Narrow Results

Our aim is studying the thermodynamics of cosmological models including initial and final de Sitter eras. For this propose, bearing Cai–Kim temperature in mind, we investigate the thermodynamic properties of a dark energy (DE) candidate with variable energy density, and show that the state parameter of this dark energy candidate $({\omega }_D)$ should obey the ${\omega }_D\ne -1$ constraint, whiles there is no interaction between the fluids filled the universe, and the universe is not in the de Sitter eras. Additionally, based on the thermal fluctuation theory, we study the possibility of inducing fluctuations to the entropy of the DE candidate due to a mutual interaction between the cosmos sectors. Therefore, we find a relation between the thermal fluctuations and the mutual interaction between the cosmos sectors, whiles the DE candidate has a varying energy density. Finally, bearing the coincidence problem in mind, we derive a constraint on the vacuum energy, and investigate its relation with the entropy evolution of the DE candidate. We also point to a model with initial and final de Sitter eras in which a gravitationally induced particle production process leads to change the expansion eras, whiles the corresponding pressure is considered as the cause of current accelerated phase. We study its thermodynamics, and show that such processes may also leave thermal fluctuations into the system. We also find an expression between the thermal fluctuations and the particle production rate. Finally, we use Hayward–Kodama temperature to get a relation for the horizon entropy in models including the gravitationally induced particle production process. Our study shows that the first law of thermodynamics is available on the apparent horizon whiles, the gravitationally induced particle production process, as the DE candidate, may add an additional term to the Bekenstein limit of the horizon. The relation between the validity of the second law of thermodynamics and the gravitationally particle production process is also studied.

The impact of thermal fluctuations on the thermodynamics of Born–Infeld–anti-de Sitter black hole is being investigated. For this purpose, we analyze the consequences of logarithmic corrections on thermodynamics potentials like Helmholtz and Gibbs. We find out the relations for critical points and stability and observe that thermal corrections play a vital role in them.

In this paper, we discuss remnants of the Bardeen regular black hole motivated by using the concept of thermal fluctuations. First, we derive the equilibrium values of various thermodynamic quantities like entropy, Hawking temperature, pressure, internal energy, Helmholtz free energy and Gibbs free energy in the non-extended phase space. We then discuss geometrothermodynamics (GTD) of Bardeen black hole to study its stability. Next, we estimate the size of black hole remnant in terms of some known parameters of the black hole solution. Motivated by the fact that estimation of size, characteristics and stability of remnants of black holes could further increase our understanding of binary collisions, information loss paradox and dark energy, the black hole remnant, which gives an idea about stable mass left over after evaporation of black hole, is seen to owe its presence due to thermal fluctuations. We see that the thermal fluctuations bring an overall increase in entropy curve. However, in presence of thermal fluctuations, a positive kink, which signifies a maximum increase in the value of entropy, occurs at a certain value of horizon, which is exactly equal to the remnant radius. We observe that the thermal fluctuations, which are characteristics of quantum gravity, lead to stable values of thermodynamic quantities near the remnant radius. In presence of thermal fluctuations, we then derive various corrected thermodynamic potentials and also discuss the validity of first law of black hole thermodynamics for Bardeen black hole.

In this paper, we explore thermodynamics, thermal stability, effects of logarithmic corrections on thermodynamic quantities and phase transitions of spherically symmetric regular black hole with the de Sitter core. We first calculate the expressions for Hawking temperature as well as heat capacity and investigate its thermal stability. We also discuss the effects of logarithmic corrections on thermodynamical quantities such as pressure, Gibbs–Helmholtz free energy, internal energy and enthalpy of the system. Finally, we analyze the behavior of Hawking temperature as well as specific heat capacity of the regular black hole versus entropy for different values of the de Sitter parameter $(b)$. It is found that Hawking temperature changes its phase from positive to negative and heat capacity changes its phase from negative to positive for large values of $b$.

In this article, we address the problem of Euler's buckling instability in a charged semi-flexible polymer that is under the action of a compressive force. We consider this instability as a phase transition and investigate the role of thermal fluctuations in the buckling critical force. By performing molecular dynamic simulations, we show that the critical force decreases when the temperature increases. Repulsive electrostatic interaction in the finite temperature is in competition with thermal fluctuations to increase the buckling threshold.

Synthesis of the Y₂Ba₅Cu₈O₁₇ superconducting material by the standard solid state reaction is reported. DC resistivity measurements reveal a bulk T_c = 104.95 K which was determined by the criterion of the maximum in the numerical temperature derivative of electrical resistivity. Structure characterization was performed by means of the X-ray diffraction (XRD) technique. A Rietveld refinement of XRD patterns shows that the material crystallizes in an orthorhombic structure, space group Pmm2 with cell parameters a = 3.8712(0) Å, b = 3.8481(4) Å and c = 27.1601(4) Å. In order to study the pairing mechanism close to T_c, conductivity fluctuation analysis was performed by the method of logarithmic temperature derivative of the conductivity excess. Close and above T_c, the conductivity fluctuation analysis reveal the occurrence of two fluctuation regimes characterized by the critical exponents λ_3D = 0.52 and λ_1D = 1.51, corresponding to 3D and 1D Gaussian regimes, respectively. The correlations of the critical exponents with the dimensionality of the fluctuation system for each Gaussian regime were performed by using the Aslamazov–Larkin theory.

In this study, we carried out the analysis of the thermal fluctuations on the dynamics of small Josephson junction (JJ). An expression for the fluctuation of Coulomb blockade edge in the case of low and high growing rate of voltage was obtained. It was shown that dynamics of small-sized JJ under thermal fluctuations is determined by the energy ratio-parameter, temperature and growing rate of voltage.

The transient dynamics of long overlap Josephson junctions in the frame of the sine-Gordon model with a white noise source is investigated. The effect of noise delayed decay is observed for the case of overdamped sine-Gordon equation. It is shown that this noise induced effect, in the range of small noise intensities, vanishes for junction lengths greater than several Josephson penetration lengths.

In this paper, we consider a charged BTZ black hole in asymptotically AdS spacetime of massive gravity to study the effect of the thermal fluctuations on the black hole thermodynamics. We consider the Einstein–Born–Infeld solution and investigate critical points and stability. We also compare the results with the case of Einstein–Maxwell solutions. Besides, we find that thermal fluctuations, which appear as a logarithmic term in the entropy, affect the stability of the black hole and change the phase transition point. Moreover, we study the geometrical thermodynamics and find that the behavior of the linear Maxwell solution is the same as the nonlinear one.

The S-shaped heat capacity, which has recently been claimed to be a fingerprint of the superfluid-to-normal phase transition in nuclei, is studied in the case of ¹⁶⁶Er element. The calculations are performed by means of the modified Bardeen–Cooper–Schrieffer (MBCS) approach that takes into account the thermal fluctuation. The obtained results are compared to the experimental data and to the FT-BCS theoretical predictions. The present study illustrates the effect of the fluctuations of the quasiparticle (QP) number on the heat capacity.

The thermal properties of Tin isotopes such as 68≤N≤78, are studied. The calculations are performed by means of the modified Lipkin–Nogami (MLN) approach that takes into account the thermal and quantal fluctuations. The obtained results are compared to the conventional finite-temperature Bardeen–Cooper–Schrieffer (FTBCS) approach and to the modified Bardeen–Cooper–Schrieffer (MBCS) method. The numerical results illustrate the effect of the statistical and quantal fluctuations on the description of the phenomenon of pairing phase transition.

We present analytical and simple expressions to determine the free energy, internal energy, entropy, as well as the pressure acting at the interface of a perfectly conducting rectangular Casimir piston. We show that infrared divergencies linear in temperature become cancelled within the piston configuration, and show a continuous behavior consistent with intuitive expectations.