2,106 research outputs found
3-D Model of Broadband Emission from Supernova Remnants Undergoing Non-linear Diffusive Shock Acceleration
We present a 3-dimensional model of supernova remnants (SNRs) where the
hydrodynamical evolution of the remnant is modeled consistently with nonlinear
diffusive shock acceleration occuring at the outer blast wave. The model
includes particle escape and diffusion outside of the forward shock, and
particle interactions with arbitrary distributions of external ambient
material, such as molecular clouds. We include synchrotron emission and
cooling, bremsstrahlung radiation, neutral pion production, inverse-Compton
(IC), and Coulomb energy-loss. Boardband spectra have been calculated for
typical parameters including dense regions of gas external to a 1000 year old
SNR. In this paper, we describe the details of our model but do not attempt a
detailed fit to any specific remnant. We also do not include magnetic field
amplification (MFA), even though this effect may be important in some young
remnants. In this first presentation of the model we don't attempt a detailed
fit to any specific remnant. Our aim is to develop a flexible platform, which
can be generalized to include effects such as MFA, and which can be easily
adapted to various SNR environments, including Type Ia SNRs, which explode in a
constant density medium, and Type II SNRs, which explode in a pre-supernova
wind. When applied to a specific SNR, our model will predict cosmic-ray spectra
and multi-wavelength morphology in projected images for instruments with
varying spatial and spectral resolutions. We show examples of these spectra and
images and emphasize the importance of measurements in the hard X-ray, GeV, and
TeV gamma-ray bands for investigating key ingredients in the acceleration
mechanism, and for deducing whether or not TeV emission is produced by IC from
electrons or neutral pions from protons.Comment: 12 pages, 9 figures, accepted by Apj, 24 June 200
Effects of Zeeman spin splitting on the modular symmetry in the quantum Hall effect
Magnetic-field-induced phase transitions in the integer quantum Hall effect
are studied under the formation of paired Landau bands arising from Zeeman spin
splitting. By investigating features of modular symmetry, we showed that
modifications to the particle-hole transformation should be considered under
the coupling between the paired Landau bands. Our study indicates that such a
transformation should be modified either when the Zeeman gap is much smaller
than the cyclotron gap, or when these two gaps are comparable.Comment: 8 pages, 4 figure
An experimental study on (2) modular symmetry in the quantum Hall system with a small spin-splitting
Magnetic-field-induced phase transitions were studied with a two-dimensional
electron AlGaAs/GaAs system. The temperature-driven flow diagram shows the
features of the (2) modular symmetry, which includes distorted
flowlines and shiftted critical point. The deviation of the critical
conductivities is attributed to a small but resolved spin splitting, which
reduces the symmetry in Landau quantization. [B. P. Dolan, Phys. Rev. B 62,
10278.] Universal scaling is found under the reduction of the modular symmetry.
It is also shown that the Hall conductivity could still be governed by the
scaling law when the semicircle law and the scaling on the longitudinal
conductivity are invalid. *corresponding author:[email protected]: The revised manuscript has been published in J. Phys.: Condens.
Matte
Nuclear Stopping as A Probe to In-medium Nucleon-nucleon Cross Section in Intermediate Energy Heavy Ion Collisions
Using an isospin-dependent quantum molecular dynamics, nuclear stopping in
intermediate heavy ion collisions has been studied. The calculation has been
done for colliding systems with different neutron-proton ratios in beam energy
ranging from 15MeV/u to 150MeV/u. It is found that, in the energy region from
above Fermi energy to 150MeV/u, nuclear stopping is very sensitive to the
isospin dependence of in-medium nucleon-nucleon cross section, but insensitive
to symmetry potential. From this investigation, we propose that nuclear
stopping can be used as a new probe to extract the information on the isospin
dependence of in-medium nucleon-nucleon cross section in intermediate energy
heavy ion collisions
Macroscopic Quantum Coherence in Small Antiferromagnetic Particle and the Quantum Interference Effects
Starting from the Hamiltonian operator of the noncompensated two-sublattice
model of a small antiferromagnetic particle, we derive the effective Lagrangian
of a biaxial antiferromagnetic particle in an external magnetic field with the
help of spin-coherent-state path integrals. Two unequal level-shifts induced by
tunneling through two types of barriers are obtained using the instanton
method. The energy spectrum is found from Bloch theory regarding the periodic
potential as a superlattice. The external magnetic field indeed removes
Kramers' degeneracy, however a new quenching of the energy splitting depending
on the applied magnetic field is observed for both integer and half-integer
spins due to the quantum interference between transitions through two types of
barriers.Comment: 9 pages, Latex, 4 Postscript figure
Tunnel splitting and quantum phase interference in biaxial ferrimagnetic particles at excited states
The tunneling splitting in biaxial ferrimagnetic particles at excited states
with an explicit calculation of the prefactor of exponent is obtained in terms
of periodic instantons which are responsible for tunneling at excited states
and is shown as a function of magnetic field applied along an arbitrary
direction in the plane of hard and medium axes. Using complex time
path-integral we demonstrate the oscillation of tunnel splitting with respect
to the magnitude and the direction of the magnetic field due to the quantum
phase interference of two tunneling paths of opposite windings . The
oscillation is gradually smeared and in the end the tunnel splitting
monotonously increases with the magnitude of the magnetic field when the
direction of the magnetic field tends to the medium axis. The oscillation
behavior is similar to the recent experimental observation with Fe
molecular clusters. A candidate of possible experiments to observe the effect
of quantum phase interference in the ferrimagnetic particles is proposed.Comment: 15 pages, 5 figures, acceptted to be pubblished in Physical Review
Structural Characterization And Condition For Measurement Statistics Preservation Of A Unital Quantum Operation
We investigate the necessary and sufficient condition for a convex cone of
positive semidefinite operators to be fixed by a unital quantum operation
acting on finite-dimensional quantum states. By reducing this problem to
the problem of simultaneous diagonalization of the Kraus operators associated
with , we can completely characterize the kind of quantum states that are
fixed by . Our work has several applications. It gives a simple proof of
the structural characterization of a unital quantum operation that acts on
finite-dimensional quantum states --- a result not explicitly mentioned in
earlier studies. It also provides a necessary and sufficient condition for what
kind of measurement statistics is preserved by a unital quantum operation.
Finally, our result clarifies and extends the work of St{\o}rmer by giving a
proof of a reduction theorem on the unassisted and entanglement-assisted
classical capacities, coherent information, and minimal output Renyi entropy of
a unital channel acting on finite-dimensional quantum state.Comment: 9 pages in revtex 4.1, minor revision, to appear in J.Phys.
Rigidity of compact Riemannian spin Manifolds with Boundary
In this article, we prove new rigidity results for compact Riemannian spin
manifolds with boundary whose scalar curvature is bounded from below by a
non-positive constant. In particular, we obtain generalizations of a result of
Hang-Wang \cite{hangwang1} based on a conjecture of Schroeder and Strake
\cite{schroeder}.Comment: English version of "G\'eom\'etrie spinorielle extrins\`eque et
rigidit\'es", Corollary 6 in Section 3 added, to appear in Letters Math. Phy
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