Scientific American

Published by Nature Publishing Group
Online ISSN: 1946-7087
Print ISSN: 0036-8733
Earth's heat keeps continents afloat and land above sea level
Fossil fuels exact the biggest toll in terms of lives lost
Physicists speak of the world as being made of particles and force fields, but it is not at all clear what particles and force fields actually are in the quantum realm. The world may instead consist of bundles of properties, such as color and shape
This article explores the influences of light on human health and suggests that exposure to artificial light may have harmful effects. The effects of ligght on mammalian tissue are either direct or indirect, depending on whether the immediate cause is a photochemical reaction within the tissue or a neural or neuroendocrine signal generated by a photoreceptor cell. Light exerts an indirect effect on the ovaries of rats and this effect is mediated by photoceptive cells in the retina. The light cycles involved in night and day and changing day lenght appear to be associated with rhythmic changes in mammalian biological functions such as body temperature. Light levels and rhythms also influence the maturation and subsequent cyclic activity in the gonads of mammals, with the particular response seemingly dependent on whether the species ovulated once a year or at regular intervals. Ovulation can be accelerated in diurnally active, monestrous animals by exposing them to artificially long days. Pineal activity in rats can be suppressed by exposing the animals continuously to light. Such findings on the multiple and disparate effects of light suggest the view that health considerations should be incorporated into the design of light environments. The illumination provided by artificial indoor lighting is often less than 10% of the light normally available outdoors. It is urged that decisions on lighting be based on knowledge of man's biological needs as well as economic and technoloical considerations.
The current population growth rate is unique in mankinds experience. The world is currently adding nearly 80 million people every year. Earlier the high fertility was balanced by a high mortality rate. In the 1970s the rate of increase has slightly exceeded 2% a year. Continuation of this rate would result in doubling the population within 35 years. The developed countries are now close to replacement levels. The underdeveloped countries are growing fast. Even if the U.S. replacement level of fertility persists there will not be zero growth for 50 or 60 years at which time its population will be 40% greater. The crude death rates for underdeveloped countries are about 14/1000 of population as compared with 9/1000 in the developed countries. The overall crude birthrates of 39/1000 population in underdeveloped countries is compared with 17/1000 in developed countries. It is predicted that the world population will increase to between 6.5 and 8.5 billion in the next 75 years with nearly all the growth in the underdeveloped countries. Final stabilization of the world population may not occur at less than 10-15 billion with 8 billion the minimum prediction. The human population is in migration from the agricultural villages to the industrial and commercial cities. The predominant view is that in underdeveloped countries rapid population growth is such a serious hindrance to development that the reduction of fertility rates will greatly enhance social and economic progress. Another view is that population growth is not always an obstacle to development. Reorganization of society redistribution of income and rectification of social injustice are emphasized as equally important. To change fertility rates there are 5 courses of action available to governments: persuade manipulate services change incentives transform social institutions and coerce. Family planning can claim some successes. However there is widespread recognition that the world must accommodate to several billion more people in the coming decades and that the curve of growth will take a long time to level off and the earlier it begins to level off the better.
The first attempt to treat an inherited human disease by inserting a healthy gene into a patient is now under way. Although such therapies have the potential to treat some of the 4,00 known genetic disorders, many obstacles remain. The most challenging is to assure that therapeutic genes are expressed adequately and persistently in the body.
The body water is about 60% of the body weight, approximately 42 liters in an average 70-kg adult (plasma volume 3L, blood volume 5.5L, extracellular fluids outside plasma 12L); higher values of b.w. are found in infants (77%) and lower in elderly subjects; → see also adme, geriatric evaluations.
Much of the life-sustaining resource is traded across national borders
The wisdom of crowds can be brilliant. It can also be corrupt
To this day, scientists struggle with that question. A better definition can influence which animals make the endangered list
What's the best way to boost sales or handle competing resellers? By lab-testing business ideas, Kay-Yut Chen gets rid of some of the guesswork
Risk management is the process that allows business managers to balance operational and economic costs of protective measures and achieve gains in mission capability by protecting business processes that support the business objectives or mission of the enterprise. Senior management must ensure that the enterprise has the capabilities needed to accomplish its mission. Most organizations have tight budgets for security. To get the best bang for the security buck, management needs a process to determine spending.
Why digital design doesn't have to imitate the physical world
Yes. And no. For time to end seems both impossible and inevitable. Recent work in physics suggests a resolution to the paradox
The pace of living quickens continuously, yet a full understanding of things temporal still eludes us
The major provisions of the Clean Air Act of 1970 were summarized and their implementations discussed. It required that emissions from new automobiles be reduced by 90% during the period from 1971 to 1976. The law also had requirements for emissions by new industrial installations such as electric power plants, oil refineries, and copper smelters and with a special category of ''hazardous pollutants''. Once standards were established, the states were directed to prepare implementation plans for the Environmental Protection Agency. In order to control emissions of air pollutants from new industrial plants, Congress attempted to prevent promoters and local governments in sparsely populated areas from attracting industry with promises that no undue fuss would be made over air pollution. Only in the case of the automobile regulations did Congress itself set standards instead of delegating the responsibility to the EPA. Many problems were encountered in attempting to meet national air quality standards. Controversies involving enforcement of the Clean Air Act concerned the use of mathematical models of air pollution. A cost-benefit-method of deciding what measures to adopt for the control of air pollution was needed. A cost-benefit analysis assigns numerical values to such effects of air pollution as impairment ofmore » health, damage to buildings and crops and degradation of the quality of life. Presently the Act's doctrine of establishing air-quality standards probably is the best approach to the problem of air pollution.« less
Top-cited authors
Abdul Rahman
  • Linton University College
Rasheedul Haque
  • Linton University College
Charles Stevens
  • University of California, San Diego
Gan Connie
  • Xiamen University Malaysia
Michael Triantafyllou
  • Massachusetts Institute of Technology