2,042 research outputs found
A momentum filter for atomic gas
We propose and demonstrate a momentum filter for atomic gas based on a
designed Talbot-Lau interferometer. It consists in two identical optical
standing wave pulses separated by a delay equal to odd multiples of the half
Talbot time. The one dimensional momentum width along the long direction of a
cigar shape condensate is rapidly and greatly purified to a minimum, which
corresponds to the ground state energy of the confining trap in our experiment.
We find good agreement between theoretical analysis and experimental results.
The filter is also effective for non-condensed cold atoms and could be applied
widely.Comment: 9 pages, 6 figures, accepted by New Journal of Physic
Increasing stability estimates for the inverse potential scattering problems
This paper is mainly concerned with the inverse scattering problem of
determining the unknown potential for the classical Schr\"odinger equation in
two and three dimensions. We establish the increasing stability of the inverse
scattering problem from either multi-frequency near-field data or
multi-frequency far-field pattern. The stability estimate consists of the
Lipschitz type data discrepancy and the logarithmic high frequency tail of the
potential function, where the latter decreases as the upper bound of the
frequency increases. A novel method is proposed for the proof, which is based
on choosing appropriate incident plane waves and an application of the
quantitative analytic continuation. A key ingredient in the analysis is
employing scattering theory to obtain an analytic region and resolvent
estimates in this region for the resolvent in two and three dimensions. We
further apply this method to study the inverse scattering problem of
determining both the magnetic potential and electric potential for the
three-dimensional magnetic Schr\"odinger equation
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.
Effective preparation and collisional decay of atomic condensate in excited bands of an optical lattice
We present a method for the effective preparation of a Bose-Einstein
condensate (BEC) into the excited bands of an optical lattice via a
standing-wave pulse sequence. With our method, the BEC can be prepared in
either a single Bloch state in a excited-band, or a coherent superposition of
states in different bands. Our scheme is experimentally demonstrated by
preparing a Rb BEC into the -band and the superposition of - and
-band states of a one-dimensional optical lattice, within a few tens of
microseconds. We further measure the decay of the BEC in the -band state,
and carry an analytical calculation for the collisional decay of atoms in the
excited-band states. Our theoretical and experimental results consist well.Comment: 9 pages, 5 figures, Accepted by Phys. Rev.
Effects of dietary compound acidifiers supplementation on growth performance and intestinal health of juvenile American eels (Anguilla rostrata) cultured in cement tanks
This experiment was conducted to investigate the effects of compound acidifiers (CAs) on the growth performance and intestinal health of juvenile American eels (Anguilla rostrata) cultured in cement tanks. Six cement tanks with similar fish size and weight (approximately 4 g/fish and 87 kg/tank) were randomly divided into control group and CAs group with three replicates each. The fish of two groups were fed commercial diet and commercial diet supplemented with 4 g/kg CAs, respectively. The trial period was 56 days. The dietary CAs supplementation significantly increased final fish weight, weight gain rate, specific growth rate and feed intake (P0.05). Protease activity in intestine was increased significantly by CAs supplementation (P0.05). CAs supplementation significantly increased the villi length and thickness of the intestinal muscular layer (P<0.05). Dietary CAs supplementation increased the richness and the diversity of intestinal microbiota. At the phylum level, the higher relative abundances of Proteobacteria, Actinobacteria and Bacteroidetes and the lower relative abundance of Firmicutes were observed in CAs group compared to the control group. At the genus level, dietary CAs supplementation significantly increased the relative abundances of Faecalitalea, Sphingomonas, Sutterella and Mycobacterium (P<0.05). In conclusion, the dietary 4 g/kg CAs supplementation might improve the growth performance and intestinal health of juvenile American eels cultured in cement tanks
Learned Spatio-Temporal Texture Descriptors for RGB-D Human Action Recognition
Due to the recent arrival of Kinect, action recognition with depth images has attracted researchers' wide attentions and various descriptors have been proposed, where Local Binary Patterns (LBP) texture descriptors possess the properties of appearance invariance. However, the LBP and its variants are most artificially-designed, demanding engineers' strong prior knowledge and not discriminative enough for recognition tasks. To this end, this paper develops compact spatio-temporal texture descriptors, i.e. 3D-compact LBP (3D-CLBP) and local depth patterns (3D-CLDP), for color and depth videos in the light of compact binary face descriptor learning in face recognition. Extensive experiments performed on three standard datasets, 3D Online Action, MSR Action Pairs and MSR Daily Activity 3D, demonstrate that our method is superior to most comparative methods in respects of performance and can capture spatial-temporal texture cues in videos
Real-time Accurate Runway Detection based on Airborne Multi-sensors Fusion
Existing methods of runway detection are more focused on image processing for remote sensing images based on computer vision techniques. However, these algorithms are too complicated and time-consuming to meet the demand for real-time airborne application. This paper proposes a novel runway detection method based on airborne multi-sensors data fusion which works in a coarse-to-fine hierarchical architecture. At the coarse layer, a vision projection model from world coordinate system to image coordinate system is built by fusing airborne navigation data and forward-looking sensing images, then a runway region of interest (ROI) is extracted from a whole image by the model. Furthermore, EDLines which is a real-time line segments detector is applied to extract straight line segments from ROI at the fine layer, and fragmented line segments generated by EDLines are linked into two long runway lines. Finally, some unique runway features (e.g. vanishing point and runway direction) are used to recognise airport runway. The proposed method is tested on an image dataset provided by a flight simulation system. The experimental results show that the method has advantages in terms of speed, recognition rate and false alarm rate
The thermal and electrical properties of the promising semiconductor MXene Hf2CO2
In this work, we investigate the thermal and electrical properties of
oxygen-functionalized M2CO2 (M = Ti, Zr, Hf) MXenes using first-principles
calculations. Hf2CO2 is found to exhibit a thermal conductivity better than
MoS2 and phosphorene. The room temperature thermal conductivity along the
armchair direction is determined to be 86.25-131.2 Wm-1K-1 with a flake length
of 5-100 um, and the corresponding value in the zigzag direction is
approximately 42% of that in the armchair direction. Other important thermal
properties of M2CO2 are also considered, including their specific heat and
thermal expansion coefficients. The theoretical room temperature thermal
expansion coefficient of Hf2CO2 is 6.094x10-6 K-1, which is lower than that of
most metals. Moreover, Hf2CO2 is determined to be a semiconductor with a band
gap of 1.657 eV and to have high and anisotropic carrier mobility. At room
temperature, the Hf2CO2 hole mobility in the armchair direction (in the zigzag
direction) is determined to be as high as 13.5x103 cm2V-1s-1 (17.6x103
cm2V-1s-1), which is comparable to that of phosphorene. Broader utilization of
Hf2CO2 as a material for nanoelectronics is likely because of its moderate band
gap, satisfactory thermal conductivity, low thermal expansion coefficient, and
excellent carrier mobility. The corresponding thermal and electrical properties
of Ti2CO2 and Zr2CO2 are also provided here for comparison. Notably, Ti2CO2
presents relatively low thermal conductivity and much higher carrier mobility
than Hf2CO2, which is an indication that Ti2CO2 may be used as an efficient
thermoelectric material.Comment: 26 pages, 5 figures, 2 table
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