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Search Results: 1 - 10 of 144510 matches for " F. Cilento "
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Dumbarton Oaks. Byzantine Studies Dumbarton Oaks. Byzantine Studies
Adele Cilento
Reti Medievali Rivista , 2002, DOI: 10.6092/1593-2214/266
Abstract: Review of Dumbarton Oaks. Byzantine Studies Recensione a Dumbarton Oaks. Byzantine Studies
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.
Retos del hábitat urbano venezolano
Alfredo Cilento Sarli
Espacio Abierto , 2000,
Abstract: A partir de una visión comprehensiva de la situación de los asentamientos humanos venezolanos a finales del siglo XX, en este ensayo se plantean una serie de retos, como lineamientos de política que deberían tener vigencia durante un lapso no menor de diez a quince a os, dirigidos al logro de un hábitat urbano sostenible política, social, económica, técnica y ambientalmente.
Capacidad de resistencia, vulnerabilidad y cultura de riesgos
Alfredo Cilento Sarli
Espacio Abierto , 2005,
Abstract: La ocurrencia de cataclismos como sismos, aludes, tsunamis, huracanes, entre otros, constituyen amenazas naturales para los seres vivos, pero los seres humanos son los que convierten las amenazas en contingencias desastrosas. Por ello, la lucha contra los desastres provocados por los hombres y mujeres que habitan el planeta, es la batalla por el logro de una cultura de seguridad y prevención, respetuosa del medio ambiente natural y de la calidad del medio construido. Esa cultura deriva de la capacidad de resistencia de la población, y de una adecuada educación y preparación para enfrentar las contingencias antes de que ocurran, durante su ocurrencia y después de ocurridas. El fin determinante es el de salvar vidas y propiedades, y recuperar las facilidades para la vida y el trabajo, corrigiendo las fallas y vicios existentes antes de ocurrida la contingencia. En el desarrollo de esa cultura de seguridad el papel de las comunidades educativas, académicas y científicas es preponderante, al igual que la justa evaluación de la capacidad de resistencia de la sociedad, como elemento clave en los estudios de vulnerabilidad de los asentamientos humanos. En este trabajo se plantean algunos de los esfuerzos atribuibles a los actores mencionados, particularmente a las universidades públicas, dentro del marco de la Década de la Educación para el Desarrollo Sostenible 2005-2014, designada por Naciones Unidas.
Thermo-mechanical behavior of surface acoustic waves in ordered arrays of nanodisks studied by near infrared pump-probe diffraction experiments
C. Giannetti,B. Revaz,F. Banfi,M. Montagnese,G. Ferrini,F. Cilento,S. Maccalli,P. Vavassori,G. Oliviero,E. Bontempi,L. E. Depero,V. Metlushko,F. Parmigiani
Physics , 2007, DOI: 10.1103/PhysRevB.76.125413
Abstract: The ultrafast thermal and mechanical dynamics of a two-dimensional lattice of metallic nano-disks has been studied by near infrared pump-probe diffraction measurements, over a temporal range spanning from 100 fs to several nanoseconds. The experiments demonstrate that, in these systems, a two-dimensional surface acoustic wave (2DSAW), with a wavevector given by the reciprocal periodicity of the array, can be excited by ~120 fs Ti:sapphire laser pulses. In order to clarify the interaction between the nanodisks and the substrate, numerical calculations of the elastic eigenmodes and simulations of the thermodynamics of the system are developed through finite-element analysis. At this light, we unambiguously show that the observed 2DSAW velocity shift originates from the mechanical interaction between the 2DSAWs and the nano-disks, while the correlated 2DSAW damping is due to the energy radiation into the substrate.
Evidence of a photoinduced non-thermal superconducting-to-normal-state phase transition in overdoped Bi$_{2}$Sr$_{2}$Ca$_{0.92}$Y$_{0.08}$Cu$_{2}$O$_{8+δ}$
G. Coslovich,C. Giannetti,F. Cilento,S. Dal Conte,G. Ferrini,P. Galinetto,M. Greven,H. Eisaki,M. Raichle,R. Liang,A. Damascelli,F. Parmigiani
Physics , 2010, DOI: 10.1103/PhysRevB.83.064519
Abstract: Here we report extensive ultrafast time-resolved reflectivity experiments on overdoped Bi$_{2}$Sr$_{2}$Ca$_{1-x}$Y$_x$Cu$_{2}$O$_{8+\delta}$ single crystals (T$_C$=78 K) aimed to clarify the nature of the superconducting-to-normal-state photoinduced phase transition. The experimental data show the lack of the quasiparticles decay time divergence at the fluence required to induce this phase transition, in contrast to the thermally-driven phase transition observed at T$_C$ and at variance with recently reported photoinduced charge-density-wave and spin-density-wave to metal phase transitions. Our data demonstrate the non-thermal character of the superconducting-to-normal-state photoinduced phase transition. The data have been analyzed using an ad-hoc developed time-dependent Rothwarf-Taylor model, opening the question on the order of this non-equilibrium phase transition.
Competition between the Pseudogap and Superconducting States of Bi$_{2}$Sr$_{2}$Ca$_{0.92}$Y$_{0.08}$Cu$_{2}$O$_{8+δ}$ Single Crystals Revealed by Ultrafast Broadband Optical Reflectivity
G. Coslovich,C. Giannetti,F. Cilento,S. Dal Conte,T. Abebaw,D. Bossini,G. Ferrini,H. Eisaki,M. Greven,A. Damascelli,F. Parmigiani
Physics , 2013, DOI: 10.1103/PhysRevLett.110.107003
Abstract: Ultrafast broadband transient reflectivity experiments are performed to study the interplay between the non-equilibrium dynamics of the pseudogap and the superconducting phases in Bi$_{2}$Sr$_{2}$Ca$_{0.92}$Y$_{0.08}$Cu$_{2}$O$_{8+\delta}$. Once superconductivity is established the relaxation of the pseudogap proceeds $\sim$ 2 times faster than in the normal state, and the corresponding transient reflectivity variation changes sign after $\sim$ 0.5 ps. The results can be described by a set of coupled differential equations for the pseudogap and for the superconducting order parameter. The sign and strength of the coupling term suggest a remarkably weak competition between the two phases, allowing their coexistence.
The momentum and photon energy dependence of the circular dichroic photoemission in the bulk Rashba semiconductors BiTeX (X = I, Br, Cl)
A. Crepaldi,F. Cilento,M. Zacchigna,M. Zonno,J. C. Johannsen,C. Tournier-Colletta,L. Moreschini,I. Vobornik,F. Bondino,E. Magnano,H. Berger,A. Magrez,Ph. Bugnon,G. Autés,O. V. Yazyev,M. Grioni,F. Parmigiani
Physics , 2014, DOI: 10.1103/PhysRevB.89.125408
Abstract: Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important candidates for developing spintronics devices, because of the coexistence of spin-split bulk and surface states, along with the ambipolar character of the surface charge carriers. The need of studying the spin texture of strongly spin-orbit coupled materials has recently promoted circular dichroic Angular Resolved Photoelectron Spectroscopy (cd-ARPES) as an indirect tool to measure the spin and the angular degrees of freedom. Here we report a detailed photon energy dependent study of the cd-ARPES spectra in BiTeX (X = I, Br and Cl). Our work reveals a large variation of the magnitude and sign of the dichroism. Interestingly, we find that the dichroic signal modulates differently for the three compounds and for the different spin-split states. These findings show a momentum and photon energy dependence for the cd-ARPES signals in the bulk Rashba semiconductor BiTeX (X = I, Br, Cl). Finally, the outcome of our experiment indicates the important relation between the modulation of the dichroism and the phase differences between the wave-functions involved in the photoemission process. This phase difference can be due to initial or final state effects. In the former case the phase difference results in possible interference effects among the photo-electrons emitted from different atomic layers and characterized by entangled spin-orbital polarized bands. In the latter case the phase difference results from the relative phases of the expansion of the final state in different outgoing partial waves.
Evidence of reduced surface electron-phonon scattering in the conduction band of Bi_{2}Se_{3} by non-equilibrium ARPES
A. Crepaldi,F. Cilento,B. Ressel,C. Cacho,J. C. Johannsen,M. Zacchigna,H. Berger,Ph. Bugnon,C. Grazioli,I. C. E. Turcu,E. Springate,K. Kern,M. Grioni,F. Parmigiani
Physics , 2013, DOI: 10.1103/PhysRevB.88.121404
Abstract: The nature of the Dirac quasiparticles in topological insulators calls for a direct investigation of the electron-phonon scattering at the \emph{surface}. By comparing time-resolved ARPES measurements of the TI Bi_{2}Se_{3} with different probing depths we show that the relaxation dynamics of the electronic temperature of the conduction band is much slower at the surface than in the bulk. This observation suggests that surface phonons are less effective in cooling the electron gas in the conduction band.
Disentangling the electronic and phononic glue in a high-Tc superconductor
Stefano Dal Conte,Claudio Giannetti,Giacomo Coslovich,Federico Cilento,Davide Bossini,Tadesse Abebaw,Franceco Banfi,Gabriele Ferrini,Hiroshi Eisaki,Martin Greven,Andrea Damascelli,Dirk van der Marel,F. Parmigiani
Physics , 2012, DOI: 10.1126/science.1216765
Abstract: Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamen- tal step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (\Omega) dependent bosonic function, \Pi(\Omega). We perform optical spectroscopy on Bi2212 crystals with simultaneous time- and frequency-resolution; this technique allows us to disentangle the electronic and phononic contributions by their different temporal evolution. The strength of the interaction ({\lambda}~1.1) with the electronic excitations and their spectral distribution fully account for the high critical temperature of the superconducting phase transition.
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