234 research outputs found
Comparative Study on Instructors’ and Students’ Code-Switching in an EFL Class
This study investigates code-switching (CS) occurred between instructors and students in an English as a foreign language (EFL) class at an international college in China. Questionnaires and in-class observations were carried out among both instructors and students to elicit the data. Three aspects are investigated: frequency of CS, reasons for CS and attitudes towards CS. It was found that (1) English (TL) stays dominant while Chinese (L1) was auxiliary in an EFL class. (2) Most instructors and students use code-switching in class, which can be attributed to many factors. For students, low English proficiency was the underlying reason, while for instructors, major reason lies in translating important parts. Most of them are positive towards CS. Pedagogical implications of the findings were also discussed. Overall, this study contributes to teaching English as a foreign language (TEFL) based on empirical and experimental results.
Asymptotic enumeration of bipartite graphs, tournaments, digraphs and eulerian digraphs with multiple edges
The observation of diffraction phases in matter wave scattering
We study the diffraction phase of different orders via the Dyson expansion
series, for ultracold atomic gases scattered by a standing-wave pulse. As these
diffraction phases are not observable in a single pulse scattering process, a
temporal Talbot-Lau interferometer consisting of two standing-wave pulses is
demonstrated experimentally with a Bose-Einstein condensate to explore this
physical effect. The role of the diffraction phases is clearly shown by the
second standing-wave pulse in the relative population of different momentum
states. Our experiments demonstrate obvious effects beyond the Raman-Nath
method, while agree well with our theory by including the diffraction phases.
In particular, the observed asymmetry in the dependence of the relative
population on the interval between two standing-wave pulses reflects the
diffraction phase differences. The role of interatomic interaction in the
Talbot-Lau interferometer is also discussed.Comment: 7 pages, 3 figures, accepted by Phys. Rev.
Manipulating the momentum state of a condensate by sequences of standing wave pulses
We analyze the effects of sequences of standing wave pulses on a
Bose-Einstein condensate (BEC). Experimental observations are in good agreement
with a numerical simulation based on the band structure theory in the optical
lattice. We also demonstrate that a coherent control method based on such
sequences of pulses is very efficient for experimentally designing specific
momentum states.Comment: 6 pages; 5 figures; submitted to PR
Asymmetric superradiant scattering and abnormal mode amplification induced by atomic density distortion
The superradiant Rayleigh scattering using a pump laser incident along the
short axis of a Bose-Einstein condensate with a density distortion is studied,
where the distortion is formed by shocking the condensate utilizing the
residual magnetic force after the switching-off of the trapping potential. We
find that very small variation of the atomic density distribution would induce
remarkable asymmetrically populated scattering modes by the matter-wave
superradiance with long time pulse. The optical field in the diluter region of
the atomic cloud is more greatly amplified, which is not an ordinary mode
amplification with the previous cognition. Our numerical simulations with the
density envelop distortion are consistent with the experimental results. This
supplies a useful method to reflect the geometric symmetries of the atomic
density profile by the superradiance scattering.Comment: 7pages,4 figures, Optical Express 21,(2013)1437
Observation of a red-blue detuning asymmetry in matter-wave superradiance
We report the first experimental observations of strong suppression of
matter-wave superradiance using blue-detuned pump light and demonstrate a
pump-laser detuning asymmetry in the collective atomic recoil motion. In
contrast to all previous theoretical frameworks, which predict that the process
should be symmetric with respect to the sign of the pump-laser detuning, we
find that for condensates the symmetry is broken. With high condensate
densities and red-detuned light, the familiar distinctive multi-order,
matter-wave scattering pattern is clearly visible, whereas with blue-detuned
light superradiance is strongly suppressed. In the limit of a dilute atomic
gas, however, symmetry is restored.Comment: Accepted by Phys. Rev. Let
FF-LINS: A Consistent Frame-to-Frame Solid-State-LiDAR-Inertial State Estimator
Most of the existing LiDAR-inertial navigation systems are based on
frame-to-map registrations, leading to inconsistency in state estimation. The
newest solid-state LiDAR with a non-repetitive scanning pattern makes it
possible to achieve a consistent LiDAR-inertial estimator by employing a
frame-to-frame data association. In this letter, we propose a robust and
consistent frame-to-frame LiDAR-inertial navigation system (FF-LINS) for
solid-state LiDARs. With the INS-centric LiDAR frame processing, the keyframe
point-cloud map is built using the accumulated point clouds to construct the
frame-to-frame data association. The LiDAR frame-to-frame and the inertial
measurement unit (IMU) preintegration measurements are tightly integrated using
the factor graph optimization, with online calibration of the LiDAR-IMU
extrinsic and time-delay parameters. The experiments on the public and private
datasets demonstrate that the proposed FF-LINS achieves superior accuracy and
robustness than the state-of-the-art systems. Besides, the LiDAR-IMU extrinsic
and time-delay parameters are estimated effectively, and the online calibration
notably improves the pose accuracy. The proposed FF-LINS and the employed
datasets are open-sourced on GitHub (https://github.com/i2Nav-WHU/FF-LINS)
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