698 research outputs found
Investigation of clouds spatial distribution using ground-based lidar
Certain investigations of spatial distribution of clouds by employing ground based lidar are presented. The great changeability is one of the main properties of the clouds in the boundary layer. As a result, their optical properties change rapidly which complicates the modeling of cloud evolution. Suitable equipped lidars are widely used for diagnostics of the clouds via a number of scattering and absorption processes. In particular, lidar can provide information on the distribution of meteorological parameters and of the other important cloud characteristics both in vertical and horizontal directions. Herein the time and spatial distribution of the aerosol backscattering coefficient of S sub t and S sub c type clouds are investigated by means of a correlation analysis of the lidar obtained data provided from several arbitrary directions and heights
Laser sounding of instantaneous and mean speed of wind using correlation method
The correlation methods for laser sounding of wind speed are based on mutual processing of lidar signals scattered from several spatially separated volumes at each altitude investigated. The time of atmospheric aerosol transport between the scattering volumes estimated by the position of maximum of the mutual correlation function is the measure of corresponding wind speed. In this case the distance between the scattering volumes (the measuring base), defining the time of aerosol movement through the measuring base also determines the lidar possibilities for measuring the instantaneous (during the time interval of several seconds) or the mean wind speed (some minutes). Based on the experimental investigations performed using two lidars, these possibilites are analyzed
High Dielectric Permittivity in AFeBO Nonferroelectric Perovskite Ceramics (A - Ba, Sr, Ca; B - Nb, Ta, Sb)
AFeBO(A- Ba, Sr, Ca; B-Nb, Ta, Sb) ceramics were
synthesized and temperature dependencies of the dielectric permittivity were
measured at different frequencies. The experimental data obtained show very
high values of the dielectric permittivity in a wide temperature interval that
is inherent to so-called high-k materials. The analyses of these data establish
a Maxwell-Wagner mechanism as a main source for the phenomenon observed.Comment: 6 pages, 7 figure
A theoretical study on the mechanisms of formation of primal carbon clusters and nanoparticles in space
We present a computational study of assembling carbon clusters and nanophases
in space from carbon aggregations. Geometry optimizations and
Density-functional-based tight-binding (SCC-DFTB) dynamics methods are employed
to predict carbon clusters, their time evolution, and their stability. The
initial density of the aggregates is found to be of primary importance for the
structural properties of the clusters. Aggregates with sufficiently low initial
density yield clusters with approximately equal prevalence of sp and sp2
hybridized states and almost missing sp3 ones. The increase in the initial
density results in sp2-dominant molecules that resemble the carbon skeleton of
polycyclic aromatic hydrocarbons (PAHs). Larger initial aggregations with
tetrahedral interatomic orientation result in sp2-dominant multi-dimensional
polymers. Such materials are highly porous and resemble axially bound
nanotubes. Some resultant clusters resemble fullerene building blocks. Spheroid
nanoparticles resembling improper fullerenes are predicted by metadynamics,
aimed at inter-fragment coupling reactions. One such structure has the lowest
binding energy per atom among the studied molecules. All zero-dimensional
forms, obtained by the simulations, conform to the experimentally detected
types of molecules in space. The theoretical IR spectrum of the clusters
closely resembles that of fullerene C70 and therefore such imperfect structures
may be mistaken for known fullerenes in experimental infrared (IR) telescope
studies
The geometry of a vorticity model equation
We provide rigorous evidence of the fact that the modified
Constantin-Lax-Majda equation modeling vortex and quasi-geostrophic dynamics
describes the geodesic flow on the subgroup of orientation-preserving
diffeomorphisms fixing one point, with respect to right-invariant metric
induced by the homogeneous Sobolev norm and show the local existence
of the geodesics in the extended group of diffeomorphisms of Sobolev class
with .Comment: 24 page
Upper limits for a narrow resonance in the reaction p + p -> K^+ + (Lambda p)
The reaction pp -> K^+ + (Lambda p) has been measured at T_p = 1.953 GeV and
\Theta = 0 deg with a high missing mass resolution in order to study the Lambda
p final state interaction. Narrow S = -1 resonances predicted by bag model
calculations are not visible in the missing mass spectrum. Small structures
observed in a previous experiment are not confirmed. Upper limits for the
production cross section of a narrow resonance are deduced for missing masses
between 2058 and 2105 MeV/c^2.Comment: 8 pages, 5 figure
Cross section of the reaction close to threshold
We have measured inclusive data on -meson production in collisions
at COSY J\"ulich close to the hyperon production threshold and determined the
hyperon-nucleon invariant mass spectra. The spectra were decomposed into three
parts: , and . The cross section for the
channel was found to be much smaller than a previous measurement in
that excess energy region. The data together with previous results at higher
energies are compatible with a phase space dependence.Comment: accepted by Phys. lett. B some typos correcte
Detailed comparison of the pp -> \pi^+pn and pp -> \pi^+d reactions at 951 MeV
The positively charged pions produced in proton-proton collisions at a beam
momentum of 1640 MeV/c were measured in the forward direction with a high
resolution magnetic spectrograph. The missing mass distribution shows the bound
state (deuteron) clearly separated from the continuum. Despite the very
good resolution, there is no evidence for any significant production of the
system in the spin-singlet state. However, the cross section ratio is about twice as large as
that predicted from -wave final-state-interaction theory and it is suggested
that this is due to -state effects in the system.Comment: 8 pages, 3 figure
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