Crack growth in transforming ceramics under cyclic tensile loads

The mechanisms of stable growth of short fatigue cracks (crack length up to 1 mm) at room temperature in magnesia-partially stabilized zirconia subjected to cyclic tensile loads were investigated. Single edge-notched specimens were fractured in the four-point bend configuration under cyclic and quasi-static tensile loads. At a load ratio of 0.1, the threshold stress intensity factor range, K, for fracture initiation in cyclic tension is as low as 3.4 M Pam^1/2, and catastrophic failure occurs at K=6.6 M Pam^1/2. For crack length less than 1 mm and for plane strain conditions, growth rates are highly discontinuous, and periodic crack arrest is observed after growth over distances of the order of tens of micrometres. Crack advance could only be resumed with an increase in the far-field stress intensity range. The mechanisms of short crack advance in cyclic tension are similar to those observed under quasi-static loads, and the tensile fatigue effect appears to be a manifestation of static failure modes. A model is presented to provide an overall framework for the tensile fatigue crack growth characteristics of partially stabilized zirconia. Experimental results are also described to demonstrate the possibility of stable room temperature crack growth under cyclic tension in fine-grained tetragonal zirconia polycrystals, partially stabilized with Y₂O₃. The growth of cracks in transformation-toughened ceramics is found to be strongly influenced by the crack size and shape, stress state and specimen geometry.     

Tensile Fracture Toughness Measurements in Ceramics

A novel procedure is outlined whereby fracture toughness values for ceramics can be measured under uniaxial tension (mode I) in specimens containing a fatigue crack. Circumferentially notched rods of rapolycrystalline aluminum oxide were precracked in cyclic compression to introduce a fatigue crack at room temperature, following the technique proposed by Suresh and co-workers.^7,10,11 Subsequently, the precracked rods were fractured in pure tension. Highly reproducible values of fracture toughness were obtained using this method.     

Generalized differentiability and integrability for fuzzy set-valued functions on time scales

This paper deals with the fuzzy set-valued functions of real variables on time scale whose values are normal, convex, upper semicontinuous and compactly supported fuzzy sets in \(\mathbb {R}^{n}\). We introduce and study the fundamental properties of new class of derivative called generalized delta derivative (\(\Delta _{g}\)-derivative) and generalized delta integral (\(\Delta _{g}\)-integral) for such fuzzy functions.     

Proteomic Biomarkers of the Apnea Hypopnea Index and Obstructive Sleep Apnea: Insights into the Pathophysiology of Presence,Severity, and Treatment Response

Obstructive sleep apnea (OSA), a disease associated with excessive sleepiness and increased cardiovascular risk, affects an estimated 1 billion people worldwide. The present study examined proteomic biomarkers indicative of presence, severity, and treatment response in OSA. Participants (n = 1391) of the Stanford Technology Analytics and Genomics in Sleep study had blood collected and completed an overnight polysomnography for scoring the apnea–hypopnea index (AHI). A highly multiplexed aptamer-based array (SomaScan) was used to quantify 5000 proteins in all plasma samples. Two separate intervention-based cohorts with sleep apnea (n = 41) provided samples pre- and post-continuous/positive airway pressure (CPAP/PAP). Multivariate analyses identified 84 proteins (47 positively, 37 negatively) associated with AHI after correction for multiple testing. Of the top 15 features from a machine learning classifier for AHI ≥ 15 vs. AHI < 15 (Area Under the Curve (AUC) = 0.74), 8 were significant markers of both AHI and OSA from multivariate analyses. Exploration of pre- and post-intervention analysis identified 5 of the 84 proteins to be significantly decreased following CPAP/PAP treatment, with pathways involving endothelial function, blood coagulation, and inflammatory response. The present study identified PAI-1, tPA, and sE-Selectin as key biomarkers and suggests that endothelial dysfunction and increased coagulopathy are important consequences of OSA, which may explain the association with cardiovascular disease and stroke.     

Structural and Spectroscopic Studies of Sm3+/CdS Nanocrystallites in Sol–Gel TiO2-ZrO2 Matrix

A sol–gel method was used to prepare titania-zirconia matrices doped with Sm³⁺/CdS nanocrystallites. The structural properties of the matrices were characterized using transmission electron microscopy (TEM), thermogravimetric analysis (TGA), differential thermal analysis (DTA), and Fourier-transform infrared spectroscopy studies. The thermal stability of the material was determined by TGA/DTA analysis. The absorption spectrum shows the characteristic peaks of the Sm³⁺ ions and the absorption peak corresponding to the CdS nanocrystallites. The optical bandgap and size of the CdS nanoparticles were calculated from the absorption spectrum. From TEM, the interplanar distance (d) was estimated to be 3.533 Å, which matches with the (1 0 0) plane of bulk CdS. The measurements yield a nanocrystallite size of around 7.8 nm. The optical absorption and emission spectra confirmed the formation of CdS nanoparticles along with samarium ions in the titania-zirconia matrices. The fluorescence intensity of the samarium ions was found to be greatly enhanced by codoping with CdS nanocrystallites.