Microstructure of stomaflex based magnetic elastomers

Stomaflex elastomers filled with two types of magnetic particles (nano- and micro-sized) were investigated. It was observed that doping with Fe₃O₄ nanoparticles and applying a magnetic field during the polymerisation process led to a significant change in the local structure of the elastomer. Decreases in the quasi-crystalline phase concentration, in the average size of the crystalline blocks, and in the ordering distance were observed after doping the elastomer with magnetite nanoparticles. After filling the polymer with Fe₃O₄ nanoparticles, yet the elastomer fractal dimension changes. For the elastomer filled with a large amount of Fe microparticles (75% particle concentration) a texture effect is observed, and this effect is larger for the samples polymerised in a magnetic field. At all microparticle concentrations, these elastomers exhibit surface fractal structure.     

Isotope ratio monitoring gas chromatography/Mass spectrometry of D/H by high temperature conversion isotope ratio mass spectrometry

Of all the elements, hydrogen has the largest naturally occurring variations in the ratio of its stable isotopes (D/H). It is for this reason that there has been a strong desire to add hydrogen to the list of elements amenable to isotope ratio monitoring gas chromatography/mass spectrometry (irm-GC/MS). In irm-GC/MS the sample is entrained in helium as the carrier gas, which is also ionized and separated in the isotope ratio mass spectrometer (IRMS). Because of the low abundance of deuterium in nature, precise and accurate on-line monitoring of D/H ratios with an IRMS requires that low energy helium ions be kept out of the m/z 3 collector, which requires the use of an energy filter. A clean mass 3 (HD(+.)) signal which is independent of a large helium load in the electron impact ion source is essential in order to reach the sensitivity required for D/H analysis of capillary GC peaks. A new IRMS system, the DELTA(plus)XL(trade mark), has been designed for high precision, high accuracy measurements of transient signals of hydrogen gas. It incorporates a retardation lens integrated into the m/z 3 Faraday cup collector. Following GC separation, the hydrogen bound in organic compounds must be quantitatively converted into H(2) gas prior to analysis in the IRMS. Quantitative conversion is achieved by high temperature conversion (TC) at temperatures >1400 degrees C. Measurements of D/H ratios of individual organic compounds in complicated natural mixtures can now be made to a precision of 2 per thousand (delta notation) or, better, with typical sample amounts of approximately 200 ng per compound. Initial applications have focused on compounds of interest to petroleum research (biomarkers and natural gas components), food and flavor control (vanillin and ethanol), and metabolic studies (fatty acids and steroids). Copyright 1999 John Wiley & Sons, Ltd.     

Li–Zn ferrites with nonmagnetic additives

The authors investigated the effect of small additive amounts of non-magnetic ions as Na¹⁺, Ca²⁺, Zr²⁺, Sb³⁺ and binary or ternary combinations of these ions on some physical properties of the (Li_0.5Fe_0.5)_0.6Zn_0.4Fe₂O₄ ferrite used in high frequency. It was found that by the segregation of these additives on the grain boundaries, the grain growth is diminished and much higher sintered densities are obtained in several cases, though not all. We established that additives such as Na₂O, CaO, ZrO₂ enhance the rate of sintering, giving a speedy start to the sintering process. All additives improve the electrical resistivity due to insulating intergranular layers generated by segregation of additives.     

LiFe5O8 and BaFe12O19 Fine Particles Crystallised in a Glassy Matrix

We investigated the magnetic and microstructure properties of the Fe₂O₃ - Li₂O - B₂O₃ and Fe₂O₃ - BaO - B₂O₃ - Sb₂O₃ glass strips (with dimensions 50 mm long, 6 mm wide and about 30-100 mikrometer thick) subjected to various heat treatments. The irreversible structure changes produced by heat treatments, were investigated by X-ray diffraction and magnetic measurements. The magnetic behaviour is discussed in terms of the evolution of the size of LiFe₅O₈ and BaFe₁₂O₁₉ crystals dispersed in the glassy matrix, with thermal annealing.     

Bioleaching of UO2 2+ ions from a Romanian poor uranium ore

The present paper deals with an experimental study on the bioleaching of a poor uranium ore by means of hydrophytic plants Lemna minor and Riccia fluitans, under various operating conditions. The maximum degree of bioleaching (42%) of the reduced uranium species to U(VI) has been attained for the ore-Lemna minor-alkaline carbonate solution system. The UO₂ ²⁺ ions amount accumulated in the plants is negligible as compared to the dissolved quantity, owing to the ionic competition between uranyl ions and the cations necessary to the mineral nutrition. The X-ray diffraction patterns prove that the uranium species in pyrochlore mineral are completely oxidized to U(VI), while thucolite is only partially turned into UO₂ ²⁺ ions, in the presence of living plants.     

How does cold constrain life cycles of terrestrial plants and animals?

Short summer seasons with low thermal energy input characterise polar ecosystems. Climatic variables and physical isolation of terrestrial habitats act as selective filters which must be passed to allow colonisation, establishment and survival in these extreme environments. Life history studies of the terrestrial biota of such ecosystems give little evidence of adaptive responses to low temperatures having evolved in situ, even though behavioural, ecophysiological and biochemical features allowing tolerance of the likely extremes are well-developed. Observed life history strategies are often consistent with the general predictions of adversity (A) or stress (S) selection. However, biota successful in these extreme environments may be better-grouped by the lack of particular life history features, rather than common possession.