Study of catalytic homogeneous electrochemical reactions with reciprocal derivative chronopotentiometry using exponential time currents at spherical electrodes: Discrimination between transient and stationary conditions

Catalytic homogeneous electrochemical reactions have been studied with reciprocal derivative chronopotentiometry (RDCP) using an exponential time current both under transient and stationary conditions. The general expressions for the chronopotentiometric potential–time and derivative curves obtained are applicable for spherical electrodes of any radius, including planar electrodes and ultramicroelectrodes as limiting cases. The use of this programmed current has the particularity that it enables to achieve a stationary state very quickly, even when the chemical rate constants are not very high and, under these conditions a simple and quantitative characterisation of catalytic processes can be carried out. Moreover, the RDCP response is always peak-shaped, even for very high homogeneous rate constants for which the stationary response in cyclic voltammetry has a sigmoid feature. The experimental verification of the theoretical predictions has been carried out by analysing the electrocatalytic reduction of the heteropolyanion PW₁₂O₄₀^3? in an aqueous sulphuric media with an excess of nitrite.     

Sensory adaptation as Kalman filtering: theory and illustration with contrast adaptation

Sensory adaptation allows biological systems to adjust to variations in the environment. A recent theoretical work postulated that the goal of adaptation is to minimize errors in the performance of particular tasks. The proposed minimization was Bayesian and required prior knowledge of the environment and of the limitations of the mechanisms processing the information. One problem with that formulation is that the environment changes in time and the theory did not specify how to know what the current state of the environment is. Here, we extend that theory to estimate optimally the environmental state from the temporal stream of responses. We show that such optimal estimation is a generalized form of Kalman filtering. An application of this new Kalman-filtering framework is worked out for retinal contrast adaptation. It is shown that this application can account for surprising features of the data. For example, it accounts for the differences in responses to increases and decreases of mean contrasts in the environment. In addition, it accounts for the two-phase decay of contrast gain when the mean contrast in the environment rises suddenly. The success of this and related theories suggest that sensory adaptation is a form of constrained biological optimization.     

Coincidence detection with dynamic synapses

Recent experimental findings show that the efficacy of transmission in cortical synapses depends on presynaptic activity. In most neural models, however, the synapses are regarded as static entities where this dependence is not included. We study the role of activity-dependent (dynamic) synapses in neuronal responses to temporal patterns of afferent activity. Our results demonstrate that, for suitably chosen threshold values, dynamic synapses are capable of coincidence detection (CD) over a much larger range of frequencies than static synapses. The phenomenon appears to be valid for an integrate-and-fire as well as a Hodgkin-Huxley neuron and various types of CD tasks.     

Atrial activity extraction for atrial fibrillation analysis using blind source separation

This contribution addresses the extraction of atrial activity (AA) from real electrocardiogram (ECG) recordings of atrial fibrillation (AF). We show the appropriateness of independent component analysis (ICA) to tackle this biomedical challenge when regarded as a blind source separation (BSS) problem. ICA is a statistical tool able to reconstruct the unobservable independent sources of bioelectric activity which generate, through instantaneous linear mixing, a measurable set of signals. The three key hypothesis that make ICA applicable in the present scenario are discussed and validated: 1) AA and ventricular activity (VA) are generated by sources of independent bioelectric activity; 2) AA and VA present non-Gaussian distributions; and 3) the generation of the surface ECG potentials from the cardioelectric sources can be regarded as a narrow-band linear propagation process. To empirically endorse these claims, an ICA algorithm is applied to recordings from seven patients with persistent AF. We demonstrate that the AA source can be identified using a kurtosis-based reordering of the separated signals followed by spectral analysis of the sub-Gaussian sources. In contrast to traditional methods, the proposed BSS-based approach is able to obtain a unified AA signal by exploiting the atrial information present in every ECG lead, which results in an increased robustness with respect to electrode selection and placement.     

Qualitative differences between implicit and explicit sequence learning.

Four experiments investigate the differences between implicit and explicit sequence learning concerning their resilience to structural and superficial task changes. A superficial change that embedded the SRT task in the context of a selection task, while maintaining the sequence, did selectively hinder the expression of implicit learning. In contrast, a manipulation that maintained the task surface, but decreased the sequence validity, affected the expression of learning specifically when it was explicit. These results are discussed in the context of a dynamic framework (Cleeremans & Jime'nez, 2002), which assumes that implicit knowledge is specially affected by contextual factors and that, as knowledge becomes explicit, it allows for the development of relevant metaknowledge that modulates the expression of explicit knowledge. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conductive‐diamond electrochemical advanced oxidation of naproxen in aqueous solution: optimizing the process

BACKGROUND: Electrochemical advanced oxidation treatment using boron‐doped diamond (BDD) electrodes is a promising technology to treat small amounts of toxic and biorefractory pollutants in water. This process has been tested on the degradation of naproxen, a common pollutant drug present in surface waters. To optimize the process a series of experiments have been designed to study the interaction between four variables: pH (over the range 5–11); current (0–320 mA cm^?2); supporting Na₂SO₄ electrolyte concentration (0–0.375 mol L^?1); and solution flow rate (Q_v) between 3.64 and 10.8 cm³ min^?1. RESULTS: Among these variables the influence of current was the greatest, the second was the salt concentration, the third flow rate, and the fourth pH. An ANOVA test reported significance for seven of the fourteen variables involved and the degradation of naproxen was optimized using response surface methodology. CONCLUSIONS: Optimum conditions for naproxen removal (100%) were found to be pH = 10.70, Q_v = 4.10 cm³ min^?1, current density = 194 mA cm^?2 using a supporting electrolyte concentration of 0.392 mol L^?1. Copyright © 2010 Society of Chemical Industry     

Nonconventional Production of Glass Nanofibers by Laser Spinning

The production of very long glass nanofibers with lengths up to several centimeters was demonstrated using the Laser Spinning technique. It employs a laser to melt a small volume of a solid precursor material while a high‐pressure gas jet drags the molten material away. Thus, the molten material forms glass fibers as result of its viscous elongation by the drag force and rapid cooling promoted by the gas jet. High quantities of nanofibers can be quickly produced with tailored chemical compositions. Previously reported analyses of the process revealed that the dimensions and temperature of the molten volume together with its viscosity to surface tension ratio are the main factors governing the formation of the nanofibers. Therefore, the influence of the working conditions on these parameters must be understood to control the efficiency of the process. In this work, we demonstrate that the surface tension of the melt can be controlled independently of its temperature, and consequently of its viscosity, by adjusting the relative humidity of the gas jet. This outcome increases the productivity of the process and expands its capability for the synthesis of glass nanofibers from fragile melts.     

Examiner trust in applicants to the European Patent Office: country specificities

Indicators based on the probability of applicant citations in patents have been used to emphasize the importance of distinguishing applicant and examiner citations. However, the interpretation of these indicators and of the presence of applicant citations in European Patent Office (EPO) examiner reports is still uncertain. Based on interviews with patent examiners and patent applicants, we develop the idea that applicant citations in EPO examiner reports indicate examiner trust in applicants, and that this trust varies according to national patterns. Using EPO data for over 3,500,000 citations during 1997–2007, we verify that examiner trust in applicants is higher in granted patents. Examiners trust applicants from scientifically or economically strong countries, from member states of the European Patent Organization, and from the same country of the examiners.