5,589 research outputs found
Measurement of the solar system acceleration using the Earth scale factor
We propose an alternative method to detect the secular aberration drift
induced by the solar system acceleration due to the attraction to the Galaxy
centre. This method is free of the individual radio source proper motion caused
by intrinsic structure variation. We developed a procedure to estimate the
scale factor directly from very long baseline interferometry (VLBI) data
analysis in a source-wise mode within a global solution. The scale factor is
estimated for each reference radio source individually as a function of
astrometric coordinates (right ascension and declination). This approach splits
the systematic dipole effect and uncorrelated motions on the level of
observational parameters. We processed VLBI observations from 1979.7 to 2016.5
to obtain the scale factor estimates for more than 4,000 reference radio
sources. We show that the estimates highlight a dipole systematics aligned with
the direction to the centre of the Galaxy. With this method we obtained a
Galactocentric acceleration vector with an amplitude of 5.2 0.2 \mu as/yr
and direction and .Comment: accepted to A&
On the VLBI measurement of the Solar System acceleration
We propose new estimates of the secular aberration drift, mainly due to the
rotation of the Solar System about the Galactic center, based on up-to-date
VLBI observations and and improved method of outlier elimination. We fit
degree-2 vector spherical harmonics to extragalactic radio source proper motion
field derived from geodetic VLBI observations spanning 1979-2013. We pay
particular attention to the outlier elimination procedure to remove outliers
from (i) radio source coordinate time series and (ii) the proper motion sample.
We obtain more accurate values of the Solar system acceleration compared to
those in our previous paper. The acceleration vector is oriented towards the
Galactic center within 7 deg. The component perpendicular to the Galactic plane
is statistically insignificant. We show that an insufficient cleaning of the
data set can lead to strong variations in the dipole amplitude and orientation,
and statistically biased results.Comment: Accepted for publication in A&
Electromagnetic modulation of monochromatic neutrino beams
A possibility to produce a modulated monochromatic neutrino beam is
discussed. Monochromatic neutrinos can be obtained in electron capture by
nuclei of atoms or ions, in particular, by nuclei of hydrogen-like ions. It is
shown that monochromatic neutrino beam from such hydrogen-like ions with nuclei
of non-zero spin can be modulated because of different probabilities of
electron capture from hyperfine states. Modulation arises by means of inducing
of electromagnetic transitions between the hyperfine states. Requirements for
the hydrogen-like ions with necessary properties are discussed. A list of the
appropriate nuclei for such ions is presented.Comment: 11 pages, 1 figure, minor corrections to match the final published
versio
The influence of Galactic aberration on precession parameters determined from VLBI observations
The influence of proper motions of sources due to Galactic aberration on
precession models based on VLBI data is determined. Comparisons of the linear
trends in the coordinates of the celestial pole obtained with and without
taking into account Galactic aberration indicate that this effect can reach 20
as per century, which is important for modern precession models. It is
also shown that correcting for Galactic aberration influences the derived
parameters of low-frequency nutation terms. It is therefore necessary to
correct for Galactic aberration in the reduction of modern astrometric
observations
Microscopic theory of spin-orbit torques and skyrmion dynamics
We formulate a general microscopic approach to spin-orbit torques in thin
ferromagnet/heavy-metal bilayers in linear response to electric current or
electric field. The microscopic theory we develop avoids the notion of spin
currents and spin-Hall effect. Instead, the torques are directly related to a
local spin polarization of conduction electrons, which is computed from
generalized Kubo-St\v{r}eda formulas. A symmetry analysis provides a one-to-one
correspondence between polarization susceptibility tensor components and
different torque terms in the Landau-Lifshitz-Gilbert equation for
magnetization dynamics. The spin-orbit torques arising from Rashba or
Dresselhaus type of spin-orbit interaction are shown to have different
symmetries. We analyze these spin-orbit torques microscopically for a generic
electron model in the presence of an arbitrary smooth magnetic texture. For a
model with spin-independent disorder we find a major cancelation of the
torques. In this case the only remaining torque corresponds to the
magnetization-independent Edelstein effect. Furthermore, our results are
applied to analyze the dynamics of a Skyrmion under the action of electric
current.Comment: 13 pages, 4 figure
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