Thermal-Microstructural Analysis of Anodic and Electrolytic Copper Solidification: Simulation and Experimental Validation

This work analyzes the solidification process of anodic and electrolytic copper. The aim of this study is to perform an experimental validation of numerical results computed using a proposed thermal formulation including microstructural evolution. To this end, a set of experiments is carried out testing primary and eutectic phase formation in copper. To evaluate the formation of different microstructural phases, anodic copper (99.80 pct purity, approximately) and electrolytic copper (99.99 pct purity, approximately) are used. Primary and eutectic phases evolve in anodic copper; meanwhile, only a primary phase is obtained in electrolytic copper. The effect of heat extraction conditions is evaluated using sand, graphite, and steel molds to promote different cooling rates. The proposed microstructural model takes into account nucleation and grain growth laws based on thermal undercooling together with microstructural evolution. The primary copper evolution model is based on solute diffusion at the grain scale and on the dendrite top-growing kinetic; meanwhile, the eutectic evolution is assumed proportional to the copper initial composition and eutectic undercooling. The corresponding numerical formulation is solved in the framework of the finite-element method. Finally, the computed temperature histories and final values for the grain density and radius, including primary or dendritic phase and eutectic solid volumetric fractions, are all compared and validated with the experimental measurements.     

Kinetics of L-tryptophan production from indole and L-serine catalyzed by whole cells with tryptophanase activity

The essential amino acid L-tryptophan can be produced by a condensation reaction between indole and L-serine, catalyzed by whole cells of Escherichia coli B1t-7A with tryptophanase activity. The reaction was previously studied using soluble tryptophanase, a kinetic mechanism proposed and the catalytic properties of the enzyme described. It is important, however, to determine the kinetic parameters of the reaction catalyzed by whole cells, if the process is to be designed with the catalyst in this form. The reaction stoichiometry was established, a mole of product being formed from a mole of each reactant, with no indication of side reactions under the conditions used. The two-substrate reaction kinetics were characterized and modelled, assuming an enzyme-substituted mechanism and no product inhibition. Theoretical consumption rates of indole were compared with experimental values obtained in a batch reactor system. The K(m) values of whole cells towards L-serine and indole were 1.79 M and 0.07 M, respectively. These values are, as expected, considerably higher than their counterparts for soluble tryptophanase.     

ATR-FTIR Study of the Decomposition of Acetic Anhydride on Fosfotungstic Wells–Dawson Heteropoly Acid Using Concentration-Modulation Excitation Spectroscopy

The decomposition of acetic anhydride in liquid phase on a fosfotungstic Wells–Dawson heteropoly acid (HPA) was investigated by in situ ATR-FTIR spectroscopy. Transient and concentration-modulation excitation spectroscopy (MES) experiments in combination with phase-sensitive detection (PSD) were used to monitor the solid–liquid interface. The MES method is based on the periodic variation of a parameter of the reaction media such as, the reactant concentration. That periodic alteration causes varying infrared signals of the surface adsorbed species that are subsequently demodulated with the PSD methodology. Thus, the separation of the static signals from the changing ones is achieved, and species with different response can be observed in the spectra. Using MES-PSD coupled with ATR-FTIR, acetic anhydride was observed to decompose to acetic acid, acetate and acyl [CH₃C(O)⁺] species, involving Brønsted acid sites of the HPA catalyst. The CH₃C(O)⁺ is a very unstable intermediate species and it is the key intermediate in the Friedel–Crafts acylation reactions. Moreover, the acetate groups are spectator species since remain strongly adsorbed on the catalyst surface and do not further react.     

Robust h-index

Scientometrics - The h-index is the most used measurement of impact for researchers. Sites such as Web of Science, Google Scholar, Microsoft Academic, and Scopus leverage it to show and compare the...     

A nature-inspired biomarker for mental concentration using a single-channel EEG

Neural Computing and Applications - We developed a system for measuring the attentional process during the performance of specific activities. The proposed biomarker device is able to estimate the...     

Decoration of Squalenoyl-Gemcitabine Nanoparticles with Squalenyl-Hydroxybisphosphonate for the Treatment of Bone Tumors

Therapeutic perspectives of bone tumors such as osteosarcoma remain restricted due to the inefficacy of current treatments. We propose here the construction of a novel anticancer squalene-based nanomedicine with bone affinity and retention capacity. A squalenyl-hydroxybisphosphonate molecule was synthetized by chemical conjugation of a 1-hydroxyl-1,1-bisphosphonate moiety to the squalene chain. This amphiphilic compound was inserted onto squalenoyl-gemcitabine nanoparticles using the nanoprecipitation method. The co-assembly led to nanoconstructs of 75 nm, with different morphology and colloidal properties. The presence of squalenyl-hydroxybisphosphonate enhanced the nanoparticles binding affinity for hydroxyapatite, a mineral present in the bone. Moreover, the in vitro anticancer activity was preserved when tested in commercial and patient-treated derived pediatric osteosarcoma cells. Further in vivo studies will shed light on the potential of these nanomedicines for the treatment of bone sarcomas.     

Probability density functions for bubble size distribution in air–water systems in stirred tanks

Bubble size distribution (BSD) is relevant to the design of gas–liquid systems, as it determines the interfacial area available in heat and mass transfer processes. Although data on BSD in stirred aerated tanks are available, a systematic comparison of alternative modeling functions for these data is lacking. In this work, BSDs obtained in air–water dispersions in a stirred aerated tank with a Rushton turbine and BSDs available in the literature for similar systems were modeled by 14 empirical probability density functions (PDFs). It was found that both the distribution of Nukiyama–Tanasawa with three adjustable parameters and the Rosin–Rammler distribution with two adjustable parameters reasonably fit original and literature BSDs. It is also concluded that it is possible to correlate the PDF parameters with the power dissipated by the agitator in the liquid phase, allowing the BSD to be modeled with only two parameters in a range of dissipated power from 0.5 to 2.3?kW/m³. BSDs thus modeled provide good predictions of average bubble size.     

A domain specific language notation for a language learning activity generation tool

Multimedia Tools and Applications - Globalization has increased the need for society to master new languages. This need has encouraged the launch of many applications dedicated to language...