Consensus formation on adaptive networks

The structure of a network can significantly influence the properties of the dynamical processes which take place on them. While many studies have been devoted to this influence, much less attention has been devoted to the interplay and feedback mechanisms between dynamical processes and network topology on adaptive networks. Adaptive rewiring of links can happen in real life systems such as acquaintance networks where people are more likely to maintain a social connection if their views and values are similar. In our study, we consider different variants of a model for consensus formation. Our investigations reveal that the adaptation of the network topology fosters cluster formation by enhancing communication between agents of similar opinion, though it also promotes the division of these clusters. The temporal behavior is also strongly affected by adaptivity: while, on static networks, it is influenced by percolation properties, on adaptive networks, both the early and late time evolution of the system are determined by the rewiring process. The investigation of a variant of the model reveals that the scenarios of transitions between consensus and polarized states are more robust on adaptive networks.Comment: 11 pages, 14 figure

CLC, a promising concept with challenging development issues

Chemical Looping Combustion (CLC) is a promising technique to achieve fuel combustion in a nitrogen free atmosphere, therefore giving the possibility to separate and store or use CO2. Several potential applications are considered in the field of power generation with gas, liquid and solid fuels. In the Carbon Capture, Storage and Utilization (CCSU) context, energy penalty is reduced compared to other routes. In addition, other applications of Chemical Looping are considered in the field of H2 production or gasification for instance. In the past years, a huge effort has been conducted worldwide to investigate CLC materials and process issues. In 2008, IFPEN and Total have started an ambitious collaboration to develop CLC applications. Nowadays, the CLC concept is well demonstrated at the pilot scale. The next step is to demonstrate the technology over time at larger scale. However, for further developments, the challenges are numerous and will be discussed, both on market and technical aspects. Short term market is limited. Uncertainties around CO2 emission market and storage issues are related to CO2 policy and public acceptance of storage which still must evolve in the right direction... Financing of demonstration units in this context is challenging and other applications of CLC have to be investigated. The industrial use of synthetic metal oxides or natural ores at large scale generates a lot of issues related to availability, price, waste disposal, health and safety, additionally to chemical and mechanical stability over time, reactivity, and oxygen transfer capacity. Chemical looping reactor and process technology concepts have to be explored, developed, modeled and scaled-up in order to ensure adequate power production together with good gas solid contact and reaction requirement, controlled circulation of mixtures of particle (oxygen carrier, ash, solid fuel for instance). All these points should be considered at very large scale for CCS applications in order to minimize energy penalty and cost in severe operating conditions (temperatures above 800°C and intense solid circulation). Technical challenges remain to be solved and proven with large demonstration over long periods of time. In this context, research in the field of fluidization technology is essential and we will address a couple of key points already investigated at IFPEN and related to control of solid circulation, oxygen carrier attrition, conceptual design of CLC reactors and process performance

Spectral Analysis of Multi-dimensional Self-similar Markov Processes

In this paper we consider a discrete scale invariant (DSI) process $\{X(t), t\in {\bf R^+}\}$ with scale $l>1$. We consider to have some fix number of observations in every scale, say $T$, and to get our samples at discrete points $\alpha^k, k\in {\bf W}$ where $\alpha$ is obtained by the equality $l=\alpha^T$ and ${\bf W}=\{0, 1,...\}$. So we provide a discrete time scale invariant (DT-SI) process $X(\cdot)$ with parameter space $\{\alpha^k, k\in {\bf W}\}$. We find the spectral representation of the covariance function of such DT-SI process. By providing harmonic like representation of multi-dimensional self-similar processes, spectral density function of them are presented. We assume that the process $\{X(t), t\in {\bf R^+}\}$ is also Markov in the wide sense and provide a discrete time scale invariant Markov (DT-SIM) process with the above scheme of sampling. We present an example of DT-SIM process, simple Brownian motion, by the above sampling scheme and verify our results. Finally we find the spectral density matrix of such DT-SIM process and show that its associated $T$-dimensional self-similar Markov process is fully specified by $\{R_{j}^H(1),R_{j}^H(0),j=0, 1,..., T-1\}$ where $R_j^H(\tau)$ is the covariance function of $j$th and $(j+\tau)$th observations of the process.Comment: 16 page

Mobility and Social Network Effects on Extremist Opinions

Understanding the emergence of extreme opinions and in what kind of environment they might become less extreme is a central theme in our modern globalized society. A model combining continuous opinions and observed discrete actions (CODA) capable of addressing the important issue of measuring how extreme opinions might be has been recently proposed. In this paper I show extreme opinions to arise in a ubiquitous manner in the CODA model for a multitude of social network structures. Depending on network details reducing extremism seems to be possible. However, a large number agents with extreme opinions is always observed. A significant decrease in the number of extremists can be observed by allowing agents to change their positions in the network.Comment: 7 pages, 8 figures, discussion expanded, new references, new figure

A BCG with Offset Cooling:Is the AGN Feedback Cycle Broken in A2495?

We present a combined radio/X-ray analysis of the poorly studied galaxy cluster A2495 (z = 0.07923) based on new EVLA and Chandra data. We also analyze and discuss Hα emission and optical continuum data retrieved from the literature. We find an offset of ∼6 kpc between the cluster brightest cluster galaxy (BCG) (MCG+02-58-021) and the peak of the X-ray emission, suggesting that the cooling process is not taking place on the central galaxy nucleus. We propose that sloshing of the intracluster medium (ICM) could be responsible for this separation. Furthermore, we detect a second, ∼4 kpc offset between the peak of the Hα emission and that of the X-ray emission. Optical images highlight the presence of a dust filament extending up to ∼6 kpc in the cluster BCG and allow us to estimate a dust mass within the central 7 kpc of 1.7 × 105 M . Exploiting the dust-to-gas ratio and the L Hα-M mol relation, we argue that a significant amount (up to 109 M ) of molecular gas should be present in the BCG of this cluster. We also investigate the presence of ICM depressions, finding two putative systems of cavities; the inner pair is characterized by t age ∼ 18 Myr and P cav ∼ 1.2 × 1043 erg s-1, the outer one by t age ∼ 53 Myr and P cav ∼ 5.6 × 1042 erg s-1. Their age difference appears to be consistent with the freefall time of the central cooling gas and with the offset timescale estimated with the Hα kinematic data, suggesting that sloshing is likely playing a key role in this environment. Furthermore, the cavities' power analysis shows that the active galactic nucleus energy injection is able to sustain the feedback cycle, despite cooling being offset from the BCG nucleus.</p

Probing microscopic origins of confined subdiffusion by first-passage observables

Subdiffusive motion of tracer particles in complex crowded environments, such as biological cells, has been shown to be widepsread. This deviation from brownian motion is usually characterized by a sublinear time dependence of the mean square displacement (MSD). However, subdiffusive behavior can stem from different microscopic scenarios, which can not be identified solely by the MSD data. In this paper we present a theoretical framework which permits to calculate analytically first-passage observables (mean first-passage times, splitting probabilities and occupation times distributions) in disordered media in any dimensions. This analysis is applied to two representative microscopic models of subdiffusion: continuous-time random walks with heavy tailed waiting times, and diffusion on fractals. Our results show that first-passage observables provide tools to unambiguously discriminate between the two possible microscopic scenarios of subdiffusion. Moreover we suggest experiments based on first-passage observables which could help in determining the origin of subdiffusion in complex media such as living cells, and discuss the implications of anomalous transport to reaction kinetics in cells.Comment: 21 pages, 3 figures. Submitted versio

Fractional Langevin equation

We investigate fractional Brownian motion with a microscopic random-matrix model and introduce a fractional Langevin equation. We use the latter to study both sub- and superdiffusion of a free particle coupled to a fractal heat bath. We further compare fractional Brownian motion with the fractal time process. The respective mean-square displacements of these two forms of anomalous diffusion exhibit the same power-law behavior. Here we show that their lowest moments are actually all identical, except the second moment of the velocity. This provides a simple criterion which enables to distinguish these two non-Markovian processes.Comment: 4 page

The response function of a sphere in a viscoelastic two-fluid medium

In order to address basic questions of importance to microrheology, we study the dynamics of a rigid sphere embedded in a model viscoelastic medium consisting of an elastic network permeated by a viscous fluid. We calculate the complete response of a single bead in this medium to an external force and compare the result to the commonly-accepted, generalized Stokes-Einstein relation (GSER). We find that our response function is well approximated by the GSER only within a particular frequency range determined by the material parameters of both the bead and the network. We then discuss the relevance of this result to recent experiments. Finally we discuss the approximations made in our solution of the response function by comparing our results to the exact solution for the response function of a bead in a viscous (Newtonian) fluid.Comment: 12 pages, 2 figure

Integrated Filterbank for DESHIMA: A Submillimeter Imaging Spectrograph Based on Superconducting Resonators

An integrated filterbank (IFB) in combination with microwave kinetic inductance detectors (MKIDs), both based on superconducting resonators, could be used to make broadband submillimeter imaging spectrographs that are compact and flexible. In order to investigate the possibility of adopting an IFB configuration for DESHIMA (Delft SRON High-redshift Mapper), we study the basic properties of a coplanar-waveguide-based IFB using electromagnetic simulation. We show that a coupling efficiency greater than 1/2 can be achieved if transmission losses are negligible. We arrive at a practical design for a 9 pixel x 920 color 3 dimensional imaging device that fits on a 4 inch wafer, which instantaneously covers multiple submillimeter telluric windows with a dispersion of f/df = 1000.Comment: 6 pages, 4 figures, submitted to LTD-14 / Journal of Low Temperature Physic