Browsing by Author "Deighan, John"

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    The effect of cropping systems on the pest complex in Virginia soybeans and calibration of the sweep net and ground cloth sampling methods for use in these cropping systems
    Deighan, John (Virginia Polytechnic Institute and State University, 1983)
    Increasing numbers of soybean fields in Virginia are double-cropped, immediately following spring harvest of barley or wheat. Most of these fields are planted in notillage systems. Early planted soybeans are sometimes planted with a grain drill in very narrow rows (ca. 18 cm. apart). The effect that these practices have on arthropod populations is not well understood. Also, sampling methods developed for conventionally tilled, wide row systems may be more or less efficient in the double-cropped and drilled cropping systems. Ten sample pairs were obtained from each of 150 fields between 1980 and 1982 in conventional, drilled, and double-cropped soybean fields. The first sample of each pair was collected with a 38 cm. diameter sweep net (25 sweeps per sample) and the other sample was collected with a 0.91 meter ground cloth. In addition, after each ground cloth sample was obtained, the foliage and base of the plants in the 0.91 m sample were searched for additional arthropods not counted on the ground cloth. Regression relationships were developed and are presented which relate sweep net counts to ground cloth counts. Also, estimates of the percent of selected species missed with the ground cloth may be used to obtain absolute estimates of arthropod densities. Throughout the 1981 and 1982 growing seasons weekly sweep net samples were obtained from three fields planted to each of the following cropping systems: full season, conventionally tilled; full season, drilled; no-till, double-cropped after barley; and no-till, double-cropped after wheat. Analyses were perforrried to determine which species were most abundant in which cropping systems. Also, a principal components analysis was performed to determine the factors that caused the observed differences.
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    Effects of Illumination and Viewing Angle on the Modeling of Flicker Perception in CRT Displays
    Sidebottom, Shane D. (Virginia Tech, 1997-03-21)
    This study evaluated the usefulness of a psychophysical model as part of a new ANSI/HFES 100 standard for CRT flicker. A graph based flicker prediction method developed from Farrell, 1987 was evaluated. The Farrell model is based on phosphor persistence, screen luminance, display size, and viewing distance. The graph based method assumes a worse case scenario (i.e. a white display screen shown on a display with P4 phosphor). While the Farrell model requires photometric measurements to be taken using special equipment, the graph based method require a knowledge of the display size, viewing distance, screen luminance, and refresh rate. Ten participants viewed different display sizes from different eccentricities under different levels of illumination and luminance. In each condition the display's refresh rate was manipulated using the Method of Limits to determine the critical flicker frequency (CFF). An Analysis of Variance was used to detirmine significant effects on CFF. CFF increased with increasing luminance and display size. Adequate illumination significantly increased CFF. A viewing eccentricity of 30 degrees (measured horizontally from the center of the screen) produced the highest CFF values. Under the conditions of 30 degrees eccentricity and 250 to 500 lux illumination, observed 50% CFF threshold values exceeded the 90% CFF threshold values predicted by the graph based method. This study demonstates that when tested under the same conditions it was developed under, the Farrell method successfully predicts flicker perception; however, when tested under conditions representative of real world working conditions, the Farrell model fails to predict flicker perception. New parameters for the model are suggested.
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    Effects of Interface Format, Feedback Style, and System Lag on the Usability of Hand-Held Internet Controllers
    Ergen, Feyza F. (Virginia Tech, 1996-12-17)
    The increasing popularity of the World Wide Web (WWW) has created a new market: Web access through television to accommodate those who either cannot afford existing hardware or are intimidated by computers. Current efforts to combine the WWW and television have targeted potential novice users. One of the approaches for creating a WWW browsing system that is both simple to use and inexpensive is the utilization of the existing cable system to provide Web access through television. Some unique characteristics of this browsing system are fast access to the Web, the use of nine buttons on a universal remote control, and an index structure for reaching Web sites. Since browsing the Web through television is relatively new, many interface issues need to be examined. The purpose of this research was to investigate potential user interface designs for this WWW browser and to evaluate the usability of the nine-button interface. Sixteen volunteers participated in the experiment and were asked to navigate to specific Web sites with two interface formats, five different system lag times (0.2, 0.7, 1.3, 2.0, and 3.0 seconds), and three feedback styles (active feedback, passive feedback and no feedback). Participants were prescreened for their experience with computers and browsing the Web. The experiment was conducted in a living room setting to simulate real life situations and participants were given a total of 42 tasks to complete throughout the experiment. Each task consisted of navigating through the tree structure with either one of the two interface formats until reaching a designated Web site. The number of errors committed and task completion times were recorded. In addition, participants were asked to rate the WWW browser system after each task as well as after the entire experiment. Participants preferred the 0.2 second system lag and the active feedback style. Overall, they committed fewer errors and took less time to complete tasks with the tabbing interface than with the one-to-one mapping interface. Experienced participants committed more errors than did the inexperienced ones. Increase of system lag time was determined to have a greater adverse effect on the tabbing interface than on the one-to-one mapping interface.
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    Hierarchical Constraint Satisfaction as a Model for Adding Types with Inheritance to Prolog
    Chitale, Chandan; Deighan, John; Roach, John W. (Department of Computer Science, Virginia Polytechnic Institute & State University, 1990)
    Prolog is a language based on first order logic. It uses resolution as a rule of inference, and unification is the heart of resolution. Prolog operates on the Herbrand universe, a single, unstructured domain. In problems with large structured domains, the number of resolution steps may become large. We have incorporated type inheritance into Prolog to exploit large structured domains to write more concise code and to obtain shorter proofs. Types are subuniverses corresponding to sets of objects. The subset of relation between types induces a hierarchy on the universe. We used the hierarchical constraint satisfaction concept to incorporate these extensions into Prolog. We also provide a formal proof that our typed unification extends standard Prolog and directly augments the Warren Abstract Machine (WAM) concept.
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    Improving Access to Computer Displays: Readability for Visually Impaired Users
    Bangor, Aaron W. (Virginia Tech, 1998-08-06)
    In the field of human factors engineering the issue of how to present electronic text to people has been studied intensely for over 35 years. However, one major consideration that has largely been overlooked in these studies is how visual impairments affect reading of computer text. Specifically, the issue of how text can be modified to improve readability of CRTs for individuals with low vision. A 2x5x2x3 (visual capability, font size, polarity, and contrast) mixed-factor, repeated-measures experimental design was used to determine if changes in font size, contrast polarity, and/or contrast can improve reading speeds and reduce error rate for people with low vision. The results of this experiment show that alterations in text can be made that do not affect unimpaired vision readers while dramatically improving the reading capabilities of the impaired vision population. For character size, 12 and 14 point font sizes were found to be too small for the visually impaired population examined. In general, 18 and 30 point font sizes were equal to each other and to the 24 point font size, but for some interactions these two were found to produce longer response times and higher error rates. Thus, a 24 point font size is recommended. Unlike previous research with visually impaired participants, this experiment found that negative (white-on-black) polarity worsened reading performance. It is thought that this discrepancy is a result of polarity's interaction with small font sizes. For this reason, it is recommended that for font sizes of 18 points and below, positive polarity should be used. For 24 and 30 point sizes either polarity is satisfactory, though previous research (Legge, Pelli, Rubin, and Schleske, 1985b; NRC, 1995; Rubin and Legge, 1989) suggests negative polarity might be better for some visually impaired readers.. Contrasts of 3:1, 7:1, and 18:1 were used in this experiment and had no significant effect for either vision group. However, contrast did significantly interact with both font size and polarity. For font sizes of 18 points or below, it is recommended that contrasts of 18:1 be used for either polarity, but this is very important if negative polarity is used. The above recommendations are based on a small group of impaired vision readers. Visual impairments vary widely and the sample used in this experiment represented only a portion of them, with respect to both cause and severity. Wherever possible, computer text should be tailored to the unique needs of its users.
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    Objective Image Quality of CRT Displays under Ambient Glare: Assessing the ISO 9241-7 Ergonomic Technical Standard
    Kempic, Joy III (Virginia Tech, 1998-04-10)
    This thesis assessed the readability of CRT displays viewed under ambient lighting conditions and then evaluated the findings with respect to the ISO 9241-7 standard. More specifically, two phases of work were conducted in this thesis. In Phase 1, seven monitors were evaluated photometrically according to the ISO 9241-7 standard to determine whether they were Class I, II, or III in positive and negative polarity. Additionally, six filters were attached to each of the monitors and their ISO Class also was assessed. All monitor/filter combinations yielded either Class I or II in positive polarity and Class II, III or failed in negative polarity. In Phase 2, fourteen participants were asked to read Tinker passages from seven display/filter combinations (tested in Phase 1) under five lighting conditions and two screen polarities. The purpose of the Phase 2 was to determine if people perform differently for Class I, II, or III monitor/filter combinations. The dependent measures were the time to read the Tinker passage (reading time) and the ability to identify the out of context word in each passage (accuracy). An Analysis of Variance was used to determine the significant effects of reading time and accuracy. The ANOVA results indicate that specular glare interferes significantly more with reading time than does diffuse glare. Diffuse (200 lux) and Specular reading times also were correlated against two ISO metrics: screen image luminance ratio (Diffuse, 200 lux) and specular reflection luminance ratio. Reading times did not correlate with the screen image luminance ratio, but they did correlate with one of the ISO specular reflection luminance ratios. The results of this thesis indicate that the ISO standard should not equally weight the screen image and the specular reflection luminance ratios. Additionally, the results indicate that it is not necessary to have separate ISO Classes for positive and negative polarity. Furthermore, people did not read differently for Class I, II, or III monitor/filter combinations. Finally, the data of this investigation provide an initial human factors database for use in assessing the validity of ISO 9241-7.
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    Subjective Image Quality of CRT Displays under Ambient Glare: Assessing the ISO 9241-7 Ergonomic Technical Standard
    Olacsi, Gary S. III (Virginia Tech, 2004-02-24)
    This thesis evaluates the ISO 9241 Part 7, Ergonomic requirements for office work with visual display terminals (VDTs) - Part 7: Requirements for display with reflections. The thesis involved two phases of effort that evaluated the photometric measurements required in the ISO standard in terms of subjective image quality judgments. In phase one, seven monitors were evaluated photometrically according to the ISO 9241-7 standard to determine whether they were Class I, II, or III. Additionally, glare filters were attached to monitors to see if they change the ISO classification of the monitor. The results of phase one indicated that positive polarity always yielded either Class I or Class II because the Large Source, Screen Image Luminance Ratio (LR BDS/FDS) and the Specular Reflection Luminance Ratio (LR BDS/BD) always passed. Conversely, negative polarity always produced Class II or Class III because the Small Source, Specular Reflection Luminance Ratio (LR BDS/BD) failed every time. Also, the AF 150 and HF 300 were the best filters for reducing glare on monitors. The BF 10 and AF 100 or AF 200 ,on the other hand, were the worst because they intensified screen reflections. In phase two, human image quality judgments were collected to determine if people rated Class I, II, or III monitor-filter combinations differently under different lighting and different screen polarity conditions. Specifically, phase two assessed the effects of seven monitor/add-on glare filter combinations, five ambient lighting conditions, and two screen polarities on subjective image quality ratings. Each participant provided subjective image quality judgments by viewing alphanumeric text on the CRT screens. Subjective scale values also were correlated with ISO classifications and two ISO metrics: screen image luminance ratio (Diffuse, 200 lux) and specular reflection image luminance ratio. The ANOVA findings indicated that specular glare significantly degrades image quality ratings more than diffuse glare. The author contends that this finding is the result of an experimental context effect. In other words, the specular glare was so influential on subjective ratings of image quality that subjects paid little or no attention to reductions in contrast from the diffuse lighting conditions. The correlation analysis showed that the specular reflection luminance ratio and the negative polarity classifications did index subjective quality ratings. Finally, this thesis establishes a human factors basis to justify the measurement requirements in the ISO 9241-7 standard. Specifically, the findings show that it underemphasizes the contribution of the specular reflection luminance ratio' and overemphasizes the contribution of the screen image luminance ratio to compliance classification calculations, because the procedure gives equal weight to both ratios.
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    VPI PROLOG compiler project report
    Deighan, John (Virginia Tech, 1991-11-15)
    This project report documents a PROLOG compiler based on an abstract machine design published by David H. D. Warren. The implementation is actually a low-level intermediate language generator and interpreter. However, it is customary among PROLOG users to call this a compiler, since most PROLOG implementations are pure interpreters, i.e. they store PROLOG code as lists which mirror the source clauses. This compiler imcorporates many extensions to the abstract machine described by Dr. Warren.
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    VPI Prolog User Manual
    Roach, John W.; Deighan, John (Department of Computer Science, Virginia Polytechnic Institute & State University, 1990)
    This paper documents how a user may work with the VPI Prolog compiler. The user interface functions called debugging environment and input/output are all described in detail. Anyone using this manual should be able to program effectively using VPI Prolog.