129 research outputs found
Beyond the Singularity of the 2-D Charged Black Hole
Two dimensional charged black holes in string theory can be obtained as exact
(SL(2,R)xU(1))/U(1) quotient CFTs. The geometry of the quotient is induced from
that of the group, and in particular includes regions beyond the black hole
singularities. Moreover, wavefunctions in such black holes are obtained from
gauge invariant vertex operators in the SL(2,R) CFT, hence their behavior
beyond the singularity is determined. When the black hole is charged we find
that the wavefunctions are smooth at the singularities. Unlike the uncharged
case, scattering waves prepared beyond the singularity are not fully reflected;
part of the wave is transmitted through the singularity. Hence, the physics
outside the horizon of a charged black hole is sensitive to conditions set
behind the past singularity.Comment: 19 pages, 5 figures; v2: refs added, minor typos corrected; v3:
references on the infinite blue shift at the inner horizon and minor
corrections adde
On the accretion disc properties in eclipsing dwarf nova EM Cyg
In this paper we analyzed the behavior of the unusual dwarf nova EM Cyg using
the data obtained in April-October, 2007 in Vyhorlat observatory (Slovak
Republic) and in September, 2006 in Crimean Astrophysical Observatory
(Ukraine). During our observations EM Cyg has shown outbursts in every 15-40
days. Because on the light curves of EM Cyg the partial eclipse of an accretion
disc is observed we applied the eclipse mapping technique to reconstruct the
temperature distribution in eclipsed parts of the disc. Calculations of the
accretion rate in the system were made for the quiescent and the outburst
states of activity for different distances.Comment: 6 pages, 3 figures, accepted in Astrophysics and Space Scienc
Half-metallicity and Slater-Pauling behavior in the ferromagnetic Heusler alloys
Introductory chapter for the book "Halfmetallic Alloys - Fundamentals and
Applications" to be published in the series Springer Lecture Notes on Physics,
P. H. Dederichs and I. Galanakis (eds). It contains a review of the theoretical
work on the half-metallic Heusler alloys.Comment: Introductory chapter for the book "Halfmetallic Alloys - Fundamentals
and Applications" to be published in the series Springer Lecture Notes on
Physics, P. H. Dederichs and I. Galanakis (eds
Anthropogenic Space Weather
Anthropogenic effects on the space environment started in the late 19th
century and reached their peak in the 1960s when high-altitude nuclear
explosions were carried out by the USA and the Soviet Union. These explosions
created artificial radiation belts near Earth that resulted in major damages to
several satellites. Another, unexpected impact of the high-altitude nuclear
tests was the electromagnetic pulse (EMP) that can have devastating effects
over a large geographic area (as large as the continental United States). Other
anthropogenic impacts on the space environment include chemical release ex-
periments, high-frequency wave heating of the ionosphere and the interaction of
VLF waves with the radiation belts. This paper reviews the fundamental physical
process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure
OGLE-2018-BLG-0022: A Nearby M-dwarf Binary
We report observations of the binary microlensing event OGLE-2018-BLG-0022, provided by the Robotic Observations of Microlensing Events (ROME)/Reactive Event Assessment (REA) Survey, which indicate that the lens is a low-mass binary star consisting of M3 (0.375 ± 0.020 M⊙) and M7 (0.098 ± 0.005 M⊙) components. The lens is unusually close, at 0.998 ± 0.047 kpc, compared with the majority of microlensing events, and despite its intrinsically low luminosity, it is likely that adaptive optics observations in the near future will be able to provide an independent confirmation of the lens masses
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Maritime aerosol network as a component of AERONET - First results and comparison with global aerosol models and satellite retrievals
The Maritime Aerosol Network (MAN) has been collecting data over the oceans since November 2006. Over 80 cruises were completed through early 2010 with deployments continuing. Measurement areas included various parts of the Atlantic Ocean, the Northern and Southern Pacific Ocean, the South Indian Ocean, the Southern Ocean, the Arctic Ocean and inland seas. MAN deploys Microtops hand-held sunphotometers and utilizes a calibration procedure and data processing traceable to AERONET. Data collection included areas that previously had no aerosol optical depth (AOD) coverage at all, particularly vast areas of the Southern Ocean. The MAN data archive provides a valuable resource for aerosol studies in maritime environments. In the current paper we present results of AOD measurements over the oceans, and make a comparison with satellite AOD retrievals and model simulations
Epidemiology of Escherichia coli bacteraemia in England: results of an enhanced sentinel surveillance programme
Background: Escherichia coli causes over one third of the bacteraemia cases in England each year, and the incidence of these infections is increasing. Aim: To determine the underlying risk factors associated with E. coli bacteraemia. Methods: A three month enhanced sentinel surveillance study involving 35 National Health Service hospitals was undertaken in the winter of 2012/13 to collect risk factor information and further details on the underlying source of infection to augment data already collected by the English national surveillance programme. Antimicrobial susceptibility results for E. coli isolated from blood and urine were also collected. Findings: A total of 1,731 cases of E. coli bacteraemia were included. The urogenital tract was the most commonly reported source of infection (51.2% of cases) with prior treatment for a urinary tract infection being the largest independent effect associated with this infection source. Half of all patients had prior healthcare exposure in the month prior to the bacteraemia with antimicrobial therapy and urinary catheterisation being reported in one third and one fifth of these patients. Prior healthcare exposure was associated with a higher proportion of antibiotic non-susceptibility in the blood culture isolates (P=0.001). Conclusion: Analysis of risk factors suggests potential community and hospital-related interventions particularly better use of urinary catheters and improved antibiotic management of urinary tract infections. As part of the latter strategy, antibiotic resistance profiles need to be closely monitored to ensure treatment guidelines are up to date to limit inappropriate empiric therapy
The L 98-59 System: Three Transiting, Terrestrial-Size Planets Orbiting A Nearby M Dwarf
We report the Transiting Exoplanet Survey Satellite (TESS) discovery of three terrestrial-size planets transiting L 98-59 (TOI-175, TIC 307210830)—a bright M dwarf at a distance of 10.6 pc. Using the Gaia-measured distance and broadband photometry, we find that the host star is an M3 dwarf. Combined with the TESS transits from three sectors, the corresponding stellar parameters yield planet radii ranging from 0.8 R⊕ to 1.6 R⊕. All three planets have short orbital periods, ranging from 2.25 to 7.45 days with the outer pair just wide of a 2:1 period resonance. Diagnostic tests produced by the TESS Data Validation Report and the vetting package DAVE rule out common false-positive sources. These analyses, along with dedicated follow-up and the multiplicity of the system, lend confidence that the observed signals are caused by planets transiting L 98-59 and are not associated with other sources in the field. The L 98-59 system is interesting for a number of reasons: the host star is bright (V = 11.7 mag, K = 7.1 mag) and the planets are prime targets for further follow-up observations including precision radial-velocity mass measurements and future transit spectroscopy with the James Webb Space Telescope; the near-resonant configuration makes the system a laboratory to study planetary system dynamical evolution; and three planets of relatively similar size in the same system present an opportunity to study terrestrial planets where other variables (age, metallicity, etc.) can be held constant. L 98-59 will be observed in four more TESS sectors, which will provide a wealth of information on the three currently known planets and have the potential to reveal additional planets in the system
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