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Δημοσιεύσεις σε διεθνή επιστημονικά περιοδικά
 
1. G. P. Veldes, J. Cuevas,P. G.Kevrekidis, and D. J. Frantzeskakis, Coupled backward- and forward-propagating solitons in a composite right- and left- handed transmission line, Phys. Rev. E 88, 013203 (2013).
 Περίληψη/Abstract:   We study the coupling between backward- and forward-propagating wave modes, with the same group velocity, in a composite  right/left-handed nonlinear transmission line. Using an asymptotic multiscale expansion technique, we derive a system of two coupled nonlinear Schrodinger equations governing the evolution of the envelopes of these modes. We show that this system supports a variety of backward- and forward propagating vector solitons, of the bright-bright, bright-dark and dark-bright type. Performing systematic numerical simulations in the framework of the original lattice that models the transmission line, we study the propagation properties of the derived vector soliton solutions. We show that all types of the predicted solitons exist, but differ on their robustness: only bright-bright solitons propagate undistorted for long times, while the other types are less robust, featuring shorter lifetimes. In all cases, our analytical predictions are in a very good agreement with the results of the simulations, at least up to times of the order of the solitons' lifetimes. 
 
2. G.P. Veldes, J. Borhanian, M. McKerr, V. Saxena, D.J. Frantzeskakis and I. Kourakis, Electromagnetic Rogue Waves in Beam-Plasma Interactions, J. Opt. 15, 064003 (2013).
 Περίληψη/Abstract: The occurrence of rogue waves (freak waves) associated with electromagnetic pulse propagation interacting with a plasma is investigated, from first principles. A multiscale technique is employed to solve the fluid-Maxwell equations describing a weakly nonlinear circularly polarized electromagnetic pulses in magnetized plasmas. A nonlinear Schrodinger (NLS) type equation is shown to govern the amplitude of the vector potential. A set of non-stationary envelope solutions of the NLS equation are considered, as potential candidates for modeling of rogue waves (freak waves) in beam-plasma interactions, namely in the form of the Peregrine soliton, the Akhmediev breather and the Kuznetsov-Ma breather. The variation of the structural properties of the latter structures with relevant plasma parameters is investigated, in particular focusing on the ratio between the (magnetic field dependent) cyclotron (gyro-) frequency and the plasma frequency. 
3. G. P. Veldes, J. Cuevas,P. G.Kevrekidis, and D. J. Frantzeskakis, Quasidiscrete microwave solitons in a split-ring-resonator-based left-handed coplanar waveguide, Phys. Rev. E 83, 046608 (2011).
Περίληψη/Abstract: We study experimentally, analytically and numerically the backward-wave propagation, and formation of discrete bright and dark solitons in a nonlinear electrical lattice. We observe experimentally that a focusing (defocusing) effect occurs above (below) a certain carrier frequency threshold, and backwardpropagating bright (dark) discrete solitons are formed. We develop a discrete model emulating the relevant circuit and benchmark its linear properties against the experimental dispersion relation. Using a perturbation method, we derive a nonlinear Schrödinger equation, that predicts accurately the carrier frequency threshold. Finally, we use numerical simulations to corroborate our findings and monitor the space–time evolution of the discrete solitons.
 
4. L. Q. English, S. G. Wheeler, Y. Shen, G. P. Veldes, N.Whitaker,P. G.Kevrekidis, and D. J. Frantzeskakis, Backward-wave propagation and discrete solitons in a left-handed electrical lattice, Phys. Lett.A 375, 1242 (2011).
Περίληψη/Abstract: We study the propagation of quasidiscrete microwave solitons in a nonlinear left-handed coplanar waveguide coupled with split-ring resonators. By considering the relevant transmission line analog, we derive a nonlinear lattice model which is studied analytically by means of a quasidiscrete approximation. We derive a nonlinear Schr¨odinger equation, and find that the system supports bright envelope soliton solutions in a relatively wide subinterval of the left-handed frequency band. We perform systematic numerical simulations, in the framework of the nonlinear lattice model, to study the propagation properties of the quasidiscrete microwave solitons. Our numerical findings are in good agreement with the analytical predictions, and suggest that the predicted structures are quite robust and may be observed in experiments.
 
Διπλωματικές εργασίες
1.  Γ. Π. Βελντές, «Θεωρία πληροφορίας και χωρητικότητα καναλιού στις Τηλεπικοινωνίες», Διπλωματική εργασία, Τμήμα Φυσικής (ΜΔΕ Ηλεκτρονικής & Ραδιοηλεκτρολογίας), Ε.Κ.Π.Α., 1996.
2.  Γ. Π. Βελντές,  «Θεωρία δειγματοληψίας στις Tηλεπικοινωνίες. Θεώρημα Shannon», Διπλωματική εργασία, Τμήμα Φυσικής, Ε.Κ.Π.Α., 1995.