Configurations in 4-cycle systems

A 4-cycle system of order n, denoted by 4CS(n), exists if and only if nequivalent to1 (mod 8). There are four configurations which can be formed by two 4-cycles in a 4CS(n). Formulas connecting the number of occurrences of each such configuration in a 4CS(n) are given. The number of occurrences of each configuration is determined completely by the number d of occurrences of the configuration D consisting of two 4-cycles sharing a common diagonal. It is shown that for every nequivalent to1 (mod 8) there exists a 4CS(n) which avoids the configuration D, i.e. for which d=0. The exact upper bound for d in a 4CS(n) is also determined.

Belgrade vs. Serbia: Spatial re-configurations of belonging

This article explores the relationship between the nation, the city, narratives, and belonging in Serbia through an analysis of narratives of a set of 30 interviews with young Belgrade intellectuals aged 23-35. I argue that what appears to be emerging in post-Milosevic Serbia is a new articulation and a new scale of belonging. Most of my informants are mobilising their city identities, moving from a national to an urban perspective. They imaginatively defend their city identity through a discourse that, others' its newcomers, i.e. the rural residents. However, the article is critical of their articulated dichotomous rhetoric of 'Us, the City Cosmopolitans' vs. I Them, the Rural Nationalists' My overall aim is to offer an analysis of the Serbian case, where one sees that the city of Belgrade has become a microcosm and a symbolic expression for modernity, resistance, openness and democracy. However, instead of seeing urbanity as the only locus of modernity, one needs to understand that urbanity does not one-dimensionally lead to the urbanisation of the mind, implying that once you have cities, or live in a city, there is a specific urban, cosmopolitan experience.

Determination of the anomeric configurations of 2,3,4,6-tetra-O-acetyl-D-mannopyranosyl azide

The structures of 2,3,4,6-tetra-O-acetyl-alpha-D-mannopyranosyl azide and 2,3,4,6-tetra-O-acetyl-beta-D-mannopyranosyl azide were determined using X-ray crystallographic and one-dimensional NOESY techniques.

Simulation of a complete reflected shock tunnel showing a vortex mechanism for flow contamination

Simulations of a complete reflected shock tunnel facility have been performed with the aim of providing a better understanding of the flow through these facilities. In particular, the analysis is focused on the premature contamination of the test flow with the driver gas. The axisymmetric simulations model the full geometry of the shock tunnel and incorporate an iris-based model of the primary diaphragm rupture mechanics, an ideal secondary diaphragm and account for turbulence in the shock tube boundary layer with the Baldwin-Lomax eddy viscosity model. Two operating conditions were examined: one resulting in an over-tailored mode of operation and the other resulting in approximately tailored operation. The accuracy of the simulations is assessed through comparison with experimental measurements of static pressure, pitot pressure and stagnation temperature. It is shown that the widely-accepted driver gas contamination mechanism in which driver gas 'jets' along the walls through action of the bifurcated foot of the reflected shock, does not directly transport the driver gas to the nozzle at these conditions. Instead, driver gas laden vortices are generated by the bifurcated reflected shock. These vortices prevent jetting of the driver gas along the walls and convect driver gas away from the shock tube wall and downstream into the nozzle. Additional vorticity generated by the interaction of the reflected shock and the contact surface enhances the process in the over-tailored case. However, the basic mechanism appears to operate in a similar way for both the over-tailored and the approximately tailored conditions.