Vortex shedding from a row of square bars

Interactions of wakes in a flow past a row of square bars, which is placed across a uniform flow, are investigated by numerical simulations and experiments on the tassumption that the flow is two-dimensional and incompressible. At small Reynolds numbers the flow is steady and symmetric with respect not only to streamwise lines through the center of each square bar but also to streamwise centerlines between adjacent square bars. However, the steady symmetric flow becomes unstable at larger Reynolds numbers and make a transition to a steady asymmetric flow with respect to the centerlines between adjacent square bars in some cases or to an oscillatory flow in other cases. It is found that vortices are shed synchronously from adjacent square bars in the same phase or in anti-phase depending upon the distance between the bars when the flow is oscillatory. The origin of the transition to the steady asymmetric flow is identified as a pitchfork bifurcation, while the oscillatory flows with synchronous shedding of vortices are clarified to originate from a Hopf bifurcation. The critical Reynolds numbers of the transitions are evaluated numerically and the bifurcation diagram of the flow is obtained.

Energy security in the news:North/South perspectives

Analysis of newspaper reporting on the topic of energy security in eight countries – four from the global North (France, Germany, the UK, and the United States) and four from the global South (China, India, Brazil, and South Africa) – produces no support for the thesis that news is disseminated from core countries to the periphery and semi-periphery. There is an important difference between China and the other three fast-developing countries and a highly asymmetric flow of news not aligned to old core-periphery boundaries. In general, energy security is mainly covered in trade and business outlets and less in newspapers with mass circulation, indicating that the topic is still an elite concern. In some instances, attention has surged at the same time in different countries. But very few of these instances show a homogenous coverage across countries. Despite increasingly globalised media, news is created and consumed at a national level.