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MLE (Maximum Likelihood Estimator) reconstruction of a brain phantom using a Monte Carlo transition matrix and a statistical stopping rule
In order to study properties of the Maximum Likelihood Estimator (MLE) algorithm for image reconstruction in Positron Emission Tomographyy (PET), the algorithm is applied to data obtained by the ECAT-III tomograph from a brain phantom. The procedure for subtracting accidental coincidences from the data stream generated by this physical phantom is such that he resultant data are not Poisson distributed. This makes the present investigation different from other investigations based on computer-simulated phantoms. It is shown that the MLE algorithm is robust enough to yield comparatively good images, especially when the phantom is in the periphery of the field of view, even though the underlying assumption of the algorithm is violated. Two transition matrices are utilized. The first uses geometric considerations only. The second is derived by a Monte Carlo simulation which takes into account Compton scattering in the detectors, positron range, etc. in the detectors. It is demonstrated that the images obtained from the Monte Carlo matrix are superior in some specific ways. A stopping rule derived earlier and allowing the user to stop the iterative process before the images begin to deteriorate is tested. Since the rule is based on the Poisson assumption, it does not work well …
Date:
October 1, 1987
Creator:
Veklerov, E.; Llacer, J. & Hoffman, E.J.
Object Type:
Article
System:
The UNT Digital Library
The effects of halides on the performance of coal gas-fueled molten carbonate fuel cells: Final report, October 1986-October 1987
This report presents the results of a program to determine the probable tolerable limits of hydrogen chloride and hydrogen fluoride present in the fuel and oxidant streams of molten carbonate fuel cells that are operating on gasified coal. A literature survey and thermodynamic analyses were performed to determine the likely effects of halides on cell performance and materials. Based on the results of these studies, accelerated corrosion experiments and electrode half-cell performance tests were conducted using electrolyte which contained chloride and fluoride. These data and the results of previous in-cell tests were used to develop a computer for predicting the performance decay due to these halides. The tolerable limits were found to be low (less than 1 PPM) and depend on the power plant system configuration, the operating conditions of the fuel cell stack, the cell design and initial electrolyte inventory, and the ability of the cell to scrub low levels of halide from the reactant streams. The primary decay modes were conversion of the electrolyte from pure carbonate to a carbonate-halide mixture and accelerated electrolyte evaporation. 75 figs., 16 tabs.
Date:
October 1, 1987
Creator:
Magee, T. P.; Kunz, H. R.; Krasij, M. & Cote, H. A.
Object Type:
Report
System:
The UNT Digital Library
Combustion of ultrafine coal/water mixtures and their application in gas turbines: Final report
The feasibility of using coal-water fuels (CWF) in gas turbine combustors has been demonstrated in recent pilot plant experiments. The demands of burning coal-water fuels with high flame stability, complete combustion, low NO/sub x/ emission and a resulting fly ash particle size that will not erode turbine blades represent a significant challenge to combustion scientists and engineers. The satisfactory solution of these problems requires that the variation of the structure of CWF flames, i.e., the fields of flow, temperature and chemical species concentration in the flame, with operating conditions is known. Detailed in-flame measurements are difficult at elevated pressures and it has been proposed to carry out such experiments at atmospheric pressure and interpret the data by means of models for gas turbine combustor conditions. The research was carried out in five sequential tasks: cold flow studies; studies of conventional fine-grind CWF; combustion studies with ultrafine CWF fuel; reduction of NO/sub x/ emission by staged combustion; and data interpretation-ignition and radiation aspects. 37 refs., 61 figs., 9 tabs.
Date:
October 1, 1987
Creator:
Toqan, M.A.; Srinivasachar, S.; Staudt, J.; Varela, F. & Beer, J.M.
Object Type:
Report
System:
The UNT Digital Library
1987 Oak Ridge model conference: Proceedings
A conference sponsored by the United States Department of Energy (DOE), was held on waste management. Topics included waste management, site remediation, waste minimization, economic and social aspects of waste management, and waste management training. Several case studies of US DOE facilities are included. Individual projects are processed separately for the data bases. (CBS)
Date:
October 1, 1987
Creator:
unknown
Object Type:
Article
System:
The UNT Digital Library
An overview of the IAEA Safety Series on procedures for evaluating the reliability of predictions made by environmental transfer models
The International Atomic Energy Agency is preparing a Safety Series publication on practical approaches for evaluating the reliability of the predictions made by environmental radiological assessment models. This publication identifies factors that affect the reliability of these predictions and discusses methods for quantifying uncertainty. Emphasis is placed on understanding the quantity of interest specified by the assessment question and distinguishing between stochastic variability and lack of knowledge about either the true value or the true distribution of values for quantity of interest. Among the many approaches discussed, model testing using independent data sets (model validation) is considered the best method for evaluating the accuracy in model predictions. Analytical and numerical methods for propagating the uncertainties in model parameters are presented and the strengths and weaknesses of model intercomparison exercises are also discussed. It is recognized that subjective judgment is employed throughout the entire modelling process, and quantitative reliability statements must be subjectively obtained when models are applied to different situations from those under which they have been tested. (6 refs.)
Date:
October 1, 1987
Creator:
Hoffman, F. W. & Hofer, E.
Object Type:
Article
System:
The UNT Digital Library
Aurora status and plans
Aurora is a short wavelength (248 nm) 10 to kJ KrF laser systems in the ICF program at Los Alamos National Laboratory. It is both an experiment in driver technology and a means for studying target performance using KrF laser light. Both features will be used to help evaluate the uv excimer laser as a viable fusion driver. The system has been designed to employ several electron-beam pumped amplifiers in series, with a final aperture of one meter square, to amplify 96 angularly mulitplexed 5 ns beamlets to the 10 kJ level. In Phase I, 48 of these beamlets are brought to target by demultiplexing and focusing with f26 optics. The beamlet ensemble, contained within an f1.9 bundle, is focused as a single beam;however, pointing is done individually. Spot size in the target plane is variable from 0.1-4 mm, with maximum averaged intensity of )similarreverse arrowto) 4 x 10/sup 15/ Wcm/sup 2/. The illumination geometry is designed specifically for several classes of important target physics experiments. These include: energy flow, symmetry and preheat studies related to indirectly driven targets;x-ray conversion and plasma coupling characterization on disc targets, and hydrodynamic instability studies in planar geometry. System integration is proceeding toward initial …
Date:
October 1, 1987
Creator:
Kristal, R.; Blair, L. S.; Burrows, M. D.; Cartwright, D. C.; Goldstone, P. D.; Greene, D. P. et al.
Object Type:
Article
System:
The UNT Digital Library
Reanalysis of Zion risk
As part of the NUREG-1150 efforts, Brookhaven National Laboratory (BNL) has undertaken a risk analysis of Zion Unit 1 adopting the methodology developed at Sandia National Laboratories (SNL) under the Severe Accident Risk Rebaselining Program. Results of the preliminary version of the analysis are reported here. Completion plans for the Zion study are described also.
Date:
October 1, 1987
Creator:
Park, C.K.; Unwin, S.D.; Cazzoli, E.; Tingle, A. & Chun, M.
Object Type:
Article
System:
The UNT Digital Library
Portable Pbars, traps that travel
The advent of antiproton research utilizing relatively small scale storage devices for very large numbers of these particles opens the possibility of transporting these devices to a research site removed from the accelerator center that produced the antiprotons. Such a portable source of antiprotons could open many new areas of research and make antiprotons available to a new research community. At present antiprotons are available at energies down to 1 MeV. From a portable source these particles can be made available at energies ranging from several tens of kilovolts down to a few millielectron volts. These low energies are in the domain of interest to the atomic and condensed matter physicist. In addition such a source can be used as an injector for an accelerator which could increase the energy domain even further. Moreover, the availability of such a source at a university will open research with antiprotons to a broader range of students than possible at a centralized research facility. This report focuses on the use of ion traps, in particular cylindrical traps, for the antiproton storage device. These devices store the charged antiprotons in a combination of electric and magnet fields. At high enough density and low enough …
Date:
October 1, 1987
Creator:
Howe, S.D.; Hynes, M.V. & Picklesimer, A.
Object Type:
Article
System:
The UNT Digital Library
Solubility and superconductivity in RE(Ba sub 2-x RE sub x )Cu sub 3 O sub 7+. delta. (RE = Nd, Sm, Eu, Gd, Dy)
Solid solutions of RE(Ba{sub 2-x}RE{sub x})Cu{sub 3}O{sub 7- {delta}}(RE=Nd,Sm,Eu,Gd,Dy) for x=0 to x=0.5 have been investigated. X-ray and resistivity measurements show that there exists a solid solution region, through which, the structure changes from orthorhombic to tetragonal and the superconducting properties are depressed. The solubility limits depend strongly on the size of the rare-earth ion, with the smallest (Dy) showing no appreciable solubility. The superconducting transition temperature versus x for all of the rare-earth ion substitutions falls on a universal curve, indicating that the Ba sites are extremely ionic and magnetically isolated. 20 refs., 4 figs.
Date:
October 1, 1987
Creator:
Zhang, K.; Dabrowski, B.; Segre, C.U.; Hinks, D.G.; Schuller, I.K.; Jorgensen, J.D. et al.
Object Type:
Report
System:
The UNT Digital Library
Performance evaluation of PEP
An investigation of collective effects has been undertaken to assess the possibilities for using the low emittance operating mode of the PEP storage ring as a dedicated source of synchrotron radiation. Beam current limitations associated with longitudinal and transverse instabilities, and the expected emittance growth due to intrabeam scattering have been studied as a function of beam energy. Calculations of the beam lifetime due to Touschek and gas scattering are presented, and the growth times of coupled-bunch instabilities are estimated. In general, the results are encouraging, and no fundamental problems have been uncovered. It appears that beam currents up to about 10 mA per bunch should be achievable, and that the emittance growth is not a severe problem at an energy of about 8 GeV. A feedback system to deal with coupled-bunch instabilities is likely to be required. 7 refs., 13 figs.
Date:
October 1, 1987
Creator:
Zisman, M. S.
Object Type:
Article
System:
The UNT Digital Library
Radioactivation in ''quiet'' sections of the SSC (Superconducting Super Collider)
Estimation of induced radioactivity in the ''quiet'' sections of the SSC is approached using elementary methods. Estimates are given of total activity and residual dose rates on the surface of magnets in the quiet regions, as well as estimates of the activation of tunnel concrete. The residual radioactivity produced in the magnets and concrete walls of the ''quiet'' regions of the SSC are found to be quite small and of little radiological impact, but that simple scaling could yield results for more ''lossy'' regions. (LEW)
Date:
October 1, 1987
Creator:
Cossairt, J.D.
Object Type:
Article
System:
The UNT Digital Library
Effect of experimental variables on flash thermal diffusivity data analysis
Flash thermal diffusivity data are usually analyzed with a thermal model which assumes axial heat conduction and uniform illumination of the flashed surface. For high accuracy data reduction, it becomes important to bound to the errors caused by radial heat flow and by non-uniform laser beam profiles. These effects are examined analytically for a case in which the incident laser beam is confined to a radius smaller than the sample radius. The dependence of the output of an averaging detector on the magnitude of the radial heat transfer coefficient is presented and the linear dependence of radial and axial loss sensitivity coefficients is discussed. From this discussion, we conclude that inclusion of radial loss effects in analysis of the thermal response of multilayer structures is not important unless the radial loss factor is very large. Analytical results are presetned for the temperature vs. time response of a two layer composite sample with interfacial thermal resistance and high thermal losses at the sample faces. The use of these results to reduce data for two multilayer samples is presented to show the utility of new data reduction techniques.
Date:
October 1, 1987
Creator:
Sweet, J.N.
Object Type:
Article
System:
The UNT Digital Library
A search for supersymmetric electrons with the Mark II detector at PEP (Positron Electron Project)
An experimental search for selectrons, the supersymmetric partner of the electron, has been performed at the PEP storage ring at SLAC using the Mark II detector. The experimental search done was based upon hypothetical reaction in e/sup +/e/sup -/ interactions at PEP center of mass energies of 29 GeV. In this reaction the selectrons, e-tilde, are assumed produced by the interaction of one of initial state electrons with a photon radiated from the other initial state electron. This latter electron is assumed to continue down the beam pipe undetected. The photon and electron then produce a selectron and a photino, ..gamma..-tilde, in the supersymmetric analog of Compton scattering. The photino is assumed to be the lightest supersymmetric particle, and as such, does not interact in the detector, thereby escaping detection very much like a neutrino. The selectron is assumed to immediately decay into an electron and photino. This electron is produced with large p perpendicular with respect to the beam pipe, since it must balance the transverse momentum carried off by the photinos. Thus, the experimental signature of the process is a single electron in the detector with a large unbalanced tranverse momentum. No events of this type were observed …
Date:
October 1, 1987
Creator:
LeClaire, B.W.
Object Type:
Report
System:
The UNT Digital Library
Engineering design of a liquid metal cooled self-pumped limiter for a tokamak reactor
A lithium cooled self-pumped limiter has been designed as the impurity control system for the TPSS high-..beta.. power reactor conceptual design. The limiter removes helium by trapping impinging helium ions in freshly deposited vanadium surface layers in a slot region. No hydrogen is removed and no pumps or vacuum penetrations are used, thereby eliminating penetration shielding and reducing tritium handling. The limiter is composed of a vanadium alloy structure with a 2mm tungsten cladding on the front face and leading edges for sputtering control. Up to approx.3cm of vanadium trapping material is deposited in the slot region during 5 years of operation. A key design feature is the use of a calcium oxide electrical insulator which coats the limiter coolant channels to reduce MHD pressure drops. A combination of high lithium coolant velocity, made possible by the insulator, and mid-limiter manifolding has been used to obtain acceptable material temperatures with moderately high heat fluxes (3 to 5 mw/m/sup 2/). Overall, a limiter lifetime of approx.5 years is predicted by stress and lifetime analysis. This would permit maintenance free impurity control operation between first wall/blanket replacement periods. 4 refs., 3 figs., 1 tab.
Date:
October 1, 1987
Creator:
Brooks, J. N.; Cha, Y.; Hassanein, A.; Majumdar, S.; Mattas, R. F. & Smith, D. L.
Object Type:
Article
System:
The UNT Digital Library
Status of the silicon strip vertex detector for the Mark II experiment at the SLC
We are constructing a silicon strip vertex detector to be used in the Mark II detector in the study of Z/sup 0/ decays at the SLAC Linear Collider. The status of the project, including the performance of the individual silicon detector modules, is presented. 6 refs., 8 figs., 2 tabs.
Date:
October 1, 1987
Creator:
Adolphsen, C.; Gratta, G.; Litke, A.; Schwarz, A.; Turala, M.; Breakstone, A. et al.
Object Type:
Article
System:
The UNT Digital Library
Estimation of aerial deposition and foliar uptake of xenobiotics: Assessment of current models
This report reviews existing mathematical and/or computer simulation models that estimate xenobiotic deposition to and transport through (both curricular and stomatal) vegetative surfaces. The report evaluates the potential for coupling the best of those models to the existing Uptake, Translocation, Accumulation, and Biodegradation model to be used for future xenobiotic exposure assessments. Here xenobiotic compounds are defined as airborne contaminants, both organic and gaseous pollutants, that are introduced into the environment by man. Specifically this document provides a detailed review of the state-of-the-art models that addressed aerial deposition of particles and gases to foliage; foliar and cuticular transport, metabolism, and uptake of organic xenobiotics; and stomatal transport of gaseous and volatile organic xenobiotic pollutants. Where detailed information was available, parameters for each model are provided on a chemical by chemical as well as species by species basis. Sufficient detail is provided on each model to assess the potential for adapting or coupling the model to the existing UTAB plant exposure model. 126 refs., 6 figs., 10 tabs.
Date:
October 1, 1987
Creator:
Link, S. O.; Fellows, R. J.; Cataldo, D. A.; Droppo, J. G. & Van Voris, P.
Object Type:
Report
System:
The UNT Digital Library
The status of the SLAC Linear Collider and of the Mark II detector
At SLAC we are currently involved in the exciting challenge of commissioning the first example of a new type of colliding beam accelerator, the SLAC Linear Collider, or SLC. The goals of the SLC are two-fold. It will explore the concept of linear colliders, and it will allow the study of physics on the Z/sup 0/ resonance. It accomplishes these goals by exploiting the existing SLAC linac and the large visible cross-section of approximately thirty nanobarns of the Z/sup 0/. The MARK II detector will have the opportunity to be first to explore the physics in this regime. This paper briefly reports the status of the SLC and of the MARK II as of early October 1987, at which time commissioning efforts were interrupted in order to place the MARK II detector at the collision point and to incorporate some improvements to the SLC. The first portion of this report highlights some of the milestones achieved in the SLC commissioning and some of the problems encountered. The last portion outlines improvements made to the MARK II for physics at the SLC. 10 refs., 12 figs., 1 tab.
Date:
October 1, 1987
Creator:
Lankford, A.J.
Object Type:
Article
System:
The UNT Digital Library
Prospects of stable high-density dispersion fuels
The majority of research and test reactors around the world employ aluminum fuel element designs that contain dispersed powders of uranium compounds as fuel. Specifically, two compounds are used: (1) uranium oxide (U/sub 3/O/sub 8/) and (2) an uranium aluminide mixed phase composed of the intermetallic compounds UAl/sub 2/, UAl/sub 3/, and UAl/sub 4/, all made with highly enriched uranium (HEU), i.e., 93% /sup 235/U. The reduction of /sup 235/U enrichment to below 20%, to so-called low enriched uranium (LEU), requires the use of higher density fuels for those applications where increased fuel loading is not feasible. Fuel dispersant loading is, in practice, limited to approximately 45 vol %. Fuel development in the Reduced Envichment Research and Test Reactors (RERTR) program has focused on uranium silicides (U/sub 3/Si and U/sub 3/Si/sub 2/) as the most promising high-density fuels. The compounds of U/sub 6/Fe and U/sub 6/Mn as well as U/sub 3/Si containing Cu were tested as part of the search for stable very-high-density fuels. The problem of breakaway swelling in high-density fuel compounds is attributed to radiation-induced amorphization of these compounds. Alloy additions are a possible means by which the crystal structure of very-high-density compounds can be strengthened and preserved …
Date:
October 1, 1987
Creator:
Hofman, G.L. & Neimark, L.A.
Object Type:
Article
System:
The UNT Digital Library
Fermi surface and effective masses for the heavy-electron superconductor UPt sub 3
Local-density-approximation (LDA) calculations for the Fermi-surface extremal cross-sectional areas of UPt{sub 3} are presented and compared to deHaas-van Alphen experiments of Taillefer et al. The topology of the calculated surfaces is in excellent agreement with experiment and allows a determination of the directional dependence of the anisotropic mass-renormalization factor. The source of this renormalization is briefly discussed. 12 refs., 4 figs., 2 tabs.
Date:
October 1, 1987
Creator:
Norman, M. R.; Albers, R. C.; Boring, A. M.; Christensen, N. E. (Argonne National Lab., IL (USA); Los Alamos National Lab., NM (USA) & Max-Planck-Institut fuer Festkoerperforschung, Stuttgart (Germany, F.R.))
Object Type:
Report
System:
The UNT Digital Library
Effect of decontamination on aging processes and considerations for life extension
The basis for a recently initiated program on the chemical decontamination of nuclear reactor components and the possible impact of decontamination on extended-life service is described. The incentives for extending plant life beyond the present 40-year limit are discussed, and the possible aging degradation processes that may be accentuated in extended-life service are described. Chemical decontamination processes for nuclear plant primary systems are summarized with respect to their corrosive effects on structural alloys, particularly those in the aged condition. Available experience with chemical cleaning processes for the secondary side of PWR steam generators is also briefly considered. Overall, no severe materials corrosion problems have been found that would preclude the use of these chemical processes, but concerns have been raised in several areas, particularly with respect to corrosion-related problems that may develop during extended service.
Date:
October 1, 1987
Creator:
Diercks, D. R.
Object Type:
Article
System:
The UNT Digital Library
Procedures manual for the Evaluated Nuclear Structure Data File
This manual is a collection of various notes, memoranda and instructions on procedures for the evaluation of data in the Evaluated Nuclear Structure Data File (ENSDF). They were distributed at different times over the past few years to the evaluators of nuclear structure data and some of them were not readily avaialble. Hence, they have been collected in this manual for ease of reference by the evaluators of the international Nuclear Structure and Decay Data (NSDD) network contribute mass-chains to the ENSDF. Some new articles were written specifically for this manual and others are reivsions of earlier versions.
Date:
October 1, 1987
Creator:
Bhat, M.R. (ed.)
Object Type:
Report
System:
The UNT Digital Library
Container materials for isolation of radioactive waste in salt
The workshop reviewed the extensive data on the corrosion resistance of low-carbon steel in simulated salt repository environments, determined whether these data were sufficient to recommend low-carbon steel for fabrication of the container, and assessed the suitability of other materials under consideration in the SRP. The panelists determined the need for testing and research programs, recommended experimental approaches, and recommended materials based on existing technology. On the first day of the workshop, presentations were made on waste package requirements; the expected corrosion environment; degradation processes, including a review of data from corrosion tests on carbon steel; and rationales for container design and materials, modeling studies, and planned future work. The second day was devoted to a panel caucus, presentation of workshop findings, and open discussion. 76 refs., 2 figs., 3 tabs.
Date:
October 1, 1987
Creator:
Streicher, M.A. & Andrews, A. (eds.)
Object Type:
Article
System:
The UNT Digital Library
A qualitative study of wake fields for very short bunches
A qualitative treatment is given of both single and multiple cavity wakefields, with the intent of providing some physical insight into the energy and bunch length dependencies. (LEW)
Date:
October 1, 1987
Creator:
Palmer, Robert B.
Object Type:
Article
System:
The UNT Digital Library
Hadron-quark phase transition in dense stars
An equation of state is computed for a plasma of one flavor quarks interacting through some phenomenological potential, at zero temperature. Assuming that the confining potential is scalar and color-independent, it is shown that the quarks undergo a first-order mass phase transition. In addition, due to the way screening is introduced, all the thermodynamic quantities computed are independent of the actual shape of the interquark potential. This equation of state is then generalized to a several quark flavor plasma and applied to the study of the hadron-quark phase transition inside a neutron star. 45 refs., 4 figs.
Date:
October 1, 1987
Creator:
Grassi, F.
Object Type:
Article
System:
The UNT Digital Library