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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
MTX (Microwave Tokamak Experiment) facility and machine grounding plan
A key issue in the design of fusion research experiments and their related facilities is the control of ground currents. Because of the large magnetic field, high voltages and high currents present in most of these installations, it is essential to avoid ground loops, and to control ground currents during both normal operations and fault conditions. This paper describes the grounding policy that was developed for MTX. The vault area was divided into zones, and each of the four walls was treated as a separate grounding area. Cable runs and magnet buss bars were run into the machine radially. The paper also describes the steps taken to isolate diagnostic signals and power for pumps and instruments. The paper outlines some of the field calculations used to predict problem areas, and to reveal voltage isolation levels that were required. The paper includes the active ground fault detection system used to insure the integrity of the ground system. 2 refs., 5 figs.
Date:
October 7, 1987
Creator:
Bell, H.H.; Rice, B.W.; Petersen, D.E. & Herrera, C.H.
Object Type:
Article
System:
The UNT Digital Library
Magnet power system for the Microwave Tokamak Experiment (MTX)
The system configuration, layout, and general philosophy for the MTX magnet power system is described. The vast majority of the magnet power equipment was quite successfully used on the ALCATOR-C experiment at the Massachusetts Institute of Technology. The AC power for the magnet system at MIT was obtained from a 225MVA alternator. The power for the system at LLNL is obtained directly from the local utility's 230 kV line. This installation, therefore, necessitates the addition of a great deal of equipment in ranges from new switchgear in the substation to using existing switchgear obtained from MIT as contractors for intershop electrical isolation as well as safety isolation for personnel entry into the experimental area. Additionally, some discussion is made of the unique layout of this facility and the tradeoffs made to accommodate them. 2 refs., 6 figs.
Date:
October 7, 1987
Creator:
Jackson, M.C. & Musslewhite, R.C.
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
Enhanced durability and reactivity for zinc ferrite desulfurization sorbent
AMAX Research Development Center (AMAX R D) has been investigating methods for improving the reactivity and durability of the zinc ferrite desulfurization sorbent. Zinc ferrite sorbents are intended for use in desulfurization of hog coal gas in integrated gasification combined cycle (IGCC) or molten carbonate fuel cell (MCFC) applications. The reactivity of the sorbent may be defined as its sulfur sorption capacity at the breakthrough point in a bench-scale fixed-bed reactor. The durability may be defined as the ability of the sorbent to maintain its reactivity and other important physical characteristics such as size, strength, and specific surface area during 10 cycles of sulfidation and regeneration. Two base case sorbents, spherical pellets and cylindrical extrudes used in related METC sponsored projects, are being used to provide a basis for the comparison of physical characteristics and chemical reactivity.
Date:
October 27, 1987
Creator:
Jha, M. C. & Berggren, M. H.
Object Type:
Report
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
[Pamphlet: March on Washington for Lesbian & Gay Rights]
A March on Washington for Lesbian & Gay Rights pamphlet, containing demands, related events, and a call to action.
Date:
October 1987
Creator:
National March on Washington Committee
Object Type:
Pamphlet
System:
The UNT Digital Library
[Letter from James R. Miller to Carl L. Yeckel, October 8, 1987]
Letter from James R. Miller to Carl L. Yeckel, of the Carl B. and Florence E. King Foundation, on October 8, 1987, mentioning the recent visit of Julian C. Stanley to the university, and thanking Yeckel for his consideration of their proposal. Stanley's letter of thanks to Alfred Hurley is included.
Date:
October 8, 1987
Creator:
Miller, James R.
Object Type:
Letter
System:
The UNT Digital Library
Oklahoma's Residential High School: Cultivating Scholars
First page of an article on the creation of a special residential high school in Oklahoma, wherein Texas is mentioned as a state that has already done so.
Date:
October 26, 1987
Creator:
unknown
Object Type:
Article
System:
The UNT Digital Library
Academy awaits board completion, first meeting
Newspaper clipping of an article by Jay Johnson, noting that the TAMS advisory board is more than half complete, and that Dr. Rogers Redding hopes to have it filled and meeting within a few weeks.
Date:
October 2, 1987
Creator:
Johnson, Jay
Object Type:
Clipping
System:
The UNT Digital Library
[Letter from E. L. Langley to Alfred F. Hurley, October 19, 1987]
Letter from E. L. Langley to Alfred F. Hurley, on October 19, 1987, sending a copy of a letter from Gibson D. Lewis appointing Langley to the Academics of Mathematics and Science Advisory Board.
Date:
October 19, 1987
Creator:
Langley, E. L.
Object Type:
Letter
System:
The UNT Digital Library
[Letter from Valleau Wilkie, Jr. to James J. Muro, October 8, 1987]
Letter from Valleau Wilkie, Jr. to James J. Muro, on October 8, 1987, informing him that Muro's request for a grant to North Texas State University for the Texas Academy of Mathematics and Science has been denied, although he promises that it will be revisited in early 1988.
Date:
October 8, 1987
Creator:
Wilkie, Valleau, Jr.
Object Type:
Letter
System:
The UNT Digital Library
A Review and Analysis of Fortran 8x
The ANSI Standards Subcommittee X3J3 on Fortran has recently completed a draft proposed standard for the Fortran programming language. The draft proposed standard, known informally as Fortran 8x, is a revision of the current standard X3.9-1978, known informally as Fortran 77. This report is a review of Fortran 8x and consists of a series of six articles. The first article gives a general overview of Fortran 8x. The next three articles give brief discussions of the array facilities; the enhanced numeric facilities; and user-defined data types, procedure interfaces, and the new program unit called a module. The fifth article provides a brief analysis of the controversial issues discussed by X3J3 (including both the accepted and rejected facilities for Fortran 8x). The sixth article gives a brief comparison with Ada. The report concludes with a summary giving information on how and where to express opinions of the draft proposed standard.
Date:
October 1987
Creator:
Smith, Brian T.
Object Type:
Report
System:
The UNT Digital Library
Application of a Multigrid Method to a Buoyancy-Induced Flow Problem
The numerical prediction of buoyancy-induced flows provides special difficulties for standard numerical techniques associated with velocity-buoyancy coupling. We present a multigrid algorithm based upon a novel relaxation scheme that handles this coupling correctly. Numerical experiments have been performed that show that this approach is reasonably efficient and robust for a range of Rayleigh numbers and a variety of cycling strategies.
Date:
October 1987
Creator:
Thompson, C. P.; Leaf, G. K. & Vanka, S. P.
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
High-field superconducting solenoids for the TIBER II PF (poloidal-field) system
The poloidal-field (PF) coil set for the Tokamak Ignition/Burn Engineering Reactor (TIBER-II) consists of 24 solenoid modules, 16 of which are stacked inside the toroidal-field (TF) system at the center of the machine. These central solenoid modules operate at high-current densities, and maximum fields at the windings approach 14 T. Although TIBER-II is designed for steady-state operation with noninductive current drive, other operating scenarios are also considered. In the pulsed or inductive mode, PF coil currents are ramped to induce plasma current. In this mode, peak fields approaching 14 T appear on the central solenoid modules at the ends of the stack; the required current densities in these modules approach 40 A . mm/sup 2/. The central solenoid modules are layer wound using cable-in-conduit conductor (CICC) with (NbTi)/sub 3/Sn composite strands for improved high-field performance. Layer winding permits grading the conductor for maximum overall winding-pack current density and also results in less wasted space in the radial build of the machine. Cooling connections may be made at each layer of a module as needed. Current leads to the modules are routed through the high-field central bore. The central solenoid modules can easily support the centering load of the PF system, …
Date:
October 7, 1987
Creator:
Kerns, J. A.; Miller, J. R. & Summers, L. T.
Object Type:
Article
System:
The UNT Digital Library