27,355 research outputs found
Electronic structure induced reconstruction and magnetic ordering at the LaAlOSrTiO interface
Using local density approximation (LDA) calculations we predict
GdFeO-like rotation of TiO octahedra at the -type interface between
LaAlO and SrTiO. The narrowing of the Ti bandwidth which results
means that for very modest values of , LDA calculations predict charge
and spin ordering at the interface. Recent experimental evidence for magnetic
interface ordering may be understood in terms of the close proximity of an
antiferromagnetic insulating ground state to a ferromagnetic metallic excited
state
Flavor Evolution of the Neutronization Neutrino Burst from an O-Ne-Mg Core-Collapse Supernova
We present results of 3-neutrino flavor evolution simulations for the
neutronization burst from an O-Ne-Mg core-collapse supernova. We find that
nonlinear neutrino self-coupling engineers a single spectral feature of
stepwise conversion in the inverted neutrino mass hierarchy case and in the
normal mass hierarchy case, a superposition of two such features corresponding
to the vacuum neutrino mass-squared differences associated with solar and
atmospheric neutrino oscillations. These neutrino spectral features offer a
unique potential probe of the conditions in the supernova environment and may
allow us to distinguish between O-Ne-Mg and Fe core-collapse supernovae.Comment: 4 pages, 2 figures. Version accepted by PR
Neutrino Mass Hierarchy and Stepwise Spectral Swapping of Supernova Neutrino Flavors
We examine a phenomenon recently predicted by numerical simulations of
supernova neutrino flavor evolution: the swapping of supernova and
energy spectra below (above) energy \EC for the normal
(inverted) neutrino mass hierarchy. We present the results of large-scale
numerical calculations which show that in the normal neutrino mass hierarchy
case, \EC decreases as the assumed
effective vacuum mixing angle () is decreased.
However, these calculations also indicate that \EC is essentially independent
of the vacuum mixing angle in the inverted neutrino mass hierarchy case. With a
good neutrino signal from a future Galactic supernova, the above results could
be used to determine the neutrino mass hierarchy even if is too
small to be detected in terrestrial neutrino oscillation experiments.Comment: 4 pages, 2 figures. Version accepted by PR
Magnetoresistance due to Domain Walls in Micron Scale Fe Wires with Stripe Domains
The magnetoresistance (MR) associated with domain boundaries has been
investigated in microfabricated bcc Fe (0.65 to 20 m linewidth) wires with
controlled stripe domains. Domain configurations have been characterized using
magnetic force microscopy. MR measurements as a function of field angle,
temperature and domain configuration are used to estimate MR contributions due
to resistivity anisotropy and domain walls. Evidence is presented that domain
boundaries enhance the conductivity in such microstructures over a broad range
of temperatures (1.5 K to 80 K).Comment: 8 pages, 3 postscript figures, and 2 jpg images (Fig 1 and 2) to
appear in IEEE Transactions on Magnetics (Fall 1998
Exploration of Resonant Continuum and Giant Resonance in the Relativistic Approach
Single-particle resonant-states in the continuum are determined by solving
scattering states of the Dirac equation with proper asymptotic conditions in
the relativistic mean field theory (RMF). The regular and irregular solutions
of the Dirac equation at a large radius where the nuclear potentials vanish are
relativistic Coulomb wave functions, which are calculated numerically.
Energies, widths and wave functions of single-particle resonance states in the
continuum for ^{120}Sn are studied in the RMF with the parameter set of NL3.
The isoscalar giant octupole resonance of ^{120}Sn is investigated in a fully
consistent relativistic random phase approximation. Comparing the results with
including full continuum states and only those single-particle resonances we
find that the contributions from those resonant-states dominate in the nuclear
giant resonant processes.Comment: 16 pages, 2 figure
Electric Transport Theory of Dirac Fermions in Graphene
Using the self-consistent Born approximation to the Dirac fermions under
finite-range impurity scatterings, we show that the current-current correlation
function is determined by four-coupled integral equations. This is very
different from the case for impurities with short-range potentials. As a test
of the present approach, we calculate the electric conductivity in graphene for
charged impurities with screened Coulomb potentials. The obtained conductivity
at zero temperature varies linearly with the carrier concentration, and the
minimum conductivity at zero doping is larger than the existing theoretical
predictions, but still smaller than that of the experimental measurement. The
overall behavior of the conductivity obtained by the present calculation at
room temperature is similar to that at zero temperature except the minimum
conductivity is slightly larger.Comment: 6 pages, 3 figure
Retraction of articles by H. Zhong et al.
Retraction of 41 articles by H. Zhong et al.
Density Fluctuation Effects on Collective Neutrino Oscillations in O-Ne-Mg Core-Collapse Supernovae
We investigate the effect of matter density fluctuations on supernova
collective neutrino flavor oscillations. In particular, we use full
multi-angle, 3-flavor, self-consistent simulations of the evolution of the
neutrino flavor field in the envelope of an O-Ne-Mg core collapse supernova at
shock break-out (neutrino neutronization burst) to study the effect of the
matter density "bump" left by the He-burning shell. We find a seemingly
counterintuitive increase in the overall electron neutrino survival probability
created by this matter density feature. We discuss this behavior in terms of
the interplay between the matter density profile and neutrino collective
effects. While our results give new insights into this interplay, they also
suggest an immediate consequence for supernova neutrino burst detection: it
will be difficult to use a burst signal to extract information on fossil
burning shells or other fluctuations of this scale in the matter density
profile. Consistent with previous studies, our results also show that the
interplay of neutrino self-coupling and matter fluctuation could cause a
significant increase in the electron neutrino survival probability at very low
energyComment: 12 pages, 11 figures. This is a pre-submission version of the pape
Coherent Development of Neutrino Flavor in the Supernova Environment
We calculate coherent neutrino and antineutrino flavor transformation in the
supernova environment, for the first time including a self-consistent treatment
of forward scattering-induced coupling and entanglement of intersecting
neutrino/antineutrino trajectories. For the atmospheric neutrino mass-squared
difference we find that in the normal (inverted) mass hierarchy the more
tangentially-propagating (radially-propagating) neutrinos and antineutrinos can
initiate collective, simultaneous medium-enhanced flavor conversion of these
particles across broad ranges of energy and propagation direction. Accompanying
alterations in neutrino/antineutrino energy spectra and/or fluxes could affect
supernova nucleosynthesis and the expected neutrino signal.Comment: 4 pages, 3 figure
Concave Switching in Single and Multihop Networks
Switched queueing networks model wireless networks, input queued switches and
numerous other networked communications systems. For single-hop networks, we
consider a {()-switch policy} which combines the MaxWeight policies
with bandwidth sharing networks -- a further well studied model of Internet
congestion. We prove the maximum stability property for this class of
randomized policies. Thus these policies have the same first order behavior as
the MaxWeight policies. However, for multihop networks some of these
generalized polices address a number of critical weakness of the
MaxWeight/BackPressure policies.
For multihop networks with fixed routing, we consider the Proportional
Scheduler (or (1,log)-policy). In this setting, the BackPressure policy is
maximum stable, but must maintain a queue for every route-destination, which
typically grows rapidly with a network's size. However, this proportionally
fair policy only needs to maintain a queue for each outgoing link, which is
typically bounded in number. As is common with Internet routing, by maintaining
per-link queueing each node only needs to know the next hop for each packet and
not its entire route. Further, in contrast to BackPressure, the Proportional
Scheduler does not compare downstream queue lengths to determine weights, only
local link information is required. This leads to greater potential for
decomposed implementations of the policy. Through a reduction argument and an
entropy argument, we demonstrate that, whilst maintaining substantially less
queueing overhead, the Proportional Scheduler achieves maximum throughput
stability.Comment: 28 page
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