Showing papers in "Scientific American in 1997"

Creating False Memories

Abstract: Researchers are showing how suggestion and imagination can be used to create "memories" of events that did not actually occur.

Global Population and the Nitrogen Cycle

Abstract: During the 20th century, humanity has almost quadrupled its numbers. Although many factors have fostered this unprecedented expansion, its continuation during the past generation would not have been at all possible without a widespread—yet generally unappreciated— activity: the synthesis of ammonia.2 The ready availability of ammonia, and other nitrogen-rich fertilizers derived from it, has effectively done away with what for ages had been a fundamental restriction on food production. The world’s population now has enough to eat (on the average) because of numerous advances in modern agricultural practices. But human society has one key chemical industry to thank for that abundance— the producers of nitrogen fertilizer. Why is nitrogen so important? Compared with carbon, hydrogen and oxygen, nitrogen is only a minor constituent of living matter. But whereas the three major elements can move readily from their huge natural reservoirs through the food and water people consume to become a part of their tissues, nitrogen remains largely locked in the atmosphere. Only a puny fraction of this resource exists in a form that can be absorbed by growing plants, animals and, ultimately, human beings. Yet nitrogen is of decisive importance. This element is needed for DNA and RNA, the molecules that store and transfer genetic information. It is also required to make proteins, those indispensable messengers, receptors, catalysts and structural components of all plant and animal cells. Humans, like other higher animals, cannot synthesize these molecules using the nitrogen found in the air and have to acquire nitrogen compounds from food. There is no substitute for this intake, because a minimum quantity (consumed as animal or plant protein) is needed for proper nutrition. Yet getting nitrogen from the atmosphere to crops is not an easy matter. The relative scarcity of usable nitrogen can be blamed on that element’s peculiar chemistry. Paired nitrogen atoms make up 78 percent of the atmosphere, but they are too stable to transform easily into a reactive form that plants can take up. Lightning can cleave these strongly bonded molecules; however, most natural nitrogen “fixation” (the splitting of paired nitrogen molecules and subsequent incorporation of the element into the chemically reactive compound ammonia) is done by certain bacteria. The most important nitrogen-fixing bacteria are of the genus Rhizobium, symbionts that create nodules on the roots of leguminous plants, such as beans or acacia trees. To a lesser extent, cyanobacteria (living either freely or in association with certain plants) also fix nitrogen.

Managing human error in aviation.

Abstract: SUBTITLE: MISTAKES BY FLIGHT CREWS CONTRIBUTE TO MORE THAN TWO-THIRDS OF AVIATION ACCIDENTS: TRAINING TO ENHANCE TEAM PERFORMANCE MAY REDUCE POTENTIALLY FATAL ERRORS.

The past and future of global mobility

Abstract: How much will people travel in the future? Which modes of transport will they use? Where will traffic be most intense? The answers are critical for planning infrastructures and for assessing the consequences of mobility. They will help societies anticipate environmental problems such as regional acid rain and global warming, which are partially caused by transport emissions. These questions also lie at the center of efforts to estimate the future size of markets for transportation hardware -- aircraft, automobiles, buses and trains. In this research, the authors have tried to answer these questions for 11 geographic regions specifically and more generally for the world. Historical statistics for trains, buses, automobiles and high-speed transport were used to compose a scenario for the future volume of passenger travel, as well as the relative prevalence of different forms of transportation through the year 2050.

Fighting Computer Viruses

Abstract: Much of their popular presence is attributable to an obvious but deep biological analogy: computer viruses replicate by attaching themselves to a host (a program or computer instead of a biological cell) and co-opting the host's resources to make copies of themselves. Symptoms can range from unpleasant to fatal. Computer viruses spread from program to program and computer to computer, much as biological viruses spread within individuals and among individual members of a society. There are other computer pathogens, such as the "worms" that occasionally afflict networks and the "Trojan horses" that put a deceptively friendly face on malicious programs, but viruses are the most common computer ill by far.

Divided We Fall: Cooperation among Lions

Abstract: In the popular imagination, lions hunting for food present a marvel of group choreography: in the dying light of sunset, a band of stealthy cats springs forth from the shadows like trained assassins and surrounds its unsuspecting prey. The lions seem to be archetypal social animals, rising above petty dissension to work together toward a common goal—in this case, their next meal. But after spending many years observing these creatures in the wild, we have acquired a less exalted view. Our investigations began in 1978, when we inherited the study of the lion population in Serengeti National Park in Tanzania, which George B. Schaller of Wildlife Conservation International of the New York Zoological Society

Gene therapy for cancer.

Abstract: Initiation of clinical trials of gene therapies for cancer has been made possible by two major technological advances: the ability to clone genes that constitute the genetic basis of carcinogenesis or that have therapeutic potential, and the development of an increasing number of gene transfer methods. As a result, 30 experimental trials of gene therapy for the treatment of human cancer have been approved in the United States of America. Here, we discuss the current status of gene therapy for cancer together with future directions for its development.