Open Physics Volume 8 Issue 5

Open Physics

Volume 8 Issue 5

Contents
Journal Overview

A Q-Ising model application for linear-time image segmentation

Frank Bentrem July 22, 2010

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Abstract

A computational method is presented which efficiently segments digital grayscale images by directly applying the Q-state Ising (or Potts) model. Since the Potts model was first proposed in 1952, physicists have studied lattice models to gain deep insights into magnetism and other disordered systems. For some time, researchers have realized that digital images may be modeled in much the same way as these physical systems (i.e., as a square lattice of numerical values). A major drawback in using Potts model methods for image segmentation is that, with conventional methods, it processes in exponential time. Advances have been made via certain approximations to reduce the segmentation process to power-law time. However, in many applications (such as for sonar imagery), real-time processing requires much greater efficiency. This article contains a description of an energy minimization technique that applies four Potts (Q-Ising) models directly to the image and processes in linear time. The result is analogous to partitioning the system into regions of four classes of magnetism. This direct Potts segmentation technique is demonstrated on photographic, medical, and acoustic images.

Lévy flights and Lévy-Schrödinger semigroups

Piotr Garbaczewski July 22, 2010

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Abstract

We analyze two different confining mechanisms for Lévy flights in the presence of external potentials. One of them is due to a conservative force in the corresponding Langevin equation. Another is implemented by Lévy-Schrödinger semigroups which induce so-called topological Lévy processes (Lévy flights with locally modified jump rates in the master equation). Given a stationary probability function (pdf) associated with the Langevin-based fractional Fokker-Planck equation, we demonstrate that generically there exists a topological Lévy process with the same invariant pdf and in reverse.

Effect of Bohm potential on a charged gas

Domiziano Mostacci, Vincenzo Molinari, Francesco Pizzio July 22, 2010

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Abstract

Bohm’s interpretation of Quantum Mechanics leads to the derivation of a Quantum Kinetic Equation (QKE): in the present work, propagation of waves in charged quantum gases is investigated starting from this QKE. Dispersion relations are derived for fully and weakly degenerate fermions and bosons (for the latter above critical temperature) and the differences discussed. Use of a kinetic equation permits investigation of “Landau-type” damping: it is found that the presence of damping in fermion gases is dependent upon the degree of degeneracy, whereas it is always present in boson gases. In fully degenerate fermions a phenomenon appears that is akin to the “zero sound” propagation.

Alternative method for the measurement of the temperature of a Bose-Einstein condensate

Abel Camacho, Luis Barragán-Gil, Alfredo Macías July 22, 2010

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Abstract

Usually the temperature in a Bose-Einstein condensate is experimentally deduced resorting to the comparison between the Maxwell-Boltzmann velocity distribution function and the density profile in momentum space. Though a successful method it is merely an approximation, since it also implies the use of classical statistical mechanics at temperatures close to the condensation temperature where quantum effects play a relevant role and cannot be neglected. The present work puts forward an alternative method in which we use an ultra-intense light pulse and a nonlinear optical material as detectors for differences in times-of-flight, and in this way the temperature is deduced.

Nonextensive thermal sources of cosmic rays

Grzegorz Wilk, Zbigniew Włodarczyk July 22, 2010

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Abstract

The energy spectrum of cosmic rays exhibits power-like behavior with a very characteristic ‘knee’ structure. We consider a possibility that such a spectrum could be generated by some specific nonstatistical temperature fluctuations in the source of cosmic rays with the ‘knee’ structure reflecting an abrupt change of the pattern of such fluctuations. This would result in a generalized nonextensive statistical model for the production of cosmic rays. The possible physical mechanisms leading to these effects are discussed together with the resulting chemical composition of the cosmic rays, which follows the experimentally observed abundance of nuclei.

Jet methods in time-dependent Lagrangian biomechanics

Tijana Ivancevic July 22, 2010

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Abstract

In this paper we propose the time-dependent generalization of an ‘ordinary’ autonomous human biomechanics, in which total mechanical + biochemical energy is not conserved. We introduce a general framework for time-dependent biomechanics in terms of jet manifolds associated to the extended musculo-skeletal configuration manifold, called the configuration bundle. We start with an ordinary configuration manifold of human body motion, given as a set of its all active degrees of freedom (DOF) for a particular movement. This is a Riemannian manifold with a material metric tensor given by the total mass-inertia matrix of the human body segments. This is the base manifold for standard autonomous biomechanics. To make its time-dependent generalization, we need to extend it with a real time axis. By this extension, using techniques from fibre bundles, we defined the biomechanical configuration bundle. On the biomechanical bundle we define vector-fields, differential forms and affine connections, as well as the associated jet manifolds. Using the formalism of jet manifolds of velocities and accelerations, we develop the time-dependent Lagrangian biomechanics. Its underlying geometric evolution is given by the Ricci flow equation.

Calculation of atomic spontaneous emission rate in 1D finite photonic crystal with defects

Adam Rudziński, Paweł Szczepański July 22, 2010

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Abstract

We derive an expression for the spontaneous-emission rate in finite one-dimensional photonic crystals with arbitrary defects, using the effective resonator model to describe electromagnetic field distributions in the structure. We obtain explicit formulae for contributions from different modes, i.e. radiation, substrate and guided modes. Formal calculations are illustrated by a few numerical examples, which demonstrate that application of the effective resonator model simplifies the interpretation of results.

Intermodal interference of the lowest-order modes in hollow core optical waveguide with dielectric walls

Ivan Martincek, Dusan Pudis July 22, 2010

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Abstract

This paper deals with intermodal interference of lowest-order modes in a hollow core optical waveguide investigated theoretically and experimentally. We describe detection and excitation methods for investigation of intermodal interference in the spectral and spatial domains in the presented waveguide. In addition an analytical expression for the description of measured dependencies is also presented.

Luminescent properties and the morphology of SrMoO4:Eu3+ powders synthesized via combining sol-gel and solid-state route

Qiong Wei, Donghua Chen July 22, 2010

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Abstract

SrMoO4:Eu3+ red phosphors were prepared by combining sol-gel and solid-state route. Citric acid and ethylenediaminetetraacetic acid (EDTA), employed as the chelating agents, were added to the aqueous solutions of metal nitrates. X-ray diffraction (XRD) and photoluminescent spectra techniques (PL) were used to characterize the resultant powders. The results indicated the obtained SrMoO4:Eu3+ phosphors were fine powders with a particle size of 50 nm. The effects of synthesizing conditions were also investigated and optimized, which included the synthesis temperature and the activator concentration on the luminescent intensity. Compared with SrMoO4:Eu3+ phosphors prepared by Solid-state reaction SrMoO4:Eu3+ phosphors prepared by combining sol-gel and solid-state route showed appropriate particle size and a higher emission intensity.

Cosmological implications of the tetron model of elementary particles

Bodo Lampe July 22, 2010

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Abstract

Based on a possible solution to the tetron spin problem, a modification of the standard Big Bang scenario is suggested, where the advent of a space-time manifold is connected to the appearance of tetronic bound states. The metric tensor is constructed from tetron constituents and the reason for cosmic inflation is elucidated. Furthermore, there are natural dark matter candidates in the tetron model. The ratio of ordinary to dark matter in the universe is calculated to be 1:5.

First-principles study of electronic and optical properties of BaS, BaSe and BaTe

Zhenbao Feng, Haiquan Hu, Zengtao Lv, Shouxin Cui July 22, 2010

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Abstract

The optimized crystal structure, energy band structures, density of states (DOS) and optical properties of BaX (X=S, Se and Te) were investigated by the full potential linearized augmented plane wave plus local orbitals method (FP-LAPW+lo). The exchange-correlation potential was treated using the generalized gradient approximation (GGA). We have used also Engel and Vosko GGA (EV-GGA) formalism to improve the band gap results. The calculated results such as band gaps, dielectric constants and reflectivity spectra showed good agreement with the experimental data. The effect of the spin-orbit coupling (SOC) on the optical properties was also studied and found to be very small, especially in the low-energy region.

Molecular dynamics simulation of zirconia melting

Sergio Davis, Anatoly Belonoshko, Anders Rosengren, Adri Duin, Börje Johansson July 22, 2010

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Abstract

The melting point for the tetragonal and cubic phases of zirconia (ZrO2) was computed using Z-method microcanonical molecular dynamics simulations for two different interaction models: the empirical Lewis-Catlow potential versus the relatively new reactive force field (ReaxFF) model. While both models reproduce the stability of the cubic phase over the tetragonal phase at high temperatures, ReaxFF also gives approximately the correct melting point, around 2900 K, whereas the Lewis-Catlow estimate is above 6000 K.

Photovoltaic cells based on nickel phthalocyanine and zinc oxide formed by atomic layer deposition

Pavlo Stakhira, Georgij Pakhomov, Vlad Cherpak, Dmitro Volynyuk, Grzegorz Luka, Marek Godlewski, Elżbieta Guziewicz, Zenon Hotra July 22, 2010

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The introduction of an ultrathin zinc oxide (ZnO) layer formed by the atomic layer deposition (ALD) technique was found to improve the operation parameters of nickel phthalocyanine (NiPc) based photovoltaic cells with a transparent bottom electrode, indium tin oxide (ITO). This improvement is attributed to several reasons, such as I) increase of photovoltaic yield in ITO/p-NiPc/n-ZnO/Al cells incorporating a hybrid heterojunction as compared to single-layer ITO/NiPc/Al cells, II) enhancement of the overall spectral response in the double-layer cells and III) extension of long-term operational stability.

New parameters of many-body potentials: studying the thermal and mechanical properties of noble metals

Xin Qi, Xue-Song Yan, Lei Yang July 22, 2010

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New parameters of nearest-neighbor EAM (1N-EAM), n-th neighbor EAM (NN-EAM), and the second-moment approximation to the tight-binding (TB-SMA) potentials are obtained by fitting experimental data at different temperatures. In comparison with the available many-body potentials, our results suggest that the 1N-EAM potential with the new parameters is the best description of atomic interactions in studying the thermal expansion of noble metals. For mechanical properties, it is suggested that the elastic constants should be calculated in the experimental zero-stress states for all three potentials. Furthermore, for NNEAM and TB-SMA potentials, the calculated results approach the experimental data as the range of the atomic interaction increases from the first-neighbor to the sixth-neighbor distance.

B and N-doped double walled carbon nanotube: a theoretical study

Welber Mendes Lima, David Azevedo, Silvete Guerini July 22, 2010

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Abstract

The structural and electronic properties of boron and nitrogen atom substitutional doping in (8,0)@(13,0) (semiconductor@semiconductor) and (6,0)@(13,0) (metallic@semiconductor) double walled carbon nanotubes, were obtained by using the first-principle calculations based on the density functional theory. In this framework, the electronic density plays a central role and it was obtained from a self-consistent field form. When boron or nitrogen substitutes a carbon atom the structure remains practically the same with negligible deformation observed around defects in all configurations considered. The electronic band structure results indicate that the boron doped systems behave as a p-type impurity, however, the nitrogen doped systems behave as an n-type impurity. In all the systems investigated here, we found that, in the cases of semiconductor@semiconductor tubes, they were the easiest to incorporate a B atom in the outer-wall and an N atom in the inner-wall of the nanotube.

The multi-dimensional q-deformed bosonic Newton oscillator and its inhomogeneous quantum invariance group

Azmi Altıntaş, Metin Arık, Ali Arıkan July 22, 2010

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We obtain the inhomogeneous invariance quantum group for the multi-dimensional q-deformed bosonic Newton oscillator algebra. The homogenous part of this quantum group is given by the multiparameter quantum group $$ GL_{X;q_{ij} } $$ of Schirrmacher where q ij’s take some special values. We find the R-matrix which gives the non-commuting structure of the quantum group for the two dimensional case.

Non-physical consequences of the muffin-tin-type intra-molecular potential

Miron Amusia, Arkadiy Baltenkov July 22, 2010

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We demonstrate, using a simple model, that, in the frame of muffin-tin-like potential, non-physical peculiarities appear in molecular photoionization cross-sections that are a consequence of “jumps” in the potential and its first derivative at some radius. The magnitude of non-physical effects is of the same order as the physical oscillations in the cross-section of a diatomicmolecule. The role of the size of these “jumps” is illustrated by choosing three values for it. The results obtained are connected to the previously studied effect of non-analytic behavior as a function of r, the potential V(r) acting upon a particle on its photoionization cross-section. In reality, such potential has to be analytic in magnitude and have a first derivative function in r. The introduction of non-analytic features in model V(r) leads to non-physical features — oscillations, additional maxima, and so forth — in the corresponding cross-section.

First-principles investigation of the vibrational properties of 3-tert-butylcyclohexene

Katalin Gaál-Nagy July 22, 2010

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I present a first-principles investigation of the vibrational properties of the chiral molecule 3-tert-butylcyclohexene. The vibrational density of states (vDOS) of the two existing conformers has been calculated ab initio within the framework of density-functional theory and density-functional perturbation theory, using both the local-density approximation and the generalized-gradient approximation for the exchange-correlation potential. The vDOS of the two conformers are very similar. The vDOS has been investigated with respect to contributions of the cyclohexene ring and the tert-butyl group and also regarding the localization of vibrational modes. Additionally, the eigendisplacements of characteristic modes of 3-tert-butylcyclohexene have been analyzed.

Approximate analytical solutions of the effective mass Dirac equation for the generalized Hulthén potential with any κ-value

Altuğ Arda, Ramazan Sever, Cevdet Tezcan July 22, 2010

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The Dirac equation, with position-dependent mass, is solved approximately for the generalized Hulthén potential with any spin-orbit quantum number κ. Solutions are obtained by using an appropriate coordinate transformation, reducing the effective mass Dirac equation to a Schrödinger-like differential equation. The Nikiforov-Uvarov method is used in the calculations to obtain energy eigenvalues and the corresponding wave functions. Numerical results are compared with those given in the literature. Analytical results are also obtained for the case of constant mass and the results are in good agreement with the literature.

Probing superfluidity of periodically trapped ultracold atoms in a cavity by transmission spectroscopy

Aranya Bhattacherjee, Tarun Kumar, Man Mohan July 22, 2010

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We study a system of periodic Bose-condensed atoms coupled to cavity photons using the input-output formalism of [14]. We show for the first time that the cavity will either act as a through-pass Lorentzian filter when the superfluid fraction of the condensate is minimum, or completely reflect the input field when the superfluid fraction is maximum. We show that by monitoring the ratio between the transmitted field and the reflected field, one can estimate the superfluid fraction.

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