8,221 research outputs found
Long term cognitive outcomes of early term (37-38 weeks) and late preterm (34-36 weeks) births: a systematic review
Background: There is a paucity of evidence regarding long-term outcomes of late preterm (34-36 weeks) and early term (37-38 weeks) delivery. The objective of this systematic review was to assess long-term cognitive outcomes of children born at these gestations. Methods: Four electronic databases (Medline, Embase, clinicaltrials.gov and PsycINFO) were searched. Last search was 5 th August 2016.  Studies were included if they reported gestational age, IQ measure and the ages assessed. The protocol was registered with the International prospective register of systematic reviews (PROSPERO Record CRD42015015472). Two independent reviewers assessed the studies. Data were abstracted and critical appraisal performed of eligible papers. Results: Of 11,905 potential articles, seven studies reporting on 41,344 children were included. For early term births, four studies (n = 35,711) consistently showed an increase in cognitive scores for infants born at full term (39-41 weeks) compared to those born at early term (37-38 weeks) with increases for each week of term (difference between 37 and 40 weeks of around 3 IQ points), despite differences in age of testing and method of IQ/cognitive testing. Four studies (n = 5644) reporting childhood cognitive outcomes of late preterm births (34 - 36 weeks) also differed in study design (cohort and case control); age of testing; and method of IQ testing, and found no differences in outcomes between late preterm and term births, although risk of bias was high in included studies. Conclusion: Children born at 39-41 weeks have higher cognitive outcome scores compared to those born at early term (37-38 weeks). This should be considered when discussing timing of delivery. For children born late preterm, the data is scarce and when compared to full term (37-42 weeks) did not show any difference in IQ scores
Interplay between static and dynamic polar correlations in relaxor Pb(Mg_{1/3}Nb_{2/3})O_{3}
We have characterized the dynamics of the polar nanoregions in
Pb(MgNb)O (PMN) through high-resolution neutron
backscattering and spin-echo measurements of the diffuse scattering cross
section. We find that the diffuse scattering intensity consists of \emph{both}
static and dynamic components. The static component first appears at the Curie
temperature K, while the dynamic component freezes completely
at the temperature T K; together, these components account for
all of the observed spectral weight contributing to the diffuse scattering
cross section. The integrated intensity of the dynamic component peaks near the
temperature at which the frequency-dependent dielectric constant reaches a
maximum (T) when measured at 1 GHz, i. e. on a timescale of
ns. Our neutron scattering results can thus be directly related to dielectric
and infra-red measurements of the polar nanoregions. Finally, the global
temperature dependence of the diffuse scattering can be understood in terms of
just two temperature scales, which is consistent with random field models.Comment: (8 pages, 5 figures, submitted to Phys. Rev. B
Correlation measurements in high-multiplicity events
Requirements for correlation measurements in high--multiplicity events are
discussed. Attention is focussed on detection of so--called hot spots,
two--particle rapidity correlations, two--particle momentum correlations (for
quantum interferometry) and higher--order correlations. The signal--to--noise
ratio may become large in the high--multiplicity limit, allowing meaningful
single--event measurements, only if the correlations are due to collective
behavior.Comment: MN 55455, 20 pages, KSUCNR-011-92 and TPI-MINN-92/47-T (revised).
Revised to correct typo in equation (30), and to fill in a few steps in
calculations. Now published as Phys. Rev. C 47 (1993) 232
Hadron production in Au-Au collisions at RHIC
We present an analysis of particle production yields measured in central
Au-Au collisions at RHIC in the framework of the statistical thermal model. We
demonstrate that the model extrapolated from previous analyses at SPS and AGS
energy is in good agreement with the available experimental data at GeV implying a high degree of chemical equilibration. Performing a
fit to the data, the range of thermal parameters at chemical freezeout
is determined. At present, the best agreement of the model and the data is
obtained with the baryon chemical potential MeV and
temperature MeV. More ratios, such as multistrange baryon to
meson, would be required to further constrain the chemical freezeout
conditions. Extrapolating thermal parameters to higher energy, the predictions
of the model for particle production in Au-Au reactions at GeV
are also given.Comment: Final version, minor changes to text and figures. To appear in Phys.
Lett.
Helical spin-waves, magnetic order, and fluctuations in the langasite compound Ba3NbFe3Si2O14
We have investigated the spin fluctuations in the langasite compound
Ba3NbFe3Si2O14 in both the ordered state and as a function of temperature. The
low temperature magnetic structure is defined by a spiral phase characterized
by magnetic Bragg peaks at q=(0,0,tau ~ 1/7) onset at TN=27 K as previously
reported by Marty et al. The nature of the fluctuations and temperature
dependence of the order parameter is consistent with a classical second order
phase transition for a two dimensional triangular antiferromagnet. We will show
that the physical properties and energy scales including the ordering
wavevector, Curie-Weiss temperature, and the spin-waves can be explained
through the use of only symmetric exchange constants without the need for the
Dzyaloshinskii-Moriya interaction. This is accomplished through a set of
``helical" exchange pathways along the c direction imposed by the chiral
crystal structure and naturally explains the magnetic diffuse scattering which
displays a strong vector chirality up to high temperatures well above the
ordering temperature. This illustrates a strong coupling between magnetic and
crystalline chirality in this compound.Comment: 16 pages, 16 figures, submitted to Physical Review
Van Vleck excitons in Ca2RuO4
A framework is presented for modeling and understanding magnetic excitations
in localized, intermediate coupling magnets where the interplay between
spin-orbit coupling, magnetic exchange, and crystal field effects are known to
create a complex landscape of unconventional magnetic behaviors and ground
states. A spin-orbit exciton approach for modeling these excitations is
developed based upon a Hamiltonian which explicitly incorporates single-ion
crystalline electric field and spin exchange terms. This framework is then
leveraged to understand a canonical Van Vleck singlet ground
state whose excitations are coupled spin and crystalline electric field levels.
Specifically, the anomalous Higgs mode [Jain et al. Nat. Phys. 13, 633 (2017)],
spin-waves [S. Kunkem\"{o}ller et al. Phys. Rev. Lett. 115, 247201 (2015)], and
orbital excitations [L. Das et al. Phys. Rev. X 8, 011048 (2018)] in the
multiorbital Mott insulator CaRuO are captured and good agreement is
found with previous neutron and inelastic x-ray spectroscopic measurements.
Furthermore, our results illustrate how a crystalline electric field-induced
singlet ground state can support coherent longitudinal, or amplitude
excitations, and transverse wavelike dynamics. We use this description to
discuss mechanisms for accessing a nearby critical point.Comment: 18 pages, 8 figure
- …