Strength Improvement in Transformation-Toughened Alumina by Selective Phase Transformation

A1₂O₃-15 vol% ZrO₂ bar-shaped ceramic specimens were fabricated in the green state in such a way that the near surface regions consisted of A1₂O₃ and unstabilized ZrO₂ while the bulk consisted of A1₂O₃ and partially stabilized ZrO₂. After sintering, specimens had macroscopic residual compressive surface stresses and balancing interior tensile stresses due to the tetragonal-to-monoclinic phase transformation in the outer layers which occurs during cooling. The depth of the surface region was controlled during green forming. Residual surface compressive stresses at room temperature varied between 100 and 400 MPa depending on the outer-layer thickness. The increased strengths of the three-layer specimens were obtained in the as-fired unground condition, demonstrating that the stresses introduced are the result of transformation of tetragonal zirconia into monoclinic polymorph which occurred upon cooling from the sintering temperature. Specimens with residual surface compressive stresses were 200 MPa stronger at 750°C than monolithic specimens, demonstrating the viability of this approach for improving elevated-temperature mechanical properties.     

Mixed-Mode Fracture of Ceramics in Diametral Compression

Mixed-mode fracture of a glass-ceramic and an alumina ceramic from inclined Knoop indenter flaws was studied in diametral compression and four-point-bend tests. In annealed specimens the directions of extension of the cracks and mode I and mode II stress-intensity factors at fracture were analyzed and compared to the predictions of a maximum crack-tip hoop stress theory. Knoop flaws in all cases extended in directions normal to the principal maximum tension rather than in the direction of maximum hoop stress near the crack tip. Mixed-mode fracture envelopes assessed in experiments, particularly with the diametral-compression test, showed significant deviation to higher K_II values relative to the fracture-mechanics predictions. As a consequence, an apparent K _IIc value assessed in the diametral-compression test was approximately twice the value of K _Ic.     

EVALUATION OF PEPPER (CAPSICUM ANNUUM) FOR MANAGEMENT OF DIABETES AND HYPERTENSION

Natural α‐amylase and α‐glucosidase inhibitors from food‐grade plants offer an attractive strategy to control postprandial hyperglycemia for type 2 diabetes management. Concurrently associated macrovascular complication of hypertension can be managed by similar extracts by inhibition of angiotensin I‐converting enzyme (ACE ). In this study, nine types of pepper were investigated for inhibitory activity against said enzymes. Several pepper extracts had high α‐glucosidase inhibitory activity, which was not correlated to total phenolic content and free radical scavenging‐linked antioxidant activity. Select extracts such as Green pepper and Long hot pepper had less or no inhibitory effect on the α‐amylase activity, which indicates the potential for reduced side effects. Among various water extracts, Yellow, Cubanelle and Red pepper had the highest ACE inhibitory activity. Therefore, combinations of pepper could be screened for dietary management of type 2 diabetes, associated hypertension and microvascular complications linked to oxidative dysfunction, and provide the basis for clinical studies.     

BIOLOGICAL FUNCTIONALITY OF ELLAGIC ACID: A REVIEW

Phenolic phytochemicals such as ellagic acid are important components of fruits and vegetables and are partly responsible for their beneficial health effects against oxidation‐linked chronic diseases such as cancer and cardiovascular diseases. It is believed that phytochemicals such as ellagic acid function either by countering the negative effects of oxidative stress by directly acting as an antioxidant or by activating/inducing cellular antioxidant enzyme systems. These models are limited in explaining the more comprehensive antioxidant‐related functions of phytochemicals in maintaining specific cellular homeostasis which contributes to its preventive mode of action and beneficial effects across diverse biological systems and cell types. In this article, we have revised the existing models and have proposed a comprehensive model for the antioxidant response‐linked mechanism of the action of ellagic acid from fruits at the early stages of host cellular response by the modulation of enzyme response to maintain cellular homeostasis in eukaryotes and by inhibiting the survival in pathogenic prokaryotes.     

SYNERGISM OF CRANBERRY PHENOLICS WITH ELLAGIC ACID AND ROSMARINIC ACID FOR ANTIMUTAGENIC AND DNA PROTECTION FUNCTIONS

Several studies have shown the antimutagenic DNA protective functions of some naturally occurring phenolic phytochemicals. Emerging research also indicates that synergistic functionality of these phytochemicals in whole foods benefits the management of many diseases. Here we have investigated the potential antimutagenic properties of cranberry phenolics, ellagic acid (EA), rosmarinic acid (RA) and their synergistic interactions on enhancing antimutagenic properties in Salmonella typhimurium tester system against mutagens sodium azide and N‐methyl‐N′‐nitro‐N‐nitrosoguanidine. Ability of these phytochemical treatments to protect oxidative damage to DNA was also investigated using the supercoiled DNA strand scission assay. Results showed that EA was most effective in inhibiting the mutations in S. typhimurium system, whereas RA and EA were equally effective in protecting the DNA from oxidative damage. Results also showed that the antimutagenic functionality of cranberry powder (CP) made from juice extracts was significantly enhanced when 30% (w/w) of phenolics in CP was substituted with RA and EA possibly because of synergistic redox modulation that can influence mutagen function. It is also suggested that the synergistic mixture of cranberry phenolics with RA could also be protecting the cell from mutations by modulating DNA repair systems.     

Strength-Grain Size Relations in Polycrystalline Ceramics

A model is presented to explain the strength-grain size behavior of ceramics exhibiting duplex microstructures and of ceramics with uniform coarse-grained microstructures. Using an energy balance analysis, the model shows that in most ceramics an hitiipl flaw contained within a single large grain will initially propagate and then arrest after entering the region of increased fracture-surface energy. The arrested flaw will subsequently propagate to failure at the value OF the critical stress intensity factor. Using the data in the literature, a strength-(grain size)^−1/2 plot for MgAl₂O₄ was generated.     

Comparison of modeling methods for wind power prediction: a critical study

Prediction of power generation of a wind turbine is crucial, which calls for accurate and reliable models. In this work, six different models have been developed based on wind power equation, concept of power curve, response surface methodology (RSM) and artificial neural network (ANN), and the results have been compared. To develop the models based on the concept of power curve, the manufacturer’s power curve, and to develop RSM as well as ANN models, the data collected from supervisory control and data acquisition (SCADA) of a 1.5 MW turbine have been used. In addition to wind speed, the air density, blade pitch angle, rotor speed and wind direction have been considered as input variables for RSM and ANN models. Proper selection of input variables and capability of ANN to map input-output relationships have resulted in an accurate model for wind power prediction in comparison to other methods.