Universality of citation distributions: towards an objective measure of scientific impact

We study the distributions of citations received by a single publication within several disciplines, spanning broad areas of science. We show that the probability that an article is cited $c$ times has large variations between different disciplines, but all distributions are rescaled on a universal curve when the relative indicator $c_f=c/c_0$ is considered, where $c_0$ is the average number of citations per article for the discipline. In addition we show that the same universal behavior occurs when citation distributions of articles published in the same field, but in different years, are compared. These findings provide a strong validation of $c_f$ as an unbiased indicator for citation performance across disciplines and years. Based on this indicator, we introduce a generalization of the h-index suitable for comparing scientists working in different fields.Comment: 7 pages, 5 figures. accepted for publication in Proc. Natl Acad. Sci. US

The egalitarian effect of search engines

Search engines have become key media for our scientific, economic, and social activities by enabling people to access information on the Web in spite of its size and complexity. On the down side, search engines bias the traffic of users according to their page-ranking strategies, and some have argued that they create a vicious cycle that amplifies the dominance of established and already popular sites. We show that, contrary to these prior claims and our own intuition, the use of search engines actually has an egalitarian effect. We reconcile theoretical arguments with empirical evidence showing that the combination of retrieval by search engines and search behavior by users mitigates the attraction of popular pages, directing more traffic toward less popular sites, even in comparison to what would be expected from users randomly surfing the Web.Comment: 9 pages, 8 figures, 2 appendices. The final version of this e-print has been published on the Proc. Natl. Acad. Sci. USA 103(34), 12684-12689 (2006), http://www.pnas.org/cgi/content/abstract/103/34/1268

Percolation and Critical Behaviour in SU(2) Gauge Theory

The paramagnetic-ferromagnetic transition in the Ising model can be described as percolation of suitably defined clusters. We have tried to extend such picture to the confinement-deconfinement transition of SU(2) pure gauge theory, which is in the same universality class of the Ising model. The cluster definition is derived by approximating SU(2) by means of Ising-like effective theories. The geometrical transition of such clusters turns out to describe successfully the thermal counterpart for two different lattice regularizations of (3+1)-d SU(2).Comment: Lattice 2000 (Finite Temperature), 4 pages, 4 figures, 2 table

Center clusters in the Yang-Mills vacuum

Properties of local Polyakov loops for SU(2) and SU(3) lattice gauge theory at finite temperature are analyzed. We show that spatial clusters can be identified where the local Polyakov loops have values close to the same center element. For a suitable definition of these clusters the deconfinement transition can be characterized by the onset of percolation in one of the center sectors. The analysis is repeated for different resolution scales of the lattice and we argue that the center clusters have a continuum limit.Comment: Table added. Final version to appear in JHE

An NMR Analog of the Quantum Disentanglement Eraser

We report the implementation of a three-spin quantum disentanglement eraser on a liquid-state NMR quantum information processor. A key feature of this experiment was its use of pulsed magnetic field gradients to mimic projective measurements. This ability is an important step towards the development of an experimentally controllable system which can simulate any quantum dynamics, both coherent and decoherent.Comment: Four pages, one figure (RevTeX 2.1), to appear in Physics Review Letter

An Introduction to Community Detection in Multi-layered Social Network

Social communities extraction and their dynamics are one of the most important problems in today's social network analysis. During last few years, many researchers have proposed their own methods for group discovery in social networks. However, almost none of them have noticed that modern social networks are much more complex than few years ago. Due to vast amount of different data about various user activities available in IT systems, it is possible to distinguish the new class of social networks called multi-layered social network. For that reason, the new approach to community detection in the multi-layered social network, which utilizes multi-layered edge clustering coefficient is proposed in the paper.Comment: M.D. Lytras et al. (Eds.): WSKS 2011, CCIS 278, pp. 185-190, 201

Alkaline static feed electrolyzer based oxygen generation system

In preparation for the future deployment of the Space Station, an R and D program was established to demonstrate integrated operation of an alkaline Water Electrolysis System and a fuel cell as an energy storage device. The program's scope was revised when the Space Station Control Board changed the energy storage baseline for the Space Station. The new scope was aimed at the development of an alkaline Static Feed Electrolyzer for use in an Environmental Control/Life Support System as an oxygen generation system. As a result, the program was divided into two phases. The phase 1 effort was directed at the development of the Static Feed Electrolyzer for application in a Regenerative Fuel Cell System. During this phase, the program emphasized incorporation of the Regenerative Fuel Cell System design requirements into the Static Feed Electrolyzer electrochemical module design and the mechanical components design. The mechanical components included a Pressure Control Assembly, a Water Supply Assembly and a Thermal Control Assembly. These designs were completed through manufacturing drawing during Phase 1. The Phase 2 effort was directed at advancing the Alkaline Static Feed Electrolyzer database for an oxygen generation system. This development was aimed at extending the Static Feed Electrolyzer database in areas which may be encountered from initial fabrication through transportation, storage, launch and eventual Space Station startup. During this Phase, the Program emphasized three major areas: materials evaluation, electrochemical module scaling and performance repeatability and Static Feed Electrolyzer operational definition and characterization

Phase transitions in the Interacting Boson Fermion Model: the gamma-unstable case

The phase transition around the critical point in the evolution from spherical to deformed gamma-unstable shapes is investigated in odd nuclei within the Interacting Boson Fermion Model. We consider the particular case of an odd j=3/2 particle coupled to an even-even boson core that undergoes a transition from spherical U(5) to gamma-unstable O(6) situation. The particular choice of the j=3/2 orbital preserves in the odd case the condition of gamma-instability of the system. As a consequence, energy spectrum and electromagnetic transitions, in correspondence of the critical point, display behaviours qualitatively similar to those of the even core. The results are also in qualitative agreement with the recently proposed E(5/4) model, although few differences are present, due to the different nature of the two schemes.Comment: In press in PRC as rapid communication. 7 pages, 4 figure

Detailed analysis of quantum phase transitions within the u(2)u(2) algebra

We analyze in detail the quantum phase transitions that arise in models based on the $u(2)$ algebraic description for bosonic systems with two types of scalar bosons. First we discuss the quantum phase transition that occurs in hamiltonians that admix the two dynamical symmetry chains $u(2)\supset u(1)$ and $u(2)\supset so(2)$ by diagonalizing the problem exactly in the $u(1)$ basis. Then we apply the coherent state formalism to determine the energy functional. Finally we show that a quantum phase transition of a different nature, but displaying similar characteristics, may arise also within a single chain just by including higher order terms in the hamiltonian.Comment: 5 figure

Las tentaciones de Jesús (Mt 4,1-11) en clave intertextual

El episodio de las tentaciones de Jesús por el diablo (Mt 4,1-11; Mc 1,12-13; Lc 4,1-13) plantea diversos retos a la exégesis moderna. Junto a las cuestiones de historicidad, aparecen enseguida cuestiones de orden literario (las fuentes, la forma y la redacción) y teológico. Es evidente que el relato de las tentaciones de Jesús remite a las tentaciones de Israel: Ex 16; Dt 8,2-5 / Ex 17,1-7; Dt 6,16 / Ex 23,20-33; Dt 6,12-15. Pero, por otra parte, un análisis literario de Mt 4,1-11 hace notar semejanzas sorprendentes con Mt 14,13-33 (la introducción mediante «Juan Bautista», el uso selectivo y ordenado de adverbios, unos escenarios gráficos afines, unos temas iguales y una lexicografía casi idéntica). La abundancia y el orden de las similitudes entre ambos pasajes invitan a pensar en una elaboración consciente y pretendida por el autor. Existe, por tanto, una relación literaria entre las tentaciones de Israel, las tentaciones de Jesús (Mt 4,1-11) y los tres milagros de Jesús (Mt 14,13-33). El estudio de los pasajes muestra que Mt 4,1-11 ilumina enormemente el significado de Mt 14,13-33, y viceversa. Esta relación entre Mt 4,1-11 y Mt 14,13-33 se enriquece si el análisis se prolonga a Jn 6,1-21 (paralelo de Mt 14,13-33); un pasaje en el que gran parte de la exégesis moderna ve reflejadas las tentaciones de Jesús (ausentes en el cuarto evangelio). Aquí, el análisis literario necesita del teológico. En la Biblia, «tentación» es un concepto religioso que afecta a la alianza entre Dios y el hombre. Los agentes pueden ser el mismo Señor (con sentido de prueba), el hombre (duda) y el diablo (seducción). Pueden sufrir tentación el Señor o el hombre pero nunca el diablo. Las tentaciones de Jesús son específicas por dos notas: Jesús es tentado por el diablo en cuanto Hijo de Dios, y además es seducido para formar una alianza alternativa contra Dios Padre. Los textos estudiados así lo muestran, cada uno a su manera.The episode of Jesus’ temptations by the devil (Mt 4: 1-11; Mc 1: 12-13; Lk 4: 1-13) proposes several challenges to modern exegesis. Along with the topic of historicity, issues of theological and literary order (fonts, form and redaction) soon appear. Clearly, the story of the temptations of Jesus refers to the temptations of Israel: Ex 16; Dt 8: 2-5 / Ex 17: 1-7; Dt 6: 16 / Ex 23: 20-33; Dt 6: 12-15. But on the other hand, a literary analysis of Mt 4:1-11 noted striking similarities with Mt 14:13-33 (the introduction by «John the Baptist», selective and orderly use of adverbs, some scenarios related, a same issues and an almost identical lexicography). The abundance and the order of the similarities between the two passages invite to think of a development conscious and intended by the author. There is therefore a literary relationship between the temptations of Israel, the temptations of Jesus (Mt 4:1-11) and the three miracles of Jesus (Mt 14:13-33). The study shows that Mt 4: 1-11 greatly illuminates the meaning of Mt 14: 13- 33, and vice versa. This relationship between Mt 14: 13-33 and Mt 4:1 -11 became richer by the analysis of Jn 6: 1-21 (parallel of Mt 14:13-33); a passage in which several authors see the temptations of Jesus (absent in the fourth Gospel). Here, we need also a theological analysis. In the Bible, «temptation» is a religious concept that affects the covenant between God and man. Agents can be the Lord (testing), the man (doubting) and the devil (seducing). They can suffer temptation the Lord or the man but never the devil. The temptations of Jesus are specific for two notes: Jesus is tempted by the devil as Son of God, and is also enticed to form an alternative alliance against God, the Father. The texts of Matthew studied show it, each one in their own way