1,342 research outputs found
Quantification of depth of anesthesia by nonlinear time series analysis of brain electrical activity
We investigate several quantifiers of the electroencephalogram (EEG) signal
with respect to their ability to indicate depth of anesthesia. For 17 patients
anesthetized with Sevoflurane, three established measures (two spectral and one
based on the bispectrum), as well as a phase space based nonlinear correlation
index were computed from consecutive EEG epochs. In absence of an independent
way to determine anesthesia depth, the standard was derived from measured blood
plasma concentrations of the anesthetic via a pharmacokinetic/pharmacodynamic
model for the estimated effective brain concentration of Sevoflurane. In most
patients, the highest correlation is observed for the nonlinear correlation
index D*. In contrast to spectral measures, D* is found to decrease
monotonically with increasing (estimated) depth of anesthesia, even when a
"burst-suppression" pattern occurs in the EEG. The findings show the potential
for applications of concepts derived from the theory of nonlinear dynamics,
even if little can be assumed about the process under investigation.Comment: 7 pages, 5 figure
Morphology of radio relics-II. Properties of polarized emission
Radio relics are diffuse radio sources in galaxy clusters that are associated with merger shock waves. Detailed observations of radio relics in total intensity and in polarization show complex structures on kiloparsec scales. The relation between the observed features and the underlying morphology of the magnetic field is not clear. Using 3D magneto-hydrodynamical simulations, we study the polarized emission produced by a shock wave that propagates through a turbulent medium that resembles the intracluster medium. We model the polarized synchrotron emission on the basis of diffusive shock acceleration of cosmic ray electrons. We find that the synchrotron emission produced in a shocked turbulent medium can reproduce some of the observed features in radio relics. Shock compression can give rise to a high polarization fraction at the shock front and a partial alignment of the polarization E-vectors with the shock normal. Our work confirms that radio relics can also be formed in an environment with a tangled magnetic field. We also discuss the effect of Faraday rotation intrinsic to the source, and how our results depend on the angular resolution of observations
Systematic study of X-ray Cavities in the brightest galaxy of the Draco Constellation NGC 6338
We present results based on the systematic analysis of currently available
Chandra archive data on the brightest galaxy in the Draco constellation NGC
6338, in order to investigate the properties of the X-ray cavities. In the
central ~6 kpc, at least a two and possibly three, X-ray cavities are evident.
All these cavities are roughly of ellipsoidal shapes and show a decrement in
the surface brightness of several tens of percent. In addition to these
cavities, a set of X-ray bright filaments are also noticed which are spatially
coincident with the H{\alpha} filaments over an extent of 15 kpc. The H{\alpha}
emission line filaments are perpendicular to the X- ray cavities. Spectroscopic
analysis of the hot gas in the filaments and cavities reveal that the X-ray
filaments are cooler than the gas contained in the cavities. The emission line
ratios and the extended, asymmetric nature of the H{\alpha} emission line
filaments seen in this system require a harder ionizing source than that
produced by star formation and/or young, massive stars. Radio emission maps
derived from the analysis of 1.4 GHz VLA FIRST survey data failed to show any
association of these X-ray cavities with radio jets, however, the cavities are
filled by radio emission. The total power of the cavities is 17\times 1042 erg
s-1 and the ratio of the radio luminosity to cavity power is ~ 10-4, implying
that most of the jet power is mechanical.Comment: The paper contains 12 figures and 3 tables, Accepted 2011 December 7
for publication in MNRA
Multiplex real-time PCR and blood culture for identification of bloodstream pathogens in patients with suspected sepsis
n/
Revealing the magnetic field in a distant galaxy cluster: discovery of the complex radio emission from MACS J0717.5 +3745
Aims. To study at multiple frequencies the radio emission arising from the
massive galaxy cluster MACS J0717.5+3745 (z=0.55). Known to be an extremely
complex cluster merger, the system is uniquely suited for an investigation of
the phenomena at work in the intra-cluster medium (ICM) during cluster
collisions. Methods. We use multi-frequency and multi-resolution data obtained
with the Very Large Array radio telescope, and X-ray features revealed by
Chandra, to probe the non-thermal and thermal components of the ICM, their
relations and interactions. Results. The cluster shows highly complex radio
emission. A bright, giant radio halo is detected at frequencies as high as 4.8
GHz. MACS J0717.5+3745 is the most distant cluster currently known to host a
radio halo. This radio halo is also the most powerful ever observed, and the
second case for which polarized radio emission has been detected, indicating
that the magnetic field is ordered on large scales.Comment: 14 pages, 13 figures, Astronomy and Astrophysics, accepte
The "toothbrush-relic": evidence for a coherent linear 2-Mpc scale shock wave in a massive merging galaxy cluster?
Some merging galaxy clusters host diffuse extended radio emission, so-called
radio halos and relics. Here we present observations between 147 MHz and 4.9
GHz of a new radio-selected galaxy cluster 1RXS J0603.3+4214 (z=0.225). The
cluster is also detected as an extended X-ray source in the RASS. It hosts a
large bright 1.9 Mpc radio relic, an elongated ~2 Mpc radio halo, and two
smaller radio relics. The large radio relic has a peculiar linear morphology.
For this relic we observe a clear spectral index gradient, in the direction
towards the cluster center. We performed Rotation Measure (RM) Synthesis
between 1.2 and 1.7 GHz. The results suggest that for the west part of the
large relic some of the Faraday rotation is caused by ICM and is not only due
to galactic foregrounds. We also carried out a detailed spectral analysis of
this radio relic and created radio color-color diagrams. We find (i) an
injection spectral index of -0.6 to -0.7, (ii) steepening spectral index and
increasing spectral curvature in the post-shock region, and (iii) an overall
power-law spectrum between 74 MHz and 4.9 GHz with \alpha=-1.10 \pm 0.02.
Mixing of emission in the beam from regions with different spectral ages is
probably the dominant factor that determines the shape of the radio spectra.
Changes in the magnetic field, total electron content, or adiabatic
gains/losses do not play a major role. A model in which particles are
(re)accelerated in a first order Fermi process at the front of the relic
provides the best match to the observed spectra. We speculate that in the
post-shock region particles are re-accelerated by merger induced turbulence to
form the radio halo as the relic and halo are connected. The 1RXS J0603.3+4214
merger is probably more complex than the "simple'" binary merger events that
are thought to give rise to symmetric double radio relics.Comment: 22 pages, 22 figures, accepted for publication in A\&A on September
3, 201
Relics as probes of galaxy cluster mergers
Galaxy clusters grow by mergers with other clusters and galaxy groups. These
mergers create shocks within the intracluster medium (ICM). It is proposed that
within the shocks particles can be accelerated to extreme energies. In the
presence of a magnetic field these particles should then form large regions
emitting synchrotron radiation, creating so-called radio relics. An example of
a cluster with relics is CIZA J2242.8+5301. Here we present hydrodynamical
simulations of idealized binary cluster collisions with the aim of constraining
the merger scenario for this cluster. We conclude that by using the location,
size and width of double radio relics we can set constraints on the mass
ratios, impact parameters, timescales, and viewing geometries of binary cluster
merger events.Comment: Accepted for publication in special issue of Journal of Astrophysics
and Astronomy: conference proceedings of "Diffuse Relativistic Plasmas"
conference, Bangalore, 1-4 March 2011, 4 pages, 2 figure
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