58,115 research outputs found
Subtracting the photon noise bias from single-mode optical interferometer visibilities
I present in this paper a method to subtract the bias due to source photon
noise from visibilities measured with a single-mode optical interferometer.
Properties of the processed noise are demonstrated and examples of subtraction
on real data are presented.Comment: To appear in Astronomy & Astrophysic
Identification of the dimethylamine-trimethylamine complex in the gas phase
We have identified the dimethylamine-trimethylamine complex (DMA-TMA) at room temperature in the gas phase. The Fourier transform infrared (FTIR) spectrum of DMA-TMA in the NH-stretching fundamental region was obtained by spectral subtraction of spectra of each monomer. Explicitly correlated coupled cluster calculations were used to determine the minimum energy structure and interaction energy of DMA-TMA. Frequencies and intensities of NH-stretching transitions were also calculated at this level of theory with an anharmonic oscillator local mode model. The fundamental NH-stretching intensity in DMA-TMA is calculated to be approximately 700 times larger than that of the DMA monomer. The measured and calculated intensity is used to determine a room temperature equilibrium constant of DMA-TMA of 1.7 × 10⁻³ atm⁻¹ at 298 K
The calibration of interferometric visibilities obtained with single-mode optical interferometers. Computation of error bars and correlations
I present in this paper a method to calibrate data obtained from optical and
infrared interferometers. I show that correlated noises and errors need to be
taken into account for a very good estimate of individual error bars but also
when model fitting the data to derive meaningful model parameters whose
accuracies are not overestimated. It is also shown that under conditions of
high correlated noise, faint structures of the source can be detected. This
point is important to define strategies of calibration for difficult programs
such as exoplanet detection. The limits of validity of the assumptions on the
noise statistics are discussed
On the Approximability and Hardness of the Minimum Connected Dominating Set with Routing Cost Constraint
In the problem of minimum connected dominating set with routing cost
constraint, we are given a graph , and the goal is to find the
smallest connected dominating set of such that, for any two
non-adjacent vertices and in , the number of internal nodes on the
shortest path between and in the subgraph of induced by is at most times that in . For general graphs, the only
known previous approximability result is an -approximation algorithm
() for by Ding et al. For any constant , we
give an -approximation
algorithm. When , we give an -approximation
algorithm. Finally, we prove that, when , unless , for any constant , the problem admits no
polynomial-time -approximation algorithm, improving
upon the bound by Du et al. (albeit under a stronger hardness
assumption)
Neutral triplet Collective Mode as a new decay channel in Graphite
In an earlier work we predicted the existence of a neutral triplet collective
mode in undoped graphene and graphite [Phys. Rev. Lett. {\bf 89} (2002) 16402].
In this work we study a phenomenological Hamiltonian describing the interaction
of tight-binding electrons on honeycomb lattice with such a dispersive neutral
triplet boson. Our Hamiltonian is a generalization of the Holstein polaron
problem to the case of triplet bosons with non-trivial dispersion all over the
Brillouin zone. This collective mode constitutes an important excitation branch
which can contribute to the decay rate of the electronic excitations. The
presence of such collective mode, modifies the spectral properties of electrons
in graphite and undoped graphene. In particular such collective mode, as will
be shown in this paper, can account for some part of the missing decay rate in
a time-domain measurement done on graphite
Implications of chiral symmetry on -wave pionic resonances and the scalar charmed mesons
The chiral symmetry of QCD requires energy-dependent pionic strong
interactions at low energies. This constraint, however, is not fulfilled by the
usual Breit--Wigner parameterization of pionic resonances, leading to masses
larger than the real ones. We derive relations between nonleptonic three-body
decays of the -meson into a -meson and a pair of light pseudoscalar
mesons based on SU(3) chiral symmetry. Employing effective field theory
methods, we demonstrate that taking into account the final-state interactions,
the experimental data of the decays , , , and
can all be described by the nonperturbative
- scattering amplitudes previously obtained from a
combination of chiral effective field theory and lattice QCD calculations. The
results provide a strong support of the scenario that the broad scalar charmed
meson should be replaced by two states, the lower one of which
has a mass of around 2.1 GeV, much smaller than that extracted from
experimental data using a Breit--Wigner parameterization.Comment: 26 pages, 9 figuere
One-loop renormalization of the chiral Lagrangian for spinless matter fields in the SU(N) fundamental representation
We perform the leading one-loop renormalization of the chiral Lagrangian for
spinless matter fields living in the fundamental representation of SU(N). The
Lagrangian can also be applied to any theory with a spontaneous symmetry
breaking of to and spinless matter fields in
the fundamental representation. For QCD, the matter fields can be kaons or
pseudoscalar heavy mesons. Using the background field method and heat kernel
expansion techniques, the divergences of the one-loop effective generating
functional for correlation functions of single matter fields are calculated up
to . They are absorbed by counterterms not only from the
third order but also from the second order chiral Lagrangian.Comment: 13 page
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