Institute of Atomic Physics of romenia

Bucharest, Romania

Institute of Atomic Physics of romenia

Bucharest, Romania
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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.


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.


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.


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.


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.


Apostol M.,Institute of Atomic Physics of romenia | Ganciu M.,Institute of Atomic Physics of romenia
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2010

The coherent interaction of the electromagnetic radiation with an ensemble of polarizable, identical particles with two energy levels is investigated in the presence of external electromagnetic fields. The coupled non-linear equations of motion are solved in the stationary regime and in the limit of small coupling constants. It is shown that an external electromagnetic field may induce a macroscopic occupation of both the energy levels of the particles and the corresponding photon states, governed by a long-range order of the quantum phases of the internal motion (polarization) of the particles. A lasing effect is thereby obtained, controlled by the external field. Its main characteristics are estimated for typical atomic matter and atomic nuclei. For atomic matter the effect may be considerable (for usual external fields), while for atomic nuclei the effect is extremely small (practically insignificant), due to the great disparity in the coupling constants. In the absence of the external field, the solution, which is non-analytic in the coupling constant, corresponds to a second-order phase transition (super-radiance), which was previously investigated. © 2010 Elsevier B.V. All rights reserved.


Apostol M.,Institute of Atomic Physics of romenia
Solid State Communications | Year: 2012

Non-inertial electromagnetic effects in matter, i.e. electromagnetic fields created by a non-inertial motion of material bodies, are discussed within the Drude-Lorentz (plasma) model of matter polarization. It is shown that an oscillatory motion of a point-like body, or wavelike motion in an extended body gives rise to electromagnetic fields with the same frequency as the frequency of the original motion, while shock-like movements of a point-like body generate electromagnetic fields with the characteristic (atomic scale) frequency of the bodies. The polarization of a rigid body induced by rotations is discussed in various circumstances. A uniform rotation produces a static electric field in a dielectric and a stationary current (and a static magnetic field) in a conductor. The latter corresponds to the gyromagnetic effect (while the former may be called the gyroelectric effect). Both fields are computed for a sphere and the gyromagnetic coefficient is derived. A non-uniform rotation induces emission of electromagnetic fields. The equations of motion for the polarization are linearized for slight non-uniformities of the angular velocity and solved both for a dielectric and a conducting sphere. The electromagnetic field emitted by a dielectric spherically shaped body in (a slightly) non-uniform rotation has the characteristic (atomic scale) frequency of the body (slightly shifted by the uniform part of the angular frequency). In the same conditions, a conducting sphere emits an electromagnetic field whose frequency is double the uniform part of the angular frequency. © 2012 Elsevier Ltd. All rights reserved.


Apostol M.,Institute of Atomic Physics of romenia
Romanian Journal of Physics | Year: 2013

The motion of an electromagnetic pulse (signal) through the surface of a semiinfinite (half-space) polarizable body is investigated. The incident pulse of electromagnetic radiation propagating in vacuum is assumed to be of finite duration and finite spatial extension. As regards its extension along the transverse directions, two cases are considered. First, we assume a large (infinite) extension (in comparison with the wavelength), as for a plane wave (beam, ray); second, a very narrow pulse is assumed (zero thickness, close to the diffraction limit). In its motion the pulse encounters the plane surface of a semi-infinite polarizable body (a half-space) and penetrates into the body. The body reacts through its polarization degrees of freedom, which obey the wellknown Drude-Lorentz (plasma) equation of motion. It is shown that the beam obeys the well-known refraction law (Fresnel equations), with a specific discussion, which is provided. For the narrow pulse, both the normal and oblique incidence are analysed. It is shown that far away from the incidence direction (large transverse distance r) the motion is governed by the polaritonic eigenmodes, which yields a pulse, approximately of the same shape as the original one, propagating with the group velocity and with an amplitude which decreases as 1=r2. The group velocity is always smaller than the speed of light in vacuum c. In the vicinity of the propagation direction (small distance r), the original pulse is almost entirely preserved, including its propagation velocity c, with a distorted amplitude, which depends on the transverse direction. This picture is in fact the diffraction limit of the narrow pulse. The transmitted coefficient is computed for normal incidence. The reflected pulse is also computed, as well as the refracted pulse for oblique incidence. While the reflection law is preserved (reflection angle is equal to the incidence angle), the refraction law is different from Snell's law of refraction of a plane wave, in the sense that the highly localized (narrow) pulse along the transverse direction preserves its propagation direction on entering into the body.


Apostol M.,Institute of Atomic Physics of romenia
Physica B: Condensed Matter | Year: 2013

The eigenfrequencies are identified for two electromagnetically coupled semi-infinite solids with plane-parallel surfaces (two half-spaces) separated by a third, polarizable body. The corresponding van der Waals-London and Casimir forces are calculated from the zero-point energy (vacuum fluctuations) of the normal modes. It is shown how the results can be extended to bodies of any shape; in particular, the force is given for a sphere interacting with a half-space. The calculations are performed using the well-known Drude-Lorentz (plasma) model of (non-magnetic) polarizable matter. The polarization degrees of freedom are explicitly introduced. It is shown that the polarization dynamical variables for the two bodies are coupled through the electromagnetic field, very similar with two infinite sets of coupled harmonic oscillators. © 2012 Elsevier B.V.


Apostol M.,Institute of Atomic Physics of romenia | Vaman G.,Institute of Atomic Physics of romenia
Progress In Electromagnetics Research B | Year: 2010

We derive van der Waals-London and Casimir forces by calculating the eigenmodes of the electromagnetic field interacting with two semi-infinite bodies (two halves of space) with parallel surfaces separated by distance d. We adopt simple models for metals and dielectrics, well-known in the elementary theory of dispersion. In the non-retarded (Coulomb) limit we get a d -3-force (van der Waals-London force), arising from the zero-point energy (vacuum fluctuations) of the surface plasmon modes. When retardation is included we obtain a d -4-(Casimir) force, arising from the zero-point energy of the surface plasmon-polariton modes (evanescent modes) for metals, and from propagating (polaritonic) modes for identical dielectrics. The same Casimir force is also obtained for "fixed surfaces" boundary conditions, irrespective of the pair of bodies. The approach is based on the equation of motion of the polarization and the electromagnetic potentials, which lead to coupled integral equations. These equations are solved, and their relevant eigenfrequencies branches are identified.

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