Papers by Deshawn Johnson
The deformation and fracture of polycarbonate and polycarbonate toughened with methyl-methacrylat... more The deformation and fracture of polycarbonate and polycarbonate toughened with methyl-methacrylate shell/polybutadiene core sub-micron particles are investigated. The effects of strain rate, temperature, and notch stress triaxiality on deformation and fracture are studied. The Arruda-Boyce constitutive model for glassy polymers and finite element simulations are used to simulate the deformation of the polycarbonate homopolymer subjected to compression and tension under un-notched and notched conditions. Compression of polycarbonate in uniaxial compression is found to exhibit an initially elastic response followed by yield, then strain softening and strain hardening at large strains. The yield stress is found to be dependent on temperature and strain rate. Yield stress is shown to increase with increasing strain rate and decrease with increasing temperature. Load-displacement behavior of un-notched polycarbonate is shown to exhibit an initially elastic response followed by macroscopic yield, then a load drop, and then a load plateau as the neck stably propagates, soon after the neck has propagated the full length of the specimen it begins to travel into the grip region, ductile failure occurs due to extensive stretching. The fracture is surface initiated. The load at yield is shown to be dependent on temperature and displacement rate. The load at yield increases with increasing strain rate and decreases with increasing temperature. Notched tension specimens are shown to exhibit an initially elastic behavior. Mildly notched specimens tested at room temperature are shown to fail in a ductile manner similar to un-notched specimens. More severely notched specimens, and the moderately notched specimen tested at 100 C are shown to fail in a brittle manner where the brittle failure is found to be internally initiated. The un-notched and notched tension test data together with simulation results
Assessing the learning style preferences of adult workers (consumers) with moderate to severe int... more Assessing the learning style preferences of adult workers (consumers) with moderate to severe intellectual disabilities and accommodating the consumer's learning style preference during the job training process is a critical feature of quality supported employment services and an under-explored area of applied research. However, before evaluating the effects of learning style preferences on job training outcomes, consumers must first demonstrate the skills to express learning preferences. This research sought to demonstrate a method of assessing the learning style preference of consumers with moderate to severe intellectual disabilities and to investigate which of two instructional interventions, when matched with the consumers preferred learning style, would have the greatest impact on consumer job performance. Three independent variables were included in this study: (1) the consumer's learning style preference, (2) auditory instructional cues, and (3) visual instructional cues. The dependent variable was the accuracy of job task performance for each consumer under the alternating instructional interventions. ^ Four participants participated in the exploratory phase (phase I) of the study and three participants participated in the empirical phase (phase II) of the study. Phase I involved a descriptive analysis. Consumer learning style was assessed utilizing the Learning Style Inventory-Primary (Perrin, 1991), which was modified for use with the participant group. Phase II involved single-subject research design principles. Specifically, an alternating treatment withdrawal design was utilized to determine which instructional strategy (auditory or visual cues) when matched with the consumer's preferred learning style, had the greatest impact on the dependent variable. An Independent t-Test and a Helmert Contrast were used to determine statistical significance between conditions. An alpha level of .05 was set for determining significance. ^ Results indicate that learning style preferences for consumers with moderate to severe intellectual disabilities can be reliably assessed. Analysis of the data indicated that there was a significant difference in the effect of the two instructional interventions on consumer job performance. When the instructional intervention was congruent with the consumer's learning style, the greater the improvement in job performance. When the intervention was incongruent to the consumer's preferred learning style, a lesser degree of improved job performance would result. ^
Nihon University Journal of Medicine, 2002
We conducted a longitudinal study to identify factors associated with bone mass increase in middl... more We conducted a longitudinal study to identify factors associated with bone mass increase in middle school students because bone mass increase tends to be greatest at this stage life. The subjects comprised 84 students (40males, 44 females) attending a public middle school who were monitored for three years between 1998 and 2000. Bone mineral density was measured at the calcaneus using an ultrasonic analyzer (Aloka Inc., AOS-100). At the same time, various anthropometric measurements were taken and a survey was conducted to investigate the lifestyles of the students. Bone mass was assessed in terms of the osteo sono-assessment index (OSI). The OSI for female students was higher than that for male students at all grades, but there were no significant differences. At each grade, there was a significant correlation between bone mass and anthropometric measurements, particularly height. Furthermore, the results of multiple regression analysis, which investigated the degree of bone mass increase from the seventh through ninth grades as a dependent variable and anthropometric measurements and lifestyle as explanatory variables, showed that the degree of bone mass increase was greater for middle school students who exercised during the fourth, fifth and/or sixth grades.
Background/Question/Methods A current debate is whether community composition is primarly structu... more Background/Question/Methods A current debate is whether community composition is primarly structured by deterministic (e.g. Niche theory) or stochastic factors (e.g. Neutral theory). Niche theory suggests individuals with given traits for survival in a habitat with certain environmental conditions and interspecific interactions will determine community composition, while Neutral theory suggests individuals of similar trophic status do not differ in birth, death and dispersal rates and will stochastically determine community composition. Some have suggested that the importance of deterministic vs. stochastic factors varies due to the harshness of environmental conditions. Communities in harsh conditions are theorized to assemble deterministically producing similar species compositions among sites, while communities in benign conditions should assemble stochastically producing dissimilar compositions. We tested this by sampling aquatic invertebrates in ten wetland mesocosms (10 m X 20...
ABSTRACT Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2... more ABSTRACT Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2001. Includes bibliographical references (leaves 217-220). by Michael DeShawn Johnson. S.M.
Assessing the learning style preferences of adult workers (consumers) with moderate to severe int... more Assessing the learning style preferences of adult workers (consumers) with moderate to severe intellectual disabilities and accommodating the consumer's learning style preference during the job training process is a critical feature of quality supported employment services and an under-explored area of applied research. However, before evaluating the effects of learning style preferences on job training outcomes, consumers must first demonstrate the skills to express learning preferences. This research sought to demonstrate a method of assessing the learning style preference of consumers with moderate to severe intellectual disabilities and to investigate which of two instructional interventions, when matched with the consumers preferred learning style, would have the greatest impact on consumer job performance. Three independent variables were included in this study: (1) the consumer's learning style preference, (2) auditory instructional cues, and (3) visual instructiona...
IEEE Transactions on Engineering Management, 2010
... for Product Families: A Process-Based Cost-Modeling Approach Michael DeShawn Johnson, Member,... more ... for Product Families: A Process-Based Cost-Modeling Approach Michael DeShawn Johnson, Member, IEEE, and Randolph Kirchain AbstractTo be competitive in today's global economy, firms must deliver more products that are viable in the marketplace for shorter times. ...
Sustainable Dev. L. & Pol'y, 2008
The goal of most firms is to deliver products that satisfy customer needs. Delivering a variety o... more The goal of most firms is to deliver products that satisfy customer needs. Delivering a variety of differentiated products allows firms to satisfy the broadest range of customers. There is, however, a fundamental tension between this product differentiation and product cost. The use of product platforms allows a firm to reduce this tension, offering variety while also benefiting from the economics of mass production for shared components. The selection of components and subassemblies for platforming can have wide ranging effects on both product performance and cost. This thesis addresses the latter by presenting a methodology to assess product development costs, the amount of part sharing in a product family, and the effects of platforming on development, fabrication, and assembly costs for product families. Ordinal metrics are presented to assess the performance of product families. The methodology of process-based cost modeling, used to estimate product fabrication and assembly costs, is also posed. A method for determining the allocation of costs for parts and subassemblies shared among product family variants is outlined. A process-based cost model of the automotive product development process is presented. This model uses product part and subassembly characteristics to estimate the engineering effort required at various stages of the development process. Product development cycle time is also estimated. Linear regression analysis is used to determine which part and subassembly characteristics affect engineering effort. Additional development costs, such as computer hardware and software, overhead, and physical prototypes are also taken into account. Two automotive body architectures are analyzed to determine the cost savings from platforming: a tubular architecture (low tooling cost; high variable costs) and a traditional unibody architecture. Of the two designs, the tubular architecture is found to have less cost savings from platforming, even though the tubular architecture shares more parts. The higher fraction of variable costs and lower tooling cost, reduce the opportunity for sharing in the tubular architecture. Two instrument panel (IP) beam designs are also compared to study the effects of parts consolidation. A magnesium die cast IP beam is compared to a functionally equivalent steel IP beam that contains over six times as many parts. Development costs are found to make parts consolidation an attractive option, while this consolidation is found to reduce the opportunity for sharing and thus cause the magnesium IP beam family to be a more costly option than the steel design. Across all case studies, the fabrication and assembly of products are found to account for the majority of product cost; the majority of cost savings from platforming however, come from reduced development and assembly costs. Additionally, production volume and product lifetime are found to have large effects on which product architecture performs better. A significant perspective result, which emerged, was that the part sharing metric weighted by fabrication investment is found to be the most effective predictor of cost savings of the metrics tested.
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Papers by Deshawn Johnson