Importance-sampling computation of statistical properties of coupled oscillators

We introduce and implement an importance-sampling Monte Carlo algorithm to study systems of globally-coupled oscillators. Our computational method efficiently obtains estimates of the tails of the distribution of various measures of dynamical trajectories corresponding to states occurring with (exponentially) small probabilities. We demonstrate the general validity of our results by applying the method to two contrasting cases: the driven-dissipative Kuramoto model, a paradigm in the study of spontaneous synchronization; and the conservative Hamiltonian mean-field model, a prototypical system of long-range interactions. We present results for the distribution of the finite-time Lyapunov exponent and a time-averaged order parameter. Among other features, our results show most notably that the distributions exhibit a vanishing standard deviation but a skewness that is increasing in magnitude with the number of oscillators, implying that non-trivial asymmetries and states yielding rare/atypical values of the observables persist even for a large number of oscillators.Comment: 11 pages, 4 figures; v2: minor changes, close to the published version, title changed to conform to PRE guideline

Robustness of Reliability Predictions for a Series System of Identical Components

Robustness of reliability predictions for series systems with identical components, assuming exponential failure distributio

Teacher-student relationships in primary schools in Perth

This study investigated teacher-student relationships at Perth metropolitan schools in Western Australia. From the literature, three key social and emotional aspects that affect teacher-student relationships, namely, Connectedness, Availability and Communication, were identified as important to good, positive teacher-student relationships. Data were collected in four parts: (1) through a teacher questionnaire; (2) through a student questionnaire; (3) through teacher interviews; and (4) through student interviews. The three relationship aspects formed the structure of a teacher questionnaire in which ten stem-items were conceptualised from easy to hard - four stem-items for Connectedness, three for Availability, and three for Communication - and answered in three perspectives: (1) an idealistic attitude, this is what I would like to happen; (2) a self-perceived Capability, this is what I am capable of, and (3) Actual Behaviour, this is what actually happens, using three ordered response categories: not at all or some of the time (score 1), most of the time (score 2), and almost always (score 3). The same three aspects formed the structure of a student questionnaire in which ten stem-items were conceptualised from easy to hard and answered in two perspectives: (1)a realistic view, this is what does happen; and (2) an idealistic view, this is what I wish would happen. Questionnaire data were collected from 43 primary teachers concerning 139 teacher-student relationships and 139 primary school students. Interview data were collected from 25 primary teachers and 139 students gave either, or both, a brief written comment and some verbal answers to relationship questions

Exploring young children\u27s knowledge of their social network, their social competence, and links to their social behaviour

The primary focus of this study is to explore young children\u27s knowledge of their social network and their social competence and the links with their social behaviour. The secondary focus is to investigate ways in which young children may be helped to articulate such knowledge. The six participants were pairs of five-year old children selected from three pre-primary classes located in a common school. Each pair comprised a socially able and a less socially able child as selected by their class teacher. Self-reports, dialogue-interviews, video-taped vignettes and dolls were used to help the participants talk about their knowledge of their social networks and their social competence. Classroom observations were made to determine the extent to which children\u27s reports aligned with their social behaviour. Results showed that young children are able to articulate knowledge about the abstract concepts regarding their social world. The study found that the children who knew more about their social network also knew more about behaving in socially competent ways and exhibited a greater degree of those behaviours. The children who knew less about their social network also knew less about behaving in socially competent ways and exhibited a lesser degree of social competence. Resulting implications include increasing teacher awareness of the kinds of social stresses facing many pre-primary children today, and implementing strategies in the classroom for maximising children\u27s knowledge about their social networks and social competence

Sampling motif-constrained ensembles of networks

The statistical significance of network properties is conditioned on null models which satisfy spec- ified properties but that are otherwise random. Exponential random graph models are a principled theoretical framework to generate such constrained ensembles, but which often fail in practice, either due to model inconsistency, or due to the impossibility to sample networks from them. These problems affect the important case of networks with prescribed clustering coefficient or number of small connected subgraphs (motifs). In this paper we use the Wang-Landau method to obtain a multicanonical sampling that overcomes both these problems. We sample, in polynomial time, net- works with arbitrary degree sequences from ensembles with imposed motifs counts. Applying this method to social networks, we investigate the relation between transitivity and homophily, and we quantify the correlation between different types of motifs, finding that single motifs can explain up to 60% of the variation of motif profiles.Comment: Updated version, as published in the journal. 7 pages, 5 figures, one Supplemental Materia

Stochastic urban pluvial flood hazard maps based upon a spatial-temporal rainfall generator

It is a common practice to assign the return period of a given storm event to the urban pluvial flood event that such storm generates. However, this approach may be inappropriate as rainfall events with the same return period can produce different urban pluvial flooding events, i.e., with different associated flood extent, water levels and return periods. This depends on the characteristics of the rainfall events, such as spatial variability, and on other characteristics of the sewer system and the catchment. To address this, the paper presents an innovative contribution to produce stochastic urban pluvial flood hazard maps. A stochastic rainfall generator for urban-scale applications was employed to generate an ensemble of spatially—and temporally—variable design storms with similar return period. These were used as input to the urban drainage model of a pilot urban catchment (~9 km2) located in London, UK. Stochastic flood hazard maps were generated through a frequency analysis of the flooding generated by the various storm events. The stochastic flood hazard maps obtained show that rainfall spatial-temporal variability is an important factor in the estimation of flood likelihood in urban areas. Moreover, as compared to the flood hazard maps obtained by using a single spatially-uniform storm event, the stochastic maps generated in this study provide a more comprehensive assessment of flood hazard which enables better informed flood risk management decisions