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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.
Ključne besede: Black Holes, Classical Theories of Gravity, Space-Time Symmetries
Objavljeno v RUNG: 10.03.2016; Ogledov: 4690; Prenosov: 0
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Opis: The large-scale distribution of arrival directions of high-energy cosmic rays is a key observable in attempts to understanding their origin. The dipole and quadrupole moments are of special interest in revealing potential anisotropies. An unambiguous measurement of these moments as well as of the full set of spherical harmonic coefficients requires full-sky coverage. This can be achieved by combining data from observatories located in both the northern and southern hemispheres. To this end, a joint analysis using data recorded at the Pierre Auger Observatory and the Telescope Array above 10[sup]19 eV has been performed. Thanks to the full-sky coverage, the measurement of the dipole moment reported in this study does not rely on any assumption on the underlying flux of cosmic rays. As well, the resolution on the quadrupole and higher order moments is the best ever obtained. The resulting multipolar expansion of the flux of cosmic rays allows a series of anisotropy searches to be performed, and in particular to report on the first angular power spectrum of cosmic rays. This allows a comprehensive description of the angular distribution of cosmic rays above 10[sup]19 eV.
Ključne besede: Pierre Auger Observatory, Telescope Array, high-energy cosmic rays, large-scale anisotropies, angular power spectrum
Objavljeno v RUNG: 08.03.2016; Ogledov: 4471; Prenosov: 189
Celotno besedilo (462,61 KB)

Opis: We have conducted three searches for correlations between ultra-high energy cosmic rays detected by the Telescope Array and the Pierre Auger Observatory, and high-energy neutrino candidate events from IceCube. Two cross-correlation analyses with UHECRs are done: one with 39 cascades from the IceCube ‘high-energy starting events’ sample and the other with 16 high-energy ‘track events’. The angular separation between the arrival directions of neutrinos and UHECRs is scanned over. The same events are also used in a separate search using a maximum likelihood approach, after the neutrino arrival directions are stacked. To estimate the significance we assume UHECR magnetic deflections to be inversely proportional to their energy, with values 3◦, 6◦ and 9◦ at 100 EeV to allow for the uncertainties on the magnetic field strength and UHECR charge. A similar analysis is performed on stacked UHECR arrival directions and the IceCube sample of through-going muon track events which were optimized for neutrino point- source searches.
Ključne besede: ultra-high energy cosmic rays, Pierre Auger Observatory, Telescope Array, high-energy neutrinos, IceCube, correlation search
Objavljeno v RUNG: 08.03.2016; Ogledov: 4931; Prenosov: 192
Celotno besedilo (1,11 MB)

Opis: Several studies have shown that traditional standardised aphasia tests may not be sensitive enough to adequately assess linguistic deficits and recovery patterns in persons with aphasia. As a result, both functional and structural methods for the ana- lysis of connected language samples from people with aphasia have been devised (see Armstrong, 2000; Prins & Bastiaanse, 2004). The present article focuses on our attempt to provide a comprehensive, multi-level procedure for both structural and functional analysis of narrative discourse produced by speakers with brain damage. Accordingly, we will describe a method for analysis of connected language samples elicited on single picture and cartoon story description tasks. This method has proven sensitive in the assessment of language deficits in many neurogenic populations. A comprehensive description of the language production sys- tem, a thorough discussion of the different approaches to discourse analysis in persons with aphasia, and the procedure for the analysis of narrative discourse are detailed. The characteristics of the eliciting stimuli, the procedures for their administration and the transcription of the language samples are carefully explained. The analysis focuses on four main aspects of linguistic processing: productivity, lexical and grammatical pro- cessing, narrative organisation, and informativeness. To further illustrate the analytic procedure, two case reports and an appendix with the analysis of a narrative sample are provided. We will provide direct evidence of the usefulness of the multi-level procedure for discourse analysis for assessing changes in discourse performance of two persons with fluent aphasia, with different aetiologies, that were not captured by tradi- tional standardised aphasia tests. The method of analysis presented in this paper has strong grounds in linguistic and psychological theories of linguistic structure and functioning. It also has the advantage of being both quantitative and functional as it captures selective aspects of linguistic processing, and can provide relevant information about the person's communicative and informative skills.
Ključne besede: aphasia, language, narrative analysis
Objavljeno v RUNG: 07.03.2016; Ogledov: 4397; Prenosov: 1
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Opis: Mild traumatic brain injury (mTBI) represents a condition whose cognitive and behavioral sequelae are often underestimated, even when it exerts a profound impact on the patients’ every-day life. The present study aimed to analyze the features of narrative discourse impairment in a group of adults with mTBI. 10 mTBI non-aphasic speakers (GCS > 13) and 13 neurologically intact participants were recruited for the experiment. Their cognitive, linguistic and narrative skills were thoroughly assessed. The group of mTBIs exhibited normal phonological, lexical and grammatical skills. However, their narratives were characterized by the pres- ence of frequent interruptions of ongoing utterances, derailments and extraneous utterances that at times made their discourse vague and ambiguous. They produced more errors of global coherence [F (1; 21)1⁄424.242; p1⁄4.000; h2p1⁄40. 536] and fewer Lexical Information Units [F (1; 21) 1⁄4 7.068; p 1⁄4 .015; h2p 1⁄4 .252]. The errors of global coherence correlated negatively with non- perseverative errors on the WCST (r 1⁄4 1⁄4.755; p < .012). The mac- rolinguistic problems made their narrative samples less informa- tive than those produced by the group of control participants. These disturbances may reflect a deficit at the interface between cognitive and linguistic processing rather than a specific linguistic disturbance. These findings suggest that also persons with mild forms of TBI may experience linguistic disturbances that may hamper the quality of their every-day life.
Ključne besede: mild traumatic brain injury, narrative analysis, neurolinguistics, neuropsychology
Objavljeno v RUNG: 07.03.2016; Ogledov: 4761; Prenosov: 1
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