403 research outputs found
Imaging of an early memory trace in the Drosophila mushroom body
Extensive molecular, genetic, and anatomical analyses have suggested that olfactory memory is stored in the mushroom body (MB), a higher-order olfactory center in the insect brain. The MB comprises three subtypes of neurons with axons that extend into different lobes. A recent functional imaging study has revealed a long-term memory trace manifested as an increase in the Ca(2+) activity in an axonal branch of a subtype of MB neurons. However, early memory traces in the MB remain elusive. We report here learning-induced changes in Ca(2+) activities during early memory formation in a different subtype of MB neurons. We used three independent in vivo and in vitro preparations, and all of them showed that Ca(2+) activities in the axonal branches of alpha'/beta' neurons in response to a conditioned olfactory stimulus became larger compared with one that was not conditioned. The changes were dependent on proper G-protein signaling in the MB. The importance of these changes in the Ca(2+) activity of alpha'/beta' neurons during early memory formation was further tested behaviorally by disrupting G-protein signaling in these neurons or blocking their synaptic outputs during the learning and memory process. Our results suggest that increased Ca(2+) activity in response to a conditioned olfactory stimulus may be a neural correlate of early memory in the MB
River Dike Failure in Japan by Earthquakes in 1993
Hokkaido, Japan was attacked by earthquakes of magnitude 7.8 twice in January and July, 1993. One is the Kushiro-Oki Earthquake and the other the Hokkaido Nansei-Oki Earthquake. River dikes were severely damaged by liquefaction of sand. The former caused liquefaction of subsided dike materials and the latter caused liquefaction of sand of the foundation bed. Relations between dimensional elements of dike and peat bed and stress relaxation within dike were analyzed. Old channels recently filled with sandy materials were distinguished from pointbar zones in ancient river bed covered with silty sediment, based on degree of damage due to liquefaction. Repairing works were completed by the end of the year precedent the snow season
Soft x-ray magnetic circular dichroism study of weakly ferromagnetic ZnVO thin film
We performed a soft x-ray magnetic circular dichroism (XMCD) study of a
ZnVO thin film which showed small ferromagnetic moment. Field and
temperature dependences of V 2 XMCD signals indicated the coexistence of
Curie-Weiss paramagnetic, antiferromagnetic, and possibly ferromagnetic V ions,
quantitatively consistent with the magnetization measurements. We attribute the
paramagnetic signal to V ions substituting Zn sites which are somewhat
elongated along the c-axis
Spin Driven Jahn-Teller Distortion in a Pyrochlore system
The ground-state properties of the spin-1 antiferromagnetic Heisenberg model
on the corner-sharing tetrahedra, pyrochlore lattice, is investigated. By
breaking up each spin into a pair of 1/2-spins, the problem is reduced to the
equivalent one of the spin-1/2 tetrahedral network in analogy with the valence
bond solid state in one dimension. The twofold degeneracy of the spin-singlets
of a tetrahedron is lifted by a Jahn-Teller mechanism, leading to a cubic to
tetragonal structural transition. It is proposed that the present mechanism is
responsible for the phase transition observed in the spin-1 spinel compounds
ZnVO and MgVO.Comment: 4 pages, 3 eps figures, REVTeX, to appear in Phys. Rev. Let
Species of Bursaphelenchus Fuchs, 1937 (Nematoda: Parasitaphelenchidae) and other nematode genera associated with insects from Pinus pinaster in Portugal
Insects associated with maritime pine, Pinus pinaster, in Portugal were collected
and screened for the presence of Bursaphelenchus species. Nematodes were
identified using Internal Transcribed Spacers-Restriction Fragment Length
Polymorphism (ITS-RFLP) analysis of dauer juveniles and morphological
identification of adults that developed from dauer juveniles on fungal cultures
or on cultures in pine wood segments at 26 C. Several associations are
described: Bursaphelenchus teratospicularis and Bursaphelenchus sexdentati are
associated with Orthotomicus erosus; Bursaphelenchus tusciae, B. sexdentati and/or
Bursaphelenchus pinophilus with Hylurgus ligniperda and Bursaphelenchus hellenicus
with Tomicus piniperda, Ips sexdentatus and H. ligniperda. An unidentified
Bursaphelenchus species is vectored by Hylobius sp. The previously reported
association of Bursaphelenchus xylophilus with Monochamus galloprovincialis
was confirmed. The association of Bursaphelenchus leoni with Pityogenes sp. is
not definitively established and needs further studies for clarification.
Other nematode genera besides Bursaphelenchus were found to be associated
with the insects sampled, including two different species of Ektaphelenchus, Parasitorhabditis
sp., Parasitaphelenchus sp., Contortylenchus sp. and other unidentified
nematodes. The Ektaphelenchus species found in O. erosus is morphologically
similar to B. teratospicularis found in the same insect; adults of both the species
are found in cocoon-like structures under the elytra of the insects.
Introduction
Approximately one third of the nematodes belonging to
the order Aphelenchida Siddiqi, 1980 are associated with
insects (Poinar, 1983). These nematodes establish a variety
of associations with the insects, which may be
described as commensalism, e.g. phoresy (to the benefit
of the nematode but not affecting the insect), mutualism
(both the organisms benefit) or parasitism (nematodes
benefit at the expense of the insect) (Giblin-Davis,
2004).
Most Bursaphelenchus Fuchs, 1937 species are mycetophagous,
feeding on fungi in the galleries of bark beetles
and thu
High-energy spectroscopic study of the III-V nitride-based diluted magnetic semiconductor GaMnN
We have studied the electronic structure of the diluted magnetic
semiconductor GaMnN ( = 0.0, 0.02 and 0.042) grown on Sn-doped
-type GaN using photoemission and soft x-ray absorption spectroscopy. Mn
-edge x-ray absorption have indicated that the Mn ions are in the
tetrahedral crystal field and that their valence is divalent. Upon Mn doping
into GaN, new state were found to form within the band gap of GaN, and the
Fermi level was shifted downward. Satellite structures in the Mn 2 core
level and the Mn 3 partial density of states were analyzed using
configuration-interaction calculation on a MnN cluster model. The deduced
electronic structure parameters reveal that the - exchange coupling in
GaMnN is stronger than that in GaMnAs.Comment: 6pages, 10figures. To be published to Phys. Rev.
Metal-insulator Crossover Behavior at the Surface of NiS_2
We have performed a detailed high-resolution electron spectroscopic
investigation of NiS and related Se-substituted compounds
NiSSe, which are known to be gapped insulators in the bulk at all
temperatures. A large spectral weight at the Fermi energy of the room
temperature spectrum, in conjunction with the extreme surface sensitivity of
the experimental probe, however, suggests that the surface layer is metallic at
300 K. Interestingly, the evolution of the spectral function with decreasing
temperature is characterized by a continuous depletion of the single-particle
spectral weight at the Fermi energy and the development of a gap-like structure
below a characteristic temperature, providing evidence for a metal-insulator
crossover behavior at the surfaces of NiS and of related compounds. These
results provide a consistent description of the unusual transport properties
observed in these systems.Comment: 12 pages, 3 figure
Soft x-ray magnetic circular dichroism study of Ca_1-xSr_xRuO_3 across the ferromagnetic quantum phase transition
Ca_1-xSr_xRuO_3, which is ferromagnetic for Sr concentration x > 0.3, has
been studied by x-ray magnetic circular dichroism (XMCD) in Ru 3p and O 1s
core-level x-ray absorption. XMCD signals appear at x ~ 0.3 and monotonically
increases with x in the ferromagnetic phase. While the monotonic increase of
the XMCD signals with x is of a typical Stoner-type, the absence of appreciable
change in the spectral line shapes of both the Ru 3p and O 1s XMCD spectra
indicate that the itinerant-electron ferromagnetism in Ca_1-xSr_xRuO_3 is
influenced by strong electron correlation.Comment: 5 pages, 4 figures, accepted in Phys. Rev. B 1 page, correct the 4th
affiliation 5 page, modifiy 9th referenc
- …