3,980 research outputs found
A target guided subband filter for acoustic event detection in noisy environments using wavelet packets
This paper deals with acoustic event detection (AED), such as screams, gunshots, and explosions, in noisy environments. The main aim is to improve the detection performance under adverse conditions with a very low signal-to-noise ratio (SNR). A novel filtering method combined with an energy detector is presented. The wavelet packet transform (WPT) is first used for time-frequency representation of the acoustic signals. The proposed filter in the wavelet packet domain then uses a priori knowledge of the target event and an estimate of noise features to selectively suppress the background noise. It is in fact a content-aware band-pass filter which can automatically pass the frequency bands that are more significant in the target than in the noise. Theoretical analysis shows that the proposed filtering method is capable of enhancing the target content while suppressing the background noise for signals with a low SNR. A condition to increase the probability of correct detection is also obtained. Experiments have been carried out on a large dataset of acoustic events that are contaminated by different types of environmental noise and white noise with varying SNRs. Results show that the proposed method is more robust and better adapted to noise than ordinary energy detectors, and it can work even with an SNR as low as -15 dB. A practical system for real time processing and multi-target detection is also proposed in this work
Vortex-lattice structures in rotating Bose-Fermi superfluid mixtures
The system of Bose-Fermi superfluid mixture offers a playground to explore
rich macroscopic quantum phenomena. In a recent experiment of Yao {\it et al.}
[Phys. Rev. Lett. {\bf 117}, 145301 (2016)], K-Li superfluid
mixture is implemented. Coupled quantized vortices are generated via rotating
the superfluid mixture, and a few unconventional behaviors on the formations of
vortex numbers are observed, which can be traced to boson-fermion interactions.
Here we provide a theoretical insight into the unconventional behaviors
observed in the experiment. To this end, the orbital-free density functional
theory is hired, and its utility is validated by making comparison of numerical
results and full microscopic theory for vortex lattices in strongly interacting
Fermi superfluids alone. We also predict interesting phenomena which can be
readily explored experimentally, including the novel structures of vortex
lattices in Bose-Fermi superfluid mixtures in phase-separated regimes, and
attractive interactions between vortex lines belonging to distinct superfluids.Comment: 27 pages, 9 figures, Submission to SciPost Physic
The effects of large extra dimensions on associated production at linear colliders
In the framework of the large extra dimensions (LED) model, the effects of
LED on the processes \rrtth and \eetth at future linear colliders are
investigated in both polarized and unpolarized collision modes. The results
show that the virtual Kaluza-Klein (KK) graviton exchange can significantly
modify the standard model expectations for these processes with certain
polarizations of initial states. The process \rrtth with
allows the effective scale to be probed up to 7.8 and 8.6 TeV in
the unpolarized and , J=2 polarized collision
modes, respectively. For the \eetth process with , the upper
limits of to be observed can be 6.7 and 7.0 TeV in the unpolarized
and , , polarized collision modes,
respectively. We find the \rrtth channel in J=2 polarized photon collision mode
provides a possibility to improve the sensitivity to the graviton tower
exchange.Comment: To be appeard in Physical Review
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