Bulletin of the Lebedev Physics Institute最新文献

We report simulation and resolution evaluation of monolithic position sensitive detectors with different surfaces. The best result was obtained using a combination of rough polishing of the crystal surface and a Teflon wrapper with a resolution in the interaction depth of dZ = 0.89 ± 0.01 mm. The best planar resolution dX = 0.53 ± 0.01 mm is obtained for a finely polished plate with an ESR film. The diffuse reflector also demonstrates an increase in light collection by 33% compared to the specular one.

The paper demonstrates a method for calculating spiral beams of a given configuration based on a linear combination of displaced Gaussian beams. A new method for generating spiral beams is implemented. The effect of scaling the phase distribution on the quality of the generated light fields is experimentally investigated. The synthesized fields are tested in an experiment on optical manipulation of ensembles of single microparticles.

Ionization waves (IWs) of positive polarity are studied experimentally in several sealed discharge tubes containing neon at pressures of 0.6‒15 Torr and surrounded with a grounded metal screen. The IWs arise at the stage single-electrode breakdown development at moderate overvoltage conditions, and belong to “slow” ionization waves (velocity of 10⁵‒10⁸ cm/s). The wave propagation is accompanied by a monotonic loss of velocity and the electric potential magnitude at the IW front, indicating its significant spatial attenuation. The IWs are studied by recording x‒t diagrams supplemented with measurements of instantaneous velocities, front potentials, and attenuation coefficients at various pressures and applied voltages. An exponential nature of a decrease in the front potential and instantaneous velocity of the IWs with the distance traveled is established. It is found that the scales of the exponential decrease in both quantities do not coincide. The obtained results can be useful in planning experiments on breakdown in long tubes, ionization wave modeling, as well as their technological implementation

An experimental study of self-organization processes that arise during evaporation of droplets of a colloidal solution of nanocarbon in ethanol from the surface of quartz glass is presented. The influence of the distilled-water content in the colloidal solution and the temperature gradient on the substrate on the distribution of nanoparticles and their agglomerates over the contact area of the drop with the surface are discussed. The evaporation of a multicomponent droplet is examined and described from the viewpoint of mass transfer by identifying the characteristic mechanisms of fluid motion in the droplet as the main cause of motion of nanocarbon nanoparticles. A detailed analysis of nanolayers and nanoparticle agglomerates deposited by droplet coating is performed, and the optimal conditions in terms of the substrate temperature and the pure-water content are determined, under which the most uniform spatial distribution of nanoparticles over the contact area of the droplet with the substrate is observed, as well as additional regimes with spatially uniform distributions of nanoparticle agglomerates (more than 10 μm).

As part of the program for upgrading a stratospheric radiosonde for cosmic rays, an electronic barorelay was developed using modern circuitry elements. This article considers its design and characteristics. The results of test flights with the electronic barorelay and flights with a mechanical barorelay during similar solar activity in 1978 are also compared. According to the results of all tests, it is recommended to use an electronic barorelay in the radiosonde circuit.

For the first time, the secondary diamond nucleation processes are compared during the growth of polycrystalline diamond films by the MPCVD method with addition of nitrogen and ammonia. An ammonia molecule (NH₃) has a lower ionization energy than a nitrogen molecule (N₂) in microwave plasma. It has been established that when using ammonia, the transition to the nanocrystalline structure of diamond occurs at significantly lower concentrations than when using nitrogen.

The treatment efficacy of PEF processing is directly subject to its electric field distribution in the treatment zone. A reliable and efficient model to predict the distribution plays a crucial role for clarifying the treatment mechanism and for improving the treatment effect. A lattice Boltzmann model (LBM) to describe the electric field distribution in a co-linear PEF processing was developed. Based on the assumption that PEF does not cause a time varying magnetic field, the simulation was carried out by using the charge conservation equation. For a two-dimensional LBM, we specified the macroscopic boundary condition for electric potential at high voltage and ground electrodes, and bounce-back boundary condition for electric potential at the insulator. Our model was validated by comparing with previous results based on the finite element method (FEM) for the existing co-linear treatment chambers. We suggested another type of treatment chamber with “holo-elliptical” geometry by which the uniformity of electric field was remarkably improved. Our model encourages further investigation to clear the mechanism of PEF treatment and to design more effective device.

Compressed sampling allows to accurately reconstruct a sparse signal even in case of incomplete signal measurements. In this paper, we apply this method to single-pixel imaging and explore the possibilities of image reconstruction by sampling it with an incomplete set of binary light patterns. Using computer simulation, we optimize the image sampling process and find parameters of light patterns such that single-pixel imaging works best.

The paper examines the possibilities of using the multifrequency synthesis method to improve the quality of images obtained by the space-ground very long baseline radio interferometer mode of the Millimetron observatory. Simulation of imaging observations for the close vicinity of the supermassive black hole M87 was carried out. The advantages of multifrequency synthesis compared to single-frequency observations are shown. The requirements and limitations of its applicability to space-ground interferometry with the Millimetron observatory are formulated.

Geomagnetic radio emission from an extensive atmospheric shower (EAS) is calculated in a kinetic model where, in contrast to previous models, the radiation of each electron and positron of the shower disk is calculated taking into account their spatial distribution in the disk, the disk evolution along the EAS track, energy spectrum and multiple scattering. Radio emission spectra are found at distances of 100 and 800 m from the vertical EAS axis in the frequency range of 40 to 340 MHz with a resolution of 20 MHz.