Centrality indices are an essential concept in network analysis. For those based on shortest-path distances the computation is at least quadratic in the number of nodes, since it usually involves solving the single-source shortest-paths (SSSP) problem from every node. Therefore, exact computation is infeasible for many large networks of interest today. Centrality scores can be estimated, however, from a limited number of SSSP computations. We present results from an experimental study of the quality of such estimates under various selection strategies for the source vertices.

ZFIN, the Zebrafish Model Organism Database, http://zfin.org, serves as the central repository and web-based resource for zebrafish genetic, genomic, phenotypic and developmental data. ZFIN manually curates comprehensive data for zebrafish genes, phenotypes, genotypes, gene expression, antibodies, anatomical structures and publications. A wide-ranging collection of web-based search forms and tools facilitates access to integrated views of these data promoting analysis and scientific discovery. Data represented in ZFIN are derived from three primary sources: curation of zebrafish publications, individual research laboratories and collaborations with bioinformatics organizations. Data formats include text, images and graphical representations. ZFIN is a dynamic resource with data added daily as part of our ongoing curation process. Software updates are frequent. Here, we describe recent additions to ZFIN including (i) enhanced access to images, (ii) genomic features, (iii) genome browser, (iv) transcripts, (v) antibodies and (vi) a community wiki for protocols and antibodies.

Abstract. We present a novel sampling-based approximation technique for classical multidimensional scaling that yields an extremely fast layout algorithm suitable even for very large graphs. It produces layouts that compare favorably with other methods for drawing large graphs, and it is among the fastest methods available. In addition, our approach allows for progressive computation, i.e. a rough approximation of the layout can be produced even faster, and then be refined until satisfaction.

ZFIN, the Zebrafish Model Organism Database (http://zfin.org), is the central resource for zebrafish genetic, genomic, phenotypic and developmental data. ZFIN curators manually curate and integrate comprehensive data involving zebrafish genes, mutants, transgenics, phenotypes, genotypes, gene expressions, morpholinos, antibodies, anatomical structures and publications. Integrated views of these data, as well as data gathered through collaborations and data exchanges, are provided through a wide selection of web-based search forms. Among the vertebrate model organisms, zebrafish are uniquely well suited for rapid and targeted generation of mutant lines. The recent rapid production of mutants and transgenic zebrafish is making management of data associated with these resources particularly important to the research community. Here, we describe recent enhancements to ZFIN aimed at improving our support for mutant and transgenic lines, including (i) enhanced mutant/transgenic search functionality; (ii) more expressive phenotype curation methods; (iii) new downloads files and archival data access; (iv) incorporation of new data loads from laboratories undertaking large-scale generation of mutant or transgenic lines and (v) new GBrowse tracks for transgenic insertions, genes with antibodies and morpholinos.

We study the quantum phase transition in the two-dimensional random Ising model in a transverse field by Monte Carlo simulations. We find results similar to those known analytically in onedimension. At the critical point, the dynamical exponent is infinite and the typical correlation function decays with a stretched exponential dependence on distance. Away from the critical point there are Griffiths-McCoy singularities, characterized by a single, continuously varying exponent, z ′ , which diverges at the critical point, as in one-dimension. Consequently, the zero temperature susceptibility diverges for a range of parameters about the transition.PACS numbers: 75.50. Lk, 75.10.Nr, 75.40.Gb Though classical phase transitions occurring at finite temperature are very well understood, our knowledge of quantum transitions at T = 0 is relatively poor, at least for systems with quenched disorder. There is, however, considerable interest in these systems since they (i) exhibit new universality classes, and (ii) display "GriffithsMcCoy" 1,2 singularities even away from the critical point, due to rare regions with stronger than average interactions.Just as the simplest model with a classical phase transition is the Ising model, the simplest random model with a quantum transition is arguably the Ising model in a transverse field whose Hamiltonian is given byHere the {σ α i } are Pauli spin matrices, and the nearest neighbor interactions J ij and transverse fields h i are both independent random variables. This model should provide a reasonable description of the experimental system 6 LiHo x Y 1−x F 4 and may also be an appropriate model 7 to describe non-fermi liquid behavior in certain f -electron systems.Naturally the random transverse field Ising model has been quite extensively studied and many surprising analytical results are available 3-5 for the case of dimension d = 1. For example, the dynamic critical exponent, z, is infinite. Instead of a characteristic time scale ξ τ varying as a power of a characteristic length scale ξ according to ξ τ ∼ ξ z , one has instead an exponential relation 3 ξ τ ∼ exp(const. ξ ψ ), where ψ = 1/2. This is called activated dynamical scaling. In addition, distributions of the equal-time σ z i -σ z i+r correlations, are very broad. As a result average and typical 8 correlations behave rather differently, since the average is dominated by a few rare (and hence atypical ) points. At the critical point, for example, the average correlation function falls off with a power of the distance r as C av (r) ∼ r −η , where 3η = (3 − √ 5)/2 ≃ 0.38 whereas the typical value falls off much faster, as a stretched exponential C typ (r) ∼ exp(−const. r σ ), with σ = 1/2. As the critical point is approached, the average and typical correlation lengths both diverge but with different exponents 3 , i.e. ξ av ∼ δ −νav ; ξ typ ∼ δ −νtyp , where δ is the deviation from criticality, and ν av = 2, ν typ = 1. Finally, there are strong Griffiths-McCoy singularities at low temperature even away from the critical p...