4,579 research outputs found
Reversible electrowetting and trapping of charge: model and experiments
We derive a model for voltage-induced wetting, so-called electrowetting, from
the principle of virtual displacement. Our model includes the possibility that
charge is trapped in or on the wetted surface. Experimentally, we show
reversible electrowetting for an aqueous droplet on an insulating layer of 10
micrometer thickness. The insulator is coated with a highly fluorinated layer
impregnated with oil, providing a contact-angle hysteresis lower than 2
degrees. Analyzing the data with our model, we find that until a threshold
voltage of 240 V, the induced charge remains in the liquid and is not trapped.
For potentials beyond the threshold, the wetting force and the contact angle
saturate, in line with the occurrence of trapping of charge in or on the
insulating layer. The data are independent of the polarity of the applied
electric field, and of the ion type and molarity. We suggest possible
microscopic origins for charge trapping.Comment: 13 pages & 5 figures; the paper has been accepted for publication in
Langmui
Spin-dependent transport in metal/semiconductor tunnel junctions
This paper describes a model as well as experiments on spin-polarized tunnelling with the aid of optical spin orientation. This involves tunnel junctions between a magnetic material and gallium arsenide (GaAs), where the latter is optically excited with circularly polarized light in order to generate spin-polarized carriers. A transport model is presented that takes account of carrier capture in the semiconductor surface states, and describes the semiconductor surface in terms of a spin-dependent energy distribution function. The so-called surface spin-splitting can be calculated from the balance of the polarized electron and hole flow in the semiconductor subsurface region, the polarized tunnelling current across the tunnel barrier between the magnetic material and the semiconductor surface, and the spin relaxation at the semiconductor surface.
Measurements are presented of the circular-polarization-dependent photocurrent (the so-called helicity asymmetry) in thin-film tunnel junctions of Co/Al2O3/GaAs. In the absence of a tunnel barrier, the helicity asymmetry is caused by magneto-optical effects (magnetic circular dichroism). In the case where a tunnel barrier is present, the data cannot be explained by magneto-optical effects alone; the deviations provide evidence that spin-polarized tunnelling due to optical spin orientation occurs. In Co/τ-MnAl/AlAs/GaAs junctions no deviations from the magneto-optical effects are observed, most probably due to the weak spin polarization of τ-MnAl along the tunnelling direction; the latter is corroborated by bandstructure calculations. Finally, the application of photoexcited GaAs for spin-polarized tunnelling in a scanning tunnelling microscope is discussed.
Probing cell membrane mechanics by magnetic particle actuation and 3D rotational particle tracking
The mechanical properties of the cell membrane and the actin cortex determine a variety of cellular processes. An accurate description of their mechanics and dynamics necessitates a measurement technique that can capture the inherent anisotropy of the system. We combine magnetic particle actuation with rotational and translational particle tracking to simultaneously measure the mechanical stiffness of the membrane and the actin cortex in living cells in three rotational and two translational directions. We demonstrate the technique by targeting various types of membrane receptors. When using particles that bind via integrins, we measured an isotropic stiffness and a characteristic power-law dependence of the shear modulus on the applied frequency. When using particles functionalized with immunoglobulin G, we measured an anisotropic stiffness with a strongly reduced value in one dimension. We suggest that the observed reduced stiffness is caused by a local detachment of the membrane from the subjacent cytoskeletal cortex. Furthermore, we use functionalized particles as phagocytic targets for macrophages. Although phagocytosis is an inherently mechanical process, little is known about the forces and energies that a cell requires for internalization. We use our technique to measure the stiffnesses of the phagocytic cup as a function of time. The measured values and their time-dependence can be interpreted with a model of a pre-stressed membrane connected to an elastically deformable actin cortex. A comparison of model and data allows a determination of the speed at which the membrane advances around the particle. This approach is a novel way of measuring the progression of phagocytic cups and their mechanical properties in real-time. We expect that our technique will enable new insights into the mechanical properties of cells and will help to better understand numerous cellular processes
Tomato chlorotic mottle virus is a target of RNA silencing but the presence of specific short interfering RNAs dois not guarantee resistance in transgenic plants.
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Previous issue date: 2008-01-2
Schapenhouderij nog steeds geen vetpot
Dat blijkt uit de deeladministra-ties die het Landbouw-Economisch Instituut (LEI-DLO) samen met de Dienst Landbouw Voorlichting (DLV) bijhoudt
Characterization of Municipal, Construction and Demolition Wastes for Energy Production Through Gasification - A Case Study for a Portuguese Waste Management Company
Gasification of wastes is considered a promising alternative for
energy generation due to its lower environmental impacts when compared with
conventional landfilling and incineration. Valorisation of such wastes improves
sustainability of resource management and of energy production. However, an
appropriate characterisation of wastes in terms of physical and chemical properties
is essential for the prediction of their behaviour during gasification,
allowing to identify possible problems for the environment and installed
equipment and also to define which materials present a greater energy potential.
This study aimed to characterise 10 different fractions from municipal, construction
and demolition wastes received in different fluxes by a Portuguese
waste management company. These fractions included wood (44.83 wt%),
plastic (22.15 wt%), paper/card (0.04 wt%), mixtures of paper and plastic (14.67
wt%) and sewage sludge (18.31 wt%). For this purpose, determination of
density, proximate and ultimate analysis, higher heating value (HHV), thermogravimetric
profiles and inorganic composition of ashes were performed for
each fraction. Analysis revealed that plastics and their mixtures with paper/card
possess the highest HHV’s (25–45 MJ/kg db), thus exhibiting a greater capacity
for energy production. High levels of ashes found in dried sewage sludge (50 wt
% db) indicate that a lot of by-product will be generated after gasification,
possibly increasing the treatment costs. A gasification unit operating at 50 kg/h
and admitting a mixture of all these wastes would generate 109.7 kW of total
power, having capacity to receive more waste fluxes along the year.info:eu-repo/semantics/acceptedVersio
Lattice sites of ion-implanted Li in diamond
Published in: Appl. Phys. Lett. 66 (1995) 2733-2735
citations recorded in [Science Citation Index]
Abstract: Radioactive Li ions were implanted into natural IIa diamonds at temperatures between 100 K and 900 K. Emission channelling patterns of a-particles emitted in the nuclear decay of 8Li (t1/2 = 838 ms) were measured and, from a comparison with calculated emission channelling and blocking effects from Monte Carlo simulations, the lattice sites taken up by the Li ions were quantitatively determined. A fraction of 40(5)% of the implanted Li ions were found to be located on tetrahedral interstitial lattice sites, and 17(5)% on substitutional sites. The fractions of implanted Li on the two lattice sites showed no change with temperature, indicating that Li diffusion does not take place within the time window of our measurements.
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