ac conductivity of anhydrous pellicular zirconium phosphate in hydrogen form

Aqueous suspensions of delaminated zirconium phosphate have been recently obtained in our laboratory by a suitable intercalation-deintercalation of alkylamines. By filtering these suspensions thin and flexible sheets or pellicles of lamellar α-zirconium phosphate, with the most part of the layers oriented parallel to the pellicle surface, can be easily prepared. ac conductivity measurements have been carried out, in the temperature range 150–300°C, on pellets made of α-Zr(HPO₄)₂ pressed pellicles, oriented both parallel and perpendicular to the electric field. Independently of the pellet orientation, a slope variation was observed in the Arrhenius plot at about 220°C. As already found for the α-Zr(HPO₄)₂ powder, this is associated with a phase transition at this temperature, which causes a discontinuous change of the interlayer distance from 7.4 Å to 6.8 Å. The conductivity of samples oriented parallel to the electric field ($\text{～10}{}^{\mathrm{?4}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}\text{at}\text{300°}\text{C}$) is about two orders higher than the conductivity of the anhydrous microcrystalline powder, which, in turn, is higher than that of perpendicularly oriented samples ($\text{～3 × 10}{}^{\mathrm{?7}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}\text{at}\text{300°}\text{C}$).     

Nonlinear evolution equations andH theorems

We prove a structure theorem for evolution equations in the state space of a discrete classical system fulfilling a class ofH theorems. TheseH theorems are proved to give strong implications on the time behavior of the solutions. All the results are demonstrated by examples (Boltzmann-like equations, for example).     

Non-stationary random response of a finite cable

Numerous problems of current concern involve the designs of aerodynamic systems which either travel at high speeds or contain structural elements which are excited by moving pressure fluctuations. In a number of recent papers responses of dynamic systems to random excitation have been considered. The appropriate theory for calculating the mean square response of linear systems to both stationary and non-stationary random excitation is well known [1–7]. In this paper, the mean square response of a finite cable to non-stationary random excitation is considered. The non-stationary random excitation is of the form s(t) = e(t)α(t), where e(t) is a well defined envelope function and α (t) is the Guassian, narrow band, stationary part of the excitation which has zero mean. Both the unit step and rectangular step functions are used for the envelope function, and both white noise and noise with an exponentially decaying harmonic correlation function are used to prescribe the statistical property of the excitation. The results obtained are shown to be a complete expression for the mean square response when checked for accuracy by reduction to expressions previously obtained by Lyon [4]. It is felt that these results will aid the design of both linear and two-dimensional aerodynamic systems excited by random pressure fluctuations.     

Addition of organometallic radicals to organic substrates. Reaction between manganese decacarbonyl and α-dicarbonyl compounds

Some o-quinones and 1,2-diketones were allowed to react with manganese pentacarbonyl radicals generated in situ and the resulting persistent paramagnetic adducts studied by ESR spectroscopy. The evolution of carbon monoxide during the reaction together with the symmetrical distribution of the spin density in the organic framework (as implied by the spectral data) indicated chelation of a Mn(CO)₄ moiety by the two oxygens of the dicarbonyl substrates.One or more carbon monoxide groups can be replaced by compounds containing nitrogen, phosphorus, arsenic or antimony as binding sites. A conjugative transfer of spin density is proposed for the last three classes of substituents, while a σ mechanism is probably involved in the case of nitrogen-containing ligands.     

A problem relating to positive linear maps on matrix algebras

In this paper we investigate conditions under which two finite-dimensional density matrices can be transformed simultaneously into two other ones by means of a positive linear map which maps density matrices into density matrices. The result of this paper provides a complete answer in case of the matrix algebra of two-by-two matrices.     

Determination of urea in blood plasma by enzyme-pH electrode

Combination of gel-entrapped urease with a pH electrode can be used to measure plasma urea, provided that the response is related to an auxiliary pH electrode. The response time is 1–3 min and electrodes can be used for up to one week. Good correlation was obtained for routine samples with a spectrophotometric diacetyl monoxime method (y = 0.952x + 0.224, r = 0.996).     

A simple,direct synthesis of 3-vinylindoles from the carbocation-catalysed dehydrative cross-coupling of ketones and indoles. A combined experimental and computational study

A straightforward synthesis of a library of largely new 3-vinylindoles via a clean dehydrative coupling reaction between ketones and indoles has been developed. Highly stable, non-nucleophilic aryl(2-methylindol-3-yl)methylium salts have been used as efficient Lewis acid catalysts. The advantages of the reaction are the use of equimolar amounts of inexpensive and easily available reagents, the low catalyst amount, high atom efficiency, the production of only one molecule of water as a by-product and the mild reaction conditions. Computational studies of two specific reaction mechanism instances show that both steric and electronic effects heavily influence the nature of the final products, whether a methyl group in position 2 of the indole is present or absent.     

Contribution of individual flavonoids in Lysimachia species to the antioxidant capacity based on HPLC-DPPH assay

Quantitative phytochemical characterisation of the chief flavonoid aglycones in the hydrolysed Lysimachia extracts revealed the dominance of kaempferol, quercetin and myricetin in L. vulgaris, L. nummularia, L. punctata, L. christinae, L. ciliata and L. clethroides, respectively. Due to the significant radical scavenging capacity of the samples, the contribution of the individual aglycones to the total antioxidant activity became of interest. Therefore, a HPLC method coupled to pre-column DPPH scavenging assay was developed. Differences in the six Lysimachia species’ phenolic composition regarding their participation to the antioxidant activity were revealed. The participation of the three investigated flavonoids to the radical quenching activity was the highest (91.2%) in the L. vulgaris sample, the lowest in L. christinae sample with 29.6%. In L. vulgaris sample, the 76.3% contribution of quercetin to the scavenger capacity was the highest peak area decrement ratio among the investigated samples.