8,303 research outputs found
The political dimension of seasonal allocations: Developing a seasonal allocation strategy in a water-short system in Sri Lanka
Water allocation, Irrigation programs, Reservoirs, Participatory management, Farmer participation, Water rights, Irrigated farming, Rice, Water shortage, Farmers' attitudes, Farmer-agency interactions, Sri Lanka
Reflection high-energy electron diffraction experimental analysis of polycrystalline MgO films with grain size and orientation distributions
Analysis of biaxial texture of MgO films grown by ion-beam-assisted deposition (IBAD) has been performed using a quantitative reflection high-energy electron diffraction (RHEED) based method. MgO biaxial texture is determined by analysis of diffraction spot shapes from single RHEED images, and by measuring the width of RHEED in-plane rocking curves for MgO films grown on amorphous Si3N4 by IBAD using 750 eV Ar+ ions, at 45° incidence angle, and MgO e-beam evaporation. RHEED-based biaxial texture measurement accuracy is verified by comparison with in-plane and out-of-plane orientation distribution measurements made using transmission electron microscopy and x-ray rocking curves. In situ RHEED measurements also enable the analysis of the evolution of the biaxial texture which narrows with increasing film thickness. RHEED-based measurements of IBAD MgO biaxial texture show that the minimum in-plane orientation distribution depends on the out-of-plane orientation distribution, and indicates that the minimum obtainable in-plane orientation on distribution is 2°
The Yale-Potsdam Stellar Isochrones (YaPSI)
We introduce the Yale-Potsdam Stellar Isochrones (YaPSI), a new grid of
stellar evolution tracks and isochrones of solar-scaled composition. In an
effort to improve the Yonsei-Yale database, special emphasis is placed on the
construction of accurate low-mass models (Mstar < 0.6 Msun), and in particular
of their mass-luminosity and mass-radius relations, both crucial in
characterizing exoplanet-host stars and, in turn, their planetary systems. The
YaPSI models cover the mass range 0.15 to 5.0 Msun, densely enough to permit
detailed interpolation in mass, and the metallicity and helium abundance ranges
[Fe/H] = -1.5 to +0.3, and Y = 0.25 to 0.37, specified independently of each
other (i.e., no fixed Delta Y/Delta Z relation is assumed). The evolutionary
tracks are calculated from the pre-main sequence up to the tip of the red giant
branch. The isochrones, with ages between 1 Myr and 20 Gyr, provide UBVRI
colors in the Johnson-Cousins system, and JHK colors in the homogeneized
Bessell & Brett system, derived from two different semi-empirical Teff-color
calibrations from the literature. We also provide utility codes, such as an
isochrone interpolator in age, metallicity, and helium content, and an
interface of the tracks with an open-source Monte Carlo Markov-Chain tool for
the analysis of individual stars. Finally, we present comparisons of the YaPSI
models with the best empirical mass- luminosity and mass-radius relations
available to date, as well as isochrone fitting of well-studied steComment: 17 pages, 14 figures; accepted for publication in the Astrophysical
Journa
{Tris[2-(imidazol-2-ylmethylimino)ethyl]methylammonium}iron(II) tris(perchlorate) dihydrate
The title complex, [Fe(C19H27N10)](ClO4)3·2H2O, is a new polymorph of an iron(II) Schiff base complex of tris(2-aminoethyl)methylammonium with imidazole-2-carboxaldehyde. The octahedral FeII atom is bound to three facial imidazole N atoms with average Fe—Nimidazole and Fe—Nimine bond distances of 1.963 (5) and 1.951 (5) Å, respectively. The central N atom of the tripodal ligand is outside the bonding distance at 3.92 Å. The crystal packing is stabilized by the hydrogen-bonding interactions between the two water molecules (acceptor) and two of the three imidazole NH groups (donor). The third imidazole NH group (donor) forms a hydrogen bond to one of the three perchlorate counter-ions (acceptor)
The magnetic phase of the perovskite CaCrO studied with SR
We investigated the magnetic phase of the perovskite CaCrO by using the
muon spin relaxation technique accompanied by susceptibility measurements. A
thermal hysteresis loop is identified with a width of about 1 K at the
transition temperature. Within the time scale of the muon lifetime, a static
antiferromagnetic order is revealed with distinct multiple internal fields
which are experienced in the muon interstitial sites below the phase-transition
temperature, . Above , lattice deformations are indicated by
transverse-field muon-spin rotation and relaxation suggesting a magneto-elastic
mechanism.Comment: 5 pages, 4 figures. Accepted for publication in PR
Late-Type Stars in M31. I.: A Photometric Study of AGB Stars and Metallicity Gradients.
We have imaged five 7\arcmin \x 7\arcmin\ fields in M31 spanning
galactocentric radii from 4 to 32 kpc along the SW-major axis. The fields were
observed through two broad-band (\V\ and \I) and two narrow-band (\CN\ and
\TiO) filters. The broad-band data were used to construct \IvsVI\
color-magnitude diagrams (CMDs) and, in some of our fields, we found
significant numbers of stars in the Cepheid instability strip. A distance
modulus for the Cepheids in the middle field was found that agreed well with
other values in the literature values. The width of the giant branch (GB) in
the \IvsVI\ CMD of all 5 fields was investigated, and we show that in four of
the fields a likely explanation for the GB width is a combination of {\it both}
metallicity and mass variations. Using the broad-band data, the asymptotic
giant branch (AGB) luminosity functions (LFs) were measured in the five fields,
and we show that differences exist between these LFs. We speculate on how the
different star forming histories in the fields may lead to the observed AGB LFs
and GB widths. Using the narrow-band data along with the broad-band data we
separated the AGB stars into carbon-rich (C) and oxygen-rich (M) types. The
carbon stars LFs were used to obtain an estimate for the distance modulus of
M31 which agrees with the value derived from Cepheids. The ratio of C- to
M-stars (C/M) is believed to be an indicator of gaseous chemical abundance at
the time of formation of these stars. We show that the C/M ratio increases
smoothly with galactocentric distance, suggesting an inverse correlation with
metallicity. This is the first demonstration of this effect within a single
extragalactic system. We find that differences in the width of the GB and the
AGB LFs do not significantly affect the C/M ratio. We consider the effect of
the increasing C/M ratio on the ISM in M31, and cite evidence in favor of a
model where the grain composition in M31 is a function of galactocentric
distance.Comment: UUencoded compressed postscript, 3 Figs. available on request.
(Contact [email protected]
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