22,004 research outputs found
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
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
No experimental evidence for local competition in the nestling phase as a driving force for density-dependent avian clutch size
Full text link1. In birds, local competition for food between pairs during the nestling phase may affect nestling growth and survival. A decrease in clutch size with an increase in breeding density could be an adaptive response to this competition. To investigate whether breeding density causally affected the clutch size of great tits (Parus major), we manipulated breeding density in three out of eight study plots by increasing nest-box densities. We expected clutch size in these plots to be reduced compared to that in control plots.
2. We analysed both the effects of variation in annual mean density (between-year comparisons) and experimental density (within-year comparison between plots) on clutch size variation, the occurrence of second broods and nestling growth. We examined within-female variation in clutch size to determine whether individual responses explain the variation over years.
3. Over the 11 years, population breeding density increased (from 0·33 to 0·50 pairs ha–1) while clutch size and the occurrence of second broods decreased (respectively from 10·0 to 8·5 eggs and from 0·39 to 0·05), consistent with a negative density-dependent effect for the whole population. Nestling growth showed a declining but nonsignificant trend over years.
4. The decline in population clutch size over years was primarily explained by changes occurring within individuals rather than selective disappearance of individuals laying large clutches.
5. Within years, breeding density differed significantly between manipulated plots (0·16 pairs ha–1 vs. 0·77 pairs ha–1) but clutch size, occurrence of second broods and nestling growth were not affected by the experimental treatment, resulting in a discrepancy between the effects of experimental and annual variation in density on reproduction.
6. We discuss two hypotheses that could explain this discrepancy: (i) the decline in breeding performance over time was not due to density, but resulted from other, unknown factors. (ii) Density did cause the decline in breeding performance, but this was not due to local competition in the nestling phase. Instead, we suggest that competition acting in a different phase (e.g. before egg laying or after fledgling) was responsible for the density effect on clutch size among years.
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
Modern Medival Monasteries: Two Modern Dutch Monasteries compared to the Benedictine Ideal
No full textIn the 19th century the interest in monasteries and monastic life returned, leading to the design of the Abbey of Egmond by architect A.J. Kropholler in 1929 and the design of St. Benedictusberg in Vaals by architect Dom Hans van der Laan.This research investigates how the architects A.J. Kropholler and Dom Hans van der Laan incorporated the Benedictine Rule into their modern abbeys. Specifically, it examines the historical context of the Dutch abbeys and the development of monastic architecture, drawing on Wolfgang Braunfels’ Monasteries of Western Europe as a foundation for contextualizing the St. Gall Utopia. Additionally, it explores the design principles and philosophies that influenced the layout and construction of the Dutch abbeys under investigation, through an analysis of the floor plans and layouts of the abbeys, as well as interviews with a current monk or an employee at both Dutch abbeys.The thesis is structured into four chapters, beginning with an examination of the Benedictine Rule and Utopia of St. Gall, followed by separate analyses of St. Adalbert’s Abbey in Egmond by A.J. Kropholler and the St. Benedictusberg Abbey in Vaals by Dom Hans van der Laan. The final chapter compares the two Dutch abbeys with each other and the Utopia of St. Gall. The study is limited by the scope of the two Dutch abbeys chosen for analysis, but it offers insights into how the architects of the abbeys incorporated the Benedictine Rule into their designs, and sheds light on the role of monasteries in modern society.The spaces for the three main pillars of the Benedictine Rule are integrated in both Dutch Abbeys. However this research shows that the role in society for Monasteries has changed. The essential elements of the St. Gall Utopia can still be recognized in both floor plans, however the size and clustering of several functions changed.ABSTRACTAR2A011Architectural History ThesisArchitecture, Urbanism and Building Science
Computing with cables: Towards massively parallel neuro computers
No full textElectrical Engineering, Mathematics and Computer Scienc
Direct numerical simulation of the flow in a flue pipe
No full textThe flow behavior of a geometrically simplified flue pipe has been investigated by direct numerical simulation for jet Reynolds numbers of Re = 368; 490; 613. The flow process starts with the formation of a planar ring vortex at the flue exit, which travels towards the upper lip of the pipe. In the following Kelvin-Helmholtz instability appears at both sides of the jet, vortices are formed and an oscillating lateral movement of the jet set in. The vortices interacts with the upper lip, which leads to the generation of further opposite rotating vortices. After resonance is established in the pipe, the frequency spectrum of the quasi periodic state shows the expected fundamental frequency as well as several harmonics
- …
