Studying the control properties of complex networks provides insight into how designers and engineers can influence these systems to achieve a desired behavior. Topology of a network has been shown to strongly correlate with certain control properties; here we uncover the fundamental structures that explain the basis of this correlation. We develop the control profile, a statistic that quantifies the different proportions of control-inducing structures present in a network. We find that standard random network models do not reproduce the kinds of control profiles that are observed in real-world networks. The profiles of real networks form three well-defined clusters that provide insight into the high-level organization and function of complex systems.
The way players form into groups in online games reveals that hierarchies are an inevitable product of the human condition, say complexity scientists.
“Remarkably, the online players exhibit the same type of structured hierarchical layers as the societies studied by anthropologists, where each of these layers is three to four times the size of the lower layer,” say Fuchs and co.
That’s an interesting result. That the same hierarchy emerges in wildly different situations suggests that whatever produces this effect is independent of the environment. In other words, it must be an innate property of human social behavior.
Some people are more susceptible to conspiracy theories than others, say computational social scientists who have studied how false ideas jump the “credulity barrier” on Facebook.
Conspiracy theories seem to come about by a process in which ordinary satirical commentary or obviously false content somehow jumps the credulity barrier. And that seems to happen through groups of people who deliberately expose themselves to alternative sources of news.
Human conflict, geopolitical crises, terrorist attacks, and natural disasters can turn large parts of energy distribution networks offline. Europe's current gas supply network is largely dependent on deliveries from Russia and North Africa, creating vulnerabilities to social and political instabilities. During crises, less delivery may mean greater congestion, as the pipeline network is used in ways it has not been designed for. Given the importance of the security of natural gas supply, we develop a model to handle network congestion on various geographical scales. We offer a resilient response strategy to energy shortages and quantify its effectiveness for a variety of relevant scenarios. In essence, Europe's gas supply can be made robust even to major supply disruptions, if a fair distribution strategy is applied.
The combination of the network theoretic approach with recently available abundant economic data leads to the development of novel analytic and computational tools for modelling and forecasting key economic indicators. The main idea is to introduce a topological component into the analysis, taking into account consistently all higher-order interactions. We present three basic methodologies to demonstrate different approaches to harness the resulting network gain. First, a multiple linear regression optimisation algorithm is used to generate a relational network between individual components of national balance of payment accounts. This model describes annual statistics with a high accuracy and delivers good forecasts for the majority of indicators. Second, an early-warning mechanism for global financial crises is presented, which combines network measures with standard economic indicators. From the analysis of the cross-border portfolio investment network of long-term debt securities, the proliferation of a wide range of over-the-counter-traded financial derivative products, such as credit default swaps, can be described in terms of gross-market values and notional outstanding amounts, which are associated with increased levels of market interdependence and systemic risk. Third, considering the flow-network of goods traded between G-20 economies, network statistics provide better proxies for key economic measures than conventional indicators. For example, it is shown that a country's gate-keeping potential, as a measure for local power, projects its annual change of GDP generally far better than the volume of its imports or exports.
It is commonly believed that information spreads between individuals like a pathogen, with each exposure by an informed friend potentially resulting in a naive individual becoming infected. However, empirical studies of social media suggest that individual response to repeated exposure to information is far more complex. As a proxy for intervention experiments, we compare user responses to multiple exposures on two different social media sites, Twitter and Digg. We show that the position of exposing messages on the user-interface strongly affects social contagion. Accounting for this visibility significantly simplifies the dynamics of social contagion. The likelihood an individual will spread information increases monotonically with exposure, while explicit feedback about how many friends have previously spread it increases the likelihood of a response. We provide a framework for unifying information visibility, divided attention, and explicit social feedback to predict the temporal dynamics of user behavior.
Decentralised networks are naturally robust against certain types of attack. Now one mathematician says advanced geometry shows how to make them even more robust.
One of the common myths about the internet is that it was originally designed during the Cold War to survive nuclear attack. Historians of the internet are quick to point out that this was not at all one of the design goals of the early network, although the decentralised nature of the system turns out to make it much more robust than any kind of centralised network.
Nevertheless, the internet is still vulnerable. For example, the magnitude 9 earthquake and resulting tsunami that struck Japan on 11 March 2011, caused huge damage to the Japanese telecommunications infrastructure.
The Japanese telecom company NTT says it lost 18 exchange buildings and 65,000 telegraph poles in the disaster which also damaged 1.5 million fixed line circuits and 6300 kilometres of cabling.
That raises an interesting question: could the spatial layout of the internet be made any more robust against this kind of damage?
When Romanian singer Maria Tanase died in 1963, almost a million people flooded onto the streets of Bucharest for her funeral. A brief, grainy archival snippet on the internet reveals a sea of mourners parting around Tanase's open coffin and overflowing from every balcony.
''Maria Tanase was greatly loved and greatly respected in Romania,'' says violinist Alexander Balanescu. ''And her funeral was like a state funeral. People from that generation who were there … still remember that day.''
Balanescu was only nine at the time, and left Romania permanently a few years later, but he remembers hearing Tanase's music as a child, and listening to his parents' rapturous accounts of her live performances. It took many decades though, for those memories to resurface as the inspiration for one of his most personal projects.
A Hungarian team has created the first drones that can fly as a coordinated flock. The researchers watched as the ten autonomous robots took to the air in a field outside Budapest, zipping through the open sky, flying in formation or even following a leader, all without any central control.
The documentary revisits the unresolved question of “Who were the Dacians?” It focuses on the Roman Emperor Trajan’s six-year long two military campaigns against Dacia and its King Decebal between 101 and 106 AD. The documentary is not a literal history but an attempt to link past (who were the Dacians) to the present (what is the legacy) visible in the core regions of the Dacian Kingdom surrounding Sarmizgetusa, its center of power and sanctuary. Dacian Carpathian Mountain fortresses are a UNESCO Heritage Site. The film uses Trajan’s column in Rome, also a UNESCO Heritage Site, and its extensive bas-relief depictions combined with illustrations by artist Radu Oltean and contemporary on-location videography to create an artistic interpretation of the events and to cover on-going archaeological research.
Researchers from the Santa Fe Institute and the Smithsonian Institution have pieced together a highly detailed picture of feeding relationships among 700 mammal, bird, reptile, fish, insect, and plant species from a 48 million year old lake and forest ecosystem.
Their analysis of fossilized remains from the Messel deposit near Frankfurt, Germany, provides the most compelling evidence to date that ancient food webs were organized much like modern food webs. Their paper describing the research appears online and open access this week in Proceedings of the Royal Society B: Biological Sciences.
Subterranean ants and termites are leading researchers and prospectors alike, to gold and other minerals in the northern Yilgarn district.
"There's been anecdotal evidence of it in the Kalgoorlie area since the 1920s," entomologist Aaron Stewart says.
Following an earlier study of a termite that builds nests mostly above ground (Tumulitermes tumuli), they have extended their research to a subterranean termite species (Schedorhinotermes actuosus) and an ant (Rhtidoponera mayri).
"Termite mounds, subterranean termites and ants have the ability to vertically transport indicators [like gold] from 1.4m depth," their paper says.
"The ant species studied brings larger concentrations of gold to the surface than the termites studied."
How generosity among strangers becomes socially contagious.
In recent years, social scientists have conducted experiments demonstrating that the effect of a single act of kindness can in fact ripple through a social network, setting off chains of generosity that reach far beyond the original act. But whether it is enough to merely witness a generous act, rather than actually benefit from one, has been an open question.
Origami, the Japanese art of paper folding, has evolved considerably since it appeared in the western world over a century ago. Folding is simple, easy and cheap. So it’s no wonder that scientists and engineers have begun to exploit it in all kinds of innovative ways. They now use origami to construct everything from molecular machines to space telescopes.
Today, Manu Prakash and pals at Stanford University in California, reveal how they’ve designed and built an origami microscope that is constructed largely out of folded paper and costs less than a dollar to make. And they say their device could revolutionize the way billions of people see the world around them.
Prakash and co call their device the Foldscope and say it can be assembled from a flat sheet of paper in under 10 minutes.
Power grids, road maps, and river streams are examples of infrastructural networks which are highly vulnerable to external perturbations. An abrupt local change of load (voltage, traffic density, or water level) might propagate in a cascading way and affect a significant fraction of the network. Almost discontinuous perturbations can be modeled by shock waves which can eventually interfere constructively and endanger the normal functionality of the infrastructure. We study their dynamics by solving the Burgers equation under random perturbations on several real and artificial directed graphs. Even for graphs with a narrow distribution of node properties (e.g., degree or betweenness), a steady state is reached exhibiting a heterogeneous load distribution, having a difference of one order of magnitude between the highest and average loads. Unexpectedly we find for the European power grid and for finite Watts-Strogatz networks a broad pronounced bimodal distribution for the loads. To identify the most vulnerable nodes, we introduce the concept of node-basin size, a purely topological property which we show to be strongly correlated to the average load of a node.
Effective point-of-use devices for providing safe drinking water are urgently needed to reduce the global burden of waterborne disease. Here we show that plant xylem from the sapwood of coniferous trees – a readily available, inexpensive, biodegradable, and disposable material – can remove bacteria from water by simple pressure-driven filtration. Approximately 3 cm3 of sapwood can filter water at the rate of several liters per day, sufficient to meet the clean drinking water needs of one person. The results demonstrate the potential of plant xylem to address the need for pathogen-free drinking water in developing countries and resource-limited settings.
Has natural selection led to adaptations of Lévy flight foraging, as stated on the respective Wikipedia page? Random walks with scale-free jump length distributions were indeed shown to optimize the search for sparse targets as supported by extensive movement data of many animal species and humans. Here we demonstrate that small variations of the search conditions strongly modify these claims: In the presence of a bias, underwater currents for sea predators or winds for airborne searchers, a Lévy searcher easily overshoots the target, and Brownian strategies become advantageous. Even in the absence of a bias, there exist conditions for which a Brownian strategy may effect faster target localization. Our results show clear limitations for the universality of Lévy flight foraging.