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ARL

United States Army Research Laboratory
Country: United States
7 Projects, page 1 of 2
  • Funder: UKRI Project Code: NE/V008099/1
    Funder Contribution: 73,366 GBP
    Partners: ARL, KCL

    Our current capabilities for predicting amounts of sand moved by wind over beaches and in deserts perform poorly when tested in the natural environment. Accurate predictions are crucial, however, to many practical problems in resource management and environmental engineering, such as beach deflation, coastal dune and habitat development, soil erosion, and dust emissions into the atmosphere. The principal limitation of the current models is that they calculate transport rate only as a function of a single time-averaged wind speed. We know, however, that wind-blown sand - even over uniform beaches and desert surfaces - displays intricate and shifting spatial patterns, most visibly in the form of streamers or so-called 'sand-snakes'. Previous research has suggested that these patterns are formed by individual gusts, or eddies, of wind that generate and drive the streamers over the surface. The research project will determine the precise functional relationships between eddies in natural winds and resultant sand transport over the surface, with the goal of establishing a new quantitative and predictive model that explicitly incorporates parameters related to the turbulence. We do this by applying state-of-the-art video imaging technology in field experiments on a beach. The International Partner is deploying a laboratory-grade measurement system for tracking eddies in the wind as well as airborne sand grains through a powerful laser beam, filmed by multiple high-speed video cameras from different viewing angles. The PI will add to this his technique of filming streamers with ordinary GoPro sports cameras and analysing the footage to measure the movements and grain densities of these patterns as they approach and enter the laser beam. The combination of these two types of Particle Image Velocimetry on different spatial scales allows us to interrogate the precise links between wind turbulence and sand movement so that we can establish a mathematical model.

  • Funder: UKRI Project Code: NE/H004238/1
    Funder Contribution: 371,897 GBP
    Partners: ARL, University of Leeds, Miami University

    The exchange of heat and moisture between the ocean and atmosphere depends upon turbulent mixing in the lower atmosphere; this depends strongly on the wind speed. At very high wind speeds the sea surface becomes dominated by breaking waves, whitecaps, and sea spray. The water droplets lofted into the lower atmosphere by turbulent air motions will undergo two interactions with the air around them. First, if they are at a different temperature from the air, they will cool or warm until their temperature matches that of the air; secondly, they will start to evaporate, contributing water vapour to the air. Evaporation requires energy, which is obtained initially by a cooling of the droplet, and then a transfer of heat from the air to the droplet. The net result of these processes is a transfer of heat and moisture between ocean and air at some altitude above the surface. The simplified mathematical descriptions of of heat and moisture exchange used within weather forecast and climate models assume that all the heat and moisture exchange takes place at the surface, thus they may provide the wrong values at high wind speeds. The difficulty of making appropriate measurements under severe storm conditions at sea means that there are very few measurements available with which to evaluate whether the spray generated actually has a significant impact or not. Theoretical studies disagree strongly about the importance of the effect. In this study we will instrument autonomous buoys, specifically designed to operate in extreme conditions, to measure the turbulent exchange of heat, moisture, momentum, and sea-spray between the atmosphere and ocean, along measurements of wave state, turbulence in the surface layer of the ocean, the extent of wave breaking, and mean conditions in the surface layers of the ocean and atmosphere. The data obtained will be used to evaluate the air-sea exchange, and determine the contribution of the sea spray to the total exchange of heat and moisture. The measurements will also be used to better define the rate of sea-spray aerosol generation under high winds, and the influence of wave state on the production rate, both of which are poorly defined. Improving understanding of air-sea interaction is particularly important for high wind conditions, because the development and track of severe storms - hurricanes and typhoons - is critically dependent on the heat and moisture input and frictional drag at the surface. This study will ultimately lead to improved prediction of severe tropical storms. The study will be carried out in close collaboration with the University of Miami, Florida, who operate the buoys from which the measurements will be made. The buoys will be deployed in the East/South China Sea in June 2010 and recovered during October 2010.

  • Funder: UKRI Project Code: EP/K029398/1
    Funder Contribution: 1,314,140 GBP
    Partners: UT, Imperial College London, ARL, Sharp Laboratories of Europe (United Kingdom)

    Solar panel prices are plummeting and they are becoming more widespread, but the impact they can actually make to the carbon problem is ultimately limited by their efficiency. Even if the panels could be made for almost nothing, and if we all covered our roofs with them, at their present working efficiency they could only generate a small fraction of the year-round electricity we have become used to using. This project aims to develop a radically new way of harvesting solar power that has the potential to improve this conversion efficiency by a factor of 5, and so to put solar power in a position to make a major contribution to the carbon mitigation issue. The science behind our approach stems from the fact that behind the familiar beauty of the Rainbow lies a vexing problem if you want to the power of sunlight. Solar cells work by absorbing quanta of light, so-called photons, in a way that makes the electrons inside them jump from one energy level to a higher one, like a rung in a ladder. It's these electron jumps that capture the sunlight's energy The problem with sunlight is that each colour in the rainbow is made from different energy photons. No matter what rung height you decide on, some of the lower energy photons (at the red end of the rainbow) are lost because they can't power the jump. Others (at the blue end) have more energy than the rung spacing, so only part of their energy gets captured. A detailed analysis shows that, no matter what rung size you settle on, the best, the very best you can ever do is the so-called "Shockley-Queisser" efficiency limit, of 31%, and most actual solar cells struggle to reach half of this. Our research programme sets out to smash this "Shockley-Queisser" limit. We plan to do this by using quantum mechanics to design an energy level structure into the solar cell which is analogous to a ladder with a range of uneven rung spacings. Each rung grabs a different part of the rainbow with high efficiency, and some are designed so that one photon can make an electron jump up two rungs at a time. To do this we use a revolutionary approach that exploits the sort of nano-technology that gave us the lasers that power computer printers, the internet and DVD drives. Theory indicates that efficiencies up to 89% are possible. We hope and believe that demonstrating even part of this improvement will permanently change the way we design solar cells and dramatically improve the chances of solar power being adapted on a scale that is wide enough to have a genuine positive environmental impact. This cell also develops much more voltage than present designs, which makes its electrical output easier to use. As well as determining the rung spacing, we also use the nano-technology to add an extra , and critical twist, a new idea we are calling a "Quantum Ratchet". This can be thought of as, say, a small hollow in each rung, so that if an electron makes it up that far, the likelihood is that it will stay there long enough to absorb another photon and hop up to the next rung, rather than losing its captured energy by sliding back down. At the moment we are proposing to get as far as demonstrating and optimising the concept, using comparatively expensive test cells and complex laser spectroscopy in a University lab. Even that is a major undertaking though. It will occupy a focussed team of ~ 9 scientists for 4 years, all working towards the same goal if we are to have even a chance of success, but we all believe the results will be worth it.

  • Funder: UKRI Project Code: NE/G000123/1
    Funder Contribution: 47,555 GBP
    Partners: ARL, MET, University of Bergen, NOC

    In 2006 scientists from the UK's National Oceanography Centre, Southampton (NOCS) installed additional sensors to measure the rate at which the atmosphere and ocean exchange heat, CO2 and momentum. The behaviour of theses exchanges or 'fluxes' is complicated and is affected by many other processes. For example, the CO2 flux may depend on wind speed, air temperature and humidity, sea temperature, sea state, wave breaking, whitecap coverage, CO2 concentration of the water and CO2 concentration in the atmosphere. All these processes need to be measured as well, so that the behaviour of the flux can be understood. The Polarfront was already equipped with a ship borne wave recorder (SBWR) which makes direct measurements of the wave heights, but this system does not measure the direction of the waves. As part of the NOCS project a wave radar system (WAVEX) was also installed to provide wave direction. The WAVEX does not make direct height measurements, but combining its directional data with the height data from the SBWR gives a very detailed description of the sea state - the Polarfront is the only ship in the world to have both systems. NOCS added digital cameras to the ship's bridge to obtain whitecap fraction and sea spikes in the wave radar data will be used to obtained wave breaking statistics. The fluxes are very difficult to measure directly and such measurements are usually only made from research ships, during short cruises of only a few weeks. To date very few measurements have been made of the CO2 flux and none have been made over the open ocean for winds of more than 15 m/s. In contrast, the NOCS systems on the Polarfront have operated continuously since they were installed in September 2006 and measurements in mean wind speeds of more than 25 m/s have already been made. Obtaining high wind speed data is important because the fluxes increase rapidly with increasing wind speed. The Polarfront was chosen for the project since it is dedicated to meteorological observations, unlike any other ship in the world. It also occupies a location where high wind speeds and therefore large fluxes often occur. To understand the interaction between the various forcing process requires a large data set obtained under as wide a range of conditions as possible. Extending the measurement program from 2 years to 3 years (as originally planned) would significantly increase the data available for analysis and would only increase the cost of the project by 12%.

  • Funder: UKRI Project Code: EP/I004475/1
    Funder Contribution: 1,172,100 GBP
    Partners: ARL, Imperial College London, University of Oxford, University of Liverpool, Radboud University Nijmegen

    An important phenomenon in Nature is that of organization of many objects interacting together, which results into new entities with properties that are much more than the sum of the parts . For example the ability to think is a property of the brain as a whole and is the result of interactions that involves numerous neurons exchanging information in an organized way and is not a property of a single individual neuron. Similarly, in many technologically-important materials electrons also show a certain degree of order in that they correlate their motion with one another to avoid the strong repulsion that arise when they are brought close together. Such correlation effects can lead to surprising emergent material properties, which often can not be predicted in advance, such as superconductivity, where current flows with no resistance due to the fact that electrons travel in pairs in a very robust way. This proposal is to explore superconductivity and other novel form of electronic order stabilized by strong correlations in complex materials that are often not found in Nature but are artificially synthesized with the purpose to achieve certain material functionality. In 2008 the discovery of superconductivity a large class of materials based on Iron stimulated a revolution in condensed matter physics. This was most unexpected as usually Iron has strong ferromagnetic properties (attracting metals) that would normally destroy a superconducting state by breaking the special pairing between electrons. The large number of structural combinations in which iron-based superconductivity is found has raised the hope that the periodic table still holds the key to the discovery of new materials with extremely high superconducting temperatures which one day will revolutionize our way of living. In my first project I propose to take on the challenge of exploring deep into the nature of structural configurations, predicting electronic behaviors and testing experimentally novel superconductors. My second project aims to explore how electrons organize themselves in the presence of frustrated magnetic interactions. Imagine a restaurant with a number of triangular tables and a large number of male and female guests; if one tries to arrange guests such that everybody sits next to a person of the opposite sex, it cannot be realized even for one single table and many equally-unsatisfactory arrangements exist. The same kind of decision has to be made by magnetic spins which can point up or down on a triangular lattice and they cannot decide, so become frustrated. How electrons organize themselves and how they travel in such circumstances remains a mystery. Another amazing unexplored behaviour is that in which electrons are able to flow freely on the surface of a material but not inside it, giving rise to an insulator with a surface that conducts electricity. In this kind of topological insulator, as also in certain frustrated systems, conventional laws of physics do not apply as particles could be found in a superposition of several states at the same time, property that could be important for use in future quantum computers.For this research I use and plan to develop the most advanced tools for probing electron correlations in micron-size single crystalline materials using the highest magnetic fields in the world (a million times larger than earth's magnetic field), low temperatures near absolute zero and extreme high pressures to tune interactions and probe new electronic phases of matter.