update.520 (fwd)

[Jim Choate]

---------- Forwarded message ----------
Date: Fri, 12 Jan 2001 13:50:22 -0500 (EST)
From: AIP listserver <physnews at aip.org>
To: physnews-mailing at aip.org
Subject: update.520

PHYSICS NEWS UPDATE                         
The American Institute of Physics Bulletin of Physics News
Number 520  January 12, 2001   by Phillip F. Schewe, James
Riordon, and Ben Stein   

PLANETARY OCTAVE.  Johannes Kepler succeeded in

[ SSZ: Text deleted ]

TILTING AT OPTICAL WINDMILLS. One of the greatest
challenges facing engineers who design tiny
microelectromechanical systems (MEMS) is finding ways to
power machines that often measure only microns across. The
answer, it seems, may be blowing in the optical wind. Researchers
at the Hungarian Academy of Sciences have built resin-based
structures that operate on principles similar to those that propel
windmills. Rather than extracting energy from wind, however, the
new devices are driven by beams of light. In one demonstration of
the potential for light-powered machinery, an optical vane turned a
series of interlinked cogwheels, each only 5 microns in diameter.  
The researchers (P l Ormos, pali at everx.szbk.u-szeged.hu,
36-62-433-465) manufactured various shapes for their devices,
including helixes and propellers, by curing resin with focused laser
light. A particularly promising structure that resembles a common
lawn sprinkler (see figure at
http://www.aip.org/physnews/graphics) spins at several revolutions
per second when illuminated by a 20 milliwatt laser beam. In
addition to providing torque to miniature gears, pumps, and other
micro-machines, the light-powered rotors could be used to measure
fluid properties on micrometer scales. Alternatively, it may be
possible to study the mechanical properties of certain molecules,
such as proteins or DNA, by fixing one end to a surface, attaching
a rotor to the other end, and using light to apply a twisting force.
(P‚ter Galajda; P l Ormos, Applied Physics Letters, 8 January
2001.)

ARRAYS OF LOW-TEMPERATURE SENSORS can now be
serviced by a single SQUID
detector operating in a multiplex mode for the first time. A
SQUID, short for superconducting quantum interference device,
can detect very small magnetic fields in the following way: a 
SQUID circuit consists basically of a superconducting loop
interrupted at two points by a thin insulator gap through which
pairs (Cooper pairs) of electrons must tunnel (that is, in their
wavelike capacity the electrons can pass through an otherwise
forbidden zone) to maintain a flowing current. This whole process
is sensitive to any magnetic flux threading the circuit. The addition
of more flux will cause a slight voltage increase across the gap.
Thus a SQUID operates as a flux-to-voltage converter, but can also
be used to read small currents. Physicists at UC Berkeley (contact
Jongsoo Yoon, 510-642-8809, yoon at cfpa.berkeley.edu) have now
developed a SQUID-based multiplexer which can interrogate
arrays of many low-temperature sensors all at once. This makes
possible arrays of a thousand or more sensors for
magnetoencephalography (which maps magnetic fields from brain
activity) and arrays of several thousands of a voltage-biased
superconducting bolometers,  or VSBs, employing tens of
multiplexers. Such large VSB arrays are being developed for the
next generation of spacecraft-based astronomical
observations to detect radiation from interstellar dust and to
explore the earliest history of the Universe by measuring the
cosmic microwave background radiation. The multiplexer is also
useful for arrays of sensors for the detection of ultraviolet light and
X-rays.(Yoon et al., Applied Physics Letters, 15 January 2000.)

CORRECTION.  The correct acronym for the rainfall measuring
satellite (Update 518) is TRMM (not TRIM), and its correct
website is http://trmm.gsfc.nasa.gov/