To see the other types of publications on this topic, follow the link: LD5655.V856 1987.S524.
Dissertations / Theses on the topic 'LD5655.V856 1987.S524'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'LD5655.V856 1987.S524.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Shakya, Keshab M. "Land use planning with multiobjective programming: a model for forest development in the hills of Nepal." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/49893.
Full textAbstract:
A land use planning model was developed for long term planning of renewable natural resources development in the Hills of Nepal. Considerable emphasis was placed upon identifying land use planning problems for the prevalent limited market economy and subsistence farming system.
A multiobjective programming model was chosen for modeling the land use planning problem. The model accommodated five objectives: namely, increasing food, fodder, and fuelwood production and decreasing soil loss and cost. A weighting technique within the multiobjective framework was developed to facilitate land use planning as a socio-political decision making process. The application of the model was demonstrated with data from Phewatal watershed.
The model generated technically efficient alternative land use plans. It also generated information on time flow of achievement levels of the objectives and their trade-offs in each alternative plan. Very few alternative plans were generated when the periodic growth rates on achievement levels of the objectives were tightly constrained. The model also provided information on periodic deficit and surplus achievements of the objectives. This information provided the guidelines for evaluating the plans.
The model provided a useful mathematical structure for analyzing land use planning as an integrated planning process coordinating multi-sectoral objectives in time and space. A foundation has been laid for constructing comprehensive land use planning models in subsistence farming economy in developing nations. The model was run on a commercially available software package and a portable personal computer. Therefore, the model can be applied in the field situation in many developing countries.Ph. D.
incomplete_metadata
2
Shands, Nancy. "The lonely voyage: support or isolation for gay men with AIDS?" Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/43893.
Full textAbstract:
Twenty-five gay men, 20 with Acquired Immune Deficiency
Syndrome (AIDS) and 5 with either AIDS Related Complex (ARC)
or who tested positive for the AIDS virus, were asked in
semi-structured interviews whether they felt supported or
isolated. Areas covered included society in general,
employment, housing, health care, insurance, religion,
families of origin, ex-wives, children, friends and lovers.
Subjects indicated that fear of AIDS, homophobia, and death
anxiety were all present in certain circumstances, but there
was no attempt to differentiate between these three possible
causes of social isolation in this exploratory study.Master of Science
3
Shalev, Doron. "Prediction model for the onset of edge-effect delamination at holes in composite laminates." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/81007.
Full textAbstract:
Composite laminates are prone to delamination at free edges, straight edges or at holes, due to the mismatch at interfaces where two adjacent plies have different fiber orientations and/or different material properties. The linear analysis of the mismatch at the edge results in a mathematical singularity. That phenomenon occurs in a boundary layer and has to be treated mathematically and physically as such. In the literature it is called the "Boundary Layer Effect" or simply the "Edge Effect". It is of great importance to recognize and be able to predict delamination locations at edges prone to such events. The goal of this research was to create a model capable of providing such a prediction. In an effort to generalize the model, the more complicated case of a free edge at holes in the composite laminate was chosen rather than the case of a straight free edge.
A sequel of three major efforts was completed: 1) Development of the analysis of the free-edge effect at a hole in a composite laminate, 2) Performance of an extensive experimental program to provide data for the creation of the prediction model, and 3) On the basis of the analysis, establishment of the model, and comparison with the experimental results.
The prediction model consists of two major products of the analysis, the order of the singularity and the strain energy release rate. Both are useful in locating the interface most prone to delaminate and the point along the hole circumference where it initiates.
Two material systems (AS4/3501-6 and AS4/1808) and two stacking sequences [(0/45/0/-45)s)₄] and [ (0/45/90/-45)s)₄]s , quasi-orthotropic and quasi-isotropic respectively, were quasi-statically tested under tension and compression. The specimens were X-rayed after each loading stage in order to locate the initiation of delaminations. The fact that both materials consisted of the same type of fibers, was an excellent opportunity to examine the performance of the matrix and its influence on the process of delamination. Matrix dependent behavior was successfully examined and studied through the experiments and the prediction model. Results showed good correlation and high sensitivity to the type of matrix material involved.Ph. D.
4
Skiles, Jean Ann. "Chromic acid anodized Ti-6Al-4V: its characterization and its single lap bond strength to heat resistant adhesives." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53661.
Full textAbstract:
Anodized Ti-6Al-HV/adhesive bonds exhibit improved corrosion resistance and a higher strength-to-weight ratio compared to conventional metal bonding techniques for primary and/or secondary structural applications. This work was conducted to identify chromic acid (CA) anodization and bond process conditions which produced durable, structural anodized Ti-6Al-4V/heat resistant single lap bonds and to understand why these conditions were necessary. A structural single lap bond was defined as a bond tested at 298K ≤ 0.5 month after bonding and with a strength ≥ 6.9 MPa, based upon values reported in structural adhesive manufacturers' product literature. A durable, structural single lap bond was defined as a bond with a strength ≥ 6.9 MPa strength at 298K after 9 months aging at 433K. Heat resistant adhesives tested had reported service temperatures ≥ 423K, and were: polysulfone; eolyethersulfone; polyphenylquinoxaline; polyetherimide, both unfilled and 20% glass filled; and 50% calcium carbonate filled polyimide.
Hydrofluoric acid (HF) added to the CA anodization solution was necessary to produce structural bonds. CA/HF oxide was more porous, and thicker than the CA anodic oxide (140 nm vs. 20 nm), perhaps promoting physical and oxide/adhesive interphase mechanical interlock. Structural, durable CA/HF anodized Ti-6Al-4V-adhesive bonds were produced for all adhesives tested except for the filled polyimide (5.5 MPa). The filler may have occluded oxide pores and prevented optimal adhesive/oxide interphase interlock, and there may have been competition of polyimide for calcium carbonate filler and for oxide. Average oxide thickness values of 65 to 410 nm did not affect bond strength; structural bonds were produced in all cases. CA/HF initial current density of 20 Amperes per square meter produced 33% stronger polysulfone bonds than 30 Amperes per square meter. Polysulfone microstructure may have been chemically degraded by the unnecessarily high fluoride concentration in the oxide from the higher current density. Lica® 44 titanate primer did not significantly influence bond strength or durability, except when unfilled polyetherimide was the adhesive. Polyphenylquinoxaline bond processing influenced bond strength. Structural bonds resulted for all the CA/HF anodization and process conditions described above. Single Iap bond fracture initiated in the adhesive (polymer) fillet. Fracture propagation in the bond overlap was through the polymer/anodic oxide interphase and/or cohesively in the polymer.Ph. D.
5
Shull, Bruce Colin. "Molecular cloning and analysis of the genome of bovine parvovirus." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/49895.
Full textAbstract:
The genome of bovine parvovirus (BPV) has been cloned by blunt end ligation of double-stranded virion DNA into the plasmid pUC8. The resulting genomic clones were infectious after transfection into bovine fetal lung (BFL) cells. Sequencing of the plasmids demonstrated that deletions were common at both ends of the cloned BPV genome. Deletions of up to 34 bases at the 3’ end lowered but did not abolish infectivity, while a deletion of 52 bases eliminated infectivity, End label analysis demonstrated the repair of deletions of up to 34 bases at the 3’ end or 35 bases at the 5’ end to the wild type length. Mutually inverted sequence orientations of the palindromic termini, known as the flip and flop forms, can occur during replication of parvovirus DNA. Cloning of BPV terminal sequences permitted the identification of the 3’ flop sequence inversion as a natural component of BPV DNA. This is the first report of sequence inversions within the 3’ end of an autonomous parvovirus. Clones with the 3’ flop or flip conformations were equally infectious. Wild type virion DNA was shown to have predominantly the 3’ flip conformation but a significant amount of 3’ flop was also detected. At the 5’ end, both the flip and flop sequence conformations were identified in nearly equal amounts. The progeny virion DNA from transfection of genomic clones had the same ratio of flip to flop as did wild type at both the 3’ and 5’ ends, regardless of the starting terminal conformations of the genomic clone. These data suggest that, while sequence inversion occurs at both termini during BPV DNA replication, some mechanism exists for the preferential replication of the 3’ flip conformation. Replicative form DNA from BPV infected cells had the same ratio of flip and flop at each end and the same termini as virion DNA. A set of deletion and frameshift mutants affecting each of the coding regions of BPV was constructed using one of the genomic clones. None of these mutants was infectious when transfected into BFL cells, which demonstrates that all three of the major open reading frames are essential for the production of infectious virus.Ph. D.
incomplete_metadata
6
Sherertz, Peter Chamness. "Catabolic substrate utilization patterns: varying humidity and dietary regimens in the American cockroach Periplaneta americana (L.) (Dictyoptera: Blattidae)." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/71182.
Full textAbstract:
Changes in metabolic substrate utilization patterns resulting from exposure to varying humidity and dietary regimens were examined in the adult, male American cockroach. A series of respirometric experiments were conducted to monitor changes in respiratory quotient (RQ), oxygen quotient (QO₂), food and water consumption and body weight. Also, a series of radiolabel experiments, utilizing injected ¹⁴C-glucose and ¹⁴C-palmitic acid, were conducted to determine radiolabel content (after exposure to varying humidity and dietary regimens) in whole body, feces, ¹⁴CO₂, hemolymph, fat body tissue and cuticle. The results of these two series of experiments were compared to determine the overall effects of humidity and diet on catabolic substrate utilization pattern changes in the American cockroach.
In these experiments, variation in dietary regimens appeared to play a more significant role than humidity variations with respect to significant differences observed in insect RQ, QO₂, body weight and radiolabel incorporation in whole body, ¹⁴CO₂ , hemolymph, and fat body tissue. However, humidity significantly affected radiolabel incorporation in fat body tissue in the glucose experiments and ¹⁴CO₂ in the palmitic acid experiments.
RQ and QO₂ data from the respirometric experiments and ¹⁴CO₂ data from the radiolabel experiments suggested that cockroaches deprived of food, but provided water to drink, change their metabolic substrate utilization pattern from initial catabolic substrates such as carbohydrates to lipid-based substrates. Also, cockroaches deprived of either water (FO) or food and water (OO) appeared to change metabolic substrate utilization patterns toward carbohydrates, but the final carbohydrate metabolic substrates are still unknown.
Cockroaches provided water, but no food, showed a change from initial RQ values (low humidity OW = 0.92 and medium humidity OW = 0.86) to terminal RQ values (low humidity OW = 0.71 and medium humidity OW = 0.68) representative of lipid-based substrate metabolism. There was also an unexplained decrease in QO₂ (initial low humidity OW = 0.45 ul/mg/hr and terminal low humidity OW = 0.28 ul/mg/hr; initial medium humidity OW = 0.35 ul/mg/hr and terminal medium humidity OW = 0. 30 ul/mg/hr). Also, cockroaches deprived of water (FO) or food and water (OO) showed an overall experimental rise in RQ values (initial low humidity FO = 0.87; and terminal low humidity FO = 0.87; initial medium humidity FO = 0.82 and terminal medium humidity FO = 0.85: initial low humidity OO = 0.79 and terminal low humidity OO = 0.88; initial medium humidity OO = 0. 75 and terminal medium humidity OO = 0.87). In addition, these same insects showed an overall experimental increase in QO₂ (initial low humidity FO = 0. 34 ul/mg/hr and terminal low humidity FO = 0.43 ul/mg/hr; initial medium humidity FO = 0.45 ul/mg/hr and terminal medium humidity FO = 0.49 ul/mg/hr: initial low humidity OO = 0.37 ul/mg/hr and terminal low humidity OO = 0.53 ul/mg/hr; initial medium humidity OO = 0.32 ul/mg/hr and terminal medium humidity OO = 0.45 ul/mg/hr), and in the radiolabelled glucose study OO insects showed an almost complete cessation of ¹⁴CO₂ release at 2 days (d). Terminal body weights differed significantly among cockroaches provided with both food and water (controls = FW), only water (OW), only food (FO) and no food or water (OO). Insects deprived of either water (FO) or food and water (OO) had significantly lower terminal body weights than those insects provided either water or food and water. Whole body water content increased and dry weight decreased in insects provided only water to drink.Ph. D.
7
Sind, Paula M. "The effects of structural and overlay design parameters of membrane switches on the force exerted by users." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54421.
Full textAbstract:
Two experiments were conducted to evaluate the effects on applied force of structural design parameters and feedback conditions inherent in the aesthetic overlay of membrane switch touchpads. In the first experiment, which evaluated structure, 12 males and 12 females keyed 100 4-digit sequences into a computer using 6 of a total of 12 touchpads which differed in membrane ply thickness, spacer thickness, and spacer aperture diameter. The same task was completed by nine males and nine females in the second experiment, which evaluated feedback conditions inherent in flat, embossed, domed, embossed with dome, flat with escutcheon, and domed keycap aesthetic overlays.
The apparatus employed for force measures was a force platform system integrating seven strain gauge force transducers. Subjects received auditory feedback for correct actuations.
Results of the studies indicate that applied forces are correlated quite highly with the required actuation force (RAF) of the switch (r = 0.89, p < 0.01). However, membrane switch structure had a significant effect on the applied forces, even after the effects of RAF were controlled. Feedback conditions inherent in the aesthetic overlay also had an effect on the forces applied. A significant preference for RAF was found in the structure experiment. There were no significant differences among touchpads with respect to preference for feedback conditions inherent in different aesthetic overlays.Ph. D.
8
Shagena, Elizabeth C. "Comparison of packed and wide-bore, open-tubular gas chromatographic columns." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45896.
Full textAbstract:
Wide-bore, fused-silica capillary columns can be an excellent replacement for packed columns in many cases. They can provide higher surface inertness and thermal stability, as well as higher efficiency or speed of analysis. Wide-bore, open-tubular (WBOT) columns with thick films have higher sample capacities than conventional narrow-bore capillary columns and can be used in unmodified packed-column gas chromatographs.
The majority of gas chromatographic analyses are still performed using packed columns. Many chromatographers associate open-tubular columns exclusively with split injection, often perceived as less repeatable or quantitative. Also, many packed-column methods use application-specific stationary phases which are not readily available on capillary columns. WBOT columns with standard phases can often be substituted due to higher available efficiencies. While several studies have been published on qualitative differences, there is little comparative quantitative data available on O.53â mm I.D. and packed columns.
Master of Science
9
Shah, Mahesh. "A heuristic method for the optimal design of water distribution systems." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/88600.
Full textAbstract:
The water distribution system design problem consists of finding a minimum cost combination of network layout and sizes of system components so as to satisfy flow demands, minimum and maximum head requirements and a reliability criterion. A two step procedure is proposed to find a near optimal design. The first step considers obtaining a near optimal tree layout using a heuristic tree search algorithm. Two different methods are followed for the tree search - one for single source networks and the other for multiple source networks. The second step adds loop forming redundant links to the tree layout in such a way that every demand node has two paths from source node(s). The methodology is applied to a single source network and a multiple source network. In both the cases better results arc achieved than those obtained previously by other researchers.Master of Science
10
Shappell, Nancy W. "Calcium: some aspects of subcellular accumulation and distribution in milk." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/81003.
Full textAbstract:
Distribution and bioavailability of ⁴⁷calcium in milk labeled by extrinsic and intrinsic methods was investigated. Milk from Sprague Dawley rats was labeled by both methods, and milk from a cow was labeled by the extrinsic method. Retention of ⁴⁷Ca from milks administered to young male Sprague Dawley rats was determined through whole body counting for 6 days after administration of milk. Percent of ⁴⁷Ca dose retained was 72% for extrinsically labeled cow milk, 62% for extrinsically labeled rat milk, and 55% for intrinsically labeled rat milk. Samples were fractionated by ultracentrifugation and by gel exclusion chromatography. ⁴⁷Calcium distributions in rat milk labeled intrinsically or extrinsically were similar. The majority of ⁴⁷Ca was found in a particulate, > 30,000 molecular weight fraction (about 60% for cow milk, about 90% rat milks). The amount of milk calcium retained by rats appeared to be related to the amount of noncasein micelle-associated calcium.
When administered by intraperitoneal injection into rats, ⁴⁵Ca specific activity of milk peaked in 60 to 90 minutes. Specific activity was highest in cytosol, and lower in Golgi apparatus and rough endoplasmic reticulum. Specific activities in subcellular fractions changed in parallel with specific activities of milk. Rapid turnover of Ca was observed in endoplasmic reticulum and Golgi apparatus; this was expected since secretory proteins and associated Ca are transported through these organelles for secretion.
In vitro ⁴⁵Ca accumulation was compared in Golgi apparatus and endoplasmic reticulum from liver and mammary gland of lactating Dunkin Hartley guinea pigs. In the presence of ATP, highest accumulation per unit total fraction protein was found in Golgi apparatus (mammary gland 28% of available ⁴⁵Ca, liver 11%) while 8% was accumulated by endoplasmic reticulum fractions. Calcium accumulation was not the result of binding, as preincubation of vesicles with calcium ionophore resulted in less than 10% of the accumulation found without ionophore. The ATPase inhibitor sodium orthovanadate, and the ATP analog AMP-PNP, reduced ⁴⁵Ca accumulation in all fractions. Protonophore caused a small reduction in ⁴⁵Ca accumulation in all cases. Citrate accumulation by fractions was not observed under conditions used for ⁴⁵Ca accumulation.Ph. D.
11
Shilts, Lee G. "Adolescent substance use and family dynamics." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/77837.
Full textAbstract:
The purpose of this research project was to explore the family structural variables of cohesion and adaptability as well as extracurricular activities, peer influences, and personal attitudes as they were manifested in adolescents classified as nonusers, users, and/or abusers of alcohol/drugs. Two hundred and thirty-seven adolescents responded to written questionnaires including the Alcohol and Drug Use Index, a reduced form of the Family Adaptability and Cohesion Evaluation Scales (FACES III), the Student Attitude and Behavior Questionnaire, and a Demographic Questionnaire. Information was obtained on age and grade level, gender and ethnicity, parental characteristics, and student's educational aspirations in an effort to identify factors associated with teenage alcohol/drug use. Some of the major findings suggested that the users/abusers groups reported less involvement with their families, educational pursuits, and extracurricular activities when compared to their nondrug using counterparts. The statistical analysis also confirmed some aspects of structural family therapy theory and refuted other aspects. The results of this study were also compared to prior research on adolescent substance use. These results further expanded the understanding of factors associated with adolescent use/abuse of alcohol/drugs.Ph. D.
12
Shankaranarayanan, N. K. "Mode-mode interference in optical fibers: analysis and experiment." Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45891.
Full textAbstract:
Interference between the modes of an optical fiber generates specific mode (intensity) patterns which get modulated by disturbances in the optical fiber system. Mode-mode interference has been analyzed from first principles and a model based on differential phase modulation presented. Mode-mode interference effects such as intensity modulation of the mode patterns are directly related to differential phase modulation between modes which arises due to the difference between the propagation constants of the constituent modes. Practical implementation of modal methods involves selective launching of modes and processing of the output pattern to demodulate the information.
Axial strain has been chosen as the modulating mechanism in experiments designed to quantify mode-mode interference effects. Quasi-statically varying strain as well as vibrational strain was used to study 'dc' and 'ac' mechanisms. Specific mode combinations have been excited and their radiation patterns identified. Mode pattern changes have been described. Experimental observations and results correlate very well with analysis.
Master of Science
13
Shankar, Uday J. "Singular-perturbation analysis of climb-cruise-dash optimization." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/45736.
Full textAbstract:
The method of singular-perturbation analysis is applied to the determination of range-fuel-time optimal aircraft trajectories.
The problem is shown to break down into three sub-problems which are studied separately. In particular, the inner layer containing the altitude path-angle dynamics is analyzed in detail. The outer solutions are discussed in an earlier work.
As a step forward in solving the ensuing nonlinear two-point boundary-value problem, linearization of the equations is suggested. Conditions for the stability of the linearized boundary-layer equations are discussed. Also, the question of parameter selection to fit the solution to the split boundary conditions is resolved. Generation of feedback laws for the angle-of-attack from the linear analysis is discussed.
Finally, the techniques discussed are applied to a numerical example of a missile. The linearized feedback solution is compared to the exact solution obtained using a multiple shooting method.Master of Science
14
Sharony, Yaakov. "Control of flexible spacecraft during a minimum-time maneuver." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/77834.
Full textAbstract:
The problem of simultaneous maneuver and vibration control of a flexible spacecraft can be solved by means of a perturbation approach whereby the slewing of the spacecraft regarded as rigid represents the zero-order problem and the control of elastic vibration, as well as of elastic perturbations from the rigid-body maneuver, represents the first-order problem. The zero-order control is to be carried out in minimum time, which implies on-off control. On the other hand, the perturbed model is described by a high-order set of linear time-varying ordinary differential equations subjected to persistent, piecewise-constant disturbances caused by inertial forces resulting from the maneuver. This dissertation is concerned primarily with the control of the perturbed model during maneuver.
On-line computer limitations dictate a reduced-order compensator, thus only a reduced-order model (ROM) is controlled while the remaining states are regarded as residual. Hence, the problem reduces to 1) control in a short time period of a linear time-varying ROM subject to constant disturbances and 2) mitigation of control and observation spillover effects, as well as modeling errors, in a way that the full modeled system remains finite-time stable.
The control policy is based on a compensator, which consists of a Luenberger observer and a controller. The main features of the control design are: (1) the time-varying ROM is stabilized within the finite-time interval by an optimal linear quadratic regulator, (2) a weighted norm spanning the full modeled state is minimized toward the end of the time interval, and (3) the supremum"time constant" of the full modeled system is minimized, while (1) serves as a constraint, thus resulting in a finite-time stable modeled system. The above developments are illustrated by means of a numerical example.Ph. D.
15
Shelhamer, Susan Smith. "An evaluation of a summer migrant education program." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/51931.
Full textAbstract:
The purpose of this study was to investigate the relationships between school-related behaviors of migrant students enrolled in a summer program and selected factors in the home and school which may interact with academic performance.
The research strategy utilized three components to address the research questions: an ethnographic study of selected students, teachers and personnel; a teacher survey with achievement data on students; and paired student-parent interviews.
The research questions to be addressed were: (a) What educational needs were reported for migrant students by school personnel and parents? (b) what was the cultural and psychological context of the school for migrant students? (c) How did the educational values of migrant parents and students relate to academic performance and school philosophy? (d) For a migrant population, did the study habits relate to academic performance? (e) what was the relationship of English proficiency to academic performance? (f) what were the strengths and weaknesses of the program as reported by parents and program personnel and as reported through research observations?
Crosstabulations and frequencies were used to report interview data. The quantitative component utilized a regression analysis and the Developmental Research Sequence was used for ethnographic analyses.
The findings of the study indicated that the summer migrant education programs of Virginia were facilitating the pursuit of education through their programming by providing positive academic experiences. Students exhibited academic gains. In addition, the programs provided an important social function by offering full day programs and individualized health-related services. There was a lack of parental involvement that would "personalize" the program for each family if nurtured. The components of the evaluation design provided for input from a variety of sources for program improvement.Ed. D.
16
Smith, David Gilman. "Determination of chloride diffusion constants for concretes of differing water to cement ratios and admixtures." Thesis, Virginia Tech, 1988. http://hdl.handle.net/10919/43056.
Full textAbstract:
Reinforced concrete exposed to chlorides is subject to
rapid deterioration once the concentration of the chloride
ion in the concrete reaches a critical level to cause
corrosion of the reinforcing steel. The chloride ion diffuses through concrete according to Fick's Law, which is a function of time, a driving concentration, and a diffusion constant. The diffusion constant varies with temperature and
the variety of concrete .
The research included determination of diffusion
constants for six types of concretes after 8 weeks and 16 weeks of ponding with an NaC1 solution. In addition, one set of these samples was subjected to the outside environment
while the other was indoors under controlled conditions. The mixes included water to cement ratios of 0.35, 0.40, 0.45, and 0.50, and two water to cement ratios of 0.45 with 15%
cement replacement with pozblan admixtures (silica fume and
type'F flY ash). Thus, the effects of temperature, water to cement ratio, and pozzolanic admixtures in regard to the diffusion constant for concrete were found.
The method by,which a diffusion constant was found is as 1)X3% solution of-NaC1 is ponded on top of a four
inch thick 'specimen of concrete. 2) Powder samples of the
paste are taken at specified time at depths of -0.5, 1.0
1,:5, and 2-.5 inches. 3) These samples are analyzed for
chloride content by potentiometric titration. 4) The data is
fit to Fick's Law by nonlinear regression and an effective
diffusion constant determined.Master of Science
17
Affholter, Kathleen. "Synthesis and crystal chemistry of lanthanide allanites." Diss., Virginia Tech, 1987. http://hdl.handle.net/10919/37332.
Full textAbstract:
Metamictization and complex chemistry are major obstacles to the crystal chemical characterization of natural allanites. To overcome these problems, allanites, Ca(REE)Fe²+Al₂Si₃O₁₂(OH), where REE = La, La-Ce, Ce, Nd, Sm, Eu, Gd, Er, Dy, Yb and Y have been synthesized hydrothermally from unbuffered and buffered oxide mixes at 500 to 650°C, 5.5 kbar (550 MPa), and 700 to 725°C, 4 kbar (400 MPa). Although allanite is readily synthesized, high yields are obtained only for allanite-(LREE) compositions, and end"member composition is obtained only for allanite-(La). Er and Yb ions are too small to substitute at the A(2) site in allanite, but a small amount can substitute at the VI~coordinated M(3) site. Fe²+ in the M(3) site favors LREE substitution, which supports the contention that allanite is Ce'selective.Ph. D.
18
Broske, Alan D. "Investigations utilizing mono- and difunctional organo alkali metal initiators for anionic polymerization." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/74760.
Full textAbstract:
This work focused on the formation and the subsequent use of a difunctional organolithium as an anionic polymerization initiator for primarily diene monomers. The initiator was formed in nonpolar solvent such as cyclohexane and toluene by the addition of two equivalents of sec-butyllithium to one of the nonconjugated diene 1,3-bis(α-phenylethenyl)benzene.
The disappearance of the starting diene was easily followed by UV/Visible spectroscopy. Rate expressions were evaluated based on the assumptions of a consecutive reaction mechanism and association behavior of the alkyl lithium. Arrhenius behavior was observed and an activation energy of 19 Kcal/mole was determined.
Unlike the spectroscopic techniques, gas chromatography was able to separate the unreacted diene, mono-, and diaddition products but dramatic increases in sensitivity were realized by using a capillary column techniques, thus allowing the direct analysis of initiator solutions that were routinely used for high molecular weight polymerizations. Quantitative determination of all reaction components confirmed the existence of a consecutive reaction mechanism for this addition and the data strongly suggested that the second rate constant was an order of magnitude faster than the first in cyclohexane.
Using the chromatographic technique to monitor initiator formation, the dianionic diaddition product was maximized by the simple addition of more sec-butyllithium. Polydiene homopolymers were then routinely prepared with predictable molecular weights and narrow polydispersities. Successive addition of isoprene and styrene resulted in triblock copolymers that incorporated both monomers over a wide compositional range. Novel triblock systems that contained t-butyl methacrylate end blocks and an isoprene center block were prepared by addition of THF which facilitated the efficient crossover.
A new trialkyl sodium magnesiate initiator was evaluated as an alternative to alkyllithiums for the polymerization of vinyl and cyclic monomers. Homopolymerizations of isoprene and styrene showed slow initiation rates and uncontrollable molecular weights relative to sec butyllithium. This initiator also polymerized methyl methacrylate in high yields without modification of its basicity and steric bulk.Ph. D.
19
Singh, Yash Pal. "Finite element analyses of cellular cofferdams." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/49896.
Full textAbstract:
Cellular cofferdams have primarily been used as temporary systems which serve to allow construction of facilities in open bodies of water. Applications for these structures have been increasing and today they may serve as permanent retaining walls or as navigation or waterfront structures. Conventional design methods for cellular cofferdams are based on semi-empirical approaches largely developed in the 1940s and 1950s. None of the available traditional procedures are capable of predicting cofferdam deformations, a parameter of key importance to the cofferdam performance, and which is often observed during construction for purposes of safety monitoring. Also, there is evidence that much of the conventional design technology is conservative, in some cases predicting loading by more than twice that which actually occurs. Recently, the finite element method has shown promise as a tool which can be used to help resolve some of the outstanding problems with cofferdam design.
There are three primary objectives of this work: (1) enhance existing finite element program to allow for more accurate and refined analysis of cellular cofferdams, (2) use the enhanced finite element programs to assess the degree of conservatism in conventional design methods for cofferdams founded on sandy soils, and (3) use the results of parametric studies of cofferdams founded on sandy soils to develop a simplified procedure to predict cofferdam movements and determine potential for internal failure. The first of the objectives involves adding better bending elements to the program SOILSTRUCT to represent the sheet pile system In axisymmetric and plane strain analyses. Also, in the case of the plane strain program, a new method is developed to allow shear transfer through the sheet pile system. Through case history and theoretical analyses, the enhanced programs are demonstrated to yield accurate and realistic results.
Parametric studies using the axisymmetric program show that conventional design methods overpredict, in some areas strongly, the interlock forces which develop during filling of the cofferdam. Parametric studies using the plane strain program suggest that there is also considerable conservatism in design methods to predict internal stability of the cofferdam. A new, simplified method is proposed for this type of analysis. In addition, it is shown that the deformations of cofferdams on sand follow consistent trends and can be set into a nondimensionalized context which can be used to predict future cofferdam movements.Ph. D.
incomplete_metadata
20
Shafer-Millsap, V. C. "A comparative analysis of the heart rate-oxygen consumption relationship observed during Bruce protocol graded exercise stress tests and steady-state exercise." Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/90958.
Full textAbstract:
Twenty-eight endurance trained male volunteers, 18-41 years or age, were studied to determine whether the heart rate-oxygen consumption relationships observed during Bruce protocol stress tests were similar to those observed during steady-state exercise. In addition, maximal oxygen consumption and maximal heart rate values obtained during the stress tests were compared to predicted values.
The heart rate-oxygen consumption relationship observed during the stress tests was dissimilar from the relationship observed during the steady-state exercise tests. Heart rate was round to be significantly higher during the stress tests. No significant difference was round in predicted maximal oxygen consumption and maximal heart rate and actual values obtained during the stress tests.M.S.
21
Mullins, Terry W. "A coal camp and its classroom: a historical study of a Virginia coalfield community and its school 1888-1987." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/38764.
Full text
22
Chyi, Kwo-Ling. "Relationships between crystal structure, bonding and thermal stability of amphiboles." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/87181.
Full textAbstract:
The complexities in structure and chemical composition of the amphiboles and the wide range of their occurrence suggest that the amphiboles are potential index minerals for the physical conditions of their formation. Hydrothermal stability studies of several amphibole endmembers have demonstrated that the FeMg₋₁ substitution produces a wide spread in thermal stability. The crystal structure, upon substitution, responds to the differences in cation size and site occupancy, but the changes are small.
In order to correlate the observed stability variation with the observed differences in crystal structure of amphiboles, structure parameters as well as calculated bond strengths, Madelung site energies, and average bond overlap populations obtained from Extended Hückel Molecular Orbital (EHMO) calculation for different cation sites, were examined. Among the examined structural parameters, calculated Madelung site potentials, and bond strength, only the parameters involving bonds between the M(1)- and M(3)-cations with OH show higher correlations with the thermal stability as compared to those of the M(2)- and M(4)-cations. This reflects the dehydration nature of the amphibole break-down reaction, since the OH bonding with seems important in controlling the thermal stability.
Infrared absorption spectra of amphiboles show the fine structure of the hydroxyl group. The frequency of the absorption band is related directly to the strength of the OH bond. Positive correlations exist between thermal stability and OH-stretching frequency for different amphibole end-members at different temperatures. For epidote minerals, as well as for muscovite and phlogopite, high OH-stretching frequencies also correlated with the minerals having higher thermal stability. These correlations indicate that the thermal stability of many hydrous minerals may be significantly related to the localized force field around the OH bond.
The crystal structure of grunerite Klein No. 9A has been refined and compared with grunerite Klein No. 1 (Finger, 1969) and cummingtonite (Ghose, 1961; Fisher, 1966). The results show that the substitution of Fe for Mg into the cummingtonite-grunerite structure not only enlarges the octahedral layer but also affects the size of the T(1) and T(2) tetrahedra and thus increases strain on the octahedral and tetrahedral linkage. The high thermal expansion of the octahedral layer and the negligible effect of heating on the tetrahedral layer substantially increase the strain on the structure. This may also explain why the Fe-rich end member decomposes at a lower temperature than its Mg-analogue, the structure of which can accommodate the build-up of strain with increasing temperature.Ph. D.
23
Bender, Holly S. "The actions of gossypol on the physiologic antioxidant defense system." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/82901.
Full textAbstract:
Gossypol , a yellow polyphenolic pigment found in cottonseeds, is known to promote the production of reactive species of oxygen in vitro, and has toxic actions on spermatogenic epithelium, hepatocytes and cardiac myocytes in vivo. Species vary in tissue sensitivity to the toxic effects of gossypol. The spermatogenic epithelium is the most sensitive tissue to gossypol in rats, followed by the liver. Toxic effects to the rat heart are found only after prolonged administration of gossypol. The antioxidant defense system that protects cells from injury by reactive species of oxygen was examined in the present study to determine a possible pathogenesis for gossypol associated tissue damage.
The concentrations of several hepatic antioxidants including catalase, glutathione peroxidase, ascorbate and copper-zinc superoxide dismutase were decreased in gossypol treated rats. Catalase, glutathione peroxidase, ascorbate and glucose-6-phosphate dehydrogenase were decreased in the testis. In contrast, antioxidants including catalase and glutathione reductase were increased in the hearts of gossypol treated rats. The selective inhibition of testis and hepatic antioxidants may account for the greater sensitivity of these organs to reactive oxygen species generated by gossypol. The rat heart may adapt to oxidative insult by inducing the production of antioxidants.
Glucose-6-phosphate dehydrogenase activity was decreased in the testis but not liver or heart of gossypol treated rats. This important enzyme is known to produce NADPH reducing equivalents for testosterone biosynthesis and the glutathione antioxidant system. In the present study, micromolar concentrations of gossypol inhibited glucose-6-phosphate dehydrogenase in a competitive manner with respect to glucose-6-phosphate. This may explain the degeneration of spermatogenic epithelium as well as decreases in serum testosterone concentrations in gossypol treated rats.
Gossypol is known to cause infertility in women and female rats. The present study found irregularities in the estrous cycles and ultrastructural changes in endometrial macula adherentes of gossypol treated female rats.Ph. D.
24
Jurek, Michael J. "Synthesis and characterization of poly(arylene ethers) and functionalized oligomers." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/80289.
Full textAbstract:
Molecular weight control and endgroup functionalization in poly(arylene ether sulfones) has been achieved by two synthetic routes. The first utilizes DMSO/sodium hydroxide and aminophenol to introduce the amine functionality. This route, though synthetically useful, suffers from serious limitations, such as hydrolytic side reactions and oxidation of the end capping reagent. An alternative route utilized K₂CO₃/NMP as base and solvent respectively. This approach has been used with great success in the preparation of both high molecular weight polymers and functionalized oligomers. We have extended this method to include amine terminated oligomers through the use of a novel aminophenolic compound 2-p-aminophenyl-2-p-hydroxyphenylpropane or MBA. The use of MBA to introduce terminal amine functionality allowed a simpler, 1-step synthesis of controlled molecular weight oligomers to be realized. Our investigations focused on bisphenol-A based systems, but this technique may be also utilized with other bisphenols.
The synthesis and characterization of a wide variety of derivatives of these functionally terminated oligomers was demonstrated. A number of potential post reactions involving these oligomeric diamines were investigated and synthetic techniques to prepare novel block and segmented copolymers were defined. As the molecular weight of the sulfone oligomer was varied, the percent sulfone character in a given polymeric material could be systematically changed. The effect was studied in block copolymers with poly(arnide sulfones) and in novel modified epoxy and bismaleimide thermosetting systems.Ph. D.
25
Preli, Rona. "Alcoholism and family structure." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/49870.
Full textAbstract:
The purpose of this research project was to explore the structural variables of hierarchical reversals, cross generational coalitions, cohesion, and adaptability as they were manifested in families with an alcoholic member, families with a recovered member, and non-alcoholic families. One hundred and twenty-five families responded to written questionnaires including The Family Adaptability and Cohesion Evaluation Scales (FACES III), the Madanes Family Hierarchy Test (MFHT), and a Demographic Questionnaire. Adult participants also completed the Michigan Alcoholism Screening Test (MAST) to ensure that control families had no potentially alcoholic members, as well as ensuring that recovered families had no actively addicted members. Information was obtained on age, ethnicity, educational employment status, family income, and the sex of participating children, to ensure that the three groups were demographically comparable. The statistical analyses confirmed structural family therapy theory and the current research on alcoholic families. The results further expanded the understanding of the nature of coalitions and hierarchical reversals as they were manifested in these samples.Ph. D.
incomplete_metadata
26
Long, Timothy E. "Anionic synthesis and characterization of alkyl methacrylate containing polymeric systems." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/74767.
Full textAbstract:
The anionic synthesis of alkyl methacrylates has received sparse attention in comparison to the synthesis of nonpolar hydrocarbon monomers such as styrene or the dienes. The two major reasons for the sluggish synthetic development of this class of polar monomers are the protic impurities present in most commercially available grades of monomer and the inherent side reactions associated with the ester functionality during anionic polymerization. However, by very carefully controlling various synthetic parameters and utilizing rigorously purified monomers, one can take advantage of the "living" nature of this polymerization to synthesize a variety of well-defined polymeric materials.
Small variations in polymerization conditions drastically affect the properties of the polymers obtained. However, the effects depend largely upon the size of the ester alkyl group involved. The subtle relationships among such variables as ester alkyl group size, polymerization temperature, polymerization solvent and initiator have been explored and are discussed. Extensive thermal, microstructural and mechanical characterization reveal very interesting effects on the resulting polymer properties.
Styrene-acrylic, acrylic-acrylic and diene-acrylic block copolymers have been synthesized demonstrating predictable molecular weights, narrow molecular weight distributions and controlled composition. These novel block copolymers preparation selective also serve as of acid- and hydrolysis excellent precursors for the ion- containing polymers. By of certain labile poly(alkyl methacrylate) esters and subsequent neutralization, metal carboxylates were introduced into a variety of block copolymers. In addition to the preparation of surfactant-like macromolecules and blend compatibilizers, novel ion-containing block copolymers were synthesized.Ph. D.
27
Lipscomb, Abigail Allen. "Alcoholism and family relations." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/77825.
Full textAbstract:
The purpose of this study was to build upon a conceptual model of the alcoholic family system. The variables investigated were: differentiation of self, as represented by quantity and quality of involvement with family of origin; and nuclear family structure, as represented by hierarchy and primary coalition types. These variables were chosen in order to provide some theoretical understanding of how alcoholism is both maintained and transmitted by family systems.
Forty-two families in which the father was an alcoholic took part in this study. Both the alcoholics and their spouses completed an abbreviated form of the Personal Authority in the Family System Questionnaire (PAFS-Q), the Family of Origin Involvement Questionnaire, and the Madanes Family Hierarchy Test. At least one child from each family also completed the Madanes Family Hierarchy Test.
Chi-square test results indicated that these families reported significant amounts of hierarchy reversal, nonmarital primacy, and nonaverage contact with family of origin. When compared to norm group scores on the PAFS-Q, alcoholic subjects and their spouses indicated more nuclear family triangulation, intergenerational fusion, and intergenerational triangulation. Pearson Product-Moment Correlation results indicated that nuclear family triangulation was related to intergenerational fusion, presence of hierarchy reversal, and nonmarital primacy. For alcoholics only, more time spent recovering, more contact with parents, nonmarital primacy, and more intergenerational triangulation were related.
These study results were interpreted as supporting a developmental model for the maintenance and transmission of alcoholism in the family. Clinical implications include the necessity of doing family of origin work with alcoholic families as well as the importance of including as many members as are willing in family therapy.Ph. D.
28
Watson, Marlene F. "Black adolescent identity development: effects of self-esteem and family structure." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/53663.
Full textAbstract:
Black adolescent identity formation was studied within the frameworks of Erikson's psychosocial theory and structural family systems theory. Ego identity was measured by the Revised Version of the EOM-EIS, an instrument based on Erikson's theoretical formulations. Family structure was measured by FACES III and a measure of self-esteem was obtained using Rosenberg's Self-Esteem Scale. It was hypothesized that a significant relationship would exist between ego identity and family structure after controlling for self-esteem and demographic variables. Two hundred thirty-seven urban black adolescents participated in the study. Multiple regression analysis was utilized to test the hypotheses in this study. The results supported a relationship between ego identity and family structure. The results further revealed a positive relationship between high family cohesion (enmeshment) and high identity which was surprising from both Eriksonian and structural perspectives. On the other hand, this finding offered support for the cultural component of ego identity and underscored the importance of recognizing strengths in family structures even if they differ from those which family theorists and clinicians expect would work best. Self-esteem was found to be a significant predictor of ego identity but failed to differentiate among the four ego identity statuses. Females reported significantly less identity diffusion than males, providing evidence that gender differences exist in ego identity development.Ph. D.
29
Rogers, Craig A. "An axisymmetric linear/high-order finite element for filament wound composite structures." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/52316.
Full textAbstract:
The development of an axisymmetric linear by high-order finite element to model filament-wound structures is presented. The primary objective of this work was to develop a ’design code' to analyze filament wound spherical pressure vessels. In order to develop a design-oriented analysis capability which can produce accurate results rather quickly with reduced input-data requirements, the total number of system equations must be reduced. To accomplish this task, a linear by high-order element was formulated which uses a single high-order displacement field finite element to model the total thickness of an axisymmetric composite structure. The displacement order for the in-plane direction remains linear, while the transverse order is user selectable. Numerical integration for stiffnesses is evaluated with respect to varying material properties and lamirna thicknesses in each individual element. Results from a computational economy study are presented showing potential time savings of 40 percent when compared to the conventional modeling scheme of using bi-linear elements. Actual test cases indicate that computation time savings may be as great as 55 percent when using linear by fourth-order elements and 45 percent when using linear by sixth-order elements. The accuracy of the element was evaluated by comparing the finite element results to elasticity solutions for isotropic, orthotropic, and filament-wound cylindrical pressure vessels. Most of the finite element results indicated a ±3 percent maximum error of the stresses compared to the elasticity results. The new linear by high order element stress results were nominally within ±2 percent of stresses calculated with conventional bilinear elements. Comparisons of finite element results for an actual filament-wound spherical pressure vessel slowed that linear by third- or fourth-order elements may be adequate for preliminary design purposes while the higher-order elements generally correlated better with the conventional bi-linear elements. Also presented is an outline of the design code and sample results for spherically wound pressure vessels.Ph. D.
30
Lynch, Larry Allen. "Bankruptcy outcome after the point of filing." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/49853.
Full textAbstract:
The subject of corporate bankruptcy has been of interest to financial academicians and practitioners alike. Researchers have directed most of their attention to accounting-based models for predicting bankruptcy filings. Although some research has attempted to estimate the probability and costs of bankruptcy, a very limited amount is centered around the outcome of bankruptcy proceedings. Specifically, little is known about the circumstances that determine whether the firm will liquidate, successfully reorganize, or become an acquisition of another firm after filing for court protection. Given the potentially large losses to both creditors and stockholders, the determinants of bankruptcy outcome should be of considerable interest. The focus of this research is threefold. First, the factors that should have an effect on the disposition of the firm after the bankruptcy filing are examined for their influence on the disposition. Second, since there is some dispute as to the appropriate classification of acquired firms, the correct classification of acquired (or merged) firms is determined. Third, the effect of a major change in the bankruptcy law is examined.Ph. D.
incomplete_metadata
31
Staples, Steven R. "A study of tenured teacher dismissals in Virginia, 1987-1990." Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-07282008-135443/.
Full text
32
Shaffer, Damon M. "Reynolds stress measurements downstream of a turbine cascade." Thesis, Virginia Tech, 1985. http://hdl.handle.net/10919/45735.
Full textAbstract:
An experimental investigation was performed to measure Reynolds stresses in the turbulent flow downstream of a large-scale linear turbine cascade. A rotatable X-wire hot-wire probe that allows redundant data to be taken with solution for mean velocities and turbulence quantities by least-squares fitting procedures was developed. This measurement technique was verified in a fully-developed turbulent pipe flow; the results show the accuracy of the probe when used in an end-flow orientation at various incidence angles and with a multiple number of angular settings.
Traverses with a single hot-wire at mid-span near the blade row exit show very high levels of turbulence locally in the blade wake near the trailing edge which quickly lessen in magnitude downstream. The rotatable X-wire was used to obtain the Reynolds stresses on a measurement plane located 10% of an axial chord downstream of the trailing edge. Here the turbulence kinetic energy exhibits a distribution resembling the contours of total pressure loss obtained previously, but is highest in the blade wake where losses are relatively low. The turbulent shear stresses obtained are consistent in sign and magnitude with the gradients of mean velocity. The mass-averaged turbulence kinetic energy accounts for 21% of the total pressure loss at this measurement plane.Master of Science
33
Sharman, Katherine L. "Application of cost benefit analysis to the expanded food and nutrition education program." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/88626.
Full textAbstract:
In 1981, President Ronald Reagan issued Executive Order 12291 which requires Federal agencies to perform benefits assessments of proposed major regulations and prohibits them from taking regulatory action unless potential benefits exceed potential costs to society.
A review of welfare economics literature and applications of the CBA model to health, education, and nutrition is presented. CBA for use in the Cooperative Extension Service Expanded Food and Nutrition Education Program (EFNEP) is then systematically examined using the following criteria: 1) theoretical considerations - can the economic criterion appropriately be applied to EFNEP?; and 2) application of the CBA model - can it be made operational?
Following the critique of application of CBA to EFNEP, conclusions are drawn as to the appropriate use of CBA or alternative techniques in evaluating EFNEP and similar programs.Doctor of Philosophy
34
Baethgen, Walter E. "Optimizing soil and fertilizer nitrogen use by intensively managed soft red winter wheat." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/74745.
Full textAbstract:
Field experiments were conducted in the Coastal Plain and Ridge and Valley regions of Virginia during the 1981-82 through 1985-86 winter wheat growing seasons. The treatments in all experiments consisted of varying amounts of N fertilizer rates applied at Zadoks' growth stages 25 (GS 25) and 30 (GS 30). The research was divided into three studies. The first study was conducted to assess the effect of N fertilizer rates and climatic conditions on the amounts and patterns of the crop N uptake. Dry matter production and total N concentration were measured in total above ground plant material at different growth stages, as well as in leaves, stems, and spikes. Plant N uptake was affected by the climatic conditions in the different growing seasons. Temperature and precipitation variations in early spring determined the differences in amounts and patterns of the N uptake by whole plants and by the various plant portions. Maximum N uptake daily rates were obtained in the period immediately after GS 30 suggesting that this is the wheat growth stage in which the highest efficiency of N fertilizer use could be expected. Crop N uptake at GS 30 also appeared to be a potentially good indicator of the plant N requirements.
The second study was designed to develop models for determining critical N levels and optimum N fertilizer rates for winter wheat. Two nonlinear models were successfully developed to determine critical N levels at GS 30 utilizing plant N concentration at GS 30 (N%30) and crop N uptake at GS 30 (NUP30). The R² values for the models utilizing N%30 and NUP30 as independent variables were 0.87, and 0.82, respectively. Simple regression models were successfully developed to predict N rates required at GS 30 to obtain either maximum or economically optimum grain yields. The models utilized NUP30 as the independent variable and had high correlation coefficients and good predicting ability.
The objective of the third study was to determine the recommended amount of N fertilizer to be applied at GS 25 that would optimize the use of the simple linear regression models developed in the second study. Quadratic programming models were developed with the objective of maximizing marginal profit with N fertilizer application. The models were then solved to determine the amounts of N at GS 25 and at GS 30 that would produce the maximum attainable profit. Four recommended nitrogen fertilizer rates at GS 25 (N25) were evaluated: 0, 30, 60, and 100 kg N ha⁻¹. The difference (D) between the yields with maximum attainable profit (Y) and the yields when N25 was forced to be 0, 30, 60, and 100 kg N ha⁻¹ (ΥR) was then calculated (D = Y - YR). The best N25 recommendation was the one that minimized the mean value, standard deviation, and coefficient of variation of D. This methodology was used for 3 nitrogen fertilizer : wheat price ratios (2.0, 4.0, and 8.0). The results indicated that the best recommendations for N25 were 50 - 60 kg N ha⁻¹ for N fertilizer : wheat price ratios of 2.0 - 4.0, and 40 - 50 kg N haha⁻¹ for a price ratio of 8.0. Sensitivity analysis was then performed to study the effect of variations in the N fertilizer : wheat price ratio on the recommended N rates. The results indicated that the recommended N rates were essentially insensitive to the variations in the price ratio of N fertilizer : wheatPh. D.
35
Liao, Chung-Li. "An incremental total Lagrangian formulation for general anisotropic shell-type structures." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/77820.
Full textAbstract:
Based on the principle of virtual displacements, the incremental equations of motion of a continuous medium are formulated by using the total Lagrangian description. After linearization of the incremental equations of motion, the displacement finite element model is obtained, which is solved iteratively. From this displacement finite element model, four different elements, i.e. degenerated shell element, degenerated curved beam element, 3-D continuum element and solid-shell transition element, are developed for the geometric nonlinear analysis of general shell-type structures, anisotropic as well as isotropic. Compatibility and completeness requirements are stressed in modelling the general shell-type structures in order to assure the convergence of the finite-element analysis. For the transient analysis Newmark scheme is adopted for time discretization. An iterative solution procedure, either Newton-Raphson method or modified Riks/Wempner method, is employed to trace the nonlinear equilibrium path. The latter is also used to perform post-buckling analysis. A variety of numerical examples are presented to demonstrate the validity and efficiency of various elements separately and in combination. The effects of boundary conditions, lamination scheme, transverse shear deformations and geometric nonlinearity on static and transient responses are also investigated. Many of the numerical results of general shell-type structures presented here could serve as references for future investigations.Ph. D.
36
Lin, Shiang-Shin. "Frequency dependent heat generation during vibrothermographic testing of composite materials." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/77822.
Full textAbstract:
This investigation concerns the frequency dependent heat generation behavior and the heat generation mechanisms for the thermal patterns of delamination in fiber reinforced composites during a vibrothermographic test, which uses real time thermography as a nondestructive evaluation of a structure or a component excited with mechanical vibration. A local resonance model was proposed in the past to describe the frequency dependent heat generation behavior during a vibrothermographic test, and this model was used as a basis for writing software for calculating the natural frequencies of a plate with the size of delamination. Vibrothermographic tests were performed on three glass-epoxy panels that each contained four different sized simulated delaminations. Comparison between the observed vibrothermal peak frequencies and the natural frequencies predicted by the local resonance model, and investigations of the thermoelastic emission field in the delamination region using SPATE, were made to determine the validity of the local resonance model. A significant conclusion of the results is that the local resonance is indeed the mechanics model for the frequency dependent heat generation behavior.
A careful measurement of the degree of heating of both sides of [0₅] glass-epoxy panel with delaminations on the 2-3 ply interface, and comparison between the predicted heat patterns generated from a finite difference heat transfer program and observed heat patterns, was made to identify the heat generation mechanism. The results show that the majority of heat generation during vibrothermographic testing results from higher stresses or strains due to local resonance. The heat generation was affected by the combination of the principal strains and shear strain for the lower modes of resonant vibration, and was dominated by the shear strain for the higher modes of resonant vibration.
Impact damaged graphite-epoxy panels were also inspected constituting an application of vibrothermography on real damaged components. The degree of heating of the damage were measured through a frequency range, and the damage severity was inspected by ultrasonic C-scan and edge replication. From comparison of two plots of the degree of heating versus exciting frequency, either the area under the curve or the number of vibrothermal peak frequencies, the severity of the damage can be qualitatively identified.Ph. D.
37
Gunter, Mickey E. "Refractometry by total reflection." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/77798.
Full textAbstract:
Refractometry is a means to measure the refractive indices of liquids, gases, and dielectric solids, either isotropic or anisotropic, by observation of light refraction or reflection with a microscope, refractometer or other more specialized equipment. For anisotropic solids, refractometry by total reflection (RTR) is by far the simplest, most rapid, and precise method to determine the refractive indices, provided a polished surface of sufficient size exists. Its precision exceeds that for routine oil immersion techniques but compares less favorably to that for minimum deviation methods. However, minimum deviation requires large crystals and, moreover, specifically oriented prisms, one for each principal refractive index to be measured and, for triclinic crystals, one for each wavelength of measurement.
The phenomenon of polarized light reflection from randomly oriented anisotropic materials has been modeled because, only after a complete understanding of these phenomena could the R TR method be automated. The mathematics and physics required for this stem from theories and equations presented in the literature of ellipsometry, polarized light, and physical optics. These were then modified, rewritten, and unified to suit the requirements of R TR.
RTR, first used by Wollaston ( l 802a, l 802b ), was later perfected for the measurement of the refractive indices and orientation of biaxial minerals in thin section (Viola l 899a, l 899b, 1902; Comu 1901, 1902). RTR with the Abbe-Pulfrich refractometer yielded refractive indices to a precision of ±0.0002, or better. Later, Smith (1905a, 1905b) introduced a simpler refractometer, now known as the jeweler's refractometer, which had a precision of ±0.001 to ±0.002. This refractometer is still in use by gemologists. During this century familiarity with the early work has declined; thus several recent papers display a lack of knowledge of aspects of R TR which were already documented in the early 1900s.
A new automated refractometer, designed by Bloss, has precision of ±0.0002 and will be able to measure the refractive indices and orientation of a biaxial mineral in a petrographic thin section. Even for triclinic crystals, a single polished surface arbitrarily oriented will suffice for measurement of all three principal refractive indices, whatever the wavelength supplied. The design and testing of this refractometer has taken approximately three years. Two prototypes have been built and tested. Results from the second prototype are presented.Ph. D.
38
Cohen, David. "Calculation of skin-stiffener interface stresses in stiffened composite panels." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/82897.
Full textAbstract:
A method for computing the skin-stiffener interface stresses in stiffened composite panels is developed. Both geometrically linear and nonlinear analyses are considered. Particular attention is given to the flange termination region where stresses are expected to exhibit unbounded characteristics. The method is based on a finite-element analysis and an elasticity solution. The finite-element analysis is standard, while the elasticity solution is based on an eigenvalue expansion of the stress functions. The eigenvalue expansion is assumed to be valid in the local flange termination region and is coupled with the finite-element analysis using collocation of stresses on the local region boundaries. In the first part of the investigation the accuracy and convergence of the local elasticity solution are assessed using a geometrically linear analysis. It is found that the finite-element/local elasticity solution scheme produce a very accurate interface stress representation in the local flange termination region. The use of 10 to 15 eigenvalues, in the eigenvalue expansion series, and 100 collocation points results in a converged local elasticity solution. In the second part of the investigation, the local elasticity solution is extended to include geometric nonlinearities. Using this analysis procedure, the influence of geometric nonlinearities on skin-stiffener interface stresses is evaluated. It is found that in flexible stiffened skin structures, which exhibit out-of-plane deformation on the order of 2 to 4 times the skin thickness, inclusion of geometrically nonlinear effects in the calculation of interface stresses is very important. Thus, the use of a geometrically linear analysis, rather than a nonlinear analysis, can lead to considerable error in the computation of the interface stresses. Finally, using the analytical tool developed in this investigation, it is possible to study the influence of stiffener parameters on the state of interface stresses.Ph. D.
39
Strganac, Thomas W. "A numerical model of unsteady, subsonic aeroelastic behavior." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/74775.
Full textAbstract:
A method for predicting unsteady, subsonic aeroelastic responses has been developed. The technique accounts for aerodynamic nonlinearities associated with angles of attack, vortex-dominated flow, static deformations, and unsteady behavior. The angle of attack is limited only by the occurrence of stall or vortex bursting near the wing. The fluid and the wing together are treated as a single dynamical system, and the equations of motion for the structure and flowfield are integrated simultaneously and interactively in the time domain. The method employs an iterative scheme based on a predictor-corrector technique. The aerodynamic loads are computed by the general unsteady vortex-lattice method and are determined simultaneously with the motion of the wing. Because the unsteady vortex-lattice method predicts the wake as part of the solution, the history of the motion is taken into account; hysteresis is predicted. Two models are used to demonstrate the technique: a rigid wing on an elastic support experiencing plunge and pitch about the elastic axis, and an elastic wing rigidly supported at the root chord experiencing spanwise bending and twisting. The method can be readily extended to account for structural nonlinearities and/or substitute aerodynamic load models. The time domain solution coupled with the unsteady vortex-lattice method provides the capability of graphically depicting wing and wake motion.Ph. D.
40
Baker, William Maurice. "The effects of accounting reports on loan officers: an experiment." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/74747.
Full textAbstract:
This experiment examines the effects of financial reporting bases (GAAP and income tax) and service levels offered by external accountants (audits and reviews) on loan officers. The effects are measured using a loan approval decision and four perceptions: (1) appropriate interest premium, (2) likelihood of default, (3) confidence in the financial report, and (4) usefulness of the financial report.
Analysis of variance techniques are used to ascertain the effects of accounting reports on the perceptions of loan officers; legit model development is used to isolate the effects on loan approval decisions. Reviews result in higher interest premiums than audits. Loan officers also associate higher default risks with reviews and tax-basis financial reports. Loan officers are most confident with audited GAAP-basis financial reports and least confident with audited income tax basis financial reports. In addition, loan officers indicate that GAAP-basis financial reports are more useful than income-tax-basis financial reports. Neither reporting basis nor service level affected their loan-approval decisions, however.
Confirmatory and exploratory factor analyses are used to develop surrogates for decision usefulness using Statement of Financial Accounting Concepts (SFAC) Number 2. The most dependable surrogate for decision usefulness developed involves two characteristics that SFAC Number 2 suggests as being nonessential to accounting information: certainty and precision. The reporting basis affected this surrogate and decision usefulness itself in the same manner; in both cases, GAAP-basis financial reports are more useful than tax-basis financial reports.
Managers, accountants, and loan officers should be aware that using income-tax-basis financial reports can detrimentally affect loan officer perceptions of default risk, confidence, and decision usefulness. Further, using a review rather than an audit may affect loan officer perceptions of confidence and interest rates.
Future research could introduce additional independent variables. These variables include the effects of a statement of changes in financial position, financial ratios, industries, or differential reporting. Research using qualitative characteristics of accounting information could lead to strong measures of decision usefulness that would be beneficial in ascertaining effects on loan-officer perceptions and decisions.Ph. D.
41
Kosenko, Rustan. "A multimethod experimental investigation of the effect of market price knowledge on acceptable price range." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/77813.
Full textAbstract:
This dissertation reports a multimethod investigation of the relationship between market price knowledge and the width of the acceptable price range. Psychophysics and Social judgment theory are discussed as supporting the existence of acceptable price thresholds (limits) and acceptable price range. Hypotheses stemming from Social judgment theory are offered directly relating market price knowledge with the width of the acceptable price range.
The relationship between market price knowledge and acceptable price range was investigated using two different methods, the Stoetzel and the Own-Category method. Unlike the previous acceptable price limit studies, this research assessed the reliability and construct validity of each of those methods.
The research design used was a laboratory experiment with a series of 2 x 2 factorials based on the Solomon 4 group-six study design. The dependent variables were: (1) the acceptable lower price limit, (2) the acceptable upper price limit, and (3) the acceptable price range. The independent variable was market price knowledge. The two-way anova design had two factors. The first factor had two levels: absence and presence of market price knowledge. The second factor consisted of two levels: pretest and no pretest treatments.
The research hypothesis was tested using (1) two-way analysis of variance, (2) analysis of covariance using sex and prior price knowledge as covariates, and (3) paired t-tests.
Test-retest reliability of the two methods were assessed using Pearson's correlation coefficient. Pearson correlation coefficients were also used to set validity coefficients. Those coefficients were used to assess construct validity of the two measures in terms of convergent and discriminant validity within the context of Campbell and Fiske's multitrait-multimethod zero-order correlation matrix.
In general, the experimental results partially confirmed the hypothesis that the acceptable price range would be narrower for subjects possessing market price knowledge than for those subjects possessing little or no market price knowledge. The results of the Stoetzel method supported the hypothesis, but the hypothesis was not supported when the same subjects used the OwnCa Category method.
The results did support the hypothesis that the two methods were valid measures of ac~eptable price thresholds with the OwnCa Category method producing higher reliability scores than the Stoetzel method. Results of the dissertation are discussed with respect to the major findings and significance to price theory and research. The dissertation concludes with a discussion of the study limitations and directions for future research.Ph. D.
42
Beets, S. Douglas. "Effectiveness of the complaint-based enforcement system of the AICPA Code of Professional Ethics." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/82900.
Full textAbstract:
The American Institute of Certified Public Accountants (AICPA) is presently considering a proposal to revise the enforcement system of the Code of Professional Ethics from the current complaint-based mechanism to a system based on reviews of practitioners and their work. Inherent within the proposal is the conclusion that the existing enforcement provisions, based on complaints about violations, are not adequate.
Complaints about ethics violations can originate from practically anyone although two of the primary initiators of violation complaints are Certified Public Accountants (CPAs) and their clients. CPAs, however, may have limited opportunities to observe violations committed by colleagues. Clients, on the other hand, may be in a prime position to detect departures from the ethics code but may have no incentive to report violations committed by their CPAs; e.g., a violation may benefit the client.
A survey of these two groups (CPAs and clients) indicated that while both groups are familiar with the code and believe that the rules of conduct are appropriate, clients do not tend to report violations and CPAs, on average, indicated that they would report observed violations slightly more than one-half the time. These findings suggest that an enforcement system based solely on the complaints of CPAs and clients cannot be effective.Ph. D.
43
Edmisten, Keith Lynn. "Fall harvest management of alfalfa." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/82643.
Full textAbstract:
Alfalfa (Medicago sativa L.) harvest schedules are often interrupted by rainfall, unfavorable environmental conditions for growth, and unfavorable weather for hay curing. Interruptions in alfalfa harvest schedules can delay the final harvest until dates considered critical to winter survival. Harvests made between 20 September and 30 October are considered detrimental to the persistence of alfalfa stands in geographical areas such as western Virginia. The objectives of this study were to determine if a critical period for fall harvest management actually exists in Virginia, if length of the growth period prior to fall harvest (GPPFH) influences plant persistence and succeeding spring yields, and if photosynthesis offsets respiration and allows more flexible fall harvest management than is currently recommended.
Final alfalfa harvests were made 10, 20, or 30 September or 10, 20, or 30 October for 2 years in two identical experiments. Alfalfa was managed to achieve 30, 40, 50, or 60 days of growth prior to each fall harvest date. Total nonstructural carbohydrates (TNC) in tap roots and population of surviving plants were determined in December and March. Succeeding spring yields were measured in May. Zero, 45, and 60 percent shade were imposed following four fall harvest dates in a supplemental study to investigate the influence of photosynthesis on TNC levels and plant persistence. In the supplemental study, CO₂ exchange and TNC were measured at 2 week intervals in the fall following four fall harvest dates.
Harvests made during the fall period previously considered as critical did not cause over-wintering plant losses. Length of growth period prior to fall harvests was more important than date of fall harvest in making management decisions for fall harvest. Although spring yield generally increased with length of GPPFH, the spring growth appeared healthy; so one might expect a few days of delay prior to the first spring harvest to eliminate any detrimental influence of short length of GPPFH. Succeeding spring yields and TNC levels were generally high for the 50-day GPPFH, and fall harvest yield offset any reductions in spring yield observed in this study. In addition, fall harvests made with a 50-day GPPFH maintained quality and leafiness as opposed to a 60-day GPPFH.
Fall regrowth and plant maintenance were not dependent on root TNC accumulation. Photosynthesis offset TNC losses for regrowth and maintenance during the fall. High photosynthetic rates as compared to respiration occurred because temperatures were within the optimum range for photosynthesis of alfalfa during 68% of the daylight hours from September through November.
There was no critical period for fall harvest management with the environmental conditions experienced during this study. A 50 or 60-day GPPFH prior to fall harvest was adequate for plant persistence and high succeeding spring yields.Ph. D.
44
Culver, Steven Michael. "Testing a model of teacher satisfaction." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/76095.
Full textAbstract:
The primary purpose of this study was to construct and test a model of the influences affecting teachers' job satisfaction. To test the model, a representative sample (N = 512) of early-career (those with less than seven years teaching experience) public school teachers in the Commonwealth of Virginia was used.
The path model proposed is a set of structural equations that consider the job satisfaction of a teacher to be a function of four exogenous variables--the teacher's sex, age, years of teaching experience, and socioeconomic status of family of origin--and three endogenous variables--the teacher' s scholastic achievement, the school climate where the teacher is employed, and the teacher's commitment to staying in teaching. Because of possible interactions caused by differing parameters between blacks and whites, the model was analyzed separately for white teachers and for black teachers.
Results of the LISREL analyses indicated that teachers' perceptions of the school climate where they are employed and teachers' commitment to staying in teaching were the two most important influences on teacher job satisfaction. For white teachers, females tended to be more committed to teaching than did their male counterparts. For the black teachers, no such distinction was evident. Also, white females tended to be more satisfied than the white males; black females tended to be less satisfied than the black males. Perhaps most importantly, the lower achieving whites tended to be more satisfied in their teaching positions than did higher achieving whites. For blacks, no differences in the effects of achievement level were noted. These differences illustrate that the process leading to teacher job satisfaction is similar for whites and blacks, but there are critical differences within the model itself in how the variables interact with one another.
Recommendations for future research include further work with broader based populations of teachers as well as follow-up with teachers now under study. A look at politically feasible ways to improve the "quality of life" for teachers is also encouraged.Ph. D.
45
Lee, Bin. "Synthesis and characterization of high performance polytetrahydrofuran based polyurethane-urea and ionene elastomers." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/80277.
Full textAbstract:
In this thesis, the effect of interphase bonding on the cohesiveness of domain structure was addressed. The interchain attractive forces between rigid segments and the phase separation between hard and soft segments have been improved by introducing either urea groups or ionic units. The urea linkages have the possibility of extensive hydrogen bonding while ionic units interact with each other by coulombic interactions, which provide even stronger interchain associations than the hydrogen bonding effects.
This thesis addressed the preparation and characterization of polytetrahydrofuran based segmented polyurethane-urea and ionene elastomers. The urea linkages were effectively introduced to the polyurethane elastomers through an unconventional route which was based on carbamate-isocyanate interactions. The carbamates were generated principally from isocyanate functional prepolymers and tertiary alcohols. The carbamates were rearranged thermally and/or catalytically to produce amines which were rapidly converted to ureas. The effects of varying the size of the rigid and flexible segments in polyurethane elastomers on physical behavior were investigated. The importance of hydrogen bonding interactions in promoting phase separation of hard and soft segments and the cohesiveness of hard segment domain structure was demonstrated. Living, difunctional polytetrahydrofuran dioxonium ions were prepared via triflic anhydride initiation. The direct coupling of these "living" polytetrahydrofuran dioxonium ions with a ditertiary amine was used to produce a novel segmented ionene elastomer. The ionenes thus synthesized displayed interesting solution behavior and could be molded, or cast to produce good physical properties. Photochromic as well as thermochromic phenomena were also noticed in these systems.Ph. D.
46
Leleno, Joanna M. "A mathematical programming-based analysis of a two stage model of interacting producers." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/77818.
Full textAbstract:
This dissertation is concerned with the characterization, existence and computation of equilibrium solutions in a two-stage model of interacting producers. The model represents an industry involved with two major stages of production. On the production side there exist some (upstream) firms which perform the first stage of production and manufacture a semi-finished product, and there exist some other (downstream) firms which perform the second stage of production and convert this semi-finished product to a final commodity. There also exist some (vertically integrated) firms which handle the entire production process themselves.
In this research, the final commodity market is an oligopoly which may exhibit one of two possible behavioral patterns: follower-follower or multiple leader-follower. In both cases, the downstream firms are assumed to be price takers in purchasing the intermediate product. For the upstream stage, we consider two situations: a Cournot oligopoly or a perfectly competitive market.
An equilibrium analysis of the model is conducted with output quantities as decision variables. The defined equilibrium solutions employ an inverse derived demand function for the semi-finished product. This function is derived and characterized through the use of mathematical programming problems which represent the equilibrating process in the final commodity market. Based on this analysis, we provide sufficient conditions for the existence (and uniqueness) of an equilibrium solution, under various market assumptions. These conditions are formulated in terms of properties of the cost functions and the final product demand function.
Next, we propose some computational techniques for determining an equilibrium solution. The algorithms presented herein are based on structural properties of the inverse derived demand function and its local approximation. Both convex as well as nonconvex cases are considered.
We also investigate in detail the effects of various integrations among the producers on firms' profits, and on industry outputs and prices at equilibrium. This sensitivity analysis provides rich information and insights for industrial analysts and policy makers into how the foregoing quantities are effected by mergers and collusions and the entry or exit of various types of firms, as well as by differences in market behavior.Ph. D.
47
Lin, Xinli. "Isolation and characterization of new pterins from nonmethanogenic archaebacteria." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/77823.
Full textAbstract:
Several new pterins have been discovered in halophilic and thermoacidophilic archaebacteria. Two of these were identified in the extreme halophiles and were thus called halopterins. One of these halopterins is produced by Halobacterium salinarium, Halobacterium halobium, and Halococcus morrhuae and is called phosphohalopterin-1. It was given this name because it was the first halopterin discovered and it has four monophosphate esters per dimeric pterin. The proposed structure of phosphohalopterin-1 is as follows. [see document for diagram of chemical structure]
The other halopterin, which is produced by Halobacterium marismortui, Halobacterium volcanii, and Halobacterial strain GN-1, is called sulfohalopterin-2 because it has two sulfate esters per dimeric pterin and it was isolated and recognized after the isolation of phosphohalopterin-1. The proposed structure of sulfohalopterin-2 is as follows. [see document for diagram of chemical structure]
As shown above, both pterins are dimers with an ether linkage connecting the polyol side chains. Both of the halopterins are negatively charged because of the phosphate and sulfate esters on the side chains. In addition to the halopterins, a positively charged pterin has been isolated from Sulfolobus solfataricus. This pterin is very special since no positively charged unconjugated pterin had ever been found in nature before. This pterin is named solfapterin after the species name of the bacteria from which it was obtained. The structure of this pterin is still unknown but the preliminary data indicate that it is an unconjugated pterin with a polyol containing an amine on the side chain. Another positively charged pterin which is different from solfapterin was found in Thermoplasma. All of the above pterins are different from any previously described pterins and thus represent new pterins in the archaebacterial kingdom.
The discovery of these new pterins is important both to pterin biochemistry and to archaebacterial taxonomy. These discoveries also open up a new field, that is, the exploration of the function of these new pterins in norunethanogenic archaebacteria.Ph. D.
48
Allen, Caitilyn. "Evolution of a gene for pathogenicity: endo-pectate lyase." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/82610.
Full textAbstract:
Erwinia carotovora subsp. Carotovora (Ecc) and Erwinia carotovora subsp. Atroseptica (Eca) are plant pathogenic bacteria that cause soft rot disease of many plant species and blackleg disease of potatoes, respectively. Ecc and Eca attack plants by means of a group of extracellular plant tissue-degrading enzymes. which rapidly breaks down the pectic polymers that form a structurally important part of the plant cell wall, is considered central to soft rot pathogenesis. In this work, I isolated and studied the genes encoding this enzyme from Ecc and Eca. A clone library of Ecc strain EC14 was constructed using cosmid PLAFR3. This library contains 2,200 clones with an average insert size of 27 kilobases of DNA and included a proteolytic clone, five cellulolytic clones, and ten pectolytic clones. The proteolytic clone was used to complement a Tn5-induced protease mutant of Ecc; the complemented mutant was restored to near-wild type phenotype. Six of the pectolytic clones hybridized to a probe from a. previously isolated extracellular endo-pectate-pectate lyase gene from Ecc; one pectolytic clone had homology to a previously isolated clone encoding endo-polygalacturonase: three clones showed no
relationship to either of the previously characterized Ecc pectolytic enzyme genes. A clone encoding the major endo-pectate lyase gene from Ecc was chosen for subcloning and further study. I used the plasmid vector pBR322 to construct a clone bank of Eca strain SRB; of the 1700 clones screened, five were pectolytic. Two of the Eca pectolytic. clones had homology to the Ecc endo-pectate lyase gene; upon examination, they proved to contain the same insert in opposite orientations. The Ecc endo-pectate lyase had a pI of 9. 5 and a molecular weight of 33,000; the analogous Eca endo-pectate lyase had a pI of 9.2 and a molecular weight of 31,000. Both enzymes required a divalent cation for activity (preferring Ca2+ over Mg2+ over Mn2+. The restriction endonuclease maps of the two clones did not have any tested sites in common. These differences suggest that although these two genes may have originated from a common ancestral gene, considerable divergence has taken place. I analyzed the fine structure of the Ecc endo-pectate lyase gene by DNA sequencing. The coding region of the gene is preceded by E. coli-type -10 and -35 sequences and encodes an unmodified protein of 281 amine acids. A typical secretion signal peptide is not present.Ph. D.
49
Cotter, Henry Van Tuyl. "The systematics and ecology of Boletes with special reference to the Genus Suillus and its ectomycorrhizal relationships in Nepal." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/74765.
Full textAbstract:
The Suillus mycota of Nepal was studied. Nine species are recognized and described; five of the nine appear to be new species. Additional species were collected, but material was inadequate to describe them completely. Cultures of eight and synthesized ectomycorrhizae of six of the Suillus species are described. Synoptic keys to the basidiocarps and to the cultures are presented. Numerical taxonomic analyses of the cultures generated clusters which paralleled the species concepts developed using basidiocarps and ecology. Each species of Suillus from Nepal is host specific based on basidiocarp formation; all hosts are in the Pinaceae. Field associations are Suillus cf. granulatus, S. cf. placidus, S. sibiricus, and greening-foot Suillus with Pinus wallichiana; queen's Suillus with P. roxburghii; waxy Suillus with P. patula; and S. laricinus, himalayan Suillus, and orange-pored Suillus with Larix himalaica. Mycorrhizal syntheses confirmed that the six Suillus-Pinus relationships are ectomycorrhizal.
The Suillus mycota of western Virginia has 12 known species. Three, of the five which are ectomycorrhizal with Pinus strobus, have closely related counterparts in Nepal. These counterparts are ectomycorrhizal with P. wallichiana, a five-needled pine closely related to P. strobus. The existence of these three pairs of similar fungi, associated with similar pines, suggests the possibility of cladogenic speciation in parallel by the pine lineage and by its ectomycorrhizal fungal associates.
Boletinellus merulioides forms abundant sclerotia in nature throughout its range in eastern North America. Sclerotia collected in the forest germinated to form mycelial colonies that had the same appearance and microscopic characteristics as colonies derived from basidiocarps. Sclerotia which had overwintered in the forest were viable in the spring.
The spatial pattern of B. merulioides sclerotia in a forest was compared with basidiocarp frequency recorded over four years. Both estimates of the spatial pattern coincided, but year-to-year basidiocarp frequency varied greatly. Individual B. merulioides dikaryons formed large perennial patches. Basidiocarp and sclerotial densities were centered around and declined outward from Fraxinus americana trees. Boletinellus merulioides and Fraxinus pennsylvanica did not form ectomycorrhizae when grown together in growth pouches.Ph. D.
50
Connaway, Melissa Clare. "Design and characterization of zeolite supported cobalt carbonyl catalysts." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/82894.
Full textAbstract:
Transition metal compounds such as Co₂(CO)₈ have often been used to catalyze various organic reactions. Severe difficulties may be encountered when attempts are made to recover and separate the soluble catalysts. A heterogeneous system consisting of Co₂(CO)₈ impregnated on zeolites with faujasitic structure has been designed and investigated using a variety of techniques. In situ FTIR spectroscopy and carbon monoxide evolution were used to identify the major products generated, namely Co₄(CO)₁₂ and Co(CO)4-. Disproportionation may be induced thus forming Co(CO)4- and an associated cation from the supported subcarbonyls by addition of various ligands such as methanol. The location of the supported cobalt carbonyls is determined by their reactivity toward various phosphines with various kinetic diameters.
The materials prepared in this manner were found to be active in catalyzing the methanol carbonylation reaction and following thermolysis were also found to be active Fischer-Tropsch catalysts. Major products observed in the carbonylation of methanol were methyl acetate and an acetaldehyde dimethyl acetal. The supported cobalt catalyst displays greater activity than Co₂(CO)₈ in solution for the carbonylation reaction when conducted under similar conditions. In the Fischer-Tropsch process, selectivity is seen for the production of linear, short-chain hydrocarbons.Ph. D.