1,084 research outputs found
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
Electromagnetic effects of neutrinos in an electron gas
We study the electromagnetic properties of a system that consists of an
electron background and a neutrino gas that may be moving or at rest, as a
whole, relative to the background. The photon self-energy for this system is
characterized by the usual transverse and longitudinal polarization functions,
and two additional ones which are the focus of our calculations, that give rise
to birefringence and anisotropic effects in the photon dispersion relations.
Expressions for them are obtained, which depend on the neutrino number
densities and involve momentum integrals over the electron distribution
functions, and are valid for any value of the photon momentum and general
conditions of the electron gas. Those expressions are evaluated explicitly for
several special cases and approximations which are generally useful in
astrophysical and cosmological settings. Besides studying the photon dispersion
relations, we consider the macroscopic electrodynamic equations for this
system, which involve the standard dielectric and permeability constants plus
two additional ones related to the photon self-energy functions. As an
illustration, the equations are used to discuss the evolution of a magnetic
field perturbation in such a medium. This particular phenomena has also been
considered in a recent work by Semikoz and Sokoloff as a mechanism for the
generation of large-scale magnetic fields in the Early Universe as a
consequence of the neutrino-plasma interactions, and allows us to establish
contact with a specific application in a well defined context, with a broader
scope and from a very different point of view.Comment: Revtex 20 page
Metallicity Gradients in the Intracluster Gas of Abell 496
Analysis of spatially resolved ASCA spectra of the intracluster gas in Abell
496 confirms there are mild metal abundance enhancements near the center, as
previously found by White et al. (1994) in a joint analysis of Ginga LAC and
Einstein SSS spectra. Simultaneous analysis of spectra from all ASCA
instruments (SIS + GIS) shows that the iron abundance is 0.36 +- 0.03 solar
3-12' from the center of the cluster and rises ~50% to 0.53 +- 0.04 solar
within the central 2'. The F-test shows that this abundance gradient is
significant at the >99.99% level. Nickel and sulfur abundances are also
centrally enhanced. We use a variety of elemental abundance ratios to assess
the relative contribution of SN Ia and SN II to the metal enrichment of the
intracluster gas. We find spatial gradients in several abundance ratios,
indicating that the fraction of iron from SN Ia increases toward the cluster
center, with SN Ia accounting for ~50% of the iron mass 3-12' from the center
and ~70% within 2'. The increased proportion of SN Ia ejecta at the center is
such that the central iron abundance enhancement can be attributed wholly to SN
Ia; we find no significant gradient in SN II ejecta. These spatial gradients in
the proportion of SN Ia/II ejecta imply that the dominant metal enrichment
mechanism near the center is different than in the outer parts of the cluster.
We show that the central abundance enhancement is unlikely to be due to ram
pressure stripping of gas from cluster galaxies, or to secularly accumulated
stellar mass loss within the central cD. We suggest that the additional SN Ia
ejecta near the center is the vestige of a secondary SN Ia-driven wind from the
cD (following a more energetic protogalactic SN II-driven wind phase), which
was partially smothered in the cD due to its location at the cluster center.Comment: 25 pages AASTeX; 6 encapsulated PostScript figures; accepted for
publication in ApJ. Replaced with revised versio
Anisotropic multiple scattering in diffuse media
The multiple scattering of scalar waves in diffusive media is investigated by
means of the radiative transfer equation. This approach amounts to a
resummation of the ladder diagrams of the Born series; it does not rely on the
diffusion approximation. Quantitative predictions are obtained, concerning
various observables pertaining to optically thick slabs, such as the mean
angle-resolved reflected and transmitted intensities, and the shape of the
enhanced backscattering cone. Special emphasis is put on the dependence of
these quantities on the anisotropy of the cross-section of the individual
scatterers, and on the internal reflections due to the optical index mismatch
at the boundaries of the sample. The regime of very anisotropic scattering,
where the transport mean free path is much larger than the scattering
mean free path , is studied in full detail. For the first time the
relevant Schwarzschild-Milne equation is solved exactly in the absence of
internal reflections, and asymptotically in the regime of a large index
mismatch. An unexpected outcome concerns the angular width of the enhanced
backscattering cone, which is predicted to scale as
, in contrast with the generally
accepted law, derived within the diffusion approximation.Comment: 53 pages TEX, including 2 tables. The 4 figures are sent at reques
Explosive nucleosynthesis in core-collapse supernovae
The specific mechanism and astrophysical site for the production of half of
the elements heavier than iron via rapid neutron capture (r-process) remains to
be found. In order to reproduce the abundances of the solar system and of the
old halo stars, at least two components are required: the heavy r-process
nuclei (A>130) and the weak r-process which correspond to the lighter heavy
nuclei (A<130). In this work, we present nucleosynthesis studies based on
trajectories of hydrodynamical simulations for core-collapse supernovae and
their subsequent neutrino-driven winds. We show that the weak r-process
elements can be produced in neutrino-driven winds and we relate their
abundances to the neutrino emission from the nascent neutron star. Based on the
latest hydrodynamical simulations, heavy r-process elements cannot be
synthesized in the neutrino-driven winds. However, by artificially increasing
the wind entropy, elements up to A=195 can be made. In this way one can mimic
the general behavior of an ejecta where the r-process occurs. We use this to
study the impact of the nuclear physics input (nuclear masses, neutron capture
cross sections, and beta-delayed neutron emission) and of the long-time
dynamical evolution on the final abundances.Comment: 10 pages, 8 figures, invited talk, INPC 2010 Vancouver, Journal of
Physics: Conference Serie
Role of Anisotropy and Refractive Index in Scattering and Whiteness Optimization
The ability to manipulate light-matter interaction to
tailor the scattering properties of materials is crucial
to many aspects of our everyday life, from paints
to lighting, and to many fundamental concepts in
disordered photonics. Light transport and scattering
in a granular disordered medium are dictated by the
spatial distribution (structure factor) and the scattering properties (form factor and refractive index) of its
building blocks. As yet, however, the importance of
anisotropy in such systems has not been considered.
Here, we report a systematic numerical survey that
disentangles and quanti es the role of different kinds
and degrees of anisotropy in scattering optimization.
We show that ensembles of uncorrelated, anisotropic
particles with nematic ordering enables to increase
by 20% the reflectance of low-refractive index media
(n = 1.55), using only three-quarters of material
compared to their isotropic counterpart. Additionally,
these systems exhibit a whiteness comparable to
conventionally used high-refractive index media, e.g.
TiO2 (n = 2:60). Therefore, our findings not only
provide an understanding of the role of anisotropy
in scattering optimization, but they also showcase a
novel strategy to replace inorganic white enhancers
with sustainable and bio-compatible products made of
biopolymers
Intermediate Element Abundances in Galaxy Clusters
We present the average abundances of the intermediate elements obtained by
performing a stacked analysis of all the galaxy clusters in the archive of the
X-ray telescope ASCA. We determine the abundances of Fe, Si, S, and Ni as a
function of cluster temperature (mass) from 1--10 keV, and place strong upper
limits on the abundances of Ca and Ar. In general, Si and Ni are overabundant
with respect to Fe, while Ar and Ca are very underabundant. The discrepancy
between the abundances of Si, S, Ar, and Ca indicate that the alpha-elements do
not behave homogeneously as a single group. We show that the abundances of the
most well-determined elements Fe, Si, and S in conjunction with recent
theoretical supernovae yields do not give a consistent solution for the
fraction of material produced by Type Ia and Type II supernovae at any
temperature or mass. The general trend is for higher temperature clusters to
have more of their metals produced in Type II supernovae than in Type Ias. The
inconsistency of our results with abundances in the Milky Way indicate that
spiral galaxies are not the dominant metal contributors to the intracluster
medium (ICM). The pattern of elemental abundances requires an additional source
of metals beyond standard SNIa and SNII enrichment. The properties of this new
source are well matched to those of Type II supernovae with very massive,
metal-poor progenitor stars. These results are consistent with a significant
fraction of the ICM metals produced by an early generation of population III
stars.Comment: 18 pages, 11 figures, 7 tables. Submitted to Ap
Recent X-ray Observations and the Evolution of Hot Gas in Elliptical Galaxies: Evidence for Circumgalactic Gas
X-ray emitting gaseous halos, such as that in elliptical galaxies like NGC
4472, cannot have been produced solely from gas expelled from galactic stars.
In traditional models for the evolution of hot interstellar gas (cooling flows)
in ellipticals, the galaxies are assumed to have been cleared of gas by
SNII-driven winds at some early time then gas is subsequently replenished by
mass loss from an evolving population of old stars. To test this, we accurately
determine the stellar and dark halo mass of NGC 4472 using hydrostatic
equilibrium, then solve the standard time-dependent cooling flow equations to
recover the observed hot gas temperature and density distributions when evolved
to the present time. This procedure fails: the computed gas density gradient is
too steep, the total gas mass is too low, and the gas temperatures are much too
low. All variants on this basic procedure also fail: increasing the SNIa rate,
using the mass dropout assumption, arbitrarily adjusting uncertain
coefficients, etc. However, agreement is achieved if the galaxy is supplied
with additional, spatially-extended hot gas early in its evolution. This old
``circumgalactic'' gas can be retained to the present time and may be related
to cosmological ``secondary infall''.Comment: 15 pages in two-column AASTEX LaTeX including 1 table and 8 figures;
abstract corrected in replacement; accepted by Astrophysical Journa
Homodyne detection for atmosphere channels
We give a systematic theoretical description of homodyne detection in the
case where both the signal and the local oscillator pass through the turbulent
atmosphere. Imperfect knowledge of the local-oscillator amplitude is
effectively included in a noisy density operator, leading to postprocessing
noise. Alternatively, we propose a technique with monitored transmission
coefficient of the atmosphere, which is free of postprocessing noise.Comment: 9 pages, 5 figure
Characterizing the role of rice NRAMP5 in Manganese, Iron and Cadmium Transport
Metals like manganese (Mn) and iron (Fe) are essential for metabolism, while cadmium (Cd) is toxic for virtually all living organisms. Understanding the transport of these metals is important for breeding better crops. We have identified that OsNRAMP5 contributes to Mn, Fe and Cd transport in rice. OsNRAMP5 expression was restricted to roots epidermis, exodermis, and outer layers of the cortex as well as in tissues around the xylem. OsNRAMP5 localized to the plasma membrane, and complemented the growth of yeast strains defective in Mn, Fe, and Cd transport. OsNRAMP5 RNAi (OsNRAMP5i) plants accumulated less Mn in the roots, and less Mn and Fe in shoots, and xylem sap. The suppression of OsNRAMP5 promoted Cd translocation to shoots, highlighting the importance of this gene for Cd phytoremediation. These data reveal that OsNRAMP5 contributes to Mn, Cd, and Fe transport in rice and is important for plant growth and development
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