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101.
Valerio Scagnoli Claudio Mazzoli Carsten Detlefs Pascal Bernard Andrea Fondacaro Luigi Paolasini Federica Fabrizi Francois De Bergevin 《Journal of synchrotron radiation》2009,16(6):778-787
An in‐vacuum double‐phase‐plate diffractometer for performing polarization scans combined with resonant X‐ray diffraction experiments is presented. The use of two phase plates enables the correction of some of the aberration effects owing to the divergence of the beam and its energy spread. A higher rate of rotated polarization is thus obtained in comparison with a system with only a single retarder. Consequently, thinner phase plates can be used to obtain the required rotated polarization rate. These results are particularly interesting for applications at low energy (e.g. 4 keV) where the absorption owing to the phase plate(s) plays a key role in the feasibility of these experiments. Measurements by means of polarization scans at the uranium M4 edge on UO2 enable the contributions of the magnetic and quadrupole ordering in the material to be disentangled. 相似文献
102.
We define a natural ensemble of trace preserving, completely positive quantum maps and present algorithms to generate them at random. Spectral properties of the superoperator Φ associated with a given quantum map are investigated and a quantum analogue of the Frobenius-Perron theorem is proved. We derive a general formula for the density of eigenvalues of Φ and show the connection with the Ginibre ensemble of real non-symmetric random matrices. Numerical investigations of the spectral gap imply that a generic state of the system iterated several times by a fixed generic map converges exponentially to an invariant state. 相似文献
103.
Valerio Lucarini 《Journal of statistical physics》2009,134(2):381-400
Along the lines of the nonlinear response theory developed by Ruelle, in a previous paper we have proved under rather general
conditions that Kramers-Kronig dispersion relations and sum rules apply for a class of susceptibilities describing at any
order of perturbation the response of Axiom A non equilibrium steady state systems to weak monochromatic forcings. We present
here the first evidence of the validity of these integral relations for the linear and the second harmonic response for the
perturbed Lorenz 63 system, by showing that numerical simulations agree up to high degree of accuracy with the theoretical
predictions. Some new theoretical results, showing how to derive asymptotic behaviors and how to obtain recursively harmonic
generation susceptibilities for general observables, are also presented. Our findings confirm the conceptual validity of the
nonlinear response theory, suggest that the theory can be extended for more general non equilibrium steady state systems,
and shed new light on the applicability of very general tools, based only upon the principle of causality, for diagnosing
the behavior of perturbed chaotic systems and reconstructing their output signals, in situations where the fluctuation-dissipation
relation is not of great help. 相似文献
104.
Electrospray ionization mass spectrometry (ESI-MS) is being increasingly employed in the study of metal-ligand equilibria in aqueous solution. In the present work, the ESI-MS spectral changes due to different settings of the following instrumental parameters are analyzed: the solution flow rate (F(S)), the nebulizer gas flow rate (F(G)), the sprayer potential (E), and the temperature of the entrance capillary (T). Twenty-eight spectra were obtained for each of six samples containing aluminum(III) and 2,3-dihydroxypyridine at various pH, in the absence or in the presence of a buffer and of sodium ions. Among the considered instrumental parameters, T produced the largest effects on the ionic intensities. F(S) and F(G) affected the ESI-MS spectra to a lower extent than T. In the investigated conditions E had the weakest effects on the spectra.The correlations observed between the ionic intensities and these instrumental parameters were interpreted considering the presence of three kinds of perturbations occurring in the ESI-MS ion source: formation of some dimers in the droplets, different transfer efficiencies from the droplets to the gas phase for different complexes (according to their surface activity), and subsequent partial thermal decomposition of the dimers and of one of the monomeric complexes in the gas phase. Our results show that the evaluation of the effects produced in the ESI-MS spectra by a change of instrumental parameters can allow to identify the perturbations occurring when metal-ligand solutions are studied by ESI-MS. 相似文献
105.
Mattia Perrone 《Journal of Functional Analysis》2009,256(11):3471-3489
We study Haagerup inequality for radial functions on uniform lattices in semisimple Lie groups, with respect to Riemannian metrics and, in some case, to word metrics. In particular we extend the Swiatkowski-Valette results to any lattice acting properly and essentially transitively on classical buildings. 相似文献
106.
Montoro P Tuberoso CI Perrone A Piacente S Cabras P Pizza C 《Journal of chromatography. A》2006,1112(1-2):232-240
Anthocyanins in extracts of berries of Myrtus communis, prepared following a typical Sardinia myrtle liqueur recipe, were identified and quantified by HPLC coupled with electrospray/tandem mass spectrometry using, respectively, an ion trap and a triple quadrupole mass analyser. The fragmentation patterns of the anthocyanidins were dependent on the MS technique employed, and differed considerably from those previously reported. The anthocyanin profile of five anthocyanin glucosides and four anthocyanin arabinosides, the latter not previously identified in this specie, was specific for myrtle berry extracts. The quantitative compositions of extracts of myrtle berries derived from different geographical areas in Italy were compared. 相似文献
107.
Valerio Bozza 《General Relativity and Gravitation》2010,42(9):2269-2300
We review the theoretical aspects of gravitational lensing by black holes, and discuss the perspectives for realistic observations.
We will first treat lensing by spherically symmetric black holes, in which the formation of infinite sequences of higher order
images emerges in the clearest way. We will then consider the effects of the spin of the black hole, with the formation of
giant higher order caustics and multiple images. Finally, we will consider the perspectives for observations of black hole
lensing, from the detection of secondary images of stellar sources and spots on the accretion disk to the interpretation of
iron K-lines and direct imaging of the shadow of the black hole. 相似文献
108.
Changjun Gao Youjun Lu You-Gen Shen Valerio Faraoni 《General Relativity and Gravitation》2018,50(1):15
The Hawking–Penrose singularity theorem states that a singularity forms inside a black hole in general relativity. To remove this singularity one must resort to a more fundamental theory. Using a corrected dynamical equation arising in loop quantum cosmology and braneworld models, we study the gravitational collapse of a perfect fluid sphere with a rather general equation of state. In the frame of an observer comoving with this fluid, the sphere pulsates between a maximum and a minimum size, avoiding the singularity. The exterior geometry is also constructed. There are usually an outer and an inner apparent horizon, resembling the Reissner–Nordström situation. For a distant observer the horizon crossing occurs in an infinite time and the pulsations of the black hole quantum “beating heart” are completely unobservable. However, it may be observable if the black hole is not spherical symmetric and radiates gravitational wave due to the quadrupole moment, if any. 相似文献
109.
Lucarini Valerio Ragone Francesco Lunkeit Frank 《Journal of statistical physics》2017,166(3-4):1036-1064
Journal of Statistical Physics - The provision of accurate methods for predicting the climate response to anthropogenic and natural forcings is a key contemporary scientific challenge. Using a... 相似文献
110.
We construct different equivalent non-equilibrium statistical ensembles in a simple yet instructive \(N\) -degrees of freedom model of atmospheric turbulence, introduced by Lorenz in 1996. The vector field can be decomposed into an energy-conserving, time-reversible part, plus a non-time reversible part, including forcing and dissipation. We construct a modified version of the model where viscosity varies with time, in such a way that energy is conserved, and the resulting dynamics is fully time-reversible. For each value of the forcing, the statistical properties of the irreversible and reversible model are in excellent agreement, if in the latter the energy is kept constant at a value equal to the time-average realized with the irreversible model. In particular, the average contraction rate of the phase space of the time-reversible model agrees with that of the irreversible model, where instead it is constant by construction. We also show that the phase space contraction rate obeys the fluctuation relation, and we relate its finite time corrections to the characteristic time scales of the system. A local version of the fluctuation relation is explored and successfully checked. The equivalence between the two non-equilibrium ensembles extends to dynamical properties such as the Lyapunov exponents, which are shown to obey to a good degree of approximation a pairing rule. These results have relevance in motivating the importance of the chaotic hypothesis. in explaining that we have the freedom to model non-equilibrium systems using different but equivalent approaches, and, in particular, that using a model of a fluid where viscosity is kept constant is just one option, and not necessarily the only option, for describing accurately its statistical and dynamical properties. 相似文献