L.A. da Silva

Oxygen evolution in acid solution on IrO2 + TiO2 ceramic films. A study by impedance, voltammetry and SEM

Thermally prepared oxide films (2 μm) of nominal composition Ir0.3Ti0.7O2 were prepared at 350, 400, 450 and 500 °C on a Ti support. Electrochemical impedance spectroscopy (EIS) at constant potential was used in the range 0.4 to 1.6 V (rhe). The results were fitted by the equivalent circuit RΩ (RfCf)(Rct,Cdl)L. The RΩ values obtained by EIS agree with the data derived from kinetic studies. The high Rct value of the 350 °C oxide layer is attributed to the incomplete decomposition of the precursor so that some of the underlying insulating TiO2 layer remains uncovered. This view is corroborated by SEM and CV studies. Oxide layers prepared at higher temperatures are stable, the Rct values increasing with calcination temperature. This is attributed to crystallite size increasing with temperature, resulting in a lower number of active sites being exposed. For all electrodes, Rct decreases with increasing potential. Cdl depends on both surface area and applied potential. At T > 350 °C, Cdl diminishes as temperature increases, which is due to decrease in the active surface area. Analogously, Cdl is observed to increase with increasing potential, which is associated with the heterogeneity of the electrode surface.

Surface characterisation of IrO2/TiO2/CeO2 oxide electrodes and Faradaic impedance investigation of the oxygen evolution reaction from alkaline solution

Abstract Ti-supported electrodes of nominal composition Ti/Ir 0.3 Ti (0.7− x ) Ce x O 2 (0≤ x ≤0.7) were prepared by thermal decomposition of chloride precursor mixtures ( T cal =450°C; t cal =1 h; O 2 flux=5 L min −1 ). The effect of TiO 2 substitution by CeO 2 on the system surface parameters and oxygen evolution reaction was investigated by cyclic voltammetry and impedance measurements from 1.0 mol dm −3 KOH. Independent of composition, the solid state redox couple lr(III)/Ir(IV) dominates the surface properties of the anodes. Increasing the CeO 2 -content of the materials causes an increase in their active surface area, as supported by the anodic voltammetric charge, q a , and double layer capacitance, C dl , values. The small cathodic shift in E p values observed as a consequence of CeO 2 introduction into the material suggests an interaction among the components. R Ω -values ranging between 1.3 and 2.9 Ω cm 2 , independent of composition, are in excellent agreement with the results of the Tafel investigation (∼2.0 Ω cm 2 ). The R ct -values reveal all CeO 2 -containing compositions have better overall activity than the reference composition (Ti/Ir 0.3 Ti 0.7 O 2 ). Based on 1/ R ct q a behaviour, however, best site activity was found for electrodes with low CeO 2 -content (10 and 20 mol%).

Neuroanatomical approaches of the tectum-reticular pathways and immunohistochemical evidence for serotonin-positive perikarya on neuronal substrates of the superior colliculus and periaqueductal gray matter involved in the elaboration of the defensive behavior and fear-induced analgesia.

Deep layers of the superior colliculus, the dorsal periaqueductal gray matter and the inferior colliculus are midbrain structures involved in the generation of defensive behavior and fear-induced anti-nociception. Local injections of the GABA(A) antagonist bicuculline into these structures have been used to produce this defense reaction. Serotonin is thought to be the main neurotransmitter to modulate such defense reaction in mammals. This study is the first attempt to employ immunohistochemical techniques to locate serotonergic cells in the same midbrain sites from where defense reaction is evoked by chemical stimulation with bicuculline. The blockade of GABA(A) receptors in the neural substrates of the dorsal mesencephalon was followed by vigorous defensive reactions and increased nociceptive thresholds. Light microscopy immunocytochemistry with streptavidin method was used for the localization of the putative cells of defensive behavior with antibodies to serotonin in the rats midbrain. Neurons positive to serotonin were found in the midbrain sites where defensive reactions were evoked by microinjection of bicuculline. Serotonin was localized to somata and projections of the neural networks of the mesencephalic tectum. Immunohistochemical studies showed that the sites in which neuronal perikarya positive to serotonin were identified in intermediate and deep layers of the superior colliculus, and in the dorsal and ventral columns of the periaqueductal gray matter are the same which were activated during the generation of defense behaviors, such as alertness, freezing, and escape reactions, induced by bicuculline. These findings support the contention that serotonin and GABAergic neurons may act in concert in the modulation of defense reaction in the midbrain tectum. Our neuroanatomical findings indicate a direct neural pathway connecting the dorsal midbrain and monoaminergic nuclei of the descending pain inhibitory system, with profuse synaptic terminals mainly in the pontine reticular formation, gigantocellularis nucleus, and nucleus raphe magnus. The midbrain tectum-gigantocellularis complex and midbrain tectum-nucleus raphe magnus neural pathways may provide an alternative output allowing the organization of the fear-induced anti-nociception by mesencephalic networks.

Neuroanatomical and psychopharmacological evidence for interaction between opioid and GABAergic neural pathways in the modulation of fear and defense elicited by electrical and chemical stimulation of the deep layers of the superior colliculus and dorsal periaqueductal gray matter

The effects of central administration of opioid antagonists on the aversive responses elicited by electrical (at the freezing and escape thresholds) or chemical stimulation (crossings, rearings, turnings and jumps, induced by microinjections of bicuculline) of the midbrain tectum were determined. Central microinjections of naloxone and naltrexone in the mesencephalic tectum caused a significant increase in the freezing and escape thresholds elicited by electrical midbrain tectum stimulation. Furthermore, both opioid antagonists caused a significant decrease in the mean incidence of aversive behavioral responses induced by microinjections of bicuculline in the deep layers of the superior colliculus (DLSC) and in dorsal aspects of the periaqueductal gray matter (DPAG), as compared with controls. These findings suggest an opioid modulation of the GABAergic inhibitory inputs controlling the aversive behavior elicited by midbrain tectum stimulation. In fact, immunohistochemical evidence suggests that the dorsal mesencephalon is rich in beta-endorphin-containing neurons and fibers with varicosities. Iontophoretical microinjections of the neurotracer biodextran in the substantia nigra, pars reticulata (SNpr), show nigro-tectal pathways connecting SNpr with the same neural substrate of the DPAG rich in neuronal cells immunoreactive for opioid peptides. Labeled neurons of the DLSC and periaqueductal gray matter send inputs with varsicosities to ipsi- and contralateral DPAG and ipsilateral SNpr. These findings, in addition to the psychopharmacological evidence for the interaction between opioid and GABAergic mechanisms, offer a neuroanatomical basis of a possible presynaptic opioid inhibition of GABAergic nigro-tectal neurons modulating the fear in aversive structures of the cranial mesencephalon, in a short link, and maybe through a major neural circuit, also in GABA-containing perikarya of nigro-tectal neurons.

Kinetics and mechanism of oxygen evolution on IrO2-based electrodes containing Ti and Ce acidic solutions

A systematic investigation of the mechanistic features, the electrocatalytic activity, and the stability of thermally prepared ternary oxides of general formula Ir0.3Ti(0.7−xCexO2 (0 ⩽ x ⩽ 0.7) has been carried out using O2 evolution from 1.0 mol dm−3 aqueous HClO4 as a model reaction. The surface state of the electrodes was monitored in situ by recording voltammetric curves before and after each experiment. Stability was tested by cycling the electrodes between 0.4 and 1.4 V (rhe). For all compositions the anodic-to-cathodic charge ratio, qa/qc, was close to one. Variation of the negative potential limit did not reveal the occurrence of the cathodic dissolution phenomena previously observed with a similar RuO2-based system. Tafel slopes were independent of the CeO2 content, with a value around 30 mV. The reaction order with respect to H+ was zero at constant overpotential and ionic strength. Some inhibition of the oxygen evolution reaction is observed as Ti is replaced by Ce.

Neuroanatomical and neuropharmacological study of opioid pathways in the mesencephalic tectum: effect of μ1- and κ-opioid receptor blockade on escape behavior induced by electrical stimulation of the inferior colliculus

Deep layers of the superior colliculus (DLSC), the dorsal and ventral periaqueductal gray matter (PAG), and inferior colliculus (IC) are midbrain structures involved in the generation of defensive behavior. beta-Endorphin and Leu-enkephalin are some neurotransmitters that may modulate such behavior in mammals. Light microscopy immunocytochemistry with streptavidin method was used for the localization of the putative cells of defensive behavior with antibodies for endogenous opioids in rat brainstem. Midbrain structures showed positive neurons to beta-endorphin and Leu-enkephalin in similar distributions in the experimental animals, but we also noted the presence of varicose fibers positive to endogenous opioids in the PAG. Neuroanatomical techniques showed varicose fibers from the central nucleus of the inferior colliculus to ventral aspects of the PAG, at more caudal levels. Naloxonazine and nor-binaltorphimine, competitive antagonists that block mu(1)- and kappa-opioid receptors, were then used in the present work to investigate the involvement of opioid peptide neural system in the control of the fear-induced reactions evoked by electrical stimulation of the neural substrates of the inferior colliculus. The fear-like responses were measured by electrical stimulation of the central nucleus of the inferior colliculus, eliciting the escape behavior, which is characterized by vigorous running and jumping. Central administration of opioid antagonists (2.5 microg/0.2 microl and 5.0 microg/0.2 microl) was performed in non-anesthetized animals (Rattus norvegicus), and the behavioral manifestations of fear were registered after 10 min, 2 h, and 24 h of the pretreatment. Naloxonazine caused an increase of the defensive threshold, as compared to control, suggesting an antiaversive effect of the antagonism on mu(1)-opioid receptor. This finding was corroborated with central administration of nor-binaltorphimine, which also induced a decrease of the fear-like responses evoked by electrical stimulation of the inferior colliculus, since the threshold of the escape behavior was increased 2 and 24 h after the blockade of kappa-opioid receptor. These results indicate that endogenous opioids may be involved in the modulation of fear in the central nucleus of the inferior colliculus. Although the acute treatment (after 10 min) of both naloxonazine and nor-binaltorphimine causes nonspecific effect on opioid receptors, we must consider the involvement of mu(1)- and kappa-opioid receptors in the antiaversive influence of the opioidergic interneurons in the dorsal mesencephalon, at caudal level, after chronic (2-24 h) treatment of these opioid antagonists. The neuroanatomical study of the connections between the central nucleus of the inferior colliculus and the periaqueductal gray matter showed neuronal fibers with varicosities and with terminal bottons, both in the pericentral nucleus of the inferior colliculus and in ventral and dorsal parts of caudal aspects of the periaqueductal gray matter.

Surface and electrocatalytic properties of ternary oxides Ir0.3Ti(0.7−x)PtxO2. Oxygen evolution from acidic solution

Mixed oxides of nominal composition Ir0.3Ti(0.7−x)PtxO2 (0 ≤ × ≤0.7) were prepared by thermal decomposition at 400°C of suitable precursors on Ti supports. The surface properties were investigated ex situ by SEM and EDX, and in situ by cyclic voltammetry in 1 mol dm−3 HClO4 solutions. The morphology changes at about 30 mol% Pt; at lower Pt contents the surface is enriched with Ir; at higher contents it is enriched with Pt. Cyclic voltammetry showed that the surface concentration of active sites decreases with increasing Pt content. O2 evolution was studied by means of current-potential curves and reaction order determinations. The mechanism was found to change going from Ir to Pt surface sites. The electrocatalytic properties were separated from surface area effects by normalizing the current to unit surface charge. The specific activity turned out to decrease by a factor of 10 as Ti is replaced by Pt, which in turn displaces Ir from the surface of the active mixed oxides.

Absence of interleukin 22 affects the oral microbiota and the progression of induced periapical lesions in murine teeth

AIM To evaluate the absence of IL-22 on the progression of periapical lesions in wild-type (WT) and IL-22 knockout (IL-22 KO) mice. METHODOLOGY The evaluation of the oral microbial profile of mice was performed by Checkerboard DNA-DNA hybridization from saliva samples. Periapical lesions were induced in manbibular first molars by pulpal exposure and evaluated after 7, 21 and 42 days (n = 15). Haematoxylin-eosin-stained sections were analysed under conventional and fluorescence microscopy to evaluate the tissue features and size of periapical lesions and tartrate-resistant acid phosphatase histoenzymology (TRAP), Brown & Brenn staining and immunohistochemistry. The scores of the number of bacterial cells present in the oral cavity were analysed by the Mann-Whitney test, and the results and comparisons for periapical lesion size and number of osteoclasts were subjected to one-way anova and Bonferronis post-test (α = 0.05). RESULTS Significant differences were observed for bacterial load between the groups of animals for 6 bacterial species (P < 0.05), with five species found in higher levels in the WT group, and one in the IL-22 KO group. WT mice had significantly larger periapical lesions (P < 0.05) between 7 and 42 days and between 21 and 42 days, with an increase in the mean size and number of osteoclasts. IL-22 KO mice had an increase in periapical lesion size and number of osteoclasts between 7 and 21 days (P < 0.05). No differences were found between bacteria localization in the root canal system between the experimental groups. Small variations related to the location of immunostaining were found between the groups. CONCLUSION This study revealed differences in the composition of oral microbiota between mice that may be taken into account in the susceptibility to infections and development of periapical lesions. The absence of IL-22 in mice resulted in smaller periapical lesions with fewer osteoclasts at the final experimental period, suggesting the participation of IL-22 in the host immune and inflammatory response to a periradicular infection.

A Methodology Using Neural Network to Cluster Validity Discovered from a Marketing Database

The databases of real world contains a huge volume of data and among them there are hidden piles of interesting relations that are actually very hard to find out. The knowledge discovery databases (KDD) appear as a possible solution to find out such relations aiming at converting information into knowledge. However, not a data presented in the bases are useful to a KDD. Usually, data are processed before being presented to a KDD aiming at reducing the amount of data and also at selecting more relevant data to be used by the system. The purpose of this paper is to describe a validation methodology, through of a MLP neural network, to the knowledge discovered by a hybrid architecture composed by rough sets theory used to pre-processing the data to be presented to self-organizing maps neural network, which data cluster.

Medical Image Categorization Based on Wavelet Transform and Self-Organizing Map

Nowadays, images are fundamental data source in modern medicine. The images stored in a database according with categories are an important step for data mining and content-based image retrieval (CBIR). These can support doctors and students in diagnostic decisions and provide research and didactic material. This work addresses the use of discrete wavelet transform and self-organizing map (SOM) to medical image categorization. Furthermore, extensive experiments to define map size, finetune using linear vector quantization and a contrastive study with another success approach of categorization are realized.