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Oceanic internal waves generated in straits, river-sea interaction zones, and by interaction with localised topographic features often look on satellite images as a part of a ring. We study long weakly-nonlinear mode-I and mode-II internal ring waves in a three-layered fluid in the presence of a parallel linear current (i.e. a shear flow with constant vorticity), distorting the wavefronts. Previous research has shown that there exists a linear modal decomposition in the far-field set of Euler equations describing the waves, which is used to describe the wavefronts and modal structure of these internal ring waves, and to obtain an appropriate weakly-nonlinear model for the amplitudes of the waves. The curvilinear wavefronts of waves in cylindrical geometry are described by the singular solution of a nonlinear first-order differential equation. We show that there are significant differences in the shapes of the wavefronts of mode-I and mode-II internal waves propagating over the same linear shear current: the wavefront of the mode-I wave is elongated in the direction of the current, while the wavefront of the mode-II wave is squeezed in this direction. In addition, we use a finite-difference scheme to solve the derived cKdV-type amplitude equation numerically. Numerical results are obtained for mode-I and mode-II internal ring waves generated by a localised source and initially propagating in the absence of a current. We assume that a part of the ring wave then starts propagating over the linear shear current, and our modelling within the scope of the cKdV-type equation can be applied to describe the behaviour of the relevant part of the ring wave. Numerical modelling confirms the analytical predictions concerning the shape of the wavefronts, and reveals very strong dispersive effects in the upstream direction.

The UK Government has set an ambitious target to achieve 15% of final energy consumption from renewable sources by 2020. High Voltage Direct Current (HVDC) technology is an attractive solution for integrating offshore wind power farms farther from the coast. In the near future, more windfarms are likely to be connected to the UK grid using HVDC links. With the onset of this fairly new technology, new challenges are inevitable. This research is undertaken to help assist with these challenges by looking at possibilities of problems with respect to faster AC/DC interaction modes, especially, on the impact of inrush currents which occur during fault-recovery transients. In addition to that, possible mitigation strategies are also investigated. Initially, the relative merits of different transformer models are analysed with respect to inrush current transient studies. The most appropriate transformer model is selected and further validated using field measurement data. A detailed electro-magnetic-transient (EMT) model of a grid-connected MMC-HVDC system is prepared in PSCAD/EMTDC to capture the key dynamics of fault-recovery transformer inrush currents. It is shown that the transformer in an MMC system can evoke inrush currents during fault recovery, and cause transient interactions with the converter and the rest of the system, which should not be neglected. It is shown for the first time through a detailed dynamic analysis that if the current sensors of the inner-current control loops are placed at the converter-side of the transformer instead of the grid-side, the inrush currents will mainly flow from the grid and decay faster. This is suggested as a basic remedial action to protect the converter from inrush currents. Afterwards, analytical calculations of peak flux-linkage magnitude in each phase, following a voltage-sag recovery transient, are derived and verified. The effects of zero-sequence currents and fault resistance on the peak flux linkage magnitude are systematically explained. A zero-sequence-current suppression controller is also proposed. A detailed study is carried out to assess the key factors that affect the maximum peak flux-linkage and magnetisation-current magnitudes, especially with regard to fault specific factors such as fault inception angle, duration and fault-current attenuation. Subsequently, the relative merits of a prior-art inrush current mitigation strategy and its implementation challenges in a grid-connected MMC converter are analysed. It is shown that the feedforward based auxiliary flux-offset compensation scheme, as incorporated in the particular strategy, need to be modified with a feedback control technique, to alleviate the major drawbacks identified. Following that, eight different feedback based control schemes are devised, and a detailed dynamic and transient analysis is carried out to find the best control scheme. The relative merits of the identified control scheme and its implementation challenges in a MMC converter are also analysed. Finally, a detailed EMT model of an islanded MMC-HVDC system is implemented in PSCAD/EMTDC and the impacts of fault-recovery inrush currents are analysed. For that, initially, a MMC control scheme is devised in the synchronous reference frame and its controllers are systematically tuned. To obtain an improved performance, an equivalent control scheme is derived in the stationary reference frame with Proportional-Resonant controllers, and incorporated in the EMT model. Following that, two novel inrush current mitigation strategies are proposed, with the support of analytical equations, and verified.

The aim of this research was to quantify the influence of waves on arrays of tidal turbines. Experiments measured the wake of a turbine operating in combined wave-current flows, these were found to reduce velocity deficit as opposed to current only flow. The vertical region of the wake affected was dependant on the wave depth parameter, kd.RANS-BEM and Actuator Line methods were implemented within a commercial CFD code to provide computationally efficient methodologies for the simulation of both large turbine arrays and a turbine subjected to unsteady flow. For scaled experiments thrust coefficient was within 7% and 1% of the flume experiments for the RANS-BEM and Actuator Line methods respectively. The methods were found to give good prediction of a single turbine wake at distances greater than four diameters downstream, provided values of inlet turbulence intensity and length scale were equal to those measured experimentally.An unsteady Actuator Line method was used to quantify rotor loads and wake generation for a turbine operating within combined wave-current flow. The use of a streamwise pulsatile flow was found to give similar rotor and blade loads to simulations using a wave in a two phase volume of fluid simulation. The control strategy adopted by the turbine was found to greatly influence the computed rotor loads and blade bending moments. The wake generated by an Actuator Line method showed a reduction in velocity, however this was smaller than that measured experimentally for equivalent wave conditions.The accuracy with which the RANS-BEM method computed turbine loads and wakes was quantified for a number of one, two and three row arrays. The square of the disk averaged velocity encountered by turbines downstream of a single row of five turbines was found to be predicted to within 5% and 28% for an aligned and staggered arrangement respectively. For the two row arrays, the thrust of individual turbines was within 31% of the experimental measurements. The merged wake downstream of the multiple turbines was well predicted.Measurements of the wake of five porous disks showed combined wave-current flow did not alter the wake in the same manner as a single isolated disk. Measurement of wave energy over the wake showed the downstream current field altered wave propagation, causing a reduction in wave energy over the wake but an increase over the bypass flow. The accuracy of the wave model SWAN was assessed for the calculation of this change in wave characteristics. The model gave good prediction of the lateral variation of wave height over the far wake, however discrepancies in the near wake and upstream of the disk occurred.

This thesis presents a study of neutral-current π0 production from νµ interactions. The study uses data taken at the Tokai-to-Kamiokande off-axis experiment's near detector (ND280). Monte Carlo studies were used to develop selection criteria to reconstruct event signatures produced from such interactions. This physics analysis focuses on the tracker region of the ND280 subdetector. Other π0 analyses using different detector regions are either underway or completed. The physics analysis, after being developed from Monte Carlo studies, was then run on real data. This analysis goes partway towards measuring the neutral-current π0-producing neutrino interaction cross-section, by measuring the rate of such interactions in the T2K experiment's near detector, ND280.

Galvanic anode technology has in recent years come to the fore as a cost-effective method of successfully mitigating the corrosion of reinforcing steel in concrete structures. Developments in the field of cathodic protection have included the introduction of a novel Hybrid anode system, which uses the same sacrificial anode to pass a short-term impressed current before being connected to the steel directly to provide a long-term galvanic current. Galvanic and hybrid technologies are often seen as less powerful solutions in the treatment of reinforcement corrosion, and the test methodologies which determine the efficacy of cathodic protection systems favour impressed current technologies. The work completed has investigated the application of traditional and novel corrosion assessment techniques to laboratory samples to assess the protection offered by the hybrid treatment methodology in both treatment phases. In addition, the response of both galvanic and hybrid anodes to environmental conditions has been recorded and assessed before being discussed in the context of steel protection criteria. Finally, an investigation is presented into the on-site deterioration of commercially pure titanium feeder wire installed as part of the hybrid anode system and potential solutions to the problem have been documented. The research undertaken found that the hybrid anode system is capable of protecting steel in challenging, aggressive environments. This was confirmed by steel corrosion rate and indicative steel potential measurements. The responsive behaviour investigation showed that the current output of galvanic and hybrid anodes responds rapidly to changes in the corrosion risk posed to the steel and that this has a direct effect on anode system lifetimes. An assessment of the polarisation-based protection criteria applied to steel in concrete has found that the standard inhibits the use of responsive behaviour, and that revisions which consider the present risk of steel corrosion by considering the corrosion current resulting from the relative aggressivity of the concrete environment would be more valid in their application. A cathodic protection system based on the concepts of pit re-alkalisation and pH maintenance can fully utilise galvanic anode responsive behaviour. It was discovered that the deterioration of commercially pure titanium feeder wire seen on site installations was due to anodising in the presence of chloride media which had the potential to lead to pitting corrosion. The pitting risk varied depending on the duration of the treatment and proximity to the installed anode. An anodically grown oxide delayed the onset of corrosion in aqueous KBr solution, but did not significantly increase the pitting potential.

Introduction: The management of endodontic emergencies has changed over the last few decades and varies from practice to practice. This is due to the development of new materials, new irrigation techniques, and new evidence-based research which supports clinical success. An updated questionnaire is necessary to further advance the clinical knowledge in endodontic emergencies based on current practices. Therefore, the purpose of this research is to determine the difference practice modalities between members who are board certified, who are not board certified, and endodontic graduate residents. Materials and Methods: In 2021, every member of the American Association of Endodontics (n = 3157) were asked to complete a short survey about clinical practices and 394 (12.5%) completed the survey. The survey included questions regarding length of time between emergency treatment and definitive treatment, routinely prescribed antibiotics and analgesics, cone beam computed tomography use, level of pulp removal and instrumentation, and treatment modalities for teeth that exhibit swelling and drainage. The collected data were then statistically analyzed. Results: The overall preference in recommended analgesia was ibuprofen with 99.2% of all participants indicating that choice. The second most recommended analgesia was acetaminophen. It was recommended by 66.4% of all participants. The most recommended antibiotic was amoxicillin followed by clindamycin. Participants at all levels of education had similar choices in supplemental anesthesia. Board certified endodontists were more likely than non-board certified endodontists or residents to use a CBCT during endodontic emergencies (p < 0.05). Considering microscope use, board certified endodontists were more likely than non-board certified endodontists or residents to always use a microscope (p < 0.05). Most participants choice to wait 1-2 weeks from initiating treatment to completing treatment, an evidence-based recommendation. Majority of participants instrument to apex using the electronic apex locator, and completed the instrumentation in all 7 diagnoses. Among adjunct treatment, incision and drainage on average was selected over leave tooth open, insert drain, and artifistulation. Conclusion: Overall, residents and non-board certified endodontists treat patients similarly. The major differences are in CBCT use and microscope. Majority of participants instrument to the electronic apex locator reading and complete instrumentation. One major concern is the use of clindamycin which is no evidence based any longer and requires greater continued education on its prescription use in patients.

With everyday advances in technology and low-cost economics, processor systems are moving towards split grid shared power delivery networks (PDNs) while providing increased functionality and higher performance capabilities resulting in increased power consumption. Split grid refers to dividing up the power grid resources among various homogeneous and heterogeneous functional modules and processors. When the PDN is shared and common across multiple processors and function blocks, it is called a Shared PDN. In order to keep the power in control on a split-grid shared PDN, the processor system is required to operate when various hardware modules interact with each other while the supply voltage (V [subscript DD]) and clock frequency (F [subscript CLK]) are scaled. Software or hardware assisted power-collapse and low-power retention modes can be automatically engaged in the processor system. The processor system should also operate at maximum performance under power constraints while consuming the full thermal design power (TDP). The processor system should neither violate board and card current limits nor the power management integrated circuit (PMIC) limits or its slew rate requirements for current draw on the shared PDN. It is expected to operate within thermal limits below an operating temperature. The processor system is also required to detect and mitigate current violations within microseconds and temperature violations in milliseconds. The processor system is expected to be robust and should be able to tolerate voltage droops. Its importance is highlighted with the processor system being on shared PDN. Because of the sharing of the PDN, the voltage droop mitigation scheme is expected to be quick and must suppress V [subscript DD] droop propagation at the source while only introducing negligible performance penalties during this mitigation. Without a solution for V [subscript DD] droop in place, the entire V [subscript DD] of shared PDN is forced to be at a higher voltage, increasing overall system power. This can potentially affect the days of use (DoU) of battery-operated systems, and reliability and cooling of wired systems. A multi-threaded processor system is expected to monitor the current, power and voltage violations and react quickly without affecting the performance of its hardware threads while maintaining quality of service (QoS). Early high-level power estimates are a necessity to project how much power will be consumed by a future processor system. These power projections are used to plan for software use cases and to reassign power-domains of processors and function blocks belonging to the shared PDN. Additionally, it helps to re-design boards and power-cards, re-implement the PDN, change PMIC and plan for additional power, current, voltage and temperature violation related mitigation schemes if the existing solutions are insufficient. The split grid shared PDN that is implemented in a system-on-chip (SoC) is driven by low cost electronics and forces multiple voltage rails for a better energy efficiency. To support this, there is a need for incorporation of voltage levels and power-states into a processor behavioral register transfer level (RTL) model. Low power verification is a must in a split-grid PDN. To facilitate these, the RTL is annotated with voltage supplies and isolation circuits that engage and protect during power collapse scenarios across various voltage domains. The power-aware RTL design is verified, identified and corrected for low power circuit and RTL bugs prior to tape-out. The mandatory features to limit current, power, voltage and temperatures in these high performance and power hungry processor systems introduce a need to provide high level power projections for a processor system accounting for various split-grid PDN supplying V [subscript DD] to the processor, the interface bus, various function blocks, and co-processors. To solve this problem, a power prediction solution is provided that has an average-power error of 8% in prediction and works with reasonable accuracy by tracking instantaneous power for unknown software application traces. The compute time to calculate power using the generated prediction model is 100000X faster and uses 100X less compute memory compared to a commercial electronic design automation (EDA) RTL power tool. This solution is also applied to generate a digital power meter (DPM) in hardware for real-time power estimates while the processor is operational. These high-level power estimates project the potential peak-currents in these processor systems. This resulted in a need for new tests to be created and validated on silicon in order to functionally stress the split-grid shared PDN for extreme voltage droop and sustained high current usage scenarios. For this reason, functional test sequences are created for high power and voltage stress testing of multi-threaded processors. The PDN is a complex system and needs different functional test sequences to generate various kinds of high and low power instruction packets that can stress it. These voltage droop stress tests affect V [subscript MIN] margins in various voltage and frequency modes of operation in a commercial multi-threaded processor. These results underscore a need for voltage mitigation solutions. The processor system operating on a split grid shared PDN can have its V [subscript MIN] increased due to voltage stress tests or a power-virus software application. The shared PDN imposes requirements to mitigate the voltage noise at the source and avoid any possibility of increases to the shared PDN V [subscript DD]. This necessitates implementing a proactive system that can mitigate voltage droop before it occurs while lowering the processor’s minimum voltage of operation (V [subscript MIN]) to help in system power reduction. To mitigate the voltage droops, a proactive clock gating system (PCGS) is implemented with a voltage clock gate (VCG) circuit that uses a digital power meter (DPM) and a model of a PDN to predict the voltage droop before its occurrence. Silicon results show PCGS achieves 10% higher clock frequency (F [subscript CLK]) and 5% lower supply voltage (V [subscript DD]) in a 7nm processor. Questions arise about the effectiveness of PCGS over a reactive voltage droop mitigation scheme in the context of a shared PDN. This results in analysis of PCGS and its comparison against a reactive voltage droop mitigation scheme. This work shows the importance of voltage droop mitigation reaction time for a split grid shared PDN and highlights benefits of PCGS in its ability to provide better V [subscript MIN] of the entire split grid shared PDN. The silicon results from power-stress tests shows the possibility of the high-power processor system exceeding board or power-supply card current capacity and thermal violations. This requires designing a limiting system that can adapt processor performance. This limiting system is expected to meet the stringent system latency of 1 µs for sustained peak-current violations and react in the order of milli-seconds for thermal mitigation. It is also expected of this system to maintain the desired Quality of Service (QoS) of the multi-threaded processor. This results in implementation of a current and temperature limiting response circuit in a 7nm commercial processor. The randomized pulse modulation (RPM) circuit adapts processor performance and reduces current violations in the system within 1 µs and maintains thread fairness with a 0.4% performance resolution across a wide range of operation from 100% to 0.4%. Hard requirements from SoC software and hardware require the processor systems to be within the TDP and power budgets and processors sharing the split gird PDN. Power consumed by the threads (processors) are now exceeded by added functionality of new threads (processors), which could consume much higher power compared to power of previous generation processors. The threads (processors) operate cohesively in a multi-threaded processor system and though there is a large difference in magnitude of power profiles across threads (processors), the overall performance of the multi-threaded processor is not expected to be compromised. This enforces a need for a power limiting system that can specifically slow down the high-power threads (processors) to meet power-budgets and not affect performance of low-power threads. For this reason, a thread specific multi-thread power limiting (MTPL) mechanism is designed that monitors the processor power consumption using the per thread DPM (PTDPM). Implemented in 7nm for a commercial processor, silicon results demonstrate that the thread specific MTPL does not affect the performance of low power threads during power limiting until the current (power) is limited to very low values. For high power threads and during higher current (power) limiting scenarios, the thread specific MTPL shows similar performance to a conventional global limiting mechanism. Thus, the thread specific MTPL enables the multi-threaded processor system to operate at a higher overall performance compared to a conventional global mechanism across most of the power budget range. For the same power budget, the processor performance can be up to 25% higher using the thread specific MPTL compared to using a global power limiting scheme. In summary, in this dissertation design for power concepts are presented for a processor system on a split-grid shared PDN through various solutions that address challenges in high-power processors and help alleviate potential problems. These solutions range from embedding power-intent, to incorporating voltage droop prediction intelligence through power usage estimation, maintaining quality of service within a stringent system latency, to slowing down specific high-power threads of a multi-threaded processor. All these methods can work cohesively to incorporate power-awareness in the processor systems, making the processors energy efficient and operate reliably within the TDP.

Electromechanical actuators (EMAs) are seen as the future actuation technology for next-generation, energy-optimized aircraft. Implementation into primary flight control entails many challenges and requires much research, development, and experience to prove the technology’s robustness and maturity. Operation of multiple actuators on a control surface introduces a phenomenon known as force fight, where instead of equally sharing load they behave unequally or oppose each other. Force fight is well studied for hydraulic actuation systems, but limited research has been done on EMAs. The purpose of this thesis is to study force fight experimentally between two X-38 EMAs in a passive spring loaded dual EMA test rig. Static and dynamic analytical models of the test setup were created to assist the force fight study. The command to both EMAs was a 1-Hz, 5-degree-amplitude sine wave of ten cycles. Known force fight conditions of position lag, gain, and offset errors were introduced to each EMA in turn and the impacts of each condition were examined in terms of force difference and energy consumption. Torque, rotation, voltage, current, and power were measured from the test stand along with EMA controller position and current monitors for data analysis. Energy demand of the EMAs was calculated from the integral of the mechanical and electrical power. The force difference impact also was analyzed utilizing the maximum and minimum force difference as recorded on the torque cells. It was shown that all three cases, lag, gain, and offset, resulted in significant force fight between the two EMAs expressed as force difference. The magnitude of force fight was a linear function of the magnitude of the errors. In addition, both the gain and offset errors caused significant increase in total electrical energy demand, the larger the gain or offset, the higher the electrical energy demand, while the lag errors showed slight electrical energy increase. It also was shown that mechanical energy difference between the two EMAs did not increase noticeably with the increase of the errors for the gain and offset cases, while the lag test showed a significant amount of mechanical energy difference between the two EMAs. Lastly, the model prediction of the maximum and minimum force fight was shown in good agreement with the experimental test results and, therefore, it is believed that the models could serve as a tool to analyze force fight scenarios that are outside the capability of the test rig.

This laboratory study was centered on the mechanical design and interaction of the two model marine hydrokinetic (MHK) turbines arranged in a stream-wise tandem configuration. The goal was to design and machine a model MHK turbine which performs in the same fashion as full scale device. In addition, experiments were performed to determine the effect of an upstream turbine on the performance of the downstream turbine. Specifically, the study focuses on the changes in nondimensional power generation that occurred as the stream-wise spacing between devices was varied. Understanding the interaction effect between laboratory scale marine hydrokinetic devices is an important step prior to field deployment. Currently only few studies have addressed the issues of non-dimensionalizing the performance of a turbine when the turbine is operating in a non-uniform flow. This study addresses the question: to what degree is there a practical basis for comparison of marine hydrokinetic turbine performance when a turbine operates in a non-uniform flow? In other words, what is the basis for relating the off-design behavior to on-design behavior due to non-uniform inflow? Testing was conducted in the hydraulic flume facility (9.8 m long, 1.2 m wide and 0.4 m deep) at Bucknell University. Two types of turbine model were used. A two-bladed turbine with a rotor diameter of 0.1 meters and a three-bladed turbine with a rotor diameter of 0.12 meters. Multiple tests were performed for a fixed range of separation distances between each set of the devices. For each separation distance, a mechanical power extracted from the flow was measured. In addition, velocity profiles incident on the downstream turbine were measured at each separation location and used in developing velocity scales to be used in non-dimensionalizing the performance of the downstream turbine. Results demonstrate that the performance of a downstream turbine is affected by the presence of the upstream turbine. The evolution of the wake was directly related to the performance of the downstream turbine and that the velocity scale used in nondimensionalizing the performance of the downstream turbine needs to be carefully developed. Results shows that an ideal separation distance could exists between devices such that the power generation and performance of the downstream turbine are maximized.

Research on electrochemical disinfection of municipal wastewater has been conducted at the University of New Orleans using a continuous flow electrochemical reactor connected to a direct current (DC) power supply changing its polarity and varying the electrode distance. Bacterial inactivation and chlorine production were the main parameters that were recorded. After months of research, it was determined that the electrochemical disinfection reactor is efficient and has a great potential for the future. There is no need to use chlorine and it has low operation costs. The following design recommendations for an electrochemical disinfection unit were given: A detention time of 5 +- 0.3 minutes A minimum volumetric current density of 1000 amps/m3 A minimum detention current density of 80 amps.hr/m3 The combination of the three recommended design values yielded excellent disinfection efficiencies and low chlorine production.

Direct methane SOFCs, operated by supplying methane to Ni/YSZ anodes, suffer from degradation via accumulation of carbon deposits on the Ni surface. We proposed the anode modification by La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) perovskite catalyst to improve long-term stability of direct CH4-SOFCs. Coating a 40 µm thin film of LSCF on the Ni/YSZ anode surface decreased the amount of carbon deposits and slowed down the degradation rate. The improvement in the anode durability could be related to the oxidation activity of LSCF which facilitated oxidation of CH4 and carbon deposits. Analysis of the crystalline structure of LSCF revealed that LSCF was stable in the reducing anode environment under H2 and CH4 flow at 750 °C and retained its perovskite structure throughout the 475 h long-term stability test. Toward development of stable direct CH4-SOFCs we studied internal dry reforming of methane in SOFC stack. Dry reforming of CH4 with CO2 on the Ni/YSZ anode of SOFC produced H2 and CO which further underwent electrochemical oxidation for power generation. The CH4/CO2-SOFC exhibited long-term stability greater than 290 h. The stable performance of the SOFC stack was attributed to less carbon deposition on the anode as evidenced by the result of Raman spectroscopy and calculated amount of CO2 produced from oxidation of deposited carbon. For the first time, Fe-Ti-O (titania-supported iron oxide) chemical looping particle was used as a solid fuel for direct contact with the Ni/YSZ anode surface. Electrochemical oxidation of reduced Fe-Ti-O at 750 °C produced a maximum power density of 97 mW/cm2, corresponding to 84% of that in H2 fuel. The Fe-Ti-O pellets were able to generate stable electricity under repeated electrochemical oxidation and hydrogen reduction cycles. This study demonstrated that coupling a SOFC with an external reducer using Fe-Ti-O oxygen carrier is a good candidate for electricity generation. We developed two main approaches for improvement of long-term stability of direct methane SOFCs including anode modification and adjusting fuel composition for coke-free operation. We also proposed a novel concept of coupling the SOFC stack with chemical looping process and directly utilize Fe-Ti-O chemical looping particles as solid fuel for power generation in SOFC.

For humanoid robots to function in changing environments, they must be able to maintain balance similar to human beings. At present, humanoids recover from pushes by the use of either the ankles or hips and a rigid body. This method has been proven to work, but causes excessive strain on the joints of the robot and does not maximize on the capabilities of a humanlike body. The focus of this paper is to enable advanced dynamic balancing through torque classification and balance improving positional changes. For the robot to be able to balance dynamically, external torques must be determined accurately. The proposed method of this paper uses current sensing feedback at the humanoids power source to classify external torques. Through understanding the current draw of each joint, an external torque can be modeled. After being modeled, the external torque can be nullified with balancing techniques. Current sensing has the advantage that it adds detailed feedback while requiring small adjustments to the robot. Also, current sensing minimizes additional sensors, cost, and weight to the robot. Current sensing technology lies between the power supply and drive motors, thus can be implement without altering the robot. After an external torque has been modeled, the robot will undertake balancing positions to reduce the instability. The specialized positions increase the robot's balance while reducing the workload of each joint. The balancing positions incorporate the humanlike body of the robot and torque from each of the leg servos. The best balancing positions were generated with a genetic algorithm and simulated in Webots. The simulation environment provided an accurate physical model and physics engine. The genetic algorithm reduced the workload of searching the workspace of a robot with ten degrees of freedom below the waist. The current sensing theory was experimentally tested on the TigerBot, a humanoid produced by the Rochester Institute of Technology (RIT). The TigerBot has twenty three degrees of freedom that fully simulate human motion. The robot stands at thirty-one inches tall and weighs close to nine pounds. The legs of the robot have six degrees of freedom per leg, which fully mimics the human leg. The robot was awarded first place in the 2012 IEEE design competition for innovation in New York.

Abstract: For Molecular Electronics to become a viable replacement or complitment to current elec- tronic devices a fundamental understanding of device operation and functionality is needed. This work explores electron transport through diazonium derived molecular junctions via conductive atomic force microscopy to provide insight into the scalability of molecular de- vices. The attenuation coefficient and electron transport properties of nitroazobenzene on carbon; were found to be consistent with larger ensemble molecular junctions. Further, ap- plied force significantly decreased the resistance through the layer due to reduced tunneling distance and increased contact area. Electron transport through nitroazobenzene was ex- tended to gold surfaces and found to be in agreement with studies on carbon. Investigation of mixed-mode bonded layers of nitroazobenzene and dodecanethiol determined that surface coverage was controllable through solution concentration and sweep rate. Qualitatively it was observed that conductivity increased with nitroazobenzene coverage.

The electrical distribution system in the United States is considered one of the most complicated machines in existence. Electrical phenomena in such a complex system can inflict serious self-harm. This requires damage prevention from protection schemes. Until recently, there was a safe gap between capacity to deliver power and the demand. Therefore, these protection schemes focused on dependability allowing the disconnection of lines, transformers, or other devices with the purpose of isolating the faulted element. On some occasions, the disconnections made were not necessary. The other extreme of reliability calls for security. This aspect of reliability calls for the operation of the protective devices only for faults within the intended area of protection. There is a tradeoff here; where a dependable protection scheme will assuredly prevent damage, it is prone to unnecessary operation which can lead to cascading outages. Where a secure scheme will not operate unnecessarily, it is prone to pieces of the system becoming damaged when relays fail to operate properly. With microprocessor based relaying schemes, a hybrid reliability focus is attainable through adaptive relaying. Adaptive relaying describes protection schemes that adjust settings and/or logic of operations based on the prevailing conditions of the system. These adjustments can help to avoid relay miss-operation. Adjustments could include, but are not limited to, the logging of data for post-mortem analysis, communication throughout the system, as well changing relay parameters. Several concepts will be discussed, one of which will be implemented to prove the value of the new tools available.

Current-mode control is a commonly adopted method of regulation for pulse-width modulated (PWM) dc-dc power converters in industry, but is not well understood. The advantages of current-mode control over the voltage-mode control include inherent overload and short circuit protection, faster response, line-noise rejection, and multiple converter paralleling. Current-mode controlled system consists of (1) aninner-current loop and (2) an outer-voltage loop, which sets the reference voltage to the inner loop. To ensure stable operation of the multi-loop converter, all the sequential loops in the circuit should be stable with sufficient degree of stability. The research in this dissertation is focused on the relative stability of the inner-current loop in peak current-mode (PCM) controlled PWM dc-dc converters operating in CCM.The operating principle of peak current-mode control is presented. The inner-current loop dynamics of a peak current-mode controlled dc-dc converter is investigated using perturbation theory. Considering its mixed-signal (analog and digital) behavior, the current loop is modeled using sample-and-hold theory. Taking the discrete nature of the inner-current loop into account, a closed-loop transfer function for the current loop is derived in z-domain and an equivalent-hold approximation is used to derive an approximate closed-loop transfer function in the continuous s-domainusing modified Pad´e approximation. A general expression for the loop gain of the inner-loop, independent of the converter topology, is derived. Using the loop gain, a measure of relative stability of the inner loop is developed. Expressions for amountof slope compensation required at maximum duty cycle, for the inner loop to be marginally stable and to achieve a specified margin of stability, are derived. Also, expressions for maximum duty cycle at a given amount of slope compensation, for the inner loop to be marginally stable and to obtain a specified margin of stability, are derived. The control current expressions for the inner loop of peak current-mode controlled converters without and with slope compensation are derived. A procedure to design the inner-current loop is developed. Saber Sketch simulation and experimentalresults are presented to validate the presented theory.The dynamic behavior of the inner-current loop of peak current-mode controlled PWM dc-dc buck converter operating in CCM is analyzed. The critical path power stage transfer functions, the relevant inner-current loop transfer functions, and the control-to-output transfer function of peak current-mode controlled PWM dc-dc buck converter operating in CCM are derived. The presented model is validated using experimental Bode plots.

High-temperature integrated circuit (IC) design is one of the new frontiers in microelectronics that can significantly improve the performance of the electrical systems in extreme environment applications, including automotive, aerospace, well-logging, geothermal, and nuclear. Power modules (DC-DC converters, inverters, etc.) are key components in these electrical systems. Power-to-volume and power-to-weight ratios of these modules can be significantly improved by employing silicon carbide (SiC) based power switches which are capable of operating at much higher temperature than silicon (Si) and gallium arsenide (GaAs) based conventional devices. For successful realization of such high-temperature power electronic circuits, associated control electronics also need to perform at high temperature. In any power converter, gate driver circuit performs as the interface between a low-power microcontroller and the semiconductor power switches. This dissertation presents design, implementation, and measurement results of a silicon-on-insulator (SOI) based high-temperature (>200 _C) and high-voltage (>30 V) universal gate driver integrated circuit with high drive current (>3 A) for SiC power switches. This mixed signal IC has primarily been designed for automotive applications where the under-hood temperature can reach 200 _C. Prototype driver circuits have been designed and implemented in a Bipolar-CMOS- DMOS (BCD) on SOI process and have been successfully tested up to 200 _C ambient temperature driving SiC switches (MOSFET and JFET) without any heat sink and thermal management. This circuit can generate 30V peak-to-peak gate drive signal and can source and sink 3A peak drive current. Temperature compensating and temperature independent design techniques are employed to design the critical functional units like dead-time controller and level shifters in the driver circuit. Chip-level layout techniques are employed to enhance the reliability of the circuit at high temperature. High-temperature test boards have been developed to test the prototype ICs. An ultra low power on-chip temperature sensor circuit has also been designed and integrated into the gate-driver die to safeguard the driver circuit against excessive die temperature (_ 220 _C). This new temperature monitoring approach utilizes a reverse biased p-n junction diode as the temperature sensing element. Power consumption of this sensor circuit is less than 10 uW at 200 _C.

JAMES, BRADLEY ADAM. Static Generation and Suppression in Staple Fiber Yarns. (Under the direction of Dr. William Oxenham and Dr. Abdel-Fattah Seyam). Triboelectric effects have been studied since before the times of Christ. In more modern times, the evidence of danger and damage inherent with this phenomenon has become apparent. Much is known and theorized upon about how static electricity is generated, yet there is still much to learn. One of the most widely experienced effects of static buildup is caused by clothing or textile products. Industries worldwide have turned to the textiles markets to develop solutions on combating this nascence. From antistatic chemical treatments to conductive fibers added into processing, many innovative new solutions are still being developed. In order to develop more effective solutions, it is critical to understand more about the triboelectric phenomenon as it relates to the particular materials and substrates in question. Spun yarns are the most widely produced yarns for apparel in the world and are often used in conjunction with antistatic treatments. This research is intended to focus on better understanding some of the variables that affect static buildup and propagation within staple spun yarns. It will specifically focus on understanding the effects of blend, yarn structure, temperature, humidity, and tension as well as variables associated within these factors, such as hairiness and uniformity. This understanding will be developed based on statistically based trails utilizing highly technical equipment specifically developed at NC State and other equipment such as evenness testers and hairiness testers for understanding this phenomenon. Specific tests regarding fiber parameters such as hairiness and oil extractable content from polyester, innovative visual techniques, resistance testing, and voltage measurements all completed within temp/humidity controlled environments will all be used in conjunction to develop theories and understanding into the triboelectric effects of polyester and cotton staple structures. The results indicate that environmental humidity and temperature play critical roles in how staple yarns will perform. Tension plays little role into the charge generated as speed is shown to be the main contributing factor to charge generation. There are also differences observed within yarn structures as well as non-linear relationships between cotton and polyester blends. Specific reasoning has been developed based on supplemental data provided by other non-static measuring on non-electrical measuring tests. The results as well as the measuring processes themselves have led to further fields of interest in this topic which warrant further studies. This information collectively will help in understanding of physical principles of triboelectric charge and developing more effective solutions for combating static buildup as well as providing potential insight into static’s influence in the spinning procedures themselves.

Several studies suggest that childhood maltreatment has negative health consequences in adulthood. In addition, there is some evidence that the experience of childhood maltreatment is associated with less supportive relationships. Since social relationships are important for health, having less supportive relationships may affect vulnerability to negative health outcomes. This dissertation examines the effects of three subtypes of childhood maltreatment (i.e., emotional, moderate physical and severe physical) on current social relationships and physical health. The analysis is based on data from the National Survey of Midlife Development in the United States (MIDUS) 1995-1996, a nationally representative random-digit-dial sample of non-institutionalized, English-speaking adults who were aged 25-74 at the time of the survey. This dissertation addresses the following specific questions: (1) Does childhood maltreatment influence perceptions about relationships with spouse, family and friends? (2) Do the effects of childhood maltreatment on perceptions about social relationships vary with age? (3) Does childhood maltreatment affect current psychological resources, and do psychological resources mediate the links between childhood maltreatment and perceptions about social relationships? and (4) Do perceptions about social relationships and psychological resources mediate the childhood maltreatment-adult physical health relationship? The data suggest that childhood maltreatment is negatively associated with perceptions about social relationships and this association tends to be evident across the age groups studied (25 to 74 years). The data also suggest that childhood maltreatment is negatively associated with psychological resources and with physical health. Personal control and self acceptance mediated the effects of childhood maltreatment on current health, but the other examined psychological resources did not mediate this relationship. The findings provide important insights into the long-term effects of childhood maltreatment on social relationships and physical health. Implications for practice and future research are discussed. Milton, J. (1671). Paradise regained: A poem in four books. London: JM.

How do individuals represent others' current thoughts or future feelings? Five studies examined individuals' mindreading judgments. Across 4 yearly measurement occasions, 3,457 adolescents in Study I inferred parents' value beliefs by judging the importance their parents place on the adolescent doing well in math or English. Parents and adolescents reported their own value beliefs in these same two domains. Analytic interest centered on the relationships among the progression of attributions and the progressions of personal beliefs. Individual growth curves were estimated for these inferences and beliefs. The present model regressed an actor's mindreading trajectories on the belief trajectories of the actor and partner. Results revealed that the linear progression of adolescents' own value beliefs predicted the linear rate of change in their mindreading inferences more than did parents' trajectories. Study 2 extended the phenomenon to a non-academic belief (popularity) and to an affective forecast (predicted upset feelings). Study 3 replicated the phenomenon with 1,070 children in both academic (math, reading) and non-academic (popularity) belief domains. Results indicated changes in children's own beliefs predicted their mindreading inferences more than did changes in parents' own beliefs. Study 4 examined adults' mindreading accuracy across belief domains. Whereas adults demonstrated the same trend children did for popularity, both changes in parents' and changes in children's' own beliefs predicted parents' math and reading attributions. Study 5 examined income and education as moderators of belief predictions and affective forecasts.

Earthworms have been shown to effectively process biodegradable organic waste and increase the its level of available plant nutrients to plants. Earthworms are typically mechanically separated from the finished product. This study investigated the effectiveness of an electric field at separating earthworms from an organic media by repelling them. Results showed that the effectiveness of an electric field at repelling earthworms is a function of the voltage created across earthworms, which in turn is a function of electrode depth, spacing, earthworm species (and resulting diameter and resistance) and electric current level at the threshold beyond which earthworms are repelled. Each factor was shown to significantly affect the effectiveness with which earthworms were repelled. This was concluded from experiments where earthworms were placed in a soil slab at a density corresponding to 150 earthworms per liter, and effectiveness of the electric field was calculated as a function of the number of earthworms that exited the soil slab. Results showed that the effectiveness of the electric field was logarithmically proportional to the voltage generated across earthworms, at a given electrode spacing, up to the point of mortality onset. At higher voltages the electric field effectiveness decreased exponentially due to mortality. The time where all potential earthworms exited a soil slab increased exponentially up to peak effectiveness, and decreased exponentially after that. Testing the derived model showed that it applies to any soil type, since results showed that soil properties including salinity, moisture content and porosity are accounted for by soil resistance, which is used to calculate the electric current term in the model. A comparison between alternating and direct current showed an increased effectiveness of the model when alternating current was used. A model of electric current diffusion in earthworm casts suggested that at increasing voltage levels, the distance from the electric field at which an optimal electric current level can be found converges to a single value. The mathematical models derived from this study can be used for the preliminary design of an electric earthworm separator consisting of an array of current-conducting rods connected to a power or voltage source.

Advances in neural prostheses are strongly dependent on the development of microelectrodes having the ability to produce high fidelity sensation or to selectively control the activity of neural ensembles. Numerous devices have been developed to stimulate neural tissues and record neural responses. However, in order to instrument large volumes of neural tissue to allow detailed mapping of neural pathways and realistically assess the efficacy of neural prostheses, it is necessary to develop high-density three-dimensional microelectrode arrays suitable for chronic applications. This thesis research has demonstrated the feasibility of a high-density low-profile microelectrode array for selective stimulating and recording in the central nervous system. The array consists of a number of 64-site 8-channel CMOS probes, a silicon platform to support the probes on the cortical surface, spacers to hold the probes orthogonal to the platform, and a hybrid chip for platform address decoding. The CMOS probes feature on-chip current generation to deliver biphasic currents from -127muA to +127muA to selected sites with 1muA resolution and an on-chip preamplifier having a gain of 40dB from 100Hz to l0kHz. This array can be easily expandable to achieve higher density without increasing the number of interfacial leads or the complexity of on-chip circuitry. These devices are fabricated in a 3mum, p-sub/n-epi/p-well 2P/1M micromachined CMOS technology. A low-profile structure has been developed so that the probe backend supporting the CMOS circuitry can be folded parallel to the cortical surface to minimize the height of the final array above the cortex in order to keep the implant free of the skull in chronic applications. An integrated silicon/parylene batch fabrication process has been developed to incorporate parylene coating into the batch fabrication of the silicon microelectrode, which allows parylene coating and selective removal at wafer level prior to probe release. Microassembly techniques have also been developed to facilitate assembly of a robust 3D array. The functionalities of the STIM-3 probe have been demonstrated both in-vitro and in-vivo. The techniques developed in this research should allow significant advances in development of high-density chronic neural implants for use in neuroscience and should set the stage for practical neural prostheses.

A comprehensive steady-state one-dimensional photochemical model of the atmosphere of Titan has been developed. This model has included updated chemistry with a focus on rate coefficients and cross sections measured under conditions most applicable for simulation of Titan's atmosphere. Through this simulation, the physical and chemical processes which affect the altitudinal distribution of constituents in Titan's atmosphere have been explored. The model results, in comparison to previous Titan photochemical models, compares favorably with ground-based and fly-by observations of Titan's atmosphere. As a result, the model has facilitated the analysis of key questions regarding the nature of Titan's present chemistry, involving the production of key molecules and hazes. These questions include the role constituent density profiles may play in constraining methane photolysis quantum yields, the existence and formation mechanisms of benzene in Titan's atmosphere, and the chemical origin of Titan haze. Results show that the determination of CH3C2H and C3H6 abundance profiles will help constrain the CH quantum yield from methane photolysis, which varies significantly among photolytic schemes. Results also show that benzene can be formed in Titan's atmosphere, and the aromatic chemistry that ensues is the likely source of the Titan haze which enshrouds the surface. The origin of Titan's atmosphere has also been studied through a pseudo-time-dependent model which describes the evolution of the likely primordial ammonia inventory during the early stages of the solar system. Assuming an enhanced T-Tauri solar flux, the conversion of ammonia to nitrogen, in the presence of methane and water vapor, is found to be a plausible mechanism to account for the present-day nitrogen inventory. Results from this model are presented in preparation for the retrieval and interpretation of data from the Cassini-Huygens spacecraft, which will arrive at Titan in 2004.

In this dissertation I investigate the influence of firm relative performance and prior expansion experience on the likelihood and form of foreign market expansion by all firms in the United States international message telephone service industry between 1985 and 1998. Employing theories of organizational change, learning and structural inertia, I argue that firm foreign market expansion is directly affected by both firm characteristics (performance and experience) and its competitors' expansions (competitive contagion). I extend these theories by arguing that the imitative form of expansion, as captured by the influence of competitive contagion, is moderated by performance and experience. I hypothesize that there is a non-monotonic U-shaped relationship between relative performance and expansion, and that expansion experience has a monotonic positive effect on expansion. I then hypothesize that increasing relative performance and expansion experience, which decrease uncertainty in expansion, decrease the strength of imitation in expansion. I find that both performance and experience have significant monotonically positive effects on expansion. The strength of imitative expansion is unaffected by expansion experience, however rising relative performance decreases the strength of imitation. These findings lead to three theoretical implications for firm change and learning. First, the positive relationship between performance and expansion suggests that firm change research founded on the behavioral theory of the firm depends on the context of change and is potentially mis-specified in the behavioral assumption of satisficing. Second, the finding that improving performance increases the likelihood of expansion but also decreases the influence of contagion suggests that exploitative and explorative search forms are not mutually exclusive. Third, the strength of competitive contagion in expansion, even in the presence of firm characteristics, provides strong support for studies of change that include both firm and inter-firm characteristics.

An original model based upon mathematical theory and coupled with numerical methods has been developed in an effort to quantify and describe some of the aspects of submarine channel and fan development. The foundation of the model consists of the two-dimensional, vertically-integrated, time-dependent equations of turbidity currents which are based upon the laws of flow volume, momentum, and sediment conservation. The model has been extended to include nonuniform sediment and the most advanced, empirically-based expressions are implemented for model closure. In addition, a continuity equation for the bed sediment is solved in order to track bed development. A total variation diminishing (TVD) finite volume method has been utilized for solving the aforementioned system equations. Predictor-corrector time stepping is employed along with a monotone, upstream scheme for conservation laws (MUSCL) extrapolation of state variables to obtain a second-order scheme. Flux limiting is used to prevent the development of spurious oscillations. This is a state-of-the-art method that has been widely used by aerospace researchers, and has recently been implemented by hydrodynamicists to solve the shallow-water equations. The model has been modified to allow for the simulation of turbidity surges over a bed covered with ambient fluid only. This is analogous to the dry-bed dam-break problem associated with the shallow-water equations and requires special treatment. The behavior and accuracy of this modification are examined through theoretical reasoning and numerical experiments. Analytical solutions utilizing characteristic theory are developed as an original effort and used for verification of the numerics of the model. Verification of the sedimentation aspects of the model is accomplished by comparing numerical predictions with experimental data. In addition, the model is used to perform numerical experiments in an attempt to describe the behavior of turbidity currents and bed evolution under varying environments and boundary conditions. In addition, other phenomena are investigated such as aggradation, avulsion, and the channelization of deposits in a submarine environment. Finally, two applications of the model to cases in which field data are available are presented in order to demonstrate the ability of the model to simulate flow events in a natural setting.

A synthetically-accelerated response matrix method with heterogeneous coarse-mesh capability has been developed for the solution of neutral particle transport problems. Implementation of the method proceeds as follows. The transport problem domain is divided into sub-domains called regions; the equation is then discretized on each region using a relatively fine mesh. The resulting matrix equation is solved by direct inversion, yielding fine-mesh (local) response matrices. At this point a fine mesh to coarse mesh projection can be performed to generate coarse-mesh (global) response matrices, resulting in fewer unknowns in the ensuing global calculation. The synthetically-accelerated global calculation, which is performed by assembling the response matrices from all regions and using interface fluxes to link the regions, yields a converged interface flux distribution. This distribution can be used in conjunction with the previously stored fine-mesh response matrices to generate the detailed flux distribution within each region. A modified four-step procedure was created for synthetic acceleration of transport calculations which use discontinuous finite elements for spatial discretization; it can be applied in any geometry, uses a diffusion equation for acceleration, and appears to be unconditionally stable and rapidly convergent. A boundary projection acceleration scheme was created as well; it can be applied in any geometry regardless of discretization method, and appears to be rapidly convergent, but its acceleration equations may not always be as easy to solve as is a diffusion equation. A fine mesh to coarse mesh projection procedure was devised which allows fine-mesh accuracy to be obtained with a very coarse (heterogeneous) mesh. Recognizing that the important information from the global calculation is the interface flux distribution, the procedure seeks to reproduce important characteristics (such as partial currents) of the exiting angular flux from a region while representing the interior flux with a small number of unknowns.

A traditional objective of ergonomics has been to improve workspace designs through consideration of the human operator. While many reasons may explain a designer's failure to consider ergonomics in human-workspace systems, this research focused on the limitations due to (1) methods of information presentation which are incompatible with design strategies, and (2) difficulties in assessing multiple design factor interdependencies. A designer survey, administered to 40 engineers in 5 companies, quantified ergonomic design information needs and activities for three work-space applications (i.e., manual assembly, machine loading, and manual materials handling). Survey responses also identified the scope, user interface and specific input/output formats for a computer-based ergonomic design system. Distinct differences in design initiation, ergonomic information sources and design goals existed between preliminary design and detailed final design activities. A lack of complete information, reliance on previous designs as information sources and concentration on functional requirements were unique to the preliminary design stage. Reduced flexibility in design alternatives, concern for workplace health and safety, and a desire for design optimization existed in the final design stages. A complimentary research effort developed comprehensive models for operator, workspace and task information using available computer-based ergonomic analysis tools which predicted worker static strengths, reach capabilities and task motion times performance. The framework and prototype system implementation allowed interactive graphic workspace layout, task element description and operator and ergonomic design criteria specification. It provided indicators of operator performance limitations resulting from specific design conditions, and contained mechanisms for modifying and evaluating alternate designs. Persons using the system for preliminary design obtained ergonomic information through presentation of design guidelines, which identified regions of acceptable design solutions. Those involved in final design performed multiple ergonomic analyses with results conveyed through integrated tables, performance graphs, and three-dimensional enfleshed operator and workspace layouts. Formalized system demonstrations on an HP-1000 mini-computer were effective in predicting operator physical stresses associated with different tasks and investigating design alternatives. Areas for future research were identified and include development of enhanced operator performance models and organizational issues, such as where the system should be located and what type of user training is needed.

This study traces the history, evolution and current status of suicide prevention programs in the United States between 1955 and 1979 in order to determine the manner in which the movement's objectives are being addressed. The study explores the influence of organizations such as the American

According to the Standard Model of electroweak interactions, the weak charged-current has a universal V-A Lorentz structure. In order to test the charged-current coupling of the $\tau$ lepton, the chirality parameter $\xi\sb{h}$ was measured in the decays $\tau\sp-\to\pi\sp-\nu\sb\tau$ and $\tau\sp-\to\rho\sp-\nu\sb\tau.$ This measurement is based on an integrated luminosity of 148 pb$\sp{-1}$ for $\rm e\sp+e\sp-$ interactions at center-of-mass energies near the Z boson mass. These interactions were recorded with the L3 detector at the LEP $\rm e\sp+e\sp-$ collider located at CERN. The data sample consists of 41608 selected $\rm Z\to\tau\sp+\tau\sp-$ events in which at least one of the $\tau$ decays is identified as $\tau\to\pi\nu$ or $\tau\to\rho\nu.$ The chirality parameter and the average $\tau$ polarization in $\rm Z\to\tau\sp+\tau\sp-$ are measured simultaneously by using the decay spectra of individual $\tau$ decays and by exploiting the correlations between the $\tau\sp+$ and $\tau\sp-$ in an event. Assuming universality in $\tau$ decays, the results are:$$\eqalign{\xi\sb{h} &= {-}1.031 \pm 0.031 \pm 0.014\cr {\cal P}\sb\tau &= {-}0.149 \pm 0.011 \pm 0.015,\cr}$$where the first error is statistical and the second error is systematic. This value of $\xi\sb{h}$ agrees with the Standard Model construction of a pure V-A weak charged-current, and this value of ${\cal P}\sb\tau$ agrees with determinations from other experiments.

The purpose of this study was to investigate the perceptions of selected doctoral students in music education and current music education faculty, music supervisors, and music teachers (n = 22) with regard to multicultural music education and related issues. During serial interviews, the following questions were addressed: (1) What are the perceptions of prospective and current music education faculty, music supervisors and music teachers with regard to multicultural music education? (2) What personal experiences influenced those perceptions? and (3) To what extent is multicultural music education a part of their thinking about teaching? Fifteen issues were discussed: (1) parameters of multicultural music education, (2) role of gender issues, (3) authenticity, (4) availability of curriculum resources, (5) curriculum design: selection of cultures, (6) curriculum design: amount of time spent on multicultural music, (7) role of the ethnomusicologist, (8) minority hiring, (9) multicultural music education at the preservice level, (10) rationale or philosophy, (11) problems in implementation, (12) responsibility for implementation, (13) the degree of threat to music in the Western art tradition, (14) strategies for teaching music that is closely tied to religion and ritual, and (15) the relationship of multicultural music education to future trends in education. The data were presented in twenty-two case studies representing a distillation of participants' interviews. Taken collectively, these case studies provided a multi-faceted description of selected music educators' perceptions of multicultural music education. Although a range of positive and negative attitudes toward multicultural music education was displayed, the majority of participants recognized the need to reflect the changing cultural demographics of America in music classrooms, but did not believe that they had the training to do so. A sound philosophical foundation for multicultural music education was absent from much of the participants' perceptions, even among those most in favor of developing and implementing a multicultural music curriculum. These findings demonstrate the urgent need for the music education profession (1) to develop and practice a clearly articulated philosophy of music education that incorporates a multicultural perspective and (2) to implement and participate in more intensive inservice and preservice multicultural music education programs.

Density currents are typified by flows along the bottom of oceans or lakes. Such currents occur because the water flowing into the receiving water is colder, saltier or contains more suspended sediment. Numerous studies of density currents have been carried out over several years, and still inconsistencies between predictions and experimental results have not been resolved. Previous experimental studies showed density currents with slower propagation speeds and larger density current thicknesses than those prescribed by a momentum balance analysis. Modifications to the basic momentum balance analysis have been developed to account for the observed slower propagation speeds; such modifications are not predictive in that there are required empirical coefficients to describe the experimental observations. In this study various analytical models that describe density currents were evaluated in terms of their ability to reproduce the experimental results. A formulation based on energy considerations, a minimum energy condition, was studied and its applicability over the whole range of flow conditions was tested. This formulation allows for density currents with larger thicknesses and slower propagation speeds than those prescribed by any momentum balance analysis. The minimum energy formulation predicts density current characteristics in an absolute frame of reference while the formulations based on the momentum balance analysis express their results in a frame of reference moving with the current front. Therefore significant differences in predicted propagation speeds arise among the various theories in situations where the receiving fluid is allowed to move in counter or coflowing conditions. In this investigation an experimental study of density currents flowing over horizontal boundaries was performed. The experimental work consisted of density currents produced by a continuous release of a heavy fluid (salt water flow) into a lighter fluid (fresh water ambient flow). The experimental setup provided flexibility to impose arbitrary flow conditions in the receiving fluid. The experiments were performed over a wide range of flow configurations to test conditions in which significant differences between various theoretical predictions were present. Extreme conditions such as very large coflows and counterflows were tested. Measurements of frontal velocity, density profiles, total water depth and flow rates were made during the experiments. It was found in this investigation that the minimum energy formulation was able to describe density current characteristics such as front propagation speed and current thickness better than any of the other formulations reviewed. Limits on current propagation were established in terms of the maximum possible relative current thickness as described by the minimum energy condition. Counterflows were limited by a maximum intrusion flow rate and coflows were limited by a maximum propagation speed.