938 research outputs found
Evolution and Nucleosynthesis of Metal-Free Massive Stars
We calculate presupernova evolutions and supernova explosions of massive
stars (M=13-25 Mo) for various metallicities. We find the following
characteristic abundance patterns of nucleosynthesis in the metal-free (Pop
III) stars. (1) The alpha-nuclei (from C to Zn) are more efficiently produced
than other isotopes, and the abundance pattern of alpha-nuclei can be similar
to the solar abundance. In particular, near solar ratios of alpha elements/Fe
might be a signature of Pop III which could produce a large amount of Fe. (2)
The abundance ratios of odd Z to even Z elements such as Na/Mg and Al/Mg become
smaller for lower metallicity. However, these ratios almost saturate below Z <~
10^{-5}, and [Na, Al/Mg] ~ - 1 for Pop III and low metal Pop II
nucleosynthesis. This result is consistent with abundance pattern of metal poor
stars, in which these ratios also saturate around -1. We suggest that these
stars with the lowest [Na/Mg] or [Al/Mg] may contain the abundance pattern of
Pop III nucleosynthesis. (3) Metal poor stars show interesting trends in the
ratios of [Cr, Mn, Co/Fe]. We discuss that these trends are not explained by
the differences in metallicity, but by the relative thickness between the
complete and the incomplete Si burning layers. Large [Co/Fe] and small [Cr,
Mn/Fe] values found in the observations are explained if mass cut is deep or if
matter is ejected from complete Si burning layer in a form of a jet or bullets.
(4) We also find that primary ^{14}N production occurs in the massive Pop III
stars, because these stars have radiative H-rich envelopes so that the
convective layer in the He-shell burning region can reach the H-rich region.Comment: 19 pages. To appear in the proceedings of the MPA/ESO conference
``The First Stars'' (August 4-7, 1999, Garching) ed. A. Weiss etal.
(Springer
Strength of Titanium Joints Brazed with Aluminum Filler Metals(Physics, Process, Instrument & Measurement)
Aluminum Brazing Filler Metals for Making Aluminum to Titanium Joints in a Vacuum(Physics, Process, Instrument & Measurement)
Simian virus 40 chromatin showing nucleosomes in linear bead-like arrangements along extended closed circular DNA
Viral nucleoprotein complexes were extracted from nuclei of permissive cells (CV-1) infected with simian virus 40 (SV40) and examined by electron microscopy. SV40 nucleoprotein complexes (SV40 chromatin) showed nucleosomes in linear bead-like arrangements along the extended closed circular DNA. The contour length of the SV40 chromatin was only 1.0-1.8 times shorter than that of viral DNA obtained after deproteinization. The data suggest that the circular DNA in SV40 chromatin can be extended to nearly its full length without detachment of the histone complexes.</p
Hypernova Nucleosynthesis and Implications for Cosmic Chemical Evolution
We examine the characteristics of nucleosynthesis in 'hypernovae', i.e.,
supernovae with very large explosion energies (\gsim 10^{52} ergs).
Implications for the cosmic chemical evolution and the abundances in M82 are
discussed.Comment: To appear in 'Cosmic Evolution' Conference at IAP, Paris, honoring
Jean Audouze and Jim Truran, 13-17 Nov 200
Quantitative Tactile Examination Using Shape Memory Alloy Actuators for the Early Detection of Diabetic Neuropathy
Diabetic neuropathy (DPN) is asymptomatic in its early phases but can cause serious complications as it progresses. Most DPN tests are cumbersome and produce only qualitative assessments, and simpler approaches that yield quantitative results are needed. Techniques that allow patients to perform examinations themselves would be especially valuable. In this study, we focused on quantifying the decline in tactile sensation associated with DPN and developed a measurement device that used a thin shape memory alloy (SMA) wire as the actuator. An ON/OFF pulse current caused the wire to shrink and expand. This vibration was amplified by a round-headed pin, allowing even DPN patients with reduced tactile sensitivity to detect the stimuli generated when lightly touching the pin with their fingertips. The tactile stimuli were ranked into 30 levels of intensity. A key advantage of the device is that it can be used by patients themselves, returning quantified results within minutes. Although developed for DPN, the method can be applied to the detection of peripheral neuropathy in general
One-, Two-, and Three-dimensional Simulations of Oxygen Shell Burning Just Before the Core-Collapse of Massive Stars
We perform two- (2D) and three-dimensional (3D) hydrodynamics simulations of
convective oxygen shell-burning that takes place deep inside a massive
progenitor star of a core-collapse supernova. Using one dimensional (1D)
stellar evolution code, we first calculate the evolution of massive stars with
an initial mass of 9-40 . Four different overshoot parameters are
applied, and CO core mass trend similar to previous works is obtained in the 1D
models. Selecting eleven 1D models that have a silicon and oxygen coexisting
layer, we perform 2D hydrodynamics simulations of the evolution 100 s
until the onset of core-collapse. We find that convection with large-scale
eddies and the turbulent Mach number 0.1 is obtained in the models having
a Si/O layer with a scale of 10 cm, whereas most models that have an
extended O/Si layer up to a few cm exhibit lower turbulent
velocity. Our results indicate that the supernova progenitors that possess a
thick Si/O layer could provide a preferable condition for perturbation-aided
explosions. We perform 3D simulation of a 25 model, which exhibits
large-scale convection in the 2D models. The 3D model develops large () convection similar to the 2D model, however, the turbulent velocity is
lower. By estimating the neutrino emission properties of the 3D model, we point
out that a time modulation of the event rates, if observed in KamLAND and
Hyper-Kamiokande, would provide an important information about structural
changes in the presupernova convective layer.Comment: 25 pages, 17 figures, 2 tables. Accepted for publication in Ap
miRNA-based rapid differentiation of purified neurons from hPSCs advancestowards quick screening for neuronal disease phenotypes in vitro
Obtaining differentiated cells with high physiological functions by an efficient, but simple and rapid differentiation method is crucial for modeling neuronal diseases in vitro using human pluripotent stem cells (hPSCs). Currently, methods involving the transient expression of one or a couple of transcription factors have been established as techniques for inducing neuronal differentiation in a rapid, single step. It has also been reported that microRNAs can function as reprogramming effectors for directly reprogramming human dermal fibroblasts to neurons. In this study, we tested the effect of adding neuronal microRNAs, miRNA-9/9*, and miR-124 (miR-9/9*-124), for the neuronal induction method of hPSCs using Tet-On-driven expression of the Neurogenin2 gene
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