Microturbulence (
ξ
) is a key parameter introduced in stellar spectroscopy to explain the strength of saturated lines by formally incorporating an additional thermal broadening term in the line ...opacity profile. Although our Sun can serve as an important testing bench to check the usual assumption of constant
ξ
, the detailed behavior of how
ξ
varies from the disk center through the limb seems to have never been investigated so far. In order to fill this gap, local
ξ
values on the solar disk were determined from the equivalent widths of 46 Fe
i
lines at 32 points from the center to the limb by requiring the consistency between the abundances derived from lines of various strengths. The run of
ξ
with
θ
(angle between the line of sight and the surface normal) was found to be only gradual from ≈ 1.0 km s
−1
(at
sin
θ
=
0
: disk center) to ≈ 1.3 km s
−1
(at
sin
θ
≈
0.7
: two-thirds of radial distance); but thereafter increasing more steeply up to ≈ 2 km s
−1
(at
sin
θ
=
0.97
: limb). This result further suggests that the microturbulence derived from the flux spectrum of the disk-integrated Sun is
≈
20
% larger than that of the disk-center value, which is almost consistent with the prediction from 3D hydrodynamical model atmospheres.
The properties of 160 F, G, and K disk dwarfs/subgiants (including 27 planet-host stars) mostly within
$-0.6 \lesssim$
Fe/H
$\lesssim +0.4$
, the Okayama Astrophysical Observatory spectrum collection ...of which had been made open to the public recently, were extensively investigated with particular attention to determining (1) the mass and the age with the help of theoretical stellar evolution calculations, (2) the kinematic parameters of orbital motions in the Galaxy, and (3) the abundances of 15 elements (Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, and Zn) by analyzing the spectra in this database. The resulting characteristics are discussed in terms of several relevant topics of interest, such as a validity check for assuming LTE, the X/Fe vs. Fe/H diagram containing information on the chemical evolution of the Galactic disk, the age–metallicity–kinematics relation, and the difference/similarity between stars with and without planets.
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It is often assumed only limited amount of amorphous phase could generate in the oxide film of Ni-based alloy with H-participation. However, in this study, the formation of a ...remarkable amorphous layer on top of the oxide film of Ni-based Alloy 600 (Ni-15.5Cr-9.4Fe, wt.%) after oxidizing in high-temperature high-pressure water environment by in-situ H-charging condition is observed. A synergy of the film porosity and PH2O/PH2 is proposed as a plausible mechanism. Cavity layer appeared at the oxide and matrix interface, and the H-distribution are also discussed.
It has been suggested that Fe abundances of K dwarfs derived from Fe i and Fe ii lines show considerable discrepancies, and oxygen abundances determined from high-excitation O i 7771-5 triplet lines ...are appreciably overestimated (the problem becoming more serious toward lower Teff), which, however, has not yet been widely confirmed. With the aim of clarifying this issue, we spectroscopically determined the atmospheric parameters of 148 G-K dwarfs (Hyades cluster stars and field stars) by assuming the classical Fe i/Fe ii ionization equilibrium as usual, and determined their oxygen abundances by applying the non-local thermal equilibrium spectrum fitting analysis to O i 7771-5 lines. It turned out that the resulting parameters did not show any significant inconsistency with those determined by other methods (for example, the mean differences in Teff and from the well-determined solutions of Hyades dwarfs are mostly 100 K and 0.1 dex). Likewise, the oxygen abundances of Hyades stars are around O/H ∼ +0.2 dex (consistent with the metallicity of this cluster) without exhibiting any systematic Teff-dependence. Accordingly, we conclude that parameters can be spectroscopically evaluated to a sufficient precision in the conventional manner (based on the Saha-Boltzmann equation for Fe i/Fe ii) and oxygen abundances can be reliably determined from the O i 7771-5 triplet for K dwarfs as far as stars of Teff 4500 K are concerned. We suspect that previously reported strongly Teff-dependent discrepancies may have stemmed mainly from overestimation of weak-line strengths and/or improper Teff scale.
•The interaction of H and oxidation process in high temperature water were revealed.•The effects of H on oxidation was differentialized according to different chemical states of H.•H exhibited ...opposing impacts on the material’s reliability considering different oxidation sites.•A model of the interaction between H and oxidation in high temperature water was proposed.
The present research proposes the synergistic roles of H involved in the oxidation process of a Ni-based alloy in high temperature water environment, using an in-situ H-permeating method. The roles of H were differentiated according to the modification on the microstructure during oxidation in high-temperature water, as H is situated at multiple locations during permeating the material. The nature of the oxide was found to be modified significantly, however, it exhibited possibly opposing impacts on the reliability of the materials. The integrity of surface oxide film and matrix/oxide interface were degraded, yet grain boundary was protected by permeated H.
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•Three different roles of H were identified in structural modification of oxide film.•H modified the double-layer oxide film into a defective single-layer oxide film.•A redox chain ...reaction of Ni2+(NiO) → Ni0 → Ni2+(aq) selectively dissolved NiO.•Thickness of the oxide film was reduced by the in-situ charged H.•Growth of the oxide film under H charging followed a layer-by-layer mechanism.
The roles of H in the modification process of the oxide film of alloy 600 was investigated through a dual-exposed oxidation experiment with an in-situ H-charging method in a high temperature high pressure water environment. The selective dissolution of the NiO modified the oxide film into a defective and porous, single-layered Cr2O3 skeleton after oxidation with H charging. The modification process depended on three different chemical states of H with a varied distribution: i) H2 molecule in water, ii) neutral H in the grain boundary of the oxide film, and, iii) proton (H+) in the lattice of the oxide film.
The introduction of Asn‐linked glycans to nascent polypeptides occurs in the lumen of the endoplasmic reticulum of eukaryotic cells. After the removal of specific sugar residues, glycoproteins ...acquire signals in the glycoprotein quality control (GPQC) system and enter the folding cycle composed of lectin‐chaperones calnexin (CNX) and calreticulin (CRT), glucosidase II (G‐II), and UDP‐Glc:glycoprotein glucosyltransferase (UGGT). G‐II initiates glycoproteins’ entry and exit from the cycle, and UGGT serves as the “folding sensor”. This account summarizes our effort to analyze the properties of enzymes and lectins that play important roles in GPQC, especially those involved in the CNX/CRT cycle. To commence our study, general methods for the synthesis of high‐mannose‐type glycans and glycoproteins were established. Based on these, various substrates to analyze components of the GPQC were created, and properties of CRT, G‐II, and UGGT have been clarified.
High‐mannose‐type glycans are introduced to specific asparagine residues of nascent polypeptides in the endoplasmic reticulum (ER) of eukaryotic cells. They serve as key signals in the glycoprotein quality control (GPQC) system. To conduct precise analysis of GPQC, properly functionalized glycans and homogeneously glycosylated proteins were chemically synthesized and employed as substrates of components of GPQC. This Minireview highlights the strength of approaches based on chemical synthesis to understand biological events.
Abstract
In incorporating the effect of atmospheric turbulence in the broadening of spectral lines, the so-called radial–tangential macroturbulence (RTM) model has been widely used in the field of ...solar-type stars, which was devised from intuitive appearance of the granular velocity field of the Sun. Since this model assumes that turbulent motions are restricted to only radial and tangential directions, it has a special broadening function with notably narrow width due to the projection effect, the validity of which has not yet been confirmed in practice. With the aim of checking whether this RTM model adequately represents the actual solar photospheric velocity field, we carried out an extensive study on the non-thermal velocity dispersion along the line of sight (V
los) by analyzing spectral lines at various points of the solar disk based on locally averaged as well as high-spatial-resolution spectra, and found the following results. First, the center-to-limb run of V
los derived from ground-based low-resolution spectra is simply monotonic with a slightly increasing tendency, which contradicts the specific trend (an appreciable peak at θ ≃ 45°) predicted from RTM. Second, the V
los values derived from a large number of spectra based on high-resolution space observation were revealed to follow a nearly normal distribution, without any sign of the peculiar distribution expected for the RTM case. These two observational facts indicate that the actual solar velocity field is not simply dichotomous as assumed in RTM, but directionally more chaotic. We thus conclude that RTM is not an adequate model, at least for solar-type stars, as it would significantly overestimate the turbulent velocity dispersion by a factor of ∼2. The classical Gaussian macroturbulence model should be more reasonable in this respect.
UDP-glucose:glycoprotein glucosyltransferase (UGGT) functions as a sensor for monitoring the folding status of glycoproteins and transferring a glucose residue to the oligomannose-type glycans of ...misfolded glycoproteins. Recently, we showed that UGGT1 facilitates folding of denatured glycoproteins in vitro. In this review, we discuss whether UGGT–selenof complex acts as a chaperone for misfolded glycoproteins based on the recently revealed conformation and function of UGGT and the function of selenof, which is a UGGT-binding protein.
The properties of 322 intermediate-mass late-G giants (comprising 10 planet-host stars) selected as the targets of the Okayama Planet Search Program, many of which are red-clump giants, were ...comprehensively investigated by establishing their various stellar parameters (atmospheric parameters, including turbulent velocity fields, metallicity, luminosity, mass, age, projected rotational velocity, etc.), and their photospheric chemical abundances for 17 elements, in order to study their mutual dependence, connection with the existence of planets, and possible evolution-related characteristics. The metallicity distribution of planet-host giants was found to be almost the same as that of non-planet-host giants, making marked contrast to the case of planet-host dwarfs tending to be metal-rich. Generally, the metallicities of these comparatively young (typical age of
$\sim 10^{9}$
yr) giants tend to be somewhat lower than those of dwarfs at the same age, and super-metal-rich (Fe
$/$
H
$\gt$
0.2) giants appear to be lacking. Apparent correlations were found between the abundances of C, O, and Na, suggesting that the surface compositions of these elements have undergone appreciable changes due to dredge-up of H-burning products by evolution-induced deep envelope mixing, which becomes more efficient for higher mass stars.
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