2,315 research outputs found
Nuclear prolate-shape dominance with the Woods-Saxon potential
We study the prolate-shape predominance of the nuclear ground-state
deformation by calculating the masses of more than two thousand even-even
nuclei using the Strutinsky method, modified by Kruppa, and improved by us. The
influences of the surface thickness of the single-particle potentials, the
strength of the spin-orbit potential, and the pairing correlations are
investigated by varying the parameters of the Woods-Saxon potential and the
pairing interaction. The strong interference between the effects of the surface
thickness and the spin-orbit potential is confirmed to persist for six sets of
the Woods-Saxon potential parameters. The observed behavior of the ratios of
prolate, oblate, and spherical nuclei versus potential parameters are rather
different in different mass regions. It is also found that the ratio of
spherical nuclei increases for weakly bound unstable nuclei. Differences of the
results from the calculations with the Nilsson potential are described in
detail.Comment: 16 pages, 17 figure
Similarity of nuclear structure in 132Sn and 208Pb regions: proton-neutron multiplets
Starting from the striking similarity of proton-neutron multiplets in 134Sb
and 210Bi, we perform a shell-model study of nuclei with two additional protons
or neutrons to find out to what extent this analogy persists. We employ
effective interactions derived from the CD-Bonn nucleon-nucleon potential
renormalized by use of the V-low-k approach. The calculated results for 136Sb,
212Bi, 136I, and 212At are in very good agreement with the available
experimental data. The similarity between 132Sn and 208Pb regions is discussed
in connection with the effective interaction, emphasizing the role of core
polarization effects.Comment: 4 pages, 3 figures, 2 table
Sulfatide in health and disease. The evaluation of sulfatide in cerebrospinal fluid as a possible biomarker for neurodegeneration
Sulfatide (3-O-sulfogalactosylceramide, SM4) is a glycosphingolipid, highly multifunctional and particularly enriched in the myelin sheath of neurons. The role of sulfatide has been implicated in various biological fields such as the nervous system, immune system, host-pathogen recognition and infection, beta cell function and haemostasis/thrombosis. Thus, alterations in sulfatide metabolism and production are associated with several human diseases such as neurological and immunological disorders and cancers. The unique lipid-rich composition of myelin reflects the importance of lipids in this specific membrane structure. Sulfatide has been shown to be involved in the regulation of oligodendrocyte differentiation and in the maintenance of the myelin sheath by influencing membrane dynamics involving sorting and lateral assembly of myelin proteins as well as ion channels. Sulfatide is furthermore essential for proper formation of the axo-glial junctions at the paranode together with axonal glycosphingolipids. Alterations in sulfatide metabolism are suggested to contribute to myelin deterioration as well as synaptic dysfunction, neurological decline and inflammation observed in different conditions associated with myelin pathology (mouse models and human disorders). Body fluid biomarkers are of importance for clinical diagnostics as well as for patient stratification in clinical trials and treatment monitoring. Cerebrospinal fluid (CSF) is commonly used as an indirect measure of brain metabolism and analysis of CSF sulfatide might provide information regarding whether the lipid disruption observed in neurodegenerative disorders is reflected in this body fluid. In this review, we evaluate the diagnostic utility of CSF sulfatide as a biomarker for neurodegenerative disorders associated with dysmyelination/demyelination by summarising the current literature on this topic. We can conclude that neither CSF sulfatide levels nor individual sulfatide species consistently reflect the lipid disruption observed in many of the demyelinating disorders. One exception is the lysosomal storage disorder metachromatic leukodystrophy, possibly due to the genetically determined accumulation of non-metabolised sulfatide. We also discuss possible explanations as to why myelin pathology in brain tissue is poorly reflected by the CSF sulfatide concentration. The previous suggestion that CSF sulfatide is a marker of myelin damage has thereby been challenged by more recent studies using more sophisticated laboratory techniques for sulfatide analysis as well as improved sample selection criteria due to increased knowledge on disease pathology
Quasifree pion photoproduction on the deuteron in the region
Photo production of pions on the deuteron is studied in the spectator nucleon
model. The Born terms of the elementary production amplitude are determined in
pseudovector N coupling and supplied with a form factor. The
resonance is considered both in the and the channel. The parameters of
the resonance and the cutoff of the form factors are fixed on the
leading photoproduction multipoles. Results for total and differential cross
sections are compared with experimental data. Particular attention is paid to
the role of Pauli correlations of the final state nucleons in the quasifree
case. The results are compared with those for pion photoproduction on the
nucleon.Comment: 17 pages LateX2e including 5 postscript figure
Particle tracking in kaon electroproduction with cathode-charge sampling in multi-wire proportional chambers
Wire chambers are routinely operated as tracking detectors in magnetic
spectrometers at high-intensity continuous electron beams. Especially in
experiments studying reactions with small cross-sections the reaction yield is
limited by the background rate in the chambers. One way to determine the track
of a charged particle through a multi-wire proportional chamber (MWPC) is the
measurement of the charge distribution induced on its cathodes. In practical
applications of this read-out method, the algorithm to relate the measured
charge distribution to the avalanche position is an important factor for the
achievable position resolution and for the track reconstruction efficiency. An
algorithm was developed for operating two large-sized MWPCs in a strong
background environment with multiple-particle tracks. Resulting efficiencies
were determined as a function of the electron beam current and on the signal
amplitudes. Because of the different energy-losses of pions, kaons, and protons
in the momentum range of the spectrometer the efficiencies depend also on the
particle species
High-precision Studies of the He(e,ep) Reaction at the Quasielastic Peak
Precision studies of the reaction He(e,ep) using the
three-spectrometer facility at the Mainz microtron MAMI are presented. All data
are for quasielastic kinematics at MeV/c. Absolute cross
sections were measured at three electron kinematics. For the measured missing
momenta range from 10 to 165 MeV/c, no strength is observed for missing
energies higher than 20 MeV. Distorted momentum distributions were extracted
for the two-body breakup and the continuum. The longitudinal and transverse
behavior was studied by measuring the cross section for three photon
polarizations. The longitudinal and transverse nature of the cross sections is
well described by a currently accepted and widely used prescription of the
off-shell electron-nucleon cross-section. The results are compared to modern
three-body calculations and to previous data.Comment: 4 pages, 3 figures. Submitted for publication in Phys. Rev. Let
Self energies of the pion and the delta isobar from the ^3He(e,e'pi^+)^3H reaction
In a kinematically complete experiment at the Mainz microtron MAMI, pion
angular distributions of the He(e,e'H reaction have been measured
in the excitation region of the resonance to determine the
longitudinal (), transverse (), and the interference part of the
differential cross section. The data are described only after introducing
self-energy modifications of the pion and -isobar propagators. Using
Chiral Perturbation Theory (ChPT) to extrapolate the pion self energy as
inferred from the measurement on the mass shell, we deduce a reduction of the
mass of MeV/c in the
neutron-rich nuclear medium at a density of fm. Our data are consistent with the self energy
determined from measurements of photoproduction from He and heavier
nuclei.Comment: Elsart, 12 pages and 4 figures, Correspondent: Professor Dr. Dr. h.c.
mult. Achim Richter, [email protected], submitted to Phys. Rev.
Let
Polarization observables of the gamma d --> PiNN reaction in the Delta(1232)-resonance region
Polarization observables of the three charge states of the pion for the
reaction with polarized photon beam and/or oriented
deuteron target are evaluated over the whole (1232)-resonance region
adopting a nonrelativistic model based on time-ordered perturbation theory.
Results for the -meson spectra, linear photon asymmetry, vector and tensor
target asymmetries are presented. Particular attention is given, for the first
time, to double polarization asymmetries for which we present results for
and . We found that all other double
polarization asymmetries of photon and deuteron target are vanished.Comment: 17 Pages, 8 Figures, accepted for publication in Int. J. Mod. Phys.
A measurement of the axial form factor of the nucleon by the p(e,e'pi+)n reaction at W=1125 MeV
The reaction p(e,e'pi+)n was measured at the Mainz Microtron MAMI at an
invariant mass of W=1125 MeV and four-momentum transfers of Q^2=0.117, 0.195
and 0.273 (GeV/c)^2. For each value of Q^2, a Rosenbluth separation of the
transverse and longitudinal cross sections was performed. An effective
Lagrangian model was used to extract the `axial mass' from experimental data.
We find a value of M_A=(1.077+-0.039) GeV which is (0.051+-0.044) GeV larger
than the axial mass known from neutrino scattering experiments. This is
consistent with recent calculations in chiral perturbation theory.Comment: 14 pages, 5 figures, uses elsart.cl
Generalized seniority scheme in light Sn isotopes
The yrast generalized seniority states are compared with the corresponding
shell model states for the case of the Sn isotopes Sn. For most of
the cases the energies agree within 100 keV and the overlaps of the wave
functions are greater than 0.7.Comment: 8 pages, revtex. Submitted to Phys. Rev.
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