Fluidization of granular media wetted by liquid 4^4He

We explore experimentally the fluidization of vertically agitated PMMA spheres wetted by liquid $^4$He. By controlling the temperature around the $\lambda$ point we change the properties of the wetting liquid from a normal fluid (helium I) to a superfluid (helium II). For wetting by helium I, the critical acceleration for fluidization ($\Gamma_c$) shows a steep increase close to the saturation of the vapor pressure in the sample cell. For helium II wetting, $\Gamma_c$ starts to increase at about 75% saturation, indicating that capillary bridges are enhanced by the superflow of unsaturated helium film. Above saturation, $\Gamma_c$ enters a plateau regime where the capillary force between particles is independent of the bridge volume. The plateau value is found to vary with temperature and shows a peak at 2.1 K, which we attribute to the influence of the specific heat of liquid helium.Comment: 4 pages, 3 figures, Accepted by Phys. Rev. E as a rapid communicatio

Bottom-up assembly of functional intracellular synthetic organelles by droplet-based microfluidics

Bottom-up synthetic biology has directed most efforts toward the construction of artificial compartmentalized systems that recreate living cell functions in their mechanical, morphological, or metabolic characteristics. However, bottom-up synthetic biology also offers great potential to study subcellular structures like organelles. Because of their intricate and complex structure, these key elements of eukaryotic life forms remain poorly understood. Here, the controlled assembly of lipid enclosed, organelle-like architectures is explored by droplet-based microfluidics. Three types of giant unilamellar vesicles (GUVs)-based synthetic organelles (SOs) functioning within natural living cells are procedured: (A) synthetic peroxisomes supporting cellular stress-management, mimicking an organelle innate to the host cell by using analogous enzymatic modules; (B) synthetic endoplasmic reticulum (ER) as intracellular light-responsive calcium stores involved in intercellular calcium signalling, mimicking an organelle innate to the host cell but utilizing a fundamentally different mechanism; and (C) synthetic magnetosomes providing eukaryotic cells with a magnetotactic sense, mimicking an organelle that is not natural to the host cell but transplanting its functionality from other branches of the phylogenetic tree. Microfluidic assembly of functional SOs paves the way for high-throughput generation of versatile intracellular structures implantable into living cells. This in-droplet SO design may support or expand cellular functionalities in translational nanomedicine

Crown plasticity and neighborhood interactions of European beech (Fagus sylvatica L.) in an old-growth forest

Competition for canopy space is a process of major importance in forest dynamics. Although virgin and old-growth European beech (Fagus sylvatica L.) forests in Europe have been studied for many years, there are to date no studies of individual-tree crown plasticity and the way this is influenced by local neighborhood interactions in these forests. In this study, we analyzed crown plasticity and local neighborhood interactions of individual trees in the upper canopy of the old-growth beech forests of Serrahn, northeast Germany. In a 2.8-ha sample plot, we measured crown radii of all upper canopy trees and analyzed the direction and extent of crown asymmetry. Size, relative position, and distance of neighboring trees were used to construct vectors of neighborhood asymmetry within different distances from target trees. The crowns of beech trees showed strong morphological plasticity. Mean absolute and relative displacement of crown centers from the stem base were 1.95 m and 0.37, respectively. Circular–circular rank correlation coefficients between the direction of crown displacement and the direction of neighborhood pressure showed that trees strongly positioned their crowns away from local neighbors. Highest correlation coefficients were obtained when basal area and relative position of neighboring trees within a radial distance of 12 m were considered. Clark and Evans index and Ripley’s K-function showed that crowns were more regularly distributed than stems. Projected canopy cover was about 10% higher than canopy cover with simulated circular crowns. We conclude that the crowns of older beech trees have a high ability to plastically respond to changes in the local canopy conditions, enabling very effective exploitation of canopy space

Improving a joint inversion of GRACE, GPS and modelled ocean bottom pressure by using in-situ data.

To investigate the changes in ocean bottom pressure (OBP) and ocean mass Rietbroek et al. (2009) performed a joint least square inversion of weekly GRACE solutions, patterns of large-scale deformation measured by a network of GPS stations and modelled OBP from the Finite Element Sea ice Ocean Model (FESOM). The correlation of this inversion with in-situ OBP ranges between 0.7 and 0.8 in some regions but for example in the tropical Atlantic the correlation is below 0.4. To improve the agreement of the inversion with in-situ data, a part of the in-situ data is included directly into the inversion. The in-situ OBP data was taken from the global OBP data base of Macrander et al. (2010) and averaged to weekly means. Depending on the weight put on the in-situ data, the correlation and regression increases significantly to a value larger than 0.9. The variance of the system is locally reduced by almost 50% at the locations included into the inversion while the difference of the global ocean mean is on average below 10%. Furthermore the global ocean mean is used to compute a bias term for correcting the global ocean mean obtained by the FESOM model

Fingering Instability in a Water-Sand Mixture

The temporal evolution of a water-sand interface driven by gravity is experimentally investigated. By means of a Fourier analysis of the evolving interface the growth rates are determined for the different modes appearing in the developing front. To model the observed behavior we apply the idea of the Rayleigh-Taylor instability for two stratified fluids. Carrying out a linear stability analysis we calculate the growth rates from the corresponding dispersion relations for finite and infinite cell sizes. Based on the theoretical results the viscosity of the suspension is estimated to be approximately 100 times higher than that of pure water, in agreement with other experimental findings.Comment: 11 pages, 12 figures, RevTeX; final versio

Segregation in granular binary mixtures: Thermal diffusion

A recent solution of the inelastic Boltzmann equation that applies for strong dissipation and takes into account non-equipartition of energy is used to derive an explicit expression for the thermal diffusion factor. This parameter provides a criterion for segregation that involves all the parameters of the granular binary mixture (composition, masses, sizes, and coefficients of restitution). The present work is consistent with recent experimental results and extends previous results obtained in the intruder limit case.Comment: 4 figures. to be published in Europhys. Let

Innovative Service-Based Business Concepts for the Machine Tool Building Industry

Organised by: Cranfield UniversityDuring the last decade, machine tool building companies have been forced to put innovative offers on the market. Due to the technical features of their products and the prevailing organizational structures in this sector, especially product-service systems are a promising way of creating a unique selling point. In this paper, potential new business concepts for machine tool builders will be presented which aim at fulfilling basic customer needs like the increase in quality, flexibility, productivity and the reduction of lead times, costs and risks. For the implementation of these product-service systems, practical examples are given.Mori Seiki – The Machine Tool Compan