Showing papers in "Physica Scripta in 2003"

Asset Trees and Asset Graphs in Financial Markets

Abstract: This paper introduces a new methodology for constructing a network of companies called a dynamic asset graph. This is similar to the dynamic asset tree studied recently, as both are based on correlations between asset returns. However, the new modified methodology does not, in general, lead to a tree but a disconnected graph. The asset tree, due to the minimum spanning tree criterion, is forced to "accept" edge lengths that are far less optimal (longer) than the asset graph, thus resulting in higher overall length for the tree. The same criterion also causes asset trees to be more fragile in structure when measured by the single-step survival ratio. Over longer time periods, in the beginning the asset graph decays more slowly than the asset tree, but in the long run the situation is reversed. The vertex degree distributions indicate that the possible scale free behavior of the asset graph is not as evident as it is in the case of the asset tree.

Superabundant Vacancies Formed in Metal–Hydrogen Alloys

Abstract: Superabundant vacancies of metal atoms, of concentrations as high as 10 ~ 30 at %, can be formed in the presence of interstitial hydrogen as a consequence of reduction of the formation energy by trapping H atoms The equilibrium concentration and mobility of Vac-H clusters were determined by in situ XRD and resistivity measurements, and their sources were identified The binding energies of trapped H atoms were determined by thermal desorption spectroscopy Some of these experimental results are described, with particular reference to Pd, Ni and Cr

Nonlinear Dispersive Instabilities in Kelvin?Helmholtz Magnetohydrodynamic Flows

Abstract: In this paper a weakly nonlinear theory of wave propagation in superposed fluids in the presence of magnetic fields is presented. The equations governing the evolution of the amplitude of the progressive waves are reported. The nonlinear evolution of Kelvin–Helmholtz instability (KHI) is examined in 2 + 1 dimensions in the context of magnetohydrodynamics (MHD). We study the envelope properties of the 2 + 1 dimensional wave packet. We converted the resulting nonlinear equation for the evolution of the wave packets in a 2 + 1 dimensional nonlinear Schrodinger (NLS) equation by using the function transformation method into a sine–Gordon equation, which depends only on one function, ζ. We obtained rather general classes of solutions of the equation in ζ which leads to rather general soliton solutions of the 2 + 1 dimensional NLS equation. This result contains interesting specific solutions such as N multiple solitons, propagational breathers and quadratic solitons.

Recent Advances in the Study of Lanthanide Atoms and Ions

Abstract: We present an overview of the recent developments concerning the spectroscopic properties of lanthanide atoms and ions (Z = 57–71) This review is focussed on the advances made during the past twenty years regarding the analysis of the spectra, the transition probabilities, the radiative lifetimes and also the hyperfine structures and isotope shifts Theoretical aspects as well as experimental measurements are both covered in this paper including bibliographical references up to the end of 2001 Some astrophysical implications of the new atomic data concerning the chemical composition of the sun are briefly reviewed Emphasis is also put on the new database DREAM developed on a web site of Mons University in Belgium

Money in gas-like markets: Gibbs and Pareto laws

Abstract: We consider the ideal-gas models of trading markets, where each agent is identified with a gas molecule and each trading as an elastic or money-conserving (two-body) collision. Unlike in the ideal gas, we introduce a saving propensity λ of agents, such that each agent saves a fraction λ of its money and trades with the rest. We show that the steady-state money or wealth distribution in a market is Gibbs-like for λ = 0, has got a non-vanishing most-probable value for λ ≠ 0 and Pareto-like when λ is widely distributed among the agents. We compare these results with observations on wealth distributions of various countries.

Exponential Type Complex and Non-Hermitian Potentials in PT-Symmetric Quantum Mechanics

Abstract: Using the NU method [A F Nikiforov and V B Uvarov 1988 "Special Functions of Mathematical Physics" (Birkhauser, Basel)], we investigated the real eigenvalues of the complex and/or PT-symmetric, non-Hermitian and the exponential type systems, such as Poschl–Teller and Morse potentials.

Vortices in a Strongly Magnetized Electron–Positron–Ion Plasma

Abstract: A theoretical investigation has been presented for the linear and nonlinear properties of obliquely propagating coupled low-frequency electrostatic drift and ion-acoustic (ED-IA) waves in a strongly magnetized nonuniform electron–positron–ion plasma in the presence of sheared ion flow. A result from our linear analysis is that the ED-IA waves can be unstable due to the ion sheared flow. In addition, it is shown that the nonlinear equations governing the dynamics of weakly interacting ED-IA waves admit vortex solutions of two different classes viz. a vortex chain and a double vortex.

Classification of Spectral Lines by Means of their Hyperfine Structure. Application to Ta I and Ta II Levels

Abstract: A computer program for managing extended spectral line lists is presented, which allows classification of previously unknown lines via their expected hyperfine patterns. The program also includes several search strategies for finding unknown energy levels from unclassified lines. Some examples for the Ta I and the Ta II spectra are given, and the discovery of 11 Ta I levels of odd parity and 3 Ta II levels of even parity is reported. These latter levels are the highest known Ta II energy levels.

Stochastic Maps, Wealth Distribution in Random Asset Exchange Models and the Marginal Utility of Relative Wealth

Abstract: We look at how asset exchange models can be mapped to random iterated function systems (IFS) giving new insights into the dynamics of wealth accumulation in such models. In particular, we focus on the yard-sale (winner gets a random fraction of the poorer players wealth) and the theft-and-fraud (winner gets a random fraction of the loser's wealth) asset exchange models. Several special cases including 2-player and 3-player versions of these games allow us to connect the results with observed features in real economies, e.g., lock-in (positive feedback), etc. We then implement the realistic notion that a richer agent is less likely to be aggressive when bargaining over a small amount with a poorer player. When this simple feature is added to the yard-sale model, in addition to the accumulation of the total wealth by a single agent (condensation), we can see exponential and power-law distributions of wealth. Simulation results suggest that the power-law distribution occurs at the cross-over of the system from exponential phase to the condensate phase.

On the measure of nonclassicality of field states

Abstract: The degree of nonclassicality of states of a field mode is analysed considering both phase-space and distance-type measures of nonclassicality By working out some general examples, it is shown explicitly that the phase-space measure is rather sensitive to superposition of states, with finite superpositions possessing maximum nonclassical depth (the highest degree of nonclassicality) irrespective of the nature of the component states Mixed states are also discussed and examples with nonclassical depth varying between the minimum and the maximum allowed values are exhibited For pure Gaussian states, it is demonstrated that distance-type measures based on the Hilbert–Schmidt metric are equivalent to the phase-space measure Analyzing some examples, it is shown that distance-type measures are efficient to quantify the degree of nonclassicality of non-Gaussian pure states

Thick co-deposits and dust in controlled fusion devices with carbon walls : Fuel inventory and growth rate of co-deposited layers

Abstract: Recent results regarding the formation of co-deposits, fuel accumulation and overall material transport at the TEXTOR tokamak are described. Two categories of brittle flaking co-deposits were identified: (i) smooth stratified layers of a thickness of up to 50 ?m and a fuel content of up to 16 at.% , (ii) granular and columnar structures reaching 1 mm in thickness and con-taining around 0.5 at.% of fuel species. They were formed on the blades of the toroidal belt pump limiter (~15000 s of plasma operation) and on the neutral-iser plates of this limiter (~90000 s), respectively. A comparison is made to the fuel inventory measured in other controlled fusion devices with carbon walls.

A simple theoretical analysis of the effective electron mass in heavily doped III-V semiconductors in the presence of band-tails

Abstract: We study the effective electron mass at the Fermi-level on the basis of a newly formulated electron energy spectrum for heavily doped non-parabolic III–V semiconductors forming band-tails, taking n-InSb as an example. The investigation on the mass includes both the presence and absence of band-tailing states, in parabolic and non-parabolic energy band structures, respectively. The effective mass exists in the forbidden region, which is impossible without band-tailing effects. The analyses have been carried out for the Fermi-energy and other entities, like screening length and impurity screening potential, respectively. The values of the effective mass with band-tailing states are found much less as compared with in the absence of band-tails. The well-known results for unperturbed two-band model of Kane have also been obtained from our generalized analysis under certain limiting conditions.

Recent Progress in Optically Pumped Magnetometers

Abstract: Optically pumped magnetometres (OPM) are known as the most precise instruments for scalar measurement of low magnetic fields, including those of the Earth's magnetic field. For a long time OPM could not compete, in absolute accuracy, with the proton precession magnetometers, being, at the same time, much more sensitive and fast. Nowadays, due to the considerable progress in the OPM performance, several types of OPM became much more accurate than the best proton magnetometer. During the last decade the main progress was associated with OPM of the following three types: (1) The narrow-line potassium Mx-OMP with the highest shot-noise-limited resolution (about 10 fT/Hz1/2) and with an absolute accuracy better than 0.1 nT; (2) The "tandem" Mx–Mz-type magnetometer with a narrow line potassium Mz unit of enhanced absolute accuracy (of about 10 pT); (3) The laser pumped 3He free-precession magnetometer of highest absolute accuracy and lowest energy consumption. Each of these three types has its own specific features, preferable in certain applications.

The Phase of Neutrino Oscillations

Abstract: Using an analogy with the well-known double-slit experiment, we show that the standard phase of neutrino oscillations is correct, refuting recent claims of a factor of two correction. We also improve the wave packet treatment of neutrino oscillations taking into account explicitly the finite coherence time of the detection process.

Propagation of Self-Confinement Light Radiation in Inhomogeneous Air

Abstract: Propagation in the air atmosphere of a self-confined spherical layer (SSL) with life time measured in tens of seconds is considered. It is shown that SSL moves along the gradient of the air density and is deformed due to self-action effects connected with heating near objects and the surrounding air between the SSL and objects. As a result, SSL can penetrate through a tunnel which cross-section is smaller than the SSL diameter. Further, SSL can penetrate through a plane glass plate. It turns out that properties of the SSL are similar to the most puzzling and intriguing properties of ball lightning. Both objects are very sensitive to the inhomogeneity of the air density and the behaviour of the ball lightning based on stories of observers coincides with the behaviour of SSL based on application of well-known physical effects. The physical phenomena responsible for the stable existence of SSL are discussed. It is shown that an intense light circulating in the SSL increases the air refraction index on account of the self-action effect. As a result, the light circulates in an optical dielectric resonator formed by the same light.

Experimental lifetime studies of metastable levels

Abstract: Developments in vacuum technology as well as in ion trapping techniques has opened for new possibilities for experimental studies of long-lived metastable states. Since long it has been realized that such levels are of great importance for both fundamental theory and many different kinds of applications. Before the advent of modern technology it was, however, practically impossible to study forbidden transitions from metastable levels in the laboratory. In this review article some of the new experimental methods are briefly described. In particular, the laser probing technique for a stored ion beam developed at CRYRING is described. Recent results for singly charged ions with extremely complex structure are presented. Systematic effects are discussed.

Thermal Response of Tritiated Codeposits from JET and TFTR to Transient Heat Pulses

Abstract: High heat flux interactions with plasma facing components have been studied at microscopic scales. The beam from a continuous wave neodymium laser was scanned at high speed over the surface of graphite and carbon fiber composite tiles that had been retrieved from TFTR and JET after DT plasma operations. The tiles have a surface layer of amorphous hydrogenated carbon that was codeposited during plasma operations and laser scanning has released more than 80% of the codeposited tritium. The temperature rise of the codeposit was much higher than that of the manufactured material and showed an extended time history. The peak temperature varied dramatically (e.g. 1436?C compared to >2300?C) indicating strong variations in the thermal conductivity to the substrate. A digital microscope imaged the codeposit before, during and after the interaction with the laser and revealed 100-micron scale hot spots during the interaction. The heat flux produced a pattern of beads on a mixed Be/C deposit. Heat pulse durations of order 100 ms resulted in brittle destruction and material loss from the surface, whilst a duration of ? 10 ms showed minimal changes to the codeposit. These results show that reliable predictions for the response of deposition areas to off-normal events such as ELMs and disruptions in next step devices need to be based on experiments with tokamak generated codeposits.

Subordinated Brownian Motion and its Fractional Fokker–Planck Equation

Abstract: In this paper we show that the subordinated Brownian process is a stochastic solution of the fractional Fokker–Planck equation. This treatment simplifies and clarifies the derivation of some results suggested in literature.

Pattern Transfer using Step&Stamp Imprint Lithography

Abstract: Industrially efficient lithography process requires high throughput production, wafer scale patterning capable of handling wafers up to 8 inches. Nanoimprint lithography is a new candidate for patterning below 100 nm range. There are two methods to do large area imprinting: Wafer size parallel imprinting or sequential imprinting, mimicking the operation of an optical stepper. The step&stamp imprint lithography is a sequential printing method developed for patterning large areas using a small patterned stamp. A commercial flip chip bonder is used to demonstrate the process. A small silicon stamp with size of 3 × 3 mm2 was used as a mold to create test patterns on a silicon wafer. The stamp was patterned using optical lithography and dry etching, and contained test structures of 5 µm grid patterns. New thermoplastic polymers mr-I 8000, developed for imprint lithography, were used in the experiments.

Interpretation of the Hyperfine Structure of the Even Configuration System of Pr I

Abstract: Hyperfine structure analysis in the even configuration system 4f25d6s2 + 4f25d26s + 4f36s6p + 4f35d6p + 4f25d3 of Pr I has been performed applying a semi-empirical method. In the analysis the last experimental results have been used. Experimental radial parameters anlκk and bnlκk have been calculated for the configurations under study. The hyperfine structure of 546 energy levels have been interpreted. Extremely strong configuration mixing effects for almost all investigated levels have been observed.

Mechanism of Hydrogen Trapping and Transport in Carbon Materials

Abstract: Bulk hydrogen retention and hydrogen diffusion in graphite and carbon materials have been studied to estimate hydrogen recycling and tritium inventory in a fusion reactor environment. Hydrogen may permeate into a filler grain in the form of a hydrogen molecule, diffuse through crystallite boundaries and finally be trapped as hydrogen atoms at the edge surface of a crystallite. In the estimation of hydrogen transport, the activation energy of hydrogen diffusion can be determined from absorption experiments, and the activation energy of detrapping can be obtained from desorption experiments. The activation energies of hydrogen trapping are 2.6 eV in ordinary graphite and 4.4 eV for irradiated or mechanically milled graphite samples.

Nuclear Structure Studies by Direct Reaction Experiments with Stored Radioactive Beams

Abstract: The experimental conditions at the next generation facilities for stored radioactive ion beams presently proposed or under construction will provide unique opportunities for nuclear structure studies on nuclei far off stability and will enable to explore completely new and unknown regions in the chart of nuclides. In particular, the predicted luminosities will allow for the investigation of direct reactions with stored and cooled radioactive beams in inverse kinematics using internal H, He, etc. targets. Such light-ion induced direct reactions, as for example elastic and inelastic scattering, transfer, charge exchange, or knock-out reactions, have been proved in the past, for the case of stable nuclei, to be powerful tools for obtaining nuclear structure information, and were also applied within the last decade for the investigation of light exotic nuclei with radioactive beams bombarding external targets. A brief overview on the physics program planned at the future NESR storage ring at GSI, the physics questions to be addressed, the dedicated reactions to be used, and the regions of interest in the chart of nuclides is given. The advantage of using stored beams and internal targets for such investigations will depend on the specific exotic nuclei and reactions chosen. This is discussed by a comparison of the conditions for the application of internal and external targets for reaction experiments with exotic beams. For the special case of elastic proton scattering at intermediate energies a feasibility study is presented, including a discussion of the experimental scenario. This method was applied recently for the investigation of nuclear matter distributions of the light neutron-rich halo nuclei 6,8He and 11Li using external targets. A few examples of the results are briefly discussed. The use of internal targets and stored beams will allow in future to extend such investigations to a wide range of medium heavy and heavy nuclei far off stability, and will therefore be one of the key reactions of the experimental program at the future NESR facility.

Atomic and Nuclear Physics with Stored Particles in Ion Traps

Abstract: Trapping and cooling techniques play an increasingly important role in many areas of science. This review concentrates on recent applications of ion traps installed at accelerator facilities to atomic and nuclear physics such as mass spectrometry of radioactive isotopes, weak interaction studies, symmetry tests, determination of fundamental constants, laser spectroscopy, and spectroscopy of highly-charged ions. In addition, ion traps are proven to be extremely efficient devices for (radioactive) ion beam manipulation as, for example, retardation, accumulation, cooling, beam cleaning, charge-breeding, and bunching.

Extended term analysis of Mo II

Abstract: The spectrum of singly ionized molybdenum has been recorded with Fourier transform spectrometers in the wavelength interval 1500-7000 Angstrom. We report improved energy values for a total of 330 levels, 153 even and 177 odd, which belong to the 4d(5), 4d(4)5s, 4d(3)5s(2), 4d(4)6s, 4d(4)5d, 4d(4)5p and 4d(3)5s5p configurations. 110 of the levels have been found in the present analysis. We have also present calculated eigenvector components and oscillator strengths.

Testing of Tungsten and Tantalum Limiters at the TEXTOR Tokamak: Material Performance and Deuterium Retention

Abstract: Tungsten and tantalum were examined in the TEXTOR tokamak as test limiters in order to compare their performance under plasma operation and to recognise fuel recycling on endothermic (W) and exothermic (Ta) hydrogen absorbers. Differences have been noticed in the distribution and microstructure of co-deposits, in the fuel inventory in the bulk of metals and, in the deuterium release mechanism (ratio of molecules to atoms). As a result of poor thermal conductivity, the surface temperature of Ta during the power deposition was higher than that of W and it increased shot-by-shot because of the degradation of thermal properties due to surface modification. Results on thermal response, fuel recycling and inventory show that, as a candidate material for plasma facing components, tungsten is superior to tantalum.

Analytic Treatment of a Trading Market Model

Abstract: We mathematically analyze a simple market model where trading at each point in time involves only two agents with the sum of their money being conserved and with neither parties resulting with negative money after the interaction process. The exchange involves random re-distribution among the two players of a fixed fraction of their total money. We obtain a simple integral nonlinear equation for the money distribution. We find that the zero savings and finite savings cases belong to different universality classes. While the zero savings case can be solved analytically, the finite savings solution is obtained by numerically solving the integral equation. We find remarkable agreement with results obtained by other researchers using sophisticated numerical techniques (Chatterjee et al, these proceedings).

Embedded Solitons: Four-Frequency Radiation, Front Propagation and Radiation Inhibition

Abstract: Optical solitons which remain radiationless in spite of having wavenumbers immersed in the spectrum of linear waves are rather unusual. This article shows that moving solitons of this type are solutions of an extended NLS equation with third and fourth-order dispersion, and a quintic nonlinearity. The mechanism which prevents the emission of radiation in these solitons is presented. The radiation emitted when these solitons are perturbed is also studied. This radiation exhibits four propagating fronts, and the velocities of these fronts are calculated and explained.

An Inter-modulated Solitary Wave Solution for the Higher Order Nonlinear Schrödinger Equation

Abstract: We present a new type of solitary wave solution for the higher order nonlinear Schrodinger equation, which governs the propagation of subpicosecond and femtosecond optical pulses in optical fibers under certain parametric conditions. Unlike the previously solitary wave solution, the expression of this novel solution is composed of the product of bright and dark solitary waves, which can describe the propagation of dark optical pulses with finite-width background. The evolution of the solitary wave and its stability under some perturbations are investigated by using the numerical simulation methods.

Nonlinear Streaming Instability of Cylindrical Structures in Finitely Conducting Fluids under the Influence of a Radial Electric Field

Abstract: Linear and weakly nonlinear stabilities of two-layer flows between two concentric circular cylinders are investigated. Two different dielectric inviscid fluids are assumed to flow with different velocities in the two separate layers, whose interface is cylindrical. Hence the flow field is assumed to be axi-symmetric. The two fluids are influenced by a radial electric field due to surface charges at the interface. The critical magnitude of the electric field is obtained as a function of the velocity difference in the linear stability analysis. Based on the multiple scales technique, two nonlinear Schrodinger and Klein-Gordon equations are derived. The modulation instability of a finite wavetrain solution is discussed and compared with the linear instability condition. The analytical results are numerically confirmed, hence stability diagrams are obtained for different sets of physical parameters. New instability regions in the parameter space, which appear due to nonlinear effects, are shown.

Ab initio wavelengths and oscillator strengths for Cl X

Abstract: Using the configuration interaction technique, the energy spectra of 2s22p4, 2s2p5, 2s22p33s, 2s22p33p, and 2s22p33d configurations of oxygen-like chlorine Cl X have been calculated. The obtained data are used for the evaluation of wavelengths and oscillator strengths of all possible one-electron and two-electron 2s22p33p–2s2p5 electric dipole transitions. The calculated results are compared with recent experimental data.