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Kono M.,Chuo University | Vranjes J.,Institute of Physics Belgrade
Physical Review Letters | Year: 2014

Complicated wave behavior observed in the cylindrical pair-ion (fullerene) experiments by Oohara and co-workers are now identified to be low harmonic ion cyclotron waves combined with ion plasma oscillations inherent to kinetic theory. The electrostatic dispersion equation derived is based on an approximation for the current from the exact solutions of the characteristic cylindrical geometry form of the Vlasov plasma equation in a uniform magnetized plasma cylinder surrounded by a larger metal boundary outside a vacuum gap, which thus differs from that in unbounded plasmas. Positive and negative ions, differing only in the sign of their charge, respond to a potential in the same time scale and cooperate to reflect the enhanced kinetic orbital behaviors to the macroscopic propagation characteristics. In addition, the experimental value of the Larmor radius (comparable to the discharge radius but small enough to make the analytic approximation useful) makes higher harmonic ion cyclotron effects both observable and calculable with the appropriate approximation for the kinetic theory. © 2014 American Physical Society.


Grant
Agency: European Commission | Branch: FP7 | Program: | Phase: | Award Amount: 3.21M | Year: 2008

eInfrastructure in Europe has reached a mature state where the GEANT network forms a backbone on top of which a distributed computing infrastructure - the Grid - provides processing and storage services for eScience research. The South-East European eInfrastructure initiatives are committed to ensuring equal participation of the less-resourced countries of the region in European trends. SEEREN initiative has established a regional network and its GEANT connection and the SEE-GRID initiative the regional Grid. Hereby proposed SEE-GRID-SCI will leverage the SEE eInfrastructure to enable new scientific collaborations among SEE user communities. SEE-GRID-SCI will stimulate widespread integrated eInfrastructure uptake by new cross-border user groups extending over the region, fostering collaboration and providing advanced capabilities to more researchers, with an emphasis on strategic groups in seismology, meteorology and environmental protection. The initiative thus aims to have a catalytic and structuring effect on a variety of user communities that currently do not directly benefit from the available eInfrastructures. In parallel, it will enlarge the regional eInfrastructure to cater for demands of the communities: a number of new Grid clusters and countries will be added, engaging a wider range of players and expanding the provider pool. Finally, SEE-GRID-SCI will help mature and stabilise the National Grid Initiatives in the region, allowing them to join the new era of longer-term sustainable Grid infrastructure in Europe. In this context, SEE-GRID-SCI will aim to attract political and financial support for materializing the eInfrastructure vision. In longer term, SEE-GRID-SCI aspires to contribute to the stabilisation and development of South-East Europe, by easing the digital divide and stimulating eInfrastructure development and adoption by new user communities, thus enabling collaborative high-quality research across a spectrum of scientific fields.


Toback D.,Texas A&M University | Zivkovic L.,Institute of Physics Belgrade
International Journal of Modern Physics A | Year: 2015

We present a summary of results for searches for new particles and interactions at the Fermilab Tevatron collider by the CDF and the D0 experiments. These include results from Run I as well as Run II for the time period up to July 2014. We focus on searches for supersymmetry, as well as other models of new physics such as new fermions and bosons, various models of excited fermions, leptoquarks, technicolor, hidden-valley model particles, long-lived particles, extra dimensions, dark matter particles and signature-based searches. © 2015 World Scientific Publishing Company.


Djordjevic M.,Institute of Physics Belgrade
Journal of Physics: Conference Series | Year: 2016

High momentum suppression of light and heavy flavor observables is considered to be an excellent probe of jet-medium interactions in QCD matter created at RHIC and LHC. Utilizing this tool requires accurate suppression predictions for different experiments, probes and experimental conditions, and their unbiased comparison with experimental data. We developed the dynamical energy loss formalism which takes into account both radiative and collision energy loss computed within the same theoretical framework, dynamical (as opposed to static) scattering centers, finite magnetic mass, running coupling and uses no free parameters in comparison with experimental data. Within this formalism, we provide predictions, and a systematic comparison with the experimental data, for a diverse set of probes, various centrality ranges and various collision energies at RHIC and LHC. We also provide clear qualitative and quantitative predictions for the upcoming LHC experiments. A comprehensive agreement between our predictions and experimental results suggests that our dynamical energy loss formalism can well explain the jet-medium interactions in QGP, which will be further tested by the obtained predictions for the upcoming data.


Jovanovic R.,Institute of Physics Belgrade | Tuba M.,Megatrend University
Applied Soft Computing Journal | Year: 2011

The minimum weight vertex cover problem is an interesting and applicable NP-hard problem that has been investigated from many different aspects. The ant colony optimization metaheuristic is a relatively new technique that was successfully adjusted and applied to many hard combinatorial optimization problems, including the minimum weight vertex cover problem. Some kind of hybridization or exploitation of the knowledge about specific problem often greatly improves the performance of standard evolutionary algorithms. In this article we propose a pheromone correction heuristic strategy that uses information about the best-found solution to exclude suspicious elements from it. Elements are suspicious if they have some undesirable properties that make them unlikely members of the optimal solution. This hybridization improves pure ant colony optimization algorithm by avoiding early trapping in local convergence. We tested our algorithm on numerous test-cases that were used in the previous research of the same problem and our algorithm uniformly performed better, giving slightly better results in significantly shorter time. © 2011 Elsevier B.V. All rights reserved.


Ali Sekh G.,Institute of Physics Belgrade
Pramana - Journal of Physics | Year: 2013

Matter-wave bright solitons in bichromatic lattice potentials are considered and their dynamics for different lattice environments are studied. Bichromatic potentials are created from superpositions of (i) two linear optical lattices and (ii) a linear and a nonlinear optical lattice. Effective potentials are found for the solitons in both bichromatic lattices and a comparative study is done on the dynamics of solitons with respect to the effective potentials. The effects of dispersion on solitons in bichromatic lattices are studied and it is found that the dispersive spreading can be minimized by appropriate combinations of lattice and interaction parameters. Stability of nondispersive matter-wave solitons is checked from phase portrait analysis. © Indian Academy of Sciences.


Vranjes J.,R. Vandervaerenlaan 16 402 | Vranjes J.,Institute of Physics Belgrade
Astronomy and Astrophysics | Year: 2013

Context. It is generally accepted that the ion acoustic (IA) wave in plasmas containing ions and electrons with the same temperature is of minor importance due to strong damping of the wave by hot resonant ions. Aims. In this work it will be shown that the IA wave is susceptible to excitation even in hot-ion plasmas when both an electromagnetic transverse wave and a background density gradient are present in the plasma and, in addition, the wave is unstable (i.e., growing) in the case of permeating homogeneous plasmas. Methods. The multi-component fluid theory is used to describe the IA wave susceptibility for excitation in inhomogeneous plasmas and its coupling with electromagnetic waves. The growing IA wave in permeating homogeneous plasmas is described by the kinetic theory. Results. In plasmas with density and temperature gradients, the IA wave is effectively coupled with the electromagnetic waves. In comparison to the ordinary IA wave in homogeneous plasma, the Landau damping of the present wave is much smaller; to demonstrate this effect, a simple but accurate fluid model is presented for the Landau damping. In the case of permeating plasmas, a kinetic mechanism for the currentless IA wave instability is presented; it has a very low threshold for excitation compared with ordinary electron-current- driven kinetic instability. Such growing IA waves can effectively heat plasma in the upper solar atmosphere by a stochastic heating mechanism presented in the work. Conclusions. The results presented in the work suggest that the role of the IA wave in the heating of the solar atmosphere (chromosphere and corona) should be reexamined. © ESO, 2013.


Vranjes J.,R. Vandervaerenlaan 16 402 | Vranjes J.,Institute of Physics Belgrade | Krstic P.S.,University of Tennessee
Astronomy and Astrophysics | Year: 2013

Context. The lower solar atmosphere is an intrinsically multi-component and collisional environment with electron and proton collision frequencies in the range 108-1010 Hz, which may be considerably higher than the gyro-frequencies for both species. Collisions between different species are altitude dependent because of the variation in density and temperature of all species. Aims. We aim to provide a reliable quantitative set of data for collision frequencies, magnetization, viscosity, and thermal conductivity for the most important species in the lower solar atmosphere. Having such data at hand is essential for any modeling that is aimed at describing realistic properties of the considered environment. Methods. The relevant elastic and charge transfer cross sections in the considered range of collision energies are now accepted by the scientific community as known with unprecedented accuracy for the most important species that may be found in the lower solar atmosphere. These were previously calculated using a quantum-mechanical approach and were validated by laboratory measurements. Only with reliable collision data one can obtain accurate values for collision frequencies and coefficients of viscosity and thermal conductivity. Results. We describe the altitude dependence of the parameters and the different physics of collisions between charged species, and between charged and neutral species. Regions of dominance of each type of collisions are clearly identified. We determine the layers within which either electrons or ions or both are unmagnetized. Protons are shown to be unmagnetized in the lower atmosphere in a layer that is at least 1000 km thick even for a kilo-Gauss magnetic field that decreases exponentially with altitude. In these layers the dynamics of charged species cannot be affected by the magnetic field, and this fact is used in our modeling. Viscosity and thermal conductivity coefficients are calculated for layers where ions are unmagnetized. We compare viscosity and friction and determine the regions of dominance of each of the phenomena. Conclusions. We provide the most reliable quantitative values for most important parameters in the lower solar atmosphere to be used in analytical modeling and numerical simulations of various phenomena such as waves, transport and magnetization of particles, and the triggering mechanism of coronal mass ejections. © 2013 ESO.


Vranjes J.,Institute of Physics Belgrade | Kono M.,Chuo University
Physics of Plasmas | Year: 2014

Some essential features of the ion plasma wave in both kinetic and fluid descriptions are presented. The wave develops at wavelengths shorter than the electron Debye radius. Thermal motion of electrons at this scale is such that they overshoot the electrostatic potential perturbation caused by ion bunching, which consequently propagates as an unshielded wave, completely unaffected by electron dynamics. So in the simplest fluid description, the electrons can be taken as a fixed background. However, in the presence of magnetic field and for the electron gyro-radius shorter than the Debye radius, electrons can participate in the wave and can increase its damping rate. This is determined by the ratio of the electron gyro-radius and the Debye radius. In interpenetrating plasmas (when one plasma drifts through another), the ion plasma wave can easily become growing and this growth rate is quantitatively presented for the case of an argon plasma. © 2014 AIP Publishing LLC.


Researchers at Aalto University, Institute of Physics Belgrade and the Saha Institute in Kolkata have used a computational model to prove that participants make a more favorable decision to participating in scientific conferences the more often they have previously participated in the conference. The likelihood to participate grows regardless of the qualities of the conference, like its location, size or specialization.

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