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

Based on numerical and experimental studies, an analysis of the influence of the noise component in determining the spectral phase of an ultrashort pulse in the problems of reconstructing the pulse profile was carried out. Additive white noise was considered and it was shown that the error in field reconstruction becomes proportional to the product of the spectral amplitude and the error in determining the spectral phase at small values of the latter. The results obtained are applied to the technique of determining the spectral phase based on the dispersion Fourier transform. The high accuracy of the method and the possibility of its use as an effective technique were discussed. The spectral phases of double-peak pulses formed from a 120 fs laser pulse with a known spectral phase were experimentally determined, and the error in determining the spectral phase and reconstructing the pulse field was assessed.

The stationary states of an electron in a nanosized semiconductor quantum dot of spheroidal shape with a deep confining potential are considered. The discrete energy spectrum and corresponding wave functions are very sensitive to the elongation, especially in the region of high eccentricity values. The main attention is paid to identifying the patterns of the radial-angular distribution of electron wave functions, which should play an important role in the angular distribution of photons emitted by the quantum dot.

The interaction of biologically active molecules (BAM) with the biopolymer DNA, which performs the most important functions in a living organism having a double helical structure, irradiated with non-thermal electromagnetic millimeter waves, has been studied. It has been shown, that BAM (doxorubicin, mitoxantrone, and netropsin) form more stable complexes with DNA irradiated with the resonant frequencies of natural vibrations of the molecular structures of water (64.5 and 50.3 GHz). Under the influence of the above non-thermal millimeter waves, dehydration of the DNA molecule occurs, which leads to an increase in the binding constant of BAM to irradiated DNA. Calculations show that as a result of irradiation, the thermodynamic parameters of the binding of BAM to DNA change-enthalpy (ΔH) and entropy (ΔS): For all studied BAM, ΔH < 0, and ΔS > 0. The greatest change in entropy occurs for netropsin that binds externally to DNA.

The thermodynamic characteristics of an electron gas localized in a thin spherical CdSe nanolayer have been studied. The dimensions of the CdTe/CdSe core-shell type quantum dot are considered large, which allows the gas to be considered ideal. Due to the small thickness, the particle spectrum has a subband character, when a family of levels of the spherical rotator is associated with each radial quantization level. Within the framework of Boltzmann statistics, the statistical sum for the gas under study was determined, as well as the mean energy, entropy, and heat capacity. The dependences of the thermodynamic characteristics of the electron gas on the geometric parameters of a CdTe/CdSe quantum dot have been studied.

The present work investigates influence of self-focused elliptical laser beam on second harmonic generation (SHG) in cold quantum plasma (CQP). There is establishment of transverse intensity gradients on account of self-focused elliptical laser beam in relativistic plasma. These intensity gradients cause excitation of electron plasma wave (EPW) at pump beam’s frequency. Excited EPW interacts nonlinearly with pump wave thereby producing 2nd harmonics. The nonlinear differential equations representing beam waist’s behavior against normalized distance is derived through Wentzel, Kramers and Brillouin (WKB), approach and paraxial theory. Nonlinear Ordinary differential equation (ODE) is solved numerically in order to explore effect of distinct laser-plasma parameters and quantum contribution on beam waist of pump wave and 2nd harmonics efficiency. The present outcome is compared with classical relativistic plasma (CRP) case.

An X-ray point source was used to examine the diffraction behavior of a low-angle twist boundary. It is shown that when radiation is focused inside a crystal, because of the dislocation structure of the defect wall, the vertical divergence can be reduced so much that the size of the focus in this direction is significantly smaller than in the horizontal direction. This circumstance can be used to create X-ray optical elements.

The binding energy of the ground and first excited states of a hydrogen-like impurity electron in monolayer graphene is studied by a variational approach. It is shown that the binding energies of the impurity electron can be tuned by changing the value of the gap and the effective fine structure constant. An analytical expression for the dipole matrix element of the electron transition from the ground to the first excited state of a hydrogen-like impurity in graphene is found.

The structural and reflective properties (total reflectance and scattering) of black silicon layers formed by reactive ion etching have been studied. Reflectance spectra were determined in the visible, near-infrared, and near-ultraviolet wavelength ranges. The influence of etching duration on the optical behavior of black silicon layers is studied and the possibilities of their use in solar cells and photodetectors are discussed.

The stability of heterogeneous biopolymers is extremely important for maintaining their conformation and carrying out biological functions. The conformational stability of these molecules determines their ability to preserve the necessary structure for biological processes such as catalytic activity, molecular recognition, and cellular interactions. Within the framework of the Generalized Model of the Polypeptide Chain (GMPC), the correlation function of a two-component heteropolymer has been computed as a function of distance, specifically the number of repeating units between two monomers in a helical state, using the method of super-matrices. Through this research, dependencies of the correlation function on the number of repeating units between monomers in the helical state have been obtained for several realizations and different temperatures, particularly around the melting temperature. An interpolation dependency has been proposed for the curve at the melting temperature, expressed as a sum of exponential and power functions. This model allows for a more accurate description of the correlation function behavior under critical conditions close to the melting temperature. The exponential part of the model reflects intense decay of correlation at short distances, while the power function describes mild changes at longer distances.

An analysis of the properties of lead metasilicate powders synthesized by the microwave method and low-melting (900°C) glass obtained based on it has been conducted. Physical and chemical studies have shown that the synthesized lead metasilicate and the glass obtained from it are promising materials for use in various fields, namely as a wide-bandgap semiconductor, photocatalyst, and glass used for protection against ionizing radiation.