73,475 research outputs found
Spoof detection using time-delay shallow neural network and feature switching
Detecting spoofed utterances is a fundamental problem in voice-based
biometrics. Spoofing can be performed either by logical accesses like speech
synthesis, voice conversion or by physical accesses such as replaying the
pre-recorded utterance. Inspired by the state-of-the-art \emph{x}-vector based
speaker verification approach, this paper proposes a time-delay shallow neural
network (TD-SNN) for spoof detection for both logical and physical access. The
novelty of the proposed TD-SNN system vis-a-vis conventional DNN systems is
that it can handle variable length utterances during testing. Performance of
the proposed TD-SNN systems and the baseline Gaussian mixture models (GMMs) is
analyzed on the ASV-spoof-2019 dataset. The performance of the systems is
measured in terms of the minimum normalized tandem detection cost function
(min-t-DCF). When studied with individual features, the TD-SNN system
consistently outperforms the GMM system for physical access. For logical
access, GMM surpasses TD-SNN systems for certain individual features. When
combined with the decision-level feature switching (DLFS) paradigm, the best
TD-SNN system outperforms the best baseline GMM system on evaluation data with
a relative improvement of 48.03\% and 49.47\% for both logical and physical
access, respectively
Birefringence analysis of multilayer leaky cladding optical fibre
We analyse a multilayer leaky cladding (MLC) fibre using the finite element
method and study the effect of the MLC on the bending loss and birefringence of
two types of structures: (i) a circular core large-mode-area structure and (ii)
an elliptical-small-core structure. In a large-mode-area structure, we verify
that the multilayer leaky cladding strongly discriminates against higher order
modes to achieve single-mode operation, the fibre shows negligible
birefringence, and the bending loss of the fibre is low for bending radii
larger than 10 cm. In the elliptical-small-core structure we show that the MLC
reduces the birefringence of the fibre. This prevents the structure from
becoming birefringent in case of any departures from circular geometry. The
study should be useful in the designs of MLC fibres for various applications
including high power amplifiers, gain flattening of fibre amplifiers and
dispersion compensation.Comment: 18 page
Nonintegrability of (2+1)-dimensional continuum isotropic Heisenberg spin system: Painlev\'e analysis
While many integrable spin systems are known to exist in (1+1) and (2+1)
dimensions, the integrability property of the physically important (2+1)
dimensional isotropic Heisenberg ferromagnetic spin system in the continuum
limit has not been investigated in the literature. In this paper, we show
through a careful singularity structure analysis of the underlying nonlinear
evolution equation that the system admits logarithmic type singular manifolds
and so is of non-Painlev\'e type and is expected to be nonintegrable.Comment: 11 pages. to be published in Phys. Lett. A (2006
The Many Electron Ground State of the Adiabatic Holstein Model in Two and Three Dimensions
We present the complete ground state phase diagram of the Holstein model in
two and three dimension considering the phonon variables to be classical. We
first establish the overall structure of the phase diagram by using exact
diagonalisation based Monte Carlo (ED-MC) on small lattices and then use a new
``travelling cluster'' approximation (TCA) for annealing the phonon degrees of
freedom on large lattices. The phases that emerge include a Fermi liquid (FL),
with no lattice distortions, an insulating polaron liquid (PL) at strong
coupling, and a charge ordered insulating (COI) phase around half- filling. The
COI phase is separated from the Fermi liquid by a regime of phase coexistence
whose width grows with increasing electron-phonon coupling. We provide results
on the electronic density of states, the COI order parameter, and the spatial
organisation of polaronic states, for arbitrary density and electron-phonon
coupling. The results highlight the crucial role of spatial correlations in
this strong coupling problem.Comment: Final versio
Electron-hole coexistence in disordered graphene probed by high-field magneto-transport
We report on magneto-transport measurement in disordered graphene under
pulsed magnetic field of up to 57T. For large electron or hole doping, the
system displays the expected anomalous Integer Quantum Hall Effect (IQHE)
specific to graphene up to filling factor . In the close vicinity of the
charge neutrality point, the system breaks up into co-existing puddles of holes
and electrons, leading to a vanishing Hall and finite longitudinal resistance
with no hint of divergence at very high magnetic field. Large resistance
fluctuations are observed near the Dirac point. They are interpreted as the the
natural consequence of the presence of electron and hole puddles. The magnetic
field at which the amplitude of the fluctuations are the largest is directly
linked to the mean size of the puddles
All-optical switching of photonic entanglement
Future quantum optical networks will require the ability to route entangled
photons at high speeds, with minimal loss and added in-band noise, and---most
importantly---without disturbing the photons' quantum state. Here we present an
all-optical switch which fulfills these requirements and characterize its
performance at the single photon level. It exhibits a 200-ps switching window,
120:1 contrast, 1.5-dB loss, and induces no measurable degradation in the
switched photons' entangled-state fidelity (< 0.002). As a proof-of-principle
demonstration of its capability, we use the switch to demultiplex a single
quantum channel from a dual-channel, time-division-multiplexed entangled photon
stream. Furthermore, because this type of switch couples the temporal and
spatial degrees of freedom, it provides an important new tool with which to
encode multiple-qubit quantum states on a single photon
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Ultra low bending loss equiangular spiral photonic crystal fibers in the terahertz regime
An Equiangular Spiral Photonic Crystal Fiber (ES-PCF) design in Topas® for use in the Terahertz regime is presented. The design shows ultra low bending loss and very low confinement loss compared to conventional Hexagonal PCF (H-PCF). The ES-PCF has excellent modal confinement properties, together with several parameters to allow the optimization of the performance over a range of important characteristics. A full vector Finite Element simulation has been used to characterize the design which can be fabricated by a range of techniques including extrusion and drilling
Lithium hydroxide dihydrate: A new type of icy material at elevated pressure
We show that, in addition to the known monohydrate, LiOH forms a dihydrate at elevated pressure. The dihydrate involves a large number of H-bonds establishing chains along the direction. In addition, the energy surface exhibits a saddle point for proton locations along certain O interatomic distances, a feature characteristic for superprotonic conductors. However, MD simulations indicate that LiOH·2H_2O is not a superprotonic conductor and suggest the relevant interpolyhedral O–O distances being too large to allow for proton transfer between neighboring Li-coordinated polyhedra at least on the time scale of the MD-simulations
Heralding Single Photons Without Spectral Factorability
Recent efforts to produce single photons via heralding have relied on
creating spectrally factorable two-photon states in order to achieve both high
purity and high production rate. Through a careful multimode analysis, we find,
however, that spectral factorability is not necessary. Utilizing single-mode
detection, a similar or better performance can be achieved with non-factorable
states. This conclusion rides on the fact that even when using a broadband
filter, a single-mode measurement can still be realized, as long as the
coherence time of the triggering photons exceeds the measurement window of the
on/off detector.Comment: 7 pages, 5 figure
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