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

The paper presents the results of a study on the duration of latent periods (LP) of responses from single neurons in region 21a after their receptive fields (RF) are triggered by stationary flashing visual stimuli. Neurons exhibiting only ON or OFF responses demonstrate markedly reduced fluctuations in LP duration, and the mean LP duration in these neurons is much lower compared to those with ON-OFF responses. A reduced fluctuation in LP duration was noted in neurons exhibiting a tonic response pattern, which also displayed the shortest average LP duration. The most significant variations in LP durations and the highest average values were seen in ON–OFF neurons exhibiting a phasic response pattern. In only one-third of the examined neurons, the length of LP remains constant across the whole RF area; in the majority of neurons, it fluctuates based on the stimulus’s location inside the RF. The disparity in LP duration within a single RF can attain a factor of three or greater. It was also determined that the majority of neurons exhibit a significant degree of independence in the variations of LP ON and OFF components of ON–OFF responses. The acquired results suggest that the majority of RF neurons 21a area possess not only a complicated spatial organization but also an inhomogeneous discrete temporal structure.

For the process of non-degenerate parametric decay in an optical resonator, in which a quantum with energy (hbar {{{{omega }}}_{3}}) decays into two quanta with energies (hbar {{{{omega }}}_{2}}) and (hbar {{{{omega }}}_{1}}), where (hbar {{{{omega }}}_{3}} = hbar {{{{omega }}}_{2}} + hbar {{{{omega }}}_{1}}) is the possibility of forming entangled states of the field by variables of the number of photons between interacting modes of the optical system is investigated. For this purpose, we investigated the dynamics of normalized correlation functions of fluctuations of the number of photons of interacting modes using a Monte–Carlo method. It is shown that in the stationary interaction limit, the value of these correlation functions strongly depends on the value of the coupling coefficient between the modes. It is shown that strong entanglement of the state of three interacting field modes is obtained in the case of weak coupling between the modes. In the case of extreme coupling between them, the value of the correlation function of fluctuations of the number of photons of the field modes tends to unity, because of which entanglement between the states of the modes disappears.

Changes in the intensity of electron bremsstrahlung radiation when samples of metallic tungsten and optical glass containing radioactive impurities are immersed in water were experimentally studied. The bremsstrahlung intensity measurements were performed on a gamma-ray spectrometer. The results of experimental measurements performed on a pure tungsten sample are also presented for comparison. It has been shown that when materials with a radioactive impurity subject to β⁻-decay come into contact with water, X-ray radiation with an energy of 5.67 keV is generated. However, similar interactions involving materials with radioactive impurities undergoing α-decay do not generate bremsstrahlung radiation.

An algorithm has been developed for reconstructing long-lived particles (LLP) decaying in the barrel and endcap regions of the muon system of the CMS detector at the Large Hadron Collider. Calculations were done on the basis of Monte Carlo simulated data using CMSSW package, adapted to the conditions of CMS detector experimental setup of 2018. In considered process the hypothetical LLP particles are produced from decays of B mesons in proton–proton (p–p) collisions at a center-of-mass energy of 13 TeV. Decays of LLP particles in the muon system of the CMS detector are characterized by the presence of wide showers with a large multiplicity of hits from the muon chamber channels, which differs significantly from the hits of known particles, and is a good criterion for identifying LLP particles.

Various quantum chains consisting of interacting Majorana fermions with flavors are constructed. These systems are invariant with respect to the rotations and reflections in the flavor space. The entire space of states splits into sectors characterized by a specific set of fermionic parities related to different flavors. All systems under consideration satisfy the Lieb-Mattis condition. As a result, the lowest-energy states within individual sectors are nondegenerate. The sectorial ground states are combined into antisymmetric (in flavor numbers) multiplets.

Donor impurity states in a quasi-conical quantum dot are theoretically investigated. The confinement potential is considered within the framework of the model with infinite walls. The problem is considered because the impurity is located at the vertex of a quasi-conical quantum dot. Based on the hydrogen atom model, the impurity and the electron’s interaction potential is Coulomb potential. Because of the complexity, the problem is solved using the approximate finite element method (FEM). The FEM method is used to compute the energy states and wave functions of the system both in the presence and absence of the donor impurity. Based on the obtained results, the dependences of the impurity binding energy on the geometric parameters of the quasi-conical quantum dot and the probability density of the electron cloud distribution in the quantum dot are studied.

The energy losses of charged particles passing through the vacuum-tight exit windows of the operating accelerator facilities where experiments are carried out at the AANL (YerPhI), have been determined. Computation tables and graphs of the dependencies of the energy loss of the accelerated beam on its kinetic energy, the thickness of foils made of materials used in the separation windows, and the distances from the windows to the targets in the air are given.

The study of the threshold mechanical transition of Freedericksz is presented for the first time, taking into account the nonlinearity of the interaction of orientational and mechanical anisotropy, using weakly crosslinked nematic elastomers with side chains as an example. The reorientation of the director of the liquid crystal elastomer has a threshold character in cases where the mechanical stress is applied perpendicular to the initial orientation of the liquid crystal director. The threshold of reorientation of the liquid crystal molecules is analytically calculated. The experimental implementation of the proposed approach will allow us to determine one of the coefficients of nonlinear interaction.

The effect of selective reflection (SR) of laser radiation from the boundary of ⁸⁷Rb D₂-line atomic vapors and a dielectric window was studied using a nanocell (NC) with a vapor column thickness of ~300 nm. The formation of an SR with a spectral width of 25 MHz, located on atomic transitions, is demonstrated. This is a record narrowing of the 670 MHz Doppler width by a factor of 27 using single-pass geometry. The SR signal reaches several percent of the intensity of its forming radiation, and the SR amplitude’s linear dependence is maintained up to 100 mW/cm², which is almost two orders of magnitude greater than the saturation intensity of optical processes when using centimeter-long cells with atomic vapors. Such a high saturation intensity value is achieved by using the nanocell.

Second harmonic generation (SHG) of high power Cosh-Gaussian (ChG) beam in thermal quantum plasma (TQP) is explored in current investigation. Relativistic and ponderomotive nonlinearities are taken together in present investigation. Combination of relativistic-ponderomotive nonlinearities causes modification in electron mass, thereby producing density gradients inside plasma. This further produces self-focusing of main beam. The well-known WKB and paraxial approaches are used for solving main beam’s wave equation and to obtain 2nd order ordinary differential equation (ODE). There is generation of electron plasma wave (EPW) due to these density gradients. Excited EPW interacts with main beam to generate 2nd harmonics in plasma. Effects of combined relativistic-ponderomotive nonlinearities and established laser–plasma parameters on beam’s waist and SHG yield are studied in present study.