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Search Results: 1 - 10 of 300969 matches for " F De Felice "
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Naked Singularities, Cosmic Time Machines and Impulsive Events
F. de Felice
Physics , 2007, DOI: 10.1393/ncb/i2007-10397-3
Abstract: Continued gravitational collapse gives rise to curvature singularities. If a curvature singularity is globally naked then the space-time may be causally future ill-behaved admitting closed time-like or null curves which extend to asymptotic distances and generate a Cosmic Time Machine (de Felice (1995) Lecture Notes in Physics 455, 99). The conjecture that Cosmic Time Machines give rise to high energy impulsive events is here considered in more details.
A multiple choice decision analysis: an integrated QFD – AHP model for the assessment of customer needs
F De Felice, A Petrillo
International Journal of Engineering, Science and Technology , 2010,
Abstract: The aim of this work is to propose a new methodological approach to define customer specifications through the employment of an integrated Quality Function Deployment (QFD) – Analytic Hierarchy Process (AHP) model. The model, which is loosely based on QFD, incorporates the AHP approach to delineate and rank the relative importance weight of expressed judgments for customer needs and functional characteristics. The Analytic Hierarchy Process is very useful for this aim because it is a mathematically rigorous, proven process for prioritization and decision-making. By reducing complex decisions to a series of pair-wise comparisons, then synthesizing the results, decision-makers arrive at the best decision with a clear rationale for that decision. The methodology adopted in this work is directed to evaluate as well as rank the definition of the customer’s needs and functional characteristics among several alternatives. The approach has been validated in a real case study concerning the filter in ceramic material production.
Jet dynamics in black hole physics: acceleration during subparsec collimation
F. de Felice,O. Zanotti
Physics , 1999, DOI: 10.1023/A:1001925916715
Abstract: We study the processes of particle acceleration which take place in the field of a rotating black hole as part of a mechanism of formation of galactic jets within the first parsec from the central source, where gravitation is supposed to be dominant. We find the Lorentz factor that a stream of particles acquires as function of distance, when the orbital parameters vary slightly due to a local electromagnetic field or a pressure gradient.
Strains and Jets in Black Hole Fields
D. Bini,F. de Felice,A. Geralico
Physics , 2007, DOI: 10.1051/eas:0830011
Abstract: We study the behaviour of an initially spherical bunch of particles emitted along trajectories parallel to the symmetry axis of a Kerr black hole. We show that, under suitable conditions, curvature and inertial strains compete to generate jet-like structures.
A method to determine the parameters of black holes in AGNs and galactic X-ray sources with periodic modulation of variability
O. Semerak,F. de Felice,V. Karas
Physics , 1998, DOI: 10.1093/pasj/51.5.571
Abstract: We propose a simple and unambiguous way to deduce the parameters of black holes which may reside in AGNs and some types of X-ray binaries. The black-hole mass and angular momentum are determined in physical units. The method is applicable to the sources with periodic components of variability, provided one can assume the following: (i) Variability is due to a star or a stellar-mass compact object orbiting the central black hole and passing periodically through an equatorial accretion disk (variability time-scale is given by the orbital period). (ii) The star orbits almost freely, deviation of its trajectory due to passages through the disk being very weak (secular); the effect of the star on the disk, on the other hand, is strong enough to yield observable photometric and spectroscopic features. (iii) The gravitational field within the nucleus is that of the (Kerr) black hole, the star and the disk contribute negligibly.
Black holes in sources with a periodic component of variability
V. Karas,O. Semerak,F. de Felice
Physics , 1999,
Abstract: Three recent papers have been collected here, discussing the possibility and properties of periodic modulation of a signal from accreting black holes surrounded by orbiting clumps of gas.
Radon test measurements with Ce-doped yttrium aluminum oxide perovskite scintillator
W. Plastino,P. De Felice,F. de Notaristefani
Geofísica internacional , 2002,
Abstract: Scintillation properties of a Ce-doped yttrium aluminium oxide perovskite monocrystal optically coupled to a Hamamatsu H5784 photomultiplier are analyzed with a standard bialkali photocathode for radon and radon daughters gamma-ray spectrometry. Tests in water up to 100°C and in acidic solutions of HCl (37%), H2SO4 (48%) and HNO3 (65%) were performed to simulate environments of geophysical interest, such as geothermal and volcanic areas. Comparative measurements with standard radon sources provided by the National Institute for Metrology of Ionizing Radiations (ENEA) confirm the non-hygroscopic properties of the scintillator and small dependence of the light yield on temperature and HNO3.The Ce-doped yttrium aluminum oxide perovskite monocrystal shows high response stability for radon gamma-ray spectrometry in environments with large temperature gradients and high acid concentrations.
An Anisotropic Wormhole:TUNNELLING in Time and Space
M. Cavaglia' V. de Alfaro,F. de Felice
Physics , 1993, DOI: 10.1103/PhysRevD.49.6493
Abstract: We discuss the structure of a gravitational euclidean instanton obtained through coupling of gravity to electromagnetism. Its topology at fixed $t$ is $S^1\times S^2$. This euclidean solution can be interpreted as a tunnelling to a hyperbolic space (baby universe) at $t=0$ or alternatively as a static wormhole that joins the two asymptotically flat spaces of a Reissner--Nordstr\"om type solution with $M=0$.
Matter instabilities in general Gauss-Bonnet gravity
Antonio De Felice,David F. Mota,Shinji Tsujikawa
Physics , 2009, DOI: 10.1103/PhysRevD.81.023532
Abstract: We study the evolution of cosmological perturbations in f(G) gravity, where the Lagrangian is the sum of a Ricci scalar R and an arbitrary function f in terms of a Gauss-Bonnet term G. We derive the equations for perturbations assuming matter to be described by a perfect fluid with a constant equation of state w. We show that density perturbations in perfect fluids exhibit negative instabilities during both the radiation and the matter domination, irrespective of the form of f(G). This growth of perturbations gets stronger on smaller scales, which is difficult to be compatible with the observed galaxy spectrum unless the deviation from General Relativity is very small. Thus f(G) cosmological models are effectively ruled out from this Ultra-Violet instability, even though they can be compatible with the late-time cosmic acceleration and local gravity constraints.
Stabilization of partially folded states in protein folding/misfolding transitions by hydrostatic pressure
Ferreira, S.T.;Chapeaurouge, A.;De Felice, F.G.;
Brazilian Journal of Medical and Biological Research , 2005, DOI: 10.1590/S0100-879X2005000800009
Abstract: in the last few years, hydrostatic pressure has been extensively used in the study of both protein folding and misfolding/aggregation. compared to other chemical or physical denaturing agents, a unique feature of pressure is its ability to induce subtle changes in protein conformation, which allow the stabilization of partially folded intermediate states that are usually not significantly populated under more drastic conditions (e.g., in the presence of chemical denaturants or at high temperatures). much of the recent research in the field of protein folding has focused on the characterization of folding intermediates since these species appear to be involved in a variety of disease-causing protein misfolding and aggregation events. the exact mechanisms of these biological phenomena, however, are still poorly understood. here, we review recent examples of the use of hydrostatic pressure as a tool to obtain insight into the forces and energetics governing the productive folding or the misfolding and aggregation of proteins.
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