5,991 research outputs found
Topological phase transition based on the attractive Hubbard model
We theoretically investigate the effect of an attractive on-site interaction
on the two-band magnetic Dirac fermion model based on a square lattice system.
When the attractive fermion interaction is taken into account by the mean-field
approximation, a phase diagram is obtained. It is found that a quantum phase
transition from a band insulator state to quantum anomalous Hall state occurs
with increased attractive interaction. For an existing quantum anomalous Hall
state, the attractive interaction enlarges its nontrivial band gap and makes
the topological edge states more localized, which protects the transport of
linear-dispersive edge states against finite-size and further disorder effects.Comment: 5 pages, 4 figure
Pedestrian dynamics in single-file movement of crowd with different age compositions
An aging population is bringing new challenges to the management of escape
routes and facility design in many countries. This paper investigates
pedestrian movement properties of crowd with different age compositions. Three
pedestrian groups are considered: young student group, old people group and
mixed group. It is found that traffic jams occur more frequently in mixed group
due to the great differences of mobilities and self-adaptive abilities among
pedestrians. The jams propagate backward with a velocity 0.4 m/s for global
density around 1.75 m-1 and 0.3 m/s for higher than 2.3 m-1. The fundamental
diagrams of the three groups are obviously different from each other and cannot
be unified into one diagram by direct non-dimensionalization. Unlike previous
studies, three linear regimes in mixed group but only two regimes in young
student group are observed in the headway-velocity relation, which is also
verified in the fundamental diagram. Different ages and mobilities of
pedestrians in a crowd cause the heterogeneity of system and influence the
properties of pedestrian dynamics significantly. It indicates that the density
is not the only factor leading to jams in pedestrian traffic. The composition
of crowd has to be considered in understanding pedestrian dynamics and facility
design.Comment: 11 pages, 13 figures, 3 table
Fractal Metamaterial Absorber with Three-Order Oblique Cross Dipole Slot Structure and its Application for In-band RCS Reduction of Array Antennas
To miniaturize the perfect metamaterial absorber, a fractal three-order oblique cross dipole slot structure is proposed and investigated in this paper. The fractal perfect metamaterial absorber (FPMA) consists of two metallic layers separated by a lossy dielectric substrate. The top layer etched a three-order oblique fractal-shaped cross dipole slot set in a square patch and the bottom one is a solid metal. The parametric study is performed for providing practical design guidelines. A prototype with a thickness of 0.0106λ (λ is the wavelength at 3.18 GHz) of the FPMA was designed, fabricated, measured, and is loaded on a 1×10 guidewave slot array antennas to reduce the in-band radar cross section (RCS) based on their surface current distribution. Experiments are carried out to verify the simulation results, and the experimental results show that the absorption at normal incidence is above 90% from 3.17 to 3.22GHz, the size for the absorber is 0.1λ×0.1λ, the three-order FPMA is miniaturized 60% compared with the zero-order ones, and the array antennas significantly obtain the RCS reduction without the radiation deterioration
Dynamical generation of dark solitons in spin-orbit-coupled Bose-Einstein condensates
We numerically investigate the ground state, the Raman-driving dynamics and
the nonlinear excitations of a realized spin-orbit-coupled Bose-Einstein
condensate in a one-dimensional harmonic trap. Depending on the Raman coupling
and the interatomic interactions, three ground-state phases are identified:
stripe, plane wave and zero-momentum phases. A narrow parameter regime with
coexistence of stripe and zero-momentum or plane wave phases in real space is
found. Several sweep progresses across different phases by driving the Raman
coupling linearly in time is simulated and the non-equilibrium dynamics of the
system in these sweeps are studied. We find kinds of nonlinear excitations,
with the particular dark solitons excited in the sweep from the stripe phase to
the plane wave or zero-momentum phase within the trap. Moreover, the number and
the stability of the dark solitons can be controlled in the driving, which
provide a direct and easy way to generate dark solitons and study their
dynamics and interaction properties.Comment: 10 pages, 9 figur
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