290 research outputs found
The Geometry of Integrable and Superintegrable Systems
The group of automorphisms of the geometry of an integrable system is
considered. The geometrical structure used to obtain it is provided by a normal
form representation of integrable systems that do not depend on any additional
geometrical structure like symplectic, Poisson, etc. Such geometrical structure
provides a generalized toroidal bundle on the carrier space of the system.
Non--canonical diffeomorphisms of such structure generate alternative
Hamiltonian structures for complete integrable Hamiltonian systems. The
energy-period theorem provides the first non--trivial obstruction for the
equivalence of integrable systems
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
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
Long-range attraction between particles in dusty plasma and partial surface tension of dusty phase boundary
Effective potential of a charged dusty particle moving in homogeneous plasma
has a negative part that provides attraction between similarly charged dusty
particles. A depth of this potential well is great enough to ensure both
stability of crystal structure of dusty plasma and sizable value of surface
tension of a boundary surface of dusty region. The latter depends on the
orientation of the surface relative to the counter-ion flow, namely, it is
maximal and positive for the surface normal to the flow and minimal and
negative for the surface along the flow. For the most cases of dusty plasma in
a gas discharge, a value of the first of them is more than sufficient to ensure
stability of lenticular dusty phase void oriented across the counter-ion flow.Comment: LATEX, REVTEX4, 7 pages, 6 figure
Diversity of multiwavelength emission bumps in the GRB 100219A afterglow
Context. Multi-wavelength observations of gamma-ray burst (GRB) afterglows
provide important information about the activity of their central engines and
their environments. In particular, the short timescale variability, such as
bumps and/or rebrightening features visible in the multi-wavelength light
curves, is still poorly understood.
Aims. We analyze the multi-wavelength observations of the GRB100219A
afterglow at redshift 4.7. In particular, we attempt to identify the physical
origin of the late achromatic flares/bumps detected in the X-ray and optical
bands.
Methods. We present ground-based optical photometric data and Swift X-ray
observations on GRB100219A. We analyzed the temporal behavior of the X-ray and
optical light curves, as well as the X-ray spectra.
Results. The early flares in the X-ray and optical light curves peak
simultaneously at about 1000 s after the burst trigger, while late achromatic
bumps in the X-ray and optical bands appear at about 20000 s after the burst
trigger. These are uncommon features in the afterglow phenomenology.
Considering the temporal and spectral properties, we argue that both optical
and X-ray emissions come from the same mechanism. The late flares/bumps may be
produced by late internal shocks from long-lasting activity of the central
engine. An off-axis origin for a structured jet model is also discussed to
interpret the bump shapes. The early optical bump can be interpreted as the
afterglow onset, while the early X-ray flare could be caused by the internal
activity. GRB 100219A exploded in a dense environment as revealed by the strong
attenuation of X-ray emission and the optical-to-X-ray spectral energy
distribution.Comment: A&A accepte
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
Superluminal motion of a relativistic jet in the neutron star merger GW170817
The binary neutron star merger GW170817 was accompanied by radiation across
the electromagnetic spectrum and localized to the galaxy NGC 4993 at a distance
of 41+/-3 Mpc. The radio and X-ray afterglows of GW170817 exhibited delayed
onset, a gradual rise in the emission with time as t^0.8, a peak at about 150
days post-merger, followed by a relatively rapid decline. To date, various
models have been proposed to explain the afterglow emission, including a
choked-jet cocoon and a successful-jet cocoon (a.k.a. structured jet). However,
the observational data have remained inconclusive as to whether GW170817
launched a successful relativistic jet. Here we show, through Very Long
Baseline Interferometry, that the compact radio source associated with GW170817
exhibits superluminal motion between two epochs at 75 and 230 days post-merger.
This measurement breaks the degeneracy between the models and indicates that,
while the early-time radio emission was powered by a wider-angle outflow
(cocoon), the late-time emission was most likely dominated by an energetic and
narrowly-collimated jet, with an opening angle of <5 degrees, and observed from
a viewing angle of about 20 degrees. The imaging of a collimated relativistic
outflow emerging from GW170817 adds substantial weight to the growing evidence
linking binary neutron star mergers and short gamma-ray bursts.Comment: 42 pages, 4 figures (main text), 2 figures (supplementary text), 2
tables. Referee and editor comments incorporate
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
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