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Micro vs. Macro
I read the article “A New Wave of Microfluidic
Devices” with great interest. Fluidic circuits were investigated
in the 1960s as an alternative to electronic devices such as vacuum
tubes and solidstate devices. In the 1970s, I participated in an
effort to develop fluidic diodes and flip-flop devices based on
the Coanda effect, that is, the tendency of a fluid jet to follow
an adjacent curved surface.
I wish to point out that the crucial difference between macro-
and microfluidics is in the use of Newtonian and non-Newtonian fluids
as the working medium. Newtonian fluids are characterized by a linear
relationship between shear stress and strain (deformation) of the
fluid. The miniaturization of devices based on Newtonian fluids
was rendered impossible by the high pressures needed to drive these
devices to display the kind of highly nonlinear behavior required
of them to be of practical use.
Non-Newtonian fluids - characterized by a nonlinear relationship
between stress and strain—are now being used to develop miniature
fluidic devices, not only for biochemical applications as reported
in the TIP article, but also in logic and memory applications analogous
to electronic circuits. Readers of TIP will also enjoy the article
“Microfluidic memory and control devices,” by Alex Grossman
et al., Science 2003, 300, 955–958.
Anutosh
Moitra
The Boeing Co.
Seattle, Washington
Neutron generators
The article by David L. Chichester and James D. Simpson “Compact
accelerator neutron generators” describes the conventional
sealed-tube beam-on-solid-target type of neutron generator, but
it ignores two other newer neutron-generator technologies that are
easy to find on the Web.
One is a family of devices from the Lawrence Berkeley National
Laboratory (LBNL). Some of these devices have been built as laboratorylevel
development prototypes and are the basis of several papers published
in physics journals. The principle of operation can be reduced to
saying that deuterons are extracted and accelerated onto a solid
target that is arranged in different configurations, depending on
the topology of the neutron generator. LBNL is trying to find a
commercial enterprise to invest in the substantial effort to bring
these gadgets to market.
The other neutron generator has been developed as a purely commercial
marketready product by a start-up company operating from the United
Kingdom and Germany called Neutron
Systems Development (NSD) Ltd. This generator derives from inertial
electrostatic confinement (IEC) fusion research. The commercialization
effort started in the mid-1990s, when a major European aerospace
company adopted it at a time when non-core business initiatives
were encouraged. Like some of the conventional neutron generators,
it was eventually cast off by the parent corporation. In this case,
the project was reborn as an independent start-up business with
its own intellectual property. One difference between this and other
technologies is that it has no solid target to sputtererode. While
the longevity of conventional sealed-tube devices has been extended
from 500 h to a range of 3,000–4,000 h for certain beam/solid-target
sealed neutron generators, the prototype commercial IEC device reached
7,000 h before upper management effectively axed the business. Another
difference is that the neutron source geometry can be provided as
a line source or a conventional pointlike source.
The elevated concern for security screening technology has created
a market for neutron generators ordered in quantity long hoped for
by the manufacturers of neutronbased screening systems. Unfortunately,
general industrial usage has been inhibited by the relatively short
life and consequential unattractive life-cycle costs as compared
to 252Cf sources. The availability from NSD of the line-source neutron
generator, with a lifetime measured in years, will soon change the
market. Although this writer is a director of NSD and is therefore
biased, it is lamentable that the editors of The Industrial Physicist
did not check that the article was complete in its coverage, if
not impartial.
John Sved
Neutron Systems Development Ltd.
Liverpool, U.K.
[Authors reply: Of course, there are many different
ways to produce neutrons besides the one described in our article.
Unfortunately, because of space constraints, we had to cut from
our original submission a discussion of next-generation neutron
generators. Among these are accelerator designs based on radio-frequency
(RF) ion sources and systems using the IEC approach.
The RF systems are particularly interesting for industrial applications
because of their small size and high potential neutron yields
(>1 × 1012 neutrons/s). However, despite the
exciting promise of RF-based systems, they have not yet seen widespread
commercial use. For the most part, this is not due to technical
problems associated with the approach, but simply because the
final step of commercialization has not yet been taken.
A somewhat different situation exists for neutron generator
systems based on the IEC technique. Although a great deal of research
effort has been focused on these systems, specifically toward
their development for industrial applications, their commercial
success has been disappointing. Despite the development of prototype
commercial IEC neutron generators and some laboratory and field
trials, these systems have not yet found commercial acceptance
as an industrial technology. This is witnessed to, in part, by
the actions of the technology’s previous owner in canceling
its IEC development program a few years ago. It is difficult to
pinpoint the reason that this approach has not matured further,
but it may be partly due to the absence of specific information
on performance, including operating lifetime and costs, serviceability,
system reliability (in the real world, outside the laboratory),
and performance stability over time in the face of changing ambient
conditions. In some cases, the large size and power consumption
of these systems in comparison with compact-acceleratorbased neutron
generators may also be a contributing factor.
We regret that we could not describe in more detail the prospects
for future compact- accelerator neutron generators and other interesting
devices for producing neutrons, such as the IEC line source. However,
as in any article for publication, there must be a focus to avoid
exceeding reasonable burdens on the editor or the reader. In our
case, we chose to focus on systems presently suitable for commercial
use and some of their industrial applications.]
Electric grid
Eric Lerner’s article (“What’s
Wrong with the Electric Grid?”) did a good job of documenting
the situation and commenting on the failure, but I did not find
the cause of the failure in the article. Quite simply, the control
components and logic are dynamically unstable. The automatic trip
levels are too slow and set wrong, and, when they do trip, their
action is not continued in a manner that promotes stability. You
will always be able to overload a system, but that should not result
in shutting down much more than the overloaded area. When you overload
and lose the whole system, you have unqualified people responsible
for your control dynamics.
Hugh Coleman
Kelso, Washington
Why have I not seen such a clear and excellent explanation before?
The level of writing is surely not more technical than in The
New York Times science section, where one might expect to have
seen this story spelled out already.
Leonard X. Finegold
Physics Department
Drexel University
Philadelphia, Pennsylvania
I would expect a news item published in The Industrial Physicist
to get at least the basic physics right. This was not the case with
the political diatribe masquerading as the technical article “What’s
Wrong with the Electric Grid?” Heat builds up in generator
bearings due to underspeed operation? Only generators can produce
reactive power? It is true that deregulation, as it has been implemented
in the United States, has not adequately considered the operation
of the electric transmission system. It does not follow that deregulation
is inherently bad. There are good arguments on both sides of the
deregulation issue, but this article does not address them.
Wayne
E. Miller
PA Consulting Group
Broomfield, Colorado
The important milestone in the history of the North American grid
is deregulation —not the blackout. Your article
makes it clear that blackouts are the inevitable outcome of uninformed
changes in the factors that affect interruptions in the grid. And
there may be other problems as an outcome of utility companies,
formerly the willing guardians of the “system,” being
forced to play a complicated game with insufficient means.
I have a long history with Pacific Gas & Electric. The company
did a fantastic job of providing reliable, inexpensive gas and electrical
service. And if a kid was missing or someone needed help, its employees
were likely to drop everything and lend a hand. That is something
you won’t see much of in the future. The little contractors
providing power and worrying about losing slim profits are not likely
to applaud the work of their crews in some community effort they
were not authorized to support.
Had your article been published before deregulation, it could have
shed some light on issues that needed to be resolved before the
old barriers were removed—before deregulation caused the wholesale
loss of talent in the oversight of electric transmission.
The conditions that cost me my job with the utility company are
the same as those that continue to challenge our grid/interconnect.
I couldn’t believe the feds would mess with the transmission
and distribution system. I watched helplessly as it happened right
in front of me.
Many thanks to Eric J. Lerner for writing an overall explanation
that can be understood by the lay person without being oversimplified
and misleading. The scientists and engineers I worked with would
have had a hard time ignoring the truth if this article had been
available to read and share with others at that time. I only wish
someone had gotten this information into the heads of the Federal
Energy Regulatory Commission before they acted on deregulation.
Randy C. Smart
Former PG&E employee
[Eric Lerner replies: Many of the letters in this and
the last issue address the question of how to better match local
power supplies to local power needs, in order to reduce the long-distance
energy transmission that stresses the grid and contributes to
largescale blackouts. A few points need reemphasis. The changes
in the rules controlling utilities that were made in 1996–2000,
while called “deregulation,” were actually changes
in regulations, not reductions in the number of regulations. Eliminating
those changes, such as Order 888, which mandated that utilities
allow long-distance power wheeling across their lines, would not
be “a return to regulation” but a change back to older
rules. Eliminating Order 888 would certainly have the effect of
greatly cutting back on long-distance energy transmission.
Purely economic incentives that add costs to energy transmission
have their own problems. Utilities are not capable, as Bob Strachan
proposes (December 2003/January 2004, p. 8), of “owning,
buying or leasing unilateral transmission facilities” because
electricity does not flow directly from point a to point b but
takes every available route. So one utility cannot own all the
transmission facilities that its electricity flows over—unless,
as in some European countries, a single nationalized utility owns
the whole grid.
Until quite recently, nationalized, unified power grids were
the rule in Europe and much of the rest of the world, and in general,
they delivered highly reliable power at low cost. Another benefit
is that such unified nationalized systems also lack incentives
for long-distance power transmission.
Economic incentives for reactive power production also pose
difficulties, given the single-machine character of the grid.
Reactive power is not just needed in certain amounts—it
is needed in the right time and place. Utilities that have to
provide nearly all the power for their own areas have a huge incentive
to supply it when and where needed —they get the full blame
if the lights go out. But when long-distance power trading is
encouraged, responsibility becomes far more diffuse. Utilities
could produce reactive power when most convenient for themselves
rather than when needed for the system. Similarly, taxes on long-distance
transmission, which already exist in the form of fees paid by
utilities to each other, will not prevent overloading lines if
utilities find that the prices obtained more than balance the
fees.]
Correction
In December 2003/January 2004, “North
of the Border,”
by Dan Fleetwood, p. 27, Figure 2: This work was done at Bell Laboratories
in 2000–2001 by Julia Hsu before she moved to Sandia National
Laboratories, and it is not the subject of her invited talk at the
APS 2004 March meeting.
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