Neste trabalho, apresentamos a placa Arduino como uma opção de muito baixo custo para a aquisição de dados com um PC. Duas aplicações simples que mostram as potencialidades desta placa são brevemente discutidos. Palavras-chave: placa Arduino, aquisição de dados, oscilações amortecidas, transferências radiativas.We present the Arduino board as a very low cost option for data acquisition with a PC. Two simple applications that demonstrate the potential of this board are briefly discussed.

We report a detailed study of isofield magnetic relaxation and isothermal magnetization measurements with H c on an underdoped Ba0.75K0.25Fe2As2 pnictide single crystal, with superconducting transition temperature Tc = 28 K. The second magnetization peak (SMP) has been observed at temperatures below Tc/2 and vanished at higher temperatures. The observed behaviour of the SMP has been studied by measuring the magnetic field dependence of relaxation rate, R(H) and by performing the Maley's analysis. The results suggest that the crossover from collective to plastic pinning observed in the SMP disappears above 12 K with plastic pinning replacing collective pinning. An interesting H-T phase diagram is obtained. The critical current density (Jc) was estimated using Bean's model and found to be ∼ 3.4 × 10 9 A/m 2 at 10 K in the SMP region, which is comparable to an optimally doped Ba-KFe2As2 superconductor and may be exploited for potential technological applications. The pinning mechanism is found to be unconventional and does not follow the usual δl and δTc pinning models, which suggest the intrinsic nature of pinning in the compound.

A non-enzymatic formation of 5'-ADP starting from phosphorylation of 5'-AMP in the presence of either calcium phosphate or calcium pyrophosphate precipitates is reported. This reaction is taken as a model for the study of heterogeneous catalysis of transphosphorylation in prebiotic conditions. Experiments were performed in completely aqueous media and in media containing dimethyl sulfoxide (Me2SO), to simulate periods of dehydration in primitive aquatic environments. It has been observed that the nucleotide is adsorbed onto both calcium phosphate and calcium pyrophosphate in accordance with Langmuir isotherms. Adsorptive capacity and affinity of the precipitates for nucleotide are changed by the presence of Me2SO, suggesting that the interaction between biomonomers and surfaces can be modulated by the degree of hydration of the anionic components of these compounds. In completely aqueous environments, formation of 5'-ADP from 5'-AMP adsorbed on precipitates of calcium phosphate and calcium pyrophosphate is very small. However, in the presence of 60% Me2SO this synthesis increases by factors of 3 and 6 for surfaces of calcium phosphate and calcium pyrophosphate, respectively, and follows first-order kinetics. Determinations of free energy changes show that phosphorylation of 5'-AMP adsorbed to these precipitates is thermodynamically favorable. Depending on the precipitation time of the samples and the composition of the medium, structural analysis of these precipitates by electron and X-ray diffraction shows changes in their cristallinity grade. It is proposed that these changes are responsible for the modulation of the quantity of adsorbed nucleotides to the surface of solid matrices as well as the catalytic activity of the precipitates.

This report describes the characterization of a sedimentary occurrence from the Parnaíba Basin, Brazil, containing the zeolite stilbite intertwined with smectitic clay mineral. The head samples from different sites present a wide content range of the zeolitic phase -15% to 50%. The use of simple separation techniques -conventional gravitic treatmentsyields concentrates containing about 67% of the zeolitic component. Assays with the amendments of these concentrates with plant nutrients yield release rates matching those reported for similar commercial products.

Neste trabalho apresentamos os detalhes técnicos de construção de um termômetro em que as medidas de temperatura são audíveis. Inicialmente planejado para atender estudantes com deficiência visual em atividades práticas de termometria, o projeto se mostra perfeitamente adaptável para medir uma variedade de outras grandezas físicas. O projeto é baseado na placa Arduino Uno e no escudo (shield) para Arduino dedicado a reprodução de arquivos de som (Arduino MP3 shield player). A medida da temperatura é realizada com auxílio do sensor digital DS18B20 que opera na faixa de −55 a +125 oC. Todo o projeto é de fácil construção e os componentes usados são acessíveis e facilmente encontrados no mercado nacional.

Among double perovskites, the interpretation of the magnetic, thermal and transport properties of Sr(2)YRuO(6) remains a challenge. Characterization using different techniques reveals a variety of features that are not understood, described as anomalous, and yields contradictory values for several relevant parameters. We solved this situation through detailed susceptibility, specific heat, thermal expansion and x-ray diffraction measurements, including a quantitative correlation of the parameters characterizing the so-called anomalies. The emergence of short-range magnetic correlations, surviving well above the long-range transition, naturally accounts for the observed unconventional behavior of this compound. High resolution x-ray powder diffraction and thermal expansion results conclusively show that the magnetic and thermal responses are driven by lattice changes, providing a comprehensive scenario in which the interplay between the spin and structural degrees of freedom plays a relevant role.

The monoclinic double perovskite Sr 2 YRuO 6 has recently gained a renewed interest in order to get a deeper insight into the exotic magnetic ground states associated with geometric frustration. Striking discrepancies between the spin order derived from the neutron diffraction refinements and the macroscopic magnetic and thermal responses is a major challenge that must be addressed. In this work, detailed neutron diffraction measurements as a function of temperature yield a completely different interpretation of the patterns. We show that at low temperatures a spin structure of the K 2 NiF 4 -type is an accessible configuration for the magnetic ground state. In the neighborhood of the magnetic transition, this configuration evolves into a canted superstructure. The deduced temperature dependence of the canting angle exhibits two closely spaced peaks, which are in excellent agreement with the double peaks in the magnetic contribution to the specific heat and in the thermal expansion coefficient. We explain these features in terms of reorientation of the net ferromagnetic moment of the noncollinear spin state, due to the local breaking of the inversion symmetry promoted by the monoclinic distortions, with structural changes acting as the driving force.

No abstract