896 research outputs found
Relativistic Diskoseismology
We will summarize results of calculations of the modes of oscillation trapped
within the inner region of accretion disks by the strong-field gravitational
properties of a black hole (or a compact, weakly-magnetized neutron star).
Their driving and damping will also be addressed. The focus will be on the most
observable class: the analogue of internal gravity modes in stars. Their
frequencies which corrrespond to the lowest mode numbers depend almost entirely
upon only the mass and angular momentum of the black hole. Such a feature may
have been detected in the X-ray power spectra of two galactic `microquasars',
allowing the angular momentum of the black hole to be determined in one case.Comment: To be published in Physics Reports, proceedings of the conference
Astrophysical Fluids: From Atomic Nuclei to Stars and Galaxies; 10 pages, 5
postscript figure
Relativistic Iron Lines in Galactic Black Holes: Recent Results and Lines in the ASCA Archive
Recent observations with Chandra and XMM-Newton, aided by broad-band spectral
coverage from RXTE, have revealed skewed relativistic iron emission lines in
stellar-mass Galactic black hole systems. Such systems are excellent
laboratories for testing General Relativity, and relativistic iron lines
provide an important tool for making such tests. In this contribution to the
Proceedings of the 10th Annual Marcel Grossmann Meeting on General Relativity,
we briefly review recent developments and present initial results from fits to
archival ASCA observations of Galactic black holes. It stands to reason that
relativistic effects, if real, should be revealed in many systems (rather than
just one or two); the results of our archival work have borne-out this
expectation. The ASCA spectra reveal skewed, relativistic lines in XTE
J1550-564, GRO J1655-40, GRS 1915+105, and Cygnus X-1.Comment: to appear in the proc. of the 10th Annual Marcel Grossmann Meeting on
General Relativity, 5 pages, 1 figure, uses specific .cls and .sty file
Ostre zapalenie trzustki w praktyce ratownika medycznego
The aim of the work was to discuss the behavior of a paramedic in acute
pancreatitis.
Acute pancreatitis, which in 15-20% of patients is a severe inflammation with
life-threatening complications and is associated with 5% mortality, belongs to the most
common acute states in gastroenterology.
On the basis of the information gathered, the following conclusions were made:
1. Acute pancreatitis is a disease in which systemic and local changes occur.
2. The occurrence of acute abdominal symptoms in a patient treated for acute
pancreatitis may indicate gastrointestinal perforation.
3. The procedure of the paramedic in case of acute pancreatitis consists in:
conducting an interview, carrying out a quick assessment of the patient,
examining basic life parameters, conducting a physical examination of the
abdominal cavity, administering fluids, analgesics and safe transport to the
hospital
Methoden und Werkzeuge zum Einsatz von rekonfigurierbaren Akzeleratoren in Mehrkernsystemen
Rechensysteme mit Mehrkernprozessoren werden häufig um einen rekonfigurierbaren Akzelerator wie einen FPGA erweitert. Die Verlagerung von Anwendungsteilen in Hardware wird meist von Spezialisten vorgenommen. Damit Anwender selbst rekonfigurierbare Hardware programmieren können, ist mein Beitrag die komponentenbasierte Programmierung und Verwendung mit automatischer Beachtung der
Datenlokalität. So lässt sich auch bei datenintensiven Anwendungen Nutzen aus den Akzeleratoren erzielen
Joint spectral-timing modelling of the hard lags in GX 339-4: constraints on reflection models
The X-ray variations of hard state black hole X-ray binaries above 2 keV show
'hard lags', in that the variations at harder energies follow variations at
softer energies, with a time-lag \tau depending on frequency \nu approximately
as \tau \propto \nu^{-0.7}. Several models have so far been proposed to explain
this time delay, including fluctuations propagating through an accretion flow,
spectral variations during coronal flares, Comptonisation in the extended hot
corona or a jet, or time-delays due to large-scale reflection from the
accretion disc. In principle these models can be used to predict the shape of
the energy spectrum as well as the frequency-dependence of the time-lags,
through the construction of energy-dependent response functions which map the
emission as a function of time-delay in the system. Here we use this approach
to test a simple reflection model for the frequency-dependent lags seen in the
hard state of GX 339-4, by simultaneously fitting the model to the
frequency-dependent lags and energy spectrum measured by XMM-Newton in 2004 and
2009. Our model cannot simultaneously fit both the lag and spectral data, since
the relatively large lags require an extremely flared disc which subtends a
large solid angle to the continuum at large radii, in disagreement with the
observed Fe K\alpha emission. Therefore, we consider it more likely that the
lags > 2 keV are caused by propagation effects in the accretion flow, possibly
related to the accretion disc fluctuations which have been observed previously.Comment: 11 pages, 11 figures. Accepted for publication in MNRA
Exploiting the HTX-Board as a Coprocessor for Exact Arithmetics
Certain numerical computations benefit from dedicated computation units, e.g. providing increased computation accuracy. Exploiting current interconnection technologies and advances in reconfigurable logic, restrictions and drawbacks of past approaches towards application-specific units can be overcome. This paper presents our implementation of an FPGA-based hardware unit for exact arithmetics. The unit is tightly integrated into the host system using state-of-the-art HyperTransport technology. An according runtime system provides OS-level support including dynamic function resolution. The approach demonstrates suitability and applicability of the chosen technologies, setting the pace towards broadly acceptable use of reconfigurable coprocessor technology for application-specific computing
Reflection and noise in the low spectral state of GX339-4
We analyze RXTE/PCA observations of GX339-4 in the low spectral state from
1996--1997 and show that the pattern of its spectral and temporal variability
is nearly identical to that of Cyg X-1. In particular, a tight correlation
exists between the QPO centroid frequency and the spectral parameters. An
increase of the QPO centroid frequency is accompanied with an increase of the
amplitude of the reflected component and a steepening the slope of the
underlying power law. Fourier frequency resolved spectral analysis showed, that
the variability of the reflected component at frequencies higher than ~1-10 Hz
is suppressed in comparison with that of the primary emission.Comment: 4 pages, 4 figures. Accepted in Astronomy and Astrophysics Main
Journa
X-ray continuum variability of MCG-6-30-15
This paper presents a comprehensive examination of the X-ray continuum
variability of the bright Seyfert 1 galaxy MCG-6-30-15. The source clearly
shows the strong, linear correlation between rms variability amplitude and flux
first seen in Galactic X-ray binaries. The high frequency power spectral
density (PSD) of MCG-6-30-15 is examined in detail using a Monte Carlo fitting
procedure and is found to be well represented by a steep power-law at high
frequencies (with a power-law index alpha ~ 2.5), breaking to a flatter slope
(alpha ~ 1) below f_br ~ 0.6 - 2.0 x 10^-4 Hz, consistent with the previous
results of Uttley, McHardy & Papadakis. The slope of the power spectrum above
the break is energy dependent, with the higher energies showing a flatter PSD.
At low frequencies the variations between different energy bands are highly
coherent while at high frequencies the coherence is significantly reduced. Time
lags are detected between energy bands, with the soft variations leading the
hard. The magnitude of the lag is small (<200 s for the frequencies observed)
and is most likely frequency dependent. These properties are remarkably similar
to the temporal properties of the Galactic black hole candidate Cygnus X-1. The
characteristic timescales in these two types of source differ by ~10^5;
assuming that these timescales scale linearly with black hole mass then
suggests a black hole mass ~10^6 M_sun for MCG-6-30-15. We speculate that the
timing properties of MCG-6-30-15 may be analogous to those of Cyg X-1 in its
high/soft state and discuss a simple phenomenological model, originally
developed to explain the timing properties of Cyg X-1, that can explain many of
the observed properties of MCG-6-30-15.Comment: 19 pages, 24 figures, accepted for publication in MNRA
Comparison of data-driven uncertainty quantification methods for a carbon dioxide storage benchmark scenario
A variety of methods is available to quantify uncertainties arising with\-in
the modeling of flow and transport in carbon dioxide storage, but there is a
lack of thorough comparisons. Usually, raw data from such storage sites can
hardly be described by theoretical statistical distributions since only very
limited data is available. Hence, exact information on distribution shapes for
all uncertain parameters is very rare in realistic applications. We discuss and
compare four different methods tested for data-driven uncertainty
quantification based on a benchmark scenario of carbon dioxide storage. In the
benchmark, for which we provide data and code, carbon dioxide is injected into
a saline aquifer modeled by the nonlinear capillarity-free fractional flow
formulation for two incompressible fluid phases, namely carbon dioxide and
brine. To cover different aspects of uncertainty quantification, we incorporate
various sources of uncertainty such as uncertainty of boundary conditions, of
conceptual model definitions and of material properties. We consider recent
versions of the following non-intrusive and intrusive uncertainty
quantification methods: arbitary polynomial chaos, spatially adaptive sparse
grids, kernel-based greedy interpolation and hybrid stochastic Galerkin. The
performance of each approach is demonstrated assessing expectation value and
standard deviation of the carbon dioxide saturation against a reference
statistic based on Monte Carlo sampling. We compare the convergence of all
methods reporting on accuracy with respect to the number of model runs and
resolution. Finally we offer suggestions about the methods' advantages and
disadvantages that can guide the modeler for uncertainty quantification in
carbon dioxide storage and beyond
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