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

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 $H=T+V$ where $T$ 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. $q$-exponentials with $q>1$, and (ii) that in the thermodynamic limit the theory is only consistent in the range $0\leq q\leq1$ 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 ($q$-dependent) thermodynamic temperature and the generalized specific heat.Comment: To appear in EuroPhysics Letter

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

Method of comparison equations for cosmological perturbations

We apply the method of comparison equations to study cosmological perturbations during inflation, obtaining the full power spectra of scalar and tensor perturbations to first and to second order in the slow-roll parameters. We compare our results with those derived by means of other methods, in particular the Green's function method and the improved WKB approximation, and find agreement for the slow-roll structure. The method of comparison equations, just as the improved WKB approximation, can however be applied to more general situations where the slow-roll approximation fails.Comment: 20 pages, 10 figure

Improved models of melting temperature and thermal conductivity for mixed oxide fuels doped with low minor actinide contents

Recycling and burning minor actinides (MA, e.g., americium, neptunium) in mixed-oxide (MOX) nuclear fuel is a strategic option for fast reactor concepts of Generation IV to improve the sustainability of nuclear energy by reducing ultimate radioactive waste and improving the exploitation of fuel resources. Thermal conductivity and melting temperature are fundamental properties of nuclear fuels, since they determine the fuel temperature profile and the melting safety margin, respectively and affect the overall fuel performance under irradiation. The available literature on thermal properties of Am or Np- containing MOX, both experimental data and models, is currently scarce. Moreover, state-of-the-art fuel performance codes (FPCs), e.g., GERMINAL and TRANSURANUS, do not account for the effects of minor actinides on MOX fuel properties. This deliverable presents the development and validation of original correlations for the thermal conductivity and melting temperature of minor actinide-bearing MOX (U,Pu,Am,Np)O2-x based on available literature data. These correlations are derived by extending those obtained in the project for U-Pu MOX fuels with the inclusion of the effect of Am and Np content, while preserving the physically- grounded formulation depending on the most relevant parameters. Ways to improve these correlations further in the future are also discussed

Improved WKB analysis of Slow-Roll Inflation

We extend the WKB method for the computation of cosmological perturbations during inflation beyond leading order and provide the power spectra of scalar and tensor perturbations to second order in the slow-roll parameters. Our method does not require that the slow-roll parameters be constant. Although leading and next-to-leading results in the slow-roll parameters depend on the approximation technique used in the computation, we find that the inflationary theoretical predictions obtained may reach the accuracy required by planned observations. In two technical appendices, we compare our techniques and results with previous findings.Comment: REVTeX 4, 13 pages, no figures, final version to appear in Phys. Rev.

Towards grain-scale modelling of the release of radioactive fission gas from oxide fuel. Part I: SCIANTIX

When assessing the radiological consequences of postulated accident scenarios, it is of primary interest to determine the amount of radioactive fission gas accumulated in the fuel rod free volume. The state-of-the-art semi-empirical approach (ANS 5.4-2010) is reviewed and compared with a mechanistic approach to evaluate the release of radioactive fission gases. At the intra-granular level, the diffusion-decay equation is handled by a spectral diffusion algorithm. At the inter-granular level, a mechanistic description of the grain boundary is considered: bubble growth and coalescence are treated as inter- related phenomena, resulting in the grain-boundary venting as the onset for the release from the fuel pellets. The outcome is a kinetic description of the release of radioactive fission gases, of interest when assessing normal and off-normal conditions. We implement the model in SCIANTIX and reproduce the release of short-lived fission gases, during the CONTACT 1 experiments. The results show a satisfactory agreement with the measurement and with the state-of-the-art methodology, demonstrating the model soundness. A second work will follow, providing integral fuel rod analysis by coupling the code SCIANTIX with the thermo-mechanical code TRANSURANUS

Constraints on the CMB temperature redshift dependence from SZ and distance measurements

The relation between redshift and the CMB temperature, $T_{CMB}(z)=T_0(1+z)$ is a key prediction of standard cosmology, but is violated in many non-standard models. Constraining possible deviations to this law is an effective way to test the $\Lambda$CDM paradigm and search for hints of new physics. We present state-of-the-art constraints, using both direct and indirect measurements. In particular, we point out that in models where photons can be created or destroyed, not only does the temperature-redshift relation change, but so does the distance duality relation, and these departures from the standard behaviour are related, providing us with an opportunity to improve constraints. We show that current datasets limit possible deviations of the form $T_{CMB}(z)=T_0(1+z)^{1-\beta}$ to be $\beta=0.004\pm0.016$ up to a redshift $z\sim 3$. We also discuss how, with the next generation of space and ground-based experiments, these constraints can be improved by more than one order of magnitude.Comment: 27 pages, 11 figure

Plasma levels of immunosuppressive mediators during cardiopulmonary bypass

The aim of this study was to evaluate plasma levels of two mediators with immunosuppressive properties, complement fraction C3a (C3a) and transforming growth factor-β1 (TGF-β1), during extracorporeal circulation. The proliferation index after phytohaemagglutinin (PHA) stimulation of isolated peripheral blood mononuclear cells was also investigated. Sixteen patients undergoing hypothermic (n = 8, group 1) and normothermic (n = 8, group 2) cardiopulmormry bypass (CPB) were enrolled in this study. As a control, we evaluated four patients undergoing thoracovascular operations without CPB. Blood samples were collected before CPB but after anaesthesia, every 30 min during CPB, at the end of CPB and 10 min after protamine administration. Both C3a and TGF-β1 increased significantly during CPB and after protamine administration in the hypothermic as well as the normothermic group. In the latter case the increase of C3a and TGF-β1, although more prominent, was not significantl higher than in the former group. Conversely, the proliferation, index of peripheral mononuclear cells had already decreased 30 min after CPB was started and remained depressed throughout the CPB time. These results suggest a possible role of C3a and TGF-β1 in the immunological changes occurring during extracorporeal circulation