Showing papers by "Virginia Tech published in 1988"

Computer Relaying for Power Systems

Abstract: This text/reference presents a comprehensive, up-to-date account of computer relaying in power systems, based in part on the author's extensive experience in the field. Provides background material on current relaying practices, and covers the mathematical foundations for relaying algorithms. Each chapter contains helpful illustrations, examples, and problems.

A molecular sieve with eighteen-membered rings

Abstract: In this letter we describe a novel family of aluminophosphate-based molecular sieves denoted as VPI-5. These molecular sieves are the first to contain rings consisting of greater than twelve tetrahedral atoms. The large pores of the VPI-5 materials are long channels circumscribed by rings containing eighteen tetrahedral atoms and possess free diameters of approximately 12-13 A.

Clostridium difficile: its disease and toxins.

Abstract: Clostridium difficile is the etiologic agent of pseudomembranous colitis, a severe, sometimes fatal disease that occurs in adults undergoing antimicrobial therapy. The disease, ironically, has been most effectively treated with antibiotics, although some of the newer methods of treatment such as the replacement of the bowel flora may prove more beneficial for patients who continue to relapse with pseudomembranous colitis. The organism produces two potent exotoxins designated toxin A and toxin B. Toxin A is an enterotoxin believed to be responsible for the diarrhea and mucosal tissue damage which occur during the disease. Toxin B is an extremely potent cytotoxin, but its role in the disease has not been as well studied. There appears to be a cascade of events which result in the expression of the activity of these toxins, and these events, ranging from the recognition of a trisaccharide receptor by toxin A to the synergistic action of the toxins and their possible dissemination in the body, are discussed in this review. The advantages and disadvantages of the various assays, including tissue culture assay, enzyme immunoassay, and latex agglutination, currently used in the clinical diagnosis of the disease also are discussed.

Search for Neutral Metastable Penetrating Particles Produced in the SLAC Beam Dump

Abstract: A search was made for neutral objects which might be produced by 20-GeV electrons incident on the SLAC beam dump, penetrate the downstream natural shielding, and decay upstream of an electromagnetic shower calorimeter. With about 30 C of electrons dumped, no candidate events were found above an energy of \ensuremath{\sim}2 GeV. The 95%-confidence-level limit on the product of mass and lifetime of light axionlike bosons decaying primarily into two photons is determined to be greater than 1.4 keV sec. Limits on photino parameters are also given.

X charts with variable sampling intervals

Abstract: The usual practice in using a control chart to monitor a process is to take samples from the process with fixed sampling intervals. This article considers the properties of the chart when the sampling interval between each pair of samples is not fixed but rather depends on what is observed in the first sample. The idea is that the time interval until the next sample should be short if a sample shows some indication of a change in the process and long if there is no indication of a change. The proposed variable sampling interval (VSI) chart uses a short sampling interval if is close to but not actually outside the control limits and a long sampling interval if is close to target. If is actually outside the control limits, then the chart signals in the same way as the standard fixed sampling interval (FSI) chart. Properties such as the average time to signal and the average number of samples to signal are evaluated. Comparisons between the FSI and the VSI charts indicate that the VSI chart is substantially ...

The impact of divorce on children.

Abstract: With the acceleration of the divorce rate from the mid- 1960s to the early 1980s, the number of nontraditional families (such as single-parent families and reconstituted families) have increased relative to intact, first-time nuclear families, This article reviews empirical evidence addressing the relationship between divorce, family composition, and children's well-being. Although not entirely consistent, the pattern of empirical findings suggests that children's emotional adjustment, gender-role orientation, and antisocial behavior are affected by family structure, whereas other dimensions of well-being are unaffected. But the review indicates that these findings should be interpreted with caution because of the methodological deficiencies of many of the studies on which these findings are based. Several variables, including the level of family conflict, may be central variables mediating the effect of family structure on children.

Climatological observations and predicted sublimation rates at Lake Hoare, Antarctica.

Abstract: In December 1985, an automated meteorological station was established at Lake Hoare in the dry valley region of Antarctica. Here, the first year-round observations available for any site in Taylor Valley are reported. The mean annual solar flux at Lake Hoare was 92 W/sq m during 1986, the mean air temperature -17.3 C, and the mean 3-m wind speed 3.3 m/s. The local climate is controlled by the wind regime during the 4-month sunless winter and by seasonal and diurnal variations in the incident solar flux during the remainder of the year.

Polysiloxane containing copolymers: A survey of recent developments

Abstract: The principal focus of this review will be to document and discuss the recent developments in the synthesis, properties and applications of polyorganosiloxane containing block, segmented and graft copolymers and network structures. Special emphasis will be given to the synthesis and characterization of reactive, organofunctionally-terminated siloxane oligomers, which are the key starting materials or intermediates in the preparation of these well-defined copolymers. Use of these functionally terminated oligomers in the modification of network structures will be discussed. Detailed descriptions of the copolymer formation reactions and the effect of reaction variables, such as temperature and solvent, on the properties of the resultant materials will be given. Discussions of the bulk and surface morphology of siloxane containing copolymers and their blends with other polymeric systems will be provided. Potential applications of these novel materials and possible future directions in the chemistry and technology of polyorganosiloxane containing polymeric systems will also be discussed.

Bank loan-loss provisions and the income-smoothing hypothesis: An empirical analysis, 1976–1984

Abstract: This article tests an income-smoothing hypothesis for a sample of 106 large bank holding companies for the period 1976 to 1984. Our focus is on the behavior of the provision for loan losses as a function of bank income and alternative measures of business conditions likely to affect loan portfolio risk-taking or quality. Using an econometric model with pooled time-series, cross-sectional data, we find evidence of income-smoothing behavior over our test period. Our dummy-variable models indicate that regional banking companies tend to engage in income smoothing more than money-center banks. Alternative motivations for income-smoothing behavior, which include bank regulatory policy, risk management, agency theory, and compensation policy, are explored and their policy implications considered.

Masculine gender-role stress: predictor of anger, anxiety, and health-risk behaviors.

Abstract: We suggest that male gender-role identification affects whether specific situations are appraised as stressful. A questionnaire was developed to measure masculine gender-role stress (MGRS). Correlational data and multiple regression were used to validate the MGRS scale as a measure of gender-related stress in men, and compare its predictive utility with Spence's commonly-used measure of masculinity. Findings indicate that stress appraisal is gender related, that is, men experience more masculine-role stress than women. Further, the construct of MGRS was distinguished from the concept of masculinity. Finally, MGRS predicted increased anger, increased anxiety, and poorer health behaviors.

The Ethnographic Research Tradition and Mathematics Education Research.

Abstract: Although in theory ethnography has been put forward as a powerful naturalistic methodology, in practice it has rarely been used by educational researchers because of differences in assumptions, goals, and primary research questions. From my perspective as an educational anthropologist, I describe the research tradition of ethnography-its underlying assumptions, its heritage in holistic cultural anthropology, its goals and research questions, and the organization of its research methods. Throughout, I compare elements of this ethnographic tradition with more common educational research practices. In the final section, I discuss the advantages of improved communication for future research in both mathematics education and educational anthropology.

Cohesiveness and Performance on an Additive Task: Evidence for Multidimensionality.

Abstract: This experiment contrasted two predictions regarding the effects of two types of cohesiveness on the performance of American students. Task-based cohesion and interpersonal cohesion were manipulated independently. Results show that high task cohesion facilitated performance, whereas interpersonal attraction had no apparent effect on production. Increases in interpersonal cohesion did, however, result in higher task commitment and more frequent interactions among group members. A path analysis suggested that potentially beneficial effects on production of increasing task commitment were obviated by the increased conversation also resulting from interpersonal cohesion. These data suggest that cohesiveness should be conceptualized as a multidimensional rather than as a unitary variable.

Adaptive transmission system relaying

Abstract: The use of digital techniques to adapt transmission system protection and control to real-time power system changes is investigated. The discussion covers transmission system protection philosophy, transmission line protection, relay settings, transformer protection, and automatic reclosing. The tradeoff between dependability and security is examined, as well as the various conflicting criteria embodied in transmission line protection. Adaptive strategies that minimize the compromises required and thereby optimize system performance are presented. >

The sperm chromatin structure assay. Relationship with alternate tests of semen quality and heterospermic performance of bulls.

Abstract: Data obtained by the sperm chromatin structure assay (SCSA) on spermatozoa from nine bulls were correlated with fertility, measured by heterospermic performance (-0.94, P less than 0.01) and by alternate tests of sperm quality, including motility, acrosome integrity, Sephadex filtration and morphology of spermatozoa (all significant at P less than 0.05 to P less than 0.01). The SCSA uses flow cytometry to determine the susceptibility of nuclear DNA to low pH-induced denaturation in situ as measured by the ratio of acridine orange binding to double- or single-stranded DNA. The error associated with multiple SCSA measurements was relatively low. The primary finding is that the assay of chromatin structure stability performed on killed spermatozoa was as highly correlated with the heterospermic performance of semen as the best of the classical tests for semen quality. The SCSA may therefore be a highly useful technique for evaluation of sperm quality.

The Effects of Task and Interpersonal Cohesiveness on Performance of a Disjunctive Group Task1

Abstract: This experiment examined the effects of two different types of group cohesiveness on performance of a disjunctive task. Both interpersonal and task cohesiveness were varied independently. Results show that high levels of both types of cohesiveness were necessary for success on a task requiring group interaction. Groups high on one type of cohesiveness but low on another performed no better than groups low on both types of cohesiveness. These results suggest that cohesiveness should be conceptualized as a multidimensional rather than as a unitary variable. It is also suggested that the effects noted in the present study may well vary according to task characteristics.

Hoist Scheduling For A PCB Electroplating Facility

Abstract: This paper describes a model and associated algorithm for generating maximum throughput cyclic schedules for the movements of a hoist in a PCB electroplating facility. The algorithm is enumerative in nature and involves the solution of linear programming subproblems. Computational experience with schedules for real systems is presented.

Recreational Specializations and Motivations of Virginia River Anglers

Abstract: On-site interviews and a mail questionnaire survey of 377 anglers on two Virginia rivers were used to evaluate the concept of recreational specialization for differentiating angler subgroups. Specialization was defined for four dimensions of angler behavior: (1) fishery resource use, (2) experience, (3) investment, and (4) centrality of angling to lifestyle. Six types of anglers, representing low to high levels of specialization, were identified by cluster analysis. The experience dimension was the most important contributor to the framework, accounting for 24% of the variance in the data. A combination of the resource, investment, and centrality dimensions explained 48% of the variance. Highly specialized anglers were likely to cite resource-related motives (e.g., trophy fish), to rely on skill to catch fish, to prefer to catch and release larger fish, and to favor restrictive harvest regulations. Less specialized anglers cited escape and family-oriented recreation as motivations for fishing, pl...

Derivatives of eigenvalues and eigenvectors of a general complex matrix

Abstract: A survey of methods for sensitivity analysis of the algebraic eigenvalue problem for non-Hermitian matrices is presented. In addition, a modification of one method based on a better normalizing condition is proposed. Methods are classified as Direct or Adjoint and are evaluated for efficiency. Operation counts are presented in terms of matrix size, number of design variables and number of eigenvalues and eigenvectors of interest. The effect of the sparsity of the matrix and its derivatives is also considered, and typical solution times are given. General guidelines are established for the selection of the most efficient method.

The Southern Pine Beetle

Abstract: The Southern pine beetle, Dendroctonus frontalis Zimmerman (Coleoptera: Scolytidae), is the most destructive insect pest of pine forests in the southeastern United States and in parts of Mexico and Central America (Fig. 1). This is a well-worn statement but is nonetheless richly deserved and quite accurate. The beetle epitomizes the definition of its genus, killer of trees. As such, D. frontalis can overcome even vigorous trees when its populations are large. In the United States, the southern pine beetle primarily colonizes loblolly (Pinus taeda) and shortleaf (P. enchinata) pines, both of which are important sources of pulp and timber. These pines are fast-growing species, inhabiting some of the finest timber-growing land on the continent. In addition, most watersheds in the southern pine forest are dominated by these species, and in many recreational areas high-valued old growth pine prevail.

Analysis and Implications of the Edge Structure of Dioctahedral Phyllosilicates

Abstract: Crystal growth theory was applied to describe edge sites of phyllosilicates. Three face config- urations were found to exist. One face has one tetrahedral site per tetrahedral sheet and two octahedral one-coordinated sites per crystallographic area ac sin/3, where a and c are layer dimensions and/3 is the angle between them. The other two faces are similar except that they have one less octahedral site which is replaced by one Si'v-O-A1 vt site in this same ac sin/3 area. A transfer of bonding energy from the remaining octahedral site to the Si'v-O-A1 w site is believed to neutralize all edge charge on faces containing these latter sites at normally encountered pHs (pH 3-9). A similar charge rearrangement along the edges results in an apparent decrease in the permanent charge of the mineral with an increase in edge area. On the basis of such an analysis, lath-shaped illite can be described as a very fine grained dioctahedral mica in which the apparent deficient occupancy of the octahedral sheet, presence of excess water, and measurable cation-exchange capacity may in part be the result of a large ratio of edge area to total volume, with no other chemical or structural change in the mica layers. The increasing importance of edge charge relative to layer charge produces erroneous formulae for 2:1 phyllosilicates in very fine grained samples containing fewer than 2 of 3 octahedral sites occupied by cations, on the basis of a 22-charge half cell.