Incommensurate and commensurate magnetic long-range order in metallic REPd3 compounds of rare earths (RE=Nd,Tb, Dy,Er, Tm,Yb)

Compared to previous bulk magnetic measurements unusual magnetic ordering phenomena were detected by systematic neutron scattering experiments performed in the temperature range of 7 mKT300 K on the series of cubic metallic compounds REPd₃ of the rare earths RE=Nd, Tb, Dy, Er, Tm and Yb. Except for ErPd₃ withT _N =3 K the observed critical temperatures are compatible with the de Gennes scaling. The complexity of long-range magnetic ordering increases with decreasing 4f ⁿ occupancy, ranging from ferro- or ferrimagnetism in YbPd₃ and DyPd₃ via commensurate antiferromagnetic ordering in ErPd₃ and TmPd₃ [k=(1/2, 1/2, 0)] to incommensurate antiferromagnetic ordering of modulated type in TbPd₃ and NdPd₃. Both RKKY interactions, crystalline electric field, hybridization with 4d states of Pd as well as nuclear spin polarization in the case of RE=Nd appear to be of importance for the magnetic properties of REPd₃ systems.     

Improvement of the Froissart-Martin bound for complex scattering angles

Extension of the Froissart-Martin bound for complex scattering angles is improved using the solution of the Dirichlet boundary value problem for doubly connected domain. The Froissart-Martin bound for physical scattering angles is used as input value on one of the two boundaries. The obtained bound is valid in an ellipse smaller than the Lehmann-Martin one. Possiblities of further improvements and applications are discussed. Details will be published elsewhere (Chaichian M., Fischer J., Nelipa N. F.,Vrko I. Preprint of the University of Helsinki, HU-TFT-81-22, to be published).Abstract of the paper presented at the International Symposium Selected Topics in Quantum Field Theory and Mathematical Physics, Bechyn, Czechoslovakia, June 14–19, 1981.     

Ammoxidation of halogen-substituted toluenes on V-P-oxide catalysts

The ammoxidation of various halogen-substituted toluenes on crystalline vanadium phosphate catalysts was investigated. The monophosphates and the NH₄VOP₂O₇ are transformed into new NH₄-containing V-P-oxides. The (VO)₂P₂O₇ used is stable in time on stream. These structures are very active and selective ammoxidation catalysts.

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. NH₄VOP₂O₇ V-P , NH₄. (VO)₂P₂O₇ . .

     

Stress driven shear bands and the effect of confinement on their structures--a rheological, flow visualization, and Rheo-SALS study

An equimolar mixture of a cationic surfactant, cetylperidinium chloride (CPyCl), and salt sodium salicylate (NaSal) forms wormlike micelles in aqueous solutions. Under shear, the solution shows a pronounced shear-thickening behavior, which is coupled with oscillations in shear rate and the apparent viscosity. In this shear-thickening regime shear bands form, which also oscillate in position and intensity. These shear bands are visualized by direct imaging and Rheo-small angle light scattering methods. Temporal intensity fluctuations of the shear bands were evaluated using image analysis. Fourier transformations (FT) of the oscillating shear rate and intensity of the shear bands showed a single dominating frequency in the power spectrum analysis. This characteristic frequency as well as the amplitude of shear rate fluctuation was found to increase with stress. From the rheological and optical measurements, we propose that a stress driven mechanism is responsible for the formation of shear bands. Experiments performed in transparent parallel-plate geometry show dampening of the shear rate oscillations and increase in the characteristic frequency with decrease in the gap. Power spectrum analysis and the SALS measurements confirm the formation of different structures as a function of gap size in the parallel-plate geometry.     

Synthese und Struktur von Silber(II)-tetrafluoroaurat(III) Ag[AuF4]2

Synthesis and Structure of Silver(II) Tetrafluoroaurate(III) Ag[AuF₄]₂ Intensive green single crystals of Ag[AuF₄]₂ can be obtained by heating up micro crystalline Ag[AuF₄]₂ in autoclaves (p(F₂) ～ 200 bar, T ～ 400°C, t ～ 14 d). It crystallizes monoclinic, space group P2₁/n ? C; (No. 14) with a = 522.3(1), b = 1101.3(3), c = 550.5(2) pm, β = 94.98(3), Z = 2 and is isotypic with Pd[AuF₄]₂.     

Chromatographic speciation of anionic and neutral selenium compounds in Se-accumulating Brassica juncea (Indian mustard) and in selenized yeast

Selenium-accumulating plants such as Brassica juncea (Indian mustard) concentrate the element in plant shoots and roots. Such behavior may provide a cost-effective technology to clean up contaminated soils and waters that pose major environmental and human health problems (phytoremediation). Such ability to transform selenium into bioactive compounds has important implications for human nutrition and health. Element selective characterization of B. juncea grown in the presence of inorganic selenium under hydroponic conditions provides valuable information to better understand selenium metabolism in plants. The present work determines both previously observed organoselenium species such as selenomethionine and Se-methylselenocysteine and for the first time detects the newly characterized S-(methylseleno)cysteine in plant shoots and roots when grown in the presence of selenate or selenite as the only selenium source. A key feature of this study is the complementary role of selenium and sulfur specific chromatographic detection by HPLC with interfaced inductively coupled plasma mass spectrometry (ICP-MS) detection and by derivatization GC with interfaced atomic spectral emission. HPLC-ICP-MS limits of detection for such species were in the range 5-50 ng Se mL(-1) in the injected extracts. Speciation profiles are compared with those of selenium-enriched yeast by both HPLC-ICP-MS and GC-AED.     

Ansamycine, 5. Mitt., Chemie der Metacycloprodigiosine

In order to obtain a better partition of a prodigiosin derivative in biological media, two hydroxy groups were introduced into theansa-part of the molecule. The synthesis of the title compound is described in detail.     

Norrish Type I Cleavage of Aliphatic Carboxylic Acids and Esters in Solution. A CIDNP.-study

UV.-irradiation of pivalic and isobutyric acid and their methyl esters as well as of α-hydroxy isobutyric and malonic acid in solution lead to chemically induced dynamic nuclear polarization (CIDNP.) of parent compounds and of various reaction products. CIDNP.-effects and product distributions confirm α-cleavage of the C(α), CO bond to be the major mode of photodecomposition. Scavenger experiments indicate that decomposition of the molecules from a triplet excited state is roughly equally or more probable than from a singlet excited state. Quantum yields of educt disappearance are also given for the methyl esters of pivalic and isobutyric acid.