893 research outputs found

    Characterising and Testing Deep UV LEDs for Use in Space Applications

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    Deep ultraviolet (DUV) light sources are used to neutralise isolated test masses in highly sensitive space-based gravitational experiments. An example is the LISA Pathfinder charge management system, which uses low-pressure mercury lamps. A future gravitational-wave observatory such as eLISA will use UV light-emitting diodes (UV LEDs), which offer numerous advantages over traditional discharge lamps. Such devices have limited space heritage but are are now available from a number of commercial suppliers. Here we report on a test campaign that was carried out to quantify the general properties of three types of commercially available UV LEDs and demonstrate their suitability for use in space. Testing included general electrical and UV output measurements, spectral stability, pulsed performance, temperature dependence as well as thermal vacuum, radiation and vibration survivability

    The LISA PathFinder DMU and Radiation Monitor

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    The LISA PathFinder DMU (Data Management Unit) flight model was formally accepted by ESA and ASD on 11 February 2010, after all hardware and software tests had been successfully completed. The diagnostics items are scheduled to be delivered by the end of 2010. In this paper we review the requirements and performance of this instrumentation, specially focusing on the Radiation Monitor and the DMU, as well as the status of their programmed use during mission operations, on which work is ongoing at the time of writing.Comment: 11 pages, 7 figures, prepared for the Proceedings of the 8th International LISA Symposium, Classical and Quantum Gravit

    LISA and LISA PathFinder, the endeavour to detect low frequency GWs

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    This is a review about LISA and its technology demonstrator, LISA PathFinder. We first describe the conceptual problems which need to be overcome in order to set up a working interferometric detector of low frequency Gravitational Waves (GW), then summarise the solutions to them as currently conceived by the LISA mission team. This will show that some of these solutions require new technological abilities which are still under development, and which need proper test before being fully implemented. LISA PathFinder (LPF) is the the testbed for such technologies. The final part of the paper will address the ideas and concepts behind the PathFinder as well as their impact on LISA.Comment: 25 pages, 21 figures, presented at the Spanish Relativity Meeting, Mallorca September 2006. Will be published in Journal of Physics: Conference Series, IOP. To be published in Journal of Physics: Conference Series, IO

    The Labour Government, the Treasury and the £6 pay policy of July 1975

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    The 1974-79 Labour Government was elected in a climate of opinion that was fiercely opposed to government intervention in the wage determination process, and was committed to the principles of free collective bargaining in its manifestoes. However, by December 1974 the Treasury was advocating a formal incomes policy, and by July 1975 the government had introduced a £6 flat rate pay norm. With reference to archival sources, the paper demonstrates that TUC and Labour Party opposition to incomes policy was reconciled with the Treasury's advocacy by limiting the Bank of England‟s intervention in the foreign exchange market when sterling came under pressure. This both helped to achieve the Treasury's objective of improving the competitiveness of British industry, and acted as a catalyst for the introduction of incomes policy because the slide could be attributed to a lack of market confidence in British counter-inflation policy

    Slip behavior in liquid films on surfaces of patterned wettability: Comparison between continuum and molecular dynamics simulations

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    We investigate the behavior of the slip length in Newtonian liquids subject to planar shear bounded by substrates with mixed boundary conditions. The upper wall, consisting of a homogenous surface of finite or vanishing slip, moves at a constant speed parallel to a lower stationary wall, whose surface is patterned with an array of stripes representing alternating regions of no-shear and finite or no-slip. Velocity fields and effective slip lengths are computed both from molecular dynamics (MD) simulations and solution of the Stokes equation for flow configurations either parallel or perpendicular to the stripes. Excellent agreement between the hydrodynamic and MD results is obtained when the normalized width of the slip regions, a/σ≳O(10)a/\sigma \gtrsim {\cal O}(10), where σ\sigma is the (fluid) molecular diameter characterizing the Lennard-Jones interaction. In this regime, the effective slip length increases monotonically with a/σa/\sigma to a saturation value. For a/σ≲O(10)a/\sigma \lesssim {\cal O}(10) and transverse flow configurations, the non-uniform interaction potential at the lower wall constitutes a rough surface whose molecular scale corrugations strongly reduce the effective slip length below the hydrodynamic results. The translational symmetry for longitudinal flow eliminates the influence of molecular scale roughness; however, the reduced molecular ordering above the wetting regions of finite slip for small values of a/σa/\sigma increases the value of the effective slip length far above the hydrodynamic predictions. The strong inverse correlation between the effective slip length and the liquid structure factor representative of the first fluid layer near the patterned wall illustrates the influence of molecular ordering effects on slip in non-inertial flows.Comment: 12 pages, 10 figures Web reference added for animations: http://www.egr.msu.edu/~priezjev/bubble/bubble.htm

    Charge Management for Gravitational Wave Observatories using UV LEDs

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    Accumulation of electrical charge on the end mirrors of gravitational wave observatories, such as the space-based LISA mission and ground-based LIGO detectors, can become a source of noise limiting the sensitivity of such detectors through electronic couplings to nearby surfaces. Torsion balances provide an ideal means for testing gravitational wave technologies due to their high sensitivity to small forces. Our torsion pendulum apparatus consists of a movable Au-coated Cu plate brought near a Au-coated Si plate pendulum suspended from a non-conducting quartz fiber. A UV LED located near the pendulum photoejects electrons from the surface, and a UV LED driven electron gun directs photoelectrons towards the pendulum surface. We have demonstrated both charging and discharging of the pendulum with equivalent charging rates of ∼\sim105e/s10^5 e/\mathrm{s}, as well as spectral measurements of the pendulum charge resulting in a white noise level equivalent to 3×105e/Hz3\times10^5 e/\sqrt{Hz}.Comment: 5 pages, submitted to PR

    A comparison of match demands using ball-in-play vs. whole match data in elite male youth soccer players

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    Effective playing time in soccer is typically 90 seconds. This data allows practitioners to gain a deeper understanding of the physical demands imposed on players and plan sessions using targets that better represent match demands

    The South Asian genome

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    Genetics of disease Microarrays Variant genotypes Population genetics Sequence alignment AllelesThe genetic sequence variation of people from the Indian subcontinent who comprise one-quarter of the world's population, is not well described. We carried out whole genome sequencing of 168 South Asians, along with whole-exome sequencing of 147 South Asians to provide deeper characterisation of coding regions. We identify 12,962,155 autosomal sequence variants, including 2,946,861 new SNPs and 312,738 novel indels. This catalogue of SNPs and indels amongst South Asians provides the first comprehensive map of genetic variation in this major human population, and reveals evidence for selective pressures on genes involved in skin biology, metabolism, infection and immunity. Our results will accelerate the search for the genetic variants underlying susceptibility to disorders such as type-2 diabetes and cardiovascular disease which are highly prevalent amongst South Asians.Whole genome sequencing to discover genetic variants underlying type-2 diabetes, coronary heart disease and related phenotypes amongst Indian Asians. Imperial College Healthcare NHS Trust cBRC 2011-13 (JS Kooner [PI], JC Chambers)

    Form-function relationship in the amplitude and frequency modulations of infant - directed speech: A predictive processing perspective

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    Infants prefer infant-directed speech (IDS) over adult-directed speech (ADS). IDS is thought to serve specific functions compared to ADS: - Attracting infant attention to the speech signal - Conveying clear opportunities for easier word segmentation. Two independent domains of complexity that are embedded in the speech stream: - Amplitude complexity: Lower amplitude complexity associates with greater ease in identifying word boundaries ​ - ​Frequency complexity: Higher fre q uency complexity associates with more attention eliciting speech attention by inducing uncertaint
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