2,819 research outputs found
Determination of time dependent factors of coefficients in fractional diffusion equations
We consider fractional diffusion equations and study the stability of the
inverse problem of determining the time-dependent parameter in a source term or
a coefficient of zero-th order term from observations of the solution at one
point in a bounded domain
Universal Phase Diagram for High-Piezoelectric Perovskite Systems
Strong piezoelectricity in the perovskite-type PbZr(1-x)TixO3 (PZT) and
Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) systems is generally associated with the
existence of a morphotropic phase boundary (MPB) separating regions with
rhombohedral and tetragonal symmetry. An x-ray study of PZN-9%PT has revealed
the presence of a new orthorhombic phase at the MPB, and a near-vertical
boundary between the rhombohedral and orthorhombic phases, similar to that
found for PZT between the rhombohedral and monoclinic phases. We discuss the
results in the light of a recent theoretical paper by Vanderbilt and Cohen,
which attributes these low-symmetry phases to the high anharmonicity in these
oxide systems.Comment: REVTeX file. 4 pages,=A0 4 figures embedde
Phase transition in Pr0.5Ca0.5CoO3 and related cobaltites
We present an extensive investigation (magnetic, electric and thermal
measurements and X-ray absorption spectroscopy) of the Pr0.5Ca0.5CoO3 and
(Pr1-yYy)0.7Ca0.3CoO3 (y=0.0625-0.15) perovskites, in which a peculiar
metal-insulator (M-I) transition, accompanied with pronounced structural and
magnetic anomalies, occurs at 76 K and 40-132 K, respectively. The inspection
of the M-I transition using the XANES data of Pr L3-edge and Co K-edge proofs
the presence of Pr4+ ions at low temperatures and indicates simultaneously the
intermediate spin to low spin crossover of Co species on lowering the
temperature. The study thus definitively confirms the synchronicity of the
electron transfer between Pr3+ ions and Co^(3+/4+)O3 subsystem and the
transition to the low-spin, less electrically conducting phase. The large
extent of the transfer is evidenced by the good quantitative agreement of the
determined amount of the Pr4+ species, obtained either from the temperature
dependence of the XANES spectra or via integration of the magnetic entropy
change over the Pr4+ related Schottky peak in the low-temperature specific
heat. These results show that the average valence of Pr3+/Pr4+ ions increases
(in concomitance with the decrease of the formal Co valence) below TMI for
(Pr0.925Y0.075)0.7Ca0.3CoO3 up to 3.16+ (the doping level of the CoO3 subsystem
decreases from 3.30+ to 3.20+), for (Pr0.85Y0.15)0.7Ca0.3CoO3 up to 3.28+ (the
decrease of doping level from 3.30+ to 3.13+) and for Pr0.5Ca0.5CoO3 up to
3.46+ (the decrease of doping level from 3.50+ to 3.27+).Comment: 19 pages, 11 figure
Physical Properties, Star Formation, and Active Galactic Nucleus Activity in Balmer Break Galaxies at 0 < z < 1
We present a spectroscopic study with the derivation of the physical
properties of 37 Balmer break galaxies, which have the necessary lines to
locate them in star-forming-AGN diagnostic diagrams. These galaxies span a
redshift range from 0.045 to 0.93 and are somewhat less massive than similar
samples of previous works. The studied sample has multiwavelength photometric
data coverage from the ultraviolet to MIR Spitzer bands. We investigate the
connection between star formation and AGN activity via optical, mass-excitation
(MEx) and MIR diagnostic diagrams. Through optical diagrams, 31 (84%)
star-forming galaxies, 2 (5%) composite galaxies and 3 (8%) AGNs were
classified, whereas from the MEx diagram only one galaxy was classified as AGN.
A total of 19 galaxies have photometry available in all the IRAC/Spitzer bands.
Of these, 3 AGN candidates were not classified as AGN in the optical diagrams,
suggesting they are dusty/obscured AGNs, or that nuclear star formation has
diluted their contributions. Furthermore, the relationship between SFR surface
density (\Sigma_{SFR}) and stellar mass surface density per time unit
(\Sigma_{M_{\ast}/\tau}) as a function of redshift was investigated using the
[OII] \lambda3727, 3729, H\alpha \lambda6563 luminosities, which revealed that
both quantities are larger for higher redshift galaxies. We also studied the
SFR and SSFR versus stellar mass and color relations, with the more massive
galaxies having higher SFR values but lower SSFR values than less massive
galaxies. These results are consistent with previous ones showing that, at a
given mass, high-redshift galaxies have on average larger SFR and SSFR values
than low-redshift galaxies. Finally, bluer galaxies have larger SSFR values
than redder galaxies and for a given color the SSFR is larger for higher
redshift galaxies.Comment: preprint version, 36 pages, 17 figures, 3 tables, accepted for
publication in the Astrophysical Journa
Effects of Sintering Condition on the Trapped Magnetic Field Properties for MgB2 Bulks Fabricated by in-situ Capsule Method
AbstractWe have studied the trapped field properties of MgB2 bulks which were fabricated by the in-situ capsule method under various sintering temperatures of 700-900ÌŠC for 1-24h. The trapped field, BT (T), was 1.8-1.9 T for all the bulks approximately at 16K. The BT (T) values on the bulks sintered at 900ÌŠC for 6h and at 800ÌŠC for 24h were slightly lower than those of other bulks because of the decrease of critical current density, Jc, which originates from both the lower connectivity, K, and the promotion of the grain growth. The high temperature and/or the long periods sintering decrease the BT (T) value. From the obtained results, the sintering at 700-800ÌŠC for 1-6h is the optimum condition to fabricate MgB2 bulks by the capsule method
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