Non-Destructive Evaluation Of Degradation In Multi-Layered Thermal Barrier Coatings By Electrochemical Impedance Spectroscopy

Room temperature electrochemical impedance spectroscopy (EIS) was employed for damage monitoring of multi-layered commercial thermal barrier coatings (TBCs) that consist of a porous ceramic topcoat, thermally grown oxide (TGO), bond coat, and superalloy substrate. To gain a better understanding of the EIS response from multi-layered TBCs, individual constituents of TBCs, namely yttria-stabilized zirconia (YSZ) monoliths with open pores and hot extruded NiAl alloys, were examined as a function of thermal degradation by EIS and microstructural observation. Several types of commercial TBCs were then inspected by EIS, and the changes in the electrochemical resistance and capacitance were correlated to the development of microstructure and damage initiation. EIS response (Bode and Nyquist plots) were acquired from all specimens at room temperature and analyzed with an ac equivalent circuit based on the microstructural constituents to determine the electrochemical resistance and capacitance. The electrochemical resistance of the YSZ was observed to increase initially and then decrease with thermal exposure. This is attributed to the high temperature sintering and crack initiation of the YSZ, respectively. After an initial increase in electrochemical resistance of the TGO, there was a gradual decrease with localized spallation. A large-scale spallation of TGO drastically increased the electrochemical capacitance of the TGO. However, prior to spallation of TGO, the electrochemical capacitance of the TGO decreased inversely as the TGO thickness increased. Evolution in electrochemical resistance and capacitance along with microstructural correlations are discussed with respect to the potential of EIS as a non-destructive evaluation (NDE) technique for TBCs. © 2005 Elsevier B.V. All rights reserved

Damage Detection Of Thermal Barrier Coatings By Electrochemical Impedance Spectroscopy

Thermal barrier coatings (TBCs), consisting of yttria-stabilized zirconia (YSZ) on NiCoCrAlY or aluminide bond coats, protect hot-section components, such as blades and vanes of advanced gas turbine engines. Electrochemical impedance spectroscopy (EIS) is being developed as a non-destructive evaluation (NDE) technique for TBCs. For better understanding of electrochemical impedance response of TBCs and their damage after high temperature exposure (isothermal/cyclic), monolithic YSZ with open pores and alumina-forming NiAl specimens were independently examined by EIS as a function of isothermal oxidation. Impedance of the YSZ and oxidized NiAl increased with high temperature sintering and oxide-scale growth, respectively. However, the electrochemical impedance was significantly reduced when quench-cracks in sintered YSZ or spallation of oxide-scale from the NiAl were observed. These observations are correlated to the electrochemical impedance response of a TBC system consisting of electron beam physical vapor deposited (EB-PVD) YSZ and (Ni,Pt)Al bond coats as a function of isothermal oxidation

Electrochemical Impedance Spectroscopy Of Thermal Barrier Coatings As A Function Of Isothermal And Cyclic Thermal Exposure

Electrochemical impedance spectroscopy (EIS) is being developed as a non-destructive evaluation technique of thermal barrier coatings (TBCs) for life-remaining assessment and quality control. In this investigation, EIS was employed to non-destructively examine TBCs, as a function of thermal exposure during isothermal and cyclic oxidation in air at 1121 °C. TBCs examined in this study include electron beam physical vapor deposited (EB-PVD) and air-plasma sprayed ZrO2-7wt.%Y2O3 (YSZ) on NiCoCrAlY or (Ni,Pt)Al bondcoat. Electrochemical impedance response of TBC specimens at room temperature were acquired and analyzed with an AC equivalent circuit based on the multi-layered micro-constituents of TBCs. Microstructural characteristics of TBCs were also examined by optical and electron microscopy. Initial increase in the resistance of YSZ with thermal exposure was observed and related to the high temperature sintering of YSZ. The parabolic growth of TGO during high temperature oxidation was inversely proportional to the capacitance of TGO. An explanation based on electrolyte penetration into sub-critical damage is proposed for the gradual decrease in the resistances of YSZ and TGO with prolonged thermal exposure. Observation of exposed metallic bondcoat surface on the fracture surface, which provides conduction readily through electrolyte contact, was related to the abrupt and large increase in the capacitance of YSZ and TGO. © 2003 Elsevier B.V. All rights reserved

Copy number variation burden on asthma subgenome in normal cohorts identifies susceptibility markers

Purpose: Asthma is a complex disease caused by interplay of genes and environment on the genome of an individual. Copy number variations (CNVs) are more common compared to the other variations that disrupt genome organization. The effect of CNVs on asthma subgenome has been less studied compared to studies on the other variations. We report the assessments of CNV burden in asthma genes of normal cohorts carried out in different geographical areas of the world and discuss the relevance of the observation with respect to-asthma pathogenesis. Methods: CNV analysis was performed using Affymerix high-resolution arrays, and various bioinformatics tools were used to understand the influence of genes on asthma pathogenesis. Results: This study identified 61 genes associated with asthma and provided various mechanisms and pathways underlying asthma pathogenesis. CCL3L1, ADAM8, and MUC5B were the most prevalent asthma genes. Among them, CCL3L1 was found across all 12 populations in varying copy number states. This study also identified the inheritance of asthma-CNVs from parents to offspring creating the latent period for manifestation of asthma. Conclusions: This study revealed CNV burden with varying copy number states and identified susceptibility towards the disease manifestation. It can be hypothesized that primary CNVs may not be the initiating event in the pathogenesis of asthma and additional preceding mutations or CNVs may be required. The initiator or primary CNVs sensitize normal cohorts leading to an increased probability of accumulating mutations or exposure to allergic stimulating agents that can augment the development of asthma

Il-10 and il-17f promoter single nucleotide polymorphism and asthma: a case-control study in south india

Background Several studies have assessed the association between IL-17F and IL-10 promoter polymorphisms and asthma, but the results were conflicting. Furthermore, few studies have evaluated the association of cytokine polymorphisms with asthma and its clinical phenotypes. Objective This study was conducted to evaluate the association of IL-10 (interleukin 10) and IL-17F (interleukin 17F) promoter polymorphisms (rs1800871, rs1800896 and rs1889570) with asthma and its clinical phenotypes including severity, atopic status, spirometric parameters, and response to treatment in south Indian population. A sub-study was conducted to assess cytokine levels in subjects with different gene variants. Methods IL-10 and IL-17F polymorphisms were genotyped in 419 asthmatic patients and 393 controls using Mass ARRAY. Results Our results showed an association between IL-10 SNPs and mild asthma. No association was found with any of three SNPs in moderate to severe asthma. Comparison of genotype distribution of IL-17F rs1887570 AA variant among atopic and non-atopic patients showed significant difference (p = 0.024). Correlation analysis of IL-10 and IL-17F SNPs to clinical variables showed a positive correlation between IL-17F rs1887570 AA and number of allergen sensitized (rs = 0.142, p = 0.004). Significant improvement in lung function was observed after 2 months of ICS (Inhaled corticosteroids) and LABA (long acting beta 2 agonist) treatment in all subjects with no statistically significant difference among SNPs variants. Cytokines levels were similar in different SNP variants. Conclusion We observed an association between IL-10 rs1800871 and rs1800896 SNPs and mild asthma, as well as IL-17F rs1887570 AA variant and number of allergens sensitized

Molecular interaction network and pathway studies of ADAM33 potentially relevant to asthma

Background: Asthma is a complex disease caused by geneegene, geneeprotein, and proteineprotein interactionsand the influence of environment, which plays a significant role in causing asthma pathogenesis.ADAM33 is known to be an important gene involved in asthma pathogenesis. No one single gene is a causalfactor of asthma; rather, asthma is caused by a complex interaction of multiple genes having pathogeneticand protective effects. Objective: To identify and understand the interacting genes and proteins of ADAM33. Methods: The Ingenuity Pathway Analysis and GeneMANIA tools and a literature survey were used toidentify the interacting candidates of ADAM33 and the WEB-based GEne SeT AnaLysis Toolkit was used toperform enrichment analysis of the proteins identified. Results: Keeping ADAM33 as a major hub, the authors identified some proteins whose interaction withADAM33 had been associated with asthma and they recognized some proteins, such as amyloid b (A4)precursor protein, ataxin-7, a4-integrin, a5-integrin, a9-integrin, tissue inhibitor of metalloproteinase-4, andubiquilin-4, that had not been previously associated with asthma. Conclusion: The proteins identified in this study were enriched for various mechanisms that are involved inairway hyperresponsiveness, and through the interaction with ADAM33, they may have potential relevancein asthma

Serum levels of IL-10, IL-17F and IL-33 in patients with asthma: A case-control study

Objectives: The development of inflammation in asthma involves an intricate network of cytokines that recruit and activate numerous immune cells. This study was aimed to compare serum levels of IL-10, IL-17F, and IL-33 in asthmatic patients and non-asthmatic controls and correlate cytokine levels to asthma severity and various clinical, spirometric, and laboratory variables. Methods: Using ELISA, serum levels of IL-10, IL-17F, and IL-33 were evaluated in 44 asthmatics (14 mild persistent, 15 moderate persistent, and 15 severe persistent) and 44 controls. Results: This is one of the first reports showing a significant difference in serum levels of asthma-associated cytokines, anti-inflammatory IL-10, and pro-inflammatory IL-17F and IL-33, in the same subset of asthmatic patients. Our results showed diminished level of IL-10 and elevated levels of IL-17F and IL-33 in asthmatics than in controls (p\textless0.001). Assessment of cytokine levels between subjects of different gender, age group, and BMI showed non-significant differences. Correlation analysis of cytokine levels to clinical variables showed that IL-17F is associated negatively to FVC % predicted (forced vital capacity) and FEV1% predicted (forced expiratory volume in one second) and positively to number of allergens sensitized and FEV1 reversibility. A strong negative correlation was found between IL-10 and IL-33 levels (p=0.001). Conclusions: Negative correlation between IL-10 and IL-33 levels may reflect a converse relationship between anti-inflammatory and pro-inflammatory cytokines in an individually balanced pattern. The association between IL-17F level and asthmatic phenotypes such as reduced FVC and FEV1, higher degree of sensitization, and post-bronchodilator reversibility needs further assessments

Global spectrum of copy number variations reveals genome organizational plasticity and proposes new migration routes

Global spectrum of CNVs is required to catalog variations to provide a high-resolution on the dynamics of genome-organization and human migration. In this study, we performed genome-wide genotyping using high-resolution arrays and identified 44,109 CNVs from 1,715 genomes across 12 populations. The study unraveled the force of independent evolutionary dynamics on genome-organizational plasticity across populations. We demonstrated the use of CNV tool to study human migration and identified a second major settlement establishing new migration routes in addition to existing ones

Unravelling the complexity of human olfactory receptor repertoire by copy number analysis across population using high resolution arrays

Olfactory receptors (OR), responsible for detection of odor molecules, belong to the largest family of genes and are highly polymorphic in nature having distinct polymorphisms associated with specific regions around the globe. Since there are no reports on the presence of copy number variations in OR repertoire of Indian population, the present investigation in 43 Indians along with 270 HapMap and 31 Tibetan samples was undertaken to study genome variability and evolution. Analysis was performed using Affymetrix Genome-Wide Human SNP Array 6.0 chip, Affymterix CytoScan® High-Density array, HD-CNV, and MAFFT program. We observed a total of 1527 OR genes in 503 CNV events from 81.3% of the study group, which includes 67.6% duplications and 32.4% deletions encompassing more of genes than pseudogenes. We report human genotypic variation in functional OR repertoire size across populations and it was found that the combinatorial effect of both "orthologous obtained from closely related species" and "paralogous derived sequences" provide the complexity to the continuously occurring OR CNVs