Showing papers in "American Scientist in 1988"

Skill in Chess

Abstract: As genetics needs its model organisms, its Drosophila and Neurospora, so psychology needs standard task environments around which knowledge and understanding can cumulate. Chess has proved to be an excellent model environment for this purpose. About a decade ago in the pages of this journal, one of us, with Allen Newell, described the progress that had been made up to that time in using information-processing models and the techniques of computer simulation to explain human problem-solving processes. (Simon et al, 1964). A part of our article was devoted to a theory of the processes that expert chess players use in discovering checkmating combinations (Simon et al, 1962), a theory that was subsequently developed further, embodied in a running computer program, mater, and subjected to additional empirical testing. (Baylor et al, 1966).

Land Mammals and the Great American Interchange

Abstract: Xhe continents of South America, Africa, Antarctica, Australia, and India were once joined in a large land mass in the southern hemisphere called Gondwana. About 100 million years ago (mya) South America began to separate from Africa, moving in a primarily westward direction. There is no convincing geological evidence to indicate that South America had a continuous land connection with any other continent _ until about 3 mya, when the Bolivar Trough marine barrier disappeared and the Americas were united by the emergence of the Panamanian land bridge. The long-isolated continental biotas of North and South America were brought into contact, resulting in an intermingling that has come to be known as the Great American Interchange (Webb 1976; Fig. 1). The site of the former Bolivar Trough is thus the gateway for this event, de noting the historical boundary be tween two biotic provinces (Fig. 2). Although many different groups of plants and animals took part in the interchange, I will focus on land mammals, which are the most thoroughly studied of the participants. The Great American Interchange was first recog nized by Wallace (1876), but it has taken another hun dred years of intense paleontological study by Amegh ino, Matthew, Scott, Patterson, Simpson, Webb, and others to clarify patterns of dispersal (see, for example, Marshall 1981, 1985; Webb 1985; Webb and Marshall The emergence of the Panamanian land bridge three million years ago permitted the mingling of the long-separated faunas of North and South America 1982). It is only during the last decade, moreover, that greater precision in dating the sediments containing interchange taxa has provided a firm time frame for various aspects of the event. It is now possible to assess the interchange in detail, and to analyze the tempo and mode of dispersal and the rates of extinction and origina tion in successive faunas through time. As a result, the _ Great American Interchange repre sents the best-documented example in the fossil record of the intermin

Hormones and behavior: the biology of thirst and sodium appetite

Abstract: D iscussions of how hormones influence behavior have generally been limited to the effects of gonadal hor mones on reproductive behavior and have emphasized the parsimonious arrangement whereby the same hor mones involved in the biology of reproduction also influence sexual behavior. It now has become clear, however, that other hormones, in addition to their recognized influence on biological functions, can affect behavior. Specifically, peptide and steroid hormones involved in maintaining the physio logical balance, or homeostasis, of body fluids also appear to play an important role in the control of water and salt consumption. As Claude Bernard noted in the

The counterintuitive in conflict and cooperation

Abstract: Conflicts and cooperation offer two kinds of surprises: ition, mathematical analysis shows that the use of reathose generated by a participant and those generated by sonable and traditional rules of thumb can lead to surthe situation. Surprises of the first kind are familiar. For prising results for all participants. Mathematical analyses example, in The Art of War (1521), the Florentine bureau- of these models appear elsewhere. Here I describe only crat Niccolb Machiavelli counseled military commanders the models and their properties. to surprise their opponents; he gave many historical Because the training and intuition of different peoexamples of such surprises. How best to achieve surprise ple are different, one person's surprise is often another in political and military conflicts is person's so-what. In the examples

The Daedalus Project: Physiological Problems and Solutions

Abstract: In April of 1985, a team of engineers and scientists at the rations showed that our pilot would be required to Massachusetts Institute of Technology began a research produce approximately 3.0 to 3.5 watts of mechanical program with the goal of flying an aircraft from the power per kilogram of body weight to fly at all. FurtherGreek island of Crete powered only by the muscles of more, because human-powered aircraft require signifthe pilot. The project was called Daedalus, in celebration candy more power to climb than to fly on the level and of the mythical Greek inventor who constructed wings of so generally fly within a few meters of the surface, there wax and feathers with which he flew from imprisonment would be no time to glide, and the pilot would be on Crete some 3,500 years ago. In some versions of the required to produce this power continuously, with no myth, Daedalus was accompanied by his son Icarus, rest, for the entire flight. who flew too dose to the sun, against his father's The metabolic cost to the pilot of maintaining the admonition, and fell to the sea when constant mechanical power produchis wings melted. tion of 3.0 to 3.5 watts per kilogram The route proposed in the DaeThe challenge of a humanof body weight is relatively easy to dalus project, from the port city of ligh determine. Potential energy is conHeraklion on Crete to the island of powered flight lasting verted into mechanical work by the Santorini (or Thira), was 119 km, t hours oxidation of stored fuels to generate more than three times the existing Up o SIX rs posed the high-energy compounds that are world record for human-powered unique physiological necessary for both the contraction flight, Bryan Allen's 35-km crossing L s 2 r and relaxation processes in skeletal in 1979 of the English Channel in the problems ana required muscle (see Ethan Nadel's article in Gossamer Albatross (Fig. 2). In the unique solutions American Scientist, July-August 1985, years since the record was set, adfor an expanded account of energy vances in aircraft tedhnology had conversion in skeletal muscle). It is made our more ambitious attempt possible, although generally accepted that in humans only about 24% of the much needed to be learned about the physiology of the potential energy of these stored fuels can be converted to human pilot. In fact, the fundamental challenge of mechanical work during the metabolic transfers human-powered flight is the limited ability of humans to (Astrand and Rodahl 1986); this value is known as the act as a power plant. Preliminary estimates of the mechanical efficiency. The remaining 76% is converted aircraft's performance, based on previous designs, indidirectly to heat during these transfers and is of no use to cated that the Daedalus flight would last four to six the pilot. Thus, in order to generate mechanical power at hours. Before an aircraft could be designed in detail, we the rate of 3.5 W/kg, the pilot would have to maintain a needed to learn more about the physiological limits of fuel-oxidation rate of 14.6 W/kg, which requires an long-duration exercise and about possible countermeaoxygen uptake of more than 44 ml 0Q/(min kg). The sures that would postpone the onset of fatigue. We pilot has to sustain this rate of oxygen uptake, without sought an engineering model for human power producpause, to maintain steady flight. This metabolic cost is tion that we could address with the same analytical tools approximately the same as that required to pedal a an aircraft designer would use in matching power plant bicycle over level ground at a world-class speed of to airframe. It was that goal which brought the authors37 km/hr (Whitt and Wilson 1982). a physiologist and an aeronautical engineer-into colThe problem unique to the Daedalus project was laboration. whether this energy production could be sustained for Because an aircraft engine must carry its own the anticipated four to six hours of the flight. A thorough weight, its performance is often expressed in power per review of the existing literature yielded no convincing unit weight or power-to-weight ratio. Preliminary calcudata for human power production of durations beyond about three hours, and no data taking the sizes or body

Seeing stars with speckle interferometry.

Abstract: -Astronomers view the universe through an atmospher ic veil surrounding the earth that obscures a large part of the electromagnetic spectrum and distorts much of the remainder, including most visible and infrared wave lengths. Irregularities within atmospheric layers create small convection cells of air with slightly different tem peratures and densities from the air in neighboring cells, and the differential refraction induced by this condition changes rapidly as winds blow the cells across lines of sight to celestial objects. This results in an image from a point source such as a star that is greatly blurred, changing in appear ance on time scales of a few hun dredths of a second. For nearly a century, great ob servatories have been located on mountaintops selected after exhaus tive searches for sites with the most transparent and stable air above them to minimize atmospheric effects on seeing. The latest effort at survey ing sites was completed in April 1987 with the announcement by the Na tional Optical Astronomy Observa tories that the 16-m National New Technology Telescope would be lo cated on the Hawaiian volcano Mau na Kea. Mauna Kea is well known for

Knowledge and Belief: The Impact of Einstein's Relativity Theory

Abstract: Einstein's theory of the Brownian motion, his introduc tion of the light quantum, but above all his theories of special and general relativity have profoundly changed the way modern men and women think about the phenomena of inanimate nature It would actually be better to say "modern scientists" than "modern men and women" Indeed, in order to appreciate the contribu tions by Einstein in their fullness one needs to be schooled in the physicist's style of thinking and in mathematical techniques, not that difficult for special relativity but quite advanced for the case of general rela tivity It is an optimistic guess that only one in every hundred thousand people alive today has any insight into what Einstein's relativity is really all about It is of course by no means un common that only a tiny fraction of humanity has a genuine grasp of advances in science of any kind whatsoever, or even knows who made them It is therefore all the -

The physical significance of the reciprocal lattice of crystals.

Abstract: Since the discovery of Laue in 1912, the diffraction of X rays through crystals has been considered as an interference effect of waves, controlled by the Laue and Bragg rules for the direction of the diffraction maxima and supplemented by rules connecting the relative intensity of the maxima with the Fourier wave analysis of the matter distribution within the basic lattice cell. In spite of the great success of the classical wave theory it must not be forgotten, however, that the quantum theory considers waves only as a one-sided working hypothesis opposed by the hypothesis of mechanical particles. The uncertainty principle delimits the applicability of the classical theories in microscopic dimensions. There are many large-scale phenomena, however, among them the diffraction of a broad ray of light (or a cathode ray) through a large-sized crystal, which may be derived from either classical hypothesis. A mechanical theory of X-ray diffraction, resting on a re-appraisal of the Bragg reflection rule (section 1, below), was first established in 1923 by P. Duane. A similar re-interpretation of the Laue interference rules (section 2) lends a new physical significance to the concept of the reciprocal lattice of a crystal. The latter is usually considered as an abstract geometrical construction in spite of its wide usage in structural analysis. If the present article should contribute to lifting the reciprocal lattice from its abstract mathematical pedestal to a more realistic position in the physics of crystals, it will have attained its goal.