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Black hole

T Mahvelati-Shamsabadi, E K Goharshadi
Zinc sulfide is a UV-active photocatalyst and it undergoes photocorrosion under light irradiation. In this work, the defect sites on ZnS nanoparticles (NPs) surfaces were induced with the help of powerful ultrasonic waves. The defect sites caused (1) suppression of photocorrosion in a large extent under UV light irradiation and (2) enhancement of visible light photo activity. The photocorrosion inhibition was induced by raising valence band (VB) position through the formation of interstitial zinc and sulfur vacancy states in the ZnS band structure and weakening of oxidative capacity of hole...
January 2017: Ultrasonics Sonochemistry
Alastair K Denniston, Pearse A Keane
No abstract text is available yet for this article.
October 1, 2016: Investigative Ophthalmology & Visual Science
Óscar J C Dias, Jorge E Santos, Benson Way
According to heuristic arguments, global AdS_{5}×S^{5} black holes are expected to undergo a phase transition in the microcanonical ensemble. At high energies, one expects black holes that respect the symmetries of the S^{5}; at low energies, one expects "localized" black holes that appear pointlike on the S^{5}. According to anti-de Sitter/conformal field theory correspondence, N=4 supersymmetric Yang-Mills (SYM) theory on a 3-sphere should therefore exhibit spontaneous R-symmetry breaking at strong coupling...
October 7, 2016: Physical Review Letters
Kimitake Hayasaki, Abraham Loeb
Galaxy mergers produce supermassive black hole binaries, which emit gravitational waves prior to their coalescence. We perform three-dimensional hydrodynamic simulations to study the tidal disruption of stars by such a binary in the final centuries of its life. We find that the gas stream of the stellar debris moves chaotically in the binary potential and forms accretion disks around both black holes. The accretion light curve is modulated over the binary orbital period owing to relativistic beaming. This periodic signal allows to detect the decay of the binary orbit due to gravitational wave emission by observing two tidal disruption events that are separated by more than a decade...
October 21, 2016: Scientific Reports
F D Dastur
No abstract text is available yet for this article.
September 2016: Journal of the Association of Physicians of India
Jimmy A Irwin, W Peter Maksym, Gregory R Sivakoff, Aaron J Romanowsky, Dacheng Lin, Tyler Speegle, Ian Prado, David Mildebrath, Jay Strader, Jifeng Liu, Jon M Miller
A flaring X-ray source was found near the galaxy NGC 4697 (ref. 1). Two brief flares were seen, separated by four years. During each flare, the flux increased by a factor of 90 on a timescale of about one minute. There is no associated optical source at the position of the flares, but if the source was at the distance of NGC 4697, then the luminosities of the flares were greater than 10(39) erg per second. Here we report the results of a search of archival X-ray data for 70 nearby galaxies looking for similar flares...
October 19, 2016: Nature
Qingfeng Zhang, Juanmin Li, Yunyi Zhang, Zhenzhen Hu, Cong Yu
A black-hole quencher (BHQ-2) labeled DNA (Q-DNA) with a phosphorothioate backbone was covalently conjugated to the CdTe QDs during the QDs synthesis procedure. The hairpin structure of Q-DNA shortened the distance of the CdTe QDs and the BHQ-2 group, which resulted in fluorescence quenching of the QDs. The addition of target DNA or deoxyribonuclease I (DNase I) could move the BHQ-2 group away from the QDs. As a result, the fluorescence of the CdTe QDs recovered. This work provides a new way for target DNA and DNase I detection...
2016: Analytical Sciences: the International Journal of the Japan Society for Analytical Chemistry
K L Duggal
A new technique is used to study a family of time-dependent null horizons, called "Evolving Null Horizons" (ENHs), of generalized Robertson-Walker (GRW) space-time [Formula: see text] such that the metric [Formula: see text] satisfies a kinematic condition. This work is different from our early papers on the same issue where we used (1 + n)-splitting space-time but only some special subcases of GRW space-time have this formalism. Also, in contrast to previous work, we have proved that each member of ENHs is totally umbilical in [Formula: see text]...
2016: International Scholarly Research Notices
Ue-Li Pen, Neil Turok
We point out a surprising consequence of the usually assumed initial conditions for cosmological perturbations. Namely, a spectrum of Gaussian, linear, adiabatic, scalar, growing mode perturbations not only creates acoustic oscillations of the kind observed on very large scales today, it also leads to the production of shocks in the radiation fluid of the very early Universe. Shocks cause departures from local thermal equilibrium as well as create vorticity and gravitational waves. For a scale-invariant spectrum and standard model physics, shocks form for temperatures 1  GeV<T<10^{7}  GeV...
September 23, 2016: Physical Review Letters
Michael Appels, Ruth Gregory, David Kubizňák
We address a long-standing problem of describing the thermodynamics of an accelerating black hole. We derive a standard first law of black hole thermodynamics, with the usual identification of entropy proportional to the area of the event horizon-even though the event horizon contains a conical singularity. This result not only extends the applicability of black hole thermodynamics to realms previously not anticipated, it also opens a possibility for studying novel properties of an important class of exact radiative solutions of Einstein equations describing accelerated objects...
September 23, 2016: Physical Review Letters
Cesar E P Villegas, A S Rodin, Alexandra Carvalho, A R Rocha
Excitons play a key role in technological applications since they have a strong influence on determining the efficiency of photovoltaic devices. Recently, it has been shown that the allotropes of phosphorus possess an optical band gap that can be tuned over a wide range of values including the near-infrared and visible spectra, which would make them promising candidates for optoelectronic applications. In this work we carry out ab initio many-body perturbation theory calculations to study the excitonic effects on the optical properties of two-dimensional phosphorus allotropes: the case of blue and black monolayers...
October 12, 2016: Physical Chemistry Chemical Physics: PCCP
(no author information available yet)
No abstract text is available yet for this article.
October 5, 2016: Nature
L-P Euvé, F Michel, R Parentani, T G Philbin, G Rousseaux
We measured the power spectrum and two-point correlation function for the randomly fluctuating free surface on the downstream side of a stationary flow with a maximum Froude number F_{max}≈0.85 reached above a localized obstacle. On such a flow the scattering of incident long wavelength modes is analogous to that responsible for black hole radiation (the Hawking effect). Our measurements of the noise show a clear correlation between pairs of modes of opposite energies. We also measure the scattering coefficients by applying the same analysis of correlations to waves produced by a wave maker...
September 16, 2016: Physical Review Letters
Ning Bao, Adam Bouland, Stephen P Jordan
Two of the key properties of quantum physics are the no-signaling principle and the Grover search lower bound. That is, despite admitting stronger-than-classical correlations, quantum mechanics does not imply superluminal signaling, and despite a form of exponential parallelism, quantum mechanics does not imply polynomial-time brute force solution of NP-complete problems. Here, we investigate the degree to which these two properties are connected. We examine four classes of deviations from quantum mechanics, for which we draw inspiration from the literature on the black hole information paradox...
September 16, 2016: Physical Review Letters
D Ontaneda, K Sakaie, J Lin, X-F Wang, M J Lowe, M D Phillips, R J Fox
BACKGROUND AND PURPOSE: DTI is an MR imaging measure of brain tissue integrity. Little is known regarding the long-term longitudinal evolution of lesional and nonlesional tissue DTI parameters in multiple sclerosis and the present study examines DTI evolution over 4 years. MATERIALS AND METHODS: Twenty-one patients with multiple sclerosis were imaged for up to 48 months after starting natalizumab therapy. Gadolinium-enhancing lesions at baseline, chronic T2 lesions, and normal-appearing white matter were followed longitudinally...
September 22, 2016: AJNR. American Journal of Neuroradiology
Emanuele Berti, Alberto Sesana, Enrico Barausse, Vitor Cardoso, Krzysztof Belczynski
We estimate the potential of present and future interferometric gravitational-wave detectors to test the Kerr nature of black holes through "gravitational spectroscopy," i.e., the measurement of multiple quasinormal mode frequencies from the remnant of a black hole merger. Using population synthesis models of the formation and evolution of stellar-mass black hole binaries, we find that Voyager-class interferometers will be necessary to perform these tests. Gravitational spectroscopy in the local Universe may become routine with the Einstein Telescope, but a 40-km facility like Cosmic Explorer is necessary to go beyond z∼3...
September 2, 2016: Physical Review Letters
Romuald A Janik, Jakub Jankowski, Hesam Soltanpanahi
We study the poles of the retarded Green's functions of strongly coupled field theories exhibiting a variety of phase structures from a crossover up to a first order phase transition. These theories are modeled by a dual gravitational description. The poles of the holographic Green's functions appear at the frequencies of the quasinormal modes of the dual black hole background. We establish that near the transition, in all cases considered, the applicability of a hydrodynamic description breaks down already at lower momenta than in the conformal case...
August 26, 2016: Physical Review Letters
Andrea Maselli, Stefania Marassi, Valeria Ferrari, Kostas Kokkotas, Raffaella Schneider
The direct discovery of gravitational waves has finally opened a new observational window on our Universe, suggesting that the population of coalescing binary black holes is larger than previously expected. These sources produce an unresolved background of gravitational waves, potentially observable by ground-based interferometers. In this Letter we investigate how modified theories of gravity, modeled using the parametrized post-Einsteinian formalism, affect the expected signal, and analyze the detectability of the resulting stochastic background by current and future ground-based interferometers...
August 26, 2016: Physical Review Letters
Tim Johannsen, Carlos Wang, Avery E Broderick, Sheperd S Doeleman, Vincent L Fish, Abraham Loeb, Dimitrios Psaltis
The Event Horizon Telescope is a global, very long baseline interferometer capable of probing potential deviations from the Kerr metric, which is believed to provide the unique description of astrophysical black holes. Here, we report an updated constraint on the quadrupolar deviation of Sagittarius A^{*} within the context of a radiatively inefficient accretion flow model in a quasi-Kerr background. We also simulate near-future constraints obtainable by the forthcoming eight-station array and show that in this model already a one-day observation can measure the spin magnitude to within 0...
August 26, 2016: Physical Review Letters
Yi-Fu Cai, Salvatore Capozziello, Mariafelicia De Laurentis, Emmanuel N Saridakis
Over recent decades, the role of torsion in gravity has been extensively investigated along the main direction of bringing gravity closer to its gauge formulation and incorporating spin in a geometric description. Here we review various torsional constructions, from teleparallel, to Einstein-Cartan, and metric-affine gauge theories, resulting in extending torsional gravity in the paradigm of f (T) gravity, where f (T) is an arbitrary function of the torsion scalar. Based on this theory, we further review the corresponding cosmological and astrophysical applications...
October 2016: Reports on Progress in Physics
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