10,382 research outputs found
Photometric and spectroscopic variability of 53 Per
A new investigation of the variability of the SPB-type star 53 Per is
presented. The analysis of the BRITE photometry allowed us to determine eight
independent frequencies and the combination one. Five of these frequencies and
the combination one were not known before. In addition, we gathered more than
1800 new moderate and high-resolution spectra of 53 Per spread over
approximately six months. Their frequency analysis revealed four independent
frequencies and the combination one, all consistent with the BRITE results.Comment: 2 pages, accepted for publication in the Proceedings of the PAS
(Proc. of the 2nd BRITE Science conference, Innsbruck
Spectroscopy of Collective Excitations in Interacting Low-Dimensional Many-Body Systems Using Quench Dynamics
We study the problem of rapid change of the interaction parameter (quench) in
many-body low-dimensional system. It is shown that, measuring correlation
functions after the quench the information about a spectrum of collective
excitations in a system can be obtained. This observation is supported by
analysis of several integrable models and we argue that it is valid for
non-integrable models as well. Our conclusions are supplemented by performing
exact numerical simulations on finite systems. We propose that measuring power
spectrum in dynamically split 1D Bose-Einsten condensate into two coupled
condensates can be used as experimental test of our predictions.Comment: 4 pages, 2 figures; replaced with revised versio
Improvements to the Method of Dispersion Relations for B Nonleptonic Decays
We bring some clarifications and improvements to the method of dispersion
relations in the external masses variables, that we proposed recently for
investigating the final state interactions in the B nonleptonic decays. We
first present arguments for the existence of an additional term in the
dispersion representation, which arises from an equal-time commutator in the
LSZ formalism and can be approximated by the conventional factorized amplitude.
The reality properties of the spectral function and the Goldberger-Treiman
procedure to perform the hadronic unitarity sum are analyzed in more detail. We
also improve the treatment of the strong interaction part by including the
contributions of both t and u-channel trajectories in the Regge amplitudes.
Applications to the and decays are
presented.Comment: 16 pages, 4 new figures. modifications of the dispersion
representatio
Spin dynamics of a one-dimensional spin-1/2 fully anisotropic Ising-like antiferromagnet in a transverse magnetic field
We consider the one-dimensional Ising-like fully anisotropic S=1/2 Heisenberg
antiferromagnetic Hamiltonian and study the dynamics of domain wall excitations
in the presence of transverse magnetic field . We obtain dynamical spin
correlation functions along the magnetic field and
perpendicular to it . It is shown that the line shapes of
and are purely symmetric at the
zone-boundary. It is observed in for that the
spectral weight moves toward low energy side with the increase of . This
model is applicable to study the spin dynamics of CsCoCl in the presence of
weak interchain interactions.Comment: 19 pages, LaTeX, 12 eps figure
Neutron Irradiation of Mg11B2 : From the Enhancement to the Suppression of Superconducting Properties
In this letter we present the effect of neutron irradiation up to fluences of
3.9 1019 n/cm2 on the superconducting properties of MgB2. In order to obtain a
disorder structure homogeneously distributed, the experiment was carried out on
bulk samples prepared with the 11B isotope. Up to fluences of 1018 n/cm2 the
critical temperature is slightly diminished (36 K) and the superconducting
properties are significantly improved; the upper critical field is increased
from 13.5 T to 20.3 T at 12 K and the irreversibility field is doubled at 5 K.
For larger neutron fluences the critical temperature is suppressed down to 12 K
and the superconducting properties come out strongly degraded.Comment: 13 pages, 4 figures. Submitted to Appl.Phys.Let
Serendipitously Detected Galaxies in the Hubble Deep Field
We present a catalog of 74 galaxies detected serendipitously during a
campaign of spectroscopic observations of the Hubble Deep Field North (HDF) and
its environs. Among the identified objects are five candidate Ly-alpha emitters
at z > 5, a galaxy cluster at z = 0.85, and a Chandra source with a heretofore
undetermined redshift of z = 2.011. We report redshifts for 25 galaxies in the
central HDF, 13 of which had no prior published spectroscopic redshift. Of the
remaining 49 galaxies, 30 are located in the single-orbit HDF Flanking Fields.
We discuss the redshift distribution of the serendipitous sample, which
contains galaxies in the range 0.10 < z < 5.77 with a median redshift of z =
0.85, and we present strong evidence for redshift clustering. By comparing our
spectroscopic redshifts to optical/IR photometric studies of the HDF, we find
that photometric redshifts are in most cases capable of producing reasonable
predictions of galaxy redshifts. Finally, we estimate the line-of-sight
velocity dispersion and the corresponding mass and expected X-ray luminosity of
the galaxy cluster, we present strong arguments for interpreting the Chandra
source as an obscured AGN, and we discuss in detail the spectrum of one of the
candidate z > 5 Ly-alpha emitters.Comment: 18 pages, 9 figures, accepted for publication in the Astronomical
Journa
Algorithm for Adapting Cases Represented in a Tractable Description Logic
Case-based reasoning (CBR) based on description logics (DLs) has gained a lot
of attention lately. Adaptation is a basic task in the CBR inference that can
be modeled as the knowledge base revision problem and solved in propositional
logic. However, in DLs, it is still a challenge problem since existing revision
operators only work well for strictly restricted DLs of the \emph{DL-Lite}
family, and it is difficult to design a revision algorithm which is
syntax-independent and fine-grained. In this paper, we present a new method for
adaptation based on the DL . Following the idea of
adaptation as revision, we firstly extend the logical basis for describing
cases from propositional logic to the DL , and present a
formalism for adaptation based on . Then we present an
adaptation algorithm for this formalism and demonstrate that our algorithm is
syntax-independent and fine-grained. Our work provides a logical basis for
adaptation in CBR systems where cases and domain knowledge are described by the
tractable DL .Comment: 21 pages. ICCBR 201
Self-Trapped Exciton Defects in a Charge Density Wave: Electronic Excitations of BaBiO3
In the previous paper, it was shown that holes doped into BaBiO3 self-trap as
small polarons and bipolarons. These point defects are energetically favorable
partly because they undo locally the strain in the charge-density-wave (Peierls
insulator) ground state. In this paper the neutral excitations of the same
model are discussed. The lowest electronic excitation is predicted to be a
self-trapped exciton, consisting of an electron and a hole located on adjacent
Bi atoms. This excitation has been seen experimentally (but not identified as
such) via the Urbach tail in optical absorption, and the multi-phonon spectrum
of the ``breathing mode'' seen in Raman scattering. These two phenomena occur
because of the Franck-Condon effect associated with oxygen displacement in the
excited state.Comment: 5 pages with 7 embedded figures. See also cond-mat/0108089 on
polarons and bipolarons in BaBiO3 contains background informatio
Influence of cardiac motion on porcine AV node for the non-invasive treatment of atrial fibrillation with a scanned carbon ion beam
Spectator detection for the measurement of proton neutron interactions at ANKE
A telescope of three silicon detectors has been installed close to the
internal target position of the ANKE spectrometer, which is situated inside the
ultra-high vacuum of the COSY-Juelich light-ion storage ring. The detection and
identification of slow protons and deuterons emerging from a deuterium
cluster-jet target thus becomes feasible. A good measurement of the energy and
angle of such a spectator proton (p_sp) allows one to identify a reaction as
having taken place on the neutron in the target and then to determine the
kinematical variables of the ion-neutron system on an event-by-event basis over
a range of c.m. energies.
The system has been successfully tested under laboratory conditions. By
measuring the spectator proton in the p d to p_sp d pi^0 reaction in
coincidence with a fast deuteron in the ANKE Forward Detector, values of the p
n to d pi^0 total cross-section have been deduced. Further applications of the
telescope include the determination of the luminosity and beam polarisation
which are required for several experiments.Comment: 16 pages, 9 figure
- …