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March 1996
Scientific American Magazine

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Cover; March 1996; Scientific American Magazine; by Staff Editor; 1 Page(s)

Table of Contents; March 1996; Scientific American Magazine; by Staff Editor; 2 Page(s)

Letter from the Editor; March 1996; Scientific American Magazine; by John Rennie; 1 Page(s)

This issue, Scientific American runs the gamut on technology. We open with an article on how mundane, low technology can still have a terrific positive impact on a community. We close with a report on how one of the hottest high-tech areas can cause new headaches for society, even when deployed with the best of motives. Together these pieces make the point that technology is only as good or bad as what you do with it.

"Low technology," in the first case, really means first-rate civil engineering. Buses, artificial lakes and efficient roadways aren't glamorous. They don't have the show-biz appeal of virtual-reality interfaces for the Internet, or robots performing surgery, or "stealth" aircraft. But as the Brazilian city of Curitiba discovered, and as Jonas Rabinovitch and Josef Leitman recount, beginning on page 46, these unglamorous creations have greatly improved the quality of life for its two million inhabitants. As in a fine antique watch, the gears of this city mesh together exactly right, thanks to smart urban planning.

Letters to the Editors; March 1996; Scientific American Magazine; by Staff Editor; 1 Page(s)

Thanks for John Horgan's thought-provoking news story on the long-term rise in IQ scores, "Get Smart, Take a Test" ["Science and the Citizen," SCIENTIFIC AMERICAN, November 1995]. Could it be that the modern person uses a different aspect of intelligence than his counterpart of a century ago? And if the average person today utilizes left-brain processes more effectively, is it possible that other, more right-brained forms of intelligence are underdeveloped? Compare the rich verbal expressions of 19th-century writers and average citizens to works of present-day people. I'm reminded of Picasso's remark as he emerged from viewing the cave paintings in Lascaux, France: "We have invented nothing!"

The only IQ test I ever took was a Stanford-Binet, back in high school in 1947. It had a maximum score of 140. Just a decade later my daughter was given her first IQ test, in elementary school. Her tests were apparently open-ended, and she consistently scored some 25 points higher than I. She is now in her forties, and my personal, lifetime assessment is that her actual IQ is little, if any, higher than mine. Early on, nobody expected such high scores, so tests were not designed to be open-ended in their scoring system. Is this an explanation for the gradual rise in IQ tests over the years?

50, 100 and 150 Years Ago; March 1996; Scientific American Magazine; by Staff Editor; 1 Page(s)

MARCH 1946 The problem of crew comfort on the control-decks of longrange aircraft is basic to the full realization of air transport's potential value. This problem was once considered to be satisfactorily solved when the pilot had a comfortable cockpit in which to sit, but this now appears as a serious misconception. Many of the studies of crew comfort hinge on biomechanics-- the combined study of biology and mechanics. Some developments, such as the pressurized cabin, high-altitude flying suits, and improved food for both pilots and passengers, represent a tremendous amount of research work on the part of highly specialized medical men as well as aeronautical engineers.

A millionth of a second X-ray machine, designed originally for basic research, is moving straight into the practical end of factory operation. This device can look through an inch of steel at the fastest moving mechanisms ever built, and produce pictures which tell what each hidden machine part is doing. Some smart shop is going to obtain a worthwhile cost advantage over its competitors when it X-rays the operation of metal-cutting tools on a high-speed lathe working on one of the hard-to-machine alloy steels. The X-ray can look through floods of cutting oil to see how metal is cut under actual operating conditions and can determine machineability of any lot of steel on the first few turns of a lathe spindle.

Regulating the Body Business; March 1996; Scientific American Magazine; by Wallich, Mukerjee; 2 Page(s)

More than 30 years ago the science- fiction writer Larry Niven envisioned a world in which organ transplants were common. To ensure a continuing supply of organs for the public at large, draconian laws mandated capital punishment for a host of offenses, and shadowy "organ-leggers" plucked victims off the street to extend the lives of the rich and remorseless.

The world has not developed quite along the lines that Niven foresaw. Rumors of organ-theft syndicates appear to be pure urban legend. Then again, China does harvest the bodies of executed prisoners, and Austria has instituted "presumed consent" rules that permit doctors to remove organs from brain-dead patients unless specifically forbidden to do so beforehand.

Escher for the Ear; March 1996; Scientific American Magazine; by Yam; 1 Page(s)

When computer-generated tones are played repeatedly in certain sequences, they can appear to rise or descend endlessly in pitch. Other patterns of notes are heard to ascend by some people but to descend by others. Diana Deutsch, a psychologist at the University of California at San Diego, now reports that childhood plays a crucial role in how one perceives certain Escheresque melodies.

Using a computer, Deutsch constructed notes that lack a clear octave relation. For example, to make an ambiguous C note, she combines the harmonics of all C notes and manipulates their relative amplitudes (in essence, playing all six C notes on a keyboard simultaneously). As a result, a listener might be able to identify the note as C but remain unsure if it is middle C or the C an octave above or below.

Field Notes: Plane Scary; March 1996; Scientific American Magazine; by Schneider; 1 Page(s)

Many viewers had to squint at the final credits to see how the eerily realistic zero-gravity scenes in the recent movie Apollo 13 were filmed. Having no way to transport the cast to outer space, the moviemakers appealed to the next best thing: the National Aeronautics and Space Administration¿s Reduced- Gravity Office. Since the early days of the space program, that small arm of the agency has been lobbing a specially equipped KC-135A jetliner into the sky in such a way as to reproduce temporarily the weightlessness that astronauts feel in space. Curious to see how people with only ordinary amounts of the right stuff take to a taste of "zero g," I interviewed some recent passengers of NASA¿s KC-135A "Vomit Comet."

Scott F. Tibbitts, president of Starsys Research Corporation in Boulder, Colo., needed to test weightless operation of two devices his firm had developed for the upcoming Pathfinder and Cassini space probes. He decided to take advantage of a tool he had used once before--NASA¿s zero-gravity airplane.

Out of This World; March 1996; Scientific American Magazine; by Powell; 2 Page(s)

From outer space they come, striking the earth's atmosphere from all directions at nearly the speed of light. As they streak between the stars, they heat and alter the composition of giant gas clouds, subtly influencing the evolution of our entire galaxy.

They are cosmic rays, subatomic particles or atomic nuclei that carry at least a billion times the amount of energy in a photon of visible light. Ever since Austrian physicist Victor F. Hess discovered cosmic rays in 1912, astronomers have debated the origin of these enigmatic particles. Recent observations from ASCA, an astronomical satellite jointly operated by the U.S. and Japan, seem at last to have solved at least part of the puzzle.

Viral Tracers; March 1996; Scientific American Magazine; by Leutwyler; 1 Page(s)

Imagine trying to make sense of a railway map if none of the lines were labeled. It would be nearly impossible to know which trains ran between which towns. Neuroscientists long faced a similar problem: the chemicals they used to trace lines of communication between brain regions vanished after a single stop. "They only went from one station to the next," says Peter L. Strick of the Veterans Administration Medical Center in Syracuse, N.Y. Knowing but short stretches of certain tracks, he adds, made it exceedingly difficult to determine where any one train--or nerve signal--ultimately went.

Recently, though, Strick has turned to a new, more powerful technique, one that enlists itinerant viruses to chart brain circuits in monkeys. "The viruses move from one neuron to another, right on down the line," he notes. "Happily, there are strains of virus that do this by crossing over synaptic connections. " These viruses cross in only one direction. A strain of the herpes simplex type I virus, for example, follows the flow of nerve impulses through neighboring cells: the virus particles pass down a neuron's axon, across a synapse, into another neuron, down its axon, over another synapse and so on. A different strain moves in the opposite direction.

Rain Forest Crunch; March 1996; Scientific American Magazine; by Schneider; 1 Page(s)

Going up that river was like travelling back to the earliest beginnings of the world, when vegetation rioted on the earth and the big trees were kings." Joseph Conrad's evocative portrayal of the Congo would seem to apply as well to the Amazon. That river travels across the South American continent from Peru to the Atlantic Ocean, cutting through nearly four million square kilometers of undisturbed woodlands. But is the Amazon rain forest truly a primeval jungle, a steamy, green mass that has endured for millions of years? Perhaps not, according to new results from the high Andes.

The current findings challenge a perception, which first emerged in the 1970s, that tropical climates remained virtually unchanged while the great ice sheets of North America and Europe waxed and waned through a series of Pleistocene ice ages. That view was based largely on a study of microscopic shells from the ocean floor. Analyses of the kinds of creatures that had thrived in tropical seas during glacial periods indicated that the earth's equatorial regions had kept close to their presentday temperatures.

Rescuing an Endangered Tree; March 1996; Scientific American Magazine; by Nemecek; 1 Page(s)

The number of stinking yew trees, named for the pungent odor of their needles, has been dropping since the 1950s. Today the tree (Torreya taxifolia) is considered one of the rarest in North America, with only about 1,500 specimens still alive. Efforts to preserve the tree have a particular urgency: the stinking yew is related to the Pacific yew, known for the anticancer drug taxol found in its bark. But only recently have botanists identified what is killing the trees.

Gary Strobel of Montana State University, Jon Clardy of Cornell University and their colleagues report in Chemistry & Biology that the dying trees, also known as Florida torreya, are infected with the fungus Pestalotiopsis microspora, which belongs to a group of microorganisms known as endophytic fungi. Although not all endophytic fungi harm their hosts, according to Strobel the type living inside torreya trees appears to be on the edge between symbiotic and pathogenic.

Getting the Goats; March 1996; Scientific American Magazine; by Wright; 3 Page(s)

What's black and white and red all over? That's no joke on Washington State's Olympic Peninsula, where the U.S. Park Service has gruesome plans for some 300 mountain goats that inhabit the craggy peaks of Olympic National Park.

Stroke Mortality in Men Ages 35 to 74; March 1996; Scientific American Magazine; by Doyle; 1 Page(s)

In 1994 half a million Americans suffered a stroke; of these, 154,000 died, more than the number who died from any other cause except coronary heart disease. With more than three million stroke survivors currently incapacitated, it is the leading cause of disability in the U.S. Worldwide, probably more than six million people died from stroke in 1994. The disease, which occurs because of blocking or hemorrhaging of blood vessels in the brain, may result in paralysis of limbs, loss of speech, and other infirmities. The stroke mortality rate of women in most countries is 60 to 90 percent that of men, but because the rates rise steeply with age, and because women live longer than men do, more women actually die of the disease.

Differences in stroke mortality among countries are wide; for example, the former Soviet Union has a rate more than five times that of the U.S. Part of the difference, at least when comparing western countries with eastern European countries, is the result of inferior medical treatment in eastern Europe; however, risk factors, including hypertension, the dominant precursor of stroke, are higher in the East, and cigarette smoking and excessive drinking, which also contribute to the disease, are more widespread there as well. Other, more hypothetical risk factors may add to the eastern European rates, such as a scarcity of citrus fruit, a prime source of vitamin C. Vitamin C and other antioxidants block formation of free oxygen radicals, thought to play a role in the development of atherosclerosis, the underlying condition leading to blockage of arteries.

Anti Gravity: It's All Happening at the Zoo(logy Meeting); March 1996; Scientific American Magazine; by Mirsky; 1 Page(s)

In a striking example of convergent evolution, small children sitting in the backseats of cars and male fiddler crabs exhibit common behaviors. That kids in cars and crabs constantly move sideways is well established. Recent research also shows that if you wave at fiddler crabs, they wave back. This was just one of the findings reported at the annual meeting of the American Society of Zoologists (ASZ) in Washington, D.C. The ASZ conference was one of the few things that remained open in our nation¿s capital last December while Congress fiddled with the budget.

Thought to be an advertisement of territoriality, "waving" had been documented for large groups of fiddler crabs. Denise Pope of Duke University isolated the behavior, showing that an individual crab responds when it sees another individual wave its gigantic claw. She did this by cleverly incorporating a three-inch Sony Watchman screen into one wall of a tank and showing captive fiddlers videos of other fiddlers waving. Although the responding gestures were probably a direct response to a perceived threat, an alternative explanation is that the subject fiddler crabs desperately wanted the remote control in order to change channels (most likely to Baywatch).

No Light Matter; March 1996; Scientific American Magazine; by Powell; 2 Page(s)

Most people may associate helium with parties and parade balloons, but the lightest inert gas also has its serious side. Helium is used in a wide variety of scientific and technical applications, from cryogenics to arc welding. It is also one of the earth's most limited resources, found in usable concentrations in just a handful of natural gas wells in the U.S. and Canada. And yet Congress and the Clinton administration are acting to squander, rather than conserve, the helium supply, leading the American Physical Society to issue a warning against their "economically and technologically shortsighted " policies. Edward Gerjuoy of the University of Pittsburgh offers a more personal reaction: "It is morally wrong for this generation to waste a resource that might be precious to a future one."

Helium forms underground from alpha particles--essentially the nuclei of helium atoms--emitted by radioactive elements in the earth's interior. Over millions of years the gas builds up and finds its way into the underground reservoirs where natural gas also collects. Every year drilling companies collect about 3.3 billion cubic feet of helium. A similar amount simply mixes with the atmosphere when natural gas is burned. That helium is for all practical purposes lost forever (the gas can be extracted directly from the air, but only through an expensive and extremely energyhungry process).

Pass the Salt, Please; March 1996; Scientific American Magazine; by Wu; 1 Page(s)

Sodium, essential for nearly every metabolic reaction in the body, is sometimes a rare commodity, so it¿s no wonder that many animals seek out salt licks, sweat, termite mounds and Big Macs. Some moths, though, are able to meet their salt needs with an ability that would put any barfly to shame. They guzzle almost 40 milliliters of water in a few hours--the human equivalent of more than 40,000 liters, at four liters per second--to absorb the sodium they need.

Naturalists, after long observing butterflies and moths drinking water from puddles, came to suspect that the quest for salt drove the behavior. In the 1970s researchers found that when given a choice of progressively saltier solutions, butterflies usually drank from the saltiest mixture available. Now chemical ecologists Scott R. Smedley and Thomas Eisner of Cornell University have confirmed the role that "puddling" plays in sodium procurement, after studying nature¿s champion puddlers, male Gluphisia septentrionis moths.

Having It All; March 1996; Scientific American Magazine; by Wallich; 1 Page(s)

In the economist's jargon, lifetime utility is a function of money earned plus nonmonetary benefits from family and other interests. During the past 10 years or so, attention has focused on how--or whether--women can maximize their returns from both family and career. Many advocates of women's rights contend that the two ought not be mutually exclusive and decry the conditions that make it so difficult to achieve success in both.

To achieve success in both. It is hard enough to figure out how to juggle work, marriage and children in reality but perhaps even more difficult to conceive an economic analysis that would reliably indicate how well women (or men) are succeeding. Claudia Goldin, a labor economist and economic historian at Harvard University, has been tracking data collected on working women over the past century, starting with the era when work and marriage were almost polar opposites for many women. How well these statistics augur today--or even whether the right numbers are available--is unclear.

Hot Pork; March 1996; Scientific American Magazine; by Zorpette; 2 Page(s)

Over roughly four decades, immense complexes near Hanford, Wash., and Aiken, S.C., produced some 100 metric tons of plutonium, the wherewithal of the cold war. To put the metal in a pure form suitable for making weapons, it was extracted from irradiated nuclear fuel in an industrialchemical sequence known as reprocessing. In 1992, after the cold war ended, the Department of Energy, which oversees the weapons complex, halted all its reprocessing operations.

Now the DOE has announced that it will resume reprocessing on a small scale--and that it will continue work on a new reprocessing technology despite its limited need for reprocessing in the foreseeable future. The development has provoked charges, including some from within the DOE itself, that the plan is fraught with pork-barrel politics. At the same time, at least one public-interest group is challenging the need for reprocessing.

Smart Shopping; March 1996; Scientific American Magazine; by Dupont; 1 Page(s)

The Pentagon has never been a paragon of adept buying practices, but a new Defense Department initiative may help bring advanced technologies to soldiers more quickly and for less money. So far the program has delivered an unmanned reconnaissance aircraft to troops in Bosnia in record time, and its proponents believe they can simplify the Pentagon acquisition system by allowing the military "users"--the ones who take the stuff to war--to influence the design of weapons and other technologies from the beginning.

It may sound simple, but this is the Pentagon, where a system thought up in one decade might not be used by a soldier for another two. During the cold war, when the U.S. worried almost exclusively about the Soviet Union, this inertia worked because both nations knew enough about the other's weapons programs to keep pace, even with 30-year acquisition cycles. "There was a well-understood relationship between us and our military capability and them and theirs," says Jack Bachkosky, deputy undersecretary of defense for advanced technology.

Tough Stuff; March 1996; Scientific American Magazine; by Gibbs; 2 Page(s)

Ceramic composites, the darlings of the material world, have been too precious and fragile to realize their full potential. Certainly in toughness, advanced ceramics surpass metals that weigh much more. But composites' brittleness and high cost have made them impractical for many applications, such as airplane engines and heat exchangers, the performance and efficiency of which are limited by inadequate materials.

Those limits may soon be overcome-- and the cost of strong composites cut-- thanks to a new class of materials recently invented at the Georgia Technology Research Institute (GTRI). The advance simply combines two strategies long used to strengthen materials. The first is reinforcement. Much as metal rods can internally buttress concrete bridges, carbon fibers toughen ceramics grown around them. In metals, platelets of silicon carbide serve the same function. A second well-known way to make strong stuff stronger is to stack thin layers of two metals or ceramics into a laminate. The product is, like an oyster's shell, much harder than the mere sum of its parts.

Bad Timing; March 1996; Scientific American Magazine; by Seife; 1 Page(s)

A new cryptanalytic attack has shaken confidence in the security of some very popular encryption schemes--and computer experts are stunned at how easy it can be to unravel "securely" coded messages. A public- key encryption scheme uses a public key to encrypt messages, but the decryption key is kept private. Now Paul C. Kocher, a cryptography consultant, has found a back door. Kocher proved that a wily snooper can figure out what the secret key is--by keeping track of how long a computer takes to decipher messages.

Public-key cryptography relies on certain mathematical functions that are very easy to do but very hard to undo. For instance, it is easy to multiply two numbers together to get a larger number yet hard to factor a large number into its component primes.

Profile: Albert Libchaber; March 1996; Scientific American Magazine; by Mukerjee; 3 Page(s)

The walls of his bedroom are lined with books, original editions of works by the greats--Newton, Descartes, Leibniz, Galileo, Poincar., anyone I can think of. Albert Libchaber pulls out the volumes one by one, running his fingers along favorite passages and translating for my benefit. Kepler's musings, in 1611, on a snowflake: a "nothing" that reveals in its symmetry the atomic structure of matter. Hooke's drawings of a fly's eye, revealed by one of the earliest microscopes. Lyapunov's treatise on the stability of motion, presaging chaos theory. His heroes, Libchaber explains, are Huygens and Kepler: "They are more passionate, more human, more romantic, therefore less well known than Galileo or Newton." He is disappointed that I cannot name any heroes of my own; he would have liked to thrill me by pulling out their works.

Staring at Huygens's exquisite diagrams of the pendulums he crafted and studied, I suddenly see the wellspring that inspires Libchaber. "I have a feeling, if an experiment is aesthetic it will tell me something," he had said earlier in his soft, almost inaudible voice. "I will not do an experiment if it is not beautiful. " Libchaber emulates his heroes, whose genius touches him through the pages of these books. He asks direct, simple questions--doing, as someone said, 19th-century physics with 21stcentury equipment. In 1979 his precise techniques led him to see, in a tiny cell of liquid helium at the .cole Normale Sup.rieure in Paris, how a fluid's flow becomes disordered--the first close look at chaos in nature.

Urban Planning in Curitiba; March 1996; Scientific American Magazine; by Rabinovitch, Leitman; 8 Page(s)

As late as the end of the 19th century, even a visionary like Jules Verne could not imagine a city with more than a million inhabitants. Yet by the year 2010 over 500 such concentrations will dot the globe, 26 of them with more than 10 million people. Indeed, for the first time in history more people now live in cities than in rural areas.

Most modern cities have developed to meet the demands of the automobile. Private transport has affected the physical layout of cities, the location of housing, commerce and industries, and the patterns of human interaction. Urban planners design around highways, parking structures and rush-hour traffic patterns. And urban engineers attempt to control nature within the confines of the city limits, often at the expense of environmental concerns. Cities traditionally deploy technological solutions to solve a variety of challenges, such as drainage or pollution.

Collisions with Comets and Asteroids; March 1996; Scientific American Magazine; by Gehrels; 6 Page(s)

Are we going to be hit by an asteroid? Planetary scientists are divided on how worrisome the danger is. Some refuse to take it seriously; others believe the risk of dying from such an impact might even be greater than the risk of dying in an airplane crash. After years of studying the problem, I have become convinced that the danger is real. Although a major impact is unlikely, the energies released could be so horrendous that our fragile society would be obliterated.

Early in our planet's history, asteroids and comets made life possible by accreting into the earth and then by bringing water to the newborn planet. And they have already destroyed, at least once, an advanced form of that life. The dinosaurs were killed by such an impact, making way for the age of the mammals. Now for the first time, creatures have evolved to a point where they can wrest control of their fate from the heavenly bodies, but humans must come to grips with the danger.

The African AIDS Epidemic; March 1996; Scientific American Magazine; by Caldwell, Caldwell; 7 Page(s)

AIDS has swept across sub-Saharan Africa on an extraordinary scale. Two thirds of the roughly 16 million people in the world infected with the human immunodeficiency virus (HIV), which causes AIDS, live there. Half of the world's cases are found in what we call the AIDS belt--a chain of countries in eastern and southern Africa that is home to only 2 percent of the global population.

Heterosexual intercourse serves as the main vehicle for spreading HIV throughout sub-Saharan Africa. This is in stark contrast to the developed world, where the virus is most frequently transmitted during homosexual intercourse or when intravenous drug users share contaminated syringes. Attempts to halt the flood of AIDS cases in Africa will not succeed until researchers can determine what factors contribute to the remarkable prevalence of the disease among heterosexuals. Such a diagnosis will also help us figure out how likely it is that heterosexual epidemics might extend into Asia or the West.

Budding Vesicles in Living Cells; March 1996; Scientific American Magazine; by Rothman, Orci; 6 Page(s)

All nucleated cells--whether in colonies of yeast or in plants and people--have a complex internal organization resembling that of a well-run city. Perhaps most notably, cell and city both rely on the coordinated activities of specialized departments. In cells these departments are walled off by membranes and called organelles.

A brief tour of some of the more important departments in a cellular "city" might start at the outer membrane, itself an organelle. This structure is akin to the gated walls that once enclosed ancient cities, in that it controls the entry of food and other materials and the export of products manufactured within. Another critical department lies deep inside cells and serves as a manufacturing center. It is here, in the endoplasmic reticulum, that many proteins--the main working parts of cells--are produced. These newly made proteins are then transported to yet another department, the Golgi apparatus, where they are modified (often by the addition of sugars) and ultimately shipped to other destinations within or outside the cell. The Golgi, then, is a major distribution hub for our microscopic cities.

The Art and Science of Photoreconnaissance; March 1996; Scientific American Magazine; by Brugioni; 8 Page(s)

Every morning for the past 35 years, a Central Intelligence Agency officer has appeared at the White House with a printed intelligence digest and a fistful of images. These aerial and satellite photographs, perhaps half a dozen chosen from the thousands shot the previous day, show current hot spots, with attached explanatory notes. Similar packets are delivered to the secretaries of state and defense, selected members of Congress and other key officials. Over the decades, these images have had a powerful influence on U.S. policy.

Reconnaissance photographs have aided every presidential administration since that of Dwight D. Eisenhower in watching over troops stationed abroad, monitoring disarmament agreements, assessing hostile military forces and planning counterweapons programs. During its early years--the late 1950s and early 1960s--modern photoreconnaissance repeatedly provided timely intelligence, sometimes even helping to bring the superpowers back from the brink of conflict. More often than not, these images prevented dangerous surprises and showed arsenals to be less imposing, and intentions less sinister, than had been thought.

Electrons in Flatland; March 1996; Scientific American Magazine; by Kivelson, Lee, Zhang; 6 Page(s)

Since the time of the ancient Greeks, a central goal of all scientific disciplines has been to find a minimal set of basic principles that underlie diverse natural phenomena. This reductionist philosophy has succeeded well in some areas, such as high-energy physics--the study of the fundamental particles of force and matter. Here theorists have grouped all particles into a few families and expressed the basic laws of physics in terms of the interactions among them.

The situation is quite different in condensed-matter physics, which is the study of solids and liquids. Research in this century into the behavior of electrons in solids has uncovered various states of matter in which electrons organize themselves in myriad remarkable ways. For example, solids are typically either insulators (they strongly resist the flow of electric current) or metals (they conduct current well but still have a small amount of resistance). Yet under some circumstances, certain solids can enter a superconducting state, in which electric current flows without any resistance at all. The theoretical characterizations of these different states have been as diverse as the states themselves.

Caribbean Mangrove Swamps; March 1996; Scientific American Magazine; by Rützler, Feller; 6 Page(s)

One perceives a forest of jagged, gnarled trees protruding from the surface of the sea, roots anchored in deep, black, foul-smelling mud, verdant crowns arching toward a blazing sun, the whole mass buzzing with insects. These are the first impressions a visitor develops when approaching one of the most common sights on tropical shores--a mangrove swamp. Here is where land and sea intertwine, where the line dividing ocean and continent blurs. In this setting the marine biologist and forest ecologist both must work at the extreme reaches of their disciplines.

Naturalists have long struggled to de- fine, in proper ecological terms, the environment of a mangrove swamp. Is it an extreme form of coral reef or a flooded coastal forest? Compared with the tropical timberlands of some continental interiors (which can house as many as 100 species of tree on a single hectare), a mangrove forest appears puny, monotonous and depauperate. Even the relatively rich Indo-Pacific coasts boast only some 40 mangrove species along their entire length. In the Western Hemisphere only eight or so mangrove species can be found. And of this small set just three kinds of mangrove tree are truly common.

Vital Data; March 1996; Scientific American Magazine; by Beardsley; 6 Page(s)

Later this year, if a biotechnology company called Myriad Genetics has its way, thousands of healthy women in the U.S. will hear doubly bad news. First, a close relative--perhaps a sister--will announce that she has breast cancer. Second, the patient's physician thinks this particular cancer has probably been caused by a mutation that the healthy relative has an even chance of also carrying. The patient has been advised to suggest to all her female relatives that they be tested for the mutation. Women who share it may be urged to consider a prophylactic double mastectomy, as they, too, are likely to develop breast cancer. How likely? Hard to say--the mutations have not yet been thoroughly studied--but the likelihood could be as much as 85 percent.

Most people have yet to confront the dilemmas posed by tests for genes associated with serious diseases. But BRCA1, the breast cancer gene that Myriad proposes to start testing on a large scale this year, is merely one of what may become dozens that physicians will soon routinely order checked for mutations. The tests are all, to varying degrees, spin-offs of the Human Genome Project, an audacious 15-year, $3-billion federal effort to analyze the human genetic heritage in its ultimate molecular detail.

The Amateur Scientist; March 1996; Scientific American Magazine; by Carlson; 2 Page(s)

The world is held fast by molecular bonds. They shape every sight, sound and texture. All of life's processes, from respiration to reproduction to repairing DNA, are carried out entirely through interacting molecules. Even consciousness itself is regulated and structured by electrochemical interactions in our brain. Clearly, understanding the strength and nature of these bonds is vital to science. Using the device described here, you can conduct original research into the chemical nature of creation.

When molecules interact, old bonds break, and new ones form to produce various chemical species. If, on the whole, the new molecules are more tightly bound than the old were, heat is given off, and the temperature of the solution containing the reacting molecules rises. If they are less tightly bound, heat is absorbed, and the temperature falls. Measuring how much heat flows into or out of these chemical interactions reveals information about these bonds, such as the amount of energy needed to hold molecules together.

Mathematical Recreations; March 1996; Scientific American Magazine; by Stewart; 2 Page(s)

Afriend of mine, G. Keith Still, is a computer scientist who, together with two former soldiers, runs a company that handles crowd control at Wembley Stadium in England. His main professional interests involve simulating crowd dynamics and designing appropriate barriers. But Still is a very inventive person, and he recently told me about a game he came up with several years ago.

The game, which Still calls Quad, is played on a grid--11 cells high and 11 cells wide-- from which the four corner cells have been removed. That leaves 117 available cells. The two players each possess 20 pieces, either all red or all black, called quads, and seven (or for a shorter game, six) white pieces called quazars. They take turns placing one of their quads on the board in an unoccupied cell. The aim of the game is to get four of your quads at the corners of a square. The square may have edges that are parallel to those of the board, or it may be tilted.

Reviews; March 1996; Scientific American Magazine; by Kaku, Small; 5 Page(s)

Almost 20 years ago Nobel laureate I. I. Rabi, addressing a symposium at Columbia University, chided the audience of physicists for failing to communicate the excitement and drama of their discipline to the general public. To add insult to injury, he charged that even lowly science-fiction writers had done more than professional scientists to impart the romance and fascination of science to the next generation. Nothing has done more than the Star Trek phenomenon to show how right Rabi was. Since the debut of the first Star Trek television series nearly 30 years ago, an entire generation of young scientists has been weaned on the series and its spin-offs, fluent in the palace intrigues of the Klingon Empire as well as the periodic table and spectrum of subatomic particles. In my classes, I have found Star Trek to be a powerful tool for attracting students to physics and helping them grasp its concepts.

Albert Einstein once said that imagination is more important than knowledge. If he were still alive, I suppose he might have written The Physics of Star Trek himself. Sadly, it has taken three decades for someone else to take on the task: Lawrence M. Krauss, chairman of the physics department at Case Western Reserve University and author of several other, more sober-sounding science books. What took so long?

Commentary: Wonders - Symmetry and Symmetry-Breaking in South Africa; March 1996; Scientific American Magazine; by Morrison, Morrison; 3 Page(s)

Half a day's drive brings you out from the city of Cape Town, near the southern tip of South Africa, to the Cape of Good Hope and back again. The Cape's stony, salt-sprayed heathlands, austere in early spring before the myriad blossoms erupt, are now a nature preserve, wild and romantic under the steep hills that overlook rushing waters. The long fetch sends unending rollers to crash high above the tangled kelp, while seabirds cry plaintively in the half-gale aloft.

Only the smoothly paved roads and a few brief glimpses of hilltop lighthouses and radio masts remind you that five centuries have passed since Bartolomeu Dias, in command of two caravels and a storeship, first sailed around Africa's southern end in 1487, near the close of Portugal's century-long campaign to reach the Indies by the Atlantic seaway. Dias was blown by a gale past the twin points of the Cape of Good Hope and saw the place only on the way back; it was then that he fixed that buoyant name on a site that pointed to a place of safe haven.

Commentary: Connections - Satisfied Customers; March 1996; Scientific American Magazine; by Burke; 2 Page(s)

I suppose the modern department store, with its money-back-guaranteed merchandise, is one of the great examples of industrial democracy in action. Thanks to mass production and distribution, I can go back to the shop and get a free replacement for the cup that I found a flaw in last week. It was one of those willow-pattern things. Genuine Wedgwood. An ironic term, really, because Wedgwood's original stuff was fake.

Josiah Wedgwood was a potter who started his career repairing Delft chinaware (fake porcelain, first made for the Dutch middle classes who couldn't afford the sky-high prices of the real thing coming in from the Far East). Then, in 1769, he graduated to crafting his own stuff (fake Greek pieces, first made for the English middle classes who couldn't afford the sky-high prices of the real thing coming in from southern Italy).

Essay; March 1996; Scientific American Magazine; by Eisenberg; 1 Page(s)

They are known as intelligent agents, those popular new computer programs that sift through the Internet for the things that most interest us. Overwhelmed by all that information on the information highway, we instruct our agents to do a little scouting on our behalf: sort our e-mail, search for the latest articles on knee surgery or shop the World Wide Web for the cheapest compact discs.

There is a small catch, though, to all this convenience. While we or our electronic alter egos are busily looking at Web sites, a good number of the owners and advertisers on these sites are looking right back. All those mouse clicks and keystrokes--which electronic sites we visit, how long we stay and where we go before and after--are not the ephemera they seem. Clickstreams, as they are called, enjoy a digital afterlife in commercial databases, where raw statistics about our on-line behavior are transformed into useful information and then warehoused for future application, sale or barter. These are known as the Clickstreams that keep on giving--to advertisers, mass marketers and lucky venture capitalists.