Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 232-235). Also available via the Internet.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 186-201).

Thesis (Ph. D.)--University of Texas at Austin, 2005. / Supervisor: Chandrajit L. Bajaj. Vita. Includes bibliographical references.

Increased survival of presynaptic-like neuronal profiles was found in cell cultures of rat cerebellum when the non-neuronal cell numbers were reduced with an antimitotic drug. In both treated and untreated cell cultures, neurites grew onto the polylysine-coated surface of sepharose beads and formed a swelling. The neuronal swelling contained an accumulation of synaptic vesicles and a membrane density at the site of contact with the bead and was called an apparent presynaptic element. The apparent presynaptic elements in untreated cultures increased in number from the time the beads were added to the culture to 7 days incubation and then showed a decrease to one half the 7-day value at 14 days incubation. A 75% reduction in cell division of non-neuronal cells was seen in cultures exposed to a 5 × 10-6 M cytosine arabinoside (Ara-C) for 2 days. Adding polylysine-coated beads to cultures treated with Ara-C showed at 14 days incubation a 7-fold increase in the number of apparent presynaptic elements as compared to untreated cultures. Additional experiments examined the numbers of neurites on the beads and found only small differences between treated and untreated cultures. A decrease, however, was shown in the number of glial fibrillary acidic protein staining astrocytes on the surface of the beads in treated cultures. The reduction of astrocytes by Ara-C appeared to enhance the survival of apparent presynaptic elements but did not enhance the growth of neurites. These results suggest that proliferating non-neuronal cells at a site of injury in the central nervous system may inhibit the formation of synaptic contacts and the growth of neurites through the site of injury.

A functional water-conducting system, the tracheary elements of the xylem, is required to sustain plant growth and development. Tracheary element formation is dependent on many biological processes terminated by programmed cell death and cellular autolysis. The final two processes are probably dependent on the activity of hydrolytic enzymes such as XCP1 and XCP2 known to be expressed in tracheary elements during these final two processes. Thus, the transcriptional regulation of XCP1 and the function of XCP2 were investigated. Qualitative and quantitative assessments of GUS activity as directed by various fragments of the XCP1 promoter showed that a 237-bp internal region was able to drive GUS expression in a tracheary element-specific manner in Arabidopsis. A 25-bp deletion at the 3' end of this region abolished GUS expression. The 237-bp region served as bait in a yeast one-hybrid analysis. Screening of yeast colonies retrieved 109 putative positive interactions, which included a potential transcriptional regulator, indole acetic acid-induced protein 8 (IAA8). An auxin responsive element that potentially binds auxin responsive transcription factors was found within the 25-bp deletion. Cis-elements were predicted by Genomatix and Athamap computer programs. The cis-elements form pyrimidine and gibberellic acid responsive elements that can potentially bind Dof and Myb transcription factors, respectively. In an independent effort, attempts to develop a mapping population to isolate upstream regulators of XCP1 expression did not succeed. Functionally, tracheary element-specific expression of XCP2 in Arabidopsis suggested a specialized role for XCP2 in final phases of tracheary element differentiation. The function of XCP2 was assessed using T-DNA insertional mutants, post-transcriptional gene silencing, and through tracheary element-specific expression of the cysteine protease inhibitor, soyacystatin N in Arabidopsis. Our findings revealed that the absence of XCP2 expression due to T-DNA insertional mutagenesis did not affect plant growth and development in the laboratory. Soyacystatin N was an effective in vitro inhibitor of cysteine proteases. Plants expressing 35S-driven cytosolic form of soyacystatin exhibited stunting and reduced apical dominance. Plants expressing pXCP1-driven cytosolic soyacystatin did not differ from wild type plants. Additionally, transgenic plants expressing pXCP1- and 35S-directed XCP2-double-stranded RNA for the silencing of XCP2 showed no unusual phenotypes compared to their wild type counterparts / Ph. D.

The far-field underwater explosion (UNDEX) problem is a complicated problem dominated by two phenomena: the shock wave traveling through the fluid and the cavitation in the fluid. Both of these phenomena have a significant effect on the loading of ship structures subjected to UNDEX. An approach to numerically modeling these effects in the fluid and coupling to a structural model is using cavitating acoustic finite elements (CAFE) and more recently cavitating acoustic spectral elements (CASE). The use of spectral elements in CASE has shown to offer the greater accuracy and reduced computational expense when compared to traditional finite elements. However, spectral elements also increase spurious oscillations in both the fluid and structural response. This dissertation investigates the application of CAFE, CASE, and a possible improvement to CAFE in the form of a finite element flux-corrected transport algorithm, to the far-field UNDEX problem by solving a set of simplified UNDEX problems. Specifically we examine the effect of increased oscillations on structural response and the effect of errors in cavitation capture on the structural response which have not been thoroughly explored in previous work. The main contributions of this work are a demonstration of the problem dependency of increased oscillations in the structural response when applying the CASE methodology, the demonstration of how the sensitivity of errors in the structural response changes with changes in the structural model, a detailed explanation of how error in cavitation capture influences the structural response, and a demonstration of the need to accurately capture the shape and magnitude of cavitation regions in the fluid in order to obtain accurate structural response results. / Ph. D.

No description available.

Over the last 20-30 years the subject of spin in tennis has become increasingly important. A great deal of work has been done to establish the effects which, increased levels of spin have, on shots. The most prominent effect of increased spin in a tennis shot is the resulting deviation in flight which allows players to, amongst other things, strike the ball harder with top-spin in the knowledge that it will still fall inside the court due to the extra aerodynamic downward force. With such significant advantages available racket manufacturers are naturally keen to maximise spin generation. That being said, very little research has been performed into the subject of spin generation in tennis and the affecting factors. This thesis details the development of a finite element model which is to be used to allow a greater understanding of spin generation and how varying properties such as string density (the number of strings in a string-bed), gauge and orientation affect its magnitude. The primary aim, or goal, of this research is to create an FE model which can be used to model oblique impacts and measure the resulting spin. Whilst considerable focus was placed on developing novel, modelling techniques to create the FE model, a great deal of emphasis was also placed on its validation. The validity of the model was examined under static loading conditions, such as that experienced during stringing. The dynamic performance was also validated using a combination of modal analysis and high speed video of dynamic impacts. Each of the validation methods provided assurance of the models performance, with all error margins less than 5%. The two areas of the FE model which required the most attention were the interaction properties (specifically coefficient of friction (COF)) and material properties. Previous studies have sought to obtain a single value for the COF of a tennis racket/ball system but this study examines how the COF varies as the strings interact first, with themselves and secondly with the ball. Each of the validation methods (dynamic and static) were deemed successful as they provided concise data which could be readily compared with the results produced by the FE model. Having validated the model s performance, with respect to predicting outbound spin, a number of oblique impact angles were modelled to allow a greater understanding of how the mechanisms of spin generation change with the inbound trajectory of the ball. This analysis showed that for the impact conditions studied the contact time of the impact was reduced from 6.2 milliseconds to 5.7 milliseconds when the angle was increased from 32 degrees to 40 degrees. Furthermore, a number of novel string-beds were modelled, with varying string orientations (between 30 degrees and 60 degrees relative to the rackets frame) and subjected to a similar analysis procedure, with their results providing the concluding section of the thesis.

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Mechanical Engineering / Doctoral / Doctor of Philosophy