48 research outputs found
Susceptibility Amplitude Ratios Near a Lifshitz Point
The susceptibility amplitude ratio in the neighborhood of a uniaxial Lifshitz
point is calculated at one-loop level using field-theoretic and
-expansion methods. We use the Schwinger parametrization of the
propagator in order to split the quadratic and quartic part of the momenta, as
well as a new special symmetry point suitable for renormalization purposes. For
a cubic lattice (d = 3), we find the result .Comment: 7 pages, late
Surface critical exponents at a uniaxial Lifshitz point
Using Monte Carlo techniques, the surface critical behaviour of
three-dimensional semi-infinite ANNNI models with different surface
orientations with respect to the axis of competing interactions is
investigated. Special attention is thereby paid to the surface criticality at
the bulk uniaxial Lifshitz point encountered in this model. The presented Monte
Carlo results show that the mean-field description of semi-infinite ANNNI
models is qualitatively correct. Lifshitz point surface critical exponents at
the ordinary transition are found to depend on the surface orientation. At the
special transition point, however, no clear dependency of the critical
exponents on the surface orientation is revealed. The values of the surface
critical exponents presented in this study are the first estimates available
beyond mean-field theory.Comment: 10 pages, 7 figures include
Critical behavior at m-axial Lifshitz points: field-theory analysis and -expansion results
The critical behavior of d-dimensional systems with an n-component order
parameter is reconsidered at (m,d,n)-Lifshitz points, where a wave-vector
instability occurs in an m-dimensional subspace of . Our aim is
to sort out which ones of the previously published partly contradictory
-expansion results to second order in are
correct. To this end, a field-theory calculation is performed directly in the
position space of dimensions, using dimensional
regularization and minimal subtraction of ultraviolet poles. The residua of the
dimensionally regularized integrals that are required to determine the series
expansions of the correlation exponents and and of the
wave-vector exponent to order are reduced to single
integrals, which for general m=1,...,d-1 can be computed numerically, and for
special values of m, analytically. Our results are at variance with the
original predictions for general m. For m=2 and m=6, we confirm the results of
Sak and Grest [Phys. Rev. B {\bf 17}, 3602 (1978)] and Mergulh{\~a}o and
Carneiro's recent field-theory analysis [Phys. Rev. B {\bf 59},13954 (1999)].Comment: Latex file with one figure (eps-file). Latex file uses texdraw to
generate figures that are included in the tex
Exome sequencing of family trios from the National Birth Defects Prevention Study: Tapping into a rich resource of genetic and environmental data
Background: The National Birth Defects Prevention Study (NBDPS) is a multisite, population-based, case–control study of genetic and nongenetic risk factors for major structural birth defects. Eligible women had a pregnancy affected by a birth defect or a liveborn child without a birth defect between 1997 and 2011. They were invited to complete a telephone interview to collect pregnancy exposure data and were mailed buccal cell collection kits to collect specimens from themselves, their child (if living), and their child's father. Over 23,000 families representing more than 30 major structural birth defects provided DNA specimens. Methods: To evaluate their utility for exome sequencing (ES), specimens from 20 children with colonic atresia were studied. Evaluations were conducted on specimens collected using cytobrushes stored and transported in open versus closed packaging, on native genomic DNA (gDNA) versus whole genome amplified (WGA) products and on a library preparation protocol adapted to low amounts of DNA. Results: The DNA extracted from brushes in open packaging yielded higher quality sequence data than DNA from brushes in closed packaging. Quality metrics of sequenced gDNA were consistently higher than metrics from corresponding WGA products and were consistently high when using a low input protocol. Conclusions: This proof-of-principle study established conditions under which ES can be applied to NBDPS specimens. Successful sequencing of exomes from well-characterized NBDPS families indicated that this unique collection can be used to investigate the roles of genetic variation and gene–environment interaction effects in birth defect etiologies, providing a valuable resource for birth defect researchers
Decay studies of very neutron rich nuclei near 78Ni
The properties of beta-gamma and beta-delayed neutron emission from Cu76-79 and Ga83-85 were measured at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Laboratory. Selected results on the decay properties of copper isotopes are briefly presented and discusse
The \u3b2 decay of the \u3c0f5/2 ground state of 77Cu studied with 225 MeV and 0.2 MeV purified radioactive beams
Isobarically purified beams of 77Cu with energies of 225 and 0.2 MeV were used at the Holifield Radioactive Ion Beam Facility of Oak Ridge National Laboratory to study \u3b2 decay into states in 77Zn. Data taken at 225 MeV allowed the determination of absolute branching ratios relative to the decay of 77Cu for this \u3b2 decay as well as its daughters. From these we obtained a refined \u3b2-delayed neutron emission probability of 30.3(22)% and a probability that the decay proceeds through 77Zng of 49.1(26)%. A total of 64\u2002\u3b3 rays were placed in a level scheme for 77Zn containing 35 excited states including one state above the neutron separation energy, whereas two \u3b3 rays were observed for the \u3b2n branch to states in 76Zn. The growth and decay curves of some prominent \u3b3 rays indicate a single \u3b2-decaying state with a half-life of 480(9)\u2002ms. The decay pattern for 77Cu, with observed feeding of 8(3)% to 7/2+\u200277Zng and 6(3)% to 1/2-\u200277Znm, in contrast to the large feeding observed for decay of \u3c0p3/2 73Cug to 1/2-\u200273Zng, strongly suggests a \u3c0f5/2 ground state for the studied 77Cu activity