482 research outputs found
Inelastic X-Ray Scattering Study of Exciton Properties in an Organic Molecular crystal
Excitons in a complex organic molecular crystal were studied by inelastic
x-ray scattering (IXS) for the first time. The dynamic dielectric response
function is measured over a large momentum transfer region, from which an
exciton dispersion of 130 meV is observed. Semiempirical quantum chemical
calculations reproduce well the momentum dependence of the measured dynamic
dielectric responses, and thus unambiguously indicate that the lowest Frenkel
exciton is confined within a fraction of the complex molecule. Our results
demonstrate that IXS is a powerful tool for studying excitons in complex
organic molecular systems. Besides the energy position, the IXS spectra provide
a stringent test on the validity of the theoretically calculated exciton wave
functions.Comment: 4 pages, 4 figure
Mass and angular momenta of Kerr anti-de Sitter spacetimes in Einstein-Gauss-Bonnet theory
We compute the mass and angular momenta of rotating anti-de Sitter spacetimes
in Einstein-Gauss-Bonnet theory of gravity using a superpotential derived from
standard Noether identities. The calculation relies on the fact that the
Einstein and Einstein-Gauss-Bonnet vacuum equations are the same when
linearized on maximally symmetric backgrounds and uses the recently discovered
D-dimensional Kerr-anti-de Sitter solutions to Einstein's equations
Origins Space Telescope: predictions for far-IR spectroscopic surveys
We illustrate the extraordinary potential of the (far-IR) Origins Survey
Spectrometer (OSS) on board the Origins Space Telescope (OST) to address a
variety of open issues on the co-evolution of galaxies and AGNs. We present
predictions for blind surveys, each of 1000 h, with different mapped areas (a
shallow survey covering an area of 10 deg and a deep survey of 1
deg) and two different concepts of the OST/OSS: with a 5.9 m telescope
(Concept 2, our reference configuration) and with a 9.1 m telescope (Concept 1,
previous configuration). In 1000 h, surveys with the reference concept will
detect from to lines from
- star-forming galaxies and from
to lines from - AGNs. The shallow survey will detect
substantially more sources than the deep one; the advantage of the latter in
pushing detections to lower luminosities/higher redshifts turns out to be quite
limited. The OST/OSS will reach, in the same observing time, line fluxes more
than one order of magnitude fainter than the SPICA/SMI and will cover a much
broader redshift range. In particular it will detect tens of thousands of
galaxies at , beyond the reach of that instrument. The polycyclic
aromatic hydrocarbons lines are potentially bright enough to allow the
detection of hundreds of thousands of star-forming galaxies up to ,
i.e. all the way through the re-ionization epoch. The proposed surveys will
allow us to explore the galaxy-AGN co-evolution up to with very
good statistics. OST Concept 1 does not offer significant advantages for the
scientific goals presented here.Comment: 24 pages, 20 figures, 2 tables, accepted for publication in PAS
Unlikely Friends of the Authoritarian and Atheist Ruler: Religious Groups and Collective Contention in Rural China
This article examines the roles played by rural religious groups in China's local contentious politics. More specifically, it aims to explore whether religious groups stimulate or reduce collective contention when the ruler is both authoritarian and atheist. Drawing on national survey data and comparative case studies, this article finds that collective contention is less likely to occur in villages with religious groups that simultaneously overlap with secular social organizations and local authorities, and are hence more likely to serve as credible communication channels between local states and discontented citizens. This finding highlights two important issues that are often side-lined, if not outright neglected, in the existing literature. First, the relationship between religious groups and collective contention is diverse rather than uniform. Second, this relationship is shaped not only by religious groups but also by other important players in the local political arena
Charged Rotating Kaluza-Klein Black Holes Generated by G2(2) Transformation
Applying the G_{2(2)} generating technique for minimal D=5 supergravity to
the Rasheed black hole solution, we present a new rotating charged Kaluza-Klein
black hole solution to the five-dimensional Einstein-Maxwell-Chern-Simons
equations. At infinity, our solution behaves as a four-dimensional flat
spacetime with a compact extra dimension and hence describes a Kaluza-Klein
black hole. In particlar, the extreme solution is non-supersymmetric, which is
contrast to a static case. Our solution has the limits to the asymptotically
flat charged rotating black hole solution and a new charged rotating black
string solution.Comment: 24 page
On the Renormalizability of Horava-Lifshitz-type Gravities
In this note, we discuss the renormalizability of Horava-Lifshitz-type
gravity theories. Using the fact that Horava-Lifshitz gravity is very closely
related to the stochastic quantization of topologically massive gravity, we
show that the renormalizability of HL gravity only depends on the
renormalizability of topologically massive gravity. This is a consequence of
the BRST and time-reversal symmetries pertinent to theories satisfying the
detailed balance condition.Comment: 13 pages, references added, typos fixe
Geometric and thermodynamic properties in Gauss-Bonnet gravity
In this paper, the generalized second law (GSL) of thermodynamics and entropy
is revisited in the context of cosmological models in Gauss-Bonnet gravity with
the boundary of the universe is assumed to be enclosed by the dynamical
apparent horizon. The model is best fitted with the observational data for
distance modulus. The best fitted geometric and thermodynamic parameters such
as equation of state parameter, deceleration parameter and entropy are derived.
To link between thermodynamic and geometric parameters, the "entropy rate of
change multiplied by the temperature" as a model independent thermodynamic
state parameter is also derived. The results show that the model is in good
agreement with the observational analysis.Comment: 13 pages, 13 figures, to be published in Astrophysics and Space Sc
Constraints on kinematic models from the latest observational data
Kinematical models are constrained by the latest observational data from
geometry-distance measurements, which include 557 type Ia supernovae (SNIa)
Union2 data and 15 observational Hubble data. Considering two parameterized
deceleration parameter, the values of current deceleration parameter ,
jerk parameter and transition redshift , are obtained.
Furthermore, we show the departures for two parameterized kinematical models
from CDM model according to the evolutions of jerk parameter .
Also, it is shown that the constraint on jerk parameter is weak by the
current geometrical observed data.Comment: 8 pages, 2 figure
Electronic and optical properties of families of polycyclic aromatic hydrocarbons: a systematic (time-dependent) density functional theory study
Homologous classes of Polycyclic Aromatic Hydrocarbons (PAHs) in their
crystalline state are among the most promising materials for organic
opto-electronics. Following previous works on oligoacenes we present a
systematic comparative study of the electronic, optical, and transport
properties of oligoacenes, phenacenes, circumacenes, and oligorylenes. Using
density functional theory (DFT) and time-dependent DFT we computed: (i)
electron affinities and first ionization energies; (ii) quasiparticle
correction to the highest occupied molecular orbital (HOMO)-lowest unoccupied
molecular orbital (LUMO) gap; (iii) molecular reorganization energies; (iv)
electronic absorption spectra of neutral and charged systems. The
excitonic effects are estimated by comparing the optical gap and the
quasiparticle corrected HOMO-LUMO energy gap. For each molecular property
computed, general trends as a function of molecular size and charge state are
discussed. Overall, we find that circumacenes have the best transport
properties, displaying a steeper decrease of the molecular reorganization
energy at increasing sizes, while oligorylenes are much more efficient in
absorbing low-energy photons in comparison to the other classes.Comment: 26 pages, 9 figures, 4 tables, accepted for pubblication in Chemical
Physics (14/04/2011
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