Hi all,
I thought would be revelant to the probability and statistics
thread in simulating radioactive decay.
Sam Held
-----Original Message-----
From: AIP listserver [mailto:physnews@aip.org]
Sent: Friday, May 14, 1999 11:04 AM
To: physnews-mailing@aip.org
Subject: update.248
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 428 May 14, 1999 by Phillip F. Schewe and Ben Stein
PI AND RANDOM NUMBERS. Pi is a "quark" of mathematics: it
is one of the basic building blocks out of which various
geometrical and algebraic relations are built. Normally thought of
as the ratio of a circle's circumference to its diameter, pi keeps
turning up in odd places. For example, Georges Leclerc, Count de
Buffon, was the first to show a connection between pi and the
occurrence of random events. In 1777 he performed an experiment
in which needles are randomly dropped onto a surface covered
with ruled lines spaced apart by an amount equal to the size of the
needle; the fraction of times the needle comes down astride a line
is related to pi. Mathematicians have exploited this relation to
make random number generators. Sylvan Bloch (813-961-0778), of
the University of South Florida does the converse of this. He and
Robert Dressler developed software (for the classroom) for using
random numbers to generate a statistical estimation of pi. By the
way, in warped spacetime pi is not necessarily equal to the ratio of
a circle's circumference to its diameter. As an appendix to his
article in the April issue of the American Journal of Physics, Bloch
shows how "pi" varies as space becomes increasingly curved. (As
usual science journalists can obtain copies of articles from AIP
public information. For pi lore, see http://forum.swarthmore.edu/dr.math/faq/faq.pi.html.)
ATOMIC STEERING COMMITTEE. Even the smoothest-
looking coatings are very rough on the atomic scale, with islands
of atoms peppered abundantly across the microscopic landscape.
Depositing copper atoms on a Cu surface, researchers (Sebastiaan
van Dijken, University of Twente, the Netherlands,
s.vandijken@tn.utwente.nl) have identified a largely ignored
mechanism which contributes to introducing roughness in films of
atoms being deposited onto surfaces. Known as steering, it arises
when surface atoms, including already deposited ones, exert
chemical forces on incoming atoms and cause them to veer towards
the surface. This is reminiscent of how static electricity can cause
some of the milk poured from a glass to drip down the sides rather
than fall freely from the glass. Steering causes incoming atoms,
especially those approaching the surface at grazing angles, to arrive
preferentially on the top of protruding islands of atoms. Therefore,
steering can make already rough surfaces even rougher. Besides
providing insights into the causes of roughness, understanding this
effect may help researchers to prepare arrays of surface ridges,
which could serve as templates for making magnetic nanowires
and other customized materials. (S. van Dijken et al., Physical
Review Letters, 17 May 1999; figures at
www.aip.org/physnews/graphics)
KING EDWARD III of England (1312-1377) has, back to the time
of Charlemagne, about 1000 perches on his family tree. Of course
in the relatively closed world of medieval royalty, many names on
that tree appear more than once; indeed the repetition of ancestors
conforms to a predictable pattern. A new study of the statistical
properties of genealogical trees, using Edward III's pedigree as a
case history, concludes that by going about 30 generations into
your past, you and all your contemporaries will be related to
everyone who lived then, at least to those who had offspring and
who lived within that particular geographical or cultural realm.
Bernard Derrida of the Ecole Normale Superieure in Paris
(bernard.derrida@lps.ens.fr), Susanna Manrubia of the Max Planck
Institute in Berlin, and Damian Zanette (Barlioche, Argentina),
have discovered that the factors shaping the patterns of repetitions
of individuals in family trees have traits in common with the forces
that govern the behavior of granular materials and can,
furthermore, be understood using the mathematical tools applied to
a variety of phase transitions in physics. They expect their work to
have applications in the study of population genetics and
evolutionary biology. (Physical Review Letters, 1 March 1999;
view Edward's family tree at http://uts.cc.utexas.edu/~churchh/edw3chrt.html; see figure at
www.aip.org/physnews/graphics )