2,246 research outputs found
Developmental Changes and Injury Induced Disruption of the Radial Organization of the Cortex in the Immature Rat Brain Revealed by In Vivo Diffusion Tensor MRI
During brain development, morphological changes modify the cortex from its immature radial organization to its mature laminar appearance. Applying in vivo diffusion tensor imaging (DTI), the microstructural organization of the cortex in the immature rat was analyzed and correlated to neurohistopathology. Significant differences in apparent diffusion coefficient (ADC) and fractional anisotropy (FA) were detected between the external (I-III) and deep (IV-VI) cortical layers in postnatal day 3 (P3) and P6 pups. With cortical maturation, ADC was reduced in both cortical regions, whereas a decrease in FA was only seen in the deep layers. A distinct radial organization of the external cortical layers with the eigenvectors perpendicular to the pial surface was observed at both ages. Histology revealed maturational differences in the cortical architecture with increased neurodendritic density and reduction in the radial glia scaffolding. Early DTI after hypoxia-ischemia at P3 shows reduced ADC and FA in the ipsilateral cortex that persisted at P6. Cortical DTI eigenvector maps reveal microstructural disruption of the radial organization corresponding to regions of neuronal death, radial glial disruption, and astrocytosis. Thus, the combined use of in vivo DTI and histopathology can assist in delineating normal developmental changes and postinjury modifications in the immature rodent brai
An Efficient Large-Area Grating Coupler for Surface Plasmon Polaritons
We report the design, fabrication and characterization of a periodic grating
of shallow rectangular grooves in a metallic film with the goal of maximizing
the coupling efficiency of an extended plane wave (PW) of visible or
near-infrared light into a single surface plasmon polariton (SPP) mode on a
flat metal surface. A PW-to-SPP power conversion factor > 45 % is demonstrated
at a wavelength of 780 nm, which exceeds by an order of magnitude the
experimental performance of SPP grating couplers reported to date at any
wavelength. Conversion efficiency is maximized by matching the dissipative SPP
losses along the grating surface to the local coupling strength. This critical
coupling condition is experimentally achieved by tailoring the groove depth and
width using a focused ion beam.Comment: The final publication is available at http://www.springerlink.com.
http://dx.doi.org/10.1007/s11468-011-9303-
A classical theory for second-harmonic generation from metallic nanoparticles
In this article, we develop a classical electrodynamic theory to study the
optical nonlinearities of metallic nanoparticles. The quasi-free electrons
inside the metal are approximated as a classical Coulomb-interacting electron
gas, and their motion under the excitation of an external electromagnetic field
is described by the plasma equations. This theory is further tailored to study
second-harmonic generation. Through detailed experiment-theory comparisons, we
validate this classical theory as well as the associated numerical algorithm.
It is demonstrated that our theory not only provides qualitative agreement with
experiments, it also reproduces the overall strength of the experimentally
observed second-harmonic signals.Comment: 12 pages, 3 figures. Submitte
Rationale and design of the MULTISTARS AMI Trial: a randomized comparison of immediate versus staged complete revascularization in patients with ST-segment elevation myocardial infarction and multivessel disease
Background:
About half of patients with acute ST-segment elevation myocardial infarction (STEMI) present with multivessel coronary artery disease (MVD). Recent evidence supports complete revascularization in these patients. However, optimal timing of non-culprit lesion revascularization in STEMI patients is unknown because dedicated randomized trials on this topic are lacking.
Study design:
The MULTISTARS AMI trial is a prospective, international, multicenter, randomized, two-arm, open-label study planning to enroll at least 840 patients. It is designed to investigate whether immediate complete revascularization is non-inferior to staged (within 19-45 days) complete revascularization in patients in stable hemodynamic conditions presenting with STEMI and MVD and undergoing primary percutaneous coronary intervention (PCI). After successful primary PCI of the culprit artery, patients are randomized in a 1:1 ratio to immediate or staged complete revascularization. The primary endpoint is a composite of all-cause death, non-fatal myocardial infarction, ischemia-driven revascularization, hospitalization for heart failure, and stroke at 1 year.
Conclusions:
The MULTISTARS AMI trial tests the hypothesis that immediate complete revascularization is non-inferior to staged complete revascularization in stable patients with STEMI and MVD
Search for eta-mesic 4He in the dd->3He n pi0 and dd->3He p pi- reactions with the WASA-at-COSY facility
The search for 4He-eta bound states was performed with the WASA-at-COSY
facility via the measurement of the excitation function for the dd->3He n pi0
and dd->3He p pi- processes. The beam momentum was varied continuously between
2.127 GeV/c and 2.422 GeV/c, corresponding to the excess energy for the dd->4He
eta reaction ranging from Q=-70 MeV to Q=30 MeV. The luminosity was determined
based on the dd->3He n reaction and quasi-free proton-proton scattering via
dd->pp n_spectator n_spectator reactions. The excitation functions determined
independently for the measured reactions do not reveal a structure which could
be interpreted as a narrow mesic nucleus. Therefore, the upper limits of the
total cross sections for the bound state production and decay in
dd->(4He-eta)_bound->3He n pi0 and dd->(4He-eta)_bound->3He p pi- processes
were determined taking into account the isospin relation between both the
channels considered. The results of the analysis depend on the assumptions of
the N* momentum distribution in the anticipated mesic-4He. Assuming as in the
previous works, that this is identical with the distribution of nucleons bound
with 20 MeV in 4He, we determined that (for the mesic bound state width in the
range from 5 MeV to 50 MeV) the upper limits at 90% confidence level are about
3 nb and about 6 nb for npi0 and ppi- channels, respectively. However, based on
the recent theoretical findings of the N*(1535) momentum distribution in the
N*-3He nucleus bound by 3.6 MeV, we find that the WASA-at-COSY detector
acceptance decreases and hence the corresponding upper limits are 5 nb and 10
nb for npi0 and ppi- channels respectively.Comment: This article will be submitted to JHE
Charge Symmetry Breaking in dd->4He{\pi}0 with WASA-at-COSY
Charge symmetry breaking (CSB) observables are a suitable experimental tool
to examine effects induced by quark masses on the nuclear level. Previous high
precision data from TRIUMF and IUCF are currently used to develop a consistent
description of CSB within the framework of chiral perturbation theory. In this
work the experimental studies on the reaction dd->4He{\pi}0 have been extended
towards higher excess energies in order to provide information on the
contribution of p-waves in the final state. For this, an exclusive measurement
has been carried out at a beam momentum of p=1.2 GeV/c using the WASA-at-COSY
facility. The total cross section amounts to sigma(tot) = (118 +- 18(stat) +-
13(sys) +- 8(ext)) pb and first data on the differential cross section are
consistent with s-wave pion production.Comment: 14 pages, 5 figure
ABC Effect and Resonance Structure in the Double-Pionic Fusion to He
Exclusive and kinematically complete measurements of the double pionic fusion
to He have been performed in the energy region of the so-called ABC effect,
which denotes a pronounced low-mass enhancement in the -invariant mass
spectrum. The experiments were carried out with the WASA detector setup at
COSY. Similar to the observations in the basic reaction
and in the He reaction, the data reveal a correlation
between the ABC effect and a resonance-like energy dependence in the total
cross section. Differential cross sections are well described by the hypothesis
of resonance formation during the reaction process in addition to the
conventional -channel mechanism. The deduced resonance
width can be understood from collision broadening due to Fermi motion of the
nucleons in initial and final nuclei
Cross section ratio and angular distributions of the reaction p + d -> 3He + eta at 48.8 MeV and 59.8 MeV excess energy
We present new data for angular distributions and on the cross section ratio
of the p + d -> 3He + eta reaction at excess energies of Q = 48.8 MeV and Q =
59.8 MeV. The data have been obtained at the WASA-at-COSY experiment
(Forschungszentrum J\"ulich) using a proton beam and a deuterium pellet target.
While the shape of obtained angular distributions show only a slow variation
with the energy, the new results indicate a distinct and unexpected total cross
section fluctuation between Q = 20 MeV and Q = 60 MeV, which might indicate the
variation of the production mechanism within this energy interval.Comment: 9 pages, 9 figure
Neutron-Proton Scattering in the Context of the (2380) Resonance
New data on quasifree polarized neutron-proton scattering, in the region of
the recently observed resonance structure, have been obtained by
exclusive and kinematically complete high-statistics measurements with WASA at
COSY. This paper details the determination of the beam polarization, checks of
the quasifree character of the scattering process, on all obtained
angular distributions and on the new partial-wave analysis, which includes the
new data producing a resonance pole in the - coupled partial
waves at () MeV -- in accordance with the dibaryon
resonance hypothesis. The effect of the new partial-wave solution on the
description of total and differential cross section data as well as specific
combinations of spin-correlation and spin-transfer observables available from
COSY-ANKE measurements at = 2.27 GeV is discussed
Measurement of the Reaction in Search for the Recently Observed Resonance Structure in and systems
Exclusive measurements of the quasi-free reaction have
been performed by means of collisions at = 1.2 GeV using the WASA
detector setup at COSY. Total and differential cross sections have been
obtained covering the energy region = (2.35 - 2.46) GeV, which
includes the region of the ABC effect and its associated resonance structure.
No ABC effect, {\it i.e.} low-mass enhancement is found in the
-invariant mass spectrum -- in agreement with the constraint from
Bose statistics that the isovector pion pair can not be in relative s-wave. At
the upper end of the covered energy region -channel processes for Roper,
and excitations provide a reasonable description
of the data, but at low energies the measured cross sections are much larger
than predicted by such processes. Adding a resonance amplitude for the
resonance at =~2.37 GeV with =~70 MeV and observed
recently in and reactions leads to an
agreement with the data also at low energies
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