The importance of friction in mountain wave drag amplification by Scorer parameter resonance

A mechanism for amplification of mountain waves, and their associated drag, by parametric resonance is investigated using linear theory and numerical simulations. This mechanism, which is active when the Scorer parameter oscillates with height, was recently classified by previous authors as intrinsically nonlinear. Here it is shown that, if friction is included in the simplest possible form as a Rayleigh damping, and the solution to the Taylor-Goldstein equation is expanded in a power series of the amplitude of the Scorer parameter oscillation, linear theory can replicate the resonant amplification produced by numerical simulations with some accuracy. The drag is significantly altered by resonance in the vicinity of n/l_0 = 2, where l_0 is the unperturbed value of the Scorer parameter and n is the wave number of its oscillation. Depending on the phase of this oscillation, the drag may be substantially amplified or attenuated relative to its non-resonant value, displaying either single maxima or minima, or double extrema near n/l_0 = 2. Both non-hydrostatic effects and friction tend to reduce the magnitude of the drag extrema. However, in exactly inviscid conditions, the single drag maximum and minimum are suppressed. As in the atmosphere friction is often small but non-zero outside the boundary layer, modelling of the drag amplification mechanism addressed here should be quite sensitive to the type of turbulence closure employed in numerical models, or to computational dissipation in nominally inviscid simulations.

Fault tolerant decentralised K-Means clustering for asynchronous large-scale networks

The K-Means algorithm for cluster analysis is one of the most influential and popular data mining methods. Its straightforward parallel formulation is well suited for distributed memory systems with reliable interconnection networks, such as massively parallel processors and clusters of workstations. However, in large-scale geographically distributed systems the straightforward parallel algorithm can be rendered useless by a single communication failure or high latency in communication paths. The lack of scalable and fault tolerant global communication and synchronisation methods in large-scale systems has hindered the adoption of the K-Means algorithm for applications in large networked systems such as wireless sensor networks, peer-to-peer systems and mobile ad hoc networks. This work proposes a fully distributed K-Means algorithm (EpidemicK-Means) which does not require global communication and is intrinsically fault tolerant. The proposed distributed K-Means algorithm provides a clustering solution which can approximate the solution of an ideal centralised algorithm over the aggregated data as closely as desired. A comparative performance analysis is carried out against the state of the art sampling methods and shows that the proposed method overcomes the limitations of the sampling-based approaches for skewed clusters distributions. The experimental analysis confirms that the proposed algorithm is very accurate and fault tolerant under unreliable network conditions (message loss and node failures) and is suitable for asynchronous networks of very large and extreme scale.

Second tier professionals: English teachers in England

The policy context for mother-tongue educators at all levels in England has been dominated by a matrix with four key elements,running along two spectra, one of learning (content↘assessment) and one of teaching (autonomy↘accountability). In each case the trend has been towards increasing external control and decreasing professional autonomy. Whilst some imposed changes have been recognised as intrinsically valuable, the majority are viewed as detrimental to teachers' status and obstructive for students. The research community has been largely marginalised and has had little scope to influence proceedings. A rapidly developing crisis in teacher retention may yet reverse these trends as the government is forced to recognise the long-term implications of their treatment of the profession.

Sparse shape representation using the Laplace-Beltrami eigenfunctions and its application to modeling subcortical structures

We present a new sparse shape modeling framework on the Laplace-Beltrami (LB) eigenfunctions. Traditionally, the LB-eigenfunctions are used as a basis for intrinsically representing surface shapes by forming a Fourier series expansion. To reduce high frequency noise, only the first few terms are used in the expansion and higher frequency terms are simply thrown away. However, some lower frequency terms may not necessarily contribute significantly in reconstructing the surfaces. Motivated by this idea, we propose to filter out only the significant eigenfunctions by imposing l1-penalty. The new sparse framework can further avoid additional surface-based smoothing often used in the field. The proposed approach is applied in investigating the influence of age (38-79 years) and gender on amygdala and hippocampus shapes in the normal population. In addition, we show how the emotional response is related to the anatomy of the subcortical structures.

A spatio-temporal structure-based approach to drought characterisation

Drought characterisation is an intrinsically spatio-temporal problem. A limitation of previous approaches to characterisation is that they discard much of the spatio-temporal information by reducing events to a lower-order subspace. To address this, an explicit 3-dimensional (longitude, latitude, time) structure-based method is described in which drought events are defined by a spatially and temporarily coherent set of points displaying standardised precipitation below a given threshold. Geometric methods can then be used to measure similarity between individual drought structures. Groupings of these similarities provide an alternative to traditional methods for extracting recurrent space-time signals from geophysical data. The explicit consideration of structure encourages the construction of summary statistics which relate to the event geometry. Example measures considered are the event volume, centroid, and aspect ratio. The utility of a 3-dimensional approach is demonstrated by application to the analysis of European droughts (15 °W to 35°E, and 35 °N to 70°N) for the period 1901–2006. Large-scale structure is found to be abundant with 75 events identified lasting for more than 3 months and spanning at least 0.5 × 106 km2. Near-complete dissimilarity is seen between the individual drought structures, and little or no regularity is found in the time evolution of even the most spatially similar drought events. The spatial distribution of the event centroids and the time evolution of the geographic cross-sectional areas strongly suggest that large area, sustained droughts result from the combination of multiple small area (∼106 km2) short duration (∼3 months) events. The small events are not found to occur independently in space. This leads to the hypothesis that local water feedbacks play an important role in the aggregation process.

Ergonomics as authoritarian or libertarian: reflections on Ward’s politics of design

Ergonomics is intrinsically connected to political debates about the good society, about how we should live. This article follows the ideas of Colin Ward by setting the practices of ergonomics and design along a spectrum between more libertarian approaches and more authoritarian. Within Anglo-American ergonomics, more authoritarian approaches tend to prevail, often against the wishes of designers who have had to fight with their employers for best possible design outcomes. The article draws on debates about the design and manufacturing of schoolchildren’s furniture. Ergonomics would benefit from embracing these issues to stimulate a broader discourse amongst its practitioners about how to be open to new disciplines, particularly those in the social sciences.

Time and retribution

Retributivists believe that punishment can be deserved, and that deserved punishment is intrinsically good. They also believe that certain crimes deserve certain quantities of punishment. On the plausible assumption that the overall amount of any given punishment is a function of its severity and duration, we might think that retributivists (qua retributivists) would be indifferent as to whether a punishment were long and light or short and sharp, provided the offender gets the overall amount of punishment he deserves. In this paper I argue against this, showing that retributivists should actually prefer shorter and more severe punishments to longer, gentler options. I show this by focusing on, and developing a series of interpretations of, the retributivist claim that not punishing the guilty is bad, focussing on the relationship between that badness and time. I then show that each interpretation leads to a preference for shorter over longer punishment.

On the nature of large-scale mixing in the stratosphere and mesosphere

Studies of tracer transport in the stratosphere have shown that adiabatic quasi-horizontal tracer evolution is controlled primarily by the large-scale low-frequency component of the flow. This behavior is consistent with the concept of chaotic advection, wherein the Eulerian velocity field is spatially coherent and temporally quasi-regular on timescales over which the Lagrangian evolution is chaotic. In this study, winds from a middle atmosphere general circulation model (the Canadian Middle Atmosphere Model) are used to compare and contrast the nature of tracer evolution in the stratosphere and mesosphere. It is found that the concept of chaotic advection is relevant in the stratosphere but not in the mesosphere. The explanation for this behavior is the increased strength of gravity wave activity in the mesosphere as compared with the stratosphere, which leads to shallower kinetic energy spectra on synoptic scales and a much shorter Eulerian correlation time. The shallower kinetic energy spectra imply that tracer evolution in the mesosphere is spectrally local, in contrast with the spectrally nonlocal regime that prevails in the stratosphere. This means that tracer advection calculations in the mesosphere are controlled primarily by the gravity wave spectrum and are intrinsically resolution dependent.

The ideal self at play: the appeal of video games that let you be all you can be

Video games constitute a popular form of entertainment that allows millions of people to adopt virtual identities. In our research, we explored the idea that the appeal of games is due in part to their ability to provide players with novel experiences that let them “try on” ideal aspects of their selves that might not find expression in everyday life. We found that video games were most intrinsically motivating and had the greatest influence on emotions when players’ experiences of themselves during play were congruent with players’ conceptions of their ideal selves. Additionally, we found that high levels of immersion in gaming environments, as well as large discrepancies between players’ actual-self and ideal-self characteristics, magnified the link between intrinsic motivation and the experience of ideal-self characteristics during play.

Unique structural properties associated with mouse prion Δ105-125 protein

Murine prion protein deleted for residues 105-125 is intrinsically neurotoxic and mediates a TSE-like phenotype in transgenic mice. Equivalent and overlapping deletions were expressed in E.coli, purified and analyzed. Among mutants spanning the region 95-135, a construct lacking solely residues 105-125 had distinct properties when compared with the full-length prion protein 23-231 or other deletions. This distinction was also apparent followed expression in eukaryotic cells. Unlike the full-length protein, all deletion mutants failed to bind to synthetic membranes in vitro. These data suggest a novel structure for the 105-125 deleted variant that may relate to its biological properties

Organisational politics: reconciling leadership's rational-emotional paradox

Purpose – Effective leadership action requires managers to harness power that is intrinsically political. This paper aims to study and characterise the political nature of a manager's behaviour when taking leadership action. Design/methodology/approach – The methodological approach is qualitative and examines three organisations over a three-year period when these entities experienced a major product failure. The paper analyses the actual managerial behaviour of managers and provides insight into the factors that most strongly influence the effectiveness of managers when taking leadership action. Findings – Political behaviour when taking leadership action can be conceptualised in terms of rationality and emotionality. In so doing, it can be clarified how behaviour must be modified to ensure that leadership action is consistently effective. Research limitations/implications – A case study of three multinational engineering companies engaged in the design, development and manufacturing of turbomachinery provides the platform for the research. The concepts presented in the paper will require validating in other organisations of different demographic profiles. Practical implications – The concepts presented and the implications discussed provide insight into the political nature of managerial behaviour when taking leadership action. The paper highlights the practical steps individual managers can embrace to ensure that their behaviour is appropriate to context, even under the most traumatic situations. Thus, the paper provides managers with a model that facilitates effective leadership action. Originality/value – This paper provides insight into how managers behaved in circumstances that mattered to them. Through immersion in events at the time they took place, the authors captured situations in which managers were under real pressure and, in so doing, avoided the bias inherent when interviewing a manager about past events. As such, the paper concludes that the political behaviour in which managers engage when taking leadership action is rooted in the reality of the adversity that the most capable managers have both experienced and overcome. This detailed study reports behaviour in a situation where managers' business and future prospects were in jeopardy. This paper identifies why some managers were able to use the experience positively, helping them to adopt politically intrinsic behaviour to facilitate effective leadership action.

RMetS special interest group meeting: high resolution data assimilation

Data assimilation (DA) systems are evolving to meet the demands of convection-permitting models in the field of weather forecasting. On 19 April 2013 a special interest group meeting of the Royal Meteorological Society brought together UK researchers looking at different aspects of the data assimilation problem at high resolution, from theory to applications, and researchers creating our future high resolution observational networks. The meeting was chaired by Dr Sarah Dance of the University of Reading and Dr Cristina Charlton-Perez from the MetOffice@Reading. The purpose of the meeting was to help define the current state of high resolution data assimilation in the UK. The workshop assembled three main types of scientists: observational network specialists, operational numerical weather prediction researchers and those developing the fundamental mathematical theory behind data assimilation and the underlying models. These three working areas are intrinsically linked; therefore, a holistic view must be taken when discussing the potential to make advances in high resolution data assimilation.

Impact of non-hydrostatic effects and trapped lee waves on mountain wave drag in directionally sheared flow

The orographic gravity wave drag produced in flow over an axisymmetric mountain when both vertical wind shear and non-hydrostatic effects are important was calculated using a semi-analytical two-layer linear model, including unidirectional or directional constant wind shear in a layer near the surface, above which the wind is constant. The drag behaviour is determined by partial wave reflection at the shear discontinuity, wave absorption at critical levels (both of which exist in hydrostatic flow), and total wave reflection at levels where the waves become evanescent (an intrinsically non-hydrostatic effect), which produces resonant trapped lee wave modes. As a result of constructive or destructive wave interference, the drag oscillates with the thickness of the constant-shear layer and the Richardson number within it (Ri), generally decreasing at low Ri and when the flow is strongly non-hydrostatic. Critical level absorption, which increases with the angle spanned by the wind velocity in the constant-shear layer, shields the surface from reflected waves, keeping the drag closer to its hydrostatic limit. While, for the parameter range considered here, the drag seldom exceeds this limit, a substantial drag fraction may be produced by trapped lee waves, particularly when the flow is strongly non-hydrostatic, the lower layer is thick and Ri is relatively high. In directionally sheared flows with Ri = O(1), the drag may be misaligned with the surface wind in a direction opposite to the shear, a behaviour which is totally due to non-trapped waves. The trapped lee wave drag, whose reaction force on the atmosphere is felt at low levels, may therefore have a distinctly different direction from the drag associated with vertically propagating waves, which acts on the atmosphere at higher levels.

The excitation of ionospheric convection

This review presents recent observations of high-latitude ionospheric plasma convection, obtained using the EISCAT radar in the 'Polar' experiment mode. The paper is divided into two main parts. Firstly, the delay in the response of dayside high-latitude flows to changes in the interplanetary magnetic field is discussed. The results show the importance for the excitation of dayside convection of the transfer of magnetic flux from the dayside into the tail lobe. Consequently, ionospheric convection should be thought of as the sum of two intrinsically time-dependent flow patterns. The first of these patterns is directly driven by solar wind-magnetosphere coupling, dominates ionospheric flows on the dayside, is associated with an expanding polar cap area and is the F-region flow equivalent of the DP-2 E-region current system. The second of the two patterns is driven by the release of energy stored in the geomagnetic tail, dominates ionospheric flows on the nightside, is associated with a contracting polar cap and is equivalent to the DP-1, or substorm, current system. In the second half of the paper, various transient flow bursts observed in the vicinity of the dayside cusp are studied. These radar data, combined with simultaneous optical observations of transient dayside aurorae, strongly suggest that momentum is transferred across the magnetopause and into the ionosphere in a series of bursts, each associated with voltages of 30-80 kV. Similarities between these bursts and flux transfer events observed at the magnetopause are discussed.

The excitation of plasma convection in the high-latitude ionosphere

Recent observations of ionospheric flows by ground-based radars, in particular by the European Incoherent Scatter (EISCAT) facility using the “Polar” experiment, together with previous analyses of the response of geomagnetic disturbance to variations of the interplanetary magnetic field (IMF), suggest that convection in the high-latitude ionosphere should be considered to be the sum of two intrinsically time-dependent patterns, one driven by solar wind-magnetosphere coupling at the dayside magnetopause, the other by the release of energy in the geomagnetic tail (mainly by dayside and nightside reconnection, respectively). The flows driven by dayside coupling are largest on the dayside, where they usually dominate, are associated with an expanding polar cap area, and are excited and decay on ∼10-min time scales following southward and northward turnings of the IMF, respectively. The latter finding indicates that the production of new open flux at the dayside magnetopause excites magnetospheric and ionospheric flow only for a short interval, ∼10 min, such that the flow driven by this source subsequently decays on this time scale unless maintained by the production of more open flux tubes. Correspondingly, the flows excited by the release of energy in the tail, mainly during substorms, are largest on the nightside, are associated with a contracting polar cap boundary, and are excited on ∼1-hour time scales following a southward turn of the IMF. In general, the total ionospheric flow will be the sum of the flows produced by these two sources, such that due to their different response times to changes in the IMF, considerable variations in the flow pattern can occur for a given direction and strength of the IMF. Consequently, the ionospheric electric field cannot generally be regarded as arising from a simple mapping of the solar wind electric field along open flux tubes.