2,121 research outputs found
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
Neural Systems Underlying Aversive Conditioning in Humans with Primary and Secondary Reinforcers
Money is a secondary reinforcer commonly used across a range of disciplines in experimental paradigms investigating reward learning and decision-making. The effectiveness of monetary reinforcers during aversive learning and associated neural basis, however, remains a topic of debate. Specifically, it is unclear if the initial acquisition of aversive representations of monetary losses depends on similar neural systems as more traditional aversive conditioning that involves primary reinforcers. This study contrasts the efficacy of a biologically defined primary reinforcer (shock) and a socially defined secondary reinforcer (money) during aversive learning and its associated neural circuitry. During a two-part experiment, participants first played a gambling game where wins and losses were based on performance to gain an experimental bank. Participants were then exposed to two separate aversive conditioning sessions. In one session, a primary reinforcer (mild shock) served as an unconditioned stimulus (US) and was paired with one of two colored squares, the conditioned stimuli (CS+ and CS−, respectively). In another session, a secondary reinforcer (loss of money) served as the US and was paired with one of two different CS. Skin conductance responses were greater for CS+ compared to CS− trials irrespective of type of reinforcer. Neuroimaging results revealed that the striatum, a region typically linked with reward-related processing, was found to be involved in the acquisition of aversive conditioned response irrespective of reinforcer type. In contrast, the amygdala was involved during aversive conditioning with primary reinforcers, as suggested by both an exploratory fMRI analysis and a follow-up case study with a patient with bilateral amygdala damage. Taken together, these results suggest that learning about potential monetary losses may depend on reinforcement learning related systems, rather than on typical structures involved in more biologically based fears
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
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