Nonlinear behaviour of simple ionic systems in hydrogel in an electric field

The stationary behavior of ionic reaction-transport systems contained in hydrogel located between two reservoirs of electrolytes is investigated. The effects of the applied voltage, the composition of the electrolytes in the reservoirs and the distribution of fixed charge in the hydrogel on the spatial patterns of charge, electric potential, temperature and concentrations of the individual components are studied systematically by mathematical modelling. Such systems, containing only several ions (for example, Cl-, K+, OH- and H+) can function as electrolyte diodes and transistors and can exhibit oscillations and hysteresis. The mathematical description of the studied systems is based on balances of species, enthalpy and charge, on Poisson's equation and on the finite rate description of the water dissociation/recombination reaction, without assuming local electroneutrality. The modeling results are compared with experiments, including the system with hydrogel connecting reservoirs of strong base and acid studied by Noszticzius and co-workers. [L.H. Hegedus, N. Kirschner, M. Wittmann and Z. Noszticzius, J. Phys. Chem. A, 1998, 102, 6491 (ref. 1); L. H. Hegedus, N. Kirschner, M. Wittmann, P. Simon and Z. Noszticzius, Chaos, 1999, 9, 283 (ref. 2).]

Electric Field Effects on an Enzyme Membrane Oscillator

A simple two compartment model system composed of a reservoir and a reactor is studied by means of numerical bifurcation analysis. An enzyme reaction involving ionic species is assumed to take place in the reactor connected to the reservoir

Influence of an external electric field on cAMP wave patterns in aggregating Dictyostelium discoideum

Effects of an external electric field on the propagation of excitable cyclic adenosin monophosphate (cAMP) pulses in aggregating cells of Dictyostelium discoideum have been studied by means of numerical simulations. The mathematical model includes a three-variable version of the Martiel-Goldbeter kinetic model of cAMP production by cells, and diffusion and electromigration of cAMP through intercellular space. Electric field effects on the planar pulses propagating in a spatially one-dimensional system and on circular and spiral pulses propagating in a spatially two-dimensional system include changes in the propagation velocities of pulses initiated in the field-free system, the annihilation of pulses propagating towards the cathode by electric fields of high intensities, and the formation of region(s) of spontaneous excitation permanently generating trains of cAMP pulses. The spiral patterns were found to drift in the electric fields of low intensities, fields of high intensities were found to decompose the spiral arms on the side facing the negative electrode.

Properties of polyethylene films with incorporated benzoic anhydride and/or ethyl and propyl esters of 4-hydroxybenzoic acid and their suitability for food packaging

Benzoic anhydride and ethyl and propyl esters of 4-hydroxybenzoic acid (ETP and PRP, respectively, also termed parabens) incorporated into low density polyethylene (LDPE) film were studied with regard to migration into food and food simulants at 6 degrees C and 25 degrees C, and changes in selected properties of the film were investigated. Antimicrobials were incorporated into polymer film in concentrations of 5 g/kg and 10 g/kg. The addition of parabens into the polymer was more difficult than benzoic anhydride due to their volatility. For benzoic anhydride, 30-40% and 10-20% of the added amount was found to leach from the film into aqueous and olive oil food simulants, respectively. The migration into both water and olive oil followed a very similar course in the case of parabens. Migration levels over 90% and in the range of 70% to 80%, relative to the amount of agent in the film, were determined for ETP and PRP respectively. The incorporation of antimicrobials into the film significantly changed the functional characteristics of the packaging material, i.e. permeability of oxygen, carbon dioxide and water vapour, tensile strength, coefficient of friction, sealing strength and transparency. Shelf life tests with packaged cheese and toasted bread demonstrated the efficiency of the film containing 10 g/kg of BA against mould growth on the food surface during storage at 6 degrees C.

[Pedicled osteocutaneous groin flap in the compound reconstruction procedures of the fingers]

The paper presents the authors own experiences with pedicled oseocutaneous groin flaps based on superficial circumflex iliac vessels with a vascularized bone graft (size ranging from 2.5 cm to 5 cm) from the ilium. Eight patients, 7 males and 1 female, (aged 9-46 years, mean age 24 years) were treated using this method because a bone defect of the first metacarpal bone or the middle phalanx of the III finger. The flap pedicle was cut off after 17-36 days. Treatment was successful in all patients, although complications of the healing process were noted in 7 flaps. In 5 cases an inflammatory reaction around the sutures or superficial necrosis of the skin was observed. In two cases extensive infection of the flap's tissues was noted which in one case lead to partial necrosis of the soft tissues.

Evaluation of key parameters in a potentiostatic corrosion test for dental amalgam

OBJECTIVES

Participation in a Round Robin study of potentiostatic corrosion test guidelines for dental amalgam was undertaken for the purpose of developing an accurate set of draft guidelines.

METHODS

Dispersalloy, sybraloy, aristalloy, phasealloy, and tytin were used as the amalgam specimens. They were prepared following the guidelines, then coupled to a copper wire, cemented into glass tubes, and polished to a 600-grit finish. A corrosion cell was prepared using a carbon counter-electrode, a standard calomel electrode (SCE) as the reference electrode, and amalgam as the working electrode. A 37 degrees C solution of 10 g/l NaCl with a minimum volume of 300 ml was used. Within 5 min of polishing, the open circuit potential (OCP) was recorded for 10 min. Next, the specimen was polarized to 0 mV versus SCE, and the currents were recorded for a 24-h time period. Corrosion results were analyzed statistically with one-way ANOVA (p < 0.05) and the multiple comparisons Student-Newman-Keuls post-hoc test.

RESULTS

Problems that occurred with evaporation, beaker size, carbon electrode length, SCE cap removal, glass tube fracture, polishing technique, and fresh electrolyte are easily avoidable with further explanation or reminder notes. Observations made concerning starting time, initial OCP recording, millivoltage, and solution temperature were determined to be necessary for the accuracy of test results. Analysis of results should include clarification of units, and graph interpretations. Finally, the number of specimens per amalgam should be increased from one to three so that statistical analysis can be performed. Using three specimens per amalgam, the method revealed corrosion susceptibility as measured by the improved test: aristalloy > sybraloy > (dispersalloy, phasealloy, tytin).

SIGNIFICANCE

Having run the initially proposed guidelines, a number of clarifying changes were made so that the corrosion susceptibilities of five dental amalgams could be clearly differentiated.

Galvanic interaction between titanium and gallium alloy or dental amalgam

OBJECTIVES

The objective was to examine in vitro the galvanic interaction between titanium and a high-copper dental amalgam or a gallium-based direct filling alloy at different area ratios, and to relate the observed interactions to the electrochemical characteristics of the alloys.

METHODS

The tested materials were cast titanium, a single-composition, spherical high-copper amalgam, and a gallium-based direct filling alloy. Polarization curves were recorded. The galvanic couples were prepared at Ti/filling alloy ratios of 1:1, 2:1, 4:1 and 6:1. The couples were exposed to synthetic saliva at 37 degrees C and the galvanic currents and potentials were measured as a function of time. The results were analyzed by ANOVA and Tukey tests (p < or = 0.05).

RESULTS

Freshly abraded titanium initially was anodic to both the amalgam and the gallium alloy, but the polarity reversed after a period of exposure. The galvanic potential and current density increased with the increasing Ti/alloy area ratio. The potential increase was smaller and the current increase larger for the Ga alloy than for the amalgam. The difference was consistent with the polarization characteristics. The galvanic current density was of the order of 10(-8) A/cm2 for the Ti/amalgam couple, and 10(-7) to 10(-6) A/cm2 for the Ti/gallium alloy couple.

SIGNIFICANCE

The results show that the galvanic interaction between titanium and direct filling alloys is small. High copper dental amalgams should suffer little galvanic corrosion when in contact with Ti. For gallium direct filling alloys, the galvanic interaction may be more detrimental because of the inherently lower corrosion resistance.