1,947 research outputs found
Weak Pion Production off the Nucleon
We develop a model for the weak pion production off the nucleon, which
besides the Delta pole mechanism (weak excitation of the
resonance and its subsequent decay into ), includes also some background
terms required by chiral symmetry. We re-fit the form factor to
the flux averaged ANL differential cross
section data, finding a substantially smaller contribution of the Delta pole
mechanism than traditionally assumed in the literature. Within this scheme, we
calculate several differential and integrated cross sections, including pion
angular distributions, induced by neutrinos and antineutrinos and driven both
by charged and neutral currents. In all cases we find that the background terms
produce quite significant effects and that they lead to an overall improved
description of the data, as compared to the case where only the Delta pole
mechanism is considered. We also show that the interference between the Delta
pole and the background terms produces parity-violating contributions to the
pion angular differential cross section, which are intimately linked to odd
correlations in the contraction between the leptonic and hadronic tensors.
However, these latter correlations do not imply a genuine violation of time
reversal invariance because of the existence of strong final state interaction
effects.Comment: Typos corrected; comments adde
How to Block Cartel Formation and Price-Fixing
Abstract written by the AEI-Brookings Joint Center: Allowing foreign buyers of goods produced by international cartels to pursue civil antitrust damages in U.S. courts would better deter cartel formation and price-fixing than do sanctions currently imposed by global criminal and civil justice systems.Technology and Industry, Regulatory Reform, Other Topics
Folding of a donorâacceptor polyrotaxane by using noncovalent bonding interactions
Mechanically interlocked compounds, such as bistable catenanes and bistable rotaxanes, have been used to bring about actuation in nanoelectromechanical systems (NEMS) and molecular electronic devices (MEDs). The elaboration of the structural features of such rotaxanes into macromolecular materials might allow the utilization of molecular motion to impact their bulk properties. We report here the synthesis and characterization of polymers that contain Ï electron-donating 1,5-dioxynaphthalene (DNP) units encircled by cyclobis(paraquat-p-phenylene) (CBPQT4+), a Ï electron-accepting tetracationic cyclophane, synthesized by using the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). The polyrotaxanes adopt a well defined âfoldedâ secondary structure by virtue of the judicious design of two DNP-containing monomers with different binding affinities for CBPQT4+. This efficient approach to the preparation of polyrotaxanes, taken alongside the initial investigations of their chemical properties, sets the stage for the preparation of a previously undescribed class of macromolecular architectures
Flavor and Charge Symmetry in the Parton Distributions of the Nucleon
Recent calculations of charge symmetry violation(CSV) in the valence quark
distributions of the nucleon have revealed that the dominant symmetry breaking
contribution comes from the mass associated with the spectator quark
system.Assuming that the change in the spectator mass can be treated
perturbatively, we derive a model independent expression for the shift in the
parton distributions of the nucleon. This result is used to derive a relation
between the charge and flavor asymmetric contributions to the valence quark
distributions in the proton, and to calculate CSV contributions to the nucleon
sea. The CSV contribution to the Gottfried sum rule is also estimated, and
found to be small
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Survey to explore understanding of the principles of aseptic technique: Qualitative content analysis with descriptive analysis of confidence and training
BACKGROUND: In many countries, aseptic procedures are undertaken by nurses in the general ward setting, but variation in practice has been reported, and evidence indicates that the principles underpinning aseptic technique are not well understood.
METHODS: A survey was conducted, employing a brief, purpose-designed, self-reported questionnaire.
RESULTS: The response rate was 72%. Of those responding, 65% of nurses described aseptic technique in terms of the procedure used to undertake it, and 46% understood the principles of asepsis. The related concepts of cleanliness and sterilization were frequently confused with one another. Additionally, 72% reported that they not had received training for at least 5 years; 92% were confident of their ability to apply aseptic technique; and 90% reported that they had not been reassessed since their initial training. Qualitative analysis confirmed a lack of clarity about the meaning of aseptic technique.
CONCLUSION: Nurses' understanding of aseptic technique and the concepts of sterility and cleanliness is inadequate, a finding in line with results of previous studies. This knowledge gap potentially places patients at risk. Nurses' understanding of the principles of asepsis could be improved. Further studies should establish the generalizability of the study findings. Possible improvements include renewed emphasis during initial nurse education, greater opportunity for updating knowledge and skills post-qualification, and audit of practice
Gluon distributions in nucleons and pions at a low resolution scale
In this paper we study the gluon distribution functions in nucleons and pions
at a low resolution scale. This is an important issue since parton
densities at low have always been taken as an external input which is
adjusted through DGLAP evolution to fit the experimental data at higher scales.
Here, in the framework of a model recently developed, it is shown that the
hypothetical cloud of {\it neutral} pions surrounding nucleons and pions
appears to be responsible for the characteristic valence-like gluon
distributions needed at the inital low scale. As an additional result, we get
the remarkable prediction that neutral and charged pions have different
intrinsic sea flavor contents.Comment: final version to appear in Phys. Rev. D. Discussion on several points
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Parton energy loss limits and shadowing in Drell-Yan dimuon production
A precise measurement of the ratios of the Drell-Yan cross section per
nucleon for an 800 GeV/c proton beam incident on Be, Fe and W targets is
reported. The behavior of the Drell-Yan ratios at small target parton momentum
fraction is well described by an existing fit to the shadowing observed in
deep-inelastic scattering. The cross section ratios as a function of the
incident parton momentum fraction set tight limits on the energy loss of quarks
passing through a cold nucleus
A Modular Strategy for Fully Conjugated DonorâAcceptor Block Copolymers
A novel strategy for the synthesis of fully conjugated donorâacceptor block copolymers, in a single reaction step employing Stille coupling polymerization of end-functional polythiophene and AA + BB monomers, is presented. The unique donorâacceptor structure of these block copolymers provides a rich self-assembly behavior, with the first example of a fully conjugated donorâacceptor block copolymer having two separate crystalline domains being obtained
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