Showing papers by "Virginia Tech published in 1989"

The effect of price, brand name, and store name on buyers' perceptions of product quality: An integrative review.

Abstract: The authors integrate previous research that has investigated experimentally the influence of price, brand name, and/or store name on buyers’ evaluations of product quality. The meta-analysis sugge...

Analysis and evaluation of five short-term load forecasting techniques

Abstract: Load forecast has been a central and an integral process in the planning and operation of electric utilities. Many techniques and approaches have been investigated to tackle this problem in the last two decades. These are often different in nature and apply different engineering considerations and economic analyses. In this paper a comparative evaluation of five short-term load forecasting techniques is presented. These techniques are: 1. Multiple Linear Regression; 2. Stochastic Time Series; 3. General Exponential Smoothing; 4. State Space Method; and 5. Knowledge-Based Approach. The authors have applied these algorithms to obtain hourly load forecasts (for up to 24 hours) during the winter and summer peaking seasons. Thus the five forecasting methodologies have been applied to the same database and their performances are directly compared. The forecast error analyses are provided in Tables 1 and 2 for the winter and summer days respectively. As these results are based on forecasts of two single days, these should be used for comparative purposes only. Some interesting observations are made about the results presented in Tables 1 and 2. For example, for the peak summer day the transfer function (TF) approach gave the best result, whereas for the peak winter day the TF approach resulted in the next to the worst accuracy. During the peak summer day the temperature profile was typical whereas during the peak winter day the profile was unseasonal.

Response surface methodology: 1966–1988

Abstract: Response sarfxe methodology (RSM) is a collection of tools developed in the 1950s for the purpose of determining optimum operating conditions in applications in the chemical industry. This article reviews the progrrss of RSM in the general areas of experimental design and analysis and indicates how its role has been affected by advanccs in other fields of applied statistics. Current areas of research in RSM are highlighted. and areas for future research are discussed.

Biosynthesis and antioxidant function of glutathione in plants

Abstract: Le glutathion est synthetise aussi bien par les chloroplastes que par le cytosol. Avec l'ascorbate, il protege les macromolecules contre l'oxydation pouvant resulter de stress tels que les temperatures extremes, la secheresse, les herbicides, les polluants atmospheriques

Recent advances in analysis of laminated beams and plates. Part I - Sheareffects and buckling.

Abstract: A review of the recent developments in the analysis of laminated beams and plates with an emphasis on shear effects and buckling is presented. A discussion of various shear-deformation theories for plates and beams is given. The available theories are derived assuming a variation of either the in-plane displacement components or the stress components or both in the thickness coordinate. A review of the recently developed finite elements to analyze thin and thick laminated beams and plates is given next. These elements have been derived using the displacement methods, or the mixed methods or the hybrid methods. Recent studies on the buckling and postbuckling behavior of perfect and geometrically imperfect plates are described next. These behaviors have been studied using analytical, numerical, and experimental techniques. Finally, a review of the various studies on the delamination buckling and growth in beams and plates is given. Once again, the studies have been conducted using analytical, numerical, and experimental techniques. The energy release rates have been determined using closed-form solutions or using numerical differentiation. Mention also is made of studies on multiple delaminations and on dynamic response of composite laminates under impact loads.

The Effect of Bubble Size on Fine Particle Flotation

Abstract: Expressions for the probability of collision (Pc) and adhesion (Pa) have been derived for fine particle flotation by calculating the trajectory of particles as they flow past a bubble in streamline How. Three different flow regimes have been considered in the present work, i.e., Stokes, potential and intermediate. For the intermediate flow conditions in which most flotation operations are carried out, the particle trajectories have been determined using an empirical stream function derived in the present work. For the case of a very hydrophobic coal sample, the values of the probability of collection (P) determined experimentally have been found to be in close agreement with the theoretically predicted Pc values over a range of bubble and particle sizes The expression for Pa has been derived by determining the time it takes for a particle to slide along the surface of a bubble after collision. It has been assumed that the bubble-particte adhesion occurs when the sliding time is equal to or exceed...

Self-Perceptions of Black Americans: Self-Esteem and Personal Efficacy

Abstract: This study examines the determinants of personal self-esteem, racial self-esteem, and personal efficacy in a 1980 national sample of black Americans. The findings show that the three dimensions are interrelated and each is anchored in interpersonal relations with family and friends. However, the three dimensions are produced by fundamentally different processes. Personal self-esteem is most strongly influenced by microsocial relations with family, friends, and community, while personal efficacy is generated through experiences in social statuses embedded in macrosocial systems of social inequality. We conclude that black self-esteem is insulated from systems of racial inequality, while personal efficacy is not, and suggest that this explains why black Americans have relatively high self-esteem but low personal efficacy. The belief that racial discrimination, rather than individual failure, accounts for low achievement among blacks is irrelevant to personal self-esteem and personal efficacy. In contrast, racial self-esteem is produced by a combination of education, interracial contact, and ideological processes.

A manual colorimetric procedure for measuring ammonium nitrogen in soil and plant Kjeldahl digests

Abstract: The measurement of NH4+‐N in soil, and plant digests is one of the greatest needs in laboratories conducting agricultural and environmental research. Many laboratories do not have access to automated equipment for colorimetric analysis of soil and plant digests. The objective of this research was to modify an automated colorimetric analysis procedure for determining NH4+‐N in soil and plant digests for manual use, and compare the proposed technique with the standard distillation‐titration technique. The modified procedure is based on the color reaction between NH4 +‐ and a weakly alkaline mixture of Na salicylate and a chlorine source in the presence of Na nitroprusside. Wavelength scans indicated a very well defined peak for determinations at 650 nm. Time scans showed that color development in the manual procedure was rapid, 12 to 40 minutes depending on temperature, and that the color development remained stable for at least 120 minutes. Regression analysis of the results from 18 soil and 20 pl...

Recent developments in structural sensitivity analysis

Abstract: Recent developments are reviewed in two major areas of structural sensitivity analysis: sensitivity of static and transient response; and sensitivity of vibration and buckling eigenproblems. Recent developments from the standpoint of computational cost, accuracy, and ease of implementation are presented. In the area of static response, current interest is focused on sensitivity to shape variation and sensitivity of nonlinear response. Two general approaches are used for computing sensitivities: differentiation of the continuum equations followed by discretization, and the reverse approach of discretization followed by differentiation. It is shown that the choice of methods has important accuracy and implementation implications. In the area of eigenproblem sensitivity, there is a great deal of interest and significant progress in sensitivity of problems with repeated eigenvalues. In addition to reviewing recent contributions in this area, the paper raises the issue of differentiability and continuity associated with the occurrence of repeated eigenvalues.

Physical and genetic map of the major nif gene cluster from Azotobacter vinelandii.

Abstract: Determination of a 28,793-base-pair DNA sequence of a region from the Azotobacter vinelandii genome that includes and flanks the nitrogenase structural gene region was completed. This information was used to revise the previously proposed organization of the major nif cluster. The major nif cluster from A. vinelandii encodes 15 nif-specific genes whose products bear significant structural identity to the corresponding nif-specific gene products from Klebsiella pneumoniae. These genes include nifH, nifD, nifK, nifT, nifY, nifE, nifN, nifX, nifU, nifS, nifV, nifW, nifZ, nifM, and nifF. Although there are significant spatial differences, the identified A. vinelandii nif-specific genes have the same sequential arrangement as the corresponding nif-specific genes from K. pneumoniae. Twelve other potential genes whose expression could be subject to nif-specific regulation were also found interspersed among the identified nif-specific genes. These potential genes do not encode products that are structurally related to the identified nif-specific gene products. Eleven potential nif-specific promoters were identified within the major nif cluster, and nine of these are preceded by an appropriate upstream activator sequence. A + T-rich regions were identified between 8 of the 11 proposed nif promoter sequences and their upstream activator sequences. Site-directed deletion-and-insertion mutagenesis was used to establish a genetic map of the major nif cluster.

Human-computer interface development: concepts and systems for its management

Abstract: Human-computer interface management, from a computer science viewpoint, focuses on the process of developing quality human-computer interfaces, including their representation, design, implementation, execution, evaluation, and maintenance. This survey presents important concepts of interface management: dialogue independence, structural modeling, representation, interactive tools, rapid prototyping, development methodologies, and control structures. Dialogue independence is the keystone concept upon which all the other concepts depend. It is a characteristic that separates design of the interface from design of the computational component of an application system so that modifications in either tend not to cause changes in the other. The role of a dialogue developer, whose main purpose is to create quality interfaces, is a direct result of the dialogue independence concept. Structural models of the human-computer interface serve as frameworks for understanding the elements of interfaces and for guiding the dialogue developer in their construction. Representation of the human-computer interface is accomplished by a variety of notational schemes for describing the interface. Numerous kinds of interactive tools for human-computer interface development free the dialogue developer from much of the tedium of "coding" dialogue. The early ability to observe behavior of the interface—and indeed that of the whole application system—provided by rapid prototyping increases communication among system designers, implementers, evaluators, and end-users. Methodologies for interactive system development consider interface management to be an integral part of the overall development process and give emphasis to evaluation in the development life cycle. Finally, several types of control structures govern how sequencing among dialogue and computational components is designed and executed. Numerous systems for human-computer interface management are presented t o illustrate these concepts.

Hydroformylation by supported aqueous-phase catalysis: a new class of heterogeneous catalysts

Abstract: HOMOGENEOUS catalysts typically operate at relatively mild temperatures and exhibit high activities and selectivities1. However, it has long been recognized that many homogeneous reactions are not commercially viable because of problems of catalyst recovery. Thus, significant efforts have centred around the immobilization of the organometallic species responsible for catalysis2. At best, the performance of such heterogeneous catalysts only approximate those of their homogeneous counterparts. Here we describe a novel family of heterogeneous catalysts, denoted supported aqueousphase catalysts (SAPCs), designed to facilitate chemical reactions at the interface of two liquids. These catalysts consist of a watersoluble organometallic complex dissolved in a film of water which is supported on a high-surface-area hydrophilic solid. Reactions of liquid-phase organic reactants take place at the water–organic interface. Heterogeneous hydroformylation of alkenes by SAPCs containing water-soluble organometallic rhodium complexes is used to illustrate the efficacy of these new catalysts.

Biochemical and genetic analysis of the nifUSVWZM cluster from Azotobacter vinelandii.

Abstract: Azotobacter vinelandii genes contained within the major nif-cluster and designated orf6, nifU, nifS, nifV, orf7, orf8, nifW nifZ, nifM, and orf9 are organized into at least two overlapping transcriptional units. Nitrogenase derepressed crude extracts of Azotobacter vinelandii mutant strains having individual deletions located within nifU, nifS, nifV, nif, nifZ, or nifM were examined for nitrogenase component protein activities. The results of these experiments indicated that, in A. vinelandii, the nifU, nifS and nifM gene products are required for the full activation or the catalytic stability of the nitrogenase Fe protein. Deletion of the nifV gene resulted in lower MoFe protein activity, probably resulting from the accumulation of an altered FeMo-cofactor. The nifW and nifZ gene products were required for the full activation or catalytic stability of the MoFe protein. Deletion of nijZ alone or nifM alone did not appear to affect FeMo-cofactor biosynthesis. However, deletion of both niJZ and nifM eleminated either FeMo-cofactor biosynthesis or the insertion of FeMo-cofactor into the apo-MoFe protein. Other genes contained within the nifUSVWZM gene cluster (orf6, orf7, orf8, and orf9) were not required for Mo-dependent diazotrophic growth.

Nondiffracting optical fields: some remarks on their analysis and synthesis

Abstract: Recently Durnin pointed out the existence of nondiffracting beams that propagate in free space with their energy confined around their axis but that experience no spread or divergence [ J. Opt. Soc. Am. A4, 651 ( 1987)]. This Communication provides an alternative way of interpreting these results. The approach is based on the McCutchen theorem from which the necessary conditions for a nondiffracting field are derived. This description may be useful in suggesting several different means of synthesizing such fields and in providing a convenient way of estimating their practical limitations. Some examples, inspired by known techniques studied for depth of field enhancement, are briefly mentioned.

Recent Advances in Analysis of Laminated Beams and Plates, Part II: Vibrations and Wave Propagation

Abstract: A summary of the recent developments in the analysis of laminated beams and plates with an emphasis on vibrations and wave propagations in presented. First, a review of the recent studies on the free-vibration analysis of symmetrically laminated plates is given. These studies have been conducted for various geometric shapes and edge conditions. Both analytical (closed-form, Galerkin, Rayleigh-Ritz) and numerical methods have been used. Because of the importance of unsymmetrically laminated structural components in many applications, a detailed review of the various developments in the analysis of unsymmetrical ly laminated beams and plates also is given. A survey of the nonlinear vibrations of the perfect and geometrically laminated plates is presented next. It is seen that due to the bending-stretching coupling, the nonlinear behavior of the unsymmetrically laminated perfect and imperfect plates, depending upon the boundary conditions, may be hardening or softening type. Similar behavior also is observed for imperfect isotropic and laminated plates. Lastly, the developments in studying the wave propagation in laminated materials are reviewed. It is seen that a significant effort has been spent on developing appropriate continuum theories for modeling the composite materials. Some recent studies on the linear and nonlinear transient response of laminated materials also are described.

On refined computational models of composite laminates

Abstract: Finite element models of the continuum-based theories and two-dimensional plate/shell theories used in the analysis of composite laminates are reviewed. The classical and shear deformation theories up to the third-order are presented in a single theory. Results of linear and non-linear bending, natural vibration and stability of composite laminates are presented for various boundary conditions and lamination schemes. Computational modelling issues related to composite laminates, such as locking, symmetry considerations, boundary conditions, and geometric non-linearity effects on displacements, buckling loads and frequencies are discussed. It is shown that the use of quarter plate models can introduce significant errors into the solution of certain laminates, the non-linear effects are important even at small ratio of the transverse deflection to the thickness of antisymmetric laminates with pinned edges, and that the conventional eigenvalue approach for the determination of buckling loads of composite laminates can be overly conservative.

Modal Interactions in Dynamical and Structural Systems

Abstract: The authors review theoretical and experimental studies of the influence of modal interactions on the nonlinear response of harmonically excited structural and dynamical systems. In particular, they discuss the response of pendulums, ships, rings, shells, arches, beam structures, surface waves, and the similarities in the qualitative behavior of these systems. The systems are characterized by quadratic nonlinearities which may lead to two-to-one and combination autoparametric resonances. These resonances give rise to a coupling between the modes involved in the resonance leading to nonlinear periodic, quasi-periodic, and chaotic motions.

Dynamic Stability of Suddenly Loaded Structures

Abstract: I Concepts and Criteria.- 1 Introduction and Fundamental Concepts.- 2 Simple Mechanical Models.- 3 Dynamic Stability Under Constant Load Finite Duration.- 4 The Influence of Static Preloading.- II Structural Applications.- 5 The Concept of Dynamic Stability.- 6 Two-Bar Simple Frames.- 7 The Shallow Arch.- 8 The Shallow Spherical Cap.- 9 Thin Cylindrical Shells.- 10 Other Strutural Systems.- APPENDIX A.- Parametric Resonance.- APPENDIX B.- Brachistochrone Problems.- APPENDIX C.- The Influence of Small Damping.

Physical Distribution Service: A Fundamental Marketing Concept?

Abstract: This article contends that current discussion and research into the role of physical distribution service in the marketing mix are hampered by a lack of consistent definition of the concept of physical distribution service and its component dimensions. In order to clarify this concept, prerequisites for a theoretically meaningful understanding of physical distribution service are presented and supported by an integrative literature review. The implications of this undertaking are also discussed.

Synthetic fluid inclusions - VII. Re-equilibration of fluid inclusions in quartz during laboratory-simulated metamorphic burial and uplift

Abstract: P-T conditions inferred from fluid inclusions in metamorphic rocks often disagree with the values predicted from mineral equilibria calculations. These observations suggest that inclusions formed during early stages of regional metamorphism continue to re-equilibrate during burial and subsequent uplift in response to differential pressure. P-T conditions accompanying burial and uplift were experimentally simulated by initially forming pure H2O inclusions in quartz at elevated temperatures and pressures, and then re-equilibrating the inclusions in the presence of a 20 wt% NaCl solution such that final confining pressures ranged from 5 kbar above to 4 kbar below the initial internal pressure of the inclusions at the temperature of re-equilibration. In all samples re-equilibrated at confining pressures below the internal pressure, some inclusions were formed that had compositions of 20 wt% NaCl and densities in accord with the final P-T conditions. Additionally, some inclusions were observed to contain fluids of intermediate salinities (between 0 and 20 wt% NaCl). Densities of these inclusions were also consistent with formation at the re-equilibration P-T conditions. The remainder of the fluid inclusions observed in these samples contained pure H2O and their homogenization temperatures corresponded to densities intermediate between the initial and final P-T conditions. In short-term experiments (7 days) where the initial internal overpressure exceeded 1 kbar, no inclusions were found that contained the original density and none were found to have totally re-equilibrated. Instead, most H2O inclusions re-equilibrated until their internal pressures were between ∼750 and 1500 bars above the confining pressure, regardless of the initial pressure differential. In a long-term experiment (52 days), inclusions re-equilibrated at a lower confining pressure than the initial internal pressure displayed homogenization temperatures corresponding to a range in final internal pressures between 0 kbar (i.e. total re-equilibration) and 1.2 kbar above the confining pressure. In experiments where the confining pressure during re-equilibration exceeded the initial internal pressure, densities of pure H2O inclusions increased to values intermediate between the initial and final P-T conditions. Additionally, these inclusions were generally surrounded by a three-dimensional halo of smaller inclusions, also of intermediate density, resulting in a texture similar to that previously ascribed to decrepitation from internal overpressure. In extreme cases where confining pressures were 4–5 kbar above the initial pressure, the parent inclusion almost completely closed leaving only the three-dimensional array of small (5 μm) inclusions, the outline of which may be several times the volume of the original inclusion. Groups of such inclusions closely resemble textures commonly observed in medium- to high-grade metamorphic rocks. Inclusions containing 10 and 42 wt% NaCl solutions trapped at 600 °c and 3 kbar were re-equilibrated at 600 °c and 1 kbar for 5 days in dry argon to evaluate the importance of H2O diffusion as a mechanism of lowering the inclusion bulk density. Salinities of re-equilibrated inclusions obtained from freezing point depressions and halite dissolution temperatures indicate that original compositions were preserved. Density changes similar to those previously described were noted in these experiments, in inclusions showing no visible microfractures. Therefore, density variations observed in inclusions in this study, re-equilibrated under rapid deformation conditions, are considered to result from a change in the inclusion volume, without significant loss of contents by diffusion or leakage.

Buckling and vibration of laminated composite plates using various plate theories

Abstract: Analytical and finite-element solutions of the classical, first-order, and third-order laminate theories are developed to study the buckling and free-vibration behavior of cross-ply rectangular composite laminates under various boundary conditions

Measures of Modal Controllability and Observability for First- and Second-Order Linear Systems

Abstract: For a system described by the triple (A9B9C) where the matrix A has a set of distinct eigenvalues and a wellconditioned modal matrix, we propose measures of modal controllability and observability. The angles between the left eigenvectors of A and the columns of the matrix B are used to propose modal controllability measures and the angles between the rows of the matrix C, and the right eigenvectors of A are used to propose modal observability measures. Gross measures of controllabili ty of a mode from all inputs and its observability in all outputs are also proposed. These measures are related to other measures suggested in the literature. A closed-form relation between the norm of the residue and the proposed measures is given, thus linking the residue to the unobservability or uncontrollability of the mode. We finally show that the proposed measures can be applied directly to second-order models.

Applied Behavior Analysis and Social Marketing: An Integration for Environmental Preservation

Abstract: Basic principles of applied behavior analysis and social marketing are reviewed with reference to the development of action plans to protect the environment. Behavior-change procedures that have targeted environmental preservation are categorized as antecedent interventions (including education, prompting, modeling, goal setting and commitment, and engineering and design strategies) or consequence procedures (i.e., reinforcement and punishment). Although past behavior analysis research has demonstrated environmental benefits from applying certain behavior-change interventions, those studies were small-scale and short-lived. This paper offers an integrative model of applied behavior analysis and social marketing as a potential approach to large-scale and long-term intervention for environmental protection. The market analysis and segmentation phases of social marketing, for example, allow for the specialization of behavior-change strategies for particular target groups. This integration requires increased collaboration between behavior analysts and environmental psychologists who study the correlation of individuals' environmental concern and action with their attitudinal, demographic, and personality characteristics. A plea is made to replace armchair theorizing with interdisciplinary and intervention-focused environmental research.