27 research outputs found
Subtractive renormalization of the NN scattering amplitude at leading order in chiral effective theory
The leading-order nucleon-nucleon (NN) potential derived from chiral
perturbation theory consists of one-pion exchange plus a short-distance contact
interaction. We show that in the 1S0 and 3S1-3D1 channels renormalization of
the Lippmann-Schwinger equation for this potential can be achieved by
performing one subtraction. This subtraction requires as its only input
knowledge of the NN scattering lengths. This procedure leads to a set of
integral equations for the partial-wave NN t-matrix which give
cutoff-independent results for the corresponding NN phase shifts. This
reformulation of the NN scattering equation offers practical advantages,
because only observable quantities appear in the integral equation. The
scattering equation may then be analytically continued to negative energies,
where information on bound-state energies and wave functions can be extracted.Comment: 16 pages, 11 figure
Comparison of Isoscalar Vector Meson Production Cross Sections in Proton-Proton Collisions
The reaction was investigated with the TOF
spectrometer, which is an external experiment at the accelerator COSY
(Forschungszentrum J\"ulich, Germany). Total as well as differential cross
sections were determined at an excess energy of (). Using the total cross section of for the
reaction determined here and existing data for the reaction
, the ratio
turns out to be
significantly larger than expected by the Okubo-Zweig-Iizuka (OZI) rule. The
uncertainty of this ratio is considerably smaller than in previous
determinations. The differential distributions show that the
production is still dominated by S-wave production at this excess energy,
however higher partial waves clearly contribute. A comparison of the measured
angular distributions for production to published distributions for
production at shows that the data are consistent with an
identical production mechanism for both vector mesons
Proton-Antiproton Annihilation and Meson Spectroscopy with the Crystal Barrel
This report reviews the achievements of the Crystal Barrel experiment at the
Low Energy Antiproton Ring (LEAR) at CERN. During seven years of operation
Crystal Barrel has collected very large statistical samples in pbarp
annihilation, especially at rest and with emphasis on final states with high
neutral multiplicity. The measured rates for annihilation into various two-body
channels and for electromagnetic processes have been used to test simple models
for the annihilation mechanism based on the quark internal structure of
hadrons. From three-body annihilations three scalar mesons, a0(1450), f0(1370)
and f0(1500) have been established in various decay modes. One of them,
f0(1500), may be identified with the expected ground state scalar glueball.Comment: 64 pages, LATEX file, 36 figures are available as ps files at
http://afuz01.cern.ch/claude/ Submitted to Reviews of Modern Physic
Genome-wide methylation is modified by caloric restriction in<i> Daphnia magna</i>
Background
The degradation of epigenetic control with age is associated with progressive diseases of ageing, including cancers, immunodeficiency and diabetes. Reduced caloric intake slows the effects of ageing and age-related disease in vertebrates and invertebrates, a process potentially mediated by the impact of caloric restriction on epigenetic factors such as DNA methylation. We used whole genome bisulphite sequencing to study how DNA methylation patterns change with diet in a small invertebrate, the crustacean Daphnia magna. Daphnia show the classic response of longer life under caloric restriction (CR), and they reproduce clonally, which permits the study of epigenetic changes in the absence of genetic variation.
Results
Global cytosine followed by guanine (CpG) methylation was 0.7â0.9%, and there was no difference in overall methylation levels between normal and calorie restricted replicates. However, 333 differentially methylated regions (DMRs) were evident between the normally fed and CR replicates post-filtering. Of these 65% were hypomethylated in the CR group, and 35% were hypermethylated in the CR group.
Conclusions
Our results demonstrate an effect of CR on the genome-wide methylation profile. This adds to a growing body of research in Daphnia magna that demonstrate an epigenomic response to environmental stimuli. Specifically, gene Ontology (GO) term enrichment of genes associated with hyper and hypo-methylated DMRs showed significant enrichment for methylation and acyl-CoA dehydrogenase activity, which are linked to current understanding of their roles in CR in invertebrate model organisms
Elastic scattering of polarized electrons by polarized protons
Alguard MJ, Ash WW, Baum G, et al. Elastic scattering of polarized electrons by polarized protons. Phys.Rev.Lett. 1976;37(19):1258-1261