Sparse control of Hegselmann-Krause models: Black hole and declustering

International audienceThis paper elaborates control strategies to prevent clustering effects in opinion formation models. This is the exact opposite of numerous situations encountered in the literature where, on the contrary, one seeks controls promoting consensus. In order to promote declustering, instead of using the classical variance that does not capture well the phenomenon of dispersion, we introduce an entropy-type functional that is adapted to measuring pairwise distances between agents. We then focus on a Hegselmann-Krause-type system and design declustering sparse controls both in finite-dimensional and kinetic models. We provide general conditions characterizing whether clustering can be avoided as function of the initial data. Such results include the description of black holes (where complete collapse to consensus is not avoidable), safety zones (where the control can keep the system far from clustering), basins of attraction (attractive zones around the clustering set) and collapse prevention (when convergence to the clustering set can be avoided)

Small-World Brain Networks Revisited.

It is nearly 20 years since the concept of a small-world network was first quantitatively defined, by a combination of high clustering and short path length; and about 10 years since this metric of complex network topology began to be widely applied to analysis of neuroimaging and other neuroscience data as part of the rapid growth of the new field of connectomics. Here, we review briefly the foundational concepts of graph theoretical estimation and generation of small-world networks. We take stock of some of the key developments in the field in the past decade and we consider in some detail the implications of recent studies using high-resolution tract-tracing methods to map the anatomical networks of the macaque and the mouse. In doing so, we draw attention to the important methodological distinction between topological analysis of binary or unweighted graphs, which have provided a popular but simple approach to brain network analysis in the past, and the topology of weighted graphs, which retain more biologically relevant information and are more appropriate to the increasingly sophisticated data on brain connectivity emerging from contemporary tract-tracing and other imaging studies. We conclude by highlighting some possible future trends in the further development of weighted small-worldness as part of a deeper and broader understanding of the topology and the functional value of the strong and weak links between areas of mammalian cortex.DSB acknowledges support from the John D. and Catherine T. MacArthur Foundation, the Alfred P. Sloan Foundation, the Army Research Laboratory and the Army Research Office through contract numbers W911NF-10-2-0022 and W911NF-14-1-0679, the National Institute of Health (2-R01-DC-009209-11, 1R01HD086888-01, R01-MH107235, R01-MH107703, and R21-M MH-106799), the Office of Naval Research, and the National Science Foundation (BCS-1441502, CAREER PHY-1554488, and BCS-1631550).This is the final version of the article. It first appeared from Sage at http://dx.doi.org/10.1177/1073858416667720

Complexity and Criticality in financial markets: systemic risk across frequencies and cross sections

Extreme market events and systemic collapses cause most of the popular attention to finance and financial markets. Extreme phenomena and the dynamics of con- nected/interacting systems have been the subject of financial modeling since early derivatives modeling, exposure risk modeling and portfolio construction. In the present work we discuss how traditional methods have for the most part failed to properly model the interconnected global financial and economic system. This led to systemic risk events and simplistic regulation which does not properly account for its implications. Analogously, we discuss how from as early as Mandelbrot’s works on financial prices and fat tails, academics, practitioners and regulators alike were warned of fat tails in financial modeling and in particular market making and derivatives pricing. The improper modeling or dismissal of these lies at the cen- tre of financial downturns ranging from LTCM’s collapse to the quant downturn of August 2007. The solution I promote in this thesis is that of complexity and criticality. In line with this we propose two lines of work. The former analyses markets as complex networks and their structure through to practical takeaways including a proof of concept for portfolio construction. The latter instead focuses on extreme events in high frequency markets with results for both tail modeling and systemic events and practical insights from those. Recent events have shown how retail investors and their savings are now heavily involved in financial markets. We hope that our contribution of methods of practical use for proper risk modeling will encourage their adoption by practitioners and regulators with the outcome of a more stable and efficient financial system

Link communities reveal multiscale complexity in networks

Networks have become a key approach to understanding systems of interacting objects, unifying the study of diverse phenomena including biological organisms and human society. One crucial step when studying the structure and dynamics of networks is to identify communities: groups of related nodes that correspond to functional subunits such as protein complexes or social spheres. Communities in networks often overlap such that nodes simultaneously belong to several groups. Meanwhile, many networks are known to possess hierarchical organization, where communities are recursively grouped into a hierarchical structure. However, the fact that many real networks have communities with pervasive overlap, where each and every node belongs to more than one group, has the consequence that a global hierarchy of nodes cannot capture the relationships between overlapping groups. Here we reinvent communities as groups of links rather than nodes and show that this unorthodox approach successfully reconciles the antagonistic organizing principles of overlapping communities and hierarchy. In contrast to the existing literature, which has entirely focused on grouping nodes, link communities naturally incorporate overlap while revealing hierarchical organization. We find relevant link communities in many networks, including major biological networks such as protein-protein interaction and metabolic networks, and show that a large social network contains hierarchically organized community structures spanning inner-city to regional scales while maintaining pervasive overlap. Our results imply that link communities are fundamental building blocks that reveal overlap and hierarchical organization in networks to be two aspects of the same phenomenon.Comment: Main text and supplementary informatio

Limnology and biota of Lake Yindarlgooda - an inland salt lake in Western Australia under stress

Inland salt lakes of the arid and semi-arid zones of Western Australia are unique systems. An unpredictable rainfall pattern and a transient water regime ensure these lakes remain dry for much of the year. Lake Yindarlgooda in the Eastern Goldfields of Western Australia is a typical inland salt lake that has been subjected to additional stresses. This thesis is the outcome of investigations conducted on the lake from 2001 to 2003. Emphasis is on the limnology and biota of the lake, including an adjacent wetland, and impacts on the aquatic ecosystems caused predominantly by mining. Lake Yindarlgooda is a large, shallow hypersaline lake situated on the Yindarlgooda Palaeoriver. It is sodium chloride dominated and has naturally high background levels of nickel. Sites impacted by the leaching of hypersaline decant water from a leach residue storage facility (LRSF) were differentiated from control sites using multivariate statistics. Salinity was found to be a major determinant in the structure of the biological communities in the lake systems.Different biotic communities with low taxonomic diversity were recorded in Lake Yindarlgooda and Swan Refuge, a nearby hyposaline clay pan. The benthic microbial communities were dominated by halotolerant diatoms, notably Amphora coffeaeformis, Navicula incertata and Hantzschia baltica. Variation in the diatom assemblages between the playa sites and the clay pan were noted, influenced by habitat type and salinity. Within Lake Yindarlgooda, the diatom assemblages in the control and impact sites were found to be similar. A narrow salinity spectrum dictated the taxa present. Many of the benthic diatoms collected during the dry phase were encysted, having entered dormancy. The invertebrate fauna in Lake Yindarlgooda and Swan Refuge belonged to the Crustacea. A larger percentage of hyposaline invertebrate taxa were recorded from Swan Refuge, while those in Lake Yindarlgooda were typically halotolerant species. The Ostracoda showed the greatest diversity and their abundance was higher in the southern control sites while the Anostracan, Parartemia sp., dominated the northern impact sites of the playa.The riparian zone of Lake Yindarlgooda supported a diverse plant community, dominated by the Chenopodiaceae. The marginal vegetation communities along the shores of Lake Yindarlgooda were found to be similar, indicating habitat homeogeneity. Within the riparian zone both biological and physical soil crusts occupied large areas not inhabited by vascular plants. The biological soil crust identified was composed of an association between the filamentous cyanobacterium Microcoleus sp. and a moss species (Musci). Both biological and physical soil crusts were found to have functional roles in stabilising the surrounding low dunes. The soil crusts in the northern control sites were badly degraded as a result of trampling by livestock, while those in the southern control sites were protected and were intact. Only one Parartemia species was found to inhabit Lake Yindarlgooda, Parartemia n. sp. d. It was collected in salinities ranging from 50 to 140 g L-1. The population appeared to be oviparous, recruitment mostly from resting eggs. The male to female ratios varied between sites, as did the number of juveniles compared to the adults. The northern impact sites had a more mature Parartemia population than the southern control sites and appeared to have undergone a second recruitment. Examination of the surface sediment found a well established Parartemia “egg bank” in the northern impact sites with egg numbers much higher than in the southern control sites.The ultrastructure of the Parartemia resting egg was identical to that of Artemia. Differences in the external features and internal structure of the resting egg of Parartemia n sp. d and Parartemia n. sp g from Lake Miranda, another saline lake, were identified. This study showed morphological variation of the egg within Parartemia, a finding not previously recorded. Rehydration trials on the Parartemia egg bank indicated that the increase in sediment salinity from the LRSF had a negative effect on the hatching of the resting eggs. In salinities above 60 mS cm-1 hatching was less successful. The conditions provided in the trials were similar to those in Lake Yindarlgooda. The hatching technique was repeated on sediment from Lake Miranda with similar results. These trials were considered a valuable monitoring tool in the assessment of impacts on the biota of temporary lakes in the absence of water. This study demonstrated that in the absence of water the egg and spore/seed bank can be used as a proxy for monitoring temporary lakes. It was also found to be valuable in understanding the distribution and diversity of the biotic communities in Lake Yindarlgooda. This study provides the first integrated reference information on a Western Australian inland salt lake against which any future impact may be assessed

An Indicator for National Systems of Innovation - Methodology and Application to 17 Industrialized Countries

We develop a composite indicator measuring the performance of national innovation systems. The indicator takes into account both “hard” factors that are quantifiable (such as R&D spending, number of patents) and “soft” factors like the assessment of preconditions for innovation by managers. We apply the methodology to a set of 17 industrialized countries on a yearly basis between 2007 and 2009. The indicator combines results from public opinion surveys on the process of change, social capital, trust and science and technology to achieve an assessment of a country’s social climate for innovation. After calculating and ranking the innovation indictor scores for the 17 countries, we group them into three classes: innovation leader, middle group and end section. Using multiple sensitivity analysis approaches, we show that the indicator reacts robustly to different weights within these country groups. While leading countries like Switzerland, the USA and the Nordic countries have an innovation system with high scores and ranks in every sub indicator, the middle group consisting among others of Germany Japan, the UK and France, can be characterized by higher variation within ranks. In the end section, countries like Italy and Spain have bad scores for almost all indicators.National systems of innovation, Composite Indicators, Ranking

Reflections on CAIS and the IS Field from a Former Editor-in-Chief

This essay represents the lessons I learned over a three-year term serving as editor-in-chief of Communications of the Association for Information Systems (CAIS). The discussion revolves around general observations of the IS field, the relationship between these observations of the IS field and CAIS and CAIS\u27s unique mission and how that mission serves stakeholders, authors, readers, editorial team members, and touches on the logistics of managing a journal. The discussions focus on the use of theory in IS knowledge production, the meaning of a contribution, the goal of examining and challenging widely held assumptions and positions, as well as building on prior knowledge

Quantitative single-molecule mapping of neuronal proteins at the nanoscale

The advent of super-resolution microscopy, also called nanoscopy, allowed a substantial improvement of spatial resolution, opening the door for the observation of biological structures beyond the diffraction limit impossible with conventional light microscopy. Among the super-resolution techniques, single-molecule localization microscopies have proven to be a powerful tool to address many biological issues, since they provide an imaging resolution of the order of tens of nanometers and the possibility to perform quantitative measurements. Neuroscience has been one of the fields in biology to benefit most from super-resolution microscopy. During the last years, single-molecule localization microscopies have been widely exploited to study diffraction-limited subcellular structures in neurons, allowing a deeper understanding of molecular mechanisms underlying neural network functioning and its impairments in pathologies. In this thesis, we developed a tool to investigate the distribution, spatial organization, clustering, and density of neural proteins at the nanoscale. In particular, we focused on the quantitative study of synaptic neurotransmitter receptors and focal adhesions. The knowledge of the distribution and stoichiometry of synaptic proteins is fundamental to understand the regulation of the synaptic transmission in neurons. However, a detailed characterization of the protein architecture within synapses can be achieved only by visualizing them at a nanometric level. Here we propose a quantitative approach based on stochastic optical reconstruction microscopy combined with cluster analysis to investigate the molecular rearrangement of GABAA receptors into subsynaptic domains during synaptic plasticity of the inhibitory neurotransmission. This approach was also applied to the study of the adhesion machinery of mammalian cells and neurons at the interface with single-layer graphene to investigate the interaction between cells and nanostructured materials. Due to their excellent properties and biocompatibility, graphene and its derivatives are the ideal candidates for many biomedical applications, such as neural tissue engineering. However, the adhesion processes at the graphene/neuron interface are still not clear nowadays. Our method offers an easy way to study how graphene substrates can affect adhesion and migration of different types of cells

Just-ish?: Alternative justice attitudes: A randomized control trial

Responses to harm and crime in the United States typically utilize the criminal legal system’s retributive approach, which often contributes to cycles of harm rather than facilitating healing (Davis, 2019; Lenzen & Stahler, 2020). In response, alternative responses to harm like transformative and restorative justice are growing in popularity (Fileborn & Vera-Gray, 2017). These approaches to justice are often conflated, but rarely compared (Nocella & Anthony, 2011). First, a systematic literature review of transformative and restorative justice utilizing a qualitative content analysis (QCA) identified the two interventions\u27 definitions, comparisons, and perceived attitudinal outcomes. The major themes of healing for both justice processes and a distinct divestment from the current criminal legal system in transformative justice processes were identified. Second, a three-arm randomized control trial study design included a group that received no intervention (control group), a transformative justice educational intervention, and a restorative justice educational intervention. Results indicated a decrease in endorsement of retributive justice attitudes after both alternative justice educational interventions (i.e., transformative and restorative justice). Additionally, the study did not find that victimization functioned as a moderator of the effect of educational interventions on attitudes towards retributive justice approaches. Further, this study found predictive outcomes of transformative and restorative justice educational interventions on actual decisions to choose restorative and transformative justice processes above the current criminal legal system