Chemical surface deposition of CdS thin films from CdI2 aqueous solution

For the first time using CdI2 solution CdS films on glass and ITO coated glass substrates were produced by the method of layerwise chemical surface deposition (ChSD). CdS thin films with the widths from 40 nm to 100 nm were obtained for windows in solar cells based on CdS/CdTe heterojunctions. Changes of the structural and optical properties of CdS films due to air annealing are shown. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/910

Dynamical chaos in the problem of magnetic jet collimation

We investigate dynamics of a jet collimated by magneto-torsional oscillations. The problem is reduced to an ordinary differential equation containing a singularity and depending on a parameter. We find a parameter range for which this system has stable periodic solutions and study bifurcations of these solutions. We use Poincar\'e sections to demonstrate existence of domains of regular and chaotic motions. We investigate transition from periodic to chaotic solutions through a sequence of period doublings.Comment: 11 pages, 29 figures, 1 table, MNRAS (published online

Constraining spherically symmetric metrics by the gap between photon rings

Gravitational lensing of luminous matter that surrounds a black hole or some other sufficiently compact object produces an infinite sequence of images. Besides the direct (or primary) image, it comprises demagnified and deformed replicas of the original known as photon rings which are progressively nearing the boundary of the so-called shadow. In the present paper, we present analytical approximation formulas for higher-order photon rings for an asymptotically flat, static, spherically symmetric spacetime that admits a photon sphere. We consider an emission ring in the equatorial plane and an observer at arbitrary inclination far away from the center. Fixing the emission radius and leveraging the strong deflection limit, which provides an analytical logarithmic approximation for the deflection angle, we find the deformed shape of higher-order photon rings in the form of a polar equation on the observer's screen. It has been suggested by other authors to use the relative size of photon rings for characterizing the underlying spacetime. In particular, the relative separation between two neighboring photon rings, which we call "gap parameter," was considered. We obtain an analytical expression for the gap parameter of higher-order photon rings for metrics of the considered class that may depend on multiple parameters. The advantage of using this quantity is in the fact that, to within the assumed approximations, it is independent of the mass of the central object (or of some other characteristic parameter if the mass is zero) and of the distance of the observer. Measurements of the gap parameter, which may become possible in the near future, will restrict the spacetime models that are in agreement with the observations. Even without knowledge of the emission radius, it will conclusively rule out some metrics. We exemplify our calculations of the gap parameter with the Schwarzschild, Reissner-Nordstr & ouml;m, Janis-Newman-Winicour and Ellis wormhole metrics. In the second and third cases some coefficients have to be calculated numerically

Strong deflection limit analysis of black hole lensing in inhomogeneous plasma

This paper investigates gravitational lensing effects in the presence of plasma in the strong deflection limit, which corresponds to light rays circling around a compact object and forming higher-order images. While previous studies of this case have predominantly focused on the deflection of light in a vacuum or in the presence of a homogeneous plasma, this work introduces an analytical treatment for the influence of a nonuniform plasma. After recalling the exact expression for the deflection angle of photons in a static, asymptotically flat and spherically symmetric spacetime filled with cold nonmagnetized plasma, a strong deflection limit analysis is presented. Particular attention is then given to the case of a Schwarzschild spacetime, where the deflection angle of photons for different density profiles of plasma is obtained. Moreover, perturbative results for an arbitrary power-law radial density profile are also presented. These formulas are then applied to the calculation of the positions and magnifications of higher-order images, concluding that the presence of a nonuniform plasma reduces both their angular size and their magnifications, at least within the range of the power-law indices considered. These findings contribute to the understanding of gravitational lensing in the presence of plasma, offering a versatile framework applicable to various asymptotically flat and spherically symmetric spacetimes