Browsing by Author "Nelson, Mark D."

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    A Comparison of Two Methods Used to Deal with Saturation of Multiple, Redundant Aircraft Control Effectors
    Nelson, Mark D. (Virginia Tech, 2001-08-17)
    A comparison of two methods to deal with allocating controls for unattainable moments in an aircraft was performed using a testbed airframe that resembled an F/A-18 with a large control effector suite. The method of preserving the desired moment direction to deal with unattainable moments is currently used in a specific control allocator. A new method of prioritizing the pitch axis is compared to the moment-direction preservation. Realtime piloted simulations are completed to evaluate the characteristics and performance of these methods. A direct comparison between the method of preserving the moment direction by scaling the control solution vector and prioritizing the pitching moment axis is performed for a specific case. Representative maneuvers are flown with a highly unstable airframe to evaluate the ability to achieve the specific task. Flight performance and pilot interpretation are used to evaluate the two methods. Pilot comments and performance results favored the method of pitch-axis prioritization. This method provided favorable flight characteristics compared to the alternative method of preserving the moment direction for the specific tasks detailed in this paper. NOTE: An updated copy of this ETD was added on 09/28/2010.
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    The effects of an intensive vocational evaluation involving work samples on career indecision, self-esteem, and state anxiety in rehabilitation clients
    Nelson, Mark D. (Virginia Polytechnic Institute and State University, 1987)
    The work sample approach to vocational evaluation attained prominence in rehabilitation settings largely as a result of dissatisfaction with traditional evaluation methods. Although the predictive validity of work sampling is assumed superior to paper and pencil testing, it is the career development functions that makes work sampling particularly attractive. Frequently writers have extolled the career and self exploration components of work samples. Among the specific variables work samples are assumed to positively affect are anxiety about making a career choice, career decidedness, and self-esteem. However these career development benefits like the predictive validity of work sampling have largely been unexamined. This study is an initial exploratory investigation of these proposed career development functions. It seeks to determine if undergoing a work-sample-based evaluation is associated with (a) a reduction in anxiety connected with career decision-making, (b) lessened career indecision, and (c) enhanced self-esteem. To accomplish the aforementioned, 60 clients of a comprehensive rehabilitation center were administered the A-State Scale of the State-Trait Anxiety Scale, the Career Decision Scale, and the Self-Esteem Inventory prior to beginning a comprehensive work-sample-based vocational evaluation, and again after the evaluation was completed. Three different handicapping conditions were studied with an equal nuber of subjects in the three groups: (a) mentally retarded, (b) learning disabled, and (c) emotionally disturbed. Using a repeated measures multivariate analysis of variance, a change in dependent measures scores from pretesting to postesting was observed. Evaluation activities did not interact with type of handicapping condition to affect these scores. Post hoc analysis indicated positive changes occurred in anxiety associated with career decision-making and self-esteem. Super‘s (1983) model of career maturity was employed to examine the career development effects of a work—sample-based vocational evaluation. This model cites the counterproductive effects of anxiety and low self-esteem on career planning, both of which have been validated empirically. Consequently the change in the sample's anxiety and self-esteem are assumed to enhance the probability of career planning. The time between the vocational evaluation and posttesting may have been insufficient for career indecision levels to have changed. The limitations of the study, are addressed as are the implications of the study for future research.
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    Forest-Associated Fishes of the Conterminous United States
    Bury, Gwendolynn W.; Flitcroft, Rebecca; Nelson, Mark D.; Arismendi, Ivan; Brooks, Evan B. (MDPI, 2021-09-15)
    Freshwaters are important, interconnected, and imperiled. Aquatic ecosystems, including freshwater fishes, are closely tied to the terrestrial ecosystems they are embedded within, yet available spatially explicit datasets have been underutilized to determine associations between freshwater fishes and forested areas. Here, we determined the spatial co-occurrence between freshwater fish distributions and forests within 2129 watersheds of the conterminous United States. We identified 21% of freshwater fishes as associated with forested areas, and 2% as strictly present only in highly forested areas (75–100% forested). The northern coasts and southeast regions, both heavily forested, showed the largest numbers of forest-associated fishes in highly forested areas and fish species richness. Fish associated with low-forested areas occurred in the southwest and central plains. Imperiled fishes were relatively evenly distributed among percent forest categories, which was distinctly different from patterns for all fishes. The identification of forest-associated fishes provides insights regarding species-specific landscape contexts. Determining these large-scale patterns of freshwater biodiversity is necessary for conservation planning at regional levels, especially in highly impacted freshwater ecosystems.