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[EN] The study of oxygen consumption rate under¿ in vivo¿ human cornea during contact lens wear has been technically a challenge and several attempts have been made in the last 20 years to model the physiology of the human cornea during contact lens wear. Unfortunately, some of these models, based on a constant corneal oxygen consumption rate, produce areas on the cornea where the oxygen tension is negative, which has no physical sense. In order to avoid such inconsistency, different researchers have developed alternative models of oxygen consumption, which predict the likely oxygen metrics available at the interface cornea/post lens tear film by determination of oxygen flux, oxygen consumption, and oxygen tension through the different layers (endothelium, stroma, and epithelium). Although oxygen deficiency produces corneal edema, corneal swelling, hypoxia, acidosis, and other abnormalities, the estimation of the oxygen distribution below the impact of a contact lens wear is interesting to know which lens transmissibility was adequate to maintain the cornea and avoid epithelial and stromal anoxia. The estimation of minimum transmissibility for a lens for extended wear applications will be very useful for both clinicians and manufacturers. The aim of this work is to present a complete discussion based on Monod kinetics model that permits give an estimation of oxygen partial pressure distribution, the profile distribution of corneal flux and oxygen consumption rate, and finally the estimation of the relaxation mechanism of the cornea depending on the oxygen tension at the interface cornea/post lens tear film. Relaxation time in this context can quantify the capability of the corneal tissue to adapt to increasing concentrations of oxygen. It is proposed this parameter as a biological meaningful indicator of the interaction between contact lens polymers and living tissues such as the corneal cellular layer.

[EN] In this paper we show a laboratory experience describing the possibility to build a sensor using a coil to measure small thicknesses of materials with the possibility of measuring temperature simultaneously, with the same built sensor. Its operation is based on the following facts: An electric current (a.c), flows through a coil and a magnetic field appears producing self-induction characterized by an electromotive force induced in the coil, when a conductive piece is situated in front of the coil. That permits us to obtain information about the distance between the coil and the conductive piece. When this separation thickness is changing, the magnetic field around the coil changes, because the self-induction coefficient (L) is also changing. Using resistance and impedance measurements (voltage in our case) in the coil, an expression has been obtained for the determination of the thickness of a non-conductive sheet placed between a metallic plate and the coil. Calibration measurements of resistance with temperature have been obtained. The thermodynamic analysis is also presented showing the equation of state of the system between the voltage, temperature and the thickness of the non-conductive sample. The linear thermal-expansion coefficient of the sample is also determined.

[EN] In this paper, a series of composite proton exchange membranes comprising a cobaltacarborane protonated H[Co(C2B9H11)(2)] named (H[COSANE]) and polybenzimidazole (PBI) for a high temperature proton exchange membrane fuel cell (PEMFC) is reported, with the aim of enhancing the proton conductivity of PBI membranes doped with phosphoric acid. The effects of the anion [Co(C2B9H11)(2)] concentration in three different polymeric matrices based on the PBI structure, poly(2,2 '-(m-phenylene)-5,5 '-bibenzimidazole) (PBI-1), poly[2,2 '-(p-oxydiphenylene)-5,5 '-bibenzimidazole] (PBI-2) and poly(2,2 '-(p-hexafluoroisopropylidene)-5,5 '-bibenzimidazole) (PBI-3), have been investigated. The conductivity, diffusivity and mobility are greater in the composite membrane poly(2,2 '-(p-hexafluoroisopropylidene)-5,5 '-bibenzimidazole) containing fluorinated groups, reaching a maximum when the amount of H[COSANE] was 15%. In general, all the prepared membranes displayed excellent and tunable properties as conducting materials, with conductivities higher than 0.03 S cm(-1)above 140 degrees C. From an analysis of electrode polarization (EP) the proton diffusion coefficients and mobility have been calculated.

The dielectric and mechanical spectroscopies of acetate of cis- and trans-2-phenyl-5-hydroxymethyl-1,3- dioxane are reported in the frequency domain from 10−2 to 106 Hz. This ester has been selected in this study for its predominant á relaxation with regard to the â relaxation, which can be neglected. This study consists of determining an interconversion algorithm between dielectric and mechanical measurements, given by using a relation between rotational and translational complex viscosities. These important viscosities were obtained from measures of the dielectric complex permittivity and by dynamic mechanical analysis, respectively. The definitions of rotational and translational viscosities were evaluated by means of fractional calculus, by using the fit parameters of theHavriliak-Negami empirical model obtained in the dielectric and mechanical characterization of the á relaxation. This interconversion algorithm is a generalization of the break of the Stokes-Einstein-Debye relationship. It uses a power law with an exponent defined as the shape factor, which modifies the translational viscosity. Two others factors are introduced for the interconversion, a shift factor, which displaces the translational viscosity in the frequency domain, and a scale factor, which makes equal values of the two viscosities. In this paper, the shape factor has been identified as the relation between the slopes of the moduli of the complex viscosities at higher frequency. This is interpreted as the degree of kinetic coupling between the molecular rotation and translational movements. Alternatively, another interconversion algorithm has been expressed by means of dielectric and mechanical moduli.

PURPOSE: We present an analysis of the corneal oxygen consumption Qc from non-linear models, using data of oxygen partial pressure or tension (P(O2) ) obtained from in vivo estimation previously reported by other authors. (1) METHODS: Assuming that the cornea is a single homogeneous layer, the oxygen permeability through the cornea will be the same regardless of the type of lens that is available on it. The obtention of the real value of the maximum oxygen consumption rate Qc,max is very important because this parameter is directly related with the gradient pressure profile into the cornea and moreover, the real corneal oxygen consumption is influenced by both anterior and posterior oxygen fluxes. RESULTS: Our calculations give different values for the maximum oxygen consumption rate Qc,max, when different oxygen pressure values (high and low P(O2)) are considered at the interface cornea-tears film. CONCLUSION: Present results are relevant for the calculation on the partial pressure of oxygen, available at different depths into the corneal tissue behind contact lenses of different oxygen transmissibility.