The β-γ phase transition in titanite and the isosymmetric analogue in malayaite

X-ray diffraction technique and hard mode infrared spectroscopy were used to study the thermal behaviour of synthetic titanite, CaTiSiO₅, two natural titanite samples and iso-structural malayaite, CaSnSiO₅. Both pure minerals show a thermal anomaly near 500 K. Specific heat measurements show an intermediate phase in synthetic titanite. Impurities in titanite tend to suppress the discontinuity near 500 K. The β-γ transition near 820 K is not affected by Fe and Al defects in the natural material. Infrared studies in malayaite show a change of the temperature dependence of the phonon frequencies. X-ray experiments show weak structural rearrangements with heating but no evidence of a symmetry breaking phase transition near 500 K The character of the 500 K anomaly in malayaite is more similar to the β-γ transition (825 K) than the α-β Mtransition (496 K) in synthetic titanite.     

Infrared evidence for the folded-chain model of trans-1,4-polybutadiene

The influence of the first-order crystalline transformation at about 60°C on the infrared bands of trans-1,4-polybutadiene yields microscopic information that supports the two-component microcrystalline model of a folded chain having loose and tight end loops at the lamellar surfaces. The temperature dependence of the band parameters of the 908-cm^?1 vinyl band indicates that 1,2-(side vinyl) units are not easily taken into the crystalline component, thus forming long loops at the crystal surface that account for the micro-Brownian motion detected in the low-temperature phase. The results argue that infrared band parameters are excellent probes for details of the thermodynamics and morphology of polymers.     

On Free Energies of the Ising Model on the Cayley Tree

We present, for the Ising model on the Cayley tree, some explicit formulae of the free energies (and entropies) according to boundary conditions (b.c.). They include translation-invariant, periodic, Dobrushin-like b.c., as well as those corresponding to (recently discovered) weakly periodic Gibbs states. The weakly periodic measures are defined through a partition of the Cayley tree that induces a 4-edge-coloring on that tree. We compute the density of each color. We use these densities for computations of free energies corresponding to a weakly periodic b.c.     

New chiral ruthenium(II)–phosphinite complexes containing a ferrocenyl group in enantioselective transfer hydrogenations of aromatic ketones

A new and versatile class of unsymmetrical ferrocenyl-phosphinite ligands possessing a stereogenic center has been prepared from commercially available, inexpensive aminoacids such as, d-, l-phenylglycine and d-, l-phenylalanine, through a concise synthetic procedure. These ligands are not very sensitive to air and moisture, and display good enantioselectivities in the ruthenium-catalyzed asymmetric transfer hydrogenation of acetophenone derivatives, in which up to 91% ee was obtained. A comparison of the catalytic properties of amino alcohols and other analogues based on a ferrocenyl backbone is also discussed briefly. The structures of these ligands and their corresponding complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis.     

Synthesis of substituted cyclopropanes from vinylarenes and esters in the presence of Cl n AlEt3 − n and Cp2ZrCl2 as catalyst

A procedure has been developed for the selective synthesis of 1-alkoxy(cycloalkoxy)-1-alkyl-(cycloalkyl)-2-arylcyclopropanes in up to 75% yield by reaction of vinylarenes with aliphatic and cycloalkylacetic acid esters in the presence of Cl _n AlEt_{3 ? n} and Cp₂ZrCl₂ as catalyst.     

Thermodynamics and correlation functions of plasmas and electrolyte solutions

We consider multi-component electrolyte solutions and plasmas in thermal equilibrium and define thermodynamic quantities for number densities which do not necessarily satisfy the condition of charge neutrality. It is shown that these quantities play a role in compressibility theorems for the pair correlation functions and in the generalized Debye shielding length. A fourth moment condition for the pair correlation functions is derived. We discuss to what extent non-uniform systems may be described in terms of local thermodynamics with added coulomb interactions.