Journal of Contemporary Physics (Armenian Academy of Sciences)最新文献

In recent works, the full set of three-loop diagrams (of order (alpha _{s}^{2})) associated with the current-current operators O₁ and O₂ contributing to the decay amplitude for b → sγ were calculated. In this paper, one pair of these diagrams is calculated at various values of the charm-quark mass m_c using different methods, and the numerical accuracy/ease of use of these methods are compared to the analytic results obtained by others. Using the programs AMFlow and DiffExp to solve the differential equations for the master integrals, precise numerical results were obtained across a range of charm-quark mass values. In addition, asymptotic and Taylor series expansions were performed around z = ({{m_{c}^{2}} mathord{left/ {vphantom {{m_{c}^{2}} {m_{b}^{2}}}} right. kern-0em} {m_{b}^{2}}}) = 0 and z = 1/10, respectively. A fully numerical evaluation of the master integrals using PySecDec was also carried out.

In this study, we present an algorithm for simulating CT images of diverse 3D-printed samples, allowing for a comparison between simulated and real CT experiment results. The use of computer simulation enhances the understanding of the CT imaging process and aids in the development and validation of reconstruction algorithms. It is demonstrated that such an algorithm potentially may be useful for analysis of inaccuracies of real 3D-printed samples under CT investigation and can distinguish these details from filling model of these samples.

In this paper, we studied the transformation of light in a hexagonal graphene quantum dot during the generation of high harmonics in an intense laser field. A linearly polarized laser field leads to intense emission of elliptically polarized harmonics. The ellipticity and orientation of the polarization ellipse are derived from the Stokes parameters calculated, considering various polarization components. Numerical results show that the ellipticity of harmonics generated in a quantum dot can be easily tuned by changing the tilt angle of a linearly polarized laser pulse without complex control systems.

The mechanisms of charge carrier transport for alternating current in zinc oxide (ZnO) films with Li impurity, which creates acceptor and donor centers, are determined. A comparative study of the applicability of two models, quantum mechanical tunneling (QMT) and correlated barrier hopping (CBH), is carried out to interpret experimental data on alternating current electrical conductivity. Based on the analysis of the temperature dependence of conductivity at different frequencies, a choice was made in favor of the CBH model. The dependence of the thermal activation energy of conductivity on the concentration of the doping impurity Li in ZnO films is studied. It is established that the Meyer–Neldel rule, which relates the pre-exponential factor in the temperature dependence of alternating current conductivity to the activation energy, is fulfilled for compensated semiconductors in which donor and acceptor centers exist simultaneously.

The present research investigates nonlinear dynamics of q-Gaussian laser beam in Collisional Plasma considering the influence of linear absorption. In Collisional plasma, redistribution of carriers occurs as a result of non-uniform heating thereby creating density gradients inside plasma leading to beam’s self-focusing. The Paraxial ray approximation is used for obtaining the nonlinear differential equation for spot size of laser beam. The numerical solution of this differential equation is obtained by well-known Runge–Kutta 4th order method to explore the behavior of beam waist with normalized propagation distance. Effect of change in laser-plasma parameters such as beam intensity, plasma density, beam radius, absorption coefficient and q-values on beam waist of laser beam is also analyzed.

The double-slit dynamical X-ray diffraction in the transmitted beam is investigated. The features and differences are compared with the double-slit dynamical diffraction in the diffracted beam. The expressions for the period of the obtained interference fringes are found. The intensity distributions based on numerical calculations are compared with theoretical predictions based on approximate expressions.

A study of the fluorescent properties of MB complexes with ss-poly(dA), poly(rU), poly(rA), and poly(dT), as well as hybrid ds-structures poly(rA)-poly(dT) and poly(dA)-poly(rU), was carried out. Based on changes in fluorescence and absorption spectra, it was revealed that this ligand exhibits unequal affinity for homopolynucleotide sequences. Particularly, it was found that MS binds to poly(rA) with pronounced specificity, compared to ss-poly(dA), poly(rU), and poly(dT). The difference was also obtained for the interaction of MB with hybrid ds-polynucleotides poly(rA)-poly(dT) and poly(dA)-poly(rU).

The phase space of low-temperature propane oxidation in a spherical reactor has been investigated in terms of the presence of special points by registering light emission pulses resulting from the generation of weak shock waves in the near-surface layer of the reactor. The phenomenon is explained using the results of the well-known self-similar method to assert that a saddle point forms at the center of the reactor due to the convergence of the weak shock wave towards the reactor’s center. The property of the weak shock wave to reflect off surfaces, as well as from the saddle point, leads to a situation where both the periphery and the center of the reactor reflect the weak shock wave. Under these conditions, closed trajectories typically exist, onto which the trajectory of the shock wave wraps. As a result, it becomes possible to register the radiation of the shock wave occurring in the combustible mixture. Justification is provided for the possibility of experimentally registering weak shock waves in the reactor.

The methods of Circular Dichroism and UV/Vis spectrophotometry were used to study the influence of two cationic porphyrins meso-tetra-(4N-oxyethylpyridyl) porphyrin (TOEPyP4) and its Zn-containing derivative (ZnTOEPyP4) on the G-quadruplex conformation of d[5'-A(GGGTTA)₃GGG-3'] sequence of human telomeric DNA. The analysis of the results indicates a single binding site for these porphyrins, but it differs depending on the porphyrin. It is assumed that TOEPyP4 binds parallel to the quartet plane on the outer surface of the G-quadruplex (external π-π stacking), and the binding of ZnTOEPyP4 also occurs externally, but in the groove of the lateral surface of the G-quadruplex (groove binding).

We present the results of angular reflection analysis of black silicon (b-Si) layers formed by reactive ion etching. Calculations using the transfer matrix method and experimental measurements confirm the excellent antireflective properties of b-Si at light incidence angles of up to 60°. This ensures the stability of the short-circuit current in solar cells across a wide angular range, which is particularly important for the efficient operation of stationary photovoltaic stations during daytime and under cloudy conditions.