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A. A. Popov

Publications and source records attributed to A. A. Popov.

14 recordsLinked to original sources
arXiv2025

The concept of a superconducting spin flipper - neutron decelerator for a UCN source at a pulsed reactor

The work is devoted to the development of a conceptual design for a gradient spin flipper - neutron decelerator, which is the main component of a designed UCN source for a pulsed reactor. In close cooperation between the JINR group and SuperOx, a preliminary design of a stationary gradient magnet for the adiabatic spin flipper has been developed. A thorough calculation of the magnetic field configuration has been performed. The movement of neutrons in the magnetic field generated by the designed magnetic system has been simulated, and the deceleration time of neutrons in the spin flipper has been analyzed. The results obtained give grounds for hope that the idea of creating a UCN source based on pulsed accumulation in a trap using non-stationary neutron deceleration is feasible.

physics.ins-det↗
arXiv2025

To the UCN source with pulsed filling of a trap

The paper is devoted to the discussion of the possibility of creating UCN sources based on the principle of pulse accumulation (PA) in traps. The implementation of the PA principle would make it possible to create a source with a flux of UCN in a trap significantly exceeding the time average. The paper provides a comparative analysis of various approaches to the implementation of the idea of PA of UCN in traps remoted from the place of their generation. Based on this analysis, the concept of the UCN source, the creation of which is planned at the IBR-2M pulse reactor, was formulated. A distinctive feature of the designed source is a combination of several approaches to ensuring the pulsed structure of neutron bunches reaching the UCN trap. One of them is the deceleration of the pulsed flux of VCN using a resonant flipper, the second is the use of compensating time lenses.

physics.ins-det↗
arXiv2024

Laser-synthesized TiN nanoparticles as novel efficient sorbent for environmental water cleaning

Dyes used in industries such as textile, paper, and leather are known to be harmful to both human health and aquatic ecosystems. Therefore, finding effective and sustainable methods to remove dyes from wastewater is crucial for mitigating the detrimental effects of pollution.TiN nanoparticles have good absorption and conversion of light energy into thermal energy in the visible range of the spectrum, which makes them promising in various applications, from biomedical to environmental protection. In this work, it is shown that titanium nitride nanoparticles also possess promising adsorption capabilitieseffect. TiN nanoparticles were synthesized by laser ablation method in liquid. Water, acetone and acetonitrile are used as solvent. Nanoparticles were characterized by scanning and transmission microscopy, Raman spectroscopy, which showed the formation of the under-stoichiometric titanium nitride (TiN1-x). TiN nanoparticles are investigated as a promising object for high adsorption It is shown that adsorption of TiN nanoparticles is associated with the electrostatic effect and the presence of pores in the synthesized nanoparticles. Optimal dye absorption capabilities were found to be associated with a low amount of Ti vacancies and high amount of N vacancies acting as donor states. The particles synthesized in water have the highest sorption capacity of dye achieving the value of 136.5 mg/g.

cond-mat.mtrl-sci↗
arXiv2022

Temperature induced change of conformation of Sc2TbN@C80 on h-BN/Ni(111)

The conformation of molecules on surfaces is decisive for their functionality. For the case of the endofullerene paramagnet Sc2TbN@C80 the conformation is linked to an electric and a magnetic dipole moment. Therefore a workfunction change of a substrate with adsorbed molecules, qualifies the system to be magnetoelectric. One monolayer of Sc2TbN@C80 has been studied on h-BN/Ni(111). The molecules assume a hexagonally close packed lattice aligned with the substrate high symmetry directions. The structure is incommensurate and arranges at a periodicity of about 4.3x4.3 substrate unit cells. At low temperatures a (2 x 2) superstructure is observed. Angular resolved valence band photoemission spectroscopy shows a temperature induced 0.3 eV shift on the C80 molecular orbitals to lower binding energies that is parallel to a workfunction increase. From comparison of the molecular orbital angular photoemission intensity distributions it is conjectured that the molecules undergo a change in conformation between 30 and 300 K. This phase transition is centred at 125 K as observed with high resolution x-ray photoelectron spectroscopy that shows the core levels of the atomic species on the molecules to shift parallel to the workfunction. The temperature dependence of the workfunction can be described with a two level model that accounts for the disordering with an excitation energy of 60 meV into a highly degenerate ensemble. The experimental findings are backed by density functional theory calculations for the diamagnetic sibling of Sc2TbN@C80 : Sc2YN@C80 that rationalize the incommensurate structure, show a permanent dipole moment of Sc2YN@C80 and a relation between the workfunction and the orientation of the endohedral cluster.

cond-mat.mtrl-sci↗
arXiv2022

Effect of grain boundary state and grain size on the microstructure and mechanical properties of alumina obtained by SPS: A case of the amorphous layer on particle surface

The effect of temperature modes and heating rates (Vh) on the shrinkage kinetics of submicron and fine aluminum oxide powders has been studied. The objects of research comprised (i) submicron alfa-Al2O3 powder, (ii) submicron alfa-Al2O3 powder with an amorphous layer on particle surface, (iii) fine alfa-Al2O3 powder. The alumina ceramic specimens were produced by Spark Plasma Sintering (SPS). Equally fine powders (i) and (ii) were used to analyze the effect of an amorphous layer on sintering kinetics. Powders (i) and (iii) were used to analyze the effect of the initial particle size on shrinkage kinetics. Shrinkage curves were analyzed using the Young-Cutler and Coble models. It has been shown that sintering kinetics is determined by the intensity of grain boundary diffusion for submicron powders and by simultaneous lattice and grain boundary diffusion for fine powders. It has been determined that an amorphous layer on the surface of submicron alfa-Al2O3 powder affects grain boundary migration rate and the Coble equation parameters at SPS final stages. It has been suggested that abnormal characteristics of the alumina ceramics sintered from a submicron powder with an amorphous layer on the particle surface are associated with an increased concentration of defects at grain boundaries that were formed during crystallization of the amorphous layer.

cond-mat.mtrl-sci↗
arXiv2021

Transition metal dichalcogenide nanospheres for high-refractive-index nanophotonics and biomedical theranostics

Recent developments in the area of resonant dielectric nanostructures has created attractive opportunities for the concentrating and manipulating light at the nanoscale and the establishment of new exciting field of all-dielectric nanophotonics. Transition metal dichalcogenides (TMDCs) with nanopatterned surfaces are especially promising for these tasks. Still, the fabrication of these structures requires sophisticated lithographic processes, drastically complicating application prospects. To bridge this gap and broaden the application scope of TMDC nanomaterials, we report here femtosecond laser-ablative fabrication of water-dispersed spherical TMDC (MoS2 and WS2) nanoparticles (NPs) of variable size (5 - 250 nm). Such nanoparticles demonstrate exciting optical and electronic properties inherited from TMDC crystals, due to preserved crystalline structure, which offers a unique combination of pronounced excitonic response and high refractive index value, making possible a strong concentration of electromagnetic field in the nanoparticles. Furthermore, such nanoparticles offer additional tunability due to hybridization between the Mie and excitonic resonances. Such properties bring to life a number of nontrivial effects, including enhanced photoabsorption and photothermal conversion. As an illustration, we demonstrate that the nanoparticles exhibit a very strong photothermal response, much exceeding that of conventional dielectric nanoresonators based on Si. Being in a mobile colloidal state and exhibiting superior optical properties compared to other dielectric resonant structures, the synthesized TMDC nanoparticles offer opportunities for the development of next-generation nanophotonic and nanotheranostic platforms, including photothermal therapy and multimodal bioimaging.

physics.optics↗
arXiv2020

Kinetic equations for ultrarelativistic particles in a Robertson-Walker Universe and isotropization of relict radiation by gravitational interactions

Kinetic equations for ultrarelativistic particles with due account of gravitational interactions with massive particles in the Robertson-Walker universe are obtained. On the basis of an exact solution of the kinetic equations thus obtained, a conclusion is made as to the high degree of the uniformity of the relict radiation on scales with are less than $10'$.

gr-qc↗
arXiv2016

Information processing using three-qubit and qubit-qutrit encodings of noncomposite quantum systems

We study quantum information properties of a seven-level system realized by a particle in an one-dimensional square-well trap. Features of encodings of seven-level systems in a form of three-qubit or qubit-qutrit systems are discussed. We use the three-qubit encoding of the system in order to investigate subadditivity and strong subadditivity conditions for the thermal state of the particle. The qubit-qutrit encoding is employed to suggest a single qudit algorithm for calculation of parity of a bit string. Obtained results indicate on the potential resource of multilevel systems for realization of quantum information processing.

quant-ph↗
arXiv2016

Comparative performance of selected variability detection techniques in photometric time series

Photometric measurements are prone to systematic errors presenting a challenge to low-amplitude variability detection. In search for a general-purpose variability detection technique able to recover a broad range of variability types including currently unknown ones, we test 18 statistical characteristics quantifying scatter and/or correlation between brightness measurements. We compare their performance in identifying variable objects in seven time series data sets obtained with telescopes ranging in size from a telephoto lens to 1m-class and probing variability on time-scales from minutes to decades. The test data sets together include lightcurves of 127539 objects, among them 1251 variable stars of various types and represent a range of observing conditions often found in ground-based variability surveys. The real data are complemented by simulations. We propose a combination of two indices that together recover a broad range of variability types from photometric data characterized by a wide variety of sampling patterns, photometric accuracies, and percentages of outlier measurements. The first index is the interquartile range (IQR) of magnitude measurements, sensitive to variability irrespective of a time-scale and resistant to outliers. It can be complemented by the ratio of the lightcurve variance to the mean square successive difference, 1/h, which is efficient in detecting variability on time-scales longer than the typical time interval between observations. Variable objects have larger 1/h and/or IQR values than non-variable objects of similar brightness. Another approach to variability detection is to combine many variability indices using principal component analysis. We present 124 previously unknown variable stars found in the test data.

astro-ph.IM↗
arXiv2016

Bidirectional imperfect quantum teleportation with a single Bell state

We present a bidirectional modification of the standard one-qubit teleportation protocol, where both Alice and Bob transfer noisy versions of their qubit states to each other by using single Bell state and auxiliary (trigger) qubits. Three schemes are considered: the first where the actions of parties are governed by two independent quantum random triggers, the second with single random trigger, and the third as a mixture of the first two. We calculate the fidelities of teleportation for all schemes and find a condition on correlation between trigger qubits in the mixed scheme which allows us to overcome the classical fidelity boundary of 2/3. We apply the Choi-Jamiolkowski isomorphism to the quantum channels obtained in order to investigate an interplay between their ability to transfer the information, entanglement-breaking property, and auxiliary classical communication needed to form correlations between trigger qubits. The suggested scheme for bidirectional teleportation can be realized by using current experimental tools.

quant-ph↗
arXiv2013

New variable stars in the field of open cluster NGC188

A photometric study of variable stars in the field of old open cluster NGC 188 is discussed. Observations were carried out in two bands R and I for 5513 stars up to R = 17 mag in the field of 1.5 x 1.5 grad. around the cluster. The photometric data were processed by the console application "Astrokit", which corrects brightness variations associated with the variability of atmospheric transparency and carries out searching for variable stars. We found 18 new variable stars and determined the parameters of one previously known variable. Among discovered stars one is a low-amplitude pulsating variable, one is a EW eclipsing binary, six are eclipsing variables of EA type, five objects are long period variables, and for five stars variability type remains uncertain.

astro-ph.SR↗
arXiv2011

Prompt, early, and afterglow optical observations of five gamma-ray bursts (GRBs 100901A, 100902A, 100905A, 100906A, and 101020A)

We present results of the prompt, early, and afterglow optical observations of five gamma-ray bursts, GRBs 100901A, 100902A, 100905A, 100906A, and 101020A, made with the Mobile Astronomical System of TElescope-Robots in Russia (MASTER-II net), the 1.5-m telescope of Sierra-Nevada Observatory, and the 2.56-m Nordic Optical Telescope. For two sources, GRB 100901A and GRB 100906A, we detected optical counterparts and obtained light curves starting before cessation of gamma-ray emission, at 113 s and 48 s after the trigger, respectively. Observations of GRB 100906A were conducted with two polarizing filters. Observations of the other three bursts gave the upper limits on the optical flux; their properties are briefly discussed. More detailed analysis of GRB 100901A and GRB 100906A supplemented by Swift data provides the following results and indicates different origins of the prompt optical radiation in the two bursts. The light curves patterns and spectral distributions suggest a common production site of the prompt optical and high-energy emission in GRB 100901A. Results of spectral fits for GRB 100901A in the range from the optical to X-rays favor power-law energy distributions with similar values of the optical extinction in the host galaxy. GRB 100906A produced a smoothly peaking optical light curve suggesting that the prompt optical radiation in this GRB originated in a front shock. This is supported by a spectral analysis. We have found that the Amati and Ghirlanda relations are satisfied for GRB 100906A. An upper limit on the value of the optical extinction on the host of GRB 100906A is obtained.

astro-ph.HE↗
arXiv2006

Local spherically symmetric perturbations of spatially flat Friedmann models

The spherically symmetric perturbations in the spatially flat Friedman models are considered. It is assumed that the Friedmannian density and pressure are related through a linear equation of state. The perturbation is joined smoothly with an unperturbed Friedmann's background at the sound horizon of perturbation. Such junction is in accordance with the "birth" of a local perturbation as a result of the redistribution of matter. The solution of the Einstein's equations is obtained in linear approximation on a Friedmann's background near the the sound horizon of perturbation.

gr-qc↗