Measuring miniature eye movements by means of a SQUID magnetometer

A new technique to measure small eye movements is reported. The precise recording of human eye movements is necessary for research on visual fatigue induced by visual display units.1 So far all methods used have disadvantages: especially those which are sensitive or are rather painful.2,3 Our method is based on a transformation of mechanical vibrations into magnetic flux variations. In order to do this a small magnet is embedded in a close-fitting soft contact lens. The magnetic flux variations caused by eyeball movements during fixation are measured by means of a SQUID magnetometer. The recordings show the typical fixation pattern of a human eye. This pattern is composed of three kinds of movements: saccades, drift and microtremor. The last-mentioned type of movements are displacements in the order of 2 μm. It is possible to distinguish between movements which are perpendicular to each other

A new approach for managing the morphology and ecology of a coastal plain estuary

An expert team appointed by the Port of Antwerp proposed the idea of morphological dredging, aiming at steering the estuarine morphology. A pilot project was implemented, modifying the shape of a sandbar by disposing dredged material on the eroded tip of the Walsoorden sandbar. The new shape would help restoring the degraded ecology and morphology, but it also aims at modifying the flow on a crossing in the navigation channel, reducing the dredging effort if the self-dredging capacity of the flow could be increased on it.A research programme about the feasibility of the idea was conducted in 2002 and 2003, combining several tools: desk studies on historical changes with maps, field measurements, physical scale model tests and numerical simulations. The expert team concluded in 2003 that none of the results denied the feasibility of the new disposal strategy, although final judgement would only be possible after the execution of an in situ disposal test.During one month at the end of 2004, 500.000 m³ of sand was disposed with a diffuser in relatively shallow water at the seaward end of the sandbar. The experiment was well monitored with frequent multi-beam bathymetric surveys, LIDAR-flights, marked sediment tracing, in-situ sediment measurements and ecological monitoring. After one year, it was concluded that the test was a success from morphological viewpoint. Also the ecological monitoring did not reveal any significant negative changes in trends due to the disposal test.In 2006 a new disposal test was executed, using the traditional technique with hopper dredgers. Due to practical limitations, the disposal (again 500.000 m³) was spread over a 3 months period. The new experiment was again thoroughly monitored for morphology as well as for ecology. Up to now, the morphological results of the second test are satisfying. The ecological results will become available during the first half of 2007, with the preliminary results not showing any negative impact

The use of a SQUID magnetometer for middle ear research

A new technique is described for the measurement of vibrations in the temporal bones of an isolated middle ear. The precise recording of vibrations in the middle ear is of importance for the construction and improvement of a middle ear prosthesis.1 The method of measurement is based on a transformation of mechanical vibrations into magnetic flux variations. This is performed by attaching a small piece of permanent magnetic material to the eardrum or middle ear ossicles. The magnetic flux variations caused by vibrations of the eardrum or ossicles during application of sound can be measured by means of a SQUID magnetometer.\ud \ud Measurements showed that it is possible to measure vibratory displacement amplitudes of the eardrum down to about 10−10 m in a frequency range between 200 Hz and 10 kHz, although the acoustical and magnetometer conditions were not optimal. The method offers several advantages compared to already existing methods.2–5,

Morphological management in estuaries conciliating nature preservation and port accessibility

In 1999, Flanders and The Netherlands agreed to set up a common strategy for managing the Scheldt River in its estuarine reach. In 2002, both parties signed a memorandum of understanding in which was defined a ‘Long Term Vision’ strategy and its objectives. One of these is the preservation in the Western Scheldt of a dynamic and complex flood and ebb channel network, the so-called ‘multi-channel system’. The present trend, a continuation of past natural morphological evolutions combined with human interference (poldering, dredging and other river works) may jeopardise this objective. An expert team appointed by the Port of Antwerp proposed the idea of morphological dredging for curbing this negative trend, aiming at steering the estuarine morphology. In a first phase, sediment from dredging works could be used to reshape sandbars where needed. One case study is discussed in this paper, the aim being to reconstruct the eroded tip of a sandbar at a bifurcation so that the flood and ebb flows would be perseved, a condition to maintain the multi-channel system in the reach. The strategy would not only cut back on the ongoing degradation of the ecological and morphological values of the estuary, but it could also possibly help reducing the quantity of material to be dredged on the crossings by increasing the scouring or self-dredging capacity of the flow. A diffuser-type device was used to disperse the dredged material in a controlled way in shallow water along the sandbar edges. In 2002-2003, the new disposal strategy has been investigated by Flanders Hydraulics Research as a pilot project (Plaat van Walsoorden). The research programme combined three tools: field measurements, physical scale models and 3D numerical models. The results of the research work confirmed the feasibility of the idea. However, the Port of Antwerp Experts concluded that a real life (in situ) disposal test was required to give final proof of the feasibility of this new disposal strategy. At the end of 2004, 500,000m³ of sand was disposed at the seaward tip of the shoal of Walsoorden using a diffuser. The main idea was to modify the morphology of this sandbar by disposing dredged material very precisely. The amount of 500,000m³ was chosen because it is large enough to see an effect of the disposed sediment, while it is small enough to be reversible if something would go wrong. To evaluate the success of this in situ test, an extensive monitoring programme was set up, including bathymetric surveys, ecological monitoring, sediment tracing tests and sediment transport measurements. After one year of monitoring the disposed sediments, it can be concluded that the experiment is very successful. The morphological monitoring showed that almost 80% of the disposed sediments is still on the disposal location after one year. The ecological monitoring did not reveal any significant negativeimpact, neither in the intertidal areas, nor in the subtidal areas. This in situ test confirmed the feasibility of the proposed disposal strategy. An estimated volume of 4 to 5 million m³ could be disposed here to reach the proposed objectives, representing more than half of the volume dredged yearly in the Western Scheldt