Open Access Published by De Gruyter Open Access

Volume 2 Issue 1

March 2004

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Open Access March 1, 2004

Ion flux's pressure dependence in an asymmetric capacitively coupled rf discharge in NF3

Emil Mateev, Ivan Zhelyazkov

Page range: 1-11

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Abstract

Starting from an analytical macroscopic/phenomenological model yielding the self-bias voltage as a function of the absorbed radio-frequency (rf) power of an asymmetric capacitively coupled discharge in NF3 this paper studies the dependence of the ion flux onto the powered electrode on the gas pressure. An essential feature of the model is the assumption that the ions' drift velocity in the sheath near the powered electrode is proportional to E α, where E=−ΔU (U being the self-bias potential), and α is a coefficient depending on the gas pressure and cross section of elastic ion-neutral collisions. The model also considers the role of γ-electrons, stochastic heating as well as the contribution of the active electron current to the global discharge power balance. Numerically solving the model's basic equations one can extract the magnitude of the ion flux (at three different gas pressures) in a technological etching device (Alcatel GIR 220) by using easily measurable quantities, notably the self-bias voltage and absorbed rf power.

Open Access March 1, 2004

Statistical and neural net methods for automatic glaucoma diagnosis determination

František Pluháček, Jaroslav Pospíšil

Page range: 12-24

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Abstract

Two new computer diagnostic methods for the automatic determination of glaucoma diagnosis are presented and compared in this paper: the statistical method and the neural net method. Both introduced methods evaluate colour glaucomatous changes within the optic disc area. The mentioned colour changes are numerically represented using a suitable image analysis process. Next, the investigated eye is classified to three defined glaucoma-risk classes with different reliability of the diagnosis determination. The verification and the reliability comparison of both studied methods are performed by virtue of the application of this methods to a set of normal healthy optic disc images and a set of glaucomatous optic disc images.

Open Access March 1, 2004

Is there the radion in the RS2 model?

Mikhail Smolyakov, Igor Volobuev

Page range: 25-34

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Abstract

We analyse the physical boundary conditions at infinity for metric fluctuations and gauge functions in the RS2 model with matter on the brane. We argue that due to these boundary conditions the radion field cannot be gauged out in this case. Thus, it represents a physical degree of freedom of the model.

Open Access March 1, 2004

Interactions of charged dust particles in clouds of charges

Vladimir Gundienkov, Sergey Yakovlenko

Page range: 35-66

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Abstract

Two charged dust particles inside a cloud of charges are considered as Debye atoms forming a Debye molecule. Cassini coordinates are used for the numerical solution of the Poisson-Boltzmann equation for the charged cloud. The electric force acting on a dust particle by the other dust particle was determined by integrating the electrostatic pressure on the surface of the dust particle. It is shown that attractive forces appear when the following two conditions are satisfied. First, the average distance between dust particles should be approximately equal to two Debye radii. Second, attraction takes place when similar charges are concentrated predominantly on the dust particles. If the particles carry a small fraction of total charge of the same polarity, repulsion between the particles takes place at all distances. We apply our results to the experiments with thermoemission plasma and to the experiments with nuclear-pumped plasma.

Open Access March 1, 2004

Mass-transport driven by surface instabilities in metals under reactive plasma/ion beam treatment at moderate temperature

Liudvikas Pranevičius, Darius Milčius, Liudas Pranevičius, Vaiva Širvinskaitë, Jurgita Nomgaudyte, Jean-Paul Rivier, Claude Templier

Page range: 67-89

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Abstract

This paper presents a generalized approach to the mechanisms of oxidation, hydrogenation and nitriding of metals under ion irradiation with reactive particles at elevated temperatures. Experimental results on the plasma oxidation of bilayered Y/Zr films, the plasma hydrogenation of Mg films and the ion beam (1.2 keV N2+) nitriding of stainless steel are presented and discussed. We make special emphasis on the analysis of surface effects and their role in the initiation of mixing of bilayered films, the ingress of reactive species in the bulk and the restructuring of the surface layers. It is suggested that primary processes driving reactive atoms from the surface into the bulk are surface instabilities induced by thermal and ballistic surface atom relocations under reactive adsorption and ion irradiation, respectively. The diffusion of adatoms and vacancies, at temperature when they become mobile, provide the means to relax the surface energy. It is recognized that the stabilizing effect of surface adatom diffusion is significant at temperatures below 300–350°C. As the temperature increases, the role of surface adatom diffusion decreases and processes in the bulk become dominant. The atoms of subsurface monolayers occupy energetically favorable sites on the surface, and result in reduced surface energy.

Open Access March 1, 2004

Thermodynamic model of crystallization and melting of small particles

Vladimir Samsonov, Oleg Malkov

Page range: 90-103

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Abstract

The size dependence of the nanocrystal melting temperature has been investigated based on a nonequilibrium thermodynamics approach. An expression has been derived for the melting temperature that, contrary to the classical Tomson formula, takes into account the metastable character of the crystal nucleus-melt shell equilibrium. Quantitative estimations have been carried out for small spherical particles of aluminum, tin, and lead.

Open Access March 1, 2004

Glass-forming ability and thermal stability of Fe62Nb8−xZrxB30 and Fe72Zr8B20 amorphous alloys?

M. Shapaan, J. Lábár, L. Varga, J. Lendvai

Page range: 104-119

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Abstract

Glass-forming ability (GFA) and thermal stability of Fe62Nb8B30, Fe62Nb6Zr2B30 and Fe72Zr8B20 at % amorphous alloys were investigated by calorimetric (DSC and DTA) measurements. The crystallization kinetics was studied by DSC in the mode of continuous versus linear heating and it was found that both the glass transition temperature, Tg, and the crystallization peak temperature, Tp, display strong dependence on the heating rate. The partial replacement of Nb by Zr leads to lower Tg and Tx temperatures and causes a decrease of the supercooled liquid region. JMA analysis of isothermal transformation data measured between Tg and Tx suggests that the crystallization of the Fe62Nb8B30 and Fe62Nb6Zr2B30 amorphous alloys take place by three-dimensional growth with constant nucleation rate. Nb enhances the precipitation of the metastable Fe23B6 phase and stabilizes it up to the third crystallization stage. Zr addition increases the lattice constant of Fe23B6 and, at the same time, decreases the grain size.

Open Access March 1, 2004

NMR study of heterogeneity in pyridine-N-oxide...HCl crystal

Vytautas Balevicius, Alexandar Gacesa, Janez Plavec

Page range: 120-131

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Abstract

An origin of narrow 1H NMR signals in pyridine-N-oxide (PyO)...HCl crystal has been investigated by means of MAS, SPEDAS, NOESY and COSY techniques. Spectra of crystalline samples are compared with those of solid phase obtained from liquid PyO...HCl solutions (in acetonitile/H2O) after the heterogeneous phase separation. It has been concluded that partially resolved peaks in 1H NMR spectra of solids are related with heterogeneity of spin system and presence of different H-bond clusters of water molecules. NOESY spectra show no cross-peaks even at very long mixing time (500 ms). This indicates there is no exchange process between spins causing different peaks, and thus the corresponding molecular aggregates are captured in “islands of mobility8 without any channels sufficient for exchange. Appearance of MAS side bands as “pseudo8 cross-peaks in 2D NMR spectra using MAS/COSY technique is reported. In the case of accidental coincidence of spinning frequency (ωMAS) with spectral distances between some diagonal signals, intensive non-diagonal peaks are observed at the corresponding cross-positions. A misleading conclusion concerning spin coupling is easy to avoid using various ωMAS.

Open Access March 1, 2004

On the mechanism of the runaway of electrons in a gas: The upper branch of the paschen curve

Alexey Tkachev, Sergey Yakovlenko

Page range: 132-146

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Abstract

Basing on the simulation results, it is shown that the Townsend mechanism of electron multiplication in a gas at sufficiently large interelectrode distances is valid at least up to such large values of E/p at which relativistic electrons are generated. Correspondingly, the runaway electron producing in a gas is determined not by the local criteria accepted presently, but by the ratio of interelectrode distance and the characteristic electron multiplication length. It is shown that the critical discharge voltage U, at which the runaway electrons appear in a given gas, is a function of the product of the interelectrode distance by the gas pressure. This function (U-pd dependence) defines not only well-known Paschen curve but also an additional branch, which describes the absence of a self-sustained discharge at a high voltages sufficiently rapidly supplied across the electrodes. Critical discharge voltage dependence for helium and xenon are presented.

Open Access March 1, 2004

Fowler-nordheim tunnelling in Au−TiO2−Ag film structures

J. Aarik, V. Bichevin, I. Jõgi, H. Käämbre, M. Laan, V. Sammelselg

Page range: 147-159

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Abstract

I-V-characteristics have been measured for Au−TiO2−Ag structures with TiO2 layers of 30 and 180 nm thickness. The TiO2 films were grown by atomic layer deposition (ALD) technique. In the case of negative bias on the Au electrode, the conduction currents through TiO2 layers follow the Fowler-Nordheim formula for field emission over several orders of magnitude. The bulk of the currents may be attributed to tunnelling, seemingly through a Schottky barrier at the Au−TiO2 junction. In the case of reversed polarity the currents are also observed, but cannot be interpreted as tunnelling.

Open Access March 1, 2004

Fullerenes as polyradicals

Elena Sheka

Page range: 160-182

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Abstract

We present the investigation of the electronic structure of X60 molecules (X=C, Si), containing 60 odd electrons with spin-dependent interaction between them. Conditions for the electrons to be excluded from the covalent pairing are discussed. A computational spin-polarized quantum-chemical scheme is suggested to evaluate four parameters—energy of radicalization, exchange integral, atom spin density, and squared spin— to characterize the effect quantitatively. A polyradical character of the species, weak for C60 and strong for Si60, is established.

Open Access March 1, 2004

Industrial challenges for numerical simulation of crystal growth

M. Bogdanov, D. Ofengeim, A. Zhmakin

Page range: 183-203

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Abstract

Numerical simulation of industrial crystal growth is difficult due to its multidisciplinary nature and the complex geometry of the real-life growth equipment. An attempt is made to itemize physical phenomena dominant in the different methods for growth of bulk crystals from the melt and the vapor phase as well as to review corresponding numerical approaches. Academic research and industrial applications are compared. Development of a computational engine and a graphic user interface of the industry-oriented codes is discussed. A simulator for the entire growth process of bulk crystals by sublimation method is described.

Open Access March 1, 2004

A system of units compatible with geometry

Bernard Jancewicz

Page range: 204-219

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Abstract

Alternative system of fundamental units: length, time, action, electrical charge is presented instead of the present one: length, time, mass and electrical current. It contains more quantities which are scalars under scalings. Then it is possible to recognize from the unit, what kind of a geometric quantity is a given physical quantity. This is the reason why the new system of units is called compatible with geometry.

Open Access March 1, 2004

Critical fields of a superconducting cylinder

G. Zharkov

Page range: 220-240

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Abstract

The self-consistent solutions of the nonlinear Ginzburg-Landau equations, which describe the behavior of a superconducting mesoscopic cylinder in an axial magnetic field H (provided there are no vortices inside the cylinder), are studied. Different, vortex-free states (M-, e-, d-, p-), which exist in a superconducting cylinder, are described. The critical fields (H 1, H 2, H p, H i, H r), at which the first or second order phase transitions between different states of the cylinder occur, are found as functions of the cylinder radius R and the GL-parameter $$\kappa $$ . The boundary $$\kappa _c (R)$$ , which divides the regions of the first and second order (s, n)-transitions in the icreasing field, is found. It is found that at R→∞ the critical value, is $$\kappa _c = 0.93$$ . The hysteresis phenomena, which appear when the cylinder passes from the normal to superconducting state in the decreasing field, are described. The connection between the self-consistent results and the linearized theory is discussed. It is shown that in the limiting case $$\kappa \to {1 \mathord{\left/ {\vphantom {1 {\sqrt 2 }}} \right. \kern-\nulldelimiterspace} {\sqrt 2 }}$$ and R ≫ λ (λ is the London penetration length) the self-consistent solution (which correponds to the socalled metastable p-state) coincides with the analitic solution found from the degenerate Bogomolnyi equations. The reason for the existence of two critical GL-parameters $$\kappa _0 = 0.707$$ and $$\kappa _0 = 0.93$$ in, bulk superconductors is discussed.

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Open Physics is a peer-reviewed, open access, electronic journal devoted to the publication of fundamental research results in all fields of physics. The journal provides the readers with free, instant, and permanent access to all content worldwide; and the authors with extensive promotion of published articles, long-time preservation, language-correction services, no space constraints and immediate publication.
Open Physics is listed inter alia by Clarivate Analytics (formerly Thomson Reuters) - Current Contents/Physical, Chemical and Earth Sciences, JCR and SCIE. Our standard policy requires each paper to be reviewed by at least two Referees and the peer-review process is single-blind.

Special / Topical Issues:

Special Issue on Predicting Patern Alterations in Nature
Guest Editors:
Prof. Abdon Atangana, University of the Free State, South (Lead Guest Editor)
Prof. Dr. Emile Franc Goufo, University of South Africa
Prof. Dr Seda İğret Araz, Siirt University, Turkey

The journal publishes research and review articles, rapid and short communications, comments and replies that cover the following areas of physical sciences:

Acoustics
Astrophysics,
Atomic and Molecular Physics,
Biological and Medical Physics,
Complex Networks, Socio- and Econophysics,
Computational Physics,
Condensed Matter Physics,
Cosmology and Gravitation,
Fluid Mechanics,
Geophysics,
Nanophysics,
Optics and Lasers,
Particle and Nuclear Physics,
Plasma Physics,
Statistical and Nonlinear Physics,
Surface Physics,
Theoretical and Mathematical Physics.

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