1,308 research outputs found
Contribution of Type Ia and Type II Supernovae for Intra-Cluster Medium Enrichment
The origin of the chemical composition of the intracluster medium (ICM) is
discussed in this paper. In particular, the contribution from Type Ia
supernovae (SNe Ia) to the ICM enrichment is shown to exist by adopting the
fitting formulas which have been used in the analysis of the solar system
abundances. Our analysis means that we can use the frequency of SNe Ia relative
to SNe II as the better measure than for
estimating the contribution of SNe Ia. Moreover, the chemical compositions of
ICMs are shown to be similar to that of the solar system abundances. We can
also reproduce the sulfur/iron abundance ratio within a factor of 2, which
means that the abundance problem of sulfur needs not to be emphasized too
strongly. We need more precise observations to conclude whether ICMs really
suffer the shortage problem of sulfur or not.Comment: 20 pages, LaTeX text and 15 postscript figures. Accepted for
publication in Astrophysical Journa
Swelling of acetylated wood in organic liquids
To investigate the affinity of acetylated wood for organic liquids, Yezo
spruce wood specimens were acetylated with acetic anhydride, and their swelling
in various liquids were compared to those of untreated specimens. The
acetylated wood was rapidly and remarkably swollen in aprotic organic liquids
such as benzene and toluene in which the untreated wood was swollen only
slightly and/or very slowly. On the other hand, the swelling of wood in water,
ethylene glycol and alcohols remained unchanged or decreased by the
acetylation. Consequently the maximum volume of wood swollen in organic liquids
was always larger than that in water. The effect of acetylation on the maximum
swollen volume of wood was greater in liquids having smaller solubility
parameters. The easier penetration of aprotic organic liquids into the
acetylated wood was considered to be due to the scission of hydrogen bonds
among the amorphous wood constituents by the substitution of hydroxyl groups
with hydrophobic acetyl groups.Comment: to be published in J Wood Science (Japanese wood research society
Ultrastructural changes of intercellular junctions in rat ascites hepatoma cells with calcium depletion.
To analyse the effect of ethylenediamine tetraacetate (EDTA) on tumour cell adhesiveness, fine structure of intercellular junctions of rat ascites hepatoma cells AH136B and AH7974 (both forming cell islands in vivo) was first compared. The close contact of the apical portion of both cell islands was composed of tight junctions with a narrow gap. The close contact of the inner portion of AH136B cell islands was largely by simple apposition, while that of AH7974 cell islands had many intermediate junctions and desmosomes. Treatment with EDTA (2 mM) induced morphological alteration of simple apposition, intermediate junctions and desmosomes, but tight junctions remained intact. The effect of EDTA on such junctional complexes seemed to be partially reversible on readministration of Ca ions. Changes in desmosomes, as confirmed on AH7974 cells, were initiated by disappearance of the central disc of electron-dense materials, followed by marked opening of intercellular space and disappearance of endoplasmic laminar plaque. These results suggest that Ca ions may be concerned with maintaining the integrity of junctional complexes other than tight junctions
Effect of superradiance on transport of diffusing photons in cold atomic gases
We show that in atomic gases cooperative effects like superradiance and
subradiance lead to a potential between two atoms that decays like . In
the case of superradiance, this potential is attractive for close enough atoms
and can be interpreted as a coherent mesoscopic effect. The contribution of
superradiant pairs to multiple scattering properties of a dilute gas, such as
photon elastic mean free path and group velocity, is significantly different
from that of independent atoms. We discuss the conditions under which these
effects may be observed and compare our results to recent experiments on photon
transport in cold atomic gases.Comment: 4 pages and 1 figur
Iron Abundance Profiles of 12 Clusters of Galaxies Observed With BeppoSAX
We have derived azimuthally-averaged radial iron abundance profiles of the
X-ray gas contained within 12 clusters of galaxies with redshift 0.03 < z < 0.2
observed with BeppoSAX. We find evidence for a negative metal abundance
gradient in most of the clusters, particularly significant in clusters that
possess cooling flows. The composite profile from the 12 clusters resembles
that of cluster simulations of Metzler & Evrard (1997). This abundance gradient
could be the result of the spatial distribution of gas-losing galaxies within
the cluster being more centrally condensed than the primordial hot gas. Both
inside and outside the core region, we find a higher abundance in cooling flow
clusters than in non-cooling flow clusters. Outside of the cooling region this
difference cannot be the result of more efficient sputtering of metals into the
gaseous phase in cooling flow clusters, but might be the result of the mixing
of low metallicity gas from the outer regions of the cluster during a merger.Comment: 8 pages, 2 embedded Postscript figures, accepted by Astrophysical
Journa
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