85 research outputs found
Triton calculations with and exchange three-nucleon forces
The Faddeev equations are solved in momentum space for the trinucleon bound
state with the new Tucson-Melbourne and exchange three-nucleon
potentials. The three-nucleon potentials are combined with a variety of
realistic two-nucleon potentials. The dependence of the triton binding energy
on the cut-off parameter in the three-nucleon potentials is studied
and found to be reduced compared to the case with pure exchange. The
exchange parts of the three-nucleon potential yield an overall repulsive
effect. When the recommended parameters are employed, the calculated triton
binding energy turns out to be very close to its experimental value.
Expectation values of various components of the three-nucleon potential are
given to illustrate their significance for binding.Comment: 17 pages Revtex 3.0, 4 figures. Accepted for publication in Phys.
Rev.
Does The 3N-Force Have A Hard Core?
The meson-nucleon dynamics that generates the hard core of the RuhrPot
two-nucleon interaction is shown to vanish in the irreducible 3N force. This
result indicates a small 3N force dominated by conventional light
meson-exchange dynamics and holds for an arbitrary meson-theoretic Lagrangian.
The resulting RuhrPot 3N force is defined in the appendix. A completely
different result is expected when the Tamm-Dancoff/Bloch-Horowitz procedure is
used to define the NN and 3N potentials. In that approach, (e.g. full Bonn
potential) both the NN {\it and} 3N potentials contain non-vanishing
contributions from the coherent sum of meson-recoil dynamics and the
possibility of a large hard core requiring explicit calculation cannot be ruled
out.Comment: 16 pages REVTeX + 3 ps fig
Composite vertices that lead to soft form factors
The momentum-space cut-off parameter of hadronic vertex functions
is studied in this paper. We use a composite model where we can measure the
contributions of intermediate particle propagations to . We show that
in many cases a composite vertex function has a much smaller cut-off than its
constituent vertices, particularly when light constituents such as pions are
present in the intermediate state. This suggests that composite
meson-baryon-baryon vertex functions are rather soft, i.e., they have \Lambda
considerably less than 1 GeV. We discuss the origin of this softening of form
factors as well as the implications of our findings on the modeling of nuclear
reactions.Comment: REVTex, 19 pages, 5 figs(to be provided on request
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
The Puzzle and the Nuclear Force
The nucleon-deuteron analyzing power in elastic nucleon-deuteron
scattering poses a longstanding puzzle. At energies below
approximately 30 MeV cannot be described by any realistic NN force. The
inclusion of existing three-nucleon forces does not improve the situation.
Because of recent questions about the NN phases, we examine whether
reasonable changes in the NN force can resolve the puzzle. In order to do this
we investigate the effect on the waves produced by changes in different
parts of the potential (viz., the central force, tensor force, etc.), as well
as on the 2-body observables and on . We find that it is not possible with
reasonable changes in the NN potential to increase the 3-body and at the
same time to keep the 2-body observables unchanged. We therefore conclude that
the puzzle is likely to be solved by new three-nucleon forces, such as
those of spin-orbit type, which have not yet been taken into account.Comment: 35 pages in REVTeX, 1 figure in postscript and 3 figures in PiCTe
Role of Vector Mesons in High-Q^2 Lepton-Nucleon Scattering
The possible role played by vector mesons in inclusive deep inelastic
lepton-nucleon scattering is investigated. In the context of the convolution
model, we calculate self-consistently the scaling contribution to the nucleon
structure function using the formalism of time-ordered perturbation theory in
the infinite momentum frame. Our results indicate potentially significant
effects only when the vector meson---nucleon form factor is very hard.
Agreement with the experimental antiquark distributions, however, requires
relatively soft form factors for the , and vertices.Comment: 22 pages, 9 figures (available upon request); accepted for
publication in Phys.Rev.D, ADP-92-197/T12
The Pion-Nucleon Form Factor From QCD Sum Rules
QCD sum rules are used to calculate the dependence of the
coupling in the spacelike region 0.5 \ {\mbox{GeV}}^2
\lesssim q^2 \lesssim 1.5\ {\mbox{GeV}}^2. We study the Borel sum rule for the
three point function of one pseudoscalar and two nucleon currents up to order
four in the operator product expansion. The Borel transform is performed with
respect to the nucleon momenta, whereas the momentum of the pseudoscalar
vertex is kept fixed at spacelike values. The results can be well fitted using
a monopole form with a cutoff mass of about $\Lambda_\pi \approx 800 \
{\mbox{MeV}}.Comment: 13 pages (REVTEX), 6 figures as 5 postscript files (as fig.uu tarred,
compressed, uudecoded
Low infra red laser light irradiation on cultured neural cells: effects on mitochondria and cell viability after oxidative stress
<p>Abstract</p> <p>Background</p> <p>Considerable interest has been aroused in recent years by the well-known notion that biological systems are sensitive to visible light. With clinical applications of visible radiation in the far-red to near-infrared region of the spectrum in mind, we explored the effect of coherent red light irradiation with extremely low energy transfer on a neural cell line derived from rat pheochromocytoma. We focused on the effect of pulsed light laser irradiation vis-à-vis two distinct biological effects: neurite elongation under NGF stimulus on laminin-collagen substrate and cell viability during oxidative stress.</p> <p>Methods</p> <p>We used a 670 nm laser, with extremely low peak power output (3 mW/cm<sup>2</sup>) and at an extremely low dose (0.45 mJ/cm<sup>2</sup>). Neurite elongation was measured over three days in culture. The effect of coherent red light irradiation on cell reaction to oxidative stress was evaluated through live-recording of mitochondria membrane potential (MMP) using JC1 vital dye and laser-confocal microscopy, in the absence (photo bleaching) and in the presence (oxidative stress) of H<sub>2</sub>O<sub>2</sub>, and by means of the MTT cell viability assay.</p> <p>Results</p> <p>We found that laser irradiation stimulates NGF-induced neurite elongation on a laminin-collagen coated substrate and protects PC12 cells against oxidative stress.</p> <p>Conclusion</p> <p>These data suggest that red light radiation protects the viability of cell culture in case of oxidative stress, as indicated by MMP measurement and MTT assay. It also stimulates neurite outgrowth, and this effect could also have positive implications for axonal protection.</p
Primary Postnatal Dorsal Root Ganglion Culture from Conventionally Slaughtered Calves
Neurological disorders in ruminants have an important impact on veterinary health, but very few host-specific in vitro models have been established to study diseases affecting the nervous system. Here we describe a primary neuronal dorsal root ganglia (DRG) culture derived from calves after being conventionally slaughtered for food consumption. The study focuses on the in vitro characterization of bovine DRG cell populations by immunofluorescence analysis. The effects of various growth factors on neuron viability, neurite outgrowth and arborisation were evaluated by morphological analysis. Bovine DRG neurons are able to survive for more than 4 weeks in culture. GF supplementation is not required for neuronal survival and neurite outgrowth. However, exogenously added growth factors promote neurite outgrowth. DRG cultures from regularly slaughtered calves represent a promising and sustainable host specific model for the investigation of pain and neurological diseases in bovines
Self-Healing Collagen-Based Hydrogel for Brain Injury Therapy
Hydrogels derived from biopolymers, also called biohydrogels, have
shown potential for brain injury therapy due to their tunable physical, chemical,
and biological properties. Among different biohydrogels, those made from collagen
type I are very promising candidates for the reparation of nervous tissues due to its
biocompatibility, noncytotoxic properties, injectability, and self-healing ability.
Moreover, although collagen does not naturally occur in the brain, it has been
demonstrated that collagen type I, which resides in the basal lamina of the
subventricular zone in adults, supports neural cell attachment, axonal growth, and
cell proliferation due to its intrinsic content of specific cell-signaling domains. This
chapter summarizes the most relevant results obtained from both in vitro and in vivo
studies using self-healing biohydrogels based on collagen type I as key component
in the field of neuroregeneration.University of RegensburgUniversidad de La LagunaMinisterio de Ciencia, Innovación y Universidade
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