Physical and Technical Institute

Laura Yates discusses the effective cleaning properties of enzymes, and the benefits that enzymatic cleaning materials bring to infection control in healthcare settings.

In LaF3 crystals the EPR spectra of Ho3+ ion replacing La3+ ion in a C2 symmetry position were recorded and studied in the subterahertz frequency range. The parameters of splitting in the zero field, hyperfine structure constant and the value of g-factor are determined.

The nonlinear dynamics of quantum droplets in a quasi-one-dimensional BEC loaded in a two-core trap potential are investigated. The cases of standing and moving quantum droplets are considered. The frequencies of the Josephson oscillations and the condition for self-trapping are found. An analytical description is based on the variational approach to a system of coupled extended Gross-Pitaevskii (EGP) equations, including Lee-Huang-Yang correction terms. In the case of moving droplets, the system of equations describing the coupling of the relative motion of droplets in two cores with the dynamics of the relative phase and population imbalance (Josephson currents) is derived. Different regimes of droplet dynamics are found, including attraction and repulsion in dependence on the relative phase evolution. These phenomena are the realization of the Andreev-Bashkin effect for superfluids in a two-core trap potential. Analytical predictions of the model are confirmed by full numerical simulations of the coupled extended Gross-Pitaevskii equations.

In the present study, we consider the effects of vacuum birefringence and dichroism in strong electromagnetic fields. According to quantum electrodynamics, the vacuum state exhibits different refractive properties depending on the probe photon polarization and one also obtains different probabilities of the photon decay via production of electron-positron pairs. Here we investigate these two phenomena by means of several different approaches to computing the polarization operator. The external field is assumed to be a linearly polarized plane electromagnetic wave of arbitrary amplitude and frequency. Varying the probe-photon energy and the field parameters, we thoroughly examine the validity of the locally-constant field approximation (LCFA) and techniques involving perturbative expansions in terms of the external-field amplitude. Within the latter approach, we develop a numerical method based on a direct evaluation of the weak-field Feynman diagrams, which can be employed for investigating more complex external backgrounds. The polarization operator depends on two parameters: classical nonlinearity parameter ξ and the product η = ωq0/m2 of the laser field frequency ω and the photon energy q0 (m is the electron mass). The domains of validity of the approximate techniques in the ξη plane are explicitly identified.

The FLASH effect of high-energy (660 MeV) proton irradiation using the Phasotron accelerator with the capacity of delivering dose rates of 80 Gy/s has been studied and compared to the effect after exposure to proton radiation at a conventional dose rate of 3 Gy/min. After FLASH and conventional dose-rate irradiation with doses of 1.0 and 1.5 Gy, the induction of cytogenetic damage to bone marrow cells and the state of lymphoid organs (thymus and spleen) were estimated; at doses of 7.0 and 8.0 Gy, the survival rate after total irradiation of mice in vivo was analyzed; and at doses of 40 and 60 Gy, the tumor growth rate was determined after irradiation ex vivo. It has been shown that irradiation of animals using the FLASH mode at a dose of 1.5 Gy protects the proliferative activity of the spleen and also leads to a decrease in cytogenetic injuries in bone marrow erythrocytes, based on the micronucleus test, as compared to the conventional irradiation at a dose of 1.5 Gy; thus, the FLASH effect has lower toxicity compared to conventional radiation. However, irradiation of mice, the FLASH effect which delivers high doses (7.0 and 8.0 Gy) of radiation, leads to earlier death of animals compared to those exposed to conventional radiation. Only after FLASH irradiation of a suspension of Ehrlich ascites carcinoma at a dose of 40 Gy, a tumor node with further growth was formed; no tumors were formed in all other groups.

We propose a tunable THz generator built on a two-dimensional electronic analog of a conventional Helmholtz resonator. The generator excitation is provided by a flow similar to that in a whistle in conventional hydrodynamics. The output frequency, hydrodynamic parameters, and practical implementation of the THz-whistle are discussed in relation to possible applications.

Layers of TiO2 nanotubes formed through an anodization process are an area of active research in the context of innovative energy conversion and storage systems. Titanium nanotubes (TNT) have attracted attention due to their unique properties, especially their high surface-to-volume ratio, making them a desirable material for various technological applications. The anodizing method is widely used for the production of TNT due to its simplicity and relative cheapness, the method allows precise control of the thickness of TiO2 nanotubes. Anodizing can also be used to create decorative and colored coatings on titanium nanotubes. In this study, a combined structure comprising anodic TiO2 nanotubes and SrTiO3 particles was created using chemical synthesis methods. TiO2 nanotubes were prepared by anodizing in ethylene glycol containing NH4F and Н2O using a voltage of 30 volts.The anodic nanotube array, heat-treated at 450°C, was then placed in an autoclave filled with a dilute SrTiO3 solution. Scanning electron microscopy (SEM) analysis revealed that TNT are characterized by clear and open tube ends. With an average outer diameter of 1 µm and an inner diameter of 69 nm, and their length is 133 nm.

The theory of the magnetotransport in a two-component electron system with rare macroscopic defects has been developed. In such a system, the classical memory effects in the scattering of electrons by defects and a slow transfer of electrons between the components of the liquid occurring due to the electron–electron scattering play a decisive role. It has been shown that the flow regime depends on the ratio of the sample width to the characteristic internal length, which is determined by the rate of electron transfer between the components. In samples wider than the internal length, the flow of the two-component liquid as a whole is formed within the bulk of the sample and is described by the corresponding Drude formulas taking into account memory effects. In this case, the magnetoresistance is positive at low magnetic fields and negative at high fields. In samples narrower than the characteristic length, the transfers involving a change in the type of electrons do not provide enough time to form a unified liquid. As a result, the flows of different components are independent and described by their own conductivities, taking into account the memory effects, while the magnetoresistance is strictly negative.

The method of numerical integration of Euler problem of buckling of a homogeneous console with symmetrical cross section in regime of plastic deformation using Maple18 is presented. The ordinary differential equation for a transversal coordinate \(y\) was deduced which takes into consideration higher geometrical momenta of cross section area. As an argument in the equation a dimensionless console slope \(p=tg \theta\) is used which is linked in mutually unique manner with all other linear displacements. Real strain-stress diagram of metals (steel, titan) and PTFE polymers were modelled via the Maple nonlinear regression with cubic polynomial to provide a conditional yield point (\(t\),\(\sigma_f\)). The console parameters (free length \(l_0\), \(m\), cross section area \(S\) and minimal gyration moment \(J_x\)) were chosen so that a critical buckling forces \(F_\text{cr}\) corresponded to the stresses \(\sigma\) close to the yield strength \(\sigma_f\). To find the key dependence of the final slope \(p_f\) vs load \(F\) needed for the shape determination the equality for restored console length was applied. The dependences \(p_f(F)\) and shapes \(y(z)\), \(z\) being a longitudinal coordinate, were determined within these three approaches: plastic regime with cubic strain-stress diagram, tangent modulus \(E_\text{tang}\) approximations and Hook’s law. It was found that critical buckling load \(F_\text{cr}\) in plastic range nearly two times less of that for an ideal Hook’s law. A quasi-identity of calculated console shapes was found for the same final slope \(p_f\) within the three approaches especially for the metals.