In-plane Anisotropy on Resistivity and Thermopower in The Misfit Layered Oxide Bi2-xPbxSr2Co2Oy

We investigated the in-plane anisotropy on the resistivity and thermopower of Bi2-xPbxSr2Co2Oy single crystals, which have a misfit structure between the hexagonal CoO2 layer and the rock salt Bi2Sr2O4 layer. The resistivity and thermopower show significantly large anisotropy, which exceeds two at maximum. This anisotropy would come from the anisotropic pseudogap formation enhanced by the misfit structure. The thermopower changes with Pb doping to take a maximum at x=0.4. The misfit structure improves the thermoelectric properties through chemical pressure. The power factor is as large as 9 muW/cmK2 at 100 K for x=0.6, which is the highest value for thermoelectric oxides at 100 K.Comment: 4 pages, 3 figures, submitted to Jpn. J. Appl. Phy

Sublimation Temperature of Circumstellar Dust Particles and Its Importance for Dust Ring Formation

Dust particles in orbit around a star drift toward the central star by the Poynting-Robertson effect and pile up by sublimation. We analytically derive the pile-up magnitude, adopting a simple model for optical cross sections. As a result, we find that the sublimation temperature of drifting dust particles plays the most important role in the pile-up rather than their optical property does. Dust particles with high sublimation temperature form a significant dust ring, which could be found in the vicinity of the sun through in-situ spacecraft measurements. While the existence of such a ring in a debris disk could not be identified in the spectral energy distribution (SED), the size of a dust-free zone shapes the SED. Since we analytically obtain the location and temperature of sublimation, these analytical formulae are useful to find such sublimation evidences.Comment: 9 pages, 5 figures, to be published in Earth Planets Spac

Dilatonic Inflation and SUSY Breaking in String-inspired Supergravity

The theory of inflation will be investigated as well as supersymmetry breaking in the context of supergravity, incorporating the target-space duality and the nonperturbative gaugino condensation in the hidden sector. We found an inflationary trajectory of a dilaton field and a condensate field which breaks supersymmetry at once. The model satisfies the slow-roll condition which solves the eta-problem. When the particle rolls down along the minimized trajectory of the potential V(S,Y) at a duality invariant point of T=1, we can obtain the e-fold value \sim 57. And then the cosmological parameters obtained from our model well match the recent WMAP data combined with other experiments. This observation suggests one to consider the string-inspired supergravity as a fundamental theory of the evolution of the universe as well as the particle theory.Comment: 10 pages, 4 eps figures. Typos and references corrected. Final version to appear in Mod. Phys. Lett.

Real-time Failure Monitoring System for High Power IGBT Under Acceleration Test Up to 500 A Stress

Real-time failure monitoring system for IGBT module was demonstrated under 500 A power cycling test. The system successfully captured internal phenomena occurred in interface regions of the device under test. Moreover, we proposed realtime failure analysis method by combining the real-time monitoring and image processing techniques. This failure analysis method enables to distinguish the place where degradation occurs in DUT and also trace internal degradation process to failure.2014 IEEE 26th International Symposium on Power Semiconductor Devices & IC\u27s (ISPSD), Jun 15-19, 2014, Hilton Waikoloa Village, Hawaii, US

Internal Degradation Monitoring of Power Devices During Power Cycling Test

A technique to monitor internal degradation to failure of power devices in real time was proposed. Required components for this technique are (1) non-destructive inside imaging, (2) power stress control and (3) device cooling. We constructed the system with scanning acoustic tomography (SAT), DC power supply controlled by own made program and water cooling system, respectively. In the case of a TO-3P packaged MOSFET, propagation of internal degradations to failure was successfully recorded as time series data by using this system. At the present time, the system is modified for high power and large size IGBT modules.8th International Conference on Integrated Power Electronics Systems (CIPS 2014), February 25-27, 2014, Nuremberg, German

Real Time Monitoring System for Internal Process to Failure of High Power IGBT

A real time failure analysis system for widely used high power IGBT modules is proposed, which enables to inspect internal process to failure of the devices under power stress test as a movie. This system was realized by combining a scanning acoustic tomography (SAT/SAM), power stress controlling, device cooling, water jet system and chip temperature monitoring. This system successfully obtained internal images of a DUT under the load current of 200A.2013 International Conference on Solid State Devices and Materials (SSDM2013), September 24-27, 2013, Hilton Fukuoka Sea Hawk, Fukuoka, Japa

Evaporation of Fe and FeS dust in the active stage of the primordial solar nebula, and Fe/S fractionation

The evaporation kinetics of troilite and metallic iron was applied to evaporation of dust particles moving toward the protosun in the turbulent solar nebula. In the calculations, it was assumed that dust particles do not grow by collision, evaporated gas and residual dust are not separated, and dust particles move only radially along the midplane or the surface of the nebula. It was found that evaporation of metallic iron would occur almost in equilibrium both along the midplane and the surface. Troilite could survive to higher temperature than the equilibrium evaporation temperature due to its evaporation kinetics. However, the kinetic effects are not so large, and the incongruent evaporation of troilite is also regarded to occur roughly in equilibrium. The timescales for evaporation of metallic iron and troilite were compared with the timescales for drifts along r-and z-directions and that for coagulation to understand general aspects of the effect of evaporation kinetics. Since the temperature of the surface is lower than that of the midplane, dust particle at the surface can get closer to the sun than those at the midplane. This can cause Fe/S fractionation in a wide range of the nebula if effective solid-gas separation occurred