1,176 research outputs found
Gauge Field Preheating at the End of Inflation
Here we consider the possibility of preheating the Universe via the
parametric amplification of a massless, U(1) abelian gauge field. We assume
that the gauge field is coupled to the inflaton via a conformal factor with one
free parameter. We present the results of high-resolution three-dimensional
simulations of this model and show this mechanism efficiently preheats the
Universe to a radiation-dominated final state.Comment: 8 pages, 8 figure
From the Editors
Editorial introduction to the third issue of Clinical Research in Practice: The Journal of Team Hippocrates
From the editors
Editorial introduction to the second issue of Clinical Research in Practice: The Journal of Team Hippocrates
Measurements of the methane relaxation times for application to the infrared emission models of the upper atmospheres of outer planets and Titan
The 7.8 micrometer emission from the nu(sub 4) band of methane (CH4) is a regularly observed feature in the stratosphere of all the giant planets and Titan. On Jupiter, enhancements in this emission are associated with the infrared hot spots in the auroral zone. Attempts to model this phenomenon in particular, and to understand the role of methane in general, have been hampered in part by a lack of adequate laboratory measurements of the collisional relaxation times for the nu(sub 3) and nu(sub 4) levels over the appropriate temperature range. To provide this needed data, a series of laboratory experiments were initiated. In the experimental arrangement the nu(sub3) band of methane is pumped at 3.3 micrometers using a pulsed infrared source (Nd:YAG/dye laser system equipped with a wave-length extender). The radiative lifetime of the nu(sub 3) level (approximately 37 ms) is much shorter than the nu(sub 4) lifetime (approximately 390 ms); however, a rapid V-V energy transfer rate ensures that the nu(sub 4) level is substantially populated. The photoacoustic technique is used to acquire relaxation rate information. The experiments are performed using a low-temperature, low-pressure cell. Experimental apparatus and technique are described. In addition some of the experimental difficulties associated with making these measurements are discussed and some preliminary results are presented
High resolution, low temperature photoabsorption cross-section of C2H2 with application to Saturn's atmosphere
New laboratory observations of the VUV absorption cross-section of C2H2, obtained under physical conditions approximating stratospheres of the giant planets, were combined with IUE observations of the albedo of Saturn, for which improved data reduction techniques have been used, to produce new models for that atmosphere. When the effects of C2H2 absorption are accounted for, additional absorption by other molecules is required. The best-fitting model also includes absorption by PH3, H2O, C2H6 and CH4. A small residual disagreement near 1600 A suggests that an additional trace species may be required to complete the model
The Most Distant Stars in the Milky Way
We report on the discovery of the most distant Milky Way (MW) stars known to
date: ULAS J001535.72015549.6 and ULAS J074417.48253233.0. These stars
were selected as M giant candidates based on their infrared and optical colors
and lack of proper motions. We spectroscopically confirmed them as outer halo
giants using the MMT/Red Channel spectrograph. Both stars have large estimated
distances, with ULAS J001535.72015549.6 at kpc and ULAS
J074417.48253233.0 at 238 64 kpc, making them the first MW stars
discovered beyond 200 kpc. ULAS J001535.72015549.6 and ULAS
J074417.48253233.0 are both moving away from the Galactic center at km s and km s, respectively. Using their
distances and kinematics, we considered possible origins such as: tidal
stripping from a dwarf galaxy, ejection from the MW's disk, or membership in an
undetected dwarf galaxy. These M giants, along with two inner halo giants that
were also confirmed during this campaign, are the first to map largely
unexplored regions of our Galaxy's outer halo.Comment: Accepted and in print by ApJL. Seven pages, 2 figure
The Shape and Scale of Galactic Rotation from Cepheid Kinematics
A catalog of Cepheid variables is used to probe the kinematics of the
Galactic disk. Radial velocities are measured for eight distant Cepheids toward
l = 300; these new Cepheids provide a particularly good constraint on the
distance to the Galactic center, R_0. We model the disk with both an
axisymmetric rotation curve and one with a weak elliptical component, and find
evidence for an ellipticity of 0.043 +/- 0.016 near the Sun. Using these
models, we derive R_0 = 7.66 +/- 0.32 kpc and v_circ = 237 +/- 12 km/s. The
distance to the Galactic center agrees well with recent determinations from the
distribution of RR Lyrae variables, and disfavors most models with large
ellipticities at the solar orbit.Comment: 36 pages, LaTeX, 10 figure
W283 Should Tennessee Tobacco Growers Invest in Irrigation, Fertigation or Plastic Mulch?
Version 2.
The Most Distant Stars in the Milky Way
We report on the discovery of the most distant Milky Way (MW) stars known to date: ULAS J001535.72+015549.6 and ULAS J074417.48+253233.0. These stars were selected as M giant candidates based on their infrared and optical colors and lack of proper motions. We spectroscopically confirmed them as outer halo giants using the MMT/Red Channel spectrograph. Both stars have large estimated distances, with ULAS J001535.72+015549.6 at 274 ± 74 kpc and ULAS J074417.48+253233.0 at 238 ± 64 kpc, making them the first MW stars discovered beyond 200 kpc. ULAS J001535.72+015549.6 and ULAS J074417.48+253233.0 are both moving away from the Galactic center at 52 ± 10 km s–1 and 24 ± 10 km s–1, respectively. Using their distances and kinematics, we considered possible origins such as: tidal stripping from a dwarf galaxy, ejection from the MW\u27s disk, or membership in an undetected dwarf galaxy. These M giants, along with two inner halo giants that were also confirmed during this campaign, are the first to map largely unexplored regions of our Galaxy\u27s outer halo
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