Advanced glycation end products (AGEs) represent a set of molecules that contribute directly to the initiation and aggravation of diseases associated with ageing. AGEs are produced by the reaction between reducing sugars (or α-dicarbonyl compounds), proteins, and amino acid residues. Previous in vitro methods using non-enzymatic procedures described in the literature require an incubation period of 1–3 weeks to generate AGEs. In this study, the reaction time for the formation of AGEs (48 and 3 h) was significantly reduced by adaptation of methods previously described in the literature and coupling them to the free radical generation system termed hypoxanthine/xanthine oxidase assay. The incorporation of this assay into the experimental system accelerated the production of AGEs as a result of the formation of reactive oxygen species (ROS), as shown by increased fluorescence. The capacity of different classes of chemical compounds (aminoguanidine, chlorogenic acid, rutin, and methanol extracts of Hancornia speciosa Gomes) to inhibit protein glycation by acting as scavenging agents of α-dicarbonyl species was evaluated. Aminoguanidine and, especially, rutin identified in the leaf extracts of H. speciosa Gomes showed a high capacity to act as scavengers of reactive carbonyl species RCS-trapping, resulting in the inhibition of AGEs formation.
Resumo. O presente trabalho apresenta o resultado da vivência de estudantes do ensino médio da cidade de Quixadá-CE com atividades de aprendizagem cooperativa aplicadas ao ensino de química. Quatro técnicas distintas de aprendizagem cooperativa (jigsaw, método dos pares, fila cooperativa e teste cooperativo) foram empregadas como estratégias de ensino-aprendizagem. Os resultados obtidos foram analisados no que diz respeito à apreensão dos conteúdos e observou-se um ambiente menos competitivo e mais colaborativo entre os estudantes, contribuindo assim para o desenvolvimento de aprendizagem significativa. O trabalho inclui descrição das técnicas de aprendizagem cooperativa, apresentação de todo o percurso metodológico utilizado, bem como a avaliação dos resultados.
The present paper deals with a buck converter used to control the current during a welding process. The voltaic arc is modeled by a variable resistance in series with a voltage source. The step-dowi dc-dc converter is connected to the output of a conventional electromagnetic power source and it controls the energy fliix to the welding process. A histeretic current control was implemented to guarantee a constant average current during, the voltaic arc. The main power circuit is a buck converter that uses an high power IGBT module as the main switch. The freewheel path is made up of three parallel diodes. The buck converter was designed for an load Phone: 55 85 288-9617 with different qualities. So, to get a better result fiom each condition of welding, a study must be done about the current influence on it. The system here proposed is suitable for the realization of this study. The desired features fiom this power electronics module for welding are the ability to impose two current levels, one when there is an electric arc between the electrode and the work and the other one during the short circuit, when there is no arc. In order to control the current ripple in both situation mentioned above a buck converter has been suggested as an option to realize the task. current of up to 200A. A microcontrolled interface was The reasons are its simple configuration, the fact that there is developed to make it easier the hardware configuration. A a large literature about it and the energy store element is temperature sensor fiixed on the IGBT heat sink has an indication of the temlperature on the switch for monitoring placedonthe loadside. purpose. The converter characteristics are described. 11. THE BUCK CONVERTER Simulations and the experimental laboratory results are presented to show the performance of the structure. The buck converter[4] designed, simulated and implemented in laboratory is shown in Figure 1. I. LNTRODUCTION The quality of a welding process may be improved if some variables are well adjusted [1,2,3]. The current is one of them. A low ripple current who has the same medium value of another one with greater ripple, produce weld beads 0-7803-39324 67 6 E Fig. 1 -Buck converter. The equations below describing the buck converter are very known[4,6]. They describe the relation between the load voltage, the load current, the switches current and voltage and the power supply. The duty cycle D may be constant or variable. When the PWM control is used, the switching period (T) is not variable. In the case of extreme values control or hysteretic control, the frequency is variable[4,6]. V , = D . E (01) t c (02) D = -T v,,, =(l-D)-E (03) IDIODE = ILOAD -4GBT (04) The load current as a function of time may be expressed during the conduction time of the main switch and when the ffeewheeling diode is forward biased through equations (05) and (06) respectively. There is a limitation for the duty cycle when operating a IUE load. The reason is the power could become negative if the duty cycle is less than the rate betwee...
Advanced Glycation End Products (AGEs) represent a set of substances that contribute directly to the triggering and/or aggravation of pathologies associated with ageing. AGEs are produced by the reaction between reducing sugars (or α-dicarbonyl compounds) proteins and amino acid residues. Current methodologies require an incubation period of 1-3 weeks to generate AGEs. In this study the reaction time for the formation of AGEs (48 and 3 hours) is significantly reduced by coupling and adapting procedures already existing in the literature to the free radical generation system called the hypoxanthine/xanthine oxidase assay. The capacity of different classes and chemical compounds (aminoguanidine, chlorogenic acid, rutin, extracts of Hancornia speciosa Gomes) were evaluated to inhibit the protein glycation process, acting as capturing agents of α-dicarbonyl species. Aminoguanidine, rutin and the leaf extracts of Hancornia speciosa Gomes show a high capacity to act as α-dicarbonyl compound scavengers (RCS-trapping) and resulting in the inhibition of AGEs formation.
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