621 research outputs found
On the definition of temperature in FPU systems
It is usually assumed, in classical statistical mechanics, that the
temperature should coincide, apart from a suitable constant factor, with the
mean kinetic energy of the particles. We show that this is not the case for
\FPU systems, in conditions in which energy equipartition between the modes is
not attained. We find that the temperature should be rather identified with the
mean value of the energy of the low frequency modes.Comment: 12 pages, 4 Figure
FPU phenomenon for generic initial data
The well known FPU phenomenon (lack of attainment of equipartition of the
mode--energies at low energies, for some exceptional initial data) suggests
that the FPU model does not have the mixing property at low energies. We give
numerical indications that this is actually the case. This we show by computing
orbits for sets of initial data of full measure, sampled out from the
microcanonical ensemble by standard Montecarlo techniques. Mixing is tested by
looking at the decay of the autocorrelations of the mode--energies, and it is
found that the high--frequency modes have autocorrelations that tend instead to
positive values. Indications are given that such a nonmixing property survives
in the thermodynamic limit. It is left as an open problem whether mixing
obtains within time--scales much longer than the presently available ones
A New Double Glass-Steel Roof for an Auditorium in Cuneo
A new glass-steel roof for an auditorium of the “ex Sala Contrattazioni” in Cuneo(I) was built in 2009, with a design resulted winner of an architectural concourse.The construction, despite the small dimension, is the result of a design process thatinvolved many interdisciplinary professionals, from architectural conception to theconstruction phase. The main structure has a non-conventional behavior and thesteel girders support the curved glass panes with point devices. This article offersan overview of the design criteria, news on technological solutions, and unusualconstruction methods applied to this particular application
Energy Storage in a Hamiltonian System in Partial Contact with a Heat Bath
To understand the mechanism allowing for the long-term storage of excess
energy in proteins, we study a Hamiltonian system consisting of several coupled
pendula in partial contact with a heat bath. It is found that energy storage is
possible when the motion of each pendulum switches between oscillatory
(vibrational) and rotational (phase-slip) modes. The storage time increases
almost exponentially to the square root of the injected energy. The relevance
of our mechanism to protein motors is discussed.Comment: 8 pages, 4 figures, to appear in J.Phys.Soc.Jp
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