Abstract This study processed and characterized the biphasic ceramics Na2Ti3O7/Na2Ti6O13 that were obtained from semi-crystalline nanoparticles synthesized using sonochemical methods. Structural characterization techniques, such as X-ray diffraction and Raman spectroscopy, were used to identify the crystalline phases present. The Rietveld refinement revealed, among other structural parameters, the presence of two crystalline phases in compositions of 55.90% and 44.10% for sodium hexatitanate and trititanate, respectively. Via Raman spectroscopy, the presence of the main vibrational modes that correspond to the phases present in biphasic ceramics was confirmed. Finally, by using complex impedance spectroscopy, a decrease in the electrical resistance of both the grain (106 Ω-104 Ω) and its boundary (108 Ω -105 Ω) under increasing temperature was identified.

Abstract This article presents the theoretical analysis of a signal coupling between a proposed Photonic Crystal Fiber (PCF) and a Conventional Fiber with Step Index (CFSI) system. In this analysis, the Finite Element Method (FEM) and Beam Propagation Method (BPM) are applied together with Daubechies wavelets as basis function and described in the mathematical formulation. The simulations were performed casting the PCF signal into CFSI core using the PCF refractive index. For simulation purposes, the cladding material refractive index was set as 1.5% lower than the core index. The application of Daubechies wavelets as basis functions in BPM analysis presented insertion loss around 3.8% during the fiber coupling.

Abstract In this paper, an optical coupler composed by a photonic quasi-crystal fiber (PQCF) with two cores is proposed. The structure is obtained by immersion of a quasi-periodic arrangement of air holes replicated twelve-fold in a conventional fiber optical constituted of pure silica. The cores are generated from defects caused due to absence of two air holes on each identical core and horizontally equidistant from the center of PQCF. The chromatic dispersion in each fiber core is ultra-flat around 38.12 ps.nm-1.km-1 and to verify the power transfer, the signal was launched on the left core and transferred to the right core in a propagation length of approximately 3.78 cm.

Abstract The interest in biodiesel as an alternative source of energy has been extremely intensified by its use as a renewable and economically viable fuel. As a result, continuous production processes have been a requirement to supply growing demand. This work presents experimental and simulated results of two biodiesel production pilot plants and makes a comparison between the processes they use. The first one was designed with three plug flow reactors (PFRs) connected with recycle streams. The second one was composed of a reactive distillation process for biodiesel production. Repeated tests in Aspen Plus and Matlab showed that multiple PFRs with high volume are required for 98% ester conversion. However, a single unit of reactive distillation resulted in 99% conversion. In short, to produce large quantities of biodiesel this work indicates continuous reactive distillation as the most adequate process.

The ethanol production by Pichia stipitis was evaluated in a stirred tank bioreactor using semi-defined medium containing xylose (90.0 g/l) as the main carbon source. Experimental assays were performed according to a 2² full factorial design to evaluate the influence of aeration (0.25 to 0.75 vvm) and agitation (150 to 250 rpm) conditions on ethanol production. In the studied range of values, the agitation increase and aeration decrease favored ethanol production, which was maximum (26.7 g/l) using 250 rpm and 0.25 vvm, conditions that gave a volumetric oxygen transfer coefficient (kLa value) of 4.9 h-1. Under these conditions, the ethanol yield factor, ethanol productivity, and the process efficiency were 0.32 g/g, 0.32 g/l.h, and 63%, respectively. These results are promising and contribute to the development of a suitable process for ethanol production from xylose by Pichia stipitis.