1,421 research outputs found
Local redistribution of blood under the effect of fixation stress against a background of hypokinesia
Fixation stress was used as a model of emotional disturbance. The effect of previous restrictions on mobility on the local redistribution of blood resulting from fixation stress was examined. Disturbances in carbohydrate which result from prolonged hypokinesia was studied. Radioactivity was used to determine the local redistribution of blood. Modified factor analysis was used to study the results of the experiment
A VLBA survey of the core shift effect in AGN jets I. Evidence for dominating synchrotron opacity
The effect of a frequency dependent shift of the VLBI core position (known as
the "core shift") was predicted more than three decades ago and has since been
observed in a few sources, but often within a narrow frequency range. This
effect has important astrophysical and astrometric applications. To achieve a
broader understanding of the core shift effect and the physics behind it, we
conducted a dedicated survey with NRAO's Very Long Baseline Array (VLBA). We
used the VLBA to image 20 pre-selected sources simultaneously at nine
frequencies in the 1.4-15.4 GHz range. The core position at each frequency was
measured by referencing it to a bright, optically thin feature in the jet. A
significant core shift has been successfully measured in each of the twenty
sources observed. The median value of the core shift is found to be 1.21 mas if
measured between 1.4 and 15.4 GHz, and 0.24 mas between 5.0 and 15.4 GHz. The
core position, r, as a function of frequency, n, is found to be consistent with
an r n^-1 law. This behavior is predicted by the Blandford & Koenigl model of a
purely synchrotron self-absorbed conical jet in equipartition. No systematic
deviation from unity of the power law index in the r(n) relation has been
convincingly detected. We conclude that neither free-free absorption nor
gradients in pressure and/or density in the jet itself and in the ambient
medium surrounding the jet play a significant role in the sources observed
within the 1.4-15.4 GHz frequency range. These results support the
interpretation of the parsec-scale core as a continuous Blandford-Koenigl type
jet with smooth gradients of physical properties along it.Comment: 31 pages, 6 figures, 5 tables; accepted to Astronomy & Astrophysic
Symmetry, incommensurate magnetism and ferroelectricity: the case of the rare-earth manganites RMnO3
The complete irreducible co-representations of the paramagnetic space group
provide a simple and direct path to explore the symmetry restrictions of
magnetically driven ferroelectricity. The method consists of a straightforward
generalization of the method commonly used in the case of displacive modulated
systems and allows us to determine, in a simple manner, the full magnetic
symmetry of a given phase originated from a given magnetic order parameter. The
potential ferroic and magneto-electric properties of that phase can then be
established and the exact Landau free energy expansions can be derived from
general symmetry considerations. In this work, this method is applied to the
case of the orthorhombic rare-earth manganites RMnO3. This example will allow
us to stress some specific points, such as the differences between commensurate
or incommensurate magnetic phases regarding the ferroic and magnetoelectric
properties, the possible stabilization of ferroelectricity by a single
irreducible order parameter or the possible onset of a polarization oriented
parallel to the magnetic modulation. The specific example of TbMnO3 will be
considered in more detail, in order to characterize the role played by the
magneto-electric effect in the mechanism for the polarization rotation induced
by an external magnetic field.Comment: Conference: Aperiodic`0
Coherent photogalvanic effect in fluctuating superconductors
We develop a theory of the coherent photogalvanic effect (CPGE) in
low-dimensional superconductors in the fluctuating regime. It manifests itself
in the appearance of a stationary electric current of Cooper pairs under the
action of two coherent electromagnetic fields of light with frequencies lying
in the sub-terahertz range. We derive the general formula for the electric
current density, study the particular cases of linear and circular
polarizations of the external light fields, and show that the current might
have a non-monotonous spectrum at certain polarization angles and turns out
very sensitive to the proximity of the ambient temperature to the critical
temperature of superconducting transition: Approaching the critical
temperature, the peak in the spectrum becomes narrower, its frequency
experiences a redshift, and the intensity of the peak drastically grows.Comment: 5 pages, 4 figure
Disentanglement of the electronic and lattice parts of the order parameter in a 1D Charge Density Wave system probed by femtosecond spectroscopy
We report on the high resolution studies of the temperature (T) dependence of
the q=0 phonon spectrum in the quasi one-dimensional charge density wave (CDW)
compound K0.3MoO3 utilizing time-resolved optical spectroscopy. Numerous modes
that appear below Tc show pronounced T-dependences of their amplitudes,
frequencies and dampings. Utilizing the time-dependent Ginzburg-Landau theory
we show that these modes result from linear coupling of the electronic part of
the order parameter to the 2kF phonons, while the (electronic) CDW amplitude
mode is overdamped.Comment: 4 pages, 3 figures + supplementary material, accepted for publication
in Phys. Rev. Let
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
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