Secondary Crack Formation as Fracture Mechanism in Nanocomposites of Epoxy and Fullerene-Like WS2

Fullerene-like WS2 (IF-WS2) nanoparticles (NPs) were used as a toughening agent in epoxy nanocomposites. Already 0.5 % IF-WS2 by mass increased the critical energy release rate GIc by 45 % to 62 %. Conicsection-shaped crack lines were observed on the fracture surfaces in some distance to the NPs. Nanomechanical AFM modulus measurements showed, however, no measurable differences between the modulus distribution in the vicinity of the NPs and the bulk epoxy. Possible secondary crack formation at the NPs explains the crack lines nicely. The crack line geometry allows determining the relative velocity of the secondary crack. Topographic AFM showed vertical steps several hundred nanometers high at the crack lines, indicating shear fracture and suggesting the presence of numerous subsurface cracks, which might explain the toughness increase

AFM Investigation of Epoxy Fracture Surfaces Indicating Nanoplasticity

Epoxy fracture surfaces are investigated by nanomechanical atomic-force micrsocopy (AFM). Apparent nodules on these surfaces are likely AFM tip-convolution artifacts, which might also explain apparent modulus inhomogeneities. No modulus inhomogeneities are found on smooth ultramicrotome cuts. Invest igation of a copolymer shows, however, that existing inhomogeneities can be measured indeed. AFM investigation results in plastic deformation of ultramicrotome cuts already at low forces of 50 nN, which results in a blunt topographic image and an apparently increased modulus. This suggests that thin, sharp surface features are present on ultramicrotome cuts which are plastically deformed upon AFM investigation. Super-sharp AFM imaging showed a presumably more representative image of the investigated fracture surfaces, which showed numerous depressions and vertical steps a few nanometers high. This suggests that even brittle epoxy exhibits some plasticity at the nanometer scale upon fracture

Surface modification of HVOF thermal sprayed WC–CoCr coatings by laser treatment

In this work the affects of laser characteristics on microstructure and microhardness of high velocity oxygen fuel sprayed (HVOF) WC–CoCr coatings were investigated. The coating was deposited with a Sulzer Metco WokaJet™-400 kerosene fuel and the laser surface treatments were applied using CO2 laser with 10.6 μm wavelength. Large variations in surface properties were produced from variation in the laser processing parameters. In total, four levels of peak power (100, 200, 300 and 350 W), four levels of spot diameter (0.2, 0.4, 0.6 and 1 mm) and three levels of pulse repetition frequency (PRF) were investigated. An initial set of tests were followed by a more detailed 33 factorial design of experiments. Pulse repetition frequency and duty cycle were set in order to maintain the same overlap in the x and y directions for the raster scanned sample spot impact dimensions. Overlaps of 30% were used in the initial tests and 10% in the more detailed trials. The results have shown that care must be taken to keep the irradiance at a relatively low level compared to uncoated surfaces. High irradiance can in this case result in rough and porous surfaces. Lower levels of irradiance are shown to provide more uniform microstructures, reduced porosity and increased microhardness

Learning in the Palaver Hut: The ‘Africa Study Visit’ as teaching tool.

noThe aim of this article is to assess the experiential learning environment of the African Study Visit (ASV). It presents a theoretically grounded analysis of the ASV. Although field visits are not a new phenomenon within Higher Education, they seem, but with few exceptions, to be considered as an add-on teaching method. By drawing from the experiential learning literature, we demonstrate that there are sound pedagogical reasons for incorporating field visits like the ASV into the curriculum as stand-alone components. Thus, the original contribution of this article is to place the ASV within the experiential learning literature such that the theoretical, practical and conceptual benefits for students are understood. Its significance is that this article offers a set of practices from an experiential learning perspective that can be used for deepening the levels of comprehension of political issues in Africa for international studies students

The Expression of Vasoactive Intestinal Peptide Receptor 1 Is Negatively Modulated by MicroRNA 525-5p

Background: The human Vasoactive Intestinal Peptide (VIP) is a neurokine with effects on the immune system where it is involved in promoting tolerance. In this context, one of its receptors, VPAC1, has been found to be down-modulated in cells of the immune network in response to activating stimuli. In particular, the bacterial liposaccaride (LPS), a strong activator of the innate immune system, induces a rapid decrease of VPAC1 expression in monocytes and this event correlates with polymorphisms in the 3'-UTR of the gene. Methodology/Principal Findings: MicroRNA 525-5p, having as putative target the 3'-UTR region of VPAC1, has been analysed for its expression in monocytes and for its role in down-modulating VPAC1 expression. We report here that miR-525-5p is promptly up-regulated in LPS-treated monocytes. This microRNA, when co-transfected in 293T cells together with a construct containing the 3'-UTR of the VPAC1 gene, significantly reduced the luciferase activity in a standard expression assay. The U937 cell line as well as primary monocytes enforced to express miR-525-5p, both down-modulate VPAC1 expression at similar extent. Conclusions/Significance: Our results show that the response to an inflammatory stimulus elicits in monocytes a rapid increase of miR-525-5p that targets a signaling pathway involved in the control of the immune homeostasis

Nigella sativa (Black Cumin) Seed Extract Alleviates Symptoms of Allergic Diarrhea in Mice, Involving Opioid Receptors

The incidence of food hypersensitivity and food allergies is on the rise and new treatment approaches are needed. We investigated whether N. sativa, one of its components, thymoquinone, or synthetic opioid receptor (OR)-agonists can alleviate food allergy. Hence, ovalbumin (OVA) -sensitized BALB/c-mice were pre-treated either with a hexanic N. sativa seed extract, thymoquinone, kappa- (U50'4889) or mu-OR-agonists (DAMGO) and subsequently challenged intra-gastrically with OVA. All 4 treatments significantly decreased clinical scores of OVA-induced diarrhea. N. sativa seed extract, thymoquinone, and U50'488 also decreased intestinal mast cell numbers and plasma mouse mast cell protease-1 (MMCP-1). DAMGO, in contrast, had no effect on mast cell parameters but decreased IFNγ, IL-4, IL-5, and IL-10 concentration after ex vivo re-stimulation of mesenteric lymphocytes. The effects on allergy symptoms were reversible by OR-antagonist pre-treatment, whereas most of the effects on immunological parameter were not. We demonstrate that N. sativa seed extract significantly improves symptoms and immune parameters in murine OVA-induced allergic diarrhea; this effect is at least partially mediated by thymoquinone. ORs may also be involved and could be a new target for intestinal allergy symptom alleviation. N. sativa seed extract seems to be a promising candidate for nutritional interventions in humans with food allergy

AFM Investigation of Epoxy Fracture Surfaces Indicating Nanoplasticity

Epoxy fracture surfaces are investigated by nanomechanical atomic-force micrsocopy (AFM). Apparent nodules on these surfaces are likely AFM tip-convolution artifacts, which might also explain apparent modulus inhomogeneities. No modulus inhomogeneities are found on smooth ultramicrotome cuts. Invest igation of a copolymer shows, however, that existing inhomogeneities can be measured indeed. AFM investigation results in plastic deformation of ultramicrotome cuts already at low forces of 50 nN, which results in a blunt topographic image and an apparently increased modulus. This suggests that thin, sharp surface features are present on ultramicrotome cuts which are plastically deformed upon AFM investigation. Super-sharp AFM imaging showed a presumably more representative image of the investigated fracture surfaces, which showed numerous depressions and vertical steps a few nanometers high. This suggests that even brittle epoxy exhibits some plasticity at the nanometer scale upon fracture

The fires of hell and the burning of heretics in the accounts of the executions at Orleans in 1022

This article examines the significance of hell and hellfire in the sources for the first recorded burning of humans for the crime of heresy in the medieval West at Orleans in 1022. It suggests that the main sources for this event describe the execution of the heretics by fire as an enactment of their eschatological destinies. The division of humanity into two overarching communities, namely the saved and the damned, shapes both the accounts near-contemporaries offered of this event and also the context in which they placed it. The exposure and destruction of the heretics at Orleans reinforces the shared identity of Christian society. The fires of execution literally handed the heretics at Orleans off to the fires of hell, enacting in miniature the fate that awaited all those who failed to take their place within a united Christian society, be they heretics, Muslims or Jews