If you have studied thermodynamics in your life, you probably had to face with adiabatic pistons and their applications, and you probably know that one driving force for this topic has been the development of steam engines. But what happens when the dimensions of an adiabatic piston shrink down to a mesoscopic level ?

Here mesoscopic does not mean quantum mechanics, but the regime in which the mass of the piston is comparable with that of the gas, which, incidentally, seems to correspond to the typical scales of biophysics and bridges classical mechanics and quantum mechanical length scales. Crosignani and Di Porto (and little help by me) have pointed out that in this regime the fluctuations of the piston position are comparable to the piston size. As Capek and Sheehan have outlined in their book "Challenges to the Second Law Thermodynamics," this result raises serious doubts about the validity of the second law in the mesoscopic regime. Indeed, if on one hand we are not discovering a perpetuum mobile (because we are dealing with fluctuations), on the other hand "the entropy variation associated with these displacements are at odd with a standard corollary of the second law, namely" [Capek, Sheean,* ibid.*]

* A closed system in an equilibrium state, once an internal constraint is removed, eventually reaches a new equilibrium state characterized by a larger value of the entropy*

As a result, one can imagine a thermodynamic cycle which has the net effect of extracting work for its thermal surroundings (**).**

The adiabatic piston problem is continuosly attracting the interest of various researchers involved in thermodynamics, since 1965, and its extension to the mesoscopic realm is likely to play a role in thermodynamics of life and modern nano- and micro-devices as MEMS and NEMS technologies.

In this paper, we have deepened our analysis of the piston problem by comparing the cases of a diathermal piston and that of an adiabatic piston. Notably enough there is a remarkable difference between them: the adiabatic piston undergoes much larger fluctuactions (by a factor given by the square root of the ratio between the piston mass and the gas molecule mass). See cond-mat/0611323.

]]>The following is the Burgers-like equation derived for the shock wave in the fiber laser

]]>The effect is due to the fact that the velocity of a photon depends on the laser intensity. Because of the momentum conservation, also the velocity of an optically pushed object depends on the light intensity; hence the mechanical action of light can be all-optically controlled. This may be denoted to as ** the Nonlinear Balazs Block problem**.

By using this nonlinear optical effect it may be possible to design experiments in which objects are attracted or accelerated by short pulses by an amount determined by pulse energy, temporal duration and spectral content. This nonlinear mechanical action is due to a property common to any sufficiently transparent material, the optical Kerr effect, that is, an intensity dependent refractive index. Conti and Boyd consider the specific case of a thin membrane of graphene, which has a very pronounced optical Kerr effect, and predict that is may be deformed as an optical sail by light. This may have a variety of applications for laser propulsion, and for laser controlled shaping of surfaces.

The authors report a theoretical analysis, which is validated by first principles simulations of the 3D+1 nonlinear Maxwell equations by using High Performance Computing (HPC) facilities within the CINECA-ISCRA initiative.

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It is commonly accepted that the physics underlying the generation of giant oceanic RW is different from that of usual waves and that the triggering mechanism of RWs is not unique: linear effects (such as the focusing of independent wave trains) as well as the nonlinear amplification of noise may produce RWs.

In a paper published in Applied Physics Letters, Marco Leonetti and Claudio Conti use a spatial light modulator (SLM) to explore the possible speckle configurations generated by a random medium to generate and control a three-dimensional rogue wave.

They demonstrate that the SLM allows to select among all the possible realizations, the RW located at a user defined position in the shadow of the nearly totally reflecting obstacle. Moreover, by tuning the properties of the speckle pattern, the localization along the propagation axis can be controlled.

The picture below show the three-dimensional reconstruction of the observed rogue-wave.

]]>Edited by A. Adamatzky and Genaro J. Martinez, the book is entitled

part of the Series on Emergence, Complexity and Computation with artistic representations from simple mathematical models at the edge of physics and biology. The book contains a contribution by C. Conti on the Enlightened Game of Life.

The picture below shows the content of the book

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In a recent manuscript in arXiv, Marco Ornigotti, Leone di Mauro Villari, Alexander Szeimeit, and Claudio Conti study propagation invariant quantum X-waves with angular momentum. The adopted representation expresses the electromagnetic field as a quantum gas of weakly interacting bosons. The resulting spatio-temporal quantized light pulses are not subject to diffraction and dispersion, and are intrinsically resilient to disturbances in propagation. Spontaneous down-conversion generates squeezed X-waves useful for quantum protocols. Surprisingly the orbital angural momentum affects the squeezing angle, and a characteristic axicon aperture for maximal squeezing exists.

There results may boost the applications in free space of quantum optical transmission and multi-level quantum protocols, and may also be relevant for novel kinds of interferometers, as satellite-based gravitational wave detectors.

]]>The picture below shows a pictorial representation of the Gelfand triplet, the phase space of the Time Asymmetric Quantum Mechanics

]]>Leone Villari, Ewan Wright, Fabio Biancalana and Claudio Conti report on the possibility that all types of classical solitons may evaporate in the quantum regime. A paper in the arXiv contains the theory on the exact quantization of the nonlinear Schroedinger equation: solitons emit a blackbody radiation spectrum at a temperature given by the same formula of Hawking!

This result is intriguing. On one hand, because it represents the first theoretical prediction of the Hawking radiation in a fully nonlinear quantum field theory. The standard Hawking theory relies on the quantization of a linear field in a curved background. The theory may hence provide insights for a true quantum gravity based on the complete quantization of the Einstein-Hilbert equations.

On the other hand, the result is also important because the Hawking radiation from a quantum soliton may furnish a novel highly tunable quantum source with many possible applications.

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A key in soft-matter is self-organization and supra-molecular structuring, controlling these mechanisms will provide a variety of possibilities in terms of applications and fundamental studies. In this respect nonlinear optical processes in soft-matter seem to open novel roads, on one hand for investigating novel physical phenomena, on the other to fine tune and control soft-matter.

Laser-driven self-organization strongly affects laser propagation, and this feedback effect has been only recently considered in a couple of papers by us, also including complex structured soft-materials. However, if these approaches fill the gap while considering electrostrictive mechanisms and the corresponding nonlinear optical response in structured soft-matter, on the other hand they are based on a continuous description of SM, which is not expected to be valid when the dimension of the beam is comparable to that of the particles. This is exactly the opposite limit with respect to the longitudinal optical binding of an array of particles, for which various theoretical models have been reported.

In this respect the current theoretical situations is as follows: there is the theory of solitons and modulational instability that describes trapping of many particles within a continuous model, then there is the theory of optical binding that describes trapping of an array of particles (eventually including some particle-particle interaction).

There is hence the need for a comprehensive theoretical approach that accounts for both of these two limits and is able to take into account the landscape of soft-matter due to the particle-particle interaction and the way it is affected by external fields. However, the numerical simulations of the various self-organization processes in soft-matter is enormously complicated by the need of taking into account a full 3D environment and nonlinear effects. In addition soft-materials are typically characterized by complicated shapes that role out standard multiple scattering approaches, like Mie theory.

The use of modern parallel computational resources has opened the possibility to novel multidisciplinary approaches committing together molecular dynamics, for simulating soft-matter complex behaviour, and Time Domain Finite Difference Parallel Techniques, for solving the electromagnetic field dynamics.

Methodology

In a recent article some of us report on the first results on a fully-comprehensive ab-initio numerical analysis of laser propagation in a disordered medium.

A colloidal dispersion structure is obtained by a Molecular-Dynamics (MD) code, and a Maxwell's equations solver (FDTD) is used for the laser propagation. This approach has lead to the first ab-initio computation of the light diffusion constant, also including nonlinear effects, in quantitative agreement with experiments. By MD-FDTD it is possible to unveil, within a first-principle formulation, the interplay between the 3D structure of a complex material, its nonlinear response (eventually including light amplification) and the features of the transmitted laser pulses. By using this approach we are developing a comprehensive approach to the self-organization in the presence of an external field, while also including different particle-particle interaction potential and the feedback of the re-organization in the field dynamics.

* C. Conti, G. Ruocco, S. Trillo "Optical Spatial Solitons in Soft Matter" Phys. Rev. Lett. 95, 183902 (2005); C. Conti, N. Ghofraniha, G. Ruocco, S. Trillo "Laser beam filamentation in soft matter" Phys. Rev. Lett. 97, 123903 (2006) References added by Claudio Conti*

*C. Conti, L. Angelani and G. Ruocco "Light diffusion and localization in three-dimensional nonlinear disordered media" Phys. Rev. A 75, 033812 (2007)*

This is a toy model for investigating various field-driven complex systems and placing on a physical ground evolutionary schemes, which ascribe a leading role to the development of the eye. See also here.

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