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.     

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.     

The application of the genetic algorithm to the minimization of potential energy functions

We adapted the genetic algorithm to minimize the AMBER potential energy function. We describe specific recombination and mutation operators for this task. Next we use our algorithm to locate low energy conformation of three polypeptides (AGAGAGAGA, A9, and [Met]-enkephalin) which are probably the global minimum conformations. Our potential energy minima are –94.71, –98.50, and –48.94 kcal/mol respectively. Next, we applied our algorithm to the 46 amino acid protein crambin and located a non-native conformation which had an AMBER potential energy 150 kcal/mol lower than the native conformation. This is not necessarily the global minimum conformation, but it does illustrate problems with the AMBER potential energy function. We believe this occurred because the AMBER potential energy function does not account for hydration.     

Acyloxyalkylidènephosphoranes—II : Etude des ω-acyloxy n-butylidènetriphénylphosphoranes. Nouvelle voie d'accès aux dihydro-3,4 2h-pyrannes

ω-Acyloxy n-butylidenetriphenylphosphoranes give α-acyl n-butylidenetriphenylphosphoranes by intermolecular condensation in t-BuOH, and 3,4-dihydro-(2H)-pyrans by intramolecular condensation in toluene. The α-acyl n-butylidene phosphoranes, which are the tautomeric form of α-acyloxaphosphanes, do not lead to cyclobutylketones but to dihydropyrans.     

Consequence of boar edible tissue consumption on urinary profiles of nandrolone metabolites. II. Identification and quantification of 19-norsteroids responsible for 19-norandrosterone and 19-noretiocholanolone excretion in human urine

In previous work (Le Bizec et al., Rapid Commun. Mass Spectrom. 2000; 14: 1058), it was demonstrated that a boar meal intake could lead to possible false accusations of abuse of 17beta-nortestosterone in antidoping control. The aim of the present study was to identify and quantify endogenous 19-norsteroids in boar edible tissue at concentrations that can alter the steroid urinary profile in humans, and lead to excretion of 19-norandrosterone (19-NA) and 19-noretiocholanolone (19-NE). The samples were analysed in two laboratories. The methodologies used for extraction and detection (GC/MS(EI) and LC/MS/MS(APCI+)) are compared and discussed. 19-Norandrostenedione (NAED), 17beta- and 17alpha-nortestosterone (bNT, aNT), and 17beta- and 17alpha-testosterone (bT, aT) were quantified. The largest concentrations of NAED and bNT were observed in testicles (83 and 172 microg/kg), liver (17 and 63 microg/kg) and kidney (45 and 38 microg/kg). A correlation between the bNT and NAED content of a typical meal prepared with boar parts and the excreted concentrations of 19-NA and 19-NE in human urine was demonstrated.     

The toxic effect of aluminium in vines

The split-root technique was used to study the effect of varying the growth media on the elemental content of nutrient elements in the roots of grape vines. The varieties 2-1 (R99 x Jacquez) and Sauvignon blanc (Vitis vinifera) were grown in Hoagland water culture with and without added aluminium. The elemental concentrations of Mg, Al, Si, P. S, Cl, K and Ca in the dried roots were determined by PIXE. Roots grown in Al-rich media were deficient in Mg and Ca, but enriched in Al. There was a correlation between Al and Si but the uptake differed in the two varieties.     

Etude de la cristallinite de derives n-octadecyliques de l'alcool polyvinylique obtenus par greffage chimique

Differential scanning calorimetry has been used to study the heats of fusion and melting transitions of n-octadecyl derivatives of polyvinyl alcohol. These derivatives were obtained by grafting paraffinic chains on polyvinyl alcohol, at various proportions. The melting transitions are independent of the degree of substitution; the heats of fusion are proportional to the fraction of crystallizable units. Using Flory's equilibrium crystallization theory, it is possible to interpret these results assuming, as demonstrated previously, that the chemical grafting is sequential with two unreacted hydroxyl groups between two adjacent paraffinic side-chains.     

A convenient synthesis of (2-styrylchromon-8-yl)acetic acids

(2-Styrylchromon-8-yl)acetic acids, structural analogs of (flavon-8-yl)acetic acid (FAA) have been synthesized with satisfactory yields according to two different methods. The ¹H and ¹³C nmr data fovor the S-trans stereoisomers.