A mathematical model for determining the best process conditions for average Molecular weight and melt flow index of polypropylene

The present work describes a mathematical model based on a population balance approach for determining the effect of the reaction temperature and hydrogen amount on the vital final product properties including average molecular weight and polydispersity index and flow index of polypropylene and also the profile rate of the polymerization. The aim of this study was to find the best operating condition through a model which is validated by the experimental data. The software program was coded in MATLAB/SIMULINK. The model profile rates compared with the experimental results to show the accuracy of the model. In this study, it was concluded that increasing the reaction temperature until a certain limit is useful and improve some indices of the final product and after that rising the reaction temperature has a harmful effect on the indices. Exactly the same issue is true in the case of increasing the amount of hydrogen.               KEY WORDS: Mathematical modeling, Propylene polymerization, Melt flow index, Population balance, Average molecular weight, hydrogen Bull. Chem. Soc. Ethiop. 2019, 33(1), 169-182DOI: https://dx.doi.org/10.4314/bcse.v33i1.1

Antibacterial and Antifungal Activities of Punica Granatum Peel Extracts Against Oral Pathogens

Objective: Punica granatum has been used for many years in folk medicine due to several purposes. The aim of the present study was to evaluate the effect of methanolic extract of Punica granatum peel (MEPGP) against Streptococcus mutans, Staphylococcus aureus,Streptococcus salivarius, Streptococcus sanguinis, Staphylococcus epidermidis, Actynomyces viscosus, Lactobacillus acidophilus and Candida albicans.Materials and Methods: In this in vitro study, the mentioned oral organisms were cultured in blood agar and mueller-hinton media and then paper disks containing MEPGP at concentrations of 4 mg/ml, 8 mg/ml and 12 mg/ml were inserted on medias. The antimicrobialactivity was evaluated by agar disk diffusion method. The effects of three different concentrations of MEPGP against microorganisms were compared using one-way ANOVA and Tukey tests.Results: All concentrations of MEPGP had antibacterial activity against S. aureus and S.epidermidis. Only at concentration of 8 mg/ml and 12 mg/ml MEPGP was effective against L. acidophilus, S. mutans and S. salivarius. Furthermore; no concentrations ofMEPGP inhibited A. viscosus and C. albicans.Conclusion: This study suggests that MEPGP might be used as an antibacterial agent in controlling oral infections

In-situ Monitoring and Defect Detection of Selective Laser Melting Process and Impact of Process Parameters on the Quality of Fabricated SS 316L

Selective Laser Melting (SLM) is an advanced Additive Manufacturing (AM) technique for the 3D printing of metals. SLM process parameters and different types of defects that may appear during the manufacturing process affect the quality of the final product. Setting laser parameters and online defect detection contributes to improving the quality of parts fabricated through SLM technology. In this study, the effect of the process parameters on the properties of the product built by the SLM process was investigated, and an in-situ monitoring platform was developed to detect two types of defects during the SLM process. Different samples were built from stainless steel AISI 316 L powder, utilizing various laser process parameters. Using microscopy imaging technique, the melt structure features of the constructed samples were tested, and the results were analyzed. The dependency of porosity formation on laser process parameters and scan strategy was investigated. Moreover, hardness test was performed for all built samples. The platform developed for in-situ monitoring purposes includes an AM machine equipped with pulsed laser, camera, illumination system, and powerful industrial computer equipped with Cameral Link Adapter, FPGA, and Real-Time (RT) modules. An algorithm was designed using LabVIEW® software based on Particle Analysis (PA) to cease the process in the event of detection of defect in any fused layers. The first defect was caused by changing the laser spot diameter, which altered the energy intensity of the laser on the surface, and the second defect was created by the uneven thickness of powder on the platform. The monitoring system detected both defects and stopped the process immediately according to the designed algorithm. Images were taken from the melting process layer by layer using a high-performance camera.</p

Hydrogen effect modeling on Ziegler-Natta catalyst and final product properties in propylene polymerization

Hydrogen, as chain transfer agent, effects on kinetic of propylene polymerization; consequently variation of hydrogen concentration leads to change final product properties and also activates site of used catalyst. This phenomenon is one of the most important process variables is to adjust the final product properties and optimize the operating conditions. This work has attempted to present a mathematical model that cable to calculate the most important indices of end used product, such as melt flow index, number and weight average molecular weight and poly dispersity index. The model can predict profile polymerization rates determining important kinetic parameters such as the activation energy, lumped deactivation reaction initial reaction rate and deactivation constant. The mathematical model was implemented in Matlab/Simulink environment for slurry polymerization in laboratory scale. The modeling approach is based on polymer moment balance method in the slurry semi-batch reactor. In addition, in this work have provided a model that calculating fraction activated sites catalyst via hydrogen concentration. The model was validated by experimental data from lab scale, reactor. The experimental and model outputs were compared; consequently, the errors were within acceptable range.               KEY WORDS: Mathematical modeling, Propylene polymerization, Kinetics study, Hydrogen response, population balance Bull. Chem. Soc. Ethiop. 2018, 32(2), 371-386.DOI: https://dx.doi.org/10.4314/bcse.v32i2.1

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum