This study involves analyses and experiments of magnesium¡¦s hot extrusion of thin sheets and tubes. At first, hot compression tests are conducted to obtain the magnesium¡¦s plastic flow stresses in high tempearatures, which will be used in the finite element analysis. In the FE simulations of thin sheet extrusion, the flow pattern of the magnesium billet within the die, the temperature history at die exit and the elastic deformation of the die is analyzed. Sound and good thin sheets are obtained by appropriate die design, initial billet temperature and extrusion velocity¡¦s control. The goal of constant temperature extrusion is expected to achieved by controlling the extrusion velocity which will influences the billet temperature at die exit. In FE simulations of thin tube extrusion, the flow pattern of the magnesium billet within the port-holes, welding chamber and die bearing is analyzed. The elastic deformation of the die is dicussed. Extrusion of sound thin tubes is achieved by appropriate extrusion conditions. Finally, hot extrusion experiments are conducted and the experimental values of the extrusion load and dimensions of the products are compared with the analytical values to verify the validity of the analytical models.

Title from PDF of title page. / Document formatted into pages; contains 94 pages. / Thesis (M.S.Ch.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: Total pressure measurements at 303.15 K are reported for the binary systems of 2-ethoxyethanol with carbon tetrachloride, chloroform, 1,2-dichloroethane and dichloromethane. Total pressure measurements for the system of hexane and 2-ethoxyethanol were also made to check the validity of the experimental apparatus and procedure. These measurements were taken according to the static method proposed by Van Ness (1975). Data reduction was accomplished using Barker's Method. The modified Margules equation was used as a model for the excess Gibbs free energy (GE) and parameter values were obtained by regression of the experimental data. The obtained data were used to test the association model developed by Kretschmer and Wiebe (1967). In its original form, the Kretschmer-Wiebe model assumes self-association between molecules of 2-ethoxyethanol. / ABSTRACT: An extended form of the Kretschmer-Wiebe model, in which cross-association of 2-ethoxyethanol with the halogenated hydrocarbon is postulated, was examined as well. The regular solution model, which results from the above theories when all association is neglected, was also examined. It was found that the Kretschmer-Wiebe model was far superior to the regular solution model. However, the extended form of the Kretschmer-Wiebe model showed less improvement over the original form. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

During sustained voluntary contractions, the variability in motor unit interspike intervals increases with fatigue. This increase in variability may represent an adaptive mechanism to prevent fatigue. We investigated whether randomly modulating interpulse intervals (IPI) in a constant frequency stimulation protocol reduces force loss over time compared to a non-modulated constant frequency protocol. A second purpose of this study was to investigate the role of the M-wave in force generation during evoked contractions. Eight healthy subjects participated in three 3-minute fatigue protocols of the thenar muscles elicited by supramaximal stimulation of the median nerve. All three protocols had a mean IPI of 33.3ms and only differed in the type of modulation. One protocol consisted of 0% modulation ('Constant'), another protocol consisted of uniformly distributed modulation of [plus or minus]20% ('Variable'), and a third protocol consisted of ramped modulation from 0 to [plus or minus]20% ('Ramp'). There was no significant difference between overall force-time integrals for the three protocols. There was a significant reduction in M-wave amplitude for all three protocols; however, the M-wave immediately following the 'Ramp' protocol was significantly larger than the M-wave immediately following the 'Constant' protocol. We conclude that modulation is ineffective at preserving force output and somewhat effective at preserving the M-wave amplitude. The varied reductions in fatigued M-waves suggest that it is not necessarily a limiting factor in force output and that it was not necessarily linked to the force loss in this experiment. / text

The ubiquitous presence and chronic effect of pharmaceuticals is one of the emerging issues in environmental field. As a result of incomplete removal by sewage treatment plants, pharmaceuticals are released into the environment and drinking water sources. On the other hand, conventional drinking water treatment processes such as coagulation, filtration and sedimentation are reported to be ineffective at removing pharmaceuticals. Therefore, the potential presence of pharmaceuticals in finished drinking water poses a threat on public health. Antibiotics, as an important group of pharmaceuticals, are given special concerns because the potential development of bacteria-resistance. Ozonation and advanced oxidation processes are demonstrated to be quite effective at removing pharmaceuticals. The oxidation of pharmaceuticals is caused by ozone itself and hydroxyl radicals that are generated from ozone decomposition. Whether ozone or hydroxyl radicals are the primary oxidant depends on the specific pharmaceutical of interest and the background water matrix. In this research, erythromycin, a macrolide antibiotic, was chosen as the target compound because of its high detection frequency in the environment and its regulation status. The objective of this research was to investigate the removal performance of erythromycin by ozonation from the standpoint of kinetics. The effects of pH, carbonate and phosphate buffers, and initial ozone dose on ozonation of erythromycin were also studied. The second-order rate constant for the reaction between deprotonated erythromycin and ozone was determined to be 4.44x10⁹ M⁻¹·s⁻¹ while protonated erythromycin did not react with ozone. Ozone was determined to be the primary oxidant for erythromycin removal by ozonation. pH was found to have great positive impact on the degradation of erythromycin by ozonation due to the deprotonation of erythromycin at high pH. Carbonate and phosphate buffers were found to have negligible effects on the degradation of erythromycin by ozonation. Initial ozone dose showed a positive impact on the total erythromycin removal rate by ozonation. / text

This dissertation examines the effects of instantaneous constant-power loads (CPLs) on power converters. These CPLs are prevalent in distributed power architectures and are also present in certain motor-drive applications. CPLs introduce a destabilizing nonlinear effect on power converters through an inverse voltage term that leads to significant oscillations in the main bus voltage or to its collapse. Boundary control is studied in order to stabilize dc-dc converters with instantaneous CPLs. The three basic topologies are studied: buck, boost, and buck-boost. Converter dynamics are analyzed in both switching states and the various operating regions of switch interaction with a first-order switching surface are identified. The analysis reveals important characteristics of CPLs. For non-minimum phase converters, in order to avoid issues related with the fact that the closed-loop state-dependent switching function is undefined on the switching surface, reflective mode solutions to both converter systems are defined in the sense of Filippov. Sufficient conditions for large-signal stability of the closed loop converter operating points are established. It is shown that first-order switching surfaces with negative slopes achieve large-signal stability, while positive slopes lead to instability. In particular, for the boost converter it is illustrated via simulations and experiments that positive slopes may lead to another closed-loop limit cycle. It is also shown that instability as well as system-stalling, which is termed the invariant-set problem, may still occur in reflective mode. However, a hysteresis band that contains the designed boundary may be used to prevent system-stalling, and also allow for a practical implementation of the controller by avoiding chattering. Regulation is also achieved. The dynamic behavior of single-phase full-wave uncontrolled rectifiers with instantaneous CPLs is also explored. Stable operation is shown to be dependent on initial condition and circuit parameters, which must fall within reasonable ranges that validate a CPL model. A necessary condition for stable operation of the rectifier system is thus derived. Furthermore, input and output characteristics of the rectifier with a CPL are investigated, and comparisons are made with the resistive case. A more complete model for the rectifier system that incorporates line-voltage distortion is also utilized to study the rectifier system. Simulations and experimental results are included for verification. / text

Current stoichiometric spark-ignited engine technologies require costly catalytic converters for reductions in tailpipe emissions. Load control is achieved by using a throttle, which is a leading contributor to reductions in efficiency. Spark-ignited lean burn natural gas engines have been proven to be more efficient and emit fewer pollutants than their stoichiometric counterparts. Load reduction in these engines can be achieved by regulating the air/fuel ratio of the intake charge thereby reducing the efficiency penalties inherent to throttling. Partially stratified charge (PSC) can provide further reductions in emissions and improvements in efficiency by extending the lean limit of operation. PSC is achieved by the ignition of a small quantity of natural gas in the vicinity of the spark plug. This creates an easily ignitable mixture at the spark plug electrodes, thereby providing a high energy ignition source for the ultra-lean bulk charge. Stratified charge engine operation using direct injection (DI) has been proposed as a method of bridging the throttleless load reduction gap between idle and ultra-lean conditions. A previous study was conducted to determine if PSC can provide a high-energy ignition source in a direct injected stratified charge engine. Difficulties with igniting the PSC injections in an air-only bulk charge were encountered. This study focuses on a fundamental Schlieren image-based analysis of PSC combustion. Natural gas was injected through a modified spark plug located in an optically accessible combustion bomb. The relationships between PSC injection timing, fuel supply pressure and spark timing were investigated. Spark timing is defined as the duration between commanded start of injection and the time of spark. As the fuel supply pressure was increased, the minimum spark timing that lead to successful combustion also increased. The largest spark timing window that led to successful combustion was determined to be 80 ms wide at an injection fuel supply pressure of 300 psi. The amount of unburned natural gas increased with increasing spark timing. A cold flow study of the PSC injection system was also conducted. The PSC injection solenoid was found to have a consistent average injection delay of 1.95 ms. The slope of the linear response region of observed injection duration to commanded injection duration was 8.4. Due to plenum effects, the average observed injection duration of the entire PSC system was an order of magnitude longer than the commanded injection duration and was found to vary significantly with fuel supply pressure.

High performance, energy efficient logic style has always been a popular research topic in the field of very large scale integrated (VLSI) circuits because of the continuous demands of ever increasing circuit operating frequency. The invention of the dynamic logic in the 80s is one of the answers to this request as it allows designers to implement high performance circuit block, i.e., arithmetic logic unit (ALU), at an operating frequency that traditional static and pass transistor CMOS logic styles are difficult to achieve. However, the performance enhancement comes with several costs, including reduced noise margin,charge-sharing noise, and higher power dissipation due to higher data activity. Furthermore, dynamic logic has gradually lost its performance advantage over static logic due to the increased self-loading ratio in deep-submicron technology (65nm and below) because of the additional NMOS CLK footer transistor. Because of dynamic logic's limitations and diminished speed reward, a slowly rising need has emerged in the past decade to explore new logic style that goes beyond dynamic logic. In this thesis a constant delay (CD) logic style is proposed. The constant delay characteristic of this logic style regardless of the logic expression makes it suitable in implementing complicated logic expression such as addition. Moreover, CD logic exhibits a unique characteristic where the output is pre-evaluated before the inputs from the preceding stage is ready. This feature enables performance advantage over static and dynamic logic styles in a single cycle, multi-stage circuit block. Several design considerations including appropriate timing window width adjustment to reduce power consumption and maintain sufficient noise margin to ensure robust operations are discussed and analyzed. Using 65nm general purpose CMOS technology, the proposed logic demonstrates an average speed up of 94% and 56% over static and dynamic logic respectively in five different logic expressions. Post layout simulation results of 8-bit ripple carry adders conclude that CD-based design is 39% and 23% faster than the static and dynamic-based adders respectively. For ultra-high speed applications, CD-based design exhibits improved energy, power-delay product, and energy-delay product efficiency compared to static and dynamic counterparts.

Microwave tunable filters are key components in radar, satellite, wireless, and various dynamic communication systems. Compared to a traditional filter, a tunable filter is able to dynamically pass the required signal and suppress the interference from adjacent channels. In reconfigurable systems, tunable filters are able to adapt to dynamic frequency selection and spectrum access. They can also adapt to bandwidth variations to maximize data transmission, and can minimize interferences from or to other users. Tunable filters can be also used to reduce size and cost in multi-band receivers replacing filter banks. However, the tunable filter often suffers limited application due to its relatively low Q, noticeable return loss degradation, and bandwidth changing during the filter tuning. The research objectives of this thesis are to investigate the feasibility of designing high Q tunable filters based on dielectric resonators (DR) and coaxial resonators. Various structures and tuning methods that yield relatively high unloaded Q tunable filters are explored and developed. Furthermore, the method of designing high Q tunable filters with a constant bandwidth and less degradation during the tuning process has been also investigated. A series of novel structures of dielectric resonators have been proposed to realize in a high Q miniature tunable filters. The first type of TME mode DR filter is designed to be tuned by piezoelectric bending actuators outside the cavity, and has achieved a tuning range from 4.97 to 5.22 GHz and unloaded Q better than 536 over the tuning range. The second type of TME mode tunable filters are integrated with various tuning elements: GaAs varactors, MEMS switches, and MEMS capacitor banks are employed. The designed filter with MEMS switches operates at 4.72 GHz, and has achieved a tuning ratio of 3.5% with Q better than 510 over the tuning range. The designed filter with GaAs varactors operates at 4.92 GHz, and has achieved a tuning ratio of 2% with Q better than 170 over the tuning range. Finally, the designed filter with MEMS capacitor bank operates at 5.11 GHz, delivering a tuning ratio of 3.5% with Q better than 530 over the tuning range. Cavity combline/coaxial resonators are also used in the design of high Q tunable filters. This thesis presents a novel approach to design a tunable cavity combline filter tuned by a MEMS switched capacitor bank. Instead of mechanically moving the tuning disk, the cavity combline filter is tuned with capacitances loading on the tuning disks, which are electrically adjusted by MEMS switched capacitor bank. The assembled 2-pole filter operates at 2.5 GHz with a bandwidth of 22 MHz, a tuning range of 110 MHz and a Q better than 374 over the tuning range. The assembled 6-pole filter operates at 2.6 GHz with a bandwidth of 30 MHz and has a tuning range of 44 MHz. Finally, the design of high Q tunable filter with constant bandwidth is explored. A 4-pole high Q cavity combline tunable filter with constant bandwidth is demonstrated. The tuning has been realized manually and by using a piezoelectric motor respectively. The designed filter operates at 2.45 GHz and has achieved a stable bandwidth of 30 ??1.1 MHz over a tuning range of 400 MHz and an unloaded Q better than 3000. This design method for a constant bandwidth filter is applicable to both cavity combline filters and dielectric resonator filters.

In this thesis, a leading-order QCD analysis of structure functions in neutrinonucleon interactions is performed. From the CCFR nucleon structure function data, the QCD parameter Lambda has been extracted. This measurement also corresponds to a measurement of the strong coupling constant. Two fits to the data have been performed, the nonsinglet-only fit and the singlet-nonsinglet combined fit. The result for Lambda was found to be 289 +62 &iexcl / 59 &sect / 76 MeV, where the errors are statistical and systematical, respectively. This result is compared to the world-wide measurements of this quantity. In order to verify the agreement, also the logarithmic slopes of the QCD model and the structure function data are calculated and compared.

Living polytetrahydrofuran (PTHF) was terminated with sodium thiophenemethonate to yield a polymer with thiophene groups at one (PTHF1) and both ends (PTHF2). Copolymerizations of PTHF1 and PTHF2 insulating polymers with pyrrole and thiophene were achieved in water-p-toluene sulfonic acid (PTSA) and acetonitrile (AN)-tetrabutylammonium tetrafluoroborate (TBAFB) solvent-electrolyte couples via constant potential electrolysis. Characterization of the samples were performed by Nuclear Magnetic Resonance Spectroscopy (NMR), cyclic voltammetry (CV), Fourier Transform Infrared Spectroscopy (FT-IR), Thermal Analyses (TGA), (DSC) and Scanning Electron Microscopy (SEM). Electrical conductivities were measured by four-probe technique. PTHF1/PTh and PTHF2/PTh films which were deposited on ITO-glass in dichloromethane-TBAFB solvent-electrolyte couple found out to be anodically coloring copolymers that electrochemically switch between an oxidized blue and reduced red state exhibiting electrochromic behavior. Spectroelectrochemical Analysis (SEC) was run in UV-VIS region to reach a better understanding of the band structures of PTHF1/PTh and PTHF2/PTh electrochromic copolymers. Optoelectrochemical analyses were introduced as a new method for the characterization of copolymers.