Octavian Postavaru

Octavian Postavaru
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Octavian verified their affiliation via an institutional email.
Universitatea Națională de Știință și Tehnologie Politehnica București | UPB

PhD, Heidelberg University

About

47
Publications
4,351
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260
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Introduction
Field theory is fundamental for understanding elementary particles through symmetries. A key question arises: is the continuous nature of space or the discrete lattice structure more fundamental? Quantum Chromodynamics relies on three key aspects: confinement, mass discretization, and chiral symmetry breaking. While the first two are well described by lattice models, chiral symmetry breaking needs continuous spacetime. Is time on time-scale the most fundamental aspect in this context?

Publications

Publications (47)
Article
Full-text available
This paper presents the development of a fractional hybrid function composed of block-pulse functions and Fibonacci polynomials (FHBPF) for the numerical solution of multiterm variable-order fractional differential equations. By replacing x → x α in FHBPF and utilizing incomplete beta functions, we construct the method with a focus on fractional de...
Research Proposal
Full-text available
Dear Colleagues, This Special Issue, titled "New Trends in Fractional Differential Equations with Applications", aims to explore the latest advancements in the theory and applications of fractional differential equations (FDEs). It will focus on emerging methodologies for solving FDEs, including innovative analytical, numerical, and computational...
Article
Full-text available
The universe begins its expansion from dimensions below the Planck scale, where the uncertainty principle reigns. If at these dimensions the Archimedean geometry is useless, the p-adic non-Archimedean world creates an environment conducive to phenomenological modeling. The standard description of the cosmological density contrast is made by the Fou...
Article
Full-text available
The connection between gamma ray bursts and supernovae is studied using a temperature-dependent vacuum model. A harmonically bound particle–antiparticle system is consistent with both Hawking radiation and Casimir effect, therefore, the Maxwell–Sellmeier model correlates the speed of light to temperature. According to quantum field theory, Lorentz...
Article
Full-text available
It is shown that the chaotic Zeeman effect of a quantum system can be formally viewed as a result of fractional calculus. The fractional calculation brings into the equations the angle θ formed between the internal and the external magnetic field applied to the atom. The further the fractional coefficient α is from the ordinary case corresponding t...
Article
Full-text available
Classical forbidden processes paved the way for the description of mechanical systems with the help of complex Hamiltonians. Fractional integrals of complex order appear as a natural generalization of those of real order. We propose the complex fractional Euler-Lagrange equation, obtained by finding the stationary values associated with the fractio...
Article
Full-text available
In this paper we define the $p$-adic fluorescence spectrum and discuss the possibility of measuring it. The main idea is that, according to Ostrowski's theorem, the field of rational numbers can be completed topologically with both real numbers and $p$-adic numbers, and according to the principle of democracy, both possibilities should be equally i...
Article
Full-text available
The Fibonacci sequence is significant because of the so-called golden ratio, which describes predictable patterns for everything. Fibonacci polynomials are related to Fibonacci numbers, and in this paper we extend their applicability by using them to solve fractional differential equations (FDEs) and systems of fractional differential equations (SF...
Article
Full-text available
The Goolden ratio is famous for the predictability it provides both in the microscopic world as well as in the dynamics of macroscopic structures of the universe. The extension of the Fibonacci series to the Fibonacci polynomials gives us the opportunity to use this powerful tool in the study of Fredholm-Volterra integro-differential equations. In...
Article
Full-text available
We investigate the level structure of heavy hydrogenlike ions in laser beams. In heavy ions, the electrons are tightly bound by the Coulomb potential of the nucleus, which prohibits ionization even by strong lasers. However, interaction with the light field leads to dynamic shifts of the electronic energy levels. We apply a fully relativistic descr...
Article
Full-text available
In the current study, we propose a systematize technique for solving fractional delay differential equations in the Caputo sense. Therefore , we compute an exact Riemann-Liouville fractional integral operator for the generalized fractional-order hybrid of block-pulse functions and Bernoulli polynomials, and we use it in order to reduce the fraction...
Article
Full-text available
High-power lasers develop high energy per unit time, and as energy curves space, we expect atomic energy levels to change. The fluorescence spectrum is a good measurement of the matrix elements involved in the Rabi oscillation and consequently allows us to determine the scalar curvature. At high Z, electrons oppose ionization even for strong intens...
Preprint
In this paper we build the fractional hybrid function of block-pulse functions and Fibonacci polynomials (FHBPF) to numerically solve a class of multiterm variable-order fractional differential equations. We consider fractional derivatives in the Caputo sense and fractional integrals in the Riemann-Liouville sense. We construct an exact integral op...
Article
Full-text available
Through this paper, the success of dynamic equations on timescale is extended to field theory, in which only the time parameter belongs to the timescale. The method of Lie symmetries is not yet sufficiently developed on a timescale, especially in field theory, and therefore we need to present specific demonstrations of these symmetries. We begin by...
Article
Full-text available
For solving numerically fractional differential equations, we have to take into account a rising flow of works as (Dehestani et al. in Appl Math Comput 336:433–453, 2018, https://doi.org/10.1016/j.amc.2018.05.017 , Rahimkhani et al. Appl Math Model 40:8087–8107, 2016, https://doi.org/10.1016/j.apm.2016.04.026 ) that show the advantage of using the...
Article
Full-text available
In this paper, we solve Riccati equations by using the fractional-order hybrid function of block-pulse functions and Bernoulli polynomials (FOHBPB), obtained by replacing x with xα, with positive α. Fractional derivatives are in the Caputo sense. With the help of incomplete beta functions, we are able to build exactly the Riemann–Liouville fraction...
Article
Full-text available
Resonance fluorescence occurs when an atom is irradiated by a continuous monochromatic field. We analyze a ladder-type heliumlike highly charged ion, strongly coupled to two coherent light fields. The independent-particle approximation, where electron-electron correlations are neglected, works very well for few-electron ions when the nuclear charge...
Article
Full-text available
We present, an accurate and efficient computational method based on the fractional-order hybrid of block-pulse functions and Bernoulli polynomials for solving fractional optimal control problems. The Riemann–Liouville fractional integral operator for the fractional-order hybrid of block-pulse functions and Bernoulli polynomials is constructed. The...
Article
Full-text available
The time scale Fibonacci sequences satisfy the Friedmann–Lemaître–Robertson–Walker (FLRW) dynamic equation on time scale, which are an exact solution of Einstein’s field equations of general relativity for an expanding homogeneous and isotropic universe. We show that the equations of motion correspond to the one-dimensional motion of a particle of...
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Article
Full-text available
Fractional differential equations fit perfectly into nature modeling, requiring the finding of efficient numerical methods of solving them. This paper aims to propose a method for solving two-dimensional fractional order equations by constructing a new set of fractional functions called fractional-order hybrid of block-pulse functions and Bernoulli...
Article
Curvature invariants are the most natural invariants, with a wide application in science and engineering. A known condition for a Riemannian manifold to admit a minimal immersion in any Euclidean space is Ric≤0. In order to find other obstructions, one needs to introduce new types of Riemannian invariants, different in nature from classical ones (C...
Article
Full-text available
Symmetries and their associated conserved quantities are of great importance in the study of dynamic systems. In this paper, we describe nonconservative field theories on time scales—a model that brings together, in a single theory, discrete and continuous cases. After defining Hamilton’s principle for nonconservative field theories on time scales,...
Article
Full-text available
The dynamics of COVID-19 is investigated with regard to complex contributions of the omitted factors. For this purpose, we use a fractional order SEIR model which allows us to calculate the number of infections considering the chaotic contributions into susceptible, exposed, infectious and removed number of individuals. We check our model on Wuhan,...
Conference Paper
Full-text available
We present the relativistic power spectrum for the interaction of an x-ray field with an highly charged ion, obtained by solving the time-dependent Dirac equation in a two-level approximation [1]. The phenomenon of splitting of sideband peaks is obtained as a consequence of the introduction in theory of the electronic spin. Also this phenomenon tog...
Article
Full-text available
Resonance fluorescence of laser-driven atoms is studied in the relativistic regime by solving the time-dependent Dirac equation in a multi-level model. Electron spin and retardation of the electron–photon interaction give rise to new phenomena such as splitting of sideband peaks and modification of the Rabi oscillator frequencies not explainable in...
Presentation
Full-text available
This talk was given by Adrian Sabin Popescu (as PI, theory, experimental and code developer of the project) at the Astronomical Institute of the Romanian Academy, with the occasion of the official launch of the project “The Sun as a Laboratory for Bohmian Mechanics”, intended to prove the validity of de Broglie–Bohm quantum mechanics theory with th...
Presentation
Full-text available
This talk was given by Octavian Blagoi (as project's member and main responsible person with the instrumentation and observations) at the Astronomical Institute of the Romanian Academy, with the occasion of the official launch of the project “The Sun as a Laboratory for Bohmian Mechanics”, intended to prove the validity of de Broglie–Bohm quantum m...
Presentation
Full-text available
This talk was given by Dr. Octavian Postavaru (as project member and theoretical adviser) at the Astronomical Institute of the Romanian Academy, with the occasion of the official launch of the project “The Sun as a Laboratory for Bohmian Mechanics”, intended to prove the validity of de Broglie–Bohm quantum mechanics theory with the help of solar ph...
Article
Full-text available
The light-shift theory of many-electron systems in a laser field is described using the projection operators technique. In heavy ions, the electrons are tightly bound by the Coulomb potential of the nucleus, which prohibits ionization even by strong lasers. However, interaction with the monofrequent laser field leads to dynamic shifts of the electr...
Article
Full-text available
Double-polarization observables in the reaction $\vec{e}p \rightarrow e'\vec{p'}\gamma{}$ have been measured at $Q^2=0.33 (GeV/c)^2$. The experiment was performed at the spectrometer setup of the A1 Collaboration using the 855 MeV polarized electron beam provided by the Mainz Microtron (MAMI) and a recoil proton polarimeter. From the double-polariz...
Book
Full-text available
Quantum gravity is suppose to arise from a unification between relativity and quantum theory. We start this work with an overview over general relativity. The first chapter, as well the other two, is based on a series of lectures given by professor Leonard Susskind at Stanford University. Strings are very interesting objects which play a very impor...
Conference Paper
Full-text available
Intershell tri-electronic recombination (TR) is reported for highly charged ions of Ar, Fe and Kr, where simultaneously to the K-shell excitation an additional L electron is excited due to resonant recombination of a free electron. Clear evidence on quadru-electronic recombination (QR) is found too, with two additional L electrons being excited at...
Book
Full-text available
In this book we investigate strong-field relativistic processes in highly charged ions. In the first part, we study resonance fluorescence of laser-driven highly charged ions. Our ab initio approach based on the Dirac equation allows for investigating highly relativistic ions, and, consequently, provides a sensitive means to test correlated relativ...
Article
Using forced evaporative cooling on stored highly charged ions (HCIs) in an electron beam ion trap, high-resolution electronic recombination spectra were obtained. Inter-shell tri-electronic recombination is reported for HCIs, mainly for C-like ions of Ar, Fe and Kr, where simultaneously with the K-shell excitation an additional L electron is excit...
Article
Full-text available
Resonance fluorescence of laser-driven highly charged ions is studied in the relativistic regime by solving the time-dependent master equation in a multi-level model. Our ab initio approach based on the Dirac equation allows for investigating highly relativistic ions, and, consequently, provides a sensitive means to test correlated relativistic dyn...
Conference Paper
Full-text available
Export Date: 23 October 2011, Source: Scopus, Art. No.: 014014, CODEN: PHSTE, doi: 10.1088/0031-8949/2011/T144/014014
Poster
We investigate the level structure and excitation processes of few-electron ions in laser beams. Interaction with the light field leads to dynamic shifts and splitting of the electronic energy levels. We apply a fully relativistic description of the electronic states by means of the Dirac equation. The frequency spectrum of the fluorescence photons...
Poster
Full-text available
Resonance fluorescence of laser-driven atoms is studied in the relativistic regime by solving the time-dependent Dirac equation in a multi-level model. Electron spin and retardation of the electron-photon interaction give rise to phenomena such as splitting of sideband peaks and modification of the Rabi frequencies not explainable in a Schroedinger...
Thesis
Full-text available
In this thesis we investigate strong-field relativistic processes in highly charged ions. In the first part, we study resonance fluorescence of laser-driven highly charged ions in the relativistic regime by solving the time-dependent master equation in a multi-level model. Our ab initio approach based on the Diracv equation allows for investigating...
Article
Full-text available
We report the observation of trielectronic recombination with simultaneous excitation of a K-shell and an L-shell electron, hence involving three active electrons. This process was identified in the x-ray emission spectrum of recombining highly charged Kr ions. An energy resolution three times higher than any reported for this collision energy rang...
Article
Full-text available
We report the observation of trielectronic recombination with simultaneous excitation of a K-shell and an L-shell electron, hence involving three active electrons. This process was identified in the x-ray emission spectrum of recombining highly charged Kr ions. An energy resolution three times higher than any reported for this collision energy rang...
Article
Full-text available
The cross-section of the ep → e′p′γ reaction has been measured at Q 2 = 0.33 (GeV/c)2. The experiment was performed using the electron beam of the MAMI accelerator and the standard detector setup of the A1 Collaboration. The cross-section is analyzed using the low-energy theorem for virtual Compton scattering, yielding a new determination of the tw...
Poster
We investigate the level structure of heavy hydrogenlike ions in laser beams. In heavy ions, the electrons are tightly bound by the Coulomb potential of the nucleus, which prohibits ionization even by strong lasers. However, interaction with the light field leads to dynamic shifts of the electronic energy levels. We apply a fully relativistic descr...
Poster
The photorecombination of highly charged He- to B-like ions has been explored in the atomic number range Z=26 to 80 with the Heidelberg electron beam ion trap. The energies of state-selected dielectronic recombination (DR) resonances were determined over the KLL region. At the present level of experimental accuracy, it becomes possible to make a de...

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