27,186 research outputs found
Blind MultiChannel Identification and Equalization for Dereverberation and Noise Reduction based on Convolutive Transfer Function
This paper addresses the problems of blind channel identification and
multichannel equalization for speech dereverberation and noise reduction. The
time-domain cross-relation method is not suitable for blind room impulse
response identification, due to the near-common zeros of the long impulse
responses. We extend the cross-relation method to the short-time Fourier
transform (STFT) domain, in which the time-domain impulse responses are
approximately represented by the convolutive transfer functions (CTFs) with
much less coefficients. The CTFs suffer from the common zeros caused by the
oversampled STFT. We propose to identify CTFs based on the STFT with the
oversampled signals and the critical sampled CTFs, which is a good compromise
between the frequency aliasing of the signals and the common zeros problem of
CTFs. In addition, a normalization of the CTFs is proposed to remove the gain
ambiguity across sub-bands. In the STFT domain, the identified CTFs is used for
multichannel equalization, in which the sparsity of speech signals is
exploited. We propose to perform inverse filtering by minimizing the
-norm of the source signal with the relaxed -norm fitting error
between the micophone signals and the convolution of the estimated source
signal and the CTFs used as a constraint. This method is advantageous in that
the noise can be reduced by relaxing the -norm to a tolerance
corresponding to the noise power, and the tolerance can be automatically set.
The experiments confirm the efficiency of the proposed method even under
conditions with high reverberation levels and intense noise.Comment: 13 pages, 5 figures, 5 table
Drawing Binary Tanglegrams: An Experimental Evaluation
A binary tanglegram is a pair of binary trees whose leaf sets are in
one-to-one correspondence; matching leaves are connected by inter-tree edges.
For applications, for example in phylogenetics or software engineering, it is
required that the individual trees are drawn crossing-free. A natural
optimization problem, denoted tanglegram layout problem, is thus to minimize
the number of crossings between inter-tree edges.
The tanglegram layout problem is NP-hard and is currently considered both in
application domains and theory. In this paper we present an experimental
comparison of a recursive algorithm of Buchin et al., our variant of their
algorithm, the algorithm hierarchy sort of Holten and van Wijk, and an integer
quadratic program that yields optimal solutions.Comment: see
http://www.siam.org/proceedings/alenex/2009/alx09_011_nollenburgm.pd
An Improved Differential Evolution Algorithm for Maritime Collision Avoidance Route Planning
High accuracy navigation and surveillance systems are pivotal to ensure efficient ship route planning and marine safety. Based on existing ship navigation and maritime collision prevention rules, an improved approach for collision avoidance route planning using a differential evolution algorithm was developed. Simulation results show that the algorithm is capable of significantly enhancing the optimized route over current methods. It has the potential to be used as a tool to generate optimal vessel routing in the presence of conflicts
Dynamics of quantum adiabatic evolution algorithm for Number Partitioning
We have developed a general technique to study the dynamics of the quantum
adiabatic evolution algorithm applied to random combinatorial optimization
problems in the asymptotic limit of large problem size . We use as an
example the NP-complete Number Partitioning problem and map the algorithm
dynamics to that of an auxilary quantum spin glass system with the slowly
varying Hamiltonian. We use a Green function method to obtain the adiabatic
eigenstates and the minimum excitation gap, ,
corresponding to the exponential complexity of the algorithm for Number
Partitioning. The key element of the analysis is the conditional energy
distribution computed for the set of all spin configurations generated from a
given (ancestor) configuration by simulteneous fipping of a fixed number of
spins. For the problem in question this distribution is shown to depend on the
ancestor spin configuration only via a certain parameter related to the energy
of the configuration. As the result, the algorithm dynamics can be described in
terms of one-dimenssional quantum diffusion in the energy space. This effect
provides a general limitation on the power of a quantum adiabatic computation
in random optimization problems. Analytical results are in agreement with the
numerical simulation of the algorithm.Comment: 32 pages, 5 figures, 3 Appendices; List of additions compare to v.3:
(i) numerical solution of the stationary Schroedinger equation for the
adiabatic eigenstates and eigenvalues; (ii) connection between the scaling
law of the minimum gap with the problem size and the shape of the
coarse-grained distribution of the adiabatic eigenvalues at the
avoided-crossing poin
A Young Stellar Cluster in the Nucleus of NGC 4449
We have obtained 1-2 A resolution optical Echellette spectra of the nuclear
star cluster in the nearby starburst galaxy NGC 4449. The light is clearly
dominated by a very young (6-10 Myr) population of stars. For our age dating,
we have used recent population synthesis models to interpret the observed
equivalent width of stellar absorption features such as the HI Balmer series
and the CaII triplet around 8500 A. We also compare the observed spectrum of
the nuclear cluster to synthesized spectra of simple stellar populations of
varying ages. All these approaches yield a consistent cluster age. Metallicity
estimates based on the relative intensities of various ionization lines yield
no evidence for significant enrichment in the center of this low mass galaxy:
the metallicity of the nuclear cluster is about one fourth of the solar value,
in agreement with independent estimates for the disk material of NGC 4449.Comment: 24 pages (incl. 7 figures), accepted by AJ, March 2001 issue revised
version with minor changes and additions, one additional figur
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