518 research outputs found
Analytic solution of Guyer-Krumhansl equation for laser flash experiments
The existence of non-Fourier heat conduction is known for a long time in
small and low temperature systems. The deviation from Fourier's law has been
found at room temperature in heterogeneous materials like rocks and metal foams
\cite{Botetal16, Vanetal17}. These experiments emphasized that the so-called
Guyer-Krumhansl equation is adequate for modeling complex materials. In this
paper an analytic solution of Guyer-Krumhansl equation is presented considering
boundary conditions from laser flash experiment. The solutions are validated
with the help of a numerical code \cite{KovVan15} developed for generalized
heat equations
Video in e-learning systems
The world is changing rapidly in the field of multimedia and it is inevitable to prepare to
use and utilize the new teaching method. This is specifically true in the case of the use of educational
films both as video and also using such video on the Internet. Our first task is to decide whether the
development of material will be an independent film or a part of an e-learning course. In both cases
the method of construction is different. The next step is to select the target group of the film. There is a
wide scale of possible viewers or participants (who must have a certain level of basic knowledge) and
also handicapped people should be able to use the results. The final product ought to be acceptable for
e-learning and distance-learning as well. Using the information technology in education is general and
the present being of the e-learnig is part of this fact. We can use e-learning effectively only if the
system is filled up with electronic educational material. The most effective ones are the multimediamaterials.
The effectiveness of the multimedia-material can be improved with the application of video
On the rarefied gas experiments
There are limits of validity of classical constitutive laws such as Fourier
and Navier-Stokes equations, phenomena beyond those limits have been
experimentally found many decades ago. However, it is still not clear what
theory would be appropriate to model different non-classical phenomena under
different conditions considering either the low-temperature or composite
material structure. In this paper, a modeling problem of rarefied gases is
addressed. It covers the mass density dependence of material parameters, the
scaling properties of different theories and aspects of how to model an
experiment. In the following, two frameworks and their properties are
discussed. One of them is the kinetic theory based Rational Extended
Thermodynamics; the other one is the non-equilibrium thermodynamics with
internal variables and current multipliers. In order to compare these theories,
an experiment performed by Rhodes is analyzed in detail. It is shown that the
density dependence of material parameters has a severe impact on modeling
capabilities and can lead to very different results
Heat equations beyond Fourier: from heat waves to thermal metamaterials
In the past decades, numerous heat conduction models beyond Fourier have been
developed to account for the large gradients, fast phenomena, wave propagation,
or heterogeneous material structure, such as being typical for biological
systems, superlattices, or thermal metamaterials. It became a challenge to
orient among the models, mainly due to their various thermodynamic backgrounds
and possible compatibility issues. Additionally, in light of the recent
findings on the field of non-Fourier heat conduction, it is not even
straightforward how to interpret and utilize a non-Fourier heat equation,
primarily when one aims to thermally design the material structure to construct
the new generation of thermal metamaterials. Adding that numerous modeling
strategies can be found in the literature accompanying different
interpretations even for the same heat equation makes it even more difficult to
orient ourselves and find a comprehensive picture of this field of research.
Therefore, this review aims to ease the orientation among advanced heat
equations beyond Fourier by discussing properties concerning their possible
practical applications in light of experiments. We start from the simplest
model with basic principles and notions, then proceed toward the more complex
models related to coupled phenomena such as ballistic heat conduction. We do
not enter the often complicated technical details of each thermodynamic
framework but do not aim to compare each approach. However, we still briefly
present their background to highlight their origin and the limitations acting
on the models. Additionally, the field of non-Fourier heat conduction has
become quite segmented, and that paper also aims to provide a common ground, a
comprehensive mutual understanding of the basics of each model, together with
what phenomenon they can be applied to
Random transverse-field Ising chain with long-range interactions
We study the low-energy properties of the long-range random transverse-field
Ising chain with ferromagnetic interactions decaying as a power alpha of the
distance. Using variants of the strong-disorder renormalization group method,
the critical behavior is found to be controlled by a strong-disorder fixed
point with a finite dynamical exponent z_c=alpha. Approaching the critical
point, the correlation length diverges exponentially. In the critical point,
the magnetization shows an alpha-independent logarithmic finite-size scaling
and the entanglement entropy satisfies the area law. These observations are
argued to hold for other systems with long-range interactions, even in higher
dimensions.Comment: 6 pages, 4 figure
Non-equilibrium theories of rarefied gases: internal variables and extended thermodynamics
Limits of classical constitutive laws such as Fourier and Navier-Stokes
equations are discovered since decades. However, the proper extensions --
generalizations of these are not unique. They differ in the underlying physical
principles and in modeling capabilities. In this paper, two different theories
are discussed and compared to each other, namely the kinetic theory-based
Rational Extended Thermodynamics (RET) and non-equilibrium thermodynamics with
internal variables (NET-IV).
First, the paper starts with the case of rigid heat conductors summarizing
the result achieved so far. Then a typical example of compressible bodies is
shown by presenting the first generalization for rarefied gases, called
Meixner's theory. It is further extended using generalized entropy current in
the framework of NET-IV. It is shown how its structure is related to RET and
how the compatibility between them can be acquired
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