Mathematical Modeling of the Twin Roll Casting Process for Magnesium Alloy AZ31

Although Twin Roll Casting (TRC) process has been used for almost 60 years in the aluminum industry, TRC of magnesium is relatively new. In TRC, molten metal is fed onto water-cooled rolls, where it solidifies and is then rolled. Solidification of the molten metal starts at the point of first metal-roll contact and is completed before the kissing point (point of least roll separation) of the two rolls. The unique thermo-physical properties inherent to magnesium and its alloys, such as lower specific heat and latent heat of fusion and larger freezing ranges (in comparison with aluminum and steel) make it challenging for TRC of this alloy. Therefore, a comprehensive understanding of the process and the interaction between the casting conditions and strip final quality is imperative to guarantee high quality twin roll cast strip production. A powerful tool to achieve such knowledge is to develop a mathematical model of the process. In this thesis, a 2D mathematical model for TRC of AZ31 magnesium alloy has been developed and validated based on the TRC facility located at the Natural Resources Canada Government Materials Laboratory (CanmetMATERIALS) in Hamilton, ON, Canada. The validation was performed by comparing the predicted exit strip temperature and secondary dendrite arm spacing (SDAS) through the strip thickness with those measured and obtained by experiments. The model was developed in two stages, first a thermal-fluid model was developed followed by validation and then a thermal-fluid-stress model was developed. This is the first time a comprehensive thermal-fluid-stress model has been developed to simulate the TRC process for magnesium alloys. The work has led to new knowledge about the TRC process and its effects on magnesium strip quality including the following: 1) Using ALSIM and ANSYS® CFX® commercial packages a 2D mathematical model of thermal-fluid-stress behavior of the magnesium sheet during TRC was successfully developed and validated. 2) An average value of 11 kW/m2°C for the Heat Transfer Coefficient (HTC) was found to best represent the heat transfer between the roll and the strip during TRC casting of AZ31 using the CanmetMATERIALS facility. 3) Modeling results showed that increasing casting speed, casting thicker strips and applying higher HTCs led to less uniform microstructure through thickness in terms of SDAS. 4) Simulations showed the importance of casting parameters such as casting speed and set-back distance on the thermal history and stress development in the sheet during TRC; higher casting speeds led to deeper sumps and higher exit temperatures as well as lower overall rolling loads and lower total strains experienced during TRC. 5) The effect of roll diameter on the thermal history and stress development in the strip was also studied and indicated how larger roll diameters increased the surface normal stress and rolling loads but had little effect on the mushy zone thickness. 6) The correlation between the mechanisms of center-line and inverse segregation formation and thermo-mechanical behavior of the strip was performed. The modeling results suggested that increasing the set-back distance decreases the risk of both defects. Moreover, increasing the roll diameter reduces the propensity to inverse segregation but has a minor effect for center-line segregation formation

The study of mitochondrial ATP6, ND3 and COX3 gene nucleotide variations in Iranian patients with atherosclerosis by PCR-SSCP

Background and aims: Atherosclerosis is a complex arterial disease that is caused due to the interaction of genetic and environmental factors. Mutations in the mitochondrial genome have probably a direct effect on increased oxidative stress and thereby cause progression of the disease. The aim of the current study was to identify the possible nucleotide changes in the mitochondrial ATP6, ND3 and COX3 genes in Iranian patients with atherosclerosis. Methods: In this case-control study, DNA was extracted from peripheral blood of 90 patients with atherosclerosis and 95 healthy individuals by standard method. The regions of the mitochondrial genome including ATP6, ND3 and COX3 genes were studied by PCR-SSCP; and banding shift specimens were sequenced to determine the exact nucleotide changes. The obtained data were analyzed using the Fisher's exact test and GraphPad prism software. Results: The results of SSCP and DNA sequencing lead to the detection of three nucleotide changes in ATP6 gene including a synonymous polymorphism at position m.9034 G>A, and an SNP at position m.9055 G>A, in which alanine is converted to tyrosine and synonymous hetroplasmic variant at m. 9162C>T. Also, it was found three homoplasmic nucleotide variations including synonymous m.9602A>G, m.9899T>C related to histidine amino acid and homoplasmic variant m.9929C>A that resulted in changing of tyrosine to stop codon. Conclusion:. Since it has been proven, m.9055G>A variant increases the risk of developing breast cancer, and on the other hand, this polymorphism has also been reported in the Caucasian population of Parkinson's; Therefore, it can be said that the combination of this mutation with other predisposing factors increases the severity of coronary heart disease. Investigating other mitochondrial genes could be regarded important in order to find the the relationship between nucleotide changes of mitochondrial genes cardiovascular diseases

Mathematical modeling of thermo-mechanical behavior of strip during twin roll casting of an AZ31 magnesium alloy

The definitive publication is available at Elsevier via https://doi.org/10.1016/j.jma.2013.04.001 © 2013. This publisher's version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/The effect of set-back distance on the thermo-mechanical behavior of the strip during twin roll casting (TRC) of an AZ31 magnesium alloy was modeled using finite element method (FEM). Model validation was done by comparing the predicted and measured exit strip surface temperature as well as the secondary dendrite arm spacing (SDAS) through the thickness of the sheet to those measured during experiments. Model results showed as the set-back distance increases, the strip exit temperature decreases and the solidification front moves toward the entry of the roll gap. The cast strip also experiences more plastic deformation and consequently, the normal stress on the strip surface and effective strain at the strip center-line increase. Moreover, higher separating forces were predicted for longer set-back distances. Model predictions showed that changing the set-back distance by varying the final thickness has a more significant effect on the temperature and stress-strain fields than altering the nozzle opening height.Natural Sciences and Engineering Research Council of CanadaMagnesium Strategic Research Networ

A Generalization Concept of Measure by Using Binary Operations

In this paper, a generalization of the concept of measure is made using binary oprations. With this generalization, we extend the measure domain to . In the future, the properties of this new concept will be examined

Novel and heteroplasmic mutations in mitochondrial tRNA genes in Brugada syndrome

  Background: Brugada syndrome (BrS) is a rare cardiac arrhythmia characterized by sudden death associated with electrocardiogram patterns characterized by incomplete right bundle-branch block and ST-segment elevations in the anterior precordial leads. This syndrome predominantly is seen in younger males with structurally normal hearts. Mitochondrial variants particularly mt-tRNA mutations, are hot spots that lead to cardiological disorders. Previous studies have shown that mutations in mitochondrial tRNA genes play an important causal or modifying role in BrS. The present study aims to evaluate the involvement of mitochondrial tRNA genes in arrhythmogenic BrS. Methods: In this study, 40 Iranian patients were investigated for the presence of the mutations in 6 mitochondrial tRNA genes (tRNA Ile, Met, Gln, Asn, Ala and Trp) by PCR-SSCP analysis. Results: There were 4 mutations in tRNA genes, that for first time, were found in BrS patients and these mutations were not in controls. Three of them were heteroplasmic and located in tRNAGln (T4377A) and tRNAMet (G4407A and C4456T) which were assessed as pathogenic mutations. A homo­plasmic variant (5580T > C) in tRNATrp gene was located within the junction region between tRNATrp and tRNAAla genes. This mutation may disturb the processing of mt-tRNATrp. Conclusions: The results of this study suggest that mutations in mitochondrial tRNA genes might lead to deficiencies in translational process of critical proteins of the respiratory chain and potentially lead to BrS in Iranian subjects. (Cardiol J 2018; 25, 1: 113–119

Theoretical and experimental study of the protonated 2,4,6-tri(2-pyridyl)-1,3,5-triazine [TPTZH 2 ] 2+

The reaction between 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) and sulfuric acid in the presence of NH4PF6 yielded crystals of [TPTZH2](PF6)2·H2O, characterized by spectroscopic methods and single-crystal X-ray diffraction. The structural data indicat

A new precursor for preparation of magnetite (Fe3O4) nanoparticles

An anionic Fe(II) complex, (BMIM)4[Fe(CN)6] (where BMIM is 1-butyl-3-methylimidazolium), was synthesized in ionic liquid [BMIM][PF6] under reflux condition. The complex was characterized by elemental analysis and spectroscopic methods. The magnetite (Fe3O4) nanoparticles were prepared by the hydrothermal and solvothermal (in ionic liquid [BMIM][PF6]) methods from (BMIM)4[Fe(CN)6] as a precursor. The nanoparticles were characterized by X-ray diffraction (XRD), FT-IR, and scanning electron microscopy (SEM). The results show that the preparation of magnetite using the solvothermal method in [BMIM][PF6] has more advantages such as smaller size and high purity

(Carbonato-κ2 O,O′)bis­(1,10-phenan­throline-κ2 N,N′)cobalt(III) nitrate monohydrate

The crystal structure of the title compound, [Co(CO3)(C12H8N2)2]NO3·H2O, consists of CoIII complex cations, nitrate anions and uncoordinated water mol­ecules. The CoIII cation is chelated by a carbonate anion and two phenanthroline ligands in a distorted octa­hedral coordination geometry. A three-dimensional supra­molecular structure is formed by O—H⋯O and C—H⋯O hydrogen bonding, C—H⋯π and aromatic π–π stacking [centroid–centroid distance = 3.995 (1)Å] inter­actions

Bis[4-(2-benzyl­idenepropyl­idene­amino)phen­yl] ether

The title compound, C32H28N2O, is a flexible Schiff base displaying a trans configuration across the C=N double bond. It was prepared in high yield by condensation of α-methyl­cinnamaldehyde and bis­(4-amino­phen­yl) ether in methanol at room temperature. The sample, with pseudo-ortho­rhom­bic cell parameters, exhibited merohedral twinning by rotation 180° around a*, with a refined twin domain fraction of 0.722 (1). The elongated shape of the elementary cell corresponds to the shape and direction of the mol­ecules. The dihedral angle between the O-linked aromatic rings is 57.86 (8)°

Diiodido(2,3,5,6-tetrapyridin-2-yl­pyrazine-κ3 N 2,N 1,N 6)zinc(II)

In the title compound, [ZnI2(C24H16N6)], the ZnII ion is five-coordinated in a distorted trigonal-bipyramidal geometry by an N,N,N-tridentate 2,3,5,6-tetra-2-pyridinylpyrazine ligand and two iodide ions. The I− ions both occupy equatorial sites. Within the ligand, the dihedral angles between the central pyrazine ring and the two chelating pyridine (py) rings are 14.74 (17) and 26.72 (18)°. The equivalent angles for the non-coordinating py rings are 28.63 (16) and 42.19 (17)°. There is no aromatic π–π stacking in the crystal