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

Rare clustering processes in vanadium and enriched nickel nuclei were investigated. In particular, reactions involving the emission of one or two alpha particles, as well as fission processes in these targets, were studied. Calculations were performed using the TALYS code. It was found that the induced activity method can be used to investigate the probability of the ⁶⁴Ni(p, 2α n)⁵⁶Mn reaction. Calculations show that there is a real possibility of registering heavier fragments, for example, the isotope ⁴⁸Sc, which is formed during the interaction of protons with enriched nickel.

Dynamical theory of surface states of nearly free electrons in a semi-infinite crystal are investigated. In addition to the results known in the theory of Bloch wave formalism with a complex wave vector, some new results were obtained. In particular, it is shown that surface states can be realized only at sufficiently small Bragg angles. An estimate of this angle is obtained. The width of the spatial localization region of electrons near the surface is also estimated. It is found that it is of the order of several tens of Ångströms.

We realized an exhaustive study about structural, electronic and optical properties of the quaternary alloys B_{1 – x}Ga_xP_yBi_{1 – y} in zinc blend phase by applying the full-potential augmented plane wave method FP-LAPW within the scope of density functional theory DFT. Potentials were determined using modified generalized gradient GGA and Becke-Johnson approximations. We analyzed the effects of the compositions (x, y) on the lattice parameters, bulk modulus, and band gap energy, revealing a non linear dependence of these quantities. We also investigated several optical constants, including the real and imaginary parts of the dielectric function, the absorption coefficient α(ω), the refractive index n(ω), and the reflectivity. Our obtained results about lattice parameters, energetic gaps and optical constants for the binary compounds are in well correspondence with the provided experimental and theoretical values. However, for alloys, differences were observed against linearity for lattice constants and bulk modulus. Moreover, we examined the energy band of zinc-based quaternary alloys B_{1 – x}Ga_xP_yBi_{1 – y} those corresponding to ZnS lattice. It is worth mentioning that this study represents an innovative contribution in the domain of quaternary alloys, since it is the first theoretical analysis about these alloys.

The absorption and luminescence properties of Er³⁺ and Nd³⁺ ions in oxyfluoride barium boroaluminosilicate glasses of the BaO/BaF₂–SiO₂–B₂O₃–Al₂O₃ system were investigated by recording optical absorption and photoluminescence spectra. Photoluminescence of neodymium ions was exciting using laser radiation at a wavelength of 808 nm. Emission on the three main ⁴F_3/2 → ⁴I_J transitions of Nd³⁺ ions was observed at wavelengths of 890, 1060, and 1330 nm. Laser radiation at wavelengths of 808 and 980 nm was used to excite infrared emission of erbium ions at ∼1550 nm, corresponding to the ⁴I_13/2 → ⁴I_15/2 transition, as well as to excite upconversion (UC) emission of Er³⁺ ions in the visible spectral range, including blue (²H_9/2 → ⁴I_15/2), green (²H_11/2, ⁴S_3/2 → ⁴I_15/2), and red (⁴F_9/2 → ⁴I_15/2) luminescence bands.

The characteristics of circularly polarized synchrotron radiation are studied theoretically and numerically. Analytical expressions for partial contributions to the synchrotron radiation power are derived in both the non-relativistic and ultra-relativistic limits. It is demonstrated that for each harmonic exhibits a maximum in its partial contribution. As in the case of linear polarization, for each pair of adjacent harmonics, there is a threshold particle velocity at which the contribution of the harmonic with the higher number becomes more significant.

To obtain dynamical diffraction double-slit interference fringes and to achieve the necessary degree of collimation and monochromaticity of the beam, it is proposed to use double asymmetric reflection from two crystals in front of the two slits. An expression for the amplitude of the diffracted wave at the exit surface of the third crystal, placed after two slits, was found. The condition for the asymmetry coefficients of crystals under which the interference fringes will be observed is obtained. Examples show that the obtained condition makes it easy to find many cases of asymmetric double reflections, allowing the observation of dynamic-diffraction interference fringes using a non-monochromatic extended source.

A new method for recording the chirp of a femtosecond IR laser pulse is proposed, based on a non-collinear generation of the sum harmonic by a transform-limited IR femtosecond pulse and a pulse with a spectral supercontinuum. This paper presents the time dependences of the instantaneous frequency of an IR pulse with a spectral supercontinuum, obtained from two-dimensional dynamic spectrogram distributions. It is shown that the relative error in determining the chirp of a femtosecond IR laser pulse by the proposed method does not exceed 10%. The presented results can be used to develop a nonlinear optical phase correlator to determine the phase and temporal profile of a femtosecond laser pulse in the mid-IR range.

The solid-state nanopore probing technology can be useful for identifying the sequence of biological polymers. In nanopore experiments, the useful signal measured is the ionic current that passes through a nanopore while it is blocked nucleotides of a DNA molecule. The correlation between ionic blockade current passing through the nanopore, the geometric configuration of the pore, and the DNA sequence is the challenge addressed in this publication. The ionic blockade current was calculated and its histogram was constructed. An analysis of the effect of the nanopore size on the ionic blockade current was carried out. A detailed analysis of the dynamics of a DNA molecule in aqueous solution under the action of gravity, electrophoretic force and drag force is carried out. Analytical dependencies of the translocation rate of a DNA molecule through a nanopore on molecule’s approach time to the nanopore, and on the applied voltage are obtained and analyzed. Numerical calculations were performed for dsDNA. Cases of coincidence and vice versa of the direction of the applied electric field with gravity are considered. For the case where the electrophoretic force is directed opposite to gravity, DNA movement slows down and the translocation rate decreases. Recommendations are provided for increasing the accuracy of reading DNA molecules. Reducing the time it takes for DNA to approach the pore can reduce the translocation rate to hundreds and thousands of nm/s. When interpreting the dynamics of the DNA molecule in aqueous solution, a new effect is introduced, which we call the “proton seduction effect”.

The ability of a nematic liquid crystal (NLC) cell with planar and periodic orientational boundary conditions to diffract a light beam has been theoretically investigated. To create a continuously rotating structure, a small amount of cholesteric liquid crystal must be added to the NLC. Unlike known polarization gratings, diffraction on this cell can result in the absence of zero-order diffraction, i.e., 100% ± 1 orders of right- and left-elliptically (or even circular) polarized beams. The unique polarization properties of the cell with planar and periodic orientational boundary conditions can be used to develop a real-time photo-polarimeter and circular dichroism spectrograph without artifacts.

This paper examines the performance of hybrid solar photovoltaic-thermal (PVT) modules, which are more energy efficient than conventional solar photovoltaic modules due to the ability to cool the solar cells by removing heat from the heated solar cells and by generating additional thermal energy. It is shown that at low ambient temperatures, below a certain critical value, the temperature of the solar cells in a PVT module can be higher than that of a conventional photovoltaic module (the reverse process). The critical ambient temperature is examined for various PVT module designs (glazed, unglazed, with and without a thermally insulated back layer). It is experimentally shown that the critical temperature for a PVT module without an insulated back layer is 21°C, while for a module with an insulated back layer it is 25°C. To eliminate the negative effect of solar cell heating, it is necessary to consider the operating ambient temperatures and to select appropriate PVT module designs and heat removal modes.