Homogeneous explosion and shock initiation for a three-step chain-branching reaction model

The role of chain-branching cross-over temperatures in shock-induced ignition of reactive materials is studied by numerical simulation, using a three-step chainbranching reaction model. In order to provide insight into shock initiation, the simpler problem of a spatially homogeneous explosion is first considered. It is shown that for ratios of the cross-over temperature to the initial temperature, T-B, sufficiently less than unity, the homogeneous explosion can be quantitatively described by a widely used two-step model, while for T-B sufficiently above unity the homogeneous explosion can be effectively described by the standard one-step model. From the matchings between these homogeneous-explosion solutions, the parameters of the reduced models are identified in terms of those of the three-step model. When T-B is close to unity, all the reactions of the three-step model have a leading role, and hence in this case the model cannot be reduced further. In the case of shock initiation, for T-B (which is now the ratio of the cross-over temperature to the initial shock temperature) sufficiently below unity, the three-step solutions are qualitatively described by those of the matched two-step model, but there are quantitative differences due to the assumption in the reduced model that a purely chain-branching explosion occurs instantaneously. For T-B sufficiently above unity, the matched one-step model is found to effectively describe the way in which the heat release and fluid dynamics couple. For T-B close to unity, the competition between chain branching and chain termination is important from the outset. In these cases the speed at which the forward moving explosion wave that emerges from the piston is sensitive to T-B, and changes from supersonic to subsonic for a value of T-B just below unity

How quickly do publications get read? The evolution of Mendeley reader counts for new articles

This is an accepted manuscript of an article published by Wiley-Blackwell in Journal of the Association for Information Science and Technology on 29/08/2017, available online: https://doi.org/10.1002/asi.23909 The accepted version of the publication may differ from the final published version.Within science, citation counts are widely used to estimate research impact but publication delays mean that they are not useful for recent research. This gap can be filled by Mendeley reader counts, which are valuable early impact indicators for academic articles because they appear before citations and correlate strongly with them. Nevertheless, it is not known how Mendeley readership counts accumulate within the year of publication, and so it is unclear how soon they can be used. In response, this paper reports a longitudinal weekly study of the Mendeley readers of articles in six library and information science journals from 2016. The results suggest that Mendeley readers accrue from when articles are first available online and continue to steadily build. For journals with large publication delays, articles can already have substantial numbers of readers by their publication date. Thus, Mendeley reader counts may even be useful as early impact indicators for articles before they have been officially published in a journal issue. If field normalised indicators are needed, then these can be generated when journal issues are published using the online first date

How important is computing technology for library and information science research?

© 2015 Elsevier Inc. Computers in library and information science (LIS) research have been an object of study or a tool for research for at least fifty years, but how central are computers to the discipline now? This research analyses the titles, abstracts, and keywords of forty years of articles in LIS-classified journals for trends related to computing technologies. The proportion of Scopus LIS articles mentioning some aspect of computing in their title, abstract, or keywords increased steadily from 1986 to 2000, then stabilised at about two thirds, indicating a continuing dominance of computers in most LIS research. Within this general trend, many computer-related terms have peaked and then declined in popularity. For example, the proportion of Scopus LIS article titles, abstracts, or keywords that included the terms "computer" or "computing" decreased fairly steadily from about 20% in 1975 to 5% in 2013, and the proportion explicitly mentioning the web peaked at 18% in 2002. Parallel analyses suggest that computing is substantially less important in two related disciplines: education and communication, and so it should be seen as a key aspect of the LIS identity.Published versio

Theory of explosions and detonations for a three-step chain-branching chemistry model

A three-step kinetics scheme is used to model chain-branching reactions but also thermal reactions that are traditionally modelled using a one-step scheme. The chain-branching crossover temperature $T_B$ is adjusted to accommodate for the different reaction types. Two main scenarios are considered: a homogeneous reactive gas in a closed vessel, and the initiation of detonation waves in a tube induced by a shock that is driven either by a piston or a contact. In the homogeneous scenario, the reaction behaves more and more like a chain-branching reaction the smaller $T_B$ is below the initial temperature (unity in our non-dimensionalized scales). For $T_B > 1$ however, heat is released from the outset, and the reaction proceeds in a thermal manner similar to what occurs with one-step schemes. It is shown how the three-step scheme can be matched to widely used two-step and one-step models in the cases $T_B 1$ respectively. With piston-driven shock-induced detonations and for $T_B — 1$ sufficiently large, we reproduce situations similar to those which occur with one-step thermal schemes. For $T_B ~ 1$, both thermal and chain-branching effects are witnessed. With $T_B$ sufficiently below unity, chain-branching is very prominent from the outset, and since no secondary shock is formed, the situation is unlike what usually occurs with one-step thermal schemes, but is in good agreement with predictions of a simplified two-step chain-branching model. The major qualitative difference when using an acoustically permeable contact discontinuity to drive the shock instead of a piston occurs when $T_B — 1$ is sufficiently large, where we witness the temperature maximum and the fuel minimum move away from the driving surface

Small female citation advantages for US journal articles in medicine

This is an accepted manuscript of an article published by SAGE in Journal of Information Science on 16/02/2022, available online at: https://doi.org/10.1177/0165551520942729 The accepted version of the publication may differ from the final published version.Female underrepresentation continues in senior roles within academic medicine, potentially influenced by a perception that female research has less citation impact. This article provides systematic evidence of (a) female participation rates from the perspective of published journal articles in 46 Scopus medical subject categories 1996-2018 and (b) gender differences in citation rates 1996-2014. The results show female proportion increases 1996-2018 in all fields and a female majority of first authored articles in two fifths of categories, but substantial differences between fields: A paper is 7.3 times more likely to have a female first author in Obstetrics and Gynecology than in Orthopedics and Sports Medicine. Only three fields had a female last author majority by 2018, a probable side effect of ongoing problems with appointing female leaders. Female first-authored research tended to be more cited than male first-authored research in most fields (59%), although with a maximum difference of only 5.1% (log-transformed normalised citations). In contrast, male last-authored research tends to be more cited than female last-authored research, perhaps due to cases where a senior male has attracted substantial funding for a project. These differences increase if team sizes are not accounted for in the calculations. Since female first-authored research is cited slightly more than male first-authored research, properly analysed bibliometric data considering career gaps should not disadvantage female candidates for senior roles

Research co-authorship 1900-2020: Continuous, universal, and ongoing expansion

© [in press] The Authors. Published by MIT Press This is an open access article available under a Creative Commons licence.Research co-authorship is useful to combine different skillsets, especially for applied problems. Whilst it has increased over the last century, it is unclear whether this increase is universal across academic fields and which fields co-author the most and least. In response, this article assesses changes in the rate of journal article co-authorship 1900-2020 for all 27 Scopus broad fields and all 332 Scopus narrow fields. Whilst all broad fields have experienced reasonably continuous growth in co-authorship, in 2020 there were substantial disciplinary differences, from Arts and Humanities (1.3 authors) to Immunology and Microbiology (6 authors). All 332 Scopus narrow fields also experienced an increase in the average number of authors. Immunology and Classics are extreme Scopus narrow fields, as exemplified by 9.6 authors per Journal for ImmunoTherapy of Cancer article, whilst 93% of Trends in Classics articles were solo in 2020. The reason for this large difference seems to be the need for multiple complementary methods in Immunology, making it fundamentally a team science. Finally, the reasonably steady and universal increases in academic co-authorship over 121 years show no sign of slowing, suggesting that ever expanding teams are a central part of current professional science

Academic collaboration rates and citation associations vary substantially between countries and fields

Research collaboration is promoted by governments and research funders but if the relative prevalence and merits of collaboration vary internationally different national and disciplinary strategies may be needed to promote it. This study compares the team size and field normalised citation impact of research across all 27 Scopus broad fields in the ten countries with the most journal articles indexed in Scopus 2008-2012. The results show that team size varies substantially by discipline and country, with Japan (4.2) having two thirds more authors per article than the UK (2.5). Solo authorship is rare in China (4%) but common in the UK (27%). Whilst increasing team size associates with higher citation impact in almost all countries and fields, this association is much weaker in China than elsewhere. There are also field differences in the association between citation impact and collaboration. For example, larger team sizes in the Business, Management & Accounting category do not seem to associate with greater research impact, and for China and India, solo authorship associates with higher citation impact. Overall, there are substantial international and field differences in the extent to which researchers collaborate and the extent to which collaboration associates with higher citation impact

Domestic researchers with longer careers generate higher average citation impact but it does not increase over time

© The Authors. Published by MIT Press. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.1162/qss_a_00132Information about the relative strengths of scholars is needed for the efficient running of knowledge systems. Since academic research requires many skills, more experienced researchers might produce better research and attract more citations. This article assesses career citation impact changes 2001-2016 for domestic researchers (definition: first and last Scopus journal article in the same country) from the twelve nations with most Scopus documents. Careers are analysed longitudinally, so that changes are not due to personnel evolution, such as researchers leaving or entering a country. The results show that long term domestic researchers do not tend to improve their citation impact over time but tend to achieve their average citation impact by their first or second Scopus journal article. In some countries, this citation impact subsequently declines. These longer-term domestic researchers have higher citation impact than the national average in all countries, however, whereas scholars publishing only one journal article have substantially lower citation impact in all countries. The results are consistent with an efficiently functioning researcher selection system but cast slight doubt on the long-term citation impact potential of long-term domestic researchers. Research and funding policies may need to accommodate these patterns when citation impact is a relevant indicator

Microsoft Academic: A multidisciplinary comparison of citation counts with Scopus and Mendeley for 29 journals

Microsoft Academic is a free citation index that allows large scale data collection. This combination makes it useful for scientometric research. Previous studies have found that its citation counts tend to be slightly larger than those of Scopus but smaller than Google Scholar, with disciplinary variations. This study reports the largest and most systematic analysis so far, of 172,752 articles in 29 large journals chosen from different specialisms. From Scopus citation counts, Microsoft Academic citation counts and Mendeley reader counts for articles published 2007-2017, Microsoft Academic found a slightly more (6%) citations than Scopus overall and especially for the current year (51%). It found fewer citations than Mendeley readers overall (59%), and only 7% as many for the current year. Differences between journals were probably due to field preprint sharing cultures or journal policies rather than broad disciplinary differences

Differences between journals and years in the proportions of students, researchers and faculty registering Mendeley articles

This article contains two investigations into Mendeley reader counts with the same dataset. Mendeley reader counts provide evidence of early scholarly impact for journal articles, but reflect the reading of a relatively young subset of all researchers. To investigate whether this age bias is constant or varies by narrow field and publication year, this article compares the proportions of student, researcher and faculty readers for articles published 1996-2016 in 36 large monodisciplinary journals. In these journals, undergraduates recorded the newest research and faculty the oldest, with large differences between journals. The existence of substantial differences in the composition of readers between related fields points to the need for caution when using Mendeley readers as substitutes for citations for broad fields. The second investigation shows, with the same data, that there are substantial differences between narrow fields in the time taken for Scopus citations to be as numerous as Mendeley readers. Thus, even narrow field differences can impact on the relative value of Mendeley compared to citation counts