2,341 research outputs found
On classification of Poisson vertex algebras
We describe a conjectural classification of Poisson vertex algebras of CFT
type and of Poisson vertex algebras in one differential variable (= scalar
Hamiltonian operators)
Seasonal variations in Greenland Ice Sheet motion : Inland extent and behaviour at higher elevations
Peer reviewedPreprin
Minimum dissipation principle in stationary non equilibrium states
We generalize to non equilibrium states Onsager's minimum dissipation
principle. We also interpret this principle and some previous results in terms
of optimal control theory. Entropy production plays the role of the cost
necessary to drive the system to a prescribed macroscopic configuration
Quantitative analysis of Clausius inequality
In the context of driven diffusive systems, for thermodynamic transformations
over a large but finite time window, we derive an expansion of the energy
balance. In particular, we characterize the transformations which minimize the
energy dissipation and describe the optimal correction to the quasi-static
limit. Surprisingly, in the case of transformations between homogeneous
equilibrium states of an ideal gas, the optimal transformation is a sequence of
inhomogeneous equilibrium states.Comment: arXiv admin note: text overlap with arXiv:1404.646
Large deviation approach to non equilibrium processes in stochastic lattice gases
We present a review of recent work on the statistical mechanics of non
equilibrium processes based on the analysis of large deviations properties of
microscopic systems. Stochastic lattice gases are non trivial models of such
phenomena and can be studied rigorously providing a source of challenging
mathematical problems. In this way, some principles of wide validity have been
obtained leading to interesting physical consequences.Comment: Extended version of the lectures given by G. Jona-Lasinio at the 9th
Brazilian school of Probability, August 200
On the long range correlations of thermodynamic systems out of equilibrium
Experiments show that macroscopic systems in a stationary nonequilibrium
state exhibit long range correlations of the local thermodynamic variables. In
previous papers we proposed a Hamilton-Jacobi equation for the nonequilibrium
free energy as a basic principle of nonequilibrium thermodynamics. We show here
how an equation for the two point correlations can be derived from the
Hamilton-Jacobi equation for arbitrary transport coefficients for dynamics with
both external fields and boundary reservoirs. In contrast with fluctuating
hydrodynamics, this approach can be used to derive equations for correlations
of any order. Generically, the solutions of the equation for the correlation
functions are non-trivial and show that long range correlations are indeed a
common feature of nonequilibrium systems. Finally, we establish a criterion to
determine whether the local thermodynamic variables are positively or
negatively correlated in terms of properties of the transport coefficients.Comment: 4 page
Macroscopic current fluctuations in stochastic lattice gases
We study current fluctuations in lattice gases in the macroscopic limit
extending the dynamic approach to density fluctuations developed in previous
articles. More precisely, we derive large deviation estimates for the
space--time fluctuations of the empirical current which include the previous
results. Large time asymptotic estimates for the fluctuations of the time
average of the current, recently established by Bodineau and Derrida, can be
derived in a more general setting. There are models where we have to modify
their estimates and some explicit examples are introduced.Comment: 4 pages, LaTeX, Changed conten
Large deviations of the empirical current in interacting particle systems
We study current fluctuations in lattice gases in the hydrodynamic scaling
limit. More precisely, we prove a large deviation principle for the empirical
current in the symmetric simple exclusion process with rate functional I. We
then estimate the asymptotic probability of a fluctuation of the average
current over a large time interval and show that the corresponding rate
function can be obtained by solving a variational problem for the functional I.
For the symmetric simple exclusion process the minimizer is time independent so
that this variational problem can be reduced to a time independent one. On the
other hand, for other models the minimizer is time dependent. This phenomenon
is naturally interpreted as a dynamical phase transition.Comment: 26 page
Flood-risk assessment and hazard mitigation mesures : case studies and lessons learnt in Italy
The effect of climate change and the growing world population are together increaing both the chance of flooding and the consequences.
In Italy , in the wake of the floods that plagued the northen part of the country in the fifties and sixties ,a process was set in motion aimed at developing a new integrated approach to water management, at the catchment level,suitable for coping with water related disasters.In this context,three case-studies of flood risk management and hazard assessment are described
Liquid phase epitaxy and optical investigation of KYb(WO4)2 thin layers
In recent years, Yb3+ has attracted much attention as an activating ion because of its small quantum defect for laser emission from 2F5/2 to 2F7/2 at ~1.03 ”m [1], which provides high efficiency and reduced heat generation. Of high practical interest is the thin-disk laser concept [2], which possesses a tremendous advantage over rod lasers because of its axial-cooling approach and consequent weak thermal lensing and good beam quality.\ud
A promising material for Yb3+ thin-disk lasers is KYb(WO4)2 (KYbW) [3]. It can be grown from high-temperature solutions [4]. Nevertheless, the growth of high-quality, single-crystalline layers with thickness in the range of the absorption length of ~13 ”m at 981 nm has as yet not been reported. A suitable substrate material is KY(WO4)2 (KYW), but the relatively large differences in the thermal expansion coefficients between KYW and KYbW along the [100], [001], and especially [010] directions [5] favor low temperatures for the hetero-epitaxial growth.\ud
For the first time, we demonstrate liquid phase epitaxy (LPE) of KYbW layers. The layers were grown at start temperatures as low as 520°C, which is favorable in order to decrease the thermal stresses due to the differences in the thermal expansion coefficients of substrate and layer. Moreover, the choice of [010]-oriented substrates bypasses the large difference in the thermal expansion coefficient along the [010] direction. KY1-xYbx(WO4)2 layers with varying x = 0.03-1.00 were grown by LPE. The chloride solvent consisted of the eutectic composition [6] 24.4 mol.% KCl, 30.4 mol.% NaCl, and 42.2 mol.% CsCl. The growth temperature spanned the range from 580 to 500°C and the cooling rate was 0.67-1.00 Kh-1. Crack-free, transparent KYbW layers were grown on (010) substrates.\ud
Spectroscopic investigations have shown that the lifetime of ~250 ”s measured in our LPE-grown KYbW layers is dominated by radiative decay and is very similar to that measured in top-seeded-solution-grown bulk samples [4]. Fast energy migration among the Yb3+ ions and energy transfer to small amounts of Tm3+ and Er3+ ions present in the YbCl3 reagent lead to visible upconversion luminescence in the layers under 981-nm excitation.\ud
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[1] T.Y. Fan, IEEE J. Quantum Electron. 29, 1457 (1993).\ud
[2] A. Giesen, H. HĂŒgel, A. Voss, K. Wittig, U. Brauch, H. Opower, Appl. Phys. B 58, 365 (1994).\ud
[3] P. Klopp, U. Griebner, V. Petrov, X. Mateos, M.A. Bursukova, M.C. Pujol, R. SolĂ©, J. GavaldĂ , M. AguilĂł, F. GĂŒell, J. Massons, T. Kirilov, F. DĂaz, Appl. Phys. B 74, 185 (2002).\ud
[4] M.C. Pujol, M.A. Bursukova, F. GĂŒell, X. Mateos, R. SolĂ©, J. GavaldĂ , M. AguilĂł, J. Massons, F. DĂaz, P. Klopp, U. Griebner, V. Petrov, Phys. Rev. B 65, 165121 (2002).\ud
[5] M.C. Pujol, X. Mateos, R. SolĂ©, J. Massons, J. GavaldĂ , F. DĂaz, M. AguilĂł, Mater. Sci. Forum 378-381, 710 (2001).\ud
[6] D. Ehrentraut, M. Pollnau, S. KĂŒck, Appl. Phys. B 75, 59 (2002)
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