Can a Kasner Universe with a Viscous Cosmological Fluid be Anisotropic?

A Bianchi type -I metric of Kasner form is considered, when the space is filled with a viscous fluid. Whereas an ideal (nonviscous) fluid permits the Kasner metric to be anisotropic provided that the fluid satisfies the Zel'dovich equation of state, the viscous fluid does not permit the Kasner metric to be anisotropic at all. In the latter case, we calculate the Kasner (isotropic) metric expressed by the fluid's density, pressure, and bulk viscosity, at some chosen instant $t=t_0$. The equation of state is also calculated. The present paper is related to a recent Comment of Cataldo and del Campo [Phys. Rev. D, scheduled to April 15, 2000], on a previous work of the present authors [Phys. Rev. D {\bf 56}, 3322 (1997)].Comment: 8 pages, LaTeX, no figures. To appear in PR

A causal model for a closed universe

We study a closed model of a universe filled with viscous fluid and quintessence matter components. The dynamical equations imply that the universe might look like an accelerated flat Friedmann-Robertson-Walker (FRW) universe at low redshift. We consider here dissipative processes which obey a causal thermodynamics. Here, we account for the entropy production via causal dissipative inflation.Comment: 9 pages. Accepted for publication in IJMP

How ‘Smart’ Are Smart Specialization Strategies?

The introduction of smart specialization (S3) as a fundamental pillar of the 2014 reform of the EU cohesion policy is a significant strategic shift in European development intervention. S3 strategies aimed at mobilizing the economic potential of each country and region of the EU by allowing a more place-based and bottom-up approach to development. However, despite the salience that S3 has acquired in a short period of time, there has been no European-wide evaluation of the extent to which S3 strategies truly reflect the economic characteristics and potential of the territories where they are being implemented. This article examines the characteristics of S3 strategies across Europe – by focusing on their development axes, economic or scientific domains and policy priorities – to assess whether this is the case. The results show that S3 strategies display a proliferation of objectives, a problem that particularly affects areas with weaker quality of government. Moreover, strategies are generally loosely connected with the intrinsic conditions of each region and mostly mimic what neighbouring areas are doing. The lack of more concise and focused S3 strategies is likely to undermine the effectiveness of what is, otherwise, a very interesting and worthwhile policy experiment

Regular (2+1)-dimensional black holes within non-linear Electrodynamics

(2+1)-regular static black hole solutions with a nonlinear electric field are derived. The source to the Einstein equations is an energy momentum tensor of nonlinear electrodynamics, which satisfies the weak energy conditions and in the weak field limit becomes the (2+1)-Maxwell field tensor. The derived class of solutions is regular; the metric, curvature invariants and electric field are regular everywhere. The metric becomes, for a vanishing parameter, the (2+1)-static charged BTZ solution. A general procedure to derive solutions for the static BTZ (2+1)-spacetime, for any nonlinear Lagrangian depending on the electric field is formulated; for relevant electric fields one requires the fulfillment of the weak energy conditions.Comment: 5 pages, Latex, 2 figure

Effetti cardiorespiratori degli sprint ripetuti in giovani calciatori

Scopo: Nel calcio la performance dipende da attività caratterizzate da sforzi di breve durata, talora ad alta intensità, con ridotti tempi di recupero. Questo tipo di sforzo può avere maggiore potenzialità aritmogena rispetto a sforzi, anche massimali, iniziati e terminati in modo graduale. Gli sprint ripetuti permettono di valutare la performance e lo stato di allenamento in giovani calciatori. Scopo del nostro lavoro è stato quello di valutare gli effetti degli sprint ripetuti sul sistema cardiorespiratorio in giovani calciatori delle rappresentative regionali siciliane della FIGC. Metodi: Sono stati esaminati 12 calciatori, di età media di 15±1 anni. Per valutare lo stato di fitness cardiorespiratoria sono stati determinati, al test da sforzo incrementale massimale al treadmill (SI), il VO2max in ml.Kg-1.min-1 (VO2maxSI) e la FCmax in bpm (FCmaxSI). Per valutare gli effetti cardiorespiratori degli sprint ripetuti, gli atleti hanno eseguito un test da sforzo al cicloergometro a freno meccanico (SR) che prevedeva 10 sprint massimali “all-out” di 6 sec, intervallati da 30 sec di recupero passivo. Nella serie dei 10 sprint, sono stati determinati il valore più elevato di VO2 in ml.Kg-1.min-1 (VO2maxSR) e di FC in bpm (FCmaxSR). Risultati: Il valore medio di VO2maxSI (56,22±3,93 ml.Kg-1.min-1) indica che i soggetti esaminati hanno un buon livello di potenza aerobica, raggiunta ad una FCmaxSI di 190±8 bpm. I dati di VO2maxSR rilevati al test degli sprint ripetuti evidenziano un valore medio di 42,67±5,57 ml.Kg-1.min-1 (70% del VO2maxSI), raggiunto ad una FCmaxSR di 175±11 bpm (92% della FCmaxSI). Conclusioni: I dati del nostro studio indicano che nei soggetti esaminati gli sprint ripetuti determinano incrementi della frequenza cardiaca rapidi, elevati e persistenti nella fase di recupero. Questo dato deve essere preso in considerazione non solo per la valutazione della performance ma anche nella formulazione dell’idoneità a praticare la disciplina sportiva del calcio

Bianchi Type I Universes with Causal Bulk Viscous Cosmological Fluid

We consider the dynamics of a causal bulk viscous cosmological fluid filled constantly decelerating Bianchi type I space-time. The matter component of the Universe is assumed to satisfy a linear barotropic equation of state and the state equation of the small temperature Boltzmann gas. The resulting cosmological models satisfy the condition of smallness of the viscous stress. The time evolution of the relaxation time, temperature, bulk viscosity coefficient and comoving entropy of the dissipative fluid is also obtained.Comment: 11 pages, 5 figures, accepted for publication in International Journal of Modern Physics

BTZ black hole from (3+1) gravity

We propose an approach for constructing spatial slices of (3+1) spacetimes with cosmological constant but without a matter content, which yields (2+1) vacuum with $\Lambda$ solutions. The reduction mechanism from (3+1) to (2+1) gravity is supported on a criterion in which the Weyl tensor components are required to vanish together with a dimensional reduction via an appropriate foliation. By using an adequate reduction mechanism from the Pleba\'nski-Carter[A] solution in (3+1) gravity, the (2+1) BTZ solution can be obtained.Comment: 4 pages, Late

Interacting Kasner-type cosmologies

It is well known that Kasner-type cosmologies provide a useful framework for analyzing the three-dimensional anisotropic expansion because of the simplification of the anisotropic dynamics. In this paper relativistic multi-fluid Kasner-type scenarios are studied. We first consider the general case of a superposition of two ideal cosmic fluids, as well as the particular cases of non-interacting and interacting ones, by introducing a phenomenological coupling function $q(t)$. For two-fluid cosmological scenarios there exist only cosmological scaling solutions, while for three-fluid configurations there exist not only cosmological scaling ones, but also more general solutions. In the case of triply interacting cosmic fluids we can have energy transfer from two fluids to a third one, or energy transfer from one cosmic fluid to the other two. It is shown that by requiring the positivity of energy densities there always is a matter component which violates the dominant energy condition in this kind of anisotropic cosmological scenarios.Comment: Accepted for publication in Astrophysics &Space Science, 8 page

Stability of the hard-sphere icosahedral quasilattice

The stability of the hard-sphere icosahedral quasilattice is analyzed using the differential formulation of the generalized effective liquid approximation. We find that the icosahedral quasilattice is metastable with respect to the hard-sphere crystal structures. Our results agree with recent findings by McCarley and Ashcroft [Phys. Rev. B {\bf 49}, 15600 (1994)] carried out using the modified weighted density approximation.Comment: 15 pages, 2 figures available from authors upon request, (revtex), submitted to Phys. Rev.