Optimal control policies in service systems with limited information on the downstream stage

Existing models in multistage service systems assume full information on the state of downstream stages. In this paper, we investigate how much the lack of such information impacts jobs' waiting time in a two‐stage system with two types of jobs at the first stage. The goal is to find the optimal control policy for the server at the first stage to switch between type‐1 and type‐2 jobs, while minimizing the long‐run average number of jobs in the system. We identify control policies and corresponding conditions under which having no or partial information, the system can still capture the most benefit of having full information.     

Micromechanical simulation and experimental investigation of aluminum-based nanocomposites

Ceramic reinforced metal matrix nanocomposites are widely used in aerospace and auto industries due to their enhanced mechanical and physical properties. In this research, we investigate the mechanical properties of aluminum/Nano-silica composites through experiments and simulations. Aluminum/Nano-silica composite samples with different weight percentages of silica nanoparticles are prepared via powder metallurgy. In this method, Nano-silica and aluminum powders are mixed and compressed in a mold, followed by sintering at high temperatures. Uniaxial tensile testing of the nanocomposite samples shows that adding one percent of Nano-silica causes a considerable increase in mechanical properties of nanocomposite compared to pure aluminum. A computational micromechanical model, based on a representative volume element of aluminum/silica nanocomposite, is developed in a commercial finite element software. The model employs an elastoplastic material model along with a ductile damage model for aluminum matrix and linear elastic model for nano-silica particles. Via careful determination of model parameters from the experimental results of pure aluminum samples prepared by powder metallurgy, the proposed computational model has shown satisfactory agreement with experiments. The validated computational model can be used to perform a parametric study to optimize the micro-structure of nanocomposite for enhanced mechanical properties.     

Civil—military relations in Africa: Navigating uncharted waters

“Perception is a second reality!”

This essay discusses the military as a part of wider society and the interactions between the two. It argues that civil—military relations are complex and not always harmonious. In its focus on Africa, the essay describes some differences in the development of African militaries and civil—military relations on the continent as compared with the West, but argues that the differences are merely a matter of degree. As civil—military relations on the continent have been strongly influenced by its colonial history, which caused fear and even dislike of the colonial military, it still impacts on these relations in the post-colonial era. After examining the relationship between the armed forces, democracy and politics in the politically turbulent African environment, it is concluded that a simplistic definition of civil—military relations is difficult to arrive at. The essay identifies the key principles of democratic civil—military relations and, although admitting that these principles are not always easy to adhere to, argues that as Africa develops civil—military relations, African militaries have moved and will move closer to observing these principles. To enhance this process it is essential for African militaries to include civic education programmes at all levels of education and training in order to gain a better understanding of and commitment to these principles.     

Guns and butter? Military expenditure and health spending on the eve of the Arab Spring

We examine the validity of the guns-versus-butter hypothesis in the pre-Arab Spring era. Using panel data from 1995 to 2011 – the eve of the Arab uprisings – we find no evidence that increased security needs as measured by the number of domestic terrorist attacks are complemented by increased military spending or more importantly ‘crowd out’ government expenditure on key public goods such as health care. This suggests that both expenditure decisions were determined by other considerations at the government level.