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1
Yang, Eric Xian-Qing. "Extended describing function method for small-signal modeling of resonant and multi-resonant converters." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40173.
Full textAbstract:
The extended describing function method is proposed as a systematic small-signal modeling approach to nonlinear switching circuits. This method offers significant simplification upon the previous work on using the multi-variable describing functions to treat the circuit nonlinearities. As an extension to the statespace averaging method, this modeling technique can incorporate any Fourier components for good model accuracy and provides continuous-time small-signal models for PWM topologies and various soft-switching resonant topologies.
The proposed method is demonstrated using four resonant topologies and two multi-resonant topologies. These circuits are strongly oscillatory, and thus they cannot be modeled by means of traditional averaging techniques. By employing the proposed modeling method, the dynamics of the resonant converters are analyzed with emphasis on the nonlinear interaction between the switching frequency and the circuit natural resonant frequency. Equivalent circuit models are provided for more convenience of practical designs. Small-signal analysis is also performed for two challenging multi-resonant topologies with complex structure and operation. All of the theoretical models are verified experimentally and the predictions are well supported by the measurement data up to the Nyquist frequency.Ph. D.
2
Yang, Yaping. "Development of SiC whisker/chopped SiC fiber reinforced (Ca0.6,Mg0.4)Zr₄(PO₄)₆ ceramic matrix composites." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/38557.
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SiC whisker reinforced (Ca0.6,Mg0.4)Zr₄(PO₄)₆ (CMZP) matrix composites containing 10, 20, and 30 vol % whiskers were produced using a glass encapsulated hot isostatic pressing (HIPing) technique. The best HIPing temperature, pressure, and time conditions to optimize composite density and strength were determined to be 1050°C, 103 MPa, and 0.25 h.Ph. D.
3
Yang, Chia-Shing. "Theories, templates, and tools for designing and developing instructional hypermedia systems." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-170327/.
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Yarbrough, Walthea V. "Postural data incorporated into traditional work measurement." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-164306/.
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Yang, Lifeng. "Computer relaying for EHV/UHV transmission lines." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40085.
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As the power systems grow, system connections become more complex. Due to cost and environmental concern, more and more parallel lines and series compensated lines may be installed in the system. In order to efficiently use the transmission network, more nonlinear flexible devices such as the phase shifter and the advanced compensation system will be put into use. Once a fault occurs on such a system, a delay in clearing the fault is usually not permissive. This requires a new generation of relays which have high security and dependability and high operating speed. With the advent of high speed microprocessor and fiber optic communication technologies, it is possible to develop high performance relays. In this dissertation, a new generation of pilot relays and non-pilot relays were developed for a transmission line.
The pilot relays include the instantaneous percentage current differential (IPD), the phase comparison and the phasor based percentage current differential (PPD) principles. In the pilot protections the synchronized phasor measurement techniques are employed and digital CT saturation detectors are incorporated. All these schemes in primary protections feature charging current (or shunt current ) compensation. The phasor based principles are designed to work within one and a half cycles; while others based on sample by sample comparison are assumed to work in less than a cycle.
The non-pilot relays to be investigated in this dissertation include the fault location based and phase angle based directional distance relays. One cycle data window is used in the phasor calculation. Both the distance relays are assumed to make a trip decision in about one and a half cycles.
All algorithms were simulated against different fault conditions using EMTP outputs. The simulation results show all the pilot relay algorithms work well for EHV IUHV transmission lines including the series compensated lines. The fault location based distance relay works well in most cases, but it may give a wrong decision for the close-in fault with the fault resistance and may have a singularity problem. The phase angle based distance relay works very well for different fault conditions and is insensitive to fault resistance.
The modified phase angle based distance relay was also developed for the series compensated line. It would not lose the direction for faults with or without fault resistance, either for a compensated system in forward direction, or in an adjacent line in reverse direction. The overreach is within 20% of the protected zone. This relay algorithm is also based on the one-cycle data window DFT, and it can give a reliable trip decision in about two cycles.
All pilot relays with a fiber optic link and the phase angle based distance relay can constitute a new generation of protection systems for EHV IUHV transmission lines.Ph. D.
6
Yang, Lifeng. "A microprocessor based bus relay." Thesis, Virginia Tech, 1991. http://hdl.handle.net/10919/41506.
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A microprocessor based bus protection scheme has been proposed for a single bus system which employs a new technique to overcome the problem of current transformer saturation. The protection scheme uses a combination of the
percentage differential current principle and the phase comparison principle. A sampling rate of 1440 Hz is used. Existing algorithms for a saturation detector are reviewed and a new saturation detector has been developed. This new saturation detector employs the slope difference of the secondary current to determine the CT state. It has a high sensitivity and can reveal early (one-eighth cycle) saturation. With the incorporation of this new saturation detector, the bus relay can make a correct decision for either an internal or an external fault in the presence of current transformer saturation in a half cycle in most cases.
The bus protection scheme has been coded in Fortran and tested against data produced from EMTP. The simulated results from eight sets of data are presented in this thesis. All cases show that the bus protection scheme works correctly.
The algorithm for the new saturation detector will be implemented using a 32-bit microprocessor by Mr. Paul A. Dolloff.Master of Science
7
Yang, Won-Kyung. "The nursing home search and selection process : gender and relationship issues /." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06162009-063521/.
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Yang, Bing. "Action at a distance for specific repression of the glpD and glpTQ genes, and organization of the glpEGR genes of Escherichia coli K-12." Diss., This resource online, 1997. http://scholar.lib.vt.edu/theses/available/etd-10042006-143914/.
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Yarali, Abdulrahman. "Peak load estimation using load research data." Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/39154.
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Peak load estimation is a critical element in utility decision making. An electric utility must construct, maintain, and operate equipment sufficient to meet the peak, or maximum demand level. Electric utilities have utilized several methods of analyzing energy consumption which have yielded various levels of accuracy for estimating maximum demand.
In this research, a new method, Nonlinear Load Research Estimation (NLRE), is proposed to estimate the peak load and load characteristics of individual and group of different customer classes. Load research data is used to develop KWHr-to-KW conversion factors, diversity factors, and average time-varying load data as a function of customer class, month, and type of day. Load research data is used to derive monthly load
shapes by customer class. These profiles are used to apportion customer KWHr usage among billing cycles according to the split indicated by test data. This parsed KWHr can be further allocated based on type of day to estimate weekday and weekend peak values.Ph. D.
10
Yao, Aixiang. "Kinetic theory and global existence in Lp1s for a dense square-well fluid." Diss., Virginia Tech, 1995. http://hdl.handle.net/10919/39600.
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In this paper, we consider the kinetic equation for a dense square-well fluid and
the geometric factor Y _ 1, provide the related kinetic theory, and prove a global
existence theorem in L1 for the kinetic equation under rather general initial value
condition. An analogue of the classical H-theorem is verified.Ph. D.
11
Yang, Jian. "Prediction of the power losses of PWM inverter drives for permanent magnet synchronous motors." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-06112009-063124/.
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Yang, Jun. "Swan : a data structure visualization system /." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-06112009-063119/.
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Yang, Jae-Guen. "Lateral bracing forces in compressed two-span columns with initial curvature." Thesis, Virginia Tech, 1991. http://hdl.handle.net/10919/41515.
Full textAbstract:
The main purpose of this study is to find critical loads and full bracing conditions for perfect two-span columns, and to find the reaction forces at the lateral bracing supports and maximum deflections for two-span columns with initial curvature. In each case, the column under consideration may have different bending stiffnesses in each span, and the column is subjected to an axial compressive load. The braces are not assumed to be equally spaced, and may have different spring stiffnesses.
For the perfect columns, it is found that if the internal lateral support is located in the middle of the column , the column can resist a higher applied load than for any other support location. The load resisting capacity of the column depends on the lateral spring stiffness. It is also found that an ideal spring stiffness, corresponding to full bracing, only exists under special conditions.
For the imperfect columns, the initial shape is assumed to be the same as the buckling mode of the perfect column, and its size is specified. It is found that there are no reaction forces when there is full bracing. The reaction forces and maximum deflections are proportional to the size of the initial deflection, so their values for initial deflections of the same shape but different size can be determined directly from the results presented here.Master of Science
14
Yang, Cheng-liang. "Experiments to culture juvenile freshwater mussels in small tanks, floating containers and sediment beds." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-08222008-063420/.
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Yaniv, Elan. "Numerical analysis and visualization of the ionospheric Kelvin-Helmholtz instability." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-05022009-040339/.
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Yang, Chyi-Bao. "The application of overall equipment effectiveness (OEE) as a measure for improving productivity and efficiency in a typical factory environment." Master's thesis, Virginia Tech, 1995. http://hdl.handle.net/10919/46373.
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Yang, Joseph Sang-chin. "System dependability analysis and evaluation." Master's thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-03172010-020227/.
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Yanna, Marc-Gabriel. "An investigation of flow-induced vibrations of a steam-generator tube." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07212009-040348/.
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Yang, Jyh-Shing. "Hydrodynamics and heat transfer in shallow fluidized beds." Diss., Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/74741.
Full textAbstract:
The use of shallow fluidized beds for heat exchange has been suggested because they give high bed-to-surface heat transfer rate and require very low bed pressure. However, in comparison with research on deep fluidized beds, only relatively few studies have been devoted to heat transfer in shallow beds, and results from the available literature are often inconsistent. This study represents an integrated research on the hydrodynamics and bed-to-surface heat transfer in shallow beds. The results from this study provide the quantitative basis for the design and efficient operation of shallow fluidized-bed heat-recovery systems.
Based upon their physical appearance, shallow fluidized beds have been categorized into nine different types. A "phase diagram" (plot of superficial gas velocity versus static bed height) can be used to delineate the ranges of fluidization variables within which each type of shallow beds will be seen.
Pressure-drop data in gas flowing upward through a shallow bed reflect pressure recovery in jets formed immediately above a gas distributor at the bottom of the bed. Pressure-recovery data provide an effective means of distinguishing a shallow bed from a deep one, and suggest that the power consumption across a fluidized bed can be reduced dramatically by dividing a single deep bed into many multi-staged shallow beds.
A computerized light probe has been developed for measurements of particle volume-fraction distribution and its statical fluctuation (standard deviation). These data have been shown to quantitatively define: (1) different types of shallow beds; (2) relative magnitude of solid mixing; (3) bed surface and bed height; and (4) jet penetration depth.
Based upon observations of the hydrodynamic behavior of shallow fluidized beds, three regions can be identified for heat-transfer applications: a jet-affected region at the bottom, a free-board region at the top, and, sandwiched between theses, a homogeneous region. Only heat-transfer data in the homogeneous region are sufficiently well-behaved to be subjected to quantitative correlation in terms of fluidization variables. For relatively coarse particles (Geldart's Group B particles) the vigor of solid mixing can be the most important factor in affecting the heat-transfer performance. Bed voidage and static electricity effects are found to be important for smaller and/or lighter particles (i.e., Geldart's Group A particles).Ph. D.
20
Yang, C. C. "Three essays on taxation and public pricing." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54817.
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This dissertation contains three essays. They are "On Optimal Excise Taxes: Becker’s Household-Production Approach", "The Pricing of Public Intermediate Goods Revisited", and "Piecemeal Design and Reform of Commodity Taxes". In the first essay, Becker’s household production model is used to investigate optimal excise taxes. We are particularly interested in what can be said about the optimal tax structure from the information of household production activities and the new insights that can be gained into the optimal tax structure by using Becker’s approach. In the second essay, we revisit the pricing of publicly produced inputs for competitive downstream industries under a general equilibrium setting and with a general production technology. We emphasize the dependence of the price structure of the private sector upon public prices and explore the consequences on the public pricing rules with such a dependence. In the third essay, we consider the design and reform of commodity taxes with a given general income tax. The major part of the paper investigates tax reforms which are Pareto-improving from the status quo, with and without lump-sum taxes.Ph. D.
21
Yan, Run-Tao. "Enzymology of butanol formation in Clostridium Beijerinckii." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/38617.
Full textAbstract:
The present study encompasses an investigation of the expression of solvent forming enzymes and purification and characterization of butanol-forming enzymes. More sensitive and accurate procedures for the determination of acids and solvents in cultures have been developed, which led to the recognition of the onset of solvent production at the mid-exponential phase, about two h earlier than previously reported. Activities of solvent-forming enzymes started to increase about one h before the onset of measurable solvent production and the
activities of solvent-forming enzymes did not increase simultaneously. CoA-acylating aldehyde dehydrogenase (ALDH) was purified to near homogeneity. The ALDH showed a native M.. of 100,000, and a subunit Mr of 55,000. ALDH
could use either NAD(H) or NADP(H) as the coenzyme. ALDH was oxygenlabile.
The O2-inactivated enzyme could be reactivated by incubating the enzyme with CoA. Both NADH- and NADPH-dependent alcohol dehydrogenase activities were present in crude extracts. The ratio of NADPH-dependent activity to NADH-dependent activity (the PID ratio) varied in crude extracts. The PID ratio was affected by O~ ionic strength, pH, growth stage of cell, Fe in culture medium and temperature. Two ADHs have been identified in crude extracts. The NADPH-dependent ADH (P-ADH) could be separated from the NADH/NADPH-dependent ADH (D/P-ADH). The D/P-ADH has been extensively purified. The D/P-ADH showed a native Mr of 70,000 and subunits with Mr of 45,300 and 40,000. The D/P-ADH activity could be inactivated by a,a' -dipyridyl and restored by Fe2+.Ph. D.
22
Yan, JiYu. "Influence of plant growth regulators on turfgrass polar lipid composition, tolerance to drought and salinity stresses, and nutrient efficiency." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40051.
Full textAbstract:
Two groups of plant growth regulators (PGRs), seaweed extract and triazole chemical, have been used in turfgrass management for improving turf quality and strengthening turfgrass to]erance to environmental stress. In order to understand the physiological functions and stress-tolerance mechanisms of the PGRs on turfgrass, a series of studies were conducted with perennial ryegrass (Lolium perenne L.).
Ryegrass was treated with or without propiconazole (PPC) (1-( (2-(2,4- dichlorophenyl)-4-propyl-l,3-dioxolan-2yl)methyl) IH-l,2,4-triazole) and a proprietary fortified seaweed extract (FSE), which were combined with or without drought and salinity stress treatment. Total lipids, fatty acid conlposition of polar lipids, and total free and conjugated sterols were determined by the thin layer chromatograph, gas chromatograph, and scanner densitometer. This study indicates that ppe and FSE affected the unsaturation of polar lipid fatty acids and concentration of free sterols, which are major factors in changing cell membrane fluidity and permeability. The PGR-induced alteration of cell membrane lipid composition could be an adaptive process to protect plant nlembrane function under drought and salinity stresses. However, the metabolic effects of PPC and FSE may be different. It was found that PPC had a strong inl1uence on unsaturation of polar lipid fatty acids, whereas FSE had a strong effect on free sterol concentration. Furthermore, a radish cotyledon expansion bioassay analysis showed that the FSE had cytokinin or cytokinin-like activity and could stimulate endogenous cytokinins in ryegrass, whereas an inhibition of cell expansion was seen in PPC-treated plants.
The possibility of using the PGRs to reduce fertilizer requirements was also studied. A higher uptake efficiency of most essential elements was found in PPCand FSE-treatedKentucky bluegrass (Poa pratensis L.) than in the control (without PGR treatments). This effect was greater at lower than at higher fert::!L.dtion levels. The utilization efficiency of some major nutrient elements also was higher in PPCand FSE-treated bluegrass than in the control. The possibility of reducing fertilization by PGR application is positive.Ph. D.
23
Yang, Karen Y. "Supercritical fluid extraction applied to environmental pollutants from Chesapeake Bay sediment." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-08222008-063753/.
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Yang, Timothy T. "An experimental investigation of turbine blade tip heat transfer and tip gap flows in the supersonic regime." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-07112009-040445/.
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Page, Ernest H. "Simulation modeling methodology: principles and etiology of decision support." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/37951.
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Mavrogenes, John Ashby. "Geochemical studies of earth materials." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/37460.
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Tucker, Mollie Janet. "An identification of the factors that influence graduate satisfaction with a management development training program." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40083.
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Many organizations, both public and private are implementing total quality management processes and procedures to ensure customer satisfaction, promote effective leadership, and enhance productivity. The sudden emphasis on customer satisfaction is observable governmentwide as federal agencies respond to the President’s Executive Order to create a government that works better and costs less. Finding ways to improve customer satisfaction is now a high priority of these service-oriented organizations.
The purpose of this study was to identify the factors that influence graduate satisfaction with a management development training program. In order to fulfill this purpose, data were collected from a respondent population of the United States Department of the Interior graduates of the Women’s Executive Leadership Program. Two surveys were used in this study to identify the factors and determine the level of importance of the factors. Based on the objectives of the research, in addition to demographic data, survey one contained open-ended questions designed to assess the graduates’ perceptual fields relative to their expectations, strengths and weaknesses of the management development training program. Twenty-eight items were identified from the qualitative data obtained from survey one and using a Likert-type scale, graduates were asked to rate the level of importance of each item in survey two.
Graduate responses to survey two were subjected to standard statistical procedures. Results of these procedures led to the following conclusions: 1) Graduate satisfaction is influenced by professional advancement, personal growth and career development opportunities, program instruction, and program administration and management; 2) Graduates of the Women’s Executive Leadership Program are overwhelmingly satisfied with the training they received in the program; 3) Expectations of the Department of the Interior graduates are met; and 4) Further research is needed to determine the relationship between trainee satisfaction/dissatisfaction and expectations as well as the relationship between satisfaction and certain demographic and biographical characteristics.Ed. D.
28
Willems, Hans P. L. "Development of sorption technology for the cleanup of pesticide contaminated wastewater." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/37464.
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Yao, Mingdong. "Development of automatic vehicle headway control law and a simulation tool." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-01242009-063351/.
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Yang, Ning. "Multiuser detection for CDMA systems with convolutional coding." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-03042009-040425/.
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Yang, Shaokai. "Corrosion resistant CMZP and Mg-Al2TiO5coatings for SiC ceramics." Thesis, Virginia Tech, 1996. http://hdl.handle.net/10919/44351.
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Thin film coatings of (Cao.6Mg0.4)Zr4(P04)6 (CMZP) and Mg stabilized AhTiOs ( Mg-Ah Ti05 ) on dense SiC substrates were investigated using sol-gel coating techniques. The thickness and quality of both CMZP and Mg-Ah Ti05 coatings were found to depend on the solution concentration and lift rate. Double coatings were applied to obtain homogeneous and crack-free coatings. The quality of double coatings was influenced by different first and second coating thickness. The CMZP coated samples were fired in controlled atmospheres to have the pure CMZP phase. Unhydrolyzed solution of Mg-AhTiOs was utilized instead of hydrolyzed solution to improve the quality of Mg-AhTiOs coatings. Aging process was found to improve the quality of CMZP and Mg-Ah TiOs coatings. SiC samples coated with CMZP and Mg-Ah TiOs exhibited good thermal shock resistance and greatly improved the high temperature alkali corrosion resistance.Master of Science
32
Yan, Suming. "Parametric study and simulation of microbubble column flotation." Thesis, Virginia Tech, 1991. http://hdl.handle.net/10919/41528.
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A study based on a statistically designed set of experiments (Box-Behnken design) has been conducted to determine the optimum conditions for advanced physical fine coal cleaning using microbubble column flotation. The dependent variables in these experiments were mass yield and product quality (ash, sulfur and btu), while the independent variables were feed solids content, collector dosage, frother dosage, feed rate, aeration rate, and wash water rate. The most important operating parameters in order of significant were found to be aeration rate, feed rate, frother dosage and wash water rate. The test data were found to fall along a single grade-recovery curve and just below the ideal separation curve predicted by release analysis, provided that a sufficient bias flow was maintained. The test results also demonstrated that various combinations of operating conditions can be utilized to achieve the same level of metallurgical performance.
In order to develop an improved understanding of the behavior of column flotation cells, a simulation package was developed by incorporating guidelines developed from the parametric test data. Simulations were carried out by examining the effects of key parameters on the performance of a column flotation cell. The parameters that were found to have the most significant influence included column length/diameter ratio, aeration rate, feed rate, feed solids content, and pulp bubble size. It was also found that limitations arising from the carrying capacity of the froth phase can greatly impact the performance of large-scale flotation columns. It is believed that this simulator will be useful for the design, control, optimization and scale-up of column flotation.Master of Science
33
Yang, Liming. "Subnormal operators, hyponormal operators, and mean polynomial approximation." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/40103.
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We prove quasisimilar subdecomposable operators without eigenvalues have equal essential spectra. Therefore, quasisimilar hyponormal operators have equal essential spectra. We obtain some results on the spectral pictures of cyclic hyponormal operators. An algebra homomorphism π from H∞(G) to L(H) is a unital representation for T if π(1) = I and π(x) = T. It is shown that if the boundary of G has zero area measure, then the unital norm continuous representation for a pure hyponormal operator T is unique and is weak star continuous. It follows that every pure hyponormal contraction is in C.0
Let μ represent a positive, compactly supported Borel measure in the plane, C. For each t in [1, ∞ ), the space Pt(μ) consists of the functions in Lt(μ) that belong to the (norm) closure of the (analytic) polynomials. J. Thomson in [T] has shown that the set of bounded point evaluations, bpe μ, for Pt(μ) is a nonempty simply connected region G. We prove that the measure μ restricted to the boundary of G is absolutely continuous with respect to the harmonic measure on G and the space P2(μ)∩C(spt μ) = A(G), where C(spt μ) denotes the continuous functions on spt μ and A(G) denotes those functions continuous on G ¯ that are analytic on G.
We also show that if a function f in P2(μ) is zero a.e. μ in a neighborhood of a point on the boundary, then f has to be the zero function. Using this result, we are able to prove that the essential spectrum of a cyclic, self-dual, subnormal operator is symmetric with respect to the real axis. We obtain a reduction into the structure of a cyclic, irreducible, self-dual, subnormal operator. One may assume, in this inquiry, that the corresponding P2(μ) space has bpe μ = D. Necessary and sufficient conditions for a cyclic, subnormal operator Sμ with bpe μ = D to have a self-dual are obtained under the additional assumption that the measure on the unit circle is log-integrable.Ph. D.
34
Yates, Keith William. "Optimization of slender space trusses utilizing a continuum model." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-11242009-020159/.
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Yang, Zhenbiao. "Gene regulation in a pathogen-plant interaction: soft rot erwinias versus potato tubers." Diss., Virginia Tech, 1990. http://hdl.handle.net/10919/39693.
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Erwinia soft rot is a widespread disease destructive to numerous
important crop plants. Damage to plants is primarily due to celldegrading
enzymes (CDEs) secreted by the bacteria. I am interested in
potato (Solanum tuberosum) soft rot because it is of agricultural importance
and it represents an ideal model system for understanding molecular
events in plant-pathogen interactions. Much has been learned in
vitro about the molecular genetics of CDEs in the past decade; however,
little is known about their expression in plantae To study expression
of genes for these enzymes during pathogenesis and plant responses to
erwinias or their enzymes, I developed a membrane-separated system for
simultaneous studies of potato and bacterial gene expression. This system
facilitates the isolation of plant tissue-free bacterial cells and
bacteria-free plant tissue for subsequent analysis of gene expression by
RNA blot hybridization. Using this system, I demonstrated that in compatible
interactions, rnRNAs for three Erwinia carotovora subsp. carotovora
(Ecc) CDE genes were induced to high levels and were induced sequentially: exo-pectate lyase (PL), endo-PL, and then endopolygalacturonase
(PG) with maximal mRNA accumulations at 6, 9, and 12
hr, respectively. Induction of these mRNAs was well correlated with
tissue maceration. In the incompatible interaction, however, induction
of all three Ecc genes was reduced several-fold compared to the compatible
interaction. The kinetics of mRNA accumulation during pathogenesis
were distinct from those of in vitro accumulation induced by polygalacturonic
acid. My results confirm that in planta expression of
these genes was induced by exo-PL reaction products as suggested by
other researchers. In studies of plant genes correlated with plant
responses to pathogens and environmental stresses [plant defenseresponse
(PDR) genes], I also showed Ecc triggered active responses distinct
from wound responses. I used gene probes for phenylalanine ammonia-
lyase (PAL) and 3-hydroxy-3-methylglutaryl coenzyme A reductase
(HMGR), key genes in the biosynthesis of phenylpropanoid- and terpenoidderived
compounds believed to be important in plant defenses. Ecc
inoculation caused much more rapid and greater increases in PAL mRNA and
enzyme activity levels in potato tuber than wounding alone. Escherichia
coli, a non-plant pathogen, carrying a plasmid which encodes Ecc
endo-PL, also induced PAL mRNA accumulation. Ecc induced a specific
HMGR isogene (HMGR1) not activated by wounding. My results support the
existence of an HMGR mul-ci-gene family. Wounding resulted in a rapid
and transient accumulation of HMGR2 mRNA followed by a slower accumulation
of HMGR3 mRNA. These isogenes are distinct from the Ecc-induced
HMGRI gene.Ph. D.
36
Verma, Ravi Kant. "Melting and crystallization studies in a partially excluding copolymer." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40130.
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Knauss, Daniel M. "Synthesis and characterization of new polycarbonate material systems." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40208.
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Bisphenol A polycarbonate is an engineering thermosplastic which can be utilized for a variety of applications. Modifications to improve upon the properties of this useful material have been attempted since its invention. Three modifications of bisphenol A polycarbonate and its copolymers have been examined in this work.
The hydrolytic stability of copolymers of polydimethylsiloxane and polycarbonate was improved by the synthesis of pre-formed phenol functional polydimethylsiloxane oligomers in which the Si is attached directly to the aromatic ring of the hydroxyaryl functional component. In situ random block copolymers of polydimethylsiloxane and polycarbonate were synthesized by interfacial polymerization techniques. The Si-aryl bonds of the novel polydimethylsiloxane oligomers were found to impart good thermal and hydrolytiC stability to the random block copolymers.
Terminally reactive polycarbonate oligomers were also synthesized in order to form polycarbonate network materials. 4-Acetoxystyrene was utilized as a stable precursor to 4-vinylphenol which could then be used to quantitatvely control the molecular weight and functionality of the polycarbonate chains. The reactive oligomers were found to undergo a thermal cure above the respective glass transition temperatures to form insoluble networks. These network materials were found to have superior solvent resistance as compared to the linear material while retaining much of the useful mechanical properties (high fracture toughness, etc.) of bisphenol A polycarbonate. Furthermore, the glass transition temperatures of the networks were found to increase with a decrease in the molecular weight between crosslinks.
The fire resistance properties of polycarbonate were modified by the copolymerization of bisphenol A with phenol derivatives of triphenylphosphine oxide. The effect of changes in the composition were determined by differential scanning calorimetry and thermogravimetric analysis. The glass transition temperature, as well as the residual char yield at elevated temperatures was found to increase with an increase in the phosphorus monomer content as measured by the two respective methods. Cone calorimetry was also performed on the samples to determine the heat release rate, which reflected an increase in the fire resistance properties with an increase in the phosphorus content.Ph. D.
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Yang, Yu-Wen. "Behavior of three-span braced columns with equal and unequal spans." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07292009-090428/.
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Yan, Jingsheng. "Platoon modal operations under vehicle autonomous adaptive cruise control model." Thesis, This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-07102009-040612/.
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Yadav, Manjit S. "An examination of how buyers subjectively perceive and evaluate product bundles." Diss., This resource online, 1990. http://scholar.lib.vt.edu/theses/available/etd-02052007-081234/.
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Zhang, Jianhua. "Restriction fragment length polymorphism analysis of chloroplast DNA, mitochondrial DNA, and ribosomal DNA in turfgrasses." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-170748/.
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Cairney, Timothy D. "Credibility of annual management earnings forecasts : theory and evidence /." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-164623/.
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Loveday, Donald Ray. "Structure-property relationships in novel ionomers." Diss., This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-10022007-144854/.
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Tuncbilek, Cihan H. "Polynomial and indefinite quadratic programming problems: algorithms and applications." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/39040.
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Li, Chen-Chung. "Ion assisted deposition of multicomponent thin films." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40039.
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A novel in-situ stress measurement technique to study the formation kinetics of multi component oxide thin films was developed and was applied to PbTiO₃. Single phase PbTi 0₃ thin films were formed from the reaction between films in the deposited PbO ITi0₂ multilayer. The film stoichiometry was accurately controlled by depositing individual layers of the required thickness. Development of film stresses associated with the formation of the product layer at the PbO/Ti0₂ interface of the multilayers was used to monitor growth rate of the PbTiO₃ layer. It was found that growth of the PbTiO₃ phase obeyed the parabolic law and the effective activation energy was estimated to be 108 kJ/mole. It is believed that the mechanism of this reaction was dominated by grain boundary diffusion of the participating cations.Ph. D.
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Mayo, Kevin A. "Definition and evaluation of a synthesis-oriented, user-centered task analysis technique: the Task Mapping Model." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40167.
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A software system is an aggregate of communicating modules, and there are several different types of communication among these modules (direct, indirect, and global). Therefore, understanding the interfaces among these modules can characterize the system and are a major factor in the system's complexity. These interfaces could possibly also show and predict inadequacies in the reliability and maintenance of a system. Interfaces are defined early in the development life cycle at a detailed or high level design stage. Knowing that these interfaces exist and their structure leads us to measure them for an indication of the designed interface complexity. This designed interface complexity can then be utilized for software quality assurance by allowing users to choose from among several designs. With data provided by an Ada software developer, the interface complexity metrics correlated with established metrics, but also found complex interfaces that established metrics missed.Ph. D.
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Kang, Kyehong. "A structured reduced sequential quadratic programming and its application to a shape design problem." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/38565.
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The objective of this work is to solve a model one dimensional duct design problem using a particular optimization method. The design problem is formulated as an equality constrained optimization, called All at once method, so that the analysis problem is not solved until the optimal design is reached. Furthermore, the block structure in the Jacobian of the linearized constraints is exploited by decomposing the variables into the design and flow parts. To achieve this, Sequential quadratic programming with BFGS update for the reduced Hessian of the Lagrangian function is used with Variable reduction method which preserves the structure of the Jacobian in representing the null space basis matrix. By updating the reduced Hessians only of which the dimension is the number of design variables, the storage requirement for Hessians is reduced by a large amount. In addition, the flow part of the Jacobian can be computed analytically.
The algorithm with a line search globalization is described. A global and local analysis is provided with a modification of the paper by Byrd and Nocedal [Mathematical Programming 49(1991) pp 285-323] in which they analyzed the similar algorithm with the Orthogonal factorization method which assumes the orthogonality of the null space basis matrix. Numerical results are obtained and compared favorably with results from the Black box method - unconstrained optimization formulation.Ph. D.
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Flynn, Timothy M. "Evolutionary biology of the Armillaria mellea species complex." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40131.
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DNA-DNA hybridization experiments were used to examine the genetic variation that has accumulated with the North American Biological Species (NABS) of Armillaria. Forty strains including nine of the ten NABS and A. tabescens were used in this study. The normalized percent hybridization values ranged from 80%-100% similarity within a given biological species and ranged from 30%-85% among the biological species, The NPH data was summarized with UPGMA clustering analysis to give four main clustering groups, two were homogeneous and two were heterogeneous, The first included A. tabescens; the second included A. mellea; the third included A. calvescens, A. gallica, A. sinapina, NABS IX, and NABS X; the fourth included A. gemina and A. ostoyae. One cluster of two A. gallica strains shared greater similarity with NABS X than it had to four other conspecific strains, The NPH data and estimates of genome size (genetic complexity) was analyzed using a stoichiometric approach to calculate equivalents of homologous DNA and low copy repetition frequencies. Reciprocal NPH values did not predict relative genome size as expected, However, as the relative genome size increases, the equivalents of homologous DNA increases in the same proportion. This suggests that as an Armillaria genome increases in total complexity (novel sequences), certain ancestral sequences are duplicated in proportion the increase in total genetic complexity, This interpretation of the data is discussed with respect to interspecific hybridization, diploidy, and chromosomal evolution including alloploidy, aneuploidy, and chromosomal length polymorphisms.Ph. D.
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Ninnemann, Todd A. "Effects of riblets on the performance of the supersonic through-flow fan cascade blades." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/29358.
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An experimental study to determine the effects of riblets on the performance of the supersonic through-flow fan (STF) cascade blades was performed. The two-dimensional cascade was tested in the Virginia Polytechnic Institute and State University intermittent wind tunnel facility, where the Mach and Reynolds (based on chord) numbers were 2.36 and 4.8 x 10⁶ , respectively. Three different V-grooved riblet heights were tested on the blades: 0.023, 0.033, and 0.051 mm. Riblet testing were conducted at design incidence as well as at off-design conditions (incidence angles: +5, -10 deg).
The riblet effect on the performance of the STF blades was determined by measuring the total pressure profile downstream of the cascade and integrating this total pressure to obtain an overall mass-averaged loss coefficient. The riblet loss coefficient was compared with the loss coefficient of a control test case where an equivalent thickness of smooth material is applied to the blades. Results show that, at the design incidence, the 0.033 mm height riblets provided the optimal benefit, with a reduction of 8.5% in the loss coefficient compared to the control case. Smaller effects were measured at the off-design conditions.
Shadowgraph pictures were taken to study the effect of riblets on the turbulent transition location on the blades surfaces. At design incidence, the shadowgraphs revealed that the optimum height rib lets delayed the transition location on the suction surface of the blades. Therefore, it was concluded that for the 0.033 mm height riblets the decrease in the cascade's loss coefficient was the result of delayed transition in addition to a decrease in turbulent viscous losses.
A numerical simulation was conducted to investigate both rib let effects on the STF blades. The numerical study showed that only the combination of the two riblet effects was able to produce a decrease in loss coefficient that was observed experimentally. Results from the numerical study indicate, that at design incidence, 2/3 of the rib let benefit is attributed to the delayed transition effect on the blades with the other 1/3 resulting from a decrease in turbulent viscous losses.Ph. D.
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Hrubec, Theresa. "The effects of temperature, water quality and culture conditions on the immunology, hematology, and blood chemistry of hybrid striped bass." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40134.
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Sunshine and palmetto bass (different crosses of hybrid striped bass) were used to determine immunologic, hematologic and serum chemistry changes under different culture conditions. The kinetics of the humoral immune response was determined for sunshine bass acclimated to 10, 18, 24, 29°C, and to elevated ammonia (0.15 mg/L NH3) and elevated nitrate (200 mg/L). These conditions are frequently encountered in aquaculture situations. Cooler temperatures decreased both the magnitude and onset of the humoral response, being lowest at 10°C, intermediate at 18°C, the highest at 24 and 29°C. Elevated ammonia did not affect the immune response, while elevated nitrate decreased antibody production to the level of the 18°C response. Hematologic reference intervals were determined for sunshine bass in tanks and recirculating systems, and palmetto bass in tanks. Serum chemistry reference intervals were determined for sunshine bass in tanks, recirculating systems and cage systems. Greater differences were observed in reference intervals between the culture systems, than between the two types of hybrid. To determine if environmental factors influenced the differences seen in the reference, sunshine bass were acclimated to 10, 18, 24, 29°C, elevated ammonia (0.15 mg/L NH3) and elevated nitrate (200 mg/L). The hematology and serum chemistry profiles of these fish were compared with the reference intervals for sunshine bass in tanks. Leukocyte, lymphocyte and monocyte counts at 10°C, and glucose and calcium at 10 and 18°C deviated sufficiently to suggest generating separate reference intervals at these temperatures. In the nitrate treated fish, creatinine levels were elevated and chloride levels were lower than controls and outside the reference interval. These two responses were presumed to be pathologic changes associated with elevated nitrate levels due to the large deviation in the analytes and the mortalities seen in the nitrate treated fish. The remaining analytes for fish in the different environments were within or slightly outside the reference intervals. These slight changes were presumed to be due to individual variation as the reference intervals were determined for fish under relatively uniform conditions and may not be sufficiently broad to cover fish from more varied environments. With minor modification, the reference intervals should apply to sunshine bass in most situations.Ph. D.