2,658 research outputs found
Nucleon scattering on actinides using a dispersive optical model with extended couplings
Tamura coupling model has been extended to consider the coupling of
additional low-lying rotational bands to the ground state band. Rotational
bands are built on vibrational bandheads (even-even targets) or single particle
bandheads (odd- targets) including both axial and non-axial deformations.
These additional excitations are introduced as a perturbation to the underlying
axially-symmetric rigid rotor structure of the ground state rotational band.
Coupling matrix elements of the generalized optical model are derived for
extended multi-band transitions in even-even and odd- nuclei. Isospin
symmetric formulation of the optical model is employed.
A coupled-channels optical model potential (OMP) containing a dispersive
contribution is used to fit simultaneously all available optical experimental
databases including neutron strength functions for nucleon scattering on
Th, U and Pu nuclei and quasi-elastic (,)
scattering data on Th and U. Lane consistent OMP is derived for
all actinides if corresponding multi-band coupling schemes are defined.
Calculations using the derived OMP potential reproduce measured total
cross-section differences between several actinide pairs within experimental
uncertainty for incident neutron energies from 50 keV up to 150MeV. Multi-band
coupling is stronger in even-even targets due to the collective nature of the
coupling; the impact of extended coupling on predicted compound-nucleus
formation cross section reaches 5% below 3 MeV of incident neutron energy.
Coupling of ground-state rotational band levels in odd- nuclei is sufficient
for a good description of the compound-nucleus formation cross sections as long
as the coupling is saturated (a minimum of 7 coupled levels are typically
needed).Comment: 30 pages, 4 figures, 8 tables, 3 appendice
Predicting the optical observables for nucleon scattering on even-even actinides
Previously derived Lane consistent dispersive coupled-channel optical model
for nucleon scattering on Th and U nuclei is extended to
describe scattering on even-even actinides with 90--98. A
soft-rotator-model (SRM) description of the low-lying nuclear structure is
used, where SRM Hamiltonian parameters are adjusted to the observed collective
levels of the target nucleus. SRM nuclear wave functions (mixed in quantum
number) have been used to calculate coupling matrix elements of the generalized
optical model. The "effective" deformations that define inter-band couplings
are derived from SRM Hamiltonian parameters. Conservation of nuclear volume is
enforced by introducing a dynamic monopolar term to the deformed potential
leading to additional couplings between rotational bands. Fitted static
deformation parameters are in very good agreement with those derived by Wang
and collaborators using the Weizs\"acker-Skyrme global mass model (WS4),
allowing to use the latter to predict cross section for nuclei without
experimental data. A good description of scarce "optical" experimental database
is achieved. SRM couplings and volume conservation allow a precise calculation
of the compound-nucleus formation cross sections, which is significantly
different from the one calculated with rigid-rotor potentials coupling the
ground-state rotational band. Derived parameters can be used to describe both
neutron and proton induced reactions.Comment: 6 pages, 4 figures, 5 table
Hydrogen bonding in substituted nitroanilines : isolated nets in 1,3-diamino-4-nitrobenzene and continuously interwoven nets in 3,5-dinitroaniline
Peer reviewedPublisher PD
Broadband quadrature-squeezed vacuum and nonclassical photon number correlations from a nanophotonic device
We report the first demonstrations of both quadrature squeezed vacuum and
photon number difference squeezing generated in an integrated nanophotonic
device. Squeezed light is generated via strongly driven spontaneous four-wave
mixing below threshold in silicon nitride microring resonators. The generated
light is characterized with both homodyne detection and direct measurements of
photon statistics using photon number-resolving transition edge sensors. We
measure ~dB of broadband quadrature squeezing (~dB inferred
on-chip) and ~dB of photon number difference squeezing (~dB
inferred on-chip). Nearly-single temporal mode operation is achieved, with raw
unheralded second-order correlations as high as measured
(~when corrected for noise). Multi-photon events of over 10 photons
are directly detected with rates exceeding any previous quantum optical
demonstration using integrated nanophotonics. These results will have an
enabling impact on scaling continuous variable quantum technology.Comment: Significant improvements and updates to photon number squeezing
results and discussions, including results on single temporal mode operatio
Tropical tree branch-leaf nutrient scaling relationships vary with sampling location
Bivariate relationships between plant tissue nutrient concentration have largely been studied across broad environmental scales regardless of their covariation with soil and climate. Comparing leaf and branch wood concentrations of C, Ca, K, Mg, N, Na, and P for trees growing in tropical forests in Amazonia and Australia we found that the concentrations of most elements varied with sampling location, but with foliar and branch woody tissues varying from site to site in different ways. Using a Mixed Effect Model (MEM) approach it was further found that relationships between branch and leaf concentrations within individual plots differed in terms of both slope and/or significance to the ordinary least squares (OLS) estimates for most elements. Specifically, using MEM we found that within plots only K and Mg were correlated across organs, but with the K cross-organ intercept estimates varying significantly between sites. MEM analyses further showed that within-plot wood density variations were also negatively related to wood K and Na, suggesting a potentially important role for these cations in water transport and/or storage in woody tissues. The OLS method could not detect significant correlations in any of the above cases. By contrast, although Ca, N, and P leaf and wood tissue concentrations showed similar patterns when individual elements were compared across sites, MEM analyses suggested no consistent association within sites. Thus, for all these three elements, strong within-tree scaling relationships were inferred when data were analyzed across sites using OLS, even though there was no relationship within individual sites. Thus (as for Ca, N, and P) not only can a pooling of data across sites result in trait (co)variations attributable to the environment potentially being incorrectly attributed solely to the species and/or individual (the so-called “ecological fallacy”), but in some cases (as was found here for K and Na) the opposite can also sometimes occur with significant within-site covariations being obscured by large site-site variations. We refer to the latter phenomenon as “environmental obfuscation.
Performance of the reconstruction algorithms of the FIRST experiment pixel sensors vertex detector
Hadrontherapy treatments use charged particles (e.g. protons and carbon ions) to treat tumors. During a therapeutic treatment with carbon ions, the beam undergoes nuclear fragmentation processes giving rise to significant yields of secondary charged particles. An accurate prediction of these production rates is necessary to estimate precisely the dose deposited into the tumours and the surrounding healthy tissues. Nowadays, a limited set of double differential carbon fragmentation cross-section is available. Experimental data are necessary to benchmark Monte Carlo simulations for their use in hadrontherapy. The purpose of the FIRST experiment is to study nuclear fragmentation processes of ions with kinetic energy in the range from 100 to 1000 MeV/u. Tracks are reconstructed using information from a pixel silicon detector based on the CMOS technology. The performances achieved using this device for hadrontherapy purpose are discussed. For each reconstruction step (clustering, tracking and vertexing), different methods are implemented. The algorithm performances and the accuracy on reconstructed observables are evaluated on the basis of simulated and experimental data
Dispersive optical model description of nucleon scattering on Pb-Bi isotopes
A recently derived dispersive optical model potential (DOMP) for Pb
is extended to consider the non-locality in the real potential and the
shell-gap in the definition of the nuclear imaginary potentials near the Fermi
energy. The modified DOMP improves the simultaneous description of nucleon
scattering on Pb and of the Pb particle-hole bound states. The
new potential is shown to give a very good description of nucleon scattering
data on near-magic targets Pb and Bi.Comment: 9 pages, 8 figure
Electrophoresis of a rod macroion under polyelectrolyte salt: Is mobility reversed for DNA?
By molecular dynamics simulation, we study the charge inversion phenomenon of
a rod macroion in the presence of polyelectrolyte counterions. We simulate
electrophoresis of the macroion under an applied electric field. When both
counterions and coions are polyelectrolytes, charge inversion occurs if the
line charge density of the counterions is larger than that of the coions. For
the macroion of surface charge density equal to that of the DNA, the reversed
mobility is realized either with adsorption of the multivalent counterion
polyelectrolyte or the combination of electrostatics and other mechanisms
including the short-range attraction potential or the mechanical twining of
polyelectrolyte around the rod axis.Comment: 8 pages, 5 figures, Applied Statistical Physics of Molecular
Engineering (Mexico, 2003). Journal of Physics: Condensed Matters, in press
(2004). Journal of Physics: Condensed Matters, in press (2004
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