In Algeria, overgrazing has long threatened the sustainable use of the nearly 20 million hectares of steppe lands. More recently, governmental policies favouring extensive rainfed cereal cropping in the steppe region have increased anthropic pressure on this fragile environment. Low rainfall, weak crop development and sandy soils lead to a high risk of wind erosion, yet no studies have been carried out in this region to this date to quantify the effect of steppe conversion on wind erosion. A 1·3-ha field in the central steppe of Algeria (Laghouat) was converted to cropland (Hordeum Vulgare L.) and equipped with a weather station and Big Spring Number Eight sand straps to monitor climate-related parameters and sediment fluxes over a 25-month period. Threshold wind velocities (3·6 m height) varied between 6 and 7 m s À1 with a weak seasonal variation. More than 70% of the saltation-producing winds originated from the NW. For these winds, a soil loss of 155 Mg ha À1 was measured. Half of the sediment loss occurred during a single, 12-day period. Deposition of 26·5 Mg ha À1 was observed for SW winds. The measured erosion rates by far exceeded all norms of tolerable soil loss, indicating that rainfed cereal cropping is a highly unsustainable form of land use in the steppe region around Laghouat. National agricultural policies should be revised to take this into account.
Determination of residual stresses in the welded areas of metal structures is a very important operation in the mechanical construction and other fields, for the reliability and sustainability of these metal structures
The velocity of DSC grain‐boundary dislocations, with Burgers vector bg = 1/18[411], is measured for temperatures ranging from 823 to 1023 K and stresses ranging from 10 to 30 MPa, in silicon Σ = 9 bicrystals. Screw segments are heavily kinked and much faster than edge ones, parallel to the [011] tilt axis of the bicrystals, which look very rigid. The apparent activation energy for the glide of fast screw segments is ≈ 1.3 eV and the stress exponent m ≈ 2.5. Results are discussed in terms of the kink‐pair model and estimates of kink formation and migration energies, based on the core structures of kinks, satisfactorily account for the observed anisotropy of DSC dislocation motion.
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