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

A model of a molecular magnet consisting of three magnetic ions with spins (1/2, 1/2, 1) and non-conserved magnetization arising due to the heterogeneity of Lande multipliers. This study aims to explain the properties of quantum entanglement of the states of the system during magnetization (demagnetization) processes at finite temperatures. We show how the presence of inhomogeneous g-factors results in a significant enhancement of quantum entanglement and sometimes the expansion of the temperature range in which the spins (pseudospins) of magnetic ions of the model are in entangled states.

Doped (Ag + Fe) zinc targets were obtained: Zn/Ag/Fe (Zn96, Ag2, Fe 2%; Zn94, Ag2, Fe 4%; and Zn90, Ag2, Fe 8%). ZnO/Ag/Fe films with n- and p- type conductivity were obtained on glass substrates at room temperature using the method of DC-magnetron sputtering of Zn/Ag/Fe targets in a gas mixture of Ar : O₂, in a vacuum of about 0.666 Pa. The structural, electrophysical, optical, and morphological characteristics of the obtained films were studied. The research was conducted using X-ray diffraction (XRD), atomic force microscopy, UV/VIS spectroscopy, and Hall measurements. The X-ray diffraction patterns of the ZnO/Ag/Fe films with n- and p-type conductivity showed characteristic reflections of interplanar distances on glass substrates along the crystallographic directions 100, 002, and 101. The transmittance of these films is about 85–95% in the wavelength range of 400–930 nm. The ZnO/Ag/Fe films with p-type conductivity have a concentration of free carriers on the order of 10¹⁸ cm^–3. The ZnO/Ag/Fe films obtained at room temperature of the substrate can be used in the development of functional optoelectronic devices.

The binding energy of the ground state of an impurity electron in doped bilayer graphene is studied by a variational approach in momentum space using different trial functions and taking into account the screening of the Coulomb potential. A monotonic increase in the binding energy of a hydrogen-like impurity with increase of the gap and the tight binding parameter γ₁ is obtained. The results obtained on the basis of different trial functions are compared.

The process of dark pulse formation in a dispersion delay line using amplitude-phase filtering and, subsequently, self-formation of a dark soliton from it in a single-mode optical fiber has been investigated. A dispersive delay line is a system widely used in ultrashort pulse generation applications, consisting of a pair of diffraction gratings or prisms and a beam-returning mirror, in which the laser pulse is stretched and given a negative chirp. The magnitude of the error in fulfilling the conditions necessary for the self-formation of dark solitons has been estimated. A detailed study of the features of the radiation spectrum containing a dark soliton was carried out. The stability of the region corresponding to the dark soliton in the spectrum and its two-peak nature, which is of interest for ultrafast spectroscopy, were revealed.

Two X-ray LLL interferometers are investigated experimentally and with some theoretical explanations: one with a wedge-shaped mirror block and the other one is called hard. The received interference images show that the moiré images are also superposed on the pendellözung fringes in the roentgenograms obtained from the interferometers with a wedge-shaped mirror block and do not interact. The period of pendellözung fringes does not change after passing through the analyzer. The theory of the eikonal approximation of interference fringes formation in the interferometer with a wedge-shaped mirror plate gives predictions that coincide with the obtained experimental results. Unlike a typical LLL X-ray interferometer, the hard one has a base and a “ceiling”. The hard interferometer does not produce uncontrolled moiré thanks to such a structure. The latter occurs because of the interferometer plate deformations: the hard interferometer is much more sensitive to mechanical stresses and various external factors.

A comparative study of the binding parameters of cationic porphyrins CuTAllPyP4 and CoTAllPyP4 with DNA was conducted based on spectroscopic adsorption isotherms depending on the ionic strength of the solution. The obtained results show that the binding constant of the porphyrin CoTAllPyP4 with DNA is an order of magnitude lower than the binding constant of CuTAllPyP4 regardless of the ionic strength. The presence of hard allylic side radicals with increasing ionic strength increases the tendency of porphyrins to aggregate and form sandwich-like ensembles on the DNA macromolecule (H-aggregates), which leads to a hypsochromic shift in the electronic absorption spectra of the porphyrins CuTAllPyP4 and CoTAllPyP4 regardless of the type of central metal and spatial structure.

The energies of the ground 1S and first excited states 2P, 2S of a shallow donor impurity in graphene monolayer with opened energy gap in a perpendicular magnetic field are obtained using a variational approach. It is shown that the energies of the lowest states and distance between them can be tuned in the region of few ten meV by changing the value of the fine structure parameter and magnitude of the magnetic field. A model of a soft Coulomb interaction is suggested. On the basis of the results obtained, the dipole matrix elements for optical transitions 1S –2P⁺ and 2S –2P⁺ are calculated. In the next step, coherent population transfer between the two metastable states 1S and 2S produced by a single phase modulated (frequency chirped) laser pulse is considered. It is demonstrated that such population transfer may be performed without considerable population of the excited state 2P⁺ if initially population of the quantum system under consideration is localized in one of the metastable states. Additionally, the case when the system is in superposition of two metastable states initially is investigated.

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.