Nanospheres Containing Urea: Photothermic Properties

In the present research, nanospheres of chitosan (CS), maltodextrin, and sodium tripolyphosphate (STPP), loaded with urea, were synthesized by using an ionic gelation technique. In the nanosphere synthesis was used a central composite experimental design, obtaining nanospheres with an average size of 275?±?32 nm and 27.5 mV zeta potential. The nanospheres were characterized by their hydrodynamic diameter, polydispersity index, nitrogen content, and thermal properties such as thermal diffusivity (α), effusivity (e), and conductivity (k); also melting temperature was obtained by differential scanning calorimetry. The thermal properties of nanospheres show that the sample with the smallest size has a thermal diffusivity value of (14.4?±?0.4)?×?10^?8 m²·s^?1 and a thermal conductivity value of (6.4?±?0.1)?×?10^?1 W·m^?1·K^?1, and the obtained melting temperature was 157 °C. Higher concentrations of CS increase the values of these thermal properties, probably because chitosan interacts ionically with STPP forming a reticular network due to the opposite charges of both molecules.     

Probabilistic Boolean network modeling of an industrial machine

Theoretical modeling of manufacturing processes assists the design of new systems for predictions of future behavior, identifies improvement areas, and evaluates changes to existing systems. A novel approach is proposed to model industrial machines using probabilistic Boolean networks (PBNs) to study the relationship between machine components, their reliability and function. Once a machine is modeled as a PBN, through identification of regulatory nodes, predictors and selection probabilities, simulation and property verification are used to verify model correctness and behavior. Using real machine data, model parameters are estimated and a PBN is built to describe the machine, and formulate valid predictions about probability of failure through time. Two models were established: one with non-deterministic inputs (proposed), another with components’ MTBFs inputs. Simulations were used to generate data required to conduct inferential statistical tests to determine the level of correspondence between predictions and real machine data. An ANOVA test shows no difference between expected and observed values of the two models (p value = 0.208). A two-sample T test demonstrates the proposed model provides values closer to expected values; consequently, it can model observable phenomena (p value \(=\) 0.000). Simulations are used to generate data required to conduct inferential statistical tests to determine the level of correspondence between model prediction and real machine data. This research demonstrates that using PBNs to model manufacturing systems provides a new mechanism for the study and prediction of their future behavior at the design phase, assess future performance and identify areas to improve design reliability and system resilience.     

Smooth interfaces for spectral element method for the solution of incompressible Newtonian fluid flow

A smoothing technique is developed to calculate the interface conditions of spectral element method for solving the incompressible Newtonian fluid flow. The first derivative at the interface of spectral elements is calculated by using only the adjacent subdomains. Numerical simulations of an incompressible laminar fluid flow through a planar channel and a 2:1 planar contraction channel are presented for various Reynolds numbers.

A new approach for power system online DSA using distributed processing and fuzzy logic

In this paper, a new approach for power system online dynamic security assessment, as well as a tool for calculating the proposed fuzzy dynamic security index is presented. This proposal is based on a three-stage fuzzy inference system, which composes the fuzzy dynamic security index making use of seven performance indexes herein defined. The calculation of the performance indexes is based on the results obtained through dynamic simulations of the system behaviour after each one of the credible contingencies in a given operation state. With the aim of reducing the calculation time a novel distributed processing of the dynamic simulations is also developed. High voltage systems are used to illustrate the ideas presented in the paper.     

Integrated transient thermal and mechanical analysis of molded PBGApackages during thermal shock

During thermal shock, large thermal gradients exist within a molded plastic ball grid array (PBGA) package. The conventional assumption of uniform temperature distribution becomes invalid. In this paper, an integrated thermal-mechanical analysis was performed to evaluate the transient effect of thermal shock. For comparison, an isothermal analysis was also conducted. The computational fluid dynamics (CFD) method was used to obtain the thermal boundary conditions surrounding the package. The heat transfer coefficient obtained through CFD was compared to two analytical solutions. It was found that the analytical values were not acceptable in the time period of interest. Therefore, to obtain the actual maximum die stress, CFD solution has to be used instead of analytical solutions to derive the thermal boundary condition. This boundary condition was then applied to the package and a sequentially coupled heat transfer and thermal stress analysis was performed. The transient analysis has shown that high stresses occur in the die due to thermal shock, which can not be seen under the traditional isothermal assumption. The impact of plastic ball grid array (PBGA) package parameters on transient die stress was also studied, including mold thickness and substrate thickness. The results in this paper could be applied to either wire bond or flip-chip PBGA packages     

Do zoom meetings really help? A comparative analysis of synchronous and asynchronous online learning during Covid-19 pandemic

Background

Online learning and teaching were globally popularized due to the impact of Covid-19. The pandemic has made both synchronous and asynchronous online learning inevitable in regions privileged with the technological affordance.

Aims

This study was designed to examine and compare the effectiveness of both learning modes through the Community of Inquiry framework.

Materials & Methods

Comparative analyses on a sample of N = 170 undergraduate students who took both synchronous and asynchronous online courses in Spring 2021.

Results

The paired-sample T-tests results indicated a significant difference in social presence, cognitive presence and self-evaluated performance.

Discussion & Conclusion

Teaching presence significantly influenced social presence and cognitive presence in both learning modes. However, under synchronous learning mode, social presence significantly impacted self-evaluation, grades and school identification. While social presence only influenced school identification under asynchronous learning mode. Theoretical and practical implications were also included.     

On the relationship between cooling setup and warpage in injection molding

Injection molding process causes differences between designed shape and real parts, all of them associated to shrinkage phenomena. Temperature and pressure distribution during molding process originate local shrinkage, and the internal stresses induces warpage depending on the relative stiffness of each part area.     

Engineering Acidithiobacillus ferrooxidans growth media for enhanced electrochemical processing

The chemolithoautotroph Acidithiobacillus ferrooxidans has been proposed as a potential electrofuel synthetic platform, and its growth medium is engineered to increase its conductivity and energy density, thereby improving viability of the process. The ion V³⁺ is used as an indirect electron supplier together with Fe²⁺ to grow A. ferrooxidans to increase the energy density of the medium, overcoming the Fe³⁺ solubility limit. A medium containing 10 mM Fe²⁺ with 60 mM V³⁺ was able to support cell growth to a final cell concentration very similar to medium of 70 mM Fe²⁺. Integration of the biological process with an electrochemical reactor requires, for economical operation, a medium with high ionic conductivity. This is achieved by the addition of salt, and Mg²⁺ was found to be least toxic to the bacterium. A concentration of 500 mM Mg²⁺ is optimal considering constraints on bacterial growth and electrochemistry. © 2014 American Institute of Chemical Engineers AIChE J 60: 4008–4013, 2014