Sub-field normaliztion in the multiplicative case : high- and low- impact citation indicators

This paper uses high- and low-impact citation indicators for the evaluation of the citation performance of research units at different aggregate levels. To solve the problem of the assignment of individual articles to multiple sub-fields, it follows a multiplicative strategy according to which each paper is wholly counted as many times as necessary in the several categories to which it is assigned at each aggregation level. To control for wide differences in citation practices at the lowest level of aggregation, we apply a novel sub-field normalization procedure in the multiplicative case. The methodology is applied to a partition of the world into three geographical areas: the U.S., the European Union (EU), and the Rest of the World. The main findings are the following two. (i) Although normalization does not systematically bias the results against any area, it reduces the U.S./EU highimpact gap in the all-sciences case by a non-negligible 14.4%. (ii) The dominance of the U.S. over the EU in the basic and applied research published in the periodical literature is almost universal at all aggregation levels. From the high-impact perspective, for example, the U.S. is ahead of the EU in 77 out of 80 disciplines, and all of 20 fields. For all sciences as a whole, the U.S. high-impact indicator is 61% greater than that of the EU. The authors acknowledge financial support from the Santander Universities Global Division of Banco Santander. Ruiz-Castillo also acknowledges financial help from the Spanish MEC through grant SEJ2007- 67436. This paper is part of the SCIFI-GLOW Collaborative Project supported by the European Commission.s Seventh Research Framework Programme, Contract number SSH7-CT-2008-217436 European Community's Seventh Framework Program.

Sub-field normalization in the multiplicative case: average-based citation indicators

This paper investigates the citation impact of three large geographical areas –the U.S., the European Union (EU), and the rest of the world (RW)– at different aggregation levels. The difficulty is that 42% of the 3.6 million articles in our Thomson Scientific dataset are assigned to several sub-fields among a set of 219 Web of Science categories. We follow a multiplicative approach in which every article is wholly counted as many times as it appears at each aggregation level. We compute the crown indicator and the Mean Normalized Citation Score (MNCS) using for the first time sub-field normalization procedures for the multiplicative case. We also compute a third indicator that does not correct for differences in citation practices across sub-fields. It is found that: (1) No geographical area is systematically favored (or penalized) by any of the two normalized indicators. (2) According to the MNCS, only in six out of 80 disciplines –but in none of 20 fields– is the EU ahead of the U.S. In contrast, the normalized U.S./EU gap is greater than 20% in 44 disciplines, 13 fields, and for all sciences as a whole. The dominance of the EU over the RW is even greater. (3) The U.S. appears to devote relatively more –and the RW less– publication effort to subfields with a high mean citation rate, which explains why the U.S./EU and EU/RW gaps for all sciences as a whole increase by 4.5 and 5.6 percentage points in the un-normalized case.

Surface visualization via level curves and applications

Treballs Finals de Grau de Matemàtiques, Facultat de Matemàtiques, Universitat de Barcelona, Any: 2020, Director: Antoni Benseny[en] This study intends to implement a 3-D surface representation via level curves. This way of representing surfaces requires a lot of previous work. Nevertheless, it is very useful when dealing with problems where it is important to know the points of the surface that are in each level cut. A general simulator has been implemented in order to be easily adapted to different problems. The program code has been structured in a way in which it can be used for different surfaces. The simulator has been applied to the representation of zero-velocity curves of the extended planar and circular restricted 3-body problem (XPCR3BP). This project aims to be as general as possible. However, some simplifications of the surface visualization via level curves problem have been taken into consideration in order to ease the programming purposes: the problem has been implemented only for simple closed curves; and the singular level curves associated to saddle points have been considered to be homoclinic

An algorithm to reduce the occupational space in gender segregation studies.

This paper presents an algorithm based on the bootstrap to select an admissible aggregation level, that is, the minimum number of occupational categories that yield a gender segregation value not significantly smaller than that obtained from the large number of occupational categories usually available in any data set. The approach is illustrated using labour force survey data for Spain for the comparison of gender segregation in 1977 and 1992, as well as 1994 and 2000. To measure gender segregation, an additively decomposable segregation index based on the entropy concept is used. Despite a substantial simplification in the size of the occupation space, the decrease in the segregation index is very small and not significant, regardless of the year. Consequently, intertemporal changes in gender segregation can be studied using a greatly reduced classification of occupations that permits an easier interpretation of results.

Multiplicative and fractional strategies when journals are assigned to several sub-fields

In many datasets, articles are classified into sub-fields through the journals in which they have been published. The problem is that many journals are assigned to a single sub-field, but many others are assigned to several sub-fields. This paper discusses a multiplicative and a fractional strategy to deal with this situation, and introduces a normalization procedure in the multiplicative case that takes into account differences in mean citation rates across sub-fields. The empirical part studies different aspects of citation distributions under the two strategies, namely: (i) the number of articles, (ii) the mean citation rate, (iii) the broad shape of the distribution, (iv) the characterization in terms of size- and scale-invariant indicators of high- and low-impact, and (v) the presence of extreme distributions, or distributions that behave very differently from the rest. It is found that, in spite of large differences in the number of articles according to both strategies, the similarity of the citation characteristics of articles published in journals assigned to one or several sub-fields guarantees that choosing one of the two strategies may not lead to a radically different picture in practical applications. Nevertheless, the evaluation of citation excellence through a high-impact indicator may considerably differ depending on that choice.The authors acknowledge financial support by Santander Universities Global Division of Banco Santander. Ruiz-Castillo acknowledges financial support from the Spanish MEC through grant SEJ2007-67436European Community's Seventh Framework Progra

Sub-field normalization in the multiplicative case : high- and low- impact citation indicators

This paper uses high- and low-impact citation indicators for the evaluation of the citation performance of research units at different aggregate levels. To solve the problem of the assignment of individual articles to multiple sub-fields, it follows a multiplicative strategy according to which each paper is wholly counted as many times as necessary in the several categories to which it is assigned at each aggregation level. To control for wide differences in citation practices at the lowest level of aggregation, we apply a novel sub-field normalization procedure in the multiplicative case. The methodology is applied to a partition of the world into three geographical areas: the U.S., the European Union (EU), and the Rest of the World. The main findings are the following two. (i) Although normalization does not systematically bias the results against any area, it reduces the U.S./EU highimpact gap in the all-sciences case by a non-negligible 14.4%. (ii) The dominance of the U.S. over the EU in the basic and applied research published in the periodical literature is almost universal at all aggregation levels. From the high-impact perspective, for example, the U.S. is ahead of the EU in 77 out of 80 disciplines, and all of 20 fields. For all sciences as a whole, the U.S. high-impact indicator is 61% greater than that of the EU.The authors acknowledge financial support from the Santander Universities Global Division of Banco Santander. Ruiz-Castillo also acknowledges financial help from the Spanish MEC through grant SEJ2007- 67436. This paper is part of the SCIFI-GLOW Collaborative Project supported by the European Commission’s Seventh Research Framework Programme, Contract number SSH7-CT-2008-217436European Community's Seventh Framework Progra

Sub-field normalization in the multiplicative case : average-based citation indicators

This paper investigates the citation impact of three large geographical areas –the U.S., the European Union (EU), and the rest of the world (RW)– at different aggregation levels. The difficulty is that 42% of the 3.6 million articles in our Thomson Scientific dataset are assigned to several sub-fields among a set of 219 Web of Science categories. We follow a multiplicative approach in which every article is wholly counted as many times as it appears at each aggregation level. We compute the crown indicator and the Mean Normalized Citation Score (MNCS) using for the first time sub-field normalization procedures for the multiplicative case. We also compute a third indicator that does not correct for differences in citation practices across sub-fields. It is found that: (1) No geographical area is systematically favored (or penalized) by any of the two normalized indicators. (2) According to the MNCS, only in six out of 80 disciplines –but in none of 20 fields– is the EU ahead of the U.S. In contrast, the normalized U.S./EU gap is greater than 20% in 44 disciplines, 13 fields, and for all sciences as a whole. The dominance of the EU over the RW is even greater. (3) The U.S. appears to devote relatively more –and the RW less– publication effort to subfields with a high mean citation rate, which explains why the U.S./EU and EU/RW gaps for all sciences as a whole increase by 4.5 and 5.6 percentage points in the un-normalized case. The results with a fractional approach are very similar indeedFinancial support from the Santander Universities Global Division of Banco Santander. Ruiz-Castillo also acknowledges financial help from the Spanish MEC through grant SEJ2007-67436European Community's Seventh Framework Progra

Field normalization at different aggregation levels

This paper studies the impact of differences in citation practices using the model introduced in Crespo et al. (2012) according to which the number of citations received by an article depends on its underlying scientific influence and the field to which it belongs. Using a dataset of about 4.4 million articles published in 1998- 2003 with a five-year citation window, the main results are the following four. Firstly, we estimate a set of exchange rates (ERs) to express the citation counts of articles in a wide quantile interval into the equivalent counts in the all-sciences case. For example, in the fractional case we find that in 187 out of 219 sub-fields the ERs are reliable in the sense that the coefficient of variation is smaller than or equal to 0.10. ERs are estimated over the [660, 978] interval that, on average, covers about 62% of all citations. Secondly, in the fractional case the normalization of the raw data using the ERs (or the sub-field mean citations) as normalization factors reduces the importance of the differences in citation practices from 18% to 3.8% (3.4%) of overall citation inequality. Thirdly, the results in the fractional case are essentially replicated when we adopt the multiplicative approach. Fourthly, whenever we are restricted to an intermediate aggregate level with 19 fields, the estimation of the ERs and the linear normalization procedures also offer good results. However, the aggregation of normalized distributions at the lowest aggregate level using sub-field ERs (or sub-field mean citations) as normalization factors, lead to similar or slightly better results at the field levelThe authors acknowledge financial support by Santander Universities Global Division of Banco Santander. Crespo and Ruiz-Castillo also acknowledge financial help from the Spanish MEC through grants SEJ2007-67436 and ECO2010-1959

The effect on citation inequality of differences in citation practices at the Web of Sciences subject category level

This paper studies the impact of differences in citation practices at the sub-field, or Web of Science subject category level using the model introduced in Crespo et al. (2012) according to which the number of citations received by an article depends on its underlying scientific influence and the field to which it belongs. We use the same Thomson Reuters dataset of about 4.4 million articles published in 1998-2003 with a fiveyear citation window used in Crespo et al. (2013) to analyze a classification system consisting of 22 broad fields. The main results are the following four. Firstly, as expected, when the classification system goes from 22 broad fields to 219 sub-fields the effect on citation inequality of differences in citation practices increases from approximately 14% at the field level to 18% at the sub-field level. Secondly, we estimate a set of exchange rates (ERs) to express the citation counts of articles in a wide quantile interval into the equivalent counts in the all-sciences case. For example, in the fractional case we find that in 187 out of 219 sub-fields the ERs are reliable in the sense that the coefficient of variation is smaller than or equal to 0.10. ERs are estimated over the [660, 978] interval that, on average, covers about 62% of all citations. Thirdly, in the fractional case the normalization of the raw data using the ERs (or sub-field mean citations) as normalization factors reduces the importance of the differences in citation practices from 18% to 3.8% (3.4%) of overall citation inequality. Fourthly, the results in the fractional case are essentially replicated when we adopt the multiplicative approac

Stability of 3D-porous Ni/Cu cathodes under real alkaline electrolyzer operating conditions and its effect on catalytic activity

Despite the development and synthesis of new electrode materials for hydrogen generation in alkaline water electrolyzers has been a research topic widely exploited in the last years, stability tests on the obtained cathodes have been restricted to long-term potentiostatic/galvanostatic experiments which do not fulfil the real operating conditions that take place in those devices. In this work, two different Service Life Tests have been designed and implemented, aiming at including particular conditions (i.e. inverse polarity and short-circuit) in the durability and catalytic activity of cathode characterization. For this purpose, Ni/Cu bilayered porous electrodes were prepared using different Ni electrodeposition times (15, 30 and 45 min) following a double template electrochemical method. It has been confirmed that the electrode with the lowest Ni content can be considered as a promising electrocatalyst for hydrogen production under industrial conditions because of its optimal activity and stability after the two sets of testing conditions. In particular, electrochemical studies demonstrated that an inversion in polarity can positively affect the electrode performance, as a consequence of the synergetic interaction between CuO/Cu(OH)(2) and beta-Ni(OH)(2) species formed at potentials below the oxygen evolution domain.The authors gratefully acknowledge financial support given by the Generalitat Valenciana (PROMETEO/2010/023) and Spanish Government (Ministerio de Ciencia e Innovation) for the postgraduate grants AP2007-01243 (Carlos Valero-Vidal) and AP2007-03737 (Isaac Herraiz-Cardona).Valero Vidal, C.; Herraiz Cardona, I.; Pérez-Herranz, V.; Igual Muñoz, AN. (2016). Stability of 3D-porous Ni/Cu cathodes under real alkaline electrolyzer operating conditions and its effect on catalytic activity. Applied Catalysis B: Environmental. 198:142-153. doi:10.1016/j.apcatb.2016.05.030S14215319