117 research outputs found
Polarization phenomena in hyperon-nucleon scattering
We investigate polarization observables in hyperon-nucleon scattering by
decomposing scattering amplitudes into spin-space tensors, where each component
describes scattering by corresponding spin-dependent interactions, so that
contributions of the interactions in the observables are individually
identified. In this way, for elastic scattering we find some linear
combinations of the observables sensitive to particular spin-dependent
interactions such as symmetric spin-orbit (LS) interactions and antisymmetric
LS ones. These will be useful to criticize theoretical predictions of the
interactions when the relevant observables are measured. We treat vector
analyzing powers, depolarizations, and coefficients of polarization transfers
and spin correlations, a part of which is numerically examined in scattering as an example. Total cross sections are studied for polarized
beams and targets as well as for unpolarized ones to investigate spin
dependence of imaginary parts of forward scattering amplitudes.Comment: 15 pages, 8 figure
Central and tensor components of three-nucleon forces in low-energy proton-deuteron scattering
Contributions of three-nucleon forces (3NF) to proton-deuteron scattering
observables at energies below the deuteron breakup threshold are studied by
solving the Faddeev equation that includes the Coulomb interaction. At E_p=3.0
MeV, we find that the central part of a two-pion exchange 3NF removes the
discrepancy between measured cross sections and the calculated ones by
two-nucleon forces, and improves the agreement with T_{22} experimental data.
However, the tensor part of the 3NF fails in reproducing data of the analyzing
power T_{21} by giving worse agreement between the measured and the calculated.
Detailed examinations of scattering amplitudes suggest that a P-wave
contribution in spin quartet tensor amplitudes has unsuitable sign for
reproducing the T_{21} data.Comment: 6 pages, 6 figure
Analyzing power for the proton elastic scattering from neutron-rich 6He nucleus
Vector analyzing power for the proton-6He elastic scattering at 71
MeV/nucleon has been measured for the first time, with a newly developed
polarized proton solid target working at low magnetic field of 0.09 T. The
results are found to be incompatible with a t-matrix folding model prediction.
Comparisons of the data with g-matrix folding analyses clearly show that the
vector analyzing power is sensitive to the nuclear structure model used in the
reaction analysis. The alpha-core distribution in 6He is suggested to be a
possible key to understand the nuclear structure sensitivity.Comment: 5 pages, 3 figures, accepted for publication as a Rapid Communication
in Physical Review
Reaction mechanism and characteristics of T_{20} in d + ^3He backward elastic scattering at intermediate energies
For backward elastic scattering of deuterons by ^3He, cross sections \sigma
and tensor analyzing power T_{20} are measured at E_d=140-270 MeV. The data are
analyzed by the PWIA and by the general formula which includes virtual
excitations of other channels, with the assumption of the proton transfer from
^3He to the deuteron. Using ^3He wave functions calculated by the Faddeev
equation, the PWIA describes global features of the experimental data, while
the virtual excitation effects are important for quantitative fits to the
T_{20} data. Theoretical predictions on T_{20}, K_y^y (polarization transfer
coefficient) and C_{yy} (spin correlation coefficient) are provided up to GeV
energies.Comment: REVTEX+epsfig, 17 pages including 6 eps figs, to be published in
Phys. Rev.
Measurement of the tensor analyzing power T20 in the dd->^3Hen and dd->^3Hp at intermediate energies and at zero degree
The data on the tensor analyzing power T20 in the dd->^3Hen and dd-> ^3Hp
reactions at 140, 200 and 270 MeV of the deuteron kinetic energy and at zero
degree obtained at RIKEN Accelerator Research Facility are presented. The
observed positive sign of T20 clearly demonstrates the sensitivity to the D/S
wave ratios in the ^3He and ^3H in the energy domain of the measurements. The
T20 data for the ^3He-n and ^3H-p channels are in agreement within experimental
accuracy.Comment: 9 pages, 3 figures, submitted in Phys.Lett.
Proton--induced deuteron breakup at GeV energies with forward emission of a fast proton pair
A study of the deuteron breakup reaction with forward emission
of a fast proton pair with small excitation energy 3 MeV has been
performed at the ANKE spectrometer at COSY--J\"ulich. An exclusive measurement
was carried out at six proton--beam energies ~0.6,~0.7,~0.8,~0.95,~1.35,
and 1.9 GeV by reconstructing the momenta of the two protons. The differential
cross section of the breakup reaction, averaged up to over the cm
polar angle of the total momentum of the pairs, has been obtained. Since
the kinematics of this process is quite similar to that of backward elastic scattering, the results are compared to calculations based on a
theoretical model previously applied to the process.Comment: 17 pages including 6 figures and 1 table v2: minor changes; v3: minor
change of author list; v4: changes in accordance with referee remark
Analyzing power in elastic scattering of 6He from polarized proton target at 71 MeV/nucleon
The vector analyzing power has been measured for the elastic scattering of
neutron-rich 6He from polarized protons at 71 MeV/nucleon making use of a newly
constructed solid polarized proton target operated in a low magnetic field and
at high temperature. Two approaches based on local one-body potentials were
applied to investigate the spin-orbit interaction between a proton and a 6He
nucleus. An optical model analysis revealed that the spin-orbit potential for
6He is characterized by a shallow and long-ranged shape compared with the
global systematics of stable nuclei. A semimicroscopic analysis with a
alpha+n+n cluster folding model suggests that the interaction between a proton
and the alpha core is essentially important in describing the p+6He elastic
scattering. The data are also compared with fully microscopic analyses using
non-local optical potentials based on nucleon-nucleon g-matrices.Comment: 20 pages, 20 figures, accepted by Physical Review
Predicted contextual modulation varies with distance from pinwheel centers in the orientation preference map
In the primary visual cortex (V1) of some mammals, columns of neurons with the full range of orientation preferences converge at the center of a pinwheel-like arrangement, the ‘pinwheel center' (PWC). Because a neuron receives abundant inputs from nearby neurons, the neuron's position on the cortical map likely has a significant impact on its responses to the layout of orientations inside and outside its classical receptive field (CRF). To understand the positional specificity of responses, we constructed a computational model based on orientation preference maps in monkey V1 and hypothetical neuronal connections. The model simulations showed that neurons near PWCs displayed weaker but detectable orientation selectivity within their CRFs, and strongly reduced contextual modulation from extra-CRF stimuli, than neurons distant from PWCs. We suggest that neurons near PWCs robustly extract local orientation within their CRF embedded in visual scenes, and that contextual information is processed in regions distant from PWCs
Genome sequencing reveals metabolic and cellular interdependence in an amoeba-kinetoplastid symbiosis
Endosymbiotic relationships between eukaryotic and prokaryotic cells are common in nature. Endosymbioses between two eukaryotes are also known; cyanobacterium-derived plastids have spread horizontally when one eukaryote assimilated another. A unique instance of a non-photosynthetic, eukaryotic endosymbiont involves members of the genus Paramoeba, amoebozoans that infect marine animals such as farmed fish and sea urchins. Paramoeba species harbor endosymbionts belonging to the Kinetoplastea, a diverse group of flagellate protists including some that cause devastating diseases. To elucidate the nature of this eukaryote-eukaryote association, we sequenced the genomes and transcriptomes of Paramoeba pemaquidensis and its endosymbiont Perkinsela sp. The endosymbiont nuclear genome is ~9.5 Mbp in size, the smallest of a kinetoplastid thus far discovered. Genomic analyses show that Perkinsela sp. has lost the ability to make a flagellum but retains hallmark features of kinetoplastid biology, including polycistronic transcription, trans-splicing, and a glycosome-like organelle. Mosaic biochemical pathways suggest extensive ‘cross-talk’ between the two organisms, and electron microscopy shows that the endosymbiont ingests amoeba cytoplasm, a novel form of endosymbiont-host communication. Our data reveal the cell biological and biochemical basis of the obligate relationship between Perkinsela sp. and its amoeba host, and provide a foundation for understanding pathogenicity determinants in economically important Paramoeba
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