Tandem-GMA Welding of Low Alloy Structural Steel

The Tandem-GMAW method is the latest development as the consequences of improvements in the welding methods. The twin-wire and then the Tandem-method with the separate power sources has got a remarkable place in the welding of many types of materials with different joint types. The biggest advantage of Tandem welding method is the flexibility of choosing both the electrodes of different types from each other according to the type of the parent material. This is possible because of the feasibility of setting the separate welding parameters for both the wires. In this thesis work the effect of the variation in three parameters on the weld bead in Tandem-GMA welding method is studied. Theses three parameters are the wire feed rate in the slave wire, the wire feed rate in the master wire and the voltage difference in both the wires. The results are then compared to study the behaviour of the weld bead with the change in these parameters.

DSA-elektrodien testaaminen kulumisen arvioimiseksi

Työn tavoitteena oli tutkia eri mittausmenetelmillä metallipinnoitettujen elektrodien kulumista kulumiskokeiden aikana. Mittausmenetelminä olivat käytössä syklinen voltammetria, polarisaatiokäyrän määritys ja sähkökemiallinen impedanssispektrometria, jotka olivat offline-mittausmenetelmiä. Näiden menetelmien avulla pystyttiin seuraamaan yksittäisten elektrodien kulumista ajon aikana. Elektrodin pinnoitteen alkuaineiden pitoisuuksia tutkittiin myös elektronimikroskoopin röntgenspektrometrin avulla. Työn aikana tehdyissä kulumiskokeista havaittiin elektrodin kuluvan sitä nopeammin mitä suurempi on virrantiheys. Työssä tehtyjen elektronimikroskooppikokeiden avulla havaittiin, että harvinaisten metallien seostaminen pinnoitteeseen pidentää metallipinnoitetun elektrodin käyttöikää. Syklisen voltammetrian avulla pystyttiin seuraamaan elektrodin pinta-alan muuttumista ajon aikana. Työssä käytettyjen kulumiskokeiden avulla ei suoranaisesti pystytty määrittämään elektrodin jäljellä olevaa elinikää.

Optoelectronic studies in nanocrystalline silicon Schottky diodes obtained by Hot-Wire Chemical Vapour Deposition

The very usual columnar growth of nanocrystalline silicon leads to electronic transport anisotropies. Whereas electrical measurements with coplanar electrodes only provide information about the electronic transport parallel to the substrate, it is the transverse transport which determines the collection efficiency in thin film solar cells. Hence, Schottky diodes on transparent electrodes were obtained by hot-wire CVD in order to perform external quantum efficiency and surface photovoltage studies in sandwich configuration. These measurements allowed to calculate a transverse collection length, which must correlate with the photovoltaic performance of thin film solar cells. Furthermore, the density of charge trapped at localized states in the bandgap was estimated from the voltage dependence of the depletion capacitance of these rectifying contacts.

ICA Cleaning procedure for EEG signals analysis: application to Alzheimer's disease detection

To develop systems in order to detect Alzheimer’s disease we want to use EEG signals. Available database is raw, so the first step must be to clean signals properly. We propose a new way of ICA cleaning on a database recorded from patients with Alzheimer's disease (mildAD, early stage). Two researchers visually inspected all the signals (EEG channels), and each recording's least corrupted (artefact-clean) continuous 20 sec interval were chosen for the analysis. Each trial was then decomposed using ICA. Sources were ordered using a kurtosis measure, and the researchers cleared up to seven sources per trial corresponding to artefacts (eye movements, EMG corruption, EKG, etc), using three criteria: (i) Isolated source on the scalp (only a few electrodes contribute to the source), (ii) Abnormal wave shape (drifts, eye blinks, sharp waves, etc.), (iii) Source of abnormally high amplitude ( �100 �V). We then evaluated the outcome of this cleaning by means of the classification of patients using multilayer perceptron neural networks. Results are very satisfactory and performance is increased from 50.9% to 73.1% correctly classified data using ICA cleaning procedure.

Towards high-quality simultaneous EEG-fMRI at 7T: Detection and reduction of EEG artifacts due to head motion.

The enhanced functional sensitivity offered by ultra-high field imaging may significantly benefit simultaneous EEG-fMRI studies, but the concurrent increases in artifact contamination can strongly compromise EEG data quality. In the present study, we focus on EEG artifacts created by head motion in the static B0 field. A novel approach for motion artifact detection is proposed, based on a simple modification of a commercial EEG cap, in which four electrodes are non-permanently adapted to record only magnetic induction effects. Simultaneous EEG-fMRI data were acquired with this setup, at 7T, from healthy volunteers undergoing a reversing-checkerboard visual stimulation paradigm. Data analysis assisted by the motion sensors revealed that, after gradient artifact correction, EEG signal variance was largely dominated by pulse artifacts (81-93%), but contributions from spontaneous motion (4-13%) were still comparable to or even larger than those of actual neuronal activity (3-9%). Multiple approaches were tested to determine the most effective procedure for denoising EEG data incorporating motion sensor information. Optimal results were obtained by applying an initial pulse artifact correction step (AAS-based), followed by motion artifact correction (based on the motion sensors) and ICA denoising. On average, motion artifact correction (after AAS) yielded a 61% reduction in signal power and a 62% increase in VEP trial-by-trial consistency. Combined with ICA, these improvements rose to a 74% power reduction and an 86% increase in trial consistency. Overall, the improvements achieved were well appreciable at single-subject and single-trial levels, and set an encouraging quality mark for simultaneous EEG-fMRI at ultra-high field.

The Electronic Structure of Co-Sputtered Zinc Indium Tin Oxide Thin Films

Zinc indium tin oxide (ZITO) transparent conductive oxide layers were deposited via radio frequency (RF) magnetron co-sputtering at room temperature. A series of samples with gradually varying zinc content was investigated. The samples were characterized with x-ray and ultraviolet photoemission spectroscopy (XPS, UPS) to determine the electronic structure of the surface. Valence and conduction bands maxima (VBM, CBM), and work function were determined. The experiments indicate that increasing Zn content results in films with a higher defect rate at the surface leading to the formation of a degenerately doped surface layer if the Zn content surpasses 50%. Furthermore, the experiments demonstrate that ZITO is susceptible to ultraviolet light induced work function reduction, similar to what was earlier observed on ITO and TiO2 films.

Lésions induites par les pistolets à impulsion électrique de type Taser [Health Risks Concerning Electronic Control Devices]

Les pistolets à impulsion électrique (PIE) sont de plus en plus fréquemment utilisés en Europe ces dernières années, le modèle le plus connu étant le Taser®. Les connaissances scientifiques concernant les PIE et leurs effets potentiels restent toutefois limitées. Nous avons conduit une revue de littérature afin d'évaluer les implications potentielles de leur utilisation en termes de sécurité, de morbidité et de mortalité. Une exposition unique chez un individu sain peut généralement être considérée comme peu dangereuse. Les sujets à risque de complications sont les individus exposés à de multiples décharges, les personnes sous l'influence de substances psychoactives, ceux qui montrent des signes d'agitation extrême, ou encore les individus présentant des comorbidités médicales. L'éventail des complications pouvant survenir lors de leur exposition est large et inclut les lésions provoquées par les impacts des électrodes, les traumatismes liés à la chute induite par la paralysie transitoire ou des complications cardiovasculaires. Dans ce contexte, les personnes exposées doivent être examinées attentivement, et les éventuelles lésions traumatiques doivent être exclues. The use of electronic control devices (ECD), such as the Taser®, has increased in Europe over the past decade. However, scientific data concerning the potential health impact of ECD usage remains limited. We reviewed the scientific literature in order to evaluate the safety, mortality, and morbidity associated with ECD use. Exposure of a healthy individual to a single ECD electroshock can be considered generally safe. Complications can, however, occur if the patient is subject to multiple electroshocks, if the patient has significant medical comorbidities, or when exposure is associated with drug abuse or agitated delirium. The broad spectrum of potential complications associated with ECD exposure includes direct trauma caused by the ECD electrodes, injuries caused by the transient paralysis-induced fall, and cardiovascular events. An ECD-exposed patient requires careful examination during which traumatic injuries are actively sought out.

Estereosseletividade em reações eletródicas

This review discusses the present state of the art of the stereochemistry of electrochemical reactions. The extent of asymmetric induction is progressing, but in general diastereoselectivities and enantioselectivities remain behind those from chemical synthesis. In recent years, new methodological developments have been successful. Effects that play important roles in homogeneous chemistry have been used with success. Lack of expressive enantiomeric excess (ee) could be related to the absence of tightly organized structures during the reaction of interest. The highest ee might be expected for redox reactions where conformational preference in transition state plays the important role or for the ones performed while adsorbed on the electrode, and where the chiral element is also at the surface, either adsorbed or chemically bound to the surface and interacting directly with the substrate. Electroenzymatic synthesis has a promising future.

Eletrodos quimicamente modificados aplicados à eletroanálise: uma breve abordagem

Chemically modified electrodes (CMEs) have been subject of considerable attention since its inception about 23 years ago. CMEs result of a deliberate immobilization of a modifier agent onto the electrode surface obtained through chemical reactions, chemisorption, composite formation or polymer coating. This immobilization seeks transfer the physicochemical properties of the modifier to the electrode surface and thus to dictate and control the behavior of the electrode/solution interface. In recent years the interest in CMEs has increased particularly to enhance the sensitivity and/or the selectivity of electroanalytical techniques. In general higher sensitivity and/or selectivity may be achieved by exploiting one or more of the following phenomena: electrocatalysis, preconcentration and interferents exclusion. This paper deals with the application of CMEs in electroanalysis, including a brief presentation of the more general procedures that have been employed for the modification of electrode surfaces.

Transdutores potenciométricos a base de polímeros condutores: aplicações analíticas

A review is given about the most relevant advances on the analytical applications of conducting polymers in potentiometric sensors. These organic polymers represent a new class of materials with conducting properties due to its doping by ions. Several polymers already were synthesized such as polypyrrole, polyaniline, polythiophene, among others. Particular attention is devoted to the main advantages supplied by ion selective electrodes and gas sensors using conducting polymers, as well as the incorporation of bioactive elements in these polymers for the construction of biosensors. The correlation between structure, stability and ability to ion exchange of some conducting polymers applied as potentiometric transducers, is discussed.

Preparação e caracterização de eletrodos monocristalinos

Studies of the kinetics of electrocatalytic reactions on well oriented single crystal surfaces have demonstrated the influence of surface structure on the rate and mechanisms of many electrochemical processes. The preparation and characterization of these surfaces is the first step in this type of studies. In this paper, a methodology employed in order to ensure the quality and cleanliness of single crystals and their utilization as rotating electrodes is described.

Eletrólise de resíduos poluidores: I - Efluente de uma indústria liofilizadora de condimentos

Wastewater from a seasoning freeze-drying industry was electrolysed to increase its biodegradability. Stainless-steel electrodes were used at 9.09 A/m², for up to 80 min. Conductivity, pH, biochemical (BOD) and chemical (COD) oxygen demands, Daphnia similis acute toxicity bioassays, and bacteria counting through the plate count agar method were determined after different times of electrolysis. The results (e.g. higher BOD and lower COD) showed that the biodegradability of the wastewater was significantly increased; furthermore, Fe2+ ions liberated by the electrodes cause microorganisms to die and, when oxidised to Fe3+, contribute for the flocculation and sedimentation of solid residues.

Catálise eletroquímica da redução do bromato em superfícies modificadas por filmes de molibdênio

In this paper some studies concerning the electroreduction of Mo(VI) in sulphuric acid solutions are described. We have shown that at suitable experimental conditions very stable molybdenum oxide films can be electrochemically deposited at glassy carbon electrodes, the reduction of bromate occurring at less negative potentials on the modified surface. Coulometric experiments have shown that bromide is not the only product of the catalytic bromate reduction by the molybdenum film and species like BrO2 may have part in this process. Based on chronoamperometric curves recorded at -0.60 V, analytical curves have been obtained for the reduction of bromate in the 0.1 - 0.8 mM range, a limit of detection of 20 µM for bromate being determined.

Sistema com atmosfera controlada para a caracterização de sensores a gases

This paper describes a sample holder for the electrical measurement of oxides or conducting polymers in the form of pellets or films which are used as gas sensors. The system makes it possible to control the sample temperature, the gas pressure and composition. The temperature in the sample can be changed from 25ºC to 450ºC, and the gas pressure in the chamber is controlled between 5 ¥ 10-4 and 1000 mbar. The performance of the system in resistance measurements of doped tin oxide pellets and polyaniline films deposited on platinum electrodes for methane is analyzed.

Eletrodos artesanais para voltametria

This paper describes the construction and performance of homemade electrodes for voltammetric purpose using cheap materials, like pipette tips and asbestos fiber. A good cost-to-benefit relation makes this devices specially designed for student use, expecting to improve the broadcasting of electroanalytical methods in Brazilian schools.