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Investigation of Thermal Diffusion for Saline Water Conversion

Description: From Introduction: "The following sections treat in detail each of the three major phases of this investigation: ordinary diffusion coefficient studies, thermal diffusion coefficient studies, and packed thermogravitational column studies. This report is concluded with a summary of the progress achieved and a discussion of areas for future investigation."
Date: July 1964
Creator: Richardson, John L.
Partner: UNT Libraries Government Documents Department

A Summary of Recent Damage-Initiation Experiments on KDP Crystals

Description: We summarize recent investigations of the density and morphology of bulk damage in KDP crystals as a function of pulse duration, temporal profile, wavelength, and energy fluence. As previously reported by Runkel et al., we also find that the size of bulk damage sites varies roughly linearly with pulse duration for pulses between 1 ns and 9 ns. However this trend no longer applies at pulse durations below 1 ns. Experiments measuring the damage density and size distribution as a function of wavelength confirm many previous works which indicated a strong dependence of damage density with wavelength. However, we also find that the size of damage sites is relatively insensitive to wavelength. Further we see damage due to Flat-In-Time (FIT) pulses has different pulse length and fluence dependence than Gaussian pulses. We demonstrate that a simple thermal diffusion model can account for observed differences in damage densities due to square and Gaussian temporally shaped pulses of equal fluence. Moreover, we show that the key laser parameter governing size of the bulk damage sites is the length of time the pulse remains above a specific intensity. The different dependences of damage density and damage site size on laser parameters suggest different absorption mechanisms early and late in the damaging pulse.
Date: November 7, 2005
Creator: Carr, C W; Feit, M D; Rubenchik, A M; Trenholme, J B & Spaeth, M L
Partner: UNT Libraries Government Documents Department

LIQUID THERMAL DIFFUSION

Description: A revised and expanded version of NNES-DC-1. The liquid thermal diffusion method for the separation of isotopes is described. The discussion includes the experimental aspects of the method, description of equipment, and the theoretical aspects of the process as applied to the design, development, and performance criteria. A short history of the liquid thermal diffusion method from 1940 to 1945 is preserted along; with a survey of relevant literature prior to 1940. The remainder of the report is concerned with theoretical aspects. (J.R.D.)
Date: September 10, 1946
Creator: Abelson, P.H.; Rosen, N. & Hoover, J.I. eds.
Partner: UNT Libraries Government Documents Department

Forced convection and transport effects during hyperbaric laser chemical vapor deposition

Description: This work explores mass transport processes during HP-LCYD, including the transverse forced-flow of precursor gases through a nozzle to enhance fiber growth rates. The use of laser trapping and suspension of nano-scale particles in the precursor flow is also described, providing insights into the nature of the gas flow, including jetting from the fiber tip and thermodiffusion processes near the reaction zone. The effects of differing molecular-weight buffer gases is also explored in conjunction with the Soret effect, and it is found that nucleation at the deposit surface (and homogeneous nucleation in the gas phase) can be enhanced/ retarded, depending on the buffer gas molecular weight. To demonstrate that extensive microstructures can be grown simultaneously, three-dimensional fiber arrays are also grown in-parallel using diffractive optics--without delatory effects from neighboring reaction sites.
Date: January 1, 2009
Creator: Maxwell, James L; Chavez, Craig A; Espinoza, Miguel; Black, Marcie; Maskaly, Karlene & Boman, Mats
Partner: UNT Libraries Government Documents Department

Laser supported solid state absorption fronts in silica

Description: We develop a model based on simulation and experiment that explains the behavior of solid-state laser-supported absorption fronts generated in fused silica during high intensity (up to 5GW/cm{sup 2}) laser exposure. We find that the absorption front velocity is constant in time and is nearly linear in laser intensity. Further, this model can explain the dependence of laser damage site size on these parameters. This behavior is driven principally by the temperature-activated deep sub band-gap optical absorptivity, free electron transport and thermal diffusion in defect-free silica for temperatures up to 15,000K and pressures < 15GPa. The regime of parameter space critical to this problem spans and extends that measured by other means. It serves as a platform for understanding general laser-matter interactions in dielectrics under a variety of conditions.
Date: February 9, 2010
Creator: Carr, C W & Bude, J D
Partner: UNT Libraries Government Documents Department

Thermal imaging investigation of modified fused silica at surface damage sites for understanding the underlying mechanisms of damage growth

Description: We use an infrared thermal imaging system in combination with a fluorescence microscope to map the dynamics of the local surface temperature and fluorescence intensity under cw, UV excitation of laser-modified fused silica within a damage site. Based on a thermal diffusion model, we estimate the energy deposited via linear absorption mechanisms and derive the linear absorption coefficient of the modified material. The results indicate that the damage growth mechanism is not entirely based on linear absorption. Specifically, the absorption cross-section derived above would prove insufficient to cause a significant increase in the temperature of the modified material under nanosecond, pulsed excitation (via linear absorption at ICF laser fluences). In addition, irreversible changes in the absorption cross-section following extended cw, UV laser exposure were observed.
Date: November 1, 2006
Creator: Negres, R A; Burke, M W; DeMange, P; Sutton, S B; Feit, M D & Demos, S G
Partner: UNT Libraries Government Documents Department

Evaluation of UV absorption coefficient in laser-modified fused silica

Description: Laser-induced damage in transparent dielectrics leads to the formation of laser-modified material as a result of exposure to extreme localized temperatures and pressures. In this work, we used an infrared thermal imaging system in combination with a fluorescence microscope to map the dynamics of the local surface temperature and fluorescence intensity under cw, UV excitation of laser-modified fused silica within a damage site. Based on a thermal diffusion model, we estimate the energy deposited via linear absorption mechanisms and derive the absorption coefficient of the modified material. In addition, irreversible changes in the absorption following extended laser exposure were observed.
Date: August 21, 2006
Creator: Negres, R A; Burke, M W; Sutton, S B; DeMange, P; Feit, M D & Demos, S G
Partner: UNT Libraries Government Documents Department

Temperature activated absorption during laser-induced damage: The evolution of laser-supported solid-state absorption fronts

Description: Previously we have shown that the size of laser induced damage sites in both KDP and SiO{sub 2} is largely governed by the duration of the laser pulse which creates them. Here we present a model based on experiment and simulation that accounts for this behavior. Specifically, we show that solid-state laser-supported absorption fronts are generated during a damage event and that these fronts propagate at constant velocities for laser intensities up to 4 GW/cm{sup 2}. It is the constant absorption front velocity that leads to the dependence of laser damage site size on pulse duration. We show that these absorption fronts are driven principally by the temperature-activated deep sub band-gap optical absorptivity, free electron transport, and thermal diffusion in defect-free silica for temperatures up to 15,000K and pressures < 15GPa. In addition to the practical application of selecting an optimal laser for pre-initiation of large aperture optics, this work serves as a platform for understanding general laser-matter interactions in dielectrics under a variety of conditions.
Date: October 26, 2010
Creator: Carr, C W; Bude, J D; Shen, N & Demange, P
Partner: UNT Libraries Government Documents Department

Energetics of melts from thermal diffusion studies. Final report

Description: Most processes in geology are a consequence at some level of the flow of energy or mass. Heat conduction and chemical diffusion are examples of two of these sorts of flows which are driven by temperature and chemical potential imbalances, respectively. In the general case these flows may be coupled so that, for instance, a temperature gradient may result in a flow of mass as well as heat. This effect in liquids was demonstrated by Soret (1879) and bears his name. In gases or solids the phenomenon is given the general name thermal diffusion. It was the purpose of this research program to examine the Soret effect in molten silicates under laboratory conditions. Results of these experiments are used to evaluate the form and quantitative values of many thermodynamic and kinetic properties of silicate melts over a range of temperature, pressure, and bulk composition. The author published a comprehensive review and synthesis with a microscopic theoretical explanation for the effect at low pressure in silicate liquids of geological interest. He conducted experimental investigations of molecular diffusion in the absence of a thermal gradient through experiments involving dissolution of solid silicates in molten silicate and interdiffusion of species between miscible silicate liquids. Collectively these results enable the author to construct a more comprehensive model of molecular diffusion in magmatic liquids. He has applied this model to problems of magma mixing and crustal assimilation.
Date: December 1, 1998
Creator: Lesher, C.E.
Partner: UNT Libraries Government Documents Department

RHEED studies of the nucleation, growth, and mobility of Ag atoms on the Si(111)7 x 7 surface

Description: The low temperature and flux dependent growth of ultrathin Ag films on the Si(111)7x7 surface is studied with Reflection High-Energy Electron Diffraction (RHEED). The grazing incidence geometry of RHEED allows for an incident molecular beam normal to the surface, and makes it an ideal surface probe for studying ultrathin film growth in real time. Short-lived oscillations in the diffracted intensity are observed during Ag deposition at 150 K, indicating quasi-layer-by-layer growth mediated by adatom mobility. When the 150 K growth is performed over a wide range of deposition rates F, the peak intensity is observed to scale, i.e. I(Ft) depends only on the total amount deposited, which implies thermally activated diffusion is absent at 150 K. Scaling is not obeyed at higher temperatures (T{ge}473 K) for the growth of the {radical}3{times}{radical}3 R30{degrees} ({radical}3) superstructure. Testing for scaling of the diffracted intensity constitutes a new experimental method which can be applied generally to determine if thermal diffusion is active at a particular temperature. Scaling is consistent with a constant diffusion length R{sub 0}, independent of substrate temperature and deposition rate. The presence of a non-thermal diffusion mechanism (responsible for the constant diffusion length R{sub 0}) is confirmed by monitoring the flux dependence of the {radical}3 superstructure growth during deposition at T{ge}473 K. At these temperatures the total diffusion length R is given by R=R{sub 0}+(4Dt){sup 1/2}, where (4Dt){sup 1/2} is the thermal component. A non-zero intercept R{sub 0} is found by plotting the peak intensity I{sub p}{sup 1/2} (a measure of the average domain size) vs. deposition rate F{sup {minus}1/2} (F{sup {minus}1} is proportional to the available diffusion time.) From the FWHM of a low coverage (0.2 ML) {radical}3 spot, an estimation of 50 {angstrom} is made for a lower bound of the magnitude of R{sub 0}.
Date: July 1, 1993
Creator: Roos, K.R.
Partner: UNT Libraries Government Documents Department

Transient Mirror Heating Theory and Experiment in the Jefferson Lab IR Demo FEL

Description: During commissioning of the IR Demo FEL at Jefferson Lab, we noticed that the FEL exhibited a rapid power drop with time when the first set of 3 mu-m mirrors was used. Thought the rate of power drop was unexpected, it was thought that it could be due to a distortion of the mirrors during a time short compared to a the thermal diffusion time. This transient distortion might affect the laser more than the steady state distortion. This paper presents some analysis of the transient mirror heating problem and some recent experimental results using different mirror substrates and coatings. It is found that the behavior of the first mirror set cannot be reconciled with the observed power fall-off if a linear absorption is assumed. The power drop in more recent experiments is consistent with linear thermal analysis. No anomalous transient effects are seen.
Date: January 1, 2001
Creator: Benson, S.; Shinn., Michelle D. & Neil, G.R.
Partner: UNT Libraries Government Documents Department

Fundamentals of Energy Transport in Nanafluids

Description: The research objectives of this project are the development and applications of nanoparticle analyzing techniques to examine their thermal behaviors in suspension, including the thermal conductivity, thermal (Brownian) diffusion, thermophoresis and thermocapillaryphoresis.
Date: July 31, 2004
Creator: Kihm, Kenneth D.
Partner: UNT Libraries Government Documents Department

The Soret Effect in Naturally Propagating, Premixed, Lean, Hydrogen-Air Flames

Description: Comparatively little attention has been given to multicomponent diffusion effects in lean hydrogen-air flames, in spite of the importance of these flames in safety and their potential importance to future energy technologies. Prior direct numerical simulations either have considered only the mixture-averaged transport model, or have been limited to stabilized flames that do not exhibit the thermo-diffusive instability. The so-called full, multicomponent transport model with cross-diffusion is found to predict hotter, significantly faster flames with much faster extinction and division of cellular structures.
Date: June 30, 2008
Creator: Grcar, Joseph F.; Grcar, Joseph F.; Bell, John B. & Day, Marcus S.
Partner: UNT Libraries Government Documents Department

AN ORACLE CODE FOR CALCULATION OF FERMI AGES BY NUMERICAL INTEGRATION

Description: An oracle code was prepared for the calculation of Fermi ages by numerical integration. The code is designed to compute values of The effects of and fast and slow diffusion constants for two-group calculations from cross section data. The values of The effects of and the diffusion constants may be obtained for mixtures of any or all of sixteen elements. While the present tapes do not contain cross sections for sixteen different elements, cross sections may be changed in a simple and rapid manner. The thermal cross sections used for the calculation of slow diffusion constants have not yet been critically evaluated, and caution should ba exercised in their use. ( auth)
Date: April 10, 1956
Creator: Tobias, M.
Partner: UNT Libraries Government Documents Department

FINAL FOCUS ION BEAM INTENSITY FROM TUNGSTEN FOIL CALORIMETER AND SCINTILLATOR IN NDCX-I

Description: Laboratory high energy density experiments using ion beam drivers rely upon the delivery of high-current, high-brightness ion beams with high peak intensity onto targets. Solid-state scintillators are typically used to measure the ion beam spatial profile but they display dose-dependent degradation and aging effects. These effects produce uncertainties and limit the accuracy of measuring peak beam intensities delivered to the target. For beam tuning and characterizing the incident beam intensity, we have developed a cross-calibrating diagnostic suite that extends the upper limit of measurable peak intensity dynamic range. Absolute intensity calibration is obtained with a 3 {micro}m thick tungsten foil calorimeter and streak spectrometer. We present experimental evidence for peak intensity measures in excess of 400 kW/cm{sup 2} using a 0.3 MV, 25 mA, 5-20 {micro}sec K{sup +1} beam. Radiative models and thermal diffusion effects are discussed because they affect temporal and spatial resolution of beam intensity profiles.
Date: April 30, 2010
Creator: Lidia, S.M.; Bieniosek, F.; Henestroza, E.; Ni, P. & Seidl, P.
Partner: UNT Libraries Government Documents Department

Energetics of melts from thermal diffusion studies. FY 1993 progress report

Description: This research program characterizes diffusional mass transport in geological fluids in response to thermal, solubility and chemical gradients using tools of experimental petrology. Quantitative information is obtained on the thermodynamic and kinetic properties of multicomponent systems that are the basis for predictive models of chemical diffusion, mineral dissolution, and complexing in synthetic and natural silicate systems. Among the technical accomplishments related to establishing the UCD experimental petrology laboratory in the last year has been the design and construction of two compact piston-cylinder devices capable of achieving 40 kb using 1/2-in. pressure vessels (also capable of accommodating 3/4-in. vessels). These machines are now on-line and performing thermal diffusion experiments. In addition to establishing the new laboratory at UCD, the PI began studies of molecular diffusion in the absence of a thermal gradient with results published on the chemical and self diffusion of Sr and Nd in naturally-occurring silicate liquids, and self diffusivities of Si and O in basaltic liquid.
Date: December 31, 1994
Creator: Lesher, C.E.
Partner: UNT Libraries Government Documents Department

Examination of the CLIC drive beam pipe design for thermal distortion caused by distributed beam line

Description: Beam transport programs are widely used to estimate the distribution of power deposited in accelerator structures by particle beams, either intentionally as for targets or beam dumps or accidentally owing the beam loss incidents. While this is usually adequate for considerations of radiation safety, it does not reveal the expected temperature rise and its effect on structural integrity. To find this, thermal diffusion must be taken into account, requiring another step in the analysis. The method that has been proposed is to use the output of a transport program, perhaps modified, as input for a finite element analysis program that can solve the thermal diffusion equation. At Cern, the design of the CLIC beam pipe has been treated in this fashion. The power distribution produced in the walls by a distributed beam loss was found according to the widely-used electron shower code EGS4. The distribution of power density was then used to form the input for the finite element analysis pro gram ANSYS, which was able to find the expected temperature rise and the resulting thermal distortion. As a result of these studies, the beam pipe design can be modified to include features that will counteract such distortion.
Date: January 1, 1997
Creator: Johnson, C. & Kloeppel, K.
Partner: UNT Libraries Government Documents Department

Fault current limiter-predominantly resistive behavior of a BSCCO shielded-core reactor

Description: Tests were conducted to determine the electrical and magnetic characteristics of a superconductor shielded core reactor (SSCR). The results show that a closed-core SSCR is predominantly a resistive device and an open-core SSCR is a hybrid resistive/inductive device. The open-core SSCR appears to dissipate less than the closed-core SSCR. However, the impedance of the open-core SSCR is less than that of the closed-core SSCR. Magnetic and thermal diffusion are believed to be the mechanism that facilitates the penetration of the superconductor tube under fault conditions.
Date: June 30, 2000
Creator: Ennis, M. G.; Tobin, T. J.; Cha, Y. S. & Hull, J. R.
Partner: UNT Libraries Government Documents Department

ASSESSMENT OF A PARTICLE BED BASED BEAM STOP.

Description: Accelerator target/beam stop concepts able to withstand the thermal shock induced by intense, undiluted beams are being assessed in this study. Such conditions normally push target materials beyond their limits leading to limited useful life. A number of ingenious options have been attempted to help reduce the level of stress generated. Attention is paid to a very promising option that calls for a target consisting of a cooled particle bed. In such configuration the ability of the particle bed structure to diffuse and attenuate the generated thermal shock waves is being explored by performing comprehensive dynamic analyses that incorporate anticipated energy depositions, thermal diffusion, and wave propagation and attenuation. Further, options of coolant liquid filling the porous structure of the particle bed, including concerns of pressure drop and heat transfer, are evaluated for maximizing particle yield.
Date: June 3, 2002
Creator: SIMOS,N.; LUDEWIG,H.; MONTANEZ,P. & TODOSOW,M.
Partner: UNT Libraries Government Documents Department