Magnetic penetration depth in V3Si and LiTi2O4 measured by μSR

Muon spin relaxation (SR) studies have been performed in the normal spinel LiTi₂O₄ and the A-15 superconductor V₃Si to measure the magnetic penetration depth . The relaxation rate(T) 1/² in field-cooled measurements shows a sharp increase belowT _c followed by saturation at low temperatures in both systems. This feature implies an isotropic energy gap without anomalous zeros, and most likelys-wave pairing. The low temperature penetration depth (T 0) is determined to be 2100Å for LiTi₂O₄ and 1300Å for V₃Si respectively. Assuming a clean limit relation ^–2 n _s /m ^*, we derive the Fermi temperatureT _F n _s/ ^2/3 m ^* from the relaxation rate and the Sommerfeld constant asT _F ^3/4–1/4. Unlike conventional superconductors, both LiTi₂O₄ and V₃Si have a large ratio ofT _c /T _F 0.01, only slightly smaller than those ratios in more exotic superconductors.We thank C. Ballard and K. Hoyle for technical assistance. Work at Columbia University is supported by NSF Grant No. DMR-89-13784 and Packard Foundation (YJU). Ames Laboratory is operated for the U. S. Department of Energy by Iowa State University under Contract No. W-7405-Eng-82. Work at Ames was supported by the Director for Energy Research, Office of Basic Energy Sciences.     

Possible candidates for discrete gamma rays linking superdeformed and yrast states in an odd nucleus:193Pb

The francium isotopes^200–202Fr were produced in the reaction³⁵Cl+¹⁷⁰Yb using bombarding energies of 4.9–5.3 MeV/nucleon. Fusion products were separated in-flight from the primary beam using a gas-filled recoil separator. An alpha line with the alpha particle energy and half-life of (7468±9) keV and (19 ₋₆ ⁺¹³ ) ms, respectively, was assigned to²⁰⁰Fr. Previously reported decay properties of^201,202Fr were confirmed. Communicated by V. Metag     

Amperometric detection of pyridine nucleotides via immobilized viologen-accepting pyridine nucleotide oxidoreductase or immobilized diaphorase

The immobilization and electrical connection of a viologen-accepting pyridine nucleotide oxidoreductase (VAPOR) on an electrode surface by coadsorption with an amphiphilic pyrrole viologen and electropolymerization of this pyrrole monomer are described. The immobilized VAPOR catalyzes the reduction of NAD(P)(+) to NAD(P)H by the viologen redox couple (V(2+2+)). The sensitivity of this biosensor is 1.4 and 2.5 mA M(-1) cm(-2) for NAD(+) and NADP(+) respectively. The immobilization of diaphorase within a laponite gel adsorbed on an electrode surface is described. The incorporation and electropolymerization of Methylene Blue in the biolayer allows an electron transfer communication between diaphorase molecules and the electrode surface. The diaphorase electrode thus obtained responds to NADH at 0 V. The sensitivity and detection limit of this biosensor are 11.2 mA M(-1) cm(-2) and 1 muM respectively.     

Coordination properties of 6-deoxy-6-[1-(2-amino) ethylamino]-β-cyclodextrin and the ability of its copper(II) complex to recognize and separate amino acid enantiomeric pairs

The functionalized cyclodextrin 6-deoxy-6-[1-(2-amino)ethylamino]--cyclodextrin was synthesized, and an NMR, EPR, pH-metric, and calorimetric investigation was carried out in aqueous solution in order to ascertain its behaviour towards protonation and copper(II) complex formation. The thermodynamic parameters of the ternary complex formation with alanine, phenylalanine and tryptophan enantiomeric pairs were also determined (25° C andI=0.1 mol dm^–3). No thermodynamic enantioselectivity was observed in these systems, while a chiral, though poor, discrimination was observed in LEC: c.d. spectra also show enantiomeric stereoselectivity. The results of the present investigation, compared with previously reported results, suggest the occurence of acis-complex trans-complex equilibrium in such systems.     

Mortality of iterated Gallai graphs

For a finite or infinite graphG, theGallai graph (G) ofG is defined as the graph whose vertex set is the edge setE(G) ofG; two distinct edges ofG are adjacent in (G) if they are incident but do not span a triangle inG. For any positive integert, thetth iterated Gallai graph ^t (G) ofG is defined by ( ^t–1(G)), where ⁰(G):=G. A graph is said to beGallai-mortal if some of its iterated Gallai graphs finally equals the empty graph. In this paper we characterize Gallai-mortal graphs in several ways.