293 research outputs found
From Classical Trajectories to Quantum Commutation Relations
In describing a dynamical system, the greatest part of the work for a
theoretician is to translate experimental data into differential equations. It
is desirable for such differential equations to admit a Lagrangian and/or an
Hamiltonian description because of the Noether theorem and because they are the
starting point for the quantization. As a matter of fact many ambiguities arise
in each step of such a reconstruction which must be solved by the ingenuity of
the theoretician. In the present work we describe geometric structures emerging
in Lagrangian, Hamiltonian and Quantum description of a dynamical system
underlining how many of them are not really fixed only by the trajectories
observed by the experimentalist.Comment: 25 pages. Comments are welcome
Stopping of Charged Particles in a Magnetized Classical Plasma
The analytical and numerical investigations of the energy loss rate of the
test particle in a magnetized electron plasma are developed on the basis of the
Vlasov-Poisson equations, and the main results are presented. The Larmor
rotation of a test particle in a magnetic field is taken into account. The
analysis is based on the assumption that the energy variation of the test
particle is much less than its kinetic energy. The obtained general expression
for stopping power is analyzed for three cases: (i) the particle moves through
a collisionless plasma in a strong homogeneous magnetic field; (ii) the fast
particle moves through a magnetized collisionless plasma along the magnetic
field; and (iii) the particle moves through a magnetized collisional plasma
across a magnetic field. Calculations are carried out for the arbitrary test
particle velocities in the first case, and for fast particles in the second and
third cases. It is shown that the rate at which a fast test particle loses
energy while moving across a magnetic field may be much higher than the loss in
the case of motion through plasma without magnetic field.Comment: 14 pages, 3 figures, LaTe
The afterglow and host galaxy of GRB 090205: evidence for a Ly-alpha emitter at z=4.65
Gamma-ray bursts have been proved to be detectable up to distances much
larger than any other astrophysical object, providing the most effective way,
complementary to ordinary surveys, to study the high redshift universe. To this
end, we present here the results of an observational campaign devoted to the
study of the high-z GRB 090205. We carried out optical/NIR spectroscopy and
imaging of GRB 090205 with the ESO-VLT starting from hours after the event up
to several days later to detect the host galaxy. We compared the results
obtained from our optical/NIR observations with the available Swift high-energy
data of this burst. Our observational campaign led to the detection of the
optical afterglow and host galaxy of GRB 090205 and to the first measure of its
redshift, z=4.65. Similar to other, recent high-z GRBs, GRB 090205 has a short
duration in the rest-frame with T_{90,rf}=1.6 s, which suggests the possibility
that it might belong to the short GRBs class. The X-ray afterglow of GRB 090205
shows a complex and interesting behaviour with a possible rebrightening at
500-1000s from the trigger time and late flaring activity. Photometric
observations of the GRB 090205 host galaxy argue in favor of a starburst galaxy
with a stellar population younger than ~ 150 Myr. Moreover, the metallicity of
Z > 0.27 Z_Sun derived from the GRB afterglow spectrum is among the highest
derived from GRB afterglow measurement at high-z, suggesting that the burst
occurred in a rather enriched envirorment. Finally, a detailed analysis of the
afterglow spectrum shows the existence of a line corresponding to Lyman-alpha
emission at the redshift of the burst. GRB 090205 is thus hosted in a typical
Lyman-alpha emitter (LAE) at z=4.65. This makes the GRB 090205 host the
farthest GRB host galaxy, spectroscopically confirmed, detected to date.Comment: Accepted for publication in Astronomy and Astrophysics; 8 pages, 7
figure
Simultaneous multiwavelength observations of the Low/Hard State of the X-ray transient source SWIFT J1753.5-0127
We report the results of simultaneous multiwavelength observations of the
X-ray transient source SWIFT J1753.5-0127 performed with INTEGRAL, RXTE, NTT,
REM and VLA on 2005 August 10-12. The source, which underwent an X-ray outburst
since 2005 May 30, was observed during the INTEGRAL Target of Opportunity
program dedicated to new X-ray novae located in the Galactic Halo. Broad-band
spectra and fast timing variability properties of SWIFT J1753.5-0127 are
analyzed together with the optical, near infra-red and radio data. We show that
the source was significantly detected up to 600 keV with Comptonization
parameters and timing properties typical of the so-called Low/Hard State of
black hole candidates. We build a spectral energy distribution and we show that
SWIFT J1753.5-0127 does not follow the usual radio/X-ray correlation of X-ray
binaries in the Low/Hard State. We give estimates of distance and mass. We
conclude that SWIFT J1753.5-0127 belongs to the X-ray nova class and that it is
likely a black hole candidate transient source of the Galactic Halo which
remained in the Low/Hard State during its main outburst. We discuss our results
within the context of Comptonization and jet models.Comment: Accepted for publication in ApJ, 25 pages, 4 tables, 11 figures (3 in
color
Preliminary results of a systematic review focusing on the effectiveness of the interventions in preventing the progression of frailty in older adults
uropean Union’s Health Programme - Project FOCUSpublishe
Recommended from our members
A Photometric Redshift of z ~ 9.4 for GRB 090429B
Gamma-ray bursts (GRBs) serve as powerful probes of the early universe, with their luminous afterglows revealing the locations and physical properties of star-forming galaxies at the highest redshifts, and potentially locating first-generation (Population III) stars. Since GRB afterglows have intrinsically very simple spectra, they allow robust redshifts from low signal-to-noise spectroscopy, or photometry. Here we present a photometric redshift of z ~ 9.4 for the Swift detected GRB 090429B based on deep observations with Gemini-North, the Very Large Telescope, and the GRB Optical and Near-infrared Detector. Assuming a Small Magellanic Cloud dust law (which has been found in a majority of GRB sight lines), the 90% likelihood range for the redshift is 9.06 7. The non-detection of the host galaxy to deep limits (Y(AB) ~ 28, which would correspond roughly to 0.001L* at z = 1) in our late-time optical and infrared observations with the Hubble Space Telescope strongly supports the extreme-redshift origin of GRB 090429B, since we would expect to have detected any low-z galaxy, even if it were highly dusty. Finally, the energetics of GRB 090429B are comparable to those of other GRBs and suggest that its progenitor is not greatly different from those of lower redshift bursts
The Optical SN 2012bz Associated with the Long GRB 120422A
The association of Type Ic SNe with long-duration GRBs is well established.
We endeavor, through accurate ground-based observational campaigns, to
characterize these SNe at increasingly high redshifts. We obtained a series of
optical photometric and spectroscopic observations of the Type Ic SN2012bz
associated with the Swift long-duration GRB120422A (z=0.283) using the 3.6-m
TNG and the 8.2-m VLT telescopes. The peak times of the light curves of
SN2012bz in various optical filters differ, with the B-band and i'-band light
curves reaching maximum at ~9 and ~23 rest-frame days, respectively. The
bolometric light curve has been derived from individual bands photometric
measurements, but no correction for the unknown contribution in the
near-infrared (probably around 10-15%) has been applied. Therefore, the present
light curve should be considered as a lower limit to the actual UV-optical-IR
bolometric light curve. This pseudo-bolometric curve reaches its maximum (Mbol
= -18.56 +/- 0.06) at 13 +/- 1 rest-frame days; it is similar in shape and
luminosity to the bolometric light curves of the SNe associated with z<0.2 GRBs
and more luminous than those of SNe associated with XRFs. A comparison with the
model generated for the bolometric light curve of SN2003dh suggests that
SN2012bz produced only about 15% less 56Ni than SN2003dh, about 0.35 Msol.
Similarly the VLT spectra of SN2012bz, after correction for Galactic extinction
and for the contribution of the host galaxy, suggest comparable explosion
parameters with those observed in SN2003dh (EK~3.5 x 10^52 erg, Mej~7 Msol) and
a similar progenitor mass (~25-40 Msol). GRB120422A is consistent with the
Epeak-Eiso and the EX,iso-Egamma,iso-E_peak relations. GRB120422A/SN2012bz
shows the GRB-SN connection at the highest redshift so far accurately monitored
both photometrically and spectroscopically.Comment: 7 pages, 6 figures, 2 tables, accepted for publication in Astronomy &
Astrophysic
Characterization of the Prokaryotic Sodium Channel NavSp Pore with a Microfluidic Bilayer Platform
This paper describes the use of a newly-developed micro-chip bilayer platform to examine the electrophysiological properties of the prokaryotic voltage-gated sodium channel pore (NavSp) from Silicibacter pomeroyi. The platform allows up to 6 bilayers to be analysed simultaneously. Proteoliposomes were incorporated into suspended lipid bilayers formed within the microfluidic bilayer chips. The chips provide access to bilayers from either side, enabling the fast and controlled titration of compounds. Dose-dependent modulation of the opening probability by the channel blocking drug nifedipine was measured and its IC50 determined
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