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1.
Horizon Shells and BMS-like soldering transformations
Martin O'Loughlin, Matthias Blau, 2016, izvirni znanstveni članek

Opis: We revisit the theory of null shells in general relativity, with a particular emphasis on null shells placed at horizons of black holes. We study in detail the considerable freedom that is available in the case that one solders two metrics together across null hypersurfaces (such as Killing horizons) for which the induced metric is invariant under translations along the null generators. In this case the group of soldering transformations turns out to be infinite dimensional, and these solderings create non-trivial horizon shells containing both massless matter and impulsive gravitational wave components. We also rephrase this result in the language of Carrollian symmetry groups. To illustrate this phenomenon we discuss in detail the example of shells on the horizon of the Schwarzschild black hole (with equal interior and exterior mass), uncovering a rich classical structure at the horizon and deriving an explicit expression for the general horizon shell energy- momentum tensor. In the special case of BMS-like soldering supertranslations we find a conserved shell-energy that is strikingly similar to the standard expression for asymptotic BMS supertranslation charges, suggesting a direct relation between the physical properties of these horizon shells and the recently proposed BMS supertranslation hair of a black hole.
Najdeno v: ključnih besedah
Povzetek najdenega: ...Black Holes, Classical Theories of Gravity, Space-Time Symmetries...
Ključne besede: Black Holes, Classical Theories of Gravity, Space-Time Symmetries
Objavljeno: 10.03.2016; Ogledov: 1669; Prenosov: 0
.pdf Polno besedilo (333,17 KB)

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Reading Urban Space. An Evolving Lexicon
Purg Peter, 2018, samostojni strokovni sestavek ali poglavje v monografski publikaciji

Najdeno v: ključnih besedah
Ključne besede: urban, space, media
Objavljeno: 13.06.2018; Ogledov: 776; Prenosov: 0
.pdf Polno besedilo (206,95 KB)

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Subpolygroups related to a fuzzy topology
N. Abbasizadeh, Irina Cristea, Bijan Davvaz, Jianming Zhan, 2018, izvirni znanstveni članek

Najdeno v: ključnih besedah
Povzetek najdenega: ...polygroup, fuzzy topological space,(relatively) fuzzy continuity, lower (upper) fuzzy topological subpolygroup...
Ključne besede: polygroup, fuzzy topological space, (relatively) fuzzy continuity, lower (upper) fuzzy topological subpolygroup
Objavljeno: 21.08.2018; Ogledov: 503; Prenosov: 0
.pdf Polno besedilo (120,69 KB)

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Space weather research with the Pierre Auger Observatory
Miha Živec, 2019, magistrsko delo

Opis: Space weather refers to environmental conditions in the interplanetary space and Earth’s magnetosphere, ionosphere and exosphere and can influence the performance and reliability of electronics based technological systems. The major role in space weather changes plays the solar wind, a stream of charged particles (mostly electrons and protons) with energies of approximately 1 keV, that can cause geomagnetic storms and auroras. During their entry into the atmosphere, high energy cosmic rays collide with atomic nuclei of atmospheric gasses. When scattering occurs extensive air showers are created. Those cascades of secondary particles create flashes of light due to the Cherenkov effect as well as excite molecules of nitrogen gas in atmosphere, which then glow in fluorescent light. In order to observe the light created by air showers, it has to be collected with telescopes. The particles from the cascades that reach ground can be detected with surface detectors. The Pierre Auger Observatory is the largest observatory for cosmic ray measurements. It is located in Argentinian pampas covering an area of 3000 km2. It consists of 1660 surface detectors and 27 fluorescence telescopes. For cosmic rays with energies above few 1017 eV, a precise reconstruction of energy and direction of primary particle is achievable. Observatory also allows measurement of flux of incoming particles down to primary energies in ca. 10 GeV - 10 TeV interval, with a median energy ca. 80-90 GeV. This measurement capability is called "scaler" mode, since the corresponding data consist of scaler counted cascade particles with deposited energy between 15 and 100 MeV, at the average rate of 2 kHz per individual surface detector. For the purpose of this master thesis I compared the data from scaler mode measurements with measurements of neutron monitors, which are commonly used for space weather observations. With the correlation received from the comparison, I showed that scaler mode operation of Pierre Auger observatory can be used to monitor space weather events such as solar cycle and the decreases in the observed galactic cosmic ray intensity due to solar wind (Forbush decrease).
Najdeno v: ključnih besedah
Ključne besede: Pierre Auger Observatory, cosmic rays, space weather, Forbush decrease
Objavljeno: 17.09.2019; Ogledov: 324; Prenosov: 15
.pdf Polno besedilo (5,21 MB)

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