Bioatividade de ácidos húmicos: efeitos sobre o desenvolvimento radicular e sobre a bomba de prótons da membrana plasmática

A bioatividade de ácidos húmicos (AH) isolados de lodo da estação de tratamento de esgoto (AHL) e de vermicomposto (AHV) foi avaliada pela ação dessas substâncias sobre o transporte de prótons através da membrana plasmática de células de raízes de café e milho e sua relação com o desenvolvimento dessas espécies. Houve estímulo da área superficial radicular em ambas as espécies cultivadas com ambos AH, mostrando uma concentração ótima em torno de 40 mg L-1. Nessa condição, os tratamentos com AHL e AHV estimularam a H+-ATPase de membrana plasmática em plântulas de café e milho. Os AHL foram mais efetivos na promoção desses efeitos do que os AHV. A modificação do perfil cromatográfico dos AH em solução antes e após o cultivo das plântulas revelou que a interação planta-AH promoveu uma redistribuição das massas moleculares dessas substâncias, sugerindo uma dinâmica de mobilização de subunidades funcionais dos AH por exsudatos das raízes. A análise estrutural dos AH detectou a presença de grupamentos de auxina. A análise comparativa da ação desses dois AH sobre as espécies representantes de plantas monocotiledôneas (milho) e dicotiledôneas (café) apontam para a ativação da H+-ATPase de plasmalema como possível marcador metabólico de bioatividade dos ácidos húmicos.

Emissões de motor agrícola com o uso de diferentes tipos de diesel e concentrações de biodiesel na mistura combustível

Resumo: O objetivo deste trabalho foi quantificar o efeito do tipo de diesel e da concentração de biodiesel na mistura combustível sobre as emissões de gases por motor agrícola submetido a diferentes cargas. Foram testados dois tipos de diesel: S10, com baixo teor de enxofre; e S500, com alto teor de enxofre; bem como suas misturas com 5, 10, 15, 20, 50 e 100% de biodiesel. O motor, de quatro cilindros, turboalimentado e com 105 cv de potência máxima, foi submetido a oito modos de operação, sob diferentes rotações e torques. O ensaio seguiu a metodologia prevista na norma NBR ISSO 8174-4:2012, tendo-se analisado as emissões de O2, CO2, NO2, NO, CO e de hidrocarbonetos (HC). Somente as emissões de HC foram influenciadas pelo tipo de diesel utilizado. As emissões de NO2 e O2 aumentaram com o aumento da concentração de biodiesel na mistura, enquanto as emissões de CO2, NO, CO e HC diminuíram. A carga aplicada ao motor esteve diretamente relacionada às emissões, exceto para O2. O combustível S10, com 20% de biodiesel, reduz as emissões, em comparação ao diesel comercial (S500), sem perda no desempenho do motor.

Membrana de Liliequist: avaliação radiológica e suas implicações clínicas e terapêuticas

A membrana de Liliequist, de maneira simplista e sucinta, pode ser entendida como uma projeção formada pela aracnoide que se estende do dorso da sela turca aos corpos mamilares. Apesar de se tratar de uma estrutura anatômica bem conhecida pelos neurocirurgiões, muitos radiologistas não a conhecem ou não valorizam seu estudo. A avaliação por imagem desta membrana é factível e pode ser interessante para o melhor planejamento pré-operatório, avaliação pós-operatória de terceiro-ventriculostomias e entendimento dos cistos aracnoides suprasselares e hemorragias perimesencefálicas. Ilustramos neste artigo os aspectos anatômicos da membrana, sobretudo do ponto de vista de imagem, além de suas possíveis implicações clinicocirúrgicas.

Sistema automático para determinação seqüencial de cianeto livre e total empregando eletrodo tubular íon-seletivo de membrana homogênea

This study presents an automated system for potentiometric determination of free and total cyanide which employs a homogeneous membrane tubular ion-selective electrode. After the electrode is assembled, it is connected to a system composed of 3 three-way solenoid valves, sample line, carrier line, acid stream, and gas diffusion chamber. A Turbo Pascal® computer program, developed specifically for this task, automatically performs all the steps involved in data acquisition and processing. The proposed analytical procedure offers operational simplicity, since detection is performed by a tubular electrode, whose assembly is fast and easy. The system has shown reproducibility (r.s.d. < 0.5%, n=6) and high speed (30 readings/hour); it is efficient for determination of free and total cyanide in waste waters of starch processing plants. The detection limit was 1.2x10-5 and 1.5x10-5 mol L-1, for determination of free and total cyanide, respectively. The linear response range was between 1.2x10-5 and 1.0x10-2 mol L-1 for free cyanide and between 1.5x10-5 and 1.0x10-2 for total cyanide.

Extração e pré-concentração de compostos orgânicos voláteis por permeação em membrana para análise cromatográfica

This work discusses sample preparation processes for gas chromatography (GC) based on the technique of extraction through membrane permeation (MPE). The MPE technique may be easily coupled to GC via a relatively simple device, which is a module that holds the membrane and is directly connected to the GC column. The possibility of operational errors due to sample handling is substantially reduced in an MPE-GC system because the sample preparation and the chemical analysis are accomplished as a one-step process. The MPE technique is of relatively wide application as it can be used for aqueous samples, solid samples and gaseous samples. Depending on the type of sample the extraction is performed with the membrane in direct contact with the sample or in contact with its headspace. The MPE-GC technique is very useful in trace analysis, due to the time-dependent enrichment of the analyte. A typical application of MPE-GC is the analysis of VOCs present in water that may be accomplished with detection limits at the low ppb (mugL-1) level.

Os 200 anos da pilha elétrica

In celebration of the 200th anniversary of the electric pile, invented by Alessandro Volta, a synopsis of his letter to The Royal Society (London) and of his biography is presented.

Tecnologia de células a combustível

The fuel cell principle was discovered by Sir Grove 150 years ago. However material problems prohibited its commercialization for a long time. A change has been occurring during the last 30 years, so two types of fuel cell technologies can be distinguished: low and high temperature operation cells. Nowadays, only phosphoric acid cells are commercially offered as 200 kWel power plants. Membrane cells are more suitable for automobile electrotraction with a very low (or no) environmental impact. The fuel continues, however, to play a very particular role, since hydrogen is not easy to store and to transport. The more promising target is the utilization of liquid methanol. The Brazilian scenario concerning this kind of technology is discussed.

Células a combustível de baixa potência para aplicações estacionárias

A paradigmatic shift in developing fuel cell for stationary applications has been occurring in the last ten years. Previously, 100 kW class to a few MW class power plants were preferred but recently, the development has drifted towards units of only a few kW. The motivation is the present market situation, which favors disperse residential electric power generation from natural or liquefied gas. Membrane-type fuel cells are very promising for this application, due to their present state of development in the automobile industry. More recently, small ceramic fuel cells (SOFC) has also been found to be adequate for this application. Considering a family of 4 members, 1 kW (electric) units seem to be optimal for individual residences. This presentation discusses briefly the Brazilian scenario with respect to these units.

Avaliação de contaminantes inorgânicos e orgânicos em álcool combustível utilizando eletroforese capilar

This work reports the analysis of inorganic and organic contaminants in alcohol fuel samples using capillary electrophoresis. Chloride and sulfate were analyzed in nitrate/ monochloroacetic acid at 10 mmol L-1 concentration each under indirect UV detection (210 nm). The analysis of aldehydes is based on the 216 nm detection of 3-methyl-2-benzothiazoline hydrazone adducts. The running buffer consisted of 20 mmol L-1 tetraborate , 40 mmol L-1 sodium dodecyl sufate and 12 mmol L-1 beta-ciclodextrin. Both methodologies were applied to real samples indicating inorganic ion concentrations from 0.15 to 6.64 mg kg-1 and aldehydes from 32.0 to 91.3 mg L-1.

Eletroanálise de derivados acetaldeído com hidrazina e determinação em amostras de álcool combustível por voltametria de onda quadrada

A square wave voltammetric method is described for the determination of acetaldehyde using the derivatization reaction with hydrazine sulphate, based on the reduction of hydrazone generated as a product that exhibits a single well-defined peak at -1.19V in acetate buffer at pH 5. Calibration graphs were obtained from 1.0 x 10-6 mol L-1 to 10 x 10-6 mol L-1 of acetaldehyde, using a reaction time of 8 min and a hidrazine concentration of 0.02 mol L-1. The detection limit was 2.38 x 10-7 mol L-1. The method was applied satisfactorily to the determination of total aldehyde in fuel ethanol samples without any pre-treatment.

Determinação espectrofotométrica simultânea de cobre e ferro em álcool etílico combustível com reagentes derivados da ferroína

In the present work three ferroin reagents were studied for the simultaneous spectrophotometric determination of iron and copper: 1,10-phenanthroline, 2,2'-bipyridine and 2,4,6-tri(2-pyridyl)-1,3,5-triazine. Effect of pH, conditions, order reagent addition, interferences, amount of reagents, lineal range, sensitivity and stability of each system were compared. The 2,4,6-tri(2-pyridyl)-1,3,5-triazine can be used for determination of iron in the presence of copper with a detection limit of 5 µg L-1 and coefficient of variation of 2.0%; However it was not possible to determine directly copper in the presence of iron with this reagent. 1,10-phenanthroline can be used for simultaneous determination of the metallic ions with detection limits of 7 and 8 mg L-1 and coefficients of variation of 1.8 and 2.3% in the determination of iron and copper, respectively. The results showed also that 2,2'-bipyridine can be used for simultaneous determination of the metallic ions with detection limits of 11 and 32 µg L-1 and coefficients of variation of 1.9 and 2.5% in the determination of iron and copper, respectively. The reagents were used for spectrophotometric determination of iron and copper in ethanol fuel.

Pilhas a combustível de óxido sólido: materiais, componentes e configurações

In this paper the current status of fuel cells is described with particular emphasis on high (T > 800 ºC) and intermediate (T < 800 ºC) temperature solid oxide fuel cells. Also the importance of the fuel cell technology is shown. Reviewed are the fundamental features, the basic principles, types of fuel cell, fabrication methods, cell configurations and the development of components (cathodes, anodes, electrolytes, interconnect) and materials.

Reator de membrana enzimático e fluidos supercríticos: associação de processos

The aim of this work is to present the new applications of membrane technology in fat and oil processing, with emphasis on development and applications of the enzymatic membrane reactor and its association with extraction and purification technology by supercritical fluids (SCF). Combining the extraction by SCFs and the separation by membranes allows the integration of extractions reactions with selective separation by membranes through filtration of the supercritical mixture (SCF + extracted solutes). This association provides important energy savings regarding the SCF recompression costs.

Direcionamentos da tecnologia industrial de células a combustível de óxidos sólidos

This manuscript shows an overview of the solid oxide fuel cell (SOFC) technology based on industrial developments. The information presented has been collected mostly at conferences that the authors attended. It is observed that several companies have been pursuing the development of the SOFC technology. Significant advances in stability and power density have raised the economic interest in this technology recently. It is revealed that the SOFC materials are essentially the same ones that have been used in the past decades, and that the two most important designs of pre-commercial SOFC prototypes are the tubular and planar ones.

Avaliação da eficiência de uma célula a combustível estacionária de ácido fosfórico

Operation and performance of a commercial PAFC power plant were analyzed. Processes influencing energy conversion efficiency were studied in each module of the fuel cell power plant. The main processes were simulated using mass and energy balance equations, and the results were validated by means of experimental data. It was concluded that the electrical efficiency is higher in comparison with microturbines. The main result achieved is a better understanding of balance of plant processes, knowledge necessary for fuel cell power plant development.