St Petersburg Polytechnic University Journal-Physics and Mathematics最新文献

A metric, describing the field due to bodies in stationary rotation about their axes and compatible with a stationary electromagnetic field, has been studied in present paper. Using Lie symmetry reduction approach we have herein examined, under continuous groups of transformations, the invariance of field equations due to rotation in General Relativity, that are expressed in terms of coupled system of partial differential equations. We have exploited the symmetries of these equations to derive some ans$\ddot{a}$tz leading to the reduction of variables, where the analytic solutions are easier to obtain by considering the optimal system of conjugacy inequivalent subgroups. Furthermore, some solutions are considered by using numerical methods due to complexity of reduced ordinary differential equations.

Biomedical and biotechnological engineering applications of magnetic nanoparticles (MNPs) for sensors are found to be of great importance. MNPs have attracted a growing interest in the design and development of sensors and biosensors for other several fields of applications. This research dealt with a novel optimization of MNPs of precipitation method of Fe³⁺ in basic solution. Also, for a surface coat with a random poly [(methacrylic acid)-ran-(2-methacryloyloxyethyl phosphorylcholine)] (PMAMPC-MNPs) by the means of chelating carboxylic group in its structure. We proposed MNPs to be incorporated into the transducer materials used for (bio)sensor and be dispersed in the sample. These caused an attraction by an external magnetic field onto the active detection surface of the (bio)sensor. RPM AMD PC and iron atoms were used to find the optimum conditions needed to coat the surfaces of the sensor such as particle concentrations. Particle technique FT-IR and TEM techniques showed that the synthesized PMAMPC-MNPs were spherical in shape in the range of 10–60 nm coated with a polymer capable of enhancing dispersion and good stability. In addition, particles coated with polymers of this property remain stable as the catalysts in reactions allowed the colour changes. This would be able to enhance sensitivity and stability of sensors and biosensors. This can be applied to the PMAMPC-MNPs for biosensors measurement application.

The squeezed MHD flow of water based metallic nanoparticles over a porous sensor surface in the presence of heat source has been investigated. The physical significance of the problem is water based on the geometry and the interaction of copper (Cu), aluminum oxide (Al₂O₃) and SWCNTs. The governing partial differential equations of momentum and energy are converted into ODEs for assured groups of the controlling parameters. The numerical and analytical results of the ODEs are determined utilizing fourth or fifth order Fehlberg method with shooting technique and OHAM and it is analyzed that there is no import difference between them. It is investigated that in squeezing flow phenomena, the effect of nanoparticle volume fraction on SWCNTs–water in the presence of magnetic field with thermal radiation energy plays a dominant role on heat transfer as compared to the other mixtures in the flow regime.

Instantaneous dipole moments of polyalanine peptides in vacuum and in the aqueous medium have been calculated on the picosecond time scale in order to evaluate the external influence of temperature, of the electrostatic field's amplitude and direction. Computer simulation was performed using the molecular dynamics method. The dynamic scenarios induced by the external electrostatic field above 100 MV/m were obtained for polyalanine molecules of different lengths (from 2 to 24 groups) placed in vacuum and in aqueous medium, the time step of 1 fs and the simulation time up to 100 ns being taken. The simulated scenarios can be used for a further analysis and a generalized description of structural properties and conformational dynamics of molecules. The mastered software packages are appropriate for computing the representational scenarios of biomolecular behavior under various conditions.

In this article the influence of thermal radiation on magnetohydrodynamic (MHD) flow of Cu-water nanofluid past a wedge in the occurrence of viscous-Ohmic dissipation and chemical reaction has been analyzed. The non-linearity numerical approach called RKF of the 4–5th order have been used with a shooting technique to find the results of velocity, temperature and concentration field for several points of employing parameters. The skin friction coefficient, Nusselt number and Sherwood number are examined in detail and the results are illustrated by figures and tables. The outcomes declared that the concentration boundary layer width diminishes with an increase in the values of the chemical reaction parameter and velocity profiles increase with increase in the magnetic field parameter.

We have employed RMF+BCS (relativistic mean-field and Bardeen-Cooper-Schrieffer) approach to study the phenomenon of shape coexistence in N = 28 isotones towards the proton-deficient side. Our present investigations include single particle energies, deformations, binding energies as well as excitation energies. It is found that towards the proton-deficient side, N = 28 shell closure disappears due to reduced gap between neutron 1f_7/2 and 1f_5/2 and the nuclei ⁴⁰Mg, ⁴²Si, and ⁴⁴S are found to possess shape coexistence giving further support to weakening of the shell gap. These results are found in excellent match with other theoretical and experimental studies and are fortified with a variety of calculations and parameters.

A series of new greenish blue emitting halosulphate phosphors NaCd_(1−x)SO₄F: xEu²⁺ (x = 1,3,5,7 mol%) was synthesized by re-crystallization method and its phase formation was confirmed by using the x-ray powder diffraction (XRD) technique. Fourier transform infrared spectroscopy (FTIR) characterizations and SEM analysis have also been investigated to explore the existence of various stretching bands and study of particle morphology. The photoluminescence (PL) results showed that the phosphor was excited by ultraviolet (UV) light at the wavelength of 200–400 nm, and it exhibited bright greenish blue emission under 280 nm UV light. The emission spectrum showed that a single broad band centered at 500 nm, corresponding to the ₄f⁶₅d¹ →₄f⁷ transition of Eu²⁺. The Eu²⁺ concentration dependent PL in NaCdSO₄F:Eu²⁺ indicated that there was dipole–dipole interaction of Eu²⁺ ions. The critical transfer distance was around 15.51 Å. The NaCdSO₄F:Eu²⁺ halosulphate phosphor under 280 nm excitation is very suitable for UV applications in solid state lightening devices.