Thickness of the rim of an expanding lamella near the splash threshold

The evolution of the ejected liquid sheet, or lamella, created after impact of a liquid drop onto a solid surface is studied using high-speed video in order to observe the detailed time evolution of the thickness of the rim of the lamella. Since it has been suggested that splashing behavior is set at very early times after impact, we study early times up to D-0/U-0, where D-0 and U-0 are the diameter and speed of the impacting drop, respectively, for different liquid viscosities and impact speeds below the splashing threshold. Within the regime of our experiments, our results are not consistent with the idea that the lamella rim grows similar to the boundary layer thickness. Rather, we find that the rim thickness is always much larger than the boundary layer thickness, and that the rim thickness decreases with increasing impact speed. For lower impact speeds, the increase in the rim thickness is consistent with a root t response over the limited time range available, but the dependence is not simply proportional to root nu, where nu is the kinematic viscosity, and there is a strong dependence of the rim thickness on the impact speed U-0. Scaling of the rim height using a balance of inertial and surface tension forces provides some collapse of the data at lower impact speeds. We also observe an unusual plateau behavior in thickness versus time at higher impact speeds as we approach the splash threshold. (C) 2010 American Institute of Physics. [doi:10.1063/1.3313360

Bistability and regular spatial patterns in arid ecosystems.

A variety of patterns observed in ecosystems can be explained by resource–concentration mechanisms. A resource–concentration mechanism occurs when organisms increase the lateral flow of a resource toward them, leading to a local concentration of this resource and to its depletion from areas farther away. In resource–concentration systems, it has been proposed that certain spatial patterns could indicate proximity to discontinuous transitions where an ecosystem abruptly shifts from one stable state to another. Here, we test this hypothesis using a model of vegetation dynamics in arid ecosystems. In this model, a resource– concentration mechanism drives a positive feedback between vegetation and soil water availability. We derived the conditions leading to bistability and pattern formation. Our analysis revealed that bistability and regular pattern formation are linked in our model. This means that, when regular vegetation patterns occur, they indicate that the system is along a discontinuous transition to desertification. Yet, in real systems, only observing regular vegetation patterns without identifying the pattern-driving mechanism might not be enough to conclude that an ecosystem is along a discontinuous transition because similar patterns can emerge from different ecological mechanisms

Time-dependent, species-specific effects of N:P stoichiometry on grassland plant growth

N and P have different eutrophication effects on grassland communities, yet the underlying mechanisms are poorly understood. To examine plant growth in response to the varying (relative) supply of N and P, we conducted a two-year greenhouse experiment. Five grasses and three herbs were grown with three N:P supply ratios at two overall nutrient supply levels. During the first year the plant growth was relatively low at both high and low N:P supply ratios, whereas during the second year the growth was especially low at a high N:P supply ratio. This second-year low growth was attributed to the high root death rate, which was influenced by a high N:P supply ratio rather than by the nutrient supply level. Species responded differently, especially in P uptake and loss at a high N:P supply ratio. Each species seemed to have a different strategy for P limitation, e.g. an efficient P uptake or a high P resorption rate. Species typical of P-limited grasslands had neither better P uptake nor better P retention at a high N:P supply ratio. This study quantitatively demonstrates an increased plant root death triggered by strong P limitation. This finding indicates a possible extra effect of N eutrophication on ecosystem functioning via changed N:P stoichiometr

The core fundamental plane of B2 radio galaxies

The photometric, structural and kinematical properties of the centers of elliptical galaxies, harbor important information of the formation history of the galaxies. In the case of non active elliptical galaxies these properties are linked in a way that surface brightness, break radius and velocity dispersion of the core lie on a fundamental plane similar to that found for their global properties. We construct the Core Fundamental Plane (CFP) for a sizeable sample of low redshift radio galaxies and compare it with that of non radio ellipticals. To pursue this aim we combine data obtained from high resolution HST images with medium resolution optical spectroscopy to derive the photometric and kinematic properties of ~40 low redshift radio galaxies. We find that the CFPs of radio galaxies is indistinguishable from that defined by non radio elliptical galaxies of similar luminosity. The characteristics of the CFP of radio galaxies are also consistent (same slope) with those of the Fundamental Plane (FP) derived from the global properties of radio (and non radio) elliptical galaxies. The similarity of CFP and FP for radio and non radio ellipticals suggests that the active phase of these galaxies has minimal effects for the structure of the galaxies.Comment: 8 pages, 4 figures, accepted for publication in Astronomy and Astrophysic

Nutrients and Hydrology Indicate the Driving Mechanisms of Peatland Surface Patterning

Peatland surface patterning motivates studies that identify underlying structuring mechanisms. Theoretical studies so far suggest that different mechanisms may drive similar types of patterning. The long time span associated with peatland surface pattern formation, however, limits possibilities for empirically testing model predictions by field manipulations. Here, we present a model that describes spatial interactions between vegetation, nutrients, hydrology, and peat. We used this model to study pattern formation as driven by three different mechanisms: peat accumulation, water ponding, and nutrient accumulation. By on-and-off switching of each mechanism, we created a full-factorial design to see how these mechanisms affected surface patterning (pattern of vegetation and peat height) and underlying patterns in nutrients and hydrology. Results revealed that different combinations of structuring mechanisms lead to similar types of peatland surface patterning but contrasting underlying patterns in nutrients and hydrology. These contrasting underlying patterns suggest that the presence or absence of the structuring mechanisms can be identified by relatively simple short-term field measurements of nutrients and hydrology, meaning that longer-term field manipulations can be circumvented. Therefore, this study provides promising avenues for future empirical studies on peatland patternin

Sociale ondersteuning en kwaliteit van leven bij patienten met kanker.

In dit proefschrift wordt een onderzoek beschreven waarin de relatie centraal staat tussen stress, sociale steun en kwaliteit van leven bij een patiëntengroep, mensen die kanker hebben, en bij een controlegroep bestaande uit 'gezonde' mensen. ... Zie: Samenvattin