Open Access Published by De Gruyter Open Access

Volume 1 Issue 2

June 2003

Issue of Open Physics

Submit manuscript

Contents
Journal Overview

Open Access June 1, 2003

The effective absorption cross-section of thermal neutrons in a medium containing strongly or weakly absorbing centres

Krzysztof Drozdowicz, Barbara Gabańska, Andrzej Igielski, Ewa Krynicka, Urszula Woźnicka

Page range: 210-234

More Download PDF

Abstract

The structure of a heterogeneous system influences diffusion of thermal neutrons. The thermal-neutron absorption in grained media is considered in the paper. A simple theory is presented for a two-component medium treated as grains embedded in the matrix or as a system built of two types of grains (of strongly differing absorption cross-sections). A grain parameter is defined as the ratio of the effective macroscopic absorption cross-section of the heterogeneous medium to the absorption cross-section of the corresponding homogeneous medium (consisting of the same components in the same proportions). The grain parameter depends on the ratio of the absorption cross-sections and contributions of the components and on the size of grains. The theoretical approach has been verified in experiments on prepared dedicated models which have kept required geometrical and physical conditions (silver grains distributed regularly in Plexiglas). The effective absorption cross-sections have been measured and compared with the results of calculations. A very good agreement has been observed. In certain cases the differences between the absorption in the heterogeneous and homogeneous media are very significant. A validity of an extension of the theoretical model on natural, two-component, heterogeneous mixtures has been tested experimentally. Aqueous solutions of boric acid have been used as the strongly absorbing component. Fine- and coarse-grained pure silicon has been used as the second component with well-defined thermal-neutron parameters. Small and large grains of diabase have been used as the second natural component. The theoretical predictions have been confirmed in these experiments.

Open Access June 1, 2003

Elastic shape memory effect in In-Pb alloys in the temperature range 0.48–180 K

V. Natsik, L. Fomenko, S. Lubenets

Page range: 235-245

More Download PDF

Abstract

Pseudoelasticity caused by pseudotwinning in short-range ordered In-Pb alloys (6, 8 and 11.6 at. % Pb) is studied in the temperature range 0.48–180 K. The mechanical hysteresis parameters, namely, the thermodynamic stress τT which provides the reversibility of plastic deformation and the frictional stress τf which characterizes the resistance offered by crystal lattice and its defects to twin boundaries motion are estimated. It is found that athermal processes determine the reversible deformation: the mechanical parameters τT and τf do not depend on temperature and strain rate. The stress τT increases and the stress τf decreases with increasing Pb content. One of the main conditions of the exhibition of superelasticity is the fulfillment of the inequality τT>τf.

Open Access June 1, 2003

Higher harmonics in the voltage on a superconducting wire carrying AC electrical current

Riccardo Tebano, Fedor Gömöry

Page range: 246-257

More Download PDF

Abstract

The problem of determining the harmonic content in the voltage that appears on a superconducting wire carrying cosine-like AC current was resolved theoretically, using two approaches. First, the Fourier components of the voltage spectrum were found by numerical integration. Importance of individual terms was established, leading to two conclusions: a) it is the cosine component of the 3rd harmonic that represents the bulk of harmonic distortion, b) for the practical purposes it is sufficient to consider higher harmonics with n ≤ 7. Then, the analytical formulas were derived. While for the sine components a general expression containing an infinite series was found, closed-form formulas were derived for the cosine components of the harmonics 1, 3, 5, 7. Consequences of the results to the experimental technique used to study the AC transport properties of superconductors are discussed.

Open Access June 1, 2003

On the lyman problem

Václav Kolár

Page range: 258-267

More Download PDF

Abstract

This paper attempts to answer Lyman's question (1990) on the non-uniqueness in defining the 3D measure of the boundary vorticity-creation rate. Firstly, a straightforward analysis of the vorticity equation introduces a definition of a general vorticity flux-density tensor and its ‘effective’ part. The approach is strictly based on classical field theory and is independent of the constitutive structure of continuous medium. Secondly, the fundamental question posed by Lyman dealing with the ambiguity of the 3D measure of the boundary vorticity-creation rate for incompressible flow is discussed. It is shown that the original 3D measure (for an incompressible Newtonian fluid defined by Panton 1984), which is reminiscent of an analogy to Fourier's law, is in its character ‘effective’ and plays a crucial role in the prognostic vorticity transport equation. The alternative 3D measure proposed by Lyman includes, on the other hand, a ‘non-effective’ part, which plays a role in the local determination of the ‘effective’ measure as well as in a certain diagnostic integral boundary condition.

Open Access June 1, 2003

The characteristic X-ray spectra of free atoms of metals

P. Antsiferov

Page range: 268-288

More Download PDF

Abstract

The article presents the results of a study of characteristic X-ray spectra of free atoms by means of a new simple technique. A pulsed electron beam was used for evaporation and to create inner-shell vacancies in free atoms of metals. The spectra were obtained with the help of an X-ray monochromator which allowed precise comparison between the free-atoms spectra and corresponding solid-state spectra. The shifts of the peaks were measured and found to be in the range Δλ/λ≈10−5–10−4. The K-, L- and M-series spectra were studied. A number of the free-atoms spectra revealed structure which was not resolved in the solid-state spectra and which is of interest for atomic structure calculation applications. This electron beam technique for the investigation of X-ray characteristic spectra of free atoms can be used for the refinement of X-ray wavelength standards.

Open Access June 1, 2003

Entanglement in the second quantization formalism

Vlatko Vedral

Page range: 289-306

More Download PDF

Abstract

We study properties of entangled systems in the (mainly non-relativistic) second quantization formalism. This is then applied to interacting and non-interacting bosons and fermions and the differences between the two are discussed. We present a general formalism to show how entanglement changes with the change of modes of the system. This is illustrated with examples such as the Bose condensation and the Unruh effect. It is then shown that a non-interacting collection of fermions at zero temperature can be entangled in spin, providing that their distances do not exceed the inverse Fermi wavenumber. Beyond this distance all bipartite entanglement vanishes, although classical correlations still persist. We compute the entanglement of formation as well as the mutual information for two spin-correlated electrons as a function of their distance. The analogous, non-interacting collection of bosons displays no entanglement in the internal degrees of freedom. We show how to generalize our analysis of the entanglement in the internal degrees of freedom to an arbitrary number of particles.

Open Access June 1, 2003

Oscillator rule of the trap activation energies in NaCl crystals

Arseniy Gumenjuk, Sergiy Kutovyi

Page range: 307-331

More Download PDF

Abstract

The energy spectra of traps in NaCl crystals have been studied in detail by the method of thermoluminescence. Crystals of NaCl were undoped but treated thermally in different ways. The activation energies of traps form a single oscillator series, E n=ℏωTL(n+1/2), ℏωTL=903 cm-1. Contrary to other previously studied crystals with complex lattices, the corresponding line ℏωRam=ℏωTL was not found in Raman spectra of NaCl. It is assumed that the oscillator rule is governed by the polaron nature of traps. The trap activation energy is determined by the vibration level from which the transition of the charge carrier to the excited luminescence centre is made possible and depends on the distance between these centres.

Open Access June 1, 2003

Decoherence within a single atom

Gyula Bene

Page range: 332-343

More Download PDF

Abstract

An “almost diagonal” reduced density matrix (in coordinate representation) is usually a result of environment induced decherence and is considered the sign of classical behavior. We show that the proton of a ground state hydrogen atom can indeed possess such a density matrix. This example demonstrates that the “almost diagonal” structure may be derived from an interaction with a low number of degrees of freedom which play the role of the environment. We also show that decoherence effects in our example can only be observed if the interaction with the measuring device is significantly faster than the interaction with the environment (the electron). In the opposite case, when the interaction with the environment is significant during the measurement process, coherence is maintained. Finally, we propose a neutron scattering experiment on cold He atoms to observe decoherence which shows up as an additional positive contribution to the differential scattering cross section. This contribution is inversely proportional to the bombarding energy.

Open Access June 1, 2003

A thermodynamic approach to mechanical stability of nanosized particles

Vladimir Samsonov, Nikolay Sdobnyakov

Page range: 344-354

More Download PDF

Abstract

Thermodynamic stability conditions for nanoparticles (resulting from non-negativity of the second variation of the free energy) have been analyzed for two cases: (i) a nonvolatile nanosized particle with the size-dependent surface tension; (ii) the limiting case of larger objects when the surface tension takes its macroscopic value. It has been shown that the mechanical stability of a nanoparticle, i.e. its stability relative to the volume fluctuations, is defined by an interplay between the excess (“surface”) free energy and the volumetric elastic energy. According to the results obtained, noble gas clusters and metal nanoparticles satisfy the mechanical stability condition. At the same time, water nanodrops, as well as nanoparticles presented by nonpolar organic molecules, correspond to the stability limit. Among the investigated systems, the stability condition is not carried out for n-Pentane clusters.

Open Access June 1, 2003

Nematic ordering problem as the polymer problem of the excluded volume

A. Yakunin

Page range: 355-362

More Download PDF

Abstract

Based on a solution of the polymer excluded volume problem, a technique is proposed to estimate some parameters at the isotropic-nematic liquid crystal phase transition (the product of the volume fraction of hard sticks and the ratio of the stick length, L, to its diameter, D; the maximum value of this ratio at which one cannot regard the stick as hard). The critical exponents are estimated. The transition of a swelling polymer coil to ideal is revealed as the polymerization degree of a macromolecule increases. The entanglement concentration obtained agrees with experimental data for polymers with flexible chains. The number of monomers between neighbor entanglements is assumed to be the ratio L/D. A comparison of the theory with other ones and recent experimental data is made.

About this journal

Get easy access to the latest Open Physics' most cited and most downloaded papers with only one click!

Table of contents 2022 & 2021

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.

Why submit and read

Open Physics is a premier source of a high quality research. All published articles are made freely and permanently accessible online.

Authors benefit from fair and constructive peer review, language-correction services and extensive promotion of each published article.
The journal uses continuous publication model - accepted manuscripts are published quickly after the acceptance.
Thanks to Open Access, all articles are freely available to everyone, without any restrictions. There are more liberal policies on copyrights (authors retain copyright) and on self-archiving (no embargo periods). The journal is archived in Portico.

For the information on Article Processing Charges please go to Supplementary Information section below and view "Article Processing Charges" document (in PDF).
Detailed information on Editorial Policy, Publication Ethics, Instructions for Authors etc. can be found below and in the Supplementary Information section.