtree representation is presented. Hierarchical path-searching methods are introduced, which make use of this multiresolution representation, to speed up the path planning process considerably. The applicability of this approach to mobile robot path planning is discussed.

The Military And the Family As Greedy Institutions

Abstract: This paper analyzes military families as the intersection of two societal institutions, both of which make great demands on individuals in terms of commitment, loyalty, time, and energy. It shows t...

Computational Complexity of Network Reliability Analysis: An Overview

Abstract: This paper presents an overview of results related to the computational complexity of network reliability analysis problems Network reliability analysis problems deal with the determination of reliability measures for stochastic networks We show how these problems are related to the more familiar computational network problems of recognizing certain subnetworks, finding optimal subnetworks, and counting certain subnetworks We use these relationships to show that the k-terminal, the 2-terminal, and the all-terminal network reliability analysis problems are at least as hard as the renowned set of computationally difficult problems, NP-Complete Finally, we discuss the impact of these results on how one should approach problem solving in this area

Nonlinear pulse propagation in the neighborhood of the zero-dispersion wavelength of monomode optical fibers

Abstract: Nonlinear pulse propagation is investigated in the neighborhood of the zero-dispersion wavelength in monomode fibers. When the amplitude is sufficiently large to generate breathers (N > 1 solitons), it is found that the pulses break apart if λ – λ0 is sufficiently small, owing to the third-order dispersion. Here λ0 denotes the zero-dispersion wavelength. By contrast, the solitary-wave (N = 1) solution appears well behaved for arbitrary λ – λ0. Implications for communication systems and pulse compression are discussed.

An in situ HVEM study of dislocation generation at Al/SiC interfaces in metal matrix composites

Abstract: ANNEALED aluminum/silicon carbide (Al/SiC) composites exhibit a relatively high density of dislocations, which are frequently decorated with fine precipitates, in the Al matrix. This high dislocation density is the major reason for the unexpected strength of these composite materials. The large difference (10:1) between the coefficients of thermal expansion (CTE) of Al and SiC results in sufficient stress to generate dislocations at the Al/SiC interface during cooling. In thisin situ investigation, we observed this dislocation generation process during cooling from annealing temperatures using a High Voltage Electron Microscope (HVEM) equipped with a double tilt heating stage. Two types of bulk annealed composites were examined: one with SiC of discontinuous whisker morphology and one of platelet morphology. In addition, control samples with zero volume percent were examined. Both types of composites showed the generation of dislocations at the Al/SiC interface resulting in densities of at least 1013 m-2. One sample viewed end-on to the whiskers showed only a rearrangement of dislocations, whereas, the same material when sectioned so that the lengths of whiskers were in the plane of the foil, showed the generation of dislocations at the ends of the whiskers on cooling. The control samples did not show the generation of dislocations on cooling except at a few large precipitate particles. The results support the hypothesis that the high dislocation density observed in annealed composite materials is a result of differential thermal contraction of Al and SiC. The SiC particles act as dislocation sources during cooling from annealing temperatures resulting in high dislocation densities which strengthen the material.

Bacterioplankton: A Sink for Carbon in a Coastal Marine Plankton Community

Abstract: Recent determinations of high production rates (up to 30 percent of primary production in surface waters) implicate free-living marine bacterioplankton as a link in a "microbial loop" that supplements phytoplankton as food for herbivores. An enclosed water column of 300 cubic meters was used to test the microbial loop hypothesis by following the fate of carbon-14—labeled bacterioplankton for over 50 days. Only 2 percent of the label initially fixed from carbon-14—labeled glucose by bacteria was present in larger organisms after 13 days, at which time about 20 percent of the total label added remained in the particulate fraction. Most of the label appeared to pass directly from particles smaller than 1 micrometer (heterotrophic bacterioplankton and some bacteriovores) to respired labeled carbon dioxide or to regenerated dissolved organic carbon-14. Secondary (and, by implication, primary) production by organisms smaller than 1 micrometer may not be an important food source in marine food chains. Bacterioplankton can be a sink for carbon in planktonic food webs and may serve principally as agents of nutrient regeneration rather than as food.

Drop breakup in turbulent stirred‐tank contactors. Part I: Effect of dispersed‐phase viscosity

Abstract: The extent to which dispersed-phase viscosity influences equilibrium mean drop size and drop size distribution at constant interfacial tension is determined for dilute suspensions by dispersing silicone oils of various viscosity grades in water. A mechanistic model for mean drop size is developed which predicts the moderate-viscosity data and whose parameters correlate the high-viscosity results. Trends in the mean size data coincide with those for the drop size distribution, which broadens considerably as viscosity increases and suggests a dependency on breakage mechanism.

Accommodating Science The Rhetorical Life of Scientific Facts

Abstract: This article studies the fate of scientific observations as they pass from original research reports intended for scientific peers into popular accounts aimed at a general audience. Pairing article...

Mathematical models of hysteresis.

Abstract: A new approach to Preisach's hysteresis model, which emphasizes its phenomenological nature and mathematical generality, is briefly described. Then the theorem which gives the necessary and sufficient conditions for the representation of actual hysteresis nonlinearities by Preisach's model is proven. The significance of this theorem is that it establishes the limits of applicability of this model.

Profits in the Long Run

Abstract: Profits in the Long Run asks two questions: Are there persistent differences in profitability across firms? If so, what accounts for them? This book answers these questions using data for the 1000 largest US manufacturing firms in 1950 and 1972. It finds that there are persistent differences in profitability and market power across large US companies. Companies with persistently high profits are found to have high market shares and sell differentiated products. Mergers do not result in synergistic increases in profitability, but they do have an averaging effect. Companies with above normal profits have their profits lowered by mergers. Companies with initially below normal profits have them raised. In addition, the influence of other variables on long-run profitability, including risk, sales, diversification, growth and managerial control, is explored. The implications of antitrust policy are likewise addressed.

Family socialization of emotional expression and nonverbal communication styles and skills.

Abstract: Bilan de l'analyse des reponses de 64 etudiants a un questionnaire mesurant les styles familiaux d'expression emotionnelle, en vue d'etudier les effets de cette variable sur la propre expression emotionnelle des individus ainsi que sur leurs comportements et habiletes non verbales

Resource Sharing Among Sbus: Strategic Antecedents and Administrative Implications

Abstract: Despite widespread resource sharing among strategic business units (SBUs), questions such as when resource sharing is desirable and what its administrative implications are have rarely been examine...