71 research outputs found
On the Decelerating Shock Instability of Plane-Parallel Slab with Finite Thickness
Dynamical stability of the shock compressed layer with finite thickness is
investigated. It is characterized by self-gravity, structure, and shock
condition at the surfaces of the compressed layer. At one side of the shocked
layer, its surface condition is determined via the ram pressure, while at the
other side the thermal pressure supports its structure. When the ram pressure
dominates the thermal pressure, we expect deceleration of the shocked layer.
Especially, in this paper, we examine how the stratification of the
decelerating layer has an effect on its dynamical stability. Performing the
linear perturbation analysis, a {\it more general} dispersion relation than the
previous one obtained by one of the authors is derived. It gives us an
interesting information about the stability of the decelerating layer.
Importantly, the DSI (Decelerating Shock Instability) and the gravitational
instability are always incompatible. We also consider the evolution effect of
the shocked layer. In the early stages of its evolution, only DSI occurs. On
the contrary, in the late stages, it is possible for the shocked layer to be
unstable for the DSI (in smaller scale) and the gravitational instability (in
larger scale). Furthermore, we find there is a stable range of wavenumbers
against both the DSI and the gravitational instability between respective
unstable wavenumber ranges. These stable modes suggest the ineffectiveness of
DSI for the fragmentation of the decelerating slab.Comment: 17 pages, 6 figures. The Astrophysical Journal Vol.532 in pres
On the Possibility of Observing the Double Emission Line Feature of H and HD from Primordial Molecular Cloud Cores
We study the prospects for observing H and HD emission during the
assembly of primordial molecular cloud cores. The primordial molecular cloud
cores, which resemble those at the present epoch, can emerge around according to recent numerical simulations. A core typically contracts to
form the first generation of stars and the contracting core emits H and HD
line radiation. These lines show a double peak feature. The higher peak is the
H line of the (v=0) rotational transition, and the lower peak is
the HD line of the (v=0) rotational transition. The ratio of the peaks
is about 20, this value characterising the emission from primordial galaxies.
The expected emission flux at the redshift of (e.g. and ), in the (v=0) line of H occurs at a
rate Jy, and in the (v=0) line of HD at a rate
Jy. The former has a frequency of 5.33179 Hz and the latter is at 5.33388 Hz, respectively.
Since the frequency resolution of ALMA is about 40 kHz, the double peak is
resolvable. While an individual object is not observable even by ALMA, the
expected assembly of primordial star clusters on subgalactic scales can result
in fluxes at the 2000-50 Jy level. These are marginally observable. The
first peak of H is produced when the core gas cools due to HD cooling,
while the second peak of HD occurs because the medium maintains thermal balance
by H cooling which must be enhanced by three-body reactions to form H
itself.Comment: 24 pages, 5 figures. MNRAS (Accepted
Results of the search for inspiraling compact star binaries from TAMA300's observation in 2000-2004
We analyze the data of TAMA300 detector to search for gravitational waves
from inspiraling compact star binaries with masses of the component stars in
the range 1-3Msolar. In this analysis, 2705 hours of data, taken during the
years 2000-2004, are used for the event search. We combine the results of
different observation runs, and obtained a single upper limit on the rate of
the coalescence of compact binaries in our Galaxy of 20 per year at a 90%
confidence level. In this upper limit, the effect of various systematic errors
such like the uncertainty of the background estimation and the calibration of
the detector's sensitivity are included.Comment: 8 pages, 4 Postscript figures, uses revtex4.sty The author list was
correcte
Genome and Transcriptome Analysis of the Food-Yeast Candida utilis
The industrially important food-yeast Candida utilis is a Crabtree effect-negative yeast used to produce valuable chemicals and recombinant proteins. In the present study, we conducted whole genome sequencing and phylogenetic analysis of C. utilis, which showed that this yeast diverged long before the formation of the CUG and Saccharomyces/Kluyveromyces clades. In addition, we performed comparative genome and transcriptome analyses using next-generation sequencing, which resulted in the identification of genes important for characteristic phenotypes of C. utilis such as those involved in nitrate assimilation, in addition to the gene encoding the functional hexose transporter. We also found that an antisense transcript of the alcohol dehydrogenase gene, which in silico analysis did not predict to be a functional gene, was transcribed in the stationary-phase, suggesting a novel system of repression of ethanol production. These findings should facilitate the development of more sophisticated systems for the production of useful reagents using C. utilis
JASMINE: Near-infrared astrometry and time-series photometry science
The Japan Astrometry Satellite Mission for INfrared Exploration (JASMINE) is a planned M-class science space mission by the Institute of Space and Astronautical Science, the Japan Aerospace Exploration Agency. JASMINE has two main science goals. One is Galactic archaeology with a Galactic Center survey, which aims to reveal the Milky Way’s central core structure and formation history from Gaia-level (∼25 as) astrometry in the near-infrared (NIR) Hw band (1.0–1.6 m). The other is an exoplanet survey, which aims to discover transiting Earth-like exoplanets in the habitable zone from NIR time-series photometry of M dwarfs when the Galactic Center is not accessible. We introduce the mission, review many science objectives, and present the instrument concept. JASMINE will be the first dedicated NIR astrometry space mission and provide precise astrometric information on the stars in the Galactic Center, taking advantage of the significantly lower extinction in the NIR. The precise astrometry is obtained by taking many short-exposure images. Hence, the JASMINE Galactic Center survey data will be valuable for studies of exoplanet transits, asteroseismology, variable stars, and microlensing studies, including discovery of (intermediate-mass) black holes. We highlight a swath of such potential science, and also describe synergies with other missions
Energy Efficient and Intermittently Variable Ammonia Synthesis over Mesoporous Carbon-Supported Cs-Ru Nanocatalysts
The Cs-promoted Ru nanocatalysts supported on mesoporous carbon materials (denoted as Cs-Ru/MPC) and microporous activated carbon materials (denoted as Cs-Ru/AC) were prepared for the sustainable synthesis of ammonia under mild reaction conditions (<500 °C, 1 MPa). Both Ru and Cs species were homogeneously impregnated into the mesostructures of three commercial available mesoporous carbon materials annealed at 1500, 1800 and 2100 °C (termed MPC-15, MPC-18 and MPC-21, respectively), resulting in a series of Cs-Ru/MPC catalysts with Ru loadings of 2.5−10 wt % and a fixed Cs loading of 33 wt %, corresponding to Cs/Ru molar ratios of 2.5−10. However, the Ru and Cs species are larger than the pore mouths of microporous activated carbon (shortly termed AC) and, as a consequence, were mostly aggregated on the outer surface of the Cs-Ru/AC catalysts. The Cs-Ru/MPC catalysts are superior to the Cs-Ru/AC catalyst in catalysing mild ammonia synthesis, especially for the 2.5Cs-10Ru/MPC-18 catalyst with a Ru loading of 10 wt % and a Cs/Ru ratio of 2.5, which exhibited the highest activity across a wide SV range. It also showed an excellent response and stability during cycling tests over a severe temperature jump in a short time, presumably due to the open mesoporous carbon framework and suitable surface concentrations of CsOH and metallic Ru species at the catalytically active sites. This 2.5Cs-10Ru/MPC-18 catalyst with high activity, fast responsibility and good stability has potential application in intermittently variable ammonia synthesis using CO2-free hydrogen derived from electrolysis of water using renewable energy with fast variability
Mild Ammonia Synthesis over Ba-Promoted Ru/MPC Catalysts: Effects of the Ba/Ru Ratio and the Mesoporous Structure
A series of novel mesoporous carbon-supported, Ba-promoted, Ru catalysts with Ba/Ru ratios of 0.1−1.6 and a Ru loading of 10 wt% (denoted as 0.1−1.6Ba-10Ru/MPC) were prepared via stepwise impregnation of Ru and Ba precursors on the mesoporous carbon materials. The catalysts were applied to mild ammonia synthesis and compared to reference materials, including an analog of the prepared catalyst with a Ba/Ru ratio of 1.6 and a Ru loading of 10 wt% (denoted as 1.6Ba-10Ru/AC). Characterization by X-ray diffraction (XRD), nitrogen physisorption, and electronic microscopy revealed that the 0.1−1.6Ba-10Ru/MPC catalysts contained Ru particles (approximately 2 nm) that were well-dispersed on the mesoporous structure and nanostructured Ba(NO3)2 species. These species decomposed into amorphous BaOx species, acting as a promoter on the metallic Ru particles forming catalytically active sites for ammonia synthesis. All the 0.1−1.6Ba-10Ru/MPC catalysts showed a synergistic effect of the active Ba and Ru species, which were stabilized in the mesoporous carbon framework with fast molecular diffusion and could effectively catalyze mild ammonia synthesis (280−450 °C and 0.99 MPa) even under intermittently variable conditions, particularly for those with Ba/Ru ratios of >0.5. In contrast, the 1.6Ba-10Ru/AC analog showed poor activity and stability for ammonia synthesis due to the sintering of Ba and Ru particles on the outer surface of the microporous carbon framework, resulting in low molecular diffusion and weak synergistic effect of the catalytically active sites
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