A fast direct numerical simulation method for characterising hydraulic roughness

We describe a fast direct numerical simulation (DNS) method that promises to directly characterise the hydraulic roughness of any given rough surface, from the hydraulically smooth to the fully rough regime. The method circumvents the unfavourable computational cost associated with simulating high-Reynolds-number flows by employing minimal-span channels (Jimenez & Moin 1991). Proof-of-concept simulations demonstrate that flows in minimal-span channels are sufficient for capturing the downward velocity shift, that is, the Hama roughness function, predicted by flows in full-span channels. We consider two sets of simulations, first with modelled roughness imposed by body forces, and second with explicit roughness described by roughness-conforming grids. Owing to the minimal cost, we are able to conduct DNSs with increasing roughness Reynolds numbers while maintaining a fixed blockage ratio, as is typical in full-scale applications. The present method promises a practical, fast and accurate tool for characterising hydraulic resistance directly from profilometry data of rough surfaces.Comment: Published in the Journal of Fluid Mechanic

USDA PERSPECTIVE ON THE OUTLOOK FOR COTTON

Crop Production/Industries,

Constructing Cyberterrorism as a Security Threat: a Study of International News Media Coverage

This article examines the way in which the English language international news media has constructed the threat of cyberterrorism. Analysing 535 news items published by 31 different media outlets across 7 countries between 2008 and 2013, we show that this coverage is uneven in terms of its geographical and temporal distribution and that its tone is predominantly apprehensive. This article argues that, regardless of the ‘reality’ of the cyberterrorism threat, this coverage is important because it helps to constitute cyberterrorism as a security risk. Paying attention to this constitutive role of the news media, we suggest, opens up a fresh set of research questions in this context and a different theoretical approach to the study of cyberterrorism

Analogy and Authority in Cyberterrorism Discourse: An Analysis of Global News Media Coverage

This article explores constructions of cyberterrorism within the global news media between 2008 and 2013. It begins by arguing that the preoccupation with questions of definition, threat and response in academic literature on cyberterrorism is problematic, for two reasons. First, because it neglects the constitutivity of representations of cyberterrorism in the news media and beyond; and, second, because it prioritises policy-relevant research. To address this, the article provides a discursive analysis drawing on original empirical research into 31 news media outlets across the world. Although there is genuine heterogeneity in representations of cyberterrorism therein, we argue that constructions of this threat rely heavily on two strategies. First, appeals to authoritative or expert ‘witnesses’ and their institutional or epistemic credibility. And, second, generic or historical analogies, which help shape understanding of the likelihood and consequences of cyberterrorist attack. These strategies have particularly discursive importance, we argue, given the lack of readily available empirical examples of the ‘reality’ of cyberterroris

Characterization of a temperature-sensitive DNA ligase from Escherichia coli

DNA ligases are essential enzymes in cells due to their ability to join DNA strand breaks formed during DNA replication. Several temperature-sensitive mutant strains of Escherichia coli, including strain GR501, have been described which can be complemented by functional DNA ligases. Here, it is shown that the ligA251 mutation in E. coli GR501 strain is a cytosine to thymine transition at base 43, which results in a substitution of leucine by phenylalanine at residue 15. The protein product of this gene (LigA251) is accumulated to a similar level at permissive and non-permissive temperatures. Compared to wild-type LigA, at 20 °C purified LigA251 has 20-fold lower ligation activity in vitro, and its activity is reduced further at 42 °C, resulting in 60-fold lower ligation activity than wild-type LigA. It is proposed that the mutation in LigA251 affects the structure of the N-terminal region of LigA. The resulting decrease in DNA ligase activity at the non-permissive temperature is likely to occur as the result of a conformational change that reduces the rate of adenylation of the ligase