Predicting the occurrence of sand banks in the North Sea

Sand banks have a wavelength between 1 and 10 km, and they are up to several tens of meters high. Also, sand banks may have an impact on large-scale human activities that take place in the North Sea like sand mining, shipping, offshore wind farms, etc. Therefore, it is important to know where sand banks occur and what their natural behavior is. Here, we use an idealized model to predict the occurrence of sand banks in the North Sea. The aim of the paper is to research to what extent the model is able to predict the occurrence of sand banks in the North Sea. We apply a sensitivity analysis to optimize the model results for a North Sea environment. The results show that the model correctly predicts whether or not sand banks occur for two thirds of the North Sea area

An Attempt to Detect the Galactic Bulge at 12 microns with IRAS

Surface brightness maps at 12 microns, derived from observations with the Infrared Astronomical Satellite (IRAS), are used to estimate the integrated flux at this wavelength from the Galactic bulge as a function of galactic latitude along the minor axis. A simple model was used to remove Galactic disk emission (e.g. unresolved stars and dust) from the IRAS measurements. The resulting estimates are compared with predictions for the 12 micron bulge surface brightness based on observations of complete samples of optically identified M giants in several minor axis bulge fields. No evidence is found for any significant component of 12m emission in the bulge other than that expected from the optically identified M star sample plus normal, lower luminosity stars. Known large amplitude variables and point sources from the IRAS catalogue contribute only a small fraction to the total 12 micron flux.Comment: Accepted for publication in ApJ; 13 pages of text including tables in MS WORD97 generated postscript; 3 figures in postscript by Sigma Plo

Valuation of functions of the Wadden Area

The rationale of this position paper is to explore ways to employ valuation methods to assess the impacts of alternative policy decisions on the functions of the Wadden Area. Based on this rationale, this paper aims to bring an ecological-economic perspective on the benefits of the Wadden Area. It highlights key issues involved in the notion and application of monetary valuation methods for valuing the (ecological) functions of the area. It also pays attention to the development of policy handles on the basis of the outcome of the valuation of ecological functions. Particularly, the paper discuss Payment for Environmental Services (PES), which aims at preservation and protection by purchasing conservation. The use of a valuation instrument within a Payment for Environmental Services Scheme is new. Valuation is of course an established technique within a Cost-Benefit framework. However, Payment for Environmental Services is an innovative way of designing policy instruments in the collaboration between ecologists and economist

'Calving laws', 'sliding laws' and the stability of tidewater glaciers

A new calving criterion is introduced, which predicts calving where the depth of surface crevasses equals ice height above sea level. Crevasse depth is calculated from strain rates, and terminus position and calving rate are therefore functions of ice velocity, strain rate, ice thickness and water depth. We couple the calving criterion with three 'sliding laws', in which velocity is controlled by (1) basal drag, (2) lateral drag and (3) a combination of the two. In model 1, velocities and strain rates are dependent on effective pressure, and hence ice thickness relative to water depth. Imposed thinning can lead to acceleration and terminus retreat, and ice shelves cannot form. In model 2, ice velocity is independent of changes in ice thickness unless accompanied by changes in surface gradient. Velocities are strongly dependent on channel width, and calving margins tend to stabilize at flow-unit widenings. Model 3 exhibits the combined characteristics of the other two models, and suggests that calving glaciers are sensitive to imposed thickness changes if basal drag provides most resistance to flow, but stable if most resistance is from lateral drag. ice shelves can form if reduction of basal drag occurs over a sufficiently long spatial scale. In combination, the new calving criterion and the basal-lateral drag sliding function (model 3) can be used to simulate much of the observed spectrum of behaviour of calving glaciers, and present new opportunities to model ice-sheet response to climate change.</p

OH-selected AGB and post-AGB objects I.Infrared and maser properties

Using 766 compact objects from a survey of the galactic Plane in the 1612-MHz OH line, new light is cast on the infrared properties of evolved stars on the TP-AGB and beyond. The usual mid-infrared selection criteria, based on IRAS colours, largely fail to distinguish early post-AGB stages. A two-colour diagram from narrower-band MSX flux densities, with bimodal distributions, provides a better tool to do the latter. Four mutually consistent selection criteria for OH-masing red PPNe are given, as well as two for early post-AGB masers and one for all post--AGB masers, including the earliest ones. All these criteria miss a group of blue, high-outflow post-AGB sources with 60-mum excess; these will be discussed in detail in Paper II. The majority of post-AGB sources show regular double-peaked spectra in the OH 1612-MHz line, with fairly low outflow velocities, although the fractions of single peaks and irregular spectra may vary with age and mass. The OH flux density shows a fairly regular relation with the stellar flux and the envelope optical depth, with the maser efficiency increasing with IRAS colour R21. The OH flux density is linearly correlated with the 60-mum flux density.Comment: 16 pages, LaTex, 22 figures, AJ (accepted

Reicht optischer Fluß wirklich nicht zum Heimfinden?

Die Literatur legt nahe, daß selbst für einfache Orientierungs- und Heimfindeaufgaben die durch optischen Fluß gegebene Information unzureichend ist und vestibuläre und kinästhetische Reize benötigt werden. Um diese Behauptung zu testen, führten wir Dreiecksvervollständigungsexperimente in einer virtuellen Umgebung durch, die als einzige Informationsquelle optischen Fluß anbot. Die simulierte Eigenbewegung wurden visuell auf einer halbzylindrischen 180° Projektionsleinwand (7m Durchmesser) dargeboten und über Maus-Tasten gesteuert. Damit die Versuchspersonen zur Navigation nur Pfadintegration und keine Landmarkeninformation verwenden konnten, bestand die simulierte Welt lediglich aus einer 3D Punktewolke. Diese enthielt keinerlei hilfreiche Orientierungspunkte (Landmarken), vermittelte jedoch ein überzeugendes Gefühl von Eigenbewegung (Vektion). In Exp 1 sollten die Versuchspersonen Drehungen um bestimmte Winkel ausführen sowie Distanzen reproduzieren, wobei die Geschwindigkeiten randomisiert wurden. Exp 2 3 waren Dreiecksvervollständigungsexperimente: Versuchspersonen folgten zwei Schenkeln eines Dreiecks und sollten dann selbstständig zum nicht markierten Ausgangspunkt zurückfinden. In Exp 2 wurden fünf verschiedene gleichschenklige Dreiecke für Links- und Rechtsdrehungen verwendet, in Exp 3 hingegen 60 verschiedene Dreiecke mit randomisierten Schenkellängen und Winkeln. Unabhängig von der Bewegungsgeschwindigkeit konnten untrainierte Versuchspersonen in Exp 1 Drehungen und Distanzen mit nur geringfügigem systematischen Fehler ausführen. Wir fanden in Exp 2 3 generell eine lineare Korrelation zwischen ausgeführten und korrekten Werten für die Meßgrößen Drehwinkel und zurückgelegte Distanz. Für die weitere Analyse verwendeten wir deshalb für beide Meßgrößen die Steigungen der Regressionsgeraden (“Kompressionsrate”) und die Abweichungen vom korrekten Wert (signed error). Exp 2 zeigte keine signifikanten Fehler (d.h. generelle Über- oder Unterschätzung) für Drehungen oder Distanzen. Distanzantworten waren stark in Richtung Mittelwert verschoben (Kompressionsrate 0.58), Winkelantworten jedoch kaum (0.91). Für randomisierte Dreiecksgeometrien in Exp 3 reduzierte sich diese Tendenz zu mittleren Antworten für Distanzen (0.86), verstärkte sich jedoch für Drehungen (0.77). In ähnlichen Experimenten zur Dreiecksvervollständigung unter Beschränkung auf visuelle Information (Virtual Reality: Péruch et al., Perc. ‘97; Duchon et al., Psychonomics ‘99) und auf propriozeptive Reize (blindes gehen: Loomis et al., JEP ‘93) zeigte sich eine starke Tendenz zu mittleren Drehwinkeln (Kompressionsrate < 0.5), die wir nicht fanden. Die Tendenz, bei reinen Drehaufgaben in visuellen virtuellen Umgebungen nicht weit genug zu drehen (Péruch ‘97; Bakker, Presence ‘99) konnte ebenfalls nicht beobachtet werden (Exp 1). Pfadintegration aufgrund optischen Flusses erwies sich in unseren Experimenten als ausreichend und verläßlich für Orientierungs- und Heimfindeaufgaben. Vestibuläre und kinästhetische Information waren hierfür nicht erforderlich

Thermal stability of ultrasoft Fe–Zr–N films

The thermal stability of nanocrystalline ultrasoft magnetic (Fe98Zr2)1−xNx films with x = 0.10–0.25 was studied using thermal desorption spectrometry, positron beam analysis and high resolution transmission electron microscopy. The results demonstrate that grain growth during the heat treatment is accompanied by an increase of the free volume and nitrogen relocation and desorption. All these phenomena can drastically degrade the ultrasoft magnetic properties. The nitrogen desorption has already started at temperatures around 400 K. Nevertheless, most of the nitrogen leaves the sample at a temperature above 800 K. We found that nitrogen out-diffusion is significantly retarded compared with the prediction of the diffusion in bulk α-Fe. A qualitative model is proposed in which the nitrogen out-diffusion in nanocrystalline material is retarded by trapping at immobile defects, namely Zr atoms, and also by voids at grain boundaries. From a certain temperature, nitrogen migrates from the interior of the nanograins to the nanovoids at the grain boundaries and the out-diffusion to the outer surface is controlled by transport between the voids.

The footprint of cometary dust analogues: II. Morphology as a tracer of tensile strength and application to dust collection by the Rosetta spacecraft

The structure of cometary dust is a tracer of growth processes in the formation of planetesimals. Instrumentation on board the Rosetta mission to comet 67P/Churyumov- Gerasimenko captured dust particles and analysed them in situ. However, these deposits are a product of a collision within the instrument. We conducted laboratory experiments with cometary dust analogues, simulating the collection process by Rosetta instruments (specifically COSIMA, MIDAS). In Paper I we reported that velocity is a key driver in determining the appearance of deposits. Here in Paper II we use materials with different monomer sizes, and study the effect of tensile strength on the appearance of deposits. We find that mass transfer efficiency increases from $\sim$1 up to $\sim$10% with increasing monomer diameter from 0.3 $\mu$m to 1.5 $\mu$m (i.e. tensile strength decreasing from $\sim$12 to $\sim$3 kPa), and velocities increasing from 0.5 to 6 m/s. Also, the relative abundance of small fragments after impact is higher for material with higher tensile strength. The degeneracy between the effects of velocity and material strength may be lifted by performing a closer study of the deposits. This experimental method makes it possible to estimate the mass transfer efficiency in the COSIMA instrument. Extrapolating these results implies that more than half of the dust collected during the Rosetta mission has not been imaged. We analysed two COSIMA targets containing deposits from single collisions. The collision that occurred closest to perihelion passage led to more small fragments on the target.Comment: 13 pages, 11 figures, accepted for publication in MNRA

The Sa'dan Toradja Chant for the Deceased

Indonesi