On upstream blocking in a viscous diffusive stratified flow

The effect of diffusion of specie upon the flow about a transverse flat plate moving horizontally in a viscous stratified medium is considered. Asymptotic expansions are used to define a parameter regime where a viscous-diffusive-buoyancy balance is dominant. The solution, expressed in terms of an inverse Fourier transform, is numerically integrated. The results show that, as in the non-diffusive problem, a region of closed streamlines exists ahead of the body. However, unlike the case where diffusion is neglected, the density field within this recirculating region is uniquely determined and found to be statically stable. It is also found that varying the relative amount of diffusion affects not only the density distribution, but the velocity profile as well, indicating a strong coupling between the vorticity and specie equation

DEEP: a provenance-aware executable document system

The concept of executable documents is attracting growing interest from both academics and publishers since it is a promising technology for the dissemination of scientific results. Provenance is a kind of metadata that provides a rich description of the derivation history of data products starting from their original sources. It has been used in many different e-Science domains and has shown great potential in enabling reproducibility of scientific results. However, while both executable documents and provenance are aimed at enhancing the dissemination of scientific results, little has been done to explore the integration of both techniques. In this paper, we introduce the design and development of DEEP, an executable document environment that generates scientific results dynamically and interactively, and also records the provenance for these results in the document. In this system, provenance is exposed to users via an interface that provides them with an alternative way of navigating the executable document. In addition, we make use of the provenance to offer a document rollback facility to users and help to manage the system's dynamic resources

Semiparametric Bayesian inference in smooth coefficient models

We describe procedures for Bayesian estimation and testing in cross-sectional, panel data and nonlinear smooth coefficient models. The smooth coefficient model is a generalization of the partially linear or additive model wherein coefficients on linear explanatory variables are treated as unknown functions of an observable covariate. In the approach we describe, points on the regression lines are regarded as unknown parameters and priors are placed on differences between adjacent points to introduce the potential for smoothing the curves. The algorithms we describe are quite simple to implement - for example, estimation, testing and smoothing parameter selection can be carried out analytically in the cross-sectional smooth coefficient model. We apply our methods using data from the National Longitudinal Survey of Youth (NLSY). Using the NLSY data we first explore the relationship between ability and log wages and flexibly model how returns to schooling vary with measured cognitive ability. We also examine a model of female labor supply and use this example to illustrate how the described techniques can been applied in nonlinear settings

Effecten van dunning en vraat op spontane verjonging in eiken-dennenbossen

Bosbeheerders sturen spontane bosontwikkeling door dunning. Een dergelijke ingreep in het kronendak brengt meer licht in het bos en heeft daardoor effect op de bodemvegetatie. Behalve licht is begrazing door herbivoren een belangrijke factor in de bosontwikkeling. Met name loofbomen worden sterk bevreten, waardoor spontane verjonging van gemengde loofbossen in door herten en reeën begraasde terreinen op de hogere zandgronden in Nederland weinig voorkomt. In dit onderzoek is bekeken hoe natuurlijke verjonging van loofboomsoorten door middel van dunning kan worden bevorderd, en welke rol vraat door grote herbivoren daarbij speelt. Belangrijkste conclusies zijn dat sterke dunning in dit bostype leidt tot een spontane verjonging van met name de lichteisende soorten ruwe berk, zomereik en grove den. Meer schaduwverdragende soorten als wintereik en beuk komen in kleinere aantallen voor en lijken bovendien minder afhankelijk van de openheid van de opstand. Begrazing door grote herbivoren leidt tot meer licht op de bosbodem (ten gunste van de bodemvegetatie), tot een snellere toename van de bedekking van blauwe bosbes en tot een geringere afname van bochtige smele dan in onbegraasde situaties. Door vraat nemen de soorten smalle stekelvaren, liggend walstro en bochtige smele in bedekking af. Grote herbivoren beonvloeden tevens de samenstelling van de verjonging. Beuk en wintereik worden minder bevreten en dus bevoordeeld boven berk, zomereik en grove den. Beuk zal op termijn (ook of juist bij de huidige wilddruk) het bos op deze groeiplaats gaan domineren. Lijsterbes en vuilboom worden sterk bevreten; beide soorten kunnen alleen doorgroeien bij lage wilddichtheden. De lokale wilddichtheid in het gebied is gemiddeld, maar wel dermate hoog dat spontane verjonging sterk belemmerd wordt. Bij uitsluiting van begrazing zal een verjonging ontstaan, eerst gedomineerd door ruwe berk en lijsterbes, later door beuk