Studies on the β → α Phase Transition Kinetics of Ti–3.5Al–5Mo–4V Alloy under Isothermal Conditions by X-ray Diffraction

The β → α phase transition kinetics of the Ti–3.5Al–5Mo–4V alloy with two different grain sizes was investigated at the isothermal temperature of 500 °C. A method to estimate the function of the precipitate fraction of the α phase with different aging times was developed based on X-ray diffraction analysis. The value of the α precipitate fraction increased sharply at first, then increased slowly with the aging time, and finally reached equilibrium. The value of the α precipitate fraction was higher in the alloy aged for the same time at a higher solution temperature, while the size of the α precipitate was smaller at a higher solution temperature. The β → α phase transition kinetics under isothermal conditions were modeled in the theoretical frame of the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory. The kinetic parameters of JMAK deduced different transformation mechanisms. The mechanism of the phase transition in the first stage was dominated by mixed transformation mechanisms (homogeneously nucleated and acicular-grown α structure, and grain boundary-nucleated and grown α precipitate), while the second stage was the growth of the fine α precipitate, which was controlled by slow diffusion. As the aging time increased, the hardness of the Ti–3.5Al–5Mo–4V alloy increased sharply. After the hardness of the alloy reached a plateau, it began to decline. The hardness of the alloy was always higher at a higher solution temperature.

Relationship between Microstructure and Exfoliation Corrosion in Mg-14mass%Li-3mass%Al Cold-Rolled Alloy

Relationship between microstructure and exfoliation corrosion in Mg-14mass%Li-3mass%Al cold rolled material were investigated by controlling microstructure using heat treatment. The exfoliation corrosion was exhibited on the specimens with elongated microstructure by cold-rolling. Heat treatment at 200 C only recovery occurred. Recovery and recrystallization were caused by heat treatment at 300 C However, heat treated at 300 C decreased precipitate fraction. Corrosion rate of heat-treated at 200 C decreased by release the residual strain. However, heat treatment at 300 C has lower corrosion resistance than heat-treated at 200 C because it has less precipitate density than as-rolled. Exfoliation corrosion was shown in as-rolled and heat-treated at 200 C. In as-rolled exfoliation corrosion was shown more significant when reduction rate increase. In as-rolled, exfoliation corrosion was shown more significant than heat-treated at 200 C. After heat treatment to change the grain shape from elongated to equiatial, exfoliation was suppressed by the distribution of AlLi phase.

Comprehensive investigation of the enzymatic oligomerization of esculin by laccase in ethanol : water mixtures

The oligomerization of esculin by laccase in aqueous medium resulted in a precipitate fraction with excellent antioxidant properties.

Isolation of a stimulatory system in an Aloe extract

The authors' previous work on a 50% ethanol extract of Aloe vera was done to evaluate anti-inflammatory activity using the croton oil-induced ear swelling assay. The anti-inflammatory activity was found in the supernatant fraction. The supernatant fraction decreased inflammation, when applied topically, by 29.2%, and the precipitate decreased inflammation by 12.1%. However, in the present work, the precipitate fraction decreased the wound diameter by an average of 47.1% (stimulatory system). Little or no wound healing activity was found in the supernatant. Aloe vera appears to act as a modulatory system toward wounds and inflammation and is a potentially valuable tool for managing lower extremity conditions.

Hydrolysis of triolein, cholesterol oleate, and 4-methylumbelliferyl stearate by acid and neutral ester hydrolases (lipases) from pigeon adipose tissues: effect of cAMP-dependent protein kinase

The properties of ester hydrolases (lipases) in a pH 5.2 precipitate fraction from pigeon adipose tissue have been determined in assays which have used a variety of different substrate preparations. Hydrolase activity measured with an ethanolic triolein substrate dispersion was characterized as having a single pH optimum of 7.5. In contrast, assays performed with a glycerol-dispersed triolein preparation resulted in a distinct shoulder of hydrolase activity at acid pH values in addition to a pH optimum of 7.5; addition of lecithin to the glycerol- dispersed triolein substrate preparation decreased hydrolase activity at neutral and alkaline pH values but allowed a distinct acid pH optimum (at pH 5) to be observed. Assays with glycerol-dispersed preparations of cholesterol oleate and the fluorogenic substrate, 4-methylumbelliferyl stearate (MU-stearate) (both containing lecithin) also demonstrated hydrolase activity with both acid (pH 4.5) and neutral (pH 7.5–8) pH optima. Preincubation of the pigeon adipose tissue pH 5.2 precipitate fraction with Mg2+, ATP, and cAMP resulted in a time-dependent increase in triglyceride (TG) hydrolase activity determined at pH 7 with an ethanolic triolein emulsion. This cAMP-dependent activation could be blocked by the addition of skeletal muscle protein kinase inhibitor; the addition of exogenous protein kinase (PrK) could reverse this inhibition. A Mg2+-dependent deactivation of PrK-activated TG hydrolase was observed; the rate of deactivation was enhanced by the addition of an exogenous phosphoprotein phosphatase. A cAMP-dependent PrK-catalyzed activation of hydrolase activity measured at pH 7 could also be determined with glycerol-dispersed substrate preparations of triolein, cholesterol oleate, and MU-stearate. Acid hydrolase activity (measured at pH 4.5–5 with glycerol-dispersed substrates) was not increased by preincubation with ATP, cAMP, and PrK. In experiments with glycerol-dispersed substrates, the kinetic mechanism associated with activation of pigeon adipose tissue hydrolase(s) was found to be due to an increase in Vmax with little or no change in substrate affinity.