Influence of iron addition on the oxygen-deficient Sr0.85Bi0.15Co1−xFexO3−δ (0.0?x?1.0) perovskites

A series of oxygen-deficient Sr_0.85Bi_0.15Co_1−xFe_xO_3−δ (0.0?x?1.0) perovskite phases were prepared using solid-state reaction. Results of neutron powder diffraction analyses show that the introduction of Fe onto the B-site severely effects the long range coherence of the oxygen vacancy ordered, I4/mmm supercell, observed for the x=0.0 sample. For x=0.1 a smaller, a=b≈a_p, c≈2a_p, P4/mmm supercell gives the best agreement to the diffraction data, whilst phases in the range 0.2?x?0.6 adopt disordered cubic perovskite structures. Pseudo-cubic, a=b≈a_p, c≈a_p, structures are found for x?0.8. Evidence of weak superstructures, reflecting local oxygen ordering, is also obtained from electron diffraction. For all oxygen-annealed phases the average structure reverts to cubic Pm3¯m. The as-prepared samples show G-type antiferromagnetic order at room temperature. The oxygen annealed x=0.10, 0.25 and 1.0 samples display low-temperature spin-glass transitions.     

Magnetism of Co overlayers and nanostructures on W(0 0 1): A first-principles study

The magnetic properties of Co nanostructures and a Co monolayer on W(0 0 1) have been studied in the framework of density functional theory. Different geometries such as planar and three-dimensional clusters have been considered, with cluster sizes varying between 2 and 13 atoms. The calculations were performed using the real-space linear muffin-tin orbital method (RS-LMTO-ASA). With respect to the stability of the magnetic state, we predict an antiferromagnetic (AFM) structure for the ground state of the planar Co clusters and a ferromagnetic (FM) state for the three-dimensional clusters. For the three-dimensional clusters, one of the AFM arrangements leads to frustration due to the competing FM and AFM exchange interactions between different atoms in the cluster, and gives rise to a non-collinear state with energy close to that of the FM ground state. The relative role of the Co–Co and Co–W exchange interactions is also investigated.     

Electronically driven structure changes of Si captured by femtosecond electron diffraction

The excitation of a high density of carriers in semiconductors can induce an order-to-disorder phase transition due to changes in the potential-energy landscape of the lattice. We report the first direct resolution of the structural details of this phenomenon in freestanding films of polycrystalline and (001)-oriented crystalline Si, using 200-fs electron pulses. At excitation levels greater than approximately 6% of the valence electron density, the crystalline structure of the lattice is lost in <500 fs, a time scale indicative of an electronically driven phase transition. We find that the relaxation process along the modified potential is not inertial but rather involves multiple scattering towards the disordered state.     

Novel method of self‐interaction corrections in density functional calculations

It is demonstrated that the commonly applied self‐interaction correction (SIC) used in density functional theory does not remove all self‐interaction. We present as an alternative a novel method that, by construction, is totally free from self‐interaction. The method has the correct asymptotic 1/r dependence. We apply the new theory to localized f electrons in praseodymium and compare with the old version of SIC, the local density approximation (LDA) and with an atomic Hartree–Fock calculation. The results show a lowering of the f level, a contraction of the f electron cloud and a lowering of the total energy by 13 eV per 4 f electron compared to LDA. The equilibrium volume of the new SIC method is close to the ones given by LDA and the older SIC method and is in good agreement with experiment. The experimental cohesive energy is in better agreement using the new SIC method, both compared to LDA and another SIC method. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 81: 247–252, 2001     

Orthogonal signal correction, wavelet analysis, and multivariate calibration of complicated process fluorescence data

In this paper, multivariate calibration of complicated process fluorescence data is presented. Two data sets related to the production of white sugar are investigated. The first data set comprises 106 observations and 571 spectral variables, and the second data set 268 observations and 3997 spectral variables. In both applications, a single response, ash content, is modelled and predicted as a function of the spectral variables. Both data sets contain certain features making multivariate calibration efforts non-trivial. The objective is to show how principal component analysis (PCA) and partial least squares (PLS) regression can be used to overview the data sets and to establish predictively sound regression models. It is shown how a recently developed technique for signal filtering, orthogonal signal correction (OSC), can be applied in multivariate calibration to enhance predictive power. In addition, signal compression is tested on the larger data set using wavelet analysis. It is demonstrated that a compression down to 4% of the original matrix size — in the variable direction — is possible without loss of predictive power. It is concluded that the combination of OSC for pre-processing and wavelet analysis for compression of spectral data is promising for future use.     

The MAX I Facility

The 1.2 GeV synchrotron LUSY (Lund University Synchrotron), one of the first strong-focusing synchrotrons in Europe, designed for research in nuclear and particle physics, was closed in 1972. One major reason for this closing was that CERN was catching up speed and national facilities had difficulties catching up in high-energy physics.     

A self-polishing platinum ring voltammetric sensor and its application to complex media

A self-polishing voltammetric sensor was recently developed and has been applied to samples of urea, milk and sewage water. The polishing device continuously grinds a platinum ring electrode, offering a reproducible and clean electrode surface. Principal component analysis (PCA) and partial least squares (PLS) techniques were applied to interpret the data and to build prediction models. In an evaluation of samples with different urea concentrations, the grinding step allows for repeatable measurements, similar to those after electrochemical cleaning. Furthermore, for the determination of sewage water concentrations in drinking water and for the evaluation of different fat contents in milk samples, the polishing eliminates sensor drift produced by electrode fouling. The results show that the application of a self-polishing unit offers a promising tool for electrochemical studies of difficult analytes and complex media.     

A Photochemical Study of Diclofenac and Its Major Transformation Products

The photolytic transformation of 2-(2-(2,6-dichlorophenylamino)phenyl)acetic acid (diclofenac) and its transformation products (TPs) (8-chloro-9H-carbazol-1-yl) acetic acid (Cz1), 2-(2-chloro-phenylamino)-benzaldehyde (Ald) and (1,4-dioxo-4,9-dihydro-1H-carbazol-8-yl) acetic acid (Cz4) in aqueous solutions have been studied. The previously unreported TP (Cz4) was isolated by LC and completely characterized by NMR and MS. UV-absorption spectra of diclofenac and three of its TPs were determined and used to calculate disappearance quantum yields. The dominating transformation pathway of diclofenac occurs via initial formation of Cz1 and proceeds to form mainly (Cz4) over 200 min of UV-irradiation. A second minor transformation pathway, which yields Ald as the sole product, was observed only under deaerated conditions.