1,435 research outputs found
Induced ferroelectric phases in TbMn_2O_5
The magnetostructural transitions and magnetoelectric effects reported in
TbMn2O5 are described theoretically and shown to correspond to two essentially
different mechanisms for the induced ferroelectricity. The incommensurate and
commensurate phases observed between 38 and 24 K exhibit a hybrid pseudoproper
ferroelectric nature resulting from an effective bilinear coupling of the
polarization with the antiferromagnetic order parameter. This explains the high
sensitivity of the dielectric properties of the material under applied magnetic
field. Below 24 K the incommensurate phase shows a standard improper
ferroelectric character induced by the coupling of two distinct magnetic order
parameters. The complex dielectric behavior observed in the material reflects
the crossover from one to the other transition regime. The temperature
dependences of the pertinent physical quantities are worked out, and previous
theoretical models are discussed
The connection between the radio jet and the gamma-ray emission in the radio galaxy 3C 120
We present the analysis of the radio jet evolution of the radio galaxy 3C 120
during a period of prolonged gamma-ray activity detected by the Fermi satellite
between December 2012 and October 2014. We find a clear connection between the
gamma-ray and radio emission, such that every period of gamma-ray activity is
accompanied by the flaring of the mm-VLBI core and subsequent ejection of a new
superluminal component. However, not all ejections of components are associated
with gamma-ray events detectable by Fermi. Clear gamma-ray detections are
obtained only when components are moving in a direction closer to our line of
sight.This suggests that the observed gamma-ray emission depends not only on
the interaction of moving components with the mm-VLBI core, but also on their
orientation with respect to the observer. Timing of the gamma-ray detections
and ejection of superluminal components locate the gamma-ray production to
within almost 0.13 pc from the mm-VLBI core, which was previously estimated to
lie about 0.24 pc from the central black hole. This corresponds to about twice
the estimated extension of the broad line region, limiting the external photon
field and therefore suggesting synchrotron self Compton as the most probable
mechanism for the production of the gamma-ray emission. Alternatively, the
interaction of components with the jet sheath can provide the necessary photon
field to produced the observed gamma-rays by Compton scattering.Comment: Already accepted for publication in The Astrophysical Journa
X-ray Diffraction Study of Superstructure in GdBaCo2O5.5
A single crystal of GdBaCo2O5.47(2) has been studied by means of X-ray
diffraction. Appearance of superstructure reflections at T = 341.5(7) K gives
an evidence of continuous transition to the phase with unit cell doubled along
the shortest edge a1. Critical exponent for the order parameter is found to be
beta=0.33(1). The superstructure reflections are about 2-4 orders of magnitude
weaker than the basic ones. Their systematic extinction indicates the crystal
symmetry change from Pmmm to Pmma. The integrated intensities allow to
calculate displacements of atoms from the positions in the high-temperature
phase. The cobalt-ligand distances in the ordered phase are discussed in terms
of the spin-state/orbital ordering of Co3+ ions.Comment: 4 page
Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei. IV. Fine Scale Structure
We have used VLBA fringe visibility data obtained at 15 GHz to examine the
compact structure in 250 extragalactic radio sources. For 171 sources in our
sample, more than half of the total flux density seen by the VLBA remains
unresolved on the longest baselines. There are 163 sources in our list with a
median correlated flux density at 15 GHz in excess of 0.5 Jy on the longest
baselines. For about 60% of the sources, we have at least one observation in
which the core component appears unresolved (generally smaller than 0.05 mas)
in one direction, usually transverse to the direction into which the jet
extends. BL Lacs are on average more compact than quasars, while active
galaxies are on average less compact. Also, in an active galaxy the
sub-milliarcsecond core component tends to be less dominant. IDV sources
typically have a more compact, more core-dominated structure on
sub-milliarcsecond scales than non-IDV sources, and sources with a greater
amplitude of intra-day variations tend to have a greater unresolved VLBA flux
density. The objects known to be GeV gamma-ray loud appear to have a more
compact VLBA structure than the other sources in our sample. This suggests that
the mechanisms for the production of gamma-ray emission and for the generation
of compact radio synchrotron emitting features are related. The brightness
temperature estimates and lower limits for the cores in our sample typically
range between 10^11 and 10^13 K, but they extend up to 5x10^13 K, apparently in
excess of the equipartition brightness temperature, or the inverse Compton
limit for stationary synchrotron sources. The largest component speeds are
observed in radio sources with high observed brightness temperatures, as would
be expected from relativistic beaming (abridged).Comment: 31 pages, 13 figures, 4 tables, accepted for publication in the
Astronomical Journal; minor changes to the text are mad
Quasisymmetric graphs and Zygmund functions
A quasisymmetric graph is a curve whose projection onto a line is a
quasisymmetric map. We show that this class of curves is related to solutions
of the reduced Beltrami equation and to a generalization of the Zygmund class
. This relation makes it possible to use the tools of harmonic
analysis to construct nontrivial examples of quasisymmetric graphs and of
quasiconformal maps.Comment: 21 pages, no figure
Development and Study of Hard-Facing Materials on the Base of Heat-Resisting High-Hardness Steels for Plasma-Jet Hard- Facing in Shielding-Doping Nitrogen Atmosphere
The authors develop hard-facing materials on the base of heat-resisting highhardness steels for plasma-jet hard-facing in nitrogen atmosphere for manufacturing parts of mining and metallurgic equipment which significantly simplify the production process and effect a saving when producing bimetallic parts and tools
Developing and Studying the Methods of Hard-Facing with Heat-Resisting High-Hardness Steels
The authors develop the methods of hard-facing of mining-metallurgic equipment parts with heat-resisting high-hardness steels on the base of plasma-jet hard-facing in the shielding-alloying nitrogen atmosphere
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