Search results for "complex"

Linear ViscoElastic (LVE) Behaviour of Pure Bitumen via Fractional Model

2012

AbstractBy fitting experimental data from static creep/recovery carried out on pure bitumen, it is shown that the fractional model proposed enables the description of both creep and recovery behaviour with fewer parameters than those needed by other models in the literature. In particular, the model is fitted to experimental data of complex modulus |G*| and phase angle δ° obtained from Dynamic Mechanical Analysis. Lastly, it is demonstrated that when the fractional model is used, complex modulus isotherms for a range of frequencies can be created simply starting from isochronals at f = 1Hz.

Social network analysis approaches to study crime

2022

Social Network Analysis (SNA) studies groups of individuals and can be applied in a lot of areas such us organizational studies, psychology, economics, information science and criminology. One of the most important results of SNA has been the definition of a set of centrality measures (e.g., degree, closeness, betweenness, or clustering coefficient) which can be used to identify the most influential people with respect to their network of relationships. The main problem with computing centrality metrics on social networks is the typical big size of the data. From the computational point of view, SNA represents social networks as graphs composed of a set of nodes connected by another set of …

A primer on statistically validated networks

2019

In this contribution we discuss some approaches of network analysis providing information about single links or single nodes with respect to a null hypothesis taking into account the heterogeneity of the system empirically observed. With this approach, a selection of nodes and links is feasible when the null hypothesis is statistically rejected. We focus our discussion on approaches using i) the so-called disparity filter and ii) statistically validated network in bipartite networks. For both methods we discuss the importance of using multiple hypothesis test correction. Specific applications of statistically validated networks are discussed. We also discuss how statistically validated netw…

Design of a Planar Sensor Based on Split-Ring Resonators for Non-Invasive Permittivity Measurement

2023

The permittivity of a material is an important parameter to characterize the degree of polarization of a material and identify components and impurities. This paper presents a non-invasive measurement technique to characterize materials in terms of their permittivity based on a modified metamaterial unit-cell sensor. The sensor consists of a complementary split-ring resonator (C-SRR), but its fringe electric field is contained with a conductive shield to intensify the normal component of the electric field. It is shown that by tightly electromagnetically coupling opposite sides of the unit-cell sensor to the input/output microstrip feedlines, two distinct resonant modes are excited. Perturb…

A complex sampling design: a tourism case study

2009

Analysing Complex Life Sequence Data with Hidden Markov Modelling

2016

When analysing complex sequence data with multiple channels (dimensions) and long observation sequences, describing and visualizing the data can be a challenge. Hidden Markov models (HMMs) and their mixtures (MHMMs) offer a probabilistic model-based framework where the information in such data can be compressed into hidden states (general life stages) and clusters (general patterns in life courses). We studied two different approaches to analysing clustered life sequence data with sequence analysis (SA) and hidden Markov modelling. In the first approach we used SA clusters as fixed and estimated HMMs separately for each group. In the second approach we treated SA clusters as suggestive and …

Hierarchical structures in Complex Systems: from DNA to financial markets

2000

In this paper we discuss the concepts of short-range and long-range correlated stochastic processes and we investigate the presence of such variables in two model complex systems. The selected model systems are DNA sequences of complete genomes and financial time series of equities traded in a stock market. Specifically, by starting from our research results, we discuss the statistical properties of (i) coding and non-coding regions of DNA and (ii) equity returns and volatility in financial markets. The stylized facts about these variables are presented and discussed with a focus on the statistical tools already used and/or still needed to better characterize these model complex systems.

Shift-Invariant Canonical Polyadic Decomposition of Complex-Valued Multi-Subject fMRI Data with a Phase Sparsity Constraint

2020

Canonical polyadic decomposition (CPD) of multi-subject complex-valued fMRI data can be used to provide spatially and temporally shared components among groups with both magnitude and phase information. However, the CPD model is not well formulated due to the large subject variability in the spatial and temporal modalities, as well as the high noise level in complex-valued fMRI data. Considering that the shift-invariant CPD can model temporal variability across subjects, we propose to further impose a phase sparsity constraint on the shared spatial maps to denoise the complex-valued components and to model the inter-subject spatial variability as well. More precisely, subject-specific time …

Etude analytique en régime dynamique des performances thermiques des parois en blocs de terre stabilisée

2023

L’objectif visé à travers cette étude est de parvenir à dimensionner de manière optimale les épaisseurs des murs en blocs de terre stabilisée (BTS), pour obtenir un confort thermique satisfaisant à l’intérieur des constructions avec ce matériau. Pour ce faire, une méthode analytique des admittances basée sur le complexe de Fourier est utilisée. L’analyse des résultats a mis en exergue les principaux facteurs influents sur le dimensionnement idoine pour parvenir à assurer un confort thermique satisfaisant à l’intérieur de ces constructions en terre. Parmi ces facteurs, on relève les caractéristiques thermo-physiques intrinsèques des matériaux utilisés et d’autres paramètres tels que le facte…

Ferromagnetic exchange in a twisted, oxime-bridged [mniii2] dimer

2012

Journal article The dimeric complex [MnIII2(Naphth-sao)2(Naphth-saoH)2(MeOH)2][middle dot]4MeOH (1[middle dot]4MeOH), acts as a simple model complex with which to examine the magneto-structural relationship in polymetallic, oxime-bridged MnIII complexes. Dc magnetic susceptibility studies reveal that ferromagnetic exchange is mediated through the heavily twisted Mn-O-N-Mn moiety (J = +1.24 cm-1) with magnetisation measurements at low temperatures and high fields suggesting significant anisotropy. Simulations of high field, high frequency EPR data reveal a single ion anisotropy, D(MnIII) = -3.94 cm-1. Theoretical studies on simplified model complexes of 1 reveal that calculated values of the…