Study of the peak effect phenomenon in single crystals of 2H-NbSe2

The weakly pinned single crystals of the hexagonal 2H-NbSe₂ compound have emerged as prototypes for determining and characterizing the phase boundaries of the possible order-disorder transformations in the vortex matter. We present here a status report based on the ac and dc magnetization measurements of the peak effect phenomenon in three crystals of 2H-NbSe₂, in which the critical current densities vary over two orders of magnitude. We sketch the generic vortex phase diagram of a weakly pinned superconductor, which also utilizes theoretical proposals. We also establish the connection between the metastability effects and pinning.     

Total synthesis of d-(+)-biotin

A total synthesis of d-(+)-biotin is described starting from d-(+)-glucosamine using acyliminium chemistry.     

Shaping Solid-State Supramolecular Cavities: Chemically Induced Accordionlike Movement of gamma-Zirconium Phosphate Containing Polyethylenoxide Pillars

The hydrophilic oxygen atoms of polyethylenoxide chains inserted as pillars in gamma-zirconium phosphate form hydrogen bonds with the acid groups of the host. As a result the pillars are almost perpendicular to the gamma layers. Upon changing the pH level of the supernatant solution the hydrogen bonds are broken and the pillars become almost perpendicular to the layers (shown schematically). Thus there is a reversible enlargement-shortening of the interlayer space.     

Recent results from the TCV tokamak

During the first two years of operation, the TCV tokamak has produced a large variety of plasma shapes and magnetic configurations, with 1.0B _tor1.46T,I _p800kA,k2.05, –0.71. A new shape control algorithm, based on a finite element reconstruction of the plasma current in real time, has been implemented. Vertical growth rates up to 1000s^–1 have been stabilized using the external coil system. Ohmic H-modes with Troyon factors ( _tor aB/I _p) up to two and densities up to 2.25×10²⁰m^–3, corresponding to the Greenwald limit, have been obtained in diverted discharges. Limiter H-modes with line averaged electron densities up to 1.7×10²⁰m^–3 have been obtained in elongated D-shaped plasmas with 360 kAI _P600 kA.Presented at 17^th Symposium Plasma Physics and Technology, Prague, June 13–16, 1995.This work was partly supported by the Fonds National Suisse de la Recherche Scientifique.     

Pyrimidinethiol as a reagent for extraction separation of platinum metals and gold Determination of Pd(II), Os(VIII) and Ru(III)

The solvent extraction separation of Pt(IV), Pd(II), Os(VIII), Ru(III) and Au(III) from one another and also from Rh(III) and Ir(III) with 1-(2'-nitro-4'-tolyl)-4,4,6-trimethyl-(1H, 4H)-2-pyrimidinethiol has been investigated. Photometric procedures have been developed for the determination of Pd(II), Os(VIII) and Ru(III) with the same reagent. The reagent allows the enrichment of Pd(II) and Au(III) at the trace level from a large volume of aqueous medium even in the presence of base metals. The method can be used for the determination of platinum metals and gold in alloys.     

Eco‐friendly,ultrasound‐assisted,and facile synthesis of one‐pot multicomponent reaction of acridine‐1,8(2H,5H)‐diones in an aqueous solvent

A one‐pot, multistep synthesis of acridine‐1,8(2H,5H)‐diones ( 4a–m ) was achieved by three‐component reaction of dimedone ( 1 ) with an aromatic aldehyde ( 2a–m ) and an ammonium acetate ( 3 ) using water as a green solvent without any catalyst and a simple, easily handled, and ultrasonic technique as well as conventional method.