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New paradigms for the statistics profession

Description: This paper is a presentation made in support of the statistics profession. This field can say it has had a major impact in most major fields of study presently undertaken by man, yet it is not perceived as an important, or critical field of study. It is not a growth field either, witness the almost level number of faculty and new PhD`s produced over the past twenty years. The author argues the profession must do a better job of selling itself to the students it educates. Awaken them to the impact of statistics in their lives and their business worlds, so that they see beyond the formulae to the application of these principles.
Date: February 1, 1995
Creator: Iman, R. L.
Partner: UNT Libraries Government Documents Department

Convection in RR Lyrae stars

Description: Convection undoubtedly plays a strong role in defining the RR Lyrae instability strip, but its effects on amplitude, mode of pulsation, and light curve have always been problematical. One reason is simple that convective models are difficult to compute, and their accuracy is difficult to ascertain. We present results of a new convective survey of RR Lyrae stars that constitute the best models available at this time, with better boundary conditions, physics, zoning, and length of computational run than previous results.
Date: October 1, 1992
Creator: Stellingwerf, R. F. & Bono, G.
Partner: UNT Libraries Government Documents Department

Working group 1: Coronal streamers

Description: The working group on colonel streamers convened on the first day of the 2nd SOHO Workshop, which took place in Marciana Marina, Isola d`Elba, 27 September--1 October 1993. Recent progress in streamer observational techniques and theoretical modeling was reported. The contribution of streamers to the mass and energy supply for the solar wind was discussed. Moreover, the importance of thin electric current sheets for determining both the gross dynamical properties of streamers and the fine-scale filamentary structure within streamers, was strongly emphasized. Potential advances to our understanding of these areas of colonel physics that could be made by the contingent of instruments aboard SOHO were pointed out.
Date: April 1, 1994
Creator: Kopp, R. A.
Partner: UNT Libraries Government Documents Department

Do the Pop II field blue stragglers have a collisional origin?

Description: The hypothesis that the Pop II field blue stragglers have a collisional origin is considered. It appears unlikely that the majority of these stragglers were formed via collisions, but it is difficult to rule out the possibility that a small, but observable, fraction of them were.
Date: March 1, 1993
Creator: Leonard, P. J. T.
Partner: UNT Libraries Government Documents Department

Do the Pop II field blue stragglers have a collisional origin

Description: The hypothesis that the Pop II field blue stragglers have a collisional origin is considered. It appears unlikely that the majority of these stragglers were formed via collisions, but it is difficult to rule out the possibility that a small, but observable, fraction of them were.
Date: January 1, 1993
Creator: Leonard, P. J. T.
Partner: UNT Libraries Government Documents Department

Properties of multiple event gamma ray bursts

Description: We present results from a study of 37 multiple event gamma ray bursts found in the monitoring data of the PVO gamma ray burst detector. We define these bursts as those which have two or more distinct emission events separated by a return to the background intensity. Significant correlation exists between the duration of the first event and the duration of the second event, while some correlation exists between the hardness of the events and only weak correlation exists in the intensity of the events. Although the time profiles of events in a burst may be similar, as measured in the phase portrait, there is no general rule about the degree of similarity of the time profiles. Subdividing the data according to the recurrence time, we find a tendency for the strength of the correlation in the hardness to increase with decreasing separation between the events. 2 refs., 2 figs., 1 tab.
Date: December 31, 1991
Creator: Lochner, J. C.
Partner: UNT Libraries Government Documents Department

A survey of surveys

Description: A new era for the field of Galactic structure is about to be opened with the advent of wide-area digital sky surveys. In this article, the author reviews the status and prospects for research for 3 new ground-based surveys: the Sloan Digital Sky Survey (SDSS), the Deep Near-Infrared Survey of the Southern Sky (DENIS) and the Two Micron AU Sky Survey (2MASS). These surveys will permit detailed studies of Galactic structure and stellar populations in the Galaxy with unprecedented detail. Extracting the information, however, will be challenging.
Date: November 1, 1994
Creator: Kent, S. M.
Partner: UNT Libraries Government Documents Department

Nonlinear optics and organic materials

Description: We shall consider an interesting topic relating nonlinear optics and organic materials: how nonlinear optics can be used to study organic materials. One of the main differences between linear and nonlinear responses of a medium to incoming radiation is in their symmetries. It leads to the possibility that some properties of the medium could be more sensitively probed by nonlinear, rather than linear, optical means, or vise versa. A well-known example is that some vibrational modes of a medium could be Raman-active but infrared-inactive, and would be more readily observed by Raman scattering, which is a two-photon transition process. In this paper, we shall discuss, with the help of three examples, how we can use second harmonic generation (SHG) and sum frequency generation (SFG) to obtain unique information about a material. We shall focus on thin films, surfaces, and interfaces.
Date: July 1, 1994
Creator: Shen, Y. R.
Partner: UNT Libraries Government Documents Department

Angular momentum in the Local Group

Description: We briefly review models for the Local Group and the acquisition of its angular momentum. We describe early attempts to understand the origin of the spin of the galaxies discussing the hypothesis that the Local Group has little angular momentum. Finally we show that using Peebles` least action principle there should be a rather large amount of orbital angular momentum compared to the magnitude of the spin of its galaxies. Therefore the Local Group cannot be thought as tidally isolated. Using Peebles` trajectories we give a possible set of trajectories for Local Group galaxies which would predict their spin.
Date: April 1, 1994
Creator: Dunn, A. & Laflamme, R.
Partner: UNT Libraries Government Documents Department

Radial and nonradial periods and growth rates of an AI Velorum model

Description: Walraven, Walraven, and Balona recently discovered several new periodicities in addition to the well-known fundamental and first overtone periods of the high-amplitude {delta} Scuti star AI Velorum. Linear nonadiabatic pulsation calculations were performed for an AI Velorum model of mass 1.96 M{sub {circle_dot}}, 24.05 L{sub {circle_dot}}, and T{sub eff}7566 K for the radial and low-degree nonradial modes to help verify the tentative identifications made by Walraven, et al. Comparison of the calculated periods with the observations suggests some alternatives to the identifications proposed by Walraven, et al.
Date: May 1, 1992
Creator: Guzik, J. A.
Partner: UNT Libraries Government Documents Department

The influence of CDM on the dynamical estimate of {Omega} in the local neighborhood

Description: Peebles has suggested an interesting method to trace back in time positions of galaxies called the least action method. This method applied on the Local Group galaxies seems to indicate that we live in an {Omega}{approx} 0.1 Universe. We have studied a CDM N-body simulation with {Omega} = 0.2 and H = 50kms{sup {minus}1}/Mpc and compare trajectories traced back from the Least Action Principle and the center of mass of the particle forming CDM halos. We have shown that the agreement between these set of trajectories is at best qualitative. We have also shown that the line of sight peculiar velocities are underestimated. This discrepancy is due to orphans, CDM particles which do not end up in halos. By varying the density parameter {Omega} in the least action principle we show that using this method we would underestimate the density of the Universe by a factor of 4--5.
Date: December 31, 1994
Creator: Dunn, A. M. & Laflamme, R.
Partner: UNT Libraries Government Documents Department

The meaning of EROS/MACHO

Description: Most of the mass density in the Universe and in the halo of our own galaxy -- exists in the form of dark matter. Overall, the contribution of luminous matter (in stars) to the mass density of the Universe is less than 1%; primordial nucleosynthesis indicates that baryons contribute between 1% and 10% of the critical density (0.01h{sup {minus}2} {approx_lt} {Omega}{sub B} {approx_lt} 0.02h{sup {minus}2}; h = the Hubble constant in units of 100 kms{sup {minus}1}Mpc{sup {minus}1}); and other evidence indicates that the total mass density is at least 10% of critical density, and likely much greater. If the universal density is as low as 10% of the critical density there may be but one kind of dark matter. More likely, the universal density is greater than 10%. and there are two kinds of dark matter, and thus two dark matter problems: In what form does the baryonic dark matter exist? and In what form does the nonbaryonic dark matter exist? The MACHO and EROS collaborations have presented evidence for the microlensing of stars in the LMC by 10{sup {minus}1{plus_minus}1} M{sub {circle_dot}} dark objects in the halo of our own galaxy and may well have solved one of the dark matter puzzles by identifying the form of the baryonic dark matter. It is too early to make precise statements about the fraction of the mass density in the halo of our galaxy contributed by lensing objects (= f{sub m}), though the EROS/MACHO data suggest that f{sub m} is probably 0.1 or larger. Taking our galaxy to be typical and taking account a fraction f{sub m} of the mass in the portion of the halo that contributes most significantly to microlensing (within 20 kpc of the galactic center), I estimate that lensing objects contribute a fraction 0.008f{sub m}/h of the critical …
Date: November 1, 1993
Creator: Turner, M. S.
Partner: UNT Libraries Government Documents Department

Sloan Digital Sky Survey

Description: The Solan Digital Sky Survey is a project which will produce a detailed digital phometric map of half the northern sky to about 23 magnitude using a special purpose wide field telescope of 2.5 meter aperture. This map will be used to select about a million galaxies and 100,000 quasars, for which high resolution spectra will be obtained using the same telescope. A catalog will be produced of all the detected objects, about 100 million galaxies and a similar number of stars, and a million quasar candidates.
Date: November 1, 1993
Creator: Kent, S. M.
Partner: UNT Libraries Government Documents Department

Can physical stellar collisions explain the blue stragglers in the dwarf spheroidal galaxies?

Description: The hypothesis that the blue stragglers in the dwarf spheroidal galaxie have a collisional origin is considered. If all of the dark matter in these galaxies is in the form of low-mass stars and the binary frequency is {approx_equal} 50%, then it is quite possible that {approx_equal} 10% to 20% of their blue stragglers have been produced by physical stellar collisions.
Date: March 1, 1993
Creator: Leonard, P. J. T.
Partner: UNT Libraries Government Documents Department

Discussion of stress tensor nonuniqueness with application to nonuniform, particulate systems

Description: The indeterminacy of the mechanical stress tensor has been noted in several developments of expressions for stress in a system of particles. It is generally agreed that physical quantities related to the stress tensor must be insensitive to this nonuniqueness, but there is no definitive prescription for insuring it. Kroener`s tensor decomposition theorem is applied to the mechanical stress tensor {sup {sigma}}{sub ij} to show that its complete determination requires specification of its ``incompatibility,`` {epsilon}{sub ijk} {epsilon}{sub lmn} {sup {partial_derivative}}{sub j} {sup {partial_derivative}}{sub m} {sup {sigma}}{sub kn}, in addition to its divergence, which is obtained from the momentum conservation relation. For a particulate system, stress tensor incompatibility is shown to vanish to recover the correct expression for macroscopically observable traction. This result removes concern about nonuniqueness without requiring equilibrium or arbitrarily-defined force lines.
Date: June 1, 1993
Creator: Aidun, J. B.
Partner: UNT Libraries Government Documents Department

Fast pulsars, compact stars, and the strange matter hypothesis

Description: Part one of this paper deals with the recent finding of the possible existence of a mixed phase of baryon matter and quark matter inside neutron stars. In part two we review the theoretically determined minimum rotational periods of neutron stars, which serve to distinguish between pulsars that can be understood as rotating neutron stars and those that can not. Likely candidates for the latter are hypothetical strange stars. Their mass-radius relationship is discussed in the last part. It is pointed out that strange stars with a nuclear crust can give rise to the observed phenomena of pulsar glitches, thus passing the only astrophysical test of the strange-matter hypothesis existing to date.
Date: March 17, 1993
Creator: Weber, F. & Glendenning, N. K.
Partner: UNT Libraries Government Documents Department

Redshift distortions of galaxy correlation functions

Description: To examine how peculiar velocities can affect the 2-, 3-, and 4-point correlation functions, we evaluate volume-average correlations for configurations that emphasize and minimize distortions for four different volume-limited samples from each of the CfA, SSRS, and IRAS redshift catalogs. We present the results as the correlation length r{sub 0} and power index {gamma} of the 2-point correlation, {anti {Xi}}{sub 2} = (r{sub 0}/r){sup {gamma}}, and as the hierarchical amplitudes of the 3- and 4-point functions, S{sub 3} = {anti {Xi}}{sub 3}/{anti {Xi}}{sub 2}{sup 2} and S{sub 4} = {anti {Xi}}/{anti {Xi}}{sub 2}{sup 3}. We find a characteristic distortion for {anti {Xi}}{sub 2}: The slope {gamma} is flatter and the correlation length is larger in redshift space than in real space; that is, redshift distortions ``move`` correlations from small to large scales. At the largest scales, extra power in the redshift distribution is compatible with {Omega}{sup 4/7}/b {approx} 1; we find 0.53 {plus_minus} 0.15, 1.10 {plus_minus} 0.16 and 0.84 {plus_minus} 0.45 for the CfA, SSRS and IRAS catalogs. Higher order correlations {anti {Xi}}{sub 3} and {anti {Xi}}{sub 4} suffer similar redshift distortions, but in such a way that, within the accuracy of our analysis, the normalized amplitudes S{sub 3} and S{sub 4} are insensitive to this effect. The hierarchical amplitudes S{sub 3} and S{sub 4} are constant as a function of scale between 1-12 h{sup {minus}1} Mpc and have similar values in all samples and catalogues, S{sub 3} {approx} 2 and S{sub 4} {approx} 6, despite the fact that {anti {Xi}}{sub 2}, {anti {Xi}}{sub 3}, and {anti {Xi}}{sub 4} differ from one sample to another by large factors. The agreement between the independent estimations of S{sub 3} and S{sub 4} is remarkable given the different criteria in the selection of galaxies and also the difference in the resulting range of …
Date: May 12, 1993
Creator: Fry, J. N. & Gaztanaga, E.
Partner: UNT Libraries Government Documents Department

{open_quotes}High magnetic fields in the USA{close_quotes}

Description: During the past thirty years research using high magnetic fields has technically evolved in the manner, but not the magnitude, of the so-called big science areas of particle physics, plasma physics, neutron scattering, synchrotron light scattering, and astronomy. Starting from the laboratories of individual researchers it moved to a few larger universities, then to centralized national facilities with research and maintenance staffs, and, finally, to joint international ventures to build unique facilities, as illustrated by the subject of this conference. To better understand the nature of this type of research and its societal justification it is helpful to compare it, in general terms, with the aforementioned big-science fields. High magnetic field research differs from particle physics, plasma physics, and astronomy in three respects: (1) It is generic research that cuts across a wide range of scientific disciplines in physics, chemistry, biology, medicine, and engineering; (2) It studies materials and processes that are relevant for a variety of technological applications and it gives insight into biological processes; (3) It has produced, at least, comparably significant results with incomparably smaller resources. Unlike neutron and synchrotron light scattering, which probe matter, high magnetic fields change the thermodynamic state of matter. This change of state is fundamental and independent of other state variables, such as pressure and temperature. After the magnetic field is applied, various techniques are then used to study the new state.
Date: November 1, 1994
Creator: Campbell, L. J.; Parkin, D. M.; Crow, J. E.; Schneider-Muntau, H. J. & Sullivan, N. S.
Partner: UNT Libraries Government Documents Department

The second coming of cold dark matter?

Description: In recent years standard cold dark matter (CDM) theory, which enjoyed a large following throughout much of the past decade, has been abandoned by virtually all of its early supporters. The most serious argument against CDM was the incompatibility between the relatively high value of the pairwise radial velocity dispersion between galaxies, {sigma}{sub v}, inferred from numerical simulation with the much lower observational estimates. We reexamine this argument in the light of our new, high-resolution, COBE-normalized simulations and conclude that {sigma}{sub v} is significantly overestimated in simulations which do not have sufficient resolution (i.e., which have masses of galaxies comparable to the mass of N-body particles) and that it is also difficult to reliably estimate {sigma}{sub v} from the observational catalogues used for this purpose. We conclude that inflationary cosmology and CDM are not -- contrary to the presently prevailing prejudice -- incompatible with the observations of small scale peculiar velocities, as characterized, for example, by {sigma}{sub v}.
Date: December 31, 1993
Creator: Zurek, W. H.; Warren, M. S.; Quinn, P. J. & Salmon, J. K.
Partner: UNT Libraries Government Documents Department

Views of the solar system

Description: Views of the Solar System has been created as an educational tour of the solar system. It contains images and information about the Sun, planets, moons, asteroids and comets found within the solar system. The image processing for many of the images was done by the author. This tour uses hypertext to allow space travel by simply clicking on a desired planet. This causes information and images about the planet to appear on screen. While on a planet page, hyperlinks travel to pages about the moons and other relevant available resources. Unusual terms are linked to and defined in the Glossary page. Statistical information of the planets and satellites can be browsed through lists sorted by name, radius and distance. History of Space Exploration contains information about rocket history, early astronauts, space missions, spacecraft and detailed chronology tables of space exploration. The Table of Contents page has links to all of the various pages within Views Of the Solar System.
Date: February 1, 1995
Creator: Hamilton, C.
Partner: UNT Libraries Government Documents Department

The second coming of cold dark matter?

Description: While the standard cold dark matter (CDM) model has received numerous marks against it on the basis of a variety of observational data, the prediction of high {Sigma}{Upsilon}, the pairwise-velocity dispersion between galaxies, on small (megaparsec) scales was reported as perhaps one of its greatest failings. Here, we reexamine the case of CDM and {Sigma}{Upsilon}, with high-resolution numerical simulations. The statistic was measured in simulations, in artificial galaxy catalogs, and in the CfA North Forty redshift survey. In our reanalysis of the CfA data, we found that {Sigma}{Upsilon} {approximately} 500 km/s, significantly higher than the original estimates of Davis & Peebles (1983). This new value, along with our estimate of the velocity bias, leads to a virial measure of the cosmological density parameter, {Omega} {approximately} 0.9. which is more than four times the traditionally cited CfA result. Analysis the simulations indicates that while the method of Davis and Peebles works well, the {Sigma}{Upsilon} statistic itself is not generally robust: there is large scatter from catalog to catalog and evidence that the recovered {Sigma}{Upsilon} value depends strongly on a small fraction of galaxies in the central regions of rare, massive clusters. Thus, at present the CDM model cannot be deemed incompatible with observed small-scale peculiar velocities.
Date: December 31, 1994
Creator: Zurek, W. H.; Bromley, B. C. & Warren, M. S.
Partner: UNT Libraries Government Documents Department

Rapid cooling and structure of neutron stars

Description: This report discusses the following topics on neutron stars: direct URCA neutrino emission; thermal evolution models; analytic model for diffusion through the crust; and core superfluidity. (LSP).
Date: July 1, 1992
Creator: Van Riper, K. A. & Lattimer, J. M.
Partner: UNT Libraries Government Documents Department