UCSD Scientists Awarded $3-Million 'Biocomplexity' Grant, UCSD News Release 
Last year the US National Science foundation launched a
new program on 'Biocomplexity'. Now one of the awards goes to
Herbert Levine to study one of the classic biological
self-organization examples of complex systems, the slime mold
Dictyostelium
discoideum (short: "Dicty"). Like the fruitfly Drosophila
and the nematode worm C.elegans,
it is also one of the classic biological model organisms. It has
inspired StarLogo
simulations and its genome is currently analyzed by an international
research collaboration.
The UCSD lead team is going to take an integrated approach:
"In the biocomplexity award to UCSD, physicists, biologists
and computational scientists from the two universities will
attempt to connect the underlying genetic information about
Dictyostelium to its morphology and multicellular organization.
This should provide the scientists with a greater understanding of
one of the central problems of modern biology: How to form an
integrated picture of an organism that connects genetic
information to its behavioral responses.
"Dictyostelium provides the simplest example of cellular
biology mechanisms that go on everywhere," said Herbert Levine, a
professor of physics at UCSD who heads the research collaboration.
"Its motion and its response to cell signals is characteristic of
the way your cells move, but Dictyostelium does it in a much more
simple way and in a way you can investigate with genetics. In our
investigations of the organism, we will try to bring a level of
precision that will enable us to bridge the gap between genomics
and multicellular organization."" (…)
"Levine said Dictyostelium was chosen by the scientists
because it's the simplest organism in which to study the complex
phenomena they hope to investigate, such as the cell's response to
external signals that coordinate multicellular
development.
"Dictyostelium has a solitary lifestyle in which each
individual cell is on its own," he added. "But the organisms also
go through a developmental cycle in which they cooperate when food
becomes scarce-sending each other signals, aggregating together
and forming rudimentary multicellular organisms, one of which is a
slug that can crawl around looking for a better environment. In
the course of this transformation, the organism develops, in the
simplest possible form, many of the fundamental mechanisms that
work in all molecular biological systems-chemical signaling, cell
differentiation in response to external signals. Besides being
simple, everything takes place on the time scale of a day and you
can genetically engineer all sorts of variations of the individual
cells."
The UCSD scientists hope to first acquire a large base of
genetic knowledge relevant to the development of Dictyostelium,
then carry out a new generation of experiments focusing on the
cell response to external signals that coordinate multicellular
development. Finally, they plan to use computational simulations
to tie the genetic with the developmental and behavioral
information in a coordinated way."
U.S. Proposes Changes In Electricity Marketing In California, NYTimes
For a plain old physicist (not an
"econo-physicist") it is sometimes hard to comprehend the
intricate rules and laws of market economy. In ComDig 2000.30.1 we
have discussed our naïve opinion about the situation of the
electricity market in California that led to high prices and
threat of rolling power outages. This seemed to be odd since -from
all we have learned about the workings of a market- high prices
automatically will lead to a increased supply because more
expensive means of production become profitable.
In this NYTimes article we find a simple solution to the
puzzle:
"Currently, utilities can buy and sell power only through
the California Power Exchange, a state-run electricity
marketplace. The commission has proposed eliminating that
requirement so utilities can shop around for long-term electricity
contracts, a move most analysts welcomed.
(That) "is like going to a car lot and being able to buy
only one or two models."
Having a state controlled/planned market could explain both the
high prices and the short supply: If a producer would offer
electricity to the Californian market at a competitive price but
would not be admitted by the California
Power Exchange that would lead to further increase in price
and reduction in supply.
Within that restricted "state market" constraint one might also
understand the logic of: "(…) consumer demand for power
outstripped supply. As a result, the commission warned, California
officials will have to find ways to build more power plants and
transmission lines."
The Federal Energy Regulatory Commission suggested to lower the
price cap for electricity from a quarter per kilowatt hour to 15
cents. (For a comparison: both in neighboring Nevada as well as in
Finland electricity prices are well below that cap.)
Here "price cap" is defined as the price above which a power
supplier has to "explain the reasons for their bid."(sic!).
The article does not include a list of acceptable reasons, but
from a limited understanding of markets, reasons like: "we want to
make top dollars." or "we want to maximize our profits." should be
perfectly acceptable. These reasons seem to have been drivers of
innovation in the past.
There are certainly technical arguments why not everyone with a
power generator in the backyard can be allowed to feed electricity
into the power grid anytime prices are high enough to make that
profitable. But it seems that rules could be developed that focus
on protecting the stability of the power grid while extending the
range of competitive power suppliers.
-
In this study, three measures of temporal pattern
complexity were compared with regard to their perceptual validity.
The first measure, based on the work of Tanguiane (1993), uses the
idea that a temporal pattern can be described in terms of
(elaborations of) more simple patterns, which occur simultaneously
at different levels.
The second measure is based on the complexity measure for
finite sequences proposed by Lempel and Ziv (1976), which is
related to the number of steps in a self-delimiting production
process by which such a sequence is presumed to be
generated.
The third measure, newly developed here, is rooted in the
tehoretical framework of rhythm perception of Povel and Essens
(1985). it takes into account the ease of coding a temporal
pattern and the complexity of the segments resulting from this
coding. The perceptual validity of the three measures was
evaluated in an experiment in which subjects judged the complexity
of 35 temporal patterns.
Correlations between the three measures and the collected
complexity judgments indicated that the third measure is a much
beter predictor of temporal pattern complexity than the other two
measures. This is probably due to the fact that this measure,
unlike the other two, is based on an empirically tested model of
rhythm perception that takes into account the isochronous frame
against which the rhythm is perceived. Reasons for the differences
in performance between the three measures are discussed.
Taking A Look Into The Black Box Of Complex Physiological Systems, Ieee Trans. Biomed. Eng
Analysing the internal dynamical structure of
neurophysiological systems is difficult due to their complexity
and due to the fact that any observation must be more or less
non-invasive in order to not destroy the system. In this paper
methods of nonstationary time series analysis are presented that
are able to follow the time course of complex dynamic couplings
between different brainstem neurons and several signals of
physiological subsystems (e.g. respiration, heart rate, blood
pressure, electro-encephalogram (EEG), etc.), which change during
spontaneously occuring transitions (phase transitions) between
different functional states of the organism. Using nonlinear
methods like the Transinformation, the Pointwise Conditional
Coupling Divergence (PCCD), and the Instantaneous Phase, it is
shown that the analyzed transition is initiated by interactions of
brainstem neurons and higher brain structures, and how brainstem
neurons take part in the complex changes of rhythmical
coordination of the various physiological subsystems concerned.
This reveals the dynamics of transitions between physiological
states like the trophotropic (calm) and the ergotropic (active)
functional state for the first time. To follow the time course of
such an organizing process was not possible with the formerly used
linear methods (i.e. post event time histograms, covariance
functions, power spectra, etc.), but some important results of
previous investigations could be confirmed and extended now.
The brainstem neurons are part of a network which takes part in
the common basic regulation and coordination of several functional
systems of the organism. The neurons exert influences on, e.g.,
respiration, heart and vessels, motor systems and vigilance
realizing behavior patterns and receive afferent influences from
somatosensory receptors all over the body, visceral receptors -
e.g., in cardiovascular and respiratory systems - and from higher
brain structures, i.e. this common brainstem system has manifold
feedback loops. We have shown that the functional organization in
this neuronal net can change from one basic type to another under
the influence of changing afferent activities, which occurs if
internal or external conditions of the organism alter. In turn,
when the organization of the brainstem network changes, the
processing of afferent information at their input stations to the
central nervous system is altered (e.g., of baroreceptors - giving
information about blood pressure fluctuations - at the nucleus of
the solitary tract), and the activity levels of vegetative and
somatic systems and of the central nervous system are adapted to
behavior patterns as regulated by the brainstem neurons.
The results are interesting (i) for the proof of the usefulness
of nonlinear, non-stationary methods for black box analysis, and
(ii) for the further investigation of reorganization processes in
the Central Nervous System and of transitions between different
functional states of the organism (e.g. trophotropic and
ergotropic states).
How To Measure Oxidative DNA Damage In Nutritional Studies, Am.J. Clin. Nutrition
There are numerous, mostly anecdotal reports about the
health effects of anti-oxidants especially in the prevention of
cancer. Evidence for reducing oxidative damage by eating certain
fruits and vegetables has been confirmed according to the author.
The effects of other, widely popular supplements could not be
confirmed. It seems that a convincing theoretical model for how
nutrients can have an effect on oxidation of DNA is still a
challenge for future research.
Free radicals and other reactive species are constantly
generated in vivo and cause oxidative damage to DNA at a rate that
is probably a significant contributor to the age-related
development of cancer. Agents that decrease oxidative DNA damage
should thus decrease the risk of cancer development. That is,
oxidative DNA damage is a "biomarker" for identifying persons at
risk (for dietary or genetic reasons, or both) of developing
cancer and for suggesting how the diets of these persons could be
modified to decrease that risk. This biomarker concept presupposes
that we can measure oxidative damage accurately in DNA from
relevant tissues. Little information is available on whether
oxidative DNA damage in blood cells mirrors such damage in tissues
at risk of cancer development. Measurement of 8-hydroxylated
guanine (eg, as 8-hydroxy-2'-deoxyguanosine; 8OHdG) is the
commonest method of assessing DNA damage, but there is no
consensus on what the true levels are in human DNA. If the lowest
levels reported are correct, 8OHdG may be only a minor product of
oxidative DNA damage. Indeed, 8OHdG may be difficult to measure
because of the ease with which it is formed artifactually during
isolation, hydrolysis, and analysis of DNA. Mass spectrometry can
accurately measure a wide spectrum of DNA base damage products,
but the development of liquid chromatography-mass spectrometry
techniques and improved DNA hydrolysis procedures is urgently
required. The available evidence suggests that in Western
populations, intake of certain fruit and vegetables can decrease
oxidative DNA damage, whereas ascorbate, vitamin E, and
ß-carotene cannot.
-
In a comparative analysis of Poland and Ukraine, we
extend the often-confirmed hypothesis that the substantive
complexity of work in paid employment substantially affects (and
is affected by) fundamental dimensions of personality. The
extended hypothesis encompasses not only the complexity of work,
whether in paid employment or in the household but even the
complexity of activities of the unemployed and pensioners. We
hypothesize that the complexity of activities in any important
realm of life is substantially related to personality We test this
hypothesis under conditions that pose a particularly exacting
test-conditions of radical social change. We find that complexity
of activities in all these realms is substantially and
significantly related to intellectual flexibility,
self-directedness of orientation and a sense of well-being or
distress for both men and women. The consonance of these findings
with those of earlier longitudinal and simulated longitudinal
analyses of the complexity of work and personality strongly
implies that the relationships of the complexity of activities and
personality ore similarly reciprocal, even if the activities are
not ordinarily thought of as "work."
- Complexity
Of Activities And Personality Under Conditions Of
Radical Social Change: A Comparative Analysis Of
Poland And
Ukraine, Kohn
Ml, Zaborowski W, Janicka K, Mach Bw, Khmelko V,
Slomczynski Km, Heyman C, Podobnik B, Social
Psychology Quarterly, 63: (3) 187-207 Sep 2000
-
"Insects dominate the animal kingdom, both in terms of
numbers and variety. One reason for their success is their
remarkably swift and effective system of defense against
infections, which differs dramatically from the immune systems of
higher-order animals, including humans. Key to the insect immune
system is an array of small antimicrobial peptide molecules. Most
act, in essence, by latching on to the outer or inner membranes of
bacteria and punching holes in the membranes, thereby killing the
bacteria.
Now, in a new study, scientists at The Wistar Institute have
identified an intracellular target for one of these antimicrobial
molecules first isolated from a European sap-sucking insect. The
molecule itself is currently being evaluated for its potential as
an antibiotic in mammals, including humans. Knowledge of the
receptor, however, may make it possible to develop an entirely new
class of antibiotics, each rationally designed to fight a specific
disease-causing bacterium or fungus. The new findings were
published electronically on October 21 in the journal
Biochemistry." (…)
"The new receptor is a heat shock protein referred to as
DnaK. Heat shock proteins, in both bacteria and animals, play an
all-important role during infections that produce fevers. Fevers
cause the proteins that make up all cells to become misshapen, in
some cases destroying their ability to do the work for which they
were designed. Heat shock proteins help repair the problems,
correcting the shapes of the proteins and restoring them to
functionality.
The mechanism by which the sap-sucking insect's
antimicrobial molecule kills bacteria, then, is to disrupt the
bacterial heat-shock protein repair system. Importantly, this
insect peptide does not bind to the human equivalent of the DnaK
receptor, known as Hsp70, greatly enhancing its pharmaceutical
potential in humans. If the peptide bound to the human Hsp70
receptor, it and related compounds might pose a danger to human
cells.
With the receptor now identified, scientists might be able
to develop new drug compounds with improved characteristics that
act on the same site. The new compounds might be more easily
synthesized than the naturally occurring one, for example, or show
greater stability in mammalian systems. They might also be
tailored to target specific bacterial or fungal strains with
heightened effectiveness. "
-
"Researchers at the Smithsonian Environmental Research
Center (SERC), the Center of Marine Biotechnology (COMB) of the
University of Maryland Biotechnology Institute and Old Dominion
University are reporting in today's issue (November 2, 2000) of
the British journal, Nature, that ballast water discharges by the
world's ocean-going ships "create a long-distance dispersal
mechanism for human pathogens, and may be important in the
worldwide distribution of microorganisms as well as the
epidemiology of waterborne diseases affecting plants and animals."
It has long been known that such discharges have unintentionally
spread plankton, shellfish and fish from one body of water to
another, sometimes with major impacts to the receiving
ecosystem.
Lead researcher Gregory Ruiz, from SERC, reports in Nature
that he and his colleagues have found high concentrations of
discharged microbes in the ballast water of ships arriving in
Chesapeake Bay from foreign ports. Until these studies by Greg
Ruiz and his colleagues, Tonya Rawlings, Fred Dobbs, Lisa Drake,
Timothy Mullady, Anwarul Huq and Rita Colwell, the global movement
of microorganisms via ballast water discharges was virtually
ignored. The research was funded largely by the Maryland Sea Grant
and the National Sea Grant College programs.
Ruiz says, that though there is no reported evidence of
outbreaks of human diseases from non-indigenous microbes in
ballast water, the findings indicate the need for much greater
concern than has heretofore been shown.
"Despite growing concern about biological invasions and
emergent diseases, the extent and effects of the transfer of
microorganisms in ballast water are virtually unexplored," writes
Ruiz and his colleagues. "We know of no published estimates of
microbial genetic diversity in ballast water, and the fate of
microorganisms discharged from ballast tanks remains unknown.
Given the magnitude of ongoing transfer, and its potential
consequences for ecological and disease processes, large-scale
movement of microorganisms by ships merits attention from both
invasion biologists and epidemiologists."
Vibrio cholerae, for example, the bacterium that causes
human epidemic cholera, was detected in all ships tested, and
included the recently emerged serotype 0139, which was recently
isolated in Bangladesh. While V. cholerae and other potential
pathogens are normal constituents of coastal waters in the U.S.,
they do not ordinarily occur in high enough concentrations to
cause human health problems. However, with expanding world trade
and increasingly larger vessels moving among international ports,
the impact of non-indigenous microorganisms could be profound. The
study authors write that laboratory observations have "revealed
that some bacteria are viable upon arrival, and that their release
creates an opportunity for the colonization of coastal
ecosystems."
- Worldwide
Transfer Of Microorganism
Facilitated, Ballast
Water , National
Sea Grant College
Program, Science Daily,
11/3/00
- Global
Spread Of Microorganisms By
Ships, G M Ruiz, T K
Rawlings, F C Dobbs, L A Drake, T Mullady, A Huq&
R R Colwell
-
"The symptoms of fibromyalgia may be the result of a
central nervous system that "remembers" pain sensations for an
abnormally long time, according to research presented at the
American College of Rheumatology Annual Scientific Meeting Oct. 29
-- Nov. 2 in Philadelphia, Pennsylvania.
Fibromyalgia, sometimes called fibrositis, is associated
with widespread pain, stiffness and fatigue. People with
fibromyalgia are found to have multiple tender points in specific
body areas. The painful disorder affects about two percent of the
U.S. population.
Researchers at the University of Florida applied heat
stimuli to the hands of healthy controls and fibromyalgia
patients. In contrast to normal controls, fibromyalgia patients
experienced a great amount of cumulative pain from these
stimulations, indicating abnormalities in spinal cord pain
processing. Furthermore, the fibromyalgia patients experienced
residual pain when the stimuli were applied at intervals at which
the healthy controls were not affected. Normally, pain sensations
quickly subside after a single heat stimulus, but will accumulate
with repetitions if they occur frequently enough. This "pain
memory" appears to linger for an abnormally long period of time in
fibromyalgia patients.
The researchers also found that the residual pain
experienced by fibromyalgia patients was widespread and not
limited to a single area of the body.
"Because the effect of the first experimental stimulus does
not rapidly decay in fibromyalgia patients, the effect of
subsequent stimuli adds to the first, and so on, resulting in ever
increasing pain sensations," said lead investigator Roland Staud,
MD. "Our findings provide evidence for abnormal central nervous
system mechanism of pain in fibromyalgia patients and have
significant implications for future therapies, which need to
target these abnormal central pain mechanisms."
-
"Damage from heart attacks may be partially reversible
in the future, with recent discoveries being made at Ohio State
University.
Scientists here are seeking new methods for patients to grow
blood vessels in the heart to replace the ones they've lost in a
heart attack.
Nicanor I. Moldovan, assistant professor at Ohio State's new
Heart and Lung Institute and Biomedical Engineering Center, said
he and his colleagues' most recent work is a step forward to reach
that goal. The scientists reported their initial progress in a
recent issue of the journal Circulation Research.
Moldovan explained that during a heart attack, blockage in
coronary arteries leaves a portion of the victim's heart tissue
without oxygen, a condition called ischemia. When this happens,
part of the heart tissue begins to die -- an event signaled by
severe chest pain.
In his early work, Moldovan discovered that in a mouse model
of cardiac ischemia, blood-derived cells called monocytes
penetrate this damaged heart tissue, leaving behind a network of
tunnels in the tissue.
Monocytes, the largest blood cells, normally circulate
through the body to capture and ingest infectious agents such as
bacteria. Monocytes also penetrate enflamed body tissue to help
defend against infections.
For this Circulation Research study, scientists tested the
hypothesis that new blood vessels may grow in tunnels created by
monocytes. They took mouse hearts containing monocyte-caused
tunnels and transplanted them into healthy mice.
Five days later, the researchers found evidence in the
transplanted hearts that new blood vessels may have been about to
grow: stem cells -- cells that normally precede blood vessel
growth -- had begun to colonize the tunnels.
The findings point the way to a possible new therapy for
heart attack victims that will help them regenerate blood vessels
and keep damaged tissue alive, Moldovan said. "If we could create
similar tunnels in heart tissue -- with or without monocytes'
contribution -- we might be able to stimulate capillary
formation," he said.
He did admit, however, that this project is in its infancy.
He and his colleagues will have to overcome many obstacles to find
a practical way to grow functioning blood vessels, based on this
new principle, he said. The question of whether the tunnels
themselves improve heart function remains as well.
Moldovan and his colleagues are also exploring means for
growing blood vessels outside the body and then implanting them in
the tunnels in the heart tissue."
-
Adult human stem cells taken from bone marrow have
been induced to develop into a wide range of normal tissues,
including bone, cartilage, fat, tendon and muscle, when
transplanted into fetal sheep. The transplanted human cells have
persisted in various sheep tissues for over one year without
rejection by the sheep's immune system. The study offers promise
that in the future these cells may be useful for tissue repair or
regeneration and for treatment of degenerative diseases such as
muscular dystrophy.
"Although a great deal of work remains to be done, these
results suggest great potential for the use of these cells in
repair of damaged or degenerating tissues, or for generation of
new tissues, a process called tissue engineering," said Alan W.
Flake, M.D., director of The Children's Institute for Surgical
Science at The Children's Hospital of Philadelphia, who led the
study reported in the November issue of Nature Medicine. "One
possible future application might be the transplantation of normal
stem cells into a fetus diagnosed with muscular dystrophy. "These
cells could then act as a normal stem cell 'reservoir' and replace
the abnormal muscle with normal muscle as it degenerates over
time."
Stem cells are immature cells that develop into specialized
cells throughout the body, and those taken from embryos have the
broadest potential for giving rise to all the body's tissues.
However, recent studies have shown that cells with broad stem cell
potential can be found in various adult tissues as well, including
the bone marrow and nervous system.
In the study at Children's Hospital, researchers harvested
mesenchymal stem cells (MSCs) from adult bone marrow. "The
transplanted cells developed in a site-specific fashion," said Dr.
Flake. "They migrated to different parts of the sheep's body and
differentiated into types of tissue present at each site."
Because the transplanted cells carried human DNA, it was
possible to identify them in different tissue. They became cells
in skeletal muscle, heart muscle, bone, cartilage, the thymus
gland and stroma, which is supporting structure for bone marrow.
Furthermore, transplanted human MSCs were found at the site of
clipped tails in the sheep, suggesting that those cells were
involved in wound healing.
MSC transplants may have a future role in enhancing wound
healing after an injury or surgery. Additionally, said Dr. Flake,
because MSCs also develop into supporting cells in bone marrow,
they might provide a more favorable environment for the
transplanted cells used in bone marrow transplants for leukemias
and other blood-based diseases. MSCs might also be used in gene
therapy, acting as vehicles to deliver beneficial genes to
targeted tissues.
Although many institutions are currently investigating
various types of stem cells, this is the first study examining
transplantation of human MSCs in the fetal sheep model. In this
current study, human MSCs were transplanted into fetal sheep early
in gestation, at either 65 days or 85 days, before and after the
brief window of time when their immune systems mature and become
active.
One surprise of the study, according to Dr. Flake, is the
persistence of these transplanted cells even in animals that were
capable of rejecting foreign cells at the time of transplantation.
"This suggests that these cells may have special immunologic
properties that may allow transplantation between individuals or
even between species without rejection or the need for toxic
immunosuppressive drugs," added Dr. Flake.
Fundamental Decision-Making Unit Of Cells, UCSF/Science Daily
University of California, San Francisco scientists
have stripped the fundamental decision-making apparatus of a cell
down to its bare essentials, revealing the inner workings of one
of life's smallest "decision nodes" - the biochemical switches by
which cells take in multiple signals and integrate them, leading
to a course of action. The decision node they studied leads cells
to initiate movement - such as a white blood cell of the immune
system migrating towards an invading bacterium.
Defects in this key decision node protein are known to cause
immunodeficiency and other severe human illnesses. In addition,
oncogenes, the normal genes that can be converted into cancer
genes, probably code for proteins which function as
decision-making nodes, underscoring the potential value in better
understanding these pivotal proteins, says Wendell Lim, PhD, UCSF
associate professor of cellular and molecular pharmacology and
senior author on a report on the research.
The UCSF study is published in the October 27 issue of
Science. Survival of all organisms from microbes to humans depends
on the ability to react to changing conditions, and scientists
have already described many of the responses made constantly by
every cell of the body. But the mechanisms by which these
decisions are made has been unclear. How, for example, does a
white blood cell detect the presence of a bacterium and resolve to
move towards it? Such decisions often involve coordination of two
or more inputs.
Rather than a simple direct-line action such as "If A, then
B," for example, the decision might instead be "If A and B, then
C." The workings of this fundamental cellular decision-making unit
- similar to the decision-making components in a computer - has
eluded researchers until now. (…)
"We are only starting to understand this signal integrating
protein, and it is likely that in this case as in many others, the
two domains actually act in concert with at least one other domain
to make a three-way switch," Lim says.
In their study, the researchers synthesized what they call a
"mini-N-WASP protein" -- the bare bones of the node protein that
is still capable of integrating signals. They used this to tease
apart the essential steps in cellular decision-making.
"Much as we can understand how a computer works by breaking
it down to its transistors and other components, so we can
understand the complex circuits of a cell by studying its
signaling proteins like N-WASP," said Kenneth Prehoda, PhD, lead
author on the article and a post-doctoral scientist in Lim's lab.
Co authors include R. Dyche Mullins, PhD, assistant professor of
cellular and molecular pharmacology, and Jessica A. Scott, BS, a
research associate in Lim's lab, all at UCSF.
From Minority Games To Real Markets, arXiv
Abstract: We address the question of market efficiency
using the Minority Game (MG) model. First we show that removing
unrealistic features of the MG leads to models which reproduce a
scaling behavior close to what is observed in real markets. In
particular we find that i) fat tails and clustered volatility
arise at the phase transition point and that ii) the crossover to
random walk behavior of prices is a finite size effect. This, on
one hand, suggests that markets operate close to criticality,
where the market is marginally efficient. On the other it allows
one to measure the distance from criticality of real market, using
cross-over times. The artificial market described by the MG is
then studied as an ecosystem with different_species_ of traders.
This clarifies the nature of the interaction and the particular
role played by the various populations.
Links & Snippets
Further Steps Through The Marriage Problem, Author Response
The Stable Marriage Problem was born in the Sixties from
the ideas of two computer scientists. Since then, several possible
applications have been conceived. Indeed, in many different
situations we need to find the best way to match pair-wise
heterogeneous agents: we have a preference list of possible
choices and, at the same time, we are on the preference list of
the counterpart. Imagine you are looking for an apartment to rent
in a big town. You have your preferences, of course, but landlords
have theirs, and they will not give the flat to the first one who
comes and sees it.
Then, though love affairs are more intriguing, economical
applications of the Stable Marriage Problem (and its variants) may
give us some important clue in the understanding of real market
mechanisms. In the neoclassical scheme of economics, economic
agents are perfectly rational and optimize their personal utility.
A different approach, like the one brought about by the marriage
model, may allow us to describe markets in a more realistic
framework, introducing a bounded rationality in a very natural
way: as a result of a trade off between heterogeneous
individuals.
In fact the Stable Marriage Model is very flexible. One can
modify it in order to test different market hypothesis. For
example, we are now investigating the role of information in
markets. In modern markets (like in other social interactions),
producers and customers have a greater chance to meet one another,
thanks to information technology. Both of the parties, in
principle, could take advantage of this new situation: profitable
goods can now be known of by a larger number of customers,
increasing competition between firms, and more market niches can
now appear, since business opportunities are more easily
found.
Under the direction of Professor Yi-Cheng Zhang, who inspired
the original works, and with the collaboration of Cedric Frachet
and Paolo Laureti of the University of Fribourg, I am now starting
analytical and numerical studies aiming to test these ideas in a
more precise and meaningful way. In the paper cited by the New
Scientist, for example, Guido Caldarelli and I introduced a
topology in the model, in order to bound the rationality of
agents. They cannot get in touch if too far apart and, depending
on how you introduce the topology, you find different collective
behaviors, more or less predictable.
Other generalizations of the model are to be expected soon.
1 Presidential Politics: Constrained By Complexity?, Science
"This boxing in of the executive office is reminiscent of
the complexity catastrophe described by Kauffman in his NK
model of rugged fitness landscapes used to simulate
evolutionary patterns in biological systems.(…)
Despite their best efforts to distinguish themselves,
perhaps Mr. Bush and Mr. Gore appear similar because
large-scale communication, transportation, and economic
networks have resulted in a globally integrated political
economy, with many conflicting interactions. Globalization is
equivalent to increasing the "K parameter" of economic
networks, resulting in an uncorrelated landscape of mediocre
compromises among political, environmental, and cultural
systems."
Of Rice And Men, Science
"Catalytic reactions involving chlorine and bromine are
important pathways of polar stratospheric ozone loss, and
halide radicals have significant impacts on tropospheric and
mid-latitude stratospheric chemistry. As the anthropogenic
production of halogen gases decreases in accordance with the
terms of the Montreal Protocol, biogenic and other natural
sources of atmospheric halogens will become relatively more
important. Redeker et al. (p.
966) venture into this still largely unexplored
territory by measuring methyl halide emissions from rice
paddies. These data were then used to estimate global fluxes.
These results also suggest that different enzymatic pathways
synthesize methyl chloride and methyl iodide."
- Of
Rice And Men,
This Week in Science, Volume 290, Issue 5493,
11/3/00
- Emissions
of Methyl Halides and Methane from Rice
Paddies, K. R. Redeker,
N.-Y. Wang, J. C. Low, A. McMillan, S. C. Tyler, R. J.
Cicerone, Science, Vol 290, No 5493,
11/3/00
3 New Site Suggests Anasazi Exodus, Science
"For decades, scientists have puzzled over the fate of
the Anasazi, who once lived high in the cliffs of Mesa Verde in
southwestern Colorado. Whereas conventional wisdom holds that
they died off or slowly scattered, an archaeologist has now
proposed that at least some Anasazi made a more dramatic,
large-scale exodus to the south. That effort, he argues, would
have required a higher degree of social cohesion than has been
attributed to the Anasazi culture"
4 Telomere States And Cell Fates, Nature
"Telomere length has frequently been used as a means to
predict the future life of cells. But by itself it can be a
poor indicator of ageing or cell viability. What, then, is the
important property of a telomere? Here recent findings are
integrated into a new, probabilistic view of the telomere to
explain how and when it can signal not only its own fate but
also that of a cell."
5 Self-Organizing Biochemical Cycles, PNAS
Abstract: I examine the plausibility of theories that
postulate the development of complex chemical organization
without requiring the replication of genetic polymers such as
RNA. One conclusion is that theories that involve the
organization of complex, small-molecule metabolic cycles such
as the reductive citric acid cycle on mineral surfaces make
unreasonable assumptions about the catalytic properties of
minerals and the ability of minerals to organize sequences of
disparate reactions. Another conclusion is that data in the
Beilstein Handbook of Organic Chemistry that have been claimed
to support the hypothesis that the reductive citric acid cycle
originated as a self-organized cycle can more plausibly be
interpreted in a different way.
6 Neurobiologyhydrodynamic Stimuli And The Fish Lateral Line, Nature
Swarming behavior, i.e. collective movement of a large
number of individuals in the absence of global control requires
efficient communication of position information of nearest
neighbors. While birds and insects probably use predominantly
visual stimuli it has been known that certain fish species have
pressure receptors along their bodies that are sensitive to
small changes in water flow. Engelman et al have studied these
sensors in detail.
Abstract: "Sensory systems need to distinguish
biologically relevant stimuli from background noise. Here we
investigate how the lateral-line mechanosensory system of the
fish senses minute water motions in the vicinity while exposed
to running water. We find that one class of receptor in the
lateral line, the canal neuromasts, can respond to hydrodynamic
stimuli even in the presence of unidirectional water flow,
whereas superficial neuromasts, which predominate in
still-water fish, cannot."
7 Bertelsmann, Napster Make Peace, Agree On Music-Sharing Service, WSJ
"Napster was created last year by Shawn Fanning, then a
19-year-old college dropout who wanted to easily find MP3 music
files on the Internet. The software now has 38 million users
and allows them to get, without charge, practically all the
popular music they want. (…)
Another issue is the extent to which Napster will
continue to be the freewheeling, anything-goes trading site it
is today. Bertelsmann and Napster declined to talk much about
the topic Tuesday, saying that would interfere with what they
said would be future negotiations with other labels."
Well, now that Bertelsmann (who started off as a commercial
book club) the freewheeling times of Napster most likely are
over and the 38 million users will see themselves flooded with
"offers" to buy Bertelsman music. How many of the Napster users
will migrate to emerging non-commercial Napster offsprings?
8 As Publishers Perish, Libraries Feel The Pain, NYTimes
A NAME="15.8">
Scientific and medical subscription rates are soaring (up to
US$ 16,000 per year for the Journal "Brain Reseach") in spite
of the fact that: "Journal publishing's costs are minimal
because researchers contribute papers free, to advance their
careers. Others review submissions free, too, which takes care
of most of the editing. And the potential for price increases
is enormous because journals are the lifeblood of scholarship -
libraries and researchers cannot function without them.
(…)Most journal publishers report operating profit margins
of nearly 40 percent of revenue, roughly double the profit
margins in the rest of educational publishing, Mr. Nathanson of
Sanford Bernstein said."(1)
"Research librarians have asked the U.S. government to
block one of the biggest ever science publishing mergers as
part of a battle against spiraling subscription prices and the
growing concentration of ownership of academic journals. Their
target is the European journal giant Reed Elsevier, which last
week announced that it will swallow American rival Harcourt
General for $4.5 billion, creating a global company with more
than 1500 journals, including a substantial fraction of all
biomedical titles."(2)
- As
Publishers Perish, Libraries Feel The
Pain, David D.
Kirkpatrick, NYTimes, 11/3/00
- Librarians
Seek to Block Merger of Scientific Publishing
Giants , David
Malakoff, Science, Vol 290, No5493, 11/3/00, pp.
910-911
