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Search Results: 1 - 10 of 144496 matches for " F. Parmigiani "
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Ultrafast laser pulses to detect and generate fast thermo-mechanical transients in matter
C. Giannetti,F. Banfi,D. Nardi,G. Ferrini,F. Parmigiani
Physics , 2009, DOI: 10.1109/JPHOT.2009.2025050
Abstract: The use of femtosecond laser pulses to impulsively excite thermal and mechanical transients in matter has led, in the last years, to the development of picosecond acoustics. Recently, the pump-probe approach has been applied to nano-engineered materials to optically generate and detect acoustic waves in the GHz-THz frequency range. In this paper, we review the latest advances on ultrafast generation and detection of thermal gradients and pseudo-surface acoustic waves in two-dimensional lattices of metallic nanostructures. Comparing the experimental findings to the numeric analysis of the full thermo-mechanical problem, these materials emerge as model systems to investigate both the mechanical and thermal energy transfer at the nanoscale. The sensitivity of the technique to the nanostructures mass and shape variations, coupled to the phononic crystal properties of the lattices opens the way to a variety of applications ranging from hypersonic waveguiding to mass sensors with femtosecond time-resolution.ens the way to a variety of applications ranging from hypersonic waveguiding to mass sensors with femtosecond time-resolution.
Intersubjetividad y autorreferencialidad en la teoría ética de C.S. Nino
Parmigiani, Matías;
Diánoia , 2011,
Abstract: in el constructivismo ético, c.s. nino pointed out that "discussion and inter-subjective decision is the most trustable procedure when trying to arrive to moral truth". this epistemic thesis about moral knowledge clearly embraces a political assessment: in order to succeed at impartially satisfying the interests of everyone in a community, "the interchange of ideas and each person's necessity to justify in the face of the others" play a pivotal role. on the contrary, when the task in question is related to the auto-referential dimension of morality, the derivations of that thesis in nino's work become certainly unclear. by attempting to overstep this bound, i will explore in the present paper the connection that is supposed to exist between the social practice of moral communication and the discovery and justification of the auto-referential principles of behavior.
Intersubjetividad y autorreferencialidad en la teoría ética de C.S. Nino Intersubjetivity and Auto-Referentiality in C.S. Nino's Ethical Theory
Matías Parmigiani
Diánoia , 2011,
Abstract: En El constructivismo ético, C.S. Nino sostuvo que "la discusión y la decisión intersubjetiva es el procedimiento más confiable de acceso a la verdad moral". Esta tesis epistémica sobre el conocimiento moral posee claramente un costado político: a los fines de atender imparcialmente los intereses de todos los integrantes de una comunidad, "el intercambio de ideas y la necesidad de justificarse frente a los demás" acrecientan las posibilidades de éxito. Por el contrario, bastante menos claro resulta determinar en la obra de Nino las derivaciones de semejante tesis en lo tocante a la dimensión autorreferencial de la moralidad. Intentando llenar este vacío, exploraré en el presente trabajo las relaciones que deberían mediar entre la práctica social del discurso moral y el descubrimiento y la justificación de los ideales de conducta autorreferenciales. In El constructivismo ético, C.S. Nino pointed out that "discussion and inter-subjective decision is the most trustable procedure when trying to arrive to moral truth". This epistemic thesis about moral knowledge clearly embraces a political assessment: in order to succeed at impartially satisfying the interests of everyone in a community, "the interchange of ideas and each person's necessity to justify in the face of the others" play a pivotal role. On the contrary, when the task in question is related to the auto-referential dimension of morality, the derivations of that thesis in Nino's work become certainly unclear. By attempting to overstep this bound, I will explore in the present paper the connection that is supposed to exist between the social practice of moral communication and the discovery and justification of the auto-referential principles of behavior.
Ab-initio calculation of all-optical time-resolved calorimetry of nanosized systems: Evidence of nanosecond-decoupling of electron and phonon temperatures
F. Banfi,F. Pressacco,B. Revaz,C. Giannetti,D. Nardi,G. Ferrini,F. Parmigiani
Physics , 2009, DOI: 10.1103/PhysRevB.81.155426
Abstract: The thermal dynamics induced by ultrashort laser pulses in nanoscale systems, i.e. all-optical time-resolved nanocalorimetry is theoretically investigated from 300 to 1.5 K. We report ab-initio calculations describing the temperature dependence of the electron-phonon interactions for Cu nanodisks supported on Si. The electrons and phonons temperatures are found to decouple on the ns time scale at 10 K, which is two orders of magnitude in excess with respect to that found for standard low-temperature transport experiments. By accounting for the physics behind our results we suggest an alternative route for overhauling the present knowledge of the electron-phonon decoupling mechanism in nanoscale systems by replacing the mK temperature requirements of conventional experiments with experiments in the time-domain.
Pseudo-surface acoustic waves in hypersonic surface phononic crystals
D. Nardi,F. Banfi,C. Giannetti,B. Revaz,G. Ferrini,F. Parmigiani
Physics , 2009, DOI: 10.1103/PhysRevB.80.104119
Abstract: We present a theoretical framework allowing to properly address the nature of surface-like eigenmodes in a hypersonic surface phononic crystal, a composite structure made of periodic metal stripes of nanometer size and periodicity of 1 micron, deposited over a semi-infinite silicon substrate. In surface-based phononic crystals there is no distinction between the eigenmodes of the periodically nanostructured overlayer and the surface acoustic modes of the semi-infinite substrate, the solution of the elastic equation being a pseudo-surface acoustic wave partially localized on the nanostructures and radiating energy into the bulk. This problem is particularly severe in the hypersonic frequency range, where semi-infinite substrate's surface acoustic modes strongly couple to the periodic overlayer, thus preventing any perturbative approach. We solve the problem introducing a surface-likeness coefficient as a tool allowing to find pseudo-surface acoustic waves and to calculate their line shapes. Having accessed the pseudo-surface modes of the composite structure, the same theoretical frame allows reporting on the gap opening in the now well-defined pseudo-SAW frequency spectrum. We show how the filling fraction, mass loading and geometric factors affect both the frequency gap, and how the mechanical energy is scattered out of the surface waveguiding modes.
Infrared signatures of the spin-Peierls transition in CuGeO3
A. Damascelli,D. van der Marel,F. Parmigiani,G. Dhalenne,A. Revcolevschi
Physics , 1997, DOI: 10.1103/PhysRevB.56.R11373
Abstract: We investigated the infrared reflectivity of several Mg- and Si-substituted CuGeO3 single crystals. The temperature dependent b-axis and c-axis optical response is reported. For T
Infrared reflectivity of pure and doped CuGeO3
A. Damascelli,D. van der Marel,F. Parmigiani,G. Dhalenne,A. Revcolevschi
Physics , 1997, DOI: 10.1016/S0921-4526(97)00472-9
Abstract: We investigated the far- and mid-infrared reflectivity (20-6000 wavenumber) of several pure and doped CuGeO3 single crystals. The b-axis and c-axis optical response is presented for different temperatures between 4 K and 300 K. Moreover, a full group theoretical analysis of the lattice vibrational modes of CuGeO3 in the high temperature undistorted phase as well as in the low temperature spin-Peierls phase is reported and compared to the experimental results. We observe the activation of zone boundary phonons along the b axis of the crystal below the spin-Peierls transition temperature.
First evidence of transient interactions between $π\toπ^*$ optical excitations and image potential states in graphite
M. Montagnese,S. Pagliara,S. Dal Conte,G. Galimberti,G. Ferrini,F. Parmigiani
Physics , 2009,
Abstract: Here we report the experimental evidence of the interactions between the excitations of the $\pi\to\pi^*$ optical transition and the image potential states (IPS) of highly oriented pyrolitic graphite (HOPG). By using non-linear angle resolved photoelectron spectroscopy (NL-ARPES) we show that the IPS photoemission intensity, the effective mass, and the linewidth exhibit a strong variation when the photon energy is tuned across the $\pi\to\pi^*$ saddle points in the 3.1 - 4.5 eV photon energy range. A model based on the self-energy formalism is proposed to correlate the effective mass and the linewidth variations to transient many body effects, when a high carriers density (in the $10^{20}$ cm$^{-3}$ range) is created by the absorption of a coherent light pulse. This finding brings a clear evidence of a high IPS-bulk coupling in graphite and opens the way for exploiting the IPS as a sensitive, nonperturbing probe for the many-body dynamics in materials.
Quantum interferences reconstruction with low homodyne detection efficiency
M. Esposito,F. Randi,K. Titimbo,K. Zimmermann,G. Kourousias,A. Curri,R. Floreanini,F. Parmigiani,D. Fausti,F. Benatti
Physics , 2015,
Abstract: Standard quantum state reconstruction techniques indicate that a detection efficiency of $0.5$ is an absolute threshold below which quantum interferences cannot be measured. However, alternative statistical techniques suggest that this threshold can be overcome at the price of increasing the statistics used for the reconstruction. In the following we present numerical experiments proving that quantum interferences can be measured even with a detection efficiency smaller than $0.5$. At the same time we provide a guideline for handling the tomographic reconstruction of quantum states based on homodyne data collected by low efficiency detectors.
Ultrafast photodoping and effective Fermi-Dirac distribution of the Dirac particles in Bi2Se3
A. Crepaldi,B. Ressel,F. Cilento,M. Zacchigna,C. Grazioli,H. Berger,Ph. Bugnon,K. Kern,M. Grioni,F. Parmigiani
Physics , 2012, DOI: 10.1103/PhysRevB.86.205133
Abstract: We exploit time- and angle- resolved photoemission spectroscopy to determine the evolution of the out-of-equilibrium electronic structure of the topological insulator Bi2Se. The response of the Fermi-Dirac distribution to ultrashort IR laser pulses has been studied by modelling the dynamics of the hot electrons after optical excitation. We disentangle a large increase of the effective temperature T* from a shift of the chemical potential mu*, which is consequence of the ultrafast photodoping of the conduction band. The relaxation dynamics of T* and mu* are k-independent and these two quantities uniquely define the evolution of the excited charge population. We observe that the energy dependence of the non-equilibrium charge population is solely determined by the analytical form of the effective Fermi-Dirac distribution.
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