How Realistic Should Knowledge Diffusion Models Be?

Knowledge diffusion models typically involve two main features: an underlying social network topology on one side, and a particular design of interaction rules driving knowledge transmission on the other side. Acknowledging the need for realistic topologies and adoption behaviors backed by empirical measurements, it becomes unclear how accurately existing models render real-world phenomena: if indeed both topology and transmission mechanisms have a key impact on these phenomena, to which extent does the use of more or less stylized assumptions affect modeling results? In order to evaluate various classical topologies and mechanisms, we push the comparison to more empirical benchmarks: real-world network structures and empirically measured mechanisms. Special attention is paid to appraising the discrepancy between diffusion phenomena (i) on some real network topologies vs. various kinds of scale-free networks, and (ii) using an empirically-measured transmission mechanism, compared with canonical appropriate models such as threshold models. We find very sensible differences between the more realistic settings and their traditional stylized counterparts. On the whole, our point is thus also epistemological by insisting that models should be tested against simulation-based empirical benchmarks.Agent-Based Simulation, Complex Systems, Empirical Calibration and Validation, Knowledge Diffusion, Model Comparison, Social Networks

Precursors and Laggards: An Analysis of Semantic Temporal Relationships on a Blog Network

We explore the hypothesis that it is possible to obtain information about the dynamics of a blog network by analysing the temporal relationships between blogs at a semantic level, and that this type of analysis adds to the knowledge that can be extracted by studying the network only at the structural level of URL links. We present an algorithm to automatically detect fine-grained discussion topics, characterized by n-grams and time intervals. We then propose a probabilistic model to estimate the temporal relationships that blogs have with one another. We define the precursor score of blog A in relation to blog B as the probability that A enters a new topic before B, discounting the effect created by asymmetric posting rates. Network-level metrics of precursor and laggard behavior are derived from these dyadic precursor score estimations. This model is used to analyze a network of French political blogs. The scores are compared to traditional link degree metrics. We obtain insights into the dynamics of topic participation on this network, as well as the relationship between precursor/laggard and linking behaviors. We validate and analyze results with the help of an expert on the French blogosphere. Finally, we propose possible applications to the improvement of search engine ranking algorithms

Generating constrained random graphs using multiple edge switches

The generation of random graphs using edge swaps provides a reliable method to draw uniformly random samples of sets of graphs respecting some simple constraints, e.g. degree distributions. However, in general, it is not necessarily possible to access all graphs obeying some given con- straints through a classical switching procedure calling on pairs of edges. We therefore propose to get round this issue by generalizing this classical approach through the use of higher-order edge switches. This method, which we denote by "k-edge switching", makes it possible to progres- sively improve the covered portion of a set of constrained graphs, thereby providing an increasing, asymptotically certain confidence on the statistical representativeness of the obtained sample.Comment: 15 page

Information diffusion on realistic networks

Prix du meilleur article étudiantNational audienceLes modèles de diffusion d'information mettent traditionnellement en jeu un réseau sous-jacent dont la topologie reproduit certaines propriétés observées dans les réseaux réels. Toutefois, la comparaison des phénomènes de diffusion observés sur des réseaux générés par des modèles classiques avec ceux se produisant au sein de réseaux réels reste peu étudiée. Dans une démarche empiriste, nous proposons dans cette étude d'évaluer l'écart de comportement induit par l'utilisation de divers modèles stylisés, dont notamment certains réseaux dits ``sans-échelle''

Socio-semantic dynamics in a blog network

The blogosphere can be construed as a knowledge network made of bloggers who are interacting through a social network to share, exchange or produce information. We claim that the social and semantic dimensions are essentially co-determined and propose to investigate the co-evolutionary dynamics of the blogosphere by examining two intertwined issues: First, how does knowledge distribution drive new interactions and thus influence the social network topology? Second, which role structural network properties play in the information circulation in the system? We adopt an empirical standpoint by analyzing the semantic and social activity of a portion of the US political blogosphere, monitored on a period of four months

Cycles in hypergraph-based networks: signal or noise, artefacts or processes?

National audienceLes réseaux à structure de groupe sous-jacente induisent mécaniquement la création de cycles: chaque groupe peut être interprété comme un hyperlien connectant l'ensemble de ses noeuds les uns avec les autres, soit l'ajout d'une clique dans le réseau monoparti projeté. Nous nous intéresserons ici à l'origine des cycles de tailles n ($3\leq n\leq 5$) associés à des coefficients de clustering généralisés jusqu'à l'ordre 5 ($c_3$, $c_4$ et $c_5$) dans des réseaux à structure de groupe (ou d'hypergraphe) sous-jacente. Ces paramètres topologiques peuvent-ils être expliqués uniquement par le processus spécifique de génération à base d'hyperliens, ou d'autres processus doivent-ils être invoqués? Nous mesurons ainsi ces motifs cycliques sur un ensemble de réseaux réels et distinguons deux catégories de cycles - structurels ou séquentiels - dont on évalue la part respective en fonction du type de réseau et de n, puis nous estimons la quantité de chaque type de motif obtenue à partir de différents modèles aléatoires de réseaux à base d'hypergraphes, en nous appuyant sur le cadre formel récemment introduit par Mahadevan [MKFV06]. Nous nous en inspirons pour proposer un modèle original à même de reconstruire l'ensemble des motifs sur l'ensemble des graphes réels étudiés

Progress in the knowledge of 'ruby silvers': New structural and chemical data of pyrostilpnite, Ag3SbS3

AbstractThe crystal structure of pyrostilpnite from the Plaka mine, Lavrion Mining District, Greece, was refined in the space group P21/c to a final R1 index of 0.0283 on the basis of 2047 reflections with Fo > 4σ(Fo) and 65 refined parameters. Unit-cell parameters of the crystal examined are a = 6.8629(6), b = 15.8800(14), c = 6.2711(5) Å, β = 117.087(2)°, V = 608.48(9) Å3 and Z = 4. Chemical data agree with the stoichiometric formula Ag3SbS3. The crystal structure reported previously was confirmed, although a higher precision of refinement was achieved. It can be described as formed by {010} slabs running along c and connected along a through relatively longer Ag–S bonds. The analysis of the atomic displacement parameters together with a refinement with higher order tensors in the expression of the structure factors revealed no hint for pyrostilpnite as an ionic conductor. A historical background of the 'ruby silvers' is also reported

Paleotectonic evolution of the Zürcher Weinland (northern Switzerland), based on 2D and 3D seismic data

Abstract.: A new interpretation of the Permo-Carboniferous (PC) troughs in the Zürcher Weinland region in northern Switzerland is proposed on the basis of 2D and 3D reflection seismic surveys. The presence of two WSW-ENE oriented grabens separated by a crystalline basement horst block, confirmed by the Benken borehole, is well established, though the presence of PC deposits in its surroundings remains uncertain. The interpretation of the 3D seismic data shows a transtensive tectonic regime for this period confirming the results of earlier interpretations of 2D-lines. There is no evidence for a compressive Saalian phase (around 265Ma) as postulated for the PC trough west of Weiach. Several observed faults show signs of reactivation during a late Triassic inversion phase. Detailed mapping of the Mesozoic sequence reveals that further and minor reactivations along the border of the PC trough south of Benken may have influenced deposition of the younger sediments and the local structuration of the base-Tertiary unconformity. The findings of the local investigations are interpreted in the context of large-scale paleotectonic model

Narrow-line phase-locked quantum cascade laser in the 9.2 micron range

We report on the operation of a 50 mW continuous wave quantum cascade laser (QCL) in the 9.2 micrometer range, phase locked to a single mode CO2 laser with a tunable frequency offset. The wide free running emission spectrum of the QCL (3-5 MHz) is strongly narrowed down to the kHz range making it suitable for high resolution molecular spectroscopy.Comment: 4 page

Neoadjuvant Chemotherapy in Patients with Stage IV Colorectal Cancer: A Comparison of Histological Response in Liver Metastases, Primary Tumors, and Regional Lymph Nodes

Background: We report the histopathological results of a novel "inversed” strategy designed to manage patients with colorectal cancer (CRC) who have synchronous liver metastases by using chemotherapy first, liver surgery second, and resection of the primary tumor as a final step. This study was designed to compare the response to chemotherapy in liver metastases, primary tumors, and locoregional lymph nodes. Methods: Twenty-nine patients with stage IV CRC received a combination of oxaliplatin, irinotecan, 5-fluorouracil, and leucovorin (OCFL) for 3-4months. Histological response to chemotherapy was assessed by using a tumor regression grading (TRG) score based on presence of residual tumor cells and extent of fibrosis. Results: Median age of patients was 56 (range, 37-69) years. Primary tumor location was right colon (n=5), left colon (n=7), and rectum (n=17 patients). TRG scores correlated across disease sites (Spearman correlation coefficients for TRG in the primary tumor and lymph nodes was 0.59 [P=0.005]; for the primary tumor and metastases 0.44 [P=0.021]; and for lymph nodes and metastases 0.58 [P=0.006]). Complete absence or poor tumor response (TRG4/5) was significantly more frequent in primary tumors (35.7%) and locoregional lymph nodes (38%) than in liver metastases (6.9%; McNemar test, P=0.02). Two patients had a complete pathologic response (pT0N0M0). Conclusions: In patients with stage IV colorectal cancer, liver metastases exhibit a better histological response than primary tumors to OCFL neoadjuvant chemotherap