702,568 research outputs found
Direct measurements of the spin and the cyclotron gaps in a 2D electron system in silicon
Using magnetocapacitance data in tilted magnetic fields, we directly
determine the chemical potential jump in a strongly correlated two-dimensional
electron system in silicon when the filling factor traverses the spin and the
cyclotron gaps. The data yield an effective g-factor that is close to its value
in bulk silicon and does not depend on filling factor. The cyclotron splitting
corresponds to the effective mass that is strongly enhanced at low electron
densities
Determination of critical current density in melt-processed HTS bulks from levitation force measurements
A simple approach to describe the levitation force measurements on
melt-processed HTS bulks was developed. A couple of methods to determine the
critical current density were introduced. The averaged -plane
values for the field parallel to this plane were determined. The first and
second levitation force hysteresis loops calculated with these values
coincide remarkably well with the experimental data.Comment: 10 pages (tex), 2 figures (in jpeg
Lattice Dynamics in the Half-Space, II. Energy Transport Equation
We consider the lattice dynamics in the half-space. The initial data are
random according to a probability measure which enforces slow spatial variation
on the linear scale . We establish two time regimes. For
times of order , , locally the measure
converges to a Gaussian measure which is time stationary with a covariance
inherited from the initial measure (non-Gaussian, in general). For times of
order , this covariance changes in time and is governed by a
semiclassical transport equation.Comment: 35 page
Rotation Curve and Mass Distribution in the Galaxy from the Velocities of Objects at Distances up to 200 kpc
Three three-component (bulge, disk, halo) model Galactic gravitational
potentials differing by the expression for the dark matter halo are considered.
The central (bulge) and disk components are described by the Miyamoto-Nagai
expressions. The Allen-Santill'an (I), Wilkinson-Evans (II), and
Navarro-Frenk-White (III) models are used to describe the halo. A set of
present-day observational data in the range of Galactocentric distances R from
0 to 200 kpc is used to refine the parameters of these models. The model
rotation curves have been fitted to the observed velocities by taking into
account the constraints on the local matter density \rho_\odotand the force
K_{z=1.1} acting perpendicularly to the Galactic plane. The Galactic mass
within a sphere of radius 50 kpc,
M_G (R<=50 kpc)=(0.41+/-0.12)x10^12 M_\odot, is shown to satisfy all three
models. The differences between the models become increasingly significant with
increasing radius R. In model I, the Galactic mass within a sphere of radius
200 kpc turns out to be greatest among the models considered,
M_G (R<=200 kpc)=(1.45+/-0.30)x10^12 M_\odot, and the smallest value has been
found in model II,
M_G (R<=200 kpc)=(0.61+/-0.12)x10^{12} M_\odot.
In our view, model III is the best one among those considered, because it
ensures the smallest residual between the data and the constructed model
rotation curve provided that the constraints on the local parameters hold with
a high accuracy. Here, the Galactic mass is
M_G (R<=200 kpc)=(0.75+/-0.19)x10^12 M_\odot.
A comparative analysis with the models by Irrgang et al. (2013), including
those using the integration of orbits for the two globular clusters NGC 104 and
NGC 1851 as an example, has been performed. The third model is shown to have
subjected to a significant improvement.Comment: 22 pages, 7 figures, 2 table
Compatible Lie brackets related to elliptic curve
For the direct sum of several copies of sl_n, a family of Lie brackets
compatible with the initial one is constructed. The structure constants of
these brackets are expressed in terms of theta-functions associated with an
elliptic curve. The structure of Casimir elements for these brackets is
investigated. A generalization of this construction to the case of
vector-valued theta-functions is presented. The brackets define a
multi-hamiltonian structure for the elliptic sl_n-Gaudin model. A different
procedure for constructing compatible Lie brackets based on the argument shift
method for quadratic Poisson brackets is discussed.Comment: 18 pages, Late
Determination of the Solar Galactocentric distance from masers kinemics
We have determined the Galactic rotation parameters and the solar
Galactocentric distance by simultaneously solving Bottlinger's kinematic
equations using data on masers with known line-of-sight velocities and highly
accurate trigonometric parallaxes and proper motions measured by VLBI. Our
sample includes 93 masers spanning the range of Galactocentric distances R from
3 to 15 kpc. The solutions found are
\Omega_0 = 29.7+/-0.5 km s^{-1} kpc^{-1},
\Omega'_0 = -4.20+/-0.11 km s^{-1} kpc^{-2},
\Omega"_0 =0.730+/-0.029 km s^{-1} kpc^{-3}, and
R_0=8.03+/-0.12 kpc. In this case, the linear rotation velocity at the solar
distance R_0 is V_0=238+/-6 km s^{-1}.Comment: 8 pages, 2 figures, 1 table. Paper was presented at the Conference
"Modern Stellar Astronomy-2014" held in Rostov-on-Don State University on May
28-30, 2014, accepted for pubication in Baltic Astronom
OB Stars and Cepheids From the Gaia TGAS Catalogue: Test of their Distances and Proper Motions
We consider young distant stars from the Gaia TGAS catalog. These are 250
classical Cepheids and 244 OB stars located at distances up to 4 kpc from the
Sun. These stars are used to determine the Galactic rotation parameters using
both trigonometric parallaxes and proper motions of the TGAS stars. In this
case the considered stars have relative parallax errors less than 200%.
Following the well-known statistical approach, we assume that the kinematic
parameters found from the line-of-sight velocities are less dependent on
errors of distances than the found from the velocity components . From
values of the first derivative of the Galactic rotation angular velocity
, found from the analysis of velocities and
separately, the scale factor of distances is determined. We found that from the
sample of Cepheids the scale of distances of the TGAS should be reduced by 3%,
and from the sample of OB stars, on the contrary, the scale should be increased
by 9%.Comment: 5 pages, 1 figure, 2 table
A new estimate of the Local Standard of Rest from data on young Galactic objects
To estimate the peculiar velocity of the Sun with respect to the Local
Standard of Rest (LSR), we used young objects in the Solar neighborhood with
distance measurement errors within 10%-15%. These objects were the nearest
Hipparcos stars of spectral classes O--B2.5, masers with trigonometric
parallaxes measured by means of VLBI, and two samples of the youngest and
middle-aged Cepheids. The most significant component of motion of all these
stars is induced by the spiral density wave. As a result of using all these
samples and taking into account the differential Galactic rotation, as well as
the influence of the spiral density wave, we obtained the following components
of the vector of the peculiar velocity of the Sun with respect to the LSR:
(U_o,V_o,W_o)_{LSR}=
(6.0,10.6,6.5)+/-(0.5,0.8,0.3) km s^{-1}. We have found that the Solar
velocity components
(U_o)_{LSR} and
(V_o)_{LSR} are very sensitive to the Solar radial phase \chi_o in the spiral
density wave.Comment: 11 pages, 1 figure, 3 tables. Paper was presented at the Conference
"Modern Stellar Astronomy-2014" held in Rostov-on-Don State University on May
28-30. Accepted for publication in Baltic Astronom
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