1,022 research outputs found
Physics of compton scattering and x-ray spectra of weakly magnetic accreting neutron stars
No full textCompton scattering of photons by non-relativistic electrons is thought to play an important role in forming the radiation spectrum of many astrophysical systems. Here we study in detail Compton scattering of photons by electrons with non-negligible thermal and bulk velocities and apply our results to understanding the X-ray spectra of weakly magnetic accreting neutron stars.Submitted by Emily Purcell ([email protected]) on 2015-08-07T19:30:02Z
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Psaltis, Dimitrios.pdf: 2784137 bytes, checksum: 083f9d266c02b9030c8b6d56e1ec8c60 (MD5)
Psaltis, Dimitrios.pdf: 2784137 bytes, checksum: 083f9d266c02b9030c8b6d56e1ec8c60 (MD5)Made available in DSpace on 2015-08-07T19:30:02Z (GMT). No. of bitstreams: 2
Psaltis, Dimitrios.pdf: 2784137 bytes, checksum: 083f9d266c02b9030c8b6d56e1ec8c60 (MD5)
Psaltis, Dimitrios.pdf: 2784137 bytes, checksum: 083f9d266c02b9030c8b6d56e1ec8c60 (MD5)
Previous issue date: 1997-08-22Ope
High-performance Black-hole Simulations with Hybrid Architectures (GT SSE 2023 Workshop)
No full textDr. Psaltis presents his group's work on simulating black holes with hybrid CPU, GPU, and FPGA architectures at the SSE Scientific Computing Workshop in April 2023.</p
Letter. Shrinking the braneworld: black hole in a globular cluster
No full textLarge extra dimensions have been proposed as a possible solution to the hierarchy problem in physics. In one of the suggested models, the RS2 braneworld model, black holes may evaporate by Hawking radiation faster than in general relativity, on a timescale that depends on the black hole mass and on the asymptotic radius of curvature of the extra dimensions. Thus the size of the extra dimensions can be constrained by astrophysical observations. Here we point out that the black hole, recently discovered in an extragalactic globular cluster, places the strongest upper limit on the size of the extra dimensions in the RS2 model, L lsim 0.003 mm. This black hole has the virtues of old age and relatively small mass. The derived upper limit is within an order of magnitude of the absolute limit afforded by astrophysical observations of black holes
Babel, or the local distortion of the Greek language
No full textTitle: Βαβυλωνία ἤ ἡ κατά τόπους διαφθορά τῆς ἑλληνικῆς γλώσσας. Κωµωδία (Babel, or the local distortion of the Greek language: A comedy) Originally published: Ναύπλιο (Nafplio), Τυπογραφεῖsο Κωνσταντίνου Τόµπρα ἐκ Κυδωνιῶν καὶ Κωνσταντίνου Ἰωαννίδη ἐκ Σµύρνης, 1836 Language: Greek The excerpt used is from D. C. Vyzantios, Βαβυλωνία, introduction by Spyros Evangelatos (Athens: Εστία, 1993), pp.1–3. About the author Dimitrios Vyzantios (pseudonym of Dimitrios K. Hatziaslanis) [1790, Constantin..
BAYESIAN TECHNIQUES FOR COMPARING TIME-DEPENDENT GRMHD SIMULATIONS TO VARIABLE EVENT HORIZON TELESCOPE OBSERVATIONS
No full textThe Event Horizon Telescope (EHT) is a millimeter-wavelength, very-long-baseline interferometry (VLBI) experiment that is capable of observing black holes with horizon-scale resolution. Early observations have revealed variable horizon-scale emission in the Galactic Center black hole, Sagittarius. A* (Sgr A*). Comparing such observations to time-dependent general relativistic magnetohydrodynamic (GRMHD) simulations requires statistical tools that explicitly consider the variability in both the data and the models. We develop here a Bayesian method to compare time-resolved simulation images to variable VLBI data, in order to infer model parameters and perform model comparisons. We use mock EHT data based on GRMHD simulations to explore the robustness of this Bayesian method and contrast it to approaches that do not consider the effects of variability. We find that time-independent models lead to offset values of the inferred parameters with artificially reduced uncertainties. Moreover, neglecting the variability in the data and the models often leads to erroneous model selections. We finally apply our method to the early EHT data on Sgr A*.NSF [AST-1207752, AST-1440254, AST 1108753, AST 1312034, 1228509]; NASA/NSF TCAN award [NNX14AB48G]; NFS GRFP [DGE 1144085]This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
Dimitrios Tsamis Karatasos : a symbol of Greek, Serbian and Bulgarian friendship
No full textTwo Serbian texts extol the contribution of Dimitrios Tsamis Karatasos to the Balkan joint effort to throw off the Ottoman yoke. These texts are analysed by the author within the historical framework of their period, so that the man’s personality and work may be accurately evaluated from a fresh viewpoint. More specifically, the author conducts a research on the tombstone of Dimitrios Tsamis Karatasos, which he discovered himself at Naoussa, and the octet engraved on it, which is also published here. The work is illustrated by seven plates, of which four have not been published previously
The Remains of authoritarianism : bureaucracy and civil society in post-authoritarian Greece
No full textDimitrios A. Sotiropoulos. 30 cm. He presented this paper at a seminar held at the Center on October 21, 1994. - T.p. Includes bibliographical references (p. 31-35
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EXPLORING THE BLACK HOLE INFORMATION PARADOX
No full textMere weeks after Albert Einstein published his theory of general relativity, Karl Schwarzschild came up with the simplest, static solution to Einstein’s field equations. This solution implied the existence of a compact object with an infinite potential well. This implied that even photons could not crawl out of this potential well and hence the phrase ”even light cannot escape a black hole” came into being. Black holes are characterized by the existence of an event horizon, a surface that disconnects the interior regions of the black hole from the exterior universe. These compact objects existed on paper, without any direct observational evidence, for a century. However, with the recent shift in interests towards gravitational wave astronomy and the success of projects like the Event Horizon Telescope (EHT), we have been able to image the ”shadow” of the M87 black hole. General relativity predicts that the shadow of the black hole is going to be stationary while the weather around the black hole can be turbulent. The EHT project not only has the potential to look for any classical evidence for the quantum structure of black holes but also allows us to investigate further into the Black Hole Information Paradox. So, in this project, we develop a method to analyze the Fourier transforms of the perturbed metric around a black hole and describe the macroscopic consequences of each of the proposed solutions to the informatio nparadox. If we analyze the Fourier transforms of the perturbations, we can test the validity of general relativity’s prediction about the black hole’s shadow
Erratum: Korkovelos, A., et al. The role of open access data in geospatial electrification planning and the achievement of SDG7. An OnSSET-based case study for Malawi. <i>Energies</i> 2019, 12(7), 1395
No full textThe authors wish to make a change in author names (adding new author—Dimitrios Mentis) to this paper
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