The lift that keeps a plane airborne comes from air moving swiftly over the
wings. Air flows faster over the top of the curved wings than under the bottom,
a phenomenon that sets up a difference in pressure and generates lift.

Friction works against this process, dragging back and slowing down the
“boundary” layer of air closest to the surface of the wing. During takeoff, the
effect of friction is relatively insignificant. As an aircraft comes in to land,
however, it is typically travelling at less than half the takeoff speed, and the
loss of momentum caused by friction in the boundary layer is more significant
because the air is already moving more slowly over the wings. This, says
Wygnanski, can result in the boundary layer losing so much momentum that it
literally slips off the back of the wings, causing a potentially fatal loss of
lift.

Boosting the momentum of this surface layer is the key to making it stick to
the wings during landing, claim the researchers. The system they have devised
consists of a pump that fits inside the wing and blows out pulses of air through
a thin slot along the wing’s leading edge. This creates small pockets of
turbulent air or vortexes on the surface. The vortexes mix the slower air at the
boundary with the layer of fast air directly above it. This, says Wygnanski,
transfers momentum from the fast stream to the surface layer and has been found
to delay and even prevent flow separation.

A prototype wing has been tested in a wind tunnel at the Illinois Institute
of Technology. The pressure distribution around the wing was found to improve
lift at speeds approaching half the speed of sound, which is at the slower end
of typical aircraft speeds.

Engineers have used various methods to control the boundary layer before. For
example, a system used with the Lockheed F-104 Starfighter jet blew a continuous
stream of air over the wings. This system proved too power-hungry and expensive
for commercial airliners, however.

Wygnanski says his system is much more energy efficient. The oscillating
pulses mean that only a small amount of air needs to be blown through the
system—equivalent to around 10 per cent of the extra momentum a steady
blower would need to supply to achieve the same mixing effect.

Richard Wlezien at NASA Langley Research Center’s flow modelling and control
department in Virginia says the technology is very promising, but needs to be
validated in conditions which simulate flight more closely before it can be used
on commercial aircraft. “The Illinois tests were at the lower end of real flight
conditions,” he says. NASA plans to carry out trials of the technology next
year.

The risk of theft and damage to bicycles parked at railway stations puts
commuters off using bikes, says Klaus Vosseberg of the institute’s storage and
transport systems department, which built the prototype. According to Vosseberg,
around 300 000 bicycles are stolen each year in Germany, most of them from
railway stations, college campuses and shopping centres. By providing secure,
covered bike storage, the researchers hope to reduce bicycle theft and encourage
“bike and ride” initiatives.

The developers envisage that large versions could store over 3000 bikes,
although their prototype is less ambitious, with space for 16. Each space is 2
metres deep, 1.2 metres high and 0.7 metres wide. So the prototype is around 7.5
metres long, 2.7 metres wide and 3.4 metres high.

The design consists of a microprocessor-controlled carousel, equipped with
special bike supports that prevent the frames from being damaged. After being
rolled into a recess on the support, the front wheel of the bicycle is held in
place by a spring-loaded roller. The carousel then transports the bikes to the
various parking levels. The bike shed can be built into existing station
lock-ups at an estimated cost of DM2500 (ÂŁ1100) per parking space. The
system is equipped with an automatic ticketing system similar to those used in
car parks.

According to the German Railways, bicycle “garages” should be an important
feature of railway stations. Apart from reducing theft, they could help keep
bikes off station concourses, where they can cause an obstruction.

When seawater is mechanically agitated, the deeper, warmer water mixes with
the colder surface water. This process should prevent ice from building up, says
Andersen, who has tested the prototype in Canada.

The machine is 7.5 metres long. It consists of a floating helical roller,
similar to a large corkscrew, supported at either end by pontoons. The roller is
rotated in the water by an electric motor to create a train of waves several
hundred millimetres high.

According to Andersen, artificial waves have a higher height-to-length ratio
than natural waves, making them better able to displace water. As a result, more
water is drawn up from the warmer depths of the sea. Andersen says that greater
mixing occurs at the surface, just where the de-icing effect needs to be the
greatest. With a conventional propeller-driven de-icing system, mixing is less
effective because particle velocities tend towards zero near the surface, he
says.

Trials of Andersen’s system in Oshawa harbour, Ontario, have produced
artificial waves nearly 150 millimetres high, exceeding Andersen’s theoretical
projections by half. The wave train measured over 15 metres in width and 100
metres in length, and would certainly have had an effect on ice formation, he
says. Andersen also says that it takes very little energy to produce the
waves.

In Toronto harbour, a single main access channel makes the ferry berths
particularly vulnerable to ice. Ken Lundy, manager of works and chief engineer
with the Toronto Harbour Commissioners, says Andersen’s wave generator could be
used where a build up of ice in the berths tends to damage the quay. “The
machine worked well at pushing ice out of the way at Oshawa,” he says.

Meanwhile, an environmental group based in Atlanta is building a version of
the generator measuring 5 metres long to improve water quality in lakes. They
believe that better aeration will reduce problems such as excessive algal bloom,
weed growth and eutrophication.

“Most conventional machines, such as bubbler systems and wind-driven
turbines, only have an effect on vertical columns of water,” says Andersen. His
device should work over much wider areas. The mixing action of the artificial
waves extends to a depth of half the wavelength, which is equivalent to around
600 millimetres for the wave generator projector. So the device should not stir
up sediments from the lake bed.

Now German researchers have added another vital piece to the jigsaw by
linking a number of isolated nerve cells together on the surface of electronic
microchips for the first time.

Several groups have managed to grow bundles of nerve cells, or neurons, on
silicon chips (Technology, 30 March, p 20). But Peter Fromherz, professor of
membrane and neurophysics at the Max Planck Institute for Biochemistry in
Munich, says his is the only team to couple isolated neurons directly to
semiconductor transistors.

Fromherz’s first experiments were with neurons taken from leeches. Although
they could transmit electrical signals to the microchip, the leech cells could
not be persuaded to form synapses—the electrical connections that transmit
signals between neurons. By swapping the leech cells for neurons taken from
snails, Fromherz says he can now persuade the neurons to link up and build more
complex brain-like structures.

The next step is to train the synapses to link up in a way that will allow
the Max Planck team to investigate precisely how the nerve cells talk to each
other. They plan to stimulate one snail cell at a time to see how the other
cells respond. Neurons are thought to send signals when the electrical activity
reaching them from other cells in the brain reaches a threshold level.

Voltage changes in the cell membranes have previously been detected using
voltage-sensitive dyes, such as amphiphilic hemicyanine. This varies in
fluorescence according to the strength of the electrical signal. But the
sensitivity of the dye is relatively low, and it becomes toxic when it
fluoresces, says Fromherz. By coupling neurons to transistors, Fromherz and his
team hope they can watch how each cell behaves in an organised network of
thousands.

The junction between the neuron and the transistor is achieved by positioning
the cell so that its plasma membrane acts as the “gate” contact of the
transistor. The connection is maintained by immersing the system in an
electrolyte. The voltage in the cell is controlled by impaling it on a tiny
charged needle.

The neurons are encouraged to grow along pathways coated with adhesive
proteins that organise nerve cells into networks in the brain. The tracks are
about 10 micrometres wide and are laid down on the silicon using
photolithography masking techniques, similar to those used to create
conventional microchips.

The chips have been miniaturised so that a single neuron covers around 16
closely packed transistors. German electronics giant Siemens has developed a
microchip packed with up to 2000 transistors. This will allow Fromherz and his
team to lay down a network of snail neurons of a similar complexity to a leech
brain. The corrosion-resistant chip has been specially designed to work in the
saline solutions used to promote cell growth.

Meanwhile, the Max Planck team has perfected a technique for measuring the
distance between the cell membrane and the chip to which it is linked. According
to Fromherz, this distance—which is typically 70 micrometres—is
crucial for controlling the voltage in the cell. The researchers shine light on
the surface, and that light is refracted differently depending on the distance
between the chip and the neuron. So the wavelength of the reflected light
varies, showing up as different colours.