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Homoclinic orbits and chaos in a second-harmonic generating optical cavity

Description: We present two large families of Silnikov-type homoclinic orbits in a two mode-model that describes second-harmonic generation in a passive optical cavity. These families of homoclinic orbits give rise to chaotic dynamics in the model. 4 refs., 1 fig.
Date: April 1, 1997
Creator: Holm, D. & Kovacic, G., Timofeyev, I.
Partner: UNT Libraries Government Documents Department

Universality and clustering in 1 + 1 dimensional superstring-bit models

Description: We construct a 1+1 dimensional superstring-bit model for D=3 Type IIB superstring. This low dimension model escapes the problem encountered in higher dimension models: (1) It possesses full Galilean supersymmetry; (2) For noninteracting Polymers of bits, the exactly soluble linear superpotential describing bit interactions is in a large universality class of superpotentials which includes ones bounded at spatial infinity; (3) The latter are used to construct a superstring-bit model with the clustering properties needed to define an S-matrix for closed polymers of superstring-bits.
Date: March 1, 1996
Creator: Bergman, O. & Thorn, C.B.
Partner: UNT Libraries Government Documents Department

Gravitational microlensing results from MACHO

Description: The MACHO project is searching for dark qter inthe form of massive compact haio objects (Machos), by monitoring the brightness of millions of stars in the Magellanic Clouds to search for gravitational microlensing events. Analysis of our 1st 2.3 years of data for 8.5 million stars in the LMC yields 8 candidate microlensing events, well in excess of the {approx} 1 event expected from lensing by known low-mass stars. The event timescales range from 34 to 145 days, and the estimated optical depth is N 2x10{sup -7}, about half of that expected from a `standard` halo. Likelihood analysis indicates the typical lens mass is 0.5{sup +0.3}{sub -0.2}M{sub {circle_dot}}, suggesting they may be old white dwarfs.
Date: September 1, 1996
Creator: Alcock, C. & Collaboration, MACHO
Partner: UNT Libraries Government Documents Department

What will we learn from the CMB?

Description: Within the next decade, experiments measuring the anisotropies in the cosmic microwave background (CMB) will add greatly to our knowledge of the universe. There are dozens of experiments scheduled to take data over the next several years, capped by the satellite missions of NASA (MAP) and ESA (PLANCK). What will we learn from these experiments? I argue that the potential pay-off is immense: We are quite likely to determine cosmological parameters to unprecedented accuracy. This will provide key information about the theory of structure formation and even about the physics behind inflation. If the experiments succeed, can anything spoil this pay-off? I focus on three possible spoilers - foregrounds, reionization, and defect models - and argue that we have every reason to be optimistic.
Date: October 1, 1997
Creator: Dodelson, S.
Partner: UNT Libraries Government Documents Department

QSO color selection in the SDSS

Description: The Sloan Digital Sky Survey (SDSS) will image 10,000 square degrees in the north galactic cap in five filters. We hope to identify and obtain spectra for about 100,000 quasars brighter than 20th magnitude in this area. The selection will be primarily on the basis of point spread function and colors, but we will also identify quasars from a catalog of FIRST radio sources. The selection areas in color space must be determined during the testing period prior to the official start of the survey. This task may determine the length of the test period. In anticipation of this becoming the critical path, we have written a body of software that will allow us to quickly analyze a set of multicolor data and make a first cut at the selection limits.
Date: January 1, 1998
Creator: Newberg, H.J. & Yanny, B.
Partner: UNT Libraries Government Documents Department

Technicolor: status and prospects

Description: Technicolor models are briefly reviewed, and a number of promising signatures at hadron colliders are described. Low-scale technicolor should be discoverable in Run 11 of the Fermilab Tevatron; failing that, it would be hard to miss at the LHC. While technicolor models may be unfashionable, it is important to search for their signatures; we do not know how nature has chosen to break electroweak symmetry.
Date: September 1, 1997
Creator: Womersley, J.
Partner: UNT Libraries Government Documents Department

Dealing with quantum weirdness: Holism and related issues

Description: Various issues are discussed in interpretation of quantum mechanics. All these explorations point toward the same conclusion, that some systems are holistically connected, i.e., some composite systems have properties that cannot, even in principle, be reduced to the properties of its subsystems. This is argued to be the central metaphysical lesson of quantum theory; this will remain pertinent even if quantum mechanics gets replaced by a superior theory. Chap. 2 discusses nonlocality and rules out hidden-variable theories that approximately reproduce the perfect correlations of quantum mechanics, as well as theories that obey locality conditions weaker than those needed to derive Bell`s inequality. Chap. 3 shows that SQUID experiments can rule out non-invasive measurability if not macrorealism. Chap. 4 looks at interpretational issues surrounding decoherence, the dissipative interaction between a system and its environment. Decoherence klcan help ``modal`` interpretations pick out the desired ``preferred`` basis. Chap. 5 explores what varieties of causation can and cannot ``explain`` EPR correlations. Instead of relying on ``watered down`` causal explanations, we should instead develop new, holistic explanatory frameworks.
Date: December 1, 1995
Creator: Elby, A.R.
Partner: UNT Libraries Government Documents Department

Initial Stages of Yield in Nanoindentation

Description: We have used the Interracial Force Microscope" to perform nanoindentations on Au single- crystal surfaces. We have observed two distinct regimes of plastic deformation which are distinguished by the magnitude of discontinuities in load relaxation. At lower stresses, relaxation occurs in small deviations from elastic behavior, while at the higher stresses they take the form of large load drops often resulting in complete relaxation of the applied load. These major events create a relatively wide plastic zone that subsequently deepens more rapidly than it widens. We discuss these findings in terms of contrasting models of dislocation processes in the two regimes.
Date: November 24, 1998
Creator: Houston, J.E.; Jarausch, K.F.; Kiely, J.D. & Russell, P.E.
Partner: UNT Libraries Government Documents Department

Linear dichroism and resonant photoemission in Gd 011

Description: Magnetic Linear Dichroism in Angular Distributions (MLDAD) from Photoelectron Emission was used to probe the nature of Resonant Photoemission. Gd 5p and Gd 4f emission were investigated. Using novel theoretical simulations, we were able to show that temporal matching is a requirement for ``True`` Resonant Photoemission, where the Resonant Photoemission retains the characteristics of Photoelectron Emission.
Date: May 13, 1998
Creator: Mishra, S.R.; Cummins, T.R.; Gammon, W.J.; van der Laan, G.; Goodman, K.W. & Tobin, J.G.
Partner: UNT Libraries Government Documents Department

PG 0946+301: the Rosetta Stone of BALQSOs?

Description: We describe the motivation and features of a multiwavelength spectroscopic campaign on broad absorption line (BAL) QSO PG 0946+301. The main goal of this project is to determine the ionization equilibrium and abundances (IEA) in BAL outflows. Previous studies of IEA in BALQSOs were based on the assumption that the BALs are not saturated so that the column densities inferred from the apparent optical depths are realistic. This critical assumption is at odds with several recent observations and with analysis of existing data which indicate that the absorption troughs are heavily saturated even when they are not black. In addition, X-ray observations, which are important for constraining the ionizing continuum, were not available for those objects that had UV spectral data. Quantifying the level of saturation in the BALs necessitates UV spectroscopy with much higher S/N and broader-spectral coverage than currently exist. After taking into account the capabilities of available observatories, our best hope for a substantial improvement in understanding the IEA in BALQSOs is to concentrate considerable observational resources on the most promising object. Our studies of available HST and ground-based spectra show that PG 0946+301 is by far the best candidate for such a program. This BALQSO is at least five times brighter, shortward of 1000 {Angstrom}, rest frame, than any other object, and due to its low redshift it has an especially sparse Ly{alpha} forest. At the same time PG 0946+301 is a typical BALQSO and therefore its IEA should be representative. To this effect we are developing a multiwavelength spectroscopic campaign (UV, FUV, X-ray and optical) on BALQSO PG 0946+301. We discuss the goals and feasibility of each observational component: HST, FUSE, ASCA and ground-based.
Date: June 1, 1998
Creator: Arav, N., LLNL
Partner: UNT Libraries Government Documents Department

Three-Dimensional Silicon Photonic Crystals

Description: In this work, we report the realization of a series of silicon 3D photonic crystals operating in the infrared (IR), mid-IR and most importantly the near-IR (k= 1 -2pm) wavelengths. The structure maintains its crystal symmetry throughout the entire 6-inches wafer and holds a complete photonic bandgap.
Date: December 4, 1998
Creator: Biswas, R.; Fleming, J.G.; Hetherington, D.L.; Ho, K.M.; Lin, S.; Sigalas, M.M. et al.
Partner: UNT Libraries Government Documents Department

Large-scale mass power spectrum from peculiar velocities

Description: The power spectrum of mass density fluctuations is estimated from the Mark III and the SFI catalogs of peculiar velocities by applying a maximum likelihood analysis, using parametric models for the power spectrum and for the errors. Generalized CDM models with and without COBE normalization are used. The applications to the two different data sets give consistent results. The general result is a relatively high amplitude of the power spectrum, e.g., at k=0.1hMpc{sup -1} we find P(k){Omega}{sup 1.2}=(4.5{+-}2.0)x10{sup 3}(h{sup -1}Mpc){sup 3}, corresponding to {sigma}{sub 8}{Omega}{sup 0.6}=0.85{+-}0.2. Model-dependent constraints on combinations of cosmological parameters are obtained for families of COBE-normalized CDM models. these can roughly be approximated by {Omega}h{sub 60}{sup {mu}}n{sup {nu}}=0.6{+-}0.2, where {mu}=1.3 and {nu}=3.7, 2.0 for flat {Lambda}CDM models with and without tensor fluctuations respectively. For open CDM, without tensor fluctuations, the powers are {mu}=0.9 and {nu}=1.4. the quoted error-bars reflect the 90% formal likelihood uncertainty for each model and the variance among different models and between catalogs. This is a brief review of a collaborative project (for more details, see Zaroubi et al. 1997, Freudling et al. 1998). Preliminary constraints in the {Omega}-{Omega}{sub {Lambda}} plane are presented as well.
Date: October 1, 1998
Creator: Zehavi, Idit
Partner: UNT Libraries Government Documents Department

Summary of sessions on nuclear reaction mechanisms

Description: A summary is provided to the sessions on nuclear reaction mechanisms of the International Conference on Nuclear Data for Science and Technology held May 19-24, 1997 in Trieste, Italy. Brief descriptions of Fission, Optical Model, Radiative capture of fast nucleons, codes, and new approaches are provide.
Date: May 1, 1997
Creator: Dietrich, F.S.
Partner: UNT Libraries Government Documents Department

Particle physics: Themes and challenges

Description: I will devote this lecture to seven themes that express the essence of our understanding and our possibilities. These themes are: elementarity, symmetry, consistency, unity, identity, opportunity, and relevance.
Date: November 1, 1995
Creator: Quigg, C.
Partner: UNT Libraries Government Documents Department

A 2.14 ms candidate optical pulsar in SN1987A: Ten years after

Description: We have monitored Supernova 1987A in optical/near-infrared bands from a few weeks following its birth until the present time in order to search for a pulsar remnant. We have found an apparent pattern of emission near the frequency of 467.5 Hz - a 2.14 ms pulsar candidate, first detected in data taken on the remnant at the Las Campanas Observatory (LCO) 2.5-m Dupont telescope during 14-16 Feb. 1992 UT. We detected further signals near the 2.14 ms period on numerous occasions over the next four years in data taken with a variety of telescopes, data systems and detectors, at a number of ground- and space-based observatories. The sequence of detections of this signal from Feb. `92 through August `93, prior to its apparent subsequent fading, is highly improbable (< 10{sup -10} for any noise source). We also find evidence for modulation of the 2.14 ms period with a {approx}1,000 s period which, when taken with the high spindown of the source (2-3 x 10{sup -10} Hz/s), is consistent with precession and spindown via gravitational radiation of a neutron star with a non- axisymmetric oblateness of {approx}10{sup -6}, and an implied gravitational luminosity exceeding that of the Crab Nebula pulsar by an order of magnitude.
Date: September 1, 1997
Creator: Middleditch, J.; Kristian, J.A.; Kunkel, W.E.; Hill, K.M. & Watson, R.D.
Partner: UNT Libraries Government Documents Department

Matrix membranes and integrability

Description: This is a pedagogical digest of results reported in Curtright, Fairlie, {ampersand} Zachos 1997, and an explicit implementation of Euler`s construction for the solution of the Poisson Bracket dual Nahm equation. But it does not cover 9 and 10-dimensional systems, and subsequent progress on them Fairlie 1997. Cubic interactions are considered in 3 and 7 space dimensions, respectively, for bosonic membranes in Poisson Bracket form. Their symmetries and vacuum configurations are explored. Their associated first order equations are transformed to Nahm`s equations, and are hence seen to be integrable, for the 3-dimensional case, by virtue of the explicit Lax pair provided. Most constructions introduced also apply to matrix commutator or Moyal Bracket analogs.
Date: June 1, 1997
Creator: Zachos, C.; Fairlie, D. & Curtright, T.
Partner: UNT Libraries Government Documents Department

MACHO RR lyrae stars in the galactic bulge: the spatial distribution

Description: We have analyzed a sample of 1150 type ab, and 550 type c RR Lyrae stars found in 24 bulge fields of the MACHO database. These fields cover a range in Galactocentric distances from 0.3 to 1.6 kpc. In combination with the data on the outer bulge fields of Alard (1997) and Wesselink (1987), here we present the surface density distribution of bulge RR Lyrae between 0.3 and 3 kpc. The distribution along the line of sight of the bulge RR Lyrae population was examined on the basis of the mean magnitudes, and it was shown that the bulk of the RR Lyrae population is not barred (Alcock et al. 1998). There is a hint of a bar only in the RR Lyrae of the inner fields closer to the Galactic center. The red giant clump stars in the MACHO fields, however, clearly show a barred distribution, confirming the results of previous studies (e.g. Dwek et al. 1995, Stanek et al. 1996). In the MACHO fields studied there are about 550 clump giants per RR Lyrae star. The RR Lyrae trace metal-poor stars, which are a minor component of the bulge population. The clump giants, however, should trace the bulk of the metal-rich population, foUowing underlying mass of the bulge more closely. Given the different spatial distribution, we concluded that the RR Lyrae and the clump giants trace two dif+erent populations (Alcock et al. 1998). The RR Lyrae would represent the inner extension of the Galactic halo in these fields (Minniti 1996). The observed surface distribution of RR Lyrae in the bulge fields was computed after discarding background RR Lyrae that belong to the Sgr dwarf galaxy (Alard 1996, Alcock et al. 1997). This distribution yields a power law density distribution. There is no turnover or flattening of this distribution ...
Date: August 1, 1997
Creator: Minniti, D.; Alcock, C. & Alves, D.
Partner: UNT Libraries Government Documents Department