SearcharxivSearch

arXiv subjects

I. Nagy

Publications and source records attributed to I. Nagy.

At least 19 recordsLinked to original sources

Stopping power of electrons in a semiconductor channel for swift point charges

The nonperturbative kinetic framework for the stopping power of a charged-particle system for swift point projectiles is implemented. The pair-interaction potential energy required in this framework to two-body elastic scattering is based on the screened interaction energy between system particles. In such an energetically optimized modeling the swift bare projectile interacts with independent screened constituents of a fixed-density interacting many-body target. The first-order Born momentum-transfer (transport) cross section is calculated and thus a comparison with stopping data obtained [Phys. Rev. B {\bf 26}, 2335 (1982)] by swift ions, $Z_1\in{[9,17]}$ and $(v/v_0)\simeq{11}$, under channeling condition in Si is made. A quantitative agreement between the elastic scattering-based theoretical stopping and the experimentally observed reduced magnitude is found. Conventionally, such a reduced magnitude for the observable is interpreted, applying an equipartition rule, as inelastic energy loss mediated by a collective classical plasma-mode without momentum transfer to the valence-part. Beyond the leading, i.e., first-order Born-Bethe term ($Z_1^2$), the Barkas ($Z_1^3$) and Bloch ($Z_1^4$) terms are discussed, following the arguments of Lindhard for screened interaction. An extension to the case of stopping of warm dense plasma for swift charges is outlined as well.

cond-mat.quant-gas

$Z_1$-oscillation in the retarding force of metals for slow ions: Comparative study of theoretical modelings

Theoretical calculations, applying elements of the orbital-based density functional method for self-consistent screening in an electron gas to the stopping power of metals for slow projectiles are reviewed, by focusing on differences in modelings. New, two-channel-based results on the average retarding force are presented. All theoretical results are compared with pioneering experimental data, obtained for carbon target, on $Z_1$-oscillation in stopping at random collisional condition.

cond-mat.other

Two-channel approach to the average retarding force of metals for slow singly ionized projectiles

Based on the fundamental momentum-transfer theorem [Phys. Rev. Lett. 15, 11 (1965)] a novel contribution to the retarding force of metallic systems for slow intruders is derived. This contribution is associated with sudden charge-changing cycles during the path of projectiles. The sum of the novel and the well-known conventional contributions, both expressed in terms of scattering phase shifts, are used to discuss experimental data obtained for different targets. It is found that our two-channel modeling, with two nonlinear channels, improves the agreement between several data and theory and thus, as predictive modeling, can contribute to the desired convergence between experimental and theoretical attempts on the retarding force.

cond-mat.other

Correlated model atom in a time-dependent external field: Sign effect in the energy shift

In this contribution we determine the exact solution for the ground-state wave function of a two-particle correlated model atom with harmonic interactions. From that wave function, the nonidempotent one-particle reduced density matrix is deduced. Its diagonal gives the exact probability density, the basic variable of Density-Functional Theory. The one-matrix is directly decomposed, in a point-wise manner, in terms of natural orbitals and their occupation numbers, i.e., in terms of its eigenvalues and normalized eigenfunctions. The exact informations are used to fix three, approximate, independent-particle models. Next, a time-dependent external field of finite duration is added to the exact and approximate Hamiltonians and the resulting Cauchy problem is solved. The impact of the external field is investigated by calculating the energy shift generated by that time-dependent field. It is found that the nonperturbative energy shift reflects the sign of the driving field. The exact probability density and current are used, as inputs, to investigate the capability of a formally exact independent-particle modeling in time-dependent DFT as well. The results for the observable energy shift are analyzed by using realistic estimations for the parameters of the two-particle target and the external field. A comparison with the experimental prediction on the sign-dependent energy loss of swift protons and antiprotons in a gaseous He target is made.

quant-ph

Swift charged particles in a degenerate electron gas: An estimation for the Barkas effect in stopping

Applying a recently suggested new form [Phys. Rev. A {\bf 94}, 042704 (2016)] for the stopping power in terms of scattering phase shifts, here we show analytically that an exact leading phase shift may contain that information which is completely enough to characterize the asymptotic charge-sign-independent Bethe term ($\propto{Z_1^2}$) and a charge-sign-dependent Barkas term ($\propto{Z_1^3}$) in the stopping force of a degenerate electron gas for fast projectiles with charge $Z_1$. Our analytic implementation is based on a Hulthén-type potential with velocity-dependent screening. The next term in an asymptotic expansion, the Bloch term ($\propto{Z_1^4}$), measures the difference of the exact and first-order Born treatments with Coulomb potential. We found a reduced value for the Barkas term, in comparison with the conventional estimation which rests on the transport cross section.

quant-ph

Efficiency of magnetic hyperthermia in the presence of rotating and static fields

Single-domain ferromagnetic nanoparticle systems can be used to transfer energy from a time-dependent magnetic field into their environment. This local heat generation, i.e., magnetic hyperthermia, receives applications in cancer therapy which requires the enhancement of the energy loss. A possible way to improve the efficiency is to chose a proper type of applied field, e.g., a rotating instead of an oscillating one. The latter case is very well studied and there is an increasing interest in the literature to investigate the former although it is still unclear under which circumstances the rotating applied field can be more favourable than the oscillating one. The goal of this work is to incorporate the presence of a static field and to perform a systematic study of the non-linear dynamics of the magnetisation in the framework of the deterministic Landau-Lifshitz-Gilbert equation in order to calculate energy losses. Two cases are considered: the static field is either assumed to be perpendicular to the plane of rotation or situated in the plane of rotation. In the latter case a significant increase in the energy loss/cycle is observed if the magnitudes of the static and the rotating fields have a certain ratio (e.g. it should be one for isotropic nanoparticles). It can be used to "super-localise" the heat transfer: in case of an inhomogeneous applied static field, tissues are heated up only where the magnitudes of the static and rotating fields reach the required ratio.

cond-mat.soft

Exact spectral decomposition of a time-dependent one-particle reduced density matrix

We determine the exact time-dependent non-idempotent one-particle reduced density matrix and its spectral decomposition for a harmonically confined two-particle correlated one-dimensional system when the interaction terms in the Schrödinger Hamiltonian are changed abruptly. Based on this matrix in coordinate space we derivea precise condition for the equivalence of the purity and the overlap-square of the correlated and non-correlated wave functions as the system evolves in time. This equivalence holds only if the interparticle interactions are affected, while the confinement terms are unaffected within the stability range of the system. Under this condition we also analyze various time-dependent measures of entanglement and demonstrate that, depending on the magnitude of the changes made in the Schrödinger Hamiltonian, periodic, logarithmically incresing or constant value behavior of the von Neumann entropy can occur.

cond-mat.stat-mech

From single-particle physical distributions to probabilistic measures of two-particle entanglement

An inversion method is formulated for extracting entanglement-related information on two-particle interactions in a one-dimensional system from measurable one-particle position- and momentum-distribution functions. The method is based on a shell-like expansion of these norm-1 measured quantities in terms of product states taken from a parametric orthonormal complete set. The mathematical constraints deduced from these point-wise expansions are restricted by the underlying physics of our harmonically confined and interacting Heisenberg model. Based on these exact results, we introduce an approximate optimization scheme for different inter-particle interactions and discuss it from the point of view of entropic correlation measures.

quant-ph

Dynamic spectral aspects of interparticle correlation

Time-dependent quantities are calculated in the linear response limit for a correlated one dimensional model atom driven by an external quadrupolar time-dependent field. Besides the analysis of the time-evolving energy change in the correlated two-particle system, and orthogonality of initial and final states, Mehler's formula is applied in order to derive a point-wise decomposition of the time-dependent one-matrix in terms of time-dependent occupation numbers and time-dependent orthonormal, natural orbitals. Based on such exact spectral decomposition on the time domain, Rényi's entropy is also investigated. Considering the structure of the exact time-dependent one-matrix, an independent-particle model is defined from it which contains exact information on the single-particle probability density and probability current. The resulting noninteracting auxiliary state is used to construct an effective potential and discuss its applicability.

quant-ph

Variational occupation numbers to a Müller-type pair-density

Based on a parametric point-wise decomposition, a kind of isospectral deformation, of the exact one-particle probability density of an externally confined, analytically solvable interacting two-particle model system we introduce the associated parametric ($p$) one-matrix and apply it in the conventional Müller-type partitioning of the pair-density. Using the Schrödinger Hamiltonian of the correlated system, the corresponding approximate ground-state energy $E_p$ is then calculated. The optimization-search performed on $E_p$ with such restricted informations has a robust performance and results in the exact ($ex$) ground-state energy for the correlated model system $E_p=E_{ex}$.

quant-ph

Frequencies and resonances around $L_4$ in the elliptic restricted three-body problem

The stability of the Lagrangian point $L_4$ is investigated in the elliptic restricted three-body problem by using Floquet's theory. Stable and unstable domains are determined in the parameter plane of the mass parameter and the eccentricity by computing the characteristic exponents. Frequencies of motion around $L_4$ have been determined both in the stable and unstable domains and fitting functions for the frequencies are derived depending on the mass parameter and the eccentricity. Resonances between the frequencies are studied in the whole parameter plane. It is shown that the 1:1 resonances are not restricted only to single curves but extend to the whole unstable domain. In the unstable domains longer escape times of the test particle from the neighbourhood of $L_4$ are related to certain resonances, but changing the parameters the same resonances may lead to faster escape.

astro-ph.EP

Quadratic First Integrals of Kinetic Differential Equations

Classes of kinetic differential equations are delineated which do have a quadratic first integral, and classes which can not have one. Example reactions corresponding to the obtained kinetic differential equations are shown, and a few figures showing the trajectories of the corresponding systems are also included. Connections to other areas are mentioned and unsolved problems collected. The new results are theoretical, although computational tools are heavily used. Applications from biology and combustion theory will come later.

math.CA

An extensive photometric study of the Blazhko RR Lyrae star RZ Lyr

The analysis of recent, extended multicolour CCD and archive photoelectric, photographic and visual observations has revealed several important properties of RZ Lyr, an RRab-type variable exhibiting large-amplitude Blazhko modulation. On the time-base of \sim110 yr, a strict anticorrelation between the pulsation and modulation period changes is established. The light curve of RZ Lyr shows a remarkable bump on the descending branch in the small-amplitude phase of the modulation, similarly to the light curves of bump Cepheids. We speculate that the stellar structure temporally suits a 4:1 resonance between the periods of the fundamental and one of the higher-order radial modes in this modulation phase. The light-curve variation of RZ Lyr can be correctly fitted with a two-modulation-component solution; the 121 d period of the main modulation is nearly but not exactly four times longer than the period of the secondary modulation component. Using the inverse photometric method, the variations in the pulsation-averaged values of the physical parameters in different phases of both modulation components are determined.

astro-ph.SR

First Results of The Konkoly Blazhko Survey II

The two parts of the Konkoly Blazhko Survey (KBS I and II) are introduced. The most important preliminary findings of the second part are presented in comparison to the results of the first part. Two interesting cases of very strong modulation from the KBS II are also shown.

astro-ph.SR

Microscopic Reversibility or Detailed Balance in Ion Channel Models

Mass action type deterministic kinetic models of ion channels are usually constructed in such a way as to obey the principle of detailed balance (or, microscopic reversibility) for two reasons: first, the authors aspire to have models harmonizing with thermodynamics, second, the conditions to ensure detailed balance reduce the number of reaction rate coefficients to be measured. We investigate a series of ion channel models which are asserted to obey detailed balance, however, these models violate mass conservation and in their case only the necessary conditions (the so-called circuit conditions) are taken into account. We show that ion channel models have a very specific structure which makes the consequences true in spite of the imprecise arguments. First, we transform the models into mass conserving ones, second, we show that the full set of conditions ensuring detailed balance (formulated by Feinberg) leads to the same relations for the reaction rate constants in these special cases, both for the original models and the transformed ones.

q-bio.MN

Four-colour photometry of EY Dra: a study of an ultra-fast rotating active dM1-2e star

We present more than 1000-day long photometry of EY Draconis in BV(RI)C passbands. The changes in the light curve are caused by the spottedness of the rotating surface. Modelling of the spotted surface shows that there are two large active regions present on the star on the opposite hemispheres. The evolution of the surface patterns suggests a flip-flop phenomenon. Using Fourier analysis, we detect a rotation period of P_rot=0.45875d, and an activity cycle with P~350d, similar to the 11-year long cycle of the Sun. This cycle with its year-long period is the shortest one ever detected on active stars. Two bright flares are also detected and analysed.

astro-ph.SR

The Konkoly Blazhko Survey: Is light-curve modulation a common property of RRab stars?

A systematic survey to establish the true incidence rate of the Blazhko modulation among short-period, fundamental-mode, Galactic field RR Lyrae stars has been accomplished. The Konkoly Blazhko Survey (KBS) was initiated in 2004. Since then more than 750 nights of observation have been devoted to this project. A sample of 30 RRab stars was extensively observed, and light-curve modulation was detected in 14 cases. The 47% occurrence rate of the modulation is much larger than any previous estimate. The significant increase of the detected incidence rate is mostly due to the discovery of small-amplitude modulation. Half of the Blazhko variables in our sample show modulation with so small amplitude that definitely have been missed in the previous surveys. We have found that the modulation can be very unstable in some cases, e.g. RY Com showed regular modulation only during one part of the observations while during two seasons it had stable light curve with abrupt, small changes in the pulsation amplitude. This type of light-curve variability is also hard to detect in other Survey's data. The larger frequency of the light-curve modulation of RRab stars makes it even more important to find the still lacking explanation of the Blazhko phenomenon. The validity of the [Fe/H](P,phi_{31}) relation using the mean light curves of Blazhko variables is checked in our sample. We have found that the formula gives accurate result for small-modulation-amplitude Blazhko stars, and this is also the case for large-modulation-amplitude stars if the light curve has complete phase coverage. However, if the data of large-modulation-amplitude Blazhko stars are not extended enough (e.g. < 500 data points from < 15 nights), the formula may give false result due to the distorted shape of the mean light curve used.

astro-ph.SR

An extensive photometric study of the Blazhko RR Lyrae star DM Cyg

DM Cyg, a fundamental mode RRab star was observed in the 2007 and 2008 seasons in the frame of the Konkoly Blazhko Survey. Very small amplitude light curve modulation was detected with 10.57 d modulation period. The maximum brightness and phase variations do not exceed 0.07 mag and 7 min, respectively. In spite of the very small amplitude of the modulation, beside the frequency triplets characterizing the Fourier spectrum of the light curve two quintuplet components were also identified. The accuracy and the good phase coverage of our observations made it possible to analyse the light curves at different phases of the modulation separately. Utilizing the IP method (Sódor, Jurcsik and Szeidl, 2009) we could detect very small systematic changes in the global mean physical parameters of DM Cyg during its Blazhko cycle. The detected changes are similar to what we have already found for a large modulation amplitude Blazhko variable MW Lyrae. The amplitudes of the detected changes in the physical parameters of DM Cyg are only about 10% of that what have been found in MW Lyr. This is in accordance with its small modulation amplitude being about one tenth of the modulation amplitude of MW Lyr.

astro-ph.SR