Abstract
This article presents the results of processing the experimental data to determine the thickness of the snow cover in an area with a relatively flat terrain using a ground penetrating radar ...(GPR) and a laser rangefinder. It is shown that the GPR determines the thickness of the snow cover with an accuracy of 10-15 cm even in places under vegetation, however, in areas with sharp drops in the snow level, the error can be about 1 m due to the wide directional pattern of the antenna. The laser rangefinder is not suitable for measuring the thickness of the snow cover under vegetation, however, it detects local maxima and minima well, which can significantly supplement the GPR data in identifying critical zones. For surfaces that have a small area free from snow, it is possible to determine the thickness of the snow cover relative to this area with a laser rangefinder accuracy of ∼ 1 cm, but it is necessary that this surface be free of vegetation. This criterion is met, for example, the roof surfaces of large structures, such as water parks. In the case of using only a GPR, sharp drops in snow level are averaged and inaccuracies in measurements at local sites are possible. When using both instruments, it is possible to determine the snow cover with an accuracy of ∼ 10-15 cm on surfaces with vegetation and ∼ 1 cm without vegetation, which is the basis for the joint use of instruments. This work is a continuation of a series of experiments started last year.
The paper is devoted to an experimental study of the heat transfer dynamics during evaporation of a single liquid drop on a heated horizontal surface, which is a sapphire glass coated with a high ...heat-resistant black graphite paint. The method employed in research can be used to study the heat and mass transfer processes in the gas-liquid-solid contact line region with maximum heat transfer coefficient. Its particular feature as compared to the previously known methods is the solution of the initial-boundary problem for the heat conductivity equation, which in terms of mathematics is a correct problem. Using the thermography method, the sapphire surface temperature fields after single drop impingement are determined. The data obtained will be used to calculate the heat flux density in the region of the contact line of the drop.
The results of study on determining the height of the snow cover on a site with a relatively flat terrain using a laser rangefinder are presented. Data on the thickness of the snow cover was ...determined from the dependence of the difference in distances from the reflection point to the rangefinder with and without snow cover in the winter–spring period. The modeling of the determination of the thickness of the snow cover was carried out under the assumption of small irregularities of the measured surface. It is shown that the simulation data may differ from the experimental results up to ~200 mm even on relatively flat areas with a slope of less than 1°, which in some cases is insufficient to predict the impact of snow on snow-covered objects. Comparison with other methods for measuring the depth of snow cover is carried out. Possible applications of the technique used in problems of monitoring and remote sensing are discussed.
The article discusses the combination of a ground penetrating radar (GPR) with a laser rangefinder to determine the snow cover thickness, an experiment is described in accordance with the proposed ...methodology and a comparative analysis of the data obtained is carried out. The purpose of the proposed development of the combined method is to improve the accuracy of snow cover depth determination. Many tasks require high spatial resolution both in the horizontal coordinate and in the depth of the snow cover, since local excess of its critical level can lead to irreversible consequences. Such a situation can arise, for example, when avalanches come down in mountainous areas or when roofs of a large area collapse when snow accumulates on them. The accuracy of the snow depth determination obtained in the experiment is ∼ 10 cm and the resolution along the horizontal coordinate is ∼ 5 cm. The predicted distance based on the equipment used is about 500 meters. The proposed method can be used for determining the amount of snow on roofs of buildings and structures, as well as in predicting the descent of avalanches, and in search for hidden objects under the snow in emergency situations.
We have investigated the pitch angle (
) of the spiral arms of galaxies in the Hubble Space Telescope (HST) COSMOS field. The sample consists of 102 face-on galaxies with a two-armed pattern at a ...mean redshift
. The typical values of
in the arms of distant galaxies are shown to be close to those for nearby spiral galaxies. Within one galaxy the scatter of
for different arms is, on average, half the mean pitch angle. In the
range from 1 to 0 we have found a tendency for
to decrease. Our analysis of the
distributions in galaxies at different redshifts is consistent with the assumption that in most of the galaxies at
the spiral arms are tidal in origin or they arose from transient recurrent instabilities in their disks.
Abstract
We give diffraction gratings an analysis in the lensless camera’s construction, the reasons for their use in image processing, their use and the problems main positive factors associated ...with their consideration in the lensless camera’s construction. The diffraction gratings most common types examples that are currently used in the lens-free camera’s construction are given, their classification and approximate structure with giving their transfer functions mathematical description is given, and their use practical examples in solving various problems associated with image processing are considered. The various diffraction gratings basic advantages and lacks consideration analysis at lensless cameras construction and their use reasons are performed. Also, the questions connected with their further development at image processing construction and use in problems are considered.
Abstract
The inverse problems current state a general characteristic in optics is given, the approaches to their solution, their incorrect and unstable solutions cause are considered, and ...recommendations for these drawbacks elimination are given. General approaches to solving inverse problems in images reconstruction obtained in lensless cameras based on different masks are also considered, and their advantages and disadvantages in comparison with lensless lenses are pointed out, as well as their further research directions are indicated.
•Laser induced THG for CdS/PVA nanocomposites is explored at 1540 nm wavelength.•The photostimulated THG possess maxima within 22-…280 MW/cm2 power densities.•The maximal THG was observed for 13 nm ...NC sizes.•The relaxation degree of the THG after switching off laser treatment was 65%•Laser stimulated THG maxima are shifted up to 60 MW/cm2.
Laser operation by optical third harmonic generation at Er:Yb glass laser fundamental wavelength 1540 nm for the cadmium sulphide (CdS) nanocrystallites (NC) with average sizes 13 nm, 20 nm, 50 nm embedded into the poly(vinyl alcohol) (PVA) photopolymer matrices was discovered. The 300 mJ intensity modulated continuous wave (cw) Nd:YAG 1060 nm laser was used for photoinduced changes. The content of CdS NC was chosen to be 3%, 6%, 9%, 12%. The CdS NC have been synthesized using electrolytic procedure and their structural and morphological features were monitored by X-ray diffraction and transmission electron microscopy (TEM). The dependences of the THG versus the cw laser light power density at 1060 nm was studied and has shown an existence of the maxima which are strongly dependent on the NC sizes. Generally with decreasing NC sizes the laser stimulated THG was increased. The relaxation of the photoinduced changes was explored. The effect may be used for laser operation by coherent harmonic generation in the CdS/polymer nanocomposites.
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