Biomedical Engineering Reference
In-Depth Information
graphically describe how they perceive the
design problem and propose conceptual solu-
tions. Each worksheet is analogous to a bee doing
its waggle dance: Other students either agree and
maybe get inspired or actively go into a discus-
sion where they argue against the proposals on
the worksheet. This results in more distributed
learning and faster dissemination of knowledge.
The students are confronted with many partial
solutions to design problems similar to their own
and can readily determine which ones to be
inspired by. The average quality of the design
solutions is better than if the student groups had
worked alone without insight into the work of
the other groups. Instead of fearing that the other
students will steal their ideas, Hansen and Lenau
found that everyone performed better.
Complex ventilation systems run within the nest
either as (1) open systems with chimneys and
ventilation shafts or (2) closed systems, wherein
gas exchange occurs in special galleries close to
the outer surface. The interaction among tempo-
ral variations in wind speed, wind direction,
and turbulence caused by the morphology of the
ventilation system in the termite mound has
been suggested to cause a tidal gas exchange in
the mound similar to that found in human lungs
[21]
. Such passive ventilation systems have sig-
nificant biomimetic potential for use in manag-
ing the internal climate of buildings. Similar
wind-induced ventilation systems have been
found in large underground nests of leaf-cutter
ants, comprising millions of individual
workers
[22]
.
The structure of these giant nests is impres-
sive, but equally fascinating is the question of
how such elaborate structures can be constructed
by individual ants working without any central-
ized and hierarchical supervision. Recent
research shows that the nest structure appears
as an emergent property from the individual
actions of thousands of workers that indirectly
communicate through modifications of the envi-
ronment
[20, 23, 24]
. The concept that the actions
of individuals modify the environment, which
in turn modifies the behavior of other individu-
als, is known as
stigmergy
. One example of how
stigmergy can result in self-organization can be
seen in the ant “cemeteries” found outside the
nests of many species. The large aggregations of
dead ants result from the corpse-removal behav-
ior of individual ants, who pick up corpses and
then drop them as a function of the density of
corpses in the vicinity
[23]
. This means that once
a pile of corpses is starting to build up, the prob-
ability that further corpses are dropped on it
increases, which in turns results in all corpses
being dropped in a few large aggregations only.
A similar example of stigmergy is seen in
wall building by the ant
Leptothorax tuberointer-
ruptus
. These ants construct a simple circular
wall around the colony at a certain distance
13.4 COORDINATION OF LARGE
CONSTRUCTION WORK
Several different species across the animal king-
dom build structures either from internally
secreted building materials (such as silk used by
caterpillars to construct cocoons or by spiders in
their impressive aerial webs) or from externally
collected materials (such as stones and leaves
in the case of caddisfly larvae or twigs in bird's
nests). The majority of animal constructions are
built by individual animals for shelter, protec-
tion, mate attraction, or capturing prey. How-
ever, the most impressive examples of animal
architecture are the result of the collaboration
of a large number of individuals. For instance,
termite nests (also known as
mounds
) can reach
heights of several meters on the African savan-
nah, the heights exceeding more than 200 times
the size of the termite workers. In human terms,
a termite mound is as high as the Empire State
Building in New York.
Termite mounds are not only impressive
when viewed from the outside, but they also
contain many sophisticated internal adaptations
to maintain a constant indoor climate
[20]
.
