Optical conductivity of the Kondo insulator YbB_12: Gap formation and low-energy excitations

Optical reflectivity experiments have been conducted on single crystals of the Kondo insulator YbB_12 in order to obtain its optical conductivity, \sigma(\omega). Upon cooling below 70 K, a strong supression of \sigma(\omega) is seen in the far-infrared region, indicating the opening of an energy gap of ~ 25 meV. This gap development is coincident with a rapid decrease in the magnetic susceptibility, which shows that the gap opening has significant influence on magnetic properties. A narrow, asymmetric peak is observed at ~40 meV in \sigma(\omega), which is attributed to optical transitions between the Yb 4f-derived states across the gap. In addition, a broad peak is observed at ~0.25 eV. This peak is attributed to transitions between Yb 4f-derived states and p-d band, and is reminiscent of similar peaks previously observed for rare-earth hexaborides.Comment: 4 pages, 4 figure

Stable Existence of Phase IV inside Phase II under Pressure in Ce0.8_{0.8}La0.2_{0.2}B6_{6}

We investigate the pressure effect of the electrical resistivity and magnetization of Ce$_{0.8}$La$_{0.2}$B$_{6}$. The situation in which phase IV stably exists inside phase II at H=0 T could be realized by applying a pressure above $P\sim 1.1$ GPa. This originates from the fact that the stability of phase II under pressure is larger than those of phases IV and III. The results seem to be difficult to reproduce by taking the four interactions of $\Gamma_{\mathrm{5u}}$-type AFO, $O_{xy}$-type AFQ, $T_{xyz}$-type AFO, and AF exchange into account within a mean-field calculation framework.Comment: 4 pages, 5 figures, to appear in J. Phys. Soc. Jpn. 79 (2010) No.

Beitrag zum Problem über den Einflnss der Inhalation von mit CO(2) versetzter Luft auf verschiedene Symptome, die sicn bei Unterdruck einstellen

Im Jahre 1935 stellte Professor Dr. Oinuma mit seinem Kollegen bei der Besteigung des Fuji (3776 Meter uber dem Meeresspiegel) fest, dass die Inhalation von mit CO(2) versetzter Luft einen gunstigen Einfluss auf die Bergkrankheit ausubt. Wir stellten bezuglich dieses Punktes experimentelle Untersuchungen in der Unterdruckkammer unseres Laboratoriums an, unter Mithilfe unserer Kollegen als Versuchspersonen. Dabei wurden die Zusammensetzung und das Volumen der Expirationsluft, der Prozentsatz von O(2) und CO(2) der Alveolarluft (nach der Haldane'schen Methode), sowie auch die Gase im arteriellen Blut (nach der Slyke'schen Methode) gemessen. Die Resultate lassen sich folgendermassen zusammen fassen: 1) Bei allen Versuchspersonen tritt bei Unterdruck, infolge der Hyperventilation der Lunge, stets "Akapnie" ein, 2) Wird bei Unterdruck Luft eingeatmet, welcher CO(2) zugesetzt wurde, so nimmt die Atembewegung und der CO(2)- und der O(2)-gehalt der Expirationsluft und der Alveolarluft zu. Der respiratorische Quotient aber bleibt unverandert. Dies führt natürlich zu einer Zunahme des CO(2)- und O(2)-gehaltes im Blut. Diese Sauerstoffzunahme im Blut ubt demnach u. E. einen gunstigen Einfluss auf die verschiedenen Symptome aus, die unter vermindertem Luftdruck entstehen

Numerical investigation of thermodynamic effect on unsteady cavitation in cascade

In the present study, the thermodynamic effect on unsteady cavitation is investigated in cascade in water and liquid nitrogen at different freestream temperatures. Cavitation flowfield is simulated based on self-developed locally homogeneous model of a compressible gasliquid two-phase medium, which is available to treat unsteady cavitation. For calculation of thermodynamic effect on cavitation, simplified thermodynamic model for the locally homogenous medium is used where local saturated vapor pressure changes with depending on rate of heat transfer by evaporation and condensation. In the result of the numerical analysis, the difference of cavitating flowfields is reproduced numerically in water and liquid nitrogen at different freestream temperature concerning the cavity surface profile and distribution of the evaporation region. Also the thermodynamic effect on cavitation in water and liquid nitrogen is investigated by comparing the cavity volumes. Then, well known thermodynamic effect on cryogenic cavitation can be reproduced numerically in liquid nitrogen, where development of the cavity is suppressed according to increase of freestream temperature. On the other hand, the inverse thermodynamic effect, which is experimentally observed in single hydrofoil in water, is reproduced under the condition of unsteady cavitation in water in the present study.http://deepblue.lib.umich.edu/bitstream/2027.42/84272/1/CAV2009-final78.pd

Evidence for short-range antiferromagnetic fluctuations in Kondo-insulating YbB12

The spin dynamics of mixed-valence YbB12 has been studied by inelastic neutron scattering on a high-quality single crystal. In the Kondo-insulating regime realized at low temperature, the spectra exhibit a spin-gap structure with two sharp, dispersive, in-gap excitations at E = 14.5 and approximately 20 meV. The lower mode is shown to be associated with short-range correlations near the antiferromagnetic wave vector q0 = (1/2, 1/2, 1/2). Its properties are in overall agreement with those expected for a "spin exciton'' branch in an indirect hybridization gap semiconductor.Comment: 4 pages, 4 figures ; submitted to Physical Review Letter

Numerical prediction of cavitation erosion in cavitating flow

In this study bubble behavior in cavitating flow is analyzed and prediction of cavitation erosion in 2D cavitating flow around ClarkY 11.7 % hydrofoil at several cavitation is performed by impact pressure induced by bubble collapse. Our numerical method predicts that the impact energy is small if variation of cavitating flow is small and that the position of peak impact energy moves downstream with the decrease in cavitation number until the maximum sheet cavity length becomes larger than chord length. When the maximum sheet cavity length becomes larger than chord length, there are not obvious peak values and relatively weak erosion occurs. And it is found that high impact pressures are mainly induced by bubbles in a cloud and in the vicinity of sheet cavity termination during a cloud collapse. Therefore large impact energy occurs when the cloud cavity collapses near the hydrofoil, the sheet cavity termination is on the hydrofoil and the number of bubble is large in these cavities.http://deepblue.lib.umich.edu/bitstream/2027.42/84264/1/CAV2009-final67.pd

Microfabrication and Application of Series-Connected PZT Elements

AbstractThis paper presents series-connected PZT elements that yield high output voltage, and also shows complete establishment in the fabrication process. Series-connected PZT elements are realized by connecting the upper electrode of a PZT element with the lower electrode of another PZT element. Sputtered PZT thin-film has perovskite crystalline structure and piezoelectric coefficients up to 40 pC/N. To avoid troublesome wet etching, the PZT films, the electrodes, and insulation layers are dry-etched. The all dry-etching process performs multilayer wiring of the electrodes. Evaluations for the PZT elements validates that the output voltage is the sum output voltage of each single element