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Accelerated Aging (accelerated + aging)
Selected AbstractsEffect of accelerated aging on the structure and properties of monolayer and multilayer packaging filmsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008P. A. Tarantili Abstract The effect of accelerated aging on the structure and properties of single, metalized, and multilayer films used in food packaging was studied through the exposure of specimens of those films to repeated aging cycles in a weather meter under the combined action of ultraviolet, humidity, and heat. The aged specimens were tested for their mechanical properties and water vapor transmission characteristics, and the results were compared to those obtained from the original specimens. The property changes introduced into the films by aging were further explored by attenuated total reflectance spectroscopy and differential scanning calorimetry in an attempt to correlate the changes in the properties with structural characteristics. The results showed that the films made of polypropylene (PP) underwent severe chain scission upon irradiation and lost mechanical properties but still retained their impermeability to water vapor. The metallic coating could not prevent PP from degrading, as it seemed to oxidize under the aging conditions. Therefore, the metalized film showed the same mechanical response as PP, but its water impermeability dropped dramatically. Polyethylene (PE) and poly(ethylene terephthalate) (PET) films showed modest decreases in their mechanical properties, which could be attributed to crosslinking reactions taking place with PE and to the increased ultraviolet stability of PET, respectively. On the other hand, the multilayer films presented a decrease in their mechanical properties according to those of their weak component, which would be expected for a composite structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Effect of heat treatment after accelerated aging on phase transformation in 3Y-TZPJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2010I. L. Denry Abstract Our purpose was to investigate the effect of heat treatment on the reversibility of the tetragonal to monoclinic transformation in 3Y-TZP, and associated surface roughness. The goals were to determine the onset temperature of the reverse transformation, and characterize surface roughness after accelerated aging, and after aging followed by heat treatment. 3Y-TZP disc-shaped specimens were sintered at temperatures from 1300 to 1550°C. The reversibility of the transformation was investigated by X-ray diffraction (XRD) after accelerated aging, followed by heat treatment at temperatures from 350°C up to 850°C. The surface roughness (Rrms) was measured by atomic force microscopy after polishing, after accelerated aging for 1 or 10 h, and after aging followed by heat treatment. XRD showed that the fraction of m -phase increased linearly with grain size after aging for 10 h (1.0,29.8%). The transformation was reversed for all groups after heat treatment at 850°C/min., with only trace amounts of m -phase remaining for the group sintered at 1550°C. A significant increase in mean surface roughness was observed after accelerated aging (1.59,7.45 nm), compared to polished groups (0.83,1.0 nm). However, the mean surface roughness after accelerated aging for either 1 or 10 h, followed by heat treatment at 850°C/min. (1.18,2.1 nm), was not significantly different from that of the polished groups. This was attributed to the reverse transformation. XRD revealed that the monoclinic to tetragonal transformation, was complete after heat treatment at 500°C for 1 min, for specimens sintered at 1550°C and aged 10 h. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2010 [source] Inhibition of Lamin A/C Attenuates Osteoblast Differentiation and Enhances RANKL-Dependent Osteoclastogenesis,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 1 2009Martina Rauner Abstract Age-related osteoporosis is characterized by low bone mass, poor bone quality, and impaired osteoblastogenesis. Recently, the Hutchinson-Gilford progeria syndrome (HGPS), a disease of accelerated aging and premature osteoporosis, has been linked to mutations in the gene encoding for the nuclear lamina protein lamin A/C. Here, we tested the hypothesis that inhibition of lamin A/C in osteoblastic lineage cells impairs osteoblastogenesis and accelerates osteoclastogenesis. Lamin A/C was knocked-down with small interfering (si)RNA molecules in human bone marrow stromal cells (BMSCs) differentiating toward osteoblasts. Lamin A/C knockdown led to an inhibition of osteoblast proliferation by 26% and impaired osteoblast differentiation by 48% based on the formation of mineralized matrix. In mature osteoblasts, expression levels of runx2 and osteocalcin mRNA were decreased by lamin A/C knockdown by 44% and 78%, respectively. Furthermore, protein analysis showed that osteoblasts with diminished levels of lamin A/C also secreted less osteocalcin and expressed a lower alkaline phosphatase activity (,50%). Lamin A/C inhibition increased RANKL mRNA and protein levels, whereas osteoprotegerin (OPG) expression was decreased, resulting in an increased RANKL/OPG ratio and an enhanced ability to support osteoclastogenesis, as reflected by a 34% increase of TRACP+ multinucleated cells. Our data indicate that lamin A/C is essential for proper osteoblastogenesis. Moreover, lack of lamin A/C favors an osteoclastogenic milieu and contributes to enhanced osteoclastogenesis. [source] Cyclophilin D links programmed cell death and organismal aging in Podospora anserinaAGING CELL, Issue 5 2010Diana Brust Summary Cyclophilin D (CYPD) is a mitochondrial peptidyl prolyl- cis,trans -isomerase involved in opening of the mitochondrial permeability transition pore (mPTP). CYPD abundance increases during aging in mammalian tissues and in the aging model organism Podospora anserina. Here, we show that treatment of the P. anserina wild-type with low concentrations of the cyclophilin inhibitor cyclosporin A (CSA) extends lifespan. Transgenic strains overexpressing PaCypD are characterized by reduced stress tolerance, suffer from pronounced mitochondrial dysfunction and are characterized by accelerated aging and induction of cell death. Treatment with CSA leads to correction of mitochondrial function and lifespan to that of the wild-type. In contrast, PaCypD deletion strains are not affected by CSA within the investigated concentration range and show increased resistance against inducers of oxidative stress and cell death. Our data provide a mechanistic link between programmed cell death (PCD) and organismal aging and bear implications for the potential use of CSA to intervene into biologic aging. [source] The ubiquitous role of zinc in health and diseaseJOURNAL OF VETERINARY EMERGENCY AND CRITICAL CARE, Issue 3 2009DACVIM, Julia E. Cummings DVM Abstract Objective , To review zinc physiology and pathophysiology and the importance of zinc toxicity and deficiency in veterinary patients. Data Sources , A review of human and veterinary medical literature. Human Data Synthesis , There is a significant amount of original research in humans and animals on the role of zinc in multiple organ systems. There is also significant data available on human patients with zinc abnormalities. Veterinary Data Synthesis , Zinc deficiency has been studied in dogs with genetic disease and dietary deficiency leading to dermatological disease and immune deficiency. Zinc toxicity has been described after ingestion of metallic foreign bodies containing zinc. Conclusions , Historically, the role of zinc in health and disease has been studied through patients with toxicity or severe deficiency with obvious clinical signs. As the ubiquitous contribution of zinc to structure and function in biological systems was discovered, clinically significant but subtle deficiency states have been revealed. In human medicine, mild zinc deficiencies are currently thought to cause chronic metabolic derangement leading to or exacerbating immune deficiency, gastrointestinal problems, endocrine disorders, neurologic dysfunction, cancer, accelerated aging, degenerative disease, and more. Determining the causal relationships between mild zinc deficiency and concurrent disease is complicated by the lack of sensitive or specific tests for zinc deficiency. The prevalence of zinc deficiency and its contribution to disease in veterinary patients is not well known. Continued research is warranted to develop more sensitive and specific tests to assess zinc status, to determine which patients are at risk for deficiency, and to optimize supplementation in health and disease. [source] Could accelerated aging explain the excess mortality in patients with seropositive rheumatoid arthritis?ARTHRITIS & RHEUMATISM, Issue 2 2010Cynthia S. Crowson Objective To determine whether the mortality pattern in patients with seropositive rheumatoid arthritis (RA) is consistent with the concept of accelerated aging, by comparing the observed mortality rates in patients with RA with the age-accelerated mortality rates from the general population. Methods A population-based inception cohort of patients with seropositive RA (according to the American College of Rheumatology 1987 criteria) was assembled and followed up for vital status until July 1, 2008. The expected mortality rate was obtained by applying the death rates from the general population to the age, sex, and calendar year distribution of the RA population. The observed mortality was estimated using Kaplan-Meier methods. Acceleration factors for the expected mortality were estimated in accelerated failure time models. Results A total of 755 patients with seropositive RA (mean age 55.6 years, 69% women) were followed up for a mean of 12.5 years, during which 315 patients died. The expected median survival was age 82.4 years, whereas the median survival of the RA patients was age 76.7 years. Results of statistical modeling suggested that, in terms of mortality rates, patients with RA were effectively 2 years older than actual age at RA incidence, and thereafter the patients underwent 11.4 effective years of aging for each 10 years of calendar time. Conclusion The overall observed mortality experience of patients with seropositive RA is consistent with the hypothesis of accelerated aging. The causes of accelerated aging in RA deserve further investigation. [source] Auswirkungen der Matrixzusammensetzung auf die Dauerhaftigkeit von Betonen mit textilen Bewehrungen aus AR-GlasBETON- UND STAHLBETONBAU, Issue 8 2009Marko Butler Dipl.-Ing. Baustoffe; Bewehrung; Versuche Abstract Verbundmaterialien aus Feinbetonen mit textiler Bewehrung aus alkaliresistentem Glas (AR-Glas) können ausgeprägten zeitabhängigen Veränderungen hinsichtlich des mechanischen Leistungsvermögens unterliegen. Für eine zielsichere Anwendung solcher Werkstoffe im Bauwesen sind genaue Kenntnisse über die Höhe und die Ursachen dieser Leistungsverluste unabdingbar. In diesem Artikel werden anhand von Ergebnissen aktueller Untersuchungen entscheidende Mechanismen für die Alterungsprozesse dargestellt, die aus der Zusammensetzung der Feinbetone resultieren. Dazu wurden aus verschiedenen Betonzusammensetzungen, die sich maßgeblich in ihrer Hydratationskinetik und Alkalität unterschieden, textilbewehrte Dehnkörper hergestellt und nach beschleunigter Alterung geprüft. Dehnkörper aus Feinbeton mit hoher Alkalität (das Bindemittel bestand nur aus CEM I) zeigten dramatische Einbußen bei Zugfestigkeit und Bruchdehnung. Das Leistungsvermögen von Proben aus Feinbetonen mit puzzolanisch abgepufferter Bindemittelzusammensetzung und gleichzeitig reduziertem Portlandzementklinkeranteil zeigte sich dagegen weitgehend unbeeinflusst von Alterungsprozessen. Mit Hilfe von beidseitigen Garnauszugversuchen an beschleunigt gealterten Feinbetonproben wurden die für das unterschiedliche Materialverhalten verantwortlichen Degradationsmechanismen aufgeklärt. Neben der mechanischen Prüfung wurde dazu auch die Interphase zwischen Fasern und umgebendem Feinbeton mit bildgebenden und analytischen Verfahren charakterisiert. Die festgestellten Einbußen im Leistungsvermögen des Garn-Matrix-Verbundes konnten überwiegend auf die Neubildung von ungünstig strukturierten Hydratationsprodukten in der Interphase Filament-Matrix bzw. in Filamentzwischenräumen zurückgeführt werden. Die Morphologie dieser Phase wird maßgeblich von der Bindemittelzusammensetzung bestimmt. Korrosion des AR-Glases als Schadensursache kann unter ungünstigen Umständen auch eine große Rolle spielen, ist aber bei geeigneter Matrixformulierung von untergeordneter Bedeutung. Effect of Matrix Composition on the Durability of Concretes Reinforced with Glass Fibre Fabric The mechanical performance of composites made of finegrained concrete and textile reinforcement can worsen markedly with increasing age if alkali-resistant glass (AR-glass) is used as the reinforcing material. For reliable practical applications of textile-reinforced concrete, precise knowledge as to the extent and causes of such degradation is indispensable. This paper discusses important aging mechanisms resulting from the composition of fine-grained concrete. Tensile tests on composites made of different concrete compositions distinguished from one another by their hydration kinetics and alkalinity were performed before and after accelerated aging. Composites made of concrete with high alkalinity showed dramatic losses of tensile strength and strain capacity. In contrast the mechanical performance of composites whose binders had reduced Portland cement clinker content plus added puzzolana was hardly affected by the accelerated aging. To clarify the mechanisms of degradation, yarn pullout tests were performed on specimens of equal matrix composition and age. Additionally, the morphology of the interphase between matrix and fibre was characterised using direct microscopic examination and analytical methods. The new formation of unfavourably structured products of hydration in the filament-matrix interphase and/or in the empty spaces between filaments was found to be the main reason for the performance losses observed. The morphology of these hydration products is determined to a great extent by the binder composition. Under unfavourable conditions corrosion of AR-glass can occur as well and lead to distinct composite damage. However, if the formulation of the binder is proper, bulk glass corrosion is of minor importance. 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