Thermal expansion of La3S4 at low temperatures

The thermal expansion of the superconductor La₃S₄ has been investigated on a single crystal by a capacitive method between 1.6 and 14 K. The relative length change shows a well pronounced second order phase transformation near 8.05 K, which is caused by the superconducting transition. From the calculated linear thermal expansion coefficient we determine the pressure coefficient of the transition temperature and of the thermodynamic critical field as well as the thermodynamic critical field itself. Furthermore we estimate the electronic, phononic and total Grüneisen parameters. These parameters have been used to discuss on the basis of the McMillan equation the reason for the increase of the transition temperature under pressure.     

Nonequilibrium potential approach: Local and global stability of stationary patterns in an activator-inhibitor system with fast inhibition

We study the formation and global stability of stationary patterns in a finite one-dimensional reaction-diffusion model of the activator-inhibitor type. The analysis proceeds through the study of the nonequilibrium potential or Lyapunov functional for this system considering the fast inhibitor case and, in order to obtain analytical results, the adoption of a piecewise linear version of the model. We have studied the changes in relative stability among the different patterns as the ratio between the diffusion coefficients is varied and have discussed the meaning of the different contributions to the nonequilibrium potential.     

Functionals of paths of a diffusion process and the Onsager-Machlup function

The Onsager-Machlup function for a one-dimensional diffusion processX _t is obtained by means of the Radon-Nikodym derivative of the measure in function space induced byX _t with respect to the measure corresponding to an auxiliary diffusion processY _t.     

Dynamic 13C NMR studies of ligand exchange in linear (d10) silver(I) and gold(I) and square-planar (d8) rhodium(I) homoleptic metal carbonyl cations in superacidic media

The dynamic CO exchange of the monovalent metal carbonyl cations [Ag(13CO)]+, [Au(13CO)2]+-Au(13CO) SO3F and [Rh(12CO)4-x(13CO)x]+ (x < or = 1) in superacidic solutions was studied by variable-temperature 13C NMR methods. The exchange rates are strongly dependent on the acidity of the solvent, the concentration of metal carbonyl cations and temperature. Whereas a suitable exchange rate of the Ag(I) system is only accessible in magic acid (HSO3F-SbF5), the more stable Au(I) and Rh(I) systems were studied in the less acidic fluorosulfuric acid. Selected solutions of Ag(I), Rh(I) and Au(I) yielded activation barriers deltaG* of 42.7, 43.5, and 56.2 kJ mol(-1) respectively.     

Studies on the separation of anions with 8-hydroxy-quinolinium ion as counterion

Distribution constants, K_D, for 8-hydroxyquinolinium-anion pairs and for a series of inorganic and organic anions are reported between aqueous acidic phases and 1-butanol and 3-methyl-1-butanol. As expected, K_D values are larger for anions with relatively large crystal radius (e.g., Cl^- < I^- < R-SO₃^-), smaller for anions containing either hydroxyl or carboxyl groups favoring solvation by water (e.g., HSO₄^-, HSeO₃^-, H₂PO₄^-, C₆H₅COO^-, CH₃COO^-) and larger in solvents with larger solubility parameters (e.g., 4-methyl-2-pentanone < 3-methyl-1-butanol < 1-butanol). Distribution constants between aqueous solutions and 8-hydroxyquinoline immobilized (chemically) on controlled-pore glass are estimated for a series of aromatic and aliphatic sulfonates. Aromatic sulfonates show substantially larger K_D values than aliphatic sulfonates. Batch equilibration data were used to design chromatographic (liquid-solid) separation of a few sulfonates.     

Über die Bestimmung der Anzahl dreiachsiger Ellipsoide aus der Anzahl ihrer Schnittellipsen in zufälligen Schnittebenen

Summary A diagram is given for reading off the shape-factor oftri-axial ellipsoids ( = average distance between parallel tangent planes over all orientations).The knowledge of permits the calculation of the number of ellipsoids present per unit volume from the number of elliptical sections observed per unit area.     

The magnetic field dependence of the structural transition temperature in La3S4 and La3Se4

The magnetic field dependence of the structural transition temperature T_m from the cubic to the tetragonal phase has been determined for single crystals of La₃S₄ and La₃Se₄. The observed field dependence of T_m can be accounted for by the band Jahn-Teller model of the coupling of an e_g-band to the shear mode of the cubic lattice without invoking any coupling to acoustic or optical phonons.     

Elimination reactions in dimethyl sulfoxide solution. The effective base with potassium tert-butoxide.

Deuterium labeling studies have established that elimination of a cyclooctylammonium iodide with dimsyl anion in DMSO proceeds through an ylide intermediate while elimination with KOC(CH₃)₃ in DMSO involves an E2 mechanism. The effective base with KOC(CH₃)₃/DMSO is shown to be the alkoxide ion.     

High critical magnetic field superconductor La3S4

We report electrical conductivity, specific heat and magnetization measurements on La₃S₄ single crystals. The results show, that La₃S₄ is a strong coupling superconductor with a BCS coherence length of 132 Å. This extremely low value makes La₃S₄ an intrinsic high critical magnetic field superconductor with a Landau-Ginsburg parameter κ₀ of 20. For the temperature gradient of the upper critical magnetic field at the transition temperature we find values up to 35 kG/K.