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ABSTRACTIn this contribution we show our results on the magnetotactic bacterium Magnetospirillum gryphiswaldense concerning the growth of this bacterium in batch cultures, biochemical analysis (proteins and fatty acids profile), the (respiratory) oxygen consumption in iron -rich and iron-limited cultures, magneto-aerotactic behaviour of the cells, magnetic characterization of intact cells and isolated magnetosomes, and magnetosome isolation. We propose a magneto-mechanic model of magnetosome chain with special aim to further develop nanoactuators and micromanipulators and claim that magnetotactic bacteria could be used for in vivo synthesis of gold nanoparticles and for heavy metals biosorbtion.

Electron paramagnetic resonance (EPR) of Mn2+ions revealed their distribution on different structural units of a 2B2O3PbO glass matrix doped with MnO. Octahedral symmetric sites, tetragonally distorted, were detected. The progressive clustering of manganese ions was evidenced when the MnO content increased. EPR and magnetic susceptibility data revealed that both Mn2+and Mn3+ions are simultaneously present in the glass matrix and the transition from isolated ions in samples with x≤1 mol % to those involved in dipole–dipole interactions for samples with x≤30 mol % and antiferromagnetically coupled ions when x>30 mol %.

AbstractIn order to study the influence of substitutions and of the ionic radii of B’ ions on structure and phase transitions, we present some physical measurements and data on Pb2B′B″O6(B”=W, Nb, Mo) complex perovskite compounds. By Mn and Fe substitution for Mg in Pb2MgWO6compound a change in lattice parameters and shift of antiferroelectric transition temperature is observed. It appears that in all three series of compounds a linear dependence between ferroelectric or antiferroelectric transition temperature and B’ ionic radii is observed.

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EPR and magnetic susceptibility investigations on the $$x{\text{V}}_{\text{2}} {\text{O}}_{\text{5}} \cdot {\text{(100}} - {\text{x)[2P}}_{\text{2}} {\text{O}}_{\text{5}} \cdot {\text{PbO]}}$$ glass system with 020 mol %) suggests the increase of the associated ion number coupled by superexchange interactions. This result is consistent with magnetic susceptibility data for >3 mol % where the temperature dependence of magnetic susceptibility is described by the Curie–Weiss type law with a negative paramagnetic Curie temperature. The magnetic susceptibility results allowed the estimation of the V4+/V4++ V5+ratio in the sample studied.

Two vitreous oxide systems, i.e. 2B2O3· SrO and 2B2O3· SrF2containing CuO within a wide range of concentration, were investigated. The influence of a gradual increase in CuO content on the glass structure and the effect of the oxygen partial replacement by fluorine atoms were revealed. EPR absorption spectra show Cu2+ions in axially distorted octahedral environments. No clusters of Cu2+ions were detected. Mixed valence states of copper ions were revealed, especially at high CuO content. The influence of composition changes when using SrO or SrF2as network-modifiers upon the valence state and distribution of copper ions was also revealed. By means of IR spectroscopy the dependence of the BO4\BO3ratio on the CuO content and the presence of F atoms in the glass matrix was estimated.

The effects of gamma irradiation on structure and electric properties of Pb2MgWO6 (PMW) are presented. Gamma irradiation produces damage centers which introduce a lattice strain reflected in broadening of X-ray diffraction lines. Antiferroelectric transition in PMW becomes diffuse and Tc increases as a consequence of gamma-dose increases.

IR and Raman spectra of x(CuO·V2O5)(1−x)[3B2O3·K2O] glasses, with 0≤x≤0.5, have been measured and analysed in order to identify the spectral contribution of each component and to point out the role of V and Cu ions on the structure of the glass network. Thermal diffusivity of these vitreous materials, measured by photoacoustic technique, is sensitive to the microstructural changes induced by transition metal ions.

The structural investigation of the xMnO(100−x)[2P2O5·PbO)] vitreous system with 0≤x≤50mol% was realised using IR spectroscopy, electron paramagnetic resonance (EPR), magnetic susceptibility and photoacoustic (PA) measurements. The characteristic frequencies of different atomic group vibrations were identified. The dependence of the position and shape of these bands with the MnO content of these glasses was explained. The EPR and magnetic susceptibility data suggest that in these glasses the Mn ions exists only in divalent state; these ions are isolated or participate to dipole–dipole interactions. The concentration dependence of the thermal diffusivity coefficient shows that complex structural changes appear in these glasses for x≤5mol%, in agreement with IR and EPR data.

The results of X-ray, electron microscopy, magnetic measurements, Mössbauer effect, electron paramagnetic resonance and electrical resistivity studies on 20Fe2O380 [3B2O3 (1-x)PbOxGeO2] glasses are reported. Two sets of samples with 0?x?25 mol % GeO2 equilibrated at 1250° C and 1150° C, respectively, were investigated. All the samples were in the amorphous state. The number of ferrous ions in glasses equilibrated at 1250° C decreased by increasing the GeO2 content. In the case of the samples melted at 1150° C no evidence of Fe2+ ions was shown by magnetic and Mössbauer effect measurements. The magnetic susceptibility for T>80 K obeys a Curie-Weiss law and the effective moments of iron cations may be described by the free-ion values. The influence of the glass matrix composition and the equilibration temperatures on the intensities of g=2.00 and g=4.20 resonance lines is analysed. The EPR data suggest a clustering tendency of the iron ions in samples equilibrated at 1150° C. The resistivity measurements may be described by a mechanism involving electron hopping. The presence of two activation energies is shown. Finally, the experimental data are correlated in order to give a unitary description of the physical behaviour of the analysed glass system.

By using X-ray diffraction analysis, EPR and magnetic measurements, the chromium-ion distribution in xCr2O3-(1-x) [3B2O3-PbO] glasses with 0?x?35 mol% Cr2O3 was studied. EPR investigation evidenced the presence of both Cr3+ and Cr5+ ions, the latter being in small proportion, in agreement with the atomic magnetic moment values. For concentrations x?20 mol% Cr2O3 the isolated Cr3+ ions coexist with those coupled by super-exchange magnetic interactions, the isolated ones prevailing only for x<3 mol% Cr2O3. For x>20 mol % Cr2O3 microcrystalline precipitates were detected, giving rise to an antiferromagnetic transition with Néel temperature, NN?310 K and paramagnetic Curie temperature, ?p=-480 K.

Three-pulse sequences in the presence of magnetic field gradients at high magnetic fields produce multiple nonlinear stimulated echoes (NOSE) at timesnτ1after the third pulse, wherenis an integer and τ1the interval between the first two pulses. These phenomena are due to the demagnetizing field produced by the spatial modulation of the nuclear magnetization arising in the sample after the first two pulses. The theory is presented and compared with experiments. The dependence of the NOSE amplitudes on the flip angles and on the pulse intervals is described. Implications for multidimensional NMR experiments based on sequences of three or more pulses in the presence of field gradients are discussed.

A sequence of three RF pulses in the presence of magnetic field gradients at high magnetic fields (≳7 T) produces multiple nonlinear stimulated echoes (NOSE) at timesnτ1after the third pulse, wherenis an integer and τ1the interval between the first two pulses. From the classical point of view, these phenomena are due to the demagnetizing field produced by the spatial modulation of the nuclear magnetization arising in the sample after the first two pulses. In this paper the behavior of NOSE for molecules containing inequivalent uncoupled spins subject to motional averaging of short-range interactions is reported. As a consequence of the demagnetizing field the interference between the magnetizations of the different spin ensembles leads to beats in the amplitude of NOSE. A semiclassical formalism describing this dependence is established and verified in test experiments with the protons in a methyl acetate sample.

Various methods have been used to study the physical properties of the V2O5-Fe2O3 and V2O5-Fe2O3-Li2O systems, including X-ray, electron microscope, Mössbauer effect, NMR and thermogravimetric measurements. The iron ions are approximately equally distributed in substitutional and interstitial sites in the V2O5 lattice. The maximum number of iron ions dissolved in the V2O5 matrix corresponds to 4 mol % Fe2O3. In all the samples a quantity of Fe2O3 which has not been included in lattice is observed. The V2O5-Fe2O3 and V2O5-Fe2O3-Li2O systems are formed from solid solutions mixed with very small Fe2O3 particles. The analysis of the charge compensation of iron ions suggests that V2O5 is a quasi-amorphous semiconductor. Irradiation of V2O5-based samples with an electron beam induces the V2O5 platelets to convert to the VOx phase.

The results of magnetic investigations onxCoO.(1-x)[2B2O3.K2O] glasses are reported. The magnetic properties of these glasses are dependent on the CoO content. For glasses withx > > 10 mol% CoO, the Co2+ ions are coupled antiferromagnetically.

Magnetic and ESR investigations on xEu2O3(1 — x) [3B2O3 · PbO] glasses in the temperature range 77 to 300 K are reported. The experimental data show a modified Curie-Weiss behavior. The paramagnetic Curie temperatures are negative indicating an antiferromagnetic order at lower temperatures. The Curie constants indicate the presence of europium ions in two valence states (2+ and 3+), in agreement with ESR data.

Photoacoustic and UV-VIS spectroscopy, magnetic susceptibility and electron paramagnetic resonance measurements have been performed on soda-phosphate glasses in order to explain the changes in the valence states of Cr and the structure of the Cr2O3incorporated in these glasses.

EPR absorption spectra of Cu2+ were investigated in vitreous matrices of the system [70TeO2-25B2O3-5PbO] over a wide range of concentrations. The detected absorptions are strongly dependent on the matrix composition. Fluctuations of the ligand field were evident in the Cu2+ environment. The concentration of the paramagnetic species that cause the EPR absorptions decreases considerably at the upper limit of the investigated compositional range.

The thermal conductivity and thermal diffusivity of thexFe2O3 · (1-x) [3 B2O3 · PbO] glasses containing 0, 5, 15, 25, 35 and 50 mol % Fe2O3 were studied. Measurements were performed at temperatures ranging from 100 to 450 K. From the results obtained for thermal conductivity and diffusivity the specific heats of samples were calculated and comparated with those obtained from the additive rules. Our results do not prove the validity of the additive rules. The observed deviations were assigned to structural factors. By using the approximation of the Debye model the average sound velocity, the mean free path and dominant angular frequency of phonon have been calculated. The deviation of phonon mean free path from the average value as a function density fluctuations of the samples was discussed.

The biological wastewater treatment is based on biofilms activity. The biofilms can be fixed on biofilm carriers, that are made from varied materials, but most of them are made from high density polyethylene. The authors propose other mixtures of varied materials to obtain an increased load of microorganisms on biofilm carriers. During the experiments the load of microorganisms was increased up to 250% compared to the load on polyethylene biofilm carriers. Also, for the aerated biological tanks an innovative aeration system made from stainless steel pipes with fine pores (<1 mm) realized by electro-erosion, is proposed.

The temperature dependence of the magnetic susceptibility of xMnO · (1 − x)[70TeO2· 25B2O3· 5PbO] glasses with 0 10 mol% both, Mn2+and Mn3+ions are present, which explains their magnetic behaviour.

EPR and magnetic susceptibility measurements have been performed on xCr2O3· (1 − x)[Bi2O3· PbO] glasses with 0