639 research outputs found
Benchmark Calculations for the Triton Binding Energy for Modern NN Forces and the pi-pi Exchange Three-Nucleon Force
We present high precision benchmark calculations for the triton binding
energy using the most recent, phase equivalent realistic nucleon-nucleon (NN)
potentials and the Tuscon-Melbourne pi-pi three-nucleon force (3NF). That 3NF
is included with partial waves up to a total two-body angular momentum of
j_max=6. It is shown that the inclusion of the 3NF slows down the convergence
in the partial waves and j_max=5 is needed in order to achieve converged
results within a few keV. We adjust the cut-off parameter Lambda in the form
factors of the Tuscon-Melbourne 3NF separately for the different NN potentials
to the triton binding energy. This provides a set of phenomenological
three-nucleon Hamiltonians which can be tested in three-nucleon scattering and
systems with A>3. A connection between the probability to find two nucleons at
short distances in the triton and the effect of that 3NF on the triton binding
energy is pointed out.Comment: 18 pages REVTeX, 3 figure
Modern NN Force Predictions for the Total ND Cross Section up to 300 MeV
For several modern nucleon-nucleon potentials state-of-the-art Faddeev
calculations are carried out for the total cross section between 10 and
300 MeV projectile energy and compared to new high precision measurements. The
agreement between theory and data is rather good, with exception at the higher
energies where a 10% discrepancy builds up. In addition the convergence of the
multiple scattering series incorporated in the Faddeev scheme is studied
numerically with the result, that rescattering corrections remain important.
Based on this multiple scattering series the high energy limit of the total
cross section is also investigated analytically. In contrast to the naive
expectation that the total cross section is the sum of the and
total cross sections we find additional effects resulting from the rescattering
processes, which have different signs and different behavior as function of the
energy. A shadowing effect in the high energy limit only occurs for energies
higher than 300 MeV. The expressions in the high energy limit have
qualitatively a similar behavior as the exactly calculated expressions, but can
be expected to be valid quantitatively only at much higher energies.Comment: 22 pages, 5 figure
Improving hox protein classification across the major model organisms
The family of Hox-proteins has been a major focus of research for over 30 years. Hox-proteins are crucial to the correct development of bilateral organisms, however, some uncertainty remains as to which Hox-proteins are functionally equivalent across different species. Initial classification of Hox-proteins was based on phylogenetic analysis of the 60 amino acid homeodomain. This approach was successful in classifying Hox-proteins with differing homeodomains, but the relationships of Hox-proteins with nearly identical homeodomains, yet distinct biological functions, could not be resolved. Correspondingly, these 'problematic' proteins were classified into one large unresolved group. Other classifications used the relative location of the Hox-protein coding genes on the chromosome (synteny) to further resolve this group. Although widely used, this synteny-based classification is inconsistent with experimental evidence from functional equivalence studies. These inconsistencies led us to re-examine and derive a new classification for the Hox-protein family using all Hox-protein sequences available in the GenBank non-redundant protein database (NCBI-nr). We compare the use of the homeodomain, the homeodomain with conserved flanking regions (the YPWM and linker region), and full length Hox-protein sequences as a basis for classification of Hox-proteins. In contrast to previous attempts, our approach is able to resolve the relationships for the 'problematic' as well as ABD-B-like Hox-proteins. We highlight differences to previous classifications and clarify the relationships of Hox-proteins across the five major model organisms, Caenorhabditis elegans, Drosophila melanogaster, Branchiostoma floridae, Mus musculus and Danio rerio. Comparative and functional analysis of Hox-proteins, two fields crucial to understanding the development of bilateral organisms, have been hampered by difficulties in predicting functionally equivalent Hox-proteins across species. Our classification scheme offers a higher-resolution classification that is in accordance with phylogenetic as well as experimental data and, thereby, provides a novel basis for experiments, such as comparative and functional analyses of Hox-proteins.Funding for this work has been provided by the Australian Research Council, Center for Excellence Grant (CEO348212)
Discrepancies in Determinations of the Ginzburg-Landau Parameter
Long-standing discrepancies within determinations of the Ginzburg-Landau
parameter from supercritical field measurements on superconducting
microspheres are reexamined. The discrepancy in tin is shown to result from
differing methods of analyses, whereas the discrepancy in indium is a
consequence of significantly differing experimental results. The reanalyses
however confirms the lower determinations to within experimental
uncertainties.Comment: submitted to Phys. Rev.
S-35 Beta Irradiation of a Tin Strip in a State of Superconducting Geometrical Metastability
We report the first energy loss spectrum obtained with a geometrically
metastable type I superconducting tin strip irradiated by the beta-emission of
S-35. (Nucl. Instr. Meth. A, in press)Comment: Compressed PostScript (filename.ps.Z), 9 pages, 2 figure
Charge-Dependence of the Nucleon-Nucleon Interaction
Based upon the Bonn meson-exchange-model for the nucleon-nucleon ()
interaction, we calculate the charge-independence breaking (CIB) of the
interaction due to pion-mass splitting. Besides the one-pion-exchange (OPE), we
take into account the -exchange model and contributions from three and
four irreducible pion exchanges. We calculate the CIB differences in the
effective range parameters as well as phase shift differences for
partial waves up to total angular momentum J=4 and laboratory energies below
300 MeV. We find that the CIB effect from OPE dominates in all partial waves.
However, the CIB effects from the model are noticable up to D-waves and
amount to about 40% of the OPE CIB-contribution in some partial waves, at 300
MeV. The effects from 3 and 4 contributions are negligible except in
and .Comment: 12 pages, RevTex, 14 figure
The properties of the three-nucleon system with the dressed-bag model for nn interaction. I: New scalar three-body force
A multi-component formalism is developed to describe three-body systems with
nonstatic pairwise interactions and non-nucleonic degrees of freedom. The
dressed-bag model for interaction based on the formation of an
intermediate six-quark bag dressed by a -field is applied to the
system, where it results in a new three-body force between the six-quark bag
and a third nucleon. Concise variational calculations of bound states are
carried out in the dressed-bag model including the new three-body force. It is
shown that this three-body force gives at least half the total binding
energy, while the weight of non-nucleonic components in the H and He
wavefunctions can exceed 10%. The new force model provides a very good
description of bound states with a reasonable magnitude of the
coupling constant. The model can serve as a natural bridge between dynamical
description of few-nucleon systems and the very successful Walecka approach to
heavy nuclei and nuclear matter.Comment: 26 pages, Latex, 7 figure
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