From new-scr
- From: MarianMarian1234@xxxxxxxxxxx
- Date: 6 Jul 2006 03:52:26 -0700
MarianMarian1234@xxxxxxxxxxx | My Groups | Help | My Account | Sign out
Web Images Groups News Froogle Maps more »
Advanced Groups Search
Preferences
Topic in SCR-new
Start a new topic - Join this group - About group Message 1 - 1 of 1
Fixed font - Proportional font
The net reloaded
Email updates to meCancel my email updates
Only 1 message in topic - view as tree
From: Prof. Dr. Ing. IPS Raspopitul Esq. - view profile
Date: Wed, Jul 5 2006 12:01 am
Email: "Prof. Dr. Ing. IPS Raspopitul Esq." <prop...@xxxxxxxxxxxxx>
Not yet ratedRating:
hide options
Reply | Reply to Author | Forward | Print | Individual Message | Show
original | Report Abuse | Find messages by this author
The net reloaded
a.. 04 July 2006
b.. Kim Krieger
IT WAS the late 1990s, and a group of physicists had it all figured
out. A universal rule seemed to explain a vast range of behaviours in
social, biological and computer networks. Everything from how
ecosystems evolve to how the internet works seemed to follow the same
statistical pattern, called a "power law". What came as a surprise was
that this simple law implied a deep underlying principle for all these
networks.
Researchers began working with power-law models of the internet and
other systems - and that's when they made a startling observation. If
their models were correct, eliminating the most highly connected
computers would cripple data flow. Their work appeared to show that the
internet and systems like it had an "Achilles heel", and that contrary
to popular belief a few carefully targeted attacks could bring down the
entire network. The finding spawned a whole branch of research known as
"scale-free" network theory (New Scientist, 13 April 2002, p 24). The
name, which derives from the idea that members of a power-law network
have no "typical" number of connections, has since graced the covers of
the most prestigious scientific journals.
Is this an yes and no in the same time issue aka stagnation index
wishfull thinking
reinterpretation ?
You have a problem when all models where driven from Tv noncorelated to
reality
Holocaust
to real life constrains scientific filozofical models
I belive this to be partial first failed atempt of modeling an anti
Bravo California .
Now a growing number of biologists, mathematicians and computer
scientists are complaining that the idea has been overhyped, and that
the power-law pattern does not reveal anything fundamental about what
makes these networks tick. John Doyle, an expert in control and
dynamical systems at the California Institute of Technology in
Pasadena, is among those who dismiss the idea that scale-free theory
can make useful predictions. "The problem isn't hype, the problem is
it's wrong," he says. Researchers like Doyle are developing more
sophisticated tests of power laws and models of what they mean. They
have proposed theories that take into account the evolution, design and
structure of specific networks, and their ideas have led to statistical
methods for modelling forest fires, protein-protein interactions and
other biological phenomena.
http://groups.google.com/group/soc.culture.israel/browse_thread/thread/c4bb3a3f62bb37f6/a556663da3c9b5cc?q=marianmarian1234+all+names+planet&rnum=1#a556663da3c9b5cc
At heart, power laws are simple. If you plot the proportion of "nodes",
or members of the network, having a certain number of connections
versus that number of connections, a power law appears as a curve
shaped like a suicide ski slope: declining steeply at first, and then
ever more gently. This reflects the fact that most nodes have only one
or two connections to others, while just a handful of nodes have
hundreds, even thousands of links.
You still are reluctant like an virgin altough you are not like that
for quite a wile.
At least you greap something of the abiss brought by your systems on
humanity and
unprecedent situation etc
So where does the controversy come from? In physics, power laws give
powerful insights into simple systems like phase transitions from
liquids to gases. The systems that researchers began referring to as
scale-free, however, were more complex. "It was a fascination for many
of us," says physicist Albert-László Barabási of the University of
Notre Dame in Indiana, a leading author of the original scale-free
papers. "So many networks have absolutely nothing to do with each
other, but they all end up being scale-free."
Perhaps they should not have been so impressed, says Michael
Mitzenmacher, a computer scientist at Harvard University. "I think
that's a sort of lack of historical knowledge." He says the notion of a
power law is ill-defined, and what, if anything, it signifies outside
of simple systems has been debated for the past 80 years.
The most popular model to explain why power-law distributions occur in
networks is known as preferential attachment - the idea that in general
well-connected things tend to garner ever more connections. The first
widely cited appearance of this model was in a paper in 1925 that
described the power-law distribution of species among genera. It also
proposed an explanation: genera with many species were more likely to
have a random mutation in one of the species that then spawned a new
one, so genera with many species added more species faster than those
that were species-poor. In 1959, in the journal Information and
Control, Benoit Mandelbrot, famous for his work on fractals but also
prolific in statistical analysis, confronted Nobel prizewinning
economist Herbert Simon in a heated debate over whether the idea of
preferential attachment has any validity. The argument is still going
strong today, as Mitzenmacher pointed out in a 2004 paper in the
journal Internet Mathematics.
Preferential attachment has earned itself the most play on the World
Wide Web, where search-engine companies Google and AltaVista have used
ideas from scale-free theory to justify their system of ranking the
most connected web pages at the top of their search results. Scale-free
thought, however, doesn't go much further than noting the existence of
these highly connected pages and predicting that they should become
ever more highly connected.
The problem lies in making the leap from scale-free statistics to the
underlying process that determines how a particular network behaves.
"Power laws don't necessarily mean anything," says Mark Newman, a
physicist at the University of Michigan in Ann Arbor. "There's this
tendency for people to see a power law somewhere and assume that this
process is going on. This is a logical fallacy, like saying, 'Bears
like honey, my wife likes honey - therefore my wife is a bear.'"
Consider the router network that directs data through the internet, and
which was the subject of a 2000 Nature paper, co-authored by Barabási,
that brought scale-free thought into the mainstream. The router network
is not unlike a traditional telephone network, only with lines
stretched over the globe connected to routers that receive information
packets from one link and send them out on another. If you are sitting
in London and send an email to a friend in Washington DC, your email
gets routed from your computer to your internet service provider (ISP),
which may send your email to a data router in New York, which passes
your email to a router in Washington, which tosses it to your friend's
ISP and on to your friend's computer (see Diagram).
In this whole sequence, the only computers linked to more than a few
others are those operated by the ISPs, which will connect to hundreds
or thousands of subscribers. The major data routers will typically have
two to six links. If a graph is plotted showing how many of the
internet's computers have a given number of connections to other
computers, the vast majority will pile up on the far left, linked to
just a few others. Trailing out at the far right of the graph will be
the handful belonging to the ISPs. The resulting curve, which falls
steeply to start with and flattens out at its tail end, represents the
power law.
Knock out the net
After finding that this power law described the statistics of internet
routers, Barabási and colleagues used a theoretical network with the
same proportion of highly connected routers to model the net, and from
these models came the idea that eliminating highly connected routers
could shut the net down. Doyle argues that this approach, while
superficially attractive, ignores a simple fact: the highly connected
routers are ISPs on the edges of the network, close to end users
(Proceedings of the National Academy of Sciences, vol 102, p 14497).
Take down highly connected routers around the US, and you'll knock out
ISPs that serve users in certain neighbourhoods. It would, for sure, be
an annoyance for localised clusters of internet users, but the majority
of traffic flowing around the world would continue unscathed. The bulk
of internet data - be it financial trading, web surfing or massively
multi-player online games - will flow unimpeded, through routers that
have only a few links each. "There are so many routers that you'd have
to destroy a ridiculous number of them before you'd really cripple the
internet," Doyle says.
The router example reveals the weakness of scale-free models as a
predictor of how a system will behave. They simplify systems, leaving
out the details in which the devil can lurk. "The approach of
scale-free models was diametrically opposite to the types of models
that are truly useful, which are grounded in specificity," says Evelyn
Fox Keller, a historian of science at the Massachusetts Institute of
Technology. A useful model would specify what the nodes do, where they
are in the network and how their connections work.
A few researchers have proposed ways to model power-law networks to
make more useful predictions. While this has raised some hackles among
supporters of scale-free theory, even Barabási concedes that the
original ideas are not the whole story. "It is absolutely correct that
there are lots of other properties of the networks that are just as
important as the scale-free: some are fractal, some are not, some
preferentially attach, some don't," he says. Research on networks has
evolved considerably in the seven years since scale-free ideas made
their entrance, he says.
One leading alternative is known as "highly optimised tolerance", or
HOT. It originated in the late 1990s, and is the basis for a more
realistic internet model. Its most vocal proponent is Doyle. "Real
engineering and real biology are really complicated. Yet we want simple
models," he says. "With HOT we're trying to explain, in as simple
models as the scale-free models that are more faithful to the specifics
of the domain, what is general about complex networks."
The key idea of HOT is that networks evolve according to what they are
designed to do and their physical constraints. Real systems behave
differently at different size scales and locations. Take biological
cells and tissues. At one level they look like a sea of proteins. Zoom
out and you see organelle structure. Zoom out further and you see
bunches of cells stuck together to form a particular tissue. HOT's
recognition of complex systems' "self-dissimilar" structure sets it
apart from scale-free theory, which treats systems as the same if they
have the same statistics.
Yet both theories share an appreciation for power laws. HOT uses them
to gauge which aspects of the system are important. The exponent in the
power law controls the steepness of the curve, and is in turn
determined by the specific goals and constraints of the network. In the
simplest type of HOT model, called the "profit-loss-resource" model, a
complex system is boiled down to a conflict between the resource and
the loss, and HOT assumes there is one optimal way to set up the
system.
As an example, take the management of forest fires. If the profit is
timber, the loss is the amount of land that burns and the resource is
land used for fire barriers, the essential trade-off is planting trees
versus protecting them with fire barriers (Proceedings of the National
Academy of Sciences, vol 102, p 17912). Another application of HOT is
working out how to create an optimally navigable website, in which the
conflict is between small file sizes for fast downloading and
minimising the number of clicks before the user finds the desired
information. The router configuration of the internet is more
complicated - there are multiple goals, such as speed and volume of
information flow - but Doyle says HOT can treat it as an optimisation
problem too.
Where do networks go from here? The work that Doyle and others are
doing is "generally excellent", Mitzenmacher says. "They're trying to
define what it means to be scale-free." However, he cautions that
although HOT is alluringly useful, optimisation arguments cannot be the
whole answer any more than preferential attachment was. If the
universal law of networks is wrong, it seems, researchers must continue
to press on for better models, better testing and better understanding
- all seasoned with a healthy dose of scepticism.
Distorting the web
Does scale-free network theory hold for information on the World Wide
Web? In contrast to physical internet routers, well-connected web pages
do appear to collect links faster than less well-connected pages. Now
researchers from Carnegie Mellon University in Pittsburgh,
Pennsylvania, are studying how search engines like Google have altered
the statistics of the web. When users enter a search query, most never
explore beyond the first two pages of hits. If they link from their own
site to one of the pages they find, it will be one of the top-linked
pages. By listing the same top 10 or 20 pages whenever a given query is
received, search engines elevate those pages to celebrity status, and
they gain links at an inflated rate. That distorts the distribution of
links and makes it difficult for new pages to crawl up the stack.
This distortion makes for an interesting problem in network theory. A
power law can no longer fully describe the connectivity of the web.
Some researchers have suggested that putting randomness into search
results could increase the usefulness of search engines by highlighting
pages that would otherwise be at the bottom of the heap.
They have an slight issue they are at level -6 so their view is not as
it was before
if ever .
http://groups.google.com/group/humanities.philosophy.objectivism/browse_thread/thread/d4d69fe19129d520/470ad9d32b9c2f75?lnk=st&q=gargantua++god+created+intelligent+life&rnum=1&hl=en#470ad9d32b9c2f75
Whether this would work is uncertain, but predictive models might
provide an answer.
32240.jpg
18K View Download
Reply Rate this post: Text for clearing space
End of messages
No newer topics Curtea Suprema despre tribunalele Guantan. - Older
topic »
Topic in SCR-new
Google Home - Terms of Service - Privacy Policy
©2006 Google
GAIA
.
- Follow-Ups:
- Re: From new-scr
- From: Vetchnaya Slava Gueroyam
- Re: From new-scr
- Prev by Date: Re: ingleza pa'ntzelesu tutulor
- Next by Date: [scrierile] File de Pateric - Avva Sisoe cel Mare (6 Iulie)
- Previous by thread: "They have criticized us even though we are showing restraint," :0))
- Next by thread: Re: From new-scr
- Index(es):
Relevant Pages
|
