Browsing Award-winning Theses and Dissertations by Issue Date
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- Atomic Force Microscopy Study of Clay Mineral DissolutionBickmore, Barry Robert (Virginia Tech, 1999-12-09)An integrated program has been developed to explore the reactivity of 2:1 phyllosilicates (biotite and the clays montmorillonite, hectorite, and nontronite) with respect to acid dissolution using in situ atomic force microscopy (AFM). Three techniques are described which make it possible to fix these minerals and other small particles to a suitable substrate for examination in the fluid cell of the atomic force microscope. A suite of macros has also been developed for the Image SXM image analysis environment which make possible the accurate and consistent measurement of the dimensions of clay particles in a series of AFM images, so that dissolution rates can be measured during a fluid cell experiment. Particles of biotite and montmorillonite were dissolved, and their dissolution rates normalized to their reactive surface area, which corresponds to the area of their edge surfaces (Ae). The Ae-normalized rates for these minerals between pH 1-2 are all ~10E-8 mol/m2*s, and compare very well to other Ae-normalized dissolution rates in the literature. Differences between the Ae-normalized rates for biotite and the BET-normalized rates (derived from solution chemical studies) found in the literature can be easily explained in terms of the proportion of edge surface area and the formation of leached layers. However, the differences between the Ae-normalized montmorillonite rates and the literature values cannot be explained the same way. Rather, it is demonstrated that rates derived from solution studies of montmorillonite dissolution have been affected by the colloidal behavior of the mineral particles. Finally, the dissolution behavior of hectorite (a trioctahedral smectite) and nontronite ( a dioctahedral smectite) were compared. Based on the differential reactivity of their crystal faces, a model of their surface atomic structures is formulated using Hartman-Perdock crystal growth theory, which explains the observed data if it is assumed that the rate-determining step of the dissolution mechanism is the breaking of connecting bonds between the octahedral and tetrahedral sheets of the mineral structure.
- High-Resolution Mapping of the Region around the Soybean Virus Resistance Genes, Rsv1 and Rpv1Gore, Michael Allen (Virginia Tech, 2000-07-28)Soybean mosaic virus (SMV) and peanut mottle virus (PMV) are potyviruses that can cause serious yield reductions in soybean [Glycine max (L.) Merr.]. Virus resistant soybean cultivars have been released with alleles at the Rsv1 and Rpv1 locus that confer resistance to SMV and PMV, respectively. A high-resolution map-based cloning approach was undertaken to isolate Rsv1 and Rpv1 from soybean, with hopes of providing insight into this host-pathogen relationship. A mapping population of 1,056 F2 individuals was constructed from the cross of the resistant cultivar PI 96983 (Rsv1 and Rpv1) by the susceptible cultivar Lee 68 (rsv1 and rpv1). Ninety-one of the 1,056 F2 individuals had a cross-over (recombination) in the chromosomal region between microsatellite, or simple sequence repeat (SSR) marker loci Hsp176 and Sat120, and these 91 recombinant lines (RLs) were selected for further genetic analysis. Genotypes of Rsv1 and Rpv1 for the 91 RLs were obtained by inoculating their F2:3 progeny with SMV-G1 and PMV-P1, respectively. The 91 RLs also were used for mapping one random amplified polymorphic DNA (RAPD), five SSR, and 21 restriction fragment length polymorphism (RFLP) markers. Included in these RFLP markers were seven resistance gene candidate (RGC) and five resistance gene candidate flanking (RGCF) markers. RGC probes encode a protein with homology to previously cloned plant disease resistance genes, and RGCF probes are sequences obtained from the flanking regions of candidate disease resistance genes. The resultant high-resolution map consisted of 41 marker loci detected by 27 molecular markers. Rsv1 and Rpv1 cosegregated with one or more RFLP bands detected by RGCF probes: GG27-1a, 3gG2SP, and/or T3G. Analyses of the disease reaction and molecular marker data from seven RLs suggested that the map position of Rsv1 should be at a locus different from that designated by the linkage analysis software, Mapmaker 3.0. Compared to the other 89 RLs, a high percentage (>34%) of F3 plants grown from four of these seven RLs gave a necrotic reaction when inoculated with SMV-G1. From this evidence, we believed that another locus independent of Rsv1 was involved in PI 96983's response to SMV-G1. The two loci conferring resistance to SMV-G1 were designated Rsv1a and Rsv1b.
- Bacteriophage Felix O1: Genetic Characterization and Bioremedial ApplicationWhichard, Jean Marie (Virginia Tech, 2000-10-16)Bacteriophage Felix O1 was studied for applicability as a Salmonella intervention. Felix O1's potential as a Salmonella therapeutic was explored, as was its utility as a food application. Felix O1 is specific for and infects most serovars within the genus Salmonella. The entire 86.155-kb sequence of the phage's linear, double-stranded chromosome was determined. 213 open reading frames (ORFs) were found, including 23 homologues of phage genes (e<0.008). Homology searches do not indicate genes that would be expected to increase virulence of Salmonella. Thirteen T4 homologues were found, including rIIA and rIIB, rapid lysis genes of T-even phages. Site-directed mutagenesis of the rIIB region was attempted by homologous recombination with plasmids containing luxAB of Vibrio harveyi. No DrIIB luxAB+ recombinants resulted from the methods tried. Serial in vivo passage was used to select for a longer-circulating Felix O1 mutant using the modified methods of Merril et al., (1996). No difference was found in the clearance of wild-type (WT) and Felix O1 following nine serial passages. Injection of 10⁹pfus yielded 24-hour concentrations of 6.5 and 4.9 log10 pfus/ml plasma for WT and 9th passage, respectively. Both isolates were undetectable in plasma by 72 hours, but remained in spleens at 96 hours. A large-plaque Felix O1 variant (LP) isolated during in vivo serial passage was compared with WT for Salmonella growth suppression. Spectrophotometric measurement of BHI cultures indicated greater suppression of S. typhi by LP than by WT, a difference not seen with S. typhimurium DT104. Both isolates suppressed 24-hour S. typhimurium DT104 growth on experimentally-contaminated chicken frankfurters at 22°C. Untreated frankfurters yielded 6.81 log10 Salmonella cfus/g, whereas WT and LP-treated samples yielded 5.01 and 4.70 log10 cfus/g, respectively. Both phages suppressed the Salmonella typhimurium DT104 growth (p<0.0001), but the isolates did not perform differently (p=0.5088). Presence of Salmonella caused a higher yield of WT phage than from the uninoculated group (p=0.0011), but did not affect LP yield (p=0.4416). With Salmonella present, the 24-hour LP concentration was lower than WT concentration. This supports the surmised LP rapid-lysis phenotype since T4 rapid-lysis mutants typically exhibit lower burst sizes than wild-type phage.
- Equilibria of a Gyrostat with a Discrete DamperSandfry, Ralph Anthony (Virginia Tech, 2001-07-09)We investigate the relative equilibria of a gyrostat with a spring-mass-dashpot damper to gain new insights into the dynamics of spin-stabilized satellites. The equations of motion are developed using a Newton-Euler approach, resulting in equations in terms of system momenta and damper variables. Linear and nonlinear stability methods produce stability conditions for simple spins about the nominal principal axes. We use analytical and numerical methods to explore system equilibria, including the bifurcations that occur for varying system parameters for varying rotor momentum and damper parameters. The equations and bifurcations for zero rotor absolute angular momentum are identical to those for a rigid body with an identical damper. For the more general case of non-zero rotor momentum, the bifurcations are complex structures that are perturbations of the zero rotor momentum case. We examine the effects of spring stiffness, damper position, and inertia properties on the global equilibria. Stable equilibria exist for many different spin axes, including some that do not lie in the nominally principal planes. Some bifurcations identify regions where a jump phenomenon is possible. We use Liapunov-Schmidt reduction to determine an analytic relationship between parameters to determine if the jump phenomenon occurs. Bifurcations of the nominal gyrostat spin are characterized in parameter space using two-parameter continuation and the Liapunov-Schmidt reduction technique. We quantify the effects of rotor or damper alignment errors by adding small displacements to the alignment vectors, resulting in perturbations of the bifurcations for the standard model. We apply the global bifurcation results to several practical applications. We relate the general set of all possible equilibria to specific equilibria for dual-spin satellites with typical parameters. For systems with tuned dampers, where the natural frequency of the spring-mass-damper matches the gyrostat precession frequency, we show numerically and analytically that the existence of certain equilibria are related to the damper tuning condition. Finally, the global equilibria and bifurcations for varying rotor momentum provide a unique perspective on the dynamics of simple rotor spin-up maneuvers.
- Active Dynamic Analysis and Vibration Control of Gossamer Structures Using Smart MaterialsRuggiero, Eric John (Virginia Tech, 2002-05-07)Increasing costs for space shuttle missions translate to smaller, lighter, and more flexible satellites that maintain or improve current dynamic requirements. This is especially true for optical systems and surfaces. Lightweight, inflatable structures, otherwise known as gossamer structures, are smaller, lighter, and more flexible than current satellite technology. Unfortunately, little research has been performed investigating cost effective and feasible methods of dynamic analysis and control of these structures due to their inherent, non-linear dynamic properties. Gossamer spacecraft have the potential of introducing lenses and membrane arrays in orbit on the order of 25 m in diameter. With such huge structures in space, imaging resolution and communication transmissibility will correspondingly increase in orders of magnitude. A daunting problem facing gossamer spacecraft is their highly flexible nature. Previous attempts at ground testing have produced only localized deformation of the structure's skin rather than excitation of the global (entire structure's) modes. Unfortunately, the global modes are necessary for model parameter verification. The motivation of this research is to find an effective and repeatable methodology for obtaining the dynamic response characteristics of a flexible, inflatable structure. By obtaining the dynamic response characteristics, a suitable control technique may be developed to effectively control the structure's vibration. Smart materials can be used for both active dynamic analysis as well as active control. In particular, piezoelectric materials, which demonstrate electro-mechanical coupling, are able to sense vibration and consequently can be integrated into a control scheme to reduce such vibration. Using smart materials to develop a vibration analysis and control algorithm for a gossamer space structure will fulfill the current requirements of space satellite systems. Smart materials will help spawn the next generation of space satellite technology.
- Evaluating System Performance in a Complex and Dynamic EnvironmentVaneman, Warren Kenneth (Virginia Tech, 2002-12-04)Realistically, organizational and/or system efficiency performance is dynamic, non-linear, and a function of multiple interactions in production. However, in the efficiency literature, system performance is frequently evaluated considering linear combinations of the input/output variables, without explicitly taking into account the interactions and feedback mechanisms that explain the causes of efficiency behavior, the dynamic nature of production, and non-linear combinations of the input/output variables. Consequently, policy decisions based on these results may be sub-optimized because the non-linear relationships among variables, causal relationships, and feedback mechanisms are ignored. This research takes the initial steps of evaluating system efficiency performance in a dynamic environment, by relating the factors that effect system efficiency performance to the policies that govern it. First, this research extends the concepts of the static production axioms into a dynamic realm, where inputs are not instantaneously converted into outputs. The relationships of these new dynamic production axioms to the basic behaviors associated with system dynamics structures are explored. Second, this research introduces a methodological approach that combines system dynamics modeling with the measurement of productive efficiency. System dynamics is a modeling paradigm that evaluates system policies by exploring the causal relationships of the important elements within the system. This paradigm is coupled with the fundamental assumptions of production theory in order to evaluate the productive efficiency of a production system operating within a dynamic and non-linear environment. As a result, a subsystem within the system dynamics model is introduced that computes efficiency scores based on the fundamental notions of productive efficiency. The framework's ability to combine prescriptive and descriptive modeling characteristics, as well as dynamic and combinatorial complexity, can potentially have a greater impact on policy decisions and how they affect system efficiency performance. Finally, the utility of these concepts is demonstrated in an implementation case study. This methodology generates a prescriptive dynamical production frontier which defines the optimal production resources required to satisfy system requirements. Additionally, the dynamical production frontier allows for analysis for comparisons between options during a transient period, insight into possible unintended consequences, and the ability to forecast optimal times for introducing system or process improvements.
- Confronting the West: Social Movement Frames in 20th Century IranPoulson, Stephen Chastain (Virginia Tech, 2002-12-06)The Iranian Revolution of 1979 received considerable attention from modern social scientists who study collective action and revolution because it allowed them to apply their different perspectives to an ongoing social event. Likewise, this work used the Iranian experience as an exemplar, focusing on a sequence of related social movement frames that were negotiated by Iranian groups from the late 19th through the 20th century. Snow and Benford (1992) have proposed that cycles of protest are associated with the development of a movement master frame. This frame is a broad collective orientation that enables people to interpret an event in a more or less uniform manner. This study investigated how movement groups in Iran developed master frames of mobilization during periodic cycles of protests from 1890 to the present. By investigating how master frames were negotiated by social movement actors over time, this work examined both the continuity and change of movement messages during periods of heightened social protest in Iran.
- Gender, Politics, and Radioactivity Research in Vienna, 1910-1938Rentetzi, Maria (Virginia Tech, 2003-03-25)What could it mean to be a physicist specialized in radioactivity in the early 20th century Vienna? More specifically, what could it mean to be a woman experimenter in radioactivity during that time? This dissertation focuses on the lived experiences of the women experimenters of the Institut für Radiumforschung in Vienna between 1910 and 1938. As one of three leading European Institutes specializing in radioactivity, the Institute had a very strong staff. At a time when there were few women in physics, one third of the Institute's researchers were women. Furthermore, they were not just technicians but were independent researchers who published at about the same rate as their male colleagues. This study accounts for the exceptional constellation of factors that contributed to the unique position of women in Vienna as active experimenters. Three main threads structure this study. One is the role of the civic culture of Vienna and the spatial arrangements specific to the Mediziner-Viertel in establishing the context of the intellectual work of the physicists. A second concerns the ways the Institute's architecture helped to define the scientific activity in its laboratories and to establish the gendered identities of the physicists it housed. The third examines how the social conditions of the Institute influenced the deployment of instrumentation and experimental procedures especially during the Cambridge-Vienna controversy of the 1920s. These threads are unified by their relation to the changing political context during the three contrasting periods in which the story unfolds: a) from the end of the 19th century to the end of the First World War, when new movements, including feminism, Social Democracy, and Christian Socialism, shaped the Viennese political scene, b) the period of Red Vienna, 1919 to 1934, when Social Democrats had control of the City of Vienna, and c) the period from 1934 to the Anschluss in 1938, during which fascists and Nazis seized power in Austria. As I show, the careers of the Institute's women were shaped in good part by the shifting meanings, and the politics, that attached to being a "woman experimenter" in Vienna from 1910 to the beginning of the Second World War.
- Studies of the Class A High-Molecular Weight Penicillin-Binding Proteins in Bacillus subtilisMcPherson, Derrell C. (Virginia Tech, 2003-04-16)The survival of all organisms depends on their ability to perform certain enzymatic activities and the ability to construct certain structures. In prokaryotes, enzymes are required for the final reactions of peptidoglycan (PG) synthesis, the structural element of the bacterial cell wall. These proteins, known as penicillin-binding proteins (PBPs), are identified through the presence of conserved motifs within their functional domains. The Class A high-molecular weight PBPs are bifunctional, performing the penicillin-sensitive transpeptidase activity and the glycosyl transferase (GT) activity required for the polymerization of the glycan strands. The Class A PBPs in Bacillus subtilis are PBP1, PBP4, PBP2c, and PBP2d (YwheE) and they are encoded by ponA, pbpD, pbpF, and pbpG (ywhE), respectively. These proteins appear to be somewhat functionally redundant because removal of one or more does not cause any noticeable change in phenotype. However, the loss of PBP1 has previously been demonstrated in B. subtilis to cause a decreased growth rate and changes in morphology of vegetative cells, both of which are increased upon the additional loss of PBP4. Furthermore, the loss of sporulation-expressed Class A PBPs, PBP2c and 2d, causes a 10,000-fold decrease in the production of heat resistant spores. This double mutant is shown to have changes in the structural parameters of cortex PG that appear minor when compared to other strains, but are coupled with a large defect on the deposition of cortex PG, apparently from the synthesis of an abnormal germ cell wall. The Class A PBPs are believed to be the only proteins capable of performing the GT activity and it is therefore believed that cell viability requires the presence of at least one functional Class A PBP. This requirement has been demonstrated in other organisms, but a B. subtilis strain lacking all Class A PBPs is viable. The phenotypical changes seen in the PBP1 mutant are exacerbated in this strain. The GT activity remaining in this strain is sensitive to the antibiotic moenomycin in vitro whereas it appears resistant in vivo. Identification of the protein(s) performing this novel GT activity will rely on the demonstration of the GT activity in vitro.
- Carve That Opossum and Plucky, Ducky Underwear: A Narrative Inquiry of Laughter in a Preschool ClassroomSmidl, Sarah Lynn (Virginia Tech, 2003-05-06)This thesis is a narrative inquiry of laughter in a University Lab School preschool classroom that describes the many situations in which children laugh as well as laughter's importance for the children, for me, and for all of us as a whole within the context of our classroom. To date, there is a paucity of research on children's laughter, especially in young children. The majority of research that has been conducted has been quantitative in nature, with few attempts to comprehensively describe the many situations in which laughter occurs. For my study, I felt it crucial to look at, document, and describe preschoolers' laughter, taking into consideration the many facets of their school day including free play, story time, playground time, and snack time. My sample included all of my 14 preschoolers, who ranged in age from 3 years to 4 years, 4 months at the outset of the study. I also deemed it important to look at what these laughter-producing situations meant to me and the children in my classroom, including what deeper worth laughter for all of us, how we used it in the classroom, and how it helped me to grow both personally and professionally through my research.
- Pseudorotaxanes and Supramolecular Polypseudorotaxanes Based on the Dibenzo-24-Crown-8/Paraquat Recognition MotifHuang, Feihe (Virginia Tech, 2003-08-28)The research presented in this thesis focused on pseudorotaxanes and supramolecular polymers based on a new recognition motif, the dibenzo-24-crown-8/paraquat recognition motif. Main kinds of pseudorotaxanes and rotaxanes and various protocols used for the study of them were discussed first. By preparation and characterization of a series of pesudorotaxanes based on DB24C8 and paraquat derivatives, it was found that these complexes were stabilized by N+...O interactions, C-H...O hydrogen bonding, and face-to-face p-stacking interactions. Because methyl protons of paraquat are involved in hydrogen bonding to the host, the substitution of any methyl hydrogen on paraquat causes apparent association constant of the pseudorotaxane to decrease. The concentration dependence of apparent association constants, Ka,exp, of fast exchange host-guest systems was studied for the first time by using complexes based on viologens and crown ethers as examples. While the bis(hexafluorophosphate) salts of paraquat derivatives are predominantly ion paired in acetone (and other low dielectric constant solvents presumably) the complex based on dibenzo-24-crown-8 and paraquat is not ion paired in solution, resulting in concentration dependence of Ka,exp. However, four complexes of two different bis(m-phenylene)-32-crown-10 (BMP32C10) derivatives and bis(p-phenylene)-34-crown-10 (BPP3C10) with viologens are ion paired in solution, as shown by the fact that Ka,exp is not concentration dependent for these systems involving hosts with freer access to bound guests. X-ray crystal structures support these soluton-based assessments in that there is clearly ion pairing of the cationic guest and its PF6- counterions in the solid states of the latter four examples, but not in the former. The complexes based on the new dibenzo-24-crown-8/paraquat recognition motif are thus different from the complexes based on two old recognition motifs: the BPP34C10/BMP32C10-paraquat and DB24C8-ammonium motives. In order to compare these recognition motives further, the selectivity between two hosts, DB24C8 and BPP34C10, and two guests, dimethyl paraquat and dibenzyl ammnonium salt, was discussed. By individual and competitive complexation studies, it was demonstrated that DB24C8 is a better host than BPP34C10 for paraquat, and that paraquat is a better guest than dibenzyl ammonium salt for DB24C8. Finally the DB24C8-paraquat recognition motif was successfully applied in the preparation the first star-shaped supramolecular polymer based on a tetraparaquat guest and a DB24C8 functionalized polystyrene oligomer. A model system based on this guest and DB24C8 was also studied for comparison. It was found that the complexation in these two systems is cooperative, as are most biological complexations of multitopic species. Due to the ready availability of DB24C8 and paraquat derivatives, the new recognition motif should prove to be very valuable for self-assembly of other more sophisticated supramolecular systems.
- A Holistic Approach to Taxonomic Evaluation of Two Closely Related Endangered Freshwater Mussel Species, the Oyster Mussel (Epioblasma capsaeformis) and Tan Riffleshell (Epioblasma florentina walkeri) (Bivalvia: Unionidae)Jones, Jess W. (Virginia Tech, 2004-03-19)Primers for 10 polymorphic DNA microsatellite loci were developed and characterized for the endangered oyster mussel Epioblasma capsaeformis from the Clinch River, TN. Microsatellite loci also were amplified for individuals collected from the following additional populations or species: (1) E. capsaeformis from Duck River, TN; (2) E. florentina walkeri from Indian Creek, upper Clinch River, VA; (3) E. florentina walkeri from Big South Fork Cumberland River, TN; and (4) E. torulosa rangiana from Allegheny River, PA. Allelic diversity ranged from 9-20 alleles/locus, and averaged 13.6/locus for all 5 populations investigated. Average expected heterozygosity (HE) per locus ranged from 0.78-0.92, and averaged 0.86. A genetic characterization of extant populations of E. capsaeformis and E. florentina walkeri was conducted to assess taxonomic validity and to resolve conservation issues related to recovery planning. These mussel species exhibit pronounced phenotypic variation, and are difficult to characterize phylogenetically using DNA sequences. Monophyletic lineages, congruent with phenotypic variation among species, were obtained only after extensive analysis of combined mitochondrial (1378 bp of 16S, cytochrome-b, ND1) and nuclear (515 bp of ITS-1) DNA sequences. In contrast, analysis of variation at 10 hyper variable DNA microsatellite loci showed moderate to highly divergent populations based on FST values, which ranged from 0.12-0.39. Quantitative genetic variation was observed in fish host specificity, with transformation success of glochidia of E. capsaeformis significantly greater (p<0.05) on the greenside darter Etheostoma blennioides, and that of E. f. walkeri significantly greater (p<0.05) on the fantail darter E. flabellare. Lengths of glochidia differed significantly (p<0.001) between species, with sizes ranging from 241-272 μm. Underwater photographs of mantle-pads and micro-lures of female mussels documented fixed phenotypic variation between species. The texture and color of the mantle-pad of E. capsaeformis is smooth and bluish-white, while that of E. f. walkeri is pustuled and brown, with tan mottling. Based on extensive molecular, morphological, and life history data, a population of E. capsaeformis from the Duck River, TN is described and proposed as a separate species, and a population of E. f. walkeri from the upper Clinch River, VA is described and proposed as a separate subspecies. Genetic management guidelines were developed to assess taxonomic status, genetic variation of donor-recipient populations targeted for augmentation, and field and laboratory protocols to maximize genetically effective population size, minimize genetic changes in captive-reared progeny, and prevent the release of juvenile mussels into non-native drainages. A pragmatic approach to species recovery is advocated; one that incorporates the principles of conservation genetics into breeding programs, but prioritizes the immediate demographic needs of critically endangered mussel species.
- Molecular Pathogenesis and Development of a Genetically Engineered Vaccine for Type-2 Porcine CircovirusFenaux, Martijn (Virginia Tech, 2004-03-26)Porcine circovirus type 2 (PCV2) is the primary causative agent of postweaning multisystemic wasting syndrome (PMWS), whereas the ubiquitous porcine circovirus type 1 (PCV1) is nonpathogenic for pigs. Since its initial detection in a Canadian commercial swine herd in 1991, PMWS has been detected in all swine producing regions of the world and is now a serious economic problem to the swine industry. The objectives of this dissertation were to biologically, genetically and experimentally characterize both PCV1 and PCV2, to identify the genetic determinant(s) for virulence and replication, and to develop an effective genetically-engineered vaccine against PCV2 infection and PMWS. The genetic heterogeneity of PCV2 and PCV1 isolates from different geographic origins were determined. We found that, although PCV1 and PCV2 genomes were very conserved, some minor genomic variation exists among PCV1 isolates and PCV2 isolates. The nonpathogenic PCV1 and pathogenic PCV2 share only about 76% nucleotide sequence identity but have similar genomic organization. The highest sequence variability among PCV isolates is found in the immunogenic ORF2 capsid gene. Based on the sequence data in this dissertation, a universal polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay was developed that is capable of detecting all known PCV isolates and differentiating between infections by nonpathogenic PCV1 and pathogenic PCV2. In order to study the structural and functional relationship of PCV genes and to develop a genetically-engineered vaccine, we constructed infectious DNA clones of both PCV1 and PCV2. By using the PCV2 infectious clone, we showed that pigs can be infected by direct intrahepatic injection of PCV2 infectious DNA clone. The pathological lesions and clinical disease associated with PCV2 infection were more definitively characterized by using the infectious DNA clone. We found that PCV2 is the primary but not the sole causative agent of PMWS, as the full spectrum of clinical PMWS was not reproduced by the infectious PCV2 DNA clone although pathological lesions characteristic of PMWS were reproduced. A chimeric vaccine was constructed by cloning the immunogenic capsid gene of the pathogenic PCV2 into the genomic backbone of the non-pathogenic PCV1 virus. We showed that the resulting chimeric PCV1-2 vaccine virus, retained the non-pathogenic nature of PCV1 but induced a protective immune response against a wild-type PCV2 challenge. In vaccinated pigs, the chimeric PCV1-2 vaccine reduced PCV2 viremia length and serum virus loads and reduced pathological lesions such as lymphoid depletion (LD) and histiocytic replacement (HR) in lymphoid tissues, inflammation and discoloration of the lymph nodes. The amounts of PCV2 antigen and PCV2 genomic copy loads in lymph node tissues were also significantly reduced. Our results indicated that the attenuated chimeric PCV1-2 virus induces protective immunity against PCV2 infection and thus could serve as an effective vaccine against PCV2 and PMWS. To improve the safety of the vaccine, we attempted to identify the genetic determinant(s) for PCV2 virulence. An isolate of PCV2 was serially passaged for 120 times in PK-15 cells. After 120 passages, a total of two amino acid mutations were identified in the capsid protein of the passage 120 virus (VP120), P110A and R191S. Compared to other known PCV1 and PCV2 sequences, the two amino acid mutations in PCV2 VP120 are unique. The VP120 virus was biologically characterized in vitro and experimentally characterized in specific-pathogen-free (SPF) pigs. The two amino acid mutations resulted in an enhanced replication ability of PCV2 VP120 in PK-15 cells and an attenuated phenotype in infected pigs. The P110A and R191S mutations in the capsid protein either alone or collectively are likely important for PCV2 virulence and replication. In summary, we genetically characterized PCV2 isolates from different geographic regions and developed a PCR-RFLP assay. We constructed and characterized infectious DNA clones of PCV1 and PCV2, and developed a genetically engineered vaccine against PCV2 infection. We also identified the genetic determinants for PCV2 virulence and replication. The vaccine developed in this study, when it becomes available, will help the swine industry control this important pathogen.
- Intimacy and Family Among Single, Working-Class Women: A Focus on Rural AppalachiaMcCann, Brandy R. (Virginia Tech, 2004-06-10)With people living longer and coming into old age with more diverse relational experiences than previous cohorts (e.g., divorce, cohabitation), researchers anticipate that the so-called baby boomers will be more interested in pursuing romantic relationships in later life than their predecessors. On the other hand, we know that the experience of aging varies among people on the basis of their social locations (e.g., racial, gender, class). As central Appalachia is a place characterized by persistent poverty, I interviewed single, midlife White women from a community in West Virginia (N=11) to investigate (a) their experiences with family life and (b) their expectations for romantic relationships in later life. I used grounded theory methodology to develop a theory of intimacy and family life in central Appalachia. I found that the women who were more integrated into their families of origin had little or no interest in romantic relationships, regardless of their past relationship history. Women who perceived their childhoods as traumatic were less integrated into their families of origin and had a weaker sense of place, but had more interest in finding a romantic partner in later life. I concluded for those with a strong sense of place the importance of the family of origin persisted through midlife and into old age.
- Pixelating Policy: Visualizing Issue Transformation In Real and Virtual WorldsToavs, Dwight V. (Virginia Tech, 2004-12-10)This study seeks to identify and examine issue transformation in public policies, and to understand the relationship between issue transformation and policy change. The focus for this investigation, the information resources management (IRM) policy subsystem, is examined as a 28-year case study, concluding at the end of 2002. Study results are documented textually, and visually in an exploratory, "virtual reality-based" Policy World. This study examines the questions: "In what ways are the core issues underlying public policies transformed over time, and what is the relationship between issue transformation and policy change?" Using the advocacy coalition framework (ACF) for explaining policy change over considerable periods of time, this research identifies and examines the issues over which policy coalitions contend, and seeks to identify issue transformation in the IRM policy subsystem's 28-year history. Augmenting the traditional paper-based dissertation is an exploratory, "virtual reality-based" case study, called "Policy World," that visualizes both the policy subsystem environment and critical elements of the external policy system. Visually depicting the richness, texture, and artifacts of policy activities aids policy learning, and promotes understanding of the dynamic and complex environment of issue transformation and policy change. In confirming issue transformation, this study contributes to the advocacy coalition framework by detailing the initiation and maturation of a policy subsystem. In demonstrating issue transformation's role as facilitating policy continuity through policy change, this study contributes to policy theory. As a chronology of IRM's issue transformation and policy change, this study documents the rise of IT-enabled governance for public administrators and educators. Policy World provides an interactive, experiential learning environment for public administration scholars and practitioners wanting substantive knowledge of both policy theory and Federal IRM policies. Public administration literature notes both the need for and the lack of an information resource management component to public administration education. Information visualization concepts are combined with interactive designs and hosting on the World Wide Web, to provide wide access to Policy World and extend educational opportunities in public policy and information resources management wherever desired.
- The Influence of Mild Cognitive Impairment (MCI) on Marital RelationshipsWinston, Brianne L. (Virginia Tech, 2005-05-12)The purpose of this study was to examine the influence of mild cognitive impairment (MCI) on marital relationships. MCI refers to age-related decline in memory and other cognitive processes that do not necessarily interfere with daily activities or the maintenance of social relationships with others (Petersen et al., 1999). Using social exchange theory as the theoretical framework to guide this qualitative study, aspects of the marital relationship explored from the nonimpaired spouses’ perspective were couple interaction, intimacy, and the division of household labor. In-depth interviews were conducted with five husbands and five wives (M age = 76.6 yrs., S.D. = 6.64). Open-ended interview questions that focus on issues specific to the marital relationship included: (a) range of activities participated in as a couple, (b) ways of showing care or affection toward one another, and (e) management of everyday life. In addition to participating in the semi-structured interviews, the spouses completed three standardized scales (e.g., Revised Memory & Behavior Problems Checklist, Zarit Burden Interview, Center for Epidemiological Studies-Depression Scale). Their responses to these measures provided information about the memory and behavioral changes of the elder as it related to the outcomes for and responses of the spouse. Spouses noted both change and stability within their marriages. They expressed “mixed emotions” concerning the influence of MCI on both them as individuals and on their relationship. Husbands’ responses focused on the negative relationship outcomes (e.g., frustration, stress) associated with caring for a spouse with memory loss; however, wives reported higher levels of burden and depression on the standardized measures than did the husbands. Gender differences were found regarding how husbands and wives view their roles in context to the caregiving situation, as well as how they adapt and cope. Longitudinal research is needed to examine the changes in the dynamics of these late-life marital relationships over time.
- Coalition Networks and Policy Learning: Interest Groups on the Losing Side of Legal ChangeMillar, Ronald B. (Virginia Tech, 2005-12-07)Network, organizational, and policy learning literatures indicate that when interest groups face failure they will seek out alternative ideas and strategies that will enhance their potential for future success. Research with regard to interest groups and legal change has found that interest groups, using arguments that were once accepted as the legal standard for Supreme Court decisions, were unwilling or unable to alter their arguments when the Court reversed its position on these legal standards. This research project examined the conflicting findings of these literatures. Using the Advocacy Coalition Framework as a guide, this project studied the separationist advocacy coalition in cases regarding state aid to elementary and secondary sectarian schools from 1971 to 2002. The legal briefs filed by members of the separationist advocacy coalition with the Court were examined using content analysis to track changes in their legal arguments. Elite interviews were then conducted to gain an understanding of the rationale for results found in the content analysis. The research expectation was that the separationist advocacy coalition would seek out and incorporate into their briefs new and innovative legal arguments to promote their policy goals. The research results demonstrated that prior to legal change interest groups did seek out and incorporate new legal arguments borrowed from other fora and sought to expand or reinterpret established legal arguments to better aid their policy goals. The changes that seemed to have the potential for adoption by the Court were quickly incorporated into the briefs of the other members of the coalition. Following legal change interest groups continued to analyze the decisions of the Court in order to seek out the best possible legal arguments to use in their briefs; however, the main focus of legal arguments examined and used by the coalition narrowed to those cited by the swing justice in the funding cases. Two innovative arguments were developed, but were either ignored or considered unsuitable, and were not used by the other members of the coalition. Counter to this project's research expectations new and innovative legal arguments were not adopted by the coalition. As the Court discontinued the use of various legal arguments the coalition quickly responded to these changes and dropped those obsolete legal arguments. Therefore, contrary to prior research, the interest groups and the coalition altered their arguments following legal change. Only those interest groups who no longer participated in coalition discussions reverted back to using pre-legal change arguments. Learning continued to occur in the coalition following legal change; however, the focus of analysis and the pool of arguments deemed worthy of use narrowed considerably.
- Between Discipline and Profession: A History of Persistent Instability in the Field of Computer Engineering, circa 1951-2006Jesiek, Brent K. (Virginia Tech, 2006-12-13)This dissertation uses a historical approach to study the origins and trajectory of computer engineering as a domain of disciplinary and professional activity in the United States context. Expanding on the general question of "what is computer engineering?," this project investigates what counts as computer engineering knowledge and practice, what it means to be a computer engineer, and how these things have varied by time, location, actor, and group. This account also pays close attention to the creation and maintenance of the "sociotechnical" boundaries that have historically separated computer engineering from adjacent fields such as electrical engineering and computer science. In addition to the academic sphere, I look at industry and professional societies as key sites where this field originated and developed. The evidence for my analysis is largely drawn from journal articles, conference proceedings, trade magazines, and curriculum reports, supplemented by other primary and secondary sources. The body of my account has two major parts. Chapters 2 through 4 examine the pre-history and early history of computer engineering, especially from the 1940s to early 1960s. These chapters document how the field gained a partially distinct professional identity, largely in the context of industry and through professional society activities. Chapters 5 through 7 turn to a historical period running from roughly the mid 1960s to early 1990s. Here I document the establishment and negotiation of a distinct disciplinary identity and partially unique "sociotechnical settlement" for computer engineering. Professional societies and the academic context figure prominently in these chapters. This part of the dissertation also brings into relief a key argument, namely that computer engineering has historically occupied a position of "persistent instability" between the engineering profession, on the one hand, and independent disciplines such as computer science, on the other. In an Epilogue I review some more recent developments in the educational arena to highlight continued instabilities in the disciplinary landscape of computing, as well as renewed calls for the establishment of a distinct disciplinary and professional identity for the field of computer engineering. I also highlight important countervailing trends by briefly reviewing the history of the software/hardware codesign movement.
- Application of Artificial Intelligence to Wireless CommunicationsRondeau, Thomas Warren (Virginia Tech, 2007-09-20)This dissertation provides the theory, design, and implementation of a cognitive engine, the enabling technology of cognitive radio. A cognitive radio is a wireless communications device capable of sensing the environment and making decisions on how to use the available radio resources to enable communications with a certain quality of service. The cognitive engine, the intelligent system behind the cognitive radio, combines sensing, learning, and optimization algorithms to control and adapt the radio system from the physical layer and up the communication stack. The cognitive engine presented here provides a general framework to build and test cognitive engine algorithms and components such as sensing technology, optimization routines, and learning algorithms. The cognitive engine platform allows easy development of new components and algorithms to enhance the cognitive radio capabilities. It is shown in this dissertation that the platform can easily be used on a simulation system and then moved to a real radio system. The dissertation includes discussions of both theory and implementation of the cognitive engine. The need for and implementation of all of the cognitive components is strongly featured as well as the specific issues related to the development of algorithms for cognitive radio behavior. The discussion of the theory focuses largely on developing the optimization space to intelligently and successfully design waveforms for particular quality of service needs under given environmental conditions. The analysis develops the problem into a multi-objective optimization process to optimize and trade-of of services between objectives that measure performance, such as bit error rate, data rate, and power consumption. The discussion of the multi-objective optimization provides the foundation for the analysis of radio systems in this respect, and through this, methods and considerations for future developments. The theoretical work also investigates the use of learning to enhance the cognitive engine's capabilities through feed-back, learning, and knowledge representation. The results of this work include the analysis of cognitive radio design and implementation and the functional cognitive engine that is shown to work in both simulation and on-line experiments. Throughout, examples and explanations of building and interfacing cognitive components to the cognitive engine enable the use and extension of the cognitive engine for future work.
- Pathosystems Biology: Computational Prediction and Analysis of Host-Pathogen Protein Interaction NetworksDyer, Matthew D. (Virginia Tech, 2008-06-26)An important aspect of systems biology is the elucidation of the protein-protein interactions (PPIs) that control important biological processes within a cell and between organisms. In particular, at the cellular and molecular level, interactions between a pathogen and its host play a vital role in initiating infection and a successful pathogenesis. Despite recent successes in the advancement of the systems biology of model organisms to understand complex diseases, the analysis of infectious diseases at the systems-level has not received as much attention. Since pathogen related disease is responsible for millions of deaths and billions of dollars in damage to crops and livestock, understanding the mechanisms employed by pathogens to infect their hosts is critical in the development of new and effective therapeutic strategies. The research presented here is one of the first computational approaches to studying host-pathogen PPI networks. This dissertation has two main aims. First, we discuss analytical tools for studying host-pathogen networks to identify common pathways perturbed and manipulated by pathogens. We present the first global comparison of the host-pathogen PPI networks of 190 different pathogens and their interactions with human proteins. We also present the construction and analysis of three highly infectious human-bacterial PPI networks: Bacillus anthracis, Francislla tularensis, and Yersinia pestis. The second aim of the research presented here is the development of predictive models for identifying PPIs between host and pathogen proteins. We present two methods: (i) a domain-based approach that uses frequency of domain-pairs in intra-species PPIs, and (ii) a supervised machine learning method that is trained on known inter-species PPIs. The techniques developed in this dissertation, along with the informative datasets presented, will serve as a foundation for the field of computational pathosystems biology.