APRIL'S ISSUE TANGLED WITH quantum braids in “Computing with Quantum Knots,” by Graham P. Collins. Readers also learned about new vaccines coming to market that promise to conquer childhood diarrhea caused by rotavirus, a frequent killer of young children in the developing world, in “New Hope for Defeating Rotavirus,” by Roger I. Glass.

Most interesting were reader responses to another health problem, depicted by Madhusree Mukerjee, about public health scientist Smarajit Jana's work in organizing sex workers to fight HIV in India [“The Prostitutes' Union,” Insights]. Some letters demonstrated that there are those who prefer to draw a sharply defined line between science and medicine, culture and politics—an impossible luxury when scientific knowledge is applied to ameliorating human ills. Robert L. Teeter e-mailed: “Do you really think that articles on prostitution are appropriate for what used to be a dignified and respected scientific magazine?” More opinions were closer to Andy Benton's, who wrote from Flourtown, Pa.: “Thank you for sharing Jana's story. He is truly a hero of our times.”


Steve Mirsky's application of “tiny backbone living in corrosive swamp” in “Short Takes” [Anti Gravity] to describe both a kind of carp and any member of the House ethics committee surely deserves at the least a tiny Pulitzer Prize for its succinctness, completeness and brevity.

Harry Ison
Bellingham, Wash.


“The Prostitutes' Union,” by Madhusree Mukerjee [Insights], betrays an irony: India, a country with one of the oldest and deepest-rooted organized religions in history, is perhaps the first to successfully apply a purely secular solution to a problem that may be older than religion itself. Imagine if the U.S. surgeon general came up with this idea. I think the firestorm of revulsion from the religious right would overwhelm all the public health considerations. And yet in India, religious leaders became part of the solution. How sad that we have not made life better for our own sex workers because of belief systems infected with pride. I guess that is the contradiction of “scientific” America.

Carey McConnell
Palm Harbor, Fla.


As magazine editors dedicated to educating the public about scientific and technological issues, you should not perpetuate misleading descriptions, as was the case in “Big Squeeze,” by Mark Fischetti [Working Knowledge]. The article described how an airplane wing produces lift thus: “...because the wing top is curved, air streaming over it must travel farther and thus faster than air passing underneath the flat bottom.” If so, how could a plane fly upside down with the flat surface on top and the curved surface on the bottom?

In fact, if a winglike object, such as a flat plate, is inclined with respect to the airflow (relative wind), the air will travel much faster over the surface away from the wind and slower over the other surface, giving rise to a pressure differential. This difference is dependent on the wing's angle of attack (angle of the wing with respect to the relative wind) but not on one surface being more curved than the other.

A better explanation of lift is: as a wing angled up with respect to the relative wind moves through a volume of air, it deflects downward a large amount of air above and below the wing. Thus, the wing exerts a downward force to accelerate this mass of air downward (Newton's second law). The air exerts an equal but opposite force upward on the wing (Newton's third law). This upward force by the deflected volume of air is the lift. (This force also produces drag.)

Klaus Fritsch
Department of Physics
John Carroll University
University Heights, Ohio

FISCHETTI REPLIES: Numerous readers wrote to correct a common but faulty explanation of how an airplane wing creates lift, noting that it has somehow persisted for years, even in textbooks. We wrote, “...because the wing top is curved, air streaming over it must travel farther and thus faster than air passing underneath the flat bottom. According to Bernoulli's principle, the slower air below exerts more force on the wing than the faster air above, thereby lifting the plane.”

Or not. As Fritsch points out, the key factor is the wing's angle of attack, not its shape. As for the topside curvature of many wings, some readers noted that Bernoulli's principle can add a small amount of additional lift. Others pointed out that stunt planes and certain fighter aircraft have wings that are flat on top and bottom (or have equivalently curved surfaces) so they can better fly upside down. And yet the “third law” explanation is not the full story either: according to NASA, the complex “turning” of airflow, both below and above the wing, is the real driver. For a vetting of both the Newtonian and Bernoullian explanations, see www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html


In “New Hope for Defeating Rotavirus,” Roger I. Glass indicated that two rotavirus vaccines, RotaTeq and Rotarix, have recently proved highly effective in clinical trials and are soon to be marketed in a number of countries. The RotaShield rotavirus vaccine has also been shown to be highly effective in clinical trials; his discussion on RotaShield is related only to its withdrawal from the market in 1999.

Now that new scientific evidence has demonstrated that RotaShield can be safely used in infants, BIOVIRx intends to bring RotaShield back to the market, subject to appropriate regulatory approvals. Our goal is to make it affordable, because we believe that is necessary for a rotavirus vaccine to have the greatest global impact on reducing morbidity and mortality.

Leonard P. Ruiz, Jr.
President and CEO, BIOVIRx, Inc.
Shoreview, Minn.


With regard to “Computing with Quantum Knots,” by Graham P. Collins, is it possible to simulate a quantum computer on a conventional computer, at least in theory? If not, perhaps some of the difficulty in artificial intelligence is because biological systems have somehow discovered ways to use quantum effects.

John J. Boyer
God Touches Digital Ministry
Madison, Wis.

COLLINS REPLIES: It is impossible to simulate a quantum computer efficiently on a conventional classical computer. The simulation would require a vast supply of hardware to run algorithms in parallel, or it would take an extremely long time. Some researchers, most notably mathematician Roger Penrose, have speculated that biological brains might use quantum computation, but physicist Max Tegmark has argued that in the physical environment of a brain, the quantum coherence required would decay far too quickly to have any effect on the firing of neurons.

ERRATA “An Antibiotic Resistance Fighter,” by Gary Stix, noted incorrectly that mice did not develop resistance to the antibiotic ciprofloxacin. The article should have stated that the bacterium Escherichia coli did not become resistant. It also remarked that blocking the cutting of the protein LexA might undermine “drug effectiveness” in other microbes besides E. coli. Rather preventing the clipping of LexA might undermine the evolution of drug resistance in other microbes.

“Sharp Shooter,” by Steven Ashley [Technicalities], stated that the APS sensor in the Sony R1 digital camera has a low signal-to-noise ratio. It has a high signal-to-noise ratio.

CLARIFICATIONS In “The Science behind Sudoku,” by Jean-Paul Delahaye [June], the grid for puzzle e in the “Variations on a Theme” box should have included outlines for the domino pieces. Without the lines, the puzzle has two solutions. To find the correct version, go to www.sciam.com/ontheweb; visit that same site for extra puzzles and solutions to the grids in the article. (The address given in the article was incomplete.)

In Ask the Experts, Stephen M. Roth's answer to the question “Why does lactic acid build up in muscles?” stated that high lactate levels increase acidity in the muscle cells. Though associated with this condition, they are not the cause. For a more in-depth explanation, see www.sciam.com/ontheweb