Arquivo da tag: Sistemas complexos

Risk analysis for a complex world (Science Daily)

Date: November 18, 2014

Source: International Institute for Applied Systems Analysis

Summary: Developing adaptable systems for finance and international relations could help reduce the risk of major systemic collapses such as the 2008 financial crisis, according to a new analysis.


Developing adaptable systems for finance and international relations could help reduce the risk of major systemic collapses such as the 2008 financial crisis, according to a new analysis.

The increasing complexity and interconnection of socioeconomic and environmental systems leaves them more vulnerable to seemingly small risks that can spiral out of control, according to the new study, published in the journal Proceedings of the National Academy of Sciences.

The study examines risks are perceived as extremely unlikely or small, but because of interconnections or changes in systems, can lead to major collapses or crises. These risks, which the researchers term “femtorisks,” can include individuals such as terrorists, dissidents, or rogue traders, or factors like climate change, technologies, or globalization.

“A femtorisk is a seemingly small-scale event that can trigger, often through complex chains of events, consequences at much higher levels of organization,” says Princeton University professor and IIASA Distinguished Visiting Fellow Simon Levin, who adopted the term (originally suggested by co-organizer Joshua Ramo) together with an international group of experts during a 2011 IIASA conference on risk modeling in complex adaptive systems.

Levin explains, “A complex adaptive system is a system made up of individual agents that interact locally, with consequences at much higher levels of organization, which feed back in turn to affect individual behaviors. The individual agents can be anything from cells and molecules, to birds in a flock, to traders in a market, to each and every one of us in the global environment.”

The complexity of such systems makes it difficult or even impossible to model the outcomes of specific changes or risks, particularly very small or seemingly insignificant ones. The study examines several examples of such femtorisks that set off major crises, including the credit default swaps that led to the 2008 financial crisis, the recent protests in the Middle East and Ukraine that led to the broad upheavals in both regions’ political systems, and the warming temperatures in the Arctic that have led to massive international interest in the region for mining and economic development.

Risk management for an unpredictable world 

In light of such unpredictable risks, the researchers say, the most resilient management systems are those that can adapt to sudden threats that have not been explicitly foreseen. In particular, the researchers suggest a model drawing on biological systems such as the vertebrate immune system, which have evolved to respond to unpredictable threats and adapt to new situations.

“In practice it is generally impossible to identify which of these risks will end up being the important ones,” says Levin. “That is why flexible and adaptive governance is essential.”

The general principles of such management include: effective surveillance, generalized and immediate initial responses, learning and adaptive responses, and memory, say the researchers. Levin says, “We need to design systems to automatically limit the potential for catastrophic contagious spread of damage, and to complement that with effective and flexible adaptive responses.”


Journal Reference:

  1. Aaron Benjamin Frank, Margaret Goud Collins, Simon A. Levin, Andrew W. Lo, Joshua Ramo, Ulf Dieckmann, Victor Kremenyuk, Arkady Kryazhimskiy, JoAnne Linnerooth-Bayer, Ben Ramalingam, J. Stapleton Roy, Donald G. Saari, Stefan Thurner, Detlof von Winterfeldt. Dealing with femtorisks in international relationsProceedings of the National Academy of Sciences, 2014; 201400229 DOI: 10.1073/pnas.1400229111
Anúncios

Transitions between states of matter: It’s more complicated, scientists find (Science Daily)

Date: November 6, 2014

Source: New York University

Summary: The seemingly simple process of phase changes — those transitions between states of matter — is more complex than previously known. New work reveals the need to rethink one of science’s building blocks and, with it, how some of the basic principles underlying the behavior of matter are taught in our classrooms.

Melting ice. The seemingly simple process of phase changes — those transitions between states of matter — is more complex than previously known. Credit: © shefkate / Fotolia

The seemingly simple process of phase changes — those transitions between states of matter — is more complex than previously known, according to research based at Princeton University, Peking University and New York University.

Their study, which appears in the journal Science, reveals the need to rethink one of science’s building blocks and, with it, how some of the basic principles underlying the behavior of matter are taught in our classrooms. The researchers examined the way that a phase change, specifically the melting of a solid, occurs at a microscopic level and discovered that the transition is far more involved than earlier models had accounted for.

“This research shows that phase changes can follow multiple pathways, which is counter to what we’ve previously known,” explains Mark Tuckerman, a professor of chemistry and applied mathematics at New York University and one of the study’s co-authors. “This means the simple theories about phase transitions that we teach in classes are just not right.”

According to Tuckerman, scientists will need to change the way they think of and teach on phase changes.

The work stems from a 10-year project at Princeton to develop a mathematical framework and computer algorithms to study complex behavior in systems, explained senior author Weinan E, a professor in Princeton’s Department of Mathematics and Program in Applied and Computational Mathematics. Phase changes proved to be a crucial test case for their algorithm, E said. E and Tuckerman worked with Amit Samanta, a postdoctoral researcher at Princeton now at Lawrence Livermore National Laboratory, and Tang-Qing Yu, a postdoctoral researcher at NYU’s Courant Institute of Mathematical Sciences.

“It was a test case for the rather powerful set of tools that we have developed to study hard questions about complex phenomena such as phase transitions,” E said. “The melting of a relatively simple atomic solid such as a metal, proved to be enormously rich. With the understanding we have gained from this case, we next aim to probe more complex molecular solids such as ice.”

The findings reveal that phase transition can occur via multiple and competing pathways and that the transitions involve at least two steps. The study shows that, along one of these pathways, the first step in the transition process is the formation of point defects — local defects that occur at or around a single lattice site in a crystalline solid. These defects turn out to be highly mobile. In a second step, the point defects randomly migrate and occasionally meet to form large, disordered defect clusters.

This mechanism predicts that “the disordered cluster grows from the outside in rather than from the inside out, as current explanations suggest,” Tuckerman notes. “Over time, these clusters grow and eventually become sufficiently large to cause the transition from solid to liquid.”

Along an alternative pathway, the defects grow into thin lines of disorder (called “dislocations”) that reach across the system. Small liquid regions then pool along these dislocations, these regions expand from the dislocation region, engulfing more and more of the solid, until the entire system becomes liquid.

This study modeled this process by tracing copper and aluminum metals from an atomic solid to an atomic liquid state. The researchers used advanced computer models and algorithms to reexamine the process of phase changes on a microscopic level.

“Phase transitions have always been something of a mystery because they represent such a dramatic change in the state of matter,” Tuckerman observes. “When a system changes from solid to liquid, the properties change substantially.”

He adds that this research shows the surprising incompleteness of previous models of nucleation and phase changes–and helps to fill in existing gaps in basic scientific understanding.

This work is supported by the Office of Naval Research (N00014-13-1-0338), the Army Research Office (W911NF- 11-1-0101), the Department of Energy (DE-SC0009248, DE-AC52-07NA27344), and the National Science Foundation of China (CHE-1301314).


Journal Reference:

  1. A. Samanta, M. E. Tuckerman, T.-Q. Yu, W. E. Microscopic mechanisms of equilibrium melting of a solid. Science, 2014; 346 (6210): 729 DOI:10.1126/science.1253810

Important and complex systems, from the global financial market to groups of friends, may be highly controllable (Science Daily)

Date: March 20, 2014

Source: McGill University

Summary: Scientists have discovered that all complex systems, whether they are found in the body, in international finance, or in social situations, actually fall into just three basic categories, in terms of how they can be controlled.

All complex systems, whether they are found in the body, in international finance, or in social situations, actually fall into just three basic categories, in terms of how they can be controlled, researchers say. Credit: © Artur Marciniec / Fotolia

We don’t often think of them in these terms, but our brains, global financial markets and groups of friends are all examples of different kinds of complex networks or systems. And unlike the kind of system that exists in your car that has been intentionally engineered for humans to use, these systems are convoluted and not obvious how to control. Economic collapse, disease, and miserable dinner parties may result from a breakdown in such systems, which is why researchers have recently being putting so much energy into trying to discover how best to control these large and important systems.

But now two brothers, Profs. Justin and Derek Ruths, from Singapore University of Technology and Design and McGill University respectively, have suggested, in an article published in Science, that all complex systems, whether they are found in the body, in international finance, or in social situations, actually fall into just three basic categories, in terms of how they can be controlled.

They reached this conclusion by surveying the inputs and outputs and the critical control points in a wide range of systems that appear to function in completely different ways. (The critical control points are the parts of a system that you have to control in order to make it do whatever you want — not dissimilar to the strings you use to control a puppet).

“When controlling a cell in the body, for example, these control points might correspond to proteins that we can regulate using specific drugs,” said Justin Ruths. “But in the case of a national or international economic system, the critical control points could be certain companies whose financial activity needs to be directly regulated.”

One grouping, for example, put organizational hierarchies, gene regulation, and human purchasing behaviour together, in part because in each, it is hard to control individual parts of the system in isolation. Another grouping includes social networks such as groups of friends (whether virtual or real), and neural networks (in the brain), where the systems allow for relatively independent behaviour. The final group includes things like food systems, electrical circuits and the internet, all of which function basically as closed systems where resources circulate internally.

Referring to these groupings, Derek Ruths commented, “While our framework does provide insights into the nature of control in these systems, we’re also intrigued by what these groupings tell us about how very different parts of the world share deep and fundamental attributes in common — which may help unify our understanding of complexity and of control.”

“What we really want people to take away from the research at this point is that we can control these complex and important systems in the same way that we can control a car,” says Justin Ruths. “And that our work is giving us insight into which parts of the system we need to control and why. Ultimately, at this point we have developed some new theory that helps to advance the field in important ways, but it may still be another five to ten years before we see how this will play out in concrete terms.”

Journal Reference:

  1. Justin Ruths and Derek Ruths. Control Profiles of Complex NetworksScience, 2014 DOI: 10.1126/science.1242063

Could Ants Teach the Biofuel Industry a Thing or Two? (Quest)

Post by  , Producer for on Sep 26, 2013

Leafcutter ants, native to Central and South America, can't digest the leaves they rely on for food, so they cultivate these gardens of fungi and bacteria to break down plant matter for them.

Leafcutter ants, native to Central and South America, can’t digest the leaves they rely on for food, so they cultivate these gardens of fungi and bacteria to break down plant matter for them. Photo courtesy of Alex Wild; used with permission.

In the lobby of the Microbial Sciences building at the University of Wisconsin, leafcutter ants in adisplay colony hike back and forth. Improbably large leaf fragments wobble on their backs as the ants ferry them between a dwindling pile of oak leaves and a garden of fungus studded with leaves in assorted states of decay.

Made up of a single species of fungus and a handful of bacterial strains, the fungus garden breaks down the ants’ leafy harvest through an efficient natural process. It’s a process that researchers believe could be a model for producing biofuel in a more sustainable way.

As we transition away from petroleum dependence, ethanol-based biofuel has risen to the forefront as one of the most accessible sources of renewable energy. It’s produced by fermenting plant sugars, which are strung together into long chains called polysaccharides. Before the fermentation process can begin, these chains have to be snipped apart, a process that varies in difficulty depending on the type of plant being used.

Polysaccharide chains found in corn kernels — the primary biofuel crop in the U.S. — are relatively simple to break up. But corn depletes the soil and guzzles water and fertilizer, and using it for fuel siphons calories from the food supply to gas tanks.

On the other hand, perennial grasses and agricultural “waste” like cornstalks offer a biofuel source that has a lighter impact on the environment. But these woodier fibers — referred to as“cellulosic” biomass — are a tangle of robust polysaccharides that are trickier to deconstruct. Further complicating this problem, the molecular structure of plant biomass isn’t uniform. What breaks down the polysaccharides near the surface of a cornstalk or blade of grass might not work at all on those buried more deeply.

DSC_0025

University of Wisconsin researcher Frank Aylward peers into one of the lab’s many leafcutter ant colonies.

But finding efficient ways to extract energy from plants and other forms of biomass is not a new problem. In fact, it’s a problem that Earth’s plant eaters solved millions of years ago. And according to University of Wisconsin researcher Frank Aylward, if you’re looking for a model system, you can’t do better than leafcutter ants.

They may not have the imposing mien of herbivores like giraffes or elephants, but in Central and South America, leafcutter ants dominate, munching through more of the region’s foliage than any other organism.

But the ants can’t digest leaves by themselves — they have to rely on the garden’s microbes. “We sort of think of the fungus gardens as being an external gut,” Aylward explains. The garden digests biomass and reconstitutes its molecules in little nutrient packets holding a cocktail of carbohydrates, lipids, and proteins.

“The ants are essentially doing what we want to do with biofuel,” says Aylward. “They’re taking all of this recalcitrant plant biomass that’s full of all of these really complicated polymers and they’re degrading it and converting it into energy.” The transformation from leafy greens to energy source is mediated by hundreds of enzymes produced by the fungus garden’s microbes. If these enzymes chow down so efficiently on the leaves of Central America, Aylward and his coworkers wondered, could they be just as effective at breaking apart the sugars of cellulosic biomass in an industrial setting?

One model for a commercial biofuel process patterned after the fungus garden could entail splicing the genetic codes for the garden’s most effective enzymes into other microbes, prompting them to churn out biomass-digesting proteins.

But first, scientists needed to identify which enzymes the garden uses to digest leaves for the ants and which microbial residents produce them. By sequencing the genomes of the fungus and bacteria and comparing that data to the garden’s enzyme soup, Aylward and his coworkers were able to identify a fungus called Leucoagaricus gongylophorus as the garden’s biomass-degrading workhorse.

Aylward extracts a fragment of the fungus garden. This segment was near the surface, and still shows visible leaf matter; the biomass  in the garden sinks as it's broken down.

Aylward extracts a fragment of the fungus garden. This segment was near the surface, and still shows visible leaf matter; the biomass in the garden sinks as it’s broken down.

They also found that the fungus calibrates its enzyme cocktail for different stages of leaf decay. The biomass profile changes at each level in the garden — the freshest leaves sit near the top and the mostly decomposed waste material at the bottom. And Aylward found that the garden’s enzymes changed, too. That insight could provide the biofuel industry with some clues about which enzymes might excel early in the polysaccharide-decomposition process and which ones to apply later on.

Incidentally, this division of labor also reveals which enzymes the garden deploys together at each level. This is a huge boon to anyone designing industrial applications, since enzymes tend to work much better in specific combinations — and the garden has had 50 million years of symbiosis with the ants to find the most efficient combinations.

Aylward has already been approached by companies interested in synthesizing some of the garden’s enzymes and using them in biofuel production.

“It’s difficult to think that we can actually find a process that improves on nature,” Aylward points out, “so it probably makes sense to learn from it.”