Possible evolutionary transition from rapidly rotating neutron stars to strange stars due to spin-down

We present a scenario of formation of strange stars due to spin-down of {\it rapidly rotating} neutron stars left after supernova explosions . By assuming a process where the total baryon mass is conserved but the angular momentum is lost due to emission of gravitational waves and/or the magnetic braking, we find that the transition from rapidly rotating neutron stars to slowly rotating strange stars is possible; a large amount of energy $\sim 10^{53} ergs$ could be released. The liberated energy might become a new energy source for a delayed explosion of supernova. Furthermore, our scenario suggests that the supernova associated with gamma-ray bursts could become candidates for targets in the future observation of gravitational waves.Comment: 11 pages, 3 figures, Received November 5, 200

Hyperon mixing and universal many-body repulsion in neutron stars

A multi-pomeron exchange potential (MPP) is proposed as a model for the universal many-body repulsion in baryonic systems on the basis of the Extended Soft Core (ESC) bryon-baryon interaction. The strength of MPP is determined by analyzing the nucleus-nucleus scattering with the G-matrix folding model. The interaction in $\Lambda N$ channels is shown to reproduce well the experimental $\Lambda$ binding energies. The equation of state (EoS) in neutron matter with hyperon mixing is obtained including the MPP contribution, and mass-radius relations of neutron stars are derived. It is shown that the maximum mass can be larger than the observed one $2M_{\odot}$ even in the case of including hyperon mixing on the basis of model-parameters determined by terrestrial experiments

Neutron-star radii based on realistic nuclear interactions

The existence of neutron stars with $2M_\odot$ requires the strong stiffness of the equation of state (EoS) of neutron-star matter. We introduce a multi-pomeron exchange potential (MPP) working universally among 3- and 4-baryons to stiffen the EoS. Its strength is restricted by analyzing the nucleus-nucleus scattering with the G-matrix folding model. The EoSs are derived using the Brueckner-Hartree-Fock (BHF) and the cluster variational method (CVM) with the nuclear interactions ESC and AV18. The mass-radius relations are derived by solving the Tolmann-Oppenheimer-Volkoff (TOV) equation, where the maximum masses over $2M_\odot$ are obtained on the basis of the terrestrial data. Neutron-star radii $R$ at a typical mass $1.5M_\odot$ are predicted to be $12.3\!\sim\!13.0$ km. The uncertainty of calculated radii is mainly from the ratio of 3- and 4-pomeron coupling constants, which cannot be fixed by any terrestrial experiment. Though values of $R(1.5M_\odot)$ are not influenced by hyperon-mixing effects, finely-observed values for them indicate degrees of EoS softening by hyperon mixing in the region of $M\!\sim\!2M_\odot$. If $R(1.5M_\odot)$ is less than about 12.4 km, the softening of EoS by hyperon mixing has to be weak. Useful information can be expected by the space mission NICER offering precise measurements for neutron-star radii within $\pm 5\%$.Comment: 8 pages, 7 figure

Petrology of Chondrule Rims in Yamato-791498 and Asuka-881828, the Least-Altered CR Chondrites in the Japanese NIPR Collection

CR chondrites are a group of car-bonaceous chondrites with well-preserved records of formation of their components in the solar nebula. The CR chondrites have undergone a wide range of aqueous alteration from nearly anhydrous (CR2.8 or CR3.0) to extensive recrystallization of primary minerals, including replacement of coarse-grained silicates in chondrules (CR2.0). At the same time, CRs have experienced only minor thermal metamorphism except for rare CR6 samples. Identifying minimally altered CR chondrites is a priority because they preserve (1) relatively pristine records of the solar nebula and (2) minerals and textures at the beginning stages of aqueous alteration. Here we report the petrologic characteristics of Y-791498 and A-881828 as the least aqueously altered CR chondrites in the Japanese NIPR meteorite collection. Previous studies have shown that fine-grained rims on chondrules are indicators of incipient alteration of primitive CR chondrites, there-fore we focus on rims around chondrules in the two meteorites

Raman spectroscopy and petrology of Antarctic CR chondrites: Comparison with other carbonaceous chondrites

第6回極域科学シンポジウム[OA] 南極隕石11月16日（月）　国立国語研究所 2階 講

Petrological, petrofabric, and oxygen isotopic study of five ungrouped meteorites related to brachinites

Northwest Africa (NWA) 6112, Miller Range (MIL) 090206 (plus its pairs: MIL 090340 and MIL 090405), and Divnoe are olivine-rich ungrouped achondrites. We investigated and compared their petrography, mineralogy, and olivine fabrics. We additionally measured the oxygen isotopic compositions of NWA 6112. They show similar petrography, mineralogy, and oxygen isotopic compositions and we concluded that these five meteorites are brachinite clan meteorites. We found that NWA 6112 and Divnoe had a c axis concentration pattern of olivine fabrics using electron backscattered diffraction (EBSD). NWA 6112 and Divnoe are suggested to have been exposed to magmatic meltflows during their crystallization on their parent body. On the other hand, the three MIL meteorites have b axis concentration patterns of olivine fabrics. This indicates that the three MIL meteorites may be cumulates where compaction of olivine grains was dominant. Alternatively, they formed as residues and were exposed to olivine compaction. The presence of two different olivine fabric patterns implies that the parent body(s) of brachinite clan meteorites experienced diverse igneous processes

Hair mercury levels in relation to marine fish consumption among adults in Malaysia.

Consumption of carnivorous fish is one of the major sources of human exposure to methyl mercury (MeHg). This study presents the data on fish consumption habits and hair mercury levels taken from 201 adults aged between 17- 72 years from four districts in the Peninsular Malaysia. The means for total mercury (THg) ranged from 0.93 ppm-1.69 ppm. The means for females and males were 1.21 ppm (SD=0.76) and 1.48 ppm (SD=0.89) respectively. The THg level for 59.30% of the study population (26.60% female participants) exceeded the USEPA recommendation of 1 ppm. The average fish consumption was 180.19+11.34g/ day/person with higher fish consumption in both rural coastal areas compared with the urban communities (p=0.0001). Age was positively correlated with THg (rs=0.4588; p=0.0001) followed by the amount of fish eaten (rs=0.4199; p=0.0001), use of whitening cream (rs=0.2410; p=0.006), BMI (rs=0.2034; p=0.0041), location of study (rs=0.1818; p=0.01), and gender (0.1637; p=0.0241). However, we found negative correlation between the numbers of filling with THg (rs=-0.2485; p=0.004)

Amoeboid Olivine Aggregates in Antarctic CR Chondrites: Petrologic Variations Among CR Chondrites

Amoeboid olivine aggregates (AOAs) are important components of carbonaceous chondrites that are interpreted as solar nebula condensates, and can be used as sensitive indicators of metamorphic or alteration processes. We have been investigating a set of Antarctic CR chondrites from the Japanese-NIPR collection in order to study variations within the CRs in general and their AOAs in particular. Main goals are to identify variations in conditions of nebular condensation, parent body effects and terrestrial weathering

Mercury exposure in coastal communities of Kedah and Kelantan, Malaysia.

A cross-sectional study of mercury concentration in hair was conducted in two rural coastal communities of Yan (state of Kedah) and Bachok (state of Kelantan) from March to May 2006. For the comparative groups, the urban communities of Alor Setar (Kedah) and Kota Bharu (Kelantan) were chosen. This study was carried out in collaboration with the National Institute for Minamata Disease (NIMD), Minamata, Japan. A total of 201 hair samples were collected from the residents. Samples were analyzed by the NIMD, using the oxygen combustion-gold combustion method. The geometric means for total mercury in each district were 1.38 ppm (Yan), 1.20 ppm (Alor Setar), 1.24 ppm (Bachok) and 1.07 ppm (Kota Bharu). Two persons, each from Alor Setar and Kota Bharu, had high total mercury (washed sample 223.58 ppm and 803.16 ppm respectively). However, further analysis for methyl mercury showed that the levels were within 1.36 ppm and 1.91 ppm, respectively. Of the ten exposure parameters tested, only age (p < 0.001) and fish consumption (p < 0.01) appeared to have significant effect on hair mercury levels. Concerns about mercury were related to a severe outbreak of neurological disease in Minamata, Japan. In 1950s, a huge amount of methyl mercury (MeHg) formed in the chemical factory had been discharged to the Minamata Bay. Although inorganic mercury (I-Hg) was also discharged, contribution of biomethylation is considered too small for the Minamata disease. Bioaccumulation of MeHg into the aquatic food chain resulted in the neurological syndrome in adults who has eaten contaminated fish and prenatal exposures to MeHg from maternal consumption of fish which resulted in mental retardation, seizures and cerebral palsy (ATSDR, 1999; and Harada et al., 1999)