17,168 research outputs found
Three-body forces and proton-rich nuclei
We present the first study of three-nucleon (3N) forces for proton-rich
nuclei along the N=8 and N=20 isotones. Our results for the ground-state
energies and proton separation energies are in very good agreement with
experiment where available, and with the empirical isobaric multiplet mass
equation. We predict the spectra for all N=8 and N=20 isotones to the proton
dripline, which agree well with experiment for 18Ne, 19Na, 20Mg and 42Ti. In
all other cases, we provide first predictions based on nuclear forces. Our
results are also very promising for studying isospin symmetry breaking in
medium-mass nuclei based on chiral effective field theory.Comment: 5 pages, 4 figures, minor changes, published versio
Distribution Functions of the Nucleon and Pion in the Valence Region
We provide an experimental and theoretical perspective on the behavior of
unpolarized distribution functions for the nucleon and pion on the
valence-quark domain; namely, Bjorken-x \gtrsim 0.4. This domain is key to much
of hadron physics; e.g., a hadron is defined by its flavor content and that is
a valence-quark property. Furthermore, its accurate parametrization is crucial
to the provision of reliable input for large collider experiments. We focus on
experimental extractions of distribution functions via electron and muon
inelastic scattering, and from Drell-Yan interactions; and on theoretical
treatments that emphasize an explanation of the distribution functions,
providing an overview of major contemporary approaches and issues.
Valence-quark physics is a compelling subject, which probes at the heart of our
understanding of the Standard Model. There are numerous outstanding and
unresolved challenges, which experiment and theory must confront. In connection
with experiment, we explain that an upgraded Jefferson Lab facility is
well-suited to provide new data on the nucleon, while a future electron ion
collider could provide essential new data for the mesons. There is also great
potential in using Drell-Yan interactions, at FNAL, J-PARC and GSI, to push
into the large-x domain for both mesons and nucleons. We argue furthermore that
explanation, in contrast to modeling and parametrization, requires a widespread
acceptance of the need to adapt theory: to the lessons learnt already from the
methods of nonperturbative quantum field theory; and a fuller exploitation of
those methods.Comment: Review article: 133 double-spaced pages, 44 figures, 6 table
Study of vortex valve for medium temperature solid propellants
Fluid state vortex valve secondary injection control system shows considerable promise for future application to solid propellant rocket engine thrust vector control. The single axis injection system tested would be capable of providing secondary injection thrust vector control using 2000 deg F gas
Eye-controlled ''teletypewriter''
Oculometer provides dynamic measurement of subject's look direction, and its outputs can be used to generate visual display of his look pattern and/or to cause equipment operation associated with his lookpoint at given times. Measured eye-direction information could be used as control input at man/machine interface
Neutrinoless double-beta decay matrix elements in large shell-model spaces with the generator-coordinate method
We use the generator-coordinate method with realistic shell-model
interactions to closely approximate full shell-model calculations of the matrix
elements for the neutrinoless double-beta decay of Ca, Ge, and
Se. We work in one major shell for the first isotope, in the
space for the second and third, and finally in two major
shells for all three. Our coordinates include not only the usual axial
deformation parameter , but also the triaxiality angle and
neutron-proton pairing amplitudes. In the smaller model spaces our matrix
elements agree well with those of full shell-model diagonalization, suggesting
that our Hamiltonian-based GCM captures most of the important valence-space
correlations. In two major shells, where exact diagonalization is not currently
possible, our matrix elements are only slightly different from those in a
single shell.Comment: 8 pages, 7 figure
Three-nucleon forces and spectroscopy of neutron-rich calcium isotopes
We study excited-state properties of neutron-rich calcium isotopes based on
chiral two- and three-nucleon interactions. We first discuss the details of our
many-body framework, investigate convergence properties, and for two-nucleon
interactions benchmark against coupled-cluster calculations. We then focus on
the spectroscopy of 47-56Ca, finding that with both 3N forces and an extended
pfg9/2 valence space, we obtain a good level of agreement with experiment. We
also study electromagnetic transitions and find that experimental data are well
described by our calculations. In addition, we provide predictions for
unexplored properties of neutron-rich calcium isotopes.Comment: 15 pages, 22 figures, published versio
Method for repair of thin glass coatings
A method of repairing cracks or damaged areas in glass, in particular, glass coatings provided on tile. The method includes removing the damaged area using a high speed diamond burr drilling out a cavity that extends slightly into the base material of the tile. All loose material is then cleaned from the drilled out cavity and the cavity is filled adjacent the upper surface of the coating with a filler material including chopped silica fibers mixed with a binder. The filler material is packed into the cavity and a repair coating is applied by means of a brush or sprayed thereover. The repair includes borosilicate suspended in solution. Heat is applied at approximately 2100 F. for approximately five minutes for curing the coating, causing boron silicide particles of the coating to oxidize forming a very fluid boron-oxide rich glass which reacts with the other frits to form an impervious, highly refractory layer
Nuclear forces and their impact on neutron-rich nuclei and neutron-rich matter
We review the impact of nuclear forces on matter at neutron-rich extremes.
Recent results have shown that neutron-rich nuclei become increasingly
sensitive to three-nucleon forces, which are at the forefront of theoretical
developments based on effective field theories of quantum chromodynamics. This
includes the formation of shell structure, the spectroscopy of exotic nuclei,
and the location of the neutron dripline. Nuclear forces also constrain the
properties of neutron-rich matter, including the neutron skin, the symmetry
energy, and the structure of neutron stars. We first review our understanding
of three-nucleon forces and show how chiral effective field theory makes unique
predictions for many-body forces. Then, we survey results with three-nucleon
forces in neutron-rich oxygen and calcium isotopes and neutron-rich matter,
which have been explored with a range of many-body methods. Three-nucleon
forces therefore provide an exciting link between theoretical, experimental and
observational nuclear physics frontiers.Comment: 28 pages, 13 figures, 1 tabl
Research study of the vortex valve for medium-temperature solid propellants
Fluid state control system with vortex valves for solid propellant gas generator flow throttlin
Exploring sd-shell nuclei from two- and three-nucleon interactions with realistic saturation properties
We study ground- and excited-state properties of all sd-shell nuclei with
neutron and proton numbers 8 <= N,Z <= 20, based on a set of low-resolution
two- and three-nucleon interactions that predict realistic saturation
properties of nuclear matter. We focus on estimating the theoretical
uncertainties due to variation of the resolution scale, the low-energy
couplings, as well as from the many-body method. The experimental two-neutron
and two-proton separation energies are reasonably well reproduced, with an
uncertainty range of about 5 MeV. The first excited 2+ energies also show
overall agreement, with a more narrow uncertainty range of about 500 keV. In
most cases, this range is dominated by the uncertainties in the Hamiltonian.Comment: 6 pages, 4 figure
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