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

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

Microstructure and Hydroabrasive Wear Behavior of High-Velocity Oxy-Fuel Thermally Sprayed Wc-Co(Cr) Coatings

Sand erosion tests were performed on WC-Co and WC-CoCr coatings deposited by the high velocity oxy-fuel spraying method. Several analytical techniques, including X-ray diffraction, Auger electron spectroscopy and energy-dispersive spectroscopy in a transmission electron microscope were used to characterize the microstructures formed during powder processing and spraying. It was found that a substantial fraction of WC decomposed into W2C or reacted with the cobalt matrix to form ternary carbides such as Co3W3C and other mixed compounds. In both cases the binder phase had a nanocrystalline structure of size 4-8 nm containing tungsten, cobalt, carbon and chromium elements. The addition of chromium inhibits to a large extent the decomposition of WC and avoids the formation of metallic tungsten. In addition, chromium improved the erosion resistance by several times compared with the WC-Co coating. Scanning electron microscopy showed that the CoCr matrix binds carbides better than the cobalt matrix, thereby inhibiting carbide loss at the spray particle boundaries. The hydroabrasive wear behaviour of coatings and the mechanisms for material removal are discussed with respect to the microstructures formed during spraying

TRANSPORT IN OXIDESNew investigation of oxygen self-diffusion in Cu2O

On a effectué de nouvelles mesures des coefficients d'auto-diffusion de l'oxygène dans Cu2O monocristallin. Le domaine de stabilité a été exploré sous 2 pressions partielles d'oxygène : 4,6 x 10-4 atm et 0,26 atm. L'isotope stable 18O a été utilisé comme traceur. Il a été introduit soit par la méthode du dépôt mince soit par recuit sous atmosphère de teneur en 18O constante. On a mesuré les profils de diffusion par spectrométrie de masse de l'émission ionique secondaire. Ces profils obéissent bien aux solutions de l'équation de Fick. Nous obtenons comme résultat : D (cm2 .s-1) = 3 x 10-3 p0,4 O2 exp - 1,55 (eV)/ kT. Le défaut responsable de la migration de l'oxygène qui correspond à cette dépendance en pression partielle d'oxygène est l'interstitiel d'oxygène chargé une fois O'i.New measurements of oxygen self-diffusion coefficients in Cu2O have been performed on single crystals under two oxygen partial pressures (4.6 x 10-4 atm and 0.26 atm) in the stability domain. The stable isotope 18O has been used as a tracer. It has been introduced by a thin film method or by annealing under a constant 18O pressure. The diffusion profiles have been measured by secondary ion mass spectrometry. They obey quite well the solutions of Fick's equation. The results can be represented by : D (cm2 .s-1) = 3 x 10-3 p0,4 O2 exp - 1,55 (eV)/ kT. The defect responsible for the oxygen migration corresponding to the above oxygen partial pressure dependence is the singly charged oxygen interstitial O'i

Implantation of 18O+ ions in channelling directions of aluminium, copper and nickel single crystals - I. — Experimental conditions and range profile determination

18O+ ions with energies ranging from 10 to 45 keV have been implanted along the or directions of A1, Ni and Cu single crystals. The experimental techniques used to prepare the samples and to perform the implantations are described. The implantation profiles are determined with an ion probe microanalyser. They are characteristic of channelling implantation and vary with the energy of the 18O+ ions, the direction of implantation and the nature of the target.Des ions 18O+, dont l'énergie est comprise entre 10 et 45 keV, sont implantés dans des monocristaux de Al, Ni et Cu, parallèlement à des directions ou . Les techniques expérimentales utilisées pour préparer les échantillons et pour réaliser les implantations sont décrites. La détermination des profils d'implantation se fait à l'aide d'un microanalyseur à sonde ionique. Ceux-ci sont caractéristiques d'une implantation en canalisation et varient avec l'énergie des ions 18O+, la direction d'implantation et la nature du matériau étudié