HAWT near‐wake aerodynamics,Part I: axial flow conditions

An improved physical understanding of the rotor aerodynamics of a horizontal axis wind turbine (HAWT) is required to reduce the uncertainties associated with today's design codes. Wind tunnel experiments contribute to increased knowledge and enable validation and construction of models. The present study focuses on the near‐wake of a model HAWT in both axial and yawed flow conditions. At three downstream planes parallel to the rotor plane, single‐sensor hot‐film traverses are made. The phase‐locked unsteady three‐dimensional flow velocity vector is determined by a novel data reduction method. A series of two papers discusses the near‐wake aerodynamics of a model HAWT. The main goals are to obtain a detailed understanding of the near‐wake development and to arrive at a base for model construction and validation. The first paper presents the experimental setup, data reduction and the results for the baseline case (axial flow conditions). In the second paper, the results for the yawed flow cases are presented and the effect of yaw misalignment on the near‐wake development is discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

In situ TEM nanoindentation and dislocation-grain boundary interactions: a tribute to David Brandon

As a tribute to the scientific work of Professor David Brandon, this paper delineates the possibilities of utilizing in situ transmission electron microscopy to unravel dislocation-grain boundary interactions. In particular, we have focused on the deformation characteristics of Al–Mg films. To this end, in situ nanoindentation experiments have been conducted in TEM on ultrafine-grained Al and Al–Mg films with varying Mg contents. The observed propagation of dislocations is markedly different between Al and Al–Mg films, i.e. the presence of solute Mg results in solute drag, evidenced by a jerky-type dislocation motion with a mean jump distance that compares well to earlier theoretical and experimental results. It is proposed that this solute drag accounts for the difference between the load-controlled indentation responses of Al and Al–Mg alloys. In contrast to Al–Mg alloys, several yield excursions are observed during initial indentation of pure Al, which are commonly attributed to the collective motion of dislocations nucleated under the indenter. Displacement-controlled indentation does not result in a qualitative difference between Al and Al–Mg, which can be explained by the specific feedback characteristics providing a more sensitive detection of plastic instabilities and allowing the natural process of load relaxation to occur. The in situ indentation measurements confirm grain boundary motion as an important deformation mechanism in ultrafine-grained Al when it is subjected to a highly inhomogeneous stress field as produced by a Berkovich indenter. It is found that solute Mg effectively pins high-angle grain boundaries during such deformation. The mobility of low-angle boundaries is not affected by the presence of Mg.Special title: Advanced Materials and Characterization: Proceedings of the Brandon Symposium; Guest Editors: Wayne D. Kaplan and Srinivasa Ranganathan     

Influence of thermal ageing on the stability of polymer bulk heterojunction solar cells

A new approach is presented in order to improve the thermal stability of polymer: [6-6]-phenyl C₆₁ butyric acid methyl ester (PCBM) bulk heterojunction solar cells. The central idea in this approach is the use of a polymer with high glass transition temperature (T_g), well above the normal operating temperatures of the devices. In this paper, a PPV-derivative with a T_g of 150 °C was used as an electron donor and the thermal stability of the obtained solar cells was compared with solar cells based on the reference material poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene vinylene] (MDMO-PPV) with a T_g of 45 °C. The use of the material with higher glass transition temperature resulted in a significant improvement of the thermal stability of the photovoltaic parameters. Furthermore, a systematic transmission electron microscope (TEM) study demonstrates that the better thermal stability of performance coincides with a more stable active layer morphology. Both improvements are attributed to the reduced free movement of the electron donor material (PCBM) within the active layer of the solar cell.     

Pixel selection for near-infrared chemical imaging (NIR-CI) discrimination between fish and terrestrial animal species in animal protein by-product meals

This paper proposes a method based on near-infrared hyperspectral imaging for discriminating between terrestrial and fish species in animal protein by-products used in livestock feed. Four algorithms (Mahalanobis distance, Kennard-Stone, spatial interpolation, and binning) were compared in order to select an appropriate subset of pixels for further partial least squares discriminant analysis (PLS-DA). The method was applied to a set of 50 terrestrial and 40 fish meals analyzed in the 1000-1700 nm range. Models were then tested using an external validation set comprising 45 samples (25 fish and 20 terrestrial). The PLS-DA models obtained using the four subset-selection algorithms yielded a classification accuracy of 99.80%, 99.79%, 99.85%, and 99.61%, respectively. The results represent a first step for the analysis of mixtures of species and suggest that NIR-CI, providing valuable information on the origin of animal components in processed animal proteins, is a promising method that could be used as part of the EU feed control program aimed at eradicating and preventing bovine spongiform encephalopathy (BSE) and related diseases.     

Characterisation of aquatic humic and non-humic matter with size-exclusion chromatography--organic carbon detection--organic nitrogen detection (LC-OCD-OND)

Size-exclusion chromatography in combination with organic carbon detection (SEC-OCD) is an established method to separate the pool of NOM into major fractions of different sizes and chemical functions and to quantify these on the basis of organic carbon. One specific approach, also known as LC-OCD-OND, is based on the Gräntzel thin-film UV-reactor. This approach is described with recent improvements in fraction assignation (humic substances, biopolymers, building blocks, low molecular weight organic acids and neutrals, hydrophobic organic carbon), the coupling of a novel organic nitrogen detector (OND), and an improved diagram for the characterisation of aquatic humic substances (HS-diagram). The diagram replaces the operational distinction between humic and fulvic acids by a continuum ranging from aquagenic fulvic acids to pedogenic humic acids.     

Clinical evaluation of ultra-high-field MRI for three-dimensional visualisation of tumour size in uveal melanoma patients,with direct relevance to treatment planning

Objectives

To assess the tumour dimensions in uveal melanoma patients using 7-T ocular MRI and compare these values with conventional ultrasound imaging to provide improved information for treatment options.

Materials and methods

Ten uveal melanoma patients were examined on a 7-T MRI system using a custom-built eye coil and dedicated 3D scan sequences to minimise eye-motion-induced image artefacts. The maximum tumour prominence was estimated from the three-dimensional images and compared with the standard clinical evaluation from 2D ultrasound images.

Results

The MRI protocols resulted in high-resolution motion-free images of the eye in which the tumour and surrounding tissues could clearly be discriminated. For eight of the ten patients the MR images showed a slightly different value of tumour prominence (average 1.0 mm difference) compared to the ultrasound measurements, which can be attributed to the oblique cuts through the tumour made by the ultrasound. For two of these patients the more accurate results from the MR images changed the treatment plan, with the smaller tumour dimensions making them eligible for eye-preserving therapy.

Conclusion

High-field ocular MRI can yield a more accurate measurement of the tumour dimensions than conventional ultrasound, which can result in significant changes in the prescribed treatment.

     

Low-voltage low-power fully-integratable automatic gain controls

This paper discusses the design of low-voltage low-power fully-integratable automatic gain controls. Four different AGCs are presented, all consisting of three elementary building blocks: a controlled amplifier, a comparator and a voltage follower. Their design is treated separately. As an example, the final section describes an automatic gain control for hearing instruments, realized in a bipolar process.     

The effect of shear deformations in floorbeams on the moment distribution in orthotropic plated bridge decks

Floorbeams of orthotropic plated bridge decks are generally elements with a low slenderness, especially in the case of railway bridges. When loaded, such elements generate not only flexural deformations but shear deformations as well. Depending on the configuration, these shear deformations can be considerably large and should certainly not be neglected. In a design according to the Pelikan-Esslinger method, this deformation is taken into account in the second stage of the calculation of the orthotropic deck. At this stage, the additional bending moments, shear forces and floorbeam reactions due to the floorbeam flexibility are evaluated. The deflection of a directly loaded floorbeam creates a distribution of the load to adjacent non-loaded floorbeams. In addition, the deflection will affect the longitudinal ribs, increasing the sagging moments at midspan and decreasing the bending moments at the supports of the ribs provided by the floorbeams. In this paper a method is developed to take the shear deformation in the floorbeam into account, thus correcting the Pelikan-Esslinger method. The correction is especially important since the floorbeam web is frequently further weakened by cutouts for the longitudinal ribs and in some cases additional cope holes. The floorbeam web resisting the shear deformation is further reduced by these openings, increasing the importance of shear deformations even for more slender floorbeams. The validity of the proposed method is checked by full finite element calculation using shell elements which inherently comprise shear deformation. The effect of the correction on the calculations in the second stage of the calculation are relatively small for the floorbeam reactions; on the contrary, it can be quite large for the additional bending moments in the longitudinal ribs. In that case, the effect is worth considering.     

Microtubule gliding and cross-linked microtubule networks on micropillar interfaces

We combined biochemical and topographical patterning to achieve motor-driven microtubule gliding on top of microfabricated pillar arrays with limited and controllable surface interactions of gliding microtubules. Kinesins immobilized on pillar heads pushed microtubules from the top of one micropillar to the next bridging up to 20 mum deep gaps filled with buffer solution. Distances of more than 10 mum were by-passed, and microtubule buckling was occasionally observed. The velocity distributions of microtubules gliding on poly(dimethylsiloxane) (PDMS) pillars, on flat PDMS, and on glass were found to be different, most likely due to topological and/or chemical differences between the substrates. We also used pillar arrays to suspend cross-linked microtubule networks, whose structural characteristics were governed by the topographical characteristics of the pillar pattern. These experiments open new possibilities to study the dynamics and the self-organization of motor/microtubule networks in defined topologically structured environments.