993 research outputs found
A Modular Logic Approach for Expressing Web Services in XML Applying Dynamic Rules in XML
No full textRuleML is considered to be a markup language for the semantic web. It allows the enrichment of web ontologies by adding definitions of derived concepts and it enhances interoperability among different systems and tools by publishing rules in an XML format. Moreover the in-creasing demand for interfaces that enhance information sharing has given rise to XML doc-uments that include embedded calls to web services. In this paper we propose a variation of RuleML that is based on modular logic programming. Our approach is based in a two level architecture. In the first level a modular logic language, called M-log, is presented. This lan-guage encompasses several mechanisms for invoking web services. In the second level we ex-ploit the semantics of M-log to present a variation of RuleML with rich modeling capabilities. Formal foundations for this variation are given through direct translation to M-log semantics.Knowledge Management, XML, Modular Logic Programming, E-Services
Hybrid Numerical Simulations of Pulsar Magnetospheres
No full textWe continue our investigation of particle acceleration in the pulsar equatorial current sheet (ECS) that began with Contopoulos (2019) and Contopoulos & Stefanou (2019). Our basic premise has been that the charge carriers in the current sheet originate in the polar caps as electron-positron pairs, and are carried along field lines that enter the equatorial current sheet beyond the magnetospheric Y-point. In this work we investigate further the charge replenishment of the ECS. We discovered that the flow of pairs from the rims of the polar caps cannot supply both the electric charge and the electric current of the ECS. The ECS must contain an extra amount of positronic (or electronic depending on orientation) electric current that originates in the stellar surface and flows outwards along the separatrices. We develop an iterative hybrid approach that self-consistently combines ideal force-free electrodynamics in the bulk of the magnetosphere with particle acceleration along the ECS. We derive analytic approximations for the orbits of the particles, and obtain the structure of the pulsar magnetosphere for various values of the pair-formation multiplicity parameter kappa. For realistic values kappa >> 1, the magnetosphere is practically indistinguishable from the ideal force-free one, and therefore, the calculation of the spectrum of high-energy radiation must be based on analytic approximations for the distribution of the accelerating electric field in the ECS
The force-free magnetosphere of a rotating black hole
No full textWe explore the analogy with pulsars and investigate the structure of the force-free magnetosphere around a Kerr black hole. We propose that the source of the black hole magnetic field is the Poynting-Robertson effect on the plasma electrons at the inner edge of the surrounding accretion disk, the so called Cosmic Battery. The magnetospheric solution is characterized by the distributions of the magnetic field angular velocity and the poloidal electric current. These are not arbitrary. They are determined self-consistently by requiring that magnetic field lines cross smoothly the two singular surfaces of the problem, the inner ‘light surface’ located inside the ergosphere, and the outer ‘light surface’ which is the generalization of the pulsar light cylinder. The black hole forms a relativistic jet only if it is surrounded by a thick disk and/or extended disk outflows
Ioannis Dallaei De imaginibus libri IV.
No full textIncludes errata at end.Signatures: *⁸ A-2L⁸ 2M⁴ chi².Woodcut printer's device on t.p. Head- and tail-pieces, initials.Scanned copy bound with: Joannis Dallaei Apologia pro ecclesiis reformatis. Amstelodami : Apud Jodocum Jansonium, 1652.Mode of access: Internet.Binding: vellum. Author & titles written at head of spine.With his: Apologia pro ecclesiis reformatis (Amsterdam : J. Janson, 1652)
Ioannis Metaxas: Speech on the occasion of the inauguration of public works
No full textTitle: Λόγος κατά τα εγκαίνια των έργων του Σελινούντος Αιγιαλείας (Speech on the occasion of the inauguration of the public works at Selinous, Egialia) Originally published: Delivered at Selinous on 31 October 1937. Language: Greek The excerpts used are from Ioannis Metaxas, Λόγοι και Ομιλίες (Athens: Ερμής, 1992), pp. 247–255. About the author Ioannis Metaxas [1871, Ithaca (Ionian Islands)–1941, Athens]: military officer and politician. He was born into a well-known aristocratic family. In ..
Variable Nature of Magnetically Driven Ultra-fast Outflows
No full textAmong a number of active galactic nuclei that drive ionized outflows in X-rays, a low-redshift (z = 0.184) quasar, PDS 456, is long known to exhibit one of the exemplary ultra-fast outflows (UFOs). However, the physical process of acceleration mechanisms is yet to be definitively constrained. In this work, we model the variations of the Fe K UFO properties in PDS 456 over many epochs in X-ray observations in the context of magnetohydrodynamic (MHD) accretion disk winds employed in our earlier studies of similar X-ray absorbers. We applied the model to the 2013/2014 XMM-Newton/NuSTAR spectra to determine the UFO's condition; namely, velocity, ionization parameter, column density, and equivalent width (EW). Under some provisions on the dependence of X-ray luminosity on the accretion rate applicable to near-Eddington state, our photoionization calculations, coupled to a 2.5-dimensional MHD-driven wind model, can further reproduce the observed correlations of the UFO velocity and the anticorrelation of its EW with the X-ray strength of PDS 456. This work demonstrates that UFOs, even without radiative pressure, can be driven as an extreme case purely by magnetic interaction while also producing the observed spectrum and correlations
Literary Recants of a Tenth-Century Scholar: The Case of Ioannis Kaminiates
No full textThis paper seeks to interpret the attitude of Ioannis Kaminiates towards Homer, for while initially criticising his literary predecessor, the author of On the Capture of Thessaloniki later adopts many of his turns of phrase
My journey
No full textTitle: Τό ταξίδι μου (My journey) Originally published: Αθήνα, n. p., 1888 Language: Greek The excerpts used are from Ἰωάννης Ψυχάρης, Τό ταξίδι μου, ed. by Alkis Agelou (Athens: Ἐστία: Νεοελληνική Βιβλιοθήκη, 1993), pp. 37–39, 64–67, 75–76, 89. About the author Ioannis (Jean) Psicharis [1854, Odessa – 1929, Paris]: writer, linguist and critic. Psicharis was born to a well-off family. After his mother’s early death his father brought him to Istanbul in 1860, where he spent his childhood. His ..
Of this great idea
No full textTitle: Τῆς Μεγάλης αυτής Ἰδέας (Of this Great Idea) Originally published: Ιt was published in Ἠ τῆς τρίτης Σεπτεµβρίου ἐν Άθήναις Ἐθνική Συνέλευσις, Athens, Βουλή των Ελλήνων, 1844 Language: Greek The excerpts used are from Constantinos Th. Dimaras, Ελληνικός Ρωµαντισµός (Athens: Ερµής, 1985), pp. 405–406. About the author Ioannis Kolettis [1773, Sirako (Epirus) – 1847, Athens]: medical doctor, politician and writer. He was educated in his hometown of Sirako and in nearby Kalarites, both pros..
Generation and Transport of Magnetic Flux in Accretion–Ejection Flows
No full textAstrophysical accretion flows are associated with energetic emission of radiation and outflows (winds and jets). Extensive observations of these two processes in X-ray binary outbursts are available. A convincing understanding of their dynamics remains, however, elusive. The main agent that controls the dynamics is believed to be a large scale magnetic field that threads the system. We propose that during the quiescent state, the field is held in place by a delicate balance between inward advection and outward diffusion through the accreting matter. We also propose that the source of the field is a growing toroidal electric current generated by the aberrated radiation pressure on the innermost plasma electrons in orbit around the central black hole. This is the astrophysical mechanism of the Cosmic Battery. When the return magnetic field outside the toroidal electric current diffuses through the surrounding disk, the disk magnetic field and its associated accretion rate gradually increase, thus leading the system to an outburst. After the central accretion flow approaches equipartition with radiation, it is disrupted, and the Cosmic Battery ceases to operate. The outward field diffusion is then reversed, magnetic flux reconnects with the flux accumulated around the central black hole and disappears. The magnetic field and the associated accretion rate slowly decrease, and the system is gradually driven back to quiescence. We conclude that the action (or inaction) of the Cosmic Battery may be the missing key that will allow us to understand the long-term evolution of astrophysical accretion–ejection flows
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