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Boas práticas em laboratório químico
(Universidade Federal de São Carlos, 2021-03-25) Lins, Aline Obage; Faez, Roselena; https://lattes.cnpq.br/0654750186618555; https://lattes.cnpq.br/8583471973125177
A chemistry laboratory is a place for teaching, research, and extension activities, as well as for industrial use. Regardless of the purpose, the laboratory exhibits particularities that need to be previously known to avoid the occurrence of accidents. In order to recognize the laboratory spaces and to propose preventive safety measures, this work aimed to prepare a questionnaire and a manual of good laboratory practices. Accordingly, we performed a bibliographic review detailing all aspects of a laboratory. Besides, we based our highlights based on the observation of the Laboratory of Polymeric and Biosorbent Materials - Lab-MPB of the Federal University of São Carlos, in order to obtain a basis to elaborate on specific issues in this area. The results will help users to execute their activities with higher safety and efficiency.
Filmes finos supercondutores sob um campo magnético inomogêneo: diminuição da profundidade da frente de fluxo magnético
(Universidade Federal de São Carlos, 2021-03-25) Araújo, Ítalo Moreira de; Motta, Maycon; https://lattes.cnpq.br/8340540626164812; Ortiz, Wilson Aires; https://lattes.cnpq.br/0241177338066307; https://lattes.cnpq.br/1566463426300587
The phenomenon of superconductivity was discovered by scientist Heike Kamerlingh Onnes in 1911, while studying the resistivity of mercury when cooled below 4,2 K. As predicted by Alexei Abrikosov in 1957, materials from a class of superconductors - currently labeled as Type II - when in the presence of a magnetic field, do admit the entry of flux, in the form of vortices, even being in the superconducting state. A relevant problem for the application of superconductors is the movement of these vortices in the material, which generates dissipation and leads to a local increase in temperature, making the superconducting state less robust. One of the strategies used to avoid this unwanted effect, which results from the viscous movement of vortices, is the artificial inclusion of pinning centers, which act as potential wells for the vortices, making it difficult for them to move. Recently, a considerable number of studies have been directed to the so-called conformal arrangements, which are characterized by the maintenance of the hexagonal symmetry of the original vortex lattice and the introduction of a gradient in the spatial distribution of pinning centers, in the form of arcs, promoting a local increase in the critical current, especially in regimes of high fields and temperatures. In a recent study, performed using computer simulations carried out based on the Ginzburg-Landau theory, it was shown that through combinations of homogeneous and inhomogeneous magnetic fields, it is possible to produce a conformal arrangement of vortices even in a specimen without artificial inclusions. It was precisely this study that inspired the work described here. Thus, with the use of the magneto-optic imaging technique based on the Faraday Effect, the distribution of magnetic flux and the penetration depth of the flux front in the superconducting phase of the studied device was mapped. It consists of a square film of Nb, surrounded by a loop, also square, of Nb. The device was lithographed from a 200 nm thick Nb film. In all cases treated here, the applied field was always perpendicular to the plane of the device. The field profile generated by the superconducting loop was obtained by direct calculation, using the Biot-Savart Law. The superconducting ring was properly characterized, both with respect to the applied current and the applied field at a fixed temperature, in order to guarantee conditions for the device - i.e., the ring and the film inside it - to remain in the superconducting state along the experiments. We thus performed a series of comparisons of the penetration depth of the magnetic flux front using magneto-optic images, always maintaining an equal effective field condition. We used two sample cooling routines: one with field (FC, field cooling), which could be either homogeneous or inhomogeneous, and another in the absence of field (ZFC, zero field cooling). In addition, we also varied the sense of the FC field, always keeping in the same (positive) direction the homogeneous field that was applied during the experiments. The results showed a hierarchy in the penetration depth: the most profound was the negative inhomogeneous field condition, that is, the one in which antivortices were trapped in the superconductor during cooling. A significantly deeper penetration was presented for the condition of FC in a negative homogeneous field; in the sequence, the ZFC condition appears and then there is the positive homogeneous FC condition. The configuration with the lowest flux penetration depth was the one with inhomogeneous field in the same direction as the applied field. Therefore, the interactions between the vortices nucleated by the increase in the applied field and the vortices or antivortices trapped during the cooling of the film proved to be important in favor of vortex-vortex repulsion. In addition, among the five different cooling situations which we have studied, the inhomogeneous field condition is one in which the system exhibits the greater effective shielding capacity.
Número de Nielsen-Borsuk-Ulam para aplicações entre toros
(Universidade Federal de São Carlos, 2021-03-25) Melo, Givanildo Donizeti de; Vendrúscolo, Daniel; https://lattes.cnpq.br/8602232587914830; https://lattes.cnpq.br/1003922857436099
The Nielsen-Borsuk-Ulam number is a lower bound for the minimal number of pair of coincidences points such that f(x) = f(\tau(x)) in a given homotopy class of maps. In this text the Nielsen-Borsuk-Ulam number, NBU(f; \tau), is calculated for any mapsf : T^n \to T^n where T^n is the torus of dimension n with n less than or equal to 3 and \tau is any free involution in Tn. Furthermore, it is concluded that the tori T^1, T^2 and T^3 are Wecken spaces in the Nielsen-Borsuk-Ulam theory and that the triple (Tn; \tau ;Tn) don't have the Borsuk-Ulam property for any free involution \tau.
Durabilidade de compósitos cimentícios de ultra alto desempenho com incorporação de pó de vidro frente à ação de cloretos
(Universidade Federal de São Carlos, 2021-03-25) Soares, Silvete Mari; Salvador Filho, José Américo Alves; https://lattes.cnpq.br/8494783082862407; Ferreira, Fernanda Giannotti da Silva; https://lattes.cnpq.br/0329487394818763; https://lattes.cnpq.br/9291862414193425
Reinforced concrete is one of the most widely used construction materials in civil construction, in Brazil and worldwide, due to the ease of taking on different shapes and for protecting the reinforcement from external actions and, thus, guaranteeing its durability. In order to build more resistant and durable structures, reinforced concrete started to be studied not as a material of high mechanical resistance, but as a material of high performance. High performance concrete (HPC) is a concrete with high mechanical resistance and with characteristics that guarantee its greater durability in the face of aggressive environments, among other requirements. Ultra high performance concrete (UHPC) is a material that has low permeability to chlorides, moisture and oxygen with a matrix composition that has a low water / binder ratio and, therefore, exhibits high mechanical performance and against corrosion of the reinforcement, be used to repair concrete structures. UHPC is generally designed with a high cement content, ranging between 800 and 1,000 kg/m3, which affects production costs, consumes natural sources of raw material and negatively affects the environment through 〖CO〗_2 emissions. Supplementary cementitious materials (SCM) have been widely used to partially replace Portland cement in concrete, both as filling material and as pozzolanic material. In this sense, glass powder is a good alternative due to its silica-rich nature and the large amount available that, in many cases, is disposed of in landfills or not, inappropriately. The hypothesis considered is the feasibility of using glass powder at high levels to replace Portland cement, maintaining the characteristics of high mechanical resistance and durability against the action of chlorides in ultra high performance cementitious composites, providing a reduction in the consumption of Portland cement. This work is justified by the better knowledge of the use of recycled glass powder in the ultra high performance cementitious composite, especially with regard to durability against chlorides, with the analysis of several factors and possible problems that this partial substitution may cause. The general objective is to evaluate the influence of the substitution of Portland cement by different levels of recycled glass powder in an ultra high performance cementitious composite in the mechanical resistance and durability against the attack by chlorides, being one of its specific objectives to determine the ideal content of glass powder to be incorporated into cementitious composites. Cementitious composites with different contents of recyclable glass powder were developed (0%, 10%, 20%, 30% and 50%). For that, mechanical tests were carried out and related to durability, such as: water absorption, resistance to chloride penetration, penetration front, total chloride content, chloride diffusion and migration, electrical resistivity and corrosion potential of cementitious composites. Regarding the microstructure, X-ray diffraction tests, thermogravimetry, scanning electron microscopy and computed tomography were performed. The mechanical results obtained were favorable to the incorporation of glass powder at high contents, since the mechanical strength remain high. Regarding the durability against the attack of chloride ions, the results were also favorable to the incorporation of high contents of substitution of Portland cement by glass powder, indicating a high capacity of CUAD to protect steel against the action of chloride ions. And finally, it is recommended to use the 50% content of incorporation of glass powder to replace Portland cement because it has high mechanical resistance, high resistance to attack by chlorides, in addition to the use of these cementitious composites contributes to the reduction environmental pollution, since the studied incorporations are waste.
Calibração multivias em Laser-Induced Breakdown Spectroscopy (LIBS) para determinação de Ca, K e Mg em amostras de suplemento mineral para humanos
(Universidade Federal de São Carlos, 2021-03-25) Araújo, Alisson Silva de; Pereira Filho, Edenir Rodrigues; https://lattes.cnpq.br/3394181280355442; https://lattes.cnpq.br/8721646298089222
This work intends to present a new approach for modeling LIBS data resolved in time using multiway algorithms, aiming to achieve the advantage of second order. The algorithms evaluated in this study were: Multivariate Curve Resolution- Alternating Least Squares (MCR-ALS), Parallel Factor Analysis (PARAFAC) and Unfolded Partial Least-Squares with Residual Bilinearization (U-PLS/RBL). The analytes monitored in this work were Ca, K and Mg in samples of mineral supplement. This study was divided into four (4) parts. In Part 1 the validation of the algorithms was performed using samples of mixtures of the salts and bases of the studied analytes. In parts 2 and 3, mineral supplement samples were used to assess the predictive capacity of the models, with 6 samples in the calibration set (Part 2) and 17 samples in the calibration set (Part 3). Finally, conventional univariate models were built and the results obtained compared with the performance of the multivariate algorithms (Part 4). The results obtained in the first part demonstrated a good performance for the evaluated algorithms, with emphasis on the U-PLS/RBL. The values obtained for RMSEV by MCR-ALS were 3.4% pp-1, 0.4% pp-1 and 0.9% pp-1 for Ca, K and Mg, respectively. For PARAFAC the values obtained for Ca, K and Mg were 11% pp-1, 0.3% pp-1 and 1.1% pp-1, respectively. The values obtained by U-PLS/RBL were 2.5% pp-1 for Ca, 0.2% pp-1 for K and 1.2% pp-1 for Mg. As for the results obtained in Part 2, a decrease in the performance of the MCR ALS and PARAFAC algorithms was observed when the supplement samples were used as test samples, with high values of LoD and LoQ by both models for the three monitored analytes. The U-PLS/RBL showed an excellent performance, with low values of LoD and LoQ for Ca (0.4% pp-1 and 1.2% pp-1, respectively) and K (LoD: 0.1% pp-1 and LoQ: 0.2% pp-1), while for Mg some samples were below or close to loD (1.0 pp-1) and LoQ (3.0 pp-1). With the inclusion of more samples in the calibration set (Part 3) the performance of the MCR-ALS and PARAFAC algorithms improved for some analytes, however the LoD and LoQ values still remained high for the three monitored analytes. Regarding the U-PLS / RBL, there were no significant improvements for Ca and K, while for Mg a certain improvement in the values of LoD and LoQ was observed, 0.2 pp-1 and 0.7 pp-1, respectively. Conventional univariate calibration (Part 4) did not achieve good results, which was expected, since selective lines are necessary to obtain good results. Therefore, these results confirm that the U-PLS / RBL model was able to predict the analytes of interest in unknown samples, being possible to achieve the second order advantage.