A Nested Grid Particle-Mesh Code for High Resolution Simulations of Gravitational Instability in Cosmology

I describe a nested-grid particle-mesh (NGPM) code designed to study gravitational instability in three-dimensions. The code is based upon a standard PM code. Within the parent grid I am able to define smaller sub-grids allowing us to substantially extend the dynamical range in mass and length. I treat the fields on the parent grid as background fields and utilize a one-way interactive meshing. Waves on the coarse parent grid are allowed to enter and exit the subgrid, but waves from the subgrid are precluded from effecting the dynamics of the parent grid. On the parent grid the potential is computed using a standard multiple Fourier transform technique. On the subgrid I use a Fourier transform technique to compute the subgrid potential at high resolution. I impose quasi-isolated boundary conditions on the subgrid using the standard method for generating isolated boundary conditions, but rather than using the isolated Green function I use the Ewald method to compute a Green function on the subgrid which possesses the full periodicity of the parent grid. I present a detailed discussion of my methodology and a series of code tests.Comment: 13 pages, 10 figures included, uses mn.sty & epsf.sty. Accepted by MNRAS. This is the final refereed versio

Decaying Neutrinos in Galaxy Clusters

Davidsen et al. (1991) have argued that the failure to detect uv photons from the dark matter DM) in cluster A665 excludes the decaying neutrino hypothesis. Sciama et al. (1993) argued that because of high central concentration the DM in that cluster must be baryonic. We study the DM profile in clusters of galaxies simulated using the Harrison--Zel'dovich spectrum of density fluctuations, and an amplitude previously derived from numerical simulations (Melott 1984b; Anninos et al. 1991) and in agreement with microwave background fluctuations (Smoot et al. 1992). We find that with this amplitude normalization cluster neutrino DM densities are comparable to observed cluster DM values. We conclude that given this normalization, the cluster DM should be at least largely composed of neutrinos. The constraint of Davidsen et al. can be somewhat weakened by the presence of baryonic DM; but it cannot be eliminated given our assumptions.Comment: 14 pages, requires aaspp.sty. All latex, style files, and postscript files included in a uuencoded compressed-tar file. [email protected]

The Superiority of the Minimal Spanning Tree in Percolation Analyses of Cosmological Datasets

In this work we demonstrate the ability of the Minimal Spanning Tree to duplicate the information contained within a percolation analysis for a point dataset. We show how to construct the percolation properties from the Minimal Spanning Tree, finding roughly an order of magnitude improvement in the computer time required. We apply these statistics to Particle-Mesh simulations of large-scale structure formation. We consider purely scale-free Gaussian initial conditions ($P(k) \propto k^n$, with $n = -2, -1, 0 \ \& +1$) in a critical density universe. We find in general the mass of the percolating cluster is a much better quantity by which to judge the onset of percolation than the length of the percolating cluster.Comment: 7 pages, 4 figures included, uses mn.sty & epsf.sty. Accepted by MNRA

Indirect effects of invasive species affecting the population structure of an ecosystem engineer

Species invasion is of increasing concern as non-native species often have negative impacts on ecosystems that they were introduced to. Invaders negatively affect the abundance of native species due to direct interactions like predation and competition. Additionally, invaders may benefit native biota by imposing indirect effects on resident species interactions. Invaders indirectly affect resident species via both density-mediated indirect interactions (DMIIs) and trait-mediated indirect interactions (TMIIs). Previous studies on these different indirect interactions have largely examined the effects on structuring ecological systems, with paying little attention to the role of body size. Here, we experimentally demonstrate that an invasive habitat modifier of European coastal waters, the Pacific oyster (Crassostrea gigas), alters the population structure of native mussels (Mytilus edulis) by modifying the size specific predator-prey interaction between the mussels and the shore crab (Carcinus maenas). In laboratory split-plot experiments, the presence of Pacific oysters reduced the mortality of unconditioned mussels as well as mussels that were acclimatized in presence of predatory cues, while being exposed to predation by crabs of two different size classes. The reduction in mortality was size-dependent both in terms of the predators and the prey. The presence of oysters notably reduced mussel mortality in presence of small crabs, while the mortality rate in presence of big crabs was less affected. Mussels that benefited the most by the presence of oysters were those of recruitment stages, smaller than 20 mm in shell length. Our results suggest that oysters cause a strong shift in the population structure of M. edulis, reducing particularly the mortality of smaller sized mussels

Role of endothelial glycocalyx in sliding friction at the catheter-blood vessel interface

Catheterization is a common medical operation to diagnose and treat cardiovascular diseases. The blood vessel lumen is coated with endothelial glycocalyx layer (EGL), which is important for the permeability and diffusion through the blood vessels wall, blood hemodynamics and mechanotransduction. However EGL's role in catheter-blood vessel friction is not explored. We use a porcine aorta to mimic the blood vessel and a catheter loop was made to rub in reciprocating sliding mode against it to understand the role of catheter loop curvature, stiffness, normal load, sliding speed and EGL on the friction properties. Trypsin treatment was used to cause a degradation of the EGL. Decrease in catheter loop stiffness and EGL degradation were the strongest factors which dramatically increased the coefficient of friction (COF) and frictional energy dissipation at the aorta-catheter interface. Increasing sliding speed caused an increase but increase in normal load first caused a decrease and then an increase in the COF and frictional energy. These results provide the basic data for safety of operation and damage control during catheterization in patients with degraded EGL

A new (and better) way to measure individual financial capability

This study aims to validate the results of a 2012 pilot study that developed a short instrument to measure financial capability, using national survey results as reference point. More importantly, this study also develops a numerical scoring system to provide respondents with a transparent and easy to interpret method for differentiating low, moderate and high levels of personal financial literacy

Zzp'ers in beeld : een inventarisatie in de agrarische sector

Dit rapport schetst een beeld van zzp (zelfstandige zonder personeel) in de agrarische sector. In deze inventariserende studie zijn de voor% en nadelen van deze relatief nieuwe vorm van arbeid beschreven en is ingezoomd op de kansen die zzp biedt voor bepaalde doelgroepen. Het rapport omvat ook kwantitatieve informatie over de inzet van zzp'ers in de land% en tuinbouw. Verder is een aantal inhoudelijke thema's uitgewerkt, waaronder werving van zzp'ers/opdrachten, regelgeving, certificering en sociale zekerheid. Het rapport is gebaseerd op een deskstudie en een praktijkinventarisati

Tuinbouw Integraal Digitaal (TID); Inventarisatie, analyse en programmavoorstel

In dit rapport wordt de huidige situatie op het gebied van integrale digitale informatievoorzieningin de tuinbouwsector in kaart gebracht en geanalyseerd. Vervolgens worden de contouren geschetst van een mogelijk programma voor verbetering en integratie van deze digitale informatievoorziening. Hiermee wordt een overzicht geboden van de huidige initiatieven en projecten en een uitgangspunt gegeven voor de rol die het Nederlandse tuinbouwclusterwil vervullen. Het ziet voor zichzelf een richtinggevende rol weggelegd als ontwikkelaar en eigenaar van besturings- of coördinatieconcepten die gebruikt worden in ICT-systemen, informatiestromen en ketenstandaards. Het rapport onderstreept de noodzaak om tot een integrale aanpak van de digitale informatievoorziening te komen.This report charts and analyses the current situation regarding integrated digitalinformation facilities in the horticultural sector. It also suggests the outlines of a possible programme for improving the integration of these digital information facilities. Additionally it offers an overview of the current initiatives and projects and suggests a starting point for the role which the Dutch horticulture cluster wishes to fill. Dutch horticulture is aiming towards a guiding role as a developer and owner of operational and coordinating concepts which are used in ICT systems, data flows, and chain standards. The report emphasises the necessity of creating an integrated approach to digital information facilities