17,954 research outputs found
The Trouble with Hubble Types in the Virgo Cluster
Quantitative measures of central light concentration and star formation
activity are derived from R and Halpha surface photometry of 84 bright S0-Scd
Virgo Cluster and isolated spiral galaxies. For isolated spirals, there is a
good correlation between these two parameters and assigned Hubble types. In the
Virgo Cluster, the correlation between central light concentration and star
formation activity is significantly weaker. Virgo Cluster spirals have
systematically reduced global star formation with respect to isolated spirals,
with severe reduction in the outer disk, but normal or enhanced activity in the
inner disk. Assigned Hubble types are thus inadequate to describe the range in
morphologies of bright Virgo Cluster spirals. In particular, spirals with
reduced global star formation activity are often assigned misleading early-type
classifications, irrespective of their central light concentrations. 45+-25% of
the galaxies classified as Sa in the Virgo Cluster sample have central light
concentrations more characteristic of isolated Sb-Sc galaxies. The misleading
classification of low concentration galaxies with low star formation rates as
early-type spirals may account for part of the excess of `early-type' spiral
galaxies in clusters. Thus the morphology-density relationship is not all due
to a systematic increase in the bulge-to-disk ratio with environmental density.Comment: Accepted for publication in ApJ Letters. Latex aaspp4.sty, 9 pages, 2
Postscript (embedded) figures. Also available at
http://www.astro.yale.edu/koopmann/preprint.htm
Against 'green development fantasies': resource degradation and the lack of community resistance in the middle Mahakam wetlands, East Kalimantan, Indonesia
Towards a fully self-consistent spectral function of the nucleon in nuclear matter
We present a calculation of nuclear matter which goes beyond the usual
quasi-particle approximation in that it includes part of the off-shell
dependence of the self-energy in the self-consistent solution of the
single-particle spectrum. The spectral function is separated in contributions
for energies above and below the chemical potential. For holes we approximate
the spectral function for energies below the chemical potential by a
-function at the quasi-particle peak and retain the standard form for
energies above the chemical potential. For particles a similar procedure is
followed. The approximated spectral function is consistently used at all levels
of the calculation. Results for a model calculation are presented, the main
conclusion is that although several observables are affected by the inclusion
of the continuum contributions the physical consistency of the model does not
improve with the improved self-consistency of the solution method. This in
contrast to expectations based on the crucial role of self-consistency in the
proofs of conservation laws.Comment: 26 pages Revtex with 4 figures, submitted to Phys. Rev.
Charge transport in nanoscale vertical organic semiconductor pillar devices
We report charge transport measurements in nanoscale vertical pillar
structures incorporating ultrathin layers of the organic semiconductor
poly(3-hexylthiophene)(P3HT). P3HT layers with thickness down to 5 nm are
gently top-contacted using wedging transfer, yielding highly reproducible,
robust nanoscale junctions carrying high current densities (up to
A/m). Current-voltage data modeling demonstrates excellent hole injection.
This work opens up the pathway towards nanoscale, ultrashort-channel organic
transistors for high-frequency and high-current-density operation.Comment: 30 pages, 8 figures, 1 tabl
X-Ray and Infrared Enhancement of Anomalous X-ray Pulsar 1E 2259+58
The long term (~1.5 years) X-ray enhancement and the accompanying infrared
enhancement light curves of the anomalous X-ray pulsar 1E 2259+58 following the
major bursting epoch can be accounted for by the relaxation of a fall back disk
that has been pushed back by a gamma-ray flare. The required burst energy
estimated from the results of our model fits is low enough for such a burst to
have remained below the detection limits. We find that an irradiated disk model
with a low irradiation efficiency is in good agreement with both X-ray and
infrared data. Non-irradiated disk models also give a good fit to the X-ray
light curve, but are not consistent with the infrared data for the first week
of the enhancement.Comment: 17 pages, 3 figures, accepted for publication in Ap
Can learning by qualitative modelling be deployed as an effective method for learning Subject-Specific Content?
Деградация человеческого потенциала как фактор латентной составляющей деятельности высшей школы Украины
Рассмотрены проблемы тенизации и коррупционности функционирования украин-ской высшей школы на фоне вектора развития показателей потенциала населения страны.Розглянуті проблеми тінізації і коррупційності функціонування української вищої школи на тлі вектору розвитку показників потенціалу населення країни
Angle-resolved and core-level photoemission study of interfacing the topological insulator Bi1.5Sb0.5Te1.7Se1.3 with Ag, Nb and Fe
Interfaces between a bulk-insulating topological insulator (TI) and metallic
adatoms have been studied using high-resolution, angle-resolved and core-level
photoemission. Fe, Nb and Ag were evaporated onto Bi1.5Sb0.5Te1.7Se1.3 (BSTS)
surfaces both at room temperature and 38K. The coverage- and
temperature-dependence of the adsorption and interfacial formation process have
been investigated, highlighting the effects of the overlayer growth on the
occupied electronic structure of the TI. For all coverages at room temperature
and for those equivalent to less than 0.1 monolayer at low temperature all
three metals lead to a downward shift of the TI's bands with respect to the
Fermi level. At room temperature Ag appears to intercalate efficiently into the
van der Waals gap of BSTS, accompanied by low-level substitution of the Te/Se
atoms of the termination layer of the crystal. This Te/Se substitution with
silver increases significantly for low temperature adsorption, and can even
dominate the electrostatic environment of the Bi/Sb atoms in the BSTS
near-surface region. On the other hand, Fe and Nb evaporants remain close to
the termination layer of the crystal. On room temperature deposition, they
initially substitute isoelectronically for Bi as a function of coverage, before
substituting for Te/Se atoms. For low temperature deposition, Fe and Nb are too
immobile for substitution processes and show a behaviour consistent with
clustering on the surface. For both Ag and Fe/Nb, these differing adsorption
pathways leads to the qualitatively similar and remarkable behavior for low
temperature deposition that the chemical potential first moves upward (n-type
dopant behavior) and then downward (p-type behavior) on increasing coverage.Comment: 10 pages, 4 figures. In our Phys. Rev. B manuscript an error was made
in formulating the last sentence of the abstract that, unfortunately, was
missed in the page proofs. Version 2 on arxiv has the correct formulation of
this sentenc
DDO 88: A Galaxy-Sized Hole in the Interstellar Medium
We present an HI and optical study of the gas-rich dwarf irregular galaxy DDO
88. Although DDO 88's global optical and HI parameters are normal for its
morphological type, it hosts a large (3 kpc diameter) and unusually complete
ring of enhanced HI emission. The gas ring is located at approximately
one-third of the total HI radius and one-half the optically-defined Holmberg
radius, and contains 30% of the total HI of the galaxy. The ring surrounds a
central depression in the HI distribution, so it may be a shell formed by a
starburst episode. However, the UBV colors in the HI hole are not bluer than
the rest of the galaxy as would be expected if an unusual star-forming event
had taken place there recently, but there is an old (~1-3 Gyr), red cluster
near the center of the hole that is massive enough to have produced the hole in
the HI. An age estimate for the ring, however, is uncertain because it is not
observed to be expanding. An expansion model produces a lower estimate of 0.5
Gyr, but the presence of faint star formation regions associated with the ring
indicate a much younger age. We also estimate that the ring could have
dispersed by now if it is older than 0.5 Gyr. This implies that the ring is
younger than 0.5 Gyr. A younger age would indicate that the red cluster did not
produce the hole and ring. If this ring and the depression in the gas which it
surrounds were not formed by stellar winds and supernovae, this would indicate
that some other, currently unidentified, mechanism is operating.Comment: 44 pages; 16 figures. To appear in AJ, January 2005. Available from
ftp.lowell.edu, cd pub/dah/papers/d88 and http://www.fiu.edu/~simpsonc/d8
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