452 research outputs found
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 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 channels is shown to reproduce well the experimental
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 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 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 are obtained on the basis of
the terrestrial data. Neutron-star radii at a typical mass are
predicted to be 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 are not
influenced by hyperon-mixing effects, finely-observed values for them indicate
degrees of EoS softening by hyperon mixing in the region of
. If 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 .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
R Raman Spectroscopy and Petrology of Antarctic CR Chondrites: Comparison with Other Carbonaceous Chondrites
In Renazzo-like carbonaceous (CR) chondrites, abundant original Fe,Ni-metal is preserved in chrondules, but the matrix is characterized by fine-grained magnetite with phyllosilicate. This combination of reduced Fe in chrodrules with oxidized Fe and phyllosilicate in the matrix has been attributed to aqueous alteration of matrix at relatively low temperatures
- …