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updated plant in Wiesbaden, Germany, forexample, sludge spends 11 to 13 days in a trioof tanks rather than the 4 days or less ittook in a single tank before the renovation.

Different kinds of bacteria populate thevarious tanks because some tanks exposesludge to oxygen and others don’t. To fig-ure out where in the newer treatmentprocess estrogens break down, Ternes andhis colleagues in Denmark and Switzer-land studied sludge removed from 10 dif-ferent points along the flow of sewage inthe Wiesbaden plant.

The scientists found that oxygen-deprivedtanks remove most of the E1 and E2 thatenter them, while oxygenated tanks removemost of the EE2. Most important, all threehormones were undetectable—though notnecessarily entirely absent—in the plant’seffluent, the researchers report in an upcom-ing Environmental Science and Technology.

Estrogen removal is a fortunate sideeffect of multiple-tank sewage treatment,says chemist Thomas Heberer of the Tech-nical University of Berlin. The new researchshows for the first time that subjectingsludge alternately to oxygenated and oxy-gen-deprived conditions is highly effectiveat eliminating the hormones, he says. Henotes that with more-sophisticated meas-urement techniques, Ternes’ team mighthave measured traces of estrogen that sur-vived the treatment process.

The study also suggests that more-costlyexperimental techniques for treating sewage,such as injecting ozone gas into treatmenttanks or using high-tech filters, may not benecessary to remove the hormones, saysHeberer. A good next step, he suggests, wouldbe to determine whether a multiple-tankprocess also eliminates hormone-mimick-ing chemicals such as nonylphenol andbisphenol A, which have become major envi-ronmental concerns. —B. HARDER

Fast Findingson Fluid FrenzyTaking turbulence models to a new level

From blood spurting through hearts towinds buffeting cars, fluids swirl and tum-ble in complex ways that scientists struggleto understand. Now, a new means to effi-ciently depict fluid turbulence and to cal-culate its effects promises to influence many

branches of science and technology.For example, using the new method, car

designers can compute aerodynamic simu-lations of full, three-dimensional vehicles athighway speeds quickly enough to incorpo-rate the information into the design of cars,say the technique’s developers. With previ-ous methods, designers typically had timeonly to simulate two-dimensional flows or3-D models for which the car was portrayedin a simplified form or was moving at a crawl.

Two-thirds of the world’s major automak-ers have begun using the new simulations,says Hudong Chen, chief scientist at EXACorp. in Lexington, Mass., which createsand sells software based on the new simu-lation method.

Conventional methods of calculating tur-bulence treat fluids not as molecular assem-blages but as continuous substances. Thenew approach includes some of the under-lying, microscopic nature of fluids, whichsurprisingly turns out to be advantageous.

The new technique, described in theAug. 1 Science, “should become the methodof choice when fast answers are needed forfluid flows of complex geometry,” commentsDavid C. Montgomery of Dartmouth Col-lege in Hanover, N.H. Such complex flowscan occur as heat travels through electronicdevices and as plumes of pollutants infil-trate an environment, scientists say.

For more than 2 centuries, scientists havebeen using mathematical formulationscalled Navier-Stokes equations to calculatethe precise velocity, pressure, and tempera-ture of a fluid at any location and time. Yetthose equations are impossible to solve com-pletely in all but the simplest scenarios, inwhich fluids flow smoothly and steadily. Tosimulate more realistic flows on computers,scientists have long used approximations ofthe Navier-Stokes equations, but those sim-plified models can’t duplicate certain impor-

tant features of the flows. They also demandinordinate amounts of computing power.

The new method relies on a differentequation, called the Boltzmann equation,which is typically employed to predict thebehaviors of molecules in gases and liquids.More than a decade ago, researchers weresurprised to learn that using the Boltzmannequation to calculate simple fluid flows did-n’t make the simulations more difficult ortime consuming to carry out.

“It’s the counterintuitive approach,” saysSteven A. Orszag of Yale University, acoauthor of the Science paper and an EXAconsultant. “If you start from the verymicroscopic dynamics, you would thinkyou’d have to compute much too much.”

More recently, Orszag, Chen, and theircolleagues found a way to include turbu-lence in their Boltzmann equation–basedsimulations at little additional computingcost. The trick was to invent a particularmathematical representation of disruptionof particle motions by disorderly flows.

That last step was “really a breakthroughfrom my point of view,” comments RobertoBenzi of the University of Rome Tor Vergata,a pioneer in the use of the Boltzmann equa-tion for fluid flows. —P. WEISS

Untangling the BrainEnzyme countersAlzheimer’s-like snarls

An enzyme prevents brain cells in agingmice from developing knots of proteinsresembling those that are a hallmark ofAlzheimer’s disease, scientists report.Known as Pin1, the enzyme could form the

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SCIENCENEWSThis Week

PRESSED FOR TIME A simulated Le Mans race car at 160 kilometers per hour compressesthe surrounding air. In cross-sections, red depicts the top pressure reading.

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