Showing papers by "Virginia Tech published in 1993"
TL;DR: In this article, the salinity of H[sub 2]O-salt inclusions from freezing measurements is determined based on a regression of data available in the literature at that time.
1,862 citations
01 Jan 1993
TL;DR: A fluid is a substance in which the constituent molecules are free to move relative to each other, and in a solid, the relative positions of molecules remain essentially fixed under non-destructive conditions of temperature and pressure.
Abstract: A fluid is a substance in which the constituent molecules are free to move relative to each other Conversely, in a solid, the relative positions of molecules remain essentially fixed under non-destructive conditions of temperature and pressure While these definitions classify matter into fluids and solids, the fluids subdivide further into liquid and gases
1,166 citations
TL;DR: The use of time synchronizing techniques, coupled with the computer-based measurement technique, to measure phasors and phase angle differences in real time is reviewed, and phasor measurement units are discussed.
Abstract: The use of time synchronizing techniques, coupled with the computer-based measurement technique, to measure phasors and phase angle differences in real time is reviewed, and phasor measurement units are discussed. Many of the research projects concerned with applications of synchronized phasor measurements are described. These include measuring the frequency and magnitude of phasor, state estimation, instability prediction, adaptive relaying, and improved control. >
1,126 citations
TL;DR: This research concentrates on several object-oriented software metrics and the validation of these metrics with maintenance effort in two commercial systems.
1,111 citations
TL;DR: This meta-analysis surveyed 177 usable sources that reported data on gender differences on 21 different measures of sexual attitudes and behaviors and found that gender differences narrowed from the 1960s to the 1980s for many variables.
Abstract: This meta-analysis surveyed 177 usable sources that reported data on gender differences on 21 different measures of sexual attitudes and behaviors. The largest gender difference was in incidence of masturbation: Men had the greater incidence (d = .96). There was also a large gender difference in attitudes toward casual sex: Males had considerably more permissive attitudes (d = .81). There were no gender differences in attitudes toward homosexuality or in sexual satisfaction. Most other gender differences were in the small-to-moderate range. Gender differences narrowed from the 1960s to the 1980s for many variables. Chodorow's neoanalytic theory, sociobiology, social learning theory, social role theory, and script theory are discussed in relation to these findings.
1,100 citations
Journal Article•
882 citations
Book•
21 May 1993TL;DR: Ensuring Usability in Human-Computer Interaction, a Handbook of Iterative, Evaluation-Centered User Interaction Development, and Techniques for Representing user Interaction Designs.
Abstract: Ensuring Usability in Human-Computer Interaction. THE PRODUCT. User Interaction Design Guidance: Standards, Guidelines, and Style Guides. Interaction Styles. THE PROCESS. Iterative, Evaluation-Centered User Interaction Development. An Overview of Systems Analysis and Design. Techniques for Representing User Interaction Designs. More on Using the User Action Notation. Usability Specification Techniques. Rapid Prototyping of Interaction Design. Formative Evaluation. User Interface Development Tools. Making It Work: Ensuring Usability in Your Development Environment. Index.
861 citations
TL;DR: A map of the barley genome consisting of 295 loci was constructed, which includes 152 cDNA restriction fragment length polymorphism (RFLP), 114 genomic DNA RFLP, 14 random amplified polymorphic DNA (RAPD), five isozyme, two morphological, one disease resistance and seven specific amplicon polymorphism
Abstract: A map of the barley genome consisting of 295 loci was constructed. These loci include 152 cDNA restriction fragment length polymorphism (RFLP), 114 genomic DNA RFLP, 14 random amplified polymorphic DNA (RAPD), five isozyme, two morphological, one disease resistance and seven specific amplicon polymorphism (SAP) markers. The RFLP-identified loci include 63 that were detected using cloned known function genes as probes. The map covers 1,250 centiMorgans (cM) with a 4.2 cM average distance between markers. The genetic lengths of the chromosomes range from 124 to 223 cM and are in approximate agreement with their physical lengths. The centromeres were localized to within a few markers on all of the barley chromosomes except chromosome 5. Telomeric regions were mapped for the short (plus) arms of chromosomes 1, 2 and 3 and the long (minus) arm of chromosomes 7.
649 citations
TL;DR: It is shown that, although the lack of comparative data established on reference test cases prevents an accurate assessment, there have been significant improvements in approximation concepts since the introduction of approximation concepts in the mid-seventies.
Abstract: This paper reviews the basic approximation concepts used in structural optimization. It also discusses some of the most recent developments in that area since the introduction of approximation concepts in the mid-seventies. The paper distinguishes between local, medium-range and global approximations; it covers function approximations and problem approximations. It shows that, although the lack of comparative data established on reference test cases prevents an accurate assessment, there have been significant improvements. The largest number of developments have been in the areas of local function approximations and use of intermediate variable and response quantities. It appears also that some new methodologies emerge which could greatly benefit from the introduction of new computer architectures.
581 citations
TL;DR: For instance, this paper found that infants whose mothers were monolingual speakers of Spanish or English were tested with audio recordings of female strangers speaking either Spanish and English, and infants activated recordings of their native language for longer periods than the foreign language.
Abstract: Newborn infants whose mothers were monolingual speakers of Spanish or English were tested with audio recordings of female strangers speaking either Spanish or English. Infant sucking controlled the presentation of auditory stimuli. Infants activated recordings of their native language for longer periods than the foreign language.
535 citations
TL;DR: It is shown that NIFS is a pyridoxal phosphate-containing homodimer that catalyzes the formation of L-alanine and elemental sulfur by using L-cysteine as substrate, and it is proposed that an enzyme-bound cysteinyl persulfide that requires the release of the sulfur from the substrate L- Cysteine for its formation ultimately provides the inorganic sulfide required for nitrogenase metallocluster formation.
Abstract: Biological nitrogen fixation is catalyzed by nitrogenase, a complex metalloenzyme composed of two separately purifiable component proteins encoded by the structural genes nifH, nifD, and nifK. Deletion of the Azotobacter vinelandii nifS gene lowers the activities of both nitrogenase component proteins. Because both nitrogenase component proteins have metallocluster prosthetic groups that are composed of iron- and sulfur-containing cores, this result indicated that the nifS gene product could be involved in the mobilization of the iron or sulfur required for metallocluster formation. In the present work, it is shown that NIFS is a pyridoxal phosphate-containing homodimer that catalyzes the formation of L-alanine and elemental sulfur by using L-cysteine as substrate. NIFS activity is extremely sensitive to thiol-specific alkylating reagents, which indicates the participation of a cysteinyl thiolate at the active site. Based on these results we propose that an enzyme-bound cysteinyl persulfide that requires the release of the sulfur from the substrate L-cysteine for its formation ultimately provides the inorganic sulfide required for nitrogenase metallocluster formation. The recent discovery of nifS-like genes in non-nitrogen-fixing organisms also raises the possibility that the reaction catalyzed by NIFS represents a universal mechanism that involves pyridoxal phosphate chemistry, in the mobilization of the sulfur required for metallocluster formation.
TL;DR: In this article, the problem of the allocation of several airplane flight controls to the generation of specified body-axis moments is addressed, and a direct method of allocating these several controls is presented that guarantees the maximum possible moment can be generated within the constraints of the controls.
Abstract: This paper addresses the problem of the allocation of several airplane flight controls to the generation of specified body-axis moments. The number of controls is greater than the number of moments being controlled, and the ranges of the controls are constrained to certain limits. They are assumed to be individually linear in their effect throughout their ranges of motion and independent of one another in their effects. The geometries of the subset of the constrained controls and of its image in moment space are examined. A direct method of allocating these several controls is presented that guarantees the maximum possible moment can be generated within the constraints of the controls. It is shown that no single generalized inverse can yield these maximum moments everywhere without violating some control constraint. A method is presented for the determination of a generalized inverse that satisfies given specifications which are arbitrary but restricted in number. We then pose and solve a minimization problem that yields the generalized inverse that best approximates the exact solutions. The results are illustrated at each step by an example problem involving three controls and two moments.
TL;DR: In this paper, an estimator for the coefficients in a single-index selectivity bias model is considered under the assumption that the selection correction function depends on the conditional mean of some observable "selection" variable.
TL;DR: In this paper, the authors present the results of average and impulsive noise measurements inside several office buildings and retail stores at 918 MHz, 2.44 GHz, and 4 GHz with a nominal 40-MHz, 3dB RF bandwidth.
Abstract: The authors present the results of average and impulsive noise measurements inside several office buildings and retail stores. The noise measurement system operated at 918 MHz, 2.44 GHz, and 4 GHz with a nominal 40-MHz, 3-dB RF bandwidth. Omnidirectional and directional antennas were used to investigate the characteristics and sources of RF noise in indoor channels. Statistical analyses of the measurements are presented in the form of peak amplitude probability distributions, pulse duration distributions, and interarrival time distributions. Simple first-order mathematical models for these statistical characterizations are also presented. These analyses indicate that photocopiers, printers (both line printers and cash register receipt printers), elevators, and microwave ovens are significant sources of impulse noise in office and retail environments. >
TL;DR: In this article, a suite of indicators to monitor regional environmental health, similar in conception to management use of ‘leading economic indicators’, are described, where linkages between human activities and well being and the state of the environment are considered essential to the evaluation of general environmental health.
Abstract: Considerations involved in developing a suite of indicators to monitor regional environmental health, similar in conception to management use of ‘leading economic indicators’, are described. Linkages between human activities and well being and the state of the environment are considered essential to the evaluation of general environmental health. Biogeochemical and socioeconomic indicators are mutually affected by environmental degradation and examples of both categories of indicators are described. Desirable properties in indicators of environmental health vary with their specific management use. Different indicators are called for when collecting data to assess the adequacy of the environment, monitor trends over time, provide early warning of environmental degradation, or diagnose the cause of an existing problem. Tradeoffs between desirable characteristics, costs, and quality of information are inevitable when choosing indicators for management use. Decisions about what information to collect for which purpose can be made more rationally when available indicators are characterized and matched to management goals.
TL;DR: In this paper, a solution to the plane elasticity problem for a symmetrically laminated composite panel with spatially varying fiber orientations has been obtained, and the effects of the variable fiber orientation on the displacement fields, stress resultants and global stiffness are analyzed.
Abstract: A solution to the plane elasticity problem for a symmetrically laminated composite panel with spatially varying fiber orientations has been obtained. The fiber angles vary along the length of the composite laminate, resulting in stiffness properties that change as a function of location. This work presents an analysis of the stiffness variation and its effects on the elastic response of the panel. The in-plane response of a variable stiff ness panel is governed by a system of coupled elliptic partial differential equations/Solving these equations yields the displacement fields, from which the strains, stresses, and stress resultants can be subsequently calculated. A numerical solution has been obtained using an iterative collocation technique. Corresponding closed-form solutions are presented for three sets of boundary conditions, two of which have exact solutions, and therefore serve to validate the numerical model. The effects of the variable fiber orientation on the displacement fields, stress resultants, and global stiffness are analyzed.
TL;DR: In this paper, a layerwise, two-dimensional, displacement-based, finite element model of laminated composite plates is proposed to compute interlaminar stresses and other localized effects with the same level of accuracy as conventional 3D finite element models.
Abstract: The layerwise laminate theory of Reddy (1987) is used to develop a layerwise, two-dimensional, displacement-based, finite element model of laminated composite plates that assumes a piecewise continuous distribution of the tranverse strains through the laminate thickness. The resulting layerwise finite element model is capable of computing interlaminar stresses and other localized effects with the same level of accuracy as a conventional 3D finite element model. Although the total number of degrees of freedom are comparable in both models, the layerwise model maintains a 2D-type data structure that provides several advantages over a conventional 3D finite element model, e.g. simplified input data, ease of mesh alteration, and faster element stiffness matrix formulation. Two sample problems are provided to illustrate the accuracy of the present model in computing interlaminar stresses for laminates in bending and extension.
TL;DR: By assuming that unreplicated DNA interferes with M-phase initiation by activating the phosphatases that oppose MPF in the positive feedback loops, the model can simulate the effect of addition of sperm nuclei to oocyte extracts, and the lengthening of cycle times at the mid-blastula transition of intact embryos.
Abstract: To contribute to a deeper understanding of M-phase control in eukaryotic cells, we have constructed a model based on the biochemistry of M-phase promoting factor (MPF) in Xenopus oocyte extracts, where there is evidence for two positive feedback loops (MPF stimulates its own production by activating Cdc25 and inhibiting Wee1) and a negative feedback loop (MPF stimulates its own destruction by indirectly activating the ubiquitin pathway that degrades its cyclin subunit). To uncover the full dynamical possibilities of the control system, we translate the regulatory network into a set of differential equations and study these equations by graphical techniques and computer simulation. The positive feedback loops in the model account for thresholds and time lags in cyclin-induced and MPF-induced activation of MPF, and the model can be fitted quantitatively to these experimental observations. The negative feedback loop is consistent with observed time lags in MPF-induced cyclin degradation. Furthermore, our model indicates that there are two possible mechanisms for autonomous oscillations. One is driven by the positive feedback loops, resulting in phosphorylation and abrupt dephosphorylation of the Cdc2 subunit at an inhibitory tyrosine residue. These oscillations are typical of oocyte extracts. The other type is driven by the negative feedback loop, involving rapid cyclin turnover and negligible phosphorylation of the tyrosine residue of Cdc2. The early mitotic cycles of intact embryos exhibit such characteristics. In addition, by assuming that unreplicated DNA interferes with M-phase initiation by activating the phosphatases that oppose MPF in the positive feedback loops, we can simulate the effect of addition of sperm nuclei to oocyte extracts, and the lengthening of cycle times at the mid-blastula transition of intact embryos.
TL;DR: In this paper, the free space propagation of an array of optical vortices nested in a smooth (Gaussian) beam is studied in the paraxial regime, and it is shown that their relative positions, as well as their positions within the host beam are invariant upon propagation.
Abstract: Free space propagation of an array of optical vortices nested in a smooth (Gaussian) beam is studied in the paraxial regime. It is found that when the vortices have all the same charge, their relative positions, as well as their positions within the host beam are invariant upon propagation. The array simply expands or contracts with the host beam and rotates rigidly. Vortices of opposite charges, in contrast, attract each other. Pairs can collide and annihilate. As an illustration, numerical simulation is used to compare the propagation of a pair of vortices of equal charges with that of a pair of opposite charges.
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TL;DR: Woody Allen's "Husbands and Wives" as discussed by the authors examines the relationships of two married New York couples over a period of just over a year and a half, and explores the undifferentiated nature of its principle figures and what might be called the intersystemic issues between the two dyads.
Abstract: Woody Allen's film,Husbands and Wives, examines the relationships of two married New York couples over a period of just over a year-and-a-half. Through a variety of means, it explores the undifferentiated nature of its principle figures and what might be called the intersystemic issues between the two dyads. It also offers strong, though undeveloped, indications of previous sexual abuse in several of its female characters.
TL;DR: In this paper, a modified zero-crossing method using curve fitting of voltage samples is proposed, and polynomial fitting of the discrete Fourier transform (DFT) quasi-stationary phasor data for calculation of the rate of change of the positive sequence phase angle.
Abstract: Three new techniques for frequency measurement are proposed. The first is a modified zero-crossing method using curve fitting of voltage samples. The second method is based on polynomial fitting of the discrete Fourier transform (DFT) quasi-stationary phasor data for calculation of the rate of change of the positive sequence phase angle. The third method operates on a complex signal obtained by the standard technique of quadrature demodulation. All three methods are characterized by immunity to reasonable amounts of noise and harmonics in power systems. The performance of the proposed techniques is illustrated for several scenarios by computer simulation. >
TL;DR: An investigation into methods of modeling the radiation patterns of phased arrays that include the effects of radiative mutual coupling that accurately predicts the patterns of small and medium-size arrays of equally spaced elements is presented.
Abstract: Results from an investigation into methods of modeling the radiation patterns of phased arrays that include the effects of radiative mutual coupling are presented. The approaches are based on either the principle of pattern multiplication or the use of active element patterns. Theoretical derivations of the various active element pattern methods are presented. A new method, the hybrid active element pattern method, is introduced. It accurately predicts the patterns of small and medium-size arrays of equally spaced elements. Example arrays of center-fed dipoles are analyzed to verify and illustrate the representations. The results are general and can be applied to arrays of any type of element. The array patterns computed using both the classical pattern multiplication approach and the methods based on active element patterns are compared to those computed using accurate numerical codes based on the method of moments. >
TL;DR: Correlations between reproductive traits and measures of milk yield indicate that higher yield is associated phenotypically and genetically with reduced reproductive performance in lactating cows, and the extent to which negative energy balance alters hypothalamic secretion of GnRH and its effect on gonadotropin secretion and, therefore, ovarian secretion of progesterone is unknown.
TL;DR: For instance, despite claims for achievement effects for parental involvement, there is no evidence that increased parental involvement can improve U.S. student achievement as discussed by the authors, despite the claim that it is one method of improving student achievement.
Abstract: Educators and policy makers recently have touted increased parental involvement as one method of improving U.S. student achievement. Despite claims for achievement effects for parental involvement,...
TL;DR: In this paper, a meta-analysis of 40 self-help studies examining 61 treatments which used as control groups no-treatment, wait-list, or placebo comparisons was conducted.
TL;DR: The authors reviewed research findings related to teacher retention and attrition in special education and reviewed major findings from general education retention studies to provide a context for understanding special educators' career decisions, which includes three major factors: (a) external (e.g., societal, economic, and institutional), (b) employment, professional qualifications, work conditions and rewards, commitment, and employability), and (c) personal, demographics, family and cognitive/ affective).
Abstract: The primary purpose of this paper is to review research findings related to teacher retention and attrition in special education. Major findings from general education retention studies are also reviewed to provide a context for understanding special educators' career decisions. Research findings are organized around a conceptual model of teachers' career decisions that includes three major factors: (a) external (e.g., societal, economic, and institutional), (b) employment (e.g., professional qualifications, work conditions and rewards, commitment, and employability), and (c) personal (e.g., demographics, family, and cognitive/ affective). Conceptual and methodological considerations related to attrition/retention research are also considered.
TL;DR: A conceptual framework for understanding the relationship of the objective permanent (defensible space) and transient (territorial markers and incivilities) physical environment and the subjective environment to crime is presented in this paper.
TL;DR: This paper reviews techniques that have shown sufficient sensitivity and robustness to be used in test and evaluation in workload estimation situations and makes recommendations for workload estimation intest and evaluation situations.
Abstract: Research performed during the last decade on estimation of mental workload has resulted in a subset of techniques exhibiting global sensitivity. Other techniques have also been demonstrated to have...
TL;DR: The Sad-Film Scale (SFS) developed in this paper was positively associated with measures of empathy, femininity, and positive appraisals of sad emotions and was used to explore the enjoyment of sad films and to develop a scale that would reflect such gratifications.
Abstract: The concept of met emotions (appraisals of emotional reactions) was used in three studies designed to explore the enjoyment of sad films and to develop a scale that would reflect such gratifications. Study 1 showed that sad reactions in response to this type of entertainment were positively related to enjoyment and that females reported stronger reactions both in terms of enjoyment and in terms of sad responses than males. The Sad-Film Scale (SFS) developed in Study 1 was positively associated with measures of empathy, femininity, and positive appraisals of sad emotions. Study 2 found evidence of the scale's reliability and validity. Study 3 demonstrated predictive validity of the SFS in terms of the enjoyment of a specific sad film and in terms of favorable ratings of met emotions reported directly after viewing a sad film.
TL;DR: In this paper, the mass-balance equation that partitions energy of consumed food into its various physiological fates has flourished in the past 15 years and has been converted to powerful simulation tools and used in fisheries science, most often for predicting consumption by predators or projecting fish growth as a function of temperature and prey availability.
Abstract: Elaborations of the mass-balance equation that partitions energy of consumed food into its various physiological fates have flourished in the past 15 years. These bioenergetics models have been converted to powerful simulation tools and used in fisheries science, most often for predicting consumption by predators or for projecting fish growth as a function of temperature and prey availability. New uses of bioenergetics models are proliferating and range from predictions of larval survival to analysis of ecosystem function. Companion technologies such as hydroacoustics and physiological telemetry promise to further broaden the spectrum of potential applications. However, the data demands and uncertain accuracy of multiparameter models may constrain their ability to address routine fish management questions. Field measures of consumption or growth failed to corroborate bioenergetics estimates consistently (differences of at least 50%) in four of six published tests. Poor agreement could be due to i...