Right to the city, desire for the suburb?

The 2000s have been a lively decade for cities. The Worldwatch Institute estimated that 2007 was the first year in human history that more people worldwide lived in cities than the countryside. Globalisation and new digital media technologies have generated the seemingly paradoxical outcome that spatial location came to be more rather than less important, as combinations of firms, industries, cultural activities and creative talents have increasingly clustered around a select node of what have been termed “creative cities,” that are in turn highly networked into global circuits of economic capital, political power and entertainment media. Intellectually, the period has seen what the UCLA geographer Ed Soja refers to as the spatial turn in social theory, where “whatever your interests may be, they can be significantly advanced by adopting a critical spatial perspective”. This is related to the dynamic properties of socially constructed space itself, or what Soja terms “the powerful forces that arise from socially produced spaces such as urban agglomerations and cohesive regional economies,” with the result that “what can be called the stimulus of socio-spatial agglomeration is today being assertively described as the primary cause of economic development, technological innovation, and cultural creativity”

Stochastic chemical kinetics and the quasi-steady-state assumption : application to the stochastic simulation algorithm and chemical master equation

Recently the application of the quasi-steady-state approximation (QSSA) to the stochastic simulation algorithm (SSA) was suggested for the purpose of speeding up stochastic simulations of chemical systems that involve both relatively fast and slow chemical reactions [Rao and Arkin, J. Chem. Phys. 118, 4999 (2003)] and further work has led to the nested and slow-scale SSA. Improved numerical efficiency is obtained by respecting the vastly different time scales characterizing the system and then by advancing only the slow reactions exactly, based on a suitable approximation to the fast reactions. We considerably extend these works by applying the QSSA to numerical methods for the direct solution of the chemical master equation (CME) and, in particular, to the finite state projection algorithm [Munsky and Khammash, J. Chem. Phys. 124, 044104 (2006)], in conjunction with Krylov methods. In addition, we point out some important connections to the literature on the (deterministic) total QSSA (tQSSA) and place the stochastic analogue of the QSSA within the more general framework of aggregation of Markov processes. We demonstrate the new methods on four examples: Michaelis–Menten enzyme kinetics, double phosphorylation, the Goldbeter–Koshland switch, and the mitogen activated protein kinase cascade. Overall, we report dramatic improvements by applying the tQSSA to the CME solver.

A 'click approach' to the generation of novel profluorescent nitroxides

This project focused on the first application of the copper catalyzed azide alkyne cycloaddition reaction for the generation of novel profluorescent systems. Through this approach four novel profluorescent nitroxides were prepared both rapidly and in good yield from coumarin and nitroxide CuAAC coupling partners. Specifically, 7-hydroxy, 7-diethylamino, 6-bromo and unsubstituted coumarin analogues bearing an azide group in the 3-position were prepared and conjugatively joined to an alkyne isoindoline nitroxide previously reported by our group. To explore the impact of the nitroxide moiety on the fluorescence of these systems, methoxyamine analogues of the corresponding nitroxide analogues were prepared. Spectrophotometric analysis of these methoxyamine analogues revealed that the aromatic systems possessed high quantum yields. However, the quantum yield efficiency was found to be dependent on the presence of electron donating substituents in the 7-position of the coumarin motif, which enhanced the charge-transfer character of the system. Furthermore, spectrophotometric analysis of nitroxide analogues demonstrated that the triazole effectively mediated fluorophore-nitroxide communication, as evidenced by the low quantum yield values of the nitroxide analogues. These results suggest that this technique can be used to conjugatively join any azide bearing fluorescent system with the key alkyne isoindoline coupling partner allowing for the rapid generation of diverse profluorescent systems.