Barducci A.,CNR Institute of Applied Physics Nello Carrara
Journal of the Optical Society of America B: Optical Physics | Year: 2011
We describe a specific bandpass sampling procedure that provides high efficiency for interferogram sampling. This new approach is able to mitigate the important radiometric and noise disadvantages of Fourier transform spectrometry that recent theoretical investigations have pointed out. Proof of concept is given using simulations and measurements performed with a Sagnac triangular interferometer. Adopting an information-theoretic approach to spectrometry, we demonstrate the existence of important limitations to the radiometric efficiency achieved by any interferential or dispersive multiplex spectrometers. We find an extension to optics of the well-known data processing inequality, confirming that the Fellgett (multiplex) advantage is an inappropriate expectation. We give evidence of radiometric disadvantages implicit in the coded aperture architecture typical of compressive sensing. © 2011 Optical Society of America.
Siano S.,CNR Institute of Applied Physics Nello Carrara |
Salimbeni R.,CNR Institute of Applied Physics Nello Carrara
Accounts of Chemical Research | Year: 2010
Laser ablation has found numerous applications in biomedical and industrial settings but has not spread as quickly as a means of cleaning artwork. In this Account, we report recent advances in the study and application of laser cleaning to the conservation of cultural heritage. We focus on the solution of representative cleaning problems of encrusted stones, metals, and wall paintings that were achieved through the optimization of laser pulse duration. We begin by introducing the basic mechanisms involved in the laser ablation of stratified materials and the criteria for preventing undesired side effects to the substrate and then briefly present case studies for each of these materials. Laser interaction effects are reviewed in a schematic way, with a concise overview of the physical models needed to support intuitive interpretations of the phenomenology observed, both in laboratory tests and in practical applications on important artifacts. This approach aims to provide keys of generalization that will favor the rigorous application of laser cleaning, repeatability of the successful results reported in this work, and further dissemination and acceptance of the technique. The topics treated examine the ablation mechanisms along with the efficiency, gradualness, selectivity, and effectiveness of the technique as a function of the pulse duration of neodymium laser systems and the operating conditions. Physical modeling and experimental evidence support the selection of pulse durations of between several tens of nanoseconds and several tens of microseconds, making it possible to minimize the risk of photothermal and photomechanical effects and maximize the selectivity of the ablation process. The sections dedicated to stones and metals also deal with the important problem of discoloration, which has significantly slowed the spread of the laser cleaning technique. The well-known problem of a yellowish appearance after laser cleaning is shown to be closely related to the ablation process; it can therefore be prevented by a suitable selection of irradiation parameters. The metal surfaces investigated are amalgam gilding, gold leaf gilding, and, for the first time, silver artifacts. We also describe the criteria used for applying laser ablation techniques to restoring unique masterpieces, such as Lorenzo Ghibertis Porta del Paradiso and Donatellos David. Furthermore, a novel and unusual cleaning approach for archaeological silver is reported. Based on underwater laser irradiation, it provides a way to prevent oxidative effects and amplify the photomechanical coupling to the hard, thick concretions that usually accompany archaeological pieces. Finally, the experimental extension of the laser cleaning approach to wall painting and its practical use in important restoration works is presented. The practical examples reveal a significant advance in perspective for the application, which was unthinkable until recently. In sum, this Account describes novel technological and methodological contributions of laser cleaning that are having a significant impact in the field of cultural heritage conservation. © 2010 American Chemical Society.
Muniz-Miranda M.,University of Florence |
Muniz-Miranda M.,CNR Institute of Applied Physics Nello Carrara
Journal of Raman Spectroscopy | Year: 2013
The adsorption of 4-nitroanisole on silver colloidal nanoparticles was investigated by surface-enhanced Raman spectroscopy (SERS). Actually, the chemical binding with a metal substrate may play a role in changing the electronic structure of this molecule, which can be considered a push-pull chromophore, because an internal charge-transfer occurs between methoxy and nitrogroup. A SERS signal could be detected only in chloride-activated silver colloids, but the spectrum recorded with green-light excitation was not related to adsorbed 4-nitroanisole, but to its azoderivative, formed by photoreduction of the nitrogroup on the surface of the silver substrate. Copyright © 2013 John Wiley & Sons, Ltd.
Chelli R.,University of Florence |
Chelli R.,CNR Institute of Applied Physics Nello Carrara
Journal of Chemical Theory and Computation | Year: 2010
In serial generalized-ensemble simulations, the sampling of a collective coordinate of a system is enhanced through non-Boltzmann weighting schemes. A popular version of such methods is certainly the simulated tempering technique, which is based on a random walk in temperature ensembles to explore the phase space more thoroughly. The most critical aspect of serial generalized-ensemble methods with respect to their parallel counterparts, such as replica exchange, is the difficulty of weight determination. Here we propose an adaptive approach to update the weights on the fly during the simulation. The algorithm is based on generalized forms of the Bennett acceptance ratio and of the free energy perturbation. It does not require intensive communication between processors and, therefore, is prone to be used in distributed computing environments with modest computational cost. We illustrate the method in a series of molecular dynamics simulations of a model system and compare its performances to two recent approaches, one based on adaptive Bayesian-weighted histogram analysis and the other based on initial estimates of weight factors obtained by potential energy averages. © 2010 American Chemical Society.
Toci G.,CNR Institute of Applied Physics Nello Carrara
Applied Physics B: Lasers and Optics | Year: 2012
This paper reports a new theoretical model for the evaluation of the results of the so-called pinhole method for the measurement of the upper level lifetime in doped optical materials exhibiting radiation trapping effects due to resonant reabsorption of the emitted fluorescence. The model correctly predicts that the fluorescence decay has a double exponential behavior with two time constants, with the shorter one near the intrinsic decay time of the upper level, with a correction depending on the effect of the short range reabsorption. As a consequence, a new method is proposed for the data analysis and the interpretation of the results with respect to the previous literature. © Springer-Verlag 2011.
Ceccherini S.,CNR Institute of Applied Physics Nello Carrara |
Ridolfi M.,University of Bologna
Atmospheric Chemistry and Physics | Year: 2010
The variance-covariance matrix (VCM) and the averaging kernel matrix (AKM) are widely used tools to characterize atmospheric vertical profiles retrieved from remote sensing measurements. Accurate estimation of these quantities is essential for both the evaluation of the quality of the retrieved profiles and for the correct use of the profiles themselves in subsequent applications such as data comparison, data assimilation and data fusion. We propose a new method to estimate the VCM and AKM of vertical profiles retrieved using the Levenberg-Marquardt iterative technique. We apply the new method to the inversion of simulated limb emission measurements. Then we compare the obtained VCM and AKM with those resulting from other methods already published in the literature and with accurate estimates derived using statistical and numerical estimators. The proposed method accounts for all the iterations done in the inversion and provides the most accurate VCM and AKM. Furthermore, it correctly estimates the VCM and the AKM also if the retrieval iterations are stopped when a physically meaningful convergence criterion is fulfilled, i.e. before achievement of the numerical convergence at machine precision. The method can be easily implemented in any Levenberg-Marquardt iterative retrieval scheme, either constrained or unconstrained, without significant computational overhead.
Chelli R.,University of Florence |
Chelli R.,CNR Institute of Applied Physics Nello Carrara
Journal of Chemical Theory and Computation | Year: 2012
Configurational freezing (J. Chem. Theory Comput.2011, 7, 582) is a method devised for steered Monte Carlo simulations aimed at improving free energy estimates via nonequilibrium work theorems (see Jarzynski in Phys. Rev. Lett.1997, 78, 2690 and Crooks in J. Stat. Phys.1998, 90, 1481). The basic idea is to limit the sampling to particles located in the region of space where dissipation occurs, while leaving the other particles fixed. Therefore, the method is based on the reasonable assumption that dissipation is a local phenomenon in single-molecule nonequilibrium processes, a statement which holds for many processes including, for example, folding of biopolymers and protein-ligand binding/unbinding. In this article, the configurational freezing approach, based on the sampling of particles located around hot-spot sites encompassing the high dissipation domain, is supplemented by the possibility of selecting such particles (for trial Monte Carlo moves) dependent on their distance from the hot spots. This is accomplished by exploiting an extension of the Owickis preferential sampling (J. Am. Chem. Soc.1977, 99, 7413) in the original configurational freezing machinery. The combined strategy is shown to improve the accuracy of free energy estimates in physically sound cases: the calculation of the water to methane relative hydration free energy and the calculation of the potentials of mean force of two solvated methane molecules and two solvated benzene molecules along the direction connecting the centers of mass. © 2012 American Chemical Society.
Santi E.,CNR Institute of Applied Physics Nello Carrara
International Journal of Remote Sensing | Year: 2010
Microwave radiometers operating from space are one of the most promising tools for soil, snow and vegetation monitoring, due to the sensitivity of the measured emission to surface features and to the extended and recursive Earth observation. However, these potentials are partially hampered by the coarse spatial resolution, which is of the order of tens of kilometres, especially at the lower frequencies. This paper describes the results obtained by using a simple algorithm for enhancing the spatial resolution of the spaceborne microwave radiometer at C-band. The algorithm is based on the smoothing filter-based intensity modulation technique (SFIM), applied to the Advanced Microwave Remote Scanning Radiometer-Earth Observing System (AMSR-E) data collected from some reference targets, including the Amazon river basin, Lake Victoria in Africa and the Antarctic plateau. © 2010 Taylor & Francis.
Ceccherini S.,CNR Institute of Applied Physics Nello Carrara
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2012
The optimal estimation method for the retrieval of atmospheric vertical profiles uses a priori information made of a profile and its covariance matrix. The underlying assumption is that the a priori profile has an averaging kernel matrix equal to the identity. The method is herewith generalized to the case that the a priori profile has a different averaging kernel matrix. The averaging kernel matrix of the a priori profile is properly taken into account in the cost function and a rigorous and more general solution for the optimal estimation method is derived. © 2012 Elsevier Ltd.
CNR Institute of Applied Physics Nello Carrara | Date: 2012-12-19
The present invention refers to a system for the support, positioning and orientation of at least one apparatus in the space particularly, but not exclusively, used in the furnishing industry, both interior and exterior, wherein the system (10) for the support, positioning and orientation of at least one apparatus (20) in the space comprises at least one bracket element (11) for fixing the system (10) to a surface, at least one first flange element (12) provided with means (13) for receiving the at least one apparatus (20), connection means (15, 17, 18) of the orientable type arranged between the at least one bracket element (11) and the first flange element (12) suitable for the orientation and positioning of the at least one apparatus (20) in the space according to a plurality of operating positions, the system (10) being characterised in that the connection means (15, 17, 18) of the orientable type comprise at least one arm-like connection element (15) provided with a first end (31), rotatably connected to the at least one bracket element (11), and a second end (32) also rotatably connected to the at least one first flange element (12), so as to allow the orientation and positioning of the at least one apparatus (20) in the space constrained to the at least one first flange element 12.