Measuring Nonequilibrium Temperature of Forced Oscillators

The meaning of temperature in nonequilibrium thermodynamics is considered by using a forced harmonic oscillator in a heat bath, where we have two effective temperatures for the position and the momentum, respectively. We invent a concrete model of a thermometer to testify the validity of these different temperatures from the operational point of view. It is found that the measured temperature depends on a specific form of interaction between the system and a thermometer, which means the zeroth law of thermodynamics cannot be immediately extended to nonequilibrium cases.Comment: 8 page

Diffuse-interface model for rapid phase transformations in nonequilibrium systems

A thermodynamic approach to rapid phase transformations within a diffuse interface in a binary system is developed. Assuming an extended set of independent thermodynamic variables formed by the union of the classic set of slow variables and the space of fast variables, we introduce finiteness of the heat and solute diffusive propagation at the finite speed of the interface advancing. To describe the transformation within the diffuse interface, we use the phase-field model which allows us to follow the steep but smooth change of phases within the width of diffuse interface. The governing equations of the phase-field model are derived for the hyperbolic model, model with memory, and for a model of nonlinear evolution of transformation within the diffuse-interface. The consistency of the model is proved by the condition of positive entropy production and by the outcomes of the fluctuation-dissipation theorem. A comparison with the existing sharp-interface and diffuse-interface versions of the model is given.Comment: 15 pages, regular article submitted to Physical Review

Case report of simultaneous presentation of pulmonary embolism and pericardial effusion following an oncological esophagectomy

INTRODUCTION: This is the first reported case of simultaneous presentation of pulmonary embolism and pericardial effusion following esophagectomy. This case illustrates a diagnostic and therapeutic challenge exemplifying the difficulties arising from complex anticoagulant considerations in esophageal cancer. PATIENT CASE: A 72 year old male undergoes an oncological esophageal resection. Postoperatively the patient develops pulmonary embolism for which he is treated with Rivaroxaban. After starting Rivaroxaban the patient develops a large pericardial effusion. DISCUSSION: We suspect that the treatment of pulmonary embolism with Rivaroxaban had a causative role in the development of pericardial effusion. Based on literature we suspect that chemoradiotherapy increased susceptibility. CONCLUSION: Diagnosis and treatment of simultaneous pulmonary embolism and pericardial effusion remains a challenge. Special consideration should be taken when using Rivaroxaban in esophageal cancer patients; this should always be conducted in consultation with a coagulation specialist. (C) 2020 The Authors. Published by Elsevier Ltd on behalf of IJS Publishing Group Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by-nc-nd/4.0/)

The effects of nonlocality on the evolution of higher order fluxes in non-equilibrium thermodynamics

The role of gradient dependent constitutive spaces is investigated on the example of Extended Thermodynamics of rigid heat conductors. Different levels of nonlocality are developed and the different versions of extended thermodynamics are classified. The local form of the entropy density plays a crucial role in the investigations. The entropy inequality is solved under suitable constitutive assumptions. Balance form of evolution equations is obtained in special cases. Closure relations are derived on a phenomenological level.Comment: 16 pages, 1 figur

Modelling scheme for railway vehicle/track/ground dynamic interaction in the time domain

Modelling of vehicle/track/ground dynamic interaction is an important issue for railway design. Better understanding of how the moving dynamic loads are distributed through the track components to the ground can be derived from these numerical results to improve the stability of the moving train and decrease the cost of the maintenance. Nonlinear models of the ground may be required due to the large displacements induced by heavier and/or high-speed trains. The aim of this research is to develop a general modelling approach for predicting the dynamic behaviour for a variety of situations. A three-dimensional vehicle/track/ground approach in the time domain is presented. The finite element method is used to model the track/ground vibration. The equations of motion of a multi-body vehicle are implemented to couple with the ground/track system. An alternative approach to the commonly used infinite elements is proposed for modelling the far-field, based on the use of mass-proportional damping to suppress the reflections from model edges. Improved results are shown and better efficiency can be found compared to the results from models with infinite elements. Furthermore, two different geometries for the ground model, a hemispherical and a cuboid one, are discussed. The issue of transients developed by the moving load is discussed and it is shown that long models are required for load speeds close to the wavespeed in the ground to allow the results to achieve steady state. Finally, the results are benchmarked against the results from a wavenumber FE/BE model

Influence of electron and phonon temperature on the efficiency of thermoelectric conversion

In the framework of Extended Irreversible Thermodynamics it is developed a two-temperature model (for electrons and phonons, respectively) of thermoelectric effects. The expression of the maximum efficiency in terms of these two temperatures is derived as well. It is proved that, for the electron temperature higher than the phonon temperature, the two-temperature model yields an efficiency which is higher with respect to that of the single-temperature model. Two possible experiments to estimate the electron temperature are suggested

Archimedean-type force in a cosmic dark fluid: II. Qualitative and numerical study of a multistage Universe expansion

In this (second) part of the work we present the results of numerical and qualitative analysis, based on a new model of the Archimedean-type interaction between dark matter and dark energy. The Archimedean-type force is linear in the four-gradient of the dark energy pressure and plays a role of self-regulator of the energy redistribution in a cosmic dark fluid. Because of the Archimedean-type interaction the cosmological evolution is shown to have a multistage character. Depending on the choice of the values of the model guiding parameters,the Universe's expansion is shown to be perpetually accelerated, periodic or quasiperiodic with finite number of deceleration/acceleration epochs. We distinguished the models, which can be definitely characterized by the inflation in the early Universe, by the late-time accelerated expansion and nonsingular behavior in intermediate epochs, and classified them with respect to a number of transition points. Transition points appear, when the acceleration parameter changes the sign, providing the natural partition of the Universe's history into epochs of accelerated and decelerated expansion. The strategy and results of numerical calculations are advocated by the qualitative analysis of the instantaneous phase portraits of the dynamic system associated with the key equation for the dark energy pressure evolution.Comment: 15 pages, 12 figures, Part II, typos corrected, Fig.4 replaced, references correcte

Ideal gas sources for the Lemaitre-Tolman-Bondi metrics

New exact solutions emerge by replacing the dust source of the Lem\^aitre-Tolman-Bondi metrics with a viscous fluid satisfying the monatomic gas equation of state. The solutions have a consistent thermodynamical interpretation. The most general transport equation of Extended Irreversible Thermodynamics is satisfied, with phenomenological coefficients bearing a close resemblance to those characterizing a non relativistic Maxwell-Bolzmann gas.Comment: 7 pages, Plain TeX with IOP macros, important corrections to previous version, 3 figures (to appear in Classical and Quantum Gravity, June 1998

Vortex length, vortex energy and fractal dimension of superfluid turbulence at very low temperature

By assuming a self-similar structure for Kelvin waves along vortex loops with successive smaller scale features, we model the fractal dimension of a superfluid vortex tangle in the zero temperature limit. Our model assumes that at each step the total energy of the vortices is conserved, but the total length can change. We obtain a relation between the fractal dimension and the exponent describing how the vortex energy per unit length changes with the length scale. This relation does not depend on the specific model, and shows that if smaller length scales make a decreasing relative contribution to the energy per unit length of vortex lines, the fractal dimension will be higher than unity. Finally, for the sake of more concrete illustration, we relate the fractal dimension of the tangle to the scaling exponents of amplitude and wavelength of a cascade of Kelvin waves.Comment: 12 pages, 1 figur

The delayed uncoupled continuous-time random walks do not provide a model for the telegraph equation

It has been alleged in several papers that the so called delayed continuous-time random walks (DCTRWs) provide a model for the one-dimensional telegraph equation at microscopic level. This conclusion, being widespread now, is strange, since the telegraph equation describes phenomena with finite propagation speed, while the velocity of the motion of particles in the DCTRWs is infinite. In this paper we investigate how accurate are the approximations to the DCTRWs provided by the telegraph equation. We show that the diffusion equation, being the correct limit of the DCTRWs, gives better approximations in $L_2$ norm to the DCTRWs than the telegraph equation. We conclude therefore that, first, the DCTRWs do not provide any correct microscopic interpretation of the one-dimensional telegraph equation, and second, the kinetic (exact) model of the telegraph equation is different from the model based on the DCTRWs.Comment: 12 pages, 9 figure