PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 740   August 5, 2005  by Phillip F. Schewe, Ben Stein

TRACKING FLUID FLOW INSIDE A POROUS MATERIAL can now be performed with
remote MRI viewing.  MRI is an important means for sub-surface viewing of
soft objects like biological tissue or moist in solid things like rice
grains.  In a new approach, scientists at Lawrence Berkeley National
Laboratory and UC Berkeley in collaboration with Schlumberger-Doll Research
have developed a style of MRI that can be used to see how a gas flows
through a porous rock, an experimental tool with possible applications in
oil exploration, in situ monitoring of natural and manmade structures, and
industrial processes where the flow of a fluid through an opaque material
is important. To accomplish this, Josef Granwehr
(joga{at}waugh.cchem.berkeley.edu) and Yi-Qiao Song (ysong{at}SLB.com) and their
colleagues use not one radio coil but two, separated in space.  In MRI it
is customary to cause atomic nuclei in a sample (given an orientation by an
external magnet) to be disturbed by magnetic waves induced by the coil. 
The same coil is used a moment later to detect the radio waves given back
out by the target nuclei, thus providing information about their
whereabouts.  In the Berkeley setup, one coil surrounds the porous sample
and can, in combination with magnetic field gradients, selectively disturb
nuclei of the fluid in a voxel (a tiny volume element) anywhere in the
sample, while a second independent coil, positioned at the exit of the
sample, can detect the emerging material. The first coil is therefore used
to tag certain nuclei at a given point in time, while the second coil is
used to record the time of flight of the affected nuclei as they leave the
sample. Possessing location and velocity of any portion of the gas allows
researchers, in effect, to look inside the rock and watch its flowing and
unfolding.  One can trade off the minimum detectable partial pressure of
the target nuclei (tens of millibar up to one bar) for time resolution
(tens of microseconds to
milliseconds) or vice versa. (Granwehr et al., Physical Review Letters,
upcoming article)

A NEW KIND OF NANOPHOTONIC WAVEGUIDE has been created at MIT, overcoming 
several long-standing design obstacles.  The resultant device might lead to
single-photon, broadband and more compact optical transistors, switches,
memories, and time-delay devices needed for optical computing and
telecommunications.
If photonics is to keep up with electronics in the effort to produce
smaller, faster, less-power-hungry circuitry, then photon manipulation will
have to be carried out over scales of space, time, and energy hundreds or
thousands of times smaller than is possible now.  One or two of these
parameters (space, time, energy) at a time have been reduced, but until now
it has been hard to achieve all three simultaneously.  John Joannopoulos
and his MIT colleagues have succeeded in the following way.  To process a
photonic signal, they encrypt it into light waves supported on the
interface between a metal  substrate and a layer of insulating material.
These waves, called surface plasmons, can have a propagation wavelength
much smaller than the free-space optical wavelength. This achieves one of
the desired reductions: with a shorter wavelength the spatial dimension of
the device can be smaller.  Furthermore, a subwavelength plasmon is also a
very slow electromagnetic wave. Such a slower-moving wave spends more ti
me "feeling" the nonlinear properties of the device materials,
and is therefore typified by a lower device-operational-energy scale, thus
achieving another of the desired reductions. Finally, by stacking up
several insulator layers, the slow plasmon waves occupy a surprisingly
large frequency bandwidth.  Since the superposition of waves at a variety
of frequencies can add up to a pulse that is very short in the time domain,
the third of the desired scale reductions is thereby achieved. Reducing
energy loss is another great virtue of the MIT device.  The plasmons are
guided around on the photonic chip by corrugations on the nano-scale.  In
plasmonic devices the corrugations have usually been in the metal layer;
this has always led to intractable propagation losses.  However, in the MIT
device they reside in the insulator layer; this, it turns out, allows for a
drastic reduction of the losses by cooling.    (Karalis et al., Physical
Review Letters, 5 August; contact Aristeidis Karalis,
aristos{at}mit.edu)        
                        
POSSIBLE NEW PLANETS in our solar system have been spotted recently. 
Reservations about claiming new planets arises not from anything to do with
the observations, but with semantics; there is no universally accepted
definition for planet.  Even Pluto is not a planet according to some
scientists.  The two newest planet candidates are the latest residents to
be discerned in the Kuiper Belt, the zone of debris material beyond the
orbit of Neptune.  Two earlier specimens go by the name of Sedna
(www.aip.org/pnu/2004/split/677-1.html) and Quaoar
(www.aip.org/pnu/2002/split/608-3.html).  One of the new objects,
discovered by astronomers at the Sierra Nevada Observatory in Spain, is
called EL61, with an orbital radius of about 51 AU (1 AU, or astronomical
unit, is equal to the Earth-sun distance) and a size about 2/3 that of
Pluto (which itself orbits at a distance of about
32 AU).  The other object is called UB313 and was spotted by astronomers at
the Palomar observatory in California and the Gemini telescope in Hawaii. 
It orbits at a distance of 97 AU and has an estimated size larger than
Pluto).

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