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Norita Kawanaka,Rohta Takahashi,Shin Mineshige 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.3
We calculated the iron line proles for Advection-dominated accretion ow (ADAF) using numerical data for the velocity elds and we compared the results with the proles for the case when the inner edge is identical with rms, the radius of the marginally stable orbit. We can conclude that the broadened red wing of the iron line prole can be associated with a non-rotating black hole. The iron K uorescent line emitted from accretion disks provides us with plausible evidence of strong gravitational elds around black holes. When calculating the line prole, many previous studies assumed that there was no material, and no line emission, inside rms. In those studies, the broadened and red-shifted iron lines that had been observed in some Seyfert galaxies could be explained by rapidly rotating black holes because they had values smaller rms than 3rg (rms for non-rotating black holes). Some recent studies show, however, that the inner radius of an accretion disk does not always coinside with rms. We will discuss the possibility that iron line emission from inside the marginally stable orbit of a black hole might signicantly contribute to the line prole.
A Neutrino-Cooled Accretion Disk as the Central Engine of Gamma-ray Bursts
Norita Kawanaka,Shin Mineshige,Shigehiro Nagataki 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.4
It is often theoretically hypothesized that the enormous power released from gamma-ray bursts is generated by the accretion of a massive torus with approximately a solar mass onto a stellar-mass black hole. Such a torus (or disk) would become so dense and hot that the main cooling process would be neutrino radiation. We study the steady-state structure of this disk and consider the degeneracy of electrons and neutrinos, the opacity of neutrinos, and the equation of state of nuclear matter. The stability of the disk is also discussed.
Mohammad A. Hasnat,Sami Ben Aoun,Mohammed M. Rahman,Abdullah M. Asiri,Norita Mohamed 한국공업화학회 2015 Journal of Industrial and Engineering Chemistry Vol.28 No.-
Asymmetric reactors having the configuration (PtjNafionjM–Cu, M = Pt, Pd) were designed and appliedto the electrocatalytic nitrate reduction reaction (NRR) with no supporting electrolyte. Theelectrochemically–fabricated Cu–M (M = Pt, Pd) catalysts showed a highly-efficient catalytic activityby effectively reducing more than ca. 99% of nitrate ions, under static-reactor conditions, with first-orderrate constants of ca. 0.040 min 1 and ca. 0.057 min 1 for Cu–Pt and Cu–Pd, respectively. Similarreactivity trends were observed under flow mode irrespective of flow rates while NRR rates werepredominantly controlled by diffusion-limited mass-transfer. A maximum of ca. 93% nitrate removal atCu–Pd catalyst was achieved within ca. 60 min. The comparatively lower CuO content of ca. 9%, asconfirmed by XANES, resulted in a greater number of free NRR active sites inducing the superior catalyticactivity of the Cu–Pd catalyst. On the other hand, NRR product selectivity investigations showed that Cu–Pd catalyst was highly ammonia–selective with a maximum of ca. 24% selectivity at a flow rate of0.1 mL min 1, while Cu–Pt catalyst was much selective to intermediate nitrite ions reaching a maximumof ca. 35% selectivity at the same flow rate.
Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Kobayashi, M.,Moriyama, S.,Nakahata, M.,Norita, T.,Ogawa, H.,Sato, K.,Sekiya, H.,Takachio, O.,Takeda, A.,Tasaka, S.,Yamashita, M.,Yang, B.S Elsevier 2018 Nuclear Instruments & Methods in Physics Research. Vol.884 No.-
<P><B>Abstract</B></P> <P>We established a method to assay <SUP>210</SUP>Pb and <SUP>210</SUP>Po contaminations in the bulk of copper samples using a low-background alpha particle counter. The achieved sensitivity for the <SUP>210</SUP>Pb and <SUP>210</SUP>Po contaminations reaches a few mBq/kg. Due to this high sensitivity, the <SUP>210</SUP>Pb and <SUP>210</SUP>Po contaminations in oxygen free copper bulk were identified and measured for the first time. The <SUP>210</SUP>Pb contaminations of our oxygen free copper samples were 17–40 mBq/kg. Based on our investigation of copper samples in each production step, the <SUP>210</SUP>Pb in oxygen free copper was understood to be a small residual of an electrolysis process. This method to measure bulk contaminations of <SUP>210</SUP>Pb and <SUP>210</SUP>Po could be applied to other materials.</P>
Direct dark matter search by annual modulation with 2.7 years of XMASS-I data
Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Kobayashi, M.,Moriyama, S.,Nakahata, M.,Norita, T.,Ogawa, H.,Sato, K.,Sekiya, H.,Takachio, O.,Takeda, A.,Tasaka, S.,Yamashita, M.,Yang, B. American Physical Society 2018 Physical Review D Vol.97 No.10
<P>An annual modulation signal due to the Earth orbiting around the Sun would be one of the strongest indications of the direct detection of dark matter. In 2016, we reported a search for dark matter by looking for this annual modulation with our single-phase liquid xenon XMASS-I detector. That analysis resulted in a slightly negative modulation amplitude at low energy. In this work, we included more than one year of additional data, which more than doubles the exposure to 800 live days with the same 832 kg target mass. When we assume weakly interacting massive particle (WIMP) dark matter elastically scattering on the xenon target, the exclusion upper limit for the WIMP-nucleon cross section was improved by a factor of 2 to 1.9 x 10(-41) cm(2) at 8 GeV/c(2) at 90% confidence level with our newly implemented data selection through a likelihood method. For the model-independent case, without assuming any specific dark matter model, we obtained more consistency with the null hypothesis than before with a p-value of 0.11 in the 1-20 keV energy region. This search probed this region with an exposure that was larger than that of DAMA/LIBRA. We also did not find any significant amplitude in the data for periodicity with periods between 50 and 600 days in the energy region between 1 to 6 keV.</P>
XMASS Collaboration,Takiya, H.,Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Kobayashi, M.,Moriyama, S.,Nakahata, M.,Norita, T.,Ogawa, H.,Sekiya, H.,Takachio, O.,Takeda, A.,Tasaka, S.,Y North-Holland 2016 Nuclear Instruments & Methods in Physics Research. Vol.834 No.-
We report the measurement of the emission time profile of scintillation from gamma-ray induced events in the XMASS-I 832kg liquid xenon scintillation detector. Decay time constant was derived from a comparison of scintillation photon timing distributions between the observed data and simulated samples in order to take into account optical processes such as absorption and scattering in liquid xenon. Calibration data of radioactive sources, <SUP>55</SUP>Fe, <SUP>241</SUP>Am, and <SUP>57</SUP>Co were used to obtain the decay time constant. Assuming two decay components, τ<SUB>1</SUB> and τ<SUB>2</SUB>, the decay time constant τ<SUB>2</SUB> increased from 27.9ns to 37.0ns as the gamma-ray energy increased from 5.9keV to 122keV. The accuracy of the measurement was better than 1.5ns at all energy levels. A fast decay component with τ<SUB>1</SUB>~2ns was necessary to reproduce data. Energy dependencies of τ<SUB>2</SUB> and the fraction of the fast decay component were studied as a function of the kinetic energy of electrons induced by gamma-rays. The obtained data almost reproduced previously reported results and extended them to the lower energy region relevant to direct dark matter searches.