Poly(methyl methacrylate)‐modified epoxy/amine system for reactive rotational moulding: crosslinking kinetics and rheological properties

BACKGROUND: The rotational moulding of thermosetting resins is hampered by their low viscosity and the abrupt increase in their viscosity as they polymerize. This study investigates the use of poly(methylmethacrylate) (PMMA) as a rheological processing aid in reactive blends of an aromatic diepoxy resin (diglycidyl ether of bisphenol‐A, DGEBA) and an aromatic diamine (diethyltoluenediamine, DETDA) by studying the miscibility, curing, rheology, dynamic properties and morphology of the uncured solutions and of the resulting highly crosslinked polymer blends. RESULTS: The PMMA was miscible in the uncured resins as expected from consideration of their solubility parameters, and the effect of PMMA concentration on the glass transition temperature, measured via differential scanning calorimetry (DSC), was fitted to several models. Addition of PMMA significantly increased the viscosity of the uncured blend which obeyed the log‐additivity rule. The curing behaviour was monitored using DSC, infrared spectroscopy and dynamic rheology and it was found that addition of PMMA caused a small reduction in rate due to a dilution effect. The dynamic and steady shear rheologies were used to determine the gel point and gel relaxation index. Dynamic mechanical thermal analysis provided evidence for phase separation of the components into PMMA‐rich domains and an epoxy‐rich matrix and this was confirmed with electron microscopy studies. CONCLUSION: These results indicate that addition of small amounts of PMMA to DGEBA/DETDA enlarges the processing window with regards to the rotational moulding of thermosets. In addition, the blending of small amounts (ca 10 wt%) of PMMA with the DGEBA/DETDA resin appears to cause only a modest sacrifice in thermal resistance. Copyright © 2009 Society of Chemical Industry     

Hydrocephalus requiring urgent external ventricular drainage in a patient with diabetic ketoacidosis and cerebral edema: case report

OBJECTIVE AND IMPORTANCE: Neurological deterioration, typically attributed to cerebral edema, is a rare but life-threatening complication in the treatment of diabetic ketoacidosis (DKA). We report the case of a child with DKA who became comatose but demonstrated acute obstructive hydrocephalus, instead of cerebral edema. CLINICAL PRESENTATION: An 11-year-old male patient presented with new-onset insulin-dependent diabetes mellitus and DKA. He was initially responsive but, after several hours of treatment, became unresponsive, with dilated pupils and decerebrate posturing. Cranial computed tomographic scanning demonstrated obstructive hydrocephalus resulting from focal cerebellar and brain stem edema. INTERVENTION: The patient was initially managed with medical treatment but ultimately required urgent ventricular drainage to arrest a progressive herniation syndrome. To our knowledge, this report describes only the second such case reported and the first requiring urgent ventriculostomy. CONCLUSIONS: These observations emphasize the importance of recognizing hydrocephalus as a potentially reversible cause of coma in DKA and of initiating prompt neurosurgical intervention, if warranted.     

Mine blast algorithm: A new population based algorithm for solving constrained engineering optimization problems

A novel population-based algorithm based on the mine bomb explosion concept, called the mine blast algorithm (MBA), is applied to the constrained optimization and engineering design problems. A comprehensive comparative study has been carried out to show the performance of the MBA over other recognized optimizers in terms of computational effort (measured as the number of function evaluations) and function value (accuracy). Sixteen constrained benchmark and engineering design problems have been solved and the obtained results were compared with other well-known optimizers. The obtained results demonstrate that, the proposed MBA requires less number of function evaluations and in most cases gives better results compared to other considered algorithms.     

(Fe3O4)-graphene oxide as a novel magnetic nanomaterial for non-enzymatic determination of phenylalanine

Fe₃O₄-graphene oxide (GO) modified glassy carbon (GC) electrode was used as a new magnetic nanosensor for determination of phenylalanine (Phe). It was found that Fe₃O₄-GO has been stably absorbed on GC electrode modified by simple technique. The cyclic voltammograms of the modified electrode in an aqueous solution displayed a pair of well-defined, stable and irreversible reductive/oxidation redox systems. The apparent electron transfer rate constant (k_s) and transfer coefficient (α) were determined by cyclic voltammetry and were approximately 9.3 s^? 1 and 0.67, respectively. The modified electrode showed excellent catalytic activity towards the oxidation of Phe at an unusually positive potential in buffer solution. This nanosensor also displayed fast response time, high sensitivity, low detection limit and had a remarkably positive potential oxidation of Phe that decreased the effect of interferences in analysis.     

Effectiveness of clicker‐assisted teaching in improving the critical thinking of adolescent learners

The effect of the implementation of student response systems (SRSs) in teaching on the critical thinking (CT) of young students was investigated. The study benefited from a quasi‐experimental design and a pretest/posttest set‐up. Subjects consisted of 156 K‐8 students in Tehran during 2016–2017, selected through a multistage cluster sampling, and randomly assigned to either the experimental group (EG) or the control group (CG). The regular curriculum of the students contained a weekly session of a course titled “Thinking and Lifestyle.” Ten sessions of the course were conducted using SRS (aka clickers) for EG, whereas CG kept receiving the same content in the conventional form. The teaching period was followed by the posttest. ANCOVA showed that, in contrast with CG, EG scored significantly higher on CT test after the intervention. The effect was shown to be only significant for the students at the lower side of the performance spectrum. Thus, in this inaugural study of clickers in schools in Iran, it was empirically demonstrated that clickers, as a relatively new piece of technology, can be successfully utilized during early adolescence in the pedagogical strategies in general and for the improvement of CT of students in particular.     

Geometry optimization of a cylindrical fin heat sink using mine blast algorithm

The heat sinks are utilized in electronic devices to eliminate heat from the chip and efficiently transmit it to the environment. Therefore, the optimal geometry sizes of fin heat sinks are the point of concern for manufacturers and designers. For this reason, the importance of optimization techniques particularly metaheuristics is understood. The design variables are width of heat sink, number of fins, fin height, and fin diameter. The various responses that have been considered are electromagnetic emitted radiations, thermal resistance, and mass of the heat sink investigated separately and simultaneously (multi-objective). Mine blast algorithm (MBA), as a recently developed optimizer, is inspired from explosion of mines. The optimum dimensions and values for each response have been obtained by the MBA and have been compared with other optimization methods in the literature. In terms of thermal resistance and mass responses, the MBA has offered better values, while for the emitted radiations, the obtained results obtained by Taguchi-based gray relational analysis (TGRA) was preferred. For manufacturing point of view, the MBA and TGRA both suggested better and efficient design. In addition, the value path analysis has been carried out to compare the trade-off among the considered responses. Finally, parametric sensitivity analyses have been implemented for design parameters, and discussions and comparisons have been carried out for the effects of each decision variable. By considering all responses, width of heat sink and fin height are considered as the most important and effective design parameters, respectively.     

Statistical Modeling of Zr/Hf Extraction using TBP–D2EHPA Mixtures

In the present work, response surface methodology was employed for the study and prediction of Zr/Hf extraction curves in a solvent extraction system using D2EHPA-TBP mixtures. The effect of change in the levels of temperature, nitric acid concentration, and TBP/D2EHPA ratio (T/D) on the Zr/Hf extraction/separation was studied by the use of central composite design. The results showed a statistically significant effect of T/D, nitric acid concentration, and temperature on the extraction percentage of Zr and Hf. In the case of Zr, a statistically significant interaction was found between T/D and nitric acid, whereas for Hf, both interactive terms between temperature and T/D and nitric acid were significant. Additionally, the extraction curves were profitably predicted applying the developed statistical regression equations; this approach is faster and more economical compared with experimentally obtained curves.     

Selective Leaching-Recovery of Re and Mo from Out-Gas Dust of Molybdenite Roasting Furnace

Selective leaching and recovery of Mo and Re present in out-gas dust of molybdenite roasting furnace was quantitatively investigated. The effects of solid to liquid (S/L) phase ratio, sulfuric acid concentration and solution temperature on the selective extraction were determined. Considerable Mo and small amount of Re were detected in the out-gas dust of the industrial roasting furnaces. Recovery percentage of both Re and Mo increased by increasing acid concentration and solution temperature. The results also showed that the recovery percentage of Re decreased by increasing the S/L ratio. The best conditions for selective leaching was obtained as 20 min mixing in water (0 g/L sulfuric acid) with S/L ratio of 0.2 in the temperature range of 40–60 °C.     

Effect of ARB Cycle Number and Second Phase Content on Mechanical properties and Microstructure of Pb–Ag Composite

A solid state method has been found for manufacturing of lead–silver composites for use as anodes in electrowinning production. Mechanical properties and microstructure of composite were characterized via peeling, tensile and microhardness tests, and scanning electron microscopy, transmission electron microscopy and fractography. Based on the peeling test results, maximum bond strength was achieved in the presence of 0.125 wt% of Ag (1.8 N/mm). Best mechanical properties were achieved in the Pb–0.5 wt% Ag composite after 10 ARB cycles by the enhanced tensile strength rising up to 50%, yield strength up to 170%, shear strength up to 63% and hardness up to 2.6 times higher, and the strain decreasing to 68% lower. These advanced properties led to higher stiffness and considerable enhancements in dimensional stability of the anodes and they improved creep characteristics. The advanced properties of the processed Pb–Ag composite anodes could be introduced as certification for slower anode failure, upkeep, surcharge and capital expenditure of industries with essential lead anode requirement.