Showing papers by "Virginia Tech published in 1997"

Structural control: past, present, and future

Abstract: This tutorial/survey paper: (1) provides a concise point of departure for researchers and practitioners alike wishing to assess the current state of the art in the control and monitoring of civil engineering structures; and (2) provides a link between structural control and other fields of control theory, pointing out both differences and similarities, and points out where future research and application efforts are likely to prove fruitful. The paper consists of the following sections: section 1 is an introduction; section 2 deals with passive energy dissipation; section 3 deals with active control; section 4 deals with hybrid and semiactive control systems; section 5 discusses sensors for structural control; section 6 deals with smart material systems; section 7 deals with health monitoring and damage detection; and section 8 deals with research needs. An extensive list of references is provided in the references section.

Assessing the predictive validity of two methods of measuring self-image congruence

Abstract: The predictive validity of two measurement methods of self-image congruence—traditional versus new—were compared in six studies involving different consumer populations, products, consumption settings, and dependent variables (brand preference, preference for product form, consumer satisfaction/dissatisfaction, brand attitude, and program choice). The traditional method is based on tapping the subject’s perception of product-user image and the subject’s perception of his/her self-image along a predetermined set of image attributes and adding the self-congruity scores across all image dimensions. Three problems were identified and discussed in relation to the traditional method: (1) the use of discrepancy scores, (2) the possible use of irrelevant images, and (3) the use of the compensatory decision rule. The new method is based on tapping the psychological experience of self-congruity directly and globally. The findings demonstrated the predictive validity of the new method over and beyond the traditional method.

Reactive oxygen species and antioxidants: Relationships in green cells

Abstract: The imposition of oxidative stress leads to increased production of reactive oxygen species (ROS) in plant cells. Orchestrated defense processes ensue that have much in common between stresses, yet are also particular to the site of action of the stress and its concentration. Possible functional roles of these responses include, but are not restricted to, the protection of the photosynthetic machinery, the preservation of membrane integrity and the protection of DNA and proteins. Superimposed upon our understanding of cellular mechanisms for protection against abiotic stress is a newly discovered role of ROS in signalling and defense response to pathogens (J. L. Dangl, R. A. Dietrich and M. S. Richberg. 1996. Plant Cell 8: 1793–1807). Evidence to date suggests a coordinated response to ROS among different members of the superoxide dismutase (SOD) gene families. A further layer of complexity is afforded by reports of coordination of expression between ascorbate peroxidase and SOD genes. Our understanding of the signalling mechanisms that underlie these coordinated events is in its infancy. An exciting future lies ahead in which the orchestration of successful antioxidant stress responses will be gradually revealed. Current data suggest that complex regulatory mechanisms function at both the gene and protein level to coordinate antioxidant responses and that a critical role is played by organellar localization and inter-compartment coordination.

A Theoretical Analysis of Host Community Resident Reactions to Tourism

Abstract: This research organizes resident reactions to tourism in the context of a theoretical paradigm based on the principles of social exchange theory. A path model based on social exchange theory principles explains how residents weigh and balance seven factors that influence their support for tourism. The analysis demonstrates that potential for economic gain, use of the tourism resource, ecocentric attitude, and attachment to the community affect resident perceptions of the impacts and modify, both directly and indirectly, resident support for tourism.

Modeling piezoelectric stack actuators for control of micromanipulation

Abstract: A nonlinear lumped-parameter model of a piezoelectric stack actuator has been developed to describe actuator behavior for purposes of control system analysis and design, and, in particular, for microrobotic applications requiring accurate position and/or force control. In formulating this model, the authors propose a generalized Maxwell resistive capacitor as a lumped-parameter causal representation of rate-independent hysteresis. Model formulation is validated by comparing results of numerical simulations to experimental data. Validation is followed by a discussion of model implications for purposes of actuator control.

PHOAKS: a system for sharing recommendations

Abstract: The feasibility of automatic recognition of recommendations is supported by empirical results. First, Usenet messages are a significant source of recommendations of Web resources: 23% of Usenet messages mention Web resources, and ?>0% of these mentions are recommendations. Second, recommendation instances can be machine-recognized with nearly 90% accuracy. Third, some resources are recommended by more than one person. These multiconfirmed recommendations appear to be significant resources for the relevant community. Finally, the number of distinct recommenders of a resource is a tallying, and redistributing recom-

Dimensions and Levels of Trust: Implications for Commitment to a Relationship

Abstract: Previous research has found that trust is positively related to commitment in buyer-seller relationships. However, the validity of this finding is questionable because trust has been operationalized in many different ways. For example, prior research has not distinguished among levels of trust (interpersonal or organizational trust) and dimensions or motives of trust (credibility or benevolence). In this study, we distinguish among the levels and dimensions of trust. The results indicate that trust in a sales representative (interpersonal credibility) is more strongly related to commitment than trust in an organization (organizational credibility). In contrast, trust based on organizational benevolence is a stronger predictor of commitment than interpersonal benevolence.

Gas phase ozone decomposition catalysts

Abstract: Catalytic ozone decomposition is of practical significance because ozone is a toxic substance commonly found or generated in human environments (aircraft cabins, offices with photocopiers, laser printers, sterilizers). Considerable work has been done on ozone decomposition, most of it reported in the patent literature. This review provides a comprehensive summary of this literature, concentrating on analysis of the composition, preparation procedure and performance of the catalysts. This is supplemented by experimental work on kinetics and catalyst characterization which ties together the previously reported results. It is found that p-type oxide semiconductors are the most active substances for ozone decomposition. Among these MnO2 has the highest activity, explaining its prevalence in patent disclosures. The kinetics of the reaction on MnO2 is zero order in oxygen and water vapor and two-thirds order in ozone, and is consistent with the existence of a peroxo or superoxo surface intermediate.

Industry Self‐Regulation: An Institutional Perspective

Abstract: Throughout the advanced countries of the world self-regulatory regimes are being introduced. This article suggests that, at least in some contexts, industry self-regulation can be an effective and efficient means of social control that has been largely ignored by economics (which has a focus on individual rather than group behavior) and prematurely discounted by mainstream regulatory theory. The article examines the strengths and to a lesser extent the weaknesses of industry self-regulation from five closely related yet distinct vantage points: mediating institutions; industrial morality; institutionalizing responsibility; institutions responding to external pressure; and the roles of the state and third parties.

Unit sizing and control of hybrid wind-solar power systems

Abstract: The aim of this paper is to provide the core of a CAD/CAA tool that can help designers determine the optimal design of a hybrid wind-solar power system for either autonomous or grid-linked applications. The proposed analysis employs linear programming techniques to minimize the average production cost of electricity while meeting the load requirements in a reliable manner, and takes environmental factors into consideration both in the design and operation phases. While in autonomous systems, the environmental credit gained as compared to diesel alternatives can be obtained through direct optimization, in grid-linked systems emission is another variable to be minimized such that the use of renewable energy can be justified. A controller that monitors the operation of the autonomous/grid-linked systems is designed. Such a controller determines the energy available from each of the system components and the environmental credit of the system. It then gives details related to cost, unmet and spilled energies, and battery charge and discharge losses.

Measuring physical distribution service quality

Abstract: The quality of the physical distribution service industrial purchasers receive from suppliers has been shown to be an important consideration in industrial purchasing decisions. To better understand the criteria used to assess physical distribution service quality, the authors examined the literature on physical distribution and service quality and conducted interviews with purchasing managers. Based on the results of the literature reviews and interviews, plus a two-step data-gathering process, a valid and reliable measurement instrument for perceptions of physical distribution service quality (PDSQ) was developed and refined.

Validity of the age-of-onset criterion for ADHD: a report from the DSM-IV field trials.

Abstract: Objective To examine the validity of the DSM-IV requirement of an age of onset of impairment due to symptoms before 7 years of age for the diagnosis of attention-deficit/hyperactivity disorder (ADHD). Method The validity of this criterion was examined in a clinic sample of 380 youths aged 4 through 17 years by comparing youths who met symptom criteria for ADHD and either did or did not display impairment before age 7 years. Results Nearly all youths who met symptom criteria for the predominantly hyperactive-impulsive subtype also met the age of onset of impairment criterion, but 18% of youths who met symptom criteria for the combined type, and 43% of youths who met symptom criteria for the predominantly inattentive type, did not manifest impairment before 7 years. For the latter two subtypes, requiring impairment before age 7 years reduced the accuracy of identification of currently impaired cases of ADHD and reduced agreement with clinicians' judgments. Conclusions These findings raise questions about the validity of the DSM-IV definition of age of onset of ADHD. Marked differences in the ages of onset of both symptoms and impairment for the three subtypes of ADHD support the validity of distinguishing among these subtypes in DSM-IV .

Evidence that hyporheic zones increase heterotrophic metabolism and phosphorus uptake in forest streams

Abstract: We used nondisruptive, whole-stream methods to measure hydraulic characteristics, ecosystem metabolism, and phosphorus cycling in the west fork of Walker Branch (WB), Tennessee and in Hugh White Creek (HWC), North Carolina. Although similar in many of their hydrological and chemical characteristics, transient storage zone volume in HWC was relatively large (- 1.5 times that of the flowing water zone), whereas transient storage zone volume in WB was small (-0.1 times that of the flowing water zone). Both streams were highly heterotrophic (gross primary production : total respiration ratios

Human-computer interaction

Abstract: Human?computer interaction (HCI) is the area of intersection between psychology and the social sciences, on the one hand, and computer science and technology, on the other. HCI researchers analyse and design-specific user-interface technologies (e.g. three-dimensional pointing devices, interactive video). They study and improve the processes of technology development (e.g. usability evaluation, design rationale). They develop and evaluate new applications of technology (e.g. computer conferencing, software design environments). Through the past two decades, HCI has progressively integrated its scientific concerns with the engineering goal of improving theusabilityof computer systems and applications, thus establishing a body of technical knowledge and methodology. HCI continues to provide a challenging test domain for applying and developing psychology and social science in the context of technology development and use.

Responses of Antioxidants to Paraquat in Pea Leaves (Relationships to Resistance)

Abstract: Differnential sensitivity to the oxidant paraquat was observed in pea (Pisum sativum L.) based on cultivar and leaf age. To assess contributions of inductive responses of the antioxidant enzymes in short-term resistance to oxidative damage, activities of glutathione reductase (GR), superoxide dismutase (SOD), and ascorbate peroxidase (APX) and transcript levels for plastidic GR, Cu,Zn SOD, and cytosolic APX were determined. Responses to paraquat exposure from three different leaf age classes of pea were studied. Resistance was correlated with leaf age, photosynthetic rates, enzyme activities, and pretreatment levels of plastid GR and plastid Cu,Zn SOD transcripts. In response to paraquat, small increases in activities of GR and APX were observed in the more resistant leaves. These changes were not reflected at the mRNA level for the plastidic GR or Cu,Zn SOD. Paraquat-mediated increases in cytosolic APX mRNA occurred in all leaf types, irrespective of resistance. Developmentally controlled mechanisms determining basal antioxidant enzyme activities, and not inductive responses, appear to be critical factors mediating short-term oxidative stress resistance.

Core-annular flows

Abstract: This paper gives an overview of the issues posed by the science and technology of transporting heavy oils in a sheath of lubricating water. It touches on measures of energy efficiency, industrial experience, fouling, stability, models of levitation, and future directions.

Human-computer interaction: psychology as a science of design.

Abstract: Human-computer interaction (HCI) study is the region of intersection between psychology and the social sciences, on the one hand, and computer science and technology, on the other. HCI researchers analyze and design specific user interface technologies (e.g. pointing devices). They study and improve the processes of technology development (e.g. task analysis, design rationale). They develop and evaluate new applications of technology (e.g. word processors, digital libraries). Throughout the past two decades, HCI has progressively integrated its scientific concerns with the engineering goal of improving the usability of computer systems and applications, which has resulted in a body of technical knowledge and methodology. HCI continues to provide a challenging test domain for applying and developing psychological and social theory in the context of technology development and use.

A prediction model that combines rain attenuation and other propagation impairments along Earth-satellite paths

Abstract: The rapid growth of satellite services using higher frequency bands such as the Ka-band has highlighted a need for estimating the combined effect of different propagation impairments. Many projected Ka-band services will use very small terminals and, for some, rain effects may only form a relatively small part of the total propagation link margin. It is therefore necessary to identify and predict the overall impact of every significant attenuating effect along any given path. A procedure for predicting the combined effect of rain attenuation and several other propagation impairments (at frequencies between 4 and 35 GHz) along Earth-satellite paths is presented. Where an accurate model exist for some phenomena, these have been incorporated into the prediction procedure. New models were developed, however, for rain attenuation, cloud attenuation, and low-angle fading to provide more overall accuracy, particularly at very low elevation angles (<10/spl deg/). In the absence of a detailed knowledge of the occurrence probabilities of different impairments, an empirical approach is taken in estimating their combined effects. An evaluation of the procedure is made using slant-path attenuation data that have been collected with simultaneous beacon and radiometer measurements which allow a near complete account of different impairments. Results indicate that the rain attenuation element of the model provides the best average accuracy globally between 10 and 30 GHz and that the combined procedure gives prediction accuracies comparable to uncertainties associated with the year-to-year variability of path attenuation.

Lignin Impact on Fiber Degradation. 3. Reversal of Inhibition of Enzymatic Hydrolysis by Chemical Modification of Lignin and by Additives

Abstract: The impact of lignins of various origins on filter paper hydrolysis by fungal cellulase was evaluated. Powdered lignins were added to enzyme incubations, either as isolated or after thorough hydroxypropylation of phenolic sites. Extent of cellulose hydrolysis was reduced by 14−60% by the addition of up to 15% lignin to the substrate. Unmodified lignins were more detrimental to cellulose hydrolysis than hydroxypropylated lignins. The inhibitory effect of lignin addition was only partially overcome by a 10-fold increase in cellulase activity, suggesting inhibitory lignin interactions with both substrate and enzyme. Preincubation of cellulase with underivatized lignins resulted in reduced enzyme activity and soluble protein concentration in the supernatant, suggesting protein precipitation with lignin rather than reduced activity of a lignin−enzyme complex as the inhibitory mechanism. Two further experiments showed that the negative impact of lignin on cellulose hydrolysis can be counteracted by addition of ...

The matK gene: sequence variation and application in plant systematics

Abstract: Although the matK gene has been used in addressing systematic questions in four families, its potential application to plant systematics above the family level has not been investigated This paper examines the rates, patterns, and types of nucleotide substitutions in the gene and addresses its utility in constructing phylogenies above the family level Eleven complete sequences from the GenBank representing seed plants and liverworts and nine partial sequences generated for genera representing the monocot families Poaceae, Joinvilleaceae, Cyperaceae, and Smilacaceae were analyzed The study underscored the high rate of substitution in the gene and the presence of mutationally conserved sectors The use of different sectors of the gene and the cumulative inclusion of informative sites showed that the 3' region was most useful in resolving phylogeny, and that the topology and robustness of the tree reached a plateau after the inclusion of 100 informative sites from that region for the taxa used The impact of using partial sequencing on sample size is addressed The presence of a relatively conserved 3' region and the less conserved 5' region provides two sets of characters that can be used at different taxonomic levels from the tribal to the division levels

Infrared reflectivity and lattice fundamentals in anatase TiO 2 s

Abstract: Polarization-dependent far-infrared reflectivity measurements were carried out on single crystals of anatase ${\mathrm{TiO}}_{2}$ . The results were analyzed to yield the dielectric dispersion properties of anatase in the lattice fundamentals regime. The frequencies (in ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ ) of the transverse optical (TO) and longitudinal optical (LO) zone-center phonons were determined to be 367(755) for the TO (LO) of the ${\mathrm{A}}_{2\mathrm{u}}$ mode, 262(366) and 435(876) for the ${\mathrm{E}}_{\mathrm{u}}$ modes. The large TO-LO splittings were used to estimate effective charges.

Investigation of Shape Memory Polymers and Their Hybrid Composites

Abstract: In this paper, a newly developed polymer, shape memory polyurethane (SMP), will be introduced. The shape memory polymer possesses the same basic shape memory effect and elasticity memory effect as shape memory alloys. Shape memory polymers can change their elastic modulus up to 500 times around their glass transition temperatures. Both the shape memory effect and the elasticity memory effect of shape memory polymers make them a useful candidate for today's intelligent material systems and structures. This paper will introduce some of the basic characteristics of SMPs and the results of some initial investigation of SMP composites.

An Empirical Examination of the Relationship Between Ethical Climate and Ethical Behavior from Multiple Levels of Analysis

Abstract: Victor and Cullen (1988) identified several dimensions of ethical climate that exist in organizations and organizational subunits We tested the relationship between these dimensions of ethical climate and ethical behavior at different levels of analysis Using Within and Between Analysis (WABA) (cf Dansereau, Alutto and Yammarino, 1984), partial support was found for a relationship between dimensions of ethical climate and ethical behavior