Homogénéité des caractères sédimentologiques des sables ogoliens entre Nouakchott (Mauritanie) et Mbour (Sénégal)

L'étude de l'ensemble dunaire ogolien (20.000-12.000 ans BP) le long du littoral de la Mauritanie méridionale et du Sénégal permet de montrer la très grande homogénéité des caractères sédimentologiques de la nappe sableuse. Les études ultérieures permettront de préciser les limites de cette couverture sableuse ogolienne et d'expliquer les mécanismes de son homogénéisatio

Strong second harmonic generation in SiC, ZnO, GaN two-dimensional hexagonal crystals from first-principles many-body calculations

International audienceThe second harmonic generation (SHG) intensity spectrum of SiC, ZnO, GaN two-dimensional hexagonal crystals is calculated by using a real-time first-principles approach based on Green's function theory [Attaccalite et al.,Phys Rev B 2013 88, 235113]. This approach allows one to go beyond the independent particle description used in standard first-principles nonlinear optics calculations by including quasiparticle corrections (by means of the GW approximation), crystal local field effects and excitonic effects. Our results show that the SHG spectra obtained by the latter approach differ significantly from their independent particle counterparts. In particular they show strong excitonic resonances at which the SHG intensity is about two times stronger than within the independent particle approximation. All the systems studied (whose stability have been predicted theoretically) are transparent and at the same time exhibit a remarkable SHG intensity in the range of frequencies at which Ti:Sapphire and Nd:YAG lasers operate thus they can be of interest for nanoscale nonlinear frequency conversion devices. Specifically the SHG intensity at 800 nm (1.55 eV) ranges from about 40-80 pm/V in ZnO and GaN to 0.6 nm/V in SiC. The latter value in particular is 1 order of magnitude larger than values in standard nonlinear crystals

Homogénéité des caractères sédimentologiques des sables ogoliens entre Nouakchott (Mauritanie) et Mbour (Sénégal)

L'étude de l'ensemble dunaire ogolien (20.000-12.000 ans BP) le long du littoral de la Mauritanie méridionale et du Sénégal permet de montrer la très grande homogénéité des caractères sédimentologiques de la nappe sableuse. Les études ultérieures permettront de préciser les limites de cette couverture sableuse ogolienne et d'expliquer les mécanismes de son homogénéisatio

Study of Hypermetropia in a Senegalese Hospital

The cases of hypermetropia in patients aged 5 to 40 years were studied at Aristide Le Dantec hospital in Dakar. There are 85 patients including 28 men and 57 women. The average age was 22 years old. Headache was the most common reason for consultation (79.69%). The average consultation time was 6 days after onset of functional symptoms. Complications were strabismus (21.88%) and amblyopia (3.12%). A negative impact on the socio-professional level was noted in 60.94%. The treatment consisted of an optical correction by glasses in 96.87%.</p

Glucocorticoid modulation of Ca2+ homeostasis in human B lymphoblasts

We determined the effect of cortisol (200 nm for 48 h) on the intracellular Ca2+ concentration ([Ca2+]i) and parameters of Ca2+i signalling in 19 lymphoblastoid cell lines (LCLs).Using the fluorescent dye fura-2, the basal [Ca2+]i in Ca2+-containing medium was 63.5 ± 2.4 nm in vehicle (ethanol)-treated LCLs and 55.7 ± 2.6 nm (mean ±s.e.m.) in cortisol-treated LCLs.Ca2+i signalling following platelet-activating factor (PAF, 100 nm) addition was enhanced by cortisol treatment, with LCLs having small PAF responses showing the largest percentage increase after cortisol treatment. Mean peak [Ca2+]i responses to PAF were enhanced 67.0% and 55.7% in Ca2+-free and Ca2+-containing medium, respectively.The endoplasmic reticulum Ca2+-ATPase inhibitor thapsigargin (100 nm) caused a transient increase in [Ca2+]i in Ca2+-free medium in which the peak change was increased in cortisol-treated cells (98.5 ± 5.8 vs. 79.8 ± 4.5 nm). Peak changes in the freely exchangeable Ca2+ in response to 5 μm ionomycin were also enhanced in cortisol-treated cells (923.7 ± 113.9 vs. 652.2 ± 64.5 nm) and correlated to the PAF-evoked [Ca2+]i response.Cortisol-treated LCLs exposed to thapsigargin to empty intracellular Ca2+ stores (10 min treatment in Ca2+-free medium) and exposed to CaCl2 or MnCl2 had a greater rate of Ca2+ entry (18.6 ± 1.8 vs. 13.8 ± 1.5 nm s−1) and higher rate constant for Mn2+ entry (0.0345 ± 0.0029 vs. 0.0217 ± 0.0020) than vehicle-treated cells. Peak [Ca2+]i in cells exposed to CaCl2 was also enhanced (869.4 ± 114.7 vs. 562.6 ± 61.7 nm). Parameters of divalent cation influx were highly correlated to the peak [Ca2+]i elicited by thapsigargin or ionomycin.Inclusion of RU 486 (a glucocorticoid antagonist) with cortisol prevented the decrease in basal [Ca2+]i and stimulatory actions of cortisol on all Ca2+i parameters. RU 486 alone had no apparent effects on basal [Ca2+]i or Cai2+ signalling.Based on data obtained over a wide range of responses (in the presence and/or absence of cortisol or RU 486), the results show that cortisol stimulation of glucocorticoid receptors decreases basal [Ca2+]i and enhances PAF-evoked [Ca2+]i signalling, most probably through its effects on intracellular Ca2+ stores. In turn, the extent of Ca2+ entry via store-operated plasma membrane Ca2+ channels is closely linked to the size of the Ca2+ stores