109 research outputs found
Thermodynamic aspects of rock friction
Rate- and state-dependent friction law for velocity-step tests is analyzed
from a thermodynamic point of view. A simple macroscopic non-equilibrium
thermodynamic model with a single internal variable reproduces instantaneous
jump and relaxation. Velocity weakening appears as a consequence of a
plasticity related nonlinear coefficient. Permanent part of displacement
corresponds to plastic strain, and relaxation effects are analogous to creep in
thermodynamic rheology.Comment: 13 pages 3 figures. Revision: thermodynamic compatibility of velocity
weakenin
Models of ballistic propagation of heat at low temperatures
Heat conduction at low temperatures show various effects that cannot be
described by the Fourier law, like the second sound and ballistic propagation.
In this paper the performance of various theories is compared in case of
ballistic and wave like propagation of heat pulses in NaF
Microinertia and internal variables
The origin of microinertia of micromorphic theories is investigated from the
point of view of non-equilibrium thermodynamics. In the framework of dual
internal variables microinertia stems from a thermodynamic equation of state
related to the internal variable with the properties of mechanical momentum.Comment: 14 pages, no figure
Scalar, vectorial and tensorial damage parameters from the mesoscopic background
In the mesoscopic theory a distribution of different crack sizes and crack
orientations is introduced. A scalar damage parameter, a second order damage
tensor and a vectorial damage parameter are defined in terms of this
distribution function. As an example of a constitutive quantity the free energy
density is given as a function of the damage tensor. This equation is reduced
in the uniaxial case to a function of the damage vector and in case of a
special geometry to a function of the scalar damage parameter.Comment: 14 pages, 2 figure
Relativistic hydrodynamics - causality and stability
Causality and stability in relativistic dissipative hydrodynamics are
important conceptual issues. We argue that causality is not restricted to
hyperbolic set of differential equations. E.g. heat conduction equation can be
causal considering the physical validity of the theory. Furthermore we propose
a new concept of relativistic internal energy that clearly separates the
dissipative and non-dissipative effects. We prove that with this choice we
remove all known instabilities of the linear response approximation of viscous
and heat conducting relativistic fluids. In this paper the Eckart choice of the
velocity field is applied.Comment: 14 pages, 2 figures, completely revise
Thermodynamics and flow-frames for dissipative relativistic fluids
A general thermodynamic treatment of dissipative relativistic fluids is
introduced, where the temperature four vector is not parallel to the velocity
field of the fluid. Generic stability and kinetic equilibrium points out a
particular thermodynamics, where the temperature vector is parallel to the
enthalpy flow vector and the choice of the flow fixes the constitutive
functions for viscous stress and heat. The linear stability of the homogeneous
equilibrium is proved in a mixed particle-energy flow-frame.Comment: 9 page
Splitting the source term for the Einstein equation to classical and quantum parts
We consider the special and general relativistic extensions of the action
principle behind the Schr\"odinger equation distinguishing classical and
quantum contributions. Postulating a particular quantum correction to the
source term in the classical Einstein equation we identify the conformal
content of the above action and obtain classical gravitation for massive
particles, but with a cosmological term representing off-mass-shell
contribution to the energy-momentum tensor. In this scenario the - on the
Planck scale surprisingly small - cosmological constant stems from quantum
bound states (gravonium) having a Bohr radius as being \Lambda=3/a^2.Comment: 13 pages, revise
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