Elastic properties of the olivine and spinel polymorphs of Mg2GeO4, and evaluation of elastic analogues

The single-crystal elastic moduli of the olivine and spinel phases of Mg₂GeO₄ have been measured using Brillouin scattering spectra. The moduli for the olivine phase are: C₁₁ = 3.12, C₂₂ = 1.87, C₃₃ = 2.17, C₆₆ = 0.71, C₂₃ = 0.66, C₃₁ = 0.65 and C₁₂ = 0.60. The moduli for the spinel phase are: C₁₁ = 3.00, C₄₄ = 1.26 and C₁₂ = 1.18.These data are analyzed to define the best type of elastic analogue for magnesium orthosilicates. The character of the many-bodied, non-central force associated with the divalent cation is found to significantly influence the relative magnitudes of the elastic moduli. Since the nature of the many-bodied, non-central force is quite different for alkaline earth cations than for transition metal cations, we conclude that materials which contain one of these cation types is not a good analogue for materials with the other type. Magnesium orthogermanate, however, is a good analogue of magnesium orthosilicate. On the other hand, the high elastic anisotropy of the spinel phase of the germanate suggests that the germanium tetrahedron is less rigid under shear than the corresponding silicon tetrahedron. The success of the magnesium orthogermanate to model the magnesium orthosilicate is probably a result of the mechanical isolation of the tetrahedra, thus requiring the conclusions of this study to be further tested before applying them to other silicate systems.     

Farmers’ adaptive practices for drought risk reduction in the northwest region of Bangladesh

Being an agrarian region, the northwest part of Bangladesh frequently experiences recurrent droughts over the last decade. To cope with this insidious disaster, the farmers in this region practice various adaptation measures through their own efforts with institutional support. But these efforts and support are not sufficient for farmers to survive droughts. In this light, this study assesses the adaptive capacity of farmers along with institutions to develop suitable drought adaptation policy in the context of this region. The drought adaptive practices developed in this study are mainly adopted from the unique approach called socioeconomic, institutional and physical. Results reveal that establishment of mango orchard, vegetable gardening and community health care service would be helpful in enhancing drought resilience at community level. Moreover, an important policy message from this study suggests that validation of these practices through government offices, research institutes and other relevant organizations can help to develop an appropriate drought adaptation policy for this region. Similarly, by performing these practices from national to local level, farmers as well as communities in this region will be able to effectively sustain their livelihoods against droughts.