2,658 research outputs found
On the possibility of applying the quasi-isothermal St\"ackel's model to our Galaxy
An earlier derived quasi-isothermal St\"ackel's model of mass distribution in
stellar systems and the corresponding formula for space density are applied to
our Galaxy. The model rotation curve is fitted to HI kinematical data. The
structural and scale parameters of the model are estimated and the
corresponding density contours for our Galaxy are presented.Comment: 7 pages, 3 figures. Accepted for publication in Baltic Astronomy (BA
AC Conductance in Dense Array of the GeSi Quantum Dots in Si
Complex AC-conductance, , in the systems with dense
GeSi quantum dot (QD) arrays in Si has been determined from
simultaneous measurements of attenuation, ,
and velocity, , of surface acoustic waves (SAW)
with frequencies = 30-300 MHz as functions of transverse magnetic field 18 T in the temperature range = 1-20 K. It has been shown that in the
sample with dopant (B) concentration 8.2 cm at
temperatures 4 K the AC conductivity is dominated by hopping between
states localized in different QDs. The observed power-law temperature
dependence, , and weak frequency dependence,
, of the AC conductivity are consistent with
predictions of the two-site model for AC hopping conductivity for the case of
1, where is the SAW angular frequency and
is the typical population relaxation time. At 7 K the AC
conductivity is due to thermal activation of the carriers (holes) to the
mobility edge. In intermediate temperature region 4 7 K, where AC
conductivity is due to a combination of hops between QDs and diffusion on the
mobility edge, one succeeded to separate both contributions. Temperature
dependence of hopping contribution to the conductivity above 4.5 K
saturates, evidencing crossover to the regime where 1. From
crossover condition, = 1, the typical value, , of
the relaxation time has been determined.Comment: revtex, 3 pages, 6 figure
Thermoconvective flow velocity in a high-speed magnetofluid seal after it has stopped
Convective flow is investigated in the high-speed (linear velocity of the shaft seal is more than 1 m/s) magnetofluid shaft seal after it has been stopped. Magnetic fluid is preliminarily heated due to viscous friction in the moving seal. After the shaft has been stopped, nonuniform heated fluid remains under the action of a high-gradient magnetic field. Numerical analysis has revealed that in this situation, intense thermomagnetic convection is initiated. The velocity of magnetic fluid depends on its viscosity. For the fluid with viscosity of 2 × 10 -4 m 2/s the maximum flow velocity within the volume of magnetic fluid with a characteristic size of 1 mm can attain a value of 10 m/s
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