365 research outputs found
Bayesian Classifier for Medical Data from Doppler Unit
Nowadays, hand-held ultrasonic Doppler units (probes) are often used for noninvasive screening of atherosclerosis in the arteries of the lower limbs. The mean velocity of blood flow in time and blood pressures are measured on several positions on each lower limb. By listening to the acoustic signal generated by the device or by reading the signal displayed on screen, a specialist can detect peripheral arterial disease (PAD).This project aims to design software that will be able to analyze data from such a device and classify it into several diagnostic classes. At the Department of Functional Diagnostics at the Regional Hospital in Liberec a database of several hundreds signals was collected. In cooperation with the specialist, the signals were manually classified into four classes. For each class, selected signal features were extracted and then used for training a Bayesian classifier. Another set of signals was used for evaluating and optimizing the parameters of the classifier. Slightly above 84 % of successfully recognized diagnostic states, was recently achieved on the test data.
Electronic structure and magnetic properties of Li_2ZrCuO_4 - a spin 1/2 Heisenberg system in vicinity to a quantum critical point
Based on density functional calculations, we present a detailed theoretical
study of the electronic structure and the magnetic properties of the quasi-one
dimensional chain cuprate Li_2ZrCuO_4 (Li_2CuZrO_4). For the relevant ratio of
the next-nearest neighbor exchange J_2 to the nearest neighbor exchange J_1 we
find alpha = -J_2/J_1 = 0.22\pm0.02 which is very close to the critical point
at 1/4. Owing this vicinity to a ferromagnetic-helical critical point, we study
in detail the influence of structural peculiarities such as the reported Li
disorder and the non-planar chain geometry on the magnetic interactions
combining the results of LDA based tight-binding models with LDA+U derived
exchange parameters. Our investigation is complemented by an exact
diagonalization study of a multi-band Hubbard model for finite clusters
predicting a strong temperature dependence of the optical conductivity for
Li_2ZrCuO_4
Very Fast Keyword Spotting System with Real Time Factor below 0.01
In the paper we present an architecture of a keyword spotting (KWS) system
that is based on modern neural networks, yields good performance on various
types of speech data and can run very fast. We focus mainly on the last aspect
and propose optimizations for all the steps required in a KWS design: signal
processing and likelihood computation, Viterbi decoding, spot candidate
detection and confidence calculation. We present time and memory efficient
modelling by bidirectional feedforward sequential memory networks (an
alternative to recurrent nets) either by standard triphones or so called
quasi-monophones, and an entirely forward decoding of speech frames (with
minimal need for look back). Several variants of the proposed scheme are
evaluated on 3 large Czech datasets (broadcast, internet and telephone, 17
hours in total) and their performance is compared by Detection Error Tradeoff
(DET) diagrams and real-time (RT) factors. We demonstrate that the complete
system can run in a single pass with a RT factor close to 0.001 if all
optimizations (including a GPU for likelihood computation) are applied.Comment: 11 pages, 3 figure
Quantum Zakharov Model in a Bounded Domain
We consider an initial boundary value problem for a quantum version of the
Zakharov system arising in plasma physics. We prove the global well-posedness
of this problem in some Sobolev type classes and study properties of solutions.
This result confirms the conclusion recently made in physical literature
concerning the absence of collapse in the quantum Langmuir waves. In the
dissipative case the existence of a finite dimensional global attractor is
established and regularity properties of this attractor are studied. For this
we use the recently developed method of quasi-stability estimates. In the case
when external loads are functions we show that every trajectory from
the attractor is both in time and spatial variables. This can be
interpret as the absence of sharp coherent structures in the limiting dynamics.Comment: 27 page
On the correllation effect in Peierls-Hubbard chains
We reexamine the dimerization, the charge and the spin gaps of a half-filled
Peierls-Hubbard chain by means of the incremental expansion technique. Our
numerical findings are in significant quantitative conflict with recently
obtained results by M. Sugiura and Y. Suzumura [J. Phys. Soc. Jpn. v. 71 (2002)
697] based on a bosonization and a renormalization group method, especially
with respect to the charge gap. Their approach seems to be valid only in the
weakly correlated case.Comment: 7pages,4figures(6eps-files
Development of boundary layers in Euler fluids that on "activation'' respond like Navier-Stokes fluids
We consider the flow of a fluid whose response characteristics change due the
value of the norm of the symmetric part of the velocity gradient, behaving as
an Euler fluid below a critical value and as a Navier-Stokes fluid at and above
the critical value, the norm being determined by the external stimuli. We show
that such a fluid, while flowing past a bluff body, develops boundary layers
which are practically identical to those that one encounters within the context
of the classical boundary layer theory propounded by Prandtl. Unlike the
classical boundary layer theory that arises as an approximation within the
context of the Navier-Stokes theory, here the development of boundary layers is
due to a change in the response characteristics of the constitutive relation.
We study the flow of such a fluid past an airfoil and compare the same against
the solution of the Navier-Stokes equations. We find that the results are in
excellent agreement with regard to the velocity and vorticity fields for the
two cases
Some qualitative properties of the solutions of the Magnetohydrodynamic equations for nonlinear bipolar fluids
In this article we study the long-time behaviour of a system of nonlinear
Partial Differential Equations (PDEs) modelling the motion of incompressible,
isothermal and conducting modified bipolar fluids in presence of magnetic
field. We mainly prove the existence of a global attractor denoted by \A for
the nonlinear semigroup associated to the aforementioned systems of nonlinear
PDEs. We also show that this nonlinear semigroup is uniformly differentiable on
\A. This fact enables us to go further and prove that the attractor \A is
of finite-dimensional and we give an explicit bounds for its Hausdorff and
fractal dimensions.Comment: The final publication is available at Springer via
http://dx.doi.org/10.1007/s10440-014-9964-
Temperature dependent optical conductivity of undoped cuprates with weak exchange
The optical conductivity sigma(omega) is calculated at finite temperature T
for CuO_2 chain clusters within a pd-Hubbard model. Data at T = 300 K for
Li_2CuO_2 are reanalyzed within this approach. The relative weights of
Zhang-Rice singlet and triplet charge excitations near 2.5 and 4 eV,
respectively, depend strongly on T, and a rather dramatic dependence of
sigma(omega) on the ratio of the first to second neighbor exchange integrals is
predicted. On the basis of these results, information about exchange
interactionsfor frustrated edge-shared cuprates can be obtained from
T-dependent optical spectra. Our results are also relevant for magnetically
weakly coupled wide-gap insulators in general.Comment: 5 pages, 3 figure
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