227 research outputs found
On the general relativistic framework of the Sagnac effect
The Sagnac effect is usually considered as being a relativistic effect
produced in an interferometer when the device is rotating. General relativistic
explanations are known and already widely explained in many papers. Such
general relativistic approaches are founded on Einstein's equivalence principle
(EEP), which states the equivalence between the gravitational "force" and the
pseudo-force experienced by an observer in a non-inertial frame of reference,
included a rotating observer. Typically, the authors consider the so-called
Langevin-Landau-Lifschitz metric and the path of light is determined by null
geodesics. This approach partially hides the physical meaning of the effect. It
seems indeed that the light speed varies by c\pm\omega r in one or the other
direction around the disk. In this paper, a slightly different general
relativistic approach will be used. The different "gravitational field" acting
on the beam splitter and on the two rays of light is analyzed. This different
approach permits a better understanding of the physical meaning of the Sagnac
effect.Comment: 9 pages, to appear in the European Physical Journal
C. Pelloso, Socrate. La democrazia contro il libero pensiero, I grandi processi della Storia, vol. 5, Corriere della Sera, Milano, 2019, pp. 157
Breast-Lesion Characterization using Textural Features of Quantitative Ultrasound Parametric Maps
© 2017 The Author(s). This study evaluated, for the first time, the efficacy of quantitative ultrasound (QUS) spectral parametric maps in conjunction with texture-analysis techniques to differentiate non-invasively benign versus malignant breast lesions. Ultrasound B-mode images and radiofrequency data were acquired from 78 patients with suspicious breast lesions. QUS spectral-analysis techniques were performed on radiofrequency data to generate parametric maps of mid-band fit, spectral slope, spectral intercept, spacing among scatterers, average scatterer diameter, and average acoustic concentration. Texture-analysis techniques were applied to determine imaging biomarkers consisting of mean, contrast, correlation, energy and homogeneity features of parametric maps. These biomarkers were utilized to classify benign versus malignant lesions with leave-one-patient-out cross-validation. Results were compared to histopathology findings from biopsy specimens and radiology reports on MR images to evaluate the accuracy of technique. Among the biomarkers investigated, one mean-value parameter and 14 textural features demonstrated statistically significant differences (p < 0.05) between the two lesion types. A hybrid biomarker developed using a stepwise feature selection method could classify the legions with a sensitivity of 96%, a specificity of 84%, and an AUC of 0.97. Findings from this study pave the way towards adapting novel QUS-based frameworks for breast cancer screening and rapid diagnosis in clinic
On the quantization of the extremal Reissner-Nordstrom black hole
Following Rosen's quantization rules, two of the Authors (CC and FF) recently
described the Schwarzschild black hole (BH) formed after the gravitational
collapse of a pressureless "star of dust" in terms of a "gravitational hydrogen
atom". Here we generalize this approach to the gravitational collapse of a
charged object, namely, to the geometry of a Reissner-Nordstrom BH (RNBH) and
calculate the gravitational potential, the Schr\"odinger equation and the exact
solutions of the energy levels of the gravitational collapse. By using the
concept of BH effective state, previously introduced by one of us (CC), we
describe the quantum gravitational potential, the mass spectrum and the energy
spectrum for the extremal RNBH. The area spectrum derived from the mass
spectrum finds agreement with a previous result by Bekenstein. The stability of
these solutions, described with the Majorana approach to the Archaic Universe
scenario, show the existence of oscillatory regimes or exponential damping for
the evolution of a small perturbation from a stable state.Comment: 7 pages, to appear in Europhysics Letter
Charged particle scattering near the horizon
We study Maxwell theory, in the presence of charged scalar sources, near the
black hole horizon in a partial wave basis. We derive the gauge field
configuration that solves Maxwell equations in the near-horizon region of a
Schwarzschild black hole when sourced by a charge density of a localised
charged particle. This is the electromagnetic analog of the gravitational
Dray-'t Hooft shockwave near the horizon. We explicitly calculate the S-matrix
associated with this shockwave in the first quantised
formalism. We develop a theory for scalar QED near the horizon using which we
compute the electromagnetic eikonal S-matrix from elastic
scattering of charged particles exchanging soft photons in the black hole
eikonal limit. The resulting ladder resummation agrees perfectly with the
result from the first quantised formalism, whereas the field-theoretic
formulation allows for a computation of a wider range of amplitudes. As a
demonstration, we explicitly compute sub-leading corrections that arise from
four-vertices.Comment: 23 pages + appendices. v2: typos corrected, some clarifications
added. v3: fixed an incorrect Feynman diagra
Quantum oscillations in the black hole horizon
By applying Rosen's quantization approach to the historical Oppenheimer and
Snyder gravitational collapse and by setting the constraints for the formation
of the Schwarzschild black hole (SBH), in a previous paper [1] two of the
Authors (CC and FF) found the gravitational potential, the Schrodinger
equation, the solution for the energy levels, the area quantum and the quantum
representation of the ground state at the Planck scale of the SBH. Such results
are consistent with previous ones in the literature. It was also shown that the
traditional classical singularity in the core of the SBH is replaced by a
quantum oscillator describing a non-singular two-particle system where the two
components, named the "nucleus" and the "electron", strongly interact with each
other through a quantum gravitational interaction. In agreement with the de
Broglie hypothesis, the "electron" is interpreted in terms of the quantum
oscillations of the BH horizon. In other words, the SBH should be the
gravitational analogous of the hydrogen atom. In this paper, it is shown that
these results allow us to compute the SBH entropy as a function of the BH
principal quantum number in terms of Bekenstein-Hawking entropy and three
sub-leading corrections. In addition, the coefficient of the formula of
Bekenstein-Hawking entropy is reduced to a quarter of the traditional value.
Then, it is shown that, by performing a correct rescaling of the energy levels,
the semi-classical Bohr-like approach to BH quantum physics, previously
developed by one of the Authors (CC), is consistent with the obtained results
for large values of the BH principal quantum number. After this, Hawking
radiation will be analysed by discussing its connection with the BH quantum
structure. Finally, it is shown that the time evolution of the above mentioned
system solves the BH information paradox.Comment: 29 pages.Comments are welcome. arXiv admin note: text overlap with
arXiv:1912.0647
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