Investigation of the association of the 1-dodecene-lauryl alcohol bicomponent system

The 1-dodecene-lauryl alcohol bicomponent system was investigated as an exemplary one, able to form the hydrogen-bonded mixed multimers, involving the olefinic double bond π-electrons. We applied the following analytical techniques: IR spectroscopy, dielectric permeativity measurements, and examinations taking advantage of the cellulose sorbents.     

Principal component analysis application in polycyclic aromatic hydrocarbons “mussel watch” analyses for source identification

This article aims to show how a careful pre-treatment of data can be used to demonstrate various features embedded in a given data set obtained from a “mussel watch” survey, namely site- and source-specific characteristics and weather-related changes, and to provide indications so as to allow comparison with analyses performed on another substrate matrix. Polycyclic aromatic hydrocarbons (PAHs) biomonitored in the aquatic environment by means of caged mussels are compared by site and by season. Moreover, their fingerprints were compared to marine sediments and atmospheric airborne PAHs. The characterization of the sampling stations by means of the multivariate technique called principal component analysis (PCA) allows distinguishing the prevalence of pyrogenic or petrogenic types of pollution and between two kinds of combustibles. This was confirmed by jointly analyzing the percent composition of sea (mussel) and air (filter) samples.     

F + operators and classes associated with some classes of unbounded operators

In this paper we study in a unified way the classes of all weakly compact, weakly completely continuous, unconditionally converging and Rosenthal operators in relation to a naturally associated class of operators and we generalise certain results of [9] and [10] for unbounded operators acting between normed spaces. Supported in part by DGICYT Grant PB 94-1052 (Spain).     

On weighted inequalities for martingale transform operators

For 1 < p < ∞, the almost surely finiteness of is a necessary and sufficient condition in order to have almost surely convergence of the sequences {E(f|?_n)} with f ∈ L^p(v dP). This condition is also equivalent to have weighted inequalities from L^p(v dP) into L^p(u dP) for some weight u for Doob's maximal function, square function and generalized Burkholder martingale transforms. Similarly, E(u|?₁) < ∞ turns out to be necessary and sufficient for the above weighted inequalities to hold for some v.     

Numerical solution of a nonuniquely solvable Volterra integral equation using extrapolation methods

In this work the numerical solution of a Volterra integral equation with a certain weakly singular kernel, depending on a real parameter μ, is considered. Although for certain values of μ this equation possesses an infinite set of solutions, we have been able to prove that Euler's method converges to a particular solution. It is also shown that the error allows an asymptotic expansion in fractional powers of the stepsize, so that general extrapolation algorithms, like the E-algorithm, can be applied to improve the numerical results. This is illustrated by means of some examples.     

On Neumann Operators

We give a sufficient condition for the validity of the implication lim_n→∞ Tⁿx=0⇒∑^∞_n=0Tⁿxconverges, whereT:X→Xis a bounded linear operator,Xis a Banach space, andx∈X. From this condition we derive the results given by other authors. Moreover, we give some properties about the operators that verifies the above implication, which are called Neumann operators.     

Amperometric detection of cationic neurotransmitters at nafion-coated glassy carbon electrodes in flow streams

Substantial improvements in amperometric monitoring of flowing streams are obtained by using Nafion-coated working electrodes. The charged coating tends to exclude anionic and neutral interferences, thus adding a new dimension of selectivity to electrochemical detection for flow-injection and liquid-chromatographic systems. A highly selective response is observed for cationic neurotransmitters in the presence of otherwise interfering substances (e.g., ascorbic acid, uric acid, bilirubin or chlorpromazine). The permselectivity and transport characteristics are evaluated with respect to solution pH, solvent, flow rate, film thickness, and other variables. The reduced flow-rate dependence results in low noise levels and detection limits of 0.04 and 0.10 ng of norepinephrine and epinephrine, respectively. A bilayer electrode coating, with a cellulose acetate film over the Nafion layer, offers a bifunctional (selectivity, protection) capability. Applicability to urine samples is demonstrated.     

Novel conjugated molecules from oxidation of a cyclopentadienone iron tricarbonyl complex

Oxidation of tetrakis-diethylaminocyclopentadienone iron tricarbonyl (1) electrochemically or with nitrosonium hexafluorophosphate afforded the dication of tetrakisdiethylaminocyclopentadienone (3). Oxidation of 1 with bromine and aqueous workup gave diethylaminocyclobutenedione-N,N-diethylcarboxamide (4), which was also formed by the hydrolysis of 3. The structures of the products were confirmed by X-ray crystallography.