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Physics News Update
Number 696, August 12, 2004 by Phil Schewe and Ben Stein

The Massive Northeast Blackout

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

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

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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