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Magnetohydrodynamic computation of feedback stabilization of resistive-shell instabilities in the reversed field pinch
MHD computations demonstrate that feedback can sustain reversal and reduce loop voltage in resistive-shell reversed field pinch (RFP) plasmas. In the absence of a close-fitting conducting shell, feedback with conducting coils {approximately}2R/a tearing modes resonant near axis is found to restore plasma parameters to nearly their levels with a close-fitting conducting shell. When original dynamo modes are stabilized, neighboring tearing modes grow to maintain the RFP dynamo more efficiently. This suggests that experimentally observed limits on RFP pulselengths to the order of the shell time can be overcome by applying feedback to a few helical modes. Feedback with resistive coils yields information on requirements for more physically realistic feedback systems and on the potentiality of improvement of resistive-shell plasma parameters beyond the conducting-shell case. Plasma response to shell rotation is investigated, and issues relevant to mode locking and feedback rotation of individual modes are discussed.
Date:
May 1, 1993
Creator:
Zita, E. J.
System:
The UNT Digital Library
Nuclear fuel element
A nuclear fuel element and a method of manufacturing the element. The fuel element is comprised of a metal primary container and a fuel pellet which is located inside it and which is often fragmented. The primary container is subjected to elevated pressure and temperature to deform the container such that the container conforms to the fuel pellet, that is, such that the container is in substantial contact with the surface of the pellet. This conformance eliminates clearances which permit rubbing together of fuel pellet fragments and rubbing of fuel pellet fragments against the container, thus reducing the amount of dust inside the fuel container and the amount of dust which may escape in the event of container breach. Also, as a result of the inventive method, fuel pellet fragments tend to adhere to one another to form a coherent non-fragmented mass: this reduces the tendency of a fragment to pierce the container in the event of impact. 1 fig., 1 tab.
Date:
April 6, 1989
Creator:
Zocher, R.W.
System:
The UNT Digital Library
NMR Studies of the Vanadium Spin Dynamics and Spin Structure in LiV2O4, CaV2O4, and (LixV1-x)3BO5 (x is almost equal to 0.33, 0.40)
Strong electron correlation is believed to be an essential and unifying factor in diverse properties of condensed matter systems. Ground states that can arise due to electron correlation effects include Mott insulators, heavy fermion, ferromagnetism and antiferromagnetism, spin glasses, and high-temperature superconductivity. The electronic systems in transition metal oxide compounds are often highly correlated. In this thesis, the author presents experimental studies on three strongly correlated vanadium oxide compounds: LiV{sub 2}O{sub 4}, (Li{sub x}V{sub 1-x}){sub 3}BO{sub 5}, and CaV{sub 2}O{sub 4}, which have completely different ground states.
Date:
December 1, 2007
Creator:
Zong, Xiaopeng
System:
The UNT Digital Library
Device Optimization and Transient Electroluminescence Studies of Organic light Emitting Devices
Organic light emitting devices (OLEDs) are among the most promising for flat panel display technologies. They are light, bright, flexible, and cost effective. And while they are emerging in commercial product, their low power efficiency and long-term degradation are still challenging. The aim of this work was to investigate their device physics and improve their performance. Violet and blue OLEDs were studied. The devices were prepared by thermal vapor deposition in high vacuum. The combinatorial method was employed in device preparation. Both continuous wave and transient electroluminescence (EL) were studied. A new efficient and intense UV-violet light emitting device was developed. At a current density of 10 mA/cm{sup 2}, the optimal radiance R could reach 0.38 mW/cm{sup 2}, and the quantum efficiency was 1.25%. using the delayed EL technique, electron mobilities in DPVBi and CBP were determined to be {approx} 10{sup -5} cm{sup 2}/Vs and {approx} 10{sup -4} cm{sup 2}/Vs, respectively. Overshoot effects in the transient El of blue light emitting devices were also observed and studied. This effect was attributed to the charge accumulation at the organic/organic and organic/cathode interfaces.
Date:
August 5, 2003
Creator:
Zou, Lijuan
System:
The UNT Digital Library
Hydrodynamic Aspects of Boiling Heat Transfer
A study concerned with the determination of the limiting hydrodynamic conditions which characterize nucleate and transitional boiling was conducted. The critical heat flux and the minimum heat flux are derived from these hydrodynamic limits. Results of investigations of nucleate boilin g are discussed and the theory of bubble growth is extended to include the effect of non-uniform temperature fields. An equation is derived for the product bubble diameter times frequency of bubble emission, and data showing that the diameter of nucleating cavities can he related to the heat flux density and superheat difference are presented. (J.R.D.)
Date:
June 1, 1959
Creator:
Zuber, N.
System:
The UNT Digital Library
WAVELENGTH MODULATION SPECTROSCOPY OF SEMICONDUCTORS.
None
Date:
January 1, 1971
Creator:
Zucca, R. R.L.
System:
The UNT Digital Library
A theoretical study of the electronic structure of Invar Fe*3Pt and related materials
The Full Potential Linear Augmented Plane Wave (FPLAPW or FLAPW) method is used for a spin-polarized band calculation for ordered Fe{sub 3}Pt. As major purpose, the momentum distributions of the spin-polarized electrons are calculated and compared with results from a magnetic Compton scattering measurement. To get related information, the electronic behavior is also analyzed by examining the partial densities of states and the spatial electron distributions; the role of alloying effects is then explored by studying the electrons in some related alloys: Fe{sub 3}Ni, Fe{sub 3}Pd, Ni{sub 3}Pt and Co{sub 3}Pt.
Date:
January 10, 1997
Creator:
Zuo, Zhiqi
System:
The UNT Digital Library
Accelerator systems and instrumentation for the NuMI neutrino beam
None
Date:
December 1, 2005
Creator:
Zwaska, Robert Miles
System:
The UNT Digital Library
Investigation of high energy runaway electron confinement in the Oak Ridge tokamak
High energy runaway electrons in the Oak Ridge tokamak ORMAK have been investigated through measurement of the bremsstrahlung produced when these electrons leave the discharge and strike the limiting aperture of the torus. The experimental results have been interpreted in terms of a classical single-particle model appropriate for collisionless particles in a tokamak, and it has been found that most of the confinement properties of high energy runaways in ORMAK can be understood on this basis. An experiment designed to directly test this model has disclosed an anomalous transport which has been described by a runaway diffusion coefficient D approximately 10/sup 2/ to 10/sup 4/ cm/sup 2//sec appropriate for runaways near the outside of the plasma. A discussion of the possible mechanisms for this anomalous transport is given.
Date:
November 1, 1977
Creator:
Zweben, S. J.
System:
The UNT Digital Library
Direct observation of resonance effects in laser cluster interactions
Time resolved dynamics of high intensity laser interactions with atomic clusters have been studied with both theoretical analysis and experiment. A short-pulse Ti:sapphire laser system, which could produce 50 mJ of energy in a 50 fs pulse, was built to perform these experiments. The laser used a novel single grating stretcher and was pumped, in part, by a custom Nd:YLF laser system, including 19 mm Nd:YLF amplifiers. It was found that there is an optimal pulse width to maximize absorption for a given cluster size. This optimal pulse width ranged from 400 fs for 85 A radius xenon clusters to 1.2 ps for 205 {angstrom} radius xenon clusters. Using a pump-probe configuration, the absorption of the probe radiation was observed to reach a maximum for a particular time delay between pump and probe, dependent on the cluster size. The delay for peak absorption was 800, 1400, and 2100 fs for 85 {angstrom}, 130 {angstrom}, and 170 {angstrom} radius xenon clusters respectively. Model calculations suggest that these effects are due to resonant heating of the spherical plasma in agreement with the hydrodynamic interpretation of cluster interactions. While this simple hydrodynamic code produces reasonable agreement with data, it does not include bulk …
Date:
June 1, 1999
Creator:
Zweiback, J
System:
The UNT Digital Library
Time Integration Methods for Reactor Kinetics.
None
Date:
January 1, 1971
Creator:
da Nóbrega, J. A. W. & Henry, A. F.
System:
The UNT Digital Library
Electronic structure of diamond, zincblende, and chalcopyrite semiconductors
ABS>Thesis. The dependence of energy band structure and electronic charge density on pseudopotential parameters is investigated for: InSb, InAs, InP, GaP, Si, ZnGeP/sub 2/, and ZnGeAs/sub 2/. (DLC)
Date:
January 1, 1973
Creator:
de Alvarez, C.V.
System:
The UNT Digital Library
Free Convection Heat Transfer to Horizontal Cylinders From an Ordinary Fluid Containing a Volume Heat Source
Outside heat transfer coefficients for several horizontal tubes cooling an ordinary fluid containing a volume heat source by free convection were obtained experimentally. Water was used as the coolant, and a very dilute solution of HC1 was the bulk fluid. The basic equipment included a Lucite test cell which contained the bulk fluid, Cu screen grids through which an alternating current was passed to generate a volume heat source in the bulk and several horizontal 1/4 in. O.D. stainless steel tubes through which the coolant was pumped. Experiments were conducted using a single-tube, four-tube, and five-tube geometry. The heat transfer coefficients obtained were considered accurate within 8%. With single-tube cooling, the heat transfer coefficients were correlated by Nu = 0.49 (Gr Pr)/sup 1/4/. With four cooling tubes, the data were correlated by Nu = 0.59 (Gr Pr)/sup 1/4/, while with five cooling tubes the value of the coefficients in the correlation equation was Nu = 0.64 (Gr Pr)/sup 1/4/. (auth)
Date:
January 1, 1958
Creator:
de Guzman, J. P.
System:
The UNT Digital Library
Drift compression and final focus systems for heavy ion inertial fusion
Longitudinal compression of space-charge dominated beams can be achieved by imposing a head-to-tail velocity tilt on the beam. This tilt has to be carefully tailored, such that it is removed by the longitudinal space-charge repulsion by the time the beam reaches the end of the drift compression section. The transverse focusing lattice should be designed such that all parts of the beam stay approximately matched, while the beam smoothly expands transversely to the larger beam radius needed in the final focus system following drift compression. In this thesis, several drift compression systems were designed within these constraints, based on a given desired pulse shape at the end of drift compression systems were designed within these constraints, based on a given desired pulse shape at the end of drift compression. The occurrence of mismatches due to a rapidly increasing current was analyzed. In addition, the sensitivity of drift compression to errors in the initial velocity tilt and current profile was studied. These calculations were done using a new computer code that accurately calculates the longitudinal electric field in the space-charge dominated regime.
Date:
May 1, 2001
Creator:
de Hoon, M.J.L.
System:
The UNT Digital Library
Simulation of the Steady-State Transport of Radon from Oil intoHouses with Basements under Constant Negative Pressure
None
Date:
May 1, 1987
Creator:
de Oliveira Loureiro, Celso
System:
The UNT Digital Library
Mechanism of constitution liquid film migration
Liquid film migration (LFM) in liquid phase sintering classically involves a large metastable liquid volume adjacent to solid, and migration occurs at an isolated solid-liquid (S-L) interface. Constitutional liquid film migration (CLFM), discovered in alloy 718, has major characteristics similar to those of LFM, except that the metastable liquid is from the constitutional liquation of precipitates on the grain boundary. The similarity between LFM and CLFM has led to the theory that coherency lattice strain responsible for LFM is also responsible for CLFM. The coherency strain hypothesis was tested in this study by evaluating whether the Hillert model of LFM would also apply for CLFM. Experimental results of CLFM in alloy 718 showed that migration velocity followed the trend predicted by the Hillert model. This indicates that the coherency strain hypothesis of LFM also applies for CLFM and that the coherency lattice strain responsible for LFM is also the driving force for CLFM.
Date:
June 1, 1999
Creator:
unknown
System:
The UNT Digital Library
Oxidation studies on small atom doped TI*5*SI*3*
This report described the oxidation and oxidation resistance of Ti{sub 5}Si{sub 3}, along with a discussion on general material properties. Single crystal studies of Ti{sub 5}Si{sub 3}Z{sub x} are included.
Date:
November 1, 1995
Creator:
unknown
System:
The UNT Digital Library
A proper time dependent measurement of Delta M {sub D} using jet charge and soft lepton flavor tagging
This thesis presents a proper time dependent measurement of the B{sup 0}{sub d} mixing frequency {Delta}M{sub d} using jet charge and soft lepton flavor tagging in p - {anti p} collisions at {radical}s = 1.8 TeV. The measurement uses the inclusive e and {mu} trigger data of the CDF detector from an integrated luminosity of 91 pb{sub -1}. The proper time at decay is measured from a partial reconstruction of the B associated with the trigger lepton. The measurement of {Delta}M{sub d} yields {Delta}M{sub d} = 0.50 {+-} 0.05 {+-} 0.05 {bar h} ps{sup -1} where the first error is statistical and the second systematic. The flavor tagging methods used give a measured effective efficiency {epsilon}D{sup 2} of o Jet Charge: {epsilon}D{sup 2} (0.78 + 0.12 + 0.09) % o Soft Lepton: {epsilon}D{sup 2} (1.07 + 0.09 + 0.10) % where the first error is statistical and the second systematic.
Date:
August 1, 1998
Creator:
unknown
System:
The UNT Digital Library
Temperature dependence of CsI(Tl) gamma-ray excited scintillation characteristics
Gamma-ray excited emission spectrum, absolute scintillation yield, rise and decay time constants, and thermoluminescence emissions of CsI(Tl) were measured at {minus}100 to +50 C, for crystals from 4 different vendors. The thermoluminescence glow curves were the only property that varied significantly from crystal to crystal; room temperature operation in current mode could be susceptible to temperature fluctuations. The CsI(Tl) emission spectrum has emission bands peaking around 400 and 560 nm; the former band disappears between {minus}50 and {minus}75 C. The RT absolute scintillation yield was calculated to be 65,500{plus_minus}4,100 photons/MeV. The two primary decay time constants increases about exponentially with inverse temperature. An ultra-fast decay component was confirmed. Applications are discussed.
Date:
October 1, 1993
Creator:
unknown
System:
The UNT Digital Library