53 research outputs found
Electrical Resistivity Studies of Hydrogenated Pd-Zr Glasses
The effect of hydrogen absorption on the electrical resistivity is studied for Pd-Zr glasses prepared by melt-quenching using a single roll technique. The temperature coefficients of the electrical resistivity are negative over the temperature range between 4.2 and 300 K for both as-quenched Pd_Zr_ and hydrogenated Pd_Zr_H_ glasses. The results can be interpreted in terms of an acoustical phonon in case of Pd_Zr_ glass, while in Pd_Zr_H_ glass an optical phonon originating from the metal-hydrogen interaction has a significant contribution to the electrical resistivity as well as an acoustic phonons
Advanced burning stages and fate of 8-10 Mo stars
The stellar mass range 8<M/Mo<12 corresponds to the most massive AGB stars
and the most numerous massive stars. It is host to a variety of supernova
progenitors and is therefore very important for galactic chemical evolution and
stellar population studies. In this paper, we study the transition from
super-AGB star to massive star and find that a propagating neon-oxygen burning
shell is common to both the most massive electron capture supernova (EC-SN)
progenitors and the lowest mass iron-core collapse supernova (FeCCSN)
progenitors. Of the models that ignite neon burning off-center, the 9.5Mo model
would evolve to an FeCCSN after the neon-burning shell propagates to the
center, as in previous studies. The neon-burning shell in the 8.8Mo model,
however, fails to reach the center as the URCA process and an extended (0.6 Mo)
region of low Ye (0.48) in the outer part of the core begin to dominate the
late evolution; the model evolves to an EC-SN. This is the first study to
follow the most massive EC-SN progenitors to collapse, representing an
evolutionary path to EC-SN in addition to that from SAGB stars undergoing
thermal pulses. We also present models of an 8.75Mo super-AGB star through its
entire thermal pulse phase until electron captures on 20Ne begin at its center
and of a 12Mo star up to the iron core collapse. We discuss key uncertainties
and how the different pathways to collapse affect the pre-supernova structure.
Finally, we compare our results to the observed neutron star mass distribution.Comment: 20 pages, 14 figures, 1 table. Submitted to ApJ 2013 February 19;
accepted 2013 June
Development of an evaluation tool for a driving seat reducing neck injury based on mechanical impedance
The importance of developing a driving seat effective for reducing neck injuries caused by rear-end collisions has been increased to produce a safer automobile against vehicle accidents in recent years. The present paper develops a computer simulator based on a mechanical impedance model for analyzing and designing an effective driving seat reducing neck injuries. The simulator can reproduce dynamic behaviors of a dummy doll measured in an actual test of rear-end collision. Effectiveness of an active headrest, which is developed for reducing neck injuries, is quantitatively evaluated through a set of computer simulations
Nucleosynthesis Constraints on the Explosion Mechanism for Type Ia Supernovae
Observations of type Ia supernovae include information about the
characteristic nucleosynthesis associated with these thermonuclear explosions.
We consider observational constraints from iron-group elemental and isotopic
ratios, to compare with various models obtained with the most-realistic recent
treatment of electron captures. The nucleosynthesis is sensitive to the highest
white-dwarf central densities. Hence, nucleosynthesis yields can distinguish
high-density Chandrasekhar-mass models from lower-density burning models such
as white-dwarf mergers. We discuss new results of post-processing
nucleosynthesis for two spherical models (deflagration and/or delayed
detonation models) based upon new electron capture rates. We also consider
cylindrical and 3D explosion models (including deflagration,
delayed-detonation, or a violent merger model). Although there are
uncertainties in the observational constraints, we identify some trends in
observations and the models. We make a new comparison of the models with
elemental and isotopic ratios from five observed supernovae and three supernova
remnants. We find that the models and data tend to fall into two groups. In one
group low-density cores such as in a 3D merger model are slightly more
consistent with the nucleosynthesis data, while the other group is slightly
better identified with higher-density cores such as in single-degenerate 1D-3D
deflagration models. Hence, we postulate that both types of environments appear
to contribute nearly equally to observed SNIa. We also note that observational
constraints on the yields of Cr and Fe, if available, might be
used as a means to clarify the degree of geometrical symmetry of SNIa
explosions.Comment: Accepted for publication in Ap
In vivo imaging of zebrafish retinal cells using fluorescent coumarin derivatives
<p>Abstract</p> <p>Background</p> <p>The zebrafish visual system is a good research model because the zebrafish retina is very similar to that of humans in terms of the morphologies and functions. Studies of the retina have been facilitated by improvements in imaging techniques. <it>In vitro </it>techniques such as immunohistochemistry and <it>in vivo </it>imaging using transgenic zebrafish have been proven useful for visualizing specific subtypes of retinal cells. In contrast, <it>in vivo </it>imaging using organic fluorescent molecules such as fluorescent sphingolipids allows non-invasive staining and visualization of retinal cells <it>en masse</it>. However, these fluorescent molecules also localize to the interstitial fluid and stain whole larvae.</p> <p>Results</p> <p>We screened fluorescent coumarin derivatives that might preferentially stain neuronal cells including retinal cells. We identified four coumarin derivatives that could be used for <it>in vivo </it>imaging of zebrafish retinal cells. The retinas of living zebrafish could be stained by simply immersing larvae in water containing 1 μg/ml of a coumarin derivative for 30 min. By using confocal laser scanning microscopy, the lamination of the zebrafish retina was clearly visualized. Using these coumarin derivatives, we were able to assess the development of the zebrafish retina and the morphological abnormalities induced by genetic or chemical interventions. The coumarin derivatives were also suitable for counter-staining of transgenic zebrafish expressing fluorescent proteins in specific subtypes of retinal cells.</p> <p>Conclusions</p> <p>The coumarin derivatives identified in this study can stain zebrafish retinal cells in a relatively short time and at low concentrations, making them suitable for <it>in vivo </it>imaging of the zebrafish retina. Therefore, they will be useful tools in genetic and chemical screenings using zebrafish to identify genes and chemicals that may have crucial functions in the retina.</p
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