Turbulence Onset Despite Stable Laminarity Of Hagen-Poiseuille Pipe Flow, Rev. Mod. Phys. 
Now nearly 120 years have passed since Osborne Reynolds's
seminal experiments about the onset of turbulence in fast flowing
water through a pipe, but also more than 100 years of failure to
identify the transition mechanism in terms of an instability. Many
researchers, including William Thomson, Rayleigh, Orr, Sommerfeld,
Taylor, Heisenberg, Lin, Orszag and others have developed various,
sophisticated methods to find the instability of the Navier-Stokes
fluid equations for pipe flow, but failed. Only recently the
relevant mechanism seems to have been elucidated: It is claimed
that not the eigenvalue spectrum (which lies completely in the
stable range of the complex plane to the left of the imaginary
axis), but the bunching of the eigenfunctions under the coupling
to the parabolic Hagen-Poiseuille laminar background flow gives
the key.
Mathematically the shear profile of the laminar pipe flow
creates a nonnormal, linear eigenvalue problem. The fact that the
problem is not "normal" is important since it implies that not all
eigenvectors need to be orthogonal to each other and can therefore
become sensitive to perturbations in a way that is not predicted
in the traditional analysis. For instance flow perturbations not
being dominantly in the flow direction can draw energy from the
laminar flow and become amplified - though transiently only.
Simultaneously they adopt the downstream predominance. The
amplification 'level' increases with the Reynolds number. But once
being strong enough, the nonlinear interaction becomes
effective.
Recent theory shows that part of the nonlinear action
reestablishes disturbances which are mismatched relative to the
main flow. These again are able to draw energy, starting now
already from a higher amplitude level, transiently grow further,
interact anew, and so on. A feedback loop is established leading
to turbulence by an intricate balance of nonnormal and nonlinear
effects.
The characteristic signature is the existence of a "double
threshold": Two conditions must be satisfied: the Reynolds number
must be large enough and the disturbance must exceed some
threshold amplitude. The latter decreases for increasing Reynolds
number as a powerlaw with exponents around -3/2, depending on the
flow geometry as argued very recently by Trefethen et al.
The nonnormal-nonlinear turbulence onset also needs many more
degrees of freedom than standard eigenvalue instability: about 50
in models and 10^5 in realistic flows. The hydrodynamic
nonlinearity otherwise cannot make proper use of the
nonnormal-nonlinear mechanism. In models fewer variables will do,
but at the price of an artificial interaction.
The turbulence threshold also depends on the type of flow
perturbations: Tapping on the pipe or twisting it can have a much
stronger effect than perturbations, say, along the flow direction.
That explains why experimentally different onset ranges are
reported, quite in contrast to the reproducably sharp critical
Reynolds number in case of a linear instability. For a fixed type
of the disturbance but varying amplitude the double threshold
seems to be fractal as Bruno Eckhardt et al. found in simulations.
They also noted a close relation with the existence of new
stationary states having finite disturbance amplitude but being
unstable solutions of the Navier-Stokes equations. The first such
solution has been found by Nagata ten years ago.
The nonnormal-nonlinear onset mechanism immediately produces
violent, finite level turbulence with many scales. It is a new
mechanism in complex dynamical systems, adding to the bouquet of
fascinating nonlinear phenomena.
- Contributed by Siegfried
Grossmann
- The
Onset Of Shear Flow
Turbulence, Siegfried
Grossmann, Reviews of Modern Physics, Vol. 72, No. 2,
April 2000
- Minimum
Description Of The Onset Of Pipe
Turbulence, Brosa, U.,
and S. Grossmann, 1999a, Eur. Phys. J. B 9,
343-354.
One Choice Too Many In Electricity's New Free Market, NYTimes
One of the reasons, why many people were attracted to
socialism in the previous century was that the state made sure
that basic needs were affordable for everyone: Food, housing, and
medical costs were kept down by massive state interventions. It
turned out that this situation was unstable and a market economy
emerged e.g. in Russia which unofficially co-existed for a number
of years parallel to the "official" economic system. In the
meantime the US was always seen as the prime example of the
success of unconstrained market economy.
Therefore it is an interesting phenomenon that within a
successful market system there are economical islands where laws
of the market apparently are not accepted by the public. Two of
the most important areas are the energy (both in terms of
electricity) and the water market (see also ComDig
2000.30#1, 27#4
and the videos of Massoud
Amin and George
Verghese in ComDig
00-31)
California started a market experiment in the electrical power
sector and faces now attempts with a number of often ad hoc
re-regulation attempts:
"Loretta Lynch,(…), explained that the price caps would
apply only to individuals who use 500 kilowatts (sic!) or less a
month or from 60 percent to 70 percent of customers in the city.
Customers who use more than that will be charged the higher rates
in the unregulated market, she said. The decision also applies
only to small-business customers, those that use 1,500 kilowatts a
month or less. " (1)
If we model customers as intelligent, adaptive agents, how
would they respond to a state imposed price cap? Certainly
different than to largely increased costs for electricity.
"People want to make choices about clothes and restaurants
and what houses they live in, but a lot of us would rather not be
bothered with having to make a choice about electricity," said
Wendy Kaminer, a public policy fellow at the Radcliffe Institute
for Advanced Study in Cambridge, Mass. "It's not a desire to be
disempowered," Ms. Kaminer added. "It's a desire not to be
bothered." (2)
There have been other attempts to make energy consumption more
tangible to average consumers by estimating the amount of human
work that would be equivalent to the consumed energy. Instead of
abstract units of kilowatts H.P.Duerr of the Global Challenges
Network introduced the units of one "energy slave" being
equivalent to the work of a (strong) human producing 100 Watts in
a 12hr workday (7 days a week). In those energy units US consumers
employ in the average a force of 110 energy slaves compared to 60
in central Europe and 8 in China.
- (1) In
Reverse, California Acts to Cap Some Electric
Bills, The New
York Times on the Web, Tuesday, August 22,
2000
- (2) One
Choice Too Many In Electricity's New Free
Market, Kirk
Johnson, NYTimes, August 27, 2000
- Selbstbeschränkung
- Eine Unmögliche
Notwendigkeit?,
Hans-Peter Dürr, Auftaktveranstaltung der
Projektgruppe "Grüne Akademie" in der
Heinrich-Böll-Stiftung am 16./17. Juni 1998 in
Berlin
- Global
Challenges Network
-
Excerpt: "Here's a good puzzle: What motivates
thousands of computer programmers-and even the companies that
employ them- to share their code with the world? The growing use
of so-called "open source" software may not seem, at first glance,
to make much economic sense. But according to research by HBS
Professor Josh Lerner and his colleague Jean Tirole, economics,
especially labor economics, may actually help explain why open
source works as well as it does.
Delayed rewards, what Lerner and Tirole call the "signaling
incentive," include the "career concern incentive" which refers to
future job offers, shares in commercial open source-based
companies or future access to venture capital, and the "ego
gratification incentive," focused on a desire for peer
recognition. Though different in some regards, both have been
shown to be stronger when the work is visible to people the
programmer wants to impress (colleagues, venture capitalists, the
overall job market).
With immediate rewards, commercial projects have an edge as
far as money goes-the proprietary nature of the code generates
income, making it possible for firms to reward programmers with
salaries. But open source projects carry two advantages that
commercial projects can't match. One is the "alumni effect":
programmers are already used to working with the open code from
their time in schools and universities, where it was freely
available; they are able to build on knowledge they already
possess. And, two, programmers welcome the opportunity, made
possible by open source, to customize and de-bug projects, either
for personal use or to make their job easier at their
firm."
Intel: The Future Is Peer, ZDNet News
Excerpt: "The peer-to-peer networking revolution
championed by Napster will change computing, Intel Corp. believes.
And the rest of the industry better jump on board, said Pat
Gelsinger, Intel's chief technology officer, in his Intel
Developer Forum keynote speech Thursday morning.
As previously
reported, Intel is spearheading a number of efforts to
make sure that peer-to-peer networking receives wide adoption on
the part of service providers and consumers.
"We suggest that it could be ushering in the next computing
revolution," Gelsinger said. "Our job now as an industry is to
change our perspective and now build the infrastructure that
allows peer-to-peer computing to emerge in a broad way."
Not that the chip maker is embracing Napster and other
music-file sharing services that have run afoul of the recording
industry. Officially, Intel (Nasdaq: INTC) has no opinion on
Napster. However, it's quite clear Intel believes that this kind
of model will play a major role in the future of computing.
(…)"It takes on a dynamic, self-organizing nature ...
and the network brokers services to those who can partake of
them," Gelsinger said in an interview Wednesday night.
Gelsinger compares Napster to Mosaic, the first widely used
Web browser and the trigger for the Internet revolution. He also
expects peer-to-peer technology, with the aid of the working
group, to develop in much the same way the Web did. With Mosaic
came the need for standards for transfer of data (HTTP) and
security (SSL). (…)"
How Web Finance Might Untangle the Napster Mess, Businessweek
Excerpt: "If Napster can give music away, why
would anyone buy a CD? It's a good question. But the answer for
the music industry is not to rely on the courts to solve their
problem. Instead, they should follow the route taken by the
full-service brokers, who have attacked their online rivals
head-on by cutting prices and expanding their products and
services on the Web. The result has been soaring assets and
profits.
The music industry may soon have potent new ammunition to
compete. Record moguls should look closely at the latest
development in the world of online finance. New e-payments
technology being developed by Silicon Valley startup Dynamic
Transactions Inc., which runs the Web site www.PayPlace.com,
potentially offers a valuable solution to the industry's
problems.
How? By linking file-sharing technology with e-payments
technology. Any file that can be shipped on the Net from one
computer to another can be attached to an e-payment system
requiring recipients to pay money via e-mail before the file can
be executed. That means anytime a file transfer is made, record
companies get paid. Copyright protection would be ensured through
the use of separate encryption technology, such as that used by
Liquid Audio.
This person-to-person payment system is similar to that
developed by PayPal (www.paypal.com),
a unit of X.com (www.x.com).
PayPal is now widely used by eBay customers to make payments via
e-mail. Dynamic Transactions uses a similar e-mail payment system,
but adds the ability to link e-mail payments to
files."(…)
Squeezing Out Pyruvate, Science
One model for the origin of life is that the necessary
building blocks originated at hydrothermal vents in a series of
reaction steps where metal sulfides at elevated pressures and
temperatures catalyzed carbon fixation and the formation of more
complex organic molecules. Cody et al. (p. 1337; see the
Perspective by Wachtershauser) performed experiments that simulate
some of the possible conditions of marine hydrothermal systems and
show more complex organometallic species forms in this environment
that catalyze the formation of pyruvate, a critical biochemical
molecule. High pressures appear to compensate for the high
temperatures that would normally cause pyruvate to decompose.
- Life
As We Don't Know It,
Gunter Wachtershauser, Science 2000 289: p.
1307
- Primordial
Carbonylated Iron-Sulfur Compounds and the Synthesis
of Pyruvate, George D.
Cody, Nabil Z. Boctor, Timothy R. Filley, Robert M.
Hazen, James H. Scott, Anurag Sharma, and Hatten S.
Yoder Jr., Science 2000 289: 1337-1340
- This
Week In Science, Volume
289, Issue 5483, 8/25/2000
Europa's Ocean Still Afloat, Science
Interpretations of previous data from the Galileo
spacecraft have suggested that Europa, the smallest of the
Galilean satellites orbiting Jupiter, may have a layer of fluid
beneath its icy surface. Kivelson et al. (p.
1340; see the Perspective by Stevenson)
used magnetometer data collected by Galileo during the 3 January
2000 close flyby of Europa to confirm that changes in Europa's
induced magnetic field are driven by a shallow conductive layer. A
model of a spherical shell conductor located about 7.5 kilometers
below the surface with a conductivity similar to Earth's ocean
water fits their new data well.
- Europa's
Ocean--the Case
Strengthens, David
Stevenson, Science, Volume 289, Issue 5483, 8/25/2000,
p. 1305
- Galileo
Magnetometer Measurements: A Stronger Case For A
Subsurface Ocean At
Europa, Margaret G.
Kivelson, Krishan K. Khurana, Christopher T. Russell,
Martin Volwerk, Raymond J. Walker, and Christophe
Zimmer, Science, Volume 289, Issue 5483, 8/25/2000, p.
1340
- This
Week in Science, Volume
289, Issue 5483, 8/25/2000
Whistling in the Sea, Science
Dolphins have long been known to communicate by means
of a rich repertoire of vocalizations. However, studies have been
based mostly on captive individuals, and little has been known
about communication in the wild. Janik (p. 1355; see the
Perspective by Tyack) has developed a technique that allows the
measurement of vocalizations between bottlenose dolphin
individuals in the sea without the presence of human observers.
Individualsrespond to each other using learned, matching whistles
over distances of up to half a kilometer. The development of vocal
imitation is an important step in the evolution of communication
and has implications for the evolution of human language.
-
Excerpt: "Brief exposure to low levels of
nicotine, as little as that provided by a single cigarette, can
cause lasting changes in the brain's "reward" areas, report two
University of Chicago scientists in the August 2000 issue of the
journal Neuron. http://www.neuron.org/ The finding is a major
advance in understanding the process of nicotine addiction.
The researchers discovered that nicotine uses a mechanism
responsible for learning and memory to enhance the connections
between one set of nerve cells that are sensitive to the drug and
other nerve cells that register pleasure. They also demonstrate
that the first exposure to nicotine can induce an enduring "memory
trace," which amplifies the pleasing effects of the drug -- and
boosts the desire to repeat the exposure.
By uncovering the precise cellular mechanisms of nicotine's
effect, this study suggests new and more precise targets for drugs
designed to block this powerful craving.
"This appears to be the crucial first step in the process of
addiction," said neurobiologist Daniel McGehee, Ph.D., assistant
professor in the department of anesthesia and critical care at the
University of Chicago and director of the study. "Now that we know
how this happens, we can begin to search for better ways to
intervene."
The reinforcing effect of nicotine is the primary reason
people cannot quit smoking, despite widespread awareness that
smoking causes cancer, heart disease, stroke, emphysema,
bronchitis, vascular disease, cataracts, impotence and many other
health problems. Nicotine dependence has been estimated to cause
70 times more deaths in the United States than all other types of
drug dependence combined. Nearly 25 million Americans alive today
will die prematurely from smoking-related
illnesses.(…)"
-
Excerpt: How far have conflicts at the cell and
organism level influenced the evolution of multicellularity? It is
often argued that by passing through a single-cell stage during
their life cycle, organisms ensure maximal relatedness of their
constituent cells. Close genetic relatedness among component cells
might be sufficient to preserve the integration of the organism
and to reduce selfish trends at the cellular level. However, in
some lineages (most notably myxobacteria and the cellular slime
mould Dictyostelium) the multicellular body develops by
aggregation of independent cells. Given that genetically different
cells might produce a common fruiting body, mutants that
preferentially form spores are expected to have a selective
advantage at the cellular level. This possibility is supported by
two new experimental findings.
The life cycles of the prokaryotic myxobacteria and the
eukaryotic Dictyostelium show astonishing similarities. Under
nutrient-rich habitats, these soil organisms are unicellular;
however, when food sources become depleted, about
105-106 cells aggregate to form a common
fruiting body. Not all cells become spores: some of them sacrifice
their life for improved survival or dispersal of the spores. In
slime moulds, these nonspore cells constitute the stalk of the
fruiting body; in myxobacteria, these cells autolyse. If spore
cells happen to be dispersed to a nutrient-rich habitat, they
germinate to give rise to the next generation. Such a system seems
vulnerable to exploitation by parasite cells that avoid the stalk
fate in mixture with cooperative partners.
Mastering Gravity: Making Liquids Dance, CWRU/Science Daily
Excerpt: "Rosenblatt, professor of physics, suspends a
fluid such as water or glycerol, mixed with highly paramagnetic
magnesium chloride tetrahydrate, between two specially designed
pole pieces of an electromagnet. By revving up the current to the
magnet, he is able to generate an upward magnetic force on the
fluid that completely compensates the downward force due to
gravity. The result is a floating fluid.
In order to prevent the fluid from drifting off, as
astronauts tend to do during their space walks, the fluid is
tethered at two points, but is otherwise a freely floating
"bridge" suspended between the two surfaces.
When he reduces the magnetic force, he finds that the bridge
sags, and when he increases the magnetic force, the bridge arches
upward. When he wiggles the electric current in the magnet up and
down with time, the bridge dances in a pattern that is determined
by gravity and the properties of the fluid. From the motion of the
fluid bridge he is able to determine many of its physical
properties.
Suspense in Rosenblatt's laboratory hangs in the air as
computer-recorded images detail the changes in the shape of the
bridge as his assistants -- graduate students Milind Mahajan and
Shiyong Zhang -- control the magnet's power supply and
computer-assisted imaging system. If the magnetic force is changed
too much, the bridge collapses.
Images of collapsing bridges have revealed new physical
phenomena that he and his colleagues -- Philip Taylor, Perkins
Professor of Physics; J. Iwan D. Alexander, associate professor of
mechanical and aerospace engineering; and graduate student Mesfin
Tsige -- have been examining theoretically. The group reported its
findings in the Physical Review Letters article, "Collapse
Dynamics of Liquid Bridges Investigated by Time-Varying Magnetic
Levitation."
Links & Snippets
1 Collapse And Recovery Of Marine Fishes, Nature
Excerpt: " Here I show that there is very little evidence
for rapid recovery from prolonged declines, in contrast to the
perception that marine fishes are highly resilient to large
population reductions. With the possible exception of herring
and related species that mature early in life and are fished
with highly selective equipment, my analysis of 90 stocks
reveals that (…) [they] have experienced little,
if any, recovery as much as 15 years after 45-99% reductions in
reproductive biomass. Although the effects of overfishing on
single species may generally be reversible, the actual time
required for recovery appears to be considerable. "
2 Mutant Of Motor Protein Kinesin Moves In Both Directions, Nature
Excerpt: "Molecular motors move directionally to either
the plus or the minus end of microtubules or actin filaments.
Kinesin moves towards microtubule plus ends, whereas the
kinesin-related Ncd motor moves to the minus ends. The
'neck'-the region between the stalk and motor domain-is
required for Ncd to move to microtubule minus ends, but the
mechanism underlying directional motor movement is not
understood. Here we show that a single amino-acid change in the
Ncd neck causes the motor to reverse directions and move with
wild-type velocities towards the plus or minus end; thus, the
neck is functional but directionality is defective. "
3 A Deeply Knotted Protein Structure And How It Might Fold, Nature
Excerpt: " (…) A knot in an open chain (as distinct
from a closed circle) is not rigorously defined and many weak
protein knots disappear if the structure is viewed from a
different angle. Here I describe a computer algorithm to detect
knots in open chains that is not sensitive to viewpoint and
that can define the region of the chain giving rise to the
knot. It characterizes knots in proteins by the number of
residues that must be removed from each end to abolish the
knot. I applied this algorithm to the protein structure
database and discovered a deep, figure-of-eight knot in the
plant protein acetohydroxy acid isomeroreductase. I propose a
protein folding pathway that may explain how such a knot is
formed."
4 Navigation In A Small World, Nature
Abstract: "The small-world phenomenon - the principle
that most of us are linked by short chains of acquaintances -
was first investigated as a question in sociology and is a
feature of a range of networks arising in nature and
technology. Experimental study of the phenomenon revealed that
it has two fundamental components: first, such short chains are
ubiquitous, and second, individuals operating with purely local
information are very adept at finding these chains. The first
issue has been analysed, and here I investigate the second by
modelling how individuals can find short chains in a large
social network."
-
Excerpt: " Ectoparasites play important roles in the
lives of birds. Among these parasites, mites offer unique
potential because of their extraordinary ecological and
evolutionary diversity. However, the basic biology of most
mites is poorly understood, and misleading extrapolations are
sometimes made from better studied systems involving lice and
fleas. Most importantly, not all bird-associated mites are
parasitic; indeed, recent research suggests that some might
even be beneficial. Here, we summarize what is known about the
diversity of bird-mite relationships, and highlight how mites
provide an ideal tool for the study of host life histories,
sexual selection, immunocompetence and cospeciation."
6 Pretty Good Bug Found in PGP, Wired News
A NAME="12.6">
Excerpt: "Network Associates' PGP ["Pretty Good
Privacy", ed.] software has a bug that allows attackers to
trick Windows versions of PGP into not encoding secret
information properly.
A bug in newer versions of Network Associates' popular
PGP software exposes purportedly scrambled communications to
prying eyes. Network
Associates (NETA) confirmed the vulnerability on
Thursday after it was discovered by a German cryptanalyst. The
glitches allows malicious attackers to hoodwink Windows
versions of PGP into not encoding secret information properly.
"
