More Talk on Tasers

I am not surprised to see that the articles on the Taser electronic control device (ECD) [“How a Taser Works,” IEEE Spectrum,December 2007] by me and Patrick Tchou generated so much interest [see Forum, February 2008]. There are not many technical gadgets in the public eye that have had as much publicity, and certainly none have as much misinformation associated with them. Glenn Marin’s letter clearly explains why there is such a need for the ECD and why police departments throughout the English-speaking world have now standardized them.

Larry Fennigkoh’s letter is technically right on target. The pulse currents are very important in explaining the effectiveness of the ECD. The original drafts of the article included the details on the pulse currents. (Actually, the pulse charge—in microcoulombs—is the best metric of the muscle capture capability.) However, we were forced to remove these details from the article for reasons of space and clarity. The bar chart “What a Jolt” shows the pulse current, and the “Levels of Shock” graph has a comment that the current is packed into 100-microsecond pulses. Thus the article, while somewhat simplified, is not misleading in any way. The interested EE can find the detailed electrical specifications on the ECDlaw Web site.

I was a bit surprised by the comments of Martin Lurie. The introductory piece by Sandra Upson clearly discloses my relationship with Taser. The implication that the highly respected Patrick Tchou of the Cleveland Clinic (America’s top-rated heart hospital for 12 years running) would falsify data to promote a product is simply breathtaking. The suggestion that these were one-sided articles must be evaluated with the facts that they were the product of peer review by experts in the field (with no connection to Taser) and more than a year of extensive discussions separating the facts from the myths. With over 1.2 million human applications and a dozen published human medical studies, the scientific issues are now largely resolved.

Mark W. Kroll, Ph.D., FACC, FHRS

Crystal Bay, Minn.

Galileo a Loser?

Your article “No Payoff for Galileo Navigation System” [January 2008] takes the standard U.S. anti-European stance, which is disappointing (you don’t, for instance, report how far GPS is behind its promised timetable). Imagine you were a CEO of a French telecommunications company in 2002. Your CDMA network is synchronized by GPS, a system provided by the U.S. military, with no guarantees of performance. The U.S. military is preparing for war in Iraq and, because it is a war based on bogus claims, your country chooses not to participate. You are labeled “cheese-eating surrender monkeys” by the country supplying your satellite navigation system. The president of that country announces he can turn off the system whenever he wants. Wouldn’t you want a system provided by a company that guarantees a level of service?

The IEEE may be a U.S. organization, but it is also the de facto international EE organization. We international members deserve less insular reporting.

Andrew Dempster

IEEE Senior Member

Sydney, Australia

Cutting Down on CO₂

After reading “Restoring Coal’s Sheen” [Spectrum,January 2008] and “Synthetic Fuel From a Solar Collector” [Spectrum Online, January 2008], I said “Eureka!” It is possible to combine both great ideas—to produce synthetic fuel with the solar collector technology using the carbon dioxide generated by the oxyfuel process discussed in the coal article. I suggest that both groups working on those two projects (the United States’ Sandia National Labs and Sweden’s Vattenfall energy company) cooperate in order to develop a product that integrates the advantages of both. This way we will win twice: we will be able to produce electric energy in a cleaner way with a healthier atmosphere all over the planet, and we’ll be able to produce synthetic hydrocarbon fuels, allowing us to be less dependent on the fossil oil of dictatorship countries.

Moshe Goldstein

IEEE Member

Jerusalem

We Fell for Fall

IEEE Spectrum is the flagship magazine of an international organization, but frequently cultural biases from the United States slip in. Some can be amusing. In the article “Restoring Coal’s Sheen” in the January 2008 issue are found the words “Though Australia, until a new government was elected last fall…” Actually, Australia’s federal elections were in November, which is definitely late spring for the lower half of the world.

The bias does not end there. The term fall is one from American English, and I believe it refers to leaves falling in what Australians would call autumn. Australia has very few native deciduous trees, but there is one outstanding example. The flame tree keeps its leaves through autumn and winter, dropping them and covering itself in bright red flowers in late spring. It is a spectacular sight, but I am not sure it is enough to name a whole season after.

Michael O’Brien

Tarragindi, Australia

An Occupying Army

I can't understand how the propaganda for the new Afghan military academy, aka "East Point" ["Engineers Graduate From New Afghan Military Academy," January 2008] slipped into the pages of a widely known technical magazine. You found it politically correct to publish this article under the golden cover of “technical issues” (“The academy will graduate its first class of engineers this month”), presenting the good U.S. military personnel that assisted in building this little miracle. In my dictionary, when an army enters a country by force (usually called an invasion) and remains there, putting up a government, this act is known as occupation! This army can build schools, train personnel, and exploit a country’s wealth “for the sake of its citizens,” but it will always be an occupation army! Please treat this as a friendly but angry protest against issues that are better put aside when it is known that they will trigger political and not technical rivalry.

Dimitris Karavidas

Athens

Salad Bar of Doom

I was just getting started on the February 2008 issue and read the Back Story piece, “Dispatch From Down Under.” I was struck by Chris Barns’s explanation for the impact of internal combustion vehicles on the kangaroo population. While his version is prosaic, it lacks the ring of scientific credibility. Water vapor in the exhaust gases of internal combustion engines is just that: vapor. It’s going to drift and diffuse so much that it could not possibly concentrate its impact on the shoulders of the highways.

I spent a season in a remote part of the American Southwest and I was struck by the spring wildflower blooms on the desert. Every paved road had a dramatic colored border on each side. The wildflowers were at least four times as dense on the shoulders of the roads as they were 10 feet [3 meters] away from the shoulder. This was in an area that gets significant traffic in the summer months but is nearly empty the rest of the year, so in springtime there had not been more than two vehicles per day on many of these roads for months. So the idea that water vapor in the exhaust of vehicles causes the increase in vegetation just doesn’t hold water.

A much simpler explanation is that what little precipitation the area does see runs off the roads and soaks into the dirt at the shoulder. As a result, the shoulders would see substantially more moisture than the land only a few feet away. Another contributing factor may be that the road protects the moisture in the dirt beneath it from being wicked to the surface and evaporated. So the areas at the shoulders of paved roads would see more moisture, and some of that moisture would be essentially “banked” under the edge of the road for use later in the season. This would produce a very localized increase in vegetation. I expect that the same phenomenon is responsible for the increase in vegetation along the shoulders of roads in the Australian outback. Thus, even if all the vehicles were changed to battery-powered, emissions-free propulsion, Joey would still be drawn to the roadside salad bar of doom.

I’d still love to go cuddle a baby kangaroo, though.

Michael Antoniak

IEEE Member

Severna Park, Md.

The Cost of Solar Energy

I’m writing you about “How Free Is Solar Energy?” [The Data, February 2008]. In the article you report the average daily solar radiation in kilowatt-hours per square meter per day. However, the data is used to evaluate the energy that the PV can produce without taking into account the PV efficiency. At present, commercial PV panels have efficiencies between 10 percent and 20 percent, so the data reported must be reduced by this factor. Moreover, if there is no maintenance (as is usual for roof plants), the dust and aging (without taking into account possible hail) cause a reduction of the efficiency during the life of the plant. The costs to produce energy should be evaluated taking into account these factors, and resulting payback periods are much longer than the 10 to 22 months as reported in the article. I’m working in the field of renewable energies, and I would be very happy if results could be as good as reported in the article, but unfortunately they are not yet.

Luigi Piegari

Naples, Italy

Associate Editor Sandra Upson responds: The efficiency was factored into the payback-time calculations and assumed to be 13 percent for multicrystalline-silicon cells, a detail we neglected to include in the text, although we did say that the calculations were for the “most common type of module.” For the sake of space and readability, we did not go into full detail about the assumptions underlying the calculations. You can find more information about how the numbers arose in our source materials by Vasilis Fthenakis and his colleagues.

The U.S. Department of Energy, by the way, cites a similar payback-time range. A 2004 DOE fact sheet on the energy payback for PV put multicrystalline-silicon payback times at just under four years using data from 1998 (assuming 12 percent efficiency), with a projection that it would fall to about two years within the decade. The head of the department’s solar program indicated in an interview that those numbers had indeed fallen over the intervening years, although the department had not yet updated its data.