Study of the basicity of some 1,2‐diazinium ylids

In this paper we present a study concerning the basicity of some new carbanion monosubstituted pyridazinium, 3‐methyl‐pyridazinium, 3‐(p‐halogenophenyl)‐pyridazinium and phtalazinium ylids. The pk_a values of the conjugated acids (salts) of ylids have been experimentaly determinated. Consequently, we have evaluated their basicity (k_b,) using the titration curves. The basicity depends mainly on the structure of the ylids carbanion itself, however the heterocycle's structures also has some influence on bacisity. Having in view the basicity, we have established certain correlations between basicity, structure and stability of the analised ylids.     

Approximation and Complexity: Liouvillean-Type Theorems for Linear Differential Equations on an Interval

Let u,v be solutions on an interval I of linear differential equations (LDEs) P=0 , Q=0 , respectively. We obtain a lower bound on the approximation of v by u in terms of bounds on the coefficients of LDE S _i =0 (for several i ), satisfied by the i th derivative of v and by the i th derivative of a basis of the LDE P=0 . One could view this result as a differential analog of the Liouville theorem which states that two different algebraic numbers are well separated if they satisfy algebraic equations with small enough integer coefficients. Unlike the algebraic situation, in the differential setting, in order to bound from below the difference |u-v| , we need to involve not only the coefficients of P,Q themselves, but also those of S _i . September 22, 2000. Final version received: March 11, 2001.     

Selecting the nature of imprinted molecular organosilica sieves with gallic acid via thermal analyses

The stability of the organosilica–gallic acid (GA) complex, and thus the strength of initial interactions which influences directly the sorption parameters of imprinted materials, is mostly given by the nature of co-monomers. Therefore, combining tetraethoxysilane, tetrametoxysilane, vinyl triethoxysilane and vinyl benzyl triethoxysilane as functional monomers, six formulations were obtained in order to optimise the nature of imprinted sieves. Vinyl benzyl trimethylammonium chloride and tertamethyl ammonium hydroxide directed the mesophase formation. Morphology and thermal properties of imprinted organosilica sieves were evaluated and compared to those of blank polymers synthesised in the same conditions as the imprinted ones but without GA. Thermal analysis results corroborated with the morphology of imprinted sieves were confirmed by specific GA sorption tests.     

Composition of an oxide layer formed by laser radiation and the structure of an oxide-metal interface on the surface of 9XC and P6M5 tool steels according to XPS

The composition of an oxide layer formed by pulse heating in air, and the layer of the oxide-metal interface structure on the surface of 9XC and P6M5 multicomponent alloys, were investigated by X-ray photoelectron spectroscopy (XPS) using a SPECS surface analysis system.     

Thermodynamic properties of tunneling quasiparticles in graphene-based structures

Thermodynamic properties of quasiparticles in a graphene-based structures are investigated. Two graphene superconducting layers (one superconducting component is placed on the top layered-graphene structure and the other component in the bottom) separated by oxide dielectric layers and one normal graphene layer in the middle. The quasiparticle flow emerged due to external gate voltage, we considered it as a gas of electron–hole pairs whose components belong to different layers. This is a striking result in view of the complexity of these systems: we have established that specific heat exhibits universal (?T³) behavior at low T, independent from the gate voltage and the superconducting gap. The experimental observation of this theoretical prediction would be an important step towards our understanding of critical massless matter.     

Electronic structure of a PbFe1/2Nb1/2O3 single crystal in the ferroelectric and paraelectric states, according to X-Ray photoelectron spectroscopy data and first principle calculations

Electronic structure of the PbFe_1/2Nb_1/2O₃ single crystal is studied by means of X-ray photoelectron spectroscopy on an ESCALAB 250 system and first principle FEFF9 at temperatures of 296 and 403 K.     

The study of the pyrolysis products of Ni (II) and Pd (II) chelate complexes as catalysts for the oxygen electroreduction reaction

Journal of Solid State Electrochemistry - Nitrogen-doped carbon materials were prepared by the pyrolysis of carbon black Vulcan XC-72 impregnated with nitrogen-containing Pd (II) and Ni (II)...     

Effect of sintering temperature on the chemical state of ions in the Ba1 − x Sr x TiO3 (x = 0.2) system,according to X-ray photoelectron spectroscopy data

The chemical state of ions in different samples of ceramics of the Ba_{1 ? x} Sr _x TiO₃ (x = 0.2) system produced by varying only a single technological parameter (sintering temperature T _S) is studied by means of X-ray photoelectron spectroscopy. The X-ray electron spectra of the Ba4d, Sr3d, O1s, and Ti2p levels reveal well-marked fine structures. As expected, the energy position and intensity of the features of this fine structure vary with T _S.     

Around a theorem of F. Dyson and A. Lenard: Energy equilibria for point charge distributions in classical electrostatics

We discuss several results in electrostatics: Onsager’s inequality, an extension of Earnshaw’s theorem, and a result stemming from the celebrated conjecture of Maxwell on the number of points of electrostatic equilibrium. Whenever possible, we try to provide a brief historical context and references.     

Approximation and Complexity II: Iterated Integration

We introduce two classes of real analytic functions W \subset U on an interval. Starting with rational functions to construct functions in W we allow the application of three types of operations: addition, integration, and multiplication by a polynomial with rational coefficients. In a similar way, to construct functions in U we allow integration, addition, and multiplication of functions already constructed in U and multiplication by rational numbers. Thus, U is a subring of the ring of Pfaffian functions [7]. Two lower bounds on the L _∈fty -norm are proved on a function f from W (or from U , respectively) in terms of the complexity of constructing f .