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Electronic and optical properties of Quasi-2D nanostructures and exfoliated systems
(Universidade Federal de São Carlos, 2017-10-30) Meneses Gustin, Diana Mercedes; Richard, Victor Lopez; https://lattes.cnpq.br/4492188799583104; https://lattes.cnpq.br/0910995987339213
This thesis is aiming to study, according to a theoretical approaches, the electronic and optical properties of quasi-2D semiconductor quantum systems. Using the k · p model as basis we obtained a satisfactory set of results that explain certain optical processes, described below, of nanoscale confined systems such as quantum wells or monolayer atoms. The need and the systematic implementation of new and higher levels of approximation from the original electronic structure models also are themes broadly described here. One of the first contributions of this study was the verification of the necessity of a new approach to describe the phonon-carrier interactions in GaAs-based quantum wells beyond the deformation potential theory. Thus, the Frohlich interaction was considered in our model, revealing the existence of phonon assisted couplings between different states in the valence and conduction band, which resulted in significant changes in the electronic structure. The results of this approach, as well as the simulations and new predictions allowed us to explain two intriguing effects: (i) the potential observation of magneto-polarons of light-heavy holes, (ii) the relevance of 2D states as intermediaries in relaxation processes, assisted by phonons, from a 3D structure to a 0D. Another system studied was the two-dimensional molybdenum disulphide (MoS 2 ), in which the carrier scattering depends on perturbation locally induced in the material. One version of the Dirac Hamiltonian for massive particles was used. The scattering processes have been described in terms of the phase shift and the corresponding cross sections. By comparing the results of this model with those obtained using a parabolic dispersion relation with an appropriate effective mass was possible to obtain interesting information regarding the conductivity of both electronic models. The asymptotic regimes of each of the models were also studied, and for low energies, where both dispersions coincide in parabolic bands, the scattering process is dominated by channels with low angular momentum and still result in almost comparable dispersion amplitudes. On the other hand, the differential cross section in the high energy regime has the clear signature of the two scattering relations. The understanding of the electronic dynamics in these systems is promising for the design of structures with desired functionalities, as exemplified by presenting the differential cross sections for different types of scattering centers.
Imobilização de lipases pela técnica CLEA para síntese de biodiesel em reator de fluxo em vórtice
(Universidade Federal de São Carlos, 2017-10-30) Díaz-Ramos, Margarita; Kopp, Willian; https://lattes.cnpq.br/3856554957880380; Tardioli, Paulo Waldir; https://lattes.cnpq.br/0808991927126468; https://lattes.cnpq.br/0650674183874339
Due to the heterogeneity of the vegetable oils used in the synthesis of biodiesel, they can be transformed more quickly using a mixture consisting of lipases with different activities and specificities instead of single lipases. In this context, this PhD work aimed to evaluate the enzymatic synthesis of biodiesel in vortex flow reactor catalyzed with a mixture of lipases. The lipases were selected and later immobilized by a low-cost technique known as CLEA (cross-linked enzyme aggregate). Mixtures of two lipases from different sources including Thermomyces lanuginosus (TLL), Candida antarctica fraction B (CALB), porcine pancreas (PPL) and Pseudomonas fluorescens (PFL) lipases were evaluated in the transesterification of soybean oil. The mixture of 50 % of PPL and 50 % of TLL reached the highest concentration of fatty acid ethyl esters (FAEE). Under the conditions evaluated, it was obtained 22.03% in 8 h, whereas the individual lipases, TLL and PPL reached 4.32 % and 0.22 % of FAEE, respectively. These lipases were individually immobilized by CLEA technique and evaluated (individually and mixed) in the ethylic transesterification of soybean oil. The PPL CLEA, called PPL-SP-CLEA, reached around 60 % FAEE, a concentration 12 times higher than that achieved with soluble PPL after 34 h of reaction and with a 2-fold lower enzymatic loading. On the other hand, the LTL CLEA, called LTL-SDS-CLEA, was prepared using ethanol as a precipitant, the surfactant sodium dodecyl sulfate (SDS) and glutaraldehyde. The CLEAs LPP-PS-CLEA and LTL-SDS-CLEA were used in a mixture (50 % - 50 %) to catalyze the transesterification of soybean oil. The use of the mixture within 48 hours of reaction resulted in the increase of the final FAEE concentration of almost 20% relative to the individual CLEAs. Through 10 h of reaction, the mixture of CLEAs reached 90% of the FAEE mass concentration. Finally, this mixture was evaluated in the vortex flow reactor, reaching 86.1% of FAEE in 6 h of reaction and saving nearly 80% of activity through 5 cycles of reaction. The mixture of CLEAs LPP-PS-CLEA and LTL-SDS-CLEA showed to be a potential approach to improve the rate of the transesterification reaction, by the synergistic action of lipases.
Os sistemas de treinamento de força pirâmide crescente e drop-set não promovem maiores ganhos de força, massa muscular e mudanças na arquitetura muscular comparado ao treinamento de força tradicional em homens treinados
(Universidade Federal de São Carlos, 2017-10-30) Angleri, Vitor; Libardi, Cleiton Augusto; https://lattes.cnpq.br/8953409094842074; https://lattes.cnpq.br/7516265500891144
Purpose The aim of this study was to compare the effects of crescent pyramid (CP) and Drop-set (DS) systems with traditional resistance training (TRAD) with equalized total training volume (TTV) on maximum dynamic strength (1-RM), muscle cross-sectional area (CSA), pennation angle (PA) and fascicle length (FL). Methods Thirty-two volunteers had their legs randomized in a within-subject design in TRAD (3-5 sets of 6-12 repetitions at 75% 1-RM), CP (3-5 sets of 6-15 repetitions at 65-85% 1-RM) and DS (3-5 sets of ~50-75% 1-RM to muscle failure) protocols. Each leg was trained for 12 weeks. Participants had one leg fixed in the TRAD while the contralateral leg performed either CP or DS to allow for TTV equalization. Results The CSA increased significantly and similarly for all protocols (TRAD: 7.6%; CP: 7.5%; DS: 7.8%). All protocols showed significant and similar increases in leg press 45º (TRAD = 25.9%; CP = 25.9%; DS = 24.9%) and leg extension 1-RM loads (TRAD = 16.6%; CP = 16.4%; DS = 17.1%). All protocols increased PA (TRAD = 10.6%; CP = 11.0%; DS = 10.3%) and FL (TRAD = 8.9%; CP = 8.9%; DS = 9.1%) similarly. Conclusion CP and DS systems do not promote greater gains in strength muscle hypertrophy and changes in muscle architecture compared to traditional resistance training.