A Nagumo-like uniqueness result for a second order ODE

In this note, we present an extension to second order nonlinear ordinary differential equations (ODEs) of the Nagumo-like uniqueness criterion for first order ODEs established in [A. Constantin, On Nagumo's theorem, Proc. Japan Acad. 86(A) (2010), pp. 41--44]

On the uniqueness of flow in a recent tsunami model

We give an elementary proof of uniqueness for the integral curve starting from the vertical axis in the phase-plane analysis of the recent model [A. Constantin, R.S. Johnson, Propagation of very long water waves, with vorticity, over variable depth, with applications to tsunamis, Fluid Dynam. Res. 40 (2008), 175--211]. Our technique can be applied easily in circumstances where the reparametrization device from [A. Constantin, A dynamical systems approach towards isolated vorticity regions for tsunami background states, Arch. Rational Mech. Anal. doi: 10.1007/s00205-010-0347-1] might lead to some serious difficulties

On isolated vorticity regions beneath the water surface

We present a class of vorticity functions that will allow for isolated, circular vorticity regions in the background of still water preceding the arrival of a tsunami wave at the shoreline

Oscillatory solutions of some perturbed second order differential equations

We discuss the occurrence of oscillatory solutions which decay to 0 as $s\to+\infty$ for a class of perturbed second order ordinary differential equations. As opposed to other results in the recent literature, the perturbation is as small as desired in terms of its improper integrals and it is independent of the coefficients of the non-oscillatory unperturbed equation. This class of equations reveals thus a new pathology in the theory of perturbed oscillations

Anisotropic Strange Quintessence Stars in f(R)f(R) Gravity

In this paper, we have formulated the new exact model of quintessence anisotropic star in $f(R)$ theory of gravity. The dynamical equations in $f(R)$ theory with the anisotropic fluid and quintessence field have been solved by using Krori-Barua solution. In this case, we have used the Starobinsky model of $f(R)$ gravity. We have determined that all the obtained solutions are free from central singularity and potentially stable. The observed values of mass and radius of the different strange stars PSR J 1614-2230, SAXJ1808.4-3658(SS1), 4U1820- 30, PSR J 1614-2230 have been used to calculate the values of unknown constants in Krori and Barua metric. The physical parameters like anisotropy, stability and redshift of the stars have been investigated in detail.Comment: 20 Pages, 12 figures, Accepted for publication in Astrophys. Space Sci. arXiv admin note: substantial text overlap with arXiv:1412.212

A Modified Hard Thermal Loop Perturbation Theory

Based on the external perturbation that disturbs the system only slightly from its equilibrium position we make the Taylor expansion of the pressure of a quark gas. It turns out that the first term was used in the literature to construct a Hard Thermal Loop perturbation theory (HTLpt) within the variation principle of the lowest order of the thermal mass parameter. Various thermodynamic quantities within the 1-loop HTLpt encountered overcounting of the leading order (LO) contribution and also required a separation scale for soft and hard momenta. Using same variational principle we reconstruct the HTLpt at the first derivative level of the pressure that takes into account the effect of the variation of the external source through the conserved density fluctuation. This modification markedly improves those quantities in 1-loop HTLpt in a simple way instead of pushing the calculation to a considerably more complicated 2-loop HTLpt. Moreover, the results also agree with those obtained in the 2-loop approximately self-consistent \Phi-derivable Hard Thermal Loop resummation. We also discuss how this formalism can be extended for the higher order contributionsComment: Paper revised; a sec. deleted and title change

On the asymptotic integration of a class of sublinear fractional differential equations

We estimate the growth in time of the solutions to a class of nonlinear fractional differential equations $D_{0+}^{\alpha}(x-x_0) =f(t,x)$ which includes $D_{0+}^{\alpha}(x-x_0) =H(t)x^{\lambda}$ with $\lambda\in(0,1)$ for the case of slowly-decaying coefficients $H$. The proof is based on the triple interpolation inequality on the real line and the growth estimate reads as $x(t)=o(t^{a\alpha})$ when $t\to+\infty$ for $1>\alpha>1-a>\lambda>0$. Our result can be thought of as a non--integer counterpart of the classical Bihari asymptotic integration result for nonlinear ordinary differential equations. By a carefully designed example we show that in some circumstances such an estimate is optimal

On the critical exponent of \eta/s and a new exponent-less measure of fluidity

We discuss on the critical exponent of $\eta/s$ for a fluid, and propose a new exponent-less measure of fluidity based on a mode-mode coupling theory. This exhibits a remarkable universality for fluids obeying a liquid-gas phase transition both in hydrodynamic as well as in nonhydrodynamic region. We show that this result is independent of the choice of the fluid dynamics, {\em viz.}, relativistic or nonrelativistic. Quark-Gluon Plasma, being a hot relativistic and a nearly perfect fluid produced in relativistic heavy-ion collisions, is expected to obey the same universality constrained by both the viscous and the thermal flow modes in it. We also show that if the elliptic flow data in RHIC puts a constraint on $\eta/s$ then the new fluidity measure for Quark-Gluon Plasma in turn also restricts the other transport coefficient, {\it viz.}, the thermal conductivity.Comment: 4 pages and 2 figures; Title and abstract changed; discussion adde

On the Nagumo uniqueness theorem

By a convenient reparametrisation of the integral curves of a nonlinear ordinary differential equation (ODE), we are able to improve the conclusions of the recent contribution [A. Constantin, Proc. Japan Acad. {\bf 86(A)} (2010), 41--44]. In this way, we establish a flexible uniqueness criterion for ODEs without Lipschitz-like nonlinearities

Temperature dependent Nucleon Mass and entropy bound inequality

Mass of a baryon as a function of temperature is calculated using colour-singlet partition function for massless quarks (with two flavours) and abelian gluons confined in a bag with a temperature dependent bag pressure constant $B(T)$. The non-perturbative aspect of QCD interaction is included through colour-singlet restriction on quark-gluon partition function in a phenomenological way. The entropy bound inequality $S/E \ \leq \ 2\pi R/\hbar c$, where $S, \ E$ and $R$ are entropy, energy and radius, respectively of the enclosed system with $\hbar c \ = \ 197.331$ MeVfm, is found to be consistent with the equilibrium solutions of the baryon mass upto a temperature $T_E$. There is a region of temperature $T_E < T < T_C$ ($T_C$ is critical temperature for quark-gluon plasma formation) in which no admissible equilibrium states exist for the bag. We say that the system expriences a phase jump from hadron to quark-gluon plasma through thermodynamic non-equlibrium processes.Comment: Latex file(3 figures obtainable from first author