Net: not so vulnerable
A key finding from researchers who have teased out the structure
of the Internet during the past half-dozen years has been that that, though
the Internet is resistant to random failures, attacks targeting the largest
hubs could fragment the network (see Five
percent of nodes keep Net together, Hubs
increase Net risk).
A new study
by researchers from the California Institute of Technology, the University
of Adelaide in Australia, Internet2, The Institute of Physical and Chemical
Research in Japan, and AT&T Labs, however, shows that research describing
the scale-free nature of the Internet has not captured the whole picture.
In light of the new findings, it looks like the Internet is fairly
resilient to attacks.
The study showed that the Internet's network of routers, which
controls the flow of data between computers connected to the Internet,
is different than the scale-free structure of Web sites and the connections
between them. While scale-free networks have a few highly-connected sites,
or hubs, in the center and many peripheral sites with far fewer connections,
the physical router network that underpins the Internet has highly connected
hubs at its periphery and less well-connected central hubs, making it
resistant to targeted attacks.
The study took performance, constraints and trade-offs into account.
In contrast, the scale-free approach takes a statistical physics perspective
that deliberately omits particular factors of specific networks. The researchers
based their analysis on the structure of the Abilene
network, which is the backbone of the Internet2 academic network.
(The "Robust yet Fragile" Nature of the Internet, Proceedings
of the National Academy Of Sciences, October 3, 2005)
Cheap solar cells get efficient
Plastic solar cells promise to dramatically lower the cost of
generating electricity from sunlight -- once researchers figure out how
to make them more efficient.
Plastic solar cells tend to capture from 1 to 3 percent of the
energy contained in the sunlight that hits them, while standard, relatively
expensive silicon solar cells capture as much as 30 percent.
Researchers from the University of California at Los Angeles and
the National Renewable Energy Laboratory have improved the picture with
solar cell that is 4.4 percent efficient. The key to the efficiency
boost is giving the blend of plastics, or polymers, more time to dry.
The longer drying time allows the polymers to self-organize, increasing
polymer mixing and reducing electrical resistance.
Making plastic solar cells using the method is relatively easy,
paving the way for inexpensive plastic solar cells with high enough efficiencies
to be commercially viable.
The advance is the latest in a string of solar energy research
improvements and breakthroughs, including a method of spraying
on solar cell material, a material that increases efficiency by converting
energy from the full
spectrum of sunlight and a device that doubles potential solar efficiency
by generating twice
as much electricity per captured photon.
(High-efficiency Solution Processable Polymer Photovoltaic Cells
by Self-organization of Polymer Blends, Nature Materials, October
Swimming blood cells
Scientists have turned red blood cells into microbial
cyborgs by equipping them with artificial filaments and using magnetic
fields to cause the filaments to propel the cells.
The French National Center for Scientific Research (CNRS) and
Harvard University researchers created the artificial microbes in order
to better understand swimming at the microscopic level, where swimming
through water is the equivalent of swimming through honey at the human
The red blood cells' filaments consisted of one-micron-diameter
magnetic particles strung together and attached with DNA molecules. A
steady magnetic field acted to keep the artificial flagella extended while
a second, oscillating magnetic field moved the filaments to produce the
necessary swimming motions.
The method promises to be useful in precisely positioning microscopic
devices and biological entities like blood cells and in pumping tiny amounts
of fluids through biochips.
(Microscopic Artificial Swimmers, Nature, October 6, 2005)
Microbes drive sensor
Scientists are looking for ways to use simple chemistry techniques
to make electronics that are smaller, faster and cheaper than today's
chip-based devices. Researchers have recently begun using microbes in
this effort, both as templates for wires and electrodes, and also as living
components whose biological responses can play a role in the devices'
Researchers from the University of Nebraska have made a prototype
humidity sensor using Bacillus cereus bacterium coated with gold nanoparticles.
The researchers coated 5-micron long bacteria with 30-nanometer-diameter
gold nanoparticles and used a pair of thus bedecked bacterium to bridge
gold electrodes. A micron is one thousandth of a millimeter and a nanometer
is one thousandth of a micron.
The device acts as a humidity sensor because a decrease in humidity
shrinks the bacterium, shrinking the spaces between the nanoparticles
on its surface, which decreases the electrical resistance across the bacterium.
Decreasing the humidity from 20 percent to 0 percent increased the current
40 fold, making for a relatively sensitive sensor.
The work paves the the way for sensors and other devices that
combine the biological properties of living microorganisms with the electrical,
optical and/or magnetic properties of nanoparticles. Such devices promise
to be relatively inexpensive because they can be constructed using simple
chemistry rather than chipmaking methods.
(Self-assembly of Nanoparticles on Live Bacterium: an Avenue to
Fabricate Electronic Devices, Angewandte Chemie, October 10, 2005)
Bits and pieces
A laser-driven shape-shifting plastic device snares
blood clots; a rotary
motor brings molecular machines another step closer to reality; tiny
solid-state electronic heaters
and coolers bring temperature control to biochips.