Calorimetric study of the reactions of n-alkylphosphonic acids with metal oxide surfaces

The reaction enthalpies for the solution-phase self-assembly of n-alkylphosphonic acids on the surfaces of TiO2 and ZrO2 have been determined using isothermal titration calorimetry at 298 K. The reaction enthalpies were negative (exothermic) for methyl- and n-octylphosphonic acids and positive (endothermic) for n-octadecylphosphonic acid with both metal oxides. The enthalpy/energy analysis showed that the net enthalpy of the formation of self-assembled monolayers (SAMs) at solid-liquid interface can be presented as follows: DeltaHr=-D-(DeltaHsol+DeltaHdil)-(ES-ESAM), where D is the binding energy of the SAM molecules with the solid; DeltaHsol and DeltaHdil are the enthalpies of dissolution and dilution; ES and ESAM are the surface energies of bare solid and SAM, respectively. This equation predicted an increase (and the sign change) of the reaction enthalpy as the alkyl group in n-alkylphosphonic acid increased, which explained the experimental data. Using this equation, the binding energy (D) in the SAMs of n-octyl- and n-octadecylphosphonic acids were estimated: 55+/-5 kJ/mol (for ZrO2) and 58+/-7 kJ/mol (for TiO2).     

Charge-transfer complexation as a general phenomenon in the copigmentation of anthocyanins

Color intensification of anthocyanin solutions in the presence of natural polyphenols (copigmentation) is re-interpreted in terms of charge transfer from the copigment to the anthocyanin. Flavylium cations are shown to be excellent electron acceptors (E(red) approximately -0.3 V vs SCE). It is also demonstrated, for a large series of anthocyanin-copigment pairs, that the standard Gibbs free energy of complex formation decreases linearly with EA(Anthoc) - IP(Cop), the difference between the electron affinity of the anthocyanin, EA(Anthoc), and the ionization potential of the copigment, IP(Cop). Based on this correlation, copigmentation strengths of potential candidates for copigments can be predicted.     

On the Non-parametric Prediction of Conditionally Stationary Sequences

We prove the strong consistency of estimators of the conditional distribution function and conditional expectation of a future observation of a discrete time stochastic process given a fixed number of past observations. The results apply to conditionally stationary processes (a class of processes including Markov and stationary processes) satisfying a strong mixing condition, and they extend and bring together the work of several authors in the area of non-parametric estimation. One of our goals is to provide further justification for the growing practical application of non-parametric estimators in non-stationary time series and in other `non-i.i.d.' settings. Some arguments as to why such estimators should work very generally in practice, often in a nearly `optimal' way, are given. Two numerical illustrations are included, one with simulated data and the other with oceanographic data. An erratum to this article is available at .     

An orbital perturbation approach of enzymatic catalysis

An orbital perturbation approach of enzymatic catalysis is proposed. Orbital symmetry restrictions to a fast reaction pathway is lifted by first order perturbation of the catalyst potential. The drastic decrease of the energy gap is a second order effect enhance by the band-like structure of the enzymes. The model incorporates conformational specify and signals the importance of the low symmetries of the active sites. It is proposed that allosteric effects are due to shifts of the enzyme band structure.     

Comparison of neutron activation analysis from five ceramic standards of the C.R.A.M. Caen and the Perlman/Asaro-standard

The elemental concentration of the ceramic standard material F, G, H, J and K of the Centre de Recherches Archéologiques Médiévales, Université de Caen have been determined based upon the Perlman/Asaro Standard. The analysis has been done by instrumental neutron activation analysis. Results are given for Fe, Na, K, Ba, Co, Cr, Cs, Eu, Ga, La, Lu, Mn, Rb, Sc, Ta, Yb.     

Variational cellular method for polyatomic molecules: SF6

This is the third paper on the cellular method for polyatomic systems. We show how to deal with nonspherical Coulomb potentials. We also show how to modify the variational expression for the energy eigenvalues so as to obtain a faster convergence in the angular momentum series for the wavefunctions. We apply both techniques to the self-consistent calculation of SF₆. Contrary to what we obtained in CH₄ and SiH₄, the cellular method cannot yield the correct equilibrium interatomic distance in the present case. The calculated ionization potentials are in the correct order but are all shifted by 2–3 eV. This shift is attributed to the wrong expression for exchange correlation.     

Structural ordering and chemical stability of a complex perovskite oxide DyBa2ZrO5.5 with YBa2Cu3O7-δ superconductors

2 ZrO_5.5 has been synthesized by solid-state reaction. Structural ordering in this material has been studied by X-ray diffraction (XRD). The XRD spectra reveal that DyBa₂ZrO_5.5 has an ordered complex cubic perovskite structure. The presence of superstructure reflections in the XRD spectra is characteristic of A₂BB’O₆-type crystalline structure. The chemical stability of DyBa₂ZrO_5.5 with YBa₂CuO_7-δ (YBCO) superconductors has been studied by XRD and electrical resistivity measurements. These studies show that DyBa₂ZrO_5.5 is chemically stable with YBCO and there is no degradation in the superconducting transition temperature T_c of YBCO even when mixed up to 1:1 vol%, with DyBa₂ZrO_5.5 in YBCO. Detailed study of the superconducting transition region shows that T_c(onset) and T_c(0) values of pure YBCO and YBCO–DyBa₂ZrO_5.5 composites are similar in both cases. The implications are discussed. Accepted: 13 October 1997     

On End-Extensions of Models of ¬exp

Every model of IΔ₀ is the tally part of a model of the stringlanguage theory Th-FO (a main feature of which consists in having induction on notation restricted to certain AC⁰. sets). We show how to “smoothly” introduce in Th-FO the binary length function, whereby it is possible to make exponential assumptions in models of Th-FO. These considerations entail that every model of IΔ₀ + ¬exp is a proper initial segment of a model of Th-FO and that a modicum of bounded collection is true in these models. Mathematics Subject Classification: 03F30, 03C62, 68Q15.     

Large amplitude solitary waves in a multicomponent plasma with negative ions

When the concentration of negative ions is larger than a critical value, a small compressive pulse evolves into a subionic wave train and a large pulse develops into a solitary wave. The threshold amplitude and velocity of the solitary waves are measured and compared with predictions using the pseudopotential method.