14,643 research outputs found
Green's Function Monte Carlo Calculations with Two- and Three-Nucleon Interactions from Chiral Effective Field Theory
I discuss our recent work on Green's function Monte Carlo (GFMC) calculations
of light nuclei using local nucleon-nucleon interactions derived from chiral
effective field theory (EFT) up to next-to-next-to-leading order (NLO). I
present the natural extension of this work to include the consistent
three-nucleon (3N) forces at the same order in the chiral expansion. I discuss
our choice of observables to fit the two low-energy constants which enter in
the 3N sector at NLO and present some results for light nuclei.Comment: Contribution to the Proceedings of the 21st International Conference
on Few-Body Problems in Physics. May 18-22, 2015. Chicago, Illinois, US
A new method for satellite orbit determination using an operational worldwide transponder network
The method utilizes computer programs developed for the forthcoming ATS-F/NIMBUS-F tracking and data relay experiment where the basic tracking measurements are multiple path round-trip propagation times and rates. This method of orbit computation has recently been successfully evaluated by tracking a geostationary satellite (ATS-3) using an existing VHF (150 MHz) network of automatic transponders. A master station sequentially interrogates each transponder via the ATS-3. The master site is located at Schenectady, N. Y. and four automatic transponders were located at Shannon, Reykajavik, Buenos Aires, and Seattle respectively. Data at hourly intervals were collected during a 24 hour period on April 18-19, 1973. After correcting this data for known systematic errors it was provided as input to an orbit determination program where all satellite motions during signal propagation are rigorously accounted for. The resulting estimated ATS-3 orbit yielded observational residuals on the order of 100 meters. By using more than one satellite the present scheme is further capable of accurately locating several stationary or mobile terminals as part of the overall orbital solution
Quantum Monte Carlo Calculations of Light Nuclei Using Chiral Potentials
We present the first Green's function Monte Carlo calculations of light
nuclei with nuclear interactions derived from chiral effective field theory up
to next-to-next-to-leading order. Up to this order, the interactions can be
constructed in a local form and are therefore amenable to quantum Monte Carlo
calculations. We demonstrate a systematic improvement with each order for the
binding energies of and systems. We also carry out the first
few-body tests to study perturbative expansions of chiral potentials at
different orders, finding that higher-order corrections are more perturbative
for softer interactions. Our results confirm the necessity of a three-body
force for correct reproduction of experimental binding energies and radii, and
pave the way for studying few- and many-nucleon systems using quantum Monte
Carlo methods with chiral interactions.Comment: 5 pages, 3 figures, 4 tables. Updated references. Cosmetic changes to
figures, tables, and equations; added a sentence clarifying the
correspondence between our real-space cutoffs and momentum-space cutoffs.
Other sentences were reworded for clarit
Analyzing the Fierz Rearrangement Freedom for Local Chiral Two-Nucleon Potentials
Chiral effective field theory is a framework to derive systematic nuclear
interactions. It is based on the symmetries of quantum chromodynamics and
includes long-range pion physics explicitly, while shorter-range physics is
expanded in a general operator basis. The number of low-energy couplings at a
particular order in the expansion can be reduced by exploiting the fact that
nucleons are fermions and therefore obey the Pauli exclusion principle. The
antisymmetry permits the selection of a subset of the allowed contact operators
at a given order. When local regulators are used for these short-range
interactions, however, this "Fierz rearrangement freedom" is violated. In this
paper, we investigate the impact of this violation at leading order (LO) in the
chiral expansion. We construct LO and next-to-leading order (NLO) potentials
for all possible LO-operator pairs and study their reproduction of phase
shifts, the He ground-state energy, and the neutron-matter energy at
different densities. We demonstrate that the Fierz rearrangement freedom is
partially restored at NLO where subleading contact interactions enter. We also
discuss implications for local chiral three-nucleon interactions.Comment: 11 pages, 5 figure
Engaging Nursing Staff in Research: The Clinical Nurse Specialist Role in an Academic-Clinical Partnership
Purpose: The purpose of this article is to describe the processes of exploring and implementing an academic-clinical study, engaging nursing staff in research, and maintaining their enthusiasm within the context of an academic-clinical research partnership.
Description: The core competencies of the clinical nurse specialist (CNS) role address evidence-based practice, quality improvement, and research. Studies and exemplars of the CNS role in the literature illustrate expert practitioner and facilitator of evidence-based practice, but less attention is given to methods used by the CNS to engage staff in clinical research.
Outcome: The CNS was successful in obtaining staff engagement in the research project from exploration through sustainment.
Conclusion: Collaborative research between academic and clinical partners enhances the educational and professional environment for students and clinicians, promotes evidence-based practice, and from this project may promote Veteran and family-centered care. The CNS played a key role in engaging and sustaining staff commitment, which contributed to the success of this study
Chiral Three-Nucleon Interactions in Light Nuclei, Neutron- Scattering, and Neutron Matter
We present quantum Monte Carlo calculations of light nuclei, neutron-
scattering, and neutron matter using local two- and three-nucleon ()
interactions derived from chiral effective field theory up to
next-to-next-to-leading order (NLO). The two undetermined low-energy
couplings are fit to the He binding energy and, for the first time, to the
spin-orbit splitting in the neutron- -wave phase shifts.
Furthermore, we investigate different choices of local -operator structures
and find that chiral interactions at NLO are able to simultaneously
reproduce the properties of systems and of neutron matter, in
contrast to commonly used phenomenological interactions.Comment: 5 pages, 3 figures, 1 table - updated version: small wording changes,
one reference chang
Antiferromagnetic Order of the Ru and Gd in Superconducting RuSr2GdCu2O8
Neutron diffraction has been used to study the magnetic order in
RuSr{2}GdCu2O8. The Ru moments order antiferromagnetically at T{N}=136(2)K,
coincident with the previously reported onset of ferromagnetism. Neighboring
spins are antiparallel in all three directions, with a low T moment of 1.18(6)
mu {B} along the c-axis. Our measurements put an upper limit of ~0.1 mu{B} to
any net zero-field moment, with fields exceeding ~0.4T needed to induce a
measurable magnetization. The Gd ions order independently at T{N}=2.50(2)K with
the same spin configuration. PACS numbers: 74.72.Jt, 75.25.+z, 74.25.Ha,
75.30.KzComment: Four pages, Latex, 5 eps figure
Quantum Monte Carlo calculations of light nuclei with local chiral two- and three-nucleon interactions
Local chiral effective field theory interactions have recently been developed
and used in the context of quantum Monte Carlo few- and many-body methods for
nuclear physics. In this work, we go over detailed features of local chiral
nucleon-nucleon interactions and examine their effect on properties of the
deuteron, paying special attention to the perturbativeness of the expansion. We
then turn to three-nucleon interactions, focusing on operator ambiguities and
their interplay with regulator effects. We then discuss the nuclear Green's
function Monte Carlo method, going over both wave-function correlations and
approximations for the two- and three-body propagators. Following this, we
present a range of results on light nuclei: Binding energies and distribution
functions are contrasted and compared, starting from several different
microscopic interactions.Comment: 21 pages, 14 figures, published version, Editor's Suggestio
Auxiliary field diffusion Monte Carlo calculations of light and medium-mass nuclei with local chiral interactions
Quantum Monte Carlo methods have recently been employed to study properties
of nuclei and infinite matter using local chiral effective field theory
interactions. In this work, we present a detailed description of the auxiliary
field diffusion Monte Carlo algorithm for nuclei in combination with local
chiral two- and three-nucleon interactions up to next-to-next-to-leading order.
We show results for the binding energy, charge radius, charge form factor, and
Coulomb sum rule in nuclei with . Particular attention is devoted
to the effect of different operator structures in the three-body force for
different cutoffs. The outcomes suggest that local chiral interactions fit to
few-body observables give a very good description of the ground-state
properties of nuclei up to O, with the exception of one fit for the
softer cutoff which predicts overbinding in larger nuclei.Comment: 23 pages, 10 figure
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