http://dspace.nbuv.gov.ua:80/handle/123456789/114609 2026-04-17T00:09:39Z http://dspace.nbuv.gov.ua:80/handle/123456789/118054 Singular optics methods for analysis of spatial structure of diffraction field of optical elements Budnyk, O.P.; Lymarenko, R.A. The paper is devoted to developing methods of analytical and experimental investigations of diffraction and interference phenomena used in test systems for optical elements. The theoretical analysis and experimental results illustrate the possibility of describing diffraction phenomena using the objects and methods that were developed in singular optics. It was shown that a system of dislocations in singular component of diffraction field represents its topology. The diffracted field has a system of hidden optical vortices that are smoothly transformed during deformation of an aperture depending on boundary flexion. The proposed experimental proof ground can be useful for the analysis of a wavefront structure. It is also considered the technique for more accurate evaluation of Ronchi test results. The mathematical background of the Ronchi test technique is developed. It describes sufficiently well the wavefront shape, grating plate parameters, image sensor characteristics, parameters of image acquisition and restoration. The fringe pattern distributions and their spatial spectrum are calculated. Both the results of computer simulation of Ronchi fringe pattern and experimental ones obtained using image sensor and the applied image enhancement algorithms are shown. 2003-01-01T00:00:00Z http://dspace.nbuv.gov.ua:80/handle/123456789/118053 Approximation of electro-optical characteristics of ChLC at transitions from the homeotropic texture Rybalochka, A.; Chumachkova, M.; Sorokin, V. In this paper a method for an approximation of electro-optical characteristics of a cholesteric liquid crystal (ChLC) that describe behavior of a cholesteric material at transitions from the field induced homeotropic texture to the stable planar and focal conic textures have been proposed. To obtain the complete information about such behavior of a cholesteric liquid crystal a protracted experimental research is required. Proposed method allows to obtain all necessary approximated electro-optical characteristics of a cholesteric liquid crystal on the basis of experimental measuring only of four special electro-optical characteristics. 2003-01-01T00:00:00Z http://dspace.nbuv.gov.ua:80/handle/123456789/118052 New nonlinear model to determine Cgs and Cgd capacities of GaAs MESFET Merabtine, N.; Amourache, S.; Saidi, Y.; Zaabat, M.; Kenzai, Ch. New nonlinear model for simulating physical and geometrical parameters to determine the junctions capacities of "the Gallium Arsenide Metal Semiconductor Field Effect Transistor" GaAs MESFET are represented in this paper. Non linear variations of the bias and gate-source and gate-drain capacities have been found. A simulated values show excellent agreement with experimental results. 2003-01-01T00:00:00Z http://dspace.nbuv.gov.ua:80/handle/123456789/118051 Domino phase retrieval algorithm for structure determination using electron diffraction and high resolution transmission electron microscopy patterns Chukhovskii, F.N.; Poliakov, A.M.; Prokopenko, I.V. Direct method formalism to determine atomic structures using the electron diffraction data is here aimed at a general solution of the phase retrieval problem, consequently combining the electron diffraction (ED) and the high-resolution transmission electron microscopy (HRTEM) patterns in a "domino" fashion. While there are similarities to what there is in conventional (kinematical) direct methods, there remain major differences, in particular, owing to the dynamical effects in the data the ED structure factors prove to be complex and then, the positivity of the reconstructed electron density is no longer a valid constraint for 'dynamical' direct methods. Besides, due to the dynamical effects heavy atoms need not dominantly contribute the HRTEM images any more. Thus, the 'dynamical' direct methods concept has to base upon it that the phase retrieval algorithm will utilize both the dynamical ED and HRTEM data. Noteworthy is the fact that the fusion of the traditional direct method technique, which is described here, allows to realize a full phase restoration of complex structure factors. The numerical example, using the dynamical ED and HRTEM data for (Ga,In)₂SnO₅5 ceramic, shows that the method is capable of yielding unique phase retrieval solution. The clear sense is that the domino transform algorithm proposed works well and represents a valuable method for phasing diffraction patterns in electron structural crystallography using an experiment, which is readily to perform within collecting the ED and HRTEM data. 2003-01-01T00:00:00Z