361 research outputs found
On the solar cycle variation in the barometer coefficients of high latitude neutron monitors
Evaluation of barometer coefficients of neutron monitors located at high latitudes has been performed by using the results of the spherical harmonic analysis based on the records from around twenty stations for twelve years from January 1966 to December 1977. The average of data at eight stations, where continuous records are available for twelve years, show that the absolute value of barometer coefficient is in positive correlation with the cosmic ray neutron intensity. The variation rate of the barometer coefficient to the cosmic ray neutron intensity is influenced by the changes in the cutoff rigidity and in the primary spectrum
Optical conductivity of rattling phonons in type-I clathrate BaGaGe
A series of infrared-active optical phonons have been detected in type-I
clathrate BaGaGe by terahertz time-domain spectroscopy. The
conductivity spectra with the lowest-lying peaks at 1.15 and 1.80 THz are
identified with so-called rattling phonons, i.e., optical modes of the guest
ion Ba with symmetry in the oversized tetrakaidecahedral
cage. The temperature dependence of the spectra from these modes are totally
consistent with calculations based on a one-dimensional anharmonic potential
model that, with decreasing temperature, the shape becomes asymmetrically sharp
associated with a softening for the weight to shift to lower frequency. These
temperature dependences are determined, without any interaction effects, by the
Bose-factor for optical excitations of anharmonic phonons with the nonequally
spaced energy levels.Comment: 4 pages, 4 figure
Magnetic excitations in SrCu2O3: a Raman scattering study
We investigated temperature dependent Raman spectra of the one-dimensional
spin-ladder compound SrCu2O3. At low temperatures a two-magnon peak is
identified at 3160+/-10 cm^(-1) and its temperature dependence analyzed in
terms of a thermal expansion model. We find that the two-magnon peak position
must include a cyclic ring exchange of J_cycl/J_perp=0.09-0.25 with a coupling
constant along the rungs of J_perp approx. 1215 cm^(-1) (1750 K) in order to be
consistent with other experiments and theoretical results.Comment: 4 pages, 3 figure
Far-Infrared Spectroscopy in Spin-Peierls Compound CuGeO_3 under High Magnetic Fields
Polarized far-infrared (FIR) spectroscopic measurements and FIR
magneto-optical studies were performed on the inorganic spin-Peierls compound
CuGeO_3. An absorption line, which was found at 98 cm in the dimerized
phase (D phase), was assigned to a folded phonon mode of B symmetry. The
splitting of the folded mode into two components in the incommensurate phase
(IC phase) has been observed for the first time. A new broad absorption
centered at 63 cm was observed only in the axis
polarization, which was assigned to a magnetic excitation from singlet ground
state to a continuum state.Comment: 9 pages multicolREVTeX, 10 figure
Spin-phonon coupled modes in the incommensurate phases of doped CuGeO
The doping effect of the folded phonon mode at 98 cm was investigated
on the Si-doped CuGeO by magneto-optical measurements in far-infrared (FIR)
region under high magnetic field. The folded phonon mode at 98 cm
appears not only in the dimerized (D) phase but also in the
dimerized-anitiferromagnetic (DAF) phase on the doped CuGeO. The splitting
was observed in the incommensurate (IC) phase and the antiferromagnetically
ordered incommensurate (IAF) phase above . The split-off branches exhibit
different field dependence from that of the pure CuGeO in the vicinity of
, and the discrepancy in the IAF phase is larger than that in the IC
phase. It is caused by the interaction between the solitons and the impurities.Comment: 7 pages, 4 figures, resubmitted to Phys. Rev.
Reirradiation of head and neck cancer focusing on hypofractionated stereotactic body radiation therapy
Reirradiation is a feasible option for patients who do not otherwise have treatment options available. Depending on the location and extent of the tumor, reirradiation may be accomplished with external beam radiotherapy, brachytherapy, radiosurgery, or intensity modulated radiation therapy (IMRT). Although there has been limited experience with hypofractionated stereotactic radiotherapy (hSRT), it may have the potential for curative or palliative treatment due to its advanced precision technology, particularly for limited small lesion. On the other hand, severe late adverse reactions are anticipated with reirradiation than with initial radiation therapy. The risk of severe late complications has been reported to be 20- 40% and is related to prior radiotherapy dose, primary site, retreatment radiotherapy dose, treatment volume, and technique. Early researchers have observed lethal bleeding in such patients up to a rate of 14%. Recently, similar rate of 10-15% was observed for fatal bleeding with use of modern hSRT like in case of carotid blowout syndrome. To determine the feasibility and efficacy of reirradiation using modern technology, we reviewed the pertinent literature. The potentially lethal side effects should be kept in mind when reirradiation by hSRT is considered for treatment, and efforts should be made to minimize the risk in any future investigations
Pressure induced Superconductor-Insulator transition in the spinel compound CuRh2S4
We performed resistivity measurements in CuRhS under
quasi-hydrostatic pressure of up to 8.0 GPa, and found a pressure induced
superconductor-insulator (SI) transition. Initially, with increasing pressure,
the superconducting transition temperature increases from 4.7 K at
ambient pressure to 6.4 K at 4.0 GPa, but decreases at higher pressures. With
further compression, superconductivity in CuRhS disappears abruptly
at a critical pressure between 5.0 and 5.6 GPa, when it becomes an
insulator.Comment: 4 pages, 4 figure
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