Locking device with rolling detents Patent

Ball locking device which releases in response to small forces when subjected to high axial load

Segregation in a fluidized binary granular mixture: Competition between buoyancy and geometric forces

Starting from the hydrodynamic equations of binary granular mixtures, we derive an evolution equation for the relative velocity of the intruders, which is shown to be coupled to the inertia of the smaller particles. The onset of Brazil-nut segregation is explained as a competition between the buoyancy and geometric forces: the Archimedean buoyancy force, a buoyancy force due to the difference between the energies of two granular species, and two geometric forces, one compressive and the other-one tensile in nature, due to the size-difference. We show that inelastic dissipation strongly affects the phase diagram of the Brazil nut phenomenon and our model is able to explain the experimental results of Breu et al. (PRL, 2003, vol. 90, p. 01402).Comment: 5 pages, 2 figure

Amplitudes at Infinity

We investigate the asymptotically large loop-momentum behavior of multi-loop amplitudes in maximally supersymmetric quantum field theories in four dimensions. We check residue-theorem identities among color-dressed leading singularities in $\mathcal{N}=4$ supersymmetric Yang-Mills theory to demonstrate the absence of poles at infinity of all MHV amplitudes through three loops. Considering the same test for $\mathcal{N}=8$ supergravity leads us to discover that this theory does support non-vanishing residues at infinity starting at two loops, and the degree of these poles grow arbitrarily with multiplicity. This causes a tension between simultaneously manifesting ultraviolet finiteness---which would be automatic in a representation obtained by color-kinematic duality---and gauge invariance---which would follow from unitarity-based methods.Comment: 4+1+1 pages; 15 figures; details provided in ancillary Mathematica file

Skill shortages, recruitment and retention in the housebuilding sector

Purpose - The purpose of this paper is to show how internal and external labour markets operate in the construction sector, associated with different strategies taken by firms in recruiting and retaining particular groups of employees. It draws on research of the house building sector which aims to discover how far firms develop human resource policies, recruitment and retention strategies, and training and development activities in response to skill shortages. Design/methodology/approach - The paper is based on a questionnaire survey of skills shortages, recruitment and retention in house building firms, drawn from databases of social and private housebuilders and a detailed investigation of firms. Findings - The results show worsening skill shortages and hard-to-fill vacancies, particularly for site managers and tradespersons. These shortages are especially bad for house building firms, above all those with higher levels of direct employment in the social housing sector. Despite this, firms rely for operative recruitment on traditional and informal methods and procedures, on experience - not qualifications - as the main criterion, and on "poaching" - all symptomatic of a craft labour market. For managers, there is some evidence of retention measures, in particular through training and promotion, implying the development of internal labour markets. And for professionals there are indications of occupational labour markets with their dependence on institutionalised systems of training and qualifications. Originality/value - The paper shows that firms take little responsibility themselves for resolving skill shortages and establishing training needs, though national training policy is reactive and driven by employer demand. Obligatory skills certification and an institutionalised industrial training system would facilitate a move from this deadlocked situation, from craft to occupational labour markets

Critical neural networks with short and long term plasticity

In recent years self organised critical neuronal models have provided insights regarding the origin of the experimentally observed avalanching behaviour of neuronal systems. It has been shown that dynamical synapses, as a form of short-term plasticity, can cause critical neuronal dynamics. Whereas long-term plasticity, such as hebbian or activity dependent plasticity, have a crucial role in shaping the network structure and endowing neural systems with learning abilities. In this work we provide a model which combines both plasticity mechanisms, acting on two different time-scales. The measured avalanche statistics are compatible with experimental results for both the avalanche size and duration distribution with biologically observed percentages of inhibitory neurons. The time-series of neuronal activity exhibits temporal bursts leading to 1/f decay in the power spectrum. The presence of long-term plasticity gives the system the ability to learn binary rules such as XOR, providing the foundation of future research on more complicated tasks such as pattern recognition.Comment: 8 pages, 7 figure