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Lundberg, J., Nordqvist, J. & Laitinen, M. (2019). Towards a language independent Twitter bot detector. In: Navarretta Costanza et al. (Ed.), Proceedings of 4th Conference of The Association Digital Humanities in the Nordic Countries: Copenhagen, March 6-8 2019. Paper presented at 4th Conference of The Association Digital Humanities in the Nordic Countries, Copenhagen, March 6-8 2019. Copenhagen: Digital Humanities in the Nordic countries
Open this publication in new window or tab >>Towards a language independent Twitter bot detector
2019 (English)In: Proceedings of 4th Conference of The Association Digital Humanities in the Nordic Countries: Copenhagen, March 6-8 2019 / [ed] Navarretta Costanza et al., Copenhagen: Digital Humanities in the Nordic countries , 2019Conference paper, Published paper (Refereed)
Abstract [en]

This article describes our work in developing an application that recognizes automatically generated tweets. The objective of this machine learning application is to increase data accuracy in sociolinguistic studies that utilize Twitter by reducing skewed sampling and inaccuracies in linguistic data. Most previous machine learning attempts to exclude bot material have been language dependent since they make use of monolingual Twitter text in their training phase. In this paper, we present a language independent approach which classifies each single tweet to be either autogenerated (AGT) or human-generated (HGT). We define an AGT as a tweet where all or parts of the natural language content is generated automatically by a bot or other type of program. In other words, while AGT/HGT refer to an individual message, the term bot refers to non-personal and automated accounts that post content to online social networks. Our approach classifies a tweet using only metadata that comes with every tweet, and we utilize those metadata parameters that are both language and country independent. The empirical part shows good success rates. Using a bilingual training set of Finnish and Swedish tweets, we correctly classified about 98.2% of all tweets in a test set using a third language (English).

Place, publisher, year, edition, pages
Copenhagen: Digital Humanities in the Nordic countries, 2019
Keywords
Twitter, bots, bot detection, supervised machine learning
National Category
General Language Studies and Linguistics Computer and Information Sciences
Research subject
Humanities, English; Computer and Information Sciences Computer Science, Computer Science
Identifiers
urn:nbn:se:lnu:diva-81663 (URN)
Conference
4th Conference of The Association Digital Humanities in the Nordic Countries, Copenhagen, March 6-8 2019
Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2019-04-29Bibliographically approved
Lindahl, K.-O. & Nordqvist, J. (2018). Geometric location of periodic points of 2-ramified power series. Journal of Mathematical Analysis and Applications, 465(2), 762-794
Open this publication in new window or tab >>Geometric location of periodic points of 2-ramified power series
2018 (English)In: Journal of Mathematical Analysis and Applications, ISSN 0022-247X, E-ISSN 1096-0813, Vol. 465, no 2, p. 762-794Article in journal (Refereed) Published
Abstract [en]

In this paper we study the geometric location of periodic points of power series defined over fields of prime characteristic p. More specifically, we find a lower bound for the absolute value of all periodic points in the open unit disk of minimal period pn of 2-ramified power series. We prove that this bound is optimal for a large class of power series. Our main technical result is a computation of the first significant terms of the pnth iterate of 2-ramified power series. As a by-product we obtain a self-contained proof of the characterization of 2-ramified power series.

Place, publisher, year, edition, pages
Elsevier, 2018
National Category
Geometry
Research subject
Mathematics, Mathematics
Identifiers
urn:nbn:se:lnu:diva-64440 (URN)10.1016/j.jmaa.2018.05.009 (DOI)
Available from: 2017-05-29 Created: 2017-05-29 Last updated: 2019-07-09Bibliographically approved
Nordqvist, J. (2018). Ramification numbers and periodic points in arithmetic dynamical systems. (Licentiate dissertation). Växjö: Linnaeus University Press
Open this publication in new window or tab >>Ramification numbers and periodic points in arithmetic dynamical systems
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The field of discrete dynamical systems is a rich and active field of research within mathematics, with applications ranging from biology to computer science, finance, engineering and various others. In this thesis properties of certain discrete dynamical systems are studied together with number theoretic properties of the functions defining these systems. The dynamical systems studied in this thesis are defined by iteration of power series g with a fixed point at the origin, tangent to the identity, and defined over fields of prime characteristic p. We are interested in the geometric location of the periodic points in the open unit disk. Recent results have shown that there is a connection between the lower ramification numbers of g and the geometric location of the periodic points in the open unit disk. The lower ramification numbers of g can be described as the multiplicity of zero as a fixed point of p-power iterates of g.

Part of this thesis concerns characterizing power series having certain sequences of ramification numbers. The other part concerns utilizing these results in order to describe the geometric location of the periodic points in terms of their distance to the origin. More precisely, we characterize all 2-ramified power series, i.e. power series having ramification numbers of the form 2(1 + p + … + pn). Moreover, we also obtain a lower bound of the absolute value of the periodic points in the open unit disk of such series.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2018. p. 74
Series
Lnu Licentiate ; 10
Keywords
ramification numbers, local fields, arithmetic dynamics, periodic points, Nottingham group
National Category
Mathematics
Research subject
Natural Science, Mathematics
Identifiers
urn:nbn:se:lnu:diva-69926 (URN)978-91-88761-28-6 (ISBN)978-91-88761-29-3 (ISBN)
Presentation
2018-02-15, D1136, Växjö, 13:00 (English)
Opponent
Supervisors
Available from: 2018-01-17 Created: 2018-01-17 Last updated: 2018-01-17Bibliographically approved
Nordqvist, J. (2017). Characterization of 2-ramified power series. Journal of Number Theory, 174, 258-273
Open this publication in new window or tab >>Characterization of 2-ramified power series
2017 (English)In: Journal of Number Theory, ISSN 0022-314X, E-ISSN 1096-1658, Vol. 174, p. 258-273Article in journal (Refereed) Published
Abstract [en]

In this paper we study lower ramification numbers of power series tangent to the identity that are defined over fields of positive characteristics p. Let g be such a series, then g has a fixed point at the origin and the corresponding lower ramification numbers of g are then, up to a constant, the degree of the first non-linear term of p-power iterates of g. The result is a complete characterization of power series g having ramification numbers of the form 2 ( 1 + p + 
 + p n ) . Furthermore, in proving said characterization we explicitly compute the first significant terms of g at its pth iterate.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Lower ramification numbers, iterations of power series, difference equations, arithmetic dynamics
National Category
Other Mathematics
Research subject
Natural Science, Mathematics
Identifiers
urn:nbn:se:lnu:diva-58627 (URN)10.1016/j.jnt.2016.10.005 (DOI)000392902700016 ()2-s2.0-85006507544 (Scopus ID)
Note

Correction published in: Nordqvist, Jonas. 2017. Corrigendum to “Characterization of 2-ramified power series” [J. Number Theory 174 (2017) 258–273], Journal of Number Theory, 178: 208.

Available from: 2016-12-02 Created: 2016-12-02 Last updated: 2019-09-06Bibliographically approved
Chandler, R. E., Juhlin, K., Fransson, J., Caster, O., Edwards, R. I. & Norén, N. G. (2017). Current Safety Concerns with Human Papillomavirus Vaccine: A Cluster Analysis of Reports in VigiBase®. Drug Safety, 40(1), 81-90
Open this publication in new window or tab >>Current Safety Concerns with Human Papillomavirus Vaccine: A Cluster Analysis of Reports in VigiBase®
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2017 (English)In: Drug Safety, ISSN 0114-5916, E-ISSN 1179-1942, Vol. 40, no 1, p. 81-90Article in journal (Refereed) Published
Abstract [en]

INTRODUCTION: A number of safety signals-complex regional pain syndrome (CRPS), postural orthostatic tachycardia syndrome (POTS), and chronic fatigue syndrome (CFS)-have emerged with human papillomavirus (HPV) vaccines, which share a similar pattern of symptomatology. Previous signal evaluations and epidemiological studies have largely relied on traditional methodologies and signals have been considered individually.

OBJECTIVE: The aim of this study was to explore global reporting patterns for HPV vaccine for subgroups of reports with similar adverse event (AE) profiles.

METHODS: All individual case safety reports (reports) for HPV vaccines in VigiBase(®) until 1 January 2015 were identified. A statistical cluster analysis algorithm was used to identify natural groupings based on AE profiles in a data-driven exploratory analysis. Clinical assessment of the clusters was performed to identify clusters relevant to current safety concerns.

RESULTS: Overall, 54 clusters containing at least five reports were identified. The four largest clusters included 71 % of the analysed HPV reports and described AEs included in the product label. Four smaller clusters were identified to include case reports relevant to ongoing safety concerns (total of 694 cases). In all four of these clusters, the most commonly reported AE terms were headache and dizziness and fatigue or syncope; three of these four AE terms were reported in >50 % of the reports included in the clusters. These clusters had a higher proportion of serious cases compared with HPV reports overall (44-89 % in the clusters compared with 24 %). Furthermore, only a minority of reports included in these clusters included AE terms of diagnoses to explain these symptoms. Using proportional reporting ratios, the combination of headache and dizziness with either fatigue or syncope was found to be more commonly reported in HPV vaccine reports compared with non-HPV vaccine reports for females aged 9-25 years. This disproportionality remained when results were stratified by age and when those countries reporting the signals of CRPS (Japan) and POTS (Denmark) were excluded.

CONCLUSIONS: Cluster analysis reveals additional reports of AEs following HPV vaccination that are serious in nature and describe symptoms that overlap those reported in cases from the recent safety signals (POTS, CRPS, and CFS), but which do not report explicit diagnoses. While the causal association between HPV vaccination and these AEs remains uncertain, more extensive analyses of spontaneous reports can better identify the relevant case series for thorough signal evaluation.

National Category
Public Health, Global Health, Social Medicine and Epidemiology
Research subject
Health and Caring Sciences
Identifiers
urn:nbn:se:lnu:diva-56719 (URN)10.1007/s40264-016-0456-3 (DOI)27638661 (PubMedID)
Available from: 2016-10-03 Created: 2016-09-25 Last updated: 2017-11-30Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-0510-6782

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