650 research outputs found
Immersed boundary-finite element model of fluid-structure interaction in the aortic root
It has long been recognized that aortic root elasticity helps to ensure
efficient aortic valve closure, but our understanding of the functional
importance of the elasticity and geometry of the aortic root continues to
evolve as increasingly detailed in vivo imaging data become available. Herein,
we describe fluid-structure interaction models of the aortic root, including
the aortic valve leaflets, the sinuses of Valsalva, the aortic annulus, and the
sinotubular junction, that employ a version of Peskin's immersed boundary (IB)
method with a finite element (FE) description of the structural elasticity. We
develop both an idealized model of the root with three-fold symmetry of the
aortic sinuses and valve leaflets, and a more realistic model that accounts for
the differences in the sizes of the left, right, and noncoronary sinuses and
corresponding valve cusps. As in earlier work, we use fiber-based models of the
valve leaflets, but this study extends earlier IB models of the aortic root by
employing incompressible hyperelastic models of the mechanics of the sinuses
and ascending aorta using a constitutive law fit to experimental data from
human aortic root tissue. In vivo pressure loading is accounted for by a
backwards displacement method that determines the unloaded configurations of
the root models. Our models yield realistic cardiac output at physiological
pressures, with low transvalvular pressure differences during forward flow,
minimal regurgitation during valve closure, and realistic pressure loads when
the valve is closed during diastole. Further, results from high-resolution
computations demonstrate that IB models of the aortic valve are able to produce
essentially grid-converged dynamics at practical grid spacings for the
high-Reynolds number flows of the aortic root
Origin of the low-mass electron pair excess in light nucleus-nucleus collisions
We report measurements of electron pair production in elementary p+p and d+p
reactions at 1.25 GeV/u with the HADES spectrometer. For the first time, the
electron pairs were reconstructed for n+p reactions by detecting the proton
spectator from the deuteron breakup. We find that the yield of electron pairs
with invariant mass Me+e- > 0.15 GeV/c2 is about an order of magnitude larger
in n+p reactions as compared to p+p. A comparison to model calculations
demonstrates that the production mechanism is not sufficiently described yet.
The electron pair spectra measured in C+C reactions are compatible with a
superposition of elementary n+p and p+p collisions, leaving little room for
additional electron pair sources in such light collision systems.Comment: 11 pages, 2 figures, \usepackage{epsfig
Shrinking a large dataset to identify variables associated with increased risk of Plasmodium falciparum infection in Western Kenya
Large datasets are often not amenable to analysis using traditional single-step approaches. Here, our general objective was to apply imputation techniques, principal component analysis (PCA), elastic net and generalized linear models to a large dataset in a systematic approach to extract the most meaningful predictors for a health outcome. We extracted predictors for Plasmodium falciparum infection, from a large covariate dataset while facing limited numbers of observations, using data from the People, Animals, and their Zoonoses (PAZ) project to demonstrate these techniques: data collected from 415 homesteads in western Kenya, contained over 1500 variables that describe the health, environment, and social factors of the humans, livestock, and the homesteads in which they reside. The wide, sparse dataset was simplified to 42 predictors of P. falciparum malaria infection and wealth rankings were produced for all homesteads. The 42 predictors make biological sense and are supported by previous studies. This systematic data-mining approach we used would make many large datasets more manageable and informative for decision-making processes and health policy prioritization
Study of CP violation in Dalitz-plot analyses of B0 --> K+K-KS, B+ --> K+K-K+, and B+ --> KSKSK+
We perform amplitude analyses of the decays , , and , and measure CP-violating
parameters and partial branching fractions. The results are based on a data
sample of approximately decays, collected with the
BABAR detector at the PEP-II asymmetric-energy factory at the SLAC National
Accelerator Laboratory. For , we find a direct CP asymmetry
in of , which differs
from zero by . For , we measure the
CP-violating phase .
For , we measure an overall direct CP asymmetry of
. We also perform an angular-moment analysis of
the three channels, and determine that the state can be described
well by the sum of the resonances , , and
.Comment: 35 pages, 68 postscript figures. v3 - minor modifications to agree
with published versio
Observation of Orbitally Excited B_s Mesons
We report the first observation of two narrow resonances consistent with
states of orbitally excited (L=1) B_s mesons using 1 fb^{-1} of ppbar
collisions at sqrt{s} = 1.96 TeV collected with the CDF II detector at the
Fermilab Tevatron. We use two-body decays into K^- and B^+ mesons reconstructed
as B^+ \to J/\psi K^+, J/\psi \to \mu^+ \mu^- or B^+ \to \bar{D}^0 \pi^+,
\bar{D}^0 \to K^+ \pi^-. We deduce the masses of the two states to be m(B_{s1})
= 5829.4 +- 0.7 MeV/c^2 and m(B_{s2}^*) = 5839.7 +- 0.7 MeV/c^2.Comment: Version accepted and published by Phys. Rev. Let
Global Search for New Physics with 2.0/fb at CDF
Data collected in Run II of the Fermilab Tevatron are searched for
indications of new electroweak-scale physics. Rather than focusing on
particular new physics scenarios, CDF data are analyzed for discrepancies with
the standard model prediction. A model-independent approach (Vista) considers
gross features of the data, and is sensitive to new large cross-section
physics. Further sensitivity to new physics is provided by two additional
algorithms: a Bump Hunter searches invariant mass distributions for "bumps"
that could indicate resonant production of new particles; and the Sleuth
procedure scans for data excesses at large summed transverse momentum. This
combined global search for new physics in 2.0/fb of ppbar collisions at
sqrt(s)=1.96 TeV reveals no indication of physics beyond the standard model.Comment: 8 pages, 7 figures. Final version which appeared in Physical Review D
Rapid Communication
Measurement of the Bottom-Strange Meson Mixing Phase in the Full CDF Data Set
We report a measurement of the bottom-strange meson mixing phase \beta_s
using the time evolution of B0_s -> J/\psi (->\mu+\mu-) \phi (-> K+ K-) decays
in which the quark-flavor content of the bottom-strange meson is identified at
production. This measurement uses the full data set of proton-antiproton
collisions at sqrt(s)= 1.96 TeV collected by the Collider Detector experiment
at the Fermilab Tevatron, corresponding to 9.6 fb-1 of integrated luminosity.
We report confidence regions in the two-dimensional space of \beta_s and the
B0_s decay-width difference \Delta\Gamma_s, and measure \beta_s in [-\pi/2,
-1.51] U [-0.06, 0.30] U [1.26, \pi/2] at the 68% confidence level, in
agreement with the standard model expectation. Assuming the standard model
value of \beta_s, we also determine \Delta\Gamma_s = 0.068 +- 0.026 (stat) +-
0.009 (syst) ps-1 and the mean B0_s lifetime, \tau_s = 1.528 +- 0.019 (stat) +-
0.009 (syst) ps, which are consistent and competitive with determinations by
other experiments.Comment: 8 pages, 2 figures, Phys. Rev. Lett 109, 171802 (2012
Model Reduction Opportunities in Detailed Simulations of Combustion Dynamics
Rocket and gas turbine combustion dynamics involves a confluence of diverse physics and interaction across a number of system components. Any comprehensive, self-consistent numerical model is burdened by a very large computational mesh, stiff unsteady processes which limit the permissible time step, and the need to perform tedious, repeated calculations for a broad parametric range. Predictive CFD models rely on very large scale simulations and advanced hardware. Reduced Basis Methods (RBM) have grown in usage during the past decade, as promising new techniques in making large simulations more accessible. These methods create models with far fewer unknown quantities than the original system, by generating “proper” fundamental solutions and their Galerkin projections, while guaranteeing accuracy and computational efficiency. RBMs seek to reproduce full CFD solutions, rather than solutions to a simplified or linearized set of equations. We present here some recent work in this area, focusing on approaches to model large scale combustor systems. The maturation of methods leading to LES-based turbulent combustion modeling is discussed, and model reduction goals and strategies are explored from the perspective of applicability in real life problems in both gas turbine, as well as rocket engines
Saethre-Chotzen syndrome : cranofacial anomalies caused by genetic changes in the TWIST gene
In this thesis, one of the most frequently occurring and most variable craniosynostosis
syndromes was investigated; Saethre-Chotzen syndrome. Craniosynostosis is the premature
obliteration of cranial sutures in the developing embryo. It can also occur in the first few
months of life. Saethre-Chotzen syndrome is, besides craniosynostosis, characterized by
specific facial and limb abnormalities, of which the most frequently reported are ptosis,
prominent crus helicis, cutaneous syndactyly of digit 2 and 3 on both hands and feet, and
broad halluces. Saethre-Chotzen syndrome has been linked to the TWIST gene on
chromosome 7p21.1. Mutations in and variably sized deletions of this gene can be found in
patients with clinical features of Saethre-Chotzen syndrome. The latter, TWIST deletions,
often also include part of the surrounding chromosome 7p and are reported to be associated
with mental retardation. In Saethre-Chotzen patients, in whom neither a mutation nor a
deletion of TWIST had been found, the FGFR3 P250R mutation was in some cases detected.
This mutation has specifically been linked to Muenke syndrome that is characterized by unior
bicoronal synostosis and slight facial dysmorphology. However, a Saethre-Chotzen like
phenotype can also result from this mutation.
Because of the possible overlap of Saethre-Chotzen with Muenke syndrome, these syndromes
were studied in order to provide clinical criteria that discriminate between the two (chapter 4).
Many phenotypic features occur in both syndromes. In addition, although unicoronal
synostosis occurs slightly more frequently in Muenke syndrome, unicoronal and bicoronal
synostosis are seen in both syndromes. The discrimination between Saethre-Chotzen and
Muenke is often not made easily and the associated genes, TWIST and FGFR3, respectively,
are simultaneously tested for pathogenic m
W boson polarization measurement in the ttbar dilepton channel using the CDF II Detector
We present a measurement of boson polarization in top-quark decays in
events with decays to dilepton final states using of integrated luminosity in collisions collected by the
CDF II detector at the Tevatron. A simultaneous measurement of the fractions of
longitudinal () and right-handed () bosons yields the results
and . Combining this measurement
with our previous result based on single lepton final states, we obtain and . The results are consistent with standard
model expectation.Comment: Published in Phys. Lett.
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