80,500 research outputs found
On the rotation of ONC stars in the Tsallis formalism context
The theoretical distribution function of the projected rotational velocity is
derived in the context of the Tsallis formalism. The distribution is used to
estimate the average for a stellar sample from the Orion Nebula Cloud
(ONC), producing an excellent result when compared with observational data. In
addition, the value of the parameter q obtained from the distribution of
observed rotations reinforces the idea that there is a relation between this
parameter and the age of the cluster.Comment: 6 pages, 2 figure
Physical constraints on interacting dark energy models
Physical limits on the equation-of-state (EoS) parameter of a dark energy
component non-minimally coupled with the dark matter field are examined in
light of the second law of thermodynamics and the positiveness of entropy. Such
constraints are combined with observational data sets of type Ia supernovae,
baryon acoustic oscillations and the angular acoustic scale of the cosmic
microwave background to impose restrictions on the behaviour of the dark
matter/dark energy interaction. Considering two EoS parameterisations of the
type , we derive a general expression for the evolution
of the dark energy density and show that the combination of thermodynamic
limits and observational data provide tight bounds on the parameter
space.Comment: 7 pages, 4 figures. Accepted for publication in European Physical
Journal
Calibration of longwavelength exotech model 20-C spectroradiometer
A brief description of the Exotech model 20-C field spectroradiometer which measures the spectral radiance of a target in the wavelength ranges 0.37 to 2.5 microns (short wavelength unit), 2.8 to 5.6 microns and 7.0 to 14 microns (long wavelength unit) is given. Wavelength calibration of long wavelength unit was done by knowing the strong, sharp and accurately known absorption bands of polystyrene, atmospheric carbon dioxide and methyl cyclohexane (liquid) in the infrared wavelength region. The spectral radiance calibration was done by recording spectral scans of the hot and the cold blackbodies and assuming that spectral radiance varies linearly with the signal
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