Text 122, 73 rader
Skriven 2004-08-13 22:27:42 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 696
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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 696 August 12, 2004
by Phillip F. Schewe, Ben Stein

THE MASSIVE NORTHEAST BLACKOUT of a year ago not only shut off
electricity for 50 million people in the US and Canada, but also shut off the
pollution coming from fossil-fired turbogenerators in the Ohio Valley. In
effect, the power outage was an inadvertent experiment for gauging atmospheric
repose with the grid gone for the better part of the day.  And the results were
impressive.  On 15 August 2003, only 24 hours after the blackout, air was
cleaner by this amount: SO2 was down 90%, O3 down 50%, and light-scattering
particles down 70% over "normal" conditions in the same area.  The haze
reductions were made by University of Maryland scientists scooping air samples
with a light aircraft.  The observed pollutant reductions exceeded
expectations, causing the authors to suggest that the spectacular overnight
improvements in air quality "may result from underestimation of emission from
power plants, inaccurate representation of power plant effluent in emission
models or unaccounted-for atomospheric chemical reactions."  (Marufu et al.,
Geophysical Research Letters, vol 31, L13106, 2004.)

THE LONG-TERM DYNAMICS OF THE ELECTRICAL GRID are examined in new studies
conducted by Ben Carreras and his colleagues at Oak Ridge National Lab, the
University of Wisconsin, and University of Alaska.  Engineers at the utilities
are of course always looking for ways to make their systems better, especially
in the aftermath of large blackouts, such as the event on August 14, 2003. 
These post-mortem studies typically locate the sources of the outage and
suggest corrective measures to prevent that kind of collapse again, often by
strengthening the reliability of specific components. Carreras argues that a
more effective approach to mitigating electrical disasters is build more
redundancy into the system.  And to do this, he says, you need to look at how
the electrical grid, considered as a dynamic system subject to many forces,
behaves over longer periods of time.  And to do this one needs to build into
any grid model social and business forces in addition to the physics forces
that govern the movement of electricity. Thus the Oak Ridge model not only
solves the equations (governed by the so-called Kirchoff laws) that determine
how much
 power flows through specific lines in a simulated circuit, but also build in
the strain on the system over time caused by an increasing demand for power,
the addition of new generators and transmission lines, and even elements of
chance in the form of weather fluctuations and the occasional shorting caused
by warm, sagging lines contacting untrimmed trees.  The model proceeds to let
the grid evolve, and for each "day" it computes possible solutions---in the
form of successful combinations of power generation levels and subsequent
transmission of that power over existing lines, some of which come in and out
of service---for the continued running of the grid.  The model derives a
probability curve for blackouts which matches pretty well the observed outage
data for North America.  The Oak Ridge scientists believe that their model
could be used by utility companies to test grid behavior for various
network-configuration scenarios, particularly those where the grid is operating
dangerously close to a cascade threshold.  (Carreras et al., Chaos, September
2004; carreras@fed.ornl.gov)

PROTEIN-BASED NANOACTUATORS can now be controlled rapidly and reversibly by
thermoelectric signals. In a living creature, contracting or relaxing of muscle
tissue is carried out by motor proteins called actomyosin. Scientists designing
nano-scale devices would naturally like to emulate the efficiency and
compactness of the muscle-moving molecules.  A key issue is the controlled
rapid activation of the protein motors through simple means. And that's what
researchers at Florida State University have done. They have set up a flow cell
in which motor molecules (which can remain viable for days when refrigerated)
can be thermally activated into motion in a controllable and reversible way
using only input wires which provide a controlled amount of heat. An important
goal of this work, according to Goran Mihajlovic (goran@martech.fsu.edu), is to
use the protein motors to power linear motion of nanowires; if the wires are
themselves magnetic (such as nickel), then the motion could be monitored via a
field sensor, such as a micro-Hall probe. The result would a bi-directional
nano-actuator, controlled electrically but powered with biological energy. 
Possible future applications include a role in bioanalysis chips and gene
delivery.  (Mihajlovic et al., Applied Physics Letters, 9 August 2004)

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 * Origin: Big Bang (1:106/2000.7)