MAGNETIC STRIPS TO SIMULATE LAYERED BRITTLE SOLIDS IN CLEAVAGE AND FRACTURE EXPERIMENTS

A characteristic of the fracture and cleavage experiments is that they are usually intrinsically destructive. Cracks do not completely heal in an unstressed system, even in crystals such as mica. Here, we used magnetic solids composed of magnetic strips for the non-destructive cleavage and brittle fracture experiments. Between the magnetic strips materials with different mechanical characteristics can be inserted, such as Teflon or foam strips, to change the mechanical properties of the solid. For the cleavage experiments, we developed an apparatus where parameters such as the main involved force can be measured easily. By inserting flaws, the magnetic solid can be used in dynamic fracture experiments, with the advantages of simulating macroscopically a non-destructive experiment in an easier way, that happen in real materials with much higher velocities. The apparatus and the used magnetic solid may be useful for demonstrations of fractures in classes.     

Pesticide residues in herbs and their transfer for infusions

In this work, a cost-effective gas chromatography-mass spectrometry method was validated for the analysis of twenty-five pesticide residues in herbs and infusions using a quick, easy, cheap, effective, rugged, and safe procedure or a dispersive liquid-liquid microextraction method, respectively. Figures of merit of the method showed good accordance with current guidelines. From the 58 herb samples studied (pertaining to 20 different species), 80% presented at least one detectable pesticide, with 62% of them above the maximum residual level. Results showed that pesticide residues from naturally contaminated herbs were not transferred at a significant rate to the herbal infusions. When a control assay was conducted by spiking a blank herb sample with a large amount of each pesticide (7 mg/L) 15 analytes were detected below the limit of quantification in the infusion.