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

The optical detection of a nanosecond laser pulse in transparent ferrimagnetic single crystals of yttrium iron garnet and yttrium orthoferrite in the IR range at room temperature was experimentally studied. A linearly polarized neodymium laser (wavelength 1.06 μm) operating in the Q-switched mode was used as the source of electromagnetic radiation. The pulse duration was about 20 ns, and the peak power ∼10 MW. It was found that the ferrimagnetic detector has a sufficient response time to detect nanosecond laser pulses. The amplitude of the detected signal strongly depends on the external bias magnetic field and correlates well with the nonlinearity of the static magnetization curve of the ferrimagnetic crystal sample used.

The excitation functions in proton-induced reactions on natural gadolinium ^natGd(p,xn)^{152,153,154,156,160}Tb were calculated for terbium isotopes, which are of interest from both scientific and application points of view. The calculations were performed in wide energy range of proton beam from the corresponding thresholds of reactions up to 70 MeV. The calculations were carried out using TALYS 1.96 and EMPIRE 3.2 nuclear reaction codes. Calculations have been done by different models inherent in these codes. The obtained results are compared with published experimental data. The discrepancies between experimental and theoretical data were discussed, which indicates the need to expand the experimental data base in order to improve the theoretical models.

The effect of a millimeter-wave range of electromagnetic waves (MM EMW) on methyl or crystal violet interaction with human serum albumin (HSA) has been studied using UV-denaturation, fluorescence spectroscopy, and CD spectroscopy methods. It was revealed that MM EMW irradiation results in the weakening of the stability of HSA and decreases the interaction force between HSA and methyl violet (MV). It was also shown that MM EMW irradiation by non-resonant frequency of the water affects the structure of HSA immediately, and changes its secondary structure, while the irradiation by water-resonant frequency does not invoke structural changes, but weakens the stability to a higher degree.

The results of FDTD modeling of the spectral reflection characteristics of periodic systems with unit cells in the form of cylinders and cones corresponding to the morphology of the porous and black silicon layer presented. The antireflection behavior of these systems with a characteristic size on the order of several hundreds of nanometers is analyzed. The properties of reflection depending on the geometric parameters of unit cells and the angle of incidence of light rays are investigated. It is shown that periodic systems with cones are superior in antireflection properties to systems with cylinders.

In previous works, the electromagnetic field in an arbitrarily chosen volume is represented in vector form including surface and volume integrals using the found vector Green’s function. Surface integrals describe the diffraction of the field created by charges external to the volume, and volume integrals describe the fields created by charges moving inside the volume. In this work, passing to the Fourier transforms in the previously found vector formulas of the field, expressions for a monochromatic electromagnetic field are obtained. Integro-differential equations are also obtained for a monochromatic electromagnetic field in a non-magnetic medium, in the presence of charges with a given motion. Because both diffraction fields and the fields of charges with a given motion, as well as the fields of charges induced in the medium, are considered together, these equations are obtained for the first time.

The modeling calculation of cross-sections of residual nuclei for isotopically enriched lead (²⁰⁴Pb, ²⁰⁶Pb, ²⁰⁷Pb, and ²⁰⁸Pb) targets irradiated by 2.2 GeV/nucleon deuteron beam has been made by the Monte Carlo N-Particle Transport Code (MCNP). The experimental results were obtained on the Nuclotron of the Laboratory of High Energy Physics at the Joint Institute for Nuclear Research in Dubna. The production cross-sections of target fragments were determined for about 90 residual nuclei on each target mentioned above by the method of induced activity. The first-time irradiation has been made on the ²⁰⁴Pb in the GeV range. The comparison of theoretical computations and experimental results showed good agreement between the experiment and simulation data.

Rare decays of B-mesons allow one the investigation of physics outside of the SM. For (B to {{X}_{s}}{{gamma gamma }}) processes, the potential new physics should be visible not only for the width of the decay but also in the differential distributions for the parameters (({{s}_{1}},{{s}_{2}})), defined as ({{s}_{i}} = {{({{p}_{b}} - {{q}_{i}})}^{2}}{text{/}}m_{b}^{2}), (i = 1, 2), where ({{p}_{b}}), ({{q}_{1}},{{q}_{2}}) are the momenta of the b-quark and the two photons. In this work, the contribution of the order ({{{{alpha }}}_{s}}) of the interference of the operators ({{O}_{7}} - {{O}_{8}}) was calculated. We also consider the dependence of the results from the mass of the s-quark by changing ({{m}_{s}}) in the range of 400–600 MeV. The contribution of the interference of the operators ({{O}_{7}} - {{O}_{8}}) into the width of the decay (B to {{X}_{s}}{{gamma gamma }}) in the regions of the phase space considered is equal to 2–3%.

The results of the simulation of heat propagation processes in the multilayer detection pixel of a single-photon thermoelectric detector consisting of heat sink (Bi-2223), thermoelectric sensor (CeB₆), absorber (Bi-2223), and antireflection layer (SiO₂) arranged in series on sapphire substrate (Al₂O₃) are presented. The design of the detection pixel without an antireflection layer is also considered. Simulation of the processes of absorbed photons heat transfer is carried out based on the equation of heat propagation from a limited volume. The cases of absorption of photons with energies of 0.8–1000 eV in detection pixels with a surface of 4 and 1 µm², different thicknesses of absorber and sensor at a fixed operating temperature of the detector of 9 K are studied. Temporal dependences of voltage arising on the sensor, the equivalent power of Johnson and phonon noise are investigated, the signal-to-noise ratio is calculated, and the ways to increase this parameter are proposed.

The Jaynes-Cummings (JC) model is presented based on quantized counterpropagating waves, characteristic of a ring resonator. This model, in addition to the Hamiltonian and the operator of the number of excitations, includes an interference operator whose eigenvalues imitate the term cos 2kz of the classical picture of the field. The average number of photons, dispersion, the Mandel parameter Q, and atomic-photon entanglement in states with certain excitations are considered. The collapses and revivals are revealed, which in the standard JC model are present only in states with an indefinite number of excitations. It is shown that photons at the boundary energy levels are antibunched (with Q ≈ –1/2) regardless of the system’s parameters, and photons of other energy levels are grouped to the degree that grows with the total number of photons.

The vibrating wire monitors are used for measuring transverse pro-files of radiation beams of different nature. For increasing the accuracy of scanning, and in some cases escaping the scanning procedure (measurement of the beam profile using a matrix of wires), it is proposed to use several vibrating wires. A monitor of this kind with two vibrating wires spaced apart at some distance formed the measuring unit of the laboratory stand, developed by us for training students in accelerator technology. The features of such a two-wire monitor and, in particular, the problem of laser radiation power redistribution between the wires are discussed.