An Electronic Model for CoO2CoO_2 layer based systems: Chiral RVB metal and Superconductivity

Takada et al. have reported superconductivity in layered Na__x CoO_2.yH_2O ($T_c \approx5 K$) and more recently Wen et al. in $A_xCoO_{2+\delta}$ ($A = Na,K$)(\tc$\approx~31 K$). We model a reference neutral \cob layer as an orbitally non-degenerate spin-\half antiferromagnetic Mott insulator on a triangular lattice and Na__x CoO_2.yH_2O and $A_xCoO_{2+\delta}$ as electron doped Mott insulators described by a t-J model. It is suggested that at optimal doping chiral spin fluctuations enhanced by the dopant dynamics leads to a d-wave superconducting state. A chiral RVB metal, a PT violating state with condensed RVB gauge fields, with a possible weak ferromagnetism and low temperature p-wave superconductivity are also suggested at higher dopings.Comment: 4 pages of LaTex file, 6 figures in eps files. Typos and minor corrections mad

16-channnel Micro Magnetic Flux Sensor Array for IGBT Current Distribution Measurement

Current crowding of IGBT and power diode in a chip or among chips is a barrier to the realization of highly-reliable power module and power electronics system. Current crowding occurs because of the parasitic inductance, difference of chip characteristics or temperature imbalance among chips. Although current crowding among IGBT or power diode chips has been analysed on numerical simulations, no sensor with sufficiently high special resolution and fast measurement time has yet been demonstrated. Therefore, the author developed and demonstrated 16-channel flat sensitivity sensor array for IGBT current distribution measurement. The sensor array consists of tiny-scale film sensors with analog amps and shield case against noise. The array and digital calibration method will be applied for reliability analysis, designing and screening of IGBT modules.ESREF 2015, 26th European Symposium on Reliability of Electron Devices, Failure Physics and Analysis, Oct 5-9, 2015, Centre de Congrès Pierre Baudis, Toulouse, Franc

High-throughput and Full Automatic DBC-Module Screening Tester for High Power IGBT

We developed a high-throughput screening tester for DBC-module of IGBT. The tester realizes a new screening test with current distribution in addition to a conventional switching test. It consists of a power circuit, a replaceable test head, sensor array module and digitizer with LabVIEW program. Therefore, all kinds of DBC-modules can be screened by switching the test head. The tester acquires magnetic field signals and displays GO/NOGO judgment automatically after digital calibration and signal processing in 10 seconds. It is expected to be applied for screening in a production line and analysis in order to prevent the failure of power modules.ESREF 2015, 26th European Symposium on Reliability of Electron Devices, Failure Physics and Analysis, Oct 5-9, 2015, Centre de Congrès Pierre Baudis, Toulouse, Franc

Perceptions of the COVID-19 pandemic in Japan with respect to cultural, information, disaster and social issues

A questionnaire survey was distributed via the Internet to 600 respondents. Preliminary results revealed that most Japanese people regularly washed their hands and had low resistance to wearing masks even before the COVID-19 pandemic. Internet news was the most common source of information. Half of the respondents said they would “stay at home evacuation” if a disaster occurred during the COVID-19 pandemic, reflecting the strategy promoted to reduce crowding in evacuation shelters. If a state of emergency must be reinstated, one-third of respondents said they could bear it for a few months and another one-third for a few weeks

Semiclassical theory of electron drag in strong magnetic fields

We present a semiclassical theory for electron drag between two parallel two-dimensional electron systems in a strong magnetic field, which provides a transparent picture of the most salient qualitative features of anomalous drag phenomena observed in recent experiments, especially the striking sign reversal of drag at mismatched densities. The sign of the drag is determined by the curvature of the effective dispersion relation obeyed by the drift motion of the electrons in a smooth disorder potential. Localization plays a role in explaining activated low temperature behavior, but is not crucial for anomalous drag per se.Comment: 10 page

A Novel Longitudinal Mode in the Coupled Quantum Chain Compound KCuF3

Inelastic neutron scattering measurements are reported that show a new longitudinal mode in the antiferromagnetically ordered phase of the spin-1/2 quasi-one-dimensional antiferromagnet KCuF3. This mode signals the cross-over from one-dimensional to three-dimensional behavior and indicates a reduction in the ordered spin moment of a spin-1/2 antiferromagnet. The measurements are compared with recent quantum field theory results and are found to be in excellent agreement. A feature of the data not predicted by theory is a damping of the mode by decay processes to the transverse spin-wave branches.Comment: 9 pages of text plus 4 postscript figures (1 color

Short-Circuit Protection for an IGBT with Detecting the Gate Voltage and Gate Charge

This paper proposes a new short-circuit protection method for an IGBT. The proposed method is characterized by detecting not only gate charge but also gate voltage of the IGBT. This results in a shorter protection time, compared to the previous method that detects only the gate charge. A real-time monitoring system using an FPGA, A/D converters, and a D/A converter is used for the proposed protection method. Experimental results verify that the proposed method achieves a protection time of 390 ns, which is reduced by 68% compared to the previous method.ESREF 2014, 25th EUROPEAN SYMPOSIUM ON RELIABILITY OF ELECTRON DEVICES,FAILURE PHYSICS AND ANALYSIS, Sep 29–Oct 3, 2014, Technische Universität Berli