Ryuichi Matsuba

p-process nucleosynthesis inside supernova-driven supercritical accretion disks

We investigate p-process nucleosynthesis in a supercritical accretion disk around a compact object of 1.4 M☉, using the self-similar solution of an optically thick advection-dominated flow. Supercritical accretion is expected to occur in a supernova with fallback material accreting onto a newborn compact object. It is found that an appreciable number of p-nuclei are synthesized via the p-process in supernova-driven supercritical accretion disks (SSADs) when the accretion rate = c2/(16LEdd) > 105, where LEdd is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSADs have features similar to those of the oxygen/neon layers in Type II supernovae when the abundance of the fallback gas far from the compact object is that of the oxygen/neon layers in the progenitor. The overall abundance profile is in agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and La, are underproduced in the SSADs as in Type II supernovae. If the fallback gas is mixed with a small fraction of protons through Rayleigh-Taylor instability during the explosion, significant amounts of 92Mo are produced inside the SSADs. Isotopes 96Ru and 138La are also produced when the fallback gas contains abundant protons, although the overall abundance profile of p-nuclei is rather different from that of the solar system. The p-process nucleosynthesis in SSADs contributes to the chemical evolution of p-nuclei, in particular 92Mo, if several percent of the fallback matter are ejected via jets and/or winds.

Nucleosynthesis inside an accretion disk and disk winds related to gamma-ray bursts

We investigate nucleosynthesis inside both a gamma-ray burst accretion disk and a wind launched from an inner region of the disk using one-dimensional models of the disk and wind and a nuclear reaction network. Far from a central black hole, the composition of accreting gas is taken to be that of an O-rich layer of a massive star before core collapse. We find that the disk consists of five layers characterized by dominant elements: O16, Si28, Fe54 (and Ni56), He4, and nucleons, and the individual layers shift inward with keeping the overall profiles of compositions as the accretion rate decreases. Ni56 are abundantly ejected through the wind from the inner region of the disk with the electron fraction \simeq 0.5. In addition to iron group, elements heavier than Cu, in particular Cu63 and Zn64, are massively produced through the wind. Various neutron-rich nuclei can be also produced in the wind from neutron-rich regions of the disk, though the estimated yields have large uncertainties.We investigate nucleosynthesis inside both a gamma-ray burst accretion disk and a wind launched from an inner region of the disk using one-dimensional models of the disk and wind. Far from a central black hole, the composition of accreting gas is taken to be that of an Si-rich or O-rich layer of a massive star before core collapse. We find that the inner region of the disk comprises five layers characterized by dominant elements: 16O, 28Si, 54Fe (and 56Ni), 4He, and nucleons. As the accretion rate decreases, the individual layers shift inward, retaining the overall profiles of compositions. A massive amount of 56Ni, over 0.1 M☉, is ejected through the wind from the disk where the electron fraction 0.5. The amount of 56Ni produced through the disk wind can be responsible for the light curves observed at the late stage in hypernovae (HNe). The yields of elements heavier than Ca produced via the disk wind are comparable to or greater than those of a normal supernova and their composition is similar to that of an aspherical HN explosion. A significant amount of Ga, Ge, and Se is ejected from the disk. A variety of neutron-rich elements, as well as p-nuclei, are also appreciably produced through the disk wind.

Web-based time schedule system for multiple LMSs on the SSO/portal environment

We developed a web-based time schedule system as an important feature of the university portal along with our universitys long-term ICT (Information and Communication Technologies) plan. By using the system, students and professors can get their own course timetable in collaboration with the Student Information System (SIS). Each course name on the timetable is linked to the corresponding course page on the Learning Management System (LMS) through the Single Sign-On (SSO). The system is adapted to multiple LMSs which can be selected by the course professor. In order to widely cooperate with other systems, the system is designed by using global standards (IMS Enterprise, JSR-168 Portlet, etc.) and open source software (uPortal, CAS, JSF, Hibernate, etc.) as possible as we can. This paper shows the major functions, the measured use of the portal and the time schedule system over eight months, and the implementation especially for supporting multiple LMSs, syllabus and grade books.

P-process nucleosynthesis inside supernova-driven supercritical accretion disks

Abstract We investigate p-process nucleosynthesis in a supercritical accretion disk around a compact object of 1.4 M ⊙ . Supercritical accretion is expected to occur in a supernova (SN) with fallback material accreting onto a nascent compact object. We find that appreciable amounts of p-nuclei are synthesized via the p-process in the disk when the accretion rate M > 1.6 × 10 6 L Edd c 2 , where L Edd is the Eddington luminosity. Abundance profiles of p-nuclei ejected from SSASs have similar features to those of oxygen/neon layers in the Type II SNe when composition of the fallback gas is initially those of the oxygen/neon layers in the progenitor. The overall abundance profile is in agreement with that of the solar system. Some p-nuclei, such as Mo, Ru, Sn, and La, are underproduced in SSADs as in Type II SNe. If the fallback gas is mixed with a small fraction of proton, significant amounts of 92 Mo and 138 La are produced inside SSADs. 96 Ru, 113 Sn, and 114 Sn are also abundantly produced when the fallback gas contains abundant proton though the overall abundance profile of p-nuclei is rather different from that of the solar system.

Nucleosynthesis inside accretion disks around intermediate-mass black holes

Abstract Nucleosynthesis is investigated inside an accredition disk around a black hole of 50 – 10 3 M ⊙ located in a circumnuclear region of starburst galaxies. Nuclear reactions proceed through the hot CNO cycle to produce large amounts of 14 O and 15 O, which decay to 14 N and 15 N. The calculated N/O − O/H relation is found to be consistent with that observed in the most metal-poor galaxies. The accretion disk may be one of the promising sites of nitrogen production.

Design of a Supporting System for Consultation of Instructional Improvement

In many universities instructional designers consult and provide appropriate advice to faculty members about instructional improvement. It usually takes many times for such instructional consultation. We have developed a supporting system useful for instructional designers to provide expert advice to their clients in the instructional consultation. We made a questionnaire for evaluating a course instruction by students in an effort of the system development, in which we compose items based on ARCS motivation model. The questionnaire has superiority over existing ones in term of narrowing down the strategies of instructional improvement, so that instructional designers prepare appropriate tactics of improvement to their clients in shorter period. Then we developed a prototype system that automatically detects improvements by analyzing the result of the questionnaire, and to suggest several suitable improvement tactics. This proposal showed the possibility to semi-automate multiple steps of motivational design of instruction in relatively short time.

Lithium Production on a Low-Mass Secondary in a Black Hole Soft X-Ray Transient

We examine production of Li on the surface of a low-mass secondary in a black hole soft X-ray transient (BHSXT) through the spallation of CNO nuclei by neutrons which are ejected from a hot (>10 MeV) advection-dominated accretion flow (ADAF) around the black hole. Using updated binary parameters, cross sections of neutron-induced spallation reactions, and mass accretion rates in ADAFs derived from the spectrum fitting of multiwavelength observations of quiescent BHSXTs, we obtain the equilibrium abundances of Li by equating the production rate of Li and the mass transfer rate through accretion to the black hole. The resulting abundances are found to be in good agreement with the observed values in seven BHSXTs. We note that the abundances vary on a timescale longer than a few months in our model. Moreover, the isotopic ratio 6Li /7Li is calculated to be about 0.7-0.8 on the secondaries, which is much higher than the ratio measured in meteorites. Detection of such a high value is favorable to the production of Li via spallation and the existence of a hot accretion flow, rather than an accretion disk corona system in quiescent BHSXTs.

Production of light elements on a low-mass secondary in a soft X-ray transient

We examine production of light elements (Li, Be, & B) on the surface of a low‐mass secondary in a black hole soft X‐ray transient (BHSXT) through the spallation of CNO nuclei by neutrons which are ejected from a hot (>10 MeV) advection‐dominated accretion flow (ADAF) around the black hole. Using updated binary parameters, cross sections of neutron‐induced spallation reactions, and mass accretion rates in ADAFs derived from the spectrum fitting of multi‐wavelength observations of quiescent BHSXTs, we obtain the equilibrium abundances of Li by equating the production rate of Li and the mass transfer rate through accretion to the black hole. We find that the resulting abundances are found to be in good agreement with the observed values in seven BHSXTs. Moreover, the isotopic ratio 6Li/7Li and the abundance ratios Be/Li and B/Li are calculated to be about 0.7–0.8, 1.0–1.3, and 1.8–2.1, respectively, on the secondaries.

Crash of NIS Server Generates Unusual DNS Query Traffic

We investigated statistically on the unusual DNS query traffic from several DNS clients like Linux servers and/or PC terminals in the campus network of a university. The interesting results are: (1) The DNS query traffic includes several keywords relating with database servers in the local area network, to which the Linux servers and PC terminals are belonging. (2) These keywords are generated by network information system (NIS) server program daemons in the database servers. Recent NIS communication employs the remote procedure call (RPC) with libwrap that performs name resolution to the DNS server. From these results, we can reasonably take a workaround to refrain the unusual DNS query traffic when configuring host domain names and their IP addresses in the /etc/hosts file.

Heavy Elements Synthesized in an Accretion Disk around a Black Hole Associated with Gamma-Ray Bursts

We examine nucleosynthesis inside an accretion disk with accretion rates 0.01 - 1M s - 1 associated with gamma-ray bursts. The black hole mass is fixed to be 3M. The chemical composition of accreting gas far from the black hole is taken to be that of an oxygen-rich layer of a massive star before the collapse. The disk consists of five layers characterized by dominant elements: 1 6 O, 2 8 Si, 5 4 Fe (and 5 6 Ni), 4 He, and nucleons. As the accretion rate increases, the individual layers shift outwards with keeping the overall profiles of composition. A similar situation may be realized in an accretion disk around an intermediate mass black hole produced in a collapsing Population III supermassive star.