Thermomechanics of Solid Oxide Fuel Cell Electrode Microstructures Using Finite Element Methods: Progressive Interface Degradation under Thermal Cycling

The electrochemical performance of solid oxide fuel cell (SOFC) is significantly influenced by three-phase boundary (TPB) zones in the microstructure. TPB zones are locations where all three phases comprising the microstructure such as the two solid phases and the pore phase are present. Electrochemical reactions such as oxygen reduction occur near TPBs, and TPB density is believed to affect the polarization resistance of the cathode. In this regard, the effect of interface degradation under repeated thermal loading on the mechanical integrity and electrochemical performance of solid oxide fuel cell (SOFC) electrodes is studied through finite element simulations. Image-based 3-D models are used in this study, with additional interface zones at the boundaries between dissimilar solid phases. These interface zones are composed of 3-D cohesive elements of small thickness. The effect of interface degradation on mechanical integrity is studied by subjecting 50:50 LSM:YSZ wt.% cathode models to increasing levels of thermal load from room temperature (20°C) up to operating temperature (820°C). Energy quantities (e.g., strain energy and damage dissipation) for cathode models with and without cohesive interface zones are obtained through finite element analysis (FEA). These quantities are compared using energy balance concepts from fracture mechanics to gain insight into the effects of interface degradation on mechanical integrity

Fibrinogen Excretion in the Urine and Immunoreactivity in the Kidney Serves as a Translational Biomarker for Acute Kidney Injury

Fibrinogen (Fg) is significantly up-regulated in the kidney after acute kidney injury (AKI). We evaluated the performance of Fg as a biomarker for early detection of AKI. In rats and mice with kidney tubular damage induced by ischemia/reperfusion (I/R) or cisplatin administration, respectively; kidney tissue and urinary Fg increased significantly and correlated with histopathological injury, urinary kidney injury molecule-1 (KIM-1) and N-acetyl glucosaminidase (NAG) corresponding to the progression and regression of injury temporally. In a longitudinal follow-up of 31 patients who underwent surgical repair of abdominal aortic aneurysm, urinary Fg increased earlier than SCr in patients who developed postoperative AKI (AUC-ROC = 0.72). Furthermore, in a cohort of patients with biopsy-proven AKI (n = 53), Fg immunoreactivity in the tubules and interstitium increased remarkably and was able to distinguish patients with AKI from those without AKI (n = 59). These results suggest that immunoreactivity of Fg in the kidney, as well as urinary excretion of Fg, serves as a sensitive and early diagnostic translational biomarker for detection of AKI

Detection of Drug-Induced Acute Kidney Injury in Humans Using Urinary KIM-1, miR-21,-200c, and-423

Drug-induced acute kidney injury (AKI) is often encountered in hospitalized patients. Although serum creatinine (SCr) is still routinely used for assessing AKI, it is known to be insensitive and nonspecific. Therefore, our objective was to evaluate kidney injury molecule 1 (KIM-1) in conjunction with microRNA (miR)-21, -200c, and -423 as urinary biomarkers for drug-induced AKI in humans. In a cross-sectional cohort of patients (n = 135) with acetaminophen (APAP) overdose, all 4 biomarkers were significantly (P < .004) higher not only in APAP-overdosed (OD) patients with AKI (based on SCr increase) but also in APAP-OD patients without clinical diagnosis of AKI compared with healthy volunteers. In a longitudinal cohort of patients with malignant mesothelioma receiving intraoperative cisplatin (Cp) therapy (n = 108) the 4 biomarkers increased significantly (P < .0014) over time after Cp administration, but could not be used to distinguish patients with or without AKI. Evidence for human proximal tubular epithelial cells (HPTECs) being the source of miRNAs in urine was obtained first, by in situ hybridization based confirmation of increase in miR-21 expression in the kidney sections of AKI patients and second, by increased levels of miR-21, -200c, and -423 in the medium of cultured HPTECs treated with Cp and 4-aminophenol (APAP degradation product). Target prediction analysis revealed 1102 mRNA targets of miR-21, -200c, and -423 that are associated with pathways perturbed in diverse pathological kidney conditions. In summary, we report noninvasive detection of AKI in humans by combining the sensitivity of KIM-1 along with mechanistic potentials of miR-21, -200c, and -423

Three-Dimensional Finite Element Analysis of Solid Oxide Fuel Cell Microstructures

Finite element thermal stress analyses of solid oxide fuel cell (SOFC) electrode microstructure models are performed under various conditions to investigate mechanical integrity of electrodes under thermal loads. Image-based three-dimensional finite element models of electrode microstructures are generated from two-dimensional images of actual electrode cross-sections. Finite element thermal stress analyses of anode models under spatially uniform temperature fields of increasing magnitude are performed, and the effects of temperature-dependent material properties and plasticity on mechanical integrity are investigated. Linear elastic material models are found to underestimate the probability of failure of the anode at high temperatures. Analyses of cathode models are performed to study the effects of temperature-dependent material properties and varying phase volume fractions. An approximate heuristic scheme based on boundary pixel modification is developed, validated, and used to derive a microstructure of varying composition from the original microstructure. Limited variations in ceramic phase volume fractions are found to have limited effect on probability of failure of models having temperature-independent material properties, with higher pore volume fraction leading to higher probability of failure. Consideration of temperature-dependent material properties leads to lower probability of failure for the cathode models compared with temperature-independent material properties. Interface degradation under repeated thermal loading is simulated using cohesive elements. Effects of damage on mechanical integrity and electrochemical performance are studied. Three-phase boundary evolution due to mechanical interface damage is evaluated. Three-phase boundary density is found to decrease over a number of heating cycles, indicating that interface damage may be a major mechanism responsible for SOFC performance degradation over time

A rare case of complex odontome in posterior maxilla

Odontomas are considered to be a developmental anomalies resulting from the growth of completely differentiated epithelial and mesenchymal cells that give rise to ameloblasts and odontoblasts. A rare case of complex odontome in posterior maxilla involving maxillary sinus, associated with impacted tooth and erupting into oral cavity is presented in this article which was treated with an en block resection and palatal obturator

Quasi-static response of sandwich steel beams with corrugated cores

The response of sandwich steel beams with corrugated cores to quasi-static loading is investigated by employing experimental and computational approaches. The sandwich steel beam consists of top and bottom substrates made of AISI Steel 1018 and four corrugated core layers made of AISI Steel 1008. Various arrangements of the corrugated core layers with both uniform and graded layer thicknesses are considered. Three core arrangements with identical relative densities are used to study the effects of uniform versus graded core layer thicknesses onto the quasi-static behavior of corrugated steel beams. Finite element models are validated against quasi-static tests, and lender themselves suitable for a parametric study. A parametric study is also carried out on large-scale structural size beams of a few meters in length. The deformation modes observed in this study include core crushing, and plate bending and shear. It is found that core arrangement and beam span is key factors governing the quasi-static response of sandwich beams with corrugated cores