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Natural Aging (natural + aging)

Distribution by Scientific Domains

Polymers and Materials Science	85%

Selected Abstracts

Natural Aging in Al-Mg-Si Alloys , A Process of Unexpected Complexity,

ADVANCED ENGINEERING MATERIALS, Issue 7 2010
John Banhart
The natural aging behavior of pure ternary Al-Mg-Si alloys is investigated by measuring hardness, electrical resistivity and positron lifetime, as well as carrying out thermal analysis and atom probe microscopy. It is found that several distinct temporal stages of natural aging can be distinguished in which one of these quantities shows a characteristic behavior and that these times coincide for many of these measurements. The rate of change in the measured data is correlated with proposed solute dynamics during natural aging for both aging that takes place prior to artificial aging (natural pre-aging) and after artificial underaging (natural secondary aging) heat treatments. Controlling factors for solute dynamics are discussed. [source]

Enhanced Ability of Nanostructured Titania Film to Assist Photodegradation of Rhodamine B in Water Through Natural Aging

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2007
Jin-Ming Wu
Gradually but significantly improved abilities of titania films with various nanofeatures and crystal structures to assist photodegradation of trace rhodamine B in water were observed when the films were subjected to natural aging. The so-called natural aging behavior can be attributed to the gradual increase in the surface hydroxyl groups that are beneficial to the photocatalytic reaction. [source]

Natural Aging in Al-Mg-Si Alloys , A Process of Unexpected Complexity,

Effect of long-term natural aging on the thermal, mechanical, and viscoelastic behavior of biomedical grade of ultra high molecular weight polyethylene

JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2010
H. Fouad
Abstract In the total joint prostheses, Ultra High Molecular Weight Polyethylene (UHMWPE) may undergo an oxidative degradation in the long term. The overall properties of UHMWPE are expected to be altered due to the oxidative degradation. The goal of this study is to investigate the effects of natural aging up to 6 years in air on the thermal, mechanical, and viscoelastic properties of UHMWPE that was used in total joint replacement. The changes in UHMWPE properties due to aging are determined using Differential Scanning Calorimetry (DSC), uniaxial tensile tests, and Dynamic Mechanical Analysis (DMA). The DSC results show that the lamellar thickness and degree of crystallinity of UHMWPE specimens increase by 38% and 12% due to aging. A small shoulder region in the DSC thermograms is remarked for aged specimens, which is an indication of formation of new crystalline forms within their amorphous region. The tensile properties of aged and nonaged UHMWPE specimens show a significant decrease in the elastic modulus, yield, fracture stresses, and strain at break due to aging. The DM testing results indicate that the storage modulus and creep resistance of UHMWPE specimens decrease significantly due to aging. Also, it is remarked that the , relaxation peak for aged UHMWPE specimens occurs at lower temperature compared to nonaged ones. The significant reduction in the strength and creep resistance of UHMWPE specimens due to aging would affect the long-term clinical performance of the total joint replacement and should be taken into consideration during artificial joint design. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source]

Hedgehog signaling maintains hair follicle stem cell phenotype in young and aged human skin

AGING CELL, Issue 6 2009
Laure Rittié
Summary Skin hair follicles (HF) contain bulge stem cells (SC) that regenerate HFs during hair cycles, and repair skin epithelia following injury. As natural aging is associated with decreased skin repair capacity in humans, we have investigated the impact of age on human scalp HF bulge cell number and function. Here, we isolated human bulge cells, characterized as CD200+/KRT15+/KRT19+ cells of the HF, by dissection-combined CD200 selection in young and aged human skin. Targeted transcriptional profiling indicates that KRT15, KRT19, Dkk3, Dkk4, Tcf3, S100A4, Gas1, EGFR and CTGF/CCN2 are also preferentially expressed by human bulge cells, compared to differentiated HF keratinocytes (KC). Our results demonstrate that aging does not alter expression or localization of these HF SC markers. In addition, we could not detect significant differences in HF density or bulge cell number between young and aged human scalp skin. Interestingly, hedgehog (Hh) signaling is activated in human bulge cells in vivo, and down-regulated in differentiated HF KCs, both in young and aged skin. In addition, activation of Hh signaling by lentivirus-mediated overexpression of transcription factor Gli1 induces transcription of HF SC markers KRT15, KRT19, and Gas1, in cultured KCs. Together with previously reported knock-out mouse results, these data suggest a role for Hh signaling in maintaining bulge cell phenotype in young and aged human skin. [source]