The paper provides a literature review of the features of models of self-organization of dendritic objects.On the basis of theoretical studies, the features of scaling of dendritic structures in light fields, which manifest themselves in the form of stable local formations, have been determined. General approaches to solving a fundamental scientific problem aimed at establishing patterns that determine the quantitative relationship between the features of the structure of dendrites and their spectral characteristics are considered. Finding the characteristics of dendrites can be used in the development of new diagnostic tools for their study.
Show AbstractIron cations Fe$^{3+}$ (S = 5/2) in inorganic compounds usually effectively interact with each other along three directions, which excludes the presence of correlation effects associated with shortrange order. However, some systems with distant fragments containing Fe$^{3+}$ ions due to ligands or other nonmagnetic cations, retain signs of low-dimensional magnetic behavior both above and below the temperature of magnetic ordering. In this review, we have selected examples of iron compounds that can be attributed to the different classes of low-dimensional magnets, including magnetic clusters: dimers in Fe(Te$_{1.5}$Se$_{0.5}$)O$_5$Cl, magnetic chains in Bi$_2$Fe(SeO$_3$)$_2$OCl$_3$, Fe$_2$O(SeO$_3$)$_2$, magnetic chains with different spins Na$_x$Fe$_7$(PO$_4$)$_6$ (\textit{x} = 0, 0.65), MCuFe$_2$(VO$_4$)$_3$ (M = Li, Na), magnetic two-dimensional planes with triangular arrangement of magnetic ions MFeO$_2$ (M = Ag$^+$, Cu$^+$), MFe(MoO$_4$)$_2$ (M = K$^+$, Rb$^+$, Cs$^+$, Tl$^+$), NaFe$_3$(HPO$_3$)$_2$((H,F)PO$_2$OH)$_6$.
Show AbstractProstate cancer is common cancer affecting the prostate, a gland in the male reproductive system. Cancer develops from the tissues of the prostate when cells there mutate and multiply out of control. These can then spread (metastasize) by migrating from the prostate to other parts of the body, especially the bones and lymph nodes in the pelvis. This type of cancer usually grows slowly, but it can be treated successfully using the different treatment techniques available today. Radiation Therapy and Proton Therapy remain among the most effective techniques for the treatment of prostate cancer, they destroy the cancer cells by blocking their ability to multiply. The main objective of our work is to model the male pelvic area in the form of a mathematical phantom with real dimensions using the Monte Carlo simulation platform GEANT4, to subsequently make a dosimetric comparison between track-structure technique for photon and condensed history technique for proton to find the most effective technique which allows the minimum doses to be deposited in the organs at risk.
Show AbstractModel calculations are carried out for a few configurations of dense structures in homogeneous ground with the goal to develop the muon radiography method. The sensitivity of the method and possible role of statistical fluctuations is assessed for the cases considered. Quantitative analysis of muon radiography data is made which results may be used for the planning of the future experiments.
Show AbstractDifferential cross sections ${d\sigma _{nf,p}} \left(\theta\right/)d\Omega$ of the fission reaction of nonoriented target nuclei by cold polarized neutrons with the emission of light particles ($p$), which include prescission $\alpha$- particles and evaporative neutrons and $\gamma$-quanta, can be represented as the sum of the cross section ${d\sigma}^{0} _{nf,p}} \left(\theta\right/)d\Omega$, corresponding to unpolarized neutrons and the cross section ${d\sigma}^{1} _{nf,p}} \left(\theta\right/)d\Omega$, linearly related to the neutron polarization vector $\mathbf{\sigma}_n$.. The last cross section is expressed through the sum of P-even T-odd triple $A\left(\boldsymbol\sigma_{n} \left[\mathbf{k}_{LF} ,\mathbf{k}_{p} \right]\right)$ and quinary $B\left(\boldsymbol\sigma_{n} \left[\mathbf{k}_{LF} ,\mathbf{k}_{p} \right]\right)\left(\mathbf{k}_{LF} ,\mathbf{k}_{p} \right)$ scalar correlators, the signs of which change and do not change during the transformation $\theta \to \pi -\theta $ accordingly. Using the experimental cross sections ${d\sigma _{nf,p} (\theta)/ d\Omega} $ and ${d\sigma _{nf,p}^{0} (\theta)/ d\Omega} $ , the experimental values of the correlators considered above were found. In the work within the framework of the quantum theory of fission, taking into account the Coriolis interaction of the total spin of a compound fissile system with the orbital angular momenta of fission fragments and prescission $\alpha$-particles, it was possible satisfactory to describe the characteristics of the noted above experimental correlators in the case of the emission of prescission $\alpha$-particles and prompt neutrons and $\gamma$-quanta for most of the nuclei-targets under consideration. A noticeable discrepancy between the theoretical and experimental characteristics is observed for the triple correlator only in the case of $\alpha$-particles for the target nucleus $^{233}$U. This, apparently, can be associated with an additional mechanism of the appearance of similar correlators, connected with the influence of bending and wriggling--oscillations of compound nucleus in the vicinity of the scission point on $\alpha$-particle escaping from the nucleus neck.
Show AbstractIt is shown that the experimental energy characteristics of long-range $\alpha$-particles, considered as third particles, emitted in the ternary spontaneous and induced by neutrons fission of nuclei allow us to assume that the ternary nuclear fission belongs to the class of two-stage virtual nuclear decays, in which states of intermediate nuclei that lie outside the mass surface of the decay appear, so as in previously studied processes of double beta-decay and two-proton decay of nuclei. The ternary fission widths and the $\alpha$-particles energy distributions were calculated based on the concepts of the quantum fission theory and the proposed virtual mechanism of ternary fission, taking into account that the $\alpha$-particle is emitted from the neck of the fissile nucleus in its configuration preceding the nucleus rupture into fission fragments. An estimate of the radius of the fissile nucleus neck for spontaneous ternary fission of $^{250,252}$Cf, $^{248}$Cm, nuclei, as well as for ternary fission of $^{233,235}$U nuclei induced by neutrons is obtained from the comparison of these energy distributions with experimental α-particles distributions and is consistent with the values of similar radii from calculations of the evolution of the fissile nucleus shape based on the generalized droplet model of the nucleus.
Show AbstractIn this study, the details of design studies and obtained main parameters for dipole and combined sextupole/quadrupole magnets for the booster ring of TURKAY, namely Turkish Accelerator Center Synchrotron Radiation Facility are presented. Besides that, the corrector magnet’s testing results are demonstrated, which could be informative for the straight sections of the main ring. The measurements of the corrector magnet and the magnetic simulation results of the sextupole/quadrupole magnet are given in detail. Based on experimental results on the corrector magnet, excitation effects of the field strength of multipoles and higher-order harmonics are presented. In this frame, we used the combined function quadrupole and sextupole field approximation in the combined magnet design and COMSOL Multiphysics 3D and Creo Parametric 3D programs for 3D representations. Moreover, we used the laminated core technique to produce the corrector magnet and the rotating coil and the hall probe techniques for the measurements.
Show AbstractThis research aims to achieve the desired objectives to install the devices of the prompt gamma activation analysis technique soon. For this, we participated in the realization of models and simulations using the Monte Carlo method to know the behavior and the neutron distribution in the collimator, the sapphire, the shutter (off state), and in the shielding. So we calculated the neutron doses in 10 different positions for the purpose to increase the confidence interval of all radiation leaks.
Show AbstractThis work aims to calculate the air Kerma to ambient dose equivalent conversion coefficients $ \textit{H}^{*}(10) $, for mono-energetic photons from 0.015 to 10 MeV. A new analytical approach has been used for conversion coefficients calculation in Kerma approximation and absorbed dose terms. The obtained results in good agreement with those published in Al Kanti, 2020, and ICRU 57 were found. We concluded that new analytical fits provide a convenient approach for determining conversion coefficients for discrete incidents.
Show AbstractThe angular sensitivity of the MatriXX ionizing chambers array (IBA Dosimetry) was investigated in order to make corrections to the measured dose distribution with the aim of the accuracy improvement of intensity modulated plans verification. MatriXX in combination with the phantom was irradiated using medical linear accelerator at various gantry positions. The measured dose distribution for each irradiated angle was processed in Python3 and compared with the reference calculated one. The reference dose distribution for the corresponding geometry was obtained using the calculation in the planning system Monaco 5.10 (Elekta). Sets of correction coefficients for the angular sensitivity of the MatriXX detector array as a function of the accelerator gantry angle have been created. The angular dependence of MatriXX was analyzed statistically, after which it was decided to use a single correction factor for each row of detectors, except for angles in the ranges $90^\circ{-}95^\circ$ and~$265^\circ{-}270^\circ$, where a unique factor was applied for each detector. The use of the developed correction factors that take into account the angular sensitivity of the detectors made it possible to increase the measurement accuracy and thereby obtain better dosimetric verification results, in comparison with the measurements where the angular sensitivity was not taken into account.
Show AbstractThe averaging method is considered in general form up to the fourth order inclusive. As an example, we study the motion of charged particle in a discontinuous strong focusing magnetic field. The present technique, in particular, can be applied in the investigation of particle oscillations in undulators and particle channeling in crystals.
Show AbstractIn this paper the author considers the existence, local uniqueness and asymptotic stability of the boundary layer type solution of the nonlinear one-dimensional initial-boundary value problem with nonhomogeneous Neumann conditions. The corresponding theorems are proved for different types of quasimonotone right-hand sides of the equations using the method of upper and lower solutions and its modification --- asymptotical method of differential inequalities.
Show AbstractThe results of a theoretical study of electron beam bunching processes in high-power multicavity klystrons are presented. The studies were carried out using one-dimensional and two-dimensional numerical models for different values of the space charge parameter. The data on the effect of stratification effects on the efficiency of klystrons with a different number of cavities are presented. As a result of the optimization of the cavities parameters, the limiting efficiency values that are achievable at different values of the space charge parameter are determined. The obtained fundamental dependence of the limiting efficiency values on the space charge parameter is compared with the empirical estimates of other specialists, as well as with experimental data obtained for record klystrons in leading klystron centers in our country and abroad. It is shown that the space charge parameter is a universal characteristic that determines the dependence of the efficiency of multicavity klystrons on the properties of the electron flow used. The prospects of increasing the efficiency of multi-resonator klystrons are indicated.
Show AbstractIn this work, the interaction of a thin medium of neon gas localized in the focal region of sharply and loosly focused Gaussian, radially and azimuthally polarized fields was investigated. The distribution of fields in the focal plane was described using the Richards-Wolf theory, taking into account the presence of three spatial field components in the solution. The generated harmonics were investigated from the point of view of the intensity and polarization state described within the framework of the 3D Stokes parameters formalism. The results were studied in dependence on the distance from the focal plane to the detector, as well as their distribution in the plane perpendicular to the optical axis. The efficiency of harmonic generation in different spatial modes was investigated, as well as the topology of the spatial distribution of individual harmonics in the plane perpendicular to the optical axis.
Show AbstractThe accuracy of the determination of the parameters of the first coating layer is critical for the accuracy of monitoring of the entire deposition of optical coatings. The paper presents a nonlocal algorithm for the analysis of optical monitoring data, which makes it possible to compose a more accurate model of the layer. The capabilities of the new nonlocal algorithm are demonstrated by studying the parameters of the first coating layer formed by niobium oxide, which is one of the main film-forming materials with a high refractive index.
Show AbstractBy the example of a fiber laser based on bismuth active centers, the influence of the structural scheme of the laser on the efficiency of a regime with periodic active Q-switching is demonstrated. Numerical simulation of various circuits allows us to understand the details of the formation of the multi-peak struc-ture of the output signal and, in many cases, to increase the efficiency of Q-switching, keeping at the output a single pulse that saturates the active medium as deeply as possible. For this purpose, a method of Q-switching is proposed, based on a short-term repeated increase in Q-factor in each period. Calcula-tions have shown that this method allows one to obtain single pulses with a duration of about 0.01 times the time of a single pass through the cavity.
Show AbstractA new approach to determining the parameters of a two-dimensional electron gas (2DEG) in InGaN/GaN quantum wells is proposed. It is based on the method of terahertz (THz) spectroscopy with time resolution, within the framework of which the THz frequencies of two-dimensional plasmon resonances excited in the studied samples of InGaN/AlGaN/GaN heterostructures by femtosecond laser pulses at a wavelength of 797 nm were recorded. Oscillating behavior of the output THz radiation power with minima in the frequency range 1 - 5 THz is shown, which is associated with the excitation of plasmon oscillations in a two-dimensional electron gas localized in an InGaN/GaN quantum well. During the processing of THz spectra, the effect of renormalization of the effective mass of 2DEG, as well as phase modulation near the frequencies of plasmon resonances with an increase in the temperature of the sample from 90K to 170K, was found. The proposed method is non-contact and can be used in a wide temperature range.
Show AbstractA two-dimensional model of an arbitrary planet's magnetosphere is constructed via conformal mappings. It is assumed that the magnetopause has the paraboloidal shape. Due to this fixed geometry of the magnetopause, the magnetic moments and the size of the magnetosphere can change independently of each other, which is an advantage of this model.
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