1,542 research outputs found
The design of a thermal rectifier
The idea that one can build a solid-state device that lets heat flow more
easily in one way than in the other, forming a heat valve, is
counter-intuitive. However the design of a thermal rectifier can be easily
understood from the basic laws of heat conduction. Here we show how it can be
done. This analysis exhibits several ideas that could in principle be
implemented to design a thermal rectifier, by selecting materials with the
proper properties. In order to show the feasibility of the concept, we complete
this study by introducing a simple model system that meets the requirements of
the design
Experimental and theoretical studies of sequence effects on the fluctuation and melting of short DNA molecules
Understanding the melting of short DNA sequences probes DNA at the scale of
the genetic code and raises questions which are very different from those posed
by very long sequences, which have been extensively studied. We investigate
this problem by combining experiments and theory. A new experimental method
allows us to make a mapping of the opening of the guanines along the sequence
as a function of temperature. The results indicate that non-local effects may
be important in DNA because an AT-rich region is able to influence the opening
of a base pair which is about 10 base pairs away. An earlier mesoscopic model
of DNA is modified to correctly describe the time scales associated to the
opening of individual base pairs well below melting, and to properly take into
account the sequence. Using this model to analyze some characteristic sequences
for which detailed experimental data on the melting is available [Montrichok et
al. 2003 Europhys. Lett. {\bf 62} 452], we show that we have to introduce
non-local effects of AT-rich regions to get acceptable results. This brings a
second indication that the influence of these highly fluctuating regions of DNA
on their neighborhood can extend to some distance.Comment: To be published in J. Phys. Condensed Matte
Can we model DNA at the mesoscale ? Comment on: Fluctuations in the DNA double helix: A critical review
Comment on "Fluctuations in the DNA double helix: A critical review" by
Frank-Kamenetskii and Prakas
Bogomol'nyi solitons in a gauged sigma model
The scale invariance of the sigma model can be broken by gauging a
subgroup of the symmetry and including a Maxwell term for the
gauge field in the Lagrangian. Adding also a suitable potential one obtains a
field theory of Bogomol'nyi type with topological solitons. These solitons are
stable against rescaling and carry magnetic flux which can take arbitrary
values in some finite interval. The soliton mass is independent of the flux,
but the soliton size depends on it. However, dynamically changing the flux
requires infinite energy, so the flux, and hence the soliton size, remains
constant during time evolution.Comment: 10 pages, Latex, 2 postscript figure
Dependence of kinetic friction on velocity: Master equation approach
We investigate the velocity dependence of kinetic friction with a model which
makes minimal assumptions on the actual mechanism of friction so that it can be
applied at many scales provided the system involves multi-contact friction.
Using a recently developed master equation approach we investigate the
influence of two concurrent processes. First, at a nonzero temperature thermal
fluctuations allow an activated breaking of contacts which are still below the
threshold. As a result, the friction force monotonically increases with
velocity. Second, the aging of contacts leads to a decrease of the friction
force with velocity. Aging effects include two aspects: the delay in contact
formation and aging of a contact itself, i.e., the change of its
characteristics with the duration of stationary contact. All these processes
are considered simultaneously with the master equation approach, giving a
complete dependence of the kinetic friction force on the driving velocity and
system temperature, provided the interface parameters are known
Discreteness effects on soliton dynamics: a simple experiment
We present a simple laboratory experiment to illustrate some aspects of the
soliton theory in discrete lattices with a system that models the dynamics of
dislocations in a crystal or the properties of adsorbed atomic layers. The
apparatus not only shows the role of the Peierls-Nabarro potential but also
illustrates the hierarchy of depinning transitions and the importance of the
collective motion in mass transport.Comment: 9 pages, 4 Figures, to Appear in American Journal of Physic
- …