We made stereoscopic observations of the Vela Pulsar region with two of the 10 m diameter CANGAROO-III imaging atmospheric Cherenkov telescopes in January and February, 2004, in a search for sub-TeV gamma-rays from the pulsar and surrounding regions. We describe the observations, provide a detailed account of the calibration methods, and introduce the improved and bias-free analysis techniques employed for CANGAROO-III data. No evidence of gamma-ray emission is found from either the pulsar position or the previously reported position offset by 0.13 degree, and the resulting upper limits are a factor of five less than the previously reported flux from observations with the CANGAROO-I 3.8 m telescope. Following the recent report by the H.E.S.S. group of TeV gamma-ray emission from the Pulsar Wind Nebula, which is ∼0.5 degree south of the pulsar position, we examined this region and found supporting evidence for emission extended over ∼0.6 degree.
Sub-TeV gamma-ray emission from the northwest rim of the supernova remnant RX J0852.0À4622 was detected with the CANGAROO II telescope and recently confirmed by the HESS group. In addition, the HESS data revealed a very wide (up to 2 in diameter), shell-like profile of the gamma-ray emission. We carried out CANGAROO III observations in 2005 January and February with three telescopes and show here the results of threefold coincidence data. We confirm the HESS results about the morphology and the energy spectrum and find that the energy spectrum in the NW rim is consistent with that of the whole remnant.
We have observed the giant radio galaxy Centaurus A and the globular cluster ! Centauri in the TeV energy region using the CANGAROO III stereoscopic system. The system has been in operation since 2004 with an array of four Imaging Atmospheric Cerenkov Telescopes (IACT) with $100 m spacings. The observations were carried out in 2004 March and April. In total, approximately 10 hr of data were obtained for each target. No statistically significant gammaray signal has been found above 420 GeV over a wide angular region (a 1 radius from the pointing center), and we derive flux upper limits using the wholefield of view. Implications for the total energy of cosmic rays and the density of the cold dark matter are considered.
Ferroelectric (FE)-HfO2 based FETs (FEFETs) are one of the most promising candidates for emerging memories. However, the FE material suffers from a unique reliability phenomenon known as imprint: the coercive voltage shifts during data retention, which has been regarded as a major issue for memory operation, while the mechanism causing it is still under research. In this paper, imprint and its recovery in FE-HfO2 are investigated in detail by comprehensive electrical measurements to reveal its underlying mechanism including the cause of asymmetric coercive voltage shifts. The recovery measurements clarify that domain switching is indispensable for the recovery from imprint. The sub-loop imprint effect shows that imprint and its recovery must be independent for each domain. In addition, switching time measurements and corresponding fitting results with the nucleation-limited-switching (NLS) model strongly indicate that imprint is caused by domainseeds-pinning. Based on these results, we conclude that charge trapping and de-trapping affecting activation barriers for domain switching, accompanied by domain switching is responsible for imprint and its recovery.
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