7,213 research outputs found
Overtones of Isoscalar Giant Resonances in medium-heavy and heavy nuclei
A semi-microscopic approach based on both the
continum-random-phase-approximation (CRPA) method and a phenomenological
treatment of the spreading effect is extended and applied to describe the main
properties (particle-hole strength distribution, energy-dependent transition
density, partial direct-nucleon-decay branching ratios) of the isoscalar giant
dipole, second monopole, and second quadrupole resonances. Abilities of the
approach are checked by description of gross properties of the main-tone
resonances. Calculation results obtained for the resonances in a few singly-
and doubly-closed-shell nuclei are compared with available experimental data.Comment: 12 pages, 14 figures, submitted to Phys. Rev.
On Uniqueness of Boundary Blow-up Solutions of a Class of Nonlinear Elliptic Equations
We study boundary blow-up solutions of semilinear elliptic equations
with , or with , where is a second order
elliptic operator with measurable coefficients. Several uniqueness theorems and
an existence theorem are obtained.Comment: To appear in Comm. Partial Differential Equations; 10 page
Differential image motion in the short exposure regime
Whole atmosphere seeing \beta_0 is the most important parameter in site
testing measurements. Estimation of the seeing from a variance of differential
image motion is always biased by a non-zero DIMM exposure, which results in a
wind smoothing. In the paper, the wind effects are studied within short
exposure approximation, i.e. when the wind shifts turbulence during exposure by
distance lesser than device aperture. The method of correction for this effect
on the base of image motion correlation between adjacent frames is proposed. It
is shown that the correlation can be used for estimation of the mean wind speed
V_2 and atmospheric coherence time \tau_0. Total power of longitudinal and
transverse image motion is suggested for elimination of dependence on the wind
direction. Obtained theoretical results were tested on the data obtained on
Mount Shatdjatmaz in 2007--2010 with MASS/DIMM device and good agreement was
found.Comment: 11 pages, 8 figures. Accepted for publication in MNRA
Speckle Interferometry with CMOS Detector
In 2022 we carried out an upgrade of the speckle polarimeter (SPP) -- the
facility instrument of the 2.5-m telescope of the Caucasian Observatory of the
SAI MSU. During the overhaul, CMOS Hamamatsu ORCA-Quest qCMOS C15550-20UP was
installed as the main detector, some drawback of the previous version of the
instrument were eliminated. In this paper, we present a description of the
instrument, as well as study some features of the CMOS detector and ways to
take them into account in speckle interferometric processing. Quantitative
comparison of CMOS and EMCCD in the context of speckle interferometry is
performed using numerical simulation of the detection process. Speckle
interferometric observations of 25 young variable stars are given as an example
of astronomical result. It was found that BM And is a binary system with a
separation of 273 mas. The variability of the system is dominated by the
brightness variations of the main component. A binary system was also found in
NSV 16694 (TYC 120-876-1). The separation of this system is 202 mas.Comment: 24 pages, 27 figures. Minor style differences with respect to version
accepted to Astrophys. Bull. V. 78, no.
Low-Temperature Mobility of Surface Electrons and Ripplon-Phonon Interaction in Liquid Helium
The low-temperature dc mobility of the two-dimensional electron system
localized above the surface of superfluid helium is determined by the slowest
stage of the longitudinal momentum transfer to the bulk liquid, namely, by the
interaction of surface and volume excitations of liquid helium, which rapidly
decreases with temperature. Thus, the temperature dependence of the
low-frequency mobility is \mu_{dc} = 8.4x10^{-11}n_e T^{-20/3} cm^4 K^{20/3}/(V
s), where n_e is the surface electron density. The relation
T^{20/3}E_\perp^{-3} << 2x10^{-7} between the pressing electric field (in
kV/cm) and temperature (in K) and the value \omega < 10^8 T^5 K^{-5}s^{-1} of
the driving-field frequency have been obtained, at which the above effect can
be observed. In particular, E_\perp = 1 kV/cm corresponds to T < 70 mK and
\omega/2\pi < 30 Hz.Comment: 4 pages, 1 figur
Adsorption and two-body recombination of atomic hydrogen on He-He mixture films
We present the first systematic measurement of the binding energy of
hydrogen atoms to the surface of saturated He-He mixture films.
is found to decrease almost linearly from 1.14(1) K down to 0.39(1) K, when the
population of the ground surface state of He grows from zero to
cm, yielding the value K cm
for the mean-field parameter of H-He interaction in 2D. The experiments
were carried out with overall He concentrations ranging from 0.1 ppm to 5 %
as well as with commercial and isotopically purified He at temperatures
70...400 mK. Measuring by ESR the rate constants and for
second-order recombination of hydrogen atoms in hyperfine states and we
find the ratio to be independent of the He content and to
grow with temperature.Comment: 4 pages, 4 figures, all zipped in a sigle file. Submitted to Phys.
Rev. Let
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