Advanced, very high temperature materials that are ablation-resistant in oxidizing atmospheres are needed to withstand the severe environments found in rocket engine and aerospace vehicle applications. Boride-based coatings that form a protective layer during oxidation have been found to withstand these extreme conditions. Chemical vapor deposition has been chosen as a viable processing technique for producing these coatings. It is expected that two-phase boride coatings will have enhanced oxidation resistance over the single-phase materials by forming an oxide/glass layer to seal the base material from direct attack. Thermochemical modeling of CVD reactions was done to predict the processing conditions for the deposition of two-phase HfB₂-SiB₆ or HfB₂-SiB₄ coatings. The SOLGASMIX-PV computer program was used for these calculations, which were based on ZrCl₄, SiCl₄ BCl₃, and H₂ reactant gases. An array of temperatures (1100, 1300, and 1500K), total pressures (0.02, 0.1, and 1 atm.) and excess hydrogen concentrations (10:1, 25:1, and 50:1 H:(Zr + Si + B + Cl)) were investigated. These calculations show that two-phase HfB₂-SiB₆ and HfB₂-SiB₃ coatings are possible over a wide range of processing conditions, suggesting that a wide variety of two-phase compositions with a diverse population of microstructures can be deposited. This points to the possibility of optimizing oxidation resistance of these coatings by varying the processing conditions. A hot-wall CVD reactor was designed and constructed specifically for deposition reactions in this system. It was found to be necessary to separately deliver SiCl₄ and BCI₃ to the hot zone to prevent reactions between them and to eliminate interference with the in-situ hafnium chlorination reaction. SiB₄, rather than SiB₆, was the preferred deposition product in the Si-B-CI-H system. HfB₂ was the only compound found to deposit in the Hf-B-Cl-H system. Both borides coatings exhibited several different surface morphologies. The separate delivery of BCI₃ and SiCl₄, while necessary to prevent their gas phase reaction, caused reactant concentration gradients at the substrate surface due to poor mixing. This resulted in a variation of microstructural features across the substrate surface (both domed and faceted morphologies were deposited at the same temperatures), suggesting that reactant supersaturation is more important in determining surface morphology than temperature, pressure, and hydrogen concentration at the conditions studied. The first successful deposition of the two-phase HfB₂-SiB₄ coating was accomplished. Analysis of these two-phase coatings again reveals a broad range of microstructural characteristics, and the compositional gradients across the substrate surface also suggest the need for better gas mixing. / Ph. D.

Traditional methods commonly used to design sheet pile cellular cofferdams and bulkheads were developed in the 1940's and 1950's and are based on semi-empirical approaches. The traditional methods are limited because they do not explicitly incorporate soil-structure interactions, they do not predict deflections, and they are based on assumed failure plane orientations. In recent years, two-dimensional and three-dimensional finite element models have been developed to study the behavior of cells constructed at two project sites. Additionally, cells constructed at 11 project sites have been instrumented to quantify movements and sheet pile tensions. This investigation focused on combining the instrumentation measurements with finite element parametric studies in an effort to improve the existing design procedures. Sheet pile tensions were investigated by performing axisymmetric analyses of cell filling and developing correlations between computed tensions and cell geometry, foundation conditions, and sheet pile characteristics. To study the response of cells to lateral loading, a new crosswall model that simulates sheet pile slippage was implemented for plane-strain analyses. Cell deflection trends were investigated by performing analyses of lateral loading and developing correlations between computed deflections and cell geometry, cell fill characteristics, applied load level, and foundation conditions. The analyses were verified by measurements collected for the instrumented cells. Internal shearing mechanisms were investigated by performing plane-strain analyses of cells loaded by extreme lateral pressures and observing element failure plane orientations. The results of the study indicate that main cell sheet pile tensions depend on the amount of arching within the cells, foundation conditions, the degree of available interlock slack, and the method used for cell filling. Common wall sheet pile tensions are furthermore influenced by arc cell fill lateral pressures and by arc cell sheet pile tensions transferred through the wye pile. During lateral loading, cell deflections increase with increasing values of a newly defined parameter termed "characteristic head". During extreme lateral loading, vertical shear planes were computed to develop within the cell fill along the dredgeline and along the inboard sheet pile wall. / Ph. D.

This study examines an innovative multimedia facility created in partnership with the NewMedia Center's consortium which is a partnership between technology corporations and institutes of higher education. Findings include the discovery that the facility was itself an innovation created in response to the innovation of multimedia technology. It was also an institutional innovation that tried to assist the diffusion of multimedia technology in certain directions. The main thing it offered was access to its users the tools of multimedia but perhaps more importantly was the facility's founders ability to create the perception of momentum in the direction of a new innovation multimedia. / Ph. D.

This dissertation considers minimal risk equivariant (MRE) estimation of a location scalar μ in ensembles and mixtures of translation families having structured dispersion matrices Σ. The principal focus is the preservation of Pitman's solutions across classes of distributions. To these ends the cone S_n⁺ of positive definite matrices is partitioned into various equivalence classes. The classes 𝓝_𝑪 are indexed through matrices 𝑪 from a class 𝓒(n) comprising positive semidefinite (n×n) matrices with one-dimensional subspace spanned by the unit vector 𝟏_n'=[1, 1, ..., 1]. Here Σ∈𝓝_𝑪 has the structure Σ(y) = 𝑪+γ𝟏_n'+𝟏_ny'-γ̅𝟏_n𝟏_n', for some vector γ such that γ'𝑪_𝓒(n)⁻¹γ < γ̅, where 𝑪_𝓒(n)⁻¹ is the Moore-Penrose inverse of 𝑪. Of particular interest is the class Γ(n) = 𝓝_𝐁 with 𝐁 = [𝐈_n - (1/n)𝟏_n𝟏_n']. In addition, the equivalence classes Λ(𝐰) in S_n⁺ are indexed through elements of 𝓦(n) containing n-dimensional vectors 𝐰 such that Σ_i=1ⁿw_i = 1, where 𝐰'Σ = c𝟏_n’ for some scalar c>0. Of interest is the class Ω(n) = Λ(n⁻¹𝟏_n), containing equicorrelation matrices in the intersection Γ(n)⋂Ω(n). Ensembles of elliptically contoured distributions having dispersion matrices in the foregoing classes, and mixtures over these, are considered further with regard to Pitman estimation of μ. For elliptical random vectors 𝐗 the Pitman estimator continues to take the generalized least squares form. Further, ensembles of elliptically symmetric distributions having dispersion matrices in Ω(n) preserve the equivariant admissibility of the sample average X̅ under squared error loss. For dispersion matrices Σ in each class 𝓝_𝑪 the estimator is obtained as a correction of X̅ taking the form δ_Σ(𝐗) = X̅ -γ'𝑪⁻¹_𝓒(n)𝐗, with γ as in the expansion for Σ. This simplifies when Σ∈Γ(n) to δ_Σ(𝐗) = X̅ -γ'𝐞, where 𝐞 is the vector of residuals {e_i = x_i-x̅; i = 1, 2, ..., n}. These results carry over to dispersion mixtures of elliptically symmetric distributions when the mixing measure 𝐆 is restricted to the corresponding subsets of S⁺_n. The estimators are now given through a dispersion matrix Ψ which is the expectation of Σ over 𝐆. For mixing measures over S_n⁺, for which each conditional expectation for Σ given 𝑪 ∈ 𝓒(n) is in Ω(n), X̅ is the Pitman estimator for μ for the corresponding mixture distribution. Similar results apply for each linear estimator. In both elliptical ensembles and mixtures over these, the Pitman estimator is shown to be linear and unbiased. / Ph. D.

Many physical systems are well-modeled by queueing systems in which time is slotted, the distribution of the number of entities that arrive during a slot is dependent upon the evolution of a discrete time, discrete state Markov chain, and the number of entities that may be served during a slot is limited to some number, say R. Techniques for analyzing systems in this, or closely related, class have appeared in the literature, but distributions have been presented in only rare instances, limited to the case R = 1. Yet, distributions are very important, not only in performance evaluation, but in design, especially for sizing buffers in integrated (BISDN) communications systems and intermediate storage space designs in manufacturing systems. In this dissertation, a numerically stable methodology based on eigenanalysis and probability generating function technique has been developed for producing both occupancy and delay moments and distributions for the equilibrium process described above. Feasibility of the methodology is demonstrated through numerical results for two examples of an important subclass. Special attention is paid to obtaining accurate numerical values; and wherever available, numerical values are compared to those previously obtained in the literature. Furthermore, additional important models amenable to analysis by the same methodology are discussed and numerically feasible approaches for obtaining important performance measures are suggested. / Ph. D.

The research presented in this dissertation is carried out in two parts; the first, which is the main work of this dissertation, involves development of continuous differentiability of the solution with respect to the unknown parameters. For linear parabolic partial differential equations, only mild conditions are assumed on the admissible parameter space. The nonlinear partial differential equation we consider is a generalized Burgers’ equation, for which we establish the well-posedness and the smoothness properties of the solution with respect to the parameters. In the second part, we consider parameter identification problems for these two parameter dependent systems. The identification scheme which we use here is the quasilinearization method. Based on the results in the first part of this work, we obtain existence and local convergence of the algorithm. We also present some numerical examples which demonstrate the performance of the quasilinearization scheme. / Ph. D.

Broadband, high power, dual polarized phased arrays constructed from waveguide type elements generally require a 90 degree rotationally symmetric waveguide cross sectional geometry that can support single-mode propagation over the desired bandwidth. This dissertation presents a novel method of obtaining bandwidth enhancement of a square waveguide using both dielectric loading and mode filters that retains the 90 degree rotational symmetry. By placing two orthogonal dielectric slabs transverse to the guide, one obtains what is referred to as the crossed-septum waveguide (CSW). The bandwidth enhancement of the square waveguide is achieved by exploiting the modal symmetry properties of the electric field about a given axis within the guide. The objective is to increase the modal separation between the TE₁₀ (or TE₀₁) mode having even/odd (or odd/even) symmetry and TE,, mode having odd/odd symmetry in the guide. The TE₁₁ and TM₁₁ modes having even/even symmetry are forced to attenuate rapidly by the use of mode filters. An analysis of the CSW is performed using the mode matching technique to determine the electromagnetic fields, phase constants and modal cutoff frequencies. A numerical study of the modal cutoff frequencies as a function of septum thickness and dielectric constant is performed. The TE₂₀, mode is found to split into two distinctly different modes upon the introduction of the dielectric septum and are referred to as the 'U'-upper and 'L'-lower modes. The analysis shows that one can obtain increased cutoff frequency separation between the TE₁₀ and TE_20L modes, however the TM₁₂ mode may limit bandwidth performance. A process for designing and experimentally verifying a mode filter for supporting the dual polarization requirement is described. The mode filter consisting of a thin conductive film is demonstrated using the resonant cavity technique, and is experimentally shown to suppress unwanted TM₁₁ and TE₁₁ higher-order mode resonances. A general case multi-mode radiation analysis is used to identify dominant mode and higher-order mode far-field radiation characteristics. Co- and cross-polarization measurements are performed and show that energy can be largely confined to dominant mode. Under these conditions, the patterns are reasonably well behaved and degrade gracefully at the high frequencies. The concept is demonstrated over a 2.2:1 bandwidth. A potential application of the CSW is a phased array antenna radiating element that supports dual polarization. / Ph. D.

A combined experimental and computational study of two different swept-ramp injector configurations was conducted in a scramjet combustor. The object of the study was to determine the effect of mixing augmentation, resulting from the streamwise vortices generated by injector ramps, on scramjet engine operation characteristics, combustion, and heat transfer. Hydrogen was injected from the base of swept compression and expansion ramps in direct-connect tests that simulated flight at Mach 6.6. The experimental effort included combustor wall pressure and heat flux measurements with Gardon gages and surface thermocouples for the two injector configurations. A novel, side-view laser light sheet technique was developed to obtain images of the combustion product distribution at selected planes in the closed combustor duct downstream of the swept-compression ramp. injectors. In addition, a miniature refractory probe was developed to determine the pitot pressure at the exit of the combustor. Three-dimensional computations were made for mixing and reacting cases of the swept-compression ramp injector using the SPARK computer code. The flow field calculations were compared to the experimental measurements. The experimental tests demonstrated combustor performance with parallel injection comparable to that reported using normal injection. This unusually rapid parallel jet mixing and combustion was obtained using swept ramp injectors with near-parallel injection. The experiments and calculations showed that the injectors were effective in promoting lateral spreading of the fuel jets. The incomplete penetration of the fuel jets in the direction normal to the walls was a major limiting factor in the amount of mixing that could occur for both configurations. In addition, the proximity of the burning shear layer to the injector wall led to increased heat transfer on the injector wall. The effect of the flow structure on the heat flux was not principally through a large increase in the film coefficient caused by the vortical flow. Instead, it was due to the proximity of the reacting fuel jet to the wall, which led to high adiabatic wall temperatures near the wall. / Ph. D.

This historical study, covering the period 1900-1989, examined how team building became a discreet educational intervention in organizations. Team building, unlike other training interventions of the 1960s, continued to be used throughout the 1980s despite the major changes in organizations. The study reveals some of the story of how people in organizations worked to develop ways to get along with each other and to improve their performance. The study is divided into three time periods. The first, 1900-1950, was a period of the discovery of the value of teams in the workplace. The second period, 1950-1969, when team building emerged, was marked by an increased focus on the social interactions of managers, supervisors and workers. The third period, 1970-1989, saw team building change its focus. During the 1970s, team building became a stand alone educational process focused on solving productivity and quality problems. The factor that most influenced the evolution and development of team building was the management theory and practice of the times. Ranging from team building focused on relationships during the era of human relations, to team building focused on problem solving for total quality management, this group learning experience continued to meet the needs for training groups in organizations. / Ed. D.

In the analysis of quantal dose-response data, the most commonly used parametric procedure is logistic regression, commonly referred to as "logit analysis." The adequacy of the fit by the logistic regression curve is tested using the chi-square lack-of-fit test. If the lack-of-fit test is not significant, then the logistic model is assumed to be adequate and estimation of effective doses and confidence intervals on the effective doses can be made. When the tolerance distribution of the dose-response data is not known and cannot be assumed by the user, one can use nonparametric methods, such as kernel regression or local linear regression, to estimate the dose-response curve, effective doses, and confidence intervals. This research proposes another alternative to analyzing quantal dose-response data called model-robust quantal regression (MRQR). MRQR linearly combines the parametric and nonparametric predictions with the use of a mixing parameter. MRQR uses logistic regression as the parametric portion of the model and either kernel or local linear regression as the nonparametric portion of the model. Research has shown that the MRQR procedure can improve the fit of the dose-response curve by producing narrower confidence intervals for predictions, while providing improved precision of estimates of the effective doses with respect to logit analysis. / Ph. D.