The Experts below are selected from a list of 30858 Experts worldwide ranked by ideXlab platform
John M. Powers - One of the best experts on this subject based on the ideXlab platform.
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Accelerated Aging effects on color and translucency of flowable composites.
Journal of Esthetic and Restorative Dentistry, 2014Co-Authors: Yonca Korkmaz Ceyhan, John M. Powers, Joe C. Ontiveros, Rade D. ParavinaAbstract:Objectives: To evaluate the effect of Accelerated Aging on color and translucency parameter of composites. Materials and Methods: Filtek Supreme Ultra Flowable, shades A1, A3, White, Tetric EvoFlow, shades A1, A3, Bleach, and Filtek Z250 shades A1, A3, B1 were evaluated. Color and translucency were recorded using a spectrophotometer after 24-hour storage (baseline) and after Accelerated Aging. The data were analyzed by analysis of variance. Results: Fisher's PLSD intervals for comparisons among products and shades were 0.4, 0.1, 0.3, and 0.4 for ΔL*, Δa*, Δb*, and ΔE*, respectively. The data showed significant ΔE* and ΔL* main effects for composite product and shades (p 0.05). Conclusion: The effects of Aging on color of resin composites were composite and shade dependent. Translucency was not affected by Accelerated Aging.
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Color stability of provisional restorative materials after Accelerated Aging.
Journal of Prosthodontics, 2001Co-Authors: Pamela G. Doray, John M. PowersAbstract:PURPOSE Color of 11 provisional restorative materials (4 acrylic resins and 7 resin composites) was evaluated by reflection spectrophotometry immediately after fabrication, after Aging for 15 kJ/m(2), and after Aging for 60 kJ/m(2) to determine relative color stability under experimental Aging conditions. MATERIALS AND METHODS Specimens of provisional restorative materials were polymerized according to manufacturers' instructions and aged in an artificial Aging chamber with exposure to a total ultraviolet irradiation of 60 kJ/m(2) in increments of 15 kJ/m(2). Color was measured by CIE L*a*b* on a reflection spectrophotometer before and after Aging. Color change (Delta E*) was calculated and analyzed statistically by analysis of variance with repeated measures after 15 and 60 kJ/m(2) intervals of Aging. RESULTS Statistically significant changes in color were observed after Accelerated Aging at both the initial and final Aging intervals. Five of the 11 provisional materials tested showed perceptible color change (Delta E* from 3.6 to 9.3) after Accelerated Aging of 15 kJ/m(2). Seven of the 11 provisional materials tested showed perceptible color change (Delta E* from 3.4 to 9.4) after Accelerated Aging of 60 kJ/m(2). CONCLUSIONS Clinically perceptible color changes (Delta E* Delta 3.3) can be expected in some acrylic resin and composite resin provisional materials after Accelerated Aging.
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Accelerated Aging Affects Color Stability of Provisional Restorative Materials
Journal of Prosthodontics, 1997Co-Authors: Pamela G. Doray, John M. Powers, Xinzhi Wang, John O. BurgessAbstract:Purpose The color stability of two shades each of five acrylic resin and seven resin composite provisional restorative materials was evaluated by reflection spectrophotometry following in vitro Accelerated Aging. Materials and Methods Specimens of provisional restorative materials were polymerized according to manufacturers' instructions and aged in an artificial Aging chamber with exposure to a total ultraviolet irradiation of 60 kj/m2. Color was measured by CIE L*a*b* on a reflection spectrophotometer before and after Aging. Color change (ΔE*) was calculated and analyzed statistically. Results Statistically significant changes in color were observed after Accelerated Aging. Nine of the 12 provisional materials tested showed perceptible color change of at least one of the shades tested. The most color-stable materials were the acrylic, Alike, and the resin composites, Luxatemp and Protemp Garant, which had no perceptible color changes under these conditions. Conclusions Some acrylic resin and composite provisional materials change color significantly and perceptibly when exposed to in vitro Accelerated Aging conditions.
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Color stability of resin cements after Accelerated Aging.
International Journal of Prosthodontics, 1995Co-Authors: Farid Noie, Kathy L. O'keefe, John M. PowersAbstract:The color stability of both light- and dual-polymerized samples of three shades of three commercial resin cements was measured using a reflection spectrophotometer after Accelerated Aging over a period of 179 hours. Porcelite cement was the most color stable, followed by Optec and then 3M. The Optec and Porcelite cements changed color after Accelerated Aging, but with one exception the changes were not perceptible. Five of six 3M cements had perceptible color changes after Accelerated Aging, becoming darker and more yellow. The two lighter shades of Optec and 3M changed color more than the darker shade. Most differences between light- and dual-polymerized samples were significant but none was perceptible.
Sandrine Thérias - One of the best experts on this subject based on the ideXlab platform.
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Accelerated Aging test modeling applied to solar mirrors
npj Materials Degradation, 2019Co-Authors: Coralie Avenel, Olivier Raccurt, Jean-luc Gardette, Sandrine ThériasAbstract:The durability of solar mirrors is a critical factor for the deployment of concentrating solar power plants. Accelerated Aging test models currently applied in the polymer, electronic, and photovoltaic fields have recently been reviewed, and the issues of their application to solar mirrors have been discussed. This article first reports the results of temperature, humidity, and light irradiance Accelerated Aging tests performed to assess the dependent parameters of selected models from the literature. These parameters include the apparent activation energy for the Arrhenius temperature law, the Peck and Eyring coefficients for humidity models and the Schwarzschild coefficient for the irradiance law. The experimental values were then assessed for specular reflectance loss of solar mirrors. Finally, using these parameters, acceleration factors were calculated for solar mirrors. An effective temperature considering the Arrhenius degradation law was used rather than the commonly used mean temperature. This question is also addressed for light irradiance by using the dose instead of the mean value.
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Accelerated Aging test modeling applied to solar mirrors
npj Materials Degradation, 2019Co-Authors: Coralie Avenel, Olivier Raccurt, Jean-luc Gardette, Sandrine ThériasAbstract:The durability of solar mirrors is a critical factor for the deployment of concentrating solar power plants. Accelerated Aging test models currently applied in the polymer, electronic, and photovoltaic fields have recently been reviewed, and the issues of their application to solar mirrors have been discussed. This article first reports the results of temperature, humidity, and light irradiance Accelerated Aging tests performed to assess the dependent parameters of selected models from the literature. These parameters include the apparent activation energy for the Arrhenius temperature law, the Peck and Eyring coefficients for humidity models and the Schwarzschild coefficient for the irradiance law. The experimental values were then assessed for specular reflectance loss of solar mirrors. Finally, using these parameters, acceleration factors were calculated for solar mirrors. An effective temperature considering the Arrhenius degradation law was used rather than the commonly used mean temperature. This question is also addressed for light irradiance by using the dose instead of the mean value.
Kai Goebel - One of the best experts on this subject based on the ideXlab platform.
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Accelerated Aging in electrolytic capacitors for prognostics
2012 Proceedings Annual Reliability and Maintainability Symposium, 2012Co-Authors: Jose R. Celaya, Chetan S. Kulkarni, Sankalita Saha, Gautam Biswas, Kai GoebelAbstract:The focus of this work is the analysis of different degradation phenomena based on thermal overstress and electrical overstress Accelerated Aging systems and the use of Accelerated Aging techniques for prognostics algorithm development. Results on thermal overstress and electrical overstress experiments are presented. In addition, preliminary results toward the development of physics-based degradation models are presented focusing on the electrolyte evaporation failure mechanism. An empirical degradation model based on percentage capacitance loss under electrical overstress is presented and used in: (i) a Bayesian-based implementation of model-based prognostics using a discrete Kalman filter for health state estimation, and (ii) a dynamic system representation of the degradation model for forecasting and remaining useful life (RUL) estimation. A leave-one-out validation methodology is used to assess the validity of the methodology under the small sample size constrain. The results observed on the RUL estimation are consistent through the validation tests comparing relative accuracy and prediction error. It has been observed that the inaccuracy of the model to represent the change in degradation behavior observed at the end of the test data is consistent throughout the validation tests, indicating the need of a more detailed degradation model or the use of an algorithm that could estimate model parameters on-line. Based on the observed degradation process under different stress intensity with rest periods, the need for more sophisticated degradation models is further supported. The current degradation model does not represent the capacitance recovery over rest periods following an Accelerated Aging stress period.
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Accelerated Aging with electrical overstress and prognostics for power MOSFETs
IEEE 2011 EnergyTech, 2011Co-Authors: Sankalita Saha, Jose R. Celaya, Vladislav Vashchenko, Shompa Mahiuddin, Kai GoebelAbstract:Power electronics play an increasingly important role in energy applications as part of their power converter circuits. Understanding the behavior of these devices, especially their failure modes as they age with nominal usage or sudden fault development is critical in ensuring efficiency. In this paper, a prognostics based health management of power MOSFETs undergoing Accelerated Aging through electrical overstress at the gate area is presented. Details of the Accelerated Aging methodology, modeling of the degradation process of the device and prognostics algorithm for prediction of the future state of health of the device are presented. Experiments with multiple devices demonstrate the performance of the model and the prognostics algorithm as well as the scope of application.
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Towards Accelerated Aging methodologies and health management of Power MOSFETs (Technical Brief)
Annual Conference of the Prognostics and Health Management Society PHM 2009, 2009Co-Authors: Jose R. Celaya, Peter Wysocki, N. Patil, S Saha, Kai GoebelAbstract:Understanding Aging mechanisms of electronic components is of extreme importance in the aerospace domain where they are part of numerous critical subsystems including avionics. In particular, power MOSFETs are of special interest as they are involved in high voltage switching circuits such as drivers for electrical motors. With increased use of electronics in aircraft control, it becomes more important to understand the degradation of these components in aircraft specific environments. In this paper, we present an Accelerated Aging methodology for power MOSFETs that subject the devices to indirect thermal overstress during high voltage switching. During this Accelerated Aging process, two major modes of failure were observed - latch-up and die attach degradation. In this paper we present the details of our Aging methodology along with details of experiments and analysis of the results.
Paolo Garagnani - One of the best experts on this subject based on the ideXlab platform.
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Down syndrome, Accelerated Aging and immunosenescence
Seminars in Immunopathology, 2020Co-Authors: Noémie Gensous, Maria Giulia Bacalini, Claudio Franceschi, Paolo GaragnaniAbstract:Down syndrome is the most common chromosomal disorder, associated with moderate to severe intellectual disability. While life expectancy of Down syndrome population has greatly increased over the last decades, mortality rates are still high and subjects are facing prematurely a phenomenon of atypical and Accelerated Aging. The presence of an immune impairment in Down syndrome subjects is suggested for a long time by the existence of an increased incidence of infections, the incomplete efficacy of vaccinations, and a high prevalence of autoimmunity. Immunologic abnormalities have been described since many years in this population, both from a numerical and a functional points of view, and these abnormalities can mirror the ones observed during normal Aging. In this review, we summarize our knowledge on immunologic disturbances commonly observed in subjects with Down syndrome, and in innate and adaptive immunity, as well as regarding chronic inflammation. We then discuss the role of Accelerated Aging in these observed abnormalities and finally review the potential age-associated molecular and cellular mechanisms involved.
Kenneth T Gillen - One of the best experts on this subject based on the ideXlab platform.
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nylon 6 6 Accelerated Aging studies thermal oxidative degradation and its interaction with hydrolysis
Polymer Degradation and Stability, 2005Co-Authors: Robert Bernstein, Dora K Derzon, Kenneth T GillenAbstract:Abstract Accelerated Aging of Nylon 6.6 fibers used in parachutes has been conducted by following the tensile strength loss under both thermal–oxidative and 100% relative humidity conditions. Thermal–oxidative studies (air circulating ovens) were performed for time periods of weeks to years at temperatures ranging from 37 °C to 138 °C. Accelerated Aging humidity experiments (100% RH) were performed under both an argon atmosphere to examine the ‘pure’ hydrolysis pathway, and under an oxygen atmosphere (oxygen partial pressure close to that occurring in air) to mimic true Aging conditions. As expected the results indicated that degradation caused by humidity is much more important than thermal–oxidative degradation. Surprisingly when both oxygen and humidity were present the rate of degradation was dramatically enhanced relative to humidity Aging in the absence of oxygen. This significant and previously unknown phenomena underscores the importance of careful Accelerated Aging that truly mimics real world storage conditions.
