760 research outputs found

    Swelling strains from gamma-irradiated silica - Evaluation of results by Shelby

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    Water introduced in silica reacts with the silica network under hydroxyl generation that causes a volume swelling. This effect has been discussed quantitatively in much detail in [1] for the case of water entrance by a heat treatment procedure. In the present Report we include also data by Shelby [8] obtained by in-situ generation of hydroxyl in gamma-irradiated silica. This procedure resulted in stronger density changes compared with the heat-treated material. Independent of this fact, we can show that the same volume swelling results for both methods. As an application of the results an estimation of the molar volume of hydroxyl is made

    Inert strength measurement on silica soaked at 250°C in liquid water and water vapour

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    The effect of water soaking and heat-treatment in saturated water vapour at 250°C for 192 h on the strength of silica glass is studied. Bending strength meaurements in liquid nitrogen showed a clear increase of the inert strength for heat-treated specimens over that of the untreated material. The increase in strength is interpreted as the consequence of water diffusion into exposed surfaces of the test specimen, which results in swelling of the glass and shielding of cracks, present in the surface of the glass. Experimental results are compared with theoretical predictions

    Women’s perspectives on smartphone apps for fertility tracking and predicting conception : a mixed methods study

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    Acknowledgement We would like to thank all our survey respondents and interview participants, without whom this research would not have been possible. Additionally, we would like to thank the Clearblue team at SPD Development Company Ltd., for their assistance and support with volunteer recruitment and assistance with implementation of the research. Funding This work was conducted as an MPH research project at the University of Aberdeen. SPD Development Company Ltd. (Clearblue) provided pregnancy and ovulation tests as rewards for participants who completed interviews.Peer reviewedPublisher PD

    Evaluation of crack-terminating angles in heat-treated silica DCDC-specimens

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    Cracks terminating at free surfaces are affected by local stresses in the surface region. Under residual compression, the crack front must retard and under residual tensile stresses advance, both compared with the crack contour in the absence of stresses. This effect can be used for an estimation of residual surface stresses in silica generated during the silica/water reaction and caused by volume swelling. A strong shielding stress intensity factor of about -2.5 MPam\sqrt{m} was found for DCDC specimen heat-treated for 192h at 250°C in water. This result is a clear indication for compressive stresses developing in the water diffusion zone at the surface

    v-K-data for silica from interrupted lifetime measurements

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    Different methods were applied so far in order to determine subcritical crack growth for silica. Mostly, fracture mechanics standard tests with macro cracks were used for this purpose. In this report, we evaluated the subcritical crack growth curves from interrupted lifetime tests on silica bending specimens containing small natural flaws. The resulting v-K-curve showed crack growth rates down to 10−14^{-14} m/s indicating a threshold for subcritical crack growth at Kth_{th}≊\approxeq0.31 MPam\sqrt{m} In the plot of v=f(K/KIc_{Ic}) slight material differences could be eliminated and suitable agreement with macro-crack results by Wiederhorn and Bolz [1] on DCB-specimens and Michalske et al. [2] on DCDC-specimens could be stated

    Neuroimaging oxytocin modulation of social reward learning in schizophrenia.

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    Conventional pharmacological approaches have limited effectiveness for schizophrenia. There is interest in the application of oxytocin, which is involved in social cognition. Clinical trials have yielded mixed results, with a gap in understanding neural mechanisms. To evaluate the behavioural impact of oxytocin administration on a social learning task in individuals with schizophrenia, and elucidate any differential neural activity produced. We recruited 20 clinically stable right-handed men diagnosed with schizophrenia or schizoaffective disorder. In a double-blind cross-over randomised controlled study, 40 IU of oxytocin or placebo were administered before functional magnetic resonance imaging of participants playing a multi-round economic exchange game of trust. Participants had the role of investors (investment trials) receiving repayment on their investments (repayment trials), playing one session against a computer and a second against a player believed to be human. During investment trials, oxytocin increased neural signalling in the right lateral parietal cortex for both human and computer player trials, and attenuated signalling in the right insula for human player trials. For repayment trials, oxytocin elicited signal increases in left insula and left ventral caudate, and a signal decrease in right amygdala during the human player trials; conversely it resulted in right dorsal caudate activation during the computer player trials. We did not find a significant change in behavioural performance associated with oxytocin administration, or any associations with symptoms. During a social learning task oxytocin modulates cortical and limbic substrates of the reward-processing network. These perturbations can be putatively linked to the pathoaetiology of schizophrenia

    Progress in strength, toughness and lifetime methods for ceramics

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    Fortschritte auf dem Gebiet der Festigkeit, RisszĂ€higkeit und Lebensdauer von Keramik Zur Charakterisierung des Versagensverhaltens keramischer Werkstoffe sind Festigkeits- und RisszĂ€higkeitsmessungen erforderlich. Weist eine Keramik noch den Effekt des unterkritischen Risswachstums auf, sind auch Lebensdauermessungen unter statischer Belastung von großer Wichtigkeit. Neuere BeitrĂ€ge der Autoren zur Untersuchungs-Methodik sind in diesem Bericht zusammengefasst. Teil A befasst sich mit der Berechnung der maximalen Spannungen in runden Scheiben unter Kugelbelastung. Hierbei werden der “ball-on-ring test”, der “ball-on-3-balls test” und der kĂŒrzlich von den Verfassern entwickelte „3-balls-on-3-balls test“ betrachtet. Als praktische Anwendung der ermittelten Spannungen im “ball-on-3-balls test” wird das bei grobkörnigem Aluminiumoxid gefundene stabile Bruchverhalten als Effekt einer stark ansteigenden Risswiderstandskurve diskutiert. In Teil B wird auf eine von den Verfassern entwickelte Methode eingegangen, die es gestattet, sehr kurze Kerben mit extrem kleinen Kerbradien zu erzeugen. Bei einer ZrO2-Keramik konnten Kerbradien von unter 0.1 ÎŒm bei einer Kerbtiefe von nur 40ÎŒm erzeugt werden. Derartig kurze und scharfe Kerben sollten geeignet sein, das Verhalten natĂŒrlicher Risse in Keramiken anzunĂ€hern. Schließlich wird in Teil C ĂŒber eine Prozedur berichtet, die sich dafĂŒr eignet, eine vorhandene Anzahl an Lebensdauer-Versuchsproben optimal auszunutzen. Hierbei kann aus der erneuten Verwendung von auf niederem Lastniveau angefallenen „DurchlĂ€ufern“ zusĂ€tzliche Information ĂŒber das Risswachstumsgesetz gewonnen werden. Die Methode wird an Lebensdauermessungen von SIALON in destilliertem Wasser von 20°C demonstriert
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