1,966 research outputs found
Momentum and Coordinate Space Three-nucleon Potentials
In this paper we give explicit formulae in momentum and coordinate space for
the three-nucleon potentials due to and meson exchange, derived
from off-mass-shell meson-nucleon scattering amplitudes which are constrained
by the symmetries of QCD and by the experimental data. Those potentials have
already been applied to nuclear matter calculations. Here we display additional
terms which appear to be the most important for nuclear structure. The
potentials are decomposed in a way that separates the contributions of
different physical mechanisms involved in the meson-nucleon amplitudes. The
same type of decomposition is presented for the TM force: the
, the chiral symmetry breaking and the nucleon pair terms are isolated.Comment: LATEX, 33 pages, 3 figures (available as postscript files upon
request
Definition of valid proteomic biomarkers: a bayesian solution
Clinical proteomics is suffering from high hopes generated by reports on apparent biomarkers, most of which could not be later substantiated via validation. This has brought into focus the need for improved methods of finding a panel of clearly defined biomarkers. To examine this problem, urinary proteome data was collected from healthy adult males and females, and analysed to find biomarkers that differentiated between genders. We believe that models that incorporate sparsity in terms of variables are desirable for biomarker selection, as proteomics data typically contains a huge number of variables (peptides) and few samples making the selection process potentially unstable. This suggests the application of a two-level hierarchical Bayesian probit regression model for variable selection which assumes a prior that favours sparseness. The classification performance of this method is shown to improve that of the Probabilistic K-Nearest Neighbour model
Local three-nucleon interaction from chiral effective field theory
The three-nucleon (NNN) interaction derived within the chiral effective field
theory at the next-to-next-to-leading order (N2LO) is regulated with a function
depending on the magnitude of the momentum transfer. The regulated NNN
interaction is then local in the coordinate space, which is advantages for some
many-body techniques. Matrix elements of the local chiral NNN interaction are
evaluated in a three-nucleon basis. Using the ab initio no-core shell model
(NCSM) the NNN matrix elements are employed in 3H and 4He bound-state
calculations.Comment: 17 pages, 9 figure
A New Treatment of 2N and 3N Bound States in Three Dimensions
The direct treatment of the Faddeev equation for the three-boson system in 3
dimensions is generalized to nucleons. The one Faddeev equation for identical
bosons is replaced by a strictly finite set of coupled equations for scalar
functions which depend only on 3 variables. The spin-momentum dependence
occurring as scalar products in 2N and 3N forces accompanied by scalar
functions is supplemented by a corresponding expansion of the Faddeev
amplitudes. After removing the spin degrees of freedom by suitable operations
only scalar expressions depending on momenta remain. The corresponding steps
are performed for the deuteron leading to two coupled equations.Comment: 19 page
Quadratic momentum dependence in the nucleon-nucleon interaction
We investigate different choices for the quadratic momentum dependence
required in nucleon-nucleon potentials to fit phase shifts in high
partial-waves. In the Argonne v18 potential L**2 and (L.S)**2 operators are
used to represent this dependence. The v18 potential is simple to use in
many-body calculations since it has no quadratic momentum-dependent terms in
S-waves. However, p**2 rather than L**2 dependence occurs naturally in
meson-exchange models of nuclear forces. We construct an alternate version of
the Argonne potential, designated Argonne v18pq, in which the L**2 and (L.S)**2
operators are replaced by p**2 and Qij operators, respectively. The quadratic
momentum-dependent terms are smaller in the v18pq than in the v18 interaction.
Results for the ground state binding energies of 3H, 3He, and 4He, obtained
with the variational Monte Carlo method, are presented for both the models with
and without three-nucleon interactions. We find that the nuclear wave functions
obtained with the v18pq are slightly larger than those with v18 at
interparticle distances < 1 fm. The two models provide essentially the same
binding in the light nuclei, although the v18pq gains less attraction when a
fixed three-nucleon potential is added.Comment: v.2 important corrections in tables and minor revisions in text;
reference for web-posted subroutine adde
Charge-Symmetry Breaking and the Two-Pion-Exchange Two-Nucleon Interaction
Charge-symmetry breaking in the nucleon-nucleon force is investigated within
an effective field theory, using a classification of isospin-violating
interactions based on power-counting arguments. The relevant
charge-symmetry-breaking interactions corresponding to the first two orders in
the power counting are discussed, including their effects on the 3He-3H
binding-energy difference. The static charge-symmetry-breaking potential linear
in the nucleon-mass difference is constructed using chiral perturbation theory.
Explicit formulae in momentum and configuration spaces are presented. The
present work completes previously obtained results.Comment: 15 pages, 2 figure
Charge-Symmetry-Breaking Three-Nucleon Forces
Leading-order three-nucleon forces that violate isospin symmetry are
calculated in Chiral Perturbation Theory. The effect of the
charge-symmetry-breaking three-nucleon force is investigated in the trinucleon
systems using Faddeev calculations. We find that the contribution of this force
to the 3He - 3H binding-energy difference is approximately 5 keV.Comment: 14 pages, 3 figure
Charge-Asymmetry of the Nucleon-Nucleon Interaction
Based upon the Bonn meson-exchange model for the nucleon-nucleon ()
interaction, we study systematically the charge-symmetry-breaking (CSB) of the
interaction due to nucleon mass splitting. Particular attention is payed
to CSB generated by the -exchange contribution to the interaction,
diagrams, and other multi-meson-exchanges. We calculate the CSB
differences in the effective range parameters as well as phase shift
differences in , and higher partial waves up to 300 MeV lab. energy. We
find a total CSB difference in the singlet scattering length of 1.6 fm which
explains the empirical value accurately. The corresponding CSB phase-shift
differences are appreciable at low energy in the state. In the other
partial waves, the CSB splitting of the phase shifts is small and increases
with energy, with typical values in the order of 0.1 deg at 300 MeV in and
waves.Comment: 11 pages, RevTex, 14 figure
Three-Nucleon Force Effects in Nucleon Induced Deuteron Breakup: Predictions of Current Models (I)
An extensive study of three-nucleon force effects in the entire phase space
of the nucleon-deuteron breakup process, for energies from above the deuteron
breakup threshold up to 200 MeV, has been performed. 3N Faddeev equations have
been solved rigorously using the modern high precision nucleon-nucleon
potentials AV18, CD Bonn, Nijm I, II and Nijm 93, and also adding 3N forces. We
compare predictions for cross sections and various polarization observables
when NN forces are used alone or when the two pion-exchange Tucson-Melbourne
3NF was combined with each of them. In addition AV18 was combined with the
Urbana IX 3NF and CD Bonn with the TM' 3NF, which is a modified version of the
TM 3NF, more consistent with chiral symmetry. Large but generally model
dependent 3NF effects have been found in certain breakup configurations,
especially at the higher energies, both for cross sections and spin
observables. These results demonstrate the usefulness of the kinematically
complete breakup reaction in testing the proper structure of 3N forces.Comment: 42 pages, 20 ps figures, 2 gif figure
Highly Purified Liver Microsomal Cytochrome P450: Properties and Catalytic Mechanism
Recent studies in this laboratory on two forms of cytochrome
P450 purified to homogeneity from rabbit liver microsomes are
reviewed. The two forms, phenobarbital-inducible P450LM2 and
5,6-benzoflavone-inducible P450LM4, differ in subunit molecular
weight, identity of the C-terminal amino acid, optical and EPR
spectra, and other properties. As isolated, oxidized P450LM2 is in
the low spin state, whereas P450LM4 is largely, but non entirely, in
the high spin state. Mechanistic studies have shown the following:
(a) P450LM2 may accept two electrons, calculated per heme, from
dithionite or NADPH in the presence of catalytic amounts of the
reductase, and may donate two electrons to various oxidizing agents,
including molecular oxygen. (b) Hydrogen peroxide is formed in
the reconstituted system in the presence of NADPH and oxygen, and
the amount varies with the substrate added. (c) Hydrogen peroxide
and other hydroperoxides apparently donate the oxygen atom
inserted into substrate during hydroxylation in the absence of 0 2
and an external donor. (d) Stopped flow spectrophotometry has
provided evidence for two distinct oxygenated complexes of the
reduced cytochrome. The reductase and cytochrome b5 may play
an effector role in increasing the rate of decomposition of the
second complex during oxygen insertion into substrate. A scheme
is proposed for the mechanism of action of purified P450LM2, based
on these and other findings
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