Tracker is a piece of freeware software, designed to use video recorded images of the motion of objects as input data, and has been mostly applied in physics education to analyse and simulate physical phenomena in mechanics. In this work we report the application of Tracker to the study of experiments in electricity and magnetism using analog instruments for electrical signal measurements. As we are unable to directly video-track the motion of electrons in electric circuits, the angular deflections of the instruments’ pointers were video captured instead. The kinematic variables (angular position as a function of time) had to be related to the electrical ones (voltages and currents as a function of time). Two well-known experiments in physics teaching, the RC circuit for charging and discharging a capacitor and Faraday electromagnetic induction, were chosen to illustrate the procedures. The third experiment analysed and modeled with Tracker was the rather well-known electromagnetic retardation of disk- or cylinder-shaped magnets falling inside non-magnetic metallic pipes. Instead of metallic pipes we used an aluminum plate with an arrangement of a couple of parallelepiped-shaped magnets falling parallel to the plate. In the three cases studied, the experimental and the Tracker simulation results were in very good agreement. These outcomes show that it is possible to exploit the potential of Tracker software in areas other than mechanics, in areas where electrical signals are involved. The experiments are inexpensive and simple to perform, and are suitable for high school and introductory undergraduate courses in electricity, magnetism and electronics. We propose the use of Tracker combined with analog measuring devices to explore further its applications in electricity, magnetism, electronics and in other experimental sciences where electrical signals are involved.
From tilapia (Oreochromis niloticus) farming, the by-products have been identified as a source of collagen that could be used for the development of dermocosmetics or pharmaceutical products. However, the characteristics of collagen related to a specific strain or culture must be well defined prior to its application. Collagen was extracted from the skin of three strains of tilapia: red YY males (YY: two Y-type sex chromosomes), XX gray females, and the F1: offspring of crossing red YY males with XX gray females; at different ages in the adult phase, using acetic acid and pepsin enzyme. The characteristics of acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) were shown by SDS-PAGE band profiles to be similar to bovine collagen type I (SIGMA), the PSC of gray tilapia being more fragile to temperature changes, consistent with the results of fractional viscosity. The characteristics of the F1 progeny were prioritized for being a commercially productive and sustainable source for the extraction of collagen, and the ASC form, being the one with the greatest stability and advantage over PSC, of importance to our investigations, leads to a controlled digestion as in the case of peptide induction, and also in the development of natural products in the pharmaceutical and/or dermocosmetic industry. Evaluations of the triple helix structure by FT-IR, X-ray diffraction and UV–visible spectroscopy give similar results between the strains: red, gray, and F1, and between ages in the adult form F1 (15, 24, and 36 months of age). Consequently, the skin of tilapia in adult form is recommended sustainably for up to 24 months of age where the collagen is obtained with the use of acetic acid without enzymatic treatment.
Pure and Zn1-xCoxO nanoparticles have been synthesized by a simple sol-gel method at low temperature where neither a chelating agent nor subsequent annealing was required. The effect of Cobalt atomic fraction, ‘x’ ≤ 0.0625, on the structural and magnetic properties of the doped ZnO powders was evaluated. X-ray diffraction and Fourier-transform infrared spectroscopy analyses evidenced the exclusive formation of the ZnO-wurtzite structure; no isolated Co-phases were detected. The linear dependence of cell parameters a and c with ‘x’, suggested the actual replacement of Zn by Co ions in the oxide lattice. Micro Raman spectroscopy measurements showed a band centered at 534cm-1, which can be assigned to a local vibrational mode related to Co species, in addition to the normal modes associated with wurtzite. The intensity and broadening of this band at 534 cm-1 were enhanced by increasing ‘x’. In turn, the other bands corresponding to A1 (E2, E1) and E2High modes were red shifted at higher Co contents. Room-temperature magnetization measurements revealed the paramagnetic behavior of the Co-doped ZnO nanoparticles.
Highly monodisperse ZnO:Eu3+ nanocrystals have been synthesized by modified sol-gel method from ethanolic solutions. The effect of Eu3+ ions (x=0.05-0.30) concentration on the structural, optical and luminescent properties has been evaluated. No other than the ZnO-wurtzite phase was observed at all dopant levels, which was confirmed by FT-IR and Raman spectroscopy techniques. A blue shift of the exciton peak and the increase on the corresponding band gap were observed at increasing Europium contents, which would indicate an interaction between Eu3+ ions and the development of the ZnO host structure. The luminescence properties were also dependent on Europium contents; a systematic blue shift and enhancement of the intensity of visible luminescence peak, attributed to an increment of surface defects, was observed by a rising Europium concentration. The red luminescence band, representing the 5D0→7F0 transition, was clearly observed in nanocrystals after annealing at 300OC for one hour. The presence of this band could be considered as an evidence of the effective energy transfer from ZnO to Eu3+ ions.
Highly crystalline and transparent Eu-doped Gd 2 O 3 thin films were produced through a modified sol-gel method that did not require the use of any chelating agent. The effect of the atomic fraction of Eu 3+ ions ('x' =0.05-0.30) on the structural, optical and luminescent properties has been studied. X-ray diffraction studies showed the preferential growth of Gd 2-x Eu x O 3 thin films along the (400) plane corresponding to the cubic phase. UV-vis measurements revealed the high film transparency of the films in the visible region and a band gap value of 5.3eV. It has also been observed that the luminescence properties of the films were strongly dependent on both, the excitation wavelength and Eu concentration; the most efficient excitation conducive to red luminescence was achieved at the absorption band of Gd 2 O 3 host (229nm). Under this condition all films exhibited strong red emission that is characteristic of Eu 3+ ions. The emission intensity was also dependent on the doping level; the most intense luminescence was obtained at 'x'=0.15. The drop in the luminescence intensity observed for 'x' values higher than 0.15 was attributed to quenching concentration effect.
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