Electrical and optical characterization of thrombin-induced permeability of cultured endothelial cell monolayers on semiconductor electrode arrays

Impedance spectroscopy and phase-contrast microscopy are combined to monitor the electrical and morphological properties of human umbilical vein endothelial cell monolayers. The cells were cultured on optically transparent indium-tin-oxide (ITO) semiconductor electrode arrays coated with collagen IV, and the effect of the inflammatory mediator thrombin on monolayer permeability was monitored in real time. ITO electrodes provide several advantages for these kinds of experiments, because they are optically transparent, polarizable and highly sensitive due to the absence of insulating oxide layers. A qualitative correlation between the thrombin-induced gap formation and the electrical parameters of the cell layer is established. Received: 8 August 2000 / Accepted: 2 March 2001 / Published online: 20 June 2001     

Synthesis and in situ FTIRS characterization of conducting polymers obtained from aminobenzoic acid isomers at platinum electrodes

The electrochemical homo-polymerization of o-, m- and p-aminobenzoic acids has been performed on Pt electrodes in perchloric acid aqueous medium by cyclic scanning of the potential. Different limit potentials were employed to obtain thin polymeric films. When the switching potential was extended beyond the respective monomer oxidation peak, a rather degraded material was obtained. In situ FTIR spectroscopy has been used to characterize the redox response of films synthesized at the lower potential limits. Characteristic absorption features related with benzenoid and quinoid rings and different types of C-N bonds suggest the presence of redox processes similar to those undergone by the parent compound polyaniline. In addition, the existence of a chemical interaction between -COOH and -NH- groups in the reduced state of the three homopolymers studied can be suggested. Carbon dioxide has been detected at potentials higher than 1.0 V (RHE) irrespective of the polymeric material, thus indicating its degradation.     

Characterization of the interphase in an aluminium/epoxy joint by using controlled pressure scanning electron microscopy coupled with an energy dispersive X-ray spectrometer

The aim of this work is to introduce the use of low vacuum scanning electron microscopy (LVSEM) coupled with an X-ray energy dispersive spectrometer (EDS) in the field of structural adhesives, more precisely aluminium/epoxy resin assembly. Such assembly is characterized by the creation of an interphase resulting from the metal diffusion inside the resin during cross-linking. As the performance of the final bond is strongly links by the interphase properties, fine characterization of this interphase, in particularity the evaluation of its thickness is essential to understand the macroscopic properties of the adhesive assembly. First, the EDS acquisition parameters were investigated in order to limit the sample/resin damage/degradation due to the incident electrons beam irradiation. Then a specific methodology of stacked profiles was defined to improve the precision of the measures. To evaluate the true Al diffusion profile, the impact of the interaction volume of incident electron in the material on the Al signal variation during the interface crossing was calculated and the effect of the gas pressure on the electron beam characteristic and so on the measured profiles was examinated.According to our developed methodology and data treatments, Al diffusion profile was interpreted and interphase thickness was qualitatively determined by comparison with an experimental baseline. This innovative methodology promotes the use of LVSEM–EDS in the field of adhesive structural assemblies, but also, deals with a comparative study on the effect of the gas pressure on the EDS profile analysis.     

Heat transfer enhancement of ice storage systems: a systematic review of the literature

Journal of Thermal Analysis and Calorimetry - Thermal resistance of ice slows down the charging/discharging process of ice storage systems which results in long operating cycles and thus high...     

A CLASS OF DIFFERENTIAL SYSTEM WITH AT MOST FOUR ALGEBRAIC LIMIT CYCLES

A class of quartic and quintic differential system is introduced.We show that under suitable assumptions,one,two or four algebraic limit cycles can occur.These limit cycles are analytically given.     

A conductometric biosensor for the estimation of the number of cleaving sites in peptides and proteins

A conductometric enzyme biosensor using proteinase K was developed and then tested to relate its electrical signal to the number of proteinase K hydrolysis sites in bovine serum albumin (BSA) and angiotensin, a ten amino acid peptide, with one cleaving site.The conductometric sensor presents a large linear range of response for BSA and angiotensin ranging from 0.5 to 8 mg/l and from 4 to 8 mg/l, respectively. For a same tested concentration (mg/l), the response for native BSA is 12 times higher than for angiotensin. Aspartam was used as negative test and no response was obtained with the proteinase K biosensor. The conductometric sensor permitted also to detect difference on enzyme activity on native and non-native BSA, a response three times higher was obtained for non-native BSA.     

From the mathematical kinetic theory for active particles on the derivation of hyperbolic macroscopic tissue models

This paper deals with the derivation of macroscopic equations from the underlying kinetic model delivered by the kinetic theory of active particles with discrete microscopic states. Hyperbolic models for local density and mean velocity are obtained with the aim at adding further knowledge to mathematical methods for modelling living matter.