Biomechanical models are used in many situations to help understand the risks associated with performing different work tasks. A necessary input to most biomechanical models is the body posture of the worker. Measuring posture has proven to be a difficult and time-consuming process. The research reported in this thesis investigated if a posture can be predicted instead of measured. The posture prediction model employs a whole-body sagittal plane representation of the worker with five links using inverse kinematic procedures to calculate the postures. The model chooses a posture by optimizing an objective function using a nonlinear programming search. Three separate models have been formulated to predict the postures of 16 subjects humans performing four static sagittal lifting tasks. Each model uses a different objective function or criterion defined relative to the torques on the human joints. These criteria are labeled as Total Torque, Percent Strength, and Balance. The influence of gender, hand position, and criteria on the prediction accuracy were investigated. The results showed that there was less postural variability for higher hand positions compared to lower hand positions. For lower hand positions there were two distinct types of postures chosen by subjects which implies that there are two different types of criteria being used by subjects at these hand positions. Student t tests, which investigated the accuracy of the predictions, showed that all of the prediction errors were significantly greater than zero at α=0.05. A mixed factor, repeated measures ANOVA investigating the prediction error showed that the Total Torque criterion was more accurate than the two other criteria. / Master of Science

Computers are being used in interior design for space planning, drafting, and modeling. Advances in technology have made it possible to create graphic renderings and animations which enable designers and clients to “walk through” the designed space long before its construction. In kitchen showrooms this technology can be used as a marketing device to generate numerous three-dimensional computer models of complete kitchen setups, each capable of displaying all the possible combinations of styles and finishes available. The purpose of this study was to test the communication effectiveness of three-dimensional computer-generated models in presenting design ideas and alternatives to a client. Three forms of kitchen design presentations were compared: Line Drawings, an actual Showroom Display, and three-dimensional Computer Model. A sample of 32 residents from the town of Blacksburg, Virginia were shown the three presentations and scored each one for its efficiency of communication of specific design concepts. Their reactions to the use of computer models as presentation media were also obtained. ANOVAs and Chi Square tests were used to analyze the data. The Showroom Display was the best communicator of space and design ideas and the, Computer Model was most effective in presenting color and finish alternatives. In conclusion, the Computer Models were found to be an effective and acceptable means of kitchen design presentation. Although they cannot replace Showroom Displays, Computer Models can be used effectively and economically as an enhancement to showroom displays and can facilitate reduction of the number of displays required for effective marketing in a showroom. / Master of Science

System identification techniques were applied to obtain mathematical expressions relating column flotation operating parameters. The empirical data were derived by making individual step changes in tailings rate, wash water rate, feed rate, frother addition and air rates, while measuring the pulp level and air holdup responses. The dynamic behavior of the flotation column is also analyzed for the conditions at which the tests were performed. After converting these mathematical equations into continuous and discrete transfer function matrices, several control algorithms were simulated on this column flotation empirical representation. Suggestions are provided to deal with the complexities of the process when designing a control scheme. / Master of Science

The crystallization behavior of poly(p-phenylene sulfide) PPS has been studied. Two PPS samples with < M_w > = 43K and < M_w > = 83K were fractionated to remove low molecular weight oligomers yielding fractionated PPS samples with < M_w > = 57K and < Mw > = 113K. The fractionated samples were then treated with an ion exchange process to allow control over the nature of endgroup counterion. Isothermal rates of hulk crystallization were analyzed as a function of n1olecular weight of PPS, fractionation, and chen1ical nature of the endgroup counter-ion. Additionally the spherulitic growth rates and nucleation densities were studied as a function of the chemical nature of the endgroup counter-ion for fractionated PPS with < M_w > = 57K. As a function of endgroup counter-ion, crystal growth rates and overall rates of crystallization decreased in the following order: H > Zn > Na. No significant trends in nucleation density as a function of endgroup counter-ion were observed. Bulk crystallization rates, nucleation density, general morphological features, equilibrium melting point, and abso1ute crystalline percentage of linear and starbranched nylon-6 have been studied as a function of branch-point functionality and crystallization temperature. Overall bulk crystallization rates were described in terms of the Avrami equation. The crystallization half-times of star-branched nylon-6 as a function of <i>supercooling</i> were reduced relative to those of linear nylon-6 of comparable molecular weight. Irregularities in lame1lar structure were implied by SAXS experiments on samples with branch-point functionality as low as three. The effects of changing the block length of poly(dimethylsiloxane), PSX, blocks in poly(etheretherketone)-poly(dimethylsiloxane), PEEK-PSX, multi block copolymers and their ketimine precursors, PEEKt-PSX, were investigated. A dran1atic dependence on thermal history prior to crystallization was observed in both block copolymer systems. Block copolyn1crs crystallized from the glassy state obtained a much higher degree of crystallinity at a n1uch faster rate of crystallization than copolymers crystallized from the melt at identical crystallization temperatures. Thermal and mechanical behavior of bisphenol-A polycarbonate was studied as a function of thermal history and absorbed mass fraction of C0₂. Mechanical testing and gas absorption experiments were performed on physically aged and unaged polycarbonate. Gas absorption studies indicated that although initial diffusion was somewhat retarded in the aged samples, both aged and unaged polycarbonate samples showed identical equilibrium absorbed gas values at 6500KPa and identical gas desorption behavior. Absorbed C0₂ was shown to plasticize polycarbonate. Polymeric liquid crystalline foams were produced from star-branched polyoxybenzoate-po1yoxyphenoxybenzoate copolymers (POB-co-POPB) via gas supersaturation followed by thermal blowing. Solid state C0₂ gas absorption well as melt processability of star-branched POB-co-POPB was increased relative to the linear polymer of comparable molecular weight. While C0₂ blown foams of linear POB-co-POPB produced by the gas supersaturation technique had a relatively high density and showed highly anisotropic bubble growth, well defined, nearly isotropic foams of star-branched POB-co-POPB with mean cell size from 200 to 400μ were made using the gas supersaturation technique. / Ph. D.

The concept of soft-switching pulse-width-modulated (PWM) technique was proposed aimed at combining the advantages of both the conventional PWM technique and the resonant technique. This work presents four new families of soft-switching PWM converters: the zero-voltage-switched (ZVS) PWM converters, the zero-current-switched (ZCS) PWM converters, the zerovoltage- transition (ZVT) PWM converters, and the zero-current-transition (ZCT) PWM converters. The family of ZVS- and ZCS-PWM converters are developed to improve the performance of the ZVS and ZCS quasi-resonant converters, respectively. The principles of operations of these two families of converters are presented, and the merits and limitations are assessed. A number of experimental converters are breadboarded to verify the theoretical analysis. Both the ZVT-PWM and ZCT-PWM techniques use the concept of shunt resonant network to achieve soft-switching. In this way, the new converters achieve soft-switching without increasing the voltage and current stresses of the power switches and diodes. By using the boost topology as an example, a complete dc analysis of the ZVT-PWM and ZCT-PWM converters is presented, and the dc Voltage-conversion ratio characteristics are derived. Design trade-offs are examined, and design procedures are established. The theoretical analysis and novel features of the proposed converters are verified on a number of breadboarded converters. Finally, the typical small-signal characteristics of the ZVT -PWM converters are analyzed and verified experimentally by using the boost converter as an example. / Ph. D.

An experimental study to determine the effects of riblets on the performance of the supersonic through-flow fan (STF) cascade blades was performed. The two-dimensional cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the Mach and Reynolds (based on chord) numbers were 2.36 and 4.8 x 10⁶ , respectively. Three different V-grooved riblet heights were tested on the blades: 0.023, 0.033, and 0.051 mm. Riblet testing were conducted at design incidence as well as at off-design conditions (incidence angles: +5, -10 deg). The riblet effect on the performance of the STF blades was determined by measuring the total pressure profile downstream of the cascade and integrating this total pressure to obtain an overall mass-averaged loss coefficient. The riblet loss coefficient was compared with the loss coefficient of a control test case where an equivalent thickness of smooth material is applied to the blades. Results show that, at the design incidence, the 0.033 mm height riblets provided the optimal benefit, with a reduction of 8.5% in the loss coefficient compared to the control case. Smaller effects were measured at the off-design conditions. Shadowgraph pictures were taken to study the effect of riblets on the turbulent transition location on the blades surfaces. At design incidence, the shadowgraphs revealed that the optimum height rib lets delayed the transition location on the suction surface of the blades. Therefore, it was concluded that for the 0.033 mm height riblets the decrease in the cascade's loss coefficient was the result of delayed transition in addition to a decrease in turbulent viscous losses. A numerical simulation was conducted to investigate both rib let effects on the STF blades. The numerical study showed that only the combination of the two riblet effects was able to produce a decrease in loss coefficient that was observed experimentally. Results from the numerical study indicate, that at design incidence, 2/3 of the rib let benefit is attributed to the delayed transition effect on the blades with the other 1/3 resulting from a decrease in turbulent viscous losses. / Ph. D.

This case study determined whether there was a difference in perceptions among principals from different quality schools about the influence desegregation, supplemental financial assistance, magnet thematic activities, and increased educational opportunities had on quality in education. Since there was no significant difference in perceptions, this study also examined how the factors influenced the principals' beliefs about educational quality. Two hundred fifty-five elementary and secondary principals from four different types of organizational structures in ten states participated in the study. The participating principals responded to the Survey of principals' Attitudes Regarding Education (SPARE) which constituted the data for this investigation. The degree of achievement, student dropout, violence, and racial balance were used to determine school quality and constituted the dependent variables. Principals' perceptions about desegregation, thematic activities, supplemental financial assistance, and increased educational opportunities constituted the independent variables. The findings of this study revealed the following conclusions: (1) There was no significant difference among principals from lower, average, and higher quality schools regarding their perceptions about the influence finance, desegregation, thematic activities, and educational opportunities had on the quality of education in a school. (2) Principals believed three of the four factors including desegregation, finance, and increased educational opportunities were necessary for a school to offer quality education. (3) Principals perceived student achievement could be increased without additional financial resources; however, educational quality could not be attained without additional funds for desegregation-related services and for programs designed to improve educational opportunities for students. Based upon information obtained from the survey instruments, principals believed a quality instructional program required a curriculum with special activities designed to improve student knowledge while increasing educational opportunities for a racially diverse student body. They believed schools should be given more funds for more specialized activities. Although magnet school thematic activities accomplished the same purpose, their costs were too high for most boards of education to finance. Regular school activities would be as effective as magnet school thematic activities with similar supplementary financial resources. / Ed. D.

The quest for developing high performance materials, originally responsible for the birth and growth of the composites industry, is now responsible for the drive to produce composites which outperform those used today. A great deal of this interest lies in the use of thermoplastic polymers as the composite matrix. Thermoplastics offer the potential of improved mechanical performance, greater solvent resistance, better impact tolerance, as well as cost saving processing attributes such as infinite shelf life, the ability to be recycled, short processing time and repairability. Unfortunately, these advantages come at the expense of a very high melt viscosity which makes the prepregging process, where the fiber and polymer are combined, very difficult. To overcome this and associated difficulties a detailed analysis of thermoplastic matrix composite processing is developed. The primary area of focus involves the development of an electrostatic dry polymer powder prepregging facility. This unit is capable of the production of high quality towpreg from thermoplastic polymers and reinforcing fibers. Two approaches, statistical and stochastic, were employed to model the process of polymer deposition on the fibers in the prepregging process. These models are used to optimize the production of towpreg. A modification of the prepregging facility allows for the production of towpreg from very small (15 g) samples of polymer. This is extremely useful for analysis and performance verification of state of the art polymer systems. / Ph. D.

A software system is an aggregate of communicating modules, and there are several different types of communication among these modules (direct, indirect, and global). Therefore, understanding the interfaces among these modules can characterize the system and are a major factor in the system's complexity. These interfaces could possibly also show and predict inadequacies in the reliability and maintenance of a system. Interfaces are defined early in the development life cycle at a detailed or high level design stage. Knowing that these interfaces exist and their structure leads us to measure them for an indication of the designed interface complexity. This designed interface complexity can then be utilized for software quality assurance by allowing users to choose from among several designs. With data provided by an Ada software developer, the interface complexity metrics correlated with established metrics, but also found complex interfaces that established metrics missed. / Ph. D.

Experiments were conducted to explore physiological, pathological, and immunological aspects of stress in chickens. Mechanisms of habituation and their association with adrenal steroids were also studied. Degree of stress experienced during perinatal and neonatal stages was evaluated. In both stages, heterophilia and lymphopenia were noted and post-hatching heterophil to lymphocyte (H/L) ratios declined in a quadratic manner with age. Feed restriction elicited a similar stress response, as indicated by H/L ratios in dwarfs and normals with the effect of adapting to fasting having dissipated between 12 to 16 days. Resistance to Eimeria tenella infection was greater in normals than dwarfs, and for fasted than ad libitum fed chicks. Neither genotype nor feeding regimen had an effect on antibody response to SRBC. Frustration induced by thwarting of feeding resulted in a dramatic elevation in HIL ratios and conspicuous behavioral responses, suggesting responses to fasting may be physiologically and psychologically modulated. Provision of sand during feed withdrawal attenuated physiological responses, possibly via alteration of psychogenic components. An experiment was designed to evaluate the impact of mild feed restriction at several ages on heat tolerance. Normal chicks feed-deprived during the neonatal stage had lower H/L ratios, improved resistance to marble spleen disease and growth during heat treatment than those fed ad libitum or fasted at older ages. A companion experiment examined habituation and concomitantly the role of glucocorticoids in stress response. Neonatal fasting-induced stress responses without concurrent increases in adrenal steroidogenesis did not enhance ability of normal chicks to withstand high ambient temperatures. The hypothesis regarding modulatory roles of corticosteroids in neonatally-elicited adaptation was affirmed in a subsequent study. Feed withdrawal for 8 or 24 h at 36 days of age did not induce either H/L or plasma corticosterone response of chicks stressed early in life. In contrast, neither criterion provided evidence for adaptation to feed deprivation by neonates treated with an adrenal steroidogenesis blocker during the fast. corticosterone mediated inhibitory feedback regulation of the hypothalamic - pituitary - adrenal axis which down-regulates ACTH response was also evident. / Ph. D.