34 research outputs found
Time domain reconstruction of sound speed and attenuation in ultrasound computed tomography using full wave inversion
Ultrasound computed tomography (USCT) is a non-invasive imaging technique that provides information
about the acoustic properties of soft tissues in the body, such as the speed of sound (SS) and
acoustic attenuation (AA). Knowledge of these properties can improve the discrimination between
benign and malignant masses, especially in breast cancer studies. Full wave inversion (FWI) methods
for image reconstruction in USCT provide the best image quality compared to more approximate
methods. Using FWI, the SS is usually recovered in the time domain, and the AA is usually
recovered in the frequency domain. Nevertheless, as both properties can be obtained from the same
data, it is desirable to have a common framework to reconstruct both distributions. In this work, an
algorithm is proposed to reconstruct both the SS and AA distributions using a time domain FWI
methodology based on the fractional Laplacian wave equation, an adjoint field formulation, and a
gradient-descent method. The optimization code employs a Compute Unified Device Architecture
version of the software k-Wave, which provides high computational efficiency. The performance of
the method was evaluated using simulated noisy data from numerical breast phantoms. Errors were
less than 0.5% in the recovered SS and 10% in the AA. V
Superscaling analysis and neutrino-induced charged-current pion production at MiniBooNE kinematics
Regularization of image reconstruction in ultrasound computed tomography
We propose two regularizations techniques for a bent-ray (BR) tracing algorithm to reconstruct the speed of sound maps of breast tissues in an Ultrasound Computed Tomography (USCT) system. When high frequencies are employed, the use of BR is a good approximation to describe the propagation of the front of the pressure wave. The quantitative accuracy of the images reconstructed with the BR algorithm was evaluated without any kind of regularization, and with two regularization methods. The regularizations were based on some available a priori information, namely the known higher and lower values of the speed of sound expected in the breast tissues, and the maps of the internal structures obtained from the standard reflection ultrasound (US) imaging. The use of the proposed regularizations in the implemented algorithm improves the convergence and quality of the resulting images, although further improvements are still possible. These methods will help obtaining quantitative US images in a reasonable amount of time, expanding the possibilities and applications of this technique
Charged-Current Inclusive Neutrino Cross Sections: Superscaling Extension to the Pion Production and Realistic Spectral Function for Quasielastic Region
Universal features of correlated bursty behaviour
Inhomogeneous temporal processes, like those appearing in human
communications, neuron spike trains, and seismic signals, consist of
high-activity bursty intervals alternating with long low-activity periods. In
recent studies such bursty behavior has been characterized by a fat-tailed
inter-event time distribution, while temporal correlations were measured by the
autocorrelation function. However, these characteristic functions are not
capable to fully characterize temporally correlated heterogenous behavior. Here
we show that the distribution of the number of events in a bursty period serves
as a good indicator of the dependencies, leading to the universal observation
of power-law distribution in a broad class of phenomena. We find that the
correlations in these quite different systems can be commonly interpreted by
memory effects and described by a simple phenomenological model, which displays
temporal behavior qualitatively similar to that in real systems
Display of probability densities for data from a continuous distribution
Based on cumulative distribution functions, Fourier series expansion and
Kolmogorov tests, we present a simple method to display probability densities
for data drawn from a continuous distribution. It is often more efficient than
using histograms.Comment: 5 pages, 4 figures, presented at Computer Simulation Studies XXIV,
Athens, GA, 201
Towards a Pan-European Integrated Groundwater and Surface Water Model: Development and Applications
Polarization Transfer in the ^4He(\vec e,e'\vec p)^3H Reaction up to Q^2 = 2.6 (GeV/c)^2
We have measured the proton recoil polarization in the ^4He(\vec e,e'\vec
p)^3H reaction at Q^2 = 0.5, 1.0, 1.6, and 2.6 (GeV/c)^2. The measured ratio of
polarization transfer coefficients differs from a fully relativistic
calculation, favoring the inclusion of a predicted medium modification of the
proton form factors based on a quark-meson coupling model. In contrast, the
measured induced polarizations agree reasonably well with the fully
relativistic calculation indicating that the treatment of final-state
interactions is under control.Comment: 5 pages, 3 figures, uses revtex.sty, submitted to Physical Review
Letter
First beta-decay spectroscopy of In-135 and new beta-decay branches of In-134
The beta decay of the neutron-rich In-134 and In-135 was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number Z = 50 above the N = 82 shell. The beta-delayed gamma-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three beta-decay branches of In-134 were established, two of which were observed for the first time. Population of neutron-unbound states decaying via. rays was identified in the two daughter nuclei of In-134, Sn-134 and Sn-133, at excitation energies exceeding the neutron separation energy by 1 MeV. The beta-delayed one- and two-neutron emission branching ratios of In-134 were determined and compared with theoretical calculations. The beta-delayed one-neutron decay was observed to be dominant beta-decay branch of In-134 even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of Sn-134. Transitions following the beta decay of In-135 are reported for the first time, including. rays tentatively attributed to Sn-135. In total, six new levels were identified in Sn-134 on the basis of the beta.. coincidences observed in the In-134 and In-135 beta decays. A transition that might be a candidate for deexciting the missing neutron single-particle 13/2(+) state in Sn-133 was observed in both beta decays and its assignment is discussed. Experimental level schemes of Sn-134 and Sn-135 are compared with shell-model predictions. Using the fast timing technique, half-lives of the 2(+), 4(+), and 6(+) levels in Sn-134 were determined. From the lifetime of the 4(+) state measured for the first time, an unexpectedly large B(E2; 4(+)-> 2(+)) transition strength was deduced, which is not reproduced by the shell-model calculations.Peer reviewe