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Investigations with various inner shielding distance tests for a novel coupler-based CPT system applied for electric vehicles using electromagnetic resonant coupling and aluminium shielding material
Contactless power transfer (CPT) technology development has been driven rapidly over the past decade by the world-wide trends towards new energy explorations, and numerous reports have been presented in this area. This paper focuses on passive magnetic shielding, which acts as one of the major factors mainly determining the overall CPT system performance when discussing electromagnetic field flux distribution and its real-time effects on magnetic resonant coupling. As a well performance conductive metallic material, aluminium has been adopted to be a passive shielding material in the designed novel H-shape coupler CPT system in this paper, in order to evaluate and find out the optimal inner shielding distance in between the coil and the inner shielding shell. Three inner shielding distances are applied and analyzed across a critical range of system operating frequency, by which the actual CPT system performance differences from perspectives of electromagnetics and power electronics have been illustrated and compared. As a result, it can be noticed that the 15-mm inner shielding gap CPT model is able to yield an optimal system performance with a maximum system efficiency, peak system output RMS power of over 36% and 22 kW, respectively, which also shows an optimal capability to address major concerns over electric vehicle contactless charging. Besides, along with the electromagnetic field parameters generated in the model, such as actual real-time values of flux linkage, magnetic flux density and field strength, it can be found that the 15-mm inner shielding gap prototype is able to achieve better overall magnetic field performance than 5-mm and 25-mm inner shielding distance CPT models
BCS-BEC crossover and quantum phase transition for 6Li and 40K atoms across Feshbach resonance
We systematically study the BCS-BEC crossover and the quantum phase
transition in ultracold 6Li and 40K atoms across a wide Feshbach resonance. The
background scattering lengths for 6Li and 40K have opposite signs, which lead
to very different behaviors for these two types of atoms. For 40K, both the
two-body and the many-body calculations show that the system always has two
branches of solutions: one corresponds to a deeply bound molecule state; and
the other, the one accessed by the current experiments, corresponds to a weakly
bound state with population always dominantly in the open channel. For 6Li,
there is only a unique solution with the standard crossover from the weakly
bound Cooper pairs to the deeply bound molecules as one sweeps the magnetic
field through the crossover region. Because of this difference, for the
experimentally accessible state of 40K, there is a quantum phase transition at
zero temperature from the superfluid to the normal fermi gas at the positive
detuning of the magnetic field where the s-wave scattering length passes its
zero point. For 6Li, however, the system changes continuously across the zero
point of the scattering length. For both types of atoms, we also give detailed
comparison between the results from the two-channel and the single-channel
model over the whole region of the magnetic field detuning.Comment: 7 pages, 6 figure
A computer vision approach to classification of birds in flight from video sequences
Bird populations are an important bio-indicator; so collecting reliable data is useful for ecologists helping conserve and manage fragile ecosystems. However, existing manual monitoring methods are labour-intensive, time-consuming, and error-prone. The aim of our work is to develop a reliable system, capable of automatically classifying individual bird species in flight from videos. This is challenging, but appropriate for use in the field, since there is often a requirement to identify in flight, rather than when stationary. We present our work in progress, which uses combined appearance and motion features to classify and present experimental results across seven species using Normal Bayes classifier with majority voting and achieving a classification rate of 86%
A QM/MM equation-of-motion coupled-cluster approach for predicting semiconductor color-center structure and emission frequencies
Valence excitation spectra are computed for all deep-center silicon-vacancy
defect types in 3C, 4H, and 6H silicon carbide (SiC) and comparisons are made
with literature photoluminescence measurements. Nuclear geometries surrounding
the defect centers are optimized within a Gaussian basis-set framework using
many-body perturbation theory or density functional theory (DFT) methods, with
computational expenses minimized by a QM/MM technique called SIMOMM. Vertical
excitation energies are subsequently obtained by applying excitation-energy,
electron-attached, and ionized equation-of-motion coupled-cluster (EOMCC)
methods, where appropriate, as well as time-dependent (TD) DFT, to small models
including only a few atoms adjacent to the defect center. We consider the
relative quality of various EOMCC and TD-DFT methods for (i) energy-ordering
potential ground states differing incrementally in charge and multiplicity,
(ii) accurately reproducing experimentally measured photoluminescence peaks,
and (iii) energy-ordering defects of different types occurring within a given
polytype. The extensibility of this approach to transition-metal defects is
also tested by applying it to silicon-substitutional chromium defects in SiC
and comparing with measurements. It is demonstrated that, when used in
conjunction with SIMOMM-optimized geometries, EOMCC-based methods can provide a
reliable prediction of the ground-state charge and multiplicity, while also
giving a quantitative description of the photoluminescence spectra, accurate to
within 0.1 eV of measurement in all cases considered.Comment: 13 pages, 4 figures, 6 tables, 5 equations, 100 reference
Superfluidity of fermions with repulsive on-site interaction in an anisotropic optical lattice near a Feshbach resonance
We present a numerical study on ground state properties of a one-dimensional
(1D) general Hubbard model (GHM) with particle-assisted tunnelling rates and
repulsive on-site interaction (positive-U), which describes fermionic atoms in
an anisotropic optical lattice near a wide Feshbach resonance. For our
calculation, we utilize the time evolving block decimation (TEBD) algorithm,
which is an extension of the density matrix renormalization group and provides
a well-controlled method for 1D systems. We show that the positive-U GHM, when
hole-doped from half-filling, exhibits a phase with coexistence of
quasi-long-range superfluid and charge-density-wave orders. This feature is
different from the property of the conventional Hubbard model with positive-U,
indicating the particle-assisted tunnelling mechanism in GHM brings in
qualitatively new physics.Comment: updated with published version
Topology of Knotted Optical Vortices
Optical vortices as topological objects exist ubiquitously in nature. In this
paper, by making use of the -mapping topological current theory, we
investigate the topology in the closed and knotted optical vortices. The
topological inner structure of the optical vortices are obtained, and the
linking of the knotted optical vortices is also given.Comment: 11 pages, no figures, accepted by Commun. Theor. Phys. (Beijing, P.
R. China
Phase diagram of a polarized Fermi gas across a Feshbach resonance in a potential trap
We map out the detailed phase diagram of a trapped ultracold Fermi gas with
population imbalance across a wide Feshbach resonance. We show that under the
local density approximation, the properties of the atoms in any (anisotropic)
harmonic traps are universally characterized by three dimensionless parameters:
the normalized temperature, the dimensionless interaction strength, and the
population imbalance. We then discuss the possible quantum phases in the trap,
and quantitatively characterize their phase boundaries in various typical
parameter regions.Comment: 9 pages, 4 figure
A new topological aspect of the arbitrary dimensional topological defects
We present a new generalized topological current in terms of the order
parameter field to describe the arbitrary dimensional topological
defects. By virtue of the -mapping method, we show that the topological
defects are generated from the zero points of the order parameter field , and the topological charges of these topological defects are topological
quantized in terms of the Hopf indices and Brouwer degrees of -mapping
under the condition that the Jacobian . When , it is shown that there exist the crucial case of branch process.
Based on the implicit function theorem and the Taylor expansion, we detail the
bifurcation of generalized topological current and find different directions of
the bifurcation. The arbitrary dimensional topological defects are found
splitting or merging at the degenerate point of field function but
the total charge of the topological defects is still unchanged.Comment: 24 pages, 10 figures, Revte
Direct measurement of decoherence for entanglement between a photon and stored atomic excitation
Violations of a Bell inequality are reported for an experiment where one of
two entangled qubits is stored in a collective atomic memory for a user-defined
time delay. The atomic qubit is found to preserve the violation of a Bell
inequality for storage times up to 21 microseconds, 700 times longer than the
duration of the excitation pulse that creates the entanglement. To address the
question of the security of entanglement-based cryptography implemented with
this system, an investigation of the Bell violation as a function of the
cross-correlation between the generated nonclassical fields is reported, with
saturation of the violation close to the maximum value allowed by quantum
mechanics.Comment: 4 pages, 3 figures. Minor changes. Published versio
Correlations in interference and diffraction
Quantum formalism of Fraunhofer diffraction is obtained. The state of the
diffraction optical field is connected with the state of the incident optical
field by a diffraction factor. Based on this formalism, correlations of the
diffraction modes are calculated with different kinds of incident optical
fields. Influence of correlations of the incident modes on the diffraction
pattern is analyzed and an explanation of the ''ghost'' diffraction is
proposed.Comment: 16 pages, 2 figures, Latex, to appear in J. Mod. Op
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