314 research outputs found
Content analysis of children's programs on Boston's television stations
Thesis (Ed.M.)--Boston Universit
Zero Sound and First Sound in a Disk-Shaped Normal Fermi gas
We study the zero sound and the first sound in a dilute and ultracold
disk-shaped normal Fermi gas with a strong harmonic confinement along the axial
direction and uniform in the two planar directions. Working at zero temperature
we calculate the chemical potential of the fermionic fluid as a function
of the uniform planar density and find that changes its slope in
correspondence to the filling of harmonic axial modes (shell effects). Within
the linear response theory, and under the random phase approximation, we
calculate the velocity of the zero sound. We find that also
changes its slope in correspondence of the filling of the harmonic axial modes
and that this effect depends on the Fermi-Fermi scattering length . In the
collisional regime, we calculate the velocity of first sound showing that
displays jumps at critical densities fixed by the scattering length
. Finally, we discuss the experimental achievability of these zero sound
and first sound waves with ultracold alkali-metal atoms.Comment: 9 pages, 5 figures, editorially approved for publication on Phys.
Rev.
Molecular Gas in the Powerful Radio Nucleus of the Ultraluminous Infrared Galaxy PKS 1345+12
Millimeter CO(1-0) interferometry and high resolution, Hubble Space Telescope
(HST) 1.1, 1.6, and 2.2 micron imaging of the radio compact galaxy PKS 1345+12
are presented. With an infrared luminosity of 2x10^{12} L_sun, PKS 1345+12 is a
prime candidate for studying the link between the ultraluminous infrared galaxy
phenomenon and radio galaxies. These new observations probe the molecular gas
distribution and obscured nuclear regions of PKS 1345+12 and provide
morphological support for the idea that the radio activity in powerful radio
galaxies is triggered by the merger of gas rich galaxies. Two nuclei separated
by 2" (4.0 kpc) are observed in the near-infrared; the extended southeastern
nucleus has colors consistent with reddened starlight, and the compact
northwestern nucleus has extremely red colors indicative of an optical quasar
with a warm dust component. Further, the molecular gas, 3mm continuum, and
radio emission are coincident with the redder nucleus, confirming that the
northwestern nucleus is the site of the AGN and that the molecular gas is the
likely fuel source.Comment: LaTex, 5 pages with 1 postscript and 1 jpg figure, ApJ Letters, in
press (August 20, 1999
Hidden order in bosonic gases confined in one dimensional optical lattices
We analyze the effective Hamiltonian arising from a suitable power series
expansion of the overlap integrals of Wannier functions for confined bosonic
atoms in a 1d optical lattice. For certain constraints between the coupling
constants, we construct an explicit relation between such an effective bosonic
Hamiltonian and the integrable spin- anisotropic Heisenberg model. Therefore
the former results to be integrable by construction. The field theory is
governed by an anisotropic non linear -model with singlet and triplet
massive excitations; such a result holds also in the generic non-integrable
cases. The criticality of the bosonic system is investigated. The schematic
phase diagram is drawn. Our study is shedding light on the hidden symmetry of
the Haldane type for one dimensional bosons.Comment: 5 pages; 1 eps figure. Revised version, to be published in New. J.
Phy
A Supernova Factory in Mrk 273?
We report on 1.6 and 5.0 GHz observations of the ultraluminous infrared
galaxy (ULIRG) Mrk 273, using the European VLBI Network (EVN) and the
Multi-Element Radio-Linked Interferometer Network (MERLIN). We also make use of
published 1.4 GHz VLBA observations of Mrk 273 by Carilli & Taylor (2000). Our
5 GHz images have a maximum resolution of 5-10 mas, which corresponds to linear
resolutions of 3.5-7 pc at the distance of Mrk 273, and are the most sensitive
high-resolution radio observations yet made of this ULIRG. Component N1, often
pinpointed as a possible AGN, displays a steep spectral index (); hence it is very difficult to reconcile
with N1 being an AGN, and rather suggests that the compact nonthermal radio
emission is produced by an extremely high luminous individual radio supernova
(RSN), or a combination of unresolved emission from nested supernova remnants
(SNR), luminous RSNe, or both. Component N2 is partly resolved out into several
compact radio sources --none of which clearly dominates-- and a region of
extended emission about 30 pc in size. The integrated spectral index of this
region is flat (), which can be interpreted as due to a
superposition of several unresolved components, e.g., RSNe or SNRs, whose radio
emission peaks at different frequencies and is partially free-free absorbed.
The overall extended radio emission from component N is typical of nonthermal,
optically thin radio emission (), and its 1.4 GHz
luminosity ( WHz) is
consistent with being produced by relativistic electrons diffused away from
supernova remnants in an outburst.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society Main Journal. 6 pages, 3 figure
Molecular Gas and Nuclear Activity in Radio Galaxies Detected by IRAS
This paper reports the latest results from a millimeter-wave (CO)
spectroscopic survey of IRAS-detected radio galaxies with L_1.4GHz ~ 10^23-28
W/Hz in the redshift range z ~ 0.02-0.15. The IRAS flux-limited sample contains
33 radio galaxies with different radio morphologies and a broad range of
infrared luminosities L_IR = 10^9-12 L_sun), allowing for an investigation of
(a) whether low-z radio-selected AGN reside in molecular gas-rich host galaxes,
and (b) whether the CO properties are correlated with the properties of the
host galaxy or the AGN. All of the radio galaxies in Mazzarella et al. (1993)
and Mirabel et al. (1989) have been reobserved. Three new CO detections have
been made, raising the total number of CO detections to nine and setting the
survey detection rate at ~ 25%. Many of the CO lines have double-peaked
profiles, and the CO line widths are broad (average Delta v_FWHM ~ 500+/-130
km/s), exceeding the average CO widths of both ultraluminous infrared galaxies
(300+/-90 km/s) and Palomar-Green QSOs (260+/-160 km/s), and thus being
indicative of massive host galaxies. The CO luminosities translate into
molecular gas masses of ~ 0.4-7x10^9 M_sun, however, the 3-sigma CO upper
limits for nondetections do not rule out a molecular gas mass as high as that
of the Milky Way (~ 3x10^9 M_sun). Optical images of eight out of nine
molecular gas-rich radio galaxies show evidence of close companions and/or
tidal features. Finally, there is no obvious correlation between radio power
and molecular gas mass. However, it is notable that only one F-R II galaxy out
of 12 is detected in this CO survey; the remaining detections are of galaxies
hosting F-R I and compact radio jets.Comment: LaTex, 33 pages, including 1 jpg figure and 14 postscript figures,
ApJS, in press (August 2005
Analysis of the NGXO Telescope X-Ray Hartmann Data
Next Generation X-Ray Optics (NGXO) team at the Goddard Space Flight Center (GSFC) has been developing a new silicon-based grazing incidence mirror technology for future high resolution x-ray astronomical missions. Recently, the GSFC team completed the construction of first few mirror modules that contain one pair of mirrors. One of the mirror pairs was tested in GSFC 600-m long beamline facility and Panter (Neuried, Germay) 120-m long x-ray beamline facility. Both full aperture x-ray tests, Hartmann tests, and focal plane sweeps were completed. In this paper we present the data analysis process and compare the results from our models to measured x-ray centroid data, x-ray performance data, and out of focus images of the mirror pair
Visual and Near-Infrared Imaging of Ultraluminous Infrared Galaxies: The IRAS 2 Jy Sample
New near-infrared and visual images at 2.2 μm and 6550 Å are presented for 46 galaxies having infrared luminosities of L_(IR) > 8.5 x 10^(11) L_⊙, 60 μm flux densities greater than 1.94 Jy, and declinations greater than -35°. These galaxies make up a significant fraction of a complete, northern hemisphere sample of ultraluminous infrared galaxies. Visual and/or near-infrared imaging data now exist for 56 ultraluminous infrared galaxies out to nearly 50 000 km s^(-1). Of these 56 galaxies, 53 (95%) show evidence for current or past interactions. Among these systems, there are a large variety of visual morphologies, including strongly interacting pairs with apparent tidal tails, as well as single, distorted galaxies with close double nuclei. There are three galaxies which, to the limits of the imaging data, do not appear to have suffered a recent interaction or merger. Approximately 47% (25/53) of the interacting systems have double nuclei, with projected nuclear separations ranging from 0.3 to 48 kpc. Seven systems have nuclear separations larger than 10 kpc. If the 53 interacting galaxies are viewed as stages in the evolution of pairs of interacting spiral galaxies to a single, luminous AGN or starburst, the present imaging data can be used to estimate the lifetime of the bright infrared phase. Including only those sample galaxies with morphological evidence for interactions, we calculate a lower and an upper limit to the lifetime of the ultraluminous infrared phase of the sample as a whole to be 2 x 10^8 and 2 x 10^9 yr, respectively. Comparison of these dynamical estimates to models of the mergers of gas-rich galaxies and the rates at which fuel is exhausted by starbursts or AGN suggests the lifetime of the ultraluminous phase lies much closer to the smaller of these two values. Selecting galaxies based upon luminous infrared activity clearly biases the sample towards merging galaxies with small physical separations. However, the existence of pairs with large separations indicates that the ultraluminous phase may in some cases start early during the merger process. Alternatively, these systems may contain unresolved third nuclei responsible for triggering the ultraluminous activity. We briefly compare our results to recent models of merging spiral galaxies
High Angular Resolution and Lightweight X-Ray Optics for Astronomical Missions
X-ray optics with both high angular resolution and lightweight is essential for further progress in x-ray astronomy. High angular resolution is important in avoiding source confusion and reducing background to enable the observation of the most distant objects of the early Universe. It is also important in enabling the use of gratings to achieve high spectral resolution to study, among other things, the myriad plasmas that exist in planetary, stellar, galactic environments, as well as interplanetary, inter-stellar, and inter-galactic media. Lightweight is important for further increase in effective photon collection area, because x-ray observations must take place on space platforms and the amount of mass that can be launched into space has always been very limited and is expected to continue to be very limited. This paper describes an x-ray optics development program and reports on its status that meets these two requirements. The objective of this program is to enable Explorer type missions in the near term and to enable flagship missions in the long term
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