Differential cross section for neutron-proton bremsstrahlung

The neutron-proton bremsstrahlung process $(np \to np\gamma)$ is known to be sensitive to meson exchange currents in the nucleon-nucleon interaction. The triply differential cross section for this reaction has been measured for the first time at the Los Alamos Neutron Science Center, using an intense, pulsed beam of up to 700 MeV neutrons to bombard a liquid hydrogen target. Scattered neutrons were observed at six angles between 12$^\circ$ and 32$^\circ$, and the recoil protons were observed in coincidence at 12$^\circ$, 20$^\circ$, and 28$^\circ$ on the opposite side of the beam. Measurement of the neutron and proton energies at known angles allows full kinematic reconstruction of each event. The data are compared with predictions of two theoretical calculations, based on relativistic soft-photon and non-relativistic potential models.Comment: 5 pages, 3 figure

Incretin-based therapies and diabetic retinopathy: Real-world evidence in older U.S. adults

OBJECTIVE: Recent large trials yield conflicting results on the association between incretin-based therapies (IBTs) and diabetic retinopathy (DR). We examined whether IBTs increase DR risk compared with other antihyperglycemics. RESEARCH DESIGN AND METHODS: We implementedan active comparator, new-user cohort design using anationwide 20% random sample of fee-for-service U.S. Medicare beneficiaries aged 65 years or older with Parts A, B, and D coverage between 2007 and 2015. We identified the following cohorts without prior treatment for retinopathy: dipeptidyl peptidase 4 inhibitors (DPP4i) versus sulfonylureas (SU), DPP4i versus thiazolidinediones (TZD), glucagon-like peptide-1receptor agonists (GLP1RA)versus long-acting insulin (LAI), and GLP1RA versus TZD. Primary outcome was advanced diabetic retinopathy requiring treatment (ADRRT), defined as a procedure code for retinopathy treatment. Incident diabetic retinopathy (IDR), identified by a diagnosis code, was a secondary outcome. We estimated propensity scores to balance confounders and adjusted hazard ratios (95% CI) using weighted Cox proportional hazards models. RESULTS: We identified 213, 652 eligible patients. During a median duration of 0.58 to 0.87 years across comparisons, with a rate from 6.0 to 12.8 per 1,000 person-years, IBTs were not associated with increased ADRRT or IDR risk. The adjusted hazard ratios (95% CI) for ADRRT were 0.91 (0.79-1.04) by comparing DPP4i to SU (n = 39,292 and 87,073); 0.91 (0.75-1.11), DPP4i to TZD (n = 51, 410 and 22, 231); 0.50 (0.39-0.65), GLP1RA to LAI (n = 9, 561 and 82, 849); and 0.75 (0.53-1.06), GLP1RA to TZD (n = 10, 355 and 27, 345). CONCLUSIONS: Our population-based cohort study of older U.S. adults with diabetes suggests that IBTs used for approximately 1 year do not increase the DR risk

Two‐nucleon processes in pion‐induced double charge exchange in 4He: A coincidence measurement of the 4He(π+,π− p)3p reaction

Inclusive measurements of pion double‐charge‐exchange in 3He[1] and 4He[2] in the Δ(1232) resonance region suggest the dominance of a two‐step sequential single‐charge‐exchange mechanism involving quasi‐free nucleons. To investigate this reaction mechanism, we have observed protons in coincidence with the outgoing pion in π++4He→π−+4p at Tπ+=240 MeV. Pions were detected in a magnetic spectrometer at θπ−=32°, while protons were detected in a close‐packed array of plastic scintillator telescopes covering θp=67.5°–157.5° on the same side of the beam as the spectrometer, and θp=22.5°–157.5° on the opposite side. We will present preliminary results for the distributions in energy and angle of the coincident protons. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87562/2/542_1.pd

Strange Quark Contributions to Parity-Violating Asymmetries in the Backward Angle G0 Electron Scattering Experiment

We have measured parity-violating asymmetries in elastic electron-proton and quasi-elastic electron-deuteron scattering at Q^2 = 0.22 and 0.63 GeV^2. They are sensitive to strange quark contributions to currents in the nucleon, and to the nucleon axial current. The results indicate strange quark contributions of < 10% of the charge and magnetic nucleon form factors at these four-momentum transfers. We also present the first measurement of anapole moment effects in the axial current at these four-momentum transfers.Comment: 5 pages, 2 figures, changed references, typo, and conten

Magic Numbers of Silicon Clusters

A structural model for intermediate sized silicon clusters is proposed that is able to generate unique structures without any dangling bonds. This structural model consists of bulk-like core of five atoms surrounded by fullerene-like surface. Reconstruction of the ideal fullerene geometry results in the formation of crown atoms surrounded by $\pi$-bonded dimer pairs. This model yields unique structures for \Si{33}, \Si{39}, and \Si{45} clusters without any dangling bonds and hence explains why these clusters are least reactive towards chemisorption of ammonia, methanol, ethylene, and water. This model is also consistent with the experimental finding that silicon clusters undergo a transition from prolate to spherical shapes at \Si{27}. Finally, reagent specific chemisorption reactivities observed experimentally is explained based on the electronic structures of the reagents.Comment: 4 pages + 3 figures (postscript files after \end{document}

Transverse Beam Spin Asymmetries at Backward Angles in Elastic Electron-Proton and Quasi-elastic Electron-Deuteron Scattering

We have measured the beam-normal single-spin asymmetries in elastic scattering of transversely polarized electrons from the proton, and performed the first measurement in quasi-elastic scattering on the deuteron, at backward angles (lab scattering angle of 108 degrees) for Q2 = 0.22 GeV^2/c^2 and 0.63 GeV^2/c^2 at beam energies of 362 MeV and 687 MeV, respectively. The asymmetry arises due to the imaginary part of the interference of the two-photon exchange amplitude with that of single photon exchange. Results for the proton are consistent with a model calculation which includes inelastic intermediate hadronic (piN) states. An estimate of the beam-normal single-spin asymmetry for the scattering from the neutron is made using a quasi-static deuterium approximation, and is also in agreement with theory

Measurements of electron-proton elastic cross sections for 0.4<Q2<5.5(GeV/c)20.4 < Q^2 < 5.5 (GeV/c)^2

We report on precision measurements of the elastic cross section for electron-proton scattering performed in Hall C at Jefferson Lab. The measurements were made at 28 unique kinematic settings covering a range in momentum transfer of 0.4 $<$ $Q^2$ $<$ 5.5 $(\rm GeV/c)^2$. These measurements represent a significant contribution to the world's cross section data set in the $Q^2$ range where a large discrepancy currently exists between the ratio of electric to magnetic proton form factors extracted from previous cross section measurements and that recently measured via polarization transfer in Hall A at Jefferson Lab.Comment: 17 pages, 18 figures; text added, some figures replace

Centrality dependence of charged hadron production in deuteron+gold and nucleon+gold collisions at sqrt(s_NN)=200 GeV

We present transverse momentum (p_T) spectra of charged hadrons measured in deuteron-gold and nucleon-gold collisions at \sqrts = 200 GeV for four centrality classes. Nucleon-gold collisions were selected by tagging events in which a spectator nucleon was observed in one of two forward rapidity detectors. The spectra and yields were investigated as a function of the number of binary nucleon-nucleon collisions, \nu, suffered by deuteron nucleons. A comparison of charged particle yields to those in p+p collisions show that the yield per nucleon-nucleon collision saturates with \nu for high momentum particles. We also present the charged hadron to neutral pion ratios as a function of p_T.Comment: 330 authors, 15 pages text, 16 figures, 3 tables. Submitted to Phys. Rev. Lett. v2 has minor changes to reflect revisions during review process. 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