54,786 research outputs found
An Approximate Solver for Multi-medium Riemann Problem with Mie-Gr\"uneisen Equations of State
We propose an approximate solver for multi-medium Riemann problems with
materials described by a family of general Mie-Gr\"uneisen equations of state,
which are widely used in practical applications. The solver provides the
interface pressure and normal velocity by an iterative method. The
well-posedness and convergence of the solver is verified with mild assumptions
on the equations of state. To validate the solver, it is employed in computing
the numerical flux on phase interfaces of a numerical scheme on Eulerian grids
that was developed recently for compressible multi-medium flows. Numerical
examples are presented for Riemann problems, air blast and underwater explosion
applications.Comment: 30 pages and 49 figure
Symmetry Enriched U(1) Topological Orders for Dipole-Octupole Doublets on a Pyrochlore Lattice
Symmetry plays a fundamental role in our understanding of both conventional
symmetry breaking phases and the more exotic quantum and topological phases of
matter. We explore the experimental signatures of symmetry enriched U(1)
quantum spin liquids (QSLs) on the pyrochlore lattice. We point out that the Ce
local moment of the newly discovered pyrochlore QSL candidate
CeSnO, is a dipole-octupole doublet. The generic model for these
unusual doublets supports two distinct symmetry enriched U(1) QSL ground states
in the corresponding quantum spin ice regimes. These two U(1) QSLs are dubbed
dipolar U(1) QSL and octupolar U(1) QSL. While the dipolar U(1) QSL has been
discussed in many contexts, the octupolar U(1) QSL is rather unique. Based on
the symmetry properties of the dipole-octupole doublets, we predict the
peculiar physical properties of the octupolar U(1) QSL, elucidating the unique
spectroscopic properties in the externalmagnetic fields. We further predict the
Anderson-Higgs transition from the octupolar U(1) QSL driven by the external
magnetic fields. We identify the experimental relevance with the candidate
material CeSnO and other dipole-octupole doublet systems.Comment: Published version. 6+3 pages, 3+1 figures, 1+1 table
Pyrochlore U(1) spin liquid of mixed symmetry enrichments in magnetic fields
We point out the experimental relevance and the detection scheme of symmetry
enriched U(1) quantum spin liquids (QSLs) outside the perturbative spin-ice
regime. Recent experiments on Ce-based pyrochlore QSL materials suggest that
the candidate QSL may not be proximate to the well-known spin ice regime, and
thus differs fundamentally from other pyrochlore QSL materials. We consider the
possibility of the -flux U(1) QSL favored by frustrated transverse
exchange interactions rather than the usual quantum spin ice. It was previously
suggested that both dipolar U(1) QSL and octupolar U(1) QSL can be realized for
the generic spin model for the dipole-octupole doublets of the Ce local
moments on the pyrochlore magnets CeSnO and CeZrO. We
explain and predict the experimental signatures especially the magnetic field
response of the octupolar -flux U(1) QSL. Fundamentally, this remarkable
state is a mixture of symmetry enrichments from point group symmetry and from
translational symmetry. We discuss the relevant experiments for pyrochlore U(1)
QSLs and further provide some insights to the pyrochlore Heisenberg model.Comment: 12 pages, to appear in PRResearch, a short explanation is found via
https://gangchengroup-physics.weebly.com/paper-explanation.htm
Detecting spin fractionalization in a spinon Fermi surface spin liquid
Motivated by the recent proposal of the spinon Fermi surface spin liquids for
several candidate materials such as YbMgGaO4, we explore the experimental
consequences of the external magnetic fields on this exotic state.
Specifically, we focus on the weak field regime where the spin liquid state is
well preserved and the spinon remain to be a good description of the magnetic
excitations. From the spin-1/2 nature of the spinon excitation, we predict the
unique features of the spinon continuum when the weak magnetic field is applied
to the system. Due to the small energy scale of the exchange interactions
between the local moments in the spin liquid candidate like YbMgGaO4, our
proposal for the spectral weight shifts and spectral crossing in the magnetic
fields can be immediately tested by inelastic neutron scattering experiments.
Several other experimental aspects about the spinon Fermi surface and the
spinon excitations are discussed and proposed. Our work provides an
experimental scheme to examine the fractionalized spinon excitation and the
candidate spin liquid states in YbMgGaO4, the 6H-B phase of Ba3NiSb2O9 and
other relevant materials.Comment: 9 pages, 5 figures, modified title and discussio
A Simple Two-stage Equalizer With Simplified Orthogonal Time Frequency Space Modulation Over Rapidly Time-varying Channels
In this work, we derive a equivalent delay-Doppler channel matrix of the
Orthogonal Time Frequency Space (OTFS) modulation that has not been studied in
previous literature. It has the similar structure as the banded channel matrix
of OFDM systems over rapidly time-varying channels. However, the band in the
equivalent channel matrix will no longer spread with the increase of the
Doppler spread once the length of maximum channel delay spread and the OTFS
frame duration are deter- mined. Furthermore, the equivalent channel matrix can
simplify the OTFS modulation in the transmitter side. Incorporating the
equivalent channel matrix, we propose a simple two-stage equal- izer in 1
dimensional operations for OTFS modulation. First, the receive signal is
equalized using the conventional OFDM single- tap equalizer in the frequency
domain. The multipath effects can be removed. In the second stage, another low
complexity delay- Doppler domain equalizer is employed to eliminate the effects
of the residual interference caused by the Doppler spread with the equivalent
channel matrix. The simulation results demonstrate that the proposed method is
superior to the conventional single- tap equalizer and full minimum mean
squared error (MMSE) equalizer of OFDM systems in terms of BER in high Doppler
spread scenarios.Comment: 4 page
Impurity- and Magnetic-field-induced Quasiparticle States in Chiral -wave Superconductors
Both impurity- and magnetic-field-induced quasiparticle states in chiral
-wave superconductors are investigated theoretically by solving the
Bogoliubov--de Gennes equations self-consistently. At the strong scattering
limit, we find that a universal state bound to the impurity can be induced for
both a single nonmagnetic impurity and a single magnetic impurity. Furthermore,
we find that different chiral order parameters and the corresponding
supercurrents have uniform distributions around linear impurities. Calculations
of the local density of states in the presence of an external magnetic field
show that the intensity peak of the zero-energy Majorana mode in the vortex
core can be enhanced dramatically by tuning the strength of the external
magnetic field or pairing interaction.Comment: 7 pages, 7 figure
An anisotropic spin model of strong spin-orbit-coupled triangular antiferromagnets
Motivated by the recent experimental progress on the strong
spin-orbit-coupled rare earth triangular antiferromagnet, we analyze the highly
anisotropic spin model that describes the interaction between the
spin-orbit-entangled Kramers' doublet local moments on the triangular lattice.
We apply the Luttinger-Tisza method, the classical Monte Carlo simulation, and
the self-consistent spin wave theory to analyze the anisotropic spin
Hamiltonian. The classical phase diagram includes the 120-degree state and two
distinct stripe ordered phases. The frustration is very strong and
significantly suppresses the ordering temperature in the regimes close to the
phase boundary between two ordered phases. Going beyond the semiclassical
analysis, we include the quantum fluctuations of the spin moments within a
self-consistent Dyson-Maleev spin-wave treatment. We find that the strong
quantum fluctuations melt the magnetic order in the frustrated regions. We
explore the magnetic excitations in the three different ordered phases as well
as in strong magnetic fields. Our results provide a guidance for the future
theoretical study of the generic model and are broadly relevant for strong
spin-orbit-coupled triangular antiferromagnets such as YbMgGaO4, RCd3P3,
RZn3P3, RCd3As3, RZn3As3, and R2O2CO3.Comment: 12 pages, 10 figures, 1 table. Add two families of triangular
antiferromagnets (RCd3P3, RZn3P3, RCd3As3, RZn3As3, R2O2CO3) that were
discovered recentl
Interchange reconnection associated with a confined filament eruption: Implications for the source of transient cold-dense plasma in solar winds
The cold-dense plasma is occasionally detected in the solar wind with in situ
data, but the source of the cold-dense plasma remains illusive. Interchange
reconnections (IRs) between closed fields and nearby open fields are well known
to contribute to the formation of solar winds. We present a confined filament
eruption associated with a puff-like coronal mass ejection (CME) on 2014
December 24. The filament underwent successive activations and finally erupted,
due to continuous magnetic flux cancellations and emergences. The confined
erupting filament showed a clear untwist motion, and most of the filament
material fell back. During the eruption, some tiny blobs escaped from the
confined filament body, along newly-formed open field lines rooted around the
south end of the filament, and some bright plasma flowed from the north end of
the filament to remote sites at nearby open fields. The newly-formed open field
lines shifted southward with multiple branches. The puff-like CME also showed
multiple bright fronts and a clear southward shift. All the results indicate an
intermittent IR existed between closed fields of the confined erupting filament
and nearby open fields, which released a portion of filament material (blobs)
to form the puff-like CME. We suggest that the IR provides a possible source of
cold-dense plasma in the solar wind
Stable polarization-encoded quantum key distribution in fiber
Polarizations of single-photon pulses have been controlled with long-term
stability of more than 10 hours by using an active feedback technique for
auto-compensation of unpredictable polarization scrambling in long-distance
fiber. Experimental tests of long-term operations in 50, 75 and 100 km fibers
demonstrated that such a single-photon polarization control supported stable
polarization encoding in long-distance fibers to facilitate stable one-way
fiber system for polarization-encoded quantum key distribution, providing
quantum bit error rates below the absolute security threshold.Comment: 14 pages, 4 figure
Solar jet-coronal hole collision and a related coronal mass ejection
Jets are defined as impulsive, well-collimated upflows, occurring in
different layers of the solar atmosphere with different scales. Their
relationship with coronal mass ejections (CMEs), another type of solar
impulsive events, remains elusive. Using the high-quality imaging data of
AIA/SDO, here we show a well-observed coronal jet event, in which part of the
jets, with the embedding coronal loops, runs into a nearby coronal hole (CH)
and gets bounced towards the opposite direction. This is evidenced by the
flat-shape of the jet front during its interaction with the CH and the V-shaped
feature in the time-slice plot of the interaction region. About a half-hour
later, a CME initially with a narrow and jet-like front is observed by the
LASCO C2 coronagraph, propagating along the direction of the post-collision
jet. We also observe some 304 A dark material flowing from the jet-CH
interaction region towards the CME. We thus suggest that the jet and the CME
are physically connected, with the jet-CH collision and the large- scale
magnetic topology of the CH being important to define the eventual propagating
direction of this particular jet-CME eruption
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