Volume 63, Number 12, 2018
Theoretical, Mathematical, and Computational Physics
Complex Potentials with Real Eigenvalues and the Inverse Problem R.J. Lombard, R. Mezhoud, R. Yekken Romanian Journal of Physics 63,
101 (2018)
The existence of complex potentials with real eigenvalues rises two questions. The first one concerns the determination of the local real equivalent potentials. The second one underlines the fact that any even potential with respect to $x$ in the onedimensional ($D = 1$) space has at least two complex partners with the same spectrum. The present paper illustrates this situation with a few examples.
Further Solutions of the FalknerSkan Equation Lazhar Bougoffa, Rubayyi T. Alqahtani Romanian Journal of Physics 63,
102 (2018)
In this paper, we propose a reliable treatment for the FalknerSkan equation, which can be described as the nondimensional velocity distribution in the laminar boundary layer over a flat plate. We propose an algorithm of two steps that will introduce an exact solution to the equation, followed by a correction to that solution. Three different special cases: Hiemenz flow ($\beta =1 $), Homann flow ($\beta =\tfrac {1}{2} $), and Blasius problem ($\beta =0 $) have been considered. When the pressure gradient parameter $\beta $ takes sufficiently large values, we use a transformation of variable that reduces the FalknerSkan equation into an equivalent boundary value problem in a finite domain, and we solve this problem by a different technique that allows us to find $f''(0).$ Also, various exact solutions can be obtained in a straightforward manner by using a direct method when $\beta =1.$ The new technique, as presented in this paper, has been shown to be very efficient for solving the FalknerSkan equation.
Lie Symmetry Analysis and Exact Solutions to NCoupled Nonlinear Schrödinger's Equations with Kerr and Parabolic Law Nonlinearities Yakup Yildirim, Emrullah Yasar, Houria Triki, Qin Zhou, Seithuti P. Moshokoa, Malik Zaka Ullah, Anjan Biswas, Milivoj Belic Romanian Journal of Physics 63,
103 (2018)
This paper addresses Ncoupled nonlinear Schrödinger’s equation with spatiotemporal dispersion for Kerr and parabolic laws of nonlinearity by the aid of Lie symmetry analysis. We systematically construct similarity reductions to the derived ordinary differential equations by Lie group analysis. These equations lead to exactsolutions.
Microstructural Characterization of Surface Fractals Using SmallAngle Scattering E. M. Anitas, A. M. Slyamov, Zs. Szakacs Romanian Journal of Physics 63,
104 (2018)
The microstructural properties of deterministic surface fractals with a directional growth pattern are determined from the smallangle scattering (SAS) intensity of neutrons, Xray or light, as a function of the momentum transfer. The monodisperse intensities are calculated for a system consisting of a macroscopic number of randomly oriented surface fractals with uncorrelated positions. We show that, within the model, the scattering data can be used to determine surface thickness, the size of smallest building unit, the fractal dimension or the iteration number. The obtained microstructural quantities are related to the scaling factor of the fractal. We explain these correlations and illustrate the above findings on a model of hydrant deterministic fractal.
Finite Element Approximation for the Coupled TwoDimensional Burgers' Equation Ion Aurel Cristescu Romanian Journal of Physics 63,
105 (2018)
In this work we analyze a technique to determine the approximate solution of a system of nonlinear partial differential equations: the twodimensional coupled Burgers’ equations. The proposed method combines the finite elements and homotopy analysis. It can be applied to many other nonlinear problems arising from fluid mechanics, elasticity, electrostatics, geometry, etc.. It provides the possibility to consider complex geometric forms of the problem’s domain. The numerical solutions are successfully compared with the exact ones. The computation reveals very good accordance between the convergence regions for absolute and relative errors. This fact is really important for the case when the exact solutions are unknown.
Atomic, Molecular, and Optical Physics
Scattering of a TwoDimensional SelfHealing Beam at the Interface of a Nanostructured Medium with the Vacuum V. Sergentu, V. Ursaki Romanian Journal of Physics 63,
201 (2018)
In this paper the Fresnel’s formula are generalized to the case of a twodimensional (2D) selfhealing beam incident on the interface of the vacuum with a nonmagnetic, homogeneous on average and isotropic nanostructured medium with spatial dispersion. This approach is used for simplifying the problem of finding effective parameters of the nanostructured medium. It is found that, although the 2D beam can have only a finite length and finite energy in contrast to the 3D one, conditions are provided for the conservation of beam configuration and for ensuring his selfhealing properties.
Determination of Dielectric Constant Variation Due to the Exposure to GammaRay L. C. Tugulan Romanian Journal of Physics 63,
202 (2018)
In this paper, the variation of the dielectric constant (relative electrical permittivity) as a result of the exposure to gammaray was studied. The material used in this study was BK7 type glass. Several samples were exposed to gammaray in order to obtain different absorbed dose values. Different dielectric constant values, as a function of the absorbed dose, were determined, by using photospectrometric techniques. The results showed that the dependence of the dielectric constant to the absorbed dose presents linear regions, which make the dielectric constant a quantity that can be used in gammaray dosimetry.
Physics Of Elementary Particles and Fields
Analysis of Relativistic NucleusNucleus Collisions to Search for Phase Transition A. Kamal Romanian Journal of Physics 63,
401 (2018)
We have strived to look at the behavior of Levy stability index, $\mu $ and fractal structure in the distributions of relativistic charged particles in terms of modified `$G_q^m$' moments using experimental and model (FRITIOF and HIJING, Heavy Ion Jet INteraction Generator) based simulated 14.5 GeV per nucleon $^{28}$SiAgBr collisions. The dynamical component of the multifractal moments is gleaned using correlation free Monte Carlo (MCRAND) simulated events. The results are compared with those obtained earlier using scaled factorial moments, $F_q$. The investigation reveals that the distribution of relativistic charged particles in pseudorapidity space exhibits fractal behavior, dynamical fluctuations and multifractality in both experimental and generated data. Our findings also reveal manifestation of nonthermal phase transition in the experimental data in the two approaches and the value of Levy index, $\mu $ for the experimental data is consistent with the Levy law description of density distribution of produced charged particles. Furthermore, the values of $\mu $ for the experimental data are reproduced by the FRITIOF generated data but the values of $\mu $ obtained by analysing HIJING data specifically in terms of $G_q^m$ and $F_q$ moments violate the Levy stability condition: $0 \le \mu \le 2$.
Condensed and Soft Matter Physics
On the Magnetic Behaviour of Heavy RareEarths RCo_{2} Compounds E. Burzo, L. Chioncel Romanian Journal of Physics 63,
601 (2018)
The magnetic behaviour of RCo_{2} (R = Tm, Er, Ho, Tb) compounds, above and below the Curie temperatures, $T_c$, is analysed. In the magnetic ordered phase, the exchange interactions (with spatial extension within the unit cell) are discussed in connection with R5d band polarizations. It is also shown that the exchange interactions, at $T > T_c$, are not sufficiently strong to induce the shortrange magnetic order (of Griffithstype) inferred from SANS experiments. The successive changes in the orientations of R and Co moments, as function of temperature and external field can be well described by a phenomenological model based on the energies balance, while the magnetic behaviour of cobalt is at best described by the spin fluctuations.
Superconductivity and Magnetic Studies of Bulk Y123/ BaCuO_{2} Composite A. K. StoyanovaIvanova, S. D. Terzieva, S. I. Georgieva, B. S. Blagoev, D. G. Kovacheva, A. Zaleski, V. Mikli Romanian Journal of Physics 63,
602 (2018)
In this paper we present the results of the study of ceramic composite Y123/BaCuO_{2} obtained in onestep procedure, which appears to lead to material possessing both superconducting and magnetic properties at low temperatures. By applying scanning electron microscopy (SEM), energydispersive Xray spectroscopy (EDX), spectrophotometry for oxygen index evaluation and AC and DC magnetization measurements we managed to show that if the nominal starting composition is 1:3:4 (Y:Ba:Cu) one can obtain two phase composite with 62wt% of superconducting YBCO with high critical temperature equal to 92.6 K and 38wt% of magnetic BaCuO_{2}. Stability of obtained composite in alkaline solution is superior over pure Y123 material which is important for practical application in the manufacture of batteries.
The Longitudinal Excitation Spectrum of an Elongated BoseEinstein Condensate M.C. Raportaru, R. Zus Romanian Journal of Physics 63,
603 (2018)
In this manuscript we show an efficient numerical approach for the longitudinal excitation spectrum of a quasionedimensional collisionallyinhomogeneous BoseEinstein condensate. We obtain by variational means the nonlinear ordinary differential equations of a generic longitudinal excitation and determine numerically the onset of instability, to identify which excitation is most likely to be observed experimentally. To quantify the efficiency of our approach, we study a cigarshaped condensate with weak collisionallyinhomogeneous twobody interactions and show that the position of the resonance observed in the longitudinal excitation spectrum is higher than that observed for a condensate with homogeneous twobody interactions.
Suppression of Charge and Antiferromagnetic Ordering in GaDoped La_{0.4}Ca_{0.6}MnO_{3} C. Badea, R. Tetean, I. G. Deac Romanian Journal of Physics 63,
604 (2018)
We investigate the structural, magnetic and magnetotransport properties of the Ga doped compounds La_{0.4}Ca_{0.6}Mn_{1x}Ga_{x}O_{3}. The undoped compound La_{0.4}Ca_{0.6}MnO_{3} (LCMO) shows an antiferromagnetic (AFM) ground state and charge ordering (CO) at low temperatures. The partial replacement of manganese ions by non magnetic d^{10} Ga^{3+} ions can disrupt the charge, orbital, spin ordering. The magnetic and magnetotransport measurements showed that CO and AFM phases are weakened with increasing Ga content; $T_{CO}$ and $T_N$ shift to lower temperatures. Below 100 K, the AFM/CO phase was partially transformed in ferromagnetic (FM) clusters which grow with increasing Ga content. Nonmagnetic Ga, doped in LCMO increases the magnetism in the samples. The compounds have semiconducting behavior in the whole investigated temperature range. The samples showed negative magnetoresistance (MR) that is not much affected by the Ga content. The maximum value of MR ~ 30 % (for 7 T) was always reached at the base temperature (75 K), suggesting that this behavior is mainly decided by extrinsic factors, such as grain boundaries, disorder and charge carriers localization. The magnetic and electrical properties of these compounds at low temperatures, suggest that they are composed of a mixture of charge ordered and charge disordered phases of various proportions.
Environmental and Earth Physics
Determination of Gross Alpha, Gross Beta, and Natural Radionuclides (^{210}Po, ^{210}Pb, ^{238}U, ^{232}Th and ^{40}K) Activity Concentrations in Bread and Their Contribution to the Effective Dose Violeta Pintilie, Antoaneta Ene, Lucian Puiu Georgescu, Dana Iulia Moraru, Adelina Pintilie Romanian Journal of Physics 63,
801 (2018)
In this paper the gross alpha, gross beta and natural radionuclides (^{210}Po, ^{210}Pb, ^{238}U, ^{232}Th and ^{40}K) activities were determined in bread samples collected during 20132015 from Galati, Braila and Vrancea counties, SouthEastern Romania. The concentrations of ^{210}Po and ^{210}Pb were determined after self deposition on nickel disc by gross alpha measurements. The concentrations of ^{238}U and ^{232}Th were calculated after the determination of the concentration of ^{nat}U and ^{nat}Th through spectrophotometric measurements of arsenazo IIIU^{4+} complex and arsenazo IIITh^{4+} complex, respectively. The concentrations of ^{40}K were measured by gammaspectrometry using a NaI(Tl) detector. The gross alpha and gross beta activity in bread samples ranged from 0.006 to 0.180 Bq kg^{1}, and from 21.3 to 45.7 Bq kg^{1}, respectively. The radionuclide concentrations (fresh weight) in bread ranged in the intervals 0.0140.031 Bq kg^{1} for ^{210}Po, 0.0060.080 Bq kg^{1} for ^{210}Pb, 0.0090.040 Bq kg^{1} for ^{238}U, 0.0010.021 Bq kg^{1} for ^{232}Th, and 10.431.4 Bq kg^{1} for ^{40}K. The annual effective dose obtained ranged between 0.023 µSv y^{1} (for ^{232}Th) and 19.572 µSv y^{1} (for ^{40}K).
Applied and Interdisciplinary Physics
A Method to Adjust the Impedance of the Signal Transmission Line in a MultiStrip MultiGap Resistive Plate Counter D. Bartos¸ M. Petris¸ M. Petrovici, L. Rădulescu, V. Simion Romanian Journal of Physics 63,
901 (2018)
While in a triggered experiment the matching of the signal transmission line impedance of a resistive plate counter with the one of the input of the frontend electronics is less critical, for a triggerless data recording experiment this becomes mandatory. However, impedance matching is not a straightforward solving issue, as soon as important RPC performance requirements in terms of time and position resolutions, efficiency and granularity, have to be simultaneously fulfilled. We report here a method of tunning the signal transmission line impedance of a MultiStrip MultiGap Resistive Plate Counter (MSMGRPC) which matches any input impedance of a given frontend electronics, the design of a new MSMGRPC prototype based on it and the very first results obtained with the prototype. This shows that the impedance matching can be achieved independent on counter granularity using the innovative architecture of the MSMGRPC reported here.
A New Fast Simulation Tool for the Micromegas Detectors Dan Andrei Ciubotaru, Michele Renda Romanian Journal of Physics 63,
902 (2018)
We propose a new simulation tool for the Micromegas detectors, in which the signal generated by electrons and ions is treated analytically. The description of this framework and a list of requirements are presented in this paper. We developed a prototype to verify the feasibility of this tool and we present some of the obtained results.
