5,232 research outputs found
Soil water regime and evapotranspiration of sites with trees and lawn in Moscow
No full textKeywords: Urban vegetation, Tilia cordata, linden, lawn, grass, Leaf Area Index, LAI, digital image processing, evapotranspiration, water stress, electric conductivity, salinity stress, Makkink’s radiation model, deep percolation, water infiltration, runoff, modelling Situations where tree groups of the species Tilia cordata grow together with lawn grass (trees overlapping grass) were studied on five locations in Moscow, Russia, during six periods of the growing season of 2004. The measurements included: detailed descriptions of the soil profiles, tree and lawn dimensions, and, for each period, leaf area index (LAI), soil water content, and soil electric conductivity (EC). LAI was determined through taking photos with a digital camera and processing the photos with a digital image processing program. Using weather and LAI data and vegetation dimensions, the values of potential evapotranspiration of the vegetation combinations were calculated. These calculations followed FAO guidelines for computing crop water requirements. The reference evapotranspiration was also calculated according to Makkink’s radiation model. The results resembled the values of the FAO reference. The measured values of soil water content were used to identify sites and periods with reduced evapotranspiration due to water stress. It appeared that incidence of water stress was very common. The measured soil water content values were transformed into ratios of actual evapotranspiration and potential evapotranspiration: so-called water stress factors. Using these factors, the actual evapotranspiration was calculated from the potential evapotranspiration values. The water regimes of each object and period were analysed. Deep percolation occurred in early spring and late autumn. The possibilities for rainwater to infiltrate the soil were very limited, due to degeneration of soil structure. The water balance of the root zones indicated that the root-zone volumes were smaller than in average forest conditions, and that runoff was extremely high. <br/
Drag Reduction by Applying Speedstrips on Rowing Oars
No full textAbstractThe objective of this study was to determine the advantage of the application of speedstrips to rowing oars for a lightweight single sculler. The research method comprehended three steps: (1) the analysis of the rowing oar movement, (2) the determination of the change in drag and (3) the composition of a rowing model to establish the advantage that could be achieved. The parameters needed for the model: boat velocity, oar angle velocity and power delivered by the rower, were recorded on a real single sculler. The change in drag due to speedstrips on cylinders was determined by performing wind tunnel experiments. The rowing model (Matlab) simulates a race by using real stroke data of a world-class rower as input, while calculating the drag with the coefficients determined by the wind tunnel experiments. The output of the model is the final advantage by the application of speedstrips to rowing oars. Speedstrips induce a 0.1% advantage over a 2000 m race under calm wind conditions. The advantage increases up to .4% with a headwind velocity of 5 m s-1. For bigger boats, the advantage could be even more significant
Drag and Power-loss in Rowing Due to Velocity Fluctuations
No full textAbstractThe flow motions in the turbulent boundary layer between water and a rowing boat initiate a turbulent skin friction. Reducing this skin friction results in better rowing performances. A Taylor-Couette (TC) facility was used to verify the power losses due to velocity fluctuations PV′ in relation to the total power , as a function of the velocity amplitude A. It was demonstrated that an increase of the velocity fluctuations results in a tremendous decrease of the velocity efficiency eV . The velocity efficiency eV for a typical rowing velocity amplitude A of 20 – 25% was about 0.92 – 0.95%. Suppressing boat velocity fluctuations with 60% will increase boat speed with 1.6%. Riblet surfaces were applied on the inner and outer cylinder wall to indicate the drag reducing ability of such surfaces. The results of the measurements at constant velocity are identical as the results reported earlier, while the experimental configuration was different. This confirms once more the consistency of the TC-system for drag studies. The maximum drag reduction DR was 3.4% at a Reynolds number Res 4.7 × 104, which corresponds to a shear velocity in this TC-system with water of V 4.7 m/s. For typical rowing velocity fluctuations, the riblets maintain to reduce the drag with 2.8% and corresponds to a averaged velocity increase of 0.9%. The drag reducing ability of riblets is partly lost due to velocity fluctuations with high amplitudes (A > 20%). From these results, it is concluded that the friction coefficient Cf will vary within one cycle. Higher acceleration/deceleration leads to a additional level of turbulent kinetic energy
A.J. Cronin. A doctor into lifelong writer
No full textReality and fiction might be strictly coexistent in the narrative world. The author of this article, after a deep reading of A.J. Cronin’s novels, has tried to find out the right key to penetrate into the novelist’s intricate world. After many interrogatives on A.J. Cronin both as a man and writer, the author , finally, has been able to grasp from the pages of the novelist, the suffering of a man who has made of his romance the history of his own life
Cape Leeuwin, Grass trees [picture].
No full textCondition: Good.; Title devised by cataloguer based on inscription on picture.; Part of the collection: A.J. Campbell collection, 1832-1921.; Also available in an electronic version via the Internet at: http://nla.gov.au/nla.pic-an24852395
Computing with cables: Towards massively parallel neuro computers
No full textElectrical Engineering, Mathematics and Computer Scienc
Radio Frequency Interference Mitigation in Radio Astronomy
No full textThe next generation of radio telescopes is expected to be one to two orders of magnitude more sensitive than the current generation. Examples of such new telescopes are the Low Frequency Array (LOFAR), currently under construction in the Netherlands, and the Square Kilometer Array (SKA), currently in a concept study phase. Another trend is that technological advances in the fields of electronics and communications systems have led to a vast increase in radio communication applications and systems, and also to an increasing demand for radio spectrum. These two trends, more sensitive telescopes and a much denser spectrum use, imply that radio astronomy will become more vulnerable to interference from radio transmitters. Although protection criteria exist for radio astronomy, it becomes increasingly difficult to keep the radio astronomy frequency bands free from interference. In order to mitigate interference in radio astronomical data, filtering techniques can be used. In this thesis, modern array signal processing techniques have been applied to narrow-band multichannel interference detection and excision, and to narrow-band spatial interference filtering. By investigating the subspace structure of the telescope array output covariance matrices, new results were found, such as upper limits on interference residuals after excision and spatial filtering. The effect of bandwidth, extendedness of the interfering sources, and multipath effects on the detection and spatial filter effectiveness were studied as well. The advantage of a multichannel approach over a single telescope approach was demonstrated by using experimental data from the Westerbork Synthesis Radio Telescope (WSRT). As the performance of mitigation algorithms can be improved by calibration of the telescope gains and noise powers, calibration algorithms were developed. These algorithms were verified both for single and dual polarised arrays. Finally, a LOFAR interference mitigation strategy was developed.Electrical Engineering, Mathematics and Computer Scienc
Set Functionals in Stochastic Geometry
No full textElectrical Engineering, Mathematics and Computer Scienc
Afsluiting Veersegat VIII: Ontgrondingen ten gevolge van het plaatsen van doorlaatcaissons: Rapport modelonderzoek
No full textNa het gereedkomen van het wintersluitgat in de Veerse Gatdam werd de bodem ten zuidoosten van het sluitgat achter de bezinking plaatselijk uitgeschuurd tot een diepte van N.A.P. - 36 m. Deze ontgronding was een gevolg van de wervelstraat die bij vloed van het landhoofd aan de Noordbevelandse zijde binnenwaarts trok. Door het plaatsen van de doorlaatcaissons zouden, zeker wanneer, zoals aanvankelijk in de bedoeling lag, de laatst geplaatste en de helft van de voordien geplaatste caisson gasloten zouden, blijven wervelstraten worden geïntroduceerd. Daarom is het modelonderzoek betreffende de afsluiting van het Veerse Gat voortgezet met een onderzoek naar de ontgrondingen, die in de omgeving van het sluitgat ten gevolge van het plaatsen van de doorlaatcaissons zouden kunnen optreden. In het prototype kon de ontwikkeling van de ontgrondingen, dank zij de wekelijkse peilingen die door Rijkswaterstaat werden verricht, op de voet worden gevolgd. Daardoor deed zich de gelegenheid voor de ontgrondingen in het model te vergelijken met die in het prototype. Eet bleek, dat de ontgrondingen in het samengetrokken model M 586 beter werden gereproduceerd dan in het niet samengetrokken model M 588. In een nota van het Waterloopkundig Laboratorium betreffende de afwijkingen tussen model en prototype in verband met de vormgeving van het wintersluitgat wordt als verklaring hiervoor aangegeven, dat het model M 588 in zijn geheel te ruw is en daardoor het stroombeeld niet voldoende juist weergeeft. Het onderhavige onderzoek is dan ook verricht in het samengetrokken model M 586 (schalen 150/50). Vanwege de korte tijd die beschikbaar was, zijn slechts de belangrijkste fasen uit de sluitingsperiode onderzocht.Deltawerken, Veerse Ga
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