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Surface tension measurement of glass melts by the maximum bubble pressure method
The maximum bubble pressure method was used to obtain accurate surface tension measurements. The dependence of apparent surface tension value on bubble growth time was measured for times from several to longer than a thousand seconds. The static surface tension value was obtained by extrapolating bubble growth time to infinity. The dynamic surface tension, which is familiar in colloids, could not be directly obtained because of the high viscosity of glass melt. The effects of capillary tip material and shape were also examined. This method is applicable to melts with viscosity less than 10^3.5 dPa s. The reproducibility in the measurement was within a few percent
Extremely energetic supernova explosions embedded in a massive circumstellar medium: the case of SN 2016aps
We perform one-dimensional radiation-hydrodynamic simulations of energetic
supernova ejecta colliding with a massive circumstellar medium (CSM) aiming at
explaining SN 2016aps, likely the brightest supernova observed to date. SN
2016aps was a superluminous Type-IIn SN, which released as much as erg of thermal radiation. Our results suggest that the
multi-band light curve of SN 2016aps is well explained by the collision of a
SN ejecta with the explosion energy of erg and a
wind-like CSM with the outer radius of cm, i.e.,
a hypernova explosion embedded in a massive CSM. This finding indicates that
very massive stars with initial masses larger than , which
supposedly produce highly energetic SNe, occasionally eject their hydrogen-rich
envelopes shortly before the core-collapse. We suggest that the pulsational
pair-instability SNe may provide a natural explanation for the massive CSM and
the energetic explosion. We also provide the relations between the peak
luminosity, the radiated energy, and the rise time for interacting SNe with the
kinetic energy of erg, which can be used for interpreting SN
2016aps-like objects in future surveys.Comment: 17 pages, 9 figures, accepted for publication in Ap
Study of Magnetic Excitation in Singlet-Ground-State Magnets CsFeCl and RbFeCl by Nuclear Magnetic Relaxation
The temperature dependences of spin-lattice relaxation time of
Cs in CsFeCl and Rb in RbFeCl were measured in the
temperature range between 1.5 K and 22 K, at various fields up to 7 T applied
parallel (or perpendicular) to the c-axis, and the analysis was made on the
basis of the DCEFA. The mechanism of the nuclear magnetic relaxation is
interpreted in terms of the magnetic fluctuations which are characterized by
the singlet ground state system. In the field region where the phase transition
occurs, exhibited the tendency of divergence near , and
this feature was ascribed to the transverse spin fluctuation associated with
the mode softening at the -point. It was found that the damping constant of
the soft mode is remarkably affected by the occurrence of the magnetic ordering
at lower temperature, and increases largely in the field region where the phase
transition occurs.Comment: 12 pages, 18 figures, submitted to J. Phys. Soc. Jp
Multiple losses of photosynthesis and convergent reductive genome evolution in the colourless green algae Prototheca
Autotrophic eukaryotes have evolved by the endosymbiotic uptake of photosynthetic organisms. Interestingly, many algae and plants have secondarily lost the photosynthetic activity despite its great advantages. Prototheca and Helicosporidium are non-photosynthetic green algae possessing colourless plastids. The plastid genomes of Prototheca wickerhamii and Helicosporidium sp. are highly reduced owing to the elimination of genes related to photosynthesis. To gain further insight into the reductive genome evolution during the shift from a photosynthetic to a heterotrophic lifestyle, we sequenced the plastid and nuclear genomes of two Prototheca species, P. cutis JCM 15793 and P. stagnora JCM 9641, and performed comparative genome analyses among trebouxiophytes. Our phylogenetic analyses using plastid- and nucleus-encoded proteins strongly suggest that independent losses of photosynthesis have occurred at least three times in the clade of Prototheca and Helicosporidium. Conserved gene content among these non-photosynthetic lineages suggests that the plastid and nuclear genomes have convergently eliminated a similar set of photosynthesis-related genes. Other than the photosynthetic genes, significant gene loss and gain were not observed in Prototheca compared to its closest photosynthetic relative Auxenochlorella. Although it remains unclear why loss of photosynthesis occurred in Prototheca, the mixotrophic capability of trebouxiophytes likely made it possible to eliminate photosynthesis
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