4,082 research outputs found
A digitalized solar ultraviolet spectrum
Digitalized solar ultraviolet spectrum obtained in rocket experiments for use in analysis of upper atmosphere experiment
On Type IIB Vacua With Varying Coupling Constant
We describe type IIB compactifications with varying coupling constant in
d=6,7,8,9 dimensions, where part of the ten-dimensional SL(2,Z) symmetry is
broken by a background with Gamma_0(n) or Gamma(n) monodromy for n=2,3,4. This
extends the known class of F-theory vacua to theories which are dual to
heterotic compactifications with reduced rank. On compactifying on a further
torus, we obtain a description of the heterotic moduli space of G bundles over
elliptically fibered manifolds without vector structure in terms of complex
geometries.Comment: 32 pages, 5 eps figure
Mapping 6D N = 1 supergravities to F-theory
We develop a systematic framework for realizing general anomaly-free chiral
6D supergravity theories in F-theory. We focus on 6D (1, 0) models with one
tensor multiplet whose gauge group is a product of simple factors (modulo a
finite abelian group) with matter in arbitrary representations. Such theories
can be decomposed into blocks associated with the simple factors in the gauge
group; each block depends only on the group factor and the matter charged under
it. All 6D chiral supergravity models can be constructed by gluing such blocks
together in accordance with constraints from anomalies. Associating a geometric
structure to each block gives a dictionary for translating a supergravity model
into a set of topological data for an F-theory construction. We construct the
dictionary of F-theory divisors explicitly for some simple gauge group factors
and associated matter representations. Using these building blocks we analyze a
variety of models. We identify some 6D supergravity models which do not map to
integral F-theory divisors, possibly indicating quantum inconsistency of these
6D theories.Comment: 37 pages, no figures; v2: references added, minor typos corrected;
v3: minor corrections to DOF counting in section
Recovering the effective cosmological constant in extended gravity theories
In the framework of extended gravity theories, we discuss the meaning of a
time dependent "cosmological constant" and give a set of conditions to recover
asymptotic de Sitter behaviour for a class of cosmological models independently
of initial data. To this purpose we introduce a time-dependent (effective)
quantity which asymptotically becomes the true cosmological constant. We will
deal with scalar-tensor, fourth and higher than fourth-order theories.Comment: 24 pages, Latex, submitted to Gen.Rel.and Gra
Active Galactic Nucleus Pairs from the Sloan Digital Sky Survey. I. The Frequency on ~ 5-100 kpc Scales
Galaxy-galaxy mergers and close interactions have long been regarded as a
viable mechanism for channeling gas toward the central supermassive black holes
(SMBHs) of galaxies which are triggered as active galactic nuclei (AGNs). AGN
pairs, in which the central SMBHs of a galaxy merger are both active, are
expected to be common from such events. We conduct a systematic study of 1286
AGN pairs at z ~ 0.1 with line-of-sight velocity offsets dv < 600 km/s and
projected separations r_p < 100 kpc, selected from the Seventh Data Release of
the Sloan Digital Sky Survey (SDSS). This AGN pair sample was drawn from
138,070 AGNs optically identified based on diagnostic emission line ratios
and/or line widths. The fraction of AGN pairs with 5 kpc ~< r_p < 100 kpc among
all spectroscopically selected AGNs at 0.02 < z < 0.16 is 3.6% after correcting
for SDSS spectroscopic incompleteness; ~ 30% of these pairs show morphological
tidal features in their SDSS images, and the fraction becomes >~ 80% for pairs
with the brightest nuclei. Our sample increases the number of known AGN pairs
on these scales by more than an order of magnitude. We present their AGN and
host-galaxy star formation properties in a companion paper.Comment: minor revisions; to appear in Ap
The Megamaser Cosmology Project. III. Accurate Masses of Seven Supermassive Black Holes in Active Galaxies with Circumnuclear Megamaser Disks
Observations of HO masers from circumnuclear disks in active galaxies for
the Megamaser Cosmology Project allow accurate measurement of the mass of
supermassive black holes (BH) in these galaxies. We present the Very Long
Baseline Interferometry (VLBI) images and kinematics of water maser emission in
six active galaxies: NGC~1194, NGC~2273, NGC~2960 (Mrk~1419), NGC~4388,
NGC~6264 and NGC~6323. We use the Keplerian rotation curves of these six
megamaser galaxies, plus a seventh previously published, to determine accurate
enclosed masses within the central pc of these galaxies, smaller than
the radius of the sphere of influence of the central mass in all cases. We also
set lower limits to the central mass densities of between 0.12 and 60 ~pc. For six of the seven disks, the high central
densities rule out clusters of stars or stellar remnants as the central
objects, and this result further supports our assumption that the enclosed mass
can be attributed predominantly to a supermassive black hole. The seven BHs
have masses ranging between 0.76 and 6.510. The BH mass
errors are \%, dominated by the uncertainty of the Hubble constant.
We compare the megamaser BH mass determination with other BH mass measurement
techniques. The BH mass based on virial estimation in four galaxies is
consistent with the megamaser BH mass given the latest empirical value of
, but the virial mass uncertainty is much greater. MCP
observations continue and we expect to obtain more maser BH masses in the
future.Comment: 18 pages, 4 figures. This paper has been submitted to ApJ. An updated
version of this paper will be posted when it gets accepte
Resonant particle production with non-minimally coupled scalar fields in preheating after inflation
We investigate a resonant particle production of a scalar field
coupled non-minimally to a spacetime curvature () as well as
to an inflaton field (). In the case of , effect assists -resonance in certain parameter regimes.
However, for , -resonance is not enhanced by
effect because of suppression effect as well as a back reaction effect.
If , the maximal fluctuation of produced -particle is
GeV for , which is larger than the minimally coupled case with .Comment: 33pages, 12figures. to appear in Physical Review
Opening up the Pandora's box of sustainability league tables of universities: a Kafkaesque perspective
The aim of this paper is to explore the institutional impact of sustainability league tables on current university agendas. It focuses on a narrative critique of one such league table, the UK's ‘Green League Table', compiled and reported by the student campaigning NGO, ‘People & Planet’ annually between 2007 and 2013. Through a Kafkaesque perspective, this paper offers the proposition that such league tables could be acting as an institutional hegemonic mechanism for social legitimacy, through the desire by universities to show that environmental issues are effectively under control. Espoused eco-narratives of the ‘carbon targets imperative’ and ‘engagement' can serve as a form of deception, by merely embracing the narrative as a rhetorical device. Moreover, they can serve the exclusive, particularistic self-interests of a growing legion of ‘carbon managers’, ‘sustainability managers’ and ‘environmental managers' in satisfying the neo-liberal institutional drive from their vice chancellors
Multisensory information facilitates reaction speed by enlarging activity difference between superior colliculus hemispheres in rats
Animals can make faster behavioral responses to multisensory stimuli than to unisensory stimuli. The superior colliculus (SC), which receives multiple inputs from different sensory modalities, is considered to be involved in the initiation of motor responses. However, the mechanism by which multisensory information facilitates motor responses is not yet understood. Here, we demonstrate that multisensory information modulates competition among SC neurons to elicit faster responses. We conducted multiunit recordings from the SC of rats performing a two-alternative spatial discrimination task using auditory and/or visual stimuli. We found that a large population of SC neurons showed direction-selective activity before the onset of movement in response to the stimuli irrespective of stimulation modality. Trial-by-trial correlation analysis showed that the premovement activity of many SC neurons increased with faster reaction speed for the contraversive movement, whereas the premovement activity of another population of neurons decreased with faster reaction speed for the ipsiversive movement. When visual and auditory stimuli were presented simultaneously, the premovement activity of a population of neurons for the contraversive movement was enhanced, whereas the premovement activity of another population of neurons for the ipsiversive movement was depressed. Unilateral inactivation of SC using muscimol prolonged reaction times of contraversive movements, but it shortened those of ipsiversive movements. These findings suggest that the difference in activity between the SC hemispheres regulates the reaction speed of motor responses, and multisensory information enlarges the activity difference resulting in faster responses
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