Volume 66, Number 910, 2021
In Memoriam Voicu Vlad Grecu
Romanian Journal of Physics 66,
001 (2021)
Theoretical, Mathematical, and Computational Physics
Investigation of Numerical Behavior of the GinzburgLandau Equation and DavisSkodje System via the Modified Euler Approach L. Torkzadeh Romanian Journal of Physics 66,
118 (2021)
In this paper, we present two numerical schemes based on the Euler method that can provide a suitable approximation for the solutions of Itô stochastic differential equations. The capability and efficiency of the methods are confirmed by examining two widely applied equations, namely, the stochastic GinzburgLandau equation and the DavisSkodje system. Some properties of our approximations for solutions of these equations are considered and the convergence rate and asymptotic solution are derived.
Lax Pair, Generalized Darboux Transformation, and Solitonic Solutions for a VariableCoefficient Coupled Hirota System in an Inhomogeneous Optical Fiber Meng Wang, Bo Tian Romanian Journal of Physics 66,
119 (2021)
Optical fibers, which are considered as optical waveguides, are applied to the data transmission systems on account of their high informationcarrying capacity and dielectric nature. In this paper is studied a variablecoefficient coupled Hirota system, which describes the propagation of vector optical pulses in an inhomogeneous optical fiber. For the complex wave envelopes, we obtain a Lax pair. By virtue of that Lax pair, we construct a generalized Darboux transformation. Then, the threesoliton solutions are derived accordingly, and the interactions among those solitons are investigated.
Atomic, Molecular, and Optical Physics
Modes of Appearance of a Defocusing Nonlinear Response with Increasing Electric Field in the Surface Layer of a Crystal Covered with a Fully Shielding Film S.E. Savotchenko Romanian Journal of Physics 66,
203 (2021)
We describe the appearance of a defocusing nonlinear response near the surface of the initially linear semibounded crystal with fully screening coating in dependence of electric field. We consider five different boundary modes of the surface wave propagation in two ranges of variation of the effective refractive index. We find exact analytical solutions of the nonlinear wave equation describing the new types of nonlinear surface waves. The power flux of the surface waves was calculated analytically. The dependences of the effective refractive index and frequency on the optical characteristics of the crystal are found for some types of waves.
Nuclear Physics
Extensive Study of the Positive and Negative Parity Wobbling States for an OddMass Triaxial Nucleus II: Classical Trajectories R. Poenaru, A. A. Raduta Romanian Journal of Physics 66,
309 (2021)
The wobbling properties of ^{163}Lu are described within a semiclassical view by using a new interpretation of the band structure of this isotope. Namely, the bands $TSD_2$ and $TSD_4$ are considered as Parity Partner Bands: two $\Delta I=2$ rotational bands with identical spins but opposite parity that emerge from a sole wavefunction which is an admixture of both positive and negative parity states. The classical energy function $\mathcal {H}$ of the system is obtained from the dequantization procedure of the Particle Rotor Hamiltonian, and it is expressed in terms of generalized coordinates and momenta. By analyzing its behavior near the critical points, regions where wobbling motion has a stable (unstable) character arise, this being represented by the closed (opened) trajectories surrounding these points in the contour plots. Furthermore, the two constants of motion for the deformed nucleus, i.e., the energy $E$ and total angular momentum $I$ are graphically represented as 3dimensional surfaces in the space generated by the components $I_1,I_2,I_3$ of the angular momentum. From their intersection, the classical orbits can be obtained, and their geometric interpretation gives an insight into the rotational character of ^{163}Lu. Indeed, obtaining a classical view for the motion of quantum object is a remarking feature of the present work.
Condensed and Soft Matter Physics
Viscoelastic Moduli of Homogeneous Ferrofluids R. PeredoOrtiz, K. Meza Martinez, M. HernandezContreras Romanian Journal of Physics 66,
610 (2021)
We propose a stochastic method to determine the viscosity and viscoelastic modulus of colloidal magnetic fluids. The predicted static viscosity yields the trends of the experiments as a function of the volume concentration of particles.
Plastic Deformation and Microhardness of Pb_{1x}Yb_{x}Te Single Crystals under QuasiStatic and Sclerometric Indentation Daria Grabco, Valentina Nicorici, Daria Topal, Constantin Pyrtsac, Olga Shikimaka Romanian Journal of Physics 66,
611 (2021)
In this work, the microhardness and specificity of deformation of Pb_{1x}Yb_{x}Te single crystals by quasistatic and sclerometric indentation are studied. It is shown that these crystals are distinguished by high plasticity and low microhardness both under indentation and under the movement of the indenter. An opinion is expressed that the mechanism of crystal structure compaction is involved in mass transfer during the formation of an imprint, along with the dislocation mechanism. Crystals have low sclerometric anisotropy of hardness along different crystallographic directions on the (001) plane, which is typical for crystals of a cubic system. The jumplike mechanism of the deformation process during the movement of the indenter, which is characteristic of crystals of different types, is confirmed.
The Magnetothermopower of Organic Superconductor κ(ET)_{2}Cu(NCS)_{2}: Possible Charge Density Wave Scenario Danica Krstovska, Eun Sang Choi, Eden Steven Romanian Journal of Physics 66,
612 (2021)
The interlayer magnetothermopower of the organic superconductor $\kappa \rm (ET)_2Cu(NCS)_2$ is studied at temperatures down to 0.5 K and fields up to 32 T. Analysis of the background magnetothermopower shows that at low temperatures it is negative and exhibits an upturn at higher field, producing a dip at a field close to the upper critical field $B_{c2}$. There are clear magnetothermopower quantum oscillations visible above 5 T. The obtained oscillation frequencies are in a good agreement with those previously reported on the magnetoresistance and magnetization quantum oscillations. According to our results, the magnetothermopower in $\kappa \rm (ET)_2Cu(NCS)_2$ presents features which have already been detected in YBCO and other high$T_c$ cuprates indicating that some kind of a charge density wave order is also present in the normal state of $\kappa \rm (ET)_2Cu(NCS)_2$. Most strikingly, our measurements show that there is another dip, again followed by an upturn, in the magnetothermopower of $\kappa \rm (ET)_2Cu(NCS)_2$ occurring at much higher fields than $B_{c2}$, around the magnetic breakdown field of $\sim 21$ T that is not present in $\rm YBCO$. We propose that the two induced successive phase transitions, consisting of two similarly ordered states each restricted to a finite magnetic field window are in fact charge density wave ordered states arising as a result of the layerstacking mechanism in the interlayer direction. Our results support and advance some of the previous findings that the superconductivity in the organic superconductor $\kappa \rm (ET)_2Cu(NCS)_2$ is mediated by a charge density wave order rather than antiferromagnetic fluctuation.
Polarization Anisotropy of a Microlayer of Magnetic Nanofluid in Electric and Magnetic Fields M. S. Demin, T. F. Morozova Romanian Journal of Physics 66,
613 (2021)
This article deals with the results of electric and physical tests carried out on a microlayer of a magnetic nanofluid exposed to constant electric and magnetic fields. Some dielectric hysteresis and antihysteresis loops were detected. We analyzed the cooccurring polarization anisotropy that changes the dielectric permeability of the magnetic nanofluid microlayer.
Biophysics and Medical Physics
Estimation of Absorbed Doses to Target and Healthy Tissues During ConeBeam CT Radiotherapy Imaging of the Chest M. Marjanović, Á. Tóth, B. Petrović, I. Gencel Romanian Journal of Physics 66,
707 (2021)
The aim of this study was to assess volumetric imaging dose and image quality during radiotherapy in case of Hodgkin lymphoma. The absorbed doses were measured using ionization chamber in thorax phantom. For the same setup, Monte Carlo simulations were performed. The image quality was assessed using Catphan phantom. The absorbed doses ranged from 4.4–7.7 mGy (full rotation) and 1.1–3 mGy (partial rotation). Doses from simulation ranged from 6.8–15.6 mGy (full rotation) and 1.9–10.4 mGy (partial rotation). The image quality tests have shown differences between clinical protocols. The imaging doses were smaller than prescribed doses, but shouldn't be neglected.
Environmental and Earth Physics
Seismicity, Active Stress Pattern and Fault Reactivation Potential in South Carpathians E. Oros, A. O. Placinta, I. A. Moldovan Romanian Journal of Physics 66,
811 (2021)
The paper presents a seismotectonic model of the Southern Carpathians obtained from the analysis of the seismicitystress fieldgeology and tectonics relationship. The seismicity model is based on a revised earthquake catalogue. The distribution of bvalues in the 3D space facilitated the identification of stressed areas and asperities with reactivation potential and their correlation with geological structures. The stress field has been modelled using the parameters of the stress tensor calculated by the formal inversion of the focal mechanisms. The reactivation potential of geological structures was estimated depending on the relationship between the fault planes geometry and the principal stress axes.
Applied and Interdisciplinary Physics
An Inclined Plane Based Instrument for Determining the Static Coefficient of Friction at High Temperatures M. Lukovic, J. Miljojkovic, B. Tadic Romanian Journal of Physics 66,
909 (2021)
In this paper, an instrument is presented that enables the measurement of the static coefficient of friction for contact pairs at different temperatures, normal atmospheric and low contact pressure. The instrument is based on the principle of an inclined plane and enables determination of the angle of rotation with great accuracy. The coefficients of friction are determined by measuring the angle of rotation of the instrument. Tests were conducted on stainless steel pinrod contact pair under unlubricated conditions from room temperature to a temperature of 700°C. A special heating chamber is part of the instrument that allows the metal pin to be heated to high temperatures. The results showed an increase in the values of static coefficient of friction with increasing temperature.
