954,623 research outputs found
The \chi Factor: Determining the Strength of Activity in Low Mass Dwarfs
We describe a new, distance-independent method for calculating the magnetic
activity strength in low mass dwarfs, L_{H\alpha}/L_{bol}. Using a
well-observed sample of nearby stars and cool standards spanning spectral type
M0.5 to L0, we compute ``\chi'', the ratio between the continuum flux near
H-alpha and the bolometric flux, f_{\lambda6560}/f_{bol}. This ratio may be
multiplied by the measured equivalent width of the H-alpha emission line to
yield L_{H\alpha}/L_{bol}. We provide \chi values for all objects in our
sample, as well as fits to \chi as a function of color and average values by
spectral type. This method was used by West et al.(2004) to examine trends in
magnetic activity strength in low mass stars.Comment: 11 pages, 5 figures. Accepted for publication in PAS
Square lattice Ising model susceptibility: Series expansion method and differential equation for
In a previous paper (J. Phys. A {\bf 37} (2004) 9651-9668) we have given the
Fuchsian linear differential equation satisfied by , the
``three-particle'' contribution to the susceptibility of the isotropic square
lattice Ising model. This paper gives the details of the calculations (with
some useful tricks and tools) allowing one to obtain long series in polynomial
time. The method is based on series expansion in the variables that appear in
the -dimensional integrals representing the -particle contribution to
the isotropic square lattice Ising model susceptibility . The
integration rules are straightforward due to remarkable formulas we derived for
these variables. We obtain without any numerical approximation as
a fully integrated series in the variable , where , with the conventional Ising model coupling constant. We also
give some perspectives and comments on these results.Comment: 28 pages, no figur
Determination of Wave Function Functionals: The Constrained-Search--Variational Method
In a recent paper [Phys. Rev. Lett. \textbf{93}, 130401 (2004)], we proposed
the idea of expanding the space of variations in variational calculations of
the energy by considering the approximate wave function to be a
functional of functions rather than a function. The
space of variations is expanded because a search over the functions can
in principle lead to the true wave function. As the space of such variations is
large, we proposed the constrained-search-- variational method whereby a
constrained search is first performed over all functions such that the
wave function functional satisfies a physical constraint such as
normalization or the Fermi-Coulomb hole sum rule, or leads to the known value
of an observable such as the diamagnetic susceptibility, nuclear magnetic
constant or Fermi contact term. A rigorous upper bound to the energy is then
obtained by application of the variational principle. A key attribute of the
method is that the wave function functional is accurate throughout space, in
contrast to the standard variational method for which the wave function is
accurate only in those regions of space contributing principally to the energy.
In this paper we generalize the equations of the method to the determination of
arbitrary Hermitian single-particle operators as applied to two-electron atomic
and ionic systems. The description is general and applicable to both ground and
excited states. A discussion on excited states in conjunction with the theorem
of Theophilou is provided.Comment: 26 pages, 4 figures, 5 table
Searches for Lepton Number Violation and resonances in the decays at the NA48/2 experiment
The NA48/2 experiment at CERN collected a large sample of charged kaon decays
into final states with multiple charged particles in 2003--2004. A new upper
limit on the rate of the lepton number violating decay obtained from this sample is reported:
at
90\% CL. Searches for two-body resonances in the decays
(including heavy neutral leptons~ and inflatons~) in the accessible
range of masses and lifetimes are also presented. In the absence of a signal,
upper limits are set on the products of branching ratios~ and
as functions of the resonance mass and lifetime. These limits are in the
range for resonance lifetimes below 100~ps.Comment: 8 pages. To be published in Rencontres de Moriond 2016 conference
proceeding
Recent Results from the SIMPLE Dark Matter Search
SIMPLE is an experimental search for evidence of spin-dependent dark matter,
based on superheated droplet detectors using CClF. We report
preliminary results of a 0.6 kgdy exposure of five one liter devices, each
containing 10 g active mass, in the 1500 mwe LSBB (Rustrel, France). In
combination with improvements in detector sensitivity, the results exclude a
WIMP--proton interaction above 5 pb at M = 50 GeV/c.Comment: 6 pages, 2 figures,contribution to IDM2004, Sept. 6-10, 2004,
Edinburgh, U
CHORIZOS: a CHi-square cOde for parameteRized modelIng and characteriZation of phOtometry and Spectrophotometry
We have developed a CHi-square cOde for parameteRized modelIng and
characteriZation of phOtometry and Spectrophotometry (CHORIZOS). CHORIZOS can
use up to two intrinsic free parameters (e.g. temperature and gravity for
stars; type and redshift for galaxies; or age and metallicity for stellar
clusters) and two extrinsic ones (amount and type of extinction). The code uses
chi-square minimization to find all models compatible with the observed data in
the model N-dimensional (N=1,2,3,4) parameter space. CHORIZOS can use either
correlated or uncorrelated colors as input and is especially designed to
identify possible parameter degeneracies and multiple solutions. The code is
written in IDL and is available to the astronomical community. Here we present
the techniques used, test the code, apply it to a few well-known astronomical
problems, and suggest possible applications. As a first scientific result from
CHORIZOS, we confirm from photometry the need for a revised
temperature-spectral type scale for OB stars previously derived from
spectroscopy.Comment: 32 pages, 13 figures. To appear in the September 2004 issue of PAS
Portuguese tourism demand:a dynamic panel data analysis
This article considers the determinants of Portuguese tourism demand for the period 2004-2013. The econometric methodology uses a panel unit root test and the dynamic panel data (GMM-system estimator). The different techniques of panel unit root (Levin, Lin and Chu; Im, Pesaran and Shin W-stat and augmented Dickey-Fuller - Fisher Chi-square) show that the variables used in this panel are stationary. The dynamic model proves that tourism demand is a dynamic process. The variables relative prices, income per capita, human capital and government spending encourage international tourism demand for Portugal.info:eu-repo/semantics/publishedVersio
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