30,601 research outputs found
Controllable Persistent Atom Current of Bose-Einstein Condensates in an Optical Lattice Ring
In this paper the macroscopic quantum states of Bose-Einstein condensates in
optical lattices is studied by solving the periodic Gross-Pitaevskii equation
in one-dimensional geometry. It is shown that an exact solution seen to be a
travelling wave of excited macroscopic quantum states resultes in a persistent
atom current which can be controlled by adjusting of the barrier height of the
optical periodic potential. A critical condition to generate the travelling
wave is demonstrated and we moreover propose a practical experiment to realize
the persistent atom current in a toroidal atom waveguide.Comment: 9 pages, 1 figure
Phase diagram of two-species Bose-Einstein condensates in an optical lattice
The exact macroscopic wave functions of two-species Bose-Einstein condensates
in an optical lattice beyond the tight-binding approximation are studied by
solving the coupled nonlinear Schrodinger equations. The phase diagram for
superfluid and insulator phases of the condensates is determined analytically
according to the macroscopic wave functions of the condensates, which are seen
to be traveling matter waves.Comment: 13 pages, 2 figure
Broadband RCS Reduction of Microstrip Patch Antenna Using Bandstop Frequency Selective Surface
In this article, a simple and effective approach is presented to reduce the Radar Cross Section (RCS) of microstrip patch antenna in ultra broad frequency band. This approach substitutes a metallic ground plane of a conventional patch antenna with a hybrid ground consisting of bandstop Frequency Selective Surface (FSS) cells with partial metallic plane. To demonstrate the validity of the proposed approach, the influence of different ground planes on antenna’s performance is investigated. Thus, a patch antenna with miniaturized FSS cells is proposed. The results suggest that this antenna shows 3dB RCS reduction almost in the whole out-of operating band within 1-20GHz for wide incident angles when compared to conventional antenna, while its radiation characteristics are sustained simultaneously. The reasonable agreement between the measured and the simulated results verifies the efficiency of the proposed approach. Moreover, this approach doesn’t alter the lightweight, low-profile, easy conformal and easy manufacturing nature of the original antenna and can be extended to obtain low-RCS antennas with metallic planes in broadband that are quite suitable for the applications which are sensitive to the variation of frequencies
Excitation of nonlinear ion acoustic waves in CH plasmas
Excitation of nonlinear ion acoustic wave (IAW) by an external electric field
is demonstrated by Vlasov simulation. The frequency calculated by the
dispersion relation with no damping is verified much closer to the resonance
frequency of the small-amplitude nonlinear IAW than that calculated by the
linear dispersion relation. When the wave number increases,
the linear Landau damping of the fast mode (its phase velocity is greater than
any ion's thermal velocity) increases obviously in the region of in which the fast mode is weakly damped mode. As a result, the deviation
between the frequency calculated by the linear dispersion relation and that by
the dispersion relation with no damping becomes larger with
increasing. When is not large, such as , the nonlinear IAW can be excited by the driver with the linear frequency
of the modes. However, when is large, such as
, the linear frequency can not be applied to exciting the
nonlinear IAW, while the frequency calculated by the dispersion relation with
no damping can be applied to exciting the nonlinear IAW.Comment: 10 pages, 9 figures, Accepted by POP, Publication in August 1
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Coil combination using linear deconvolution in k-space for phase imaging
Background: The combination of multi-channel data is a critical step for the imaging of phase and susceptibility contrast in magnetic resonance imaging (MRI). Magnitude-weighted phase combination methods often produce noise and aliasing artifacts in the magnitude images at accelerated imaging sceneries. To address this issue, an optimal coil combination method through deconvolution in k-space is proposed in this paper.
Methods: The proposed method firstly employs the sum-of-squares and phase aligning method to yield a complex reference coil image which is then used to calculate the coil sensitivity and its Fourier transform. Then, the coil k-space combining weights is computed, taking into account the truncated frequency data of coil sensitivity and the acquired k-space data. Finally, combining the coil k-space data with the acquired weights generates the k-space data of proton distribution, with which both phase and magnitude information can be obtained straightforwardly. Both phantom and in vivo imaging experiments were conducted to evaluate the performance of the proposed method.
Results: Compared with magnitude-weighted method and MCPC-C, the proposed method can alleviate the phase cancellation in coil combination, resulting in a less wrapped phase.
Conclusions: The proposed method provides an effective and efficient approach to combine multiple coil image in parallel MRI reconstruction, and has potential to benefit routine clinical practice in the future
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