22,643 research outputs found
On the Electronic Spectroscopy of Closed Shell Cations Derived From Resonance Stabilized Radicals: Insights From Theory and Franck-Condon Analysis
Context. Recent attention has been directed on closed-shell aromatic cations as potential carriers of the diffuse interstellar bands. The spectra of mass-selected, matrix-isolated benzylium, and tropylium cations were recently reported. The visible spectrum of benzylium exhibits a large Franck-Condon (FC) envelope, inconsistent with diffuse interstellar band carriers.
Aims. We perform a computational analysis of the experimentally studied benzylium spectrum before extending the methods to a range of larger, closed-shell aromatic cations to determine the potential for this class of systems as diffuse interstellar band carriers.
Methods. Density functional theory (DFT), time-dependant ((TD)DFT), and multi-configurational self-consistent field second-order perturbation theory (MRPT2) methods in concert with multidimensional FC analysis is used to model the benzylium spectrum. These methods are extended to larger closed-shell aromatic hydrocarbon cations derived from resonance-stabilized radicals, which are predicted to show strong S0 → Sn transitions in the visible region. The ionization energies of a range of these systems are also calculated by DFT.
Results. The simulated benzylium spectrum was found to yield excellent agreement with the experimental spectrum showing an extended progression in a low frequency (510 cm-1) ring distortion mode. The FC progression was found to be significantly quenched in the larger species: 1-indanylium, 1-naphthylmethylium, and fluorenium. Excitation and ionization energies of the closed-shell cations were found to be consistent with diffuse interstellar band carriers, with the former lying in the visible range and the latter straddling the Lyman limit in the 13−14 eV range.
Conclusions. Large closed-shell polycyclic aromatic hydrocarbon cations remain viable candidate carriers of the diffuse interstellar bands
Reduced Dynamics from the Unitary Group to Some Flag Manifolds : Interacting Matrix Riccati Equations
In this paper we treat the time evolution of unitary elements in the N level
system and consider the reduced dynamics from the unitary group U(N) to flag
manifolds of the second type (in our terminology). Then we derive a set of
differential equations of matrix Riccati types interacting with one another and
present an important problem on a nonlinear superposition formula that the
Riccati equation satisfies.
Our result is a natural generalization of the paper {\bf Chaturvedi et al}
(arXiv : 0706.0964 [quant-ph]).Comment: Latex ; 13 pages ; no figur
Viscous dark fluid universe
We investigate the cosmological perturbation dynamics for a universe
consisting of pressureless baryonic matter and a viscous fluid, the latter
representing a unified model of the dark sector. In the homogeneous and
isotropic background the \textit{total} energy density of this mixture behaves
as a generalized Chaplygin gas. The perturbations of this energy density are
intrinsically non-adiabatic and source relative entropy perturbations. The
resulting baryonic matter power spectrum is shown to be compatible with the
2dFGRS and SDSS (DR7) data. A joint statistical analysis, using also
Hubble-function and supernovae Ia data, shows that, different from other
studies, there exists a maximum in the probability distribution for a negative
present value of the deceleration parameter. Moreover,
while previous descriptions on the basis of generalized Chaplygin gas models
were incompatible with the matter power spectrum data since they required a
much too large amount of pressureless matter, the unified model presented here
favors a matter content that is of the order of the baryonic matter abundance
suggested by big-bang nucleosynthesis.Comment: 19 pages, 6 figure
5-micron photometry of late-type dwarfs
We present narrowband-M photometry of nine low-mass dwarfs with spectral
types ranging from M2.5 to L0.5. Combining the (L'-M') colours derived from our
observations with data from the literature, we find colours consistent with a
Rayleigh-Jeans flux distribution for spectral types earlier than M5, but
enhanced F_3.8/F_4.7 flux ratios (negative (L'-M') colours) at later spectral
types. This probably reflects increased absorption at M' due to the CO
fundamental band. We compare our results against recent model predictions and
briefly discuss the implications.Comment: accepted for the Astronomical Journa
Measuring the Higgs Branching Fraction into two Photons at Future Linear \ee Colliders
We examine the prospects for measuring the \gaga branching fraction of a
Standard Model-like Higgs boson with a mass of 120 GeV at the future TESLA
linear \ee collider, assuming an integrated luminosity of 1 ab and
center-of-mass energies of 350 GeV and 500 GeV. The Higgs boson is produced in
association with a fermion pair via the Higgsstrahlung process \ee ,
with \qq or \nn, or the WW fusion reaction . A relative uncertainty on BF(\hgg) of~16% can be achieved in
unpolarized \ee collisions at =~500 GeV, while for =~350
GeV the expected precision is slightly poorer. With appropriate initial state
polarizations BF(\hgg)/BF(\hgg) can be improved to 10%. If this
measurement is combined with the expected error for the total Higgs width, a
precision of 10% on the \gaga Higgs boson partial width appears feasible.Comment: 14 pages, 5 figure
Radio signatures of solar energetic particles during the 23rd solar cycle
We present the association rates between solar energetic particles (SEPs) and
the radio emission signatures in the corona and IP space during the entire
solar cycle 23. We selected SEPs associated with X and M-class flares from the
visible solar hemisphere. All SEP events are also accompanied by coronal mass
ejections. Here, we focus on the correlation between the SEP events and the
appearance of radio type II, III and IV bursts on dynamic spectra. For this we
used the available radio data from ground-based stations and the Wind/WAVES
spacecraft. The associations are presented separately for SEP events
accompanying activity in the eastern and western solar hemisphere. We find the
highest association rate of SEP events to be with type III bursts, followed by
types II and IV. Whereas for types III and IV no longitudinal dependence is
noticed, these is a tendency for a higher SEP-association rate with type II
bursts in the eastern hemisphere. A comparison with reports from previous
studies is briefly discussed.Comment: http://adsabs.harvard.edu.ezproxy.obspm.fr/abs/2013CEAB...37..541
Coal-shale interface detection system
A coal-shale interface detection system for use with coal cutting equipment consists of a reciprocating hammer on which an accelerometer is mounted to measure the impact of the hammer as it penetrates the ceiling or floor surface of a mine. A pair of reflectometers simultaneously view the same surface. The outputs of the accelerometer and reflectometers are detected and jointly registered to determine when an interface between coal and shale is being cut through
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