Linear congruence relations for 2-adic L-series at integers

In the paper we find a further generalization of congruences of the K. Hardy and K. S. Williams [5] type which seems to be a full generalization of congruences of G. Gras [4]. Moreover we extend results of [5], [7], [8], [9] and in part of [6]. We apply ideas and methods of [2], [7] and [9].     

An exactly solvable model for a ternary solution with three-body interactions and orientationally dependent bonding

A model is considered in which the bonds of a honeycomb lattice are covered by rodlike molecules of types AA, BB, and AB. Neighboring molecular ends have three-body and orientation-dependent interactions. The model is shown to be equivalent to a spin-1/2 Ising model on the same lattice with a field, but with only pairwise interactions. Symmetric and asymmetric coexistence surfaces for the separation into an AA-rich and a BB-rich phase are calculated exactly.     

Cholinesterase immobilisation on the surface of screen-printed electrodes based on concanavalin A affinity

This paper reports a new method for the immobilisation of acetylcholine esterase (AChE) on the surface of screen-printed electrodes (SPEs) based on the affinity between the glycoprotein enzyme and concavalin A (Con A). The surface of the working electrode has been modified with a Nafion layer that contains graphite, the mediator 7,7,8,8-tetracyanoquinodimethane (TCNQ) and heptylamine. The enzyme-free SPEs were characterised by cyclic voltammetry in buffer solutions and amperometry using cysteamine as analyte. The AChE immobilisation process leads to the sandwich structure: electrode-carbohydrate-Con A-enzyme. The first step of the immobilisation is the covalent activation of an amino group bound in a Nafion layer. The following steps are based on the affinity. The non-specific adsorption has been totally eliminated using BSA solutions at two different pHs. Various amounts of enzyme, from 0.1 to more than 2 mIU AChE, have been loaded on the electrode surface. The method offers the advantage of a free diffusion, which allows obtaining a response time of less than 2 min. An operational stability of more than 10 measurements was registered, while the active surface of the electrode was successfully reloaded for three consecutive times without any important change of the analytical performances.     

The partition of ethoxylated non-ionic surfactants between two non-miscible phases

The partition of a polydispersed ethoxylated non-ionic surfactant in equilibrated oil–water systems has been studied at 25 °C. The model surfactant used was a commercial sample of nonylphenol ethoxylated with 10 moles of ethylene oxide (NPEO₁₀). The partition isotherms over the range of surfactant concentration including the critical micelle concentration (CMC) were made with n-hexane, i-octane and n-decane as oil phases. Each partition isotherm exhibits a change of slope that matched the CMC value of surfactant determined by surface tension measurements on aqueous solutions. During the partition of NPEO₁₀ in the oil–water systems, the oligomer distribution in the oil and water phases changed because of fractionation. Below CMC, the mean ethoxylation degree in the oil phase was smaller, whereas in water it was higher than the mean initial value of the surfactant. Moreover, the mean ethoxylation degree in both oil and water phase was practically independent of surfactant concentration. Above CMC, the mean distribution of ethoxymers decreased in both phases. This was ascribed to the competition between micelles from water and the oil phase for the more hydrophobic species of the surfactant. The mean distribution of ethoxymers in the aqueous phase asymptoted to a value that was the mean of the surfactant itself, whereas it steeply decreased in the organic phase.     

Nonlinear calibrations on the assay of dilitiazem and two of its metabolites from plasma samples by means of liquid chromatography and ESI/MS(2) detection: application to a bioequivalence study

The assay of diltiazem (DLTZ) and its active metabolites desacetyldiltiazem (DAcD) and desmethyldiltiazem (DMeD) in plasma samples was achieved by means of an HPLC/(ESI)MS(2) method. The diastereoisomer of diltiazem, namely {(2R,3S)-5-[2-(dimethylamino)ethyl]-2-(4-methoxyphenyl)-4-oxo-2,3,4,5-tetrahydro-1,5-benzothiazepin-3-yl acetate} was used as internal standard (IS). Sample preparation was based on protein precipitation by means of organic solvent addition (acetonitrile). The isocratic elution based on a reversed-phase mechanism allows good separation of the analytes within 15 min. Atmospheric pressure electrospray ionization was used. All analytes were monitored in the MS(2)-MRM mode. A fragmentation schema is proposed for the target compounds. As the method was designed for bioequivalence purposes, a full validation procedure was considered. On validation, nonlinear calibrations were observed. Consequently, concentration intervals requiring nonlinear calibrations are discussed. Low limits of quantification in the 0.6-1 ng/mL concentration range were obtained. The analytical method was successfully applied to a single dose (120 mg), open-label, randomized, two-period, two-sequence, crossover bioequivalence study of two commercially available solid oral dosage pharmaceutical formulations (tablets).     

Error estimates for mixed finite element discretization of the Richards equation

We present a numerical scheme based on the mixed finite element method (MFEM) for the Richards equation, a nonlinear, degenerate parabolic equation. Due to the degeneracy, the solution of the equation has low regularity and therefore only lower order finite elements are recommended. We review the main posibilities for proving the convergence of the scheme. Especially for the case without using the Kirchhoff transformation a new result is given. We also briefly discuss how to solve the nonlinear fully discrete problems appearing at each time step and refer to papers where the convergence of these methods is rigurously studied. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microtubule dynamics depart from the wormlike chain model

Thermal shape fluctuations of grafted microtubules were studied using high resolution particle tracking of attached fluorescent beads. First mode relaxation times were extracted from the mean square displacement in the transverse coordinate. For microtubules shorter than approximately 10 microm, the relaxation times were found to follow an L2 dependence instead of L4 as expected from the standard wormlike chain model. This length dependence is shown to result from a complex length dependence of the bending stiffness which can be understood as a result of the molecular architecture of microtubules. For microtubules shorter than approximately 5 microm, high drag coefficients indicate contributions from internal friction to the fluctuation dynamics.     

On the metric structure of non-Kähler complex surfaces

We give a characterization of a locally conformally K?hler (l.c.K.) metric with parallel Lee form on a compact complex surface. Using the Kodaira classification of surfaces, we classify the compact complex surfaces admitting such structures. This gives a classification of Sasakian structures on compact three-manifolds. A weak version of the above mentioned characterization leads to an explicit construction of l.c.K. metrics on all Hopf surfaces. We characterize the locally homogeneous l.c.K. metrics on geometric complex surfaces, and we prove that some Inoue surfaces do not admit any l.c.K. metric. Received: 23 July 1998 / Revised: 2 June 1999     

Adsorption of poly(vinyl formamide-co-vinyl amine) onto silica particle surfaces and stability of the formed hybrid materials

In order to produce silica/polyelectrolyte hybrid materials the adsorption of the polyelectrolyte poly(vinyl formamide-co-vinyl amine), P(VFA-co-VAm) was investigated. The adsorption of the P(VFA-co-VAm) from an aqueous solution onto silica surface is strongly influenced by the pH value and ionic strength of the aqueous solution, as well as the concentration of polyelectrolyte. The adsorption of the positively charged P(VFA-co-VAm) molecules on the negatively charged silica particles offers a way to control the surface charge properties of the formed hybrid material. Changes in surface charges during the polyelectrolyte adsorption were studied by potentiometric titration and electrokinetic measurements. X-ray photoelectron spectroscopy (XPS) was employed to obtain information about the amount of the adsorbed polyelectrolyte and its chemical structure. The stability of the adsorbed P(VFA-co-VAm) was investigated by extraction experiments and streaming potential measurements. It was shown, that polyelectrolyte layer is instable in an acidic environment. At a low pH value a high number of amino groups are protonated that increases the solubility of the polyelectrolyte chains. The solvatation process is able to overcompensate the attractive electrostatic forces fixing the polyelectrolyte molecules on the substrate material surface. Hence, the polyelectrolyte layer partially undergoes dissolving process.