Brown pigments based on perovskite structure of BiFeO3−δ

Light brown inorganic pigments based on BiFeO₃ doped by Sr²⁺ cations were prepared by a conventional solid-state reaction at high temperature. This study is focused on the synthesis of Bi_1?x Sr _x FeO_3?δ powders in a range of substitution (x = 0–0.35; with step size 0.05). The main role of strontium is to overcome the defects that come to exist during the evaporation of Bi over material preparation. The substitution of trivalent bismuth ions by divalent strontium ions results in oxygen deficiency in the lattice, which was proved by both thermogravimetric analysis and elemental analysis. The substitution has a positive effect on the thermal stability of samples. The thermal stability of BiFeO₃ is 1046 K, whereas the substitution of 20 mol% of Bi³⁺ by Sr²⁺ ions shifted it to 1403 K and powder with composition Bi_0.65Sr_0.35FeO_3?δ has a thermal stability that is higher than 1434 K. An increasing range of substitution is connected with the change in the pigment color from reddish-brown to orange-brown and back to reddish-brown. The Bi_0.85Sr_0.15FeO_3?δ pigment prepared by calcination at 1273 K offers the most interesting color properties (L* = 45.57; a* = 20.38; b* = 26.23).

     

Dielectric properties of multiband electron systems II. Collective modes

Starting from the tight-binding dielectric matrix in the random phase approximation we examine the collective modes and electron-hole excitations in a two-band electronic system. For long wavelengths (q → 0), for which most of the analysis is carried out, the properties of the collective modes are closely related to the symmetry of the atomic orbitals involved in the tight-binding states. In insulators there are only inter-band charge oscillations. If atomic dipolar transitions are allowed, the corresponding collectivemodes reduce in the asymptotic limit of vanishing bandwidths to Frenkel excitons for an atomic insulator with weak on-site interactions. The finite bandwidths renormalize the dispersion of these modes and introduce a continuum of incoherent inter-band electron-hole excitations. The possible Landau damping of collective modes due to the presence of this continuum is discussed in detail. In conductors the intra-band charge fluctuations give rise to plasmons. If the atomic dipolar transitions are forbidden, the coupling of inter-band collective modes and plasmons tends to zero as q → 0. On the contrary, in dipolar conductors this coupling is strong and nonperturbative, due to the long range monopole-dipole interactions between intra-band and inter-band charge fluctuations. The resulting collective modes are hybrids of intra-band plasmons and inter-band dipolar oscillations. It is shown that the frequency of the lower hybridized longitudinal mode is proportional to the frequency of the transverse dipolar mode when the latter is small. The dielectric instability in a multi-band conductor is therefore characterized by the simultaneous softening of a transverse and a longitudinal mode, which is an important, directly measurable consequence of the present theory.     

Comment on determination of electron temperature from Langmuir probe data in tokamak edge plasma

Langmuir probe measurements of electron temperature in a plasma in the limiter shadow of a tokamak are presented together with a method of probe data analysis which takes into account the influence of the ion current vs voltage dependence in the determination of electron temperature, The method is based on the transformation of a single into a double probe characteristic. Values of the electron temperature calculated using this method are compared with the values estimated from single probe characteristic data.     

Accreditation of GMO detection laboratories: Improving the reliability of GMO detection

Reliable and efficient methods for detecting genetically modified organisms (GMOs) are essential for establishing an effective system for traceability all along the supply chain from seed producers to final consumers. The latter is especially meaningful in European Union and other countries where strict legislations on GMOs were set up. Performance of the methods used in laboratories around the world should be uniform, in order to obtain reliable and comparable results. Accreditation is a suitable system for harmonising procedures in each testing laboratory. In this paper, key elements for the accreditation of molecular biology methods for GMO detection according to ISO/IEC 17025 are described. The procedures described are also valuable for the accreditation of molecular methods for all laboratory diagnostics where qualitative and quantitative characterisation of nucleic acids is needed.     

Excitation and structure of hypernuclear resonances in (K −,π ¯0)-reactions on 1p-shell nuclei

The available experimental data on the excitation functions (EF) of the 1p-shellΛ-hy-pernuclei in (K ^?, π^?) reactions atθ _π = 0^° has been analysed in terms of shell model and weak coupling scheme. It is substantiated by the experimental data on the neutron spectroscopic factors and on the fragmentation of nuclear hole excitations. The pronounced nuclear spectroscopic characteristics in the hypernuclear spectra are indicative of a weak coupling ofΛ-hyperon with nuclear subsystem. The analysis has made it possible to determine the difference is single-particle energies ofΛ-hyperon in the 1p- and 1s-states and to obtain additional evidence for the smallness of theΛ-nucleus spin-orbit interaction. The resonance structure of EF of hypernuclei, which were not studied in (K ^?,π ₀ ^? ) reactions, is predicted. The interrelated aspects of the studies of the (K ^?,π ₀ ^? ), (K ^?,π ₀ ^? β^′), and (K ^?, π⁺) reactions which are of interest to spectroscopy ofΛ-andΣ-hypernuclei are discussed.     

A computer program for calculating Ge(Li) detector counting efficiencies for Marinelli beakers

A novel computing method has been developed to calculate the absolute photopeak efficiency of a Ge(Li) detector for Marinelli beakers of different heights and diameters and with variable density. For each point in the cylindrical sample the detection efficiency is calculated taking into account the distance from the detector and gamma-ray attenuation and the efficiency is integrated numerically over the volume of the sample. The detector is approximated as a point detector with an experimentally determined effective interaction depth. It is necessary to measure the absolute efficiency for a point source located on the detector axis and on a line beside the detector parallel to the axis. The computer program calculates the absolute counting efficiency for Marinelli beakers of any geometry and for any density. The measured and calculated values for three different densities give a good (–2.2%) overall agreement.     

Hilic MS/MS determination of amino acids in herbs of Fumaria schleicheri L., Ocimum basilicum L., and leaves of Corylus avellana L.

The aim of research was to study the content of amino acids using in extracts of Fumaria schleicheri L., Ocimum basilicum L., and Corylus avellana L. by HILIC MS/MS method. Separation of amino acids in the samples was carried out with Acquity H-class UPLC system (Waters, Milford, USA) equipped with SeQuant ZIC-Hilic collumn (2.1 × 150 mm, 3.5 μm) (Merck Millipore, Darmstadt, Germany). The MS/MS fragment ion chromatograms of the test solutions established the presence of 19 amino acids. The obtained results have shown that O. basilicum L. characterized the highest concentrations of different neurogenic amino acids (128.1 mg/kg), comparing with F. schleicheri L. and C. avellana L. (57.72 and 52.91 mg/kg, respectively).     

Molecular orbital resonance theory: A new approach to the treatment of quantum chemical problems

An alternative approach to the treatment of the quantum chemical problems combining both, the MO and VB theory, is proposed. This approach retains the concept of resonance from the VB method, but it treats each particular bond in the MO sense. The method is illustrated with a few examples. Relative stabilities of benzene, pentalene and cyclobutadiene are derived. A Hückel (4m + 2) rule is derived for the annulenes. The charge polarisation in the case of the pentalene molecule is explained. A distortion of the pentalene molecule is considered and it is shown that within this approach the distortion depends on the charge polarisation.     

Ferrous ion induced decomposition of alkyl hypochlorites

The decomposition of primary, secondary and tertiary alkyl hypochlorites induced by ferrous and other one-electron oxidizable metal ions leads to δ-chloro alcohols in yields of 34–76%. In decomposition of tertiary alkyl hypochlorites, β-fragmentation competes with intramolecular δ-chlorination. Tertiary cycloalkyl hypochlorites containing five- or six-membered rings undergo β-cleavage giving the corresponding ω-chloro ketones, while 1-methylcycloheptyl and 1-methylcyclooctyl hypochlorites by decomposition with ferrous ion proceed by transannular functionalization of δ-carbon atom and β-cleavage as a competing reaction.     

Computer program for neutron activation analysis with the SLOWPOKE reactor

A FORTRAN computer program for automatic neutron activation analysis is presented. The program locates and identifies peaks in a gamma-ray spectrum, calculates peak areas and the concentrations of the elements of interest in the sample. This program was specifically designed for the SLOWPOKE reactor, it uses a semi-absolute method and does not need standards or flux monitors. The program was written so as to minimize the computation time, and a typical 4096-channel spectrum is processed in five seconds by an IBM 360/75 computer.