Volume 72, Number 2, 2020
 
THEORETICAL, MATHEMATICAL, AND COMPUTATIONAL PHYSICS
 
Solitary waves of the Camassa-Holm derivative nonlinear Schrödinger equation
L.J. GUO, C.B. WARD, I.K. MYLONAS, P.G. KEVREKIDIS
Rom. Rep. Phys. 72, 107 (2020)
Abstract. In this paper we examine a deformation of the derivative nonlinear Schrödinger (DNLS) equation, the so-called Camassa-Holm DNLS (CH-DNLS) equation. We use two asymptotic multiscale expansion methods to reduce this model to both the modified Korteweg-de Vries (MKdV) equation and the Korteweg-de Vries (KdV) equation. Using their exact soliton solutions, we construct approximate solutions of the original CH-DNLS equation, namely dark and anti-dark solitary waves. Direct numerical simulations demonstrate the validity of these approximate solutions and illustrate their dynamical evolution, including their potential for nearly elastic head-on collisions in the case examples considered.
Article no. 107: PDF 
Transverse Kahler-Ricci flow and deformations of the metric on the Sasaki space T1,1
VLADIMIR SLESAR, MIHAI VISINESCU, GABRIEL-EDUARD VILCU
Rom. Rep. Phys. 72, 108 (2020)
Abstract. In this paper we investigate the possibility to obtain locally new Sasaki-Einstein metrics on the space T1,1 considering a deformation of the standard metric tensor field. We show that from the geometric point of view this deformation leaves the transverse and leafwise metric intact, but changes the orthogonal complement of the Reeb vector field using a particular basic function. In particular, the family of metric obtained using this method can be regarded as solutions of the equation associated to the Sasaki-Ricci flow on the underlying manifold.
Article no. 108: PDF 
Inverses of Langevin, Brillouin and related functions: a status report
VICTOR BARSAN
Rom. Rep. Phys. 72, 109 (2020)
Abstract. This paper gives a coherent and comprehensive review of the results concerning the inverses of Langevin L(x) and of Brillouin functions BJ(x) and the inverses of L(x)/x and BJ(x)/x, with main focus on the most recent developments. As these functions are used in several fields of physics, without evident interconnections-magnetism (ferromagnetism, nanomagnetism, hysteretic physics), rubber elasticity, rheology, solar energy conversion - the new results are not always efficiently transferred from a domain to another. The increasing accuracy of experimental investigations claims an increasing accuracy in the knowledge of these functions, so it is important to compare the accuracy of various approximants and even to obtain, in some cases, the exact form of the inverses of L(x), BJ(x), L(x)/x and BJ(x)/x, using the recently created theory of generalized Lambert functions. The paper contains also some new results, concerning both exact and approximate forms of the aforementioned inverse functions.
Article no. 109: PDF 
Painlevé analysis for higher–dimensional integrable shallow water waves equations with time–dependent coefficients
ABDUL-MAJID WAZWAZ
Rom. Rep. Phys. 72, 110 (2020)
Abstract. We investigate the (2+1)- and (3+1)-dimensional shallow water waves equations with time-dependent coefficients. We study the integrability of each developed model by using the Painlevé approach. Multiple soliton solutions and multiple complex soliton solutions, for each equation, are constructed using the Hirota's direct method, and the related complex criteria.
Article no. 110: PDF 
Solitons of the complex nonlinear Schrödinger equation with parity-time-symmetric linear-nonlinear lattice potentials
SYED TAHIR RAZA RIZVI, UJALA SAFDAR, ISHRAT BIBI, KASHIF ALI, QIN ZHOU
Rom. Rep. Phys. 72, 111 (2020)
Abstract. By using an inverse method, we report families of exact soliton solutions of a generalized complex nonlinear Schrödinger equation with parity-time-symmetric mixed linear-nonlinear lattice potentials. The Kerr-, parabolic-, and power-law nonlinearities are considered and analytical soliton solutions are obtained, for some special forms of complex-valued parity-time-symmetric potentials.
Article no. 111: PDF 
Stochastic simulation of epidemics using the maximum entropy principle and generalized polynomial chaos expansions
JULIA CALATAYUD, MARC JORNET
Rom. Rep. Phys. 72, 112 (2020)
Abstract. The evolution of epidemics can be better understood using compartmental models based on differential equations. Accounting for modeling and data errors, the transmission parameters of the model must be regarded as random variables. The maximum entropy principle infers consistent probability distributions for the parameters, by maximizing the ignorance on their density functions while not violating physical principles. Once the parameter estimation problem is solved, a non-intrusive approach based on generalized polynomial chaos expansions reconstructs the stochastic solution in terms of the random parameters. This allows for uncertainty quantification to obtain robust predictions for the epidemic. Also, a variance-based sensitivity analysis can be conducted to determine the parameter having the highest impact on the model output.
Article no. 112: PDF 
 
OPTICS AND PHOTONICS, PLASMAS, LASER AND BEAM PHYSICS
 
Propagation of three-dimensional extremely short optical pulses in strained carbon nanotubes
N.N. KONOBEEVA, D.S. SKVORTSOV, M.B. BELONENKO
Rom. Rep. Phys. 72, 406 (2020)
Abstract. We investigate the extremely short optical pulses in strained carbon nanotubes in the three-dimensional case. The mechanical strain is taken into account in the framework of the gauge theory. We study the influence of the value of the mechanical stretching on the pulse shape.
Article no. 406: PDF 
Optical fiber-based plasmonic sensors using aluminium oxide insulator
V.A. POPESCU
Rom. Rep. Phys. 72, 407 (2020)
Abstract. The angular and spectral interrogation methods are applied to calculation of the power loss, figure of merit and spectral and amplitude sensitivities for the TM modes in a fiber-based plasmonic sensor with four layers using a very thin aluminium oxide insulator as the interior or exterior cladding layer. The values of the effective indices calculated by using the finite element method are in agreement with an analytical method where the electromagnetic field is represented by a Bessel function of the first kind in the core region (SiO2), a linear combination of the Hankel functions in the gold and Al2O3 regions, and a modified Bessel function of the second kind in the outermost region (H2O). For a fiber with four layers and the gold layer in the exterior part of the cladding region, the limit of detection in intensity interrogation mode (7.78 × 10-8 RIU) is better than in angular interrogation mode (8.41 × 10-6 RIU).
Article no. 407: PDF 
 
CONDENSED AND SOFT MATTER PHYSICS
 
Magnetorheological suspension-based magnetoresistor: influence of temperature and magnetic field intensity on electrical resistance and apparent viscosity
I. BICA, E.M. ANITAS
Rom. Rep. Phys. 72, 501 (2020)
Abstract. We fabricate a magnetoresistor consisting of a microfiber cloth impregnated with magnetorheological suspensions (MRS), and covered by a sheath of cotton fabric with silicone rubber. The obtained magnetoresistor is investigated in a static magnetic field superimposed on a thermal field with increasing temperatures Θ over time t. We build and describe an experimental setup for measuring the electrical resistance R = R(t, Θ)H of magnetoresistor as a function of t and Θ for fixed values of magnetic field intensities H. We show that at Θ = 300 K, R = R(t)H is constant in time, and decrease with H. However, the functions R = R(t, Θ)H decrease sensibly with Θ. From these data, and by using the magnetic dipolar approximation we determine the behaviour of apparent viscosity η as a function of Θ for fixed values of H. We present and discuss the physical mechanisms responsible for the observed effects. The obtained results can be used for manufacturing of MRS based devices aimed at sensing magnetic and thermal field fluctuations.
Article no. 501: PDF 
Effect of Mn substitution on the structural, magnetic and magnetostrictive properties of Fe-Pd ferromagnetic shape memory ribbons
M. SOFRONIE, M. ENCULESCU, A.D. CRISAN, F. TOLEA
Rom. Rep. Phys. 72, 502 (2020)
Abstract. This work reports the effect of the Mn substitution, rapid solidification technique and heat treatments on the martensitic transformation, magnetic and magnetostrictive properties on the Fe70-xPd30Mnx (x = 1, 3) ferromagnetic shape memory ribbons. The samples were investigated by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy, magnetic and magnetostrictive measurements. The thermal treatments induce significant changes in the microstructure and magnetocrystalline anisotropy of the martensitic phase, for Fe67Pd30Mn3 compared to Fe69Pd30 Mn1. The competition between the magnetization orientation and twin boundary motion within martensitic variants under magnetic field evidenced in the magnetic-strain curves was discussed and correlated with the magnetic data.
Article no. 502: PDF 
Physical properties of metal oxide nanoparticles processed as thin films by MAPLE technique
A.I. RADU, M. FILIPESCU, M. DUMITRU, A. MOLDOVAN, M. DINESCU, S. ANTOHE
Rom. Rep. Phys. 72, 503 (2020)
Abstract. Metal oxide nanoparticles are intensively studied due to advantages such as low cost, easy production, compact size and simple measuring electronics. For this study, SnO2 , CeO2 and WO3 nanoparticles were processed as thin layers by matrix assisted pulsed laser evaporation technique. The morphological, structural and optical properties of the obtained layers were investigated. The achieved homogeneous distribution of nanoparticles in the layers and the high surface roughness, are properties suitable for gas sensors development.
Article no. 503: PDF 
Characterization of PBDB-T-SF: fullerene blend thin films for solar cell applications
L. HROSTEA, L. LEONTIE, M. GIRTAN
Rom. Rep. Phys. 72, 504 (2020)
Abstract. This paper presents a comparative study of two polymers: poly (3-hexylthiophene) (P3HT) and poly[(2,6-(4,8-bis(5-(2-ethylhexylthio)-4-fluorothiophen-2-yl)-benzo[1,2-b:4,5 b']dithiophene))-alt-(5,5(1',3'di2thienyl-5',7'-bis(2-ethylhexyl)benzo[1',2'-c:4',5'c']dithiophene-4,8-dione)] (PBDB-T-SF) deposited on glass and indium tin oxide (ITO) substrates by spin coating, as polymer thin films and polymer: fullerene phenyl-C61-Butyric-Acid-Methyl-Ester (PCBM) thin films (90÷300 nm thickness). The comparison concerns: i) spectral dependence of optical properties measured by spectrophotometry and ellipsometry techniques; ii) morphological characteristics by atomic force microscopy; iii) electric properties. The decisive impact of chemical structure on photovoltaic behaviour of polymer-based materials is emphasized in case of PBDB-T-SF, containing two fluorine atoms into its polymer backbone, which improve its performance in solar cell applications.
Article no. 504: PDF 
 
BIOPHYSICS AND MEDICAL PHYSICS
 
The impact of breast irradiation using thermoplastic mask on treatment delivery and acute effects
A. DINU, T. FLONTA, L.G. MARCU
Rom. Rep. Phys. 72, 603 (2020)
Abstract. Several methods of breast immobilisation exist for patients treated for left-sided breast carcinomas to reduce positioning errors and to limit dose to cardiac muscle. Thermoplastic masks are useful tools, particularly when respiratory-gated radiotherapy is not available. This study evaluates the impact of breast masks on treatment delivery and acute effects.
Article no. 603: PDF 
 
ENVIRONMENTAL AND EARTH PHYSICS
 
Statistical analysis of mineral elements content in different melliferous plants from the Dobrogea region, Romania
L. BARBES, A. BARBULESCU, G. STANCIU
Rom. Rep. Phys. 72, 705 (2020)
Abstract. Different mineral elements are essential for physiological processes in the medicinal plants and food derivative products (tea, herb extracts, tinctures, honey, pollen etc.). The aim of this paper was to study the content of nine mineral elements: K, Ca, Mg, Na, Fe, Mn, Cu, Zn, and Cd in different parts (leaves, flowers and steam or bark) of three medicinal plant with highest melliferous potential: Sambacus nigra L., Hypericum perforatum and Tilia tomentosa species, collected in May and June 2019 from wild flora of Dobrudja area. The quantitative determination of mineral elements in the components of these medicinal herbs was done by FAAS (flame atomic absorption spectrometry). Absorption of different metallic ions in melliferous plants is governed by soil characteristics such as pH, salinity, conductivity and organic matter content. In this respect, Zn average concentration ranged between 6.893 mg/kg in Sambacus nigra L. stems and 101.46 mg/kg in Tilia tomentosa bark collected from touristic camping area. The physiological activities of melliferous plants influence zinc absorption and the interactions with many elements such as Fe and Mn. The analysis of Cd in the melliferous plants indicated that Cd concentration ranged between 0.001 mg/kg in Sambacus nigra L. stems to 5.64 mg/kg in Tilia tomentosa leaves on the same polluted area by the intense road traffic, respectively.
Article no. 705: PDF 
Changes in cyclone intensity over Romania according to 12 tracking methods
ION-ANDREI NITA, LUCIAN SFICA, LIVIU APOSTOL, CRINA RADU, MARIUS-VICTOR BIRSAN, ROBERT SZEP, AGNES KERESZTESI
Rom. Rep. Phys. 72, 706 (2020)
Abstract. Extratropical cyclones are essential for climate conditions in midlatitude areas due to energy budget transfer which they sustain between the poles and tropical areas. With the multitude of cyclone tracking and detection methods developed over the years, the principal challenge focused on the agreement between them. For this purpose, we selected 12 cyclones detection methods mainly based on mean sea level pressure and 850 hPa relative vorticity parameters. Only the trajectories that crossed the Romanian territory were selected. The temporal trends in cyclone's characteristics intensity, speed, lifetime, traveled distance - were also investigated. While there is a general consensus among the methods regarding an increase in intensity of cyclones over Romania, a smaller agreement can be seen for other characteristics. For instance, we found no significant changes over the annual frequency for any group of cyclones with respect to their origins.
Article no. 706: PDF 
GPS processing tools for better impact assessment of earthquakes in Romania
E.I. NASTASE, A. MUNTEAN, S. NISTOR, B. GRECU, D. TATARU
Rom. Rep. Phys. 72, 707 (2020)
Abstract. Nowadays, advances in GNSS receivers technology and computational algorithms such as 1 Hz acquisition rate (and even more, up to 50 Hz), that are commonly available, make us search worldwide for systems & algorithms that would make possible a real‐time estimation of waveforms and coseismic displacements. The present paper highlights the results obtained in recent years by looking at the Romanian GNSS data over 3 different study cases from another perspective, aims to elaborate on a number of issues and provide some directions for future work that involve nontraditional seismological sensors such as GPS and tiltmeters following the implementation of the new generation of tools into GNSS permanent reference network data processing, in help for a more accurate assessment of the Vrancea earthquakes impact.
Article no. 707: PDF 
 
APPLIED AND INTERDISCIPLINARY PHYSICS
 
Calculation method for derived emission limits values from "Horia Hulubei" National Institute for R&D in Physics and Nuclear Engineering area
ANA STOCHIOIU
Rom. Rep. Phys. 72, 802 (2020)
Abstract. The paper presents studies devoted to the assessment of derived emission limits (DELs) for potential radionuclides emitted as gaseous and liquid effluents resulting from the nuclear activities carried out in "Horia Hulubei" National Institute of Physics and Nuclear Engineering, IFIN-HH. The radionuclides in gaseous effluents identified by qualitative and quantitative specific measurements are: Co-60, Cs-134, Cs-137, Ag-108m, Eu-152, Eu-154, Eu-155, and H-3 total. The maximum concentration was found for Co-60 in the quantum of 109 Bq·a-1. In the case of liquid effluents, a number of radionuclides, mainly C-14 in a concentration of 109 Bq·a-1 , I-123 with 108 Bq·a-1 concentration, and Tc-99m and Mo-99, in concentrations of up to 1010 Bq·a-1 were found. The calculations are based on these data and an approved annual effective dose constraint for the critical group from the Magurele town of Econstr=100 μSv·a-1.
Article no. 802: PDF 
Optical band gap as parameter in gamma-rays dosimetry (high doses)
L.-C. TUGULAN, G.-V. IOAN
Rom. Rep. Phys. 72, 803 (2020)
Abstract. Targeting the investigation of the optical band gap energy of two chosen types of optical materials when interacting with ionizing radiation, this paper was focused on a relatively high absorbed gamma-ray doses region (0.1-16) kGy. The optical materials involved in this study were ZF-7 (high lead content glass) and BK-7 (borosilicate crown glass). The potential of the optical band gap energy to be used as parameter in gamma-rays dosimetry (high doses) was also analyzed. Both the direct and indirect types of optical absorption were studied. For the direct transition, relative decreases of 14.4% (ZF-7) and 14.5% (BK-7) were found. In the case of indirect transition, the decrease was of 12.7% for ZF-7 and respectively of 15.4% for BK-7.
Article no. 803: PDF 

This is an electronic version of Volume 72 Number 2 2020
 
   
 
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