Showing papers in "Physica Scripta in 2005"
TL;DR: Sam's Interface for XAS analysis Package (SIXPack) as discussed by the authors is a graphical user interface that allows users simple manipulation and analysis of data, which is particularly useful for analysis of geochemical and environmental systems.
Abstract: SIXPack (Sam's Interface for XAS analysis Package), a graphical user interface that allows users simple manipulation and analysis of data, is presented. The modules of SIXPack allow users to: (1) load, calibrate, and average raw data files; (2) perform background subtractions; (3) perform principal component analysis and target transforms; (4) perform least squares fitting of data to standards and functions; (5) perform EXAFS fitting to FEFF phase and amplitude files; (6) create single scattering FEFF phase and amplitude files using a periodic table interface. Novel features of the program allow for the fitted correction of XANES spectra due to self-absorption effects in unknown matrices, which is particularly useful for analysis of geochemical and environmental systems. The core of the XAS analysis routine uses IFEFFIT. SIXPack is developed in Python, is installable across many operating systems and platforms, and is freely available with an Open Source license.
1,035 citations
TL;DR: A new software package for analysis of XAS data based on the IFEFFIT library of analytical and numerical algorithms and uses the perl/Tk graphics toolkit, which provides high quality analytical capabilities in a manner that is accessible to novices yet powerful enough to meet the demands of an expert.
Abstract: We introduce a new software package for analysis of XAS data. This package is based on the IFEFFIT library of analytical and numerical algorithms and uses the perl/Tk graphics toolkit. The two main components are ATHENA, a program for XAS data processing, and ARTEMIS, a program for EXAFS data analysis using theoretical standards from FEFF. These programs provide high quality analytical capabilities in a manner that is accessible to novices yet powerful enough to meet the demands of an expert. The programs run on all major platforms and are freely available under the terms of a free software license.
349 citations
TL;DR: In this paper, the fractional Hamiltonian formulation and fractional path integral quantization of Dirac and Schrodinger fields are investigated in detail, and a fractional integral quantisation of the Dirac field is proposed.
Abstract: The fractional Hamiltonian formulation and the fractional path integral quantization of fields are analysed. Dirac and Schrodinger fields are investigated in detail.
244 citations
TL;DR: The French Absorption spectroscopy beamline at the ESRF (FAME) has been operational since September 2002 as discussed by the authors, where the main optical element is a two-crystals monochromator using either Si(111 or Si(220) monocrystals so that the available energy ranges from 4 to 40 keV.
Abstract: FAME is the French Absorption spectroscopy beamline in Material and Environmental sciences at the ESRF (France), operational since September 2002. Technically speaking, the source is a 0.85 T bending magnet and the main optical element is a two-crystals monochromator using either Si(111) or Si(220) monocrystals so that the available energy ranges from 4 to 40 keV. The first crystal is liquid nitrogen cooled in order to avoid a thermal bump and thus preserve the energy resolution. The second crystal is dynamically bent during the energy scan in order to focus the beam in the horizontal plane. Two bendable mirrors are located before and after the monochromator, for beam-collimation (to optimize the energy resolution) and vertical focalization, respectively. During scans, the beam on the sample is kept constant in position and size (around 150 × 200 μm2, V × H). The high flux on the sample combined with the sensitivity of our 30-elements fluorescence detector allow to decrease the detection limit down to 10 ppm or around less than a monolayer. Moreover, quick-EXAFS acquisition is operational: the acquisition time may be reduced down to 30s.
210 citations
TL;DR: In this paper, the decay of unstable D-branes in type II string theory was studied, and the open-closed string duality proposal that arises from these studies was applied to tachyon driven cosmology.
Abstract: We begin by reviewing the results on the decay of unstable D-branes in type II string theory, and the open–closed string duality proposal that arises from these studies. We then apply this proposal to the study of tachyon driven cosmology, namely cosmological solutions describing the decay of unstable space filling D-branes. This naturally gives rise to a time reversal invariant bounce solution with positive spatial curvature. In the absence of a bulk cosmological constant the universe always begins with a big bang and ends in a big crunch. In the presence of a bulk cosmological constant one may get non-singular cosmological solutions for some special range of initial conditions on the tachyon.
137 citations
TL;DR: In this paper, the authors presented a nearly exact treatment that can be applied for any sample thickness or concentration, and retains the EXAFS oscillations in the correction term, which can be used to estimate the effect of the self-absorption of the fluorescing photon by the sample before reaching a detector.
Abstract: Extended x-ray absorption fine-structure (EXAFS) data collected in the fluorescence mode are susceptible to an apparent amplitude reduction due to the self-absorption of the fluorescing photon by the sample before it reaches a detector. Previous treatments have made the simplifying assumption that the effect of the EXAFS on the correction term is negligible, and that the samples are in the thick limit. We present a nearly exact treatment that can be applied for any sample thickness or concentration, and retains the EXAFS oscillations in the correction term.
129 citations
TL;DR: Gomez, Daniel Osvaldo as mentioned in this paper, et al. as mentioned in this paper presented the work of the Instituto de Astronomia y Fisica del Espacio (IOFES).
Abstract: Fil: Gomez, Daniel Osvaldo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina
97 citations
TL;DR: This work describes recent progress of the latest version of the REX2000 XAFS analysis package, which is an entirely new package with a user-friendly interface and simple operation.
Abstract: Today a lot of XAFS analysis software is available either free of charge, licensed or commercially. The list of the programs can be found on web sites (IXS web site displays 35 programs and ESRF web site displays 23) and there are many XAFS analysis softwares not on such lists yet. We describe recent progress of the latest version of the REX2000 XAFS analysis package. The REX2000 runs on MS-Windows family operating system, and is an entirely new package with a user-friendly interface and simple operation. The package provides many classic DATA reduction methods for EXAFS and XANES. All the parameters needed for DATA analysis can be set on graphics windows as well as numerical input. The package also has FEFF interface for multiple scattering capability.
96 citations
TL;DR: In this paper, the atomic ratio of oxygen to platinum (O/Pt) for nano-sized platinum particles on the support was determined by the amount of desorbed oxygen in He carrier (O2-TPD) during elevated temperature.
Abstract: Quantitative determination of platinum oxidation state on supported platinum catalyst was examined by using Pt LIII-edge XANES spectra. The nano-sized platinum particles on the support were partially oxidized under oxidative atmosphere. The atomic ratio of oxygen to platinum (O/Pt) for these particles could be determined by the amount of desorbed oxygen in He carrier (O2-TPD) during elevated temperature. On the other hand, the XANES spectrum of the platinum catalysts oxidized under each corresponding condition was recorded under the same condition, then the area intensity of the white line of these spectra was evaluated by a simple simulation using a set of Gaussian and arctangent functions. A good linear relationship was confirmed between the white line intensity and the atomic ratio of oxygen to platinum, meaning that the oxidation state of the platinum could be quantitatively determined by a simple XANES analysis.
89 citations
TL;DR: In this article, the development of inflationary theory and its present status, including recent progress in describing de Sitter space and inflationary universe in string theory, are discussed and discussed.
Abstract: I will discuss the development of inflationary theory and its present status, including recent progress in describing de Sitter space and inflationary universe in string theory.
75 citations
TL;DR: Using the Nikiforov-Uvarov method, an application of the relativistic Duffin-Kemmer-Petiau equation in the presence of a deformed Hulthen potential is presented in this article.
Abstract: Using the Nikiforov–Uvarov method, an application of the relativistic Duffin–Kemmer–Petiau equation in the presence of a deformed Hulthen potential is presented for spin zero particles. We derived first-order coupled differential radial equations which enable the energy eigenvalues as well as the full wavefunctions to be evaluated by using the Nikiforov–Uvarov method that can be written in terms of hypergeometric polynomials.
TL;DR: A fire-new way to construct an optical computer that expresses information by two polarized states with orthogonal vibration directions and no-intensity of light is put forward in this paper.
Abstract: A fire-new way to construct an optical computer is put forward in this paper. Distinguished from others, the optical computer in this study expresses information by two polarized states with orthogonal vibration directions and no-intensity of light, therefore it was named ternary optical computer. Constituting its general architecture by the good combination of electric control and optical calculation, the ternary optical computer employs optical fiber ring as register, semiconductor memory as ternary cell, and liquid crystal as modulator and adder. Meanwhile, an electronic computer group produces signals to control every part of the ternary optical computer. The superiority of this novel ternary optical computer was also introduced in this paper.
TL;DR: In this paper, the main notions related to the effect, its dynamics and physical picture are reviewed, and the results for neutrino oscillations in low density media with arbitrary density profile are presented.
Abstract: The MSW (Mikheyev-Smirnov-Wolfenstein) effect is the adiabatic or partially adiabatic neutrino flavor conversion in media with varying density. The main notions related to the effect, its dynamics and physical picture are reviewed. The large mixing MSW effect is realized inside the Sun providing a solution of the solar neutrino problem. The small mixing MSW effect driven by the 1–3 mixing can be realized for the supernova (SN) neutrinos. Inside collapsing stars new elements of the MSW dynamics may show up: non-oscillatory transition, non-adiabatic conversion, time dependent adiabaticity violation induced by shock waves. Effects of the resonance enhancement and the parametric enhancement of oscillations can be realized for atmospheric and accelerator neutrinos in the Earth. Precise results for neutrino oscillations in low density media with arbitrary density profile are presented and the attenuation effect is described. The area of applications is the solar and SN neutrinos inside the Earth, and the results are crucial for the neutrino oscillation tomography.
TL;DR: In this article, a non-local criterion for runaway electron generation is proposed, which results in the universal two-valued dependence of critical voltage Ucr on pd for a certain gas (p is pressure, d is interelectrode distance).
Abstract: New understanding of the mechanism of runaway electrons beam generation in gases is presented. It is shown that the Townsend mechanism of avalanche electron multiplication is valid even for strong electric fields when the electron ionization friction on the gas may be neglected. A non-local criterion for runaway electron generation is proposed. This criterion results in the universal two-valued dependence of critical voltage Ucr on pd for a certain gas (p is pressure, d is interelectrode distance). This dependence subdivides a plane (U, pd) onto an area of efficient electron multiplication and an area where the electrons leave the gas gap without multiplication. On the basis of this dependence analogs of Paschen's curves are constructed, which contain an additional new upper branch. This brunch demarcates the area of discharge and the e-beam area. Electron beams of subnanosecond pulse duration and amplitudes of hundreds of amperes have been created at atmospheric pressure in various gases. It is shown that the beam of the runaway electrons is formed at an instant when the plasma of the discharge gap approaches the anode. In this case a basic pulse of the electron beam is formed according to the non-local criterion of runaway electron generation. A volume nanosecond discharge with high specific excitation power in the absence of gap preionization by an additional external source has been realized. The role of discharge gap preionization by the fast electrons, emitted from the plasma non-uniformities on the cathode, as well as propagation of an electron multiplication wave from cathode to anode in a dense gas are considered.
TL;DR: In this paper, the authors present a matrix representation of the Dirac equation in an inhomogeneous linear medium, in presence of sources, and show that such a representation necessarily requires 8 × 8 matrices.
Abstract: Matrix representations of Maxwell's equations are very well-known. This is evident from the numerous studies on the close resemblance between the Maxwell equations in spinor form to the Dirac equation. However, all these matrix representations lack an exactness, as they assume the media to be homogeneous or/and time-independent. Moreover the final representation is given in terms of a pair of matrix equations. We present a matrix representation of Maxwell's equations in an inhomogeneous linear medium, in presence of sources. It is shown that such a representation necessarily requires 8 × 8 matrices and an explicit representation for them is presented.
TL;DR: In this article, the Schrodinger equations of diatomic molecules with empirical potential functions are solved approximately by means of the hypergeometric series method, and the potential functions may fit the experimental Rydberg-Klein-Rees curve more closely than the Morse function.
Abstract: The Schrodinger equations of diatomic molecules with empirical potential functions are solved approximately by means of the hypergeometric series method. The potential functions may fit the experimental Rydberg-Klein-Rees curve more closely than the Morse function. Rigorous solutions of Schrodinger equations are also obtained with a similar method for zero total angular momentum. The eigenfunctions of diatomic molecules, expressed in terms of Jacobi polynomial, are employed as the orthonormal basis sets, and analytic expressions of matrix elements for the position and momentum operators are given in closed form.
TL;DR: In this article, the present status of neutrino masses and mixing and some of their implications for particle physics phenomenology are reviewed and discussed in the context of particle physics physics and particle physics.
Abstract: In this talk I review the present status of neutrino masses and mixing and some of their implications for particle physics phenomenology.
TL;DR: In this paper, the authors present three characteristic types of spectra of current and continuing interest: medium/heavy species with many ionisation stages revealed in survey VUV and XUV spectra.
Abstract: The need for quantitative evaluation of complex line emission spectra as observed in hot fusion plasmas initiated a challenging development of sophisticated interpretation tools based on integrating advanced atomic modelling with detailed treatment of the plasma environment. The successful merging of the two worlds has led to routine diagnostic procedures which have contributed enormously to the understanding of underlying plasma processes and also to a wide acceptance of spectroscopy as a reliable diagnostic method. In this paper three characteristic types of spectra of current and continuing interest are presented. The first is that of medium/heavy species with many ionisation stages revealed in survey VUV and XUV spectra. Such species occur as control gases, as wall materials, as ablated heavy species and possible as layered wall dopants for monitoring erosion. The spectra are complex with line-like and quasi-continuum regions and are amenable to advanced `pattern recognition' methods. The second type is of few electron, highly ionised systems observed as line-of-sight integrated passive emission spectra in the soft x-ray region. They are analysed successfully in terms of plasma parameters through matching of observation with predicted synthetic spectra. Examples used here include highly resolved helium-like emission spectra of argon, iron and titanium observed on the tokamaks TEXTOR and Tore Supra. The third type, and the emphasis of this work, comprises spectra linked to active beam spectroscopy, that is, charge exchange recombination spectroscopy (CXRS) and beam emission spectroscopy (BES). In this case, a complex spectrum is again composed of a (usually) dominating active spectrum and an underlying passive emission spectrum. Its analysis requires modelling of both active and passive features. Examples used here are from the CXRS diagnostic at JET and TEXTOR. They display characteristic features of the main light impurity ions (C+6, He+2, N+7, Ne+10 and Ar+18), as well as that of the bulk plasma ions, H+, D+ and T+. A main conclusion is that spectral complexity is not necessarily negative, but that `complex structures' can provide a rich source of information on the plasma and its parameters—provided it is matched with integrated analysis—and that the methods can have universal applicability. In the present preparatory phase of the next generation fusion experiment ITER (International Thermonuclear Experimental Reactor) the concepts and expectations of complex spectra and integrated data analysis play an important role in the design and optimisation procedure of the ITER diagnostic assembly.
TL;DR: The cyclic universe model as discussed by the authors is an alternative cosmology, in which the universe exists in a very long-lived attractor state determined by the laws of physics, and the universe is made homogeneous and flat, and scale-invariant adiabatic perturbations are generated during an epoch of low energy acceleration.
Abstract: Inflation has been the leading early universe scenario for two decades, and has become an accepted element of the successful `cosmic concordance' model. However, there are many puzzling features of the resulting theory. It requires both high energy and low energy inflation, with energy densities differing by a hundred orders of magnitude. The questions of why the universe started out undergoing high energy inflation, and why it will end up in low energy inflation, are unanswered. Rather than resort to anthropic arguments, we have developed an alternative cosmology, the cyclic universe, in which the universe exists in a very long-lived attractor state determined by the laws of physics. The model shares inflation's phenomenological successes without requiring an epoch of high energy inflation. Instead, the universe is made homogeneous and flat, and scale-invariant adiabatic perturbations are generated during an epoch of low energy acceleration like that seen today, but preceding the last big bang. Unlike inflation, the model requires low energy acceleration in order for a periodic attractor state to exist. The key challenge facing the scenario is that of passing through the cosmic singularity at t = 0. Substantial progress has been made at the level of linearised gravity, which is reviewed here. The challenge of extending this to nonlinear gravity and string theory remains.
TL;DR: In this paper, it was shown that, given present bounds on neutrino masses, lepton number in the Universe and gravitational clustering of neutrinos, all expected laboratory effects of relic neutrions are far from observability, awaiting future technological advances to reach the necessary sensitivity.
Abstract: Neutrinos from the Big Bang are theoretically expected to be the most abundant particles in the Universe after the photons of the Cosmic Microwave Background (CMB). Unlike the relic photons, relic neutrinos have not so far been observed. The Cosmic Neutrino Background (CνB) is the oldest relic from the Big Bang, produced a few seconds after the Bang itself. Due to their impact in cosmology, relic neutrinos may be revealed indirectly in the near future through cosmological observations. In this talk we concentrate on other proposals, made in the last 30 years, to try to detect the CνB directly, either in laboratory searches (through tiny accelerations they produce on macroscopic targets) or through astrophysical observations (looking for absorption dips in the flux of Ultra-High Energy (UHE) neutrinos, due to the annihilation of these neutrinos with relic neutrinos at the Z-resonance). We concentrate mainly on the first possibility. We show that, given present bounds on neutrino masses, lepton number in the Universe and gravitational clustering of neutrinos, all expected laboratory effects of relic neutrinos are far from observability, awaiting future technological advances to reach the necessary sensitivity. The problem for astrophysical searches is that sources of UHE neutrinos at the extreme energies required may not exist. If they do exist, we could reveal the existence, and possibly the mass spectrum, of relic neutrinos, with detectors of UHE neutrinos (such as ANITA, Auger, EUSO, OWL, RICE and SalSA).
TL;DR: In this paper, the authors summarize the main concepts and discuss some of the well-known manifestations of orbital degrees of freedom, but will mostly concentrate on a more recent development in this field.
Abstract: Rich properties of systems with strongly correlated electrons, such as transition metal (TM) oxides, is largely connected with an interplay of different degrees of freedom in them: charge, spin, orbital ones as well as crystal lattice. Specific and often very important role is played by orbital degrees of freedom. They can lead to a formation of different superstructures (an orbital ordering) which are associated with particular types of structural phase transitions — one of very few examples where the microscopic origin of these transitions is really known; they largely determine the character of magnetic exchange and the type of magnetic ordering; they can also strongly influence many other important phenomena such as insulator-metal transitions (IMT), etc. In this comment I will try to shortly summarize the main concepts and discuss some of the well-known manifestations of orbital degrees of freedom, but will mostly concentrate on a more recent development in this field. More traditional material is covered in several review articles [Kugel K I and Khomskii D I 1982 Sov. Phys. Usp. 25 231, Tokura Y and Nagaosa N 2000 Science 288 462, van den Brink J et al 2002 Colossal Magnetoresistive Manganites (Kluwer)]. Although I tried to cover the main new development in this area, the choice of topics of course is influenced by my own interests; other people probably would have stressed other parts of this big field.
TL;DR: In this article, the authors developed a method for generating pair-ion plasma which consists of only positive and negative ions with equal mass, and the experimental setup is improved step by step, being suitable for plasma generation through the processes of electron-impact ionization, electron attachment and magnetic filtering.
Abstract: We have developed a novel method for generating a pair-ion plasma which consists of only positive and negative ions with equal mass. The experimental setup is improved step by step, being suitable for plasma generation through the processes of electron-impact ionization, electron attachment, and magnetic filtering. Density modulations are actively excited by a thick annulus in order to investigate collective electrostatic-modes. Three modes propagating along magnetic-field lines are experimentally found in the pair-ion plasma. The ion acoustic wave and ion plasma wave among them are theoretically predicted, but the new mode is only experimentally found in an intermediate-frequency band between the waves for the first time.
TL;DR: In this article, the dual Aharonov-Bohm effect of a magnetic monopole in the presence of a thin electric flux tube was investigated and the appearance of Berry's quantum phase in this dynamics was demonstrated.
Abstract: The quantum dynamics of a magnetic monopole in the presence of a thin electric flux is investigated. We discuss the dual Aharonov–Bohm effect and we analyze this in the point of view of the duality transformation. We also study a double slit interference experiment for a magnetic monopole in the presence of an electric vector potential. We demonstrate the appearance of Berry's quantum phase in this dynamics. The scattering of a magnetic monopole by a thin electric flux tube is studied, the scattering amplitude and the phase shift are obtained.
TL;DR: In this article, a new experimental set-up for time-resolved x-ray absorption spectroscopy (QEXAFS) experiments was described enabling the acquisition of full EXAFS spectra with a scan range of up to about 3 keV and a repetition rate of typically 10 Hz.
Abstract: The time-resolved x-ray absorption spectroscopy (QEXAFS) yields structural information about e.g. fast chemical decomposition reactions, thin film deposition, solid-state reactions, and phase transformations. Here we describe a new experimental set-up for QEXAFS experiments enabling the acquisition of full EXAFS spectra with a scan range of up to about 3 keV and a repetition rate of typically 10 Hz. Depending on photon flux and sample quality, repetition rates of up to 40 Hz can be used. The new monochromator design employs a fixed-exit channel cut crystal and a cam driven tilt table for rapid angular oscillations. The detection of fluorescence radiation or surface sensitive techniques can be applied. The new monochromator in combination with refractive x-ray lenses for beam focusing also allows XANES-microtomography in a reasonable time frame.
TL;DR: In this article, it was shown that the changes in position and shape of the x-ray edge spectra observed for the S2-S3 transition are explainable by the transformation of five-coordinated Mn(III) in a square-pyramidal geometry to six-coordinate Mn(IV).
Abstract: Photosynthetic water oxidation proceeds at a tetra-manganese complex bound to a cofactor-protein complex denoted as Photosystem II (PSII). To understand this process of fundamental importance for life on Earth, the crucial changes of the active-site occurring upon the individual transitions in the catalytic S-state cycle have been investigated by x-ray absorption spectroscopy at the Mn K-edge. For the S2-S3 transition, the changes in position and shape of the x-ray edge have been interpreted to be either associated with oxidation of Mn(III) to Mn(IV) or to formation of a ligand radical without manganese oxidation. Here we simulate XANES spectra of simple Mn-complexes using modern multiple-scattering code. Features of the XANES spectra are assigned to molecular orbitals by means of comparative semi-empirical calculations. It is concluded that the changes in position and shape of the edge spectra observed for the S2-S3 transition are explainable by the transformation of five-coordinated Mn(III) in a square-pyramidal geometry to six-coordinated Mn(IV).
TL;DR: In this paper, the authors describe a concept to realize a broadband high finesse optical cavity (white light cavity) using low-loss negative dispersive media, which allows transparency and λ-compensation, i.e. the dispersion of the medium compensates the frequency dependence of the vacuum wavelength.
Abstract: We describe a concept to realize a broadband high finesse optical cavity (white light cavity) using low-loss negative dispersive media. Two atomic systems are discussed, which allow transparency and λ-compensation, i.e. the dispersion of the medium compensates the frequency dependence of the vacuum wavelength. These atomic systems are (i) the driven two-level system and (ii) two closely spaced gain lines. We explain why the second scheme should provide better performance in terms of the realization of a white light cavity.
TL;DR: In this paper, the authors review the phenomenology of 3-ν mixing and the current data on the 3-neutrino mixing parameters and the open questions and the main goals of future research in the field of neutrinos mixing and oscillations are outlined.
Abstract: The compelling experimental evidences for oscillations of solar and atmospheric neutrinos imply the existence of 3-neutrino mixing in vacuum. We briefly review the phenomenology of 3-ν mixing, and the current data on the 3-neutrino mixing parameters. The open questions and the main goals of future research in the field of neutrino mixing and oscillations are outlined. The predictions for the effective Majorana mass |m| in (ββ)0ν-decay in the case of 3-ν mixing and massive Majorana neutrinos are reviewed. The physics potential of the experiments, searching for (ββ)0ν-decay and having sensitivity to |m| 0.01 eV, for providing information on the type of the neutrino mass spectrum, on the absolute scale of neutrino masses and on the Majorana CP-violation phases in the PMNS neutrino mixing matrix, is discussed.
TL;DR: In this article, a large number of silicate glasses containing variable amounts of iron oxide were studied by high-resolution XANES spectroscopy at the Fe K-edge to determine an accurate method to derive redox information from pre-edge features.
Abstract: A large number (67) of silicate glasses containing variable amounts of iron oxide were studied by high-resolution XANES spectroscopy at the Fe K-edge to determine an accurate method to derive redox information from pre-edge features. The glass compositions studied mimic geological magmas, ranging from basaltic to rhyolitic, dry and hydrous, with variable quench rates. The studied glasses also include more chemically simple calco-sodic silicate glass compositions. The Fe contents range from 30 wt.% to less than 2000 ppm. For most of the series of composition studied, the pre-edge information varies linearly with redox, even under high-resolution conditions. The average coordination of Fe(II) is often similar to its Fe(III) counterpart except in highly polymerized glasses because of the strong influence exerted by the tetrahedral framework on iron's sites. Natural volcanic glasses (from various volcanoes around the world) show similar variations. The average coordination of Fe(II) is often comprised between 4.5 and 5. Fe(III) shows larger variations in coordination (4 to 6, depending on composition). Bond valence models are proposed to predict the average coordination of Fe based on composition. Molecular dynamics simulations (Born–Mayer–Huggins) potentials were carried out on some compositions to estimate the magnitude of disorder effects (both static and thermal) in the XAFS analysis. XANES calculations based on the MD simulations and FEFF 8.2 show large variations in the local structures around Fe. Also, 5-coordinated Fe(III) is found to be an important moiety in ferrisilicate glasses. For Fe(II), discrepancies between glass and melt are larger and are related to its greater structural relaxation at Tg. Also, a strong destructive interference between network formers and modifiers explain the relatively weak intensity of the next-nearest neighbors contributions in the experimental spectra.
TL;DR: The Institut fur Nukleare Entsorgung (INE) at the Forschungszentrum Karlsruhe is presently constructing and will commission and operate an x-ray spectroscopy beamline dedicated to actinide research at the new synchrotron source ANKA as mentioned in this paper.
Abstract: The Institut fur Nukleare Entsorgung (INE) at the Forschungszentrum Karlsruhe is presently constructing and will commission and operate an x-ray spectroscopy beamline dedicated to actinide research at the new synchrotron source ANKA. One great advantage of the INE-Beamline is that on-site, in situ actinide research is possible for studying, e.g., solid-water interface chemical reactions, which are not possible at other facilities. The design is for a multi-purpose beamline, i.e., a number of methods (XAFS, surface sensitive and spatial resolved techniques) are possible on one and the same sample. Planned is a safe and flexible containment concept for activities up to 106 times the limit of exemption. The design will allow spectroscopic investigations using photon energies from the K edge of S (2477 eV) to the Rh K-edge (23 220 eV). The optics include collimating and focusing mirrors for a sub-mm beam dimension at the sample position. A later upgrade is planned to install auxiliary μ-focusing optics (e.g., a single bounce elliptical monocapillary or planar compound refractive lenses). The monochromator at the INE-Beamline is a Lemonnier type double-crystal x-ray monochromator (DCM), built at the Universitat Bonn, Physikalisches Institut. The pressure inside the small diameter (380 mm) vacuum housing is ~106 mbar, allowing fast changes of crystals, avoiding long pumping times. Multi-layer mirrors can be used in the DCM for wide band-pass experiments, e.g., for x-ray fluorescence analysis measurements. Installation of beamline components has been completed in October 2003. Operation begin is targeted for 2004.
TL;DR: In this article, the authors present a numerical method for solving the Laplace equation with given boundary condition, by applying the decomposition procedure of Adomian on an integral equation that results from the reformulation of the main problem.
Abstract: We present a numerical method for solving the Laplace equation with given boundary condition, by applying the decomposition procedure of Adomian on an integral equation that results from the reformulation of the main problem. The Adomian decomposition method is useful for obtaining both analytical solutions and numerical approximations of various kinds of problems. Numerical results are reported and a comparison with some other existing methods are done.