6,833 research outputs found
Ferromagnetic to antiferromagnetic transition of one-dimensional spinor Bose gases with spin-orbit coupling
We have analytically solved one-dimensional interacting two-component bosonic
gases with spin-orbit (SO) coupling by the Bethe-ansatz method. Through a gauge
transformation, the effect of SO coupling is incorporated into a spin-dependent
twisted boundary condition. Our result shows that the SO coupling can influence
the eigenenergy in a periodical pattern. The interplay between interaction and
SO coupling may induce the energy level crossing for the ground state, which
leads to a transition from the ferromagnetic to antiferromagnetic state.Comment: 6 pages, 4 figure
Characterization of Lifshitz transitions in topological nodal line semimetals
We introduce a two-band model of three-dimensional nodal line semimetals, the
Fermi surface of which at half-filling may form various one-dimensional
configurations of different topology. We study the symmetries and "drumhead"
surface states of the model, and find that the transitions between different
configurations, namely, the Lifshitz transitions, can be identified solely by
the number of gap-closing points on some high-symmetry planes in the Brillouin
zone. A global phase diagram of this model is also obtained accordingly. We
then investigate the effect of some extra terms analogous to a two-dimensional
Rashba-type spin-orbit coupling. The introduced extra terms open a gap for the
nodal line semimetals and can be useful in engineering different topological
insulating phases. We demonstrate that the behavior of surface Dirac cones in
the resulting insulating system has a clear correspondence with the different
configurations of the original nodal lines in the absence of the gap terms.Comment: 7 pages, 6 figure
The Mid-Infrared Extinction Law and its Variation in the Coalsack Nebula
In recent years the wavelength dependence of interstellar extinction from the
ultraviolet (UV), optical, through the near- and mid-infrared (IR) has been
studied extensively. Although it is well established that the UV/optical
extinction law varies significantly among the different lines of sight, it is
not clear how the IR extinction varies among various environments. In this
work, using the color-excess method and taking red giants as the extinction
tracer, we determine the interstellar extinction Alambda in the four
Spitzer/IRAC bands of the Coalsack nebula, a nearby starless dark cloud, based
on the data obtained from the 2MASS and Spitzer/GLIMPSE surveys. We select five
individual regions across the nebula that span a wide variety of physical
conditions, ranging from diffuse, translucent to dense environments, as traced
by the visual extinction, the Spitzer/MIPS 24micron emission, and CO emission.
We find that Alambda/AKs, the mid-IR extinction relative to AKs, decreases from
diffuse to dense environments, which may be explained in terms of ineffective
dust growth in dense regions. The mean extinction (relative to AKs) is
calculated for the four IRAC bands as well, which exhibits a flat mid-IR
extinction law, consistent with previous determinations for other regions. The
extinction in the IRAC 4.5micron band is anomalously high, much higher than
that of the other three IRAC bands. It cannot be explained in terms of CO and
CO2 ices. The mid-IR extinction in the four IRAC bands have also been derived
for four representative regions in the Coalsack Globule 2 which respectively
exhibit strong ice absorption, moderate or weak ice absorption, and very weak
or no ice absorption. The derived mid-IR extinction curves are all flat, with
Alambda/AKs increasing with the decrease of the H2O ice absorption optical
depth.Comment: 39 pages, 13 figures, accepted by Ap
Distances to the Supernova Remnants in the Inner Disk
Distance measurements of supernova remnants (SNRs) are essential and
important. Accurate estimates of physical size, dust masses, and some other
properties of SNRs depend critically on accurate distance measurements.
However, the determination of SNR distances is still a tough task. Red clump
stars (RCs) have a long history been used as standard candles. In this work, we
take RCs as tracers to determine the distances to a large group of SNRs in the
inner disk. We first select RC stars based on the near-infrared (IR)
color-magnitude diagram (CMD). Then, the distance to and extinction of RC stars
are calculated. To extend the measurable range of distance, we combine near-IR
photometric data from the 2MASS survey with the deeper UKIDSS and VVV surveys.
With the help of the Gaia parallaxes, we also remove contaminants including
dwarfs and giants. Because an SN explosion compresses the surrounding
interstellar medium, the SNR region would become denser and exhibit higher
extinction than the surroundings. The distance of a SNR is then recognized by
the position where the extinction and its gradient is higher than that of the
ambient medium. A total of 63 SNRs' distances in the Galactic inner disk are
determined and divided into three Levels A, B, and C with decreasing
reliability. The distances to 43 SNRs are well determined with reliability A or
B. The diameters and dust masses of SNRs are estimated with the obtained
distance and extinction.Comment: 31 pages, 25 figures, 2 tables, accepted for publication in A&
Topological invariants, zero mode edge states and finite size effect for a generalized non-reciprocal Su-Schrieffer-Heeger model
Intriguing issues in one-dimensional non-reciprocal topological systems
include the breakdown of usual bulk-edge correspondence and the occurrence of
half-integer topological invariants. In order to understand these unusual
topological properties, we investigate the topological phase diagrams and the
zero-mode edge states of a generalized non-reciprocal Su-Schrieffer-Heeger
model, based on some analytical results. Meanwhile, we provide a concise
geometrical interpretation of the bulk topological invariants in terms of two
independent winding numbers and also give an alternative interpretation related
to the linking properties of curves in three-dimensional space. For the system
under the open boundary condition, we construct analytically the wavefunctions
of zero-mode edge states by properly considering a hidden symmetry of the
system and the normalization condition with the use of biorthogonal
eigenvectors. Our analytical results directly give the phase boundary for the
existence of zero-mode edge states and unveil clearly the evolution behavior of
edge states. In comparison with results via exact diagonalization of
finite-size systems, we find our analytical results agree with the numerical
results very well.Comment: 13 pages, 9 figure
Solving time-dependent parametric PDEs by multiclass classification-based reduced order model
In this paper, we propose a network model, the multiclass
classification-based ROM (MC-ROM), for solving time-dependent parametric
partial differential equations (PPDEs). This work is inspired by the
observation of applying the deep learning-based reduced order model (DL-ROM) to
solve diffusion-dominant PPDEs. We find that the DL-ROM has a good
approximation for some special model parameters, but it cannot approximate the
drastic changes of the solution as time evolves. Based on this fact, we
classify the dataset according to the magnitude of the solutions, and construct
corresponding subnets dependent on different types of data. Then we train a
classifier to integrate different subnets together to obtain the MC-ROM. When
subsets have the same architecture, we can use transfer learning technology to
accelerate the offline training. Numerical experiments show that the MC-ROM
improves the generalization ability of the DL-ROM both for diffusion- and
convection-dominant problems, and maintains the advantage of DL-ROM. We also
compare the approximation accuracy and computational efficiency of the proper
orthogonal decomposition (POD) which is not suitable for convection-dominant
problems. For diffusion-dominant problems, the MC-ROM can save about 100 times
online computational cost than the POD with a slightly better approximation in
the reduced space of the same dimension.Comment: 19 pages, 15 figure
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