Density-driven interstitial water motion in sediments

Sediment depth distributions and fluxes of dissolved chemical substances have been interpreted as being a result of reaction, diffusion, bioturbation and irrigation1,2. However, several studies suggest that density-driven convection3 can alter the depth distribution and increase the fluxes of dissolved substances when density decreases below the sediment surface 4-7. We present here temperature-time series measurements for a freshwater lake undergoing autumn cooling. These are the first in situ observations of heat transport due to motion of interstitial waters over periods of less than 1 hour. Density, calculated from temperature, decreases with depth at the time and place that this motion occurs. © 1982 Nature Publishing Group

Beyond Solidarity and Accumulation Networks in Urban Informal African Economies

This paper examines the role and nature of entrepreneurs’ social networks in the urban informal economy of Bobo-Dioulasso (Burkina Faso). Using an original dataset, the configuration of social networks is described based on three salient dimensions: tie content, member attributes and network structure. Multidimensional analysis allows for the simultaneous consideration of all three dimensions. Our findings suggest that network configurations at play extend well beyond the standard distinction between solidarity and accumulation networks. The complex networks highlighted by this study are consistent with rapid social changes in contemporary urban Africa. They can also significantly enhance the outcomes of small businesses