4,760 research outputs found
Non-extensive entropy from incomplete knowledge of Shannon entropy?
In this paper we give an interpretation of Tsallis' nonextensive statistical
mechanics based upon the information-theoretic point of view of Luzzi et al.
[cond-mat/0306217; cond-mat/0306247; cond-mat/0307325], suggesting Tsallis'
entropy to be not a fundamental concept but rather a derived one, stemming from
an incomplete knowledge of the system, not taking properly into account its
interaction with the environment. This interpretation seems to avoid some
problems occurring with the original interpretation of Tsallis statistics.Comment: v.4. 11 pages. Title changed. Content substantially changed: added
discussion of several points raised by various referees and readers; Also
reference made to work by Luzzi, Vasconcellos, Galvao Ramos. Physica Scripta,
to appea
Constraining the evolution of the CMB temperature with SZ measurements from Planck data
The CMB temperature-redshift relation, T_CMB(z)=T_0(1+z), is a key prediction
of the standard cosmology, but is violated in many non standard models.
Constraining possible deviations to this law is an effective way to test the
LambdaCDM paradigm and to search for hints of new physics. We have determined
T_CMB(z), with a precision up to 3%, for a subsample (104 clusters) of the
Planck SZ cluster catalog, at redshift in the range 0.01-- 0.94, using
measurements of the spectrum of the Sunyaev Zel'dovich effect obtained from
Planck temperature maps at frequencies from 70 to 353 GHz. The method adopted
to provide individual determinations of T_CMB(z) at cluster redshift relies on
the use of SZ intensity change, Delta I_SZ(nu), at different frequencies, and
on a Monte-Carlo Markov Chain approach. By applying this method to the sample
of 104 clusters, we limit possible deviations of the form
T_CMB(z)=T_0(1+z)^(1-beta) to be beta= 0.022 +/- 0.018, at 1 sigma uncertainty,
consistent with the prediction of the standard model. Combining these
measurements with previously published results we get beta=0.016+/-0.012.Comment: submitted to JCAP, 21 pages, 8 figure
Questioning the validity of non-extensive thermodynamics for classical Hamiltonian systems
We examine the non-extensive approach to the statistical mechanics of
Hamiltonian systems with where is the classical kinetic energy. Our
analysis starts from the basics of the formalism by applying the standard
variational method for maximizing the entropy subject to the average energy and
normalization constraints. The analytical results show (i) that the
non-extensive thermodynamics formalism should be called into question to
explain experimental results described by extended exponential distributions
exhibiting long tails, i.e. -exponentials with , and (ii) that in the
thermodynamic limit the theory is only consistent in the range
where the distribution has finite support, thus implying that configurations
with e.g. energy above some limit have zero probability, which is at variance
with the physics of systems in contact with a heat reservoir. We also discuss
the (-dependent) thermodynamic temperature and the generalized specific
heat.Comment: To appear in EuroPhysics Letter
Investigation of Lunar Surface Chemical Contamination by LEM Descent Engine and Associated Equipment
Lunar surface and atmospheric contamination study caused by LEM rocket exhaust and inorganic, organic, and microbiological contaminant
Natural extensions and entropy of -continued fractions
We construct a natural extension for each of Nakada's -continued
fractions and show the continuity as a function of of both the entropy
and the measure of the natural extension domain with respect to the density
function . In particular, we show that, for all , the product of the entropy with the measure of the domain equals .
As a key step, we give the explicit relationship between the -expansion
of and of
Encapsulated Molecules in Carbon Nanotubes: Structure and Properties
We encapsulate a number of fullerenes inside single-walled carbon nanotubes (SWNTs) including La2@C80 and ErxSc3-xN@C80(x=0-3). The structural properties of these nanoscopic hybrid materials are described using high resolution transmission electron microscopy and electron diffraction. It is found that the encapsulated fullerenes selfassemble into long, one-dimensional chains. The thermal stability of these supramolecular assemblies are studied and large variations are found. The behavior is nominally consistent with the mass of the encapsulated metallofullerenes
tgeocad an interface between root and cad systems
In the simulation of High Energy Physics experiment a very high precision in the description of the detector geometry is essential to achieve the required performances. The physicists in charge of Monte Carlo Simulation of the detector need to collaborate efficiently with the engineers working at the mechanical design of the detector. Often, this collaboration is made hard by the usage of different and incompatible software. ROOT is an object-oriented C++ framework used by physicists for storing, analyzing and simulating data produced by the high-energy physics experiments while CAD (Computer-Aided Design) software is used for mechanical design in the engineering field. The necessity to improve the level of communication between physicists and engineers led to the implementation of an interface between the ROOT geometrical modeler used by the virtual Monte Carlo simulation software and the CAD systems. In this paper we describe the design and implementation of the TGeoCad Interface that has been developed to enable the use of ROOT geometrical models in several CAD systems. To achieve this goal, the ROOT geometry description is converted into STEP file format (ISO 10303), which can be imported and used by many CAD systems
Cross sections for geodesic flows and \alpha-continued fractions
We adjust Arnoux's coding, in terms of regular continued fractions, of the
geodesic flow on the modular surface to give a cross section on which the
return map is a double cover of the natural extension for the \alpha-continued
fractions, for each in (0,1]. The argument is sufficiently robust to
apply to the Rosen continued fractions and their recently introduced
\alpha-variants.Comment: 20 pages, 2 figure
Constraining decaying dark energy density models with the CMB temperature-redshift relation
We discuss the thermodynamic and dynamical properties of a variable dark
energy model with density scaling as , z being the
redshift. These models lead to the creation/disruption of matter and radiation,
which affect the cosmic evolution of both matter and radiation components in
the Universe. In particular, we have studied the temperature-redshift relation
of radiation, which has been constrained using a recent collection of cosmic
microwave background (CMB) temperature measurements up to . We find
that, within the uncertainties, the model is indistinguishable from a
cosmological constant which does not exchange any particles with other
components. Future observations, in particular measurements of CMB temperature
at large redshift, will allow to give firmer bounds on the effective equation
of state parameter for such types of dark energy models.Comment: 9 pages, 1 figure, to appear in the Proceedings of the 3rd
Italian-Pakistani Workshop on Relativistic Astrophysics, Lecce 20-22 June
2011, published in Journal of Physics: Conference Series (JPCS
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