ARTICLES

Urban Planning in Curitiba
Jonas Rabinovitch and Josef Leitman
Smog, gridlock, overcrowding and blight sometimes seem like the inevitable price of metropolitan growth, but a fast-rising city in southeastern Brazil has found a better way. Simple technologies, creative use of resources, and a public transportation system that is pleasant, efficient and affordable have turned Curitiba into a model of what more cities could be.

Collisions with Comets and Asteroids
Tom Gehrels
Small rocky or icy bodies, left over from the formation of the planets, normally follow distant, stable orbits, but rare mischance can send one hurtling into the inner solar system. A leader of the Spacewatch team that tracks near-earth comets and asteroids describes their awesome beauty, the odds of a collision with our world and what could be done to prevent a cataclysm.

The African AIDS Epidemic
John C. Caldwell and Pat Caldwell
The scourge of AIDS falls hard on sub-Saharan Africa. Half of all cases are found within a chain of countries home to just 2 percent of the world's population. Unlike the scenario in most regions, here the virus causing the disease spreads almost entirely through heterosexual intercourse. Only one factor seems to correlate with the exceptionally high susceptibility: lack of male circumcision.

Budding Vesicles in Cells
James E. Rothman and Lelio Orci
Inside a cell, bundles of proteins and other molecules traffic from one compartment to another inside membrane bubbles, or vesicles. How these vesicles emerge as needed from one set of intracellular organs and deliver their payload at the right destination has been an intensively studied biological mystery. A transatlantic collaboration between the authors has helped to find answers.

SCIENCE IN PICTURES
The Art and Science of Imagery Interpretation
Dino A. Brugioni
Photoreconnaissance by spy planes and satellites has pulled the superpowers back from the brink of war several times. A former image analyst for the C.I.A. shares tricks of the trade and recently declassified pictures that made history.

Electrons in Flatland
Steven Kivelson, Dung-Hai Lee and Shou-Cheng Zhang
When moving electrons are trapped in the flat space between semiconductors and exposed to a magnetic field, they exhibit an unusual behavior called the quantum Hall effect. In essence, the electrons form a distinct phase of matter. Explanations for the changes may be linked to mechanisms of superconductivity.

Caribbean Mangrove Swamps
Klaus Rützler and Ilka C. Feller
Mangroves are trees adapted for life in shallow water along the ocean's tropical shores; communities of organisms reside in and around them, creating a habitat reminiscent of both a forest and a coral reef. The authors, a marine biologist and a forest ecologist, guide us through one such mangrove swamp in Belize.

TRENDS IN HUMAN GENETICS
Vital Data
Tim Beardsley, staff writer
The Human Genome Project is years from completion, but already DNA tests for a widening array of conditions are bursting into the marketplace. Some companies are rushing into a realm as yet unmapped by medicine, ethics or law.

DEPARTMENTS

Science and the Citizen
How much for the liver?... NASA and nausea.... Helium shortage.... Brazil's lost desert.... Thirsty moths.... Viruses trace neurons.... Cosmic rays.... Escher for the ear.... Getting Washington' goats.

The Analytical Economist
Women's real economic prospects.

Technology and Business
The scoop on plutonium processing.... Military prototypes in Bosnia.... Public-key encryption at risk.

Profile
Albert Libchaber brings order to chaos studies.

Letters to the Editors
Rising IQs.... Life's purpose.... Alien abductions and Freud.

50, 100 and 150 Years Ago
1946: X-rays in factories.
1896: A pioneer of flight.
1846: Bigfoot or tall tale?

The Amateur Scientist
Measuring the strength of chemical bonds.

Mathematical Recreations
Squaring off in a board game of Quads.

Reviews and Commentaries
Star Trek physics.... Surviving the future....
Wonders, by the Morrisons: Earth's asymmetries....
Connections, by James Burke: Code and commerce.

Essay: Anne Eisenberg
Data mining and privacy invasion on the Net.