174 research outputs found
Manifestation of a nontrivial vacuum in discrete light cone quantization
We study a (1+1)-dimensional model with a light-cone zero
mode and constant external source to describe spontaneous symmetry breaking. In
the broken phase, we find degenerate vacua and discuss their stability based on
effective-potential analysis. The vacuum triviality is spurious in the broken
phase because these states have lower energy than Fock vacuum. Our results are
based on the variational principle.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Let
Brain Activity Stimulated by Prism Adaptation Tasks Utilized for the Treatment of Unilateral Spatial Neglect: A Study with fNIRS
We investigated the neurological basis for efficacy of prism adaptation therapy, which is used for the treatment of poststroke unilateral spatial neglect (USN). Study subjects were 6 USN-positive (+), 6 USN-negative patients, and 6 healthy volunteer control subjects. USN was identified by the Behavioural Inattention Test (BIT). During the tasks, brain activity was assessed with fNIRS via changes in oxyHb concentration per unit length. There was no significant difference in the number of errors in the task between the 3 groups. However, in the USN(+) group there was a significantly greater reduction in oxyHb levels in the right parietal association cortex during the prism adaptation task than in the other 2 groups (P < 0.05). There was an immediate improvement in USN symptoms as well as a significant increase in oxyHb levels during the prism adaptation in the channels covering the right frontal and parietal lobes in 2 patients in the USN(+) group (P < 0.05). This result suggested that decreased activity in the right parietal association cortex, which is related to spatial perception, during the prism adaptation task and task-induced reorganization of the right frontal and parietal areas were involved in improvement in USN symptoms
The study of quadrupole phase diagrams and the multipole fluctuations by NMR and magnetization measurements in PrTi2Al(20)
学位の種別: 課程博士審査委員会委員 : (主査)東京大学教授 瀧川 仁, 東京大学教授 芝内 孝禎, 東京大学教授 中辻 知, 東京大学教授 木村 剛, 東京大学教授 鹿野田 一司University of Tokyo(東京大学
Search for the field-induced magnetic instability around the upper critical field of superconductivity in H || c in CeCoIn5
We present nuclear spin-lattice relaxation rate (1/T1) at the Co site and
ac-susceptibility results in the normal and superconducting (SC) states of
CeCoIn5 for H || c near the SC upper critical field Hc2 above 0.1 K. At 4.2 T,
1/T1 rapidly decreases below the SC transition temperature, consistent with the
previous reports. Although the field dependence of 1/T1T at 0.1 K shows a peak
at 5.2 T above Hc2, the temperature dependence of 1/T1T at 5.2 T is independent
of temperature below 0.2 K, showing a Fermi-liquid behavior. In addition, we
found no NMR-spectrum broadening by the appearance of internal fields around
Hc2 at 0.1 K. We could not detect any field-induced magnetic instability around
Hc2 down to 0.1 K although the remarkable non-Fermi-liquid behavior towards Hc2
was observed in various physical quantities.Comment: 6 pages, 3 figure
Magnetic Instability of Pr3Ru4Sn13
We report on the quantum criticality of PrRuSn revealed by our
new material research. PrRuSn has been synthesized by flux
growth and characterized by single X-ray, powder X-ray, and powder neutron
diffraction measurements. The compound adopts a YbRhSn-type
structure with a cubic Pmn. From the magnetization at 1 T, the
effective magnetic moment was estimated to be 3.58 per Pr,
suggesting that the magnetism is mainly contributed by Pr ions. The
specific heat and magnetization show an anomaly at ~ K owing to
the phase transition. The muon spin rotation and relaxation (SR) time
spectra exhibit clear oscillations below . This suggests that the phase is
magnetically ordered. The volume fraction of the magnetic phase estimated from
the initial asymmetry is around ten percent. In addition, spin fluctuations
were observed at low temperatures. These results provide microscopic evidence
that the material is closest to the antiferromagnetically quantum critical
point with a partial order among PrSn ( Co, Ru, Rh).Comment: 14 pages, 4 figures, accepted for publication in J. Phys. Soc. Jp
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