Plasma Reduces Drag, Enhances Lift
Airplanes may some day travel the skies enveloped in glowing layers of plasma, thanks to research that shows that plasma can dramatically improve air flow. The result comes from experiments on cylinders equipped with radio frequency plasma generators. The plasma decreased the production of drag-inducing, energy-wasting vortexes behind the cylinder. Although plasma generators require energy to operate, the energy savings that come with reduced drag would far outweigh the cost of running the generators. In a recent experiment, plasma discharges decreased drag on a cylinder by 8%. This is a significant drag reduction, which could lead to major fuel savings if the technology can be successfully applied to aircraft. In addition, the technique could be useful in other industrial applications where gas flow is important.
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EA10480
Team spirit links millions of online gamers to urban street gangs
What do the 11 million players of the world's most popular Internet
game World of Warcraft, have in common with street-gang members in
downtown Long Beach, California? They are both driven by the same team
spirit, according to a recent study by an interdisciplinary team of
physicists, gaming experts, and gang sociologists. In 1828 Bulwer-
Lytton Pelham said "It is literally true in the systematised roguery
of London, that 'birds of a feather flock together", an idea which
stems back to ancient Greek times in the apocryphal book of
Ecclesiasticus and which underpins much of our current theories about
how animals group or flock. However, while members of a given species
(e.g. birds) undoubtedly group together, the researchers found that
such groups actually prefer a diversity of *characters*. It is like a
successful Superbowl team -- they are all football players, yet they
would be doomed to failure if they were all quarterbacks, no matter
how great they were individually. Sounds reasonable, but proving it
was hard since it required state-of-the-art databases and also
exhaustive comparisons between team-based and kin-based models. The
results are not only new for sociology, they represent new physics in
that a full mathematical description requires generalizing coalescence-
fragmentation theory to include the distinct 'character' of individual
objects. Practical applications could eventually include the
predictive evolution of human groups in other online and offline
scenarios, including terrorist activity.
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LA12436
A model of navigation in social networks deciphered
Two groups, one in Switzerland (EPFL) and the other a collaboration
between Israel (Bar-Ilan) and US (Clarkson) universities,
simultaneously and independently unfolded a paradigmatic model of
searching in social networks, partly unsolved for almost a decade.
It is well known that individuals in a social network are separated by
just "six degrees", that is, six steps on the network. Yet the
question of how these short paths are actually found is still open. In
a seminal paper published in 2000, Jon Kleinberg proposed a social
network model in which long-range links render a social network
``small-world’’, and at the same time provide the means for efficient
delivery of messages (Nature 406, 845). However, only approximate
estimates, in the form of upper and lower bounds, were known for the
actual delivery time. After almost a decade, the two groups have
finally succeeded in deriving an exact expression for the dependence
of the delivery time on the number of individuals, partly confirming
Kleinberg’s conjectures on the nature of the long-range links that
makes the search process effective. Remarkably, the two groups have
used different mathematical approaches, nevertheless reaching the very
same conclusions. The proposed solution has also enriched our
understanding of the conditions that make networks navigable: it
addresses the issues of network construction and maintenance costs and
the possibility of losing messages, which are further criteria that
must be taken into account for network models and search algorithms to
be relevant for real networks.
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LE11894
Splitting spacetime back into space and time as a road to Quantum
Gravity
Despite the tremendous individual successes of General Relativity and
Quantum Field Theory, conventional approaches at merging them in order
to construct a theory of Quantum Gravity generally fail. Petr Horava
has recently proposed that such difficulties might be overcome by
refraining from treating space and time on equal footing at small
scales, with the hope of arranging for an approximate recovery of the
notion of spacetime and the related symmetries (Lorentz invariance)
only at relatively low energies.
In our article we begin to connect these abstract ideas with
observational reality: based on Horava's initial proposal we develop
step by step a theory that in principle has enough richness to be
compatible with experiments. It contains an adjustable Newton's
constant and an independently adjustable cosmological constant. The
departure of the theory from the standard spacetime picture is
characterized by a relatively small set of coupling constants, and
kept under tight control. There are still many detailed precision
tests that this model would have to pass before physicists would
consider it a serious candidate for a quantum theory of gravity. At
present, it is promising and seems to have all the right ingredients.
