A role-based perspective on leadership as a network of relationships.

The research described in this article seeks to address the question of the extent to which a role-based perspective can provide insight into the distributed and networked form of leadership

Development of improved blade tip endplate concepts for low-noise operation in industrial fans

The application of improved blade tip geometries is studied with the aim of identifying an effective design concept for industrial fan passive noise control. The concept developed optimizes a datum blade by means of profiled endplates at the tip, reducing fan noise by changing the tip leakage flow behaviour. Experimental and computational investigations have been carried out on a family of axial fans, in fully ducted configuration, to establish the aerodynamic merits of the proposed blade tip design concept. The flow mechanisms in the fan tip region are correlated to specific blade design features that promote a reduction of the fan aero-acoustic signature in both tonal and broadband noise components. The tip vortical flow structures are characterized, and their role in creation of overall stage acoustic emissions clarified. The reported research identifies modification of tip geometry as markedly affecting the multiple vortex behaviour of blade tip leakage flow by altering the near-wall fluid flow paths on both blade surfaces. Blade tip endplates were also demonstrated to influence the rotor loss behaviour in the blade tip region. Improvement of rotor efficiency was correlated to the control of tip leakage flows

Nonlinear resonant tunneling in systems coupled to quantum reservoirs

An adiabatic approximation in terms of instantaneous resonances is developed to study the steady-state and time-dependent transport of interacting electrons in biased resonant tunneling heterostructures. The resulting model consists of quantum reservoirs coupled to regions where the system is described by nonlinear ordinary differential equations and has a general conceptual interest.Comment: 4 pages, 3 postscript figure

Anomalous quantum reflection of Bose-Einstein condensates from a silicon surface: the role of dynamical excitations

We investigate the effect of inter-atomic interactions on the quantum-mechanical reflection of Bose-Einstein condensates from regions of rapid potential variation. The reflection process depends critically on the density and incident velocity of the condensate. For low densities and high velocities, the atom cloud has almost the same form before and after reflection. Conversely, at high densities and low velocities, the reflection process generates solitons and vortex rings that fragment the condensate. We show that this fragmentation can explain the anomalously low reflection probabilities recently measured for low-velocity condensates incident on a silicon surface.Comment: 5 figures, 5 pages, references correcte

Flight range, fuel load and the impact of climate change on the journeys of migrant birds

Collection of biometric data was supported by the Natural Environment Research Council (NE/I028068/1) to JAT and the USUK Fulbright Commission and the Oxford Clarendon Fund to C.S. This research was funded by a Durham University Seedcorn grant to SGW. Production of the underlying SDMs was funded by a National Environment Research Council training grant (NE/J500215/1).Climate change is predicted to increase migration distances for many migratory species, but the physiological and temporal implications of longer migratory journeys have not been explored. Here, we combine information about species' flight range potential and migratory refuelling requirements to simulate the number of stopovers required and the duration of current migratory journeys for 77 bird species breeding in Europe. Using tracking data, we show that our estimates accord with recorded journey times and stopovers for most species. We then combine projections of altered migratory distances under climate change with models of avian flight to predict future migratory journeys. We find that 37% of migratory journeys undertaken by long-distance migrants will necessitate an additional stopover in future. These greater distances and the increased number of stops will substantially increase overall journey durations of many long-distance migratory species, a factor not currently considered in climate impact studies.Publisher PDFPeer reviewe

Creation of solitons and vortices by Bragg reflection of Bose-Einstein condensates in an optical lattice

We study the dynamics of Bose-Einstein condensates in an optical lattice and harmonic trap. The condensates are set in motion by displacing the trap and initially follow simple semiclassical paths, shaped by the lowest energy band. Above a critical displacement, the condensate undergoes Bragg reflection. For high atom densities, the first Bragg reflection generates a train of solitons and vortices, which destabilize the condensate and trigger explosive expansion. At lower densities, soliton and vortex formation requires multiple Bragg reflections, and damps the center-of-mass motion.Comment: 5 pages including 5 figures (for higher resolution figures please email the authors

The Dynamic Characteristics of a High Pressure Turbine Stage in a Transient Wind Tunnel

ABSTRACT A new transient facility for the study of time averaged and unsteady aerodynamics and heat transfer in a high pressure turbine was recently commissioned. During the facility design a high priority was placed on ease of access to the turbine blading to facilitate the development of blade mounted instrumentation. The turbine disc was cantilevered on a shaft by a thin annular link, with the shaft passing back through the disc to a single row and matched pair of relatively closely spaced bearings. The bearings were originally designed for use in a marine gas turbine. Due to the facility's novel mode of operation the bearings were working well beyond some of their original design limits, primarily due to the high turbine acceleration and the high speed/low load condition at the end of facility operation. During the facility design a programme of work was undertaken to predict its dynamic performance. This was continued during commissioning to measure actual facility performance. In this paper the predicted dynamic performance of the disc/shaft assembly and its bearing system are presented. The programme of work undertaken during the facility commissioning phase to ascertain actual dynamic performance is described, and the results discussed. Finally, the technique developed to field balance the rotating assembly following changes to blade instrumentation is described

Not in my back yard! Sports stadia location and the property market

In recent years sports stadia have been built in the UK, not only for their intended sporting purpose but with the twin aim of stimulating economic and physical regeneration. However, proposals to locate stadia in urban areas often prompt a negative reaction from local communities, fearing a decline in property prices. This paper will use a case study of the Millennium Stadium in Cardiff and the City of Manchester Stadium to illustrate that in contrast to this widely held belief, sports stadia can actually enhance the value of residential property. Furthermore, it will argue that stadia also contribute indirectly to property value through the creation of pride, confidence and enhanced image of an area.</p