



Volume 70, Number 1, 2018 







Foreword
The Editorial Board of Romanian Reports in Physics
Rom. Rep. Phys. 70, 001 (2018)


THEORETICAL, MATHEMATICAL, AND COMPUTATIONAL PHYSICS. HISTORY AND PHILOSOPHY OF PHYSICS 






The first seventy volumes of Romanian Reports in Physics: A brief survey of the Romanian Physics Community
V.I. Vlad, V. Baran, A.I. Nicolin, D. Mihalache
Rom. Rep. Phys. 70, 101 (2018)
Abstract. To mark the publication of the seventieth volume of Romanian Reports in Physics,
printed before 1992 under the Romanian name Studii si Cercetari de Fizica, we briefly review here its history in the broader context of the
evolution of Romanian Physics within the past seven decades, and outline some of the research topics that are representative both for the journal
and the Romanian physics community at large. Our review takes the form of a historical resource article that references a comprehensive list of
papers authored or coauthored by Romanian physicists in the period 19502017, selected to be indicative for the research interests of the authors
and scientifically significant. Our survey covers theoretical, experimental, and computational physics articles from the main research and
academic centers in Romania and sketches the scientific profiles of a series of Romanian physicists. 




Special types of elastic resonant soliton solutions of the KadomtsevPetviashvili II equation
S. Chen, Y. Zhou, F. Baronio, D. Mihalache
Rom. Rep. Phys. 70, 102 (2018)
Abstract. Special types of exact two and threesoliton solutions in terms of
hyperbolic cosines to the KadomtsevPetviashvili II equation are presented, exhibiting rich intriguing interaction patterns on a finite
background. The behavior of each line soliton in the far region can be characterized analytically. It is revealed that under certain
conditions, there may appear an isolated bump in the interaction center, which is much higher in peak amplitude than the surrounding line
solitons, and the more line solitons interact, the higher isolated bump will form. These results may provide a clue to generation of extreme
highamplitude waves, in a reservoir of small waves, based on nonlinear interactions between the involved waves. 




Dynamics of quantum interferometric power in Gaussian open systems
A. Isar
Rom. Rep. Phys. 70, 103 (2018)
Abstract. We describe the dynamics of the interferometric power in a system composed of
two bosonic modes immersed in a thermal reservoir, in the framework of the theory of open systems based on completely positive quantum dynamical
semigroups. The time evolution of the interferometric power is described in terms of the covariance matrix for Gaussian initial states. We
show that, independent of the initial state, the Gaussian interferometric power is monotonically decreasing in time, and in the limit of large
times it asymptotically decreases to a zero value. 




Entanglement versus quantum degree of polarization
I. Ghiu
Rom. Rep. Phys. 70, 104 (2018)
Abstract. In this article we make a comparison between the behavior of entanglement and
quantum degree of polarization for a special class of states of the radiation field, namely the Belltype diagonal mixed states. For the
threephoton mixed states we have plotted the concurrence and the Chernoff quantum degree of polarization in terms of the parameter, which
defines the state. We find that the entanglement and the quantum degree of polarization are incomparable measures. 




Fingerprints of global classical phasespace structure in quantum spectra
S. MiclutaCampeanu, M.C. Raportaru, A.I. Nicolin, V. Baran
Rom. Rep. Phys. 70, 105 (2018)
Abstract. We consider a model based on two coupled fourthorder oscillators that
describes the intrinsic quadrupole vibrations of atomic nuclear surface in order to investigate the classicalquantum correspondence. We
explore the role of the classical phasespace structure upon the statistical properties of energy levels distribution of the associated quantum
system. A mixed distribution function, encoding two possible mechanisms for energy levels generation is proposed. Its features can be related
to the relative weight of the regular and irregular volumes in the classical phasespace.

Supplementary Web Material:
Archive 


ATOMIC, MOLECULAR, AND NUCLEAR PHYSICS 






Fission times and pairing properties
M. Mirea, A. Sandulescu
Rom. Rep. Phys. 70, 201 (2018)
Abstract. The dissipated energy is calculated for different values of the tunneling
velocity by solving the timedependent pairing equations. Two models are used for the pairing interaction: a constant value of the pairing
interaction and the density dependent delta interaction. The timedependent pairing equations supply an average value of the dissipated
energy at scission. This average value is compared with experimental data. An average tunneling velocity is deduced by selecting the value
that gives the best agreement between experimental and theoretical dissipation energies. The tunneling velocity is strongly model dependent,
giving much lower values for the formalism that involves statedependent pairing interactions than that characterized by the constant pairing.
The investigation is made for the fission of ^{232}Th, along a fission trajectory that connects the ground state of the parent nucleus to the
scission configuration. This fission trajectory is obtained from the least action principle. The rearrangement of the single particle level
scheme is supplied by the WoodsSaxon twocenter shell model. 




Charge polarization and the elongation of the fissioning nucleus at scission
C. Ishizuka, S. Chiba, N. Carjan
Rom. Rep. Phys. 70, 202 (2018)
Abstract. The deviation ΔZ = < Z >  Z_{UCD}, of the charge of a
fission fragment with given mass number A_{F}, from the unchanged charge distribution is calculated by the minimization of
the total macroscopic energy at scission. The scission configuration is approximated by two spherical fragments with masses and charges
(A_{1}, Z_{2}) and (A_{2}, Z_{2}) separated by a distance d between their interior surfaces. An analytical
formula for ΔZ is deduced and applied to the nucleus ^{236}U at different mass divisions. A qualitative agreement with
experimental data for the ^{235}U(n_{th},f) reaction is obtained for a wide range of d values
(from 6 fm to 12 fm). When the generally accepted variation of the distance d with the mass asymmetry is introduced, the agreement becomes quantitative. 




Cross sections for electron capture in Li^{3+}+H(1s) collisions in Debye plasmas
M.C. Raportaru, L. Barandovski, N. Stojanov, D. Jakimovski
Rom. Rep. Phys. 70, 203 (2018)
Abstract. Electron capture in collisions of Li^{3+} ion with hydrogen atom in
ground state in Debye plasma is studied by employing the twocenter atomic orbital closecoupling method. The plasma screened interaction of
the electron with the two centers is represented by the DebyeHuckel potential, appropriate for a wide class of laboratory and astrophysical
plasmas (Debye plasmas). The sensitivity of nlselective capture sections to interaction screening, as well as the electron capture
enhancement in Debye plasmas in the lowenergy region are confirmed. The bellshaped local maxima of the dependence of the 2l partial sections
in a region of screening length D, for lower energy, is attributed to the proximity (and intersection) of the energies of the initial and final
levels in that region.


PHYSICS OF ELEMENTARY PARTICLES AND FIELDS 






Mass Ansatze for the standard model fermions from a composite perspective
A.H. Fariborz, R. Jora, S. Nasri
Rom. Rep. Phys. 70, 301 (2018)
Abstract. We consider a composite model in which the Standard Model fermions
are bound states of elementary spin 1/2 particles, the preons, situated in the conjugate product representation of the color group.
In this framework we propose and analyze two mass Ansatze, one for the leptons, the other one for the quarks, based on mass formulae
of the GellMannOkubo type. We find that these mass Ansatze can give an adequate description of the known Standard Model fermion masses. 

OPTICS AND PHOTONICS, PLASMA, LASER AND BEAM PHYSICS 






Optical solitons in systems of twolevel atoms
S.V. Sazonov
Rom. Rep. Phys. 70, 401 (2018)
Abstract. A scientificmethodical review of the derivation of nonlinear evolution
equations describing the interaction of laser pulses with a system of twolevel atoms and having solutions in the form of optical solitons
is presented. Regimes of propagation of resonant and quasiresonant envelope solitons, as well as fewopticalcycle solitons with temporal
durations from nano to femtoseconds, are considered. The review is a short travel guide to selected problems of soliton propagation in media
consisting of twolevel atoms. 




Broadly peak power and pulse width tunable dissipative soliton resonance generation in figure of eight fiber laser
M. Salhi, G. Semaan, F. Ben Braham, A. Niang, F. Bahloul, F. Sanchez
Rom. Rep. Phys. 70, 402 (2018)
Abstract. We experimentally demonstrate a broadly tunable dissipative soliton resonance
dualamplifier figureofeight fiber laser emission. The peak power is tuned continuously from 8.8 to 41.4 W by the first amplifier and pulse
width from 84 to 416 ns by the second one. 




Influence of initial shape of threedimensional fewcycle optical pulse on its propagation in topological insulator thin films
N.N. Konobeeva, M.B. Belonenko
Rom. Rep. Phys. 70, 403 (2018)
Abstract. We consider the propagation of threedimensional fewcycle optical pulses in
topological insulator thin films within the framework of an effective longwave Hamiltonian in the case of low temperature. The key features of
the propagation dynamics of input Gaussian, Bessel, and Airy pulse shapes are revealed.





Application of a transfer matrix method to hollowcore Bragg fiber with a gold layer
V.A. Popescu
Rom. Rep. Phys. 70, 404 (2018)
Abstract. For a hollowcore Bragg fiber, the field is represented by a Bessel function of
the first kind in the core region, a linear combination of Bessel functions of the first and second kinds in the dielectric interior layers, a
linear combination of the Hankel functions in the gold region and a Hankel function of the first kind in the external infinite medium. Our
analytical method is applied for different structures made from 19, 11, and 5 layers. When a high index material just before the outermost
region of a hollowcore Bragg fiber is replaced by a gold layer, the optical confinement for the TE _{01} mode in the core is increased about ten
times. If the gold layer is located between the first and the penultimate layer, the loss for the same mode is increased.





Silicon microring within a fiber laser cavity for highrepetitionrate pulse train generation
M. Meisterhans, A. Coillet, F. Amrani, O. Demichel, J.B. Jager, P. Noe, JM. Fedeli, F. de Fornel, Ph. Grelu, B. Cluzel
Rom. Rep. Phys. 70, 405 (2018)
Abstract. We investigate the generation of trains of short optical pulses whose
repetition frequency is imposed by the free spectral range of a silicon microring resonator embedded into a fiber laser cavity. According to
the microresonator selected in a silicononinsulator chip, the pulse trains are obtained with repetition frequencies ranging from 110 GHz
to 450 GHz. Regimes where multiple pulses are generated in the microresonator are also shown, and nonlinear broadening of the laser lines is
observed.





Cavity solitons: Dissipative structures in nonlinear photonics
M. Tlidi, K. Panajotov
Rom. Rep. Phys. 70, 406 (2018)
Abstract. In the first part of this article, we briefly overview the formation of
dissipative structures in various out of equilibrium systems. In the second part, we address the formation of localized structures often
called cavity solitons in nonlinear optics. We will focus on the interaction between cavity solitons, the polarization properties, and
the effect of delay feedback control. The following systems will be discussed: passive resonators such as optical fibers, whispering
gallery mode cavities, integrated ring resonators, lefthanded materials, and vertical cavity surface emitting lasers with or without
saturable absorption. The year 2017 marks the 50th anniversary of the scientific concept named dissipative structures that was put forward
by Ilya Prigogine. This paper is dedicated to honor the memory of Ilya Prigogine on the occasion of the anniversary in 2017 of 100 years
from his birthday. The aim of this article is to provide a list of selected subjects on some important properties of cavity solitons as
generic examples of dissipative structures and their applicability in diverse fields of photonics and nonlinear sciences. Therefore, this
paper is meant for active research physicists and engineers working in nonlinear optics and photonics and wishing to have a quick overview
of recent developments in terms of the applicability of cavity solitons.





Enhanced cooling for stronger qubitphonon couplings
V. Ceban, M.A. Macovei
Rom. Rep. Phys. 70, 407 (2018)
Abstract. Here we present details on how the cooling effects of an optomechanical
system are affected beyond the secular approximation. To this end, a laser driven twolevel quantum dot (QD) embedded in a phononic nanocavity
is investigated for moderately strong QDphonon couplings regimes. For these regimes, the use of a secular approximation within the QDphonon
interaction terms is no longer justified as the rapidly oscillating terms cannot be neglected from the system dynamics. Therefore, one shows
that although being small, their contribution plays an important role when quantum cooling is achieved. The main contribution of the fast
oscillating terms is analytically estimated and one compares how the quantum cooling dynamics changes within or beyond the secular
approximation. The behavior of the quantum cooling effect is investigated in the steadystate regime via the phonon field statistics.





Optical solitons in PTsymmetric potentials with competing cubicquintic nonlinearity: existence, stability, and dynamics
P. Li, L. Li, D. Mihalache
Rom. Rep. Phys. 70, 408 (2018)
Abstract. We address the properties of optical solitons that form in media with competing
cubicquintic nonlinearity and paritytime ( PT)symmetric complexvalued external potentials. The model describes the propagation of
solitons in nonlinear optical waveguides with balanced gain and loss. We study the existence, stability, and robustness of fundamental,
dipole, and multipole stationary solutions in this PTsymmetric system. The corresponding eigenvalue spectra diagrams for fundamental,
dipole, tripole, and quadrupole solitons are presented. We show that the eigenvalue spectra diagrams for fundamental and dipole solitons merge
at a coalescence point W_{c1}, whereas the corresponding diagrams for tripole and quadrupole solitons merge at a larger
coalescence point W_{c2}. Beyond these two merging points, i.e., when the gainloss strength parameter
W_{0} exceeds the corresponding coalescence points, the eigenvalue spectra cease to exist. The stability of the stationary
solutions is investigated by performing the linear stability analysis and the robustness to propagation of these stationary solutions is
checked by using direct numerical simulations.


CONDENSED AND SOFT MATTER PHYSICS 






From high magnetization ferrofluids to nanomicro composite magnetorheological fluids: properties and applications
D. SusanResiga, L. Vekas
Rom. Rep. Phys. 70, 501 (2018)
Abstract. Recent results are reviewed on the synthesis and properties of high
magnetization ferrofluids and ferrofluid based magnetorheological (MR) fluids. Structural characteristics at nanometer level, colloidal
behavior in specific environments, magnetic and flow behavior of a large variety of ferrofluids and some newly developed nanomicro
composite magnetizable fluids were evaluated by transmission electron microscopy (TEM/HRTEM), Xray photoelectron spectroscopy (XPS),
dynamic (DLS) and static light scattering (SLS), small angle neutron scattering (SANS), small angle Xray scattering (SAXS), vibrating
sample magnetometry (VSM), Mossbauer spectroscopy, rheomagnetorheometry, chemiluminiscence (CL), and differential scanning calorimetry
(DSC). The paper is focused mainly on the synthesis and properties of longterm colloidal stability and high magnetization sealing fluids
and of ferrofluid based magnetorheological fluids with improved kinetic stability and high MR response.





Composite solitons in twodimensional spinorbit coupled selfattractive BoseEinstein condensates in free space
H. Sakaguchi, B. Li, E.Ya. Sherman, B.A. Malomed
Rom. Rep. Phys. 70, 502 (2018)
Abstract. We review properties of twodimensional matterwave solitons, governed
by the spinor system of GrossPitaevskii equations with cubic nonlinearity, including spinorbit coupling and the Zeeman splitting. In
contrast to the collapse instability typical for the free space, spinorbit coupling gives rise to stable solitary vortices. These are
semivortices with a vortex in one spin component and a fundamental soliton in the other, and mixed modes, with topological charges
0 and ±1 present in both components. The semivortices and mixed modes realize the ground state of the system, provided that the
selfattraction in the spinor components is, respectively, stronger or weaker than their crossattraction. The modes of both types degenerate
into unstable Townes solitons when their norms attain the respective critical values, while there is no lower norm threshold for the stable
modes existence. With the Galilean invariance lifted by the spinorbit coupling, moving stable solitons can exist up to a modedependent
critical velocity with two moving solitons merging into a single one as a result of collision. Augmenting the Rashba term by the Dresselhaus
coupling has a destructive effect on these states. The Zeeman splitting tends to convert the mixed modes into the semivortices, which
eventually suffer delocalization. Existence domains for the soliton families are reviewed in terms of experimentrelated quantities.





Traveling darkbright solitons in a reduced spinorbit coupled system: application to BoseEinstein condensates
J. d'Ambroise, D.J. Frantzeskakis, P.G. Kevrekidis
Rom. Rep. Phys. 70, 503 (2018)
Abstract. In the present work, we explore the potential of spinorbit (SO) coupled
BoseEinstein condensates to support multicomponent solitonic states in the form of darkbright (DB) solitons. In the case where Raman
linear coupling between components is absent, we use a multiscale expansion method to reduce the model to the integrable Mel'nikov system.
The soliton solutions of the latter allow us to reconstruct approximate traveling DB solitons for the reduced SO coupled system. For
small values of the formal perturbation parameter, the resulting waveforms propagate undistorted, while for large values thereof, they
shed some dispersive radiation, and subsequently distill into a robust propagating structure. After quantifying the relevant radiation
effect, we also study the dynamics of DB solitons in a parabolic trap, exploring how their oscillation frequency varies as a function of
the bright component mass and the Raman laser wavenumber.





Rogue waves in ultracold bosonic seas
E.G. Charalampidis, J. CuevasMaraver, D.J. Frantzeskakis, P.G. Kevrekidis
Rom. Rep. Phys. 70, 504 (2018)
Abstract. In this work, we numerically consider the initial value problem for
nonlinear Schrodinger (NLS)type models arising in the physics of ultracold bosonic gases, with generic Gaussian wavepacket initial data.
The corresponding Gaussian's width and, wherever relevant, also its amplitude serve as control parameters. First, we explore the
onedimensional, standard NLS equation with general power law nonlinearity, in which large amplitude excitations reminiscent of Peregrine
solitons or regular solitons appear to form, as the width of the relevant Gaussian is varied. Furthermore, the variation of the nonlinearity
exponent aims at exploring the interplay between rogue waves and the emergence of collapse. The robustness of the main features to noise in
the initial data is also confirmed. To better connect our study with the physics of atomic condensates, and explore the role of dimensionality
effects, we also consider the nonpolynomial Schrodinger equation, as well as the full threedimensional NLS equation, and examine the degree
to which relevant considerations generalize.






This is an electronic version of Volume 70 Number 1 2018




