Time filter

Source Type

Leblond H.,University of Angers | Mihalache D.,University of Angers | Mihalache D.,Horia Hulubei National Institute of Physics and Nuclear Engineering | Mihalache D.,Academy of Romanian Scientists
Physics Reports | Year: 2013

In the past years there was a huge interest in experimental and theoretical studies in the area of few-optical-cycle pulses and in the broader fast growing field of the so-called extreme nonlinear optics. This review concentrates on theoretical studies performed in the past decade concerning the description of few optical cycle solitons beyond the slowly varying envelope approximation (SVEA). Here we systematically use the powerful reductive expansion method (alias multiscale analysis) in order to derive simple integrable and nonintegrable evolution models describing both nonlinear wave propagation and interaction of ultrashort (femtosecond) pulses. To this aim we perform the multiple scale analysis on the Maxwell-Bloch equations and the corresponding Schrödinger-von Neumann equation for the density matrix of two-level atoms. We analyze in detail both long-wave and short-wave propagation models. The propagation of ultrashort few-optical-cycle solitons in quadratic and cubic nonlinear media are adequately described by generic integrable and nonintegrable nonlinear evolution equations such as the Korteweg-de Vries equation, the modified Korteweg-de Vries equation, the complex modified Korteweg-de Vries equation, the sine-Gordon equation, the cubic generalized Kadomtsev-Petviashvili equation, and the two-dimensional sine-Gordon equation. Moreover, we consider the propagation of few-cycle optical solitons in both (1+1)- and (2+1)-dimensional physical settings. A generalized modified Korteweg-de Vries equation is introduced in order to describe robust few-optical-cycle dissipative solitons. We investigate in detail the existence and robustness of both linearly polarized and circularly polarized few-cycle solitons, that is, we also take into account the effect of the vectorial nature of the electric field. Some of these results concerning the systematic use of the reductive expansion method beyond the SVEA can be relatively easily extended to few-cycle solitons in the general case of multilevel atoms. Prospects of the studies overviewed in this work are given in the conclusions. © 2012 Elsevier B.V.


Budaca R.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

An analytical expression for the energy spectrum of the ground and β bands was obtained through the JWKB approximation in the axially symmetric γ-rigid regime of the Bohr-Mottelson Hamiltonian with an oscillator potential and a sextic anharmonicity in the β shape variable. Due to the scaling property of the problem, the resulting energy depends up to an overall multiplicative constant on a single parameter. Studying the behavior of the energy spectrum as a function of the free parameter, one establishes the present model's place among other prolate γ-rigid models and in the more general extent of collective solutions. The agreement with experiment is achieved through model fits for few nuclei. © 2014 The Author.


Stoica O.C.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Annals of Physics | Year: 2014

A series of old and recent theoretical observations suggests that the quantization of gravity would be feasible, and some problems of Quantum Field Theory would go away if, somehow, the spacetime would undergo a dimensional reduction at high energy scales. But an identification of the deep mechanism causing this dimensional reduction would still be desirable. The main contribution of this article is to show that dimensional reduction effects are due to General Relativity at singularities, and do not need to be postulated ad-hoc. Recent advances in understanding the geometry of singularities do not require modification of General Relativity, being just non-singular extensions of its mathematics to the limit cases. They turn out to work fine for some known types of cosmological singularities (black holes and FLRW Big-Bang), allowing a choice of the fundamental geometric invariants and physical quantities which remain regular. The resulting equations are equivalent to the standard ones outside the singularities.One consequence of this mathematical approach to the singularities in General Relativity is a special, (geo)metric type of dimensional reduction: at singularities, the metric tensor becomes degenerate in certain spacetime directions, and some properties of the fields become independent of those directions. Effectively, it is like one or more dimensions of spacetime just vanish at singularities. This suggests that it is worth exploring the possibility that the geometry of singularities leads naturally to the spontaneous dimensional reduction needed by Quantum Gravity. © 2014 Elsevier Inc.


Mihalache D.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Romanian Journal of Physics | Year: 2014

A brief up-to-date survey of recent theoretical and experimental studies of the formation, stability and robustness of multidimensional localized structures in optics and Bose-Einstein condensate in a variety of physical settings is given.


Zamfir N.V.,Horia Hulubei National Institute of Physics and Nuclear Engineering
European Physical Journal: Special Topics | Year: 2014

The field of the uncharted territory of high-intensity laser interaction with matter is confronted with new exotic phenomena and, consequently, opens new research perspectives. The intense laser beams interacting with a gas or solid target generate beams of electrons, protons and ions. These beams can induce nuclear reactions. Electrons also generate ions high-energy photons via bremsstrahlung processes which can also induce nuclear reactions. In this context a new research domain began to form in the last decade or so, namely nuclear physics with high power lasers. The observation of high brilliance proton beams of tens of MeV energy from solid targets has stimulated an intense research activity. The laser-driven particle beams have to compete with conventional nuclear accelerator-generated beams. The ultimate goal is aiming at applications of the laser produced beams in research, technology and medicine. The mechanism responsible for ion acceleration are currently subject of intensive research in many laboratories in the world. The existing results, experimental and theoretical, and their perspectives are reviewed in this article in the context of IZEST and the scientific program of ELI-NP. © 2014 EDP Sciences and Springer.


Zamfir N.V.,Horia Hulubei National Institute of Physics and Nuclear Engineering
EPJ Web of Conferences | Year: 2014

Extreme Light Infrastructure (ELI) is one of the 48 infrastructures of the European Strategic Forum for Research Infrastructure (ESFRI) roadmap and represents a major step forward in quest for producing extreme electromagnetic fields. Extreme Light Infrastructure - Nuclear Physics (ELI-NP) is one of the three pillars of the ELI initiative, which aims to use extreme electromagnetic fields for nuclear physics research. A high power laser system and a very brilliant gamma beam are the two main research equipment at the core of ELI-NP. Their targeted operational parameters are described. The related experimental areas are also presented, together with the main directions of the proposed scientific programme. © Owned by the authors, published by EDP Sciences, 2014.


Mirea M.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Physical Review C - Nuclear Physics | Year: 2011

The intrinsic excitation energy of fission fragments is dynamically evaluated in terms of the time-dependent pairing equations. These equations are corroborated with two conditions. One of them fixes the number of particles and the other separates the pairing active spaces associated to the two fragments in the vicinity of the scission configuration. The fission path is obtained in the frame of the macroscopic-microscopic model. The single-particle-level schemes are obtained within the two-center Woods-Saxon shell model. It is shown that the available intrinsic dissipated energy is not shared proportionally to the masses of the two fission fragments. If the heavy fragment possesses nucleon numbers close to the magic ones, the accumulated intrinsic excitation energy is lower than that of the light fragment. © 2011 American Physical Society.


Nicolin A.I.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

We investigate analytically the dynamics of a trapped, quasi-one- dimensional Bose-Einstein condensate subject to resonant and nonresonant periodic modulation of the transverse confinement. The dynamics of the condensate is described variationally through a set of coupled ordinary differential equations, and the period of the excited waves is determined analytically using a Mathieu-type analysis. For a modulation frequency equal to that of the radial confinement we show that the predicted period of the resonant wave is in agreement with the existing experimental results. Finally, we present a detailed comparison between the resonant waves and the Faraday waves that emerge outside of resonance. © 2011 American Physical Society.


Mihalache D.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Romanian Reports of Physics | Year: 2012

I provide a brief overview of recent theoretical and experimental studies of unique spatiotemporal dynamics of linear and nonlinear light bullets in a variety of relevant physical settings.


Mirea M.,Horia Hulubei National Institute of Physics and Nuclear Engineering
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2012

The energy sorting at scission is treated fully microscopically in terms of the time dependent pairing equations. These equations for the intrinsic motion are mixed with a dynamical particle number projection condition on the primary fragments. The shape sequences during the disintegration resort from the minimal action principle. For this purpose, the potential energy is computed within the macroscopic-microscopic approach and the inertia within semi-adiabatic cranking approximation. The disentanglement of the wave function in two semi-spaces is realized within the Woods-Saxon two-center shell model. That allows a separation of the pairing field onto two sub-spaces. It is shown that the excitation energies of the fission fragments depend on a delicate interplay between their structure at and their deformations at scission. © 2012 Elsevier B.V.

Loading Horia Hulubei National Institute of Physics and Nuclear Engineering collaborators
Loading Horia Hulubei National Institute of Physics and Nuclear Engineering collaborators