Natural additives with antioxidant properties can be used as biodegradable and sustainable alternatives to synthetic products, because they can inhibit the biodiesel oxidation reaction, increasing oxidative stability and extending its storage period. This research evaluated the efficiency of jabuticaba peels, gabiroba leaves, and hibiscus flowers in ethanolic extracts, analyzing through the simplex-centroid design, the induction periods (IP) and rate constants (k) of the biodiesel oxidation reaction at 110 °C. Antioxidant activity was observed in all extracts, either decreasing k or increasing the IP. The mathematical models obtained showed coefficients of determination greater than 0.9400, a non-significant lack of fit at the 5% level, and low dispersion between predicted and experimental data, indicating that the 1st order reaction fit was appropriate and can be used for predictive purposes. In this work, the optimization was performed with maximization of IP and minimization of k showing that the mixture containing 25% of jabuticaba peels extract and 75% of gabiroba leaves extract was the most suitable, because proportionally increased the IP and decreased k of the biodiesel oxidation reaction. It is possible to suggest the use of jabuticaba peels extract or gabiroba leaves extract as well as various combinations between them as antioxidant additives.

Abstract Background Agriculture in South America (SA) had a great expansion in the last decades and weed control changed accordingly with region and crop practices. Objective The objective of this review is to present the history of herbicide use and discuss the main changes in weed management in SA. Methods Herbicide use quantities were obtained from official institutions and commercial organizations in Argentina, Brazil, Chile, Paraguay and Uruguay. Data were summarized per active ingredient, herbicide mode of action or crop. The evolution of the cultivated area of the main crops in each country, and the crop and weed management associated to it were considered to discuss the importance and the consequences of the main herbicides used. Results In 2019 the most used herbicides in Brazil were glyphosate, 2,4-D, atrazine, paraquat and diuron representing 62, 15, 7, 5 and 2% of the total amount used. In Argentina, the increasing selection of herbicide resistant populations (4 cases/year), resulted in utilization of older chemistries. Weed control in Uruguay is traditionally benefited from crop/pasture rotations but recently is also facing problems of continuous cropping systems. Agriculture in Chile is more diverse, but similar patterns and problems of herbicide use are present. Conclusions Intensification of agriculture, no-tillage, glyphosate resistant crops, and herbicide resistant weeds were the most important drivers of herbicide use changes in SA. Integrated weed management is unpostponable to provide sustainable increasing food production in SA.

RESUMO Objetivou-se com este trabalho avaliar o efeito do primeiro desbaste sobre a morfometria de um plantio de Tectona grandis L.f. (teca). O delineamento experimental foi o de blocos ao acaso, com quatro tratamentos e três repetições sendo: T1 = testemunha (sem desbaste), T2, T3 e T4 = remoção da área basal de 20%, 30% e 40% respectivamente. As variáveis morfométricas avaliadas foram: proporção de copa (PC), índice de abrangência (IA), grau de esbeltez (GE), índice de saliência (IS), formal de copa (FC) e comprimento de copa (CC). A aplicação de desbastes em teca influenciou significativamente em todas as variáveis morfométricas avaliadas, com exceção de proporção de copa (PC) e índice de saliência (IS). As intensidades de desbastes (20%, 30% e 40%) não apresentaram diferença significativa para as variáveis: altura comercial do fuste (HF), comprimento de copa (CC), diâmetro de copa (DC), proporção de copa (PC) e forma de copa (FC) da Tectona grandis até o quarto ano pós-desbaste.

ABSTRACT The aim of this study was to evaluate the effect of first thinning on the morphometry of trees in a forest plantation of Tectona grandis Lf (teak). The experimental design used was randomized block with four treatments and three replications were: T1 = control treatment (no thinning), T2, T3 end T4 with the removal of basal area the 20, 30 and 40% respectively. The evaluated morphometric variables were: crown proportion (PC), coverage index (AI), slenderness degree (GE), salience index (IS), crown form (FC) and crown length (CC). The application of thinning in teak, significantly influenced in all morphometric variables analyzed, except for the proportion of room (PC) and the projection index (SI). The thinning intensities (20%, 30% and 40%) presented no significant differences for variables: commercial bole height (HF), crown length (CL), crown diameter (DC), crown proportion (PC) and crown form (FC) of teak to the fourth post-thinning year.

O estudo da eletricidade nos cursos de graduação em Física pode ser mais motivador e eficiente se agregar novos desafios, como o uso de circuitos eletrônicos. Neste trabalho, exploramos os recursos eletrônicos do Arduino, de sensores de corrente elétrica baseados em indução eletromagnética, de resistores, de capacitores e de programas de computador. Apresentamos os resultados obtidos e os métodos para visualizar a forma de onda da corrente elétrica de alguns eletrodomésticos e o espectro de frequência destas formas de onda.

The study of electricity in undergraduate programs in physics can be more motivating and efficient if to add new challenges such as the use of electronic circuits. In this paper, we explore the electronic resources of Arduino, electric current sensors based on electromagnetic induction, resistors, capacitors and computer software. We present the results and the methods to display the waveform of the electric current of some home appliances and the spectrum of frequency of these waveforms.

Apresentamos neste trabalho um dispositivo de baixo custo para medidas de intervalos de tempo, velocidades e acelerações, bastante útil no problema de queda livre e em outros experimentos de mecânica. Construímos uma photogate usando a porta de jogos do PC para fazer aquisição de dados e para obter a aceleração da gravidade. Obtemos boa concordância dos dados experimentais com um modelo teórico de um corpo em queda livre. Nosso trabalho ressalta uma forma de medir com precisão curtos intervalos de tempo, e abre novas possibilidades de aplicação ao ensino de física.

We present in this work a low-cost device for measurements of time intervals, velocities and acelerations, useful in the free-fall problem and others experiments in mechanics. We have constructed a homemade photogate using the PC gameport to make data acquisition and to obtain the acceleration of gravity. We have obtained good agreement of the experimental data and theoretical model of a free falling body. Our work provide a way to measure short time intervals with good accuracy, and open new possibilities of applications in physics teaching.