Elio Miraldi - Academia.edu (original) (raw)
Papers by Elio Miraldi
12th European Conf. on Thermophysical Properties, 1990
In order to study the relation between the ohmic resistance measured in a thin conducting ribbon ... more In order to study the relation between the ohmic resistance measured in a thin conducting ribbon and the length of a transversal cut, we employ a one-parameter deformed exponential and logarithm that were recently introduced in the framework of a generalized statistical mechanics. The analytical results have been compared with the data that was experimentally obtained and numerically computed with the boundary element method. Remarkably, the new deformed functions that interpolate between the standard functions and the power law functions, allow the best fit of the experimental data to be obtained for a wide range of the cut length.
Molecular Crystals and Liquid Crystals, 1982
ABSTRACT A simple method for measuring the elastic Frank constants of a nematic liquid crystal is... more ABSTRACT A simple method for measuring the elastic Frank constants of a nematic liquid crystal is described. The method consists in measuring the attenuation of a laser beam transmitted through the specimen as a function of the angle of incidence and making a best fitting by using the results of a theory developed in a previous paper.Some experimental results concerning MBBA liquid crystals are reported and discussed.
Journal de Physique, 1984
2014 Nous étudions la déformation statique d'un film nématique homéotrope au voisinage de la tran... more 2014 Nous étudions la déformation statique d'un film nématique homéotrope au voisinage de la transition de Freedericksz en fonction de l'intensité et de la direction du champ magnétique. Nous montrons qu'une technique interférométrique en incidence oblique permet de contrôler l'orthogonalité du champ magnétique et du directeur avec une précision de 0,01 degré et d'éliminer pratiquement cette source d'erreur dans les mesures de champ critique.
Il Nuovo Cimento B, 1981
ricevuto il 21 Luglio 1981) S u m m a r y .
Il Nuovo Cimento B, 1980
ABSTRACT A general optimal method for the measurement of viscoelastic constants of nematic liquid... more ABSTRACT A general optimal method for the measurement of viscoelastic constants of nematic liquid crystals by light scattering is given. It is shown that, under suitable scattering conditions, several causes of error, like the multiple-scattering effect, the light scattering by crystal defects and the necessity of changing the liquid-crystal alignment in some type of measurements can be removed. The theory allows us to relate the experimental results obtained in such optimal conditions with all the viscoelastic constants characterizing the nematic liquid crystal. Some experimental results are given which show the validity of the theory. They also extend the range of spectral power density measurements of the scattered light down to very low frequency (0.1 Hz) by the use of an oblique-incidence scattering geometry. Si propone un metodo generale ottimizzato per misurare le costanti viscoelastiche di cristalli liquidi nematici per mezzo dell'analisi della luce diffusa. Si dimostra che, in opportune condizioni sperimentali, possono essere evitate parecchie cause di errore, come l'effetto della diffusione multipla, la luce diffusa dai difetti del cristallo e la necessità di cambiare l'allineamento del cristallo liquido per effettuare le diverse misure. La teoria permette di porre in relazione i risultati sperimentali ottenuti in tali condizioni ottimali con tutte le costanti viscoelastiche che caratterizzano il cristallo liquido nematico. Si presentano alcuni dati sperimentali che confermano la validità della teoria. Essi inoltre estendono l'intervallo delle misure di densità spettrale della luce diffusa fino a frequenze bassissime (0.1 Hz) con l'uso di una geometria sperimentale con incidenza obliqua. Предлагается общий оптимальный метод для измерения упруговязких постоянных нематических жидких кристаллов с помощью рассеяния света. Показывается, что при определенных условиях некоторые причины, вызываюшие ошибки, такие как, многократное рассеяние, рассеяние света на дефектах кристалла и необходимость изменения ориентации жидкого кристалла в некотором типе измерений, могут быть устранены. Предложенная теория позволяет связать экспериментальные результаты, полученные при таких оптимальных условиях, с упрутовязкими постояннымы, характеризующими нематический жидкий кристалл. Приводятся некоторые экспериментальные результаты, которые показывают справедливость этой теории. Эти результаты обобщаются на спектральную область рассеянного света вплоть до очень низких частог (0.1 Гц), используя геометрию рассеяния при наклонном падении.
Japanese Journal of Applied Physics, 1984
ABSTRACT The general theory developed by the authors for the light propagation in cholesteric liq... more ABSTRACT The general theory developed by the authors for the light propagation in cholesteric liquid crystals has been applied to the analysis of the high resolution reflectance spectra measured in a monodomain sample, in various optical conditions and in a wide wavelength range by Takezoe et al. The dispersion relation for the refractive indices obtained by the same authors has been taken into account. The agreement between theory and experiment is excellent. The Oseen's optical model and the local uniaxiality of the medium are confirmed. The polarization properties of the first order Bragg reflection peaks and the general behaviour of the interference curves are related to the properties of the internal eigenmodes. A full explanation of the beat or swell structure of the interference fringes is given.
12th European Conf. on Thermophysical Properties, 1990
In order to study the relation between the ohmic resistance measured in a thin conducting ribbon ... more In order to study the relation between the ohmic resistance measured in a thin conducting ribbon and the length of a transversal cut, we employ a one-parameter deformed exponential and logarithm that were recently introduced in the framework of a generalized statistical mechanics. The analytical results have been compared with the data that was experimentally obtained and numerically computed with the boundary element method. Remarkably, the new deformed functions that interpolate between the standard functions and the power law functions, allow the best fit of the experimental data to be obtained for a wide range of the cut length.
Molecular Crystals and Liquid Crystals, 1982
ABSTRACT A simple method for measuring the elastic Frank constants of a nematic liquid crystal is... more ABSTRACT A simple method for measuring the elastic Frank constants of a nematic liquid crystal is described. The method consists in measuring the attenuation of a laser beam transmitted through the specimen as a function of the angle of incidence and making a best fitting by using the results of a theory developed in a previous paper.Some experimental results concerning MBBA liquid crystals are reported and discussed.
Journal de Physique, 1984
2014 Nous étudions la déformation statique d'un film nématique homéotrope au voisinage de la tran... more 2014 Nous étudions la déformation statique d'un film nématique homéotrope au voisinage de la transition de Freedericksz en fonction de l'intensité et de la direction du champ magnétique. Nous montrons qu'une technique interférométrique en incidence oblique permet de contrôler l'orthogonalité du champ magnétique et du directeur avec une précision de 0,01 degré et d'éliminer pratiquement cette source d'erreur dans les mesures de champ critique.
Il Nuovo Cimento B, 1981
ricevuto il 21 Luglio 1981) S u m m a r y .
Il Nuovo Cimento B, 1980
ABSTRACT A general optimal method for the measurement of viscoelastic constants of nematic liquid... more ABSTRACT A general optimal method for the measurement of viscoelastic constants of nematic liquid crystals by light scattering is given. It is shown that, under suitable scattering conditions, several causes of error, like the multiple-scattering effect, the light scattering by crystal defects and the necessity of changing the liquid-crystal alignment in some type of measurements can be removed. The theory allows us to relate the experimental results obtained in such optimal conditions with all the viscoelastic constants characterizing the nematic liquid crystal. Some experimental results are given which show the validity of the theory. They also extend the range of spectral power density measurements of the scattered light down to very low frequency (0.1 Hz) by the use of an oblique-incidence scattering geometry. Si propone un metodo generale ottimizzato per misurare le costanti viscoelastiche di cristalli liquidi nematici per mezzo dell'analisi della luce diffusa. Si dimostra che, in opportune condizioni sperimentali, possono essere evitate parecchie cause di errore, come l'effetto della diffusione multipla, la luce diffusa dai difetti del cristallo e la necessità di cambiare l'allineamento del cristallo liquido per effettuare le diverse misure. La teoria permette di porre in relazione i risultati sperimentali ottenuti in tali condizioni ottimali con tutte le costanti viscoelastiche che caratterizzano il cristallo liquido nematico. Si presentano alcuni dati sperimentali che confermano la validità della teoria. Essi inoltre estendono l'intervallo delle misure di densità spettrale della luce diffusa fino a frequenze bassissime (0.1 Hz) con l'uso di una geometria sperimentale con incidenza obliqua. Предлагается общий оптимальный метод для измерения упруговязких постоянных нематических жидких кристаллов с помощью рассеяния света. Показывается, что при определенных условиях некоторые причины, вызываюшие ошибки, такие как, многократное рассеяние, рассеяние света на дефектах кристалла и необходимость изменения ориентации жидкого кристалла в некотором типе измерений, могут быть устранены. Предложенная теория позволяет связать экспериментальные результаты, полученные при таких оптимальных условиях, с упрутовязкими постояннымы, характеризующими нематический жидкий кристалл. Приводятся некоторые экспериментальные результаты, которые показывают справедливость этой теории. Эти результаты обобщаются на спектральную область рассеянного света вплоть до очень низких частог (0.1 Гц), используя геометрию рассеяния при наклонном падении.
Japanese Journal of Applied Physics, 1984
ABSTRACT The general theory developed by the authors for the light propagation in cholesteric liq... more ABSTRACT The general theory developed by the authors for the light propagation in cholesteric liquid crystals has been applied to the analysis of the high resolution reflectance spectra measured in a monodomain sample, in various optical conditions and in a wide wavelength range by Takezoe et al. The dispersion relation for the refractive indices obtained by the same authors has been taken into account. The agreement between theory and experiment is excellent. The Oseen's optical model and the local uniaxiality of the medium are confirmed. The polarization properties of the first order Bragg reflection peaks and the general behaviour of the interference curves are related to the properties of the internal eigenmodes. A full explanation of the beat or swell structure of the interference fringes is given.