Properties of long superconducting variable thickness bridges

We have studied the properties of long (lengthL20m) superconducting threads (Pb of Sn) formed by pulse electrical breakdown in monocrystalline silicon. These variable thickness bridges have well defined dc and ac Josephson effects in wide temperature range. Some interesting results on the quasiparticle subharmonic gap structures are also reported.The authors would like to express their thanks to J.Móza and A.Neasová for technical assistance.     

Zur quantitativen Bestimmung von Jod in Milch

Zusammenfassung Die vonBarker und Mitarbeitern angegebene Methode der Blutjodbestimmung ist sehr einfach und genau. Sie wird auch zur Bestimmung des Jods in Milch empfohlen.

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Summary The blood iodine determination devised byBarker and associates is very simple and accurate. It is likewise recommended for the determination of iodine in milk.

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Résumé La méthode décrite parBarker et collaborateurs pour le dosage de l'iode dans le sang est simple et précise. Elle est également recommandée pour le dosage de l'iode dans le lait.

     

Thermal research of montmorillonite synthetized from the oxides SiO2-Al2O3-MgO-CaO

The thermal behaviour of synthetic montmorillonite of relatively simple chemical composition has been studied and interpreted. Montmorillonite was prepared by hydrothermal synthesis at 300° and 8.8 MPa during 165 hours. With the methods of DTA, DTG, TG, X-ray diffraction analysis, infrared spectroscopy and electron microscopy it was proved that the synthetic montmorillonite is a monomineral sample and no differences from natural montmorillonite were observed.

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Zusammenfassung Das thermische Verhalten synthetischer Montmorillonite verhältnismässig einfacher chemischer Zusammensetzung wurde untersucht und gedeutet. Montmorillonit wurde durch hydrothermische Synthese bei 300°C und 8.8 MPa in 165 Stunden hergestellt. Durch die Methoden der DTA, DTG, TG, Röntgendiffraktionsanalyse, Infrarotspektroskopie und Elektronenmikroskopie wurde erwiesen, daß synthetische Montmorillonit eine monominerale Probe ist und keine Abweichungen von natürlichem Montmorillonit beobachtet werden konnten.

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. 165 300° 8.8 . , , , , , .

     

Counter current extraction separation of rare earth traces

The discontinuous counter current extraction separation of radioactive traces of rare earth elements from each other was successfully performed by using a 96 stage automatic microscale counter current apparatus. Choice of the optimum composition of the aqueous phase (var. HNO₃ conc.) and organic phase [di-(2-ethylhexyl) phosphoric acid (HDEHP) in toluene] was made on the basis of the results of liquid-liquid extraction measurements. Providing sufficient content of HDEHP in the organic phase, the presence of macroamounts of uranium(VI) did not interfere with the individual separation of rare earth traces. Consequently, uranium was retained in the organic phase, while separated rare earth traces were redistributed into the aqueous phase. The methods of liquid-liquid extraction and extraction chromatography based on the use of HDEHP were compared. The present results confirm that the liquid-liquid extraction has the advantage to be selective for the separation of rare earth traces from each other and from the macroamount of uranium(VI).     

Apparent molar volumes and expansibilities of 1-octanol, 1-nonanol,and 1-decanol in dilute cyclohexane solutions

The densities of solutions of 1-octanol, 1-nonanol, and 1-decanol in cyclohexane up to concentrations of 1.56 mol kg^–1 were measured at temperatures between 20 and 60°C. The apparent molar volumes and expansibilities were found to be linearly dependent on solute concentration. The excess molar volume and the excess thermal expansion coefficient of the solute were derived from the partial molar volume of the solute at infinite dilution and the solute densities. In addition, the limiting partial molar volume of the solute is discussed in terms of the scaled particle theory.     

Separation and preconcentration of131I− and131IO 3 − in a liquid-liquid system

The application of isotope exchange in a liquid-liquid system for the separation and preconcentration of¹³¹I^– and¹³¹IO^3/– from water is described. For this purpose a solution of elemental iodine in tri-n-butyl phosphate diluted with toluene was used. The influence of various factors on the separation efficiency of¹³¹I was investigated. These are: time of the exchange, concentration of a carrier in the aqueous phase, concentration of I₂ in the organic phase, volume ratio of the phases, pH, foreign ions, storage of the organic phase, etc. The method is quite rapid and the selective preconcentration of these chemical forms of radioiodine from water can be accomplished even in the presence of the most important fission products. This method makes also possible to separate these chemical forms from each other under controlled pH conditions. The activity of the separated radioiodine can be measured advantageously, e.g., by homogeneous liquid scintillation counting after decolourization of the organic phase.     

Synthesis, crystal structures and magnetic properties of cyanide- and phenolate-bridged [M(III)NiII]2 tetranuclear complexes (M=Fe and Cr)

The binuclear complex NiII2L(H2O)2(ClO4)2(1) and the neutral tetranuclear bimetallic compounds [{M(III)(phen)(CN)4}2{NiII2L(H2O)2}].2CH3CN with M=Fe (2) and Cr (3)[H2L=11,23-dimethyl-3,7,15,19-tetraazatricyclo[19.3.1.1(9,13)]hexacosa-2,7,9,11,13(26),14,19,21(25),22,24-decaene-25,26-diol] have been synthesized and the structures of and determined by single crystal X-ray diffraction. and are isostructural compounds whose structure is made up of centrosymmetric binuclear cations [Ni2(L)(H2O)2]2+ and two peripheral [M(phen)(CN)4]- anions [M=Fe (2) and Cr (3)] acting as monodentate ligands towards the nickel atoms through one of their four cyanide nitrogen atoms. The environment of the metal atoms in 2 and 3 is six-coordinated: two phen-nitrogen and four cyanide-carbon atoms at the iron and chromium atoms and a water molecule, one cyanide-nitrogen and two phenolate-oxygens and two imine-nitrogens from the binucleating ligand L2- at the nickel atom build distorted octahedral surroundings. The values of the FeNi and CrNi separations through the single cyanide bridge are 5.058(1) and 5.174(2)A respectively, whereas the Ni-Ni distances across the double phenolate bridge are 3.098(2)(2) and 3.101(1) A (3). The magnetic properties of have been investigated in the temperature range 1.9-290 K. The magnetic behaviour of corresponds to that of an antiferromagnetically coupled nickel(II) dimer with J=-61.0(1) cm-1, the Hamiltonian being defined as H=-J S(A).S(B). An overall antiferromagnetic behaviour is observed for and with a low-lying singlet spin state. The values of the intramolecular magnetic couplings are J(Fe-Ni)=+17.4(1) cm-1 and J(Ni-Ni(a))=-44.4(1) cm-1 for and J(Cr-Ni)=+11.8(1) cm-1 and J(Ni-Ni(a))=-44.6(1) cm-1 for [H=-J(M-Ni)(S(M).S(Ni)+S(Ma).S(Nia))-J(Ni-Nia)S(Ni)S(Nia)]. Theoretical calculations using methods based on density functional theory (DFT) have been employed on in order to analyze the efficiency of the exchange pathways involved and also to substantiate the exchange coupling parameters.     

New 3d–4f supramolecular systems constructed by [Fe(bipy)(CN)4] and partially blocked lanthanide cations

The reaction of acetonitrile (1–5) and mixed acetonitrile/water 1:1 (6–9) solutions containing the cyanide-bearing [Fe(bipy)(CN)₄]⁻ building block (bipy = 2,2′-bipyridine) and the partially blocked [Ln(bpym)]³⁺ cation (Ln = lanthanide trivalent cation and bpym = 2,2′-bipyrimidine) has afforded two new families of 3d–4f supramolecular assemblies of formula [Ln(bpym)(NO₃)₂(H₂O)₃][Fe(bipy)(CN)₄] · H₂O · CH₃CN [Ln = Sm (1), Gd (2), Tb (3), Dy (4) and Ho (5)] and [Ln(bpym)(NO₃)₂(H₂O)₄][Fe(bipy)(CN)₄] [Ln = Pr (6), Nd (7), Sm (8), Gd (9)]. They crystallize in the P2₁/c (1–5) and P2/c (6–9) space groups and their structures are made up of [Fe(bipy)(CN)₄]⁻ anions (1–9) and [Ln(bpym)(NO₃)₂(H₂O)_n]⁺ cations [n = 3 (1–5) and 4 (6–9)] with uncoordinated water and acetonitrile molecules (1–5) which are interlinked through an extensive network of hydrogen bonds and π–π stacking into three-dimensional motifs. Both families have in common the occurrence of the low-spin iron(III) unit [Fe(bipy)(CN)₄]⁻ where two bipy–nitrogen and four cyanide–carbon atoms build a somewhat distorted octahedral surrounding around the iron atom [Fe–N = 1.980(3)–1.988(3) Å (1–5) and 1.988(2)–1.992(2) Å (6–9); Fe–C = 1.904(5)–1.952(4) Å (1–5) and 1.911(2)–1.948(3) Å (6–9)]. The main structural difference between both families concerns the environment of the lanthanide atom which is nine- (1–5)/10-coordinated (6–9) with a chelating bpym, two bidentate nitrate and three (1–5)/four (6–9) water molecules building distorted monocapped (1–5)/bicapped (6–9) square antiprisms. This different lanthanide environment is at the origin of the different hydrogen bonding pattern of the two families of compounds.     

Aspidosperma Alkaloids. A New Didehydrodimerization Mode of β-Anilinoacrylic Alkaloids by Anodic Oxidation

A regio- and stereoselective didehydrodimerization procedure, whose key step involves the anodic oxidation, allows the conversion of β-anilinoacrylic alkaloids belonging to the Aspidosperma class, typified by tabersonine ( 1 ) and its 3-oxo derivative 2 , into the hitherto unknown 16,10′-didehydro dimers 3 and 7 , respectively.