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Turing Machines

At its logical base every digital computer embodies one of these pencil-and-paper devices invented by the British mathematician A. M. Turing. The machines mark off the limits of computability

By John E. Hopcroft

The Inflationary Universe

A new theory of cosmology suggests that the observable universe is embedded in a much larger region of space that had an extraordinary growth spurt a fraction of a second after the primordial big bang

By Alan H. Guth and Paul J. Steinhardt

Steel Minimills

At a time in the U.s. when some large steel plants that start with iron ore are being shut down, smaller plants that start with scrap steel and market a limited line of products locally are doing well

By Jack Robert Miller

Parasites that Change the Behavior of their Host

In doing so they make the host more vulnerable to predation by their next host. Among such parasites are certain thorny-headed worms, which infest pill bugs that are later eaten by songbirds

By Janice Moore

Oceanic Fracture Zones

They complicate the pattern discerned in the theory of plate tectonics by dissecting the edges of the plates that compose the ocean floor. Some of them are the width of an ocean basin

By Kathleen Crane and Enrico Bonatti

Island Epidemics

Epidemics are patterns in time and space that can best be perceived when they are studied in a small, isolated population. An example is provided by a study of a century of measles epidemics in Iceland

By Andrew Cliff and Peter Haggett

How Receptors Bring Proteins and Particles into Cells

Receptor-mediated endocytosis is a process whereby cells can take up specific large molecules. In most cases a receptor, having delivered its ligand, is recycled to the plasma membrane to bind more ligand

By Alice Dautry-Varsat and Harvey F. Lodish

An Indian Hunters' Camp for 20,000 Years

A rock shelter in western Pennsylvania was periodically occupied from about 19,000 B.C. to A.D. 1000. The extreme age of the site bears on the question of when men entered the Western Hemisphere

By J. M. Adovasio and R. C. Carlisle


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