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Multiphoton processes in the field of two-frequency circularly polarized plane electromagnetic waves

Description: The authors solve Dirac`s equation for an electron in the field of a two-frequency plane electromagnetic wave, deriving general formulae for the probabilities of radiation of a photon by the electron, and for the probabilities for pair production by a photon when the two-frequency wave is circularly polarized. In contrast to the case of a monochromatic-plane electromagnetic wave, when an electron is in the field of a two-frequency circularly polarized wave, besides the absorption of multiphotons and emission of simple harmonics of the individual waves, stimulated multiphoton emission processes and various composite harmonic-photon emission processes are occurred: when a high-energy photon is in a such a field, multiphoton processes also follow the pair production processes.
Date: July 1, 1997
Creator: Yu, An & Takahashi, H.
Partner: UNT Libraries Government Documents Department

Design considerations for a thermophotovoltaic energy converter using heat pipe radiators

Description: The purpose of this paper is to discuss concepts for using high temperature heat pipes to transport energy from a heat source to a thermophotovoltaic (TPV) converter. Within the converter, the condenser portion of each heat pipe acts as a photon radiator, providing a radiant flux to adjacent TPV cells, which in turn create electricity. Using heat pipes in this way could help to increase the power output and the power density of TPV systems. TPV systems with radiator temperatures in the range of 1,500 K are expected to produce as much as 3.6 W/cm{sup 3} of heat exchanger volume at an efficiency of 20% or greater. Four different arrangements of heat pipe-TPV energy converters are considered. Performance and sizing calculations for each of the concepts are presented. Finally, concerns with this concept and issues which remain to be considered are discussed.
Date: June 1, 1997
Creator: Ashcroft, J. & DePoy, D.
Partner: UNT Libraries Government Documents Department

Minimum entropy production of neutrino radiation in the steady state

Description: A thermodynamical minimum principle valid for photon radiation is shown to hold for arbitrary geometries. It is successfully extended to neutrinos, in the zero mass and chemical potential case, following a parallel development of photon and neutrino statistics. This minimum principle stems more from that of Planck than that of classical Onsager-Prigogine irreversible thermodynamics. Its extension from bosons to fermions suggests that it may have a still wider validity. 14 refs.
Date: August 1, 1997
Creator: Essex, C. & Kennedy, D.C.
Partner: UNT Libraries Government Documents Department

Double opposite-end tubesheet design for a thermovoltaic energy converter

Description: A method and apparatus are disclosed for the direct conversion of energy by thermovoltaic energy conversion having first and second tubesheets, at least one photon emitter plate secured to and extending from the first tubesheet, at least one cold plate secured to and extending from the second tubesheet, a plurality of thermovoltaic cells disposed along oppositely disposed exterior surfaces of the cold plate, and means cooperating with the tubesheet for maintaining a vacuum between the photon emitter plate and the cold plate.
Date: December 1, 1997
Creator: Ashcroft, John M.; Campbell, Brain C. & DePoy, David M.
Partner: UNT Libraries Government Documents Department

X-ray emission from a high-atomic-number z-pinch plasma created from compact wire arrays

Description: Thermal and nonthermal x-ray emission from the implosion of compact tungsten wire arrays in 5-MA Saturn discharges is reported. The timing of multiple implosions and the thermal x-ray spectra (1 to 10 keV) agree with 2D radiation-hydrocode simulations. Nonthermal x-ray emission (10 to 100 keV) correlates with pinch spots distributed along the z-axis. The similarities of the measured nonthermal spectrum, yield, and pinch-spot emission with those of 0.8-MA, single- exploded-wire discharges on Gamble-II suggest a common nonthermal- production mechanism. Nonthermal x-ray yields are lower than expected from current scaling of Gamble II results, suggesting that implosion geometries are not as efficient as single-wire geometries for nonthermal x-ray production. The instabilities, azimuthal asymmetries, and inferred multiple implosions that accompany the implosion geometry lead to larger, more irregular pinch spots, a likely reason for reduced nonthermal efficiency. A model for nonthermal-electron acceleration across magnetic fields in highly- collisional, high-atomic-number plasmas combined with 1D hydrocode simulations of Saturn compact loads predicts weak nonthermal x-ray emission.
Date: June 1, 1996
Creator: Sanford, T.W.L.; Mosher, D. & De Groot, J.S.
Partner: UNT Libraries Government Documents Department

Novel Nanoparticles for Ultrasensitive Detection and Spectroscopy. Final Report

Description: The long-term objective of this DOE project was to develop a new class of metal nanoparticles with novel optical properties for ultrasensitive detection and spectroscopy. The specific aims were (1) to prepare and screen colloidal silver and gold nanoparticles with novel optical properties; (2) to characterize the intrinsic size-dependent properties of these nanoparticles and to identify the factors responsible for efficient optical enhancement; (3) to determine the characteristics and origins of intermittent photon emission in single metal particles; and (4) to develop methodologies for enriching these novel particles and for fabricating thin nanoparticle films.
Date: June 23, 2003
Creator: Nie, Shuming
Partner: UNT Libraries Government Documents Department

The {alpha}-induced thick-target {gamma}-ray yield from light elements

Description: The {alpha}-induced thick-target {gamma}-ray yield from light elements has been measured in the energy range 5.6 MeV {le} E{sub {alpha}} {le} 10 MeV. The {gamma}-ray yield for > 2.1 MeV from thick targets of beryllium, boron nitride, sodium fluoride, magnesium, aluminum and silicon were measured using the {alpha}-particle beam from the Lawrence Berkeley Laboratories 88 in. cyclotron. The elemental yields from this experiment were used to construct the {alpha}-induced direct production {gamma}-ray spectrum from materials in the SNO detector, a large volume ultra-low background neutrino detector located in the Creighton mine near Sudbury, Canada. This background source was an order of magnitude lower than predicted by previous calculations. These measurements are in good agreement with theoretical calculations of this spectrum based on a statistical nuclear model of the reaction, with the gross high energy spectrum structure being reproduced to within a factor of two. Detailed comparison of experimental and theoretical excitation population distribution of several residual nuclei indicate the same level of agreement within experimental uncertainties.
Date: October 1994
Creator: Heaton, R. K.
Partner: UNT Libraries Government Documents Department

Finite pulse effects in self-amplified-spontaneous emission

Description: The authors study the effects of the electron density profile on self-amplified-spontaneous-emission (SASE). A general formalism in the linear regime is developed by deriving the coupled Maxwell-Klimontovich equations for an arbitrary density profile and including the effects of the energy spread, diffraction, and the betatron oscillation. An explicit solution is obtained for the one-dimensional (1-D) case. The temporal and the spectral intensity profiles of SASE depend linearly on the initial electron correlation function. The correlation function consists of two terms, a term giving rise to the usual spontaneous radiation and its amplification to SASE, and a term representing the coherent bunched beam effect. The latter term has been neglected so far in the treatments of SASE, but it could be significant when there is a variation in the electron density at a length scale comparable to the wavelength. The theory reproduces the well-known results when the electron density is uniform. It also reproduces a recent theory for a finite top-hat density profile and a vanishing energy spread.
Date: September 1, 1994
Creator: Kim, Kwang-Je & Hahn, Sang June
Partner: UNT Libraries Government Documents Department

Efficient multi-exciton emission from quantum dots.

Description: The fundamental spontaneous emission rate an emitter can be modified by its photonic environment. By enhancing the spontaneous emission rate, there is a possibility of extracting multi-exciton energies through radiative decay. In this report, we explore using high Q and small volume cavities to enhance the spontaneous emission rate. We observed greater than 50 folds enhancement in the spontaneous emission from photonic crystal waveguide or microcavity using close-packed monolayer of PbS quantum dot emitters.
Date: September 1, 2010
Creator: Luk, Ting Shan
Partner: UNT Libraries Government Documents Department

Obwervation of 10 {mu}m Smith-Purcell radiation from 45 MeV electrons

Description: Using the high-brightness, high-energy electron beam at the Brookhaven Accelerator Test Facility we observe forward directed Smith-Purcell radiation in the mid-infrared spectral regime. This radiation can prove useful as a source of infrared radiation for other scientific studies as well as a providing a precursor investigation of the inverse process, namely the acceleration of electrons by means of the coupling of laser light with electrons via micro-structures.
Date: February 1, 1997
Creator: Fernow, R.C.; Robertson, S.H.; Brownell, J.H. & Walsh, J.E.
Partner: UNT Libraries Government Documents Department

Combustion powered thermophotovoltaic emitter system

Description: The US Naval Academy (USNA) has recently completed an engineering design project for a high temperature thermophotovoltaic (TPV) photon emitter. The final apparatus was to be portable, completely self contained, and was to incorporate cycle efficiency optimization such as exhaust stream recuperation. Through computer modeling and prototype experimentation, a methane fueled emitter system was designed from structural ceramic materials to fulfill the high temperature requirements necessary for high system efficiency. This paper outlines the engineering design process, discusses obstacles and solutions encountered, and presents the final design.
Date: July 1, 1995
Creator: McHenry, R.S.
Partner: UNT Libraries Government Documents Department

Thermovoltaic in-situ mirror cell

Description: A photovoltaic cell used in a direct energy conversion generator for converting heat to electricity includes a reflective layer disposed within the cell between the active layers of the cell and the cell substrate. The reflective layer reflects photons of low energy back to a photon producing emitter for reabsorption by the emitter, or reflects photons with energy greater than the cell bandgap back to the cell active layers for conversion into electricity. The reflective layer can comprise a reflective metal such as gold while the substrate can comprise a heavily doped silicon or a metal.
Date: December 31, 1995
Creator: Campbell, B.C.
Partner: UNT Libraries Government Documents Department

Temperature profiles of impacts

Description: Similarity solutions determine the profiles of density and temperature from impacts, which determine the scaling of the temperature and optical depth on material parameters, time, screening, and impactor size. This note uses scaling results derived earlier for the growth, size, and temperature produced by impacts to discuss the radial temperature profiles they produce. While the plasmas cool in milliseconds, they offer unique information about the thermodynamic state and material properties of the target material. The brightness temperature can be estimated from known two-dimensional similarity solutions. Regions close to unit optical thickness contribute effectively to the radiation, hence, they determine the plasma brightness temperature. The estimates of temperature as a function of time can be combined with the estimates of the exit hole size to estimate the total observable signal, which should be readily observable from distances of hundreds of kilometers.
Date: May 1, 1997
Creator: Canavan, G. H.
Partner: UNT Libraries Government Documents Department

Direct photons at CDF

Description: Direct Photon measurements from the CDF experiment will be described. These include the inclusive photon pt spectrum, photon+jet angular distributions, diphoton production, photon+2jet production, and photon+charm production. Comparisons to QCD predictions will be made.
Date: October 1, 1996
Creator: Nodulman, L.
Partner: UNT Libraries Government Documents Department

Design of High Sensitivity, High Resolution Compact Single Photon Imaging Devices for Small Animal and Dedicated Breast Imaging

Description: Imaging the biodistribution of single photon emitting radiotracers in small animals and in the breast with high resolution and high sensitivity is an important challenge. Recent work has shown that single photon emission computed tomography (SPECT) imaging of small objects with coded aperture collimators and iterative image reconstruction may provide an order of magnitude increase in sensitivity yet maintain high spatial resolution. We propose a new system design with compact detectors for single photon small animal and breast imaging. Key features are (1) mulitpinhole masks for improved sensitivity, (2) pixellated NaI(Tl) scintillator arrays with small crystals for high resolution and (3) flat panel or flangeless compact position sensitive photomultiplier tubes. Analyses for a multipinhole small animal device with four 10 cm x 20 cm detectors and 1.5 mm detector resolution indicate that 0.9-1.3 mm resolution in image space could be achieved for 0.5-0.8 mm diameter pinholes with geometric sensitivity of 0.2-0.6%, where a point in the brain is imaged through 20 pinholes/mask. A design for a multipinhole breast imager incorporates 20 cm x 20 cm pixellated detectors and lower magnification. Predicted image resolution in the center of the field of view is 1.9 mm for 0.8 mm pinholes, with sensitivity of about 0.045% in the center of the field of view for breast tissue imaged through 20 pinholes/mask. Additional modeling, iterative image reconstruction, device component and phantom tests are desirable to optimize device specifications.
Date: December 1, 2001
Creator: Smith, Mark F.; Majewski, Stan; Meikle, Steven R.; Weisenberger, Andrew G.; Popov, Vladmimir & Wojcik, Randolph F.
Partner: UNT Libraries Government Documents Department

Graphical Analysis of PET Data Applied to Reversible and Irreversible Tracers

Description: Graphical analysis refers to the transformation of multiple time measurements of plasma and tissue uptake data into a linear plot, the slope of which is related to the number of available tracer binding sites. This type of analysis allows easy comparisons among experiments. No particular model structure is assumed, however it is assumed that the tracer is given by bolus injection and that both tissue uptake and the plasma concentration of unchanged tracer are monitored following tracer injection. The requirement of plasma measurements can be eliminated in some cases when a reference region is available. There are two categories of graphical methods which apply to two general types of ligands--those which bind reversibly during the scanning procedure and those which are irreversible or trapped during the time of the scanning procedure.
Date: November 18, 1999
Creator: Logan, Jean
Partner: UNT Libraries Government Documents Department

Electromagnetic signatures of QGP (photons): Experimental status

Description: The direct photon measurement can provide information about the thermal evolution of the hot dense nuclear matter produced in ultra- relativistic heavy-ion collisions. However, the measurement of the transverse momentum distribution of the thermal photons is essential to obtain detailed information, in particular, about the short-lived initial hot phase. To date there has been no confirmed observation of direct thermal photon radiation in the transverse momentum region below about 3 GeV/c. On the other hand, the upper limit on the direct photon yield in S + Au reactions at large transverse momenta determined by the WA80 experiment has been shown to imply that the initial temperature of the system must be relatively low (< 250 MeV). Such low temperatures imply that the system has access to a large number of degrees of freedom, consistent with QGP formation or with a hadronic system consisting of the full spectrum of known resonances up to large mass, but inconsistent with a hadronic gas of only the lowest lying resonances. It is an interesting question how a hadronic gas consisting of the full spectrum of resonances could come into chemical equilibrium already during the initial phase of the interaction. Preliminary results from WA98 for Pb + Pb reactions indicate that there is no significant integrated direct photon excess in central collisions compared to peripheral collisions. This conclusion is based on the variation of the ratio of the electromagnetic to total transverse energy with centrality, which is consistent with no increase. The analysis of the photon data obtained with the WA98 leadglass detector is underway. Comparison of the preliminary inclusive photon spectrum to recent theoretical predictions for the thermal direct photon signal indicate that it may be observable for the case of a hadron gas, but is likely below the expected level of sensitivity for ...
Date: August 1, 1997
Creator: Awes, T.C. & collaboration, WA98
Partner: UNT Libraries Government Documents Department

The Study of Phosphors Efficiency and Homogeneity using a Nuclear Microprobe

Description: Ion Beam Induced Luminescence (IBIL) and Ion Beam Induced Charge Collection (IBICC) have been applied in the study of the luminescence emission efficiency and investigation of the homogeneity of the luminescence emission in phosphors. The IBIL imaging was performed by using sharply focused ion beams or broad/partially-focused ion beams. The luminescence emission homogeneity in samples was examined to reveal possible distributed crystal-defects that may lead to the inhomogeneity of the luminescence emission in samples.The purpose of the study is to search for suitable luminescent thin films that have high homogeneity of luminescence emission, large IBIL efficiency under heavy ion excitation, and can be placed as a thin layer on the top of microelectronic devices to be analyzed with Ion Photon Emission Microscopy (IPEM). The emission yield was found to be low for organic materials, due to saturation of the light output dependence on the energy deposition of heavy ions. The emission yield of a typical Bicron plastic scintillator is about 70 photons/ion/micron. Inorganic materials may have higher IBIL yield under high-energy and heavy-ion excitation, but the challenging problem is the inhomogeneity of the IBIL emission. The IBIL image techniques are applied in the investigation of the homogeneity of a GaN epitaxial thin film, a zircon single crystal and a thin layer coated by Thiogallate(EuII) ceramic.
Date: December 8, 2000
Creator: YANG,C.; DOYLE,BARNEY L.; NIGAM,M.; EL BOUANANI,M.; DUGGAN,J.L. & MCDANIEL,F.D.
Partner: UNT Libraries Government Documents Department

Radiative corrections and parity violating electron-nucleon scattering

Description: Radiative corrections to the parity-violating asymmetry measured in elastic electron-proton scattering are analyzed in the framework of the Standard Model. We include the complete set of one-loop contributions to one quark current amplitudes. The contribution of soft photon emission to the asymmetry is also calculated, giving final results free of infrared divergences. The one quark radiative corrections, when combines with previous work on many quark effects and recent SAMPLE experimental data, are used to place some new constraints on electroweak form factors of the nucleon.
Date: November 1, 2002
Creator: Barkanova, S.; Aleksejevs, A. & Blunden, P.G.
Partner: UNT Libraries Government Documents Department

Workshop on standards for photonic streak camera characterization

Description: A summary paper proposing standardization of definitions and parameter measurements related to photonic streak cameras was generated at the 16th International Congress of High Speed Photography and Photonics at Strasborg, France (August 1984). An international committee appointed by the general Workshop on Picosecond Streak Cameras met and discussed the areas appropriate for standardization and proposed specific definitions, measurements and complementary parameter sets to be used in characterizing photonic streak cameras. These proposals were compiled into a summary paper by the committee co-chairmen, Noel Fleurot (CEA-Limeil) and Gary L. Stradling (Los Alamos National Laboratory), with the intent that it be distributed to interested streak camera users and manufacturers and that appropriate improvements and additions be solicited.
Date: January 1, 1985
Creator: Stradling, G.L.
Partner: UNT Libraries Government Documents Department

The parallel implementation of a backpropagation neural network and its applicability to SPECT image reconstruction

Description: The objective of this study was to determine the feasibility of using an Artificial Neural Network (ANN), in particular a backpropagation ANN, to improve the speed and quality of the reconstruction of three-dimensional SPECT (single photon emission computed tomography) images. In addition, since the processing elements (PE)s in each layer of an ANN are independent of each other, the speed and efficiency of the neural network architecture could be better optimized by implementing the ANN on a massively parallel computer. The specific goals of this research were: to implement a fully interconnected backpropagation neural network on a serial computer and a SIMD parallel computer, to identify any reduction in the time required to train these networks on the parallel machine versus the serial machine, to determine if these neural networks can learn to recognize SPECT data by training them on a section of an actual SPECT image, and to determine from the knowledge obtained in this research if full SPECT image reconstruction by an ANN implemented on a parallel computer is feasible both in time required to train the network, and in quality of the images reconstructed.
Date: December 31, 1992
Creator: Kerr, J. P.
Partner: UNT Libraries Government Documents Department

Estimation of the parameter covariance matrix for aone-compartment cardiac perfusion model estimated from a dynamic sequencereconstructed using map iterative reconstruction algorithms

Description: In dynamic cardiac SPECT estimates of kinetic parameters ofa one-compartment perfusion model are usually obtained in a two stepprocess: 1) first a MAP iterative algorithm, which properly models thePoisson statistics and the physics of the data acquisition, reconstructsa sequence of dynamic reconstructions, 2) then kinetic parameters areestimated from time activity curves generated from the dynamicreconstructions. This paper provides a method for calculating thecovariance matrix of the kinetic parameters, which are determined usingweighted least squares fitting that incorporates the estimated varianceand covariance of the dynamic reconstructions. For each transaxial slicesets of sequential tomographic projections are reconstructed into asequence of transaxial reconstructions usingfor each reconstruction inthe time sequence an iterative MAP reconstruction to calculate themaximum a priori reconstructed estimate. Time-activity curves for a sumof activity in a blood region inside the left ventricle and a sum in acardiac tissue region are generated. Also, curves for the variance of thetwo estimates of the sum and for the covariance between the two ROIestimates are generated as a function of time at convergence using anexpression obtained from the fixed-point solution of the statisticalerror of the reconstruction. A one-compartment model is fit to the tissueactivity curves assuming a noisy blood input function to give weightedleast squares estimates of blood volume fraction, wash-in and wash-outrate constants specifying the kinetics of 99mTc-teboroxime for theleftventricular myocardium. Numerical methods are used to calculate thesecond derivative of the chi-square criterion to obtain estimates of thecovariance matrix for the weighted least square parameter estimates. Eventhough the method requires one matrix inverse for each time interval oftomographic acquisition, efficient estimates of the tissue kineticparameters in a dynamic cardiac SPECT study can be obtained with presentday desk-top computers.
Date: January 1, 2004
Creator: Gullberg, Grant T.; Huesman, Ronald H.; Reutter, Bryan W.; Qi,Jinyi & Ghosh Roy, Dilip N.
Partner: UNT Libraries Government Documents Department