Bruno Crosignani - Academia.edu (original) (raw)
Papers by Bruno Crosignani
The limits of the Second Law of Thermodynamics, which reigns undisputed in the macroscopic world,... more The limits of the Second Law of Thermodynamics, which reigns undisputed in the macroscopic world, are investigated at the mesoscopic level, corresponding to spatial dimensions of a few microns. An extremely simple isolated system, modeled after Callen's adiabatic piston, [1] can, under appropriate conditions, be described as a self-organizing Brownian motor and shown to exhibit a perpetuum mobile behavior.
A detailed analysis of the adiabatic-piston problem reveals peculiar dynamical features that chal... more A detailed analysis of the adiabatic-piston problem reveals peculiar dynamical features that challenge the general belief that isolated systems necessarily reach a static equilibrium state. In particular, the fact that the piston behaves like a perpetuum mobile, i.e., it never stops but keeps wandering, undergoing sizable oscillations, around the position corresponding to maximum entropy, has remarkable implications on the entropy variations of the system and on the validity of the second law when dealing with systems of mesoscopic dimensions. Comment: 6 pages, 4 figures, First International Conference on Quantum Limits to the Second Law
The validity of the Second Law of thermodynamics, indisputable in the macroscopic world, is chall... more The validity of the Second Law of thermodynamics, indisputable in the macroscopic world, is challenged at the mesoscopic level: a mesoscopic isolated system, possessing spatial dimensions of the order of a few microns, is capable, as shown by a straightforward kinetic analysis, to exhibit a perpetuum mobile behavior associated with large negative variations of the Clausius entropy of the system. This violation of the Second Law is expedient for devising a cyclic process through which an isolated system can extract energy from a surrounding thermal bath.
We present a comparison between the random motion of an adiabatic and a diathermal piston sliding... more We present a comparison between the random motion of an adiabatic and a diathermal piston sliding in a perfect gas. In particular, their dynamical behaviour, if investigated by means of Langevin's approach, shows the amplitude of the adiabatic-piston random displacements around the equilibrium position to be much larger (by a factor (M/m)^(1/2), where M and m are the piston mass and the mass of the single gas molecule) than that of the diathermal piston. The origin of this intriguing difference, which is accounted for in the frame of Langevin's approach, is also explored in terms of a space-phase analysis.
NATO Science Series: B:, 2002
A series presenting the results of activities sponsored by the NATO Science Committee, which aims... more A series presenting the results of activities sponsored by the NATO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division
Journal of the Optical Society of America, 1978
Journal of the Optical Society of America, 1977
A coupled system of equations governing the propagation of a signal in a statistical ensemble of ... more A coupled system of equations governing the propagation of a signal in a statistical ensemble of multimode optical fibers is presented. It describes, besides the usual average modal powers, the evolution of the interference terms between the mode amplitudes and of the modal power fluctuations. Our procedure allows us to treat the general nonstationary nonmonochromatic case of an arbitrary signal fed into the lightguide by a source possessing a finite spectral bandwidth. The introduction of modal power fluctuations permits us to establish a theorem connecting the value of the modal power, averaged over the fiber ensemble, with the actual one concerning a single fiber. These two values coincide, in the polychromatic case, for large values of the fiber length, thus providing the main result of the paper, that is the justification of the statistical approach to the problem of propagation. Furthermore, the analysis of the interference terms presents evidence for the difference between the propagation of an amplitude-modulated and a frequency-modulated signal.
Journal of the Optical Society of America, 1982
The phase variations associated with the intensity-dependent part of the refractive index assume ... more The phase variations associated with the intensity-dependent part of the refractive index assume different values for the different propagation modes of an optical fiber. As a consequence, intensity fluctuations of the exciting source are converted into relative phase fluctuations, which give rise to an amplitude-dependent modal noise.
Physical review. A, Jan 15, 1988
... Page 2. 38 HAMILTONIAN DESCRIPTION OF NONLINEAR PROPAGATION. . . 4037 II. HAMILTONIAN FORMALI... more ... Page 2. 38 HAMILTONIAN DESCRIPTION OF NONLINEAR PROPAGATION. . . 4037 II. HAMILTONIAN FORMALISM The electromagnetic field propagating insidea mul-timode fiber can be written as modal amplitude. ... E(r,z, t)= QE(r)e ' " ' 4(z,t), n(r, ~)=n, (r, co)+nzI, (2) ...
Optics Communications, 2002
We present a formalism describing optical propagation in a homogeneous medium of a fully vectoria... more We present a formalism describing optical propagation in a homogeneous medium of a fully vectorial highly nonparaxial field, characterized by a waist smaller than the wavelength. The method allows us to derive an analytical expression for a field possessing an initial Gaussian transverse distribution of width w, in the extreme nonparaxial regime w < k, valid for propagation distances z J d, where d ¼ w 2 =k is the diffraction length. Ó
Optics and Photonics News, 2002
We present a conclusive answer to Bertrand's paradox, a long standing open issue in the basic phy... more We present a conclusive answer to Bertrand's paradox, a long standing open issue in the basic physical interpretation of probability. The paradox deals with the existence of mutually inconsistent results when looking for the probability that a chord, drawn at random in a circle, is longer than the side of an inscribed equilateral triangle. We obtain a unique solution by substituting chord drawing with the throwing of a straw of finite length L on a circle of radius R, thus providing a satisfactory operative definition of the associated experiment. The obtained probability turns out to be a function of the ratio L/R, as intuitively expected.
Springer Series in Optical Sciences, 2006
Optics and Photonics News, 1994
REFERENCES 1. M. Segev et al., "Spatial solitons in photorefractive media," Phy... more REFERENCES 1. M. Segev et al., "Spatial solitons in photorefractive media," Phys. Rev. Lett. 68, 923 (1992). 2. B. Crosignani et al., "Self-trapping of optical beams in photorefractive media," J. Opt. Soc. Am. B 10, 446 (1993). 3. G. Duree et al., "Observation of self-trapping ...
Journal of the Optical Society of America, 1982
A set of equations describing pulse propagation in multimode optical fibers in the presence of an... more A set of equations describing pulse propagation in multimode optical fibers in the presence of an intensity-dependent refractive index is derived by taking advantage of the coupled-mode theory usually employed for describing the influence of fiber imperfections on linear propagation. This approach takes into account in a natural way the role of the waveguide structure in terms of the propagation constants and the spatial configurations of the propagating modes and can be applied to the most general refractive-index distribution. The conditions under which soliton propagation and longitudinal self-confinement can be achieved are examined.
Optics and Photonics News, 1993
The limits of the Second Law of Thermodynamics, which reigns undisputed in the macroscopic world,... more The limits of the Second Law of Thermodynamics, which reigns undisputed in the macroscopic world, are investigated at the mesoscopic level, corresponding to spatial dimensions of a few microns. An extremely simple isolated system, modeled after Callen's adiabatic piston, [1] can, under appropriate conditions, be described as a self-organizing Brownian motor and shown to exhibit a perpetuum mobile behavior.
A detailed analysis of the adiabatic-piston problem reveals peculiar dynamical features that chal... more A detailed analysis of the adiabatic-piston problem reveals peculiar dynamical features that challenge the general belief that isolated systems necessarily reach a static equilibrium state. In particular, the fact that the piston behaves like a perpetuum mobile, i.e., it never stops but keeps wandering, undergoing sizable oscillations, around the position corresponding to maximum entropy, has remarkable implications on the entropy variations of the system and on the validity of the second law when dealing with systems of mesoscopic dimensions. Comment: 6 pages, 4 figures, First International Conference on Quantum Limits to the Second Law
The validity of the Second Law of thermodynamics, indisputable in the macroscopic world, is chall... more The validity of the Second Law of thermodynamics, indisputable in the macroscopic world, is challenged at the mesoscopic level: a mesoscopic isolated system, possessing spatial dimensions of the order of a few microns, is capable, as shown by a straightforward kinetic analysis, to exhibit a perpetuum mobile behavior associated with large negative variations of the Clausius entropy of the system. This violation of the Second Law is expedient for devising a cyclic process through which an isolated system can extract energy from a surrounding thermal bath.
We present a comparison between the random motion of an adiabatic and a diathermal piston sliding... more We present a comparison between the random motion of an adiabatic and a diathermal piston sliding in a perfect gas. In particular, their dynamical behaviour, if investigated by means of Langevin's approach, shows the amplitude of the adiabatic-piston random displacements around the equilibrium position to be much larger (by a factor (M/m)^(1/2), where M and m are the piston mass and the mass of the single gas molecule) than that of the diathermal piston. The origin of this intriguing difference, which is accounted for in the frame of Langevin's approach, is also explored in terms of a space-phase analysis.
NATO Science Series: B:, 2002
A series presenting the results of activities sponsored by the NATO Science Committee, which aims... more A series presenting the results of activities sponsored by the NATO Science Committee, which aims at the dissemination of advanced scientific and technological knowledge, with a view to strengthening links between scientific communities. The series is published by an international board of publishers in conjunction with the NATO Scientific Affairs Division
Journal of the Optical Society of America, 1978
Journal of the Optical Society of America, 1977
A coupled system of equations governing the propagation of a signal in a statistical ensemble of ... more A coupled system of equations governing the propagation of a signal in a statistical ensemble of multimode optical fibers is presented. It describes, besides the usual average modal powers, the evolution of the interference terms between the mode amplitudes and of the modal power fluctuations. Our procedure allows us to treat the general nonstationary nonmonochromatic case of an arbitrary signal fed into the lightguide by a source possessing a finite spectral bandwidth. The introduction of modal power fluctuations permits us to establish a theorem connecting the value of the modal power, averaged over the fiber ensemble, with the actual one concerning a single fiber. These two values coincide, in the polychromatic case, for large values of the fiber length, thus providing the main result of the paper, that is the justification of the statistical approach to the problem of propagation. Furthermore, the analysis of the interference terms presents evidence for the difference between the propagation of an amplitude-modulated and a frequency-modulated signal.
Journal of the Optical Society of America, 1982
The phase variations associated with the intensity-dependent part of the refractive index assume ... more The phase variations associated with the intensity-dependent part of the refractive index assume different values for the different propagation modes of an optical fiber. As a consequence, intensity fluctuations of the exciting source are converted into relative phase fluctuations, which give rise to an amplitude-dependent modal noise.
Physical review. A, Jan 15, 1988
... Page 2. 38 HAMILTONIAN DESCRIPTION OF NONLINEAR PROPAGATION. . . 4037 II. HAMILTONIAN FORMALI... more ... Page 2. 38 HAMILTONIAN DESCRIPTION OF NONLINEAR PROPAGATION. . . 4037 II. HAMILTONIAN FORMALISM The electromagnetic field propagating insidea mul-timode fiber can be written as modal amplitude. ... E(r,z, t)= QE(r)e ' " ' 4(z,t), n(r, ~)=n, (r, co)+nzI, (2) ...
Optics Communications, 2002
We present a formalism describing optical propagation in a homogeneous medium of a fully vectoria... more We present a formalism describing optical propagation in a homogeneous medium of a fully vectorial highly nonparaxial field, characterized by a waist smaller than the wavelength. The method allows us to derive an analytical expression for a field possessing an initial Gaussian transverse distribution of width w, in the extreme nonparaxial regime w < k, valid for propagation distances z J d, where d ¼ w 2 =k is the diffraction length. Ó
Optics and Photonics News, 2002
We present a conclusive answer to Bertrand's paradox, a long standing open issue in the basic phy... more We present a conclusive answer to Bertrand's paradox, a long standing open issue in the basic physical interpretation of probability. The paradox deals with the existence of mutually inconsistent results when looking for the probability that a chord, drawn at random in a circle, is longer than the side of an inscribed equilateral triangle. We obtain a unique solution by substituting chord drawing with the throwing of a straw of finite length L on a circle of radius R, thus providing a satisfactory operative definition of the associated experiment. The obtained probability turns out to be a function of the ratio L/R, as intuitively expected.
Springer Series in Optical Sciences, 2006
Optics and Photonics News, 1994
REFERENCES 1. M. Segev et al., "Spatial solitons in photorefractive media," Phy... more REFERENCES 1. M. Segev et al., "Spatial solitons in photorefractive media," Phys. Rev. Lett. 68, 923 (1992). 2. B. Crosignani et al., "Self-trapping of optical beams in photorefractive media," J. Opt. Soc. Am. B 10, 446 (1993). 3. G. Duree et al., "Observation of self-trapping ...
Journal of the Optical Society of America, 1982
A set of equations describing pulse propagation in multimode optical fibers in the presence of an... more A set of equations describing pulse propagation in multimode optical fibers in the presence of an intensity-dependent refractive index is derived by taking advantage of the coupled-mode theory usually employed for describing the influence of fiber imperfections on linear propagation. This approach takes into account in a natural way the role of the waveguide structure in terms of the propagation constants and the spatial configurations of the propagating modes and can be applied to the most general refractive-index distribution. The conditions under which soliton propagation and longitudinal self-confinement can be achieved are examined.
Optics and Photonics News, 1993