71,995 research outputs found
Non-stationary heat conduction in one-dimensional chains with conserved momentum
The Letter addresses the relationship between hyperbolic equations of heat
conduction and microscopic models of dielectrics. Effects of the non-stationary
heat conduction are investigated in two one-dimensional models with conserved
momentum: Fermi-Pasta-Ulam (FPU) chain and chain of rotators (CR). These models
belong to different universality classes with respect to stationary heat
conduction. Direct numeric simulations reveal in both models a crossover from
oscillatory decay of short-wave perturbations of the temperature field to
smooth diffusive decay of the long-wave perturbations. Such behavior is
inconsistent with parabolic Fourier equation of the heat conduction. The
crossover wavelength decreases with increase of average temperature in both
models. For the FPU model the lowest order hyperbolic Cattaneo-Vernotte
equation for the non-stationary heat conduction is not applicable, since no
unique relaxation time can be determined.Comment: 4 pages, 5 figure
Towards a microscopic understanding of phonon heat conduction
Heat conduction by phonons is a ubiquitous process that incorporates a wide
range of physics and plays an essential role in applications ranging from space
power generation to LED lighting. Heat conduction has been studied for over two
hundred years, yet many microscopic aspects of heat conduction have remained
unclear in most crystalline solids, including which phonons carry heat and how
natural and artificial structures scatter specific phonons. Fortunately, recent
advances in both computation and experiment are enabling an unprecedented
microscopic view of thermal transport by phonons. In this topical review, we
provide an overview of these methods, the insights they are providing, and
their impact on the science and engineering of heat conduction
Emergence of non-Fourier hierarchies
The non-Fourier heat conduction phenomenon on room temperature is analyzed
from various aspects. The first one shows its experimental side, in what form
it occurs and how we treated it. It is demonstrated that the Guyer-Krumhansl
equation can be the next appropriate extension of Fourier's law for room
temperature phenomena in modeling of heterogeneous materials. The second
approach provides an interpretation of generalized heat conduction equations
using a simple thermomechanical background. Here, Fourier heat conduction is
coupled to elasticity via thermal expansion, resulting in a particular
generalized heat equation for the temperature field. Both of the aforementioned
approaches show the size dependency of non-Fourier heat conduction. Finally, a
third approach is presented, called pseudo-temperature modeling. It is shown
that non-Fourier temperature history can be produced by mixing different
solutions of Fourier's law. That kind of explanation indicates the
interpretation of underlying heat conduction mechanics behind non-Fourier
phenomena
Information filtering via biased heat conduction
Heat conduction process has recently found its application in personalized
recommendation [T. Zhou \emph{et al.}, PNAS 107, 4511 (2010)], which is of high
diversity but low accuracy. By decreasing the temperatures of small-degree
objects, we present an improved algorithm, called biased heat conduction (BHC),
which could simultaneously enhance the accuracy and diversity. Extensive
experimental analyses demonstrate that the accuracy on MovieLens, Netflix and
Delicious datasets could be improved by 43.5%, 55.4% and 19.2% compared with
the standard heat conduction algorithm, and the diversity is also increased or
approximately unchanged. Further statistical analyses suggest that the present
algorithm could simultaneously identify users' mainstream and special tastes,
resulting in better performance than the standard heat conduction algorithm.
This work provides a creditable way for highly efficient information filtering.Comment: 4 pages, 3 figure
The evolution of interstellar clouds in a streaming hot plasma including heat conduction
To examine the evolution of giant molecular clouds in the stream of a hot
plasma we performed two-dimensional hydrodynamical simulations that take full
account of self-gravity, heating and cooling effects and heat conduction by
electrons. We use the thermal conductivity of a fully ionized hydrogen plasma
proposed by Spitzer and a saturated heat flux according to Cowie & McKee in
regions where the mean free path of the electrons is large compared to the
temperature scaleheight. Significant structural and evolutionary differences
occur between simulations with and without heat conduction. Dense clouds in
pure dynamical models experience dynamical destruction by Kelvin-Helmholtz (KH)
instability. In static models heat conduction leads to evaporation of such
clouds. Heat conduction acting on clouds in a gas stream smooths out steep
temperature and density gradients at the edge of the cloud because the
conduction timescale is shorter than the cooling timescale. This diminishes the
velocity gradient between the streaming plasma and the cloud, so that the
timescale for the onset of KH instabilities increases, and the surface of the
cloud becomes less susceptible to KH instabilities. The stabilisation effect of
heat conduction against KH instability is more pronounced for smaller and less
massive clouds. As in the static case more realistic cloud conditions allow
heat conduction to transfer hot material onto the cloud's surface and to mix
the accreted gas deeper into the cloud.Comment: 19 pages, 12 figures, accepted in Astronomy and Astrophysic
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