Quantifying the 'end of history' through a Bayesian Markov-chain approach

Political regimes have been changing throughout humanhistory. After the apparent triumph of liberal democracies atthe end of the twentieth century, Francis Fukuyama andothers have been arguing that humankind is approaching an‘end of history’(EoH) in the form of a universality of liberaldemocracies. This view has been challenged by recentdevelopments that seem to indicate the rise of defectivedemocracies across the globe. There has been no attempt toquantify the expected EoH with a statistical approach. In thisstudy, we model the transition between political regimes as aMarkov process and—using a Bayesian inference approach—we estimate the transition probabilities between politicalregimes from time-series data describing the evolution ofpolitical regimes from 1800 to 2018. We then compute thesteady state for this Markov process which represents amathematical abstraction of the EoH and predicts thatapproximately 46% of countries will be full democracies.Furthermore, we find that, under our model, the fraction ofautocracies in the world is expected to increase for the nexthalf-century before it declines. Using random-walk theory, wethen estimate survival curves of different types of regimes andestimate characteristic lifetimes of democracies and autocraciesof 244 years and 69 years, respectively. Quantifying theexpected EoH allows us to challenge common beliefs aboutthe nature of political equilibria. Specifically, we find nostatistical evidence that the EoH constitutes a fixed, completeomnipresence of democratic regimes

Topological data analysis of truncated contagion maps

The investigation of dynamical processes on networks has been one focus for the study of contagion processes. It has been demonstrated that contagions can be used to obtain information about the embedding of nodes in a Euclidean space. Specifically, one can use the activation times of threshold contagions to construct contagion maps as a manifold-learning approach. One drawback of contagion maps is their high computational cost. Here, we demonstrate that a truncation of the threshold contagions may considerably speed up the construction of contagion maps. Finally, we show that contagion maps may be used to find an insightful low-dimensional embedding for single-cell RNA-sequencing data in the form of cell-similarity networks and so reveal biological manifolds. Overall, our work makes the use of contagion maps as manifold-learning approaches on empirical network data more viable. It is known that the analysis of spreading processes on networks may reveal their hidden geometric structures. These techniques, called contagion maps, are computationally expensive, which raises the question of whether they can be methodologically improved. Here, we demonstrate that a truncation (i.e., early stoppage) of the spreading processes leads to a substantial speedup in the computation of contagion maps. For synthetic networks, we find that a carefully chosen truncation may also improve the recovery of hidden geometric structures. We quantify this improvement by comparing the topological properties of the original network with the constructed contagion maps by computing their persistent homology. Finally, we explore the embedding of single-cell transcriptomics data and show that contagion maps can help us to distinguish different cell types

New magnetic phase in metallic V_{2-y}O_3 close to the metal insulator transition

We have observed two spin density wave (SDW) phases in hole doped metallic V_{2-y}O_3, one evolves from the other as a function of doping, pressure or temperature. They differ in their response to an external magnetic field, which can also induce a transition between them. The phase boundary between these two states in the temperature-, doping-, and pressure-dependent phase diagram has been determined by magnetization and magnetotransport measurements. One phase exists at high doping level and has already been described in the literature. The second phase is found in a small parameter range close to the boundary to the antiferromagnetic insulating phase (AFI). The quantum phase transitions between these states as a function of pressure and doping and the respective metamagnetic behavior observed in these phases are discussed in the light of structurally induced changes of the band structure.Comment: REVTeX, 8 pages, 12 EPS figures, submitted to PR

Individual nodes contribution to the mesoscale of complex networks

The analysis of complex networks is devoted to the statistical characterization of the topology of graphs at different scales of organization in order to understand their functionality. While the modular structure of networks has become an essential element to better apprehend their complexity, the efforts to characterize the mesoscale of networks have focused on the identification of the modules rather than describing the mesoscale in an informative manner. Here we propose a framework to characterize the position every node takes within the modular configuration of complex networks and to evaluate their function accordingly. For illustration, we apply this framework to a set of synthetic networks, empirical neural networks, and to the transcriptional regulatory network of the Mycobacterium tuberculosis. We find that the architecture of both neuronal and transcriptional networks are optimized for the processing of multisensory information with the coexistence of well-defined modules of specialized components and the presence of hubs conveying information from and to the distinct functional domains

Impartial Selection and the Power of Up to Two Choices

ta no_volume: no_number: no_pages: A:X–A:Y no_year: pdf: publications/bfk_impartial.pdf no_tr: no_http: slides: publications/slides_wine15.pdf keywords: web,recent,journal cvnote: \contrib33%ta no_volume: no_number: no_pages: A:X–A:Y no_year: pdf: publications/bfk_impartial.pdf no_tr: no_http: slides: publications/slides_wine15.pdf keywords: web,recent,journal cvnote: \contrib33%We study mechanisms that select members of a set of agents based on nominations by other members and that are impartial in the sense that agents cannot influence their own chance of selection. Prior work has shown that deterministic mechanisms for selecting any fixed number k of agents are severely limited and cannot extract a constant fraction of the nominations of the k most highly nominated agents. We prove here that this impossibility result can be circumvented by allowing the mechanism to sometimes but not always select fewer than k agents. This added flexibility also improves the performance of randomized mechanisms, for which we show a separation between mechanisms that make exactly two or up to two choices and give upper and lower bounds for mechanisms allowed more than two choices

Transport, magnetic, thermodynamic and optical properties in Ti-doped Sr_2RuO_4

We report on electrical resistivity, magnetic susceptibility and magnetization, on heat capacity and optical experiments in single crystals of Sr_2Ru_(1-x)Ti_xO_4. Samples with x=0.1 and 0.2 reveal purely semiconducting resistivity behavior along c and the charge transport is close to localization within the ab-plane. A strong anisotropy in the magnetic susceptibility appears at temperatures below 100 K. Moreover magnetic ordering in c-direction with a moment of order 0.01 mu_B/f.u. occurs at low temperatures. On doping the low-temperature linear term of the heat capacity becomes reduced significantly and probably is dominated by spin fluctuations. Finally, the optical conductivity reveals the anisotropic character of the dc resistance, with the in-plane conductance roughly following a Drude-type behavior and an insulating response along c

Magnetic properites of the Heavy Fermion Antiferromagnets YbNiAl and YbPtAl

Measurements of electrical resistivity and Hall effect as a function of magnetic field on the Heavy Fermion Systems YbNiAl and YbPtAl are presented. Both compounds order antiferro magnetically and show metamagnetic behavior in a magnetic field. Scaling behavior of the magnetoresistance above TN suggests that the paramagnetic regime for YbNiAl can be described in terms of a single ion Kondo effect.Comment: 12 pages including 5 figures (submitted to the SCES 94 Conference, Ansterdam