Digital Commons Network^™

The Analysis And Simulation Of Hybrid Stepping Motors Using The Phase Plane Approach, Timothy James Harned

Doctoral Dissertations

Stepping motors have become very popular electromechanical interface devices because they are easy to interface to digital control logic. The most popular stepping motor currently used is the hybrid design stepping motor. It incorporates an efficient magnetic structure to obtain a high output torque, while maintaining a position resolution of fifty parts per million.

All stepping motors are nonlinear devices and, therefore, control strategies have been difficult to develop and implement. A second order, nonlinear model was developed by Gauthier to describe the permanent magnet stepping motor. The results of this model are displayed using the phase plane and considerable …

A Management Training Model For Engineers In Saudi Arabia, Majid Al-Kassabi

Doctoral Dissertations

“Great economic growth has occurred in Saudi Arabia in the last decade creating overwhelming demands for professionally trained people. The emerging Saudi professionals are mostly engineers who have been put in managerial positions without the benefit of managerial training.

Objectives of this research were 1) To identify the skills needed by engineers to become managers; 2) To identify problems and constraints inherent in management training programs; 3) To identify the impact of a model training program on the individual; and 4) The impact of a model training program on the firm.

A training program was implemented using an experimental group …

Dissolution Of Multi-Component Systems, Robin Ashley Murphy

Doctoral Dissertations

"The validity of ideal barrier layer diffusion kinetics was examined in the NaCl/KCl - glycerol and Al₂O₃-CaO-Al₂O₃-SiO₂/slag corrosion systems. Single crystals and dense polycrystalline plates of pure NaCl or KCl exhibit steady-state corrosion rates within 10%, of calculated theoretical values, while dense mixtures of the two salts corrode at rates higher than either pure material. The results are compared to the grooving phenomena of NaCl/KCl bicrystals.

Polycrystalline Al₂O₃ is shown to corrode at the same rate as single crystal sapphire at 1400°C in CaO-SiO₂-Al_{2 …}

Electrochemical Evaluation Of Zinc Electrolyte, Rajesh Kumar Singh

Doctoral Dissertations

"The polarization characteristics of acidified zinc sulfate electrolyte with varying solution chemistries were examined by cyclic voltammetry. An attempt was made to correlate the polarization results with the morphological and current efficiency data in order to develop a better understanding of the more fundamental aspects of impurity and additive behavior during the zinc electrodeposition process.

A statistical screening design program was conducted to determine the effects of certain operating parameters on the nucleation potential of zinc from sulfate electrolyte. The variables studied included: solution temperature, H₂SO₄ and Zn concentration, and scan rate. The solution temperature was found to be the …

An Analysis Of Mill Sound Levels To Aid In The Control And Understanding Of The Grinding Process, Scott Douglas Morrison

Doctoral Dissertations

“An experimental study has been made to evaluate the relationships between grinding parameters and the directional sound levels emitted from the collision of the grinding media with the mill wall for a laboratory batch ball mill.

Discrete frequency and single frequency band sound pressure level measurements were performed to investigate the changes in sound levels with grind time. It was demonstrated that the reduction in sound levels with grind time observed for a narrow sized feed can be used to indicate optimum breakage rates, overall time-based particle size distribution, and ore character.

The relationships established with the discrete frequency and …

Corrosion In Magnesium And A Magnesium Alloy (Az91c) As Modified By Ion Implantation, Sanay Akavipat

Doctoral Dissertations

"Magnesium and a magnesium alloy (AZ9 1C) have been ion implanted over a range of ion s energies (50 to 150 keV) and doses (1 x 10¹⁶ to 2 x 10¹⁷ ions/cm²) to modify the corrosion properties of the metals. The corrosion tests were done by anodic polarization in chloride -free and chloride containing aqueous solutions of a borated-boric acid with a pH of 9.3. Anodic polarization measurements showed that some implantations could greatly reduce the corrosion current densities at all impressed voltages and also increased slightly the pitting potential, which indicated the onset of the …

Numerical Simulation Of Mixing Processes In Two-Dimensional Channel Flows, Milan Karel Straka

Doctoral Dissertations

"Recently, considerable interest has arisen in the numerical simulation of laminar and turbulent transport phenomena. More knowledge in this field is needed to improve predictions of heat and mass transfer processes in a variety of technical fields.

In this work a new computationally efficient transport model is developed. It consists of partially parabolized time-dependent equations of motion, continuity, and concentration of nonconservative species. Pertinent equations are solved numerically for both laminar and turbulent flow.

Results of calculations of laminar flow in the entry region of a parallel-plate channel agree well with the work of other authors. For turbulent flows, the …

A Parallel Branch And Bound Algorithm For Integer Linear Programming Models, Rochelle L. Boehning

Doctoral Dissertations

"A parallel branch and bound algorithm is developed for use with MIMD computers to study the efficiency of parallel processors on general integer linear programming problems. The Haldi and IBM test problems and a System Design model are used in the implementation of the algorithm. Initially the algorithm solves the Haldi and IBM test problems on a single processor computer which simulates a multiple processor computer. The algorithm is then implemented on the Denelcor HEP multiprocessor using two of the IBM problems to compare the results of the simulation to the results using an MIMD computer. Finally the algorithm is …

Kinetics And Reactor Design In The Pyrolysis Of Tar Sands, Charles Arthur Lechner

Doctoral Dissertations

"Data from the thermal decomposition of bitumen from Utah tar sands was obtained and analysed with both isothermal and non-isothermal chemical reaction models. The use of a power rate law to describe the complex kinetics of pyrolysis gave agreement with the experimental data that was approximate, but adequate for design purposes. The results indicated a reaction rate that was second order in bitumen content, with an activation energy of about 17 to 20 kcal/gmol.

Data for the boiling point distribution of the products was consistent with a change of mechanism from vaporization to pyrolysis as the samples are heated. Higher …

Mass Transport Considerations In Electrometallurgical Reactions, Jose Rolando Sami Cuzmar

Doctoral Dissertations

"The research program described is divided into three segments. In the first part, the morphology and kinetic studies of Cd²⁺ removal from ZnSO₄ solutions using Zn dust as a reducing agent are presented. In the absence of impurities, the morphology of the Cd deposit shows the formation of two-dimensional or leaf-like dendrites capable of interlocking and forming agglomerates or balls. The size and strength of the agglomerates depend on the initial Cd²⁺ concentration to Zn metal surface area ratio, the rate of Cd ²⁺ removal, and the reactor geometry. The presence of additives, like Cu²⁺ and …

Complex Frequency Analysis Of Damped Thin-Walled Beams With Open Cross Sections (Coupled, Vibration), Mohamed Fouad Ahmad

Doctoral Dissertations

The dynamic equilibrium equations for thin-walled beams of open cross section are derived with reference to an arbitrary system of coordinates. Exact stress resultant-displacement relation of the bending theory of cylindrical shells has been used and therefore the shell curvature, secondary warping, and rotary inertia effects are included in the derivation.

The equilibrium equations have been referred to principal coordinates in order to reduce the coupling between the different displacement components. The principal coordinates and the associated cross sectional properties for some sections have been studied. This study has indicated that the shell curvature and secondary warping effects cannot be …

Estimation Of United States Import Demand And Export Supply In A Multi-Input Multi-Output Model, Using Human Capital And R & D As Factors Of Production (Research, Development), Evangelos Nikolaou Charos

Doctoral Dissertations

Traditionally the estimation of the import and export functions has been done by specifying either linear or loglinear functions of some income and relative price variables then using, usually, ordinary least squares technique. This procedure is subject to a wide range of criticisms due to its lack of theoretical foundation and because of its implicit assumptions. In this thesis import and export functions will be derived within a more general theoretical framework first introduced by Samuelson and investigated empirically by Foley and Sidrauski in their treatment of the production side of the economy. This more general framework was also used …

Ecology Of Rocky Subtidal Communities: The Role Of Modiolus Modiolus (L) And The Influence Of Disturbance, Competition, And Mutualism, Jon Drew Witman

Doctoral Dissertations

This study presents an analysis of physical and biological processes regulating the structure of rocky subtidal communities off coastal New Hampshire and southern Maine, USA, with emphasis on the ecology of the horse mussel Modiolus modiolus (L.). Quantitative sampling and multivariate analysis revealed 3 communities: (1) Modiolus community; (2) 30 m community of species with highest densities outside mussel beds; (3) 8-18 m community of species with maximal densities outside mussel beds.

Controlled field experiments, a natural grazing experiment, and long-term photographic monitoring (5 yrs) enabled patterns of Modiolus community structure to be related to the processes maintaining them. Bivalve, …

Thermogravimetric And Electrical Conductivity Studies Of Mg-Doped Lacro₃ And La-Doped Srtio₃, Brian Keith Flandermeyer

Doctoral Dissertations

"Mg-doped LaCrO₃ and La-doped SrTiO₃ are perovskite compounds that display electrical conductivity which is a function of partial pressure of oxygen (po2). It has been proposed that acceptor-doped LaCrO₃ becomes highly resistive at low po2's due to ionic compensation of the acceptor-dopant present by oxygen vacancies. SrTiO₃ has been thought to absorb O₂ into a crystallographic shear structure and exsolve strontium vacancies which can then ionically compensate the La present and give a high resistance at high po2's.

Given these models, relationships between weight loss and conductivity vs. po₂ are developed for both these …

Fixed Bed Sorption With Recycle, John Thomas Casey

Doctoral Dissertations

"A mathematical model that describes single and multicomponent recycle-sorption systems is constructed. The model accounts for the generation of species by chemical reactions occurring in a single perfectly mixed tank, in the bulk fluid of the sorbent bed, and in the pores of the adsorbent particles.

Results are shown for single zeroth, first and second order reversible reactions as well as a network consisting of two first or second order reactions which may occur in series or parallel. For systems in which a single reaction occurs, both linear and non-linear equilibrium adsorption isotherms are considered. If multiple reactions occur, then …

Applications Of Finite And Wave Envelope Element Approximations To Acoustic Radiation From Turbofan Engine Inlets In Flight, A. V. Parrett

Doctoral Dissertations

"The problem of acoustic radiation from turbofan engine inlets in flow has not lent itself fully to analysis by numerical means because of the large domains and high frequencies involved. This project has extended the use of finite elements and wave envelope elements, elements which simulate decay and wavelike behaviour in their interpolation functions, from the no-flow case in which they have been proven, to cases incorporating mean flow. By employing an irrotational mean flow assumption, the acoustics problem has been posed in an axisymmetric formulation in terms of acoustic velocity potential, thus minimising computer solution storage requirements. The wave …

Unsteady-State Cylindrical, Spherical And Linear Flow In Porous Media, Allan Jeffrey Anthony Joseph

Doctoral Dissertations

"The general problem of unsteady flow phenomena in porous media as considered in this investigation. Emphasis was placed upon the short-term flow characteristics within cylindrical, spherical and linear reservoir geometries, and practical analysis methods were developed for each problem. Additionally, nonlinear unsteady flow behavior in infinite reservoirs was considered. Each solution obtained could optionally be implemented by hand or computer, and several FORTRAN subprograms were also presented.

At present, the only way to analyze pressure transient data prior to the development of the "semi log straight line" is by type curve matching techniques. However, this study indicated that a reliable …

The Modeling And Control Of Freeze Dryers, Martin James Millman

Doctoral Dissertations

"Two models of the freeze drying process were constructed and used to study various operational policies in order to determine the policy that would provide the shortest drying times.

The sublimation model which accounts only for the removal of frozen water, is found to predict shorter times for the free water removal phase than the sorption-sublimation model which properly accounts for the removal of frozen and bound water.

This study shows that the policy which produces the shortest free water removal phase, also produces the shortest overall drying time. This policy, predicted by both models, holds the chamber pressure at …

A Study Of The Permeability Of Clays Subjected To Organic And Inorganic Permeants, Janardanan O. Uppot

Doctoral Dissertations

"Two types of clays, a magnesium montrnorillonite and a kaolinite, were subjected to precise permeability tests in specially designed triaxial permeameters, using organic and inorgani c permeants, to study the changes in permeability due to the reaction between clays and permeants. The organic permeants were an acid (acetic acid), a base (aniline), a neutral polar fluid (methanol), a neutral nonpolar fluid (xylene), as well as EDTA and its sodium salt. The inorganic permeants were aqueous solutions of aluminum, magnesium, sodium, calcium, barium and strontium.

The clay samples were prepared by consolidating from slurry; they were subjected to back-pressure saturation and …

A Study Of The Microorganisms Inhabiting Rotating Biological Contactor Biofilms During Various Operating Conditions, Nancy Edna Kinner

Doctoral Dissertations

The microbial ecology of rotating biological contactors (RBC) is a combination of complex interrelationships among bacteria, protozoa, and metazoa and their perceived environment. Since very little information is available on the microorganisms inhabiting the biofilms, the major objective of this research was to increase the understanding of the biological interactions occurring in RBC biofilms as a function of organic loading. Biofilms, in pilot-scale RBCs receiving 2.0, 4.0, and 6.0 g TOC/m('2)(.)d of settled domestic sewage, were examined using light and electron microscopy. The microbial community, composed of filamentous and unicellular bacteria, zooflagellates, amoebae, ciliates, nematodes, and rotifers is complex and …

Effects Of Rotary Inertia And Shear Deformation On Extensional Vibrations Of Continuous Circular Curved Beams, Mohamed El-Said Said Issa

Doctoral Dissertations

This dissertation is devoted to the dynamic analysis of continuous circular curved beams. The dynamic stiffness matrix is derived for the determination of natural frequencies of continuous curved beams undergoing in-plane vibrations. The formulation of stiffness matrix may be widely applied to problems with various consideration of Bernoulli-Euler Theory, Rayleigh Theory and Timoshenko Theory. Using this formulation for dynamic loading, the fixed-end moment, shear and thrusts for concentrated and distributed loads have been derived. Two continuous circular curved beams subjected to free and forced vibrations are given to illustrate the application of the proposed method and to show the effects …

Digital Analysis Of Pulse Code Modulated Signals In Telecommunications Channels, Edmund Littlefield Chase

Doctoral Dissertations

In this dissertation the techniques required to test pulse code modulated telecommunications channels are developed using the fast Fourier transform. The techniques are then applied through the design and assembly of the corresponding hardware. Windowing of data to improve spectral estimation is discussed as well as the conditions where special test signals may be synthesized to preclude the need for windowing. Conjugate-periodic functions encountered in prime radix transforms are defined and their fast transform techniques are developed.

Truss Analysis Using Singular Imbedding Method, Thiem Jenngamkul

Doctoral Dissertations

In structural analysis and design of trussed structures, the Singular Imbedding Method is applied and formulated to handle joint displacement, member force, and member stress constraints. There are two structural systems, namely, a Displacement Constraining System (DC) and a Force Constraining System (FC) that are developed for constraining joint displacements and member forces, respectively. The formulation of this method is based upon three sets of equations; equilibrium conditions, compatibility relationships, and Hooke's law of material.

The final structural stiffness matrix equations are constructed for the different types of constraints. The unknown member areas are determined from the final structural stiffness …

The Influence Of Additives And Their Interactions On Copper Electrorefining, Chwan-Tsann Wang

Doctoral Dissertations

"Protein colloid (glue), thiourea, Avitone and chloride ion are the most common additives used electrorefining copper. The polarization behavior of these additives, single and combined, was studied by cyclic voltammetry techniques in conjunction with stationary and rotating disc electrodes. In the stationary electrode work, different protein colloids give substantially different results in polarization or interaction with other additives. The role played by Avitone is not clear, but it does somewhat modify other additives in the electrolyte. Thiourea can cause a depolarized peak and a polarized plateau depending on the concentration, the other additives present and the potential selected. Chloride ion …

The Precambrian Volcanic Stratigraphy And Petrology Of The Des Arc Ne 7 1/2 Minute Quadrangle, South Central St. Francois Mountains, Missouri, Vernon Max Brown

Doctoral Dissertations

"The Precambrian volcanics in the Des Arc NE 7½ minute quadrangle are composed predominantly of rhyolitic ash-flow tuffs with minor rhyolitic, trachytic, and andesitic lavas, and basaltic dikes. Thirty-seven volcanic units were identified, mapped, and informally named. A minimum of 1,000 meters of volcanic section is present. The rhyolites consist of phenocrysts of albitized alkali feldspar, albitic plagioclase, quartz, opaques, and ferromagnesium relicts set in a devitrified and locally recrystallized felsitic matrix. Pumice and lithophysal structures are common in the ash flows.

Chemically, the rhyolites are quite similar. The potassium to sodium ratio in individual units, however, tends to vary …

The Performance Of Full Response Multi-H Modems In Practical Environments, Mark Alan Wickert

Doctoral Dissertations

The power and bandwidth efficiency of multi-h continuous- phase modulation (CPM) schemes in practical environments are considered. Specific impairments considered are transmitter filtering, amplitude limiting, and receiver symbol timing, phase error, and decision depth sensitivities. A coherent receiver model is employed which uses the Viterbi algorithm (VA) to perform maximum likelihood sequence estimation. For (2/4,3/4), ll (3/8,4/8) and (4/8,5/8) linear phase codes, a signal-to noise ratio (SNR) power gain of 1.85 dB, 1.9 dB, and 2.4 dB at a bit error rate (BER) of 10^-5 over differentially coded minimum-shift keyed (MSK) modulation are obtained, respectively. With transmitter filtering the …

Nonuniformly And Randomly Sampled Systems, George Dimitrios Kontopidis

Doctoral Dissertations

Problems with missing data, sampling irregularities and randomly sampled systems are the topics covered by this dissertation.

The spectral analysis of a series of periodically repeated sampling patterns is developed. Parameter estimation of autoregressive moving average models using partial observations and an algorithm to fill in the missing data are proved and demonstrated by simulation programs. Interpolation of missing data using bandlimiting assumptions and discrete Fourier transform techniques is developed. Representation and analysis of randomly sampled linear systems with independent and identically distributed sampling intervals are studied. The mean, and the mean-square behavior of a multiple-input multiple-output randomly sampled system …

A Residential Electrical Load Model, Charles Francis Walker

Doctoral Dissertations

This work develops a time varying residential electric load model based on the philosophy that the availability of people to turn on electrical appliances and their tendency to do so at particular times are significant factors in determining the time varying nature of the residential load. Additional contributions to the load are the result of peoples availability and tendency to perform direct actions (e.g. dish washing) that indirectly cause electrical appliances (e.g. water heaters) to turn on and off under the control of their sensors. The availability and tendencies of the residents also affect, to some extent, the contribution to …

The Comic Dimension: A New Reading Of William Carlos Williams' Long Poem "Paterson", Kathleen Douglas Matthews

Doctoral Dissertations

When Williams decided in the early forties to accelerate work on the "magnum opus" he had begun fifteen years earlier, his ambitions were enormous, yet the literary establishment treated him more like a pygmy than a giant. T. S. Eliot, reigning literary pontiff, embraced the European literary tradition and ignored Williams as he had for years while Pound used Italy as a base for the economic and political tirades which eventually had him condemned as a traitor. In his long poem Paterson, Williams felt abandoned with the momentous task of discovering a poetics to fit the American idiom. His poem …

Decentralized Control Of Distributed Processing Systems, Ahmed Kamal Ezzat

Doctoral Dissertations

This thesis presents a methodology for implementing decentralized scheduling for distributed systems. The environment in which the controlling entities make decisions is stochastic and can be described as uncertain since each entity may have a different view of the system state. As a consequence, these entities may make inconsistent decisions.

The methodology is based on defining the system state as a set of distributions and using a queueing model to predict the future behaviour of the system. The predicted state is used to schedule the individual job tasks based on minimum predicted job response time.

A hypothetical real system is …