11,961 research outputs found
Microscopic Restoration of Proton-Neutron Mixed Symmetry in Weakly Collective Nuclei
Starting from the microscopic low-momentum nucleon-nucleon interaction V{low
k}, we present the first systematic shell model study of magnetic moments and
magnetic dipole transition strengths of the basic low-energy one-quadrupole
phonon excitations in nearly-spherical nuclei. Studying in particular the
even-even N=52 isotones from 92Zr to 100Cd, we find the predicted evolution of
the predominantly proton-neutron non-symmetric state reveals a restoration of
collective proton-neutron mixed-symmetry structure near mid-shell. This
provides the first explanation for the existence of pronounced collective
mixed-symmetry structures in weakly-collective nuclei.Comment: 5 Pages, 3 figure
Chiral three-nucleon interaction and the carbon-14 dating beta decay
We present a shell model calculation for the beta decay of 14-C to the 14-N
ground-state, treating the relevant nuclear states as two 0p-holes in an 16-O
core. Employing the universal low-momentum nucleon-nucleon potential V(low-k)
only, one finds that the Gamow-Teller matrix element is too large to describe
the known (very long) lifetime of 14-C. As a novel approach to the problem, we
invoke the chiral three-nucleon force (3NF) at leading order and derive from it
a density-dependent in-medium NN interaction. Including this effective
in-medium NN interaction, the Gamow-Teller matrix element vanishes for a
nuclear density close to that of saturated nuclear matter. The genuine
short-range part of the three-nucleon interaction plays a particularly
important role in this context, since the medium modifications to the pion
propagator and pion-nucleon vertex (due to the long-range 3NF) tend to cancel
out in the relevant observable. We discuss also uncertainties related to the
off-shell extrapolation of the in-medium NN interaction. Using the off-shell
behavior of V(low-k) as a guide, we find that these uncertainties are rather
small.Comment: 22 pages, 11 figure
Low momentum nucleon-nucleon potential and shell model effective interactions
A low momentum nucleon-nucleon (NN) potential V-low-k is derived from meson
exhange potentials by integrating out the model dependent high momentum modes
of V_NN. The smooth and approximately unique V-low-k is used as input for shell
model calculations instead of the usual Brueckner G matrix. Such an approach
eliminates the nuclear mass dependence of the input interaction one finds in
the G matrix approach, allowing the same input interaction to be used in
different nuclear regions. Shell model calculations of 18O, 134Te and 135I
using the same input V-low-k have been performed. For cut-off momentum Lambda
in the vicinity of 2 fm-1, our calculated low-lying spectra for these nuclei
are in good agreement with experiments, and are weakly dependent on Lambda.Comment: 5 pages, 5 figure
Supernova neutrinos in the light of FCNC
We study the effect of including flavor changing neutral currents (FCNC) in
the analysis of the neutrino signal of a supernova burst. When we include the
effect of the FCNC which are beyond the standard model (SM) in the study of the
MSW resonant conversion, we obtain dramatic changes in the \Delta
m^2-sin^2(2\theta) probability contours for neutrino detection.Comment: 8 pages in ReVTeX,3 figures. Revised manuscript submitted to Phys.
Rev.
Identification of mixed-symmetry states in an odd-mass nearly-spherical nucleus
The low-spin structure of 93Nb has been studied using the (n,n' gamma)
reaction at neutron energies ranging from 1.5 to 3.0 MeV and the 94Zr(p,2n
gamma)93Nb reaction at bombarding energies from 11.5 to 19 MeV. States at
1779.7 and 1840.6 keV, respectively, are proposed as mixed-symmetry states
associated with the coupling of a proton hole in the p_1/2 orbit to the 2+_1,ms
state in 94Mo. These assignments are derived from the observed M1 and E2
transition strengths to the symmetric one-phonon states, energy systematics,
spins and parities, and comparison with shell model calculations.Comment: 5 pages, 3 figure
Hot new directions for quasi-Monte Carlo research in step with applications
This article provides an overview of some interfaces between the theory of
quasi-Monte Carlo (QMC) methods and applications. We summarize three QMC
theoretical settings: first order QMC methods in the unit cube and in
, and higher order QMC methods in the unit cube. One important
feature is that their error bounds can be independent of the dimension
under appropriate conditions on the function spaces. Another important feature
is that good parameters for these QMC methods can be obtained by fast efficient
algorithms even when is large. We outline three different applications and
explain how they can tap into the different QMC theory. We also discuss three
cost saving strategies that can be combined with QMC in these applications.
Many of these recent QMC theory and methods are developed not in isolation, but
in close connection with applications
Mass Hierarchies and the Seesaw Neutrino Mixing
We give a general analysis of neutrino mixing in the seesaw mechanism with
three flavors. Assuming that the Dirac and u-quark mass matrices are similar,
we establish simple relations between the neutrino parameters and individual
Majorana masses. They are shown to depend rather strongly on the physical
neutrino mixing angles. We calculate explicitly the implied Majorana mass
hierarchies for parameter sets corresponding to different solutions to the
solar neutrino problem.Comment: 11 pages, no figures, replaced with final version. Minor corrections
and one typo corrected. Added one referenc
Solar Neutrinos and the Violation of Equivalence Principle
In this Brief Report, a non-standard solution to the solar neutrino problem
is revisited. This solution assumes that neutrino flavors could have different
couplings to gravity, hence, the equivalence principle is violated in this
mechanism. The gravity induced mixing has the potential of accounting for the
current solar neutrino data from several experiments even for massless
neutrinos. We fit this solution to the total rate of neutrino events in the
SuperKamiokande detector together with the total rate from other detectors and
also with the most recent results of the SuperKamiokande results for the
recoil-electron spectrum.Comment: 6 pages, 4 figures, submitted to Phys.Rev.
Lack of clustering in low-redshift 21-cm intensity maps cross-correlated with 2dF galaxy densities
We report results from 21-cm intensity maps acquired from the Parkes radio
telescope and cross-correlated with galaxy maps from the 2dF galaxy survey. The
data span the redshift range and cover approximately 1,300
square degrees over two long fields. Cross correlation is detected at a
significance of . The amplitude of the cross-power spectrum is low
relative to the expected dark matter power spectrum, assuming a neutral
hydrogen (HI) bias and mass density equal to measurements from the ALFALFA
survey. The decrement is pronounced and statistically significant at small
scales. At , the cross power spectrum is more
than a factor of 6 lower than expected, with a significance of .
This decrement indicates either a lack of clustering of neutral hydrogen (HI),
a small correlation coefficient between optical galaxies and HI, or some
combination of the two. Separating 2dF into red and blue galaxies, we find that
red galaxies are much more weakly correlated with HI on scales, suggesting that HI is more associated with blue
star-forming galaxies and tends to avoid red galaxies.Comment: 12 pages, 3 figures; fixed typo in meta-data title and paper author
Modeling the effects of concentration of solid nanoparticles in liquid feedstock injection on high-velocity suspension flame spray process
This paper presents the effects of the concentration of solid nanoparticles in the liquid feedstock injection on the
high-velocity suspension flame spray (HVSFS) process. Four different concentrations of solid nanoparticles in suspension
droplets with various droplet diameters are used to study gas dynamics, vaporization rate, and secondary breakup. Two types of
injections, viz. surface and group, are used. The group-type injection increases the efficiency of droplet disintegration and the
evaporation process and reduces the gas cooling. The initiation of the fragmentation process is difficult for small droplets carrying
a high concentration of nanoparticles. Also, smaller droplets undergo rapid vaporization, leaving clogs of nanoparticles in the
middle of the barrel. For larger droplets, severe fragmentation occurs inside the combustion chamber. For a higher concentration
of nanoparticles, droplets exit the gun without complete evaporation. The results suggest that, in coating applications involving a
higher concentration of nanoparticles, smaller droplet sizes are preferred
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