Sonic anemometers in aeolian sediment transport research

Fast-response wind and turbulence instruments, including sonic anemometers, are used more and more in aeolian sediment transport research. These instruments give information on mean wind, but also on fluctuations and turbulent statistics, such as the uw covariance, which is a direct measure of Reynolds' stress (RS) and friction velocity. This paper discusses the interpretation of sonic anemometer data, the transformations needed to get proper results and turbulence spectra, and how they are influenced by instrument size, sampling frequency, and measurement height. Turbulence spectra characterize how much the different frequencies in the turbulent signals contribute to the variance of wind speed, or to the covariance of horizontal and vertical wind speed. They are important in determining the measurement strategy when working with fast-response instruments, such as sonic anemometers, and are useful for interpreting the measurement results. Choices on the type of sonic anemometer, observation height, sampling period, sampling frequency, and filtering can be made on the basis of expected high and low-frequency losses in turbulent signals, which are affected by those variables, as well as wind speed and atmospheric stability. Friction velocity and RS, important variables in aeolian sediment transport research, are very sensitive to tilt or slope errors. During a field experiment, the slope sensitivity of the RS was established as 9% per degree of slope, which is 1.5 times the value reported in literature on the basis of theoretical considerations. An important reason for the difference probably is the large influence of streamline curvature on turbulence statistics and thereby on the slope sensitivity of the RS. An error of 9% per degree of slope in the RS will translate into an error of approximately 4% per degree of slope in the calculated friction velocity. Space-time correlation of the horizontal wind speed is much larger than that of the vertical wind speed and the instantaneous RS. This largely explains why, in previous studies, a poor correlation was found between instantaneous RS measured at 3 in height and saltation flux near the surface, whereas the correlation between wind speed at some height and saltation flux was much better. Therefore, the poor correlation between RS away from the surface and saltation flux does not contradict that saltation flux is caused by RS. (C) 2003 Elsevier B.V. All rights reserved

Uitvoeringsprogramma Monitoring en Evaluatie Pilot Zandmotor

Dit uitvoeringsprogramma beschrijft de evaluatiesystematiek en het monitoringplan voor de pilot Zandmotor voor de periode 2011 tot en met 2021. Om te komen tot het monitoringprogramma zijn evaluatiefactsheets opgesteld waarin de hoog abstracte doelen en beheersdoelstellingen uit het Monitoring en Evaluatie Plan Zandmotor (DHV, 2010) zijn vertaald in specifieke en concrete evaluatievragen, hypothesen en informatiebehoeften

Verkenning herstelmogelijkheden duindynamiek Westduinen (Schouwen)

Op verzoek van OBN deskundigenteam Duin- en Kustlandschap, Provincie Zeeland, en de twee grote duinbeheerders Staatsbosbeheer en Natuurmonumenten op Schouwen is een verkenning uitgevoerd naar de herstelmogelijkheden van duindynamiek in de Meeuwenduinen en de Zeepeduinen (beide onder de noemer Westduinen Schouwen in dit rapport). De herstelmaatregelen zijn opgesteld na bestudering van de verstuivingsgeschiedenis van het gebied, vooral aan de hand van de afname oppervlaktes kaal zand. Ook is de interne opbouw bestudeerd door middel van grondradar en zijn geselecteerde duinafzettingen in de tijd geplaatst door middel van luminescentie dateringen (dit is nieuw voor Nederland)

CP violating asymmetries in single top quark production at the Tevatron p pbar collider

Analytic expressions for the angular distributions of the $b$-quarks associated with single $t$-quark production in $p \bar p \to W^* \to t \bar b \to b \bar b W$ and of the leptons from the subsequent decay $W \to l\nu$ are obtained in the laboratory system. CP violation in the $t$-production vertex is assumed. Different angular and total cross section CP violating asymmetries are considered. Relations testing CP violation solely in the $t$-decay vertex are also obtained. A numerical analysis is performed in the MSSM with a CP violating phase of the trilinear coupling $A_{\tilde t}$. The asymmetries are typically of the order $10^{-3}$ - $10^{-4}$.Comment: The numerical results are corrected and some changes that meet the requirements of Phys. Rev. D are mad

Tidal inlet function: field evidence and numerical simulation in the INDIA project

In recognition of the environmentally sensitive nature of inlets and of a requirement to improve present knowledge of their function, the INDIA project has studied a small natural tidal inlet located in the Ría Formosa, Algarve, Portugal. The project has used state-of-the-art field equipment to study present day processes, and a range of numerical models to extend the spatial and temporal range of the measurements. Underpinned by knowledge of inlet evolution over several years, and by knowledge of other inlet systems, a conceptual model describing the medium-to long-term evolution of the inlet is presented. Key elements of the model are then examined with reference to field observations and to numerical simulations of tides, waves, sediments and morphology. Supported by historical evidence of inlet evolution in the Ría Formosa, the picture that emerges of inlet dynamics is essentially one of relative simplicity and predictability in the short-to medium-term

Can Mobile Phone Data Improve Emergency Response to Natural Disasters?

Peter Gething and Andrew Tatem discuss the potential impact of mobile phone positioning data on disaster response and highlight challenges that must be addressed if use of this technology is to develop