1,464 research outputs found
Collision Integrals for the Exponential Attractive Potential
Numerical integration calculation of collision integrals for exponential attractive potential of gase
Automatic calculation of the transport collision integrals with tables for the morse potential
Computer program for calculation of transport collision integrals with tables for Morse potentia
Regular obstructed categories and TQFT
A proposal of the concept of -regular obstructed categories is given. The
corresponding regularity conditions for mappings, morphisms and related
structures in categories are considered. An n-regular TQFT is introduced. It is
shown the connection of time reversibility with the regularity.Comment: 22 pages in Latex. To be published in J. Math. Phy
Using Focus Groups to Assess Educational Programming Needs in Forestry
Extension professionals are continually faced with the challenge of effectively communicating relevant information to an ever-evolving audience with diverse interests. Using focus group data, this article highlights specific educational programming needs of nonindustrial private forest landowners (NIPFs) in Mississippi. Findings indicate NIPFs are more likely to adopt new ideas if educational programming is tailored to their specific needs, consequently indicating the need to group the audience by their interests. Data also emphasize the importance of employing new technology as means for communicating more efficiently
Preliminary Parallaxes of 40 L and T Dwarfs from the U.S. Naval Observatory Infrared Astrometry Program
We present preliminary trigonometric parallaxes and proper motions for 22 L
dwarfs and 18 T dwarfs measured using the ASTROCAM infrared imager. Relative to
absolute parallax corrections are made by employing 2MASS and/or SDSS
photometry for reference frame stars. We combine USNO infrared and optical
parallaxes with the best available CIT system photometry to determine M_J, M_H,
and M_K values for 37 L dwarfs between spectral types L0 to L8 and 19 T dwarfs
between spectral types T0.5 and T8 and present selected absolute magnitude
versus spectral type and color diagrams, based on these results. Luminosities
and temperatures are estimated for these objects. Of special interest are the
distances of several objects which are at or near the L-T dwarf boundary so
that this important transition can be better understood. The previously
reported early-mid T dwarf luminosity excess is clearly confirmed and found to
be present at J, H, and K. The large number of objects that populate this
luminosity excess region indicates that it cannot be due entirely to selection
effects. The T dwarf sequence is extended to M_J~16.9 by 2MASS J041519-0935
which, at d = 5.74 pc, is found to be the least luminous [log(L/L_sun)=-5.58]
and coldest (T_eff~760 K) brown dwarf known. Combining results from this paper
with earlier USNO CCD results we find that, in contrast to the L dwarfs, there
are no examples of low velocity (V_tan < 20 km/s) T dwarfs. We briefly discuss
future directions for the USNO infrared astrometry program.Comment: 73 pages, 9 figures, 9 tables, accepted for publication in The
Astronomical Journa
Parallax and Luminosity Measurements of an L Subdwarf
We present the first parallax and luminosity measurements for an L subdwarf,
the sdL7 2MASS J05325346+8246465. Observations conducted over three years by
the USNO infrared astrometry program yield an astrometric distance of
26.7+/-1.2 pc and a proper motion of 2.6241+/-0.0018"/yr. Combined with
broadband spectral and photometric measurements, we determine a luminosity of
log(Lbol/Lsun) = -4.24+/-0.06 and Teff = 1730+/-90 K (the latter assuming an
age of 5-10 Gyr), comparable to mid-type L field dwarfs. Comparison of the
luminosity of 2MASS J05325346+8246465 to theoretical evolutionary models
indicates that its mass is just below the sustained hydrogen burning limit, and
is therefore a brown dwarf. Its kinematics indicate a ~110 Myr, retrograde
Galactic orbit which is both eccentric (3 <~ R <~ 8.5 kpc) and extends well
away from the plane (Delta_Z = +/-2 kpc), consistent with membership in the
inner halo population. The relatively bright J-band magnitude of 2MASS
J05325346+8246465 implies significantly reduced opacity in the 1.2 micron
region, consistent with inhibited condensate formation as previously proposed.
Its as yet unknown subsolar metallicity remains the primary limitation in
constraining its mass; determination of both parameters would provide a
powerful test of interior and evolutionary models for low-mass stars and brown
dwarfs.Comment: Accepted to ApJ 10 September 2007; 13 pages, 5 figures, 3 tables,
formatted in emulateapj styl
On the Munn-Silbey approach to polaron transport with off-diagonal coupling
Improved results using a method similar to the Munn-Silbey approach have been
obtained on the temperature dependence of transport properties of an extended
Holstein model incorporating simultaneous diagonal and off-diagonal
exciton-phonon coupling. The Hamiltonian is partially diagonalized by a
canonical transformation, and optimal transformation coefficients are
determined in a self-consistent manner. Calculated transport properties exhibit
substantial corrections on those obtained previously by Munn and Silbey for a
wide range of temperatures thanks to a numerically exact evaluation and an
added momentum-dependence of the transformation matrix. Results on the
diffusion coefficient in the moderate and weak coupling regime show distinct
band-like and hopping-like transport features as a function of temperature.Comment: 12 pages, 6 figures, accpeted in Journal of Physical Chemistry B:
Shaul Mukamel Festschrift (2011
Frenkel and charge transfer excitons in C60
We have studied the low energy electronic excitations of C60 using momentum
dependent electron energy-loss spectroscopy in transmission. The momentum
dependent intensity of the gap excitation allows the first direct experimental
determination of the energy of the 1Hg excitation and thus also of the total
width of the multiplet resulting from the gap transition. In addition, we could
elucidate the nature of the following excitations - as either Frenkel or charge
transfer excitons.Comment: RevTEX, 3 Figures, to appear in Phys. Rev.
Additional Ultracool White Dwarfs Found in the Sloan Digital Sky Survey
We identify seven new ultracool white dwarfs discovered in the Sloan Digital
Sky Survey (SDSS). The SDSS photometry, spectra, and proper motions are
presented, and additional BVRI data are given for these and other previously
discovered ultracool white dwarfs. The observed colors span a remarkably wide
range, qualitatively similar to colors predicted by models for very cool white
dwarfs. One of the new stars (SDSS J1251+44) exhibits strong collision-induced
absorption (CIA) in its spectra, while the spectra and colors of the other six
are consistent with mild CIA. Another of the new discoveries (SDSS J2239+00A)
is part of a binary system -- its companion is also a cool white dwarf, and
other data indicate that the companion exhibits an infrared flux deficiency,
making this the first binary system composed of two CIA white dwarfs. A third
discovery (SDSS J0310-00) has weak Balmer emission lines. The proper motions of
all seven stars are consistent with membership in the disk or thick disk.Comment: Accepted for Astrophysical Journal. 16 pages (includes 3 figures
Target Selection for the SDSS-IV APOGEE-2 Survey
APOGEE-2 is a high-resolution, near-infrared spectroscopic survey observing
roughly 300,000 stars across the entire sky. It is the successor to APOGEE and
is part of the Sloan Digital Sky Survey IV (SDSS-IV). APOGEE-2 is expanding
upon APOGEE's goals of addressing critical questions of stellar astrophysics,
stellar populations, and Galactic chemodynamical evolution using (1) an
enhanced set of target types and (2) a second spectrograph at Las Campanas
Observatory in Chile. APOGEE-2 is targeting red giant branch (RGB) and red
clump (RC) stars, RR Lyrae, low-mass dwarf stars, young stellar objects, and
numerous other Milky Way and Local Group sources across the entire sky from
both hemispheres. In this paper, we describe the APOGEE-2 observational design,
target selection catalogs and algorithms, and the targeting-related
documentation included in the SDSS data releases.Comment: 19 pages, 6 figures. Accepted to A
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