50-nm Self-Aligned and “Standard” T-gate InP pHEMT Comparison: The Influence of Parasitics on Performance at the 50-nm Node

Continued research into the development of III-V high-electron mobility transistors (HEMTs), specifically the minimization of the device gate length, has yielded the fastest performance reported for any three terminal devices to date. In addition, more recent research has begun to focus on reducing the parasitic device elements such as access resistance and gate fringing capacitance, which become crucial for short gate length device performance maximization. Adopting a self-aligned T-gate architecture is one method used to reduce parasitic device access resistance, but at the cost of increasing parasitic gate fringing capacitances. As the device gate length is then reduced, the benefits of the self-aligned gate process come into question, as at these ultrashort-gate dimensions, the magnitude of the static fringing capacitances will have a greater impact on performance. To better understand the influence of these issues on the dc and RF performance of short gate length InP pHEMTs, the authors present a comparison between In_0.7Ga_0.3As channel 50-nm self-aligned and "standard" T-gate devices. Figures of merit for these devices include transconductance greater than 1.9 S/mm, drive current in the range 1.4 A/mm, and fT up to 490 GHz. Simulation of the parasitic capacitances associated with the self-aligned gate structure then leads a discussion concerning the realistic benefits of incorporating the self-aligned gate process into a sub-50-nm HEMT system     

Mechanistic studies of the photocatalytic oxidation of microcystin-LR: an investigation of byproducts of the decomposition process

Microcystins (cyclic heptapeptides) are produced by a number of freshwater cyanobacteria and cause concern in potable water supplies due to their acute and chronic toxicity. The present study reports the structural characterization of the degradation products of the photocatalytic oxidation of microcystin-LR, so aiding the mechanistic understanding of this process. TiO2 photocatalysis is a promising technology for removal of these toxins from drinking water. However, before it can be adopted in any practical application it is necessary to have a sufficient knowledge of degradation byproducts and their potential toxicity. Liquid chromatography-mass spectrometry analysis demonstrated that the major destruction pathway of microcystin appears to be initiated via three mechanisms: UV irradiation, hydroxyl radical attack, and oxidation. UV irradiation caused geometrical isomerization of microcystin converting the (4E), (6E) of the Adda configuration to (4E), 6(Z) or 4(Z), 6(E). Hydroxyl radical attack on the conjugated diene structure of Adda moiety produced dihyroxylated products. Further oxidation cleaved the hydroxylated 4-5 and/or 6-7 bond of Adda to form aldehyde or ketone peptide residues, which then were oxidized into the corresponding carboxylic acids. Photocatalysis also hydrolyzed the peptide bond on the ring structure of microcystin to form linear structures although this appeared to be a minor pathway.     

Deliberately Losing Control of C−H Activation Processes in the Design of Small-Molecule-Fragment Arrays Targeting Peroxisomal Metabolism

Combined photochemical arylation, “nuisance effect” (S_NAr) reaction sequences have been employed in the design of small arrays for immediate deployment in medium-throughput X-ray protein–ligand structure determination. Reactions were deliberately allowed to run “out of control” in terms of selectivity; for example the ortho-arylation of 2-phenylpyridine gave five products resulting from mono- and bisarylations combined with S_NAr processes. As a result, a number of crystallographic hits against NUDT7, a key peroxisomal CoA ester hydrolase, have been identified.     

A survey of scheduling metrics and an improved ordering policy for list schedulers operating on workloads with dependencies and a wide variation in execution times

This paper considers the dynamic scheduling of parallel, dependent tasks onto a static, distributed computing platform, with the intention of delivering fairness and quality of service (QoS) to users. The key QoS requirement is that responsiveness is maintained for workloads with a wide range of execution times (minutes to months) even under transient periods of overload. A survey of schedule QoS metrics is presented, classified into those dealing with responsiveness, fairness and utilisation. These metrics are evaluated as to their ability to detect undesirable features of schedules. The Schedule Length Ratio (SLR) metric is shown to be the most helpful for measuring responsiveness in the presence of dependencies. A novel list scheduling policy called Projected-SLR is presented that delivers good responsiveness and fairness by using the SLR metric in its scheduling decisions. Projected-SLR is found to perform equally as well in responsiveness, fairness and utilisation as the best of the other scheduling policies evaluated (Shortest Remaining Time First/SRTF), using synthetic workloads and an industrial trace. However, Projected-SLR does this with a guarantee of starvation-free behaviour, unlike SRTF.     

Tropical Architecture and the West Indies: from military advances and tropical medicine,to Robert Gardner-Medwin and the networks of tropical modernism

The history of modern Tropical Architecture has largely focused on the region of West Africa, however this paper demonstrates that additional strains were being developed elsewhere, preceding the African examples. Indeed, Tropical Architecture, far from being a mid-twentieth century phenomenon, has a much longer history, stretching back into the colonial settlements of the eighteenth century and continued by the tropical medicine contributions of the early twentieth century, particularly in the British West Indies. This paper considers some of these early examples, before investigating the work produced by Robert Gardner-Medwin, along with his small team that included Leo De Syllas and Gordon Cullen, during the Second World War in the West Indies. Their work there as part of the ‘development and welfare’ programme was considered, ‘building research’, concerned with materials, pragmatic decisions and housing, and, whilst it was unacknowledged at the time, was clearly indebted to the earlier military and hygiene models. Nevertheless, the work they undertook was highly influential in the development of modern tropical architecture, and in particular the buildings that were later produced in West Africa: it helped to formalise this canon, and unified the previously fragmented and disparate out-workings of the Metropolis. Gardner-Medwin, therefore, can be considered an agent of Empire, a key-player in the extension of British architects operating as the knowledge makers, not only in the period of colonial rule, but crucially, afterwards. This is further manifest through his involvement in UN housing missions to South East Asia and his contribution to the Tropical Architecture Conference held at University College, London, in 1953.     

The Limehouse Link: the architectural and cultural history of a monumental road tunnel in London's Docklands

In the Docklands area of London lies the ‘Limehouse Link’, a dual-bore road tunnel used by around 80,000 cars each day. A monumental and highly expensive piece of construction, the Limehouse Link has nonetheless received almost no attention from architectural historians or others concerned with the history of construction, engineering or urban development.

This article provides an introduction to the Limehouse Link, explaining some of the fundamental characteristics of its construction and position in London's urban landscape. More importantly, the article then considers how one might understand an everyday yet monumental construction such as this: a tunnel without obvious aesthetic form, design intent or symbolic meaning, but which nonetheless has an undeniable presence in the city. The Limehouse Link is therefore interpreted in terms of the car driver's immersive experience of the tunnel, more active constructions of this experience through sensory qualities of sound, representations of the tunnel in different media and art, ways of knowing the history of Limehouse, and, in particular, as a kind of aesthetic experience. The article concludes that driving through the Limehouse Link is to engage in a different way of knowing the postmodern city.