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91.
We study the relation between the recently defined localizable entanglement and generalized correlations in quantum spin systems. Differently from the current belief, the localizable entanglement is always given by the average of a generalized string. Using symmetry arguments we show that in most spin-1/2 and spin-1 systems the localizable entanglement reduces to the spin-spin or string correlations, respectively. We prove that a general class of spin-1 systems, which includes the Heisenberg model, can be used as a perfect quantum channel. These conclusions are obtained in analytic form and confirm some results found previously on numerical grounds. 相似文献
92.
The equilibration dynamics of a closed quantum system is encoded in the long-time distribution function of generic observables. In this Letter we consider the Loschmidt echo generalized to finite temperature, and show that we can obtain an exact expression for its long-time distribution for a closed system described by a quantum XY chain following a sudden quench. In the thermodynamic limit the logarithm of the Loschmidt echo becomes normally distributed, whereas for small quenches in the opposite, quasicritical regime, the distribution function acquires a universal double-peaked form indicating poor equilibration. These findings, obtained by a central limit theorem-type result, extend to completely general models in the small-quench regime. 相似文献
93.
Phase solubility and FTIR-ATR studies of idebenone/sulfobutyl ether β-cyclodextrin inclusion complex
C.?CannavàEmail author V.?Crupi M.?Guardo D.?Majolino R.?Stancanelli S.?Tommasini C.?A.?Ventura V.?Venuti 《Journal of inclusion phenomena and macrocyclic chemistry》2013,75(3-4):255-262
The favourable accessibility offered by sulfobutyl ether β-cyclodextrin (SBE-β-CD) for the complexation with idebenone (IDE) has been probed, as a function of temperature, in liquid state, by phase solubility study, and, in solid state, by FTIR-ATR technique. The phase solubility results indicated the formation of a IDE/SBE-β-CD inclusion complex with 1:1 molar ratio (AL type diagram), whose apparent stability constants at T = 300, 310, and 320 K have been estimated according to the Higuchi–Connors method. The formation of the inclusion complex has been confirmed on a freeze-dried and a co-precipitated product by FTIR-ATR spectroscopy, monitoring the changes induced by complexation on some characteristic vibrational bands of IDE. Quantitative studies, performed in a wide T range, from T = 250 K to T = 340 K, allowed us to extract information on the effect of temperature on the different hydrogen-bonded environments involving host, guest, and crystallization water molecules. Again, complexation is proved to enhance the stability of the guest, at least in the explored T range. 相似文献
94.
Della Valle RG Venuti E Brillante A Girlando A 《The journal of physical chemistry. A》2008,112(29):6715-6722
Using sexithiophene as a benchmark compound, we present a very effective strategy for searching the potential energy minima of a crystalline material, described in terms of rigid molecules with Coulombic and atom-atom interactions. The strategy involves uniform sampling of the many-body energy hypersurface, mechanical identification of all constraints deriving from the crystallographic symmetry, and a "sight-resight" method, originally introduced in wildlife ecology, for assessing the completeness of the search. Thousands of distinct potential energy minima, with a surprising variety of structural arrangements, are identified for sexithiophene. Despite the large number of competing minima, the system presents a small number of deep minima, with very different structures and not particularly congested in energy or density. The two deepest minima correspond to the structures of the two known experimental polymorphs, which are satisfactorily described. 相似文献
95.
Giovanni Barbera Germana Barone Vincenza Crupi Francesca Longo Domenico Majolino Paolo Mazzoleni Giuseppe Sabatino Davide Tanasi Valentina Venuti 《Journal of Non》2012,358(12-13):1554-1561
In the present work, we report on a detailed characterization of Late Roman and Byzantine (from 2nd to 8th century A.D.) glass specimen found in Catania (Sicily, Southern Italy) by the employment of two complementary techniques, namely scanning electron microscopy coupled with energy-dispersive spectrometry (SEM–EDS) and Fourier transform infrared (FT-IR) absorbance spectroscopy. The glass fragments come from archaeological excavations in the courtyard of St. Agata la Vetere's church in Catania. In particular, compositional data were obtained by scanning SEM–EDS measurements and the investigation of the degradation on the surface of the glass specimen was made combining the SEM–EDS observations with those performed through FT-IR absorbance. The whole set of results contributed to define the provenance of the specimens. Furthermore, the data furnished new evidences of the technical development of glass production in Late Roman and Byzantine period in Catania. 相似文献
96.
Steady combustion waves in one space dimension are studied by means of fluid-dynamic reactive Navier?CStokes equations derived from kinetic theory. By using the conservation laws, the problem is reduced to a three-dimensional dynamical system, with different solutions of deflagration or detonation type according to several various sub-regions in the parameter space. The delicate question of the flame eigenvalue is addressed, and a suitable numerical algorithm is used in order to catch these special solutions and to deal with the relevant unstable equilibrium states. Numerical examples of smooth weak deflagrations or detonations are shown. 相似文献
97.
Nicolas G. Martinelli Yoann Olivier Dr. Stavros Athanasopoulos Dr. Mari‐Carmen Ruiz Delgado Dr. Kathryn R. Pigg Demétrio A. da Silva Filho Dr. Roel S. Sánchez‐Carrera Dr. Elisabetta Venuti Raffaele G. Della Valle Prof. Jean‐Luc Brédas Prof. David Beljonne Dr. Jérôme Cornil Dr. 《Chemphyschem》2009,10(13):2265-2273
We have performed classical molecular dynamics simulations and quantum‐chemical calculations on molecular crystals of anthracene and perfluoropentacene. Our goal is to characterize the amplitudes of the room‐temperature molecular displacements and the corresponding thermal fluctuations in electronic transfer integrals, which constitute a key parameter for charge transport in organic semiconductors. Our calculations show that the thermal fluctuations lead to Gaussian‐like distributions of the transfer integrals centered around the values obtained for the equilibrium crystal geometry. The calculated distributions have been plugged into Monte‐Carlo simulations of hopping transport, which show that lattice vibrations impact charge transport properties to various degrees depending on the actual crystal structure. 相似文献
98.
Fabrizio Bardelli Germana Barone Vincenza Crupi Francesca Longo Giacomo Maisano Domenico Majolino Paolo Mazzoleni Valentina Venuti 《Journal of synchrotron radiation》2012,19(5):782-788
The present work reports a detailed investigation on the speciation of iron in the pigments of decorated pottery fragments of cultural heritage relevance. The fragments come from the Gioiosa Guardia archaeological site in the area of the `Strait of Messina' (Sicily, Southern Italy), and date back to VI–V century BC. The purpose of this study is to characterize the main pigmenting agents responsible for the dark‐red coloration of the specimens using non‐destructive analytical techniques such as synchrotron radiation X‐ray absorption spectroscopy (SR‐XAS), a well established technique for cultural heritage and environmental subjects. Absorption spectra were collected at the Fe K‐edge on the Italian beamline for absorption and diffraction (BM8‐GILDA) at the European Synchrotron Radiation Facility in Grenoble (France). In order to determine the speciation of Fe in the samples, principal component analysis and least‐squares fitting procedures were applied to the near‐edge part of the absorption spectra (XANES). Details on the local structure around the Fe sites were obtained by analyzing the extended part of the spectra (EXAFS). Furthermore, an accurate determination of the average Fe oxidation state was carried out through analysis of the pre‐edge peaks of the absorption spectra. Samples resulted composed of an admixture of Fe2O3 (hematite or maghemite) and magnetite (Fe3O4), occurring in different relative abundance in the dark‐ and light‐colored areas of the specimens. The results obtained are complementary to information previously obtained by means of instrumental neutron activation analysis, Fourier transform infrared absorbance and time‐of‐flight neutron diffraction. 相似文献
99.