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Distribution selection in statistical simulation studies

Description: The statistics profession has been remiss in exploiting the numerous advances in simulation methodology. The purpose of this article is to outline progress in variate generation relevant to the conduct of statistical simulation studies. The emphasis is on multivariate distributions, a thriving area of research. 11 refs.
Date: January 1, 1986
Creator: Johnson, M.E.
Partner: UNT Libraries Government Documents Department

Modeling and generating input processes

Description: This tutorial paper provides information relevant to the selection and generation of stochastic inputs to simulation studies. The primary area considered is multivariate but much of the philosophy at least is relevant to univariate inputs as well. 14 refs.
Date: January 1, 1987
Creator: Johnson, M.E.
Partner: UNT Libraries Government Documents Department

Extragalactic origin of gamma-ray bursts. Revision 1

Description: Detectors of gamma-rays carried by satellites and later by high-flying balloons showed the existence of events lasting from fifteen milliseconds to about a hundred seconds, arriving from all directions in space. A few hundred events have been observed in a little more than a decade. The energy of gamma-rays range from a few kilovolts to millions of volts. Recent evidence indicates that considerable energy may be carried at least in some cases even above 10 MeV. But the bulk of the energy appeared to be emitted between 100 and 200 keV. The observed intensities range between 10/sup -3/ and 10/sup -7/ ergs/cm/sup 2/. The simple facts about intensity distribution are compatible with two extreme assumptions but exclude intermediate hypotheses. Either the events occur in our own galaxy in a region smaller than the thickness of the galaxy or they are of extragalactic origin and come from distant galaxies. Practically all attempted explanations have made the former explanation which requires that a mass of approximately 10/sup 20/ grams impinges on a neutron star (assuming a near to 100% conversion of gravitational energy available on the surface of the neutron star or 10/sup 20/ ergs/gram into gamma-rays which, of course, is unrealistic). In case of an extragalactic origin, the neutron star must attract and convert, as we shall see, about 2 x 10/sup 30/ grams or 10/sup -3/ of the solar mass. It is perhaps the size of such events which deterred a detailed discussion of this alternative. Montgomery Johnson and I have tried to assume these big collisions, explore the consequences, and I shall talk about this extragalactic hypothesis.
Date: November 2, 1984
Creator: Johnson, M. & Teller, E.
Partner: UNT Libraries Government Documents Department

On the extragalactic origin of gamma-ray bursts

Description: A theory to explain the origin of extragalactic gamma ray bursts is presented. Collisions of black dwarf and neutron stars with a subsequent fragmentation of the dwarf producing relativistic particle accelerations toward the neutron star and a resulting turbulent flow of material at the neutron star surface is postulated. (DWL)
Date: November 2, 1984
Creator: Johnson, M. & Teller, E.
Partner: UNT Libraries Government Documents Department

delta. /sub 33/ resonance in pion nucleus elastic, single, and double charge exchange scattering

Description: The ..delta../sub 33/ resonance is strongly excited in pion-nucleon scattering, but there is clearly only a limited amount of information that can be learned in scattering the pion from an isolated nucleon. One learns that there is a resonance of mass 1232 MeV, width 115 MeV, and, if one is willing to introduce a dynamical model, something about the off-shell extension of the amplitude. One stands to learn much more from pion-nucleus scattering because in this case the ..delta../sub 33/ resonance has an opportunity to scatter from nucleons, and how this occurs is not well understood. What do we know about the ..delta..-N interaction for pion-nucleus scattering. The isobar-hole model was invented to deal directly with the ..delta../sub 33/-nucleus dynamics, and a phenomenological determination of the isobar shell-model potential was attempted. The unknown dynamics deltaU/sub ..delta../ is contained in a central isoscalar spreading potential of strength W/sub 0/ and a spin orbit potential deltaU/sub 0/ = W/sub 0/rho + spin-orbit. The real part of W/sub 0/rho is measured relative to the nucleon-nucleus potential. From a more theoretical point of view, one would like to be able to calculate deltaU/sub ..delta../, including its isospin dependence, from an underlying dynamical model which is formulated in terms of the basic effective meson-baryon couplings. Some salient properties of these couplings can be determined from models of quark-bag structure, which raises the exciting possibility of learning about these fundamental issues from pion scattering. Attempts at Los Alamos to build a theoretical framework to deal with these and other issues are described. (WHK)
Date: January 1, 1983
Creator: Johnson, M.B.
Partner: UNT Libraries Government Documents Department

Recent developments in the understanding of pion-nucleus scattering

Description: A development of the theory of pion-nucleus scattering is given in a field theoretical framework. The theory is designed to describe pion elastic scattering and single- and double-charge exchange to isobaric analog states. An analysis of recent data at low and resonance energies is made. Strong modifications to the simple picture of the scattering as a succession of free pion-nucleon interactions are required in order to understand the data. The extent to which the experiment is understood in terms of microscopic theory is indicated. 71 references.
Date: January 1, 1983
Creator: Johnson, M.B.
Partner: UNT Libraries Government Documents Department

Self-consistent theory of hadron-nucleus scattering. Application to pion physics

Description: The requirement of using self-consistent amplitudes to evaluate microscopically the scattering of strongly interacting particles from nuclei is developed. Application of the idea to a simple model of pion-nucleus scattering is made. Numerical results indicate that the expansion of the optical potential converges when evaluated in terms of fully self-consistent quantities. A comparison of the results to a recent determination of the spreading interaction in the phenomenological isobar-hole model shows that the theory accounts for the sign and magnitude of the real and imaginary part of the spreading interaction with no adjusted parameters. The self-consistnt theory has a strong density dependence, and the consequences of this for pion-nucleus scattering are discussed. 18 figures, 1 table.
Date: January 1, 1980
Creator: Johnson, M.B.
Partner: UNT Libraries Government Documents Department

Calculation of transmission line impedances using the ANSYS finite element program

Description: This paper describes numerical techniques for calculating the capacitance of an arbitrary two conductor structure. For two dimensional structures the capacitance per unit length can be easily related to the characteristic impedance of a transmission line with the same cross section. Note that this is true for lines operated below their cut off frequency, i.e., TEM mode only. Thus, one can compute the impedance of an arbitrarily shaped line. The method using the ANSYS finite element program is being used to design the high voltage transmission line for the Yale streamer chamber. This line has a transition piece between two different cross sections. It is being modeled by taking several slices throughout the transition region.
Date: June 29, 1984
Creator: Johnson, M.E.
Partner: UNT Libraries Government Documents Department

Pion scattering and nuclear dynamics

Description: A phenomenological optical-model analysis of pion elastic scattering and single- and double-charge-exchange scattering to isobaric-analog states is reviewed. Interpretation of the optical-model parameters is briefly discussed, and several applications and extensions are considered. The applications include the study of various nuclear properties, including neutron deformation and surface-fluctuation contributions to the density. One promising extension for the near future would be to develop a microscopic approach based on powerful momentum-space methods brought to existence over the last decade. In this, the lowest-order optical potential as well as specific higher-order pieces would be worked out in terms of microscopic pion-nucleon and delta-nucleon interactions that can be determined within modern meson-theoretical frameworks. A second extension, of a more phenomenological nature, would use coupled-channel methods and shell-model wave functions to study dynamical nuclear correlations in pion double charge exchange. 35 refs., 11 figs., 1 tab.
Date: January 1, 1988
Creator: Johnson, M.B.
Partner: UNT Libraries Government Documents Department

Statistical analysis in nuclear accountability: a simulation approach

Description: This paper describes a computer simulation approach to modeling material balances and to deriving the limits of error attributable to measurement procedures. A new probability distribution is presented which is useful in the computer simulations. This distribution permits the investigator to assess the sensitivity of initial distributional assumptions on the computed limits of error. The simulation approach is illustrated with a case study example.
Date: January 1, 1978
Creator: Johnson, M.E.; Tietjen, G.L. & Johnson, M.M.
Partner: UNT Libraries Government Documents Department

Magnetic Particle Recovery of Serial Numbers

Description: One method used by crime labs to recover obliterated serial numbers in steel firearms (ferrous samples) is the magnetic particle technique. The use of this method is predicated on the detection of metal deformation present under stamped serial numbers after the visible stamp has been removed. Equipment specialized for this detection is not used in these attempts; a portable magnetic yoke used typically for flaw detection on large weldments or structures, along with dry visible magnetic powders, have been the tools of criminologists working in this area. Crime labs have reported low success rates using these tools [1, 2]. This is not surprising when one considers that little formal development has apparently evolved for use in such investigations since the publication of seminal work in this area some time ago [3]. The aim of this project is to investigate specific aspects of magnetic particle inspection for serial number recovery. This includes attempts to understand the magnetic characteristics of different steels that affect their performance in the test, such as varying results for carbon steels and alloy steels after different thermal and forming treatments. Also investigated are the effects of the nature of the sample magnetization (AC, rectified DC, and true DC) and the use of various detection media, such as visible powders and fluorescent sprays, on test outcome. Additionally, some aspects of surface preparation of firearm samples prior to number recovery were included in this work. The scope of this report includes a brief overview of the magnetic particle inspection method in general and its applications to forensic serial number recovery. This is followed by a description of how such investigations were simulated on lab samples, including a look at how the microstructure of a given steel will affect its performance in the test. Investigations into the serial number recovery ...
Date: October 1, 2003
Creator: Utrata, D. & Johnson, M.J.
Partner: UNT Libraries Government Documents Department

Light-front nuclear shell-model

Description: I examine the effects of nuclear structure on high-energy, high-momentum transfer processes, specifically the EMC effect. For pedagogical reasons, a fictitious but simple two-body system consisting of two equal-mass particles interacting in a harmonic oscillator potential has been chosen. For this toy nucleus, I utilize a widely-used link between instant-form and light-front dynamics, formulating nuclear structure and deep-inelastic scattering consistently in the laboratory system. Binding effects are compared within conventional instant-form and light-front dynamical frameworks, with appreciable differences being found in the two cases. 20 refs.
Date: January 1, 1990
Creator: Johnson, M.B.
Partner: UNT Libraries Government Documents Department

Triggering, front-end electronics, and data acquisition for high-rate beauty experiments

Description: The working group explored the feasibility of building a trigger and an electronics data acquisition system for both collider and fixed target experiments. There appears to be no fundamental technical limitation arising from either the rate or the amount of data for a collider experiment. The fixed target experiments will likely require a much higher rate because of the smaller cross section. Rates up to one event per RF bucket (50 MHz) appear to be feasible. Higher rates depend on the details of the particular experiment and trigger. Several ideas were presented on multiplicity jump and impact parameter triggers for fixed target experiments. 14 refs., 3 figs.
Date: April 1, 1988
Creator: Johnson, M. & Lankford, A.J.
Partner: UNT Libraries Government Documents Department

Theory of pion scattering by nuclei II

Description: The Chew-Low theory is used to calculate the scattering of a pion by a nucleon inside nuclear matter. Together with the standard relation between refractive index and forward scattering, this yields the wave number of a pion inside nuclear matter. Singularities appearing in earlier theories are avoided. (auth)
Date: February 1, 1974
Creator: Bethe, H.A. & Johnson, M.B.
Partner: UNT Libraries Government Documents Department