A phenomenological approach to normal form modeling: a case study in laser induced nematodynamics

An experimental setting for the polarimetric study of optically induced dynamical behavior in nematic liquid crystal films has allowed to identify most notably some behavior which was recognized as gluing bifurcations leading to chaos. This analysis of the data used a comparison with a model for the transition to chaos via gluing bifurcations in optically excited nematic liquid crystals previously proposed by G. Demeter and L. Kramer. The model of these last authors, proposed about twenty years before, does not have the central symmetry which one would expect for minimal dimensional models for chaos in nematics in view of the time series. What we show here is that the simplest truncated normal forms for gluing, with the appropriate symmetry and minimal dimension, do exhibit time signals that are embarrassingly similar to the ones found using the above mentioned experimental settings. The gluing bifurcation scenario itself is only visible in limited parameter ranges and substantial aspect of the chaos that can be observed is due to other factors. First, out of the immediate neighborhood of the homoclinic curve, nonlinearity can produce expansion leading to chaos when combined with the recurrence induced by the homoclinic behavior. Also, pairs of symmetric homoclinic orbits create extreme sensitivity to noise, so that when the noiseless approach contains a rich behavior, minute noise can transform the complex damping into sustained chaos. Leonid Shil'nikov taught us that combining global considerations and local spectral analysis near critical points is crucial to understand the phenomenology associated to homoclinic bifurcations. Here this helps us construct a phenomenological approach to modeling experiments in nonlinear dissipative contexts.Comment: 25 pages, 9 figure

Pattern forming instability induced by light in pure and dye-doped nematic liquid crystals

We study theoretically the instabilities induced by a linearly polarized ordinary light wave incident at a small oblique angle on a thin layer of homeotropically oriented nematic liquid crystal with special emphasis on the dye-doped case. The spatially periodic Hopf bifurcation that occurs as the secondary instability after the stationary Freedericksz transition is analyzed.Comment: 8 pages, 7 figures, LaTeX, accepted to Phys. Rev.

Electromagnetic trapping of chiral molecules: orientational effects of the irradiating beam

The photonic interaction generally responsible for the electromagnetic trapping of molecules is forward-Rayleigh scattering, a process that is mediated by transition electric dipoles connecting the ground electronic state and virtual excited states. Higher order electric and magnetic multipole contributions to the scattering amplitude are usually negligible. However, on consideration of chiral discrimination effects (in which an input light of left-handed circular polarization can present different observables compared to right-handed polarization, or molecules of opposite enantiomeric form respond differently to a set circular polarization), the mechanism must be extended to specifically accommodate transition magnetic dipoles. Moreover, it is important to account for the fact that chiral molecules are necessarily non-spherical, so that their interactions with a laser beam will have an orientational dependence. Using quantum electrodynamics, this article quantifies the extent of the energetic discrimination that arises when chiral molecules are optically trapped, placing particular emphasis on the orientational effects of the trapping beam. An in-depth description of the intricate ensemble-weighted method used to incorporate the latter is presented. It is thus shown that, when a mixture of molecular enantiomers is irradiated by a continuous beam of circularly polarized light, a difference arises in the relative rates of migration of each enantiomer in and out of the most intense regions of the beam. In consequence, optical trapping can be used as a means of achieving enantiomer separation

Fonti antiche sui fiumi. Il racconto multimediale nel Museo Consentia Itinera tra ricerca scientifica e nuove forme di comunicazione e divulgazione / Ancient sources on the rivers. The multimedia story in the Museum Consentia Itinera between scientific research and new forms of communication and dissemination

Il saggio intende chiarire il valore della tecnologia digitale applicata in ambito museale nel trasferimento e nella comunicazione dei contenuti scientifici rivolti alla collettività, pur nella varietà dei pubblici, attraverso il caso di studio del Museo multimediale Consentia Itinera, istituito dalla Fondazione Attilio ed Elena Giuliani nel novembre 2017. Basato sulla letteratura su fiumi e culture fluviali studiata per la realizzazione di alcune sale immersive del museo, il testo procede lungo tre direzioni: dapprima viene proposta una rilettura sintetica delle fonti antiche sul fiume Krathis che è stato celebrato nei versi di Eliano, Strabone, Euripide e Ovidio e che è protagonista dello storytelling in Consentia Itinera nonché in numerose opere degli artisti  protagonisti  delle  Residenze  Artistiche  BoCS  Art  ideate  dal Comune di Cosenza dal 2015; in secondo luogo si cerca di chiarire come il museo multimediale restituisca le fonti antiche alla comunità nel rispetto del rigore metodologico e della coerenza scientifica e, infine, si evidenzia l’importante plus valore scientifico e divulgativo seguito dal Museo Consentia Itinera con una pratica museale permanente. Nel testo si cerca inoltre di esporre le nuove competenze scientifiche ed emotive che il museo offre al pubblico con varie soluzioni tecnologiche.This essay want to clarify the value of digital technologies in the museums for the promotion and communication of thescientific research to the communities. As a case study the Multimedial Museum Consentia Itinera founded in November 2017 thanks to Attilio and Elena Giuliani Foundation, in Cosenza. The work will proceed in three directions and  it is based on literature about rivers and rivers cultures studied for the realization of this museum. In the first paragraph we propose a syntheticrereading of the ancients sources about the river Krathis which was celebrated in famous verses of Eliano, Strabone, Euripide andOvidio and which is the protagonist of the artworks of the artists living in Cosenza, during the Artistic Residences BoCS Art from 2015. Secondly we try to explane how Consentia Itinera returns the ancients sources to the community while respectingmethodological rigor and scientific coherence. At the end, we conclude highlighting the important “plus valore” both scientific and popular followed by the Museum Consentia Itinera with a permanent museum practice. In the text we try to exhibit the newscientific and emotional skills that the Museum offers to the publics with various technological solutions.

Polarization holograms allow highly efficient generation of complex light beams

We report a viable method to generate complex beams, such as the non-diffracting Bessel and Weber beams, which relies on the encoding of amplitude information, in addition to phase and polarization, using polarization holography. The holograms are recorded in polarization sensitive films by the interference of a reference plane wave with a tailored complex beam, having orthogonal circular polarizations. The high efficiency, the intrinsic achromaticity and the simplicity of use of the polarization holograms make them competitive with respect to existing methods and attractive for several applications. Theoretical analysis, based on the Jones formalism, and experimental results are shown