ISOTHERMAL CURING KINETICS OF POLYMETHACRYLIMIDE/NANO-SiO2 COMPOSITES BASED ON A DYNAMIC THERMOMECHANICAL ANALYSIS

The isothermal curing kinetics of polymethacrylimide/nano-SiO2 composites were investigated using a dynamic thermomechanical analysis. The relative conversion was defined with the storage modulus. The Avrami model-fitting method, Friedman method and integral method were applied to analyze the curing kinetics. The storage modulus and loss modulus increased appreciably, spanning three orders of magnitude throughout the curing. The frequency correlation of the relative conversion was noticeable at 180 °C because the glass transition took place when the curing degree was not high enough. The Avrami model-fitting analysis gave good fits for the experimental data. The activation energy calculated with the Avrami equation changed from 65.46 kJ/mol to 25.28 kJ/mol at 180–190 °C, while at 190–200 °C, the activation energy changed from 107.14 kJ/mol to 63.82 kJ/mol. The model-free analysis revealed the dependence of the activation energy on the relative conversion. The activation energy increased from 104.3 kJ/mol to 130.6 kJ/mol with the use of the Friedman method when the relative conversion ranged between 0.4–0.8. Similarly, the activation energy calculated with the integral method increased from 71.5 kJ/mol to 103.4 kJ/mol. When the relative conversion exceeded 0.8, the activation energy decreased gradually. The mobility of the reactive groups was hindered and the crosslinking density of the composite was much higher. The curing kinetics became diffusion controlled. The activation energy of the PMI/SiO2 composite was greater than that of PMI, which could be attributed to the hindrance effect caused by nano-SiO2.

Carbon Nanotube-Graphene Hybrid Electrodes with Enhanced Thermo-Electrochemical Cell Properties

Carbon nanotube-Graphene (CNT-Gr) hybrids were prepared on stainless steel substrates by the electrophoretic deposition (EPD) to make the thermo-electrochemical cell (TEC) electrodes. The as-obtained TEC electrodes were investigated by the SEM, XRD, Raman spectroscopy, tensile, and surface resistance tests. These hybrid electrodes exhibited significant improved TEC performances compared to the pristine CNT electrode. In addition, these hybrid electrodes could be optimized by tuning the contents of the graphene in the hybrids, and the CNT-Gr-0.1 hybrid electrode showed the best TEC performance with the current density of 62.8 A·m−2 and the power density of 1.15 W·m−2, 30.4% higher than the CNT electrode. The enhanced TEC performance is attributed to improvements in the electrical and thermal conductivities, as well as the adhesion between the CNT-Gr hybrid and the substrate. Meanwhile, the relative conversion efficiency of the TECs can reach 1.35%. The investigation suggests that the growth of CNT-Gr hybrid electrodes by the EPD technique may offer a promising approach for practical applications of the carbon nanomaterial-based TEC electrodes.

Technological Parameters of Epoxidation of Sesame Oil with Performic Acid

The course of epoxidation of sesame oil (SO) with performic acid formed „in situ” by the reaction of 30 wt% hydrogen peroxide and formic acid in the presence of sulfuric acid(VI) as a catalyst was studied. The most advantageous of the technological independent parameters of epoxidation are as follows: temperature 80°C, H2O2/ C=C 3.5:1, HCOOH/C=C 0.8:1, amount of catalyst as H2SO4/(H2O2+HCOOH) 1 wt%, stirring speed at least 700 rpm, reaction time 6 h. The iodine number (IN), epoxy number (EN), a relative conversion to oxirane (RCO) and oxirane oxygen content (EOe) were determined every hour during the reaction. Under optimal conditions the sesame oil conversion amounted to 90.7%, the selectivity of transformation to epoxidized sesame oil was equal to 93.2%, EN = 0.34 mol/100 g, IN = 0.04 mol/100 g oil (10.2 g/100 g oil), a relative conversion to oxirane RCO = 84.6%, and oxirane oxygen content of EOe = 5.5%.

Time Scales of Southern Ocean Eddy Equilibration

Stratification in the Southern Ocean is determined primarily by a competition between westerly wind-driven upwelling and baroclinic eddy transport. This study investigates the time scales of equilibration of the Southern Ocean in response to changing winds through an idealized channel model. An analytical framework describing the energetic pathways between wind input, available potential energy (APE), eddy kinetic energy (EKE), and dissipation provides a simple theory of the phase and amplitude response to oscillating wind stress. The transient ocean response to variable winds lies between the two limits of Ekman response (high frequency), characterized by the isopycnal slope responding directly to wind stress, and “eddy saturation” (low frequency), wherein a large fraction of the anomalous wind work goes into mesoscale eddies. The crossover time scale is the time scale of meridional eddy diffusive transport across the Antarctic Circumpolar Current (ACC) front. For wind variability with a period of 3 months (high-frequency forcing), the relative conversion of wind work to APE/EKE is 11, while for a period of 16 years (low-frequency forcing), the relative conversion to APE/EKE reduces to 3. The system’s frequency response is characterized by a complex transfer function. Both the phase and amplitude response of EKE and APE predicted by the linear analytic framework are verified using multiple ensemble experiments in an eddy-resolving (4-km horizontal resolution) isopycnal coordinate model. The results from the numerical experiments show agreement with the linear theory and can be used to explain certain features observed in previous modeling studies and observations.

A Study of Isothermal Curing of PMI Using DMA

The isothermal curing of polymethacrylimide (PMI) is studied through the use of dynamic mechanical analysis (DMA). Based on the growth rate of measured dynamic mechanical property, the relative conversion is defined to investigate the evolution of storage modulusE′at different curing temperatures. Hsich’s nonequilibrium thermodynamic fluctuation theory, Avrami equation, and isoconversional methods are used to analyze isothermal cure kinetics of PMI. The results show that there are different increase modes ofE′at low temperature range and high temperature range, respectively. In low temperature range, the relative conversion curves include a transitional stage which is found to be strongly frequency-dependent, but this stage is not observed in the relative conversion curve in high temperature range. During the isothermal curing process, the relative evolution ofE′can be described by Hsich’s nonequilibrium thermodynamic fluctuation theory and Avrami equation. Moreover, the values and evolutions of activation energy are different in two temperature ranges, which suggest that the curing mechanism probably has changed.

Epoxidation of Palm Kernel Oil-Based Crude Oleic Acid

Most vegetable oils have high content of unsaturated bond and can be converted into epoxidized fatty acids. These days, epoxidized vegetable oils are great concern as they are obtained from sustainable, renewable natural resources and are environmental friendly. The epoxidation of palm oleic acid was carried out by using in situ generated performic acid (HCOOOH) to produce epoxidized oleic acid. The degree of temperature, the molar ratio of formic acid or hydrogen peroxide and types of catalyst was considered. Epoxidation results were based on complete conversion oxirane, rate of epoxidation and stability of the oxirane. It was found that a maximum relative conversion oxirane (RCO) of epoxide is 88% at optimal condition.

The Study of Welding Power-Arc System Stability Based on DFCD

Regarding welding power-arc system stability (WPSS) as the research object, the paper uses differential theory and considers the full load conditions from the external circuit on the course of dynamic welding, and some models about WPSS are found, they can obtain the analytic expression of system stability coefficient, and a qualitative analysis of WPSS' conditions is so born, on this basis, by the method of the relative conversion of current deviation, a dynamic factor of current deviation (DFCD) is obtained by analytical equation，then to quantify stability of the system by the way of decay time of deviation. Test's results, based on analysis of voltage and current waveforms, are the same to quantify the WPSS based on DFCD.

Characterization of Two Novel Homozygous Missense Mutations Involving Codon 6 and 259 of Type II 3β-Hydroxysteroid Dehydrogenase (3βHSD) Gene Causing, Respectively, Nonsalt-Wasting and Salt-Wasting 3βHSD Deficiency Disorder1

We identified two homozygous missense mutations in the human type II 3β-hydroxysteroid dehydrogenase (3βHSD) gene, the first in codon 6 of exon II [CTT (Leu) to TTT (Phe)] in a male infant with hyperpigmented scrotum and hypospadias, raised as a male and no apparent salt-wasting since neonatal age, and the second in codon 259 of exon IV [ACG (Thr) to ATG (Met)] in a male pseudohermaphrodite with labial scrotal folds, microphallus, chordee, and fourth degree hypospadias, raised as a female and with salt-wasting disorder since neonatal age. In vitro transient expression of mutant type II 3βHSD complementary DNAs of L6F, T259M, as well as T259R for comparison was examined by a site-directed mutagenesis and transfection of construct into COS-1 and COS-7 cells. Northern blot analysis revealed expression of similar amounts of type II 3βHSD messenger ribonucleic acid from the COS-1 cells transfected by L6F, T259M, T259R, and wild-type (WT) complementary DNAs. Western immunoblot analysis revealed a similar amount of L6F mutant protein compared to WT enzyme from COS-1 cells, but neither L6F from COS-7 cells nor T259M or T259R mutant protein in COS-1 or COS-7 cells was detectable. Enzyme activity in intact COS-1 cells using 1 μmol/L pregnenolone as substrate in the medium after 6 h revealed relative conversion rates of pregnenolone to progesterone of 46% by WT enzyme, 22% by L6F enzyme, and 8% by T259M enzyme and less than 4% activity by T259R enzyme. Using 1 μmol/L dehydroepiandrosterone as substrate, the relative conversion rate of dehydroepiandrosterone to androstenedione after 6 was 89% by WT enzyme, 35% by L6F enzyme, 5.1% by T259M enzyme and no activity by T259R enzyme. However, the L6F mutant 3βHSD activity, despite its demonstration in the intact cells, was not detected in homogenates of COS-1 cells or in immunoblots of COS-7 cells, suggestive of the relatively unstable nature of this protein in vitro, possibly attributable to the decreased 3βHSD activity. In the case of T259M and T259R mutations, consistently undetectable proteins in both COS cells despite detectable messenger ribonucleic acids indicate severely labile proteins resulting in either no or very little enzyme activity, and these data further substantiate the deleterious effect of a structural change in this predicted putative steroid-binding domain of the gene. In conclusion, the findings of the in vitro study of mutant type II 3βHSD enzyme activities correlated with a less severe clinical phenotype of nonsalt-wasting and a lesser degree of genital ambiguity in the patient with homozygous L6F mutation compared to a more severe clinical phenotype of salt-wasting and severe degree of genital ambiguity in the patient with homozygous T259M mutation in the gene.