Text 239, 81 rader
Skriven 2004-11-17 19:41:11 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 709
===============
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 709 November 17, 2004
by Phillip F. Schewe, Ben Stein
                        
WHAT PROPELS A BOOK TO THE TOP OF ONLINE SALES CHARTS?  Is the latest
bestseller simply the product of clever marketing or has it truly permeated
society?  Will its popularity wane as quickly as it appeared or will the book
be a classic for future generations? Though these questions seem to lay outside
the realm of science, scientists can actually obtain deep insights into these
issues by using the tools of statistical physics, which can predict the rates
at which certain events occur, such as the number of aftershocks following a
major earthquake or the number of large avalanches in a given sandpile.  Using
a unique database of the Amazon.com rankings of book sales, scientists (Thomas
Gilbert, UC-Berkeley, 510-642-5295, tgilbert@haas.berkeley.edu) followed the
chart histories of books that reached the top 50 in sales.  The researchers
found that the bestsellers generally reach their sales peaks in one of two
ways, which they classify as "exogenous shocks" (e.g., a rave review in the New
York Times) and "endogenous shocks" (e.g., word of mouth).  An endogenous shock
appears slowly but results in a long-lived growth and decline of sales owing to
small but very extensive interactions in the network of buyers.  For example,
"The Divine Secrets of the Ya-Ya Sisterhood," reached the bestseller lists two
years after it came out (and without a major marketing campaign) by making the
rounds of book-discussion clubs and inspiring women to form "Ya-Ya Sisterhood"
groups of their own. In contrast, an exogenous shock (rave review) appears
suddenly and propels a book to bestseller status; however, these sales
typically decline rapidly, much more quickly than those that made the charts
via word-of-mouth.  In either case, single triggering events (e.g., a mention
on "Oprah") appear to have much less effect on the sales history of a book than
the actions of interconnected groups of people, who may pick up the book after
multiple conversations with acquaintances or by hearing about the book 
secondhand or by remembering a friend's recommendation months or even years
after the book comes out. According to the researchers, marketing agencies
could apply their method of classifying and analyzing bestsellers to measure
and to maximize the impact of their publicity on the network of potential
buyers.  (Sornette, Deschatres, Gilbert, and Ageon, Physical Review Letters,
prob 26 November 2004).

ATOM  LITHOGRAPHY, shooting sculpted beams of atoms at a substrate, can create
lines of deposited atoms with widths as narrow as 50 nm. Two groups in Holland
have separately carried out experiments in which atoms, heated in an oven,
released through a baffle, "cooled" by laser rays striking the beam at right
angles, and then focused in optical microlenses consisting of opposing laser
beams.  In the case of physicists at Eindhoven University of Technology
(contact Ton van Leeuwen, 31-40-2474094, k.a.h.v.leeuwen@tue.nl) the best
resulting grid of iron atoms had lines only 50 nm wide and spaced consistently
186 nm apart (see figure at www.aip.org/png).  The researchers expect to
achieve 10-nm lines, but their chief aim is to move from producing simple grid
patterns to making more elaborate patterns with holographic and other
techniques. They are also pursuing a "single-point writer" option, in which the
full atomic beam will be focused to a single, very intense spot.  What is the
advantage of such slow atom-beam approach to lithography?  Mainly it is the
directness of the method for inscribing microcircuitry (no etching or use of
masks) and exercising great control over line width and spacing.  The
researchers also admit that there are imposing technological hurdles to using
this approach on an industrial scale.  Short-term applications would most
likely be for making MEMS-like structures (teSligte et al., Applied Physics
Letters, 8 November 2004; text at www.aip.org/physnews/select; lab website at
www.phys.tue.nl/aow).  The other Dutch group, at Radboud University Nijmegen
have laid down their own grid of iron atoms with lines 95 nm in width, 186 nm
apart, and covering an area of 1.6 x .4 mm^2. (Myszkiewicz et al., Applied
Physics Letters, 25 Oct; contact Theo Rasing, 31-24-3653102) The two groups are
now working together on some joint ventures.

AN AVALANCHE SPIN-VALVE TRANSISTOR switches a current "on" or "off"depending on
whether the magnetizations of two thin films are parallel (large
current) or anti-parallel (small current).  Such a spintronic transistor is
somewhat like the giant magnetoresistance (GMR) read heads in hard drives, but
is 10 to 100 times more sensitive.  The usual drawback of spin-valve
transistors, a weak output current, is, in the Harvard lab of Venkatesh
Narayanamurti, overcome by using an avalanche process much like the one used in
photodetectors---an incoming electron ionizes several secondary electrons, each
of which ionizes still more electrons, adding up in the end to a sizable
current.  One of the team members, Kasey Russell (kasey.russell@gmail.com,
617-496-5471) says that the extra sensitivity and strong output could lead to
use of the device in magnetic storage technologies. (Russell et al., Applied
Physics Letters, 8 November 2004; lab website at
http://www.deas.harvard.edu/venky/research.html#overview)

---
 * Origin: Big Bang (1:106/2000.7)