24,218 research outputs found
Blind Normalization of Speech From Different Channels
We show how to construct a channel-independent representation of speech that
has propagated through a noisy reverberant channel. This is done by blindly
rescaling the cepstral time series by a non-linear function, with the form of
this scale function being determined by previously encountered cepstra from
that channel. The rescaled form of the time series is an invariant property of
it in the following sense: it is unaffected if the time series is transformed
by any time-independent invertible distortion. Because a linear channel with
stationary noise and impulse response transforms cepstra in this way, the new
technique can be used to remove the channel dependence of a cepstral time
series. In experiments, the method achieved greater channel-independence than
cepstral mean normalization, and it was comparable to the combination of
cepstral mean normalization and spectral subtraction, despite the fact that no
measurements of channel noise or reverberations were required (unlike spectral
subtraction).Comment: 25 pages, 7 figure
Simple Model for Attraction between Like-Charged Polyions
We present a simple model for the possible mechanism of appearance of
attraction between like charged polyions inside a polyelectrolyte solution. The
attraction is found to be short ranged, and exists only in presence of
multivalent counterions. The attraction is produced by the correlations in the
condensed layers of counterions surrounding each polyion, and appears only if
the number of condensed counterions exceeds the threshold, ,
where is the valence of counterions and is the polyion charge.Comment: 4 pages, 4 eps figures, also available at
http://www.if.ufrgs.br/~arenzon Figure added and a more detailed discussion
of conclusion
The nature of attraction between like charged rods
Comment on the paper of Ha and Liu (Phys. Rev. Lett. {\bf 79}, 1289 (1997))
regarding the nature of attraction between like charged rods. We demostrate
that their results do not produce the correct low temperature limit.Comment: Comment to appear in Phys. Rev. Let
Signature for the Shape of the Universe
If the universe has a nontrivial shape (topology) the sky may show multiple
correlated images of cosmic objects. These correlations can be couched in terms
of distance correlations. We propose a statistical quantity which can be used
to reveal the topological signature of any Robertson-Walker (RW) spacetime with
nontrivial topology. We also show through computer-aided simulations how one
can extract the topological signatures of flat, elliptic, and hyperbolic RW
universes with nontrivial topology.Comment: 11 pages, 3 figures, LaTeX2e. This paper is a direct ancestor of
gr-qc/9911049, put in gr-qc archive to make it more accessibl
The mean-field theory for attraction between like-charged macromolecules
A mean-field theory based on Gibbs-Bogoliubov inequality is constructed to
study the interactions between two like-charged polyions. It is shown that
contrary to the previously established paradigm, a properly constructed
mean-field theory can quantitatively account for the attractive interactions
between two like-charged rods.Comment: 5 pages, 2 figures, elsart.sty neede
Charge reversal of colloidal particles
A theory is presented for the effective charge of colloidal particles in
suspensions containing multivalent counterions. It is shown that if colloids
are sufficiently strongly charged, the number of condensed multivalent
counterion can exceed the bare colloidal charge leading to charge reversal.
Charge renormalization in suspensions with multivalent counterions depends on a
subtle interplay between the solvation energies of the multivalent counterions
in the bulk and near the colloidal surface. We find that the effective charge
is {\it not} a monotonically decreasing function of the multivalent salt
concentration. Furthermore, contrary to the previous theories, it is found that
except at very low concentrations, monovalent salt hinders the charge reversal.
This conclusion is in agreement with the recent experiments and simulations
Use of 2G coated conductors for efficient shielding of DC magnetic fields
This paper reports the results of an experimental investigation of the
performance of two types of magnetic screens assembled from YBa2Cu3O7-d (YBCO)
coated conductors. Since effective screening of the axial DC magnetic field
requires the unimpeded flow of an azimuthal persistent current, we demonstrate
a configuration of a screening shell made out of standard YBCO coated conductor
capable to accomplish that. The screen allows the persistent current to flow in
the predominantly azimuthal direction at a temperature of 77 K. The persistent
screen, incorporating a single layer of superconducting film, can attenuate an
external magnetic field of up to 5 mT by more than an order of magnitude. For
comparison purposes, another type of screen which incorporates low critical
temperature quasi-persistent joints was also built. The shielding technique we
describe here appears to be especially promising for the realization of large
scale high-Tc superconducting screens.Comment: 8 pages, 3 figure
Metastability of Asymptotically Well-Behaved Potential Games
One of the main criticisms to game theory concerns the assumption of full
rationality. Logit dynamics is a decentralized algorithm in which a level of
irrationality (a.k.a. "noise") is introduced in players' behavior. In this
context, the solution concept of interest becomes the logit equilibrium, as
opposed to Nash equilibria. Logit equilibria are distributions over strategy
profiles that possess several nice properties, including existence and
uniqueness. However, there are games in which their computation may take time
exponential in the number of players. We therefore look at an approximate
version of logit equilibria, called metastable distributions, introduced by
Auletta et al. [SODA 2012]. These are distributions that remain stable (i.e.,
players do not go too far from it) for a super-polynomial number of steps
(rather than forever, as for logit equilibria). The hope is that these
distributions exist and can be reached quickly by logit dynamics.
We identify a class of potential games, called asymptotically well-behaved,
for which the behavior of the logit dynamics is not chaotic as the number of
players increases so to guarantee meaningful asymptotic results. We prove that
any such game admits distributions which are metastable no matter the level of
noise present in the system, and the starting profile of the dynamics. These
distributions can be quickly reached if the rationality level is not too big
when compared to the inverse of the maximum difference in potential. Our proofs
build on results which may be of independent interest, including some spectral
characterizations of the transition matrix defined by logit dynamics for
generic games and the relationship of several convergence measures for Markov
chains
- …