286 research outputs found
The skewness of science in 219 sub-fields and a number of aggregates
This paper studies evidence from Thomson Scientific about the citation process of 3.7 million articles published in the period 1998-2002 in 219 Web of Science categories, or sub-fields. Reference and citation distributions have very different characteristics across sub-fields. However, when analyzed with the Characteristic Scores and Scales technique, which is replication and scale invariant, the shape of these distributions over three broad categories of articles appears strikingly similar. Reference distributions are mildly skewed, but citation distributions with a five-year citation window are highly skewed: the mean is twenty points above the median, while 9-10% of all articles in the upper tail account for about 44% of all citations. The aggregation of sub-fields into disciplines and fields according to several aggregation schemes preserve this feature of citation distributions. It should be noted that when we look into subsets of articles within the lower and upper tails of citation distributions the universality partially breaks down. On the other hand, for 140 of the 219 sub-fields the existence of a power law cannot be rejected. However, contrary to what is generally believed, at the sub-field level the scaling parameter is above 3.5 most of the time, and power laws are relatively small: on average, they represent 2% of all articles and account for 13.5% of all citations. The results of the aggregation into disciplines and fields reveal that power law algebra is a subtle phenomenon.
A comparison of the scientific performance of the U.S. and the European Union at the turn of the 21st century.
In this paper, scientific performance is identified with the impact that journal articles have through the citations they receive. In 15 disciplines, as well as in all sciences as a whole, the EU share of total publications is greater than that of the U.S. However, as soon as the citations received by these publications are taken into account the picture is completely reversed. Firstly, the EU share of total citations is still greater than the U.S. in only seven fields. Secondly, the mean citation rate in the U.S. is greater than in the EU in every one of the 22 fields studied. Thirdly, since standard indicators—such as normalized mean citation ratios—are silent about what takes place in different parts of the citation distribution, this paper compares the publication shares of the U.S. and the EU at every percentile of the world citation distribution in each field. It is found that in seven fields the initial gap between the U.S. and the EU widens as we advance towards the more cited articles, while in the remaining 15 fields—except for Agricultural Sciences—the U.S. always surpasses the EU when it counts, namely, at the upper tail of citation distributions. Finally, for all sciences as a whole the U.S. publication share becomes greater than that of the EU for the top 50% of the most highly cited articles. The data used refers to 3.6 million articles published in 1998–2002, and the more than 47 million citations they received in 1998–2007Research performance; Citation analysis; Scientific ranking; European paradox;
The skewness of science in 219 sub-fields and a number of aggregates
This paper studies evidence from Thomson Scientific about the citation process of 3.7 million articles published in the period 1998-2002 in 219 Web of Science categories, or sub-fields. Reference and citation distributions have very different characteristics across sub-fields. However, when analyzed with the Characteristic Scores and Scales technique, which is size and scale independent, the shape of these distributions appear extraordinarily similar. Reference distributions are mildly skewed, but citation distributions with a five-year citation window are highly skewed: the mean is twenty points above the median, while 9-10% of all articles in the upper tail account for about 44% of all citations. The aggregation of sub-fields into disciplines and fields according to several aggregation schemes preserve this feature of citation distributions. On the other hand, for 140 of the 219 sub-fields the existence of a power law cannot be rejected. However, contrary to what is generally believed, at the sub-field level the scaling parameter is above 3.5 most of the time, and power laws are relatively small: on average, they represent 2% of all articles and account for 13.5% of all citations. The results of the aggregation into disciplines and fields reveal that power law algebra is a subtle phenomenon.
A comparison of the scientific performance of the U. S. and the European Union at the turn of the XXI century.
In this paper, scientific performance is identified with the impact journal articles achieve through the citations they receive. The empirical exercise refers to 3.6 million articles published in 1998-2002 in 22 scientific fields, and the more than 47 million citations they receive in 1998-2007. The first finding is that a failure to exclude co-authorship among member countries within the EU (European Union) may lead to a serious upward bias in the assignment of articles to this geographical area. In the second place, standard indicators, such as normalized mean citation ratios, are silent about what takes place in different parts of the citation distribution. Consequently, this paper compares the publication shares of the U.S. and the EU at every percentile of the world citation distribution in each field. In 15 disciplines, as well as in all sciences as a whole, the EU share of total publications is greater than that of the U.S. one. But as soon as the citations received by these publications are taken into account the picture is completely reversed. The mean citation rate in the U.S. is greater than in the EU in every one of the 22 fields. In seven fields, the initial gap between the U.S. and the EU widens up as we advance towards the more cited articles, while in the remaining 15 fields –except for Agricultural Sciences– the U.S. always surpasses the EU when it counts, namely, at the upper tail of citation distributions. For all sciences as a whole, the U.S publication share becomes greater than that of the EU one for the top 50% of the most highly cited articles.
Manifestaciones cutáneas del dengue. Reporte de caso y revisión de la literatura
El dengue es un arbovirosis trasmitido por el mosquito Aedes
aegypti (MAe) infectado, que se presenta de forma epidémica
o endémica en áreas tropicales y subtropicales. Sus manifestaciones
cutáneas (MC) más frecuentemente reportadas
son las lesiones eritemato-papulo-purpúricas, las cuales
se presentan a partir del segundo a quinto día de la infección.
La Organización Mundial de la Salud (OMS) reconoce que
la incidencia del dengue ha incrementado extraordinariamente
en todo el mundo. En el año 2010, se reportaron de
50 a 100 millones de casos; de éstos, 1.6 correspondieron al
continente Americano. En México la frecuencia de dengue
ha incrementado.El dengue es una enfermedad transmitida por un vector denominado mosquito
Aedes aegypti (MAe), que generalmente está infectado por el virus del serotipo 2. Predomina en
regiones tropicales y subtropicales de todo el mundo. El cuadro clínico inicia de 3 a 7 días
después de la picadura y sus manifestaciones cutáneas (MC) representan una frecuencia que va
del 20% hasta el 65%, la cual varía de acuerdo a cada país.
En México los casos han incrementado. Sus lesiones más comunes son: la mácula (M), exantema
cutáneo morbiliforme (ECM), lesiones purpúricas (LP), petequias (P), entre otras. El objetivo de
este estudio es señalar el panorama que representan las MC del dengue. Se presenta el caso
clínico de una mujer joven, en quien se destacan estas manifestaciones, las cuales formaron
parte de la tríada del dengue, sin datos de alarma. Las MC del dengue son escasamente referidas
en su descripción, por lo que abordamos este tema con el fin de detallar las lesiones encontradas
y dar pie a la observación de más casos. No son patognomónicas y generalmente no reflejan
la gravedad de la infección.
El ECM y las M forman parte de las MC más comunes. Tienen un carácter generalmente benigno.
Los frentes de las tormentas actuales pueden impactar en el incremento de nuevos casos
A comparison of the scientific performance of the U.S. and the European Union at the turn of the 21st century
In this paper, scientific performance is identified with the impact that journal
articles have through the citations they receive. In 15 disciplines, as well as in all sciences
as a whole, the EU share of total publications is greater than that of the U.S. However, as
soon as the citations received by these publications are taken into account the picture is
completely reversed. Firstly, the EU share of total citations is still greater than the U.S. in
only seven fields. Secondly, the mean citation rate in the U.S. is greater than in the EU in
every one of the 22 fields studied. Thirdly, since standard indicators—such as normalized
mean citation ratios—are silent about what takes place in different parts of the citation
distribution, this paper compares the publication shares of the U.S. and the EU at every
percentile of the world citation distribution in each field. It is found that in seven fields the
initial gap between the U.S. and the EU widens as we advance towards the more cited
articles, while in the remaining 15 fields—except for Agricultural Sciences—the U.S.
always surpasses the EU when it counts, namely, at the upper tail of citation distributions.
Finally, for all sciences as a whole the U.S. publication share becomes greater than that of
the EU for the top 50% of the most highly cited articles. The data used refers to 3.6 million
articles published in 1998–2002, and the more than 47 million citations they received in
1998–2007European Community's Seventh Framework ProgramPublicad
A comparison of the scientific performance of the U. S. and the European Union at the turn of the XXI century
In this paper, scientific performance is identified with the impact journal articles achieve through the citations they receive. The empirical exercise refers to 3.6 million articles published in 1998-2002 in 22 scientific fields, and the more than 47 million citations they receive in 1998-2007. The first finding is that a failure to exclude co-authorship among member countries within the EU (European Union) may lead to a serious upward bias in the assignment of articles to this geographical area. In the second place, standard indicators, such
as normalized mean citation ratios, are silent about what takes place in different parts of the citation distribution. Consequently, this paper compares the publication shares of the U.S. and
the EU at every percentile of the world citation distribution in each field. In 15 disciplines, as well as in all sciences as a whole, the EU share of total publications is greater than that of the U.S. one. But as soon as the citations received by these publications are taken into account the
picture is completely reversed. The mean citation rate in the U.S. is greater than in the EU in every one of the 22 fields. In seven fields, the initial gap between the U.S. and the EU widens up as we advance towards the more cited articles, while in the remaining 15 fields –except for
Agricultural Sciences– the U.S. always surpasses the EU when it counts, namely, at the upper tail of citation distributions. For all sciences as a whole, the U.S publication share becomes greater than that of the EU one for the top 50% of the most highly cited articles
The skewness of science in 219 sub-fields and a number of aggregates
This paper studies evidence from Thomson Scientific about the citation process of 3.7 million
articles published in the period 1998-2002 in 219 Web of Science categories, or sub-fields.
Reference and citation distributions have very different characteristics across sub-fields.
However, when analyzed with the Characteristic Scores and Scales technique, which is size and
scale independent, the shape of these distributions appear extraordinarily similar. Reference
distributions are mildly skewed, but citation distributions with a five-year citation window are
highly skewed: the mean is twenty points above the median, while 9-10% of all articles in the
upper tail account for about 44% of all citations. The aggregation of sub-fields into disciplines
and fields according to several aggregation schemes preserve this feature of citation
distributions. On the other hand, for 140 of the 219 sub-fields the existence of a power law
cannot be rejected. However, contrary to what is generally believed, at the sub-field level the
scaling parameter is above 3.5 most of the time, and power laws are relatively small: on
average, they represent 2% of all articles and account for 13.5% of all citations. The results of
the aggregation into disciplines and fields reveal that power law algebra is a subtle
phenomenon.European Community's Seventh Framework ProgramThe authors acknowledge financial support from the Spanish MEC through grants SEJ2007-63098,
SEJ2006-05710, SEJ2007-67135, and SEJ2007-67436. This paper is part of the SCIFI-GLOW
Collaborative Project supported by the European Commission’s Seventh Research Framework
Programme, Contract no. SSH7-CT-2008-217436
Embedded Quantum Correlations in thermalized quantum Rabi systems
We study the quantum correlations embedded in open quantum Rabi systems.
Specifically, we study how the quantum correlation depends on the coupling
strength, number of qubits, and reservoir temperatures. We numerically
calculate the quantum correlations of up to three qubits interacting with a
single field mode. We find that the embedded quantum correlations exhibit a
maximum for a given coupling strength, which depends inversely on the number of
subsystems and the reservoir temperature. We explore how this feature affects
the performance of a many-qubit Otto heat engine, finding numerical evidence of
a direct correspondence between the minimum of the extractable work and the
maximum of the embedded quantum correlations in the qubit-cavity bi-partition.
Furthermore, as we increase the number of qubits, the maximum extractable work
is reached at smaller values of the coupling strength. This work could help
design more sophisticated quantum heat engines that rely on many-body systems
with embedded correlations as working substances.Comment: 12 pages and 12 figure
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