144 research outputs found
Increased Sensitivity to Possible Muonium to Antimuonium Conversion
A new experimental search for muonium-antimuonium conversion was conducted at
the Paul Scherrer Institute, Villigen, Switzerland. The preliminary analysis
yielded one event fulfilling all required criteria at an expected background of
1.7(2) events due to accidental coincidences. An upper limit for the conversion
probability in 0.1 T magnetic field is extracted as (90%
CL).Comment: 2 figure
Solution of the Nuclear Shell Model by Symmetry-Dictated Truncation
The dynamical symmetries of the Fermion Dynamical Symmetry Model are used as
a principle of truncation for the spherical shell model. Utilizing the usual
principle of energy-dictated truncation to select a valence space, and
symmetry-dictated truncation to select a collective subspace of that valence
space, we are able to reduce the full shell model space to one of manageable
dimensions with modern supercomputers, even for the heaviest nuclei. The
resulting shell model then consists of diagonalizing an effective Hamiltonian
within the restricted subspace. This theory is not confined to any symmetry
limits, and represents a full solution of the original shell model if the
appropriate effective interaction of the truncated space can be determined. As
a first step in constructing that interaction, we present an empirical
determination of its matrix elements for the collective subspace with no broken
pairs in a representative set of nuclei with . We demonstrate
that this effective interaction can be parameterized in terms of a few
quantities varying slowly with particle number, and is capable of describing a
broad range of low-energy observables for these nuclei. Finally we give a brief
discussion of extending these methods to include a single broken collective
pair.Comment: invited paper for J. Phys. G, 57 pages, Latex, 18 figures a macro are
available under request at [email protected]
Hyperfine Structure of S-States in Muonic Helium Ion
Corrections of orders alpha^5 and alpha^6 are calculated in the hyperfine
splittings of 1S and 2S - energy levels in the ion of muonic helium. The
electron vacuum polarization effects, the nuclear structure corrections and
recoil corrections are taken into account. The obtained numerical values of the
hyperfine splittings -1334.56 meV (1S state), -166.62 meV (2S state) can be
considered as a reliable estimate for the comparison with the future
experimental data. The hyperfine splitting interval Delta_{12}=(8 Delta
E^{hfs}(2S)- Delta E^{hfs}(1S)) = 1.64 meV can be used for the check of quantum
electrodynamics.Comment: 14 pages, 5 figure
Atomic parity nonconservation and neutron radii in cesium isotopes
The interpretation of future precise experiments on atomic parity violation
in terms of parameters of the Standard Model could be hampered by uncertainties
in the atomic and nuclear structure. While the former can be overcome by
measurement in a series of isotopes, the nuclear structure requires knowledge
of the neutron density. We use the nuclear Hartree-Fock method, which includes
deformation effects, to calculate the proton and neutron densities in
{125}Cs-{139}Cs. We argue that the good agreement with the experimental charge
radii, binding energies, and ground state spins signifies that the
phenomenological nuclear force and the method of calculation that we use is
adequate. Based on this agreement, and on calculations involving different
effective interactions, we estimate the uncertainties in the differences of the
neutron radii delta_{N,N'} and conclude that they cause uncertainties in
the ratio of weak charges, the quantities determined in the atomic parity
nonconservation experiments, of less than 10^{-3}. Such an uncertainty is
smaller than the anticipated experimental error.Comment: 24 pages (RevTeX) 4 figures (Postscript/uuencoded compressed) Caltech
Preprint No. MAP-153 (March 1993
Search for the lepton-family-number nonconserving decay \mu -> e + \gamma
The MEGA experiment, which searched for the muon- and electron-number
violating decay \mu -> e + \gamma, is described. The spectrometer system, the
calibrations, the data taking procedures, the data analysis, and the
sensitivity of the experiment are discussed. The most stringent upper limit on
the branching ratio of \mu -> e + \gamma) < 1.2 x 10^{-11} was obtained
Effects of Language Context on Ratings of Shy and Unsociable Behaviors in English Language Learning Children
Purpose
The primary goal of this study was to explore the effect of the language context on the socially withdrawn behaviors of school aged-children who are English Language Learners (ELLs) from middle to high SES backgrounds. This is one of the first studies to address the frequently confused concepts of shyness and unsociability as independent constructs within the ELL population. This study also investigated the feasibility of an experimental parent and child questionnaire that examines shyness and unsociability across native and English speaking contexts.
Method
Children and parents (34 ELL and 37 native English speaking) were administered an experimental questionnaire examining shy and unsociable behavior in native language and English-speaking contexts.
Results
Parents and children from the ELL group reported significantly higher ratings of shy behavior in English versus native language contexts, whereas unsociable ratings did not differ across language contexts.
Conclusions
Shyness and unsociability are distinguishable behaviors in ELL children and these constructs should be considered when examining withdrawal. Additionally, examining ELL children’s behavior across language contexts provides a valuable method for investigating language influenced behavioral problems. This study demonstrates the need for service providers to evaluate behavior across subtype and language context before pathologizing withdrawal in ELL children
Human milk and mucosal lacto- and galacto-N-biose synthesis by transgalactosylation and their prebiotic potential in Lactobacillus species
Lacto-N-biose (LNB) and galacto-N-biose (GNB) are major building blocks of free oligosaccharides and glycan moieties of glyco-complexes present in human milk and gastrointestinal mucosa. We have previously characterized the phospho-β-galactosidase GnbG from Lactobacillus casei BL23 that is involved in the metabolism of LNB and GNB. GnbG has been used here in transglycosylation reactions, and it showed the production of LNB and GNB with N-acetylglucosamine and N-acetylgalactosamine as acceptors, respectively. The reaction kinetics demonstrated that GnbG can convert 69 ± 4 and 71 ± 1 % of o-nitrophenyl-β-D-galactopyranoside into LNB and GNB, respectively. Those reactions were performed in a semi-preparative scale, and the synthesized disaccharides were purified. The maximum yield obtained for LNB was 10.7 ± 0.2 g/l and for GNB was 10.8 ± 0.3 g/l. NMR spectroscopy confirmed the molecular structures of both carbohydrates and the absence of reaction byproducts, which also supports that GnbG is specific for β1,3-glycosidic linkages. The purified sugars were subsequently tested for their potential prebiotic properties using Lactobacillus species. The results showed that LNB and GNB were fermented by the tested strains of L. casei, Lactobacillus rhamnosus (except L. rhamnosus strain ATCC 53103), Lactobacillus zeae, Lactobacillus gasseri, and Lactobacillus johnsonii. DNA hybridization experiments suggested that the metabolism of those disaccharides in 9 out of 10 L. casei strains, all L. rhamnosus strains and all L. zeae strains tested relies upon a phospho-β-galactosidase homologous to GnbG. The results presented here support the putative role of human milk oligosaccharides for selective enrichment of beneficial intestinal microbiota in breast-fed infants
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