Injection for Information Diffusion In Social Networks

ABSTRACT We propose a new link-injection method aiming at boosting the overall diffusion of information in social networks. Our approach is based on a diffusion-coverage score of the ability of each user to spread information over the network. Candidate links for injection are identified by a matrix factorization technique and link injection is performed by attaching links to users according to their score. We additionally perform clustering to identify communities in order to inject links that cross the boundaries of such communities. In our experiments with five real world networks, we demonstrate that our method can significantly spread the information diffusion by performing limited link injection, essential to real-world applications

Structure of complex networks: Quantifying edge-to-edge relations by failure-induced flow redistribution

The analysis of complex networks has so far revolved mainly around the role of nodes and communities of nodes. However, the dynamics of interconnected systems is commonly focalised on edge processes, and a dual edge-centric perspective can often prove more natural. Here we present graph-theoretical measures to quantify edge-to-edge relations inspired by the notion of flow redistribution induced by edge failures. Our measures, which are related to the pseudo-inverse of the Laplacian of the network, are global and reveal the dynamical interplay between the edges of a network, including potentially non-local interactions. Our framework also allows us to define the embeddedness of an edge, a measure of how strongly an edge features in the weighted cuts of the network. We showcase the general applicability of our edge-centric framework through analyses of the Iberian Power grid, traffic flow in road networks, and the C. elegans neuronal network.Comment: 24 pages, 6 figure

Dual communities in spatial networks

Both human-made and natural supply systems, such as power grids and leaf venation networks, are built to operate reliably under changing external conditions. Many of these spatial networks exhibit community structures. Here, we show that a relatively strong connectivity between the parts of a network can be used to define a different class of communities: dual communities. We demonstrate that traditional and dual communities emerge naturally as two different phases of optimized network structures that are shaped by fluctuations and that they suppress failure spreading, which underlines their importance in understanding the shape of real-world supply networks

Confluence and consequence: globalisation, viscosities and transformation of HIV risk environments in Vietnam

This thesis shows that illicit drug consumers in Vietnam who administer product via injection are vulnerable actors in a paradoxical global/local phenomenon rooted in historical complexities of globalisation. Therefore, responsibility for HIV risks should be shifted upstream from the level of individuals toward institutional processes that manufacture environments of harm. At the global level, the UN Milennium Development Goals do not provide the required level of leadership on HIV prevention for drug injectors. Association between globalisation, opiates and blood-born disease in Vietnam is not new and is inseparable from historical transportation, migration and trade processes. As a key locale in the Cold War, after 1975, and 1979 in particular, Vietnam was 'at distance' from increasing intra-regional trade flows across its western frontiers and northern border. As a consequence, it was hermetically sealed to nearby HIV sub-epidemics unfolding among heroin consumers. A latent HIV risk environment awaited Vietnam should geopolitical grievances be resolved and it became re-integrated among Mekong sub-regional flows. Neo-liberal financial flows returned to Vietnam in 1993 and the Mekong was spanned in 1994. In 1995 it normalised relations with the United States, joined ASEAN and announced the resurrection of transportation linkages across the northern border with China. Mid-decade, its borders were made more porous at the same time as local opium production was reduced as part of the UN global programme against drugs. Exploiting enhanced trans-boundary mobilities intended for goods, opiate traffickers quickly transformed Vietnam into a transit nation and a market for high-quality heroin well suited to a youthful population experiencing socio-economic change including new consumerism. Following traditional pathways, a radical transformation in the fluidity of drug consumption environs ensued, enabling more widespread and efficient flows of blood across complex boundaries. Analysis reveals that a spatio-temporal confluence of structural factors has created conditions which enabled this process. These factors are overlapping and they range from global influences, such as the collapse of the USSR, to micro-economic reform such as privatisation and modernisation of the domestic pharmaceutical sector. The transformation in opiate consumption from injecting opium to heroin injecting occurred faster than expert-driven prevention systems responded, even in time and space where this was most foreseeable. Although the opiate transformation was highly predictable, there has been a time-lag of almost a decade between risk transformations and policy responses equated with harm reduction principles. The thesis shows that blame for HIV sub-epidemics in Vietnam should not be attributed to vulnerable youths and young adults. Expert-driven economic transition associated with global intergration has manufactured circumstances in which drug availability has risen dramatically at a time when employment growth has been insufficient and a commercial sex industry has expanded. This research confirms the importance of new methods of risk environment analyses, particularly in relation to trans-boundary hazards associated with global flows, including trade and human mobilities

Intracellular transport driven by cytoskeletal motors: General mechanisms and defects

Cells are strongly out-of-equilibrium systems driven by continuous energy supply. They carry out many vital functions requiring active transport of various ingredients and organelles, some being small, others being large. The cytoskeleton, composed of three types of filaments, determines the shape of the cell and plays a role in cell motion. It also serves as a road network for the so-called cytoskeletal motors. These molecules can attach to a cytoskeletal filament, perform directed motion, possibly carrying along some cargo, and then detach. It is a central issue to understand how intracellular transport driven by molecular motors is regulated, in particular because its breakdown is one of the signatures of some neuronal diseases like the Alzheimer. We give a survey of the current knowledge on microtubule based intracellular transport. We first review some biological facts obtained from experiments, and present some modeling attempts based on cellular automata. We start with background knowledge on the original and variants of the TASEP (Totally Asymmetric Simple Exclusion Process), before turning to more application oriented models. After addressing microtubule based transport in general, with a focus on in vitro experiments, and on cooperative effects in the transportation of large cargos by multiple motors, we concentrate on axonal transport, because of its relevance for neuronal diseases. It is a challenge to understand how this transport is organized, given that it takes place in a confined environment and that several types of motors moving in opposite directions are involved. We review several features that could contribute to the efficiency of this transport, including the role of motor-motor interactions and of the dynamics of the underlying microtubule network. Finally, we discuss some still open questions.Comment: 74 pages, 43 figure