134,966 research outputs found
Testing Ghasemi-Nodehi–Bambi spacetime with continuum-fitting method
No full textThe continuum-fitting method is the analysis of the thermal spectrum of the geometrically thin and optically thick accretion disk around stellar-mass black holes. A parametrization aiming to test the Kerr nature of astrophysical black holes was proposed in Ghasemi-Nodehi and Bambi in EPJC 76:290, 2016. The metric contains 11 parameters in addition to the mass and spin parameters. One can recover the Kerr case by setting all parameters to one. In this paper, I study the continuum-fitting method in a Ghasemi-Nodehi–Bambi background. I show the impact of each of the parameters on the spectra. I then employ studies and show that using the continuum-fitting method all parameters of Ghasemi-Nodehi–Bambi spacetime are degenerate. However, the parameter can be constrained in the case of a high spin value and the Ghasemi-Nodehi–Bambi black hole as reference. This degeneracy means that the spectra of the Kerr case cannot be distinguished from spectra produced in Ghasemi-Nodehi–Bambi spacetime. This is a problem as regards measuring the spin of astrophysical black holes and constrain possible deviations from the Kerr case of General Relativity
Iron line reverberation mapping in Ghasemi-Nodehi–Bambi background
No full textThe reverberation associated with the iron line is the time lag between direct photons from the corona and the photons reflected from the disk. The resulting line spectrum is called the 2D transfer function. The shape of the 2D transfer function is determined by the geometry of spacetime and the properties of BH. In a paper (Ghasemi-Nodehi and Bambi in EPJC 76:290, 2016), the authors have proposed a parametrization. This parametrization is aimed to test the Kerr nature of astrophysical black hole candidates. In this paper, I provide a reverberation mapping of the Ghasemi-Nodehi–Bambi metric in order to constrain the parameter of spacetime. All parameters can be constrained with the exception of . The parameter is harder to constrain too
Testing Ghasemi-Nodehi–Bambi metric parameters with quasi-periodic oscillations
No full textQPOs are seen as peak features in the X-ray power spectral density of stellar mass black holes and neutron stars, of which frequencies can be measured with high precision. These QPO frequencies are believed to be related to fundamental frequencies of test particles, which are mainly determined by the background metric. We consider the metric introduced in Ghasemi-Nodehi and Bambi (Eur Phys J C 76:290, 2016). The fundamental frequencies in this metric are sensitive to some of the metric parameters but insensitive to other parameters, which means, the differences in fundamental frequencies in this metric and those in the Kerr ones can be significant for small changes of some but not all parameters around the Kerr value. By comparing with the QPO observations of GRO J1655-40, we find that only one parameter of the Ghasemi-Nodehi–Bambi metric can be strongly constrained, but other parameters cannot. We also use nested algorithm to investigate whether better constraints on the Ghasemi-Nodehi–Bambi metric parameters can be obtained from QPO observations of multiple objects by simulations. We find that four parameters can be strongly constrained while other parameters cannot . Our results suggest that QPOs may be important tools for testing the Kerr metric
Ultra-high frequency, high Q/volume micromechanical resonators in a planar AlN phononic crystal
No full textCitation: Baboly, M. G., Alaie, S., Reinke, C. M., El-Kady, I., & Leseman, Z. C. (2016). Ultra-high frequency, high Q/volume micromechanical resonators in a planar AlN phononic crystal. Journal of Applied Physics, 120(3), 5. doi:10.1063/1.4958671This paper presents the first design and experimental demonstration of an ultrahigh frequency complete phononic crystal (PnC) bandgap aluminum nitride (AlN)/air structure operating in the GHz range. A complete phononic bandgap of this design is used to efficiently and simultaneously confine elastic vibrations in a resonator. The PnC structure is fabricated by etching a square array of air holes in an AlN slab. The fabricated PnC resonator resonates at 1.117 GHz, which corresponds to an out-of-plane mode. The measured bandgap and resonance frequencies are in very good agreement with the eigen-frequency and frequency-domain finite element analyses. As a result, a quality factor/volume of 7.6 x 10(17)/m(3) for the confined resonance mode was obtained that is the largest value reported for this type of PnC resonator to date. These results are an important step forward in achieving possible applications of PnCs for RF communication and signal processing with smaller dimensions. Published by AIP Publishing
Mean flow generation by Görtler Vortices in a rotating annulus with librating side walls
No full textLongitudinal libration of the cylinder side walls of a rotating annulus in the supercritical regime induces a centrifugally unstable Stokes boundary layer which generates Görtler vortices only in a portion of a libration cycle. We show for the first time that these vortices propagate into the fluid bulk and generate an azimuthal mean flow which is retrograde (prograde) over the outer (inner) cylinder side wall. Direct numerical simulations (DNS) are carried out and Reynolds-averaged equations and kinetic energy budget of mean and fluctuating flow are used as diagnostic equations to discuss the generation mechanism and scaling behavior of the azimuthal mean flow in the fluid bulk
Abbas Ghasemi Hamed "De l'obligation d'information dans le contrat. Etude comparée du droit français et droit islamique imamite" , sous la direction de M. le Professeur Francis Kernaleguen, 11 septembre 1998
No full textAbbas Ghasemi Hamed "De l'obligation d'information dans le contrat. Etude comparée du droit français et droit islamique imamite" , sous la direction de M. le Professeur Francis Kernaleguen, 11 septembre 1998. In: Revue juridique de l'Ouest, 1998-3. p. 413
Mean Flow generation due to longitudinal librations of side-walls of a rotating annulus
No full textLaboratory experiments with rotating annuli are reported that reveal a prograde jet, which is adjacent either to a (longitudinally) librating inner straight cylinder or to a librating inner truncated cone (frustum), whereas the outer cylindrical wall and bottom and top lids rotate with constant angular velocity. In the frustum case, the jet is located on a straight cylindrical surface which is circumscribed about the frustum and joins the bottom lid. These findings are supported by direct numerical simulations which show good agreement between experimental data and numerical results and, when the centrifugal instability of the Stokes boundary layer near the oscillating sidewall does not set in, highlight the important role of local dynamical processes in the corners, between the inner cylinder and the lids, in producing the prograde jet
Abbas Ghasemi Hamed "De l'obligation d'information dans le contrat. Etude comparée du droit français et droit islamique imamite" , sous la direction de M. le Professeur Francis Kernaleguen, 11 septembre 1998
No full textAbbas Ghasemi Hamed "De l'obligation d'information dans le contrat. Etude comparée du droit français et droit islamique imamite" , sous la direction de M. le Professeur Francis Kernaleguen, 11 septembre 1998. In: Revue juridique de l'Ouest, 1998-3. p. 413
DNS of inertial wave attractors in a librating annulus with height-dependent gap width
No full textDirect numerical simulations (DNS) of inertial wave attractors have been carried out in a librating Taylor-Couette system with broken mirror symmetry in the radial-axial cross-section. The inertial wave excitation mechanism and its localisation at the edges was clarified by applying boundary layer theory. Additional resonance peaks in the simulated response spectra were found to agree with low-order wave attractors obtained by geometric ray tracing. Numerics and theory are in qualitative agreement with recent lab experiments
Community-based collaborative tourism planning in islands: A cluster analysis in the context of Costa Smeralda
No full textThis study analyses residents' perceptions and attitudes towards tourism development and community integration in tourism planning in an island tourism destination whose economy is widely influenced by the presence of big external investors. Findings reveal that residents believe that tourism planning should be more sensitive to residents and tradition, and be able to guarantee a higher level of heritage proximity in order to achieve a more indigenous/endogenous-oriented development. Exploratory factor analysis and hierarchical and non-hierarchical cluster analysis were conducted. Four clusters were identified (‘enthusiastics’, ‘moderate supporters’, ‘critics’, and ‘indifferents’), with significant differences in terms of employment reliance on tourism, length of residence, contact with tourists in everyday life, and level of education. Conversely, they did not differ based on gender, age, employment status, or geographical proximity to the tourist area, thus providing some contradictory insights when compared with previous studies. From a theoretical point of view, the findings seem to suggest that studies devoted to the investigation of residents’ view and attitude toward tourism should concentrate more on the personal values of respondents and less on their socio-demographic characteristics, which often render the findings of cluster analysis very site-specific and hard to generalise. Managerial implications are discussed, and suggestions for further research are provided
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