1,423 research outputs found
Observation of GRB 030131 with the INTEGRAL satellite
A long Gamma-Ray Burst (GRB) was detected with the instruments on board the
INTEGRAL satellite on January 31 2003. Although most of the GRB, which lasted
150 seconds, occurred during a satellite slew, the automatic software of
the INTEGRAL Burst Alert System was able to detect it in near-real time. Here
we report the results obtained with the IBIS instrument, which detected GRB
030131 in the 15 keV - 200 keV energy range, and ESO/VLT observations of its
optical transient. The burst displays a complex time profile with numerous
peaks. The peak spectrum can be described by a single power law with photon
index 1.7 and has a flux of 2 photons cm s in
the 20-200 keV energy band. The high sensitivity of IBIS has made it possible
for the first time to perform detailed time-resolved spectroscopy of a GRB with
a fluence of 7 erg cm (20-200 keV).Comment: Accepted for publication in A&A, 5 pages, 4 figures, late
Effects of guanidine on synaptic transmission in the spinal cord of the frog
The effects of guanidine on motoneurons of the isolated frog spinal cord were studied by adding the drug to the solution bathing the cord during intracellular recording. Guanidine (5·10–4 M) did not alter the membrane potential of motoneurons.
The main effect was a marked increase of the amplitudes and frequencies of small spontaneously occurring inhibitory postsynaptic potentials. The hyperpolarizing component of postsynaptic potentials evoked by stimulation of dorsal roots was also enhanced by guanidine. Higher concentrations of guanidine (5·10–3 M) resulted in a very large and irreversible increase of the small spontaneously occurring inhibitory potentials, which now appeared in a regular, rhythmic pattern.
The effects of guanidine could easily be blocked by increasing the magnesium ions (15 mM) in the bath solution.
These results indicate that guanidine facilitates the release of an inhibitory transmitter in afferent terminals of the frog spinal cord either by a direct action on these terminals or indirectly by an action on nerve endings impinging on inhibitory interneurons
The Interplanetary Network Supplement to the BeppoSAX Gamma-Ray Burst Catalogs
Between 1996 July and 2002 April, one or more spacecraft of the
interplanetary network detected 787 cosmic gamma-ray bursts that were also
detected by the Gamma-Ray Burst Monitor and/or Wide-Field X-Ray Camera
experiments aboard the BeppoSAX spacecraft. During this period, the network
consisted of up to six spacecraft, and using triangulation, the localizations
of 475 bursts were obtained. We present the localization data for these events.Comment: 89 pages, 3 figures. Submitted to the Astrophysical Journal
Supplement Serie
Cosmological MHD simulations of cluster formation with anisotropic thermal conduction
(abridged) The ICM has been suggested to be buoyantly unstable in the
presence of magnetic field and anisotropic thermal conduction. We perform first
cosmological simulations of galaxy cluster formation that simultaneously
include magnetic fields, radiative cooling and anisotropic thermal conduction.
In isolated and idealized cluster models, the magnetothermal instability (MTI)
tends to reorient the magnetic fields radially. Using cosmological simulations
of the Santa Barbara cluster we detect radial bias in the velocity and magnetic
fields. Such radial bias is consistent with either the inhomogeneous radial gas
flows due to substructures or residual MTI-driven field rearangements that are
expected even in the presence of turbulence. Although disentangling the two
scenarios is challenging, we do not detect excess bias in the runs that include
anisotropic thermal conduction. The anisotropy effect is potentially detectable
via radio polarization measurements with LOFAR and SKA and future X-ray
spectroscopic studies with the IXO. We demonstrate that radiative cooling
boosts the amplification of the magnetic field by about two orders of magnitude
beyond what is expected in the non-radiative cases. At z=0 the field is
amplified by a factor of about 10^6 compared to the uniform magnetic field
evolved due to the universal expansion alone. Interestingly, the runs that
include both radiative cooling and anisotropic thermal conduction exhibit
stronger magnetic field amplification than purely radiative runs at the
off-center locations. In these runs, shallow temperature gradients away from
the cluster center make the ICM neutrally buoyant. The ICM is more easily mixed
in these regions and the winding up of the frozen-in magnetic field is more
efficient resulting in stronger magnetic field amplification.Comment: submitted to ApJ, higher resolution figures available at:
http://www.astro.lsa.umich.edu/~mateuszr
Better Nonlinear Models from Noisy Data: Attractors with Maximum Likelihood
A new approach to nonlinear modelling is presented which, by incorporating
the global behaviour of the model, lifts shortcomings of both least squares and
total least squares parameter estimates. Although ubiquitous in practice, a
least squares approach is fundamentally flawed in that it assumes independent,
normally distributed (IND) forecast errors: nonlinear models will not yield IND
errors even if the noise is IND. A new cost function is obtained via the
maximum likelihood principle; superior results are illustrated both for small
data sets and infinitely long data streams.Comment: RevTex, 11 pages, 4 figure
Globally coupled chaotic maps and demographic stochasticity
The affect of demographic stochasticity of a system of globally coupled
chaotic maps is considered. A two-step model is studied, where the intra-patch
chaotic dynamics is followed by a migration step that coupled all patches; the
equilibrium number of agents on each site, , controls the strength of the
discreteness-induced fluctuations. For small (large fluctuations) a
period-doubling cascade appears as the coupling (migration) increases. As
grows an extremely slow dynamic emerges, leading to a flow along a
one-dimensional family of almost period 2 solutions. This manifold become a
true solutions in the deterministic limit. The degeneracy between different
attractors that characterizes the clustering phase of the deterministic system
is thus the limit of the slow dynamics manifold
Cube law, condition factor and weight-length relationships: history, meta-analysis and recommendations
This study presents a historical review, a meta-analysis, and recommendations for users about weight–length relationships, condition factors and relative weight equations. The historical review traces the developments of the respective concepts. The meta-analysis explores 3929 weight–length relationships of the type W = aLb for 1773 species of fishes. It shows that 82% of the variance in a plot of log a over b can be explained by allometric versus isometric growth patterns and by different body shapes of the respective species. Across species median b = 3.03 is significantly larger than 3.0, thus indicating a tendency towards slightly positive-allometric growth (increase in relative body thickness or plumpness) in most fishes. The expected range of 2.5 < b < 3.5 is confirmed. Mean estimates of b outside this range are often based on only one or two weight–length relationships per species. However, true cases of strong allometric growth do exist and three examples are given. Within species, a plot of log a vs b can be used to detect outliers in weight–length relationships. An equation to calculate mean condition factors from weight–length relationships is given as Kmean = 100aLb−3. Relative weight Wrm = 100W/(amLbm) can be used for comparing the condition of individuals across populations, where am is the geometric mean of a and bm is the mean of b across all available weight–length relationships for a given species. Twelve recommendations for proper use and presentation of weight–length relationships, condition factors and relative weight are given
Performance Evaluation of a Biometric System Based on Acoustic Images
An acoustic electronic scanning array for acquiring images from a person using a biometric application is developed. Based on pulse-echo techniques, multifrequency acoustic images are obtained for a set of positions of a person (front, front with arms outstretched, back and side). Two Uniform Linear Arrays (ULA) with 15 λ/2-equispaced sensors have been employed, using different spatial apertures in order to reduce sidelobe levels. Working frequencies have been designed on the basis of the main lobe width, the grating lobe levels and the frequency responses of people and sensors. For a case-study with 10 people, the acoustic profiles, formed by all images acquired, are evaluated and compared in a mean square error sense. Finally, system performance, using False Match Rate (FMR)/False Non-Match Rate (FNMR) parameters and the Receiver Operating Characteristic (ROC) curve, is evaluated. On the basis of the obtained results, this system could be used for biometric applications
Peculiar Extended X-ray Emission around the "Radio-Loud" Black Hole Candidate 1E1740.7-2942
We present the discovery of peculiar extended X-ray emission around
1E1740.7-2942, a black hole candidate that is known to produce prominent,
persistent radio jets. The data was obtained with the High-Energy Transmission
Grating Spectrometer (HETGS) aboard the Chandra X-ray Observatory. The
zeroth-order image reveals an elongated feature about 3" in length that is
roughly perpendicular to the radio lobes (or jets). The feature is roughly
symmetric about the point source. It is spatially resolved in the long
direction but not in the short direction.
The position of 1E1740.7-2942 was determined with a statistical accuracy of
\~0.06" in the right ascension and ~0.04" in the declination, thanks to
Chandra's unprecedented spatial resolution. It is about 0.6" from the radio
position but the difference is well within the uncertainty in the absolute
aspect solutions of the observation. The dispersed HETGS spectra of
1E1740.7-2942 show evidence for the presence of weak, narrow emission lines,
although the statistics are quite limited. We discuss possible origins of the
extended emission and the implications of the emission lines.Comment: To appear in Ap
GJ 1252 b: A 1.2 R\u3csub\u3e⊕\u3c/sub\u3e Planet Transiting An M3 Dwarf At 20.4 pc
We report the discovery of GJ 1252 b, a planet with a radius of 1.193 ± 0.074 R⊕ and an orbital period of 0.52 days around an M3-type star (0.381 ± 0.019 M⊕, 0.391 ± 0.020 R⊕) located 20.385 ± 0.019 pc away. We use Transiting Exoplanet Survey Satellite (TESS) data, ground-based photometry and spectroscopy, Gaia astrometry, and high angular resolution imaging to show that the transit signal seen in the TESS data must originate from a transiting planet. We do so by ruling out all false-positive scenarios that attempt to explain the transit signal as originating from an eclipsing stellar binary. Precise Doppler monitoring also leads to a tentative mass measurement of 2.09 ± 0.56 M⊕. The host star proximity, brightness (V = 12.19 mag, K = 7.92 mag), low stellar activity, and the system\u27s short orbital period make this planet an attractive target for detailed characterization, including precise mass measurement, looking for other objects in the system, and planet atmosphere characterization
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