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Turbulent Dynamos and Magnetic Helicity

Description: It is shown that the turbulent dynamo alpha-effect converts magnetic helicity from the turbulent field to the mean field when the turbulence is electromagnetic while the magnetic helicity of the mean-field is transported across space when the turbulence is elcetrostatic or due to the elcetron diamagnetic effect. In all cases, however, the dynamo effect strictly conserves the total helicity expect for a battery effect which vanishes in the limit of magnetohydrodynamics. Implications for astrophysical situations, especially for the solar dynamo, are discussed.
Date: April 1, 1999
Creator: Ji, Hantao
Partner: UNT Libraries Government Documents Department

Report on Toyota/Prius Motor Torque Capability, Torque Property, No-Load Back EMF, and Mechanical Losses, Revised May 2007

Description: In today's hybrid vehicle market, the Toyota/Prius drive system is currently considered the leader in electrical, mechanical, and manufacturing innovations. It is significant that in today's marketplace, Toyota is able to manufacture and sell the vehicle for a profit. This project's objective is to test the torque capability of the 2004 Prius motor and to analyze the torque properties relating to the rotor structure. The tested values of no-load back electromotive force (emf) and mechanical losses are also presented.
Date: May 31, 2007
Creator: Hsu, J.S.; Ayers, C.W.; Coomer, C.L.; Wiles, R.H.; Burress, T.A.; Campbell, S.L. et al.
Partner: UNT Libraries Government Documents Department

Report on Toyota/Prius Motor Torque-Capability, Torque-Property, No-Load Back EMF, and Mechanical Losses

Description: In today's hybrid vehicle market, the Toyota Prius drive system is currently considered the leader in electrical, mechanical, and manufacturing innovations. It is significant that in today's marketplace, Toyota is able to manufacture and sell the vehicle for a profit. This project's objective is to test the torque capability of the 2004 Prius motor and to analyze the torque properties relating to the rotor structure. The tested values of no-load back electromotive force (emf) and mechanical losses are also presented.
Date: September 30, 2004
Creator: Hsu, J.S.
Partner: UNT Libraries Government Documents Department


Description: The voltage or electric potential difference across the terminals of a cell when no current is drawn from it. The emf of a cell is the sum of the electric potential differences (PDs) produced by a separation of charges (electrons or ions) that can occur at each phase boundary (or interface) in the cell. The magnitude of each PD depends on the chemical nature of the two contacting phases. Thus, at the interface between two different metals, some electrons will have moved from the metal with a higher free energy of electrons to the metal with a lower free energy of electrons. The resultant charge separation will produce a PD (just as charge separation produces a voltage across a capacitor) that, at equilibrium, exactly opposes further electron flow. Similarly, PDs can be produced when electrons partition across a metal/solution interface or metal/solid interface, and when ions partition across a solution/membrane/solution interface.
Date: September 16, 1998
Creator: Archer, M. D. & Feldberg, S. W.
Partner: UNT Libraries Government Documents Department

Nature and measurements of torque ripple of permanent-magnet adjustable-speed motors

Description: Torque ripple of permanent-magnet motors can be classified into four types depending on the nature of their origin. The four types are pulsating torque, fluctuating torque, reluctance cogging torque, and inertia and mechanical system torque. Pulsating torques are inherently produced by the trapezoidal back-emf`s and trapezoidal currents used in certain permanent-magnet adjustable-speed motors. The torque ripples caused by pulsating torques may be reduced by purposely produced fluctuating counter torques. Air-gap torque measurements are conducted on a sample motor. Experimental results agree with theoretical expectations.
Date: August 1, 1995
Creator: Hsu, J.S.; Scoggins, B.P.; Scudiere, M.B.; Marlino, L.D.; Adams, D.J. & Pillay, P.
Partner: UNT Libraries Government Documents Department

Extended Constant Power Speed Range of the Brushless DC Motor Through Dual Mode Inverter Control

Description: The trapezoidal back electromotive force (emf) brushless direct current (dc) motor (BDCM) with surface-mounted magnets has high-power density and efficiency especially when rare-earth magnet materials are used. Traction applications, such as electric vehicles, could benefit significantly from the use of such motors. Unfortunately, a practical means for driving the motor over a constant power speed ratio (CPSR) of 5:1 or more has not yet been developed. A key feature of these motors is that they have low internal inductance. The phase advance method is effective in controlling the motor power over such a speed range, but the current at high speed may be several times greater than that required at the base speed. The increase in current during high-speed operation is due to the low motor inductance and the action of the bypass diodes of the inverter. The use of such a control would require increased current rating of the inverter semiconductors and additional cooling for the inverter, where the conduction losses increase proportionally with current, and especially for the motor, where the losses increase with the square of the current. The high current problems of phase advance can be mitigated by adding series inductance; however, this reduces power density, requires significant increase in supply voltage, and leaves the CPSR performance of the system highly sensitive to variations in the available voltage. A new inverter topology and control scheme has been developed that can drive low-inductance BDCMs over the CPSR that would be required in electric vehicle applications. This new controller is called the dual-mode inverter control (DMIC). It is shown that the BDCM has an infinite CPSR when it is driven by the DMIC.
Date: June 23, 2000
Creator: Lawler, J.S.
Partner: UNT Libraries Government Documents Department


Description: This project will determine whether electrolytic dialysis has promise in the separation of charged particles in an aqueous solution. The ability to selectively move ions from one aqueous solution to another through a semipermeable membrane will be studied as a function of emf, amperage, and particle electrical charge. The ions selected for the study are Cl{sup -} and SO{sub 4}{sup 2-}. These ions are of particular interest because of their electrical conduction properties in aqueous solution resulting with their association with the corrosive action of metals. The studies will be performed with commercial membranes on solutions prepared in the laboratory from reagent salts. pH adjustments will be made with dilute reagent acid and base. Specific objectives of the project include testing a selected membrane currently available for electrolytic dialysis, membrane resistance to extreme pH conditions, the effectiveness of separating a mixture of two ions selected on the basis of size, the efficiency of the membranes in separating chloride (Cl{sup 1-}) from sulfate (SO{sub 4}{sup 2-}), and separation efficiency as a function of electromotive force (emf).
Date: April 1, 2000
Creator: Timpe, Ronald C.
Partner: UNT Libraries Government Documents Department

Transient Eddy Current Response Due to a Subsurface Crack in a Conductive Plate

Description: Eddy current nondestructive evaluation (NDE) is usually carried out by exciting a time harmonic field using an inductive probe. However, a viable alternative is to use transient eddy current NDE in which a current pulse in a driver coil produces a transient .eld in a conductor that decays at a rate dependent on the conductivity and the permeability of the material and the coil configuration. By using transient eddy current, it is possible to estimate the properties of the conductive medium and to locate and size potential .aws from the measured probe response. The fundamental study described in this dissertation seeks to establish a theoretical understanding of the transient eddy current NDE. Compared with the Fourier transform method, the derived analytical formulations are more convenient when the transient eddy current response within a narrow time range is evaluated. The theoretical analysis provides a valuable tool to study the effect of layer thickness, location of defect, crack opening as well as the optimization of probe design. Analytical expressions have been developed to evaluate the transient response due to eddy currents in a conductive plate based on two asymptotic series. One series converges rapidly for a short time regime and the other for a long time regime and both of them agree with the results calculated by fast Fourier transform over all the times considered. The idea of asymptotic expansion is further applied to determine the induced electromotive force (EMF) in a pick-up coil due to eddy currents in a cylindrical rod. Starting from frequency domain representation, a quasi-static time domain dyadic Green's function for an electric source in a conductive plate has been derived. The resulting expression has three parts; a free space term, multiple image terms and partial reflection terms. The dyadic Green's function serves as the kernel of an ...
Date: August 9, 2006
Creator: Fu, Fangwei
Partner: UNT Libraries Government Documents Department

Thermodynamic and nonstoichiometric behavior of the GdBa{sub 2}Cu{sub 3}O{sub x} system.

Description: Electromotive force (EMF) measurements of oxygen fugacities as a function of stoichiometry have been made on the GdBa{sub 2}Cu{sub 3}O{sub x} system in the temperature range {approximately}400-600 C by means of an oxygen titration technique with an yttria-stabilized zirconia electrolyte. Equations for the variation of oxygen partial pressure with composition and temperature have been derived from our EMF measurements. The shape of the 400 C isotherms as a function of oxygen stoichiometry for the Gd and Nd cuprate systems suggests the presence of miscibility gaps at values of x that are higher than those in the YBa{sub 2}Cu{sub 3}O{sub x} system. For a given oxygen stoichiometry, oxygen partial pressures above Gd-123 and Nd-123 cuprate systems are higher (above x = 6.5) than that for the Y-123 system. A thermodynamic assessment and intercomparison of our partial pressure measurements with the results of related measurements will be presented.
Date: September 29, 1998
Creator: Tetenbaum, M.
Partner: UNT Libraries Government Documents Department

The Alpha Dynamo Effects in Laboratory Plasmas

Description: A concise review of observations of the alpha dynamo effect in laboratory plasmas is given. Unlike many astrophysical systems, the laboratory pinch plasmas are driven magnetically. When the system is overdriven, the resultant instabilities cause magnetic and flow fields to fluctuate, and their correlation induces electromotive forces along the mean magnetic field. This alpha-effect drives mean parallel electric current, which, in turn, modifies the initial background mean magnetic structure towards the stable regime. This drive-and-relax cycle, or the so-called self-organization process, happens in magnetized plasmas in a timescale much shorter than resistive diffusion time, thus it is a fast and unquenched dynamo process. The observed alpha-effect redistributes magnetic helicity (a measure of twistedness and knottedness of magnetic field lines) but conserves its total value. It can be shown that fast and unquenched dynamos are natural consequences of a driven system where fluctuations are statistically either not stationary in time or not homogeneous in space, or both. Implications to astrophysical phenomena will be discussed.
Date: October 16, 2001
Creator: Ji, Hantao & Prager, Stewart C.
Partner: UNT Libraries Government Documents Department

Thermodynamic and nonstoichiometric behavior of promising Hi-Tc cuprate systems via EMF measurements : a short review.

Description: Electromotive force (EMF) measurements of oxygen fugacities as a function of stoichiometry have been made on the YBa{sub 2}Cu{sub 3}O{sub x}, GdBa{sub 2}Cu{sub 3}O{sub x}, NdBa{sub 2}Cu{sub 3}O{sub x} and bismuth cuprate systems in the temperature range {approximately}400-750 C by means of an oxygen titration technique with an yttria-stabilized zirconia electrolyte. The shapes of the 400 C isotherms as a function of oxygen stoichiometry for the Gd and Nd cuprate systems suggest the presence of miscibility gaps at values of x that are higher than those in the YBa{sub 2}Cu{sub 3}O{sub x} system. For a given oxygen stoichiometry, oxygen partial pressures above GdBa{sub 2}Cu{sub 3}O{sub x} and NdBa{sub 2}Cu{sub 3}O{sub x} are higher (above x=6.5) than that for the promising YBa{sub 2}Cu{sub 3}O{sub x} system. A thermodynamic assessment and intercomparison of our partial pressure measurements with the results of related measurements will be presented.
Date: February 24, 1999
Creator: Tetenbaum, M.
Partner: UNT Libraries Government Documents Department

Carbon Dioxide, Hydrographic, and Chemical Data Obtained During the R/V Hesperides Cruise in the Atlantic Ocean

Description: This data documentation discusses the procedures and methods used to measure total carbon dioxide (TCO{sub 2}), total alkalinity (TALK), and pH at hydrographic stations during the R/V Hesperides oceanographic cruise in the Atlantic Ocean (Section A5). Conducted as part of the Work Ocean Circulation Experiment (WOCE), the cruise began in Cadiz, Spain, on July 14, 1992, and ended in Miami, Florida, on August 15, 1992. Measurements made along WOCE Section A5 included CTD pressure, temperature, salinity, and oxygen; and bottle salinity, oxygen, phosphate, nitrate, nitrite, silicate, TCO{sub 2}, TALK, and pH. The TALK, TCO{sub 2}, and pH were determined from titrations of seawater collected at 33 stations. The titration systems for measuring TALK and TCO{sub 2} were calibrated in the laboratory with certified reference materials (CRMs) before the cruise to ensure traceable results. Standard reference seawater provided by Andrew Dickson of Scripps Institution of Oceanography (SIO) was used at sea to monitor the performance of the titration systems. The results agree with the laboratory results to {+-} 2 {micro}mol/kg for TALK and {+-} 1 {micro}mol/kg for TCO{sub 2}. The titration systems used to measure pH were calibrated with TRIS seawater buffers prepared in the laboratory and measured with an H{sub 2}, Pt/AgCl, Ag electrode. The initial electromotive force (emf) of the titrations was used to determine the pH. The values of pH are thought to be reliable to {+-} 0.01 and are internally consistent with the measured values of TALK and TCO{sub 2} to {+-} 7 {micro}mol/kg. The measured carbon dioxide system parameters have been used to calculate the in situ values of the fugacity of CO{sub 2} (fCO{sub 2}) for the surface water. The surface results are briefly discussed.
Date: June 9, 2000
Creator: Millero, F.J.
Partner: UNT Libraries Government Documents Department

Equilibria and Stability of JET Discharges with Zero Core Current Density

Description: Injection of Lower Hybrid Heating and Current Drive (LHCD) into the current ramp-up phase of JET [Joint European Torus] discharges can produce extremely reversed q-profiles characterized by a core region of near zero current density (within Motional Stark Effect diagnostic measurement errors). Non-inductive, off-axis co-current drive induces a back electromotive force inside the non-inductive current radius that drives a negative current in the plasma core. The core current density does not go negative, although current diffusion calculations indicate that there is sufficient LHCD to cause this. The clamping of the core current density near zero is consistent with n=0 reconnection events redistributing the core current soon after it goes negative. This is seen in reduced MHD simulations and in nonlinear resistive MHD simulations which predict that these discharges undergo n=0 reconnection events that clamp the core current near zero.
Date: October 15, 2002
Creator: Stratton, B.C.; Hawkes, N.C.; Huysmans, G.T.A.; Breslau, J.A.; Zakharov, L.E.; Alper, B. et al.
Partner: UNT Libraries Government Documents Department

Reference electrodes for solid polymer electrolytes

Description: Electrochemical experiments were conducted on a binary metallic lithium-tin alloy that may be suitable as a reference electrode of the first kind in studies of lithium-polymer batteries. Two types of tin electrodes were tested: bulk tin foil and tin thin films deposited on a stainless steel substrate. Electrochemical test cells were fabricated, with tin, metallic lithium, poly(ethylene oxide), and lithium trifluoromethanesulfonate as electrodes and polymer electrolyte material. To form the alloy, the tin electrodes were galvanostatically loaded in situ with lithium. Each cell reached one or more steady-state voltage plateaus during the electrochemical reduction of lithium cations at the tin electrode surface. The lithiated tin foil electrode (1 C/cm{sup 2} of charge passed; area {approx} 5 cm{sup 2}; thickness = 1.0 mm) demonstrated good voltage stability over months under open-circuit conditions. This electrode maintained an average open circuit voltage of 0.7336 V with only {plus_minus}0.17 mV variance. Composition of phases in the thin film electrodes (x in Li{sub x}Sn) was coulometrically varied via reversible lithium loading and unloading reactions. Results show that three different, two-phase compositions may be formed that maintain flat voltage regions at approximately 0.53, 0.63, and 0.73 V vs lithium metal.
Date: December 31, 1993
Creator: Johnson, C. S. & Dees, D. W.
Partner: UNT Libraries Government Documents Department

16,000-rpm Interior Permanent Magnet Reluctance Machine with Brushless Field Excitation

Description: The reluctance interior permanent magnet (RIPM) motor is currently used by many leading auto manufacturers for hybrid vehicles. The power density for this type of motor is high compared with that of induction motors and switched reluctance motors. The primary drawback of the RIPM motor is the permanent magnet (PM) because during high-speed operation, the fixed PM produces a huge back electromotive force (emf) that must be reduced before the current will pass through the stator windings. This reduction in back-emf is accomplished with a significant direct-axis (d-axis) demagnetization current, which opposes the PM's flux to reduce the flux seen by the stator wires. This may lower the power factor and efficiency of the motor and raise the requirement on the alternate current (ac) power supply; consequently, bigger inverter switching components, thicker motor winding conductors, and heavier cables are required. The direct current (dc) link capacitor is also affected when it must accommodate heavier harmonic currents. It is commonly agreed that, for synchronous machines, the power factor can be optimized by varying the field excitation to minimize the current. The field produced by the PM is fixed and cannot be adjusted. What can be adjusted is reactive current to the d-axis of the stator winding, which consumes reactive power but does not always help to improve the power factor. The objective of this project is to avoid the primary drawbacks of the RIPM motor by introducing brushless field excitation (BFE). This offers both high torque per ampere (A) per core length at low speed by using flux, which is enhanced by increasing current to a fixed excitation coil, and flux, which is weakened at high speed by reducing current to the excitation coil. If field weakening is used, the dc/dc boost converter used in a conventional RIPM motor may be ...
Date: October 31, 2007
Creator: Hsu, J. S.; Burress, T. A.; Lee, S. T.; Wiles, R. H.; Coomer, C. L.; McKeever, J.W. et al.
Partner: UNT Libraries Government Documents Department

An Electromotive Force Measurement System for Alloy Fuels

Description: The development of advanced nuclear fuels requires a better understanding of the transmutation and micro-structural evolution of the materials. Alloy fuels have the advantage of high thermal conductivity and improved characteristics in fuel-cladding chemical reaction. However, information on thermodynamic and thermophysical properties is limited. The objective of this project is to design and build an experimental system to measure the thermodynamic properties of solid materials from which the understanding of their phase change can be determined. The apparatus was used to measure the electromotive force (EMF) of several materials in order to calibrate and test the system. The EMF of chromel was measured from 100°C to 800°C and compared with theoretical values. Additionally, the EMF measurement of Ni-Fe alloy was performed and compared with the Ni-Fe phase diagram. The prototype system is to be modified eventually and used in a radioactive hot-cell in the future.
Date: November 1, 2010
Creator: Xing, Changhu; Jensen, Colby; Ban, Heng; Mariani, Robert & Kennedy, J. Rory
Partner: UNT Libraries Government Documents Department

Hopping conduction in high electric fields: three issues

Description: Three issues concerning phonon-assisted hopping in molecularly doped polymers are considered. The first issue is whether Arrhenius jump rates in the vicinity of room temperature arise from single- phonon or small-polaronic hopping. It is concluded that Arrhenius hopping only occurs above low temperatures through small-polaronic hopping. Second, hopping in molecularly doped polymers is compared with small- polaronic hopping of other systems. Small-polaronic hopping typically occurs between similar chemical structures whose energies are relatively insensitive to their surroundings. Thus, disorder energies experienced by carriers are often modest, values of several hundredths of an eV are common. Nonetheless, the effects of large electric fields on carrier mobilities differ significantly among disordered systems. Data reported for molecularly doped polymers is unlike that for either transition- metal-oxide or chalcogenide glasses. In no case is high-field transport well understood. Finally, I stress that steady-state flow is driven by differences in sites` quasielectrochemical potentials (QECPs). With disorder, differences of QECPs are not simply related to the driving emf. Solution of the (nonlinear) stochastic equations for the QECPs shows that bottlenecks produced by disorder result in nonohmic conduction. Solving the linearized stochastic (disordered resistor network) equations underestimates bottleneck effects. Linearization is inappropriate when interest differences in the QECPs exceed [kappa]T.
Date: October 1, 1996
Creator: Emin, D.
Partner: UNT Libraries Government Documents Department

The Aqueous Thermodynamics and Complexation Reactions of Anionic Silica Species to High Concentration: Effects on Neutralization of Leaked Tank Wastes and Migration of Radionuclides in the Subsurface

Description: Highly basic tank wastes contain several important radionuclides, including {sup 90}Sr, {sup 99}Tc, and {sup 60}Co, as well as actinide elements (i.e., isotopes of U, Pu, and Am). These highly basic tank wastes are known to have leaked into the vadose zone at the Hanford Site. Upon entering the sediments in the vadose zone, the highly basic solutions dissolve large concentrations of silica from the silica and aluminosilicate minerals present in the subsurface. These dissolution reactions alter the chemical composition of the leaking solutions, transforming them from a highly basic (as high as 2M NaOH) solution into a pore solution with a very high concentration of dissolved silica and a significantly reduced pH. This moderately basic (pH 9 to 11), high-silica solution has the potential to complex radionuclides and move through the subsurface. Such strong radionuclide complexation is a currently unconsidered transport vector that has the potential to expedite radionuclide transport through the vadose zone. These strong complexation effects have the ability to significantly alter current conceptual models of contaminant migration beneath leaking tanks. In this project, we are determining the aqueous thermodynamics and speciation of dissolved silica and silica-radionuclide complexes to high silica concentration using a combination of (1) studies of chemical species structure and composition [via nuclear magnetic resonance (NMR) and, where applicable, laser-induced fluorescence spectroscopy and x-ray absorption spectroscopy] (2) molecular simulations to help identify key species structures and assist in interpreting experimental measurements (3) fundamental physical chemistry measurements, including solubility, electromotive force, and isopiestic measurements, to obtain the necessary thermodynamic data for predicting contaminant complexation and waste neutralization reactions. The radioactive elements we are studying include Sr, Co, Cs, Am(III), and U(VI).
Date: June 1, 2002
Creator: Felmy, Andrew R.; Choppin, Gregory & Dixon, David A.
Partner: UNT Libraries Government Documents Department

Observation of SOL Current Correlated with MHD Activity in NBI-heated DIII-D Tokamak Discharges

Description: This work investigates the potential roles played by the scrape-off-layer current (SOLC) in MHD activity of tokamak plasmas, including effects on stability. SOLCs are found during MHD activity that are: (1) slowly growing after a mode-locking-like event, (2) oscillating in the several kHz range and phase-locked with magnetic and electron temperature oscillations, (3) rapidly growing with a sub-ms time scale during a thermal collapse and a current quench, and (4) spiky in temporal behavior and correlated with spiky features in Da signals commonly identified with the edge localized mode (ELM). These SOLCs are found to be an integral part of the MHD activity, with a propensity to flow in a toroidally non-axisymmetric pattern and with magnitude potentially large enough to play a role in the MHD stability. Candidate mechanisms that can drive these SOLCs are identified: (a) toroidally non-axisymmetric thermoelectric potential, (b) electromotive force (EMF) from MHD activity, and (c) flux swing, both toroidal and poloidal, of the plasma column. An effect is found, stemming from the shear in the field line pitch angle, that mitigates the efficacy of a toroidally non-axisymmetric SOLC to generate a toroidally non-axisymmetric error field. Other potential magnetic consequences of the SOLC are identified: (i) its error field can introduce complications in feedback control schemes for stabilizing MHD activity and (ii) its toroidally non-axisymmetric field can be falsely identified as an axisymmetric field by the tokamak control logic and in equilibrium reconstruction. The radial profile of a SOLC observed during a quiescent discharge period is determined, and found to possess polarity reversals as a function of radial distance.
Date: March 26, 2004
Creator: Takahashi, H.; Fredrickson, E.D.; Schaffer, M.J.; Austin, M.E.; Evans, T.E.; Lao, L.L. et al.
Partner: UNT Libraries Government Documents Department

Research, development, and demonstration of lead-acid batteries for electric vehicle propulsion. Annual report, 1979

Description: The initial phase of work comprises three factorial experiments to evaluate a variety of component combinations. Goals to be met by these batteries include the following: capacity at 3 h discharge, 20 to 30 kWh; specific energy, 40 Wh/kg; specific power, 1000 W/kg for 15 s; cycle life, 800 cycles to 80% depth; price, $50/kWh. The status of the factorial experiments is reviewed. The second phase of work, design of an advanced battery, has the following goals: 30 to 40 kWh; 60 Wh/kg; 150 W/kg for 15 s; 1000 cycles to 80% depth; $40/kWh. It is not yet possible to say whether these goals can be met. Numerous approaches are under study to increase the utilization of battery chemicals. A battery design with no live electrical connection above the battery is being developed. 52 figures, 52 tables. (RWR)
Date: June 1, 1980
Partner: UNT Libraries Government Documents Department