Walker, Gordon James This dissertation examines four issues, including: (a) whether outdoor recreation experiences not included in the Recreation Experience Preference (REP) scales exist; (b) whether these experiences can be categorized using a framework called the Recreation Experience Matrix (REM); (c) how well the Recreation Opportunity Spectrum (ROS) variables of activity, setting, and expertise explain the types of experiences outdoor recreationists receive; and (d) how well two new variables--primary mode and mode dependence--explain the types of experiences outdoor recreationists receive. In order to address these issues, an on-site questionnaire was distributed at Mount Rogers National Recreation Area in Virginia during October and November, 1995. A total of 410 people completed this questionnaire. Of these, 336 provided useable addresses for a follow-up mail-out questionnaire, with 169 (50.3%) actually returning it. After performing a variety of statistical analyses, it was found that: (a) some outdoor recreationists did report having non-REP experiences involving identity, cognition, absorption, and self-concept; (b) indirect support does exist for classifying outdoor recreation experiences using the REM framework; and (c) the ROS variables of activity, setting, and expertise, do explain some outdoor recreation experiences, as do the new variables of primary mode and mode dependence. outdoor recreation , recreation experience preference scales , recreation experience matrix , recreation opportunity spectrum Virginia Tech Forestry NDLTD:VT/3345131939761081/ http://scholar.lib.vt.edu/theses/available/etd-3345131939761081/ A'Hearn, Francis W. This study assessed the changing mission of the Industrial College of the Armed Forces as it evolved from the institution's founding as the Army Industrial College in 1924 to its 70th anniversary in 1994. The study drew heavily from archival materials in the Special Collections of the National Defense University in Washington, DC. The problem investigated in this research was to analyze how and why the institution's mission changed over time within the context of internal and external forces and events. Based upon the historical method of research, the study identified six periods in the institution's development over seven decades: its origins in the aftermath of World War I from 1918 to 1924; its growth in the interwar years, 1924 to 1940; the institution's temporary closure and subsequent reconstitution as the Industrial College of the Armed Forces during and after World War II, from 1940 to 1947; a formative period during the Cold War from 1947 to 1962; its continuing evolution throughout the Vietnam era from 1962 to 1974; and finally the College's modern development as a joint service educational institution from 1974 to 1994. The study found that the institution has changed dramatically over much of this century, just as the world and the country's national security concerns have changed profoundly in the same period. The mission of the College has evolved from a narrow focus on training military officers in procurement and industrial mobilization to that of a graduate institution dedicated to educating a select group of promising senior military and civilian officials in the political, economic, and resource dimensions of national security. Over time, the focus has shifted from training to education, from military to national issues, from internal and external educational programs to primarily internal ones, and from a predominant interest in domestic issues to an equally strong concern for international matters. The study finds that a variety of internal and external events and forces have impelled these changes. A wide range of influential individuals and stakeholders, bureaucratic power structures, governmental agencies, special review boards, and various political, economic, military, and social considerations have influenced the mission of the College. The study also concludes that several factors have likely contributed to the institution's relatively unusual longevity as a government entity. Its dual identity as an educational institution and a government organization set apart from the mainstream bureaucracy has had a favorable influence. So too has the institution been aided by the unique service it has provided to multiple customer constituencies. In fact, the College's mission has made it unique as an institution of adult education and learning in this country and perhaps the world. History , Adult Education , Armed Forces Virginia Tech Adult Education NDLTD:VT/171110282975860/ http://scholar.lib.vt.edu/theses/available/etd-171110282975860/ Bell, Tannisha D. Several studies show that African-Americans are less likely than whites to use alcohol or drugs. However, if African-Americans use drugs then they are more likely to become heavy and persistent users. African-Americans are also more likely to have a current substance abuse disorder. There is not much in the literature to explain this phenomenon. The purpose of this study is to examine the alcohol and drug abuse, use and dependence of blacks and whites in order to explain the differences in the course of the substance disorder, using data from the National Comorbidity Survey. There are many variables thought to contribute to the racial difference, such as socio-economic status (measured by income and education), religion, insurance, employment status, and marital status. The data in this literature indicate that the aforementioned variables do not explain the racial difference in substance disorders. However, after performing interaction analyses, it is clear that the effects of treatment are different for blacks and whites. Treatment is more effective for whites, and it may even cause the substance disorder to become worse for blacks. Several studies indicate that this may be the result of cultural differences between the treatment staff and the clients. African-Americans , Drugs , Substance Abuse , Race Virginia Tech Sociology NDLTD:VT/05012000-14030054/ http://scholar.lib.vt.edu/theses/available/etd-05012000-14030054/ Ahmad, Syed Alwi B. The need to construct a fermion quantum field theory in black-hole spacetimes is an acute one. The study of gravitational collapse necessitates the need of such. In this dissertation, we construct the theory of free fermions living on the static Schwarzschild black-hole and the rotating Kerr black-hole. The construction capitalises upon the fact that both black-holes are stationary axisymmetric solutions to Einstein's equation. A factorisability ansatz is developed whereby simple quantum modes can be found, for such stationary spacetimes with azimuthal symmetry. These modes are then employed for the purposes of a canonical quantisation of the corresponding fermionic theory. At the same time, we suggest that it may be impossible to extend a quantum field theory continuously across an event horizon. This split of a quantum field theory ensures the thermal character of the Hawking radiation. In our case, we compute and prove that the spectrum of neutrinos emitted from a black-hole via the Hawking process is indeed thermal. We also study fermion scattering amplitudes off the Schwarzschild black-hole. General Relativity , Quantum Field Theory Virginia Tech Physics NDLTD:VT/3621112139711101/ http://scholar.lib.vt.edu/theses/available/etd-3621112139711101/ Anderson, Alaric Lee This study investigates four aspects associated with steel joist supported wood floor systems: 1) acceptability, 2) prediction of deflection, 3) prediction of frequency, and 4) effects of diagonal bracing. Six full scale floor systems and two two-joist floor systems were constructed in the laboratory. Span length, joist spacing and diagonal bracing were the only parameters modified for each floor. Four tests were performed for each floor setup: heel drop impact, walking perpendicular and parallel to the floor joists, static concentrated load at midspan, and testing to determine subjective evaluation. Five acceptability criteria were investigated: Swedish Building Technology Design Guide, Australian Standard Domestic Metal Framing Code, Canadian Timber Floor Criterion, Murray's Criterion, and Johnson's Criterion. The results from these criteria were compared to the measured results of each floor system. Four methods to predict vertical deflection due to a static load at midspan were compared to measured values of each floor system. The effect of diagonal bracing on floor stiffness was also investigated. Results and concusions were made for each aspect investigated. none Virginia Tech Civil Engineering NDLTD:VT/133422039701091/ http://scholar.lib.vt.edu/theses/available/etd-133422039701091/ Ackley, John A. Weed management programs in ŒSuperior' potato with PRE and POST rimsulfuron treatments were investigated during 1992, 1993, and 1994. Common ragweed control by PRE combinations of metolachlor with linuron or metribuzin was higher when treatments included PRE or POST rimsulfuron. Common lambsquarters control was 93 to 96% by treatments that included POST rimsulfuron. Applications of 35 g ai/ha rimsulfuron plus 280 g ai/ha metribuzin POST controlled weeds comparable to sequential applications. Potato recovered from occasional injury caused by rimsulfuron, rimsulfuron plus metribuzin, and organophosphate insecticides combined POST with rimsulfuron plus metribuzin. Several acetolactate synthase (ALS)-inhibiting herbicides were evaluated for yellow nutsedge control in the greenhouse. Herbicides were applied POST to yellow nutsedge at actual or anticipated commercial rates. Yellow nutsedge control was 92 and 71% from halosulfuron and chlorimuron, respectively. Control ranged from 48 to 69% from primisulfuron, pyrithiobac, and rimsulfuron. Control from nicosulfuron and imazethapyr was 45 and 68%, respectively, while thifensulfuron and CGA-152005 had almost no activity on yellow nutsedge. Chlorimuron, imazethapyr, and halosulfuron were the only herbicides which reduced yellow nutsedge regrowth., Rrimsulfuron was evaluated in tomato at 26 and 35 g ai/ha, sequentially at 26 g/ha, at 26 g/ha plus metribuzin at 280 g ai/ha, and metribuzin at 280 g/ha were evaluated POST for weed control in transplanted ŒAgriset' tomato. Common lambsquarters was controlled by rimsulfuron at 35 g/ha. Rimsulfuron plus metribuzin gave consistent control of common ragweed but jimsonweed and goosegrass control was generally low. Rimsulfuron treatments caused < 12% injury to tomato. Tomato yield was consistently high in the metribuzin, metribuzin plus rimsulfuron, and rimsulfuron sequential treatments. In greenhouse studies, giant foxtail and large crabgrass control by rimsulfuron was above 95 and 85% respectively, but goosegrass was not controlled. Height of four tomato cultivars was not reduced, but dry weight of ŒFloradade' and ŒSunbeam' was reduced by rimsulfuron. In 1993, 1994 and 1995, PPI clomazone at 390 g ai/ha, POST rimsulfuron at 35 g ai/ha, and PPI trifluralin at 560 g ai/ha were evaluated for weed control in transplanted ŒKeystone RG3' bell pepper. Common lambsquarters and jimsonweed control was highest by clomazone treatments, while common ragweed control was low from all treatments. Keystone RG3 in the field and greenhouse and ŒCamelot', ŒJupiter' and ŒMemphis' in the greenhouse were injured by POST rimsulfuron and had lower height and dry weight than untreated controls. In the greenhouse, black nightshade control was below 23% and jimsonweed control was below 49% by rimsulfuron POST. The absorption, translocation, and metabolism of rimsulfuron was investigated in three Solanaceous weed species. Rimsulfuron uptake did not differ between black nightshade and eastern black nightshade while less labeled herbicide was absorbed by hairy nightshade. Black and eastern black nightshade translocated up to 50% of the labeled herbicide out of the treated leaf with 40 to 50% of the herbicide being moved to the actively growing regions of the plant. In hairy nightshade, an average 40% of the labeled herbicide was moved out of the treated leaf and less than 30% of the translocated herbicide was moved basipetally. Most major metabolites were apparent at 24 and 48 hours however, there were no differences in metabolite composition. Rimsulfuron will be an effective herbicide for use in weed management programs in potatoand tomato, however rimsulfuron causes too much injury in pepper to be used. clomazone , metribuzin , trifluralin , pepper , potato , rimsulfuron , nightshade , tomato Virginia Tech Plant Pathology, Physiology, and Weed Science NDLTD:VT/23281533974920/ http://scholar.lib.vt.edu/theses/available/etd-23281533974920/ Adams, Nicole This thesis is an attempt to reconcile the form of an idea with the form of a thing in this world to be experienced. An exploration of the meaning behind the words idea, form, making and experience begins to unite the intellect of an architect with the design of an architect. The terms are defined in the thesis and explained through the project. The thesis through the project sets out to take these terms beyond mere words and give them an opportunity to inform eachother. It is this dialectic between idea, form, making and experience that I believe to be the heart of architecture. Idea and form are inextricably tied to one another. đWhich is the origin of the other?ø is not as pertinent a question as đhow do the two inform each other?ø. Ideas change from project to project as do the forms inherent in those ideas. Preceeding both idea and material form is another type of form that is immaterial and often remains unseen. It is the character which is essential to a thing. Whether it be a place or an object, it is the quality in the thing itself. This character is the instigator of idea and form. It is the architect£s goal to make this inherent form perceivable. An architect makes idea and form manifest through a concept of making. In Notes for a Theory of Making in a Time of Necessity, Giuseppe Zambonini emphasizes that đWe must look not only at the quality of the material used and at the craft employed, but also at the quality of the thought process selecting and shaping the material. . .quality cannot be an intrinsic condition that belongs to the object . . . but rather it must express the intent by which it is created and therein the clarity and strength of the meaning being produced by its formø (Zambonini, 21). This quality of design can best be achieved the earlier making and materiality are involved in the design process. The questions of đwhat is the form of this idea?ø and đhow is this form to be made?ø begin the relationship between idea, form and making. The immediate responses may be intuitive, but the final one is the resultof numerous makings. This is why architecture is practiced. When the question arises:đhow can this form not only embody an idea but be the idea?ø, the dialogue takes on a greater import. The way in which a thing will be experienced starts to inform its making. đIt is the process that will engage both user and observer in an active, participating relationship with the work and thereby give the work its meaningø (Zambonini, 21). It is at this point that the dialectic is fully engaged. These four aspects simultaneously inform each other and nurture the project throughout its life, from drawing board, to construction to the various experiences that it will impart. It is not just one aspect, but these four in communion that are the architecture. none Virginia Tech Architecture NDLTD:VT/123322282975860/ http://scholar.lib.vt.edu/theses/available/etd-123322282975860/ Al-Yakoob, Salem Mohammed This dissertation explores mathematical programming optimization models and algorithms for routing and scheduling ships in a maritime transportation system. Literature surveyed on seaborne transportation systems indicates that there is a scarcity of research on ship routing and scheduling problems. The complexity and the overwhelming size of a typical ship routing and scheduling problem are the primary reasons that have resulted in the scarcity of research in this area. The principal thrust of this research effort is focused at the Kuwait Petroleum Corporation (KPC) Problem. This problem is of great economic significance to the State of Kuwait, whose economy has been traditionally dominated to a large extent by the oil sector. Any enhancement in the existing ad-hoc scheduling procedure has the potential for significant savings. A mixed-integer programming model for the KPC problem is constructed in this dissertation. The resulting mathematical formulation is rather complex to solve due to (1) the overwhelming problem size for a typical demand contract scenario, (2) the integrality conditions, and (3) the structural diversity in the constraints. Accordingly, attempting to solve this formulation for a typical demand contract scenario without resorting to any aggregation or partitioning schemes is theoretically complex and computationally intractable. Motivated by the complexity of the above model, an aggregate model that retains the principal features of the KPC problem is formulated. This model is computationally far more tractable than the initial model, and consequently, it is utilized to construct a good quality heuristic solution for the KPC problem. The initial formulation is solved using CPLEX 4.0 mixed integer programming capabilities for a number of relatively small-sized test cases, and pertinent results and computational difficulties are reported. The aggregate formulation is solved using CPLEX 4.0 MIP in concert with specialized rolling horizon solution algorithms and related results are reported. The rolling horizon solution algorithms enabled us to handle practical sized problems that could not be handled by directly solving the aggregate problem. The performance of the rolling horizon algorithms may be enhanced by increasing the physical memory, and consequently, better solutions can be extracted. The potential saving and usefulness of this model in negotiation and planning purposes strongly justifies the acquisition of more computing power to tackle practical sized test problems. An ad-hoc scheduling procedure that is intended to simulate the current KPC scheduling practice is presented in this dissertation. It is shown that results obtained via the proposed rolling horizon algorithms are at least as good, and often substantially better than, results obtained via this ad-hoc procedure ship scheduling , aggregation , mixed-integer programming Virginia Tech Mathematics NDLTD:VT/255314202974780/ http://scholar.lib.vt.edu/theses/available/etd-255314202974780/ Appel, Justin Ronald Flow sensitivities are the derivatives of the variables that describe the fluid flow with respect to the parameters that determine the fluid flow. Sensitivities are of interest in their own right and are also of use in flow optimization, control and design and in the calculation of perturbed flows. Problems arise in all sensitivity calculation methods in the presence of discontinuities and other complexities such as shock waves, contact discontinuities and rarefaction waves that commonly occur in super and hypersonic inviscid, compressible fluid flows. Flow sensitivities are calculated using finite difference quotients, automatic differentiation and the sensitivity equation method for a variety of numerical methods. Explanations for the inaccuracies arising in the numerical approximations and implications these inaccuracies have on different applications are discussed. Possible corrections for the inaccuracies are outlined. none Virginia Tech Mathematics NDLTD:VT/335713312971890/ http://scholar.lib.vt.edu/theses/available/etd-335713312971890/ Aliftiras, George The communications industry is experiencing an explosion in the demand for personal communications services (PCS). Several digital technologies have been proposed to replace overburdened analog systems. One system that has gained increasing popularity in North America is a 1.25 MHz Code Division Multiple Access (CDMA) system (IS-95). In CDMA systems, multiple access interference limits the capacity of any system using conventional single user correlation or matched filter receivers. Previous research has shown that multiuser detection receivers that employ interference cancellation techniques can significantly improve the capacity of a CDMA system. This thesis studies two such structures: the successive interference cancellation scheme and the parallel interference cancellation scheme. These multiuser receivers are integrated into an IS-95 compatible receiver model which is simulated in software. This thesis develops simulation software that simulates IS-95 with conventional and multiuser receivers in multipath channels and when near-far conditions exist. Simulation results present the robustness of multiuser receivers to near-far in a practical system. In addition to multiuser implemenations, quantization effects from finite bit analog to digital converters (ADC) in CDMA systems will also be simulated. multiuser receiver , CDMA , interference cancellation , quantization Virginia Tech Electrical and Computer Engineering NDLTD:VT/104722369631841/ http://scholar.lib.vt.edu/theses/available/etd-104722369631841/ Bethard, Greg L. A microcomputer simulation was developed as a tool for analyzing the dairy replacement enterprise. The simulation was constructed using a spreadsheet, and equations were developed using stepwise regression procedures. The simulation predicted BW, DMI, and fixed and variable costs for each week of a heifer£s life from birth to calving. After calving, milk yield, feed costs, and fixed costs were predicted for first lactation. Variation was estimated for each predicted variable, thus enabling normal distribution of predicted values. The simulation was used to analyze profitability of various growth rate scenarios and marginal costs associated with changing feed costs, heat detection efficiency, death loss, and abortion rate. For the growth rate analysis, six scenarios were evaluated: 1) normal growth from 5 wk to calving, 2) accelerated growth from 5 wk to calving, 3) slow growth from 5 wk to calving, 4) normal growth from 5 wk to 14 mo and accelerated growth from 14 mo to calving, 5) accelerated growth from 5 wk to 14 mo and control growth from 14 mo to calving, and 6) slow growth from 5 wk to 14 mo and accelerated growth from 14 mo to calving. Average daily gain from birth to calving was 0.78, 0.90, 0.62, 0.78, 0.75, and 0.80 kg/d, and age at calving was 25.1, 23.1, 27.4, 23.1, 23.0, and 23.1 mo, respectively. Total rearing cost from birth to calving was 1246, 1220, 1275, 1148, 1148, and 1138 $/heifer, and net profit through first lactation was 399, 407, 319, 441, 432, and 463 $/heifer, respectively. Results suggest modest growth rates from birth to calving (0.75 to 0.80 kg/d) with reduced first calving age (<24 mo) is most desirable, and delayed calving (>24 mo) is costly and merits higher growth rates with earlier breeding. Increasing feed costs, death loss at birth through weaning, or abortion rate one percentage point increased rearing costs 7.33, 2.40, and 9.10 $/heifer. Improving heat detection efficiency one percentage point reduced rearing costs $2.80/heifer. For the heat detection analysis, the relationship between age at first calving and total rearing costs was -584.38 + 73.49 x calving age in mo (R-squared = 0.97), for ages at first calving from 24.4 to 26.6 mo. Results of this research agree with field observations that managers should strive for early calving (<24 mo) and modest growth rates (0.75 to 0.80 kg/d) to maximize profitability of the replacement enterprise. In addition, death loss, abortion rate, and heat detection efficiency are variables that a manager must control to minimize heifer rearing costs. dairy , simulation , model , heifer Virginia Tech Dairy Science NDLTD:VT/831102339731121/ http://scholar.lib.vt.edu/theses/available/etd-831102339731121/ Allan, James P. The British Labour Party has spent eighteen years in opposition since 1979. During that time it lost four consecutive general elections to the Conservative Party. In 1997, however, it now looks set to win its first election since 1974. This thesis examines the Labour Party in opposition since 1979, using a theoretical framework informed by Anthony Giddens' structuration theory. Based on a dialectical notion of the structure and agency linkage, a two-tiered framework is constructed which at one level views a political party as consisting of a set of structures which can constrain and enable party leaders in their attempts to make the party electorally successful, and at another level the party is regarded as a collective agent in its own right, which in turn is subject to the effects of larger external structures. By comparing the strategies adopted by the Labour Party and its leaders since 1979, the thesis demonstrates that the apparent recovery in the Party's electoral fortunes has corresponded with an increase in the ability of agents to successfully negotiate structural constraints, whilst taking advantage of enabling structures. However, it is also clear that the transformation of Labour into an electorally viable party in 1997 is not solely the product of agency in the period since the last election; rather, it is the culmination of a longer-term process of party change. electoral performance , The Labour Party , structure and agency Virginia Tech Political Science NDLTD:VT/454016449701231/ http://scholar.lib.vt.edu/theses/available/etd-454016449701231/ Barake, Taha Mohamed A generalized analysis of multiple-clad cylindrical dielectric structures with step-index profiles is presented. This analysis yields unified expressions for fields, dispersion equation and cutoff conditions for weakly guiding optical fibers with step-index but otherwise arbitrary profiles. The formulation focuses on triple-clad fibers, but can accommodate single and double-clad fibers as special limiting cases. Using the generalized solutions, transmission properties of several types of specialty fibers for broadband applications, including dispersion-shifted, dispersion-flattened, and dispersion compensating fibers, are studied. Improved designs for dispersion-shifted and dispersion compensating fibers are achieved. Fiber parameters and material compositions for the improved designs are provided. The proposed design for the dispersion-shifted fiber yields zero second-order as well as third-order dispersion at the 1.55 micrometer wavelength. The dispersion compensating fiber proposed here provides a large negative dispersion of about -400 ps/nm.km at the 1.55 micrometer wavelength for the fundamental mode. Numerical results for dispersion characteristics, cutoff wavelengths, and radial field distributions are provided. multiple-clad fibers , dispersion-altered fibers Virginia Tech Electrical and Computer Engineering NDLTD:VT/3034112939721181/ http://scholar.lib.vt.edu/theses/available/etd-3034112939721181/ Almajdoub, Salahuddin A. Physical design for testability (PDFT) is a strategy to design circuits in a way to avoid or reduce realistic physical faults. The goal of this work is to define and establish a speci c methodology for PDFT. The proposed design methodology includes techniques to reduce potential bridging faults in complementary metal-oxide-semiconductor (CMOS) circuits. To compare faults, the design process utilizes a new parameter called the fault index. The fault index for a particular fault is the probability of occurrence of the fault divided by the testability of the fault. Faults with the highest fault indices are considered the worst faults and are targeted by the PDFT design process to eliminate them or reduce their probability of occurrence. An implementation of the PDFT design process is constructed using several new tools in addition to other "off-the-shelf" tools. The first tool developed in this work is a testability measure tool for bridging faults. Two other tools are developed to eliminate or reduce the probability of occurrence of bridging faults with high fault indices. The row enhancer targets faults inside the logic elements of the circuit, while the channel enhancer targets faults inside the routing part of the circuit. To demonstrate the capabilities and test the eff ectiveness of the PDFT design process, this work conducts an experiment which includes designing three CMOS circuits from the ISCAS 1985 benchmark circuits. Several layouts are generated for every circuit. Every layout, except the rst one, utilizes information from the previous layout to minimize the probability of occurrence for faults with high fault indices. Experimental results show that the PDFT design process successfully achieves two goals of PDFT, providing layouts with fewer faults and minimizing the probability of occurrence of hard-to-test faults. Improvement in the total fault index was about 40 percent in some cases, while improvement in total critical area was about 30 percent in some cases. However, virtually all the improvements came from using the row enhancer; the channel enhancer provided only marginal improvements. Bridging Faults , The Labour Party , Structure and Agency , IDDQ Testing , Electoral Performance , Physical Design for Testability Virginia Tech Electrical and Computer Engineering NDLTD:VT/522014589642481/ http://scholar.lib.vt.edu/theses/available/etd-522014589642481/ Atalla, Mauro J. Accurate models are necessary in critical applications. Key parameters in dynamic systems often change during their life cycle due to repair and replacement of parts or en- vironmental changes. This dissertation presents a new approach to update system models, accounting for these changes. The approach uses frequency domain data and a neural net- work to produce estimates of the parameters being updated, yielding a model representative of the measured data. Current iterative methods developed to solve the model updating problem rely on min- imization techniques to nd the set of model parameters that yield the best match between experimental and analytical responses. Since the minimization procedure requires a fair amount of computation time, it makes the existing techniques infeasible for use as part of an adaptive control scheme correcting the model parameters as the system changes. They also require either mode shape expansion or model reduction before they can be applied, introducing errors in the procedure. Furthermore, none of the existing techniques has been applied to nonlinear systems. The neural network estimates the parameters being updated quickly and accurately without the need to measure all degrees of freedom of the system. This avoids the use of mode shape expansion or model reduction techniques, and allows for its implementation as part of an adaptive control scheme. The proposed technique is also capable of updating weakly nonlinear systems. Numerical simulations and experimental results show that the proposed method has good accuracy and generalization properties, and it is therefore, a suitable alternative for the solution of the model updating problem of this class of systems. adaptive control , neural networks , model updating Virginia Tech Engineering Science and Mechanics NDLTD:VT/274210359611541/ http://scholar.lib.vt.edu/theses/available/etd-274210359611541/ Bail, Thomas R. Flutter suppression is a problem of considerable interest in modern avionics. Flutter is a vibration caused by energy in the airstream being absorbed by a non-rigid wing. Active control is one possible method of suppressing flutter. However, due to unmeasurable aerodynamic-lag states, developing an active control using full-state feedback is not viable. The use of a state-estimator is a more practical way of developing active controllers. In this paper we investigate two control methods using state-estimators. We also use simple models of disturbances to test attenuation and robustness of each control method. Finally, a method of quantitative robust analysis is reviewed and then applied to each of the controlled systems. LQG , H , flutter , singular values Virginia Tech Mathematics NDLTD:VT/3210192049721391/ http://scholar.lib.vt.edu/theses/available/etd-3210192049721391/ Fleming, Todd B. The World Wide Web (WWW) has become the largest source of Internet traffic, but it was not designed for wireless networks. Documents with large inline images take a long time to fetch over low-bandwidth wireless networks. Radio signal dropouts cause file transfers to abort; users have to restart file transfers from the beginning. Dropouts also prevent access to documents that have not yet been visited by the user. All of these problems create user frustration and limit the utility of the WWW and wireless networks. In this work, a new Wireless World Wide Web (WWWW) proxy server and protocol were developed that address these problems. A client based on NCSA Mosaic connects to the proxy server using the new protocol, Multiple Hypertext Stream Protocol (MHSP). The proxy prefetches documents to the client, including inline images. The proxy also reduces the resolution of large bitmaps to improve performance over slow links. MHSP provides the ability to resume file transfers when the link has been broken then reestablished. The WWWW system was tested and evaluated by running script-controlled clients on different emulated network environments. This new system decreased document load time an average of 32 to 37 percent, depending on network configuration. wireless networks , WWW , MHSP , proxy , threads , protocols Virginia Tech Electrical and Computer Engineering NDLTD:VT/0521318109613220/ http://scholar.lib.vt.edu/theses/available/etd-0521318109613220/ Batongbacal, Alan L. This thesis describes the design and implementation of Chitra95, a software system developed for the visualization and analysis of time-series trace data. Chitra95 is based upon two earlier generations of Chitra and is aimed at producing a system with broad applicability and utility in this area of research. This thesis contributes to the area of software design for trace visualization and analysis by proposing a set of design principles towards achieving the goals of system extensibility, reusability, reliability, testability and verifiability. These design principles are demonstrated by Chitra95, a software architecture proposed in this thesis for visualization and analysis of time-series trace data. This architecture is novel in its combination of independence from problem domain semantics; optimization for user-extensibility and code reusability; freedom from any specific user interface model; ability to simultaneously produce an integrated application and a reusable toolkit of parts that may either be customized into a turnkey system or integrated into other software systems; support for enhanced reliability, testability and verifiability; and support for an interface to the World Wide Web and for remote execution. Finally, this thesis makes the specific contribution of a data structure for representing large traces that permits the maintainance of multiple versions of a trace and retains the ability to undo modifications made to a trace. none Virginia Tech Computer Science NDLTD:VT/310141259631631/ http://scholar.lib.vt.edu/theses/available/etd-310141259631631/ Battermann, Astrid This work is concerned with the construction of preconditioners for indefinite linear systems. The systems under investigation arise in the numerical solution of quadratic programming problems, for example in the form of Karush--Kuhn--Tucker (KKT) optimality conditions or in interior--point methods. Therefore, the system matrix is referred to as a KKT matrix. It is not the purpose of this thesis to investigate systems arising from general quadratic programming problems, but to study systems arising in linear quadratic control problems governed by partial differential equations. The KKT matrix is symmetric, nonsingular, and indefinite. For the solution of the linear systems generalizations of the conjugate gradient method, MINRES and SYMMLQ, are used. The performance of these iterative solution methods depends on the eigenvalue distribution of the matrix and of the cost of the multiplication of the system matrix with a vector. To increase the performance of these methods, one tries to transform the system to favorably change its eigenvalue distribution. This is called preconditioning and the nonsingular transformation matrices are called preconditioners. Since the overall performance of the iterative methods also depends on the cost of matrix--vector multiplications, the preconditioner has to be constructed so that it can be applied efficiently. The preconditioners designed in this thesis are positive definite and they maintain the symmetry of the system. For the construction of the preconditioners we strongly exploit the structure of the underlying system. The preconditioners are composed of preconditioners for the submatrices in the KKT system. Therefore, known efficient preconditioners can be readily adapted to this context. The derivation of the preconditioners is motivated by the properties of the KKT matrices arising in optimal control problems. An analysis of the preconditioners is given and various cases which are important for interior point methods are treated separately. The preconditioners are tested on a typical problem, a Neumann boundary control for an elliptic equation. In many important situations the preconditioners substantially reduce the number of iterations needed by the solvers. In some cases, it can even be shown that the number of iterations for the preconditioned system is independent of the refinement of the discretization of the partial differential equation. preconditioning , optimal control , quadratic programming , karush-kuhn-tucker systems , indefinite systems Virginia Tech Mathematics NDLTD:VT/12164379662151/ http://scholar.lib.vt.edu/theses/available/etd-12164379662151/ Zabaronick, Noel A. We describe a system for tracking the motion and determining the velocity of the human eye using a combination of fiber optics and imaging optics integrated with a CCD camera, a framegrabber, and a PC. Systems such as the one we describe are needed for monitoring location of interest for better human- computer interfaces and virtual reality simulations, for monitoring pilot cognitive skills during flight simulations, and for detecting the early warning signs of driver drowsiness. Where some eye-tracking devices are cumbersome because they require a person to limit head motion to remain in view of a camera or uncomfortable because they require the use of an elaborate headpiece, our proposed system is as simple to wear as a pair of eyeglasses, with the only added weight to the glasses being that of a fiber optic bundle. This fiber bundle guides the image of an 880 nm LED illuminated eye as it is reflected from a hot mirror built into the eyeglass assembly. The guided image is focused onto a CCD and the camera's output is linked to a PC framegrabber card. Software written in Microsoft Visual C++ locates the user's pupil in each video image and tracks the motion and velocity of the pupil over time. The prototype system tracks the center of the pupil to an accuracy of only 1/5 of the pupil size. This diminished accuracy results from the minimized computation scheme of pupil detection. The technique relies on edge detection and direction of image gradient over very few pixels so that the system is optimized for speed. Many other methods of pupil detection could be investigated in future research in order to optimize such a system for other parameters. none Virginia Tech Electrical and Computer Engineering NDLTD:VT/4437152139711101/ http://scholar.lib.vt.edu/theses/available/etd-4437152139711101/ Benning, Jennifer Lyn Development of Alternative Crab Claw Processing Systems to Minimize Environmental Impact by Jennifer Lyn Benning Chair: Dr. Gregory Boardman Environemental Engineering (ABSTRACT) In the recent years, environmental regulations enforced by federal, state, and local agencies have increasingly addressed water quality issues through progressively more stringent regulations. These regulations have raised concerns in the blue crab industry because processors are now subject to regulations under which new processors are unable to meet the effluent limitations with current processing techniques. This study focuses on the mechanized processing of crab claws. Currently, processors use a brine bath, referred to as the Harris Claw machine, to separate crab claw meat and shell, and this process yields a wastewater which is significantly high in pollutant strength, and is untreatable by biological methods due to the toxicity associated with the high chloride concentrations found in the waste stream. Several alternative crab claw processing systems were developed and evaluated in terms of the meat product yield, the meat product quality, and the wastewater characterization. Two alternatives involved the use of dense media, a 22.5% Staley 1300 corn syrup solution with 5.0% salt and a 30.0% Staley 1300 corn syrup solution, to separate the crab claw meat and shell. These methods, in full scale tests, produced meat yields comparable to that of the brine solution and improved the overall taste of the meat product. However, the effluents had significantly higher BOD5 concentrations. Another alternative to the Harris Claw machine, involved the design, characterization, and testing of a hydraulic separator system (HSS). The HSS was tested on a small scale, but was found to have a meat yield comparable to the Harris Claw machine. The HSS significantly improved the flavor of a final meat product, although the HSS meat product had a significantly lower shelf life than the Harris Claw machine meat product. The wastewater quality was improved, because the HSS eliminates the problems associated with a high chloride ion concentration and potentially reduces overall water consumption. waste minimization , enviromental impact , crab claw , blue crab processing Virginia Tech Environmental Engineering NDLTD:VT/1123161739741061/ http://scholar.lib.vt.edu/theses/available/etd-1123161739741061/ Berkelman, James With a population estimate of 99 pairs, the Madagascar fish-eagle (Haliaeetus vociferoides) is one of the rarest birds of prey in the world. I investigated the ecological requirements of the Madagascar fish-eagle in 1994 and 1995 to help determine management action to prevent its extinction. I investigated fish-eagle foraging ecology in 1996 to determine its prey preference and whether fish abundance and availability affect fish-eagle foraging rates and foraging success. Madagascar fish-eagle nest and perch trees were taller, broader, had more unobstructed branches, and had a greater arc of accessibility than unused trees. Perch trees also were deciduous more often and had a narrower growth form than unused trees. Nest sites had more shoreline perch trees than unused sites. Lakes occupied by fish-eagles were deeper and clearer, and had more shoreline perch trees, more fish, a greater total fish weight, and more fish species than unoccupied lakes. I developed logistic regression models to predict the probability of Madagascar fish-eagle use based on the measured habitat variables. Nest and perch tree models included tree height. The nest site model included number of shoreline perches. Lake models included number of shoreline perches and either number of fish, total fish weight, or number of fish species. These models can be used to predict fish-eagle habitat use with > 70% accuracy. Introduced tilapia, Oreochromis spp. and Tilapia spp., made up the majority of both the gill net (66.3%) and fish-eagle catch (64.7%) in similar proportion, which suggests that the fish-eagle is an opportunistic predator. Replacement of native fish species by exotics, thus, probably has not been detrimental to the island's fish-eagle population. Male fish-eagle foraging success was positively correlated with number of fish, total fish weight, and number of fish species, which suggests that declines in the fish population could adversely affect the fish-eagle population. The results of this study indicate that Madagascar fish-eagles require bodies of water with large shoreline trees and an ample fish population. I recommend greater protection of aquatic habitats, monitoring and management of freshwater fish populations, and education of local people in sustainable tree harvesting practices. lake , foraging , nest tree , madagascar fish-eagle , perch tree , habitat Virginia Tech Fisheries and Wildlife Sciences NDLTD:VT/5852152749721461/ http://scholar.lib.vt.edu/theses/available/etd-5852152749721461/ Zhang, Michael Tao This work presents the analyses and designs of high-density, low-profile power supplies, including the electrical, thermal, and EMI aspects. Emphasis is placed on forward and flyback converters. The efficiency improvements of employing synchronous rectification are theoretically derived and experimentally verified in forward and flyback converters. The performances of synchronous rectifiers in forward converters are analyzed with regards to transformer reset and SR driven method. The effectiveness of synchronous rectification in flyback converters is evaluated in various operation modes and control schemes. The paralleling techniques utilized to realize high-density, low-profile power conversion are presented. Current sharing in transformer paralleling is addressed and evaluated in forward topology. The performance and the operation principles of one-choke and two-choke interleaved forward converters are analyzed. The thermal management of high-density power supplies in sealed enclosures is optimized using computational fluid dynamics simulations. The theoretical limit of power density due to thermal constraint is determined. In addition, the thermal-design optimization guidelines are given and verified experimentally. A systematic methodology is developed to facilitate the analysis and design of conducted EMI problems in high-density power supplies. Partial element equivalent circuit method is employed for parasitic parameter extraction. Layout and packaging are optimized to minimize conducted EMI noises. Noise predictions by Saber simulations are confirmed by experimental measurements. none Virginia Tech Electrical and Computer Engineering NDLTD:VT/173510281975580/ http://scholar.lib.vt.edu/theses/available/etd-173510281975580/ Fischer, Patrick Experiments at the University of Maryland Plasma Physics Laboratory have discovered an unusual temperature response in the form of a "thermal wave" which begins at the center and propagates towards the surface of a zinc oxide sample, when heated in a microwave cavity without the presence of oxygen. This effect is believed to be caused by the irregular temperature dependence of the dielectric properties of zinc oxide, particularly dielectric loss. Two thermocouple probes were used to measure the temperature response in a small cylindrical sample of zinc oxide packed in powder insulation, and heated in a microwave oven. In order to determine if the unusual response is caused by the dielectric properties, this work uses a finite-difference mathematical model to simulate the experiments, both for the case of zinc oxide heated in ordinary air, as well as for the case of zinc oxide heated in nitrogen. A revised version of the model is used to determine if the thermocouple probe has any effect on the temperature of the sample. The spatial and temporal temperature distribution results from the model indicate that the thermocouple probe has a negligible effect on the results and that the "thermal wave" can be attributed to the irregular temperature dependence of the dielectric loss of the material. zinc oxide , microwave , heat transfer , permittivity , thermal wave Virginia Tech Mechanical Engineering NDLTD:VT/317182749721461/ http://scholar.lib.vt.edu/theses/available/etd-317182749721461/ Bhogaraju, Prabhakar V. V. I have worked on a Case-Based Reasoning (CBR) system that evaluates crop rotations for their soil erosion and risk of insect pest problems. The purpose of this system is to provide decision support for an automated whole-farm planner (CROPS). CROPS (Buick et al., 1992) generates crop rotation plans that can address some of the environmental, economic and legislative pressures facing natural resource managers. To generate and recommend a crop rotation plan CROPS requires estimates on the soil erosion risks and pesticide pollution potential of the crop rotation. In this research I have designed and prototyped a system that can assist CROPS in the process of whole-farm planning by providing information required for determining the soil erosion risks and the pesticide pollution potential of crop rotations. Inputs for the system include: a crop rotation, its tillage and residue management practices, and field conditions. Soil erosion risk is quantified using the C-value. Pest risks are likelihood of pest outbreaks that require control in a crop rotation. CBR was the chosen methodology for system implementation. In CBR, solutions to new problem situations are derived from retrieving and adapting solutions to similar problem situations experienced in the past. The system was prototyped using Esteem, a CBR development shell, and runs on a PC under the MS. Windows operating system. none Virginia Tech Entomology NDLTD:VT/5741181879602301/ http://scholar.lib.vt.edu/theses/available/etd-5741181879602301/ Bittner, Ray A. Jr. In the past, various approaches to the high performance numerical computing problem have been explored. Recently, researchers have begun to explore the possibilities of using Field Programmable Gate Arrays (FPGAs) to solve numerically intensive problems. FPGAs offer the possibility of customization to any given application, while not sacrificing applicability to a wide problem domain. Further, the implementation of data flow graphs directly in silicon makes FPGAs very attractive for these types of problems. Unfortunately, current FPGAs suffer from a number of inadequacies with respect to the task. They have lower transistor densities than ASIC solutions, and hence less potential computational power per unit area. Routing overhead generally makes an FPGA solution slower than an ASIC design. Bit-oriented computational units make them unnecessarily inefficient for implementing tasks that are generally word-oriented. And finally, in large volumes, FPGAs tend to be more expensive per unit due to their lower transistor density. To combat these problems, researchers are now exploiting the unique advantage that FPGAs exhibit over ASICs: reconfigurability. By customizing the FPGA to the task at hand, as the application executes, it is hoped that the cost-performance product of an FPGA system can be shown to be a better solution than a system implemented by a collection of custom ASICs. Such a system is called a Configurable Computing Machine (CCM). Many aspects of the design of the FPGAs available today hinder the exploration of this field. This thesis addresses many of these problems and presents the embodiment of those solutions in the Colt CCM. By offering word grain reconfiguration and the ability to partially reconfigure at computational element resolution, the Colt can offer higher effective utilization over traditional FPGAs. Further, the majority of the pins of the Colt can be used for both normal I/O and for chip reconfiguration. This provides higher reconfiguration bandwidth contrasted with the low percentage of pins used for reconfiguration of FPGAs. Finally, Colt uses a distributed reconfiguration mechanism called Wormhole Run-Time Reconfiguration (RTR) that allows multiple data ports to simultaneously program different sections of the chip independently. Used as the primary example of Wormhole RTR in the patent application, Colt is the first system to employ this computing paradigm. VLSI , data flow , DSP , wormhole run-time reconfiguration , FPGA Virginia Tech Electrical and Computer Engineering NDLTD:VT/38419290973280/ http://scholar.lib.vt.edu/theses/available/etd-38419290973280/ Zhong, Caoyuan This research develops an object-oriented approach to model airport ground network traffic operations. A generic modeling library is developed as a tool kit to model the basic traffic operations in the airfield using an object-oriented approach. The proposed generic modeling library for airfield operations is a collection of predefined abstract components implemented in the Java object-oriented programming language. Classes are defined and used as the basic components in a variety of airfield operation modeling, simulations, and optimizations. The generic airport modeling framework consists of a set the components that are necessary for modeling the basic activities of airfield traffic operations. By using the multi-threading techniques, components are integrated into the proposed modeling framework. Unlike traditional sequential simulation model, this framework organizes simulation activities into four major groups which are: flight schedule, aircraft movement, time, and animation. Instead of using built-in control logic, the framework adapts an open system policy which gives the flexibility to the end users to incorporate the user-preferred control logic into the end models. Another purpose in this research is to provide a future mechanism to study airfield ground traffic automated control systems with Just-In-Time forecasting and model system performance in a real-time ATC environment. The proposed generic library could be implemented into a Internet/intranet ready application which can query real time information and provide real time advice to pilots and air traffic controllers. This study is one of a few current research projects that are of using multiple threading technique to study traffic operation problems. The proposed generic library is originally implemented with C++ and, in the final stage, with Java, a truly cross-platform object-oriented language. Application written in Java can run on most of the mainstream computer operating systems without modifications. Although the proposed library is for airfield traffic control system, it could also be extended into air traffic control system as well as advanced transportation system. airport , simulation , object-oriented modeling , java Virginia Tech Civil Engineering NDLTD:VT/353622132974710/ http://scholar.lib.vt.edu/theses/available/etd-353622132974710/ Blanks, Joseph E. A simple, effective design for enclosing portable generators to reduce the radiated noise is an idea that seems to be desired by the consumers in this market. This investigation is to determine the feasibility of producing such an enclosure for a generator. Several engineering aspects are incorporated in the design of the enclosure. The first, and probably the most paramount, are the acoustical effects of the enclosure itself. The investigation follows the theories for insertion loss of a close fitting enclosure. The thesis examines the system behavior of a close fitting enclosure that most acoustic text books ignore and how the material stiffness, density and source-to-enclosure distance affect the insertion loss and effectiveness of the enclosure. Measured and theoretical sound pressure level around the generator before and after the application of the enclosure are presented using standards described by ISO standard 1344. The second important consideration for the enclosure design involves the heat transfer characteristics. The requirements of cooling air to the generator are discussed. Also presented are some acoustic design considerations to prevent any "direct line of sight" to any of the necessary openings which will help in the overall insertion loss. The use of an optimal engineering design technique is presented, demonstrating its strengths and weakness in this application. The optimization method used for the study is the Hooke and Jeeves, or pattern search method. This method solved for the optimum material properties in approximately 30 iterations depending on the initial starting points and the desired weighting parameters. acoustic isolation , insertion loss , passive acoustical treatment , close fitting enclosure , optimization , acoustic enclosure Virginia Tech Mechanical Engineering NDLTD:VT/145110201974500/ http://scholar.lib.vt.edu/theses/available/etd-145110201974500/ Bolling, John Glenn Control Allocation as it pertains to aerospace vehicles, describes the way in which control surfaces on the outside of an aircraft are deflected when the pilot moves the control stick inside the cockpit. Previously, control allocation was performed by a series of cables and push rods, which connected the 3 classical control surfaces (ailerons, elevators, and rudder), to the 3 cockpit controls (longitudinal stick, lateral stick, and rudder pedals). In modern tactical aircraft however, it is not uncommon to find as many as 10 or more control surfaces which, instead of being moved by mechanical linkages, are connected together by complex electrical and/or hydraulic circuits. Because of the large number of effectors, there can no longer be a one-to-one correspondence between surface deflections on the outside of the cockpit to pilot controls on the inside. In addition, these exterior control surfaces have limits which restrict the distance that they can move as well as the speed at at which they can move. The purpose of Constrained Control Allocation is to deflect the numerous control surfaces in response to pilot commands in the most efficient combinations, while keeping in mind that they can only move so far and so fast. The implementation issues of Constrained Control Allocation techniques are discussed, and an aerodynamic model of a highly modified F-15 aircraft is used to demonstrate the various aspects of Constrained Control Allocation. This work was conducted under NASA research grant NAG-1-1449 supervised by John Foster of the NASA Langley Research Center flight control , control allocation , F-15 Virginia Tech Aerospace and Ocean Engineering NDLTD:VT/1111112749721461/ http://scholar.lib.vt.edu/theses/available/etd-1111112749721461/ Feldman, Michael A. A new software tool was needed for flight planning of a high altitude, low speed unmanned aerial vehicle which would be flying in winds close to the actual airspeed of the vehicle. An energy modeled NLP formulation was used to obtain results for a variety of missions and wind profiles. The energy constraint derived included terms due to the wind field and the performance index was a weighted combination of the amount of fuel used and the final time. With no emphasis on time and with no winds the vehicle was found to fly at maximum lift to drag velocity, Vmd. When flying in tail winds the velocity was less than Vmd, while flying in head winds the velocity was higher than Vmd. A family of solutions was found with varying times of flight and varying fuel amounts consumed which will aid the operator in choosing a flight plan depending on a desired landing time. At certain parts of the flight, the turning terms in the energy constraint equation were found to be significant. An analysis of a simpler vertical plane cruise optimal control problem was used to explain some of the characteristics of the vertical plane NLP results. optimization , optimal control , aircraft performance Virginia Tech Aerospace and Ocean Engineering NDLTD:VT/17616979652211/ http://scholar.lib.vt.edu/theses/available/etd-17616979652211/ Zhu, Ping Today, the workplace is undergoing dramatic changes, featuring increased team activities and informal interactions. The work place neighborhood is a design concept derived from a city planning theory that may solve the workplace design problems arising from these changes, and provided a focus for this project. The Educational Technology office area of the Advanced Communication and Information Technology Center (ACITC) possesses the features representing the general workplace tendency today. The purpose of this project was to develop a workplace neighborhood space prototype for this office area. This prototype will provide a work environment conducive to team efforts and informal interactions and a workplace neighborhood space model for future reference. The project had three design phases: design programming, design development, and design evaluation and revision. During the design programming, a survey questionnaire was distributed to all of the 12 Educational Technology employees and behavioral mapping observations were conducted. Then, a conceptual plan, a series of workplace space patterns and a floor plan were developed for the workplace neighborhood space prototype. Finally, computer models were prepared for three neighborhood units for design evaluation. The result of the design evaluation indicated that the concerns between individual and group work spaces were not solved. The space prototype was revised, and a computer model of the revised space prototype was prepared. The revised space prototype met the work patterns of the employees more closely and reflected the design concept of workplace neighborhood more clearly space , design , workplace , neighborhood Virginia Tech Housing, Interior Design and Resource Management NDLTD:VT/2720162749721461/ http://scholar.lib.vt.edu/theses/available/etd-2720162749721461/ Yagow, Eugene R. The Agricultural Nonpoint Source model (AGNPS) is a single-event grid-based model used for simulating runoff, sediment and nutrients from agricultural areas. This study involved using geographic information system (GIS) spatial data and functionality to improve the spatial and temporal assignment of parameter values for the AGNPS 5.0 model and incorporated methods for representing urban fringe land uses and their nonpoint source (NPS) pollution contributions in model inputs. Auxiliary procedures for modeling with AGNPS were developed both for enhancing input into the model and for enhancing modeled output. On an event basis, one procedure automated the creation of complex-formatted AGNPS 5.0 model input files using GIS as a spatial data manager. One pair of alternative procedures were developed to automate the assignment of parameter values on an event basis. One procedure used typical average annual parameter values, and the second assigned parameter values using adaptations of existing time-dependent relationships. On a monthly basis, a sequencing procedure was created to perform multiple runs with the model for a list of storms while updating parameters for each event and aggregating monthly modeled spatial output. Another pair of alternative procedures were developed to facilitate the simulation of monthly output from AGNPS modeled events. The first of these aggregated event output for all storms in each month, while the second supplemented the aggregated output with baseflow and septic system loads. The study area was the 6,500 ha urbanizing Bull Run watershed in northern Virginia, which was modeled as 14,621 cells. Databases were assembled and 109 selected storm events within a 16-year period were modeled using the above procedures. Event data were added together, where necessary, to correspond with observed data from composite-sampled intervals. Output from the two event parameterization procedures were compared with monitored loads calculated for 89 composite periods, while output from the two monthly simulation procedures were compared with monthly monitored data for 23 complete months. The monitored-modeled comparisons were considered inconclusive. Evidence strongly suggested that the rainfall records from a rain gauge outside the watershed did not correspond well with monitored runoff. The average runoff produced with the AGNPS model from the 109 selected storms amounted to 40.7% of rainfall, consistent with the calculated long-term average of 38% for the Bull Run watershed. A nonpoint source pollution index was developed to utilize monthly modeled total nitrogen, total phosphorus, and suspended sediment. Individual rating curves were developed to separately transform loads and concentrations of each pollutant into sub-index values. The maximum sub-index from each parameter was added together and averaged for the index. The index was calculated at the watershed outlet from monitored data, and in a spatially-distributed fashion along all streams from simulated output. geographic information systems , index , model interface , nonpoint source pollution Virginia Tech Biological Systems Engineering NDLTD:VT/18441213972900/ http://scholar.lib.vt.edu/theses/available/etd-18441213972900/ Yatsko, Michael S Ethnic festivals are dynamic socio-spatial phenomena in American society in which rationalized spaces are transformed into “festival space” and the cultural landscapes within the boundaries of the festivals are transfigured into festival landscapes. The landscapes of ethnic festivals generate, via a colorful assortment of cultural performances and symbols, metaphors of ethnicity and spatial expressions of social processes which influence ethnic groups. As a metaphor of ethnicity, festival landscapes have become both a tool for the ethnic boundary maintenance of ethnic groups and a form of symbolic ethnicity for many assimilated individuals. This thesis analyzes the landscape of the Basque festival, Jaialdi ’95, as a tool for the ethnic boundary maintenance for the American Basque community and the Basque colony in Boise, Idaho, and as a form of symbolic ethnicity for assimilated American Basques. none Virginia Tech Geography NDLTD:VT/2230102449761431/ http://scholar.lib.vt.edu/theses/available/etd-2230102449761431/ Zhou, Hongyi High density polyethylene (HDPE) films having simple and well-defined stacked lamellar morphology, either with or without a distinct presence of row-nucleated fibril structures, have been utilized as model materials to carry out investigations on solid state structure-property relationships. Four different subjects that were addressed are: 1) mechanical properties and deformation morphologies, 2) orientation anisotropy of the dynamic mechanical a relaxation, 3) orientation dependence of creep behavior, and 4) crystalline lamellar thickness and its distribution. For the first three topics, appropriate mechanical tests, including tensile (INSTRON), creep (TMA), and dynamic mechanical (DMTA) tests, were performed at different angles with respect to the original machine direction (MD) of the melt extruded films; morphological changes as a result of these mechanical tests were detected by WAXS, SAXS, and TEM. For the forth topic, crystalline lamellar thickness and its distribution were determined by DSC, SAXS, TEM and AFM experiments. In the large strain deformation study (chapter 4.0), samples were stretched at 00ʻ, 45ʻ and 90ʻ angles with respect to the original MD. A distinct orientation dependence of the tensile behavior was observed and correlated to the corresponding deformation modes and morphological changes, namely 1) lamellar separation and fragmentation by chain slip for the 00ʻ stretch, 2) lamellar break-up via chain pull-out for the 90ʻ stretch, and 3) lamellar shear, rotation and break-up through chain slip and/or tilt for the 45ʻ stretch. A strong strengthening effect was observed for samples with row-nucleated fibril structures at the 00ʻ stretch; whereas for the 90ʻ stretch, the presence of such structures significantly limited deformability of the samples. In the dynamic strain mechanical a relaxation study (chapter 5.0), samples were tested at nine different angles with respect to the original MD, and the morphologies of samples before and after the dynamic tests were also investigated. The mechanical dispersions for the 00ʻ and 90ʻ tests were believed to arise essentially from the crystalline phase, and they contain contributions from two earlier recognized sub-relaxations of aI and aII. While for the 45ʻ test, in addition to a high temperature aII relaxation, a interlamellar shear induced low temperature mechanical relaxation was also observed. It is concluded that the low temperature relaxation is related to the characteristics of the interface between the crystalline lamellae and amorphous layers. In the small strain creep study (chapter 6.0), samples were tested at the 00ʻ, 45ʻ and 90ʻ angles at the original MD. Both creep strain and creep rate for samples at the three angles were very different. An Eyring-rate model was utilized to analysis the observed creep behavior, and structural parameters associated with this model, including population of creep sites, activation energy and volume, were obtained by fitting the experimental data to the Eyring-rate equation. It was concluded that the plateau creep rate in these model materials is primarily controlled by the density and physical state of tie-chains in the amorphous phase. For the lamellar thickness and distribution study, DSC, SAXS, TEM and AFM experiments were conducted for samples having a well-defined stacked lamellar morphology. It was found that the most probable lamellar thickness from SAXS and TEM agreed very well; however, these values did not match with those obtained by DSC and AFM. It was pointed out that the use of DSC to determine lamellar thickness and distribution is so sensitive to heating rate and numerical values for the parameters in the Gibbs-Thomson equation that it is not believed to be suitable for quantitative analysis. polyethylene , tensile property , mechanical relaxation , creep , lamellar thickness Virginia Tech Materials Science and Engineering NDLTD:VT/33501632971610/ http://scholar.lib.vt.edu/theses/available/etd-33501632971610/ Waldhart, Chris It is possible to create laminae that have spatially varying fiber orientation with a tow placement machine. A laminate which is composed of such plies will have stiffness properties which vary as a function of position. Previous work had modelled such variable-stiffness laminae by taking a reference fiber path and creating subsequent paths by shifting the reference path. This thesis introduces a method where subsequent paths are truly parallel to the reference fiber path. The primary manufacturing constraint considered in the analysis of variable-stiffness laminates was limits on fiber curvature which proved to be more restrictive for parallel fiber laminae than for shifted fiber. The in-plane responses of shifted and parallel fiber variable-stiffness laminates to either an applied uniform end shortening or in-plane shear were determined. Both shifted and parallel fiber variable-stiffness laminates can redistribute the applied load thereby increasing critical buckling loads compared to traditional straight fiber laminates. The primary differences between the two methods is that parallel fiber laminates are not able to redistribute the loading to the degree of the shifted fiber. This significantly reduces the increase in critical buckling load for parallel fiber variable-stiffness laminates over straight fiber laminates. variable-stiffness laminates , curvilinear fibers , tow placement machine , buckling Virginia Tech Engineering Science and Mechanics NDLTD:VT/520112859651791/ http://scholar.lib.vt.edu/theses/available/etd-520112859651791/ Walker, Kenroy A. This study examined the aspirations formation of disadvantaged Jamaican male youths. The design of the study was a Type 3 holistic design which considered the global nature of multiple cases, and focused on the impact of work, family, school, peers and siblings on subjects1 aspirations. Six case studies were conducted using observations, focus groups, taped interviews and document inspection techniques. Data were analyzed using McCraken1s coding techniques. The results showed that the youths1 aspirations were leveled, reflected realities of their employment possibilities, and were patterned after their father1s occupations. The youths1 reluctance to raise their aspirations signals the need for Jamaican policy makers to address the problems caused by low aspirations among youths. Recommendations for further research are offered. none Virginia Tech Curriculum and Instruction NDLTD:VT/301411131974430/ http://scholar.lib.vt.edu/theses/available/etd-301411131974430/ Walsh, Maryann Sheridan Parents with adolescents often find themselves caught in the stress and strain that normally accompanies this stage of life. It is when parents cannot meet the demands of troubled adolescents that they find themselves seeking family therapy. Most of what is reported about the process of therapy continues to be from the therapist's or reseacher's perspective. There has been an increased interest in what clients have to say about their experiences. The purpose of this study was to develop a detailed description of how parents of adolescents who attended family therapy in private practice settings viewed their experiences. Fifteen parents who had been to therapy with their adolescent were recruited by their therapist to be interviewed for this study. A multicase qualitative design and constructivist theoretical framework guided the investigation. The constant comparative analysis was used to develop four core categories that described the subtitles of parents' therapeutic experience. Five case stories illustrated the core categories and parents' quotes were used to further embellish the findings. The findings included parents' experiences prior to beginning therapy, during therapy as well as reflections in retrospect. The pre-therapy presentation, based on expectations and past experiences in treatment, affected the way parents initially approached therapy. A supportive therapeutic climate was necessary for parents to trust and become open to possibilities and do the hard work required to make changes. The story of their current experience was part of the family therapy process. Parents recognized changes and what they valued about their experiences in family therapy. parents of adolescents , clients experience , qualitative study Virginia Tech Family and Child Development NDLTD:VT/055132139711101/ http://scholar.lib.vt.edu/theses/available/etd-055132139711101/ Borisuk, Mark T. Fertilized frog eggs (and cell-free extracts) undergo periodic oscillations in the activity of "M-phase promoting factor" (MPF), the crucial triggering enzyme for mitosis (nuclear division) and cell division. MPF activity is regulated by a complex network of biochemical reactions. Novak and Tyson, and their collaborators, have been studying the qualitative and quantitative properties of a large system of nonlinear ordinary differential equations that describe the molecular details of this system as currently known. Important clues to the behavior of the model are provided by bifurcation theory, especially characterization of the codimension-1 and -2 bifurcation sets of the differential equations. To illustrate this method, I have been studying a system of 9 ordinary differentail equations that describe the frog egg cell cycle with some fidelity. I will describe the bifurcation diagram of this system in a parameter space spanned by the rate constants for cyclin synthesis and cyclin degradation. My results suggest either that the cell cycle control system should show dynamical behavior considerably more complex than the limit cycles and steady states reported so far, or that the biochemical rate constants of the system are constrained to avoid regions of parameter space where complex bifurcation points unfold. cell cycle , MPF , bifurcation theory , parameter space Virginia Tech Mathematics NDLTD:VT/1115202339731121/ http://scholar.lib.vt.edu/theses/available/etd-1115202339731121/ Bowser, Kristina L. Overtraining is a common problem in athletes that prevents many from becoming đeliteø. A decrement in an athletes£ performance is usually an indicator that overtraining syndrome may be developing. Unfortunately, there is no model that can determine overtraining. A decline in performance results in a depression in maximum muscular force. It is not known whether the force depression is a result of central or peripheral factors. In this study, the two training protocols on different legs determined whether force declines are muscular (peripheral) or psychological (central). Specifically, in this study, the subjects trained one leg at maximal intensity for two weeks, and the other trained at a low intensity for two weeks. After training for two weeks, both legs were placed on a low intensity workout to monitor the recovery process. The purpose of this study was to observe muscle strength performance decrements after overtraining one leg in comparison to properly training the other leg by knee extension exercises for two weeks in trained males. Also, after overtraining the one leg for two weeks, the leg was placed on a reduced training program in order to look at recovery if overtraining occurred. Maximal force output was measured isokinetically on the Biodex three times: pre-, post-, and final test. An analysis of this data revealed no significant changes in maximal muscular force output after a high intensity training protocol. Therefore, this investigation demonstrated that overtraining in the quadricep did not result from the two weeks of high intensity resistance training. muscle force , overtraining , weight training Virginia Tech Human Nutrition NDLTD:VT/532916102971680/ http://scholar.lib.vt.edu/theses/available/etd-532916102971680/ Boyd, Curtis Barton Approximately fifty percent of the bridges in the United States are considered deficient. The deterioration of the concrete components is a leading cause of the problem. The deterioration of concrete bridge decks is due primarily to corrosion of the reinforcing steel in the concrete. A promising solution to the problem is the use of fiber reinforced plastics (FRP) as a replacement for reinforcing steel. The use of FRP as reinforcement has the following advantages of lightweight, high tensile strength, corrosion resistance, flexibility, and electromagnetic resistance. This paper looks at the use of FRP as reinforcement in concrete beams and compares the information from deflection measurements of different configurations. Also, a material cost comparison is made to determine the cost of using the FRP reinforcement over standard steel reinforcement. Concrete bridge deck systems are designed using steel and fiber-reinforced plastics and allowable stress and load resistance factor methods. Recommendations for further study and uses of FRP are made. bridge , reinforced concrete , bridge design , FRP , fiber reinforced plastics Virginia Tech Civil Engineering NDLTD:VT/4814221949711381/ http://scholar.lib.vt.edu/theses/available/etd-4814221949711381/ Ward III, Allan The objectives of this investigation are to develop a precise, non-destructive single crystal stress measurement technique, develop a model to explain the phenomenon known as 3power slump2, and investigate the role of device processing on wafer breakage. All three objectives were successfully met. The single crystal stress technique uses a least squares analysis of X-ray diffraction data to calculate the full stress tensor. In this way, precise non-destructive stress measurements can be made with known error bars. Rocking curve analysis, stress gradient corrections, and a data reliability technique were implemented to ensure that the stress data are correct. A theory was developed to explain 3power slump2, which is a rapid decrease in the amplifying properties of microwave amplifier circuits during operation. The model explains that for the particular geometry and bias configuration of the devices studied in this research, power slump is linearly related to shear stress at values of less than 90 MPa. The microscopic explanation of power slump is that radiation enhanced dislocation glide increases the kink concentration, thereby increasing the generation center concentration in the active region of the device. These generation centers increase the total gate current, leading to a decrease in the amplifying properties of the device. Passivation layer processing has been shown to both reduce the fracture strength and increase the residual stress in GaAs wafers, making them more susceptible to wafer breakage. Bare wafers are found to have higher fracture strength than passivated wafers. Bare wafers are also found to contain less residual stress than SiON passivated wafers, which, in turn, are found to have less stress than SiN passivated wafers. Topographic imaging suggests that SiN passivated wafers have larger flaws than SiON passivated wafers, and that the distribution of flaw size among SiN passivated wafers is wider than the distribution of flaws in SiON passivated wafers. These flaws are believed to lead to breakage of the device during processing, resulting in low fabrication yield. Both the power slump model and the wafer breakage data show that these phenomena are dependent on residual stress developed in the substrate during device fabrication. Reduction of process-induced residual stress should therefore simultaneously decrease wafer breakage rates and reduce power slump during device fabrication and operation. gallium arsenide , MESFET , wafer breakage , semiconductor device , x-ray diffraction , stress Virginia Tech Materials Science and Engineering NDLTD:VT/394172159651721/ http://scholar.lib.vt.edu/theses/available/etd-394172159651721/ Warren Jr., J.E. With the increasing use of lightweight frame-type structures that span long distances, there is a need for a method to determine the probability that a structure having random initial geometric imperfections will become unstable at a load less than a spe cified fraction of the perfect critical load. The overall objective of this dissertation is to present such a method for frame-type structures that become unstable at limit points. The overall objective may be broken into three parts. The first part co ncerns the development of a three-dimensional total Lagrangian beam finite element that is used to determine the critical load for the structure. The second part deals with a least squares method for modeling the random initial imperfections using the mo de shapes from a linear buckling analysis, and a specified maximum allowable magnitude for the imperfection at any imperfect node in the structure. The third part deals with the calculation of the probability of failure using a combined response surface/ first-order second-moment method. Numerical results are presented for two example problems, and indicate that the proposed method is reasonably accurate. Several problems with the proposed method were noted during the course of this work and are discuss ed in the final chapter. Reliability , Imperfection , Stability , Finite Element , Nonlinear Virginia Tech Engineering Science and Mechanics NDLTD:VT/211714251972550/ http://scholar.lib.vt.edu/theses/available/etd-211714251972550/ Watson, George W By combining normative philosophy and empirical social science, I craft a research framework for assessing differential expectations of economic justice within the economic social contract of the United States. I argue that distinct viewsof such a contract grounded in the tradition of individualism and communitarianism manifest in people's judgments about economic justice. We empirically test these hypotheses on a sample of 270 subjects, finding broad support for the theoretical framework. none Virginia Tech Management NDLTD:VT/3213172239721111/ http://scholar.lib.vt.edu/theses/available/etd-3213172239721111/ Weissbart, Erich J THE LEACHED LAYER FORMED ON WOLLASTONITE IN AN ACID ENVIRONMENT Erich J. Weissbart (ABSTRACT) Experiments were carried out in a fixed-bed external recycle mixed flow reactor to measure the rate of dissolution and the development of a leached layer on wollastonite. Each experiment ran for approximately 24 hours and the release rates of Si and Ca in the interval from 14 to 24 hours were analyzed. Each experiment began with an incongruent stage where Ca was released faster than the silica that remained on the surface to form the leached layer. The silica release rate after 14 hours was 2.13 x 10-9 ( 1.03 x 10-9, 1 , n=67) mol/m2/sec, and this rate appeared to be independent of pH from pH 2 to 6 at 25 degrees C. BET surface area measurements of reacted wollastonite showed large increases in BET Asp over the course of experiments even though both the Ca and Si release rates decreased. These large increases of measured Asp were the result of the growing internal porosity of the leached layer, and much of this surface does not seem to contribute to Si release rates. From these data, we infer that the overall reaction for the hydrolysis of wollastonite in an acid environment is best explained by two relatively independent reactions. First, Ca is removed from the crystal leaving behind linear silica polymers; then the silica polymers are released into solution where they hydrolyze to form H4SiO4. nCaSiO3 + 2nH+ nCa2+ + (H2SiO3)n (H2SiO3)n + nH2O n(H4SiO4) As the leached layer grows in thickness, the Ca release rate slows because it is controlled by transport through the leached layer. A model of Ca diffusion through the leached layer shows that the leached layer grows thicker at lower pH and presents a longer diffusion path for Ca transport into the solution. This diffusion limited reaction offsets the faster rate of the Ca hydrolysis reaction so that at steady state the Ca rates should also become equal to the Si release rate. none Virginia Tech Geological Sciences NDLTD:VT/1554192149731401/ http://scholar.lib.vt.edu/theses/available/etd-1554192149731401/ Wilcox, Karen L. The purpose of this study was to examine privilege in families and uncover the complexities of sibling relationships in adulthood. Through interviewing 13 adult siblings and 3 mothers from 4 families my goal was to gain a clearer picture of what privilege in families means. The sample consisted of a family with 3 sisters, a family with 3 brothers and a sister, a family with 4 brothers, and a family with 2 brothers and a sister. The adult siblings ranged in age from 30 to 60, with an average age of 42. The mothers ranged in age from 62 to 70, with an average age of 67. The study was guided by three theoretical frameworks: a life course, a phenomenological, and a feminist perspective. I conducted this study utilizing an integration of qualitative and feminist methodologies. I used a snowball sampling technique to recruit participants. Data were collected through the use of qualitative in-depth interviews. The interview guides were developed based on the research questions, the review of literature, and the theories guiding the study. I draw 5 conclusions from this study. First, there is a sense of devotion to family that is both expected and fulfilled by simply spending time together, being there for each other in times of need, and at times compromising personal needs or wants. Second, there is an overarching sense of justice that is discussed in everyday language, but at the same time referred to as "something we don't ever think about." Third, descriptions of having a continuous bond among siblings is verbalized as "being the same but different" or just feeling "something in the air," while at the same time mourning the absense of something that is "gone forever." Fourth, interviewing multiple family members extends the understanding of the difficulty of taking different stories heard by each family member and fitting them together into a "family photo." Finally, maintaining an awareness of what it is like to try to "speak for your family" has a different meaning when you also hold the knowledge that everyone else is doing the same thing--but different. favoritism , brother , parental expectations , fairness , sister Virginia Tech Family and Child Development NDLTD:VT/4857172839711171/ http://scholar.lib.vt.edu/theses/available/etd-4857172839711171/ Broderick, Kevin Dee CONSTRUCTING A SUCCESSFUL THERAPEUTIC EXPERIENCE WITH ADOLESCENT CLIENTS: A QUALITATIVE STUDY OF ADOLESCENT EXPERIENCES IN FAMILY THERAPY by Kevin Dee Broderick Committee Chair: Eric McCollum Marriage and Family Therapy (ABSTRACT) Traditionally, therapists and researchers have not asked adolescents about their family therapy experience. This qualitative study was designed to solicit in-depth feedback from adolescents who have recently participated in family therapy to broaden our understanding of their experiences in counseling. Interviews were conducted with 10 adolescents, between the ages of 14 and 20, to discover what helps teenagers have a successful family therapy experience. From the interviews, five main categories emerged; (1) client/therapist relationship, (2) talking and being heard in both individual and family sessions, (3) gaining insight during therapy, (4) taking personal responsibility for making therapy work, and (5) seeing positive results. Feedback from the adolescents is used to suggest ways family therapists might enhance their effectiveness with adolescent clients and a model for treatment success is presented. none Virginia Tech Family and Child Development NDLTD:VT/492119119643530/ http://scholar.lib.vt.edu/theses/available/etd-492119119643530/ Bruner, Christopher William Stuteville Several different time-integration algorithms for the Euler equations are investigated on two distributed-memory parallel computers using an explicit message-passing paradigm: these are classic Euler Explicit, four-stage Jameson-style Runge-Kutta, Block Jacobi, Block Gauss-Seidel, and Block Symmetric Gauss-Seidel. A finite-volume formulation is used for the spatial discretization of the physical domain. Both two- and three-dimensional test cases are evaluated against five reference solutions to demonstrate accuracy of the fundamental sequential algorithms. Different schemes for communicating or approximating data that are not available on the local compute node are discussed and it is shown that complete sharing of the evolving solution to the inner matrix problem at every iteration is faster than the other schemes considered. Speedup and efficiency issues pertaining to the various time-integration algorithms are then addressed for each system. Of the algorithms considered, Symmetric Block Gauss-Seidel has the overall best performance. It is also demonstrated that using parallel efficiency as the sole means of evaluating performance of an algorithm often leads to erroneous conclusions; the clock time needed to solve a problem is a much better indicator of algorithm performance. A general method for extending one-dimensional limiter formulations to the unstructured case is also discussed and applied to Van Albada's limiter as well as Roe's Superbee limiter. Solutions and convergence histories for a two-dimensional supersonic ramp problem using these limiters are presented along with computations using the limiters of Barth & Jesperson and Venkatakrishnan--the Van Al-bada limiter has performance similar to Venkatakrishnan's. unstructured grids , parallel algorithms , computational fluid dynamics Virginia Tech Aerospace and Ocean Engineering NDLTD:VT/314610359611541/ http://scholar.lib.vt.edu/theses/available/etd-314610359611541/ Wilson II, Lawriston A An expert system to predict the fertility of beef heifers was developed using the A.I. Toolkit KAPPA-PC 2.33. The knowledge base was developed from scientific literature and from a beef cattle reproduction expert. The expert system computes an evaluation age, age both at the start and end of the breeding season, and weight per day of age to classify a heifer as having either a 3LOW2, 3GOOD2, or 3EXCELLENT2 likelihood of conception. The expert system summarizes the information that is entered into the computer and creates a text file of the summary. It also gives explanations for every prediction to help identify and alleviate any problem areas that may affect a heifer1s ability to reproduce. The program requires an IBM compatible computer installed with Windows 3.13 or greater. From simulated data for purebred or crossbred British cattle, there was 72% prediction agreement between the expert system and the expert. From analysis of historical data of Hereford-Angus crossbred cattle, heifers categorized as 3LOW2 and 3GOOD2 had significantly higher observed pregnancy rates than expected for each category. There was no significant difference between observed and expected pregnancy rates for heifers in the 3EXCELLENT2 category. Pregnancy rates for post-weaning and pre-breeding evaluations for the 3LOW2 heifers were found to be lower from the combined 3GOOD2 and 3EXCELLENT2 heifers at P=.03 and P=.06 respectively. Observed successful calving rates for heifers categorized as 3LOW2, 3GOOD2, and 3EXCELLENT2 did not differ significantly from the expected calving rates for each category. artificial intelligence , beef cattle , biological type , reproduction Virginia Tech Animal & Poultry Sciences NDLTD:VT/461113689652491/ http://scholar.lib.vt.edu/theses/available/etd-461113689652491/ Favor, Craig M. Aerobics dance floors often produce annoying floor vibrations in adjacent parts of a building due to the rhythmic impact of the aerobicists. Various types of shock absorbing aerobics and dance floors are widely used to prevent injuries to the participants, but the floors may not prevent vibrations in adjacent areas of the building. The purpose of this investigation is to evaluate a temporary "floating" concrete aerobics floor designed to prevent the force and vibrations induced by rhythmic exercises from being transmitted to the existing building floor system. The test floor is a concrete slab mounted on pressurized air springs. A series of tests was conducted to determine the vibration characteristics of the floor and the forces transferred to the supporting floor system. Experienced aerobicists compared the response of the "floating" floor to existing aerobics floors. Based on the experimental results, vibration characteristics and a prediction of the force transmitted to the supporting floor by the "floating" floor system were determined. Recommendations are made in terms of the feasibility of the "floating" floor concept, additional testing to be performed, and possible applications. none Virginia Tech Civil Engineering NDLTD:VT/91432539751141/ http://scholar.lib.vt.edu/theses/available/etd-91432539751141/ Buck, Sharon Perkins A probabilistic risk assessment (PRA) for the discharge of excessive nitrogen from nonpoint sources (NPSs) to a stream was performed for a small agricultural watershed in northern Virginia. Risk, by definition, is the product of the frequency of occurrence of an event and the consequences of that event. The purpose of this research was to determine the probability of occurrence of a nitrogen discharge event (i.e., frequency). The consequences of such a discharge event were not explicitly determined but were implicitly assumed to be negative in nature. An event tree was developed to show the basic hydrologic processes at work in a small watershed. However, the event tree could not be used to discover the causes for nitrogen loss from the watershed. Therefore, a fault tree was developed for excessive nitrogen discharge in surface runoff on any day from agricultural sources. The development of the fault tree was found to be a useful exercise in understanding the intricate cause and effect relationships between agricultural practices and NPS pollution. Based on the results, the fault tree methodology might be used as an effective teaching or communication tool. The fault tree was also evaluated quantitatively to determine a probability of occurrence for excessive nitrogen discharge to the stream on any day. Land use, fertilization, monitoring, and long-term weather records were used in conjunction with scientific judgment and expert opinion to establish the probabilities within the fault tree and to calculate the overall probability of nitrogen discharge to the stream on any day. The results obtained from the fault tree calculations tend to underestimate the importance of cropland best management practices (BMPs) over the long term, because the fault tree was developed on a daily basis (i.e., every day in a year has the same probability of a discharge event occurring). A more accurate depiction of the NPS pollution control problem was achieved by assuming the occurrence of a runoff event. A second fault tree was presented for the discharge of excessive nitrogen to the stream during a runoff event. The quantitative assessment of the new fault tree showed more clearly the impact of BMPs on reducing the likelihood of nitrogen discharge. A 0.15 decrease in the probability of nitrogen discharge during a runoff event was calculated for the Owl Run watershed from 1987 to 1993 due to the effects of BMPs installed during that time period. A 0.20 decrease was calculated for an Owl Run subwatershed for the same time period. This subwatershed isolated two major dairy operations and the effects of the BMPs installed for those dairies. Despite the success of the fault tree in mirroring changes within the watershed, the amount of data and time required to perform the quantitative assessment may limit its use in the NPS pollution control field. The basic nature of the fault tree technique also limits its usefulness in the field. One such limitation is that degrees of events cannot be expressed. For example, a BMP is either present or not present on a fault tree. There can be no indication of how effective the BMP is in preventing NPS pollution without substantially increasing the level of detail displayed by the tree. Another limitation is that the ultimate result of the fault tree calculations is a probability of occurrence. This value is not as easily understood as the output of NPS pollution computer models, for example, where the output has specific meaning and units (e.g., milligrams of nitrogen per liter of runoff). The qualitative fault tree, however, has the advantage over computer models when it comes to understanding the concepts behind the technique and being able to see the cause and effect relationships at work in the watershed. Laypersons can understand the fault tree more easily than the complex computer code and intricate equations of models. probabilistic risk assessment , nonpoint source pollution Virginia Tech Biological Systems Engineering NDLTD:VT/17391653976940/ http://scholar.lib.vt.edu/theses/available/etd-17391653976940/ Wittmer, Kenneth S Experiments were performed to document the turbulent flowfield produced downstream of an airfoil encountering an intense streamwise vortex. This type of perpendicular airfoil--vortex interaction commonly occurs in helicopter rotor flows. The experiments presented here thus provide useful information for the prediction of helicopter noise, particularly BWI noise. Three-component velocity and turbulence measurements were made in unprecedented detail using a computerized miniature four-sensor hot-wire probe system; revealing much about the structure and behavior of this flow over a range of conditions. The interaction between the vortex and the airfoil wake leaves the vortex surrounded by a large region of intense turbulence unlike the turbulence surrounding an isolated vortex. Even for close separations, the vortex core passes the airfoil virtually unchanged. However, vorticity of opposite sign is shed by the airfoil in response to the angle of attack distribution induced by the vortex resulting in an unstable circulation distribution according to Rayleigh's criterion. Simple theoretical models adequately describe the shed vorticity distribution of the airfoil and the unstable circulation distribution it imparts on the vortex. As the flow develops, the vortex continuously distorts the airfoil wake. The strain rates imparted by the vortex on the spanwise vorticity contained in the airfoil wake result in an anisotropic, turbulence producing stress field. For several chord lengths downstream, the vortex core remains laminar and little change is seen in the unstable circulation distribution. While the vortex core is laminar, turbulent fluctuations measured in the core are the result of inactive wandering motions and the characteristic length and velocity scales of the flat portion of the vortex wake appear to be appropriate scales for the fluctuations. Eventually, the vortex core becomes turbulent as indicated by an increase in high frequency velocity fluctuation levels of more than an order of magnitude. Subsequently, the circulation distribution reorganizes to a stable distribution. A loss in core circulation occurs due to a decrease in the peak tangential velocity which is proportionately larger than the increase in the vortex core radius. The peak tangential velocity decreases to the point where it is exceeded by the axial velocity deficit---another unstable situation. These effects increase with decreased separation between the vortex and the airfoil, but appear to be largely independent of airfoil angle of attack an only weakly dependent upon vortex strength. vortex , turbulence , BWI , helicopter noise , hot-wire Virginia Tech Aerospace and Ocean Engineering NDLTD:VT/31251021109643250/ http://scholar.lib.vt.edu/theses/available/etd-31251021109643250/ Cameron, Rick A. This dissertation provides a study of synchronization and quantization issues in implementing a multistage receiver in fixed-point Digital Signal Processing (DSP) hardware. Current multistage receiver analysis has neglected the effects of synchronization and quantization; however, these effects can degrade system performance and therefore decrease overall system capacity. The first objective is to analyze and simulate various effects of synchronization in a multistage system. These effects include the effect of unsynchronized users on the bit error rate (BER) of synchronized users, and determining whether interference cancellation can be used to improve the synchronization time. This information is used to determine whether synchronization will limit overall system capacity. Both analytical and simulation techniques are presented. The second objective is to study the effects of quantization on the performance of the multistage receiver. A DSP implementation of a practical receiver will require a DSP chip with a fewer number of bits than the computer chips typically used in simulation of receiver performance. Therefore, the DSP implementation performs poorer than the simulation results predict. In addition, a fixed-point implementation is often favored over a floating-point implementation, due to the high processing requirements necessitated by the high chip rate. This further degrades performance because of the limited dynamic range available with fixed-point arithmetic. The performance of the receiver using a fixed-point implementation is analyzed and simulated. We also relate these topics to other important issues in the hardware implementation of multistage receivers, including the effects of frequency offsets at the receiver and developing a multiuser air protocol interface (API). This dissertation represents a contribution to the ongoing hardware development effort in multistage receivers at Virginia Tech. interference cancellation , quantization , synchronization , CDMA Virginia Tech Electrical and Computer Engineering NDLTD:VT/23349150973140/ http://scholar.lib.vt.edu/theses/available/etd-23349150973140/ Wolf, Bettina There is a fine line between the "simple" and the "simplistic". The simple such as the plain, the pure, and the truthful holds a complexity within, which is extremely hard to obtain. It ultimately results in beauty. The simplistic embodies nothing more than obviousness and boredom. My aim is to strive for simple beauty. Concerning objects and architecture, to simplify means to reduce by eliminating the superficial and the superfluous, to unmask what is essential. Quality materials and craftsmanship are prerequisites. In combination with the accuracy of the design they help to attain the desired result which speaks of precision and clarity. wolf , simplicity , simple , beauty , art gallery Virginia Tech Architecture NDLTD:VT/431616132974710/ http://scholar.lib.vt.edu/theses/available/etd-431616132974710/ Cary, Charles William III Current procedures for estimating effective length factors for web-tapered members rely heavily on the use of charts and graphs. This makes them difficult to implement using a computer. In addition, they are often based on unrealistic assumptions. In cases where these assumptions are not satisfied, design errors may result. This investigation proposes a modification to an effective length factor expression developed by Lui (1992). This modification allows the expression to be applied to web-tapered members with good accuracy. A d