Imperial College London

DrTimEvans

Faculty of Natural SciencesDepartment of Physics

Senior Lecturer
 
 
 
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Contact

 

+44 (0)20 7594 7837t.evans Website

 
 
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Assistant

 

Mrs Graziela De Nadai-Sowrey +44 (0)20 7594 7843

 
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Location

 

609Huxley BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

89 results found

Chen B, Lin Z, Evans T, 2019, The Wikipedia Network of Mathematicians

This is data used in the paper "Analysis of the Wikipedia Network of Mathematicians". The data is taken from three snapshots of Wikipedia, taken in 2013, 2017 and 2018. It contains the raw Wikipedia data used as our source as well the results of our processing. Includes are edgelists, networks of the largest comopnent in graphml format, and tables of data on the nodes (the mathematicians). We have also included an appendix for the EPJ version of the paper, mathematiciansEPJappendix.pdf. However a complete version of this work is also at arXiv:1902.07622

Working paper

Hilton B, Sood AP, Evans TS, 2019, Predictive limitations of spatial interaction models: a non-Gaussian analysis, Publisher: arXiv

We present a method to compare spatial interaction models against data basedon well known statistical measures which are appropriate for such models anddata. We illustrate our approach using a widely used example: commuting data,specifically from the US Census 2000. We find that the radiation model performssignificantly worse than an appropriately chosen simple gravity model. Variousconclusions are made regarding the development and use of spatial interactionmodels, including: that spatial interaction models fit badly to data in anabsolute sense, that therefore the risk of over-fitting is small and addingadditional fitted parameters improves the predictive power of models, and thatappropriate choices of input data can improve model fit.

Working paper

Yao Q, Evans TS, Christensen K, 2019, How the network properties of shareholders vary with investor type and country, PLoS One, Vol: 14, Pages: 1-19, ISSN: 1932-6203

We construct two examples of shareholder networks in which shareholders are connected if they have shares in the same company. We do this for the shareholders in Turkish companies and we compare this against the network formed from the shareholdings in Dutch companies. We analyse the properties of these two networks in terms of the different types of shareholder. We create a suitable randomised version of these networks to enable us to find significant features in our networks. For that we find the roles played by different types of shareholder in these networks, and also show how these roles differ in the two countries we study.

Journal article

Ciacci A, Falkenberg M, Manani KA, Evans TS, Peters NS, Christensen Ket al., 2019, Understanding the transition from paroxysmal to persistent atrial fibrillation, Publisher: arXiv

Atrial fibrillation (AF) is the most common cardiac arrhytmia, characterisedby the chaotic motion of electrical wavefronts in the atria. In clinicalpractice, AF is classified under two primary categories: paroxysmal AF, shortintermittent episodes separated by periods of normal electrical activity, andpersistent AF, longer uninterrupted episodes of chaotic electrical activity.However, the precise reasons why AF in a given patient is paroxysmal orpersistent is poorly understood. Recently, we have introduced the percolationbased Christensen-Manani-Peters (CMP) model of AF which naturally exhibits bothparoxysmal and persistent AF, but precisely how these differences emerge in themodel is unclear. In this paper, we dissect the CMP model to identify the causeof these different AF classifications. Starting from a mean-field model wherewe describe AF as a simple birth-death process, we add layers of complexity tothe model and show that persistent AF arises from the formation of temporallystable structural re-entrant circuits that form from the interaction ofwavefront collisions during paroxysmal AF. These results are compatible withrecent findings suggesting that the formation of re-entrant drivers in fibroticborder zones perpetuates persistent AF.

Working paper

Vasiliauskaite V, Evans TS, 2019, Social success of perfumes, PLoS ONE, Vol: 14, ISSN: 1932-6203

We study data on perfumes and their odour descriptors-notes-to understand how note compositions, called accords, influence successful fragrance formulas. We obtain accords which tend to be present in perfumes that receive significantly more customer ratings. Our findings show that the most popular notes and the most over-represented accords are different to those that have the strongest effect to the perfume ratings. We also used network centrality to understand which notes have the highest potential to enhance note compositions. We find that large degree notes, such as musk and vanilla as well as generically-named notes, e.g. floral notes, are amongst the notes that enhance accords the most. This work presents a framework which would be a timely tool for perfumers to explore a multidimensional space of scent compositions.

Journal article

Patel VM, Panzarasa P, Ashrafian H, Evans TS, Kirresh A, Sevdalis N, Darzi A, Athanasiou Tet al., 2019, Collaborative patterns, authorship practices and scientific success in biomedical research: a network analysis., Journal of the Royal Society of Medicine, Vol: 112, Pages: 245-257, ISSN: 1758-1095

OBJECTIVE: To investigate the relationship between biomedical researchers' collaborative and authorship practices and scientific success. DESIGN: Longitudinal quantitative analysis of individual researchers' careers over a nine-year period. SETTING: A leading biomedical research institution in the United Kingdom. PARTICIPANTS: Five hundred and twenty-five biomedical researchers who were in employment on 31 December 2009. MAIN OUTCOME MEASURES: We constructed the co-authorship network in which nodes are the researchers, and links are established between any two researchers if they co-authored one or more articles. For each researcher, we recorded the position held in the co-authorship network and in the bylines of all articles published in each three-year interval and calculated the number of citations these articles accrued until January 2013. We estimated maximum likelihood negative binomial panel regression models. RESULTS: Our analysis suggests that collaboration sustained success, yet excessive co-authorship did not. Last positions in non-alphabetised bylines were beneficial for higher academic ranks but not for junior ones. A professor could witness a 20.57% increase in the expected citation count if last-listed non-alphabetically in one additional publication; yet, a lecturer suffered from a 13.04% reduction. First positions in alphabetised bylines were positively associated with performance for junior academics only. A lecturer could experience a 8.78% increase in the expected citation count if first-listed alphabetically in one additional publication. While junior researchers amplified success when brokering among otherwise disconnected collaborators, senior researchers prospered from socially cohesive networks, rich in third-party relationships. CONCLUSIONS: These results help biomedical scientists shape successful careers and research institutions develop effective assessment and recruitment policies that will ultimately sustain the quality of biomedical r

Journal article

Clough JR, Evans TS, 2017, Embedding graphs in Lorentzian spacetime, PLOS ONE, Vol: 12, ISSN: 1932-6203

Geometric approaches to network analysis combine simply defined models with great descriptive power. In this work we provide a method for embedding directed acyclic graphs (DAG) into Minkowski spacetime using Multidimensional scaling (MDS). First we generalise the classical MDS algorithm, defined only for metrics with a Riemannian signature, to manifolds of any metric signature. We then use this general method to develop an algorithm which exploits the causal structure of a DAG to assign space and time coordinates in a Minkowski spacetime to each vertex. As in the causal set approach to quantum gravity, causal connections in the discrete graph correspond to timelike separation in the continuous spacetime. The method is demonstrated by calculating embeddings for simple models of causal sets and random DAGs, as well as real citation networks. We find that the citation networks we test yield significantly more accurate embeddings that random DAGs of the same size. Finally we suggest a number of applications in citation analysis such as paper recommendation, identifying missing citations and fitting citation models to data using this geometric approach.

Journal article

Evans TS, Rivers RJ, 2017, Was Thebes necessary? Contingency in spatial modeling, Frontiers in Digital Humanities, Vol: 4, ISSN: 2297-2668

When data are poor, we resort to theory modeling. This is a two-step process. We have first to identify the appropriate type of model for the system under consideration and then to tailor it to the specifics of the case. To understand settlement formation, which is the concern of this article, this involves choosing not only input parameter values such as site separations but also input functions that characterizes the ease of travel between sites. Although the generic behavior of the model is understood, the details are not. Different choices will necessarily lead to different outputs (for identical inputs). We can only proceed if choices that are “close” give outcomes that are similar. Where there are local differences, it suggests that there was no compelling reason for one outcome rather than the other. If these differences are important for the historic record, we may interpret this as sensitivity to contingency. We re-examine the rise of Greek city-states as first formulated by Rihll and Wilson in 1979, initially using the same “retail” gravity model. We suggest that, although cities like Athens owe their position to a combination of geography and proximity to other sites, the rise of Thebes is the most contingent, whose success reflects social forces outside the grasp of simple network modeling.

Journal article

Goldberg SR, Anthony H, Evans TS, Modelling citation networks, Scientometrics, ISSN: 1588-2861

Journal article

Clough JR, Gollings J, Loach TV, Evans TSet al., 2015, Transitive reduction of citation networks, JOURNAL OF COMPLEX NETWORKS, Vol: 3, Pages: 189-203, ISSN: 2051-1310

Journal article

Loach TV, Evans TS, 2015, Ranking Journals Using Altmetrics, 15th International Conference of the International-Society-for-Scientometrics-and-Informetrics (ISSI) on Scientometrics and Informetrics, Publisher: INT SOC SCIENTOMETRICS & INFORMETRICS-ISSI, Pages: 89-94, ISSN: 2175-1935

Conference paper

Clough JR, Evans TS, 2015, Time & Citation Networks, 15th International Conference of the International-Society-for-Scientometrics-and-Informetrics (ISSI) on Scientometrics and Informetrics, Publisher: INT SOC SCIENTOMETRICS & INFORMETRICS-ISSI, Pages: 1073-1078, ISSN: 2175-1935

Conference paper

Goldberg SR, Anthony H, Evans TS, 2015, Do we need global and local knowledge of the citation network?, Pages: 282-283

Conference paper

Evans T, 2014, The Connected Past London 2014

A collection of material associated with The Connected Past London 2014, a one and a half day multi-disciplinary meeting held at Imperial College on the 8th and 9th of September, 2014 and attended by nearly fifty researchers.  It aims to explore how concepts and techniques from network- and complexity science can be used to study archaeological and historical data. It is part of a series of meetings organised by The Connected Past team.Slides from most (but not all) talks are provided. Most talks were also recorded but the videos are yet to be made available.

Scholarly edition

Evans TS, Rivers RJ, 2014, New approaches to Archaic Greek Settlement Structure, Les Nouvelles de l'archéologie, Vol: 135, Pages: 21-27, ISSN: 0242-7702

Recent developments in network theory have led to the creation of new Spatial Interaction Models (SIMs) and a reappraisal of existing models. Although not directed at the archaeology community, these models generalise the familiar gravitational models and Proximal Point Analysis (PPA) used by archaeologists for many years to help explain the archaeological record. However, a problem arises in archaeology that, with the increasing suite of plausible models that now exist, it is unclear how to choose one model over another. This can lead to the criticism that, if we hunt hard enough, we may be doing no more than finding a model which can be manipulated to conform to our preconceptions. In recent articles we have begun to address this criticism (Evans 2014, in press) with particular reference to the maritime networks of the MBA Aegean (Rivers 2014, in press). Different historical periods require different approaches and in this paper we continue this analysis by re-examining the onset of centralisation in mainland Greek city states of the 9th and 8th centuries BCE. Pioneering work on this archaic settlement structure was performed in 1987 by Rihll and Wilson (Rihll & Wilson 1987, 2: 5-32; 1991: 59-95), adapting a 'retail' model devised originally for urban planning. One alternative approach is given by a recent cost-benefit model termed ariadne, developed by ourselves (Evans, Knappett & Rivers 2009, 7: 451-79; Knappett, Evans & Rivers 2008, 82: 1009-84; 2011, 85: 1008-23), initially designed for Bronze Age maritime networks. A comparison of these models and other simpler SIMs for archaic settlements highlights the problems of modelling archaeological data. In particular we examine what constitutes model 'robustness' and the way in which different models handle 'contingency' when handling periods of rapid change.

Journal article

Reiss DS, Price JJ, Evans TS, 2013, Sculplexity: Sculptures of Complexity using 3D printing, EPL, Vol: 104, ISSN: 0295-5075

Journal article

Evans T, 2013, Imperial Workshop on Large Deviations Theory

Workshop on Large Deviations TheoryOn Wednesday 10th July 2013, a one day workshop on Large Deviations Theory was held at Imperial College London. It consisted of a series of invited talks by leading researchers and a session of very short talks. The aim was to connect researchers working on different aspects of Large Deviation Theory and those interested in applying these ideas. We covered a wide range of topics, trying to build capacity in this area within the UK. We covered both classical and quantum non-equilibrium systems, and applications both within physics and outside. All material related to this workshop, including some slides from the talks, are in this figshare collection.Funding was provided by the EPSRC NetworkPlus programme on Emergence and Physics far from Equilibrium.

Scholarly edition

Wilting J, Evans TS, 2013, Oscillator Synchronization in Complex Networks with Non-uniform Time Delays, Complex Networks IV, Publisher: Springer, Pages: 93-100

We investigate a population of limit-cycle Kuramoto oscillators coupled in a complex network topology with coupling delays introduced by finite signal propagation speed and embedding in a ring. By numerical simulation we find that in complete graphs velocity waves arise that were not observed before and analytically not understood. In regular rings and small-world networks frequency synchronization occurs with a large variety of phase patterns. While all these patterns are nearly equally probable in regular rings, small-world topology sometimes prefers one pattern to form for a large number of initial conditions.We propose implications of this in the context of the temporal coding hypothesis for information processing in the brain and suggest future analysis to conclude the work presented here.

Book chapter

Rivers R, Knappett C, Evans T, 2013, What makes a site important? Centrality, gateways and gravity, Network Analysis in Archaeology: New Approaches to Regional Interaction, Editors: Knappett, Publisher: OUP, Pages: 125-150

Book chapter

Rivers R, Knappett C, Evans T, 2013, Network Models and Archaeological Spaces, Computational Approaches to Archaeological Spaces, Editors: Bevan, Lake, Publisher: Left Coast Press, ISBN: 978-1-61132-346-7

Book chapter

Evans TS, Kaube BS, Hopkins N, 2012, Temporal Evolution Of Universal Performance Indicators For Academic Publication, ECCS 2012

We show universal behaviour for two indicators of the quality of publications taken from two different data sets, papers from a single institution and those on arXiv. We demonstrate this universality for different years and subjects. This distribution is well fitted by a lognormal with a variance of around 1.3, consistent with Radicchi et al (2008). We will also discuss the evolution over time of our measures describing the data and note that simple models do not have the correct temporal behaviour for our parameters. Based on arXiv:1110.3271 with additional new material.Poster given at ECCS 2012

Poster

Evans TS, Rivers RJ, Knappett C, 2012, INTERACTIONS IN SPACE FOR ARCHAEOLOGICAL MODELS, ADVANCES IN COMPLEX SYSTEMS, Vol: 15, ISSN: 0219-5259

Journal article

Clemson T, Evans TS, 2012, The emergence of leadership in social networks, PHYSICA A-STATISTICAL MECHANICS AND ITS APPLICATIONS, Vol: 391, Pages: 1434-1444, ISSN: 0378-4371

Journal article

Evans TS, Rivers RJ, 2012, Interactions in Space for Archaeological Models, Advances in Complex Systems, Vol: 15

In this article we examine a variety of quantitative models for describingarchaeological networks, with particular emphasis on the maritime networksof the Aegean Middle Bronze Age. In particular, we discriminate betweenthose gravitational networks that are most likely (maximum entropy) andmost efficient (best cost/benefit outcomes).

Journal article

Evans TS, Hopkins N, Kaube BS, 2012, Universality of Performance Indicators based on Citation and Reference Counts, Scientometrics: an international journal for all quantitative aspects of the science of science, communication in science and science policy

We find evidence for the universality of two relative bibliometric indicatorsof the quality of individual scientific publications taken from different datasets. One of these is a new index that considers both citation and referencecounts. We demonstrate this universality for relatively well cited publicationsfrom a single institute, grouped by year of publication and by faculty or bydepartment. We show similar behaviour in publications submitted to the arXive-print archive, grouped by year of submission and by sub-archive. We also findthis distribution is well fitted by a lognormal with a variance of around 1.3which is consistent with the results of Radicchi, Fortunato, and Castellano.Our work demonstrates that comparisons can be made between publications fromdifferent disciplines and publication dates, regardless of their citation countand without expensive access to the whole world-wide citation graph. Further,it shows that averages of the logarithm of such relative bibliometric indicesdeal with the issue of long tails and avoid the need for statistics based onlengthy ranking procedures.

Journal article

Evans TS, 2012, Turnover Rate of Popularity Charts in Neutral Models

It has been shown recently that in many different cultural phenomena the turnover rate on the most popular artefacts in a population exhibit some regularities. A very simple expression for this turnover rate has been proposed by Bentley et al. 2007 and its validity in two simple models for copying and innovation is investigated in this paper. It is found that the formula in Bentley et al. is an approximation of the real behaviour of the turnover rate in the Wright-Fisher model, while it is not valid in the Moran model.

Conference paper

Evans TS, Lambiotte R, Panzarasa P, 2011, Community structure and patterns of scientific collaboration in Business and Management, SCIENTOMETRICS, Vol: 89, Pages: 381-396, ISSN: 0138-9130

Journal article

Knappett C, Rivers R, Evans T, 2011, The Theran eruption and Minoan palatial collapse: new interpretations gained from modelling the maritime network, ANTIQUITY, Vol: 85, Pages: 1008-1023, ISSN: 0003-598X

Journal article

Rivers RJ, Evans TS, Knappett C, 2011, Modelling maritime interaction in the Aegean Bronze Age, II. The Theran eruption and Minoan palatial collapse, Antiquity: a quarterly review of archaeology, Vol: 85, Pages: 1008-1023

What was the effect on Late Minoan civilisation of the catastrophic destruction of Akrotiri on Thera (Santorini) by volcanic eruption? Not much, according to the evidence for continuing prosperity on Crete. But the authors mobilise their ingenious mathematical model (published in Antiquity 82: 1009–1024), this time to show that the effects of removing a major port of call could have impacted after an interval, as increased costs of transport gradually led to ever fewer routes and eventual economic collapse.

Journal article

Lambiotte R, Sinatra R, Delvenne J-C, Evans TS, Barahona M, Latora Vet al., 2011, Flow graphs: Interweaving dynamics and structure, PHYSICAL REVIEW E, Vol: 84, ISSN: 1539-3755

The behavior of complex systems is determined not only by the topological organization of their interconnections but also by the dynamical processes taking place among their constituents. A faithful modeling of the dynamics is essential because different dynamical processes may be affected very differently by network topology. A full characterization of such systems thus requires a formalization that encompasses both aspects simultaneously, rather than relying only on the topological adjacency matrix. To achieve this, we introduce the concept of flow graphs, namely weighted networks where dynamical flows are embedded into the link weights. Flow graphs provide an integrated representation of the structure and dynamics of the system, which can then be analyzed with standard tools from network theory. Conversely, a structural network feature of our choice can also be used as the basis for the construction of a flow graph that will then encompass a dynamics biased by such a feature. We illustrate the ideas by focusing on the mathematical properties of generic linear processes on complex networks that can be represented as biased random walks and their dual consensus dynamics, and show how our framework improves our understanding of these processes.

Journal article

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