529 research outputs found
Fluctuation Effects on the Transport Properties of Unitary Fermi Gases
In this letter, we investigate the fluctuation effects on the transport
properties of unitary Fermi gases in the vicinity of the superfluid transition
temperature . Based on the time-dependent Ginzburg-Landau formalism of the
BEC-BCS crossover, we investigate both the residual resistivity below
induced by phase slips and the paraconductivity above due to pair
fluctuations. These two effects have been well studied in the weak coupling BCS
superconductor, and here we generalize them to the unitary regime of ultracold
Fermi gases. We find that while the residual resistivity below increases
as one approaches the unitary limit, consistent with recent experiments, the
paraconductivity exhibits non-monotonic behavior. Our results can be verified
with the recently developed transport apparatus using mesoscopic channels.Comment: 8 pages and 4 figures including supplementary material
Evolution of Higgs mode in a Fermion Superfluid with Tunable Interactions
In this letter we present a coherent picture for the evolution of Higgs mode
in both neutral and charged -wave fermion superfluids, as the strength of
attractive interaction between fermions increases from the BCS to the BEC
regime. In the case of neutral fermionic superfluid, such as ultracold
fermions, the Higgs mode is pushed to higher energy while at the same time,
gradually loses its spectral weight as interaction strength increases toward
the BEC regime, because the system is further tuned away from Lorentz
invariance. On the other hand, when damping is taken into account, Higgs mode
is significantly broadened due to coupling to phase mode in the whole BEC-BCS
crossover. In the charged case of electron superconductor, the Anderson-Higgs
mechanism gaps out the phase mode and suppresses the coupling between the Higgs
and the phase modes, and consequently, stabilizes the Higgs mode.Comment: 5 figures, 9 pages, including supplementary materia
Wideband Optical Filters with Small Gap Coupled Subwavelength Metal Structures
In this letter, we show that the bandwidth of optical band-stop filters made
of subwavelength metal structures can be significantly increased by the strong
plasmonic near-field coupling through the corners of the periodic metal
squares. The effect of small gap coupling on the spectral bandwidth is
investigated by varying the gap size between the metal squares. An equivalent
transmission line model is used to fit the transmission and reflection spectra
of the metal filters. The transmission line model can characterize well the
metal structures with the gap size larger than the near-field decay length.
However, it fails to model the transmission and reflection spectra when the gap
size reaches the decay range of the near-field in the small gaps
Learning to Segment and Represent Motion Primitives from Driving Data for Motion Planning Applications
Developing an intelligent vehicle which can perform human-like actions
requires the ability to learn basic driving skills from a large amount of
naturalistic driving data. The algorithms will become efficient if we could
decompose the complex driving tasks into motion primitives which represent the
elementary compositions of driving skills. Therefore, the purpose of this paper
is to segment unlabeled trajectory data into a library of motion primitives. By
applying a probabilistic inference based on an iterative
Expectation-Maximization algorithm, our method segments the collected
trajectories while learning a set of motion primitives represented by the
dynamic movement primitives. The proposed method utilizes the mutual
dependencies between the segmentation and representation of motion primitives
and the driving-specific based initial segmentation. By utilizing this mutual
dependency and the initial condition, this paper presents how we can enhance
the performance of both the segmentation and the motion primitive library
establishment. We also evaluate the applicability of the primitive
representation method to imitation learning and motion planning algorithms. The
model is trained and validated by using the driving data collected from the
Beijing Institute of Technology intelligent vehicle platform. The results show
that the proposed approach can find the proper segmentation and establish the
motion primitive library simultaneously
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