1,773 research outputs found
Notions and subnotions in information structure
Three dimensions can be distinguished in a cross-linguistic account of information structure. First, there is the definition of the focus constituent, the part of the linguistic expression which is subject to some focus meaning. Second and third, there are the focus meanings and the array of structural devices that encode them. In a given language, the expression of focus is facilitated as well as constrained by the grammar within which the focus devices operate. The prevalence of focus ambiguity, the structural inability to make focus distinctions, will thus vary across languages, and within a language, across focus meanings
A data mining approach to the SAR values over large MR image repositories
Purpose: In magnetic resonance imaging, the radiofrequency energy
absorption arises as one of the main safety concerns, being mainly related with
increased body temperature. Monitoring radiofrequency absorption is achieved
by the estimation of specific absorption rate (SAR), whose implementation lies
on equipment manufacturers, which in turn are not totally enlightening about its
calculus. This work presents an exploratory approach of whole-body SAR
values stored in DICOM metadata aiming to find correlation with body weight,
body mass index (BMI), gender and pulse sequences for abdominal/pelvic
(17.812 series) and head (29.907 series) studies.
Methods and Materials: All studies were acquired in a 3 Tesla scanner with
high-performance gradients. Data were extracted using Dicoogle, a DICOM
metadata mining tool. Several DICOM tags were analysed (e.g. patient weight,
height, gender, sequence name). For each study type, specifically weighted
pulse sequences were related with weight, BMI and gender through boxplot
diagrams, statistical and effect size analysis.
Results: SAR limits were never exceeded. Generally, SAR values tended to
decrease with increasing body weight and BMI values for abdominal/pelvic
studies. On the other hand, head studies showed different trends regarding
distinct pulse sequences. SAR values tend to be higher in male individuals
(p<0,05). As expected, turbo spin echo sequences present the highest SAR
values. The values found for echo gradient spoiled sequence (FLASH) were
also high.
Conclusion: It is confirmed that SAR estimates are related with the analysed
variables. An individual examination of pulse sequences is recommended to
observe trends regarding weight, BMI or gender.publishe
Fluctuations of elastic interfaces in fluids: Theory and simulation
We study the dynamics of elastic interfaces-membranes-immersed in thermally
excited fluids. The work contains three components: the development of a
numerical method, a purely theoretical approach, and numerical simulation. In
developing a numerical method, we first discuss the dynamical coupling between
the interface and the surrounding fluids. An argument is then presented that
generalizes the single-relaxation time lattice-Boltzmann method for the
simulation of hydrodynamic interfaces to include the elastic properties of the
boundary. The implementation of the new method is outlined and it is tested by
simulating the static behavior of spherical bubbles and the dynamics of bending
waves. By means of the fluctuation-dissipation theorem we recover analytically
the equilibrium frequency power spectrum of thermally fluctuating membranes and
the correlation function of the excitations. Also, the non-equilibrium scaling
properties of the membrane roughening are deduced, leading us to formulate a
scaling law describing the interface growth, W^2(L,T)=L^3 g[t/L^(5/2)], where
W, L and T are the width of the interface, the linear size of the system and
the temperature respectively, and g is a scaling function. Finally, the
phenomenology of thermally fluctuating membranes is simulated and the frequency
power spectrum is recovered, confirming the decay of the correlation function
of the fluctuations. As a further numerical study of fluctuating elastic
interfaces, the non-equilibrium regime is reproduced by initializing the system
as an interface immersed in thermally pre-excited fluids.Comment: 15 pages, 11 figure
Integrated silicon qubit platform with single-spin addressability, exchange control and robust single-shot singlet-triplet readout
Silicon quantum dot spin qubits provide a promising platform for large-scale
quantum computation because of their compatibility with conventional CMOS
manufacturing and the long coherence times accessible using Si enriched
material. A scalable error-corrected quantum processor, however, will require
control of many qubits in parallel, while performing error detection across the
constituent qubits. Spin resonance techniques are a convenient path to parallel
two-axis control, while Pauli spin blockade can be used to realize local parity
measurements for error detection. Despite this, silicon qubit implementations
have so far focused on either single-spin resonance control, or control and
measurement via voltage-pulse detuning in the two-spin singlet-triplet basis,
but not both simultaneously. Here, we demonstrate an integrated device platform
incorporating a silicon metal-oxide-semiconductor double quantum dot that is
capable of single-spin addressing and control via electron spin resonance,
combined with high-fidelity spin readout in the singlet-triplet basis.Comment: 10 pages, 4 figure
Molecular line mapping of the giant molecular cloud associated with RCW 106 - II. Column density and dynamical state of the clumps
We present a fully sampled C^{18}O (1-0) map towards the southern giant
molecular cloud (GMC) associated with the HII region RCW 106, and use it in
combination with previous ^{13}CO (1-0) mapping to estimate the gas column
density as a function of position and velocity. We find localized regions of
significant ^{13}CO optical depth in the northern part of the cloud, with
several of the high-opacity clouds in this region likely associated with a
limb-brightened shell around the HII region G333.6-0.2. Optical depth
corrections broaden the distribution of column densities in the cloud, yielding
a log-normal distribution as predicted by simulations of turbulence.
Decomposing the ^{13}CO and C^{18}O data cubes into clumps, we find relatively
weak correlations between size and linewidth, and a more sensitive dependence
of luminosity on size than would be predicted by a constant average column
density. The clump mass spectrum has a slope near -1.7, consistent with
previous studies. The most massive clumps appear to have gravitational binding
energies well in excess of virial equilibrium; we discuss possible
explanations, which include magnetic support and neglect of time-varying
surface terms in the virial theorem. Unlike molecular clouds as a whole, the
clumps within the RCW 106 GMC, while elongated, appear to show random
orientations with respect to the Galactic plane.Comment: 17 pages, to appear in MNRA
Transport Phenomena and Structuring in Shear Flow of Suspensions near Solid Walls
In this paper we apply the lattice-Boltzmann method and an extension to
particle suspensions as introduced by Ladd et al. to study transport phenomena
and structuring effects of particles suspended in a fluid near sheared solid
walls. We find that a particle free region arises near walls, which has a width
depending on the shear rate and the particle concentration. The wall causes the
formation of parallel particle layers at low concentrations, where the number
of particles per layer decreases with increasing distance to the wall.Comment: 14 pages, 14 figure
3D Spinodal Decomposition in the Inertial Regime
We simulate late-stage coarsening of a 3D symmetric binary fluid using a
lattice Boltzmann method. With reduced lengths and times l and t respectively
(scales set by viscosity, density and surface tension) our data sets cover 1 <
l
100 we find clear evidence of Furukawa's inertial scaling (l ~ t^{2/3}),
although the crossover from the viscous regime (l ~ t) is very broad. Though it
cannot be ruled out, we find no indication that Re is self-limiting (l ~
t^{1/2}) as proposed by M. Grant and K. R. Elder [Phys. Rev. Lett. 82, 14
(1999)].Comment: 4 pages, 3 eps figures, RevTex, minor changes to bring in line with
published version. Mobility values added to Table
Spillover Effects of Studying with Immigrant Students; A Quantile Regression Approach
Abstract: We analyze how the share of immigrant children in the classroom aects the educational attainment of native Dutch children in terms of their language and math performance at the end of primary school. Our paper studies the spill-over effects at different parts of the test score distribution of native Dutch students using a quantile regression approach. We fi nd no evidence of negative spillover effects of the classroom presence of immigrant children at the median of the test score distribution. In addition, there is no indication that these spill-over effects are present at other parts of the distribution.
Sedimentation and Flow Through Porous Media: Simulating Dynamically Coupled Discrete and Continuum Phases
We describe a method to address efficiently problems of two-phase flow in the
regime of low particle Reynolds number and negligible Brownian motion. One of
the phases is an incompressible continuous fluid and the other a discrete
particulate phase which we simulate by following the motion of single
particles. Interactions between the phases are taken into account using locally
defined drag forces. We apply our method to the problem of flow through random
media at high porosity where we find good agreement to theoretical expectations
for the functional dependence of the pressure drop on the solid volume
fraction. We undertake further validations on systems undergoing gravity
induced sedimentation.Comment: 22 pages REVTEX, figures separately in uudecoded, compressed
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