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Showing papers by "University of Central Florida published in 1998"


Proceedings ArticleDOI
01 Sep 1998
TL;DR: This paper is able to tiate the service latency and improve the efficiency of mtiticast at the same time, and indicates convincingly that Patching offers .wbstanti~y better perforrnace.

602 citations


Journal ArticleDOI
TL;DR: The challenges each of these factors present to the effective design of virtual environments and systematic approaches to the resolution of each of them are discussed.
Abstract: Virtual environments are envisioned as being systems that will enhance the communication between humans and computers. If virtual systems are to be effective and well received by their users, considerable human-factors research needs to be accomplished. This paper provides an overview of many of these human-factors issues, including human performance efficiency in virtual worlds (which is likely influenced by task characteristics, user characteristics, human sensory and motor physiology, multimodal interaction, and the potential need for new design metaphors); health and safety issues (of which cybersickness and deleterious physiological aftereffects may pose the most concern); and the social impact of the technology. The challenges each of these factors present to the effective design of virtual environments and systematic approaches to the resolution of each of these issues are discussed.

549 citations


Journal ArticleDOI
25 Jun 1998-Nature
TL;DR: The shikimate pathway is an attractive target for herbicides and antimicrobial agents because it is essential in algae, higher plants, bacteria and fungi, but absent from mammals as discussed by the authors.
Abstract: Parasites of the phylum Apicomplexa cause substantial morbidity, mortality and economic losses, and new medicines to treat them are needed urgently. The shikimate pathway is an attractive target for herbicides and antimicrobial agents because it is essential in algae, higher plants, bacteria and fungi, but absent from mammals. Here we present biochemical, genetic and chemotherapeutic evidence for the presence of enzymes of the shikimate pathway in apicomplexan parasites. In vitro growth of Toxoplasma gondii, Plasmodium falciparum (malaria) and Cryptosporidium parvum was inhibited by the herbicide glyphosate, a well-characterized inhibitor of the shikimate pathway enzyme 5-enolpyruvyl shikimate 3-phosphate synthase. This effect on T. gondii and P. falciparum was reversed by treatment with p-aminobenzoate, which suggests that the shikimate pathway supplies folate precursors for their growth. Glyphosate in combination with pyrimethamine limited T. gondii infection in mice. Four shikimate pathway enzymes were detected in extracts of T. gondii and glyphosate inhibited 5-enolpyruvyl shikimate 3-phosphate synthase activity. Genes encoding chorismate synthase, the final shikimate pathway enzyme, were cloned from T. gondii and P. falciparum. This discovery of a functional shikimate pathway in apicomplexan parasites provides several targets for the development of new antiparasite agents.

473 citations


Journal ArticleDOI
01 Dec 1998
TL;DR: This paper presents the full definition of BSPlib in C, motivates the design of its basic operations, and gives examples of their use, and briefly describes applications in benchmarking, Fast Fourier Transforms, sorting, and molecular dynamics.
Abstract: BSPlib is a small communications library for bulk synchronous parallel (BSP) programming which consists of only 20 basic operations. This paper presents the full definition of BSPlib in C, motivates the design of its basic operations, and gives examples of their use. The library enables programming in two distinct styles: direct remote memory access (DRMA) using put or get operations, and bulk synchronous message passing (BSMP). Currently, implementations of BSPlib exist for a variety of modern architectures, including massively parallel computers with distributed memory, shared memory multiprocessors, and networks of workstations. BSPlib has been used in several scientific and industrial applications; this paper briefly describes applications in benchmarking, Fast Fourier Transforms (FFTs), sorting, and molecular dynamics.

343 citations


Journal ArticleDOI
TL;DR: In this article, the authors analyzed specific social activities, aspects of neighborhoods, and contribution of each to the risks of larceny victimization for college students, and found that greater specificity in measuring lifestyles is warranted, for it is not just leaving one's home and going out in public that increases one's risk for victimization (a typical finding of routine activity theory scholars), but where one goes and what one does that are the important larcene victimization predictors.
Abstract: Routine activity theory has long been plagued by a heavy reliance on proxy measures of lifestyles, which typically include demographic variables that are regularly used as measures of lifestyle and behavior. This reliance on indirect measures forces researchers to suppose how and why these indicators are related to victimization risks. Using detailed measurements of activities and specific structural aspects of communities is clearly more desirable and beneficial when seeking to explain variances in victimization risks. This research advances theoretical understandings of victimization risks through an analysis of specific social activities, aspects of neighborhoods, and contribution of each to the risks of larceny victimization for college students. We find that greater specificity in measuring lifestyles is warranted, for it is not just leaving one's home and going out in public that increases one's risk for victimization (a typical finding of routine activity theory scholars), but where one goes and what one does that are the important larceny victimization predictors.

280 citations


Journal ArticleDOI
TL;DR: The 2 most critical research issues identified were (a) standardization and use of measurement approaches for aftereffects and (b) identification and prioritization of sensorimotor discordances that drive aftere Affects.
Abstract: This report represents a committee summary of the current state of knowledge regarding aftereffects and sense of presence in virtual environments (VEs). The work presented in this article, and the proposed research agenda, are the result of a special session that was set up in the framework of the Seventh International Conference on Human Computer Interaction Recommendations were made by the committee regarding research needs in after effects and sense of presence, and, where possible, priorities were suggested. The research needs were structured in terms of the short medium, and long term and, if followed, should lead toward the effective use of VE technology. The 2 most critical research issues identified were (a) standardization and use of measurement approaches for aftereffects and (b) identification and prioritization of sensorimotor discordances that drive after effects. Identification of aftereffects countermeasures (i.e., techniques to assist users in readily transitioning between the real and vir...

279 citations


Journal ArticleDOI
TL;DR: The transition from microcrystalline to nanocrystalline diamond films grown from Ar/H2/CH4 microwave plasmas has been investigated in this article, showing that the surface morphology, the grain size, and the growth mechanism of the diamond films depend strongly on the ratio of Ar to H2 in the reactant gases.
Abstract: The transition from microcrystalline to nanocrystalline diamond films grown from Ar/H2/CH4 microwave plasmas has been investigated. Both the cross-section and plan-view micrographs of scanning electron microscopy reveal that the surface morphology, the grain size, and the growth mechanism of the diamond films depend strongly on the ratio of Ar to H2 in the reactant gases. Microcrystalline grain size and columnar growth have been observed from films produced from Ar/H2/CH4 microwave discharges with low concentrations of Ar in the reactant gases. By contrast, the films grown from Ar/H2/CH4 microwave plasmas with a high concentration of Ar in the reactant gases consist of phase pure nanocrystalline diamond, which has been characterized by transmission electron microscopy, selected area electron diffraction, and electron energy loss spectroscopy. X-ray diffraction and Raman spectroscopy reveal that the width of the diffraction peaks and the Raman bands of the as-grown films depends on the ratio of Ar to H2 in...

278 citations


Journal ArticleDOI
TL;DR: The FIB (focused ion beam) lift‐out technique is a fast method for the preparation of site‐specific TEM specimens and is a useful technique for the study of complex materials systems for TEM analysis.
Abstract: A site-specific technique for cross-section transmission electron microscopy specimen preparation of difficult materials is presented. A focused ion beam was used to slice an electron transparent membrane from a specific area of interest within a bulk sample. Micromanipulation lift-out procedures were then used to transport the electron-transparent specimen to a carbon-coated copper grid for subsequent TEM analysis. The FIB (focused ion beam) lift-out technique is a fast method for the preparation of site-specific TEM specimens. The versatility of this technique is demonstrated by presenting cross-sectioned TEM specimens from several types of materials systems, including a multi-layered integrated circuit on a Si substrate, a galvanized steel, a polycrystalline SiC ceramic fiber, and a ZnSe optical ceramic. These specimens have both complex surface geometry and interfaces with complex chemistry. FIB milling was performed sequentially through different layers of cross-sectioned materials so that preferential sputtering was not a factor in preparing TEM specimens. The FIB lift-out method for TEM analysis is a useful technique for the study of complex materials systems for TEM analysis.

245 citations


Posted Content
TL;DR: In this paper, the relationship between the short-term and long-term returns of initial public offerings (IPOs) and the reputation of the underwriters associated with the IPOs is explored.
Abstract: Explores the relationship between the short-term and long-term returns of initial public offerings (IPOs) and the reputation of the underwriters associated with the IPOs. Previous work in this area has shown that use of reputable underwriters for the IPO leads to less short-run underpricing. Data used in this analysis were collected from 2,292 IPOs that were issued between January 1979 and December 1991. The sample includes only firm commitment, domestic offerings of at least $2 million. Three ways of measuring underwriter reputation are considered: the measure developed by Johnson and Miller, the Megginson-Weiss measure, and the Carter-Manaster measure. Results show that larger and more established firms are marketed by the most prestigious investment banks for the initial IPO. In both short-term and long-term performance, the Carter-Manaster measure has the most significance. Further, the analysis shows less negative performance over the three-year period considered for IPOs that are underwritten by more prestigious investment banks. Although it is costly to compile the Carter-Manaster measure, it is shown to be the best of the three measures at controlling for underwriter prestige in IPO studies. Included in this work are the Carter-Manaster measures and the corresponding Megginson-Weiss measures for a large number of investment banks. (SRD)

244 citations


Proceedings ArticleDOI
24 Apr 1998
TL;DR: In this paper, basic types of DC-DC converter topologies are studied to investigate their self-PFC capabilities, their input characteristics are compared and their input line current waveforms are predicted.
Abstract: Basic types of DC-DC converters, when operating in discontinuous conduction mode, have self power factor correction (PFC) property, that is, if these converters are connected to the rectified AC line, they have the capability to give higher power factor by the nature of their topologies. Input current feedback is unnecessary when these converters are employed to improve power factor. In this paper, basic types of DC-DC converter topologies are studied to investigate their self-PFC capabilities. Their input characteristics are compared and their input line current waveforms are predicted.

230 citations


Journal ArticleDOI
TL;DR: Investigation of the degree to which analyzing communication sequences would contribute to the understanding of effective crew process in two simulated flight tasks indicates that pattern analyses reveal additional strong differences between performance groups that would have been overlooked by simple frequency counts of communication.
Abstract: Several models of team performance have suggested that a clearer understanding of team process is needed to determine better training formats and reduce crew-generated errors. The present study investigated the degree to which analyzing communication sequences would contribute to the understanding of effective crew process in two simulated flight tasks. The results indicate that pattern analyses reveal additional strong differences between performance groups that would have been overlooked by simple frequency counts of communication. In each case, the sequential analysis shed additional light on the communication patterns that characterize better-performing teams. These results are discussed in terms of their implications for team performance research and team training. Potential applications of this research include training needs assessment, training design, and performance measurement after training.

Journal ArticleDOI
TL;DR: In this paper, the authors design and implement a field experiment to elicit and calibrate in-sample hypothetical and actual bids given the presence of other goods and intensity of market experience.
Abstract: We design and implement a field experiment to elicit and calibrate in-sample hypothetical and actual bids given the presence of other goods and intensity of market experience. Using market goods that possess characteristics beyond the norm but yet remain deliverable, bidding behavior was consistent with theory. But we also observe the average calibration factor for hypothetical bids in the auction with other goods to be more severe (0.3) than for the auction without the goods (0.4). The results support the view that the calibration of hypothetical and actual bidding is good- and context-specific. # 1998 Elsevier Science B.V. All rights reserved.

Journal ArticleDOI
TL;DR: In this article, a nanocrystalline diamond thin film was synthesized in an Ar-CH4 microwave discharge, without the addition of molecular hydrogen, and X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy characterizations showed that the films consist of a pure crystalline diamond phase with very small grain sizes ranging from 3 to 20 nm.
Abstract: Nanocrystalline diamond thin films have been synthesized in an Ar–CH4 microwave discharge, without the addition of molecular hydrogen. X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy characterizations show that the films consist of a pure crystalline diamond phase with very small grain sizes ranging from 3 to 20 nm. Atomic force microscopy analysis demonstrates that the surfaces of the nanocrystalline diamond films remain smooth independent of the film thicknesses. Furthermore, the reactant gas pressure, which strongly affects the concentration of C2 dimer in the Ar–CH4 plasma as well as the growth rate of the films, has been found to be a key parameter for the nanocrystalline diamond thin film depositions.

Journal ArticleDOI
TL;DR: This analysis suggests that VE performance deficits result either from poor binocular disparity cues or from distortion of pictorial depth cues, and the development of virtual environments for training and the design of visual displays for virtual simulations.
Abstract: Comparing human performance in a virtual environment (VE) with performance in the real world can provide clues about which aspects of VE technology require improvement. Using a technique previously shown to measure real-world distance judgments accurately, we compared performance in a real-world environment with performance in a virtual model of that environment. The technique required participants to walk without vision to a target after viewing it for 10 s. VE distance judgments averaged 85% of the target distance, whereas real-world judgments averaged 92%. The magnitude of the relative errors in the VE was twice that in the real world, indicating that the VE degraded distance judgments. Our analysis suggests that VE performance deficits result either from poor binocular disparity cues or from distortion of pictorial depth cues. Actual or potential applications of this research include the development of virtual environments for training and the design of visual displays for virtual simulations.

Journal ArticleDOI
TL;DR: A new convolution structure for the FRFT is introduced that preserves the convolution theorem for the Fourier transform and is also easy to implement in the designing of filters.
Abstract: The fractional Fourier transform (FRFT), which is a generalization of the Fourier transform, has many applications in several areas, including signal processing and optics. Almeida (see ibid., vol.4, p.15-17, 1997) and Mendlovic et al. (see Appl. Opt., vol.34, p.303-9, 1995) derived fractional Fourier transforms of a product and of a convolution of two functions. Unfortunately, their convolution formulas do not generalize very well the classical result for the Fourier transform, which states that the Fourier transform of the convolution of two functions is the product of their Fourier transforms. This paper introduces a new convolution structure for the FRFT that preserves the convolution theorem for the Fourier transform and is also easy to implement in the designing of filters.

Journal ArticleDOI
TL;DR: In this paper, a comparative analysis of professionals' use of individual self-managing activities in functional and cross-functional units found that individual selfmanagement was beneficial for effectiveness and efficiency.
Abstract: A comparative analysis of professionals' use of individual self-managing activities in functional and cross-functional units found that individual self-management was beneficial for effectiveness i...

Posted Content
TL;DR: In this article, the authors investigated the relationship between the incidence of RAQ behaviors and auditors' personality characteristics, auditors professional characteristics and auditing firms' quality control and review procedures.
Abstract: The purpose of this study is to develop and test a more comprehensive model of factors that explain reduced audit quality (RAQ) behaviors. Specifically, this study investigates the relationship between the incidence of RAQ behaviors and auditors' personality characteristics, auditors' professional characteristics, auditing firms' quality control and review procedures, auditing firm structure, and auditors' perceptions of time budget pressure. The results suggest that auditors' perceived strength of their firm's quality control and review procedures and auditors' perceived strength of their firm's penalties for committing RAQ acts are inversely related to incidences of RAQ behaviors. Also, auditors' need for approval and need for achievement are inversely related to RAQ behaviors. No other significant relationships between RAQ behaviors and other potential explanatory factors were found. These findings suggest that firms should evaluate their control, review, and disciplinary procedures over audit program execution and improve their auditors' understanding of procedures and penalties.

Journal ArticleDOI
TL;DR: The identification of an unknown state-dependent source term in a reaction-diffusion equation is considered in this article, where integral identities are derived which relate changes in the source term to corresponding changes in measured output.
Abstract: The identification of an unknown state-dependent source term in a reaction-diffusion equation is considered. Integral identities are derived which relate changes in the source term to corresponding changes in the measured output. The identities are used to show that the measured boundary output determines the source term uniquely in an appropriate function class and to show that a source term that minimizes an output least squares functional based on this measured output must also solve the inverse problem. The set of outputs generated by polygonal source functions is shown to be dense in the set of all admissible outputs. Results from some numerical experiments are discussed.

Journal ArticleDOI
TL;DR: The current study suggests that the type of cross- training necessary to improve team performance may be related to the nature of the task and that cross-training may be effective in allowing teams to coordinate implicitly—that is, without the need to communicate overtly.
Abstract: Although previous research has shown that cross-training team members improves team performance, a number of questions remain concerning the nature of cross-training. The current study provides an extension of previous cross-training research by investigating two theoretical issues: the nature of cross-training and the joint impact of cross-training and workload on team functioning. The study examined 40 three-person teams performing a simulated radar task. Results indicated that positional rotation was an effective cross-training method for highly interdependent tasks, that cross-trained teams developed a greater degree of interpositional knowledge than did teams that were not cross-trained, and that cross-training was important only under high-workload performance conditions. The current study suggests that the type of cross-training necessary to improve team performance may be related to the nature of the task and that cross-training may be effective in allowing teams to coordinate implicitly—that is, ...

Proceedings ArticleDOI
14 Dec 1998
TL;DR: The notion of patching window is introduced, and the optimal technique outperforms the existing schemes by a significant margin, and is also up to two times better than the best Piggybacking method which provides data sharing by merging the services in progress into a single stream by altering their display rates.
Abstract: Patching has been shown to be cost efficient for video-on- demand systems. Unlike conventional multicast, patching is a dynamic multicast scheme which enables a new request to join an ongoing multicast. Since a multicast can now grow dynamically to serve new users, this approach is more efficiency than traditional multicast. In addition, since a new request can be serviced immediately without having to wait for the next multicast, true video-on-demand can be achieved. In this paper, we introduce the notion of patching window, and present a generalized patching method. We show that existing schemes are special cases with a specific patching window size. We derive a mathematical formula to help determine the optimal size for the patching window. This formula allows us to design the best patching scheme given a workload. The proposed technique is validated using simulations. They show that the analytical results are very accurate. We also provide performance results to demonstrate that the optimal technique outperforms the existing schemes by a significant margin. It is also up to two times better than the best Piggybacking method which provides data sharing by merging the services in progress into a single stream by altering their display rates.

Journal ArticleDOI
TL;DR: In this article, the authors used a comparative case study methodology to develop a theoretical model of the antecedents of effective small business geographic expansion, and found that planning helps a firm develop a set of heuristics for expansion site selection, which helps to avoid placing a site in an undesirable location.

Journal ArticleDOI
TL;DR: The degree of user sickness was tested under passive, active, and active-passive control scenarios, and the implication is that the level of user-initiated control can be manipulated to modify the deleterious effects of human-virtual environment interaction.
Abstract: Cybersickness is a pervasive and deleterious effect of human-virtual environment interaction. This paper applies motion-sickness adaptation theory to cybersickness in virtual environments to determine if the degree of user-initiated control can suppress sickness. It is suggested that if users are allowed some level of control over their movement within a virtual environment, cybersickness will not be as severe as that resulting from an enviornment in which users must follow a predetermined (i.e., scripted) path of movement. While past motion-sickness studies have examined control versus no control, the present study focuses on modifying the level of user-initiated control such that it matches the needs of the task characteristics while minimizing sickness. The degree of user sickness was tested under passive, active, and active-passive control scenarios. As measured by the Simulator Sickness Questionnaire, the active (i.e., complete control) condition reduced the severity of the symptoms experienced as compared to the passive (i.e., no control) condition, but did not do so as completely as the active-passive (i.e., coupled control) condition. The implication is that the level of user-initiated control can be manipulated to modify the deleterious effects of human-virtual environment interaction.

Journal ArticleDOI
TL;DR: Statistical models were developed to help understand the relationship between the driver age and several important accident-related factors and circumstances such as injury severity, collision types, average daily traffic, roadway character, speed ratio, alcohol involvement, and accident location and indicated significant relationships.

Journal ArticleDOI
TL;DR: In this article, the authors present a framework for delineating those conditions that might affect the utility and effectiveness of practice in training, including factors that occur prior to, during, and after practice.
Abstract: The purpose of this paper is to describe a framework for delineating those conditions that might affect the utility and effectiveness of practice in training. The framework includes factors that occur prior to, during, and after practice. Pre-practice conditions, such as attentional advice, advance organizers, goal orientation, and pre-training briefs, are designed to make the time spent in practice more efficient and useful. This paper first reviews the existing literature concerning the pre-practice conditions that have been identified. Next, a description of the underlying mechanisms for each pre-practice condition is suggested, and a set of propositions regarding these conditions is offered. Finally, past findings are summarized regarding pre-practice conditions and provide an agenda for future research.

Journal ArticleDOI
TL;DR: The study looked at the effects of sensory rearrangement caused by a HMD design that displaced the user's virtual eye position forward and above and toward the spatial position of the cameras, revealing substantial perceptual costs of the eye displacement initially, but also evidence of adaptation.
Abstract: Among the most critical issues in the design of immersive virtual environments are those that deal with the problem of technologically induced intersensory conflict and one of the results, sensorimotor adaptation. An experiment was conducted to support the design of a prototype see-through, head-mounted display (HMD). When wearing video see-through HMDs in augmented reality systems, subjects see the world around them through a pair of head-mounted video cameras. The study looked at the effects of sensory rearrangement caused by a HMD design that displaced the user's “virtual” eye position forward (165 mm) and above (62 mm) toward the spatial position of the cameras. The position of the cameras creates images of the world that are slightly downward and inward from normal. Measures of hand-eye coordination and speed on a manual pegboard task revealed substantial perceptual costs of the eye displacement initially, but also evidence of adaptation. Upon first wearing the video see-through HMD, subjects' pointing errors increased significantly along the spatial dimensions displaced (the y dimension, above-below the target, and z dimension, in front-behind the target). Speed of performance on the pegboard task decreased by 43% compared to baseline performance. Pointing accuracy improved by approximately 33% as subjects adapted to the sensory rearrangement, but it did not reach baseline performance. When subjects removed the see-through HMD, there was evidence that their hand-eye coordination had been altered. Negative aftereffects were observed in the form of greater errors in pointing accuracy compared to baseline. Although these aftereffects are temporary, the results may have serious practical implications for the use of video see-through HMDs by users (e.g., surgeons) who depend on very accurate hand-eye coordination.


Journal ArticleDOI
TL;DR: In this paper, the optical properties of silicate glasses under high-power, 850-nm femtosecond laser irradiation have been studied and it is believed that these processes result from linear and two-photon absorption of the short-wavelength component of the supercontinuum causing ionization of the glass matrix.
Abstract: The optical properties of silicate glasses under high-power, 850-nm femtosecond laser irradiation have been studied. Photoinduced processes occurred at irradiances well below the threshold for laser-induce damage. Laser spectral line broadening leading to supercontinuum generation in the visible and UV spectral regions was observed in all the glasses studied. Color-center generation and intrinsic luminescence were found in boro-silicate and alkali silicate glasses. It is believed that these processes result from linear and two-photon absorption of the short-wavelength component of the supercontinuum, causing ionization of the glass matrix. No color-center absorption in the visible region was observed in fused silica at irradiances up to the laser-damage threshold.

Journal ArticleDOI
TL;DR: In this article, the authors investigated the evolutionary trends of industry variables such as patents, product price and quantity, and number of firms from the first introduction of a product to maturity of the market.


Journal ArticleDOI
TL;DR: A novel nonlinear control scheme-robust iterative learning control (RILC) is developed, which provides a general framework targeting at synthesizing learning control and robust control methods with the help of Lyapunov's direct method to handle more general classes of nonlinear uncertain systems.