38,888 research outputs found
New transformation of Wigner operator in phase space quantum mechanics for the two-mode entangled case
As a natural extension of Fan's paper (arXiv: 0903.1769vl [quant-ph]) by
employing the formula of operators' Weyl ordering expansion and the bipartite
entangled state representation we find new two-fold complex integration
transformation about the Wigner operator (in its entangled form) in phase space
quantum mechanics and its inverse transformation. In this way, some operator
ordering problems can be solved and the contents of phase space quantum
mechanics can be enriched.Comment: 8 pages, 0 figure
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Rheo-diecasting AZ91D magnesium alloy
Magnesium recycling has become more important in today’s environmentally aware society. To prompt the usage of recycled magnesium scrap and further improve casting structure and properties, a novel physical approach, the rheo-diecasting process (RDC), has been applied in the present study to deal with AZ91D Mg-alloy directly from die-casting scrap. The experimental results show that the RDC process can be used to produce recycled AZ91D alloy with fine and uniform microstructure and a very low level of porosity. The intermetallic compounds containing the impurity elements were of fine and of spherical morphology, distributed uniformly in the alloy matrix. No oxide particle clusters or oxide films were found in the RDC microstructure. The tensile properties of the recycled AZ91D alloy were comparable to those produced by RDC from the primary alloy ingots., and much better than those produced by conventional High Pressure Die Casting (HPDC)
Early photon-shock interaction in stellar wind: sub-GeV photon flash and high energy neutrino emission from long GRBs
For gamma-ray bursts (GRBs) born in a stellar wind, as the reverse shock
crosses the ejecta, usually the shocked regions are still precipitated by the
prompt MeV \gamma-ray emission. Because of the tight overlapping of the MeV
photon flow with the shocked regions, the optical depth for the GeV photons
produced in the shocks is very large. These high energy photons are absorbed by
the MeV photon flow and generate relativistic e^\pm pairs. These pairs
re-scatter the soft X-ray photons from the forward shock as well as the prompt
\gamma-ray photons and power detectable high energy emission, significant part
of which is in the sub-GeV energy range. Since the total energy contained in
the forward shock region and the reverse shock region are comparable, the
predicted sub-GeV emission is independent on whether the GRB ejecta are
magnetized (in which case the reverse shock IC and synchrotron self-Compton
emission is suppressed). As a result, a sub-GeV flash is a generic signature
for the GRB wind model, and it should be typically detectable by the future
{\em Gamma-Ray Large Area Telescope} (GLAST). Overlapping also influence
neutrino emission. Besides the 10^{15} \sim 10^{17} eV neutrino emission
powered by the interaction of the shock accelerated protons with the
synchrotron photons in both the forward and reverse shock regions, there comes
another eV neutrino emission component powered by protons interacting
with the MeV photon flow. This last component has a similar spectrum to the one
generated in the internal shock phase, but the typical energy is slightly
lower.Comment: 7 pages, accepted for publication in Ap
The Effects of Rotation on the Evolution of Rising Omega-loops in a Stratified Model Convection Zone
We present three-dimensional MHD simulations of buoyant magnetic flux tubes
that rise through a stratified model convection zone in the presence of solar
rotation. The equations of MHD are solved in the anelastic approximation, and
the results are used to determine the effects of solar rotation on the dynamic
evolution an Omega-loop. We find that the Coriolis force significantly
suppresses the degree of fragmentation at the apex of the loop during its
ascent toward the photosphere. If the initial axial field strength of the tube
is reduced, then, in the absence of forces due to convective motions, the
degree of apex fragmentation is also reduced. We show that the Coriolis force
slows the rise of the tube, and induces a retrograde flow in both the
magnetized and unmagnetized plasma of an emerging active region.
Observationally, we predict that this flow will appear to originate at the
leading polarity, and will terminate at the trailing polarity.Comment: 25 pages, 8 figures, ApJ in pres
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Microstructural characterisation and thermal stability of an Mg-Al-Sr alloy prepared by rheo-diecasting
A commercial Mg-6Al-2Sr (AJ62) alloy has been prepared by a semisolid rheo-diecasting (RDC) process. The microstructure of the RDC alloy exhibits typical semisolid solidification features, i.e., 8.4 vol% primary α-Mg globules (23 μm in diameter), formed in the slurry maker at the primary solidification stage, uniformly distributed in the matrix of fine α-Mg grain size (8.2 μm) and intergranular eutectic Al4Sr lamellae, which resulted from secondary solidification inside the die. A ternary Mg-Al-Sr phase was also observed. Heat treatment revealed the extreme thermal stability of the RDC AJ62 alloy. The hardness showed little change up to 12 hours at 450°C, whilst the Al4Sr eutectic lamellae were broken up, spheroidised and coarsened during the annealing. The RDC alloy offers superior mechanical properties, especially ductility, over the same alloy produced by high pressure die-casting
A Reverse-Shock Model for the Early Afterglow of GRB 050525A
The prompt localization of gamma-ray burst (GRB) 050525A by {\em Swift}
allowed the rapid follow-up of the afterglow. The observations revealed that
the optical afterglow had a major rebrightening starting at days
and ending at days, which was followed by an initial power-law
decay. Here we show that this early emission feature can be interpreted as the
reverse shock emission superposed by the forward shock emission in an
interstellar medium environment. By fitting the observed data, we further
constrain some parameters of the standard fireball-shock model: the initial
Lorentz factor of the ejecta , the magnetic energy fraction
, and the medium density . These
limits are consistent with those from the other very-early optical afterglows
observed so far. In principle, a wind environment for GRB 050525A is
disfavored.Comment: 11 pages, 1 figure, accepted for publication in Ap
The composition of heavy ions in solar energetic particle events
Recent advances in determining the elemental, charge state, and isotopic composition of or approximate to 1 to or approximate to 20 MeV per nucleon ions in solar energetic particle (SEP) events and outline our current understanding of the nature of solar and interplanetary processes which may explain the observations. Average values of relative abundances measured in a large number of SEP events were found to be roughly energy independent in the approx. 1 to approx. 20 MeV per nucleon range, and showed a systematic deviation from photospheric abundances which seems to be organized in terms of the first ionization potential of the ion. Direct measurements of the charge states of SEPs revealed the surprisingly common presence of energetic He(+) along with heavy ion with typically coronal ionization states. High resolution measurements of isotopic abundance ratios in a small number of SEP events showed these to be consistent with the universal composition except for the puzzling overabundance of the SEP(22)Ne/(20)Ne relative to this isotopes ratio in the solar wind. The broad spectrum of observed elemental abundance variations, which in their extreme result in composition anomalies characteristic of (3)He rich, heavy ion rich and carbon poor SEP events, along with direct measurements of the ionization states of SEPs provided essential information on the physical characteristics of, and conditions in the source regions, as well as important constraints to possible models for SEP production
Strong GeV Emission Accompanying TeV Blazar H1426+428
For High frequency BL Lac objects (HBLs) like H1426+428, a significant
fraction of their TeV gamma-rays emitted are likely to be absorbed in
interactions with the diffuse IR background, yielding pairs. The
resulting pairs generate one hitherto undiscovered GeV emission by
inverse Compton scattering with the cosmic microwave background photons
(CMBPs). We study such emission by taking the 1998-2000 CAT data, the
reanalyzed 1999 & 2000 HEGRA data and the corresponding intrinsic spectra
proposed by Aharonian et al. (2003a). We numerically calculate the scattered
photon spectra for different intergalactic magnetic field (IGMF) strengths. If
the IGMF is about or weaker, there comes very strong GeV
emission, whose flux is far above the detection sensitivity of the upcoming
satellite GLAST! Considered its relatively high redshift (), the
detected GeV emission in turn provides us a valuable chance to calibrate the
poor known spectral energy distribution of the intergalactic infrared
background, or provides us some reliable constraints on the poorly known IGMF
strength.Comment: 5 pages, 1 figure. A&A in Pres
Solar Modulation of the Galactic Helium Spectrum Above 30 Mev Per Nucleon
Time measurements of differential energy spectra and flux of primary helium nuclei by use of charged particle telescope
Acceleration of particles in the earth's shock transition region and beyond
Acceleration of particles in earth shock transition region and beyon
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