A macroscopic model for sessile droplet evaporation on a flat surface

The evaporation of sessile droplets on a flat surface involves a complex interplay between phase change, diffusion, advection and surface forces. In an attempt to significantly reduce the complexity of the problem and to make it manageable, we propose a simple model hinged on a surface free energy-based relaxation dynamics of the droplet shape, a diffusive evaporation model and a contact line pinning mechanism governed by a yield stress. Our model reproduces the known dynamics of droplet shape relaxation and of droplet evaporation, both in the absence and in the presence of contact line pinning. We show that shape relaxation during evaporation significantly affects the lifetime of a drop. We find that the dependence of the evaporation time on the initial contact angle is a function of the competition between the shape relaxation and evaporation, and is strongly affected by any contact line pinning.Comment: 13 pages, 8 figure

Variety and regional economic growth in the Netherlands

In economic theory, one can distinguish between variety as a source of regional knowledge spillovers, called Jacobs externalities, and variety as a portfolio protecting a region from external shocks. We argue that Jacobs externalities are best measured by related variety (within sectors), while the portfolio argument is better captured by unrelated variety (between sectors). We introduce a methodology based on entropy measures to compute related variety and unrelated variety. Using data at the COROP level for the period 1996-2002, we find that Jacobs externalities enhance employment growth, while unrelated variety dampens unemployment growth. Productivity growth, by contrast, can be explained by traditional determinants including investments and R&D expenditures. Implications for regional policy in The Netherlands follow.evolutionary economic geography, new economic geography, economic variety

Compound redistribution due to droplet evaporation on a thin polymeric film: theory

A thin polymeric film in contact with a fluid body may leach low-molecular-weight compounds into the fluid. If this fluid is a small droplet, the compound concentration within the liquid increases due to ongoing leaching in combination with the evaporation of the droplet. This may eventually lead to an inversion of the transport process and a redistribution of the compounds within the thin film. In order to gain an understanding of the compound redistribution, we apply a macroscopic model for the evaporation of a droplet and combine that with a diffusion model for the compound transport. In the model, material deposition and the resulting contact line pinning are associated with the precipitation of a fraction of the dissolved material. We find three power law regimes for the size of the deposit area as a function of the initial droplet size, dictated by the competition between evaporation, diffusion and the initial compound concentrations in the droplet and the thin film. The strength of the contact line pinning determines the deposition profile of the precipitate, characterised by a pronounced edge and a linearly decaying profile towards the centre of the stain. Our predictions for the concentration profile within the solid substrate resemble patterns found experimentally.Comment: 12 pages, 10 figure

Sheared force-networks: anisotropies, yielding and geometry

A scenario for yielding of granular matter is presented by considering the ensemble of force networks for a given contact network and applied shear stress $\tau$. As $\tau$ is increased, the probability distribution of contact forces becomes highly anisotropic, the difference between average contact forces along minor and major axis grows, and the allowed networks span a shrinking subspace of all force-networks. Eventually, contacts start to break, and at the yielding shear stress, the packing becomes effectively isostatic. The size of the allowed subspace exhibits simple scaling properties, which lead to a prediction of the yield stress for packings of arbitrary contact number.Comment: 4 pages, 4 figure

Submicron active-passive integration for InP-based membranes on silicon

The high vertical index contrast and the small thickness of thin InP-based membrane structures bonded with BCB on Silicon allow the realization of very small devices. To make photonic integrated circuits with both passive and active components in these membranes, active-passive integration on a small scale is essential. In this paper we will present our results on sub-micrometer active areas for membrane applications

The tail of the contact force distribution in static granular materials

We numerically study the distribution P(f) of contact forces in frictionless bead packs, by averaging over the ensemble of all possible force network configurations. We resort to umbrella sampling to resolve the asymptotic decay of P(f) for large f, and determine P(f) down to values of order 10^{-45} for ordered and disordered systems in two and three dimensions. Our findings unambiguously show that, in the ensemble approach, the force distributions decay much faster than exponentially: P(f) ~ exp(-f^{\alpha}), with alpha \approx 2.0 for 2D systems, and alpha \approx 1.7 for 3D systems.Comment: 4 pages, 4 figures, submitted to Phys. Rev.

Dimensional Errors Due to Overhanging Features in Laser Powder Bed Fusion Parts Made of Ti-6Al-4V

The rise in popularity of Additive Manufacturing technologies and their increased adoption for manufacturing have created a requirement for their fast development and maturity. However,there is still room for improvement when compared with conventional manufacturing in terms of the predictability, quality, and robustness. Statistical analysis has proven to be an excellent tool for developing process knowledge and optimizing different processes efficiently and effectively.This paper uses a novel method for printing overhanging features in Ti-6Al-4V metal parts, by varying process parameters only within the down-facing area, and establishes a methodology for predicting dimensional errors in flat 45◦down-facing surfaces. Using the process parameters laser power, scan speed, scan spacing, scan pattern, and layer thickness, a quadratic regression equation is developed and tested. An Analysis of variance (ANOVA) analysis concluded that, within the down-facing area,the laser power is the most significant process parameter, followed by the layer thickness and scans peed. Comparatively, the scanning pattern is determined to be insignificant, which is explained by the small down-facing area where the various scanning patterns play no role. This paper also discusses the interaction effects between parameters. Some thoughts on the next steps to be taken for further validation are discussed

A tale of two charters

Charters are official commitments to quality and reform. Belgium introduced its Charter of the User of Public Services in 1993. The federal administration’s Copernicus reform began in 1999 and had a strong external outlook. It therefore may be considered as a second User Charter. In this article we focus on the administrative and political contingencies of the introduction of the two charters in Belgium. We show that actual administrative reform and political attention for administrative reform are distinct phenomena. Variations in political attention for reform depend on crises and on political realignment. Both charters were introduced in a period of disturbed relations between citizens and politics. The introduction of a User Charter and the launch of the Copernicus reform were definitely political events, and not merely administrative ones. A charter was needed to restore citizen-government relations. The charters, as pledges for reform, served as lightning rods for political discontent

Overlap Statistics of Shallow Boundary Layer Clouds: Comparing Ground-Based Observations with Large-Eddy Simulations

High-resolution ground-based measurements are used to assess the realism of fine-scale numerical simulations of shallow cumulus cloud fields. The overlap statistics of cumuli as produced by large-eddy simulations (LES) are confronted with Cloudnet data sets at the Jülich Observatory for Cloud Evolution. The Cloudnet pixel is small enough to detect cumuliform cloud overlap. Cloud fraction masks are derived for five different cases, using gridded time-height data sets at various temporal and vertical resolutions. The overlap ratio (R), i.e., the ratio between cloud fraction by volume and by area, is studied as a function of the vertical resolution. Good agreement is found between R derived from observations and simulations. An inverse linear function is found to best describe the observed overlap behavior, confirming previous LES results. Simulated and observed decorrelation lengths are smaller (∼300 m) than previously reported (\u3e1 km). A similar diurnal variation in the overlap efficiency is found in observations and simulations