Study of nuclear correlation effects via 12C(p,n)12N(g.s.,1+) at 296 MeV

We report measurements of the cross section and a complete set of polarization observables for the Gamow--Teller ${}^{12}{\rm C}(\vec{p},\vec{n}){}^{12}{\rm N}({\rm g.s.},1^+)$ reaction at a bombarding energy of 296 MeV. The data are compared with distorted wave impulse approximation calculations employing transition form factors normalized to reproduce the observed beta-decay $ft$ value. The cross section is significantly under-predicted by the calculations at momentum transfers $q \gtrsim$ 0.5 ${\rm fm^{-1}}$. The discrepancy is partly resolved by considering the non-locality of the nuclear mean field. However, the calculations still under-predict the cross section at large momentum transfers of $q$ $\simeq$ 1.6 ${\rm fm^{-1}}$. We also performed calculations employing random phase approximation response functions and found that the observed enhancement can be attributed in part to pionic correlations in nuclei.Comment: 5 figures, submitted to Phys. Lett.

The Anisotropy of Cosmic Ray Arrival Direction around 10^18eV

Anisotropy in the arrival directions of cosmic rays around 10^{18}eV is studied using data from the Akeno 20 km^2 array and the Akeno Giant Air Shower Array (AGASA), using a total of about 216,000 showers observed over 15 years above 10^{17}eV. In the first harmonic analysis, we have found significant anisotropy of $\sim$ 4 % around 10^{18}eV, corresponding to a chance probability of $\sim 10^{-5}$ after taking the number of independent trials into account. With two dimensional analysis in right ascension and declination, this anisotropy is interpreted as an excess of showers near the directions of the Galactic Center and the Cygnus region. This is a clear evidence for the existence of the galactic cosmic ray up to the energy of 10^{18}eV. Primary particle which contribute this anisotropy may be proton or neutron.Comment: 4pages, three figures, to appear in Procedings of 26th ICRC(Salt Lake City

Small-scale anisotropy of cosmic rays above 10^19eV observed with the Akeno Giant Air Shower Array

With the Akeno Giant Air Shower Array (AGASA), 581 cosmic rays above 10^19eV, 47 above 4 x 10^19eV, and 7 above 10^20eV are observed until August 1998. Arrival direction distribution of these extremely high energy cosmic rays has been studied. While no significant large-scale anisotropy is found on the celestial sphere, some interesting clusters of cosmic rays are observed. Above 4 x 10^19eV, there are one triplet and three doublets within separation angle of 2.5^o and the probability of observing these clusters by a chance coincidence under an isotropic distribution is smaller than 1 %. Especially the triplet is observed against expected 0.05 events. The cos(\theta_GC) distribution expected from the Dark Matter Halo model fits the data as well as an isotropic distribution above 2 x 10^19eV and 4 x 10^19eV, but is a poorer fit than isotropy above 10^19eV. Arrival direction distribution of seven 10^20eV cosmic rays is consistent with that of lower energy cosmic rays and is uniform. Three of seven are members of doublets above about 4 x 10^19eV.Comment: 40 pages, 12 figure, AASTeX *** Authors found a typo on Table 2 -- Energy of event 94/07/06 **

Polarization transfer measurements for 12C(p⃗,n⃗)12N(g.s.,1+)^{12}{\rm C}(\vec{p},\vec{n})^{12}{\rm N (g.s.},1^+) at 296 MeV and nuclear correlation effects

Differential cross sections and complete sets of polarization observables are presented for the Gamow-Teller $^{12}{\rm C}(\vec{p},\vec{n})^{12}{\rm N}({\rm g.s.},1^+)$ reaction at a bombarding energy of 296 MeV with momentum transfers $q$ of 0.1 to $2.2{\rm fm}^{-1}$. The polarization transfer observables are used to deduce the spin-longitudinal cross section, $ID_q$, and spin-transverse cross sections, $ID_p$ and $ID_n$. The data are compared with calculations based on the distorted wave impulse approximation (DWIA) using shell-model wave functions. Significant differences between the experimental and theoretical results are observed for all three spin-dependent $ID_i$ at momentum transfers of $q \gtrsim 0.5{\rm fm}^{-1}$, suggesting the existence of nuclear correlations beyond the shell model. We also performed DWIA calculations employing random phase approximation (RPA) response functions and found that the observed discrepancy is partly resolved by the pionic and rho-mesonic correlation effects.Comment: accepted for publication in Phys. Rev.

Extension of the Cosmic-Ray Energy Spectrum Beyond the Predicted Greisen-Zatsepin-Kuz'min Cutoff

The cosmic-ray energy spectrum above 10^{18.5} eV is reported using the updated data set of the Akeno Giant Air Shower Array (AGASA) from February 1990 to October 1997. The energy spectrum extends beyond 10^{20} eV and the energy gap between the highest energy event and the others is being filled up with recently observed events. The spectral shape suggests the absence of the 2.7 K cutoff in the energy spectrum or a possible presence of a new component beyond the 2.7 K cutoff.Comment: to be published in PRL, 3 figures, REVTEX forma

Right Isomerism of the Brain in Inversus Viscerum Mutant Mice

Left-right (L-R) asymmetry is a fundamental feature of higher-order neural function. However, the molecular basis of brain asymmetry remains unclear. We recently reported L-R asymmetry of hippocampal circuitry caused by differential allocation of N-methyl-D-aspartate receptor (NMDAR) subunit GluRε2 (NR2B) in hippocampal synapses. Using electrophysiology and immunocytochemistry, here we analyzed the hippocampal circuitry of the inversus viscerum (iv) mouse that has a randomized laterality of internal organs. The iv mouse hippocampus lacks L-R asymmetry, it exhibits right isomerism in the synaptic distribution of the ε2 subunit, irrespective of the laterality of visceral organs. This independent right isomerism of the hippocampus is the first evidence that a distinct mechanism downstream of the iv mutation generates brain asymmetry

Essential Role of Neuron-Enriched Diacylglycerol Kinase (DGK), DGKβ in Neurite Spine Formation, Contributing to Cognitive Function

BACKGROUND: Diacylglycerol (DG) kinase (DGK) phosphorylates DG to produce phosphatidic acid (PA). Of the 10 subtypes of mammalian DGKs, DGKbeta is a membrane-localized subtype and abundantly expressed in the cerebral cortex, hippocampus, and caudate-putamen. However, its physiological roles in neurons and higher brain function have not been elucidated. METHODOLOGY/PRINCIPAL FINDINGS: We, therefore, developed DGKbeta KO mice using the Sleeping Beauty transposon system, and found that its long-term potentiation in the hippocampal CA1 region was reduced, causing impairment of cognitive functions including spatial and long-term memories in Y-maze and Morris water-maze tests. The primary cultured hippocampal neurons from KO mice had less branches and spines compared to the wild type. This morphological impairment was rescued by overexpression of DGKbeta. In addition, overexpression of DGKbeta in SH-SY5Y cells or primary cultured mouse hippocampal neurons resulted in branch- and spine-formation, while a splice variant form of DGKbeta, which has kinase activity but loses membrane localization, did not induce branches and spines. In the cells overexpressing DGKbeta but not the splice variant form, DGK product, PA, was increased and the substrate, DG, was decreased on the plasma membrane. Importantly, lower spine density and abnormality of PA and DG contents in the CA1 region of the KO mice were confirmed. CONCLUSIONS/SIGNIFICANCE: These results demonstrate that membrane-localized DGKbeta regulates spine formation by regulation of lipids, contributing to the maintenance of neural networks in synaptic transmission of cognitive processes including memory