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Apostol M.,Institute of Atomic Physics of romenia
Romanian Reports in Physics | Year: 2015

It is suggested that the hadronization of the quark-gluon plasma is a first-order phase transition described by a critical curve in the temperature-(quark) density plane which terminates in a critical point. Such a critical curve is derived from the van der Waals equation and its parameters are estimated. The main assumption is that quark-gluon plasma created by high-energy nucleus-nucleus collisions is a gas of ultrarelativistic quarks in equilibrium with gluons (vanishing chemical potential, indefinite number of quarks). This plasma expands, gets cool and dilute and hadronizes at a certain transition temperature and transition density. The transition density is very close to the saturation density of the nuclear matter and, it is suggested that both these points are very close to the critical point n ≃ 1fm−3 (quark density) and T ≃ 200MeV (temperature). © 2015, Editura Academiei Romane. All rights reserved. Source


Apostol M.,Institute of Atomic Physics of romenia
Romanian Reports in Physics | Year: 2015

The “empirical” binding energy — 16Z7/3eV of heavy atoms (atomic number Z ≫ 1) is computed by a linearized version of the Thomas-Fermi model, including a Hartree-type correction. The computations are carried out by means of a variational approach. Exchange energy and corrections to the exchange energy are also estimated. This is an updated result. It is shown that giant dipole oscillations of the electrons may be induced in heavy atoms by external electromagnetic fields in the range of moderate X-rays, which, in intense fields, may lead to ionization. There are examined anharmonicities in the giant dipole oscillations, which lead to frequency shifts and highorder harmonics. Transitions to excited states and ionization of “peripheral” electrons are also investigated in the quasi-classical approximation for heavy atoms. © 2015, Editura Academiei Romane. All rights reserved. Source


Apostol M.,Institute of Atomic Physics of romenia
Journal of Modern Optics | Year: 2011

The polarization of the vacuum under the action of an external classical field of electromagnetic radiation is investigated in the stationary regime. The electron-positron pairs interact both with the external field and with their own polarization field. For a macroscopic piece of vacuum the pairs are condensed on the low-momenta states and tend to form a quasi-localized electron-positron plasma of pairs, with single-particle states labeled by the position vector. In the polarization process under the action of a classical field of radiation the electron-positron and photon dynamics can be treated by means of classical fields. Under these circumstances, the corresponding coupled non-linear equations of motion are solved. It is shown that the pair dynamics consists of quasi-stationary single-particle states, while the polarization field reduces to a static magnetic field. The singleparticle 'energy' (temporal phase) due to a monochromatic external field exhibits a spatial distribution characteristic of a stationary wave. Both the pair energy and the polarization energy are computed. Their values are extremely small, even for highly focused, reasonably high, external fields. The number of pairs is determined by the external energy. Under the action of a classical field the polarized vacuum is magnetized, and the corresponding (very low) magnetic susceptibility (the refractive index of the vacuum) is computed. © 2011 Taylor & Francis. Source


Vaman G.,Institute of Atomic Physics of romenia
Romanian Reports in Physics | Year: 2014

We establish the dispersion relation for the edge magnetoplasmons of a semi-infinite half-plane by solving the integral equations for the oscillation amplitudes of the electrons. © 2014 Romanian Reports in Physics. All rights reserved. Source


Vaman G.,Institute of Atomic Physics of romenia
Reports on Mathematical Physics | Year: 2015

We calculate electrostatic potential of a periodic lattice of arbitrary extended charges by using the Cartesian multipole formalism. This method allows the separation of the long-range potential from the contact potential (potential on the source). We write both the electrostatic potential and the interaction energy as convergent sums in the reciprocal space. © 2015 Polish Scientific Publishers. Source

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