Calculation results are presented which show how optical radiation energy is redistributed and the law of conservation of energy is fulfilled when radiation is reflected from a specular surface in a ...turbulent atmosphere. We have ascertained that if spatially limited light beams are formed due to reflection, then the energy is redistributed in a plane transversal to the light propagation direction near the strictly backward direction within a limited region no larger than several Fresnel zones. In the case of a point reflector, where a spatially unlimited reflected wave is generated, the energy redistribution occurs on a much larger scale. An increase in the mean intensity of a reflected wave within a limited region with a diameter of two Fresnel zones around the strictly backward propagation direction (backscatter enhancement effect) occurs due to the outflow of reflected wave energy in lateral directions from a huge domain, which is several orders of magnitude larger than the area where this energy is accumulated.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The ranges of the parameters of wind and temperature (refractive) turbulence are estimated corresponding to the four-point scale of turbulence intensity at flight altitudes in the free atmosphere. It ...is shown that the estimates of both the variance of the radial velocity measured with a coherent lidar in the flight direction and of the structural constant of the refractive index from the lidar measurements of the intensity of refractive turbulence in the flight direction make it possible to judge the potential danger of bumpy flight of aircraft in clear-air turbulence zones ahead of the aircraft.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Time series of the turbulent mixing layer altitude derived from the altitude-time distributions of the turbulence kinetic energy dissipation rate and of the gradient Richardson number are compared. ...We have found that the estimates of the turbulent mixing layer altitude from the altitude-time distributions of the Richardson number and of the turbulence kinetic energy dissipation rate are close only under the conditions of atmospheric boundary layer instability due to convection. In other cases, the mixing layer altitude derived from the Richardson number can be significantly underestimated.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
We study the Borel complexity of some basic families of subsets of a countable group (large, small, thin, sparse, etc.) determined by the sizes of their elements. The obtained results are applied to ...the Čech–Stone compactification 𝛽
G
of the group
G.
In particular, it is shown that the closure of the minimal ideal 𝛽
G
has the
F
𝜎𝛿
type.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
—
Experimental data on lidar signal amplification in a turbulent atmosphere and its dependence on the structure parameter of the turbulent fluctuations of the refractive index of air are presented. ...It is ascertained that the amplification coefficient first increases up to its maximum with the structure parameter of the refractive index and then decreases under the conditions of strong optical turbulence along a sounding path. The maximum of the amplification coefficient attainable at a certain distance depends on the turbulence strength during measurements. The time variations in the backscatter amplification coefficient are in a good agreement with the time variations in the structure parameter of the refractive index determined from independent measurements.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Radiophysical tools for measuring atmospheric dynamics include sodars, Doppler radars, and Doppler lidars. Among these, coherent Doppler lidars (CDLs) have been considered the best for remote ...measurement of wind turbulence. This is important not only for understanding the exchange processes in the boundary layer, but also in the applied aspect, such as aviation safety. CDLs significantly extend possibilities of experimental investigation of not only wind turbulence, but also coherent structures such as aircraft wake vortices. The authors of this book conducted field tests of the developed methods of lidar measurements of the wind velocity, atmospheric turbulence parameters, and aircraft wake vortices. This valuable resource, containing over 500 equations based on original results from the authors' work, gives professionals a comprehensive description of the operating principles of continuous wave and pulsed coherent Doppler lidars. This book studies the possibilities of obtaining information about wind turbulence from data measured by continuous wave and pulsed CDLs.
The purpose of the paper is to determine the differences in the technique of body inrun position at the beginning of take-off in junior ski jumpers of different qualifications (athletic ...preparedness).
Materials and methods. The study participants were 22 junior ski jumpers aged 14-15 (a group of junior ski jumpers) during the Ukrainian Ski Jumping Championship (October 9, 2010, Vorokhta, Ukraine) and 33 ski jumpers aged 16-17 (a group of senior ski jumpers) who took part in the international competitions “Lotos Cup” in January 2010. The study analyzed the videos of take-offs of 22 athletes aged 14-15 and 33 athletes aged 16-17. The parameters of ski jumping technique and sports results were processed on the basis of video materials of the first competition series.
Results. There are significant differences (p < 0.001) in the mean values of corresponding parameters of the body position at the beginning of take-off. The data point to a tighter tuck of the body of the athletes aged 16-17. The structure coefficients of the first canonical discriminant function indicate that the function is most significantly related to the values of angles 10 (ν); 8 (ζ); 6 (θ): the inclination angle of the segment of the straight line passing through the axes of the hip and ankle joints (ν) towards the direction of the skier’s movement; the inclination angle of the segment of the straight line passing through the general center of body weight and the axis of the ankle joint (ζ) towards the direction of the skier’s movement; the inclination angle of the head towards the trunk (θ). The athletes aged 16-17 differ from the athletes aged 14-15 by the parameters characterizing the body’s tuck in the starting position – the position at the beginning of take-off.
Conclusions. The unstandardized canonical discriminant function coefficients can be used to classify the levels of proficiency in the body’s tuck in the starting position – the position at the beginning of take-off in athletes aged 14-17.
Scattered Subsets of Groups Banakh, T. O.; Protasov, I. V.; Slobodianiuk, S. V.
Ukrainian mathematical journal,
08/2015, Volume:
67, Issue:
3
Journal Article
Peer reviewed
Open access
We define scattered subsets of a group as asymptotic counterparts of the scattered subspaces of a topological space and prove that a subset
A
of a group
G
is scattered if and only if
A
does not ...contain any piecewise shifted
IP
-subsets. For an amenable group
G
and a scattered subspace
A
of
G,
we show that
μ
(
A
) = 0 for each left invariant Banach measure
μ
on
G.
It is also shown that every infinite group can be split into ℵ
0
scattered subsets.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
A method is proposed for determining the height of the turbulent mixing layer on the basis of the vertical profiles of the dissipation rate of turbulent energy, which is estimated from lidar ...measurements of the radial wind velocity using conical scanning by a probe beam around the vertical axis. The accuracy of the proposed method is discussed in detail. It is shown that for the estimation of the mixing layer height (MLH) with the acceptable relative error not exceeding 20 %, the signal-to-noise ratio should be no less than -16 dB, when the relative error of lidar estimation of the dissipation rate does not exceed 30 %. The method was tested in a 6 d experiment in which the wind velocity turbulence was estimated in smog conditions due to forest fires in Siberia in summer 2019. The results of the experiment reveal that the relative error of determination of the MLH time series obtained by this method does not exceed 10 % in the period of turbulence development. The estimates of the turbulent mixing layer height by the proposed method are in a qualitative agreement with the MLH estimated from the distributions of the Richardson number in height and time obtained during the comparison experiment in spring 2020.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The method and results of lidar studies of spatiotemporal variability of wind turbulence in the atmospheric boundary layer are reported. The measurements were conducted by a Stream Line pulsed ...coherent Doppler lidar (PCDL) with the use of conical scanning by a probing beam around the vertical axis. Lidar data are used to estimate the kinetic energy of turbulence, turbulent energy dissipation rate, integral scale of turbulence, and momentum fluxes. The dissipation rate was determined from the azimuth structure function of radial velocity within the inertial subrange of turbulence. When estimating the kinetic energy of turbulence from lidar data, we took into account the averaging of radial velocity over the sensing volume. The integral scale of turbulence was determined on the assumption that the structure of random irregularities of the wind field is described by the von Kármán model. The domain of applicability of the used method and the accuracy of the estimation of turbulence parameters were determined. Turbulence parameters estimated from Stream Line lidar measurement data and from data of a sonic anemometer were compared.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
PDF
