266 research outputs found
Enhancement of Threshold Cross Sections by In-Medium Final State Interactions
We address the problem of pion production in low energy -nucleus
collisions. For the production mechanism we assume a simple model consisting of
a coherent sum of single pion exchange and the excitation---followed by the
decay into two pions and a nucleon---of the resonance. The
production amplitude is modified by the final state interaction between the
pions calculated using the chirally improved J\"ulich meson exchange model
including the polarization of the nuclear medium by the pions. The model
reproduces well the experimentally observed cross
sections, especially the enhancement with increasing of the
mass distribution in the threshold region.Comment: 5 pages RevTeX, 3-eps figure
Annihilation range and final-state interaction in the antiproton-proton annihilation into pi-pi+
The large set of accurate data on differential cross section and analyzing
power from the CERN LEAR experiment on in the range
from 360 to 1550 MeV/c is well reproduced within a distorted wave approximation
approach. The initial scattering wave functions originate from a
recent model. The transition operator is obtained from a combination
of the and quark-antiquark annihilation mechanisms. A good fit
to the data, in particular the reproduction of the double dip structure
observed in the analyzing powers, requires quark wave functions for proton,
antiproton, and pions with radii slightly larger than the respective measured
charge radii. This corresponds to an increase in range of the annihilation
mechanisms and consequently the amplitudes for total angular momentum J=2 and
higher are much larger than in previous approaches. The final state
wave functions, parameterized in terms of phase shifts and
inelasticities, are also a very important ingredient for the fine tuning of the
fit to the observables.Comment: 11 pages, 11 figures (Revtex 4), revised version with one additional
figure. Accepted for publication in PR
Late Paleocene Flora of the Northern Alaska Peninsula: The Role of Transberingian Plant Migrations and Climatic Change
For the first time, the Late Sagwon Flora is described from the upper beds of the Prince Creek Formation (Upper Paleocene) at the Sagavanirktok River (northern Alaska Peninsula). The flora is dominated by the angiosperm Tiliaephyllum brooksense Moiseeva et Herman sp. nov. and conifer Metasequoia occidentalis (Newb.) Chaney. The Late Sagwon Flora is most similar to the Danian or Danian-Selandian flora from the middle part of the Upper Tsagayan Subformation (Amur Region) and lower part of the Wuyun Formation (Heilongjiang Province, China). This similarity allows us to hypothesize that the genus Tiliaephyllum, which dominated in the Late Tsagayan Flora, migrated via the Bering Land Bridge from southern paleolatitudes of the Far East to high latitudes of the Arctic Pacific, due to the progressively warming climate of the Paleocene. Additional new angiosperm species are described from the Late Sagwon Flora: Archeampelos mullii Moiseeva et Herman sp. nov., Tiliaephyllum brooksense Moiseeva et Herman sp. nov., and Dicotylophyllum sagwonicum Moiseeva et Herman sp. nov
Near-threshold production of -mesons in and NN collisions and -mixing
We consider near-threshold -meson production in and
collisions. An effective Lagrangian approach with one-pion exchange is applied
to analyze different contributions to the cross section for different isospin
channels. The Reggeon exchange mechanism is also evaluated for comparison. The
results from reactions are used to calculate the contribution of the
meson to the cross sections and invariant mass distributions
of the reactions and . It is found that
the experimental observation of mesons in the reaction is much more promising than the observation of mesons in
the reaction . Effects of isospin violation in the reactions
, , and , which are induced by -- mixing, are also analyzed.Comment: 43 pages, including 16 eps figures, to be bublished in Phys. Atom.
Nucl. (Yad. Fiz.) vol. 65, No. 11 (2002
Value of prominent flow voids without cord edema in the detection of spinal arteriovenous fistulae
Purpose: To determine the prevalence of spinal dural arteriovenous fistulae (SDAVF) in patients presenting with prominent vascular flow voids on imaging without other imaging findings suggestive of SDAVF. Methods: We retrospectively identified patients from January 1, 2005 to March 1, 2012 who underwent spinal angiography for suspected SDAVF with prominent vascular flow voids on prior imaging. We excluded patients with other major spinal pathology or other imaging findings of SDAVF including cord hyperintensity, enhancement, or expansion. We calculated the proportion of patients with positive findings for SDAVF on angiography and evaluated the prevalence of SDAVF for this finding alone and in correlation with clinical findings. Results: 18 patients underwent spinal angiography for prominent flow voids on imaging without other spinal pathology or imaging findings of SDAVF. Three had a SDAVF detected on angiography. The prevalence of SDAVF in this population was low, only 17% (95% CI 6-39%). All of the patients with positive angiography findings had myelopathy, increasing the prevalence to 100% if the additional clinical finding of myelopathy was present. Conclusions: Prominent flow voids without other imaging findings suggestive of SDAVF is poorly predictive of the presence of a SDAVF, unless myelopathy is present clinically. © 2014 Alhilali et al
Near threshold enhancement of the ppbar mass spectrum in J/Psi decay
We investigate the nature of the near-threshold enhancement in the ppbar
invariant mass spectrum of the reaction J/Psi -> gamma ppbar reported recently
by the BES Collaboration. Using the Juelich NNbar model we show that the mass
dependence of the ppbar spectrum close to the threshold can be reproduced by
the S-wave ppbar final state interaction in the isospin I=1 state within the
Watson-Migdal approach. However, because of our poor knowledge of the NNbar
interaction near threshold and of the J/Psi -> gamma ppbar reaction mechanism
and in view of the controversal situation in the decay J/Psi -> pi0 ppbar,
where no obvious signs of a ppbar final state interaction are seen,
explanations other than final state interactions cannot be ruled out at the
present stage.Comment: 9 pages, 7 figure
Racemic epinephrine compared to salbutamol in hospitalized young children with bronchiolitis; a randomized controlled clinical trial [ISRCTN46561076]
BACKGROUND: Bronchiolitis is the most common cause of lower respiratory tract illness in infancy, and hospital admission rates appear to be increasing in Canada and the United States. Inhaled beta agonists offer only modest short-term improvement. Trials of racemic epinephrine have shown conflicting results. We sought to determine if administration of racemic epinephrine during hospital stay for bronchiolitis improved respiratory distress, was safe, and shortened length of stay. METHODS: The study was a randomized, double-blind controlled trial of aerosolized racemic epinephrine compared to salbutamol every one to 4 hours in previously well children aged 6 weeks to ≤ 2 years of age hospitalized with bronchiolitis. The primary outcome was symptom improvement as measured by the Respiratory Distress Assessment Instrument (RDAI); secondary outcomes were length of stay in hospital, adverse events, and report of symptoms by structured parental telephone interview one week after discharge. RESULTS: 62 children with a mean age of 6.4 months were enrolled; 80% of children had Respiratory Syncytial Virus (RSV). Racemic epinephrine resulted in significant improvement in wheezing and the total RDAI score on day 2 and over the entire stay (p < 0.05). The mean LOS in the epinephrine arm was 2.6 days (95% CI 2, 3.2) v. 3.4 days in those in the salbutamol group (95% CI 2.6, 4.2) (p > 0.05). Adverse events were not significantly different in the two arms. At one week post-discharge, over half of parents reported that their child still had a respiratory symptom and 40% had less than normal feeding. CONCLUSION: Racemic epinephrine relieves respiratory distress in hospitalized infants with bronchiolitis and is safe but does not abbreviate hospital stay. Morbidity associated with bronchiolitis as identified by parents persists for at least one week after hospital discharge in most infants
Amplicon-Dependent CCNE1 Expression Is Critical for Clonogenic Survival after Cisplatin Treatment and Is Correlated with 20q11 Gain in Ovarian Cancer
Genomic amplification of 19q12 occurs in several cancer types including ovarian cancer where it is associated with primary treatment failure. We systematically attenuated expression of genes within the minimally defined 19q12 region in ovarian cell lines using short-interfering RNAs (siRNA) to identify driver oncogene(s) within the amplicon. Knockdown of CCNE1 resulted in G1/S phase arrest, reduced cell viability and apoptosis only in amplification-carrying cells. Although CCNE1 knockdown increased cisplatin resistance in short-term assays, clonogenic survival was inhibited after treatment. Gain of 20q11 was highly correlated with 19q12 amplification and spanned a 2.5 Mb region including TPX2, a centromeric protein required for mitotic spindle function. Expression of TPX2 was highly correlated with gene amplification and with CCNE1 expression in primary tumors. siRNA inhibition of TPX2 reduced cell viability but this effect was not amplicon-dependent. These findings demonstrate that CCNE1 is a key driver in the 19q12 amplicon required for survival and clonogenicity in cells with locus amplification. Co-amplification at 19q12 and 20q11 implies the presence of a cooperative mutational network. These observations have implications for the application of targeted therapies in CCNE1 dependent ovarian cancers
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