116 research outputs found
The Peierls--Nabarro FE model in two-phase microstructures -- a comparison with atomistics
This paper evaluates qualitatively as well as quantitatively the accuracy of
a recently proposed Peierls--Nabarro Finite Element (PN-FE) model for
dislocations by a direct comparison with an equivalent molecular statics
simulation. To this end, a two-dimensional microstructural specimen subjected
to simple shear is considered, consisting of a central soft phase flanked by
two hard-phase regions. A hexagonal atomic structure with equal lattice spacing
is adopted, the interactions of which are described by the Lennard--Jones
potential with phase specific depths of its energy well. During loading, edge
dislocation dipoles centred in the soft phase are introduced, which progress
towards the phase boundaries, where they pile up. Under a sufficiently high
external shear load, the leading dislocation is eventually transmitted into the
harder phase. The homogenized PN-FE model is calibrated to an atomistic model
in terms of effective elasticity constants and glide plane properties as
obtained from simple uniform deformations. To study the influence of different
formulations of the glide plane potential, multiple approaches are employed,
ranging from a simple sinusoidal function of the tangential disregistry to a
complex model that couples the influence of the tangential and the normal
disregistries. The obtained results show that, qualitatively, the dislocation
structure, displacement, strain fields, and the dislocation evolution are
captured adequately. The simplifications of the PN-FE model lead, however, to
some discrepancies within the dislocation core. Such discrepancies play a
dominant role in the dislocation transmission process, which thus cannot
quantitatively be captured properly. Despite its simplicity, the PN-FE model
proves to be an elegant tool for a qualitative study of edge dislocation
behaviour in two-phase microstructures, although it may not be quantitatively
predictive.Comment: 29 pages, 11 figures, 5 tables, abstract shortened to fulfill 1920
character limit, small changes after revie
Parental heights and maternal education as predictors of length/height of children at birth, age 3 and 19 years, independently on diet: the ELSPAC study
BACKGROUND/OBJECTIVES: Little is currently known about the relationship between the parental diet during pregnancy and the growth of the child from early childhood until early adulthood. This study was designed to examine whether the dietary patterns of the parents during a pregnancy and of the respective child at 3 years are associated with the length/height-for-age z-score of child at birth, 3 years of age and at 19 years of age. SUBJECTS/METHODS: Dietary patterns of pregnant women and their partners, and offspring at 3 years that were enroled in the 1990-1991 period in the Czech part of the European Longitudinal Study of Pregnancy and Childhood. Multivariable linear regression models were used to estimate the relationship between the dietary patterns of parents (835 child-mother-father trios) during pregnancy and the length/height-for-age z-score of their offspring at birth, 3 years and 19 years. RESULTS: The maternal health-conscious food pattern was found to predict lower child height at 3 years, but not at birth nor at 19 years of age. An increase in the health-conscious pattern score of the maternal diet was associated with significantly lower height-for-age z-score at 3 years; however, the observed effect lost its significance after the adjustment for diet of the child at 3 years. CONCLUSIONS: After full adjustment, the only significant predictors of the height-for-age z-score of the child at 3 years were the heights of both parents and maternal education. More research into the association of maternal diet in pregnancy and height of child is necessary.European Journal of Clinical Nutrition advance online publication, 8 February 2017; doi:10.1038/ejcn.2016.244
Identified charged hadron production in p+p collisions at sqrt(s)=200 and 62.4 GeV
Transverse momentum distributions and yields for , ,
and in collisions at =200 and 62.4 GeV at midrapidity
are measured by the PHENIX experiment at the Relativistic Heavy Ion Collider
(RHIC). These data provide important baseline spectra for comparisons with
identified particle spectra in heavy ion collisions at RHIC. We present the
inverse slope parameter , mean transverse momentum and
yield per unit rapidity at each energy, and compare them to other
measurements at different in and collisions. We
also present the scaling properties such as scaling, scaling on the
spectra between different energies. To discuss the mechanism of the
particle production in collisions, the measured spectra are compared to
next-to-leading-order or next-to-leading-logarithmic perturbative quantum
chromodynamics calculations.Comment: 431 authors from 62 institutions, 32 pages, 23 figures, and 18
tables. Submitted to Physical Review C. Plain text data tables for the points
plotted in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
Quantitative Constraints on the Transport Properties of Hot Partonic Matter from Semi-Inclusive Single High Transverse Momentum Pion Suppression in Au+Au collisions at sqrt(s_NN) = 200 GeV
The PHENIX experiment has measured the suppression of semi-inclusive single
high transverse momentum pi^0's in Au+Au collisions at sqrt(s_NN) = 200 GeV.
The present understanding of this suppression is in terms of energy-loss of the
parent (fragmenting) parton in a dense color-charge medium. We have performed a
quantitative comparison between various parton energy-loss models and our
experimental data. The statistical point-to-point uncorrelated as well as
correlated systematic uncertainties are taken into account in the comparison.
We detail this methodology and the resulting constraint on the model
parameters, such as the initial color-charge density dN^g/dy, the medium
transport coefficient , or the initial energy-loss parameter epsilon_0.
We find that high transverse momentum pi^0 suppression in Au+Au collisions has
sufficient precision to constrain these model dependent parameters at the +/1
20%-25% (one standard deviation) level. These constraints include only the
experimental uncertainties, and further studies are needed to compute the
corresponding theoretical uncertainties.Comment: 422 authors, 13 pages text, RevTeX-4, 9 figures, 2 tables. This
version is updated with changes made during the review process and is now the
same as what was published in Physical Review C. Plain text data tables for
the points plotted in figures for this and previous PHENIX publications are
publicly available at http://www.phenix.bnl.gov/papers.htm
Cross section and double helicity asymmetry for eta mesons and their comparison to neutral pion production in p+p collisions at sqrt(s)=200 GeV
Measurements of double-helicity asymmetries for inclusive hadron production
in polarized p+p collisions are sensitive to helicity--dependent parton
distribution functions, in particular to the gluon helicity distribution,
Delta(g). This study focuses on the extraction of the double-helicity asymmetry
in eta production: polarized p+p --> eta + X, the eta cross section, and the
eta/pi^0 cross section ratio. The cross section and ratio measurements provide
essential input for the extraction of fragmentation functions that are needed
to access the helicity-dependent parton distribution functions.Comment: 432 authors from 62 institutions, 13 pages, 5 figures, and 3 tables.
Submitted to Physical Review D. v2 has minor changes only to update
references and reposition figures and tables. All data points plotted in
Figs. 2, 4, and 5 are given in Tables I, II, and III, respectivel
Charged hadron multiplicity fluctuations in Au+Au and Cu+Cu collisions from sqrt(s_NN) = 22.5 to 200 GeV
A comprehensive survey of event-by-event fluctuations of charged hadron
multiplicity in relativistic heavy ions is presented. The survey covers Au+Au
collisions at sqrt(s_NN) = 62.4 and 200 GeV, and Cu+Cu collisions sqrt(s_NN) =
22.5, 62.4, and 200 GeV. Fluctuations are measured as a function of collision
centrality, transverse momentum range, and charge sign. After correcting for
non-dynamical fluctuations due to fluctuations in the collision geometry within
a centrality bin, the remaining dynamical fluctuations expressed as the
variance normalized by the mean tend to decrease with increasing centrality.
The dynamical fluctuations are consistent with or below the expectation from a
superposition of participant nucleon-nucleon collisions based upon p+p data,
indicating that this dataset does not exhibit evidence of critical behavior in
terms of the compressibility of the system. An analysis of Negative Binomial
Distribution fits to the multiplicity distributions demonstrates that the heavy
ion data exhibit weak clustering properties.Comment: 464 authors from 60 institutions, 17 pages, 12 figures, 1 table.
Submitted to Physical Review C. Plain text data tables for the points plotted
in figures for this and previous PHENIX publications are (or will be)
publicly available at http://www.phenix.bnl.gov/papers.htm
Dilepton mass spectra in p+p collisions at sqrt(s)= 200 GeV and the contribution from open charm
The PHENIX experiement has measured the electron-positron pair mass spectrum
from 0 to 8 GeV/c^2 in p+p collisions at sqrt(s)=200 GeV. The contributions
from light meson decays to e^+e^- pairs have been determined based on
measurements of hadron production cross sections by PHENIX. They account for
nearly all e^+e^- pairs in the mass region below 1 GeV/c^2. The e^+e^- pair
yield remaining after subtracting these contributions is dominated by
semileptonic decays of charmed hadrons correlated through flavor conservation.
Using the spectral shape predicted by PYTHIA, we estimate the charm production
cross section to be 544 +/- 39(stat) +/- 142(syst) +/- 200(model) \mu b, which
is consistent with QCD calculations and measurements of single leptons by
PHENIX.Comment: 375 authors from 57 institutions, 18 pages, 4 figures, 2 tables.
Submitted to Physics Letters B. v2 fixes technical errors in matching authors
to institutions. Plain text data tables for the points plotted in figures for
this and previous PHENIX publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Medium modification of jet fragmentation in Au+Au collisions at sqrt(s_NN)=200 GeV measured in direct photon-hadron correlations
The jet fragmentation function is measured with direct photon-hadron
correlations in p+p and Au+Au collisions at sqrt(s_NN)=200 GeV. The p_T of the
photon is an excellent approximation to the initial p_T of the jet and the
ratio z_T=p_T^h/p_T^\gamma is used as a proxy for the jet fragmentation
function. A statistical subtraction is used to extract the direct photon-hadron
yields in Au+Au collisions while a photon isolation cut is applied in p+p. I_
AA, the ratio of jet fragment yield in Au+Au to that in p+p, indicates
modification of the jet fragmentation function. Suppression, most likely due to
energy loss in the medium, is seen at high z_T. The fragment yield at low z_T
is enhanced at large angles. Such a trend is expected from redistribution of
the lost energy into increased production of low-momentum particles.Comment: 562 authors, 70 insitutions, 8 pages, and 3 figures. Submitted to
Phys. Rev. Lett. v2 has minor changes to improve clarity. Plain text data
tables for the points plotted in figures for this and previous PHENIX
publications are (or will be) publicly available at
http://www.phenix.bnl.gov/papers.htm
Energy Loss and Flow of Heavy Quarks in Au+Au Collisions at sqrt(s_NN) = 200 GeV
The PHENIX experiment at the Relativistic Heavy Ion Collider (RHIC) has
measured electrons from heavy flavor (charm and bottom) decays for 0.3 < p_T <
9 GeV/c at midrapidity (|y| < 0.35) in Au+Au collisions at sqrt(s_NN) = 200
GeV. The nuclear modification factor R_AA relative to p+p collisions shows a
strong suppression in central Au+Au collisions, indicating substantial energy
loss of heavy quarks in the medium produced at RHIC. A large azimuthal
anisotropy, v_2, with respect to the reaction plane is observed for 0.5 < p_T <
5 GeV/c indicating non-zero heavy flavor elliptic flow. Both R_AA and v_2 show
a p_T dependence different from those of neutral pions. A comparison to
transport models which simultaneously describe R_AA(p_T) and v_2(p_T) suggests
that the viscosity to entropy density ratio is close to the conjectured quantum
lower bound, i.e., near a perfect fluid.Comment: v2 replaced Fig. 3 to fix an error in using a wrong theory curve; v3
minor changes in review process, including last 2 sentences of abstract. 422
authors, 58 institutions, 6 pages text, 3 figures, REVTeX4. Submitted to
Physical Review Letters. Plain text data tables for the points plotted in
figures available at http://www.phenix.bnl.gov/papers.htm
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