Galaxy pairs in the Sloan Digital Sky Survey - IX: Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer

Interactions between galaxies are predicted to cause gas inflows that can potentially trigger nuclear activity. Since the inflowing material can obscure the central regions of interacting galaxies, a potential limitation of previous optical studies is that obscured Active Galactic Nuclei (AGNs) can be missed at various stages along the merger sequence. We present the first large mid-infrared study of AGNs in mergers and galaxy pairs, in order to quantify the incidence of obscured AGNs triggered by interactions. The sample consists of galaxy pairs and post-mergers drawn from the Sloan Digital Sky Survey that are matched to detections by the Wide Field Infrared Sky Explorer (WISE). We find that the fraction of AGN in the pairs, relative to a mass-, redshift- and environment-matched control sample, increases as a function of decreasing projected separation. This enhancement is most dramatic in the post-merger sample, where we find a factor of 10-20 excess in the AGN fraction compared with the control. Although this trend is in qualitative agreement with results based on optical AGN selection, the mid-infrared selected AGN excess increases much more dramatically in the post-mergers than is seen for optical AGN. Our results suggest that energetically dominant optically obscured AGNs become more prevalent in the most advanced mergers, consistent with theoretical predictions.Comment: 8 pages, 7 figures accepted to MNRAS (with minor revisions

Recovering 3D structural properties of galaxies from SDSS-like photometry

Because of the 3D nature of galaxies, an algorithm for constructing spatial density distribution models of galaxies on the basis of galaxy images has many advantages over surface density distribution approximations. We present a method for deriving spatial structure and overall parameters of galaxies from images and estimate its accuracy and derived parameter degeneracies on a sample of idealised model galaxies. The test galaxies consist of a disc-like component and a spheroidal component with varying proportions and properties. Both components are assumed to be axially symmetric and coplanar. We simulate these test galaxies as if observed in the SDSS project through ugriz filters, thus gaining a set of realistically imperfect images of galaxies with known intrinsic properties. These artificial SDSS galaxies were thereafter remodelled by approximating the surface brightness distribution with a 2D projection of a bulge+disc spatial distribution model and the restored parameters were compared to the initial ones. Down to the r-band limiting magnitude 18, errors of the restored integral luminosities and colour indices remain within 0.05 mag and errors of the luminosities of individual components within 0.2 mag. Accuracy of the restored bulge-to-disc ratios (B/D) is within 40% in most cases, and becomes worse for galaxies with low B/D, but the general balance between bulges and discs is not shifted systematically. Assuming that the intrinsic disc axial ratio is < 0.3, the inclination angles can be estimated with errors < 5deg for most of the galaxies with B/D < 2 and with errors < 15deg up to B/D = 6. Errors of the recovered sizes of the galactic components are below 10% in most cases. In general, models of disc components are more accurate than models of spheroidal components for geometrical reasons.Comment: 15 pages, 13 figures, accepted for publication in RA

Large Tree Level CP Violation in e+e−→ttˉH0e^+e^-\to t\bar{t}H^0 in The Two Higgs Doublet Model

We find a large CP violation effect within the Two-Higgs-Doublet-Model for the reaction $e^+e^-\to t\bar{t}H^0$ at future linear colliders. The CP-asymmetry arises already at the tree level as a result of interference between diagrams with $H^0$ emission from $t$ (and $\bar{t}$) and its emission from a $Z^0$ and can be about 10--20\%. In the best case one needs a few hundred $t\bar{t}H^0$ events to observe CP violation at the 3$\sigma$ level.Comment: UU encoded tar compressed tex file with postscript figure

Testing Rotational Mixing Predictions with New Boron Abundances in Main Sequence B-type Stars

(Abridged) New boron abundances for seven main-sequence B-type stars are determined from HST STIS spectroscopy around the BIII 2066A line. Boron abundances provide a unique and critical test of stellar evolution models that include rotational mixing since boron is destroyed in the surface layers of stars through shallow mixing long before other elements are mixed from the stellar interior through deep mixing. Boron abundances range from 12+log(B/H) = 1.0 to 2.2. The boron abundances are compared to the published values of their stellar nitrogen abundances (all have 12+log(N/H) < 7.8, i.e., they do not show significant CNO-mixing) and to their host cluster ages (4 to 16 Myr) to investigate the predictions from models of massive star evolution with rotational mixing effects (Heger & Langer 2000). Only three stars (out of 34) deviate from the model predictions, including HD36591, HD205021, and HD30836. These three stars suggest that rotational mixing could be more efficient than currently modelled at the highest rotation rates.Comment: 10 figures, 7 tables; accepted for publication in the Astrophysical Journa

A framework for the successful implementation of food traceability systems in China

Implementation of food traceability systems in China faces many challenges due to the scale, diversity and complexity of China’s food supply chains. This study aims to identify critical success factors specific to the implementation of traceability systems in China. Twenty-seven critical success factors were identified in the literature. Interviews with managers at four food enterprises in a pre-study helped identify success criteria and five additional critical success factors. These critical success factors were tested through a survey of managers in eighty-three food companies. This study identifies six dimensions for critical success factors: laws, regulations and standards; government support; consumer knowledge and support; effective management and communication; top management and vendor support; and information and system quality

Service workload patterns for QoS-driven cloud resource management

Cloud service providers negotiate SLAs for customer services they offer based on the reliability of performance and availability of their lower-level platform infrastructure. While availability management is more mature, performance management is less reliable. In order to support a continuous approach that supports the initial static infrastructure configuration as well as dynamic reconfiguration and auto-scaling, an accurate and efficient solution is required. We propose a prediction technique that combines a workload pattern mining approach with a traditional collaborative filtering solution to meet the accuracy and efficiency requirements. Service workload patterns abstract common infrastructure workloads from monitoring logs and act as a part of a first-stage high-performant configuration mechanism before more complex traditional methods are considered. This enhances current reactive rule-based scalability approaches and basic prediction techniques by a hybrid prediction solution. Uncertainty and noise are additional challenges that emerge in multi-layered, often federated cloud architectures. We specifically add log smoothing combined with a fuzzy logic approach to make the prediction solution more robust in the context of these challenges

The Gene Ontology Resource: 20 years and still GOing strong

The Gene Ontology resource (GO; http://geneontology.org) provides structured, computable knowledge regarding the functions of genes and gene products. Founded in 1998, GO has become widely adopted in the life sciences, and its contents are under continual improvement, both in quantity and in quality. Here, we report the major developments of the GO resource during the past two years. Each monthly release of the GO resource is now packaged and given a unique identifier (DOI), enabling GO-based analyses on a specific release to be reproduced in the future. The molecular function ontology has been refactored to better represent the overall activities of gene products, with a focus on transcription regulator activities. Quality assurance efforts have been ramped up to address potentially out-of-date or inaccurate annotations. New evidence codes for high-throughput experiments now enable users to filter out annotations obtained from these sources. GO-CAM, a new framework for representing gene function that is more expressive than standard GO annotations, has been released, and users can now explore the growing repository of these models. We also provide the ‘GO ribbon’ widget for visualizing GO annotations to a gene; the widget can be easily embedded in any web page

Quenched QCD at finite density

Simulations of quenched $QCD$ at relatively small but {\it nonzero} chemical potential $\mu$ on $32 \times 16^3$ lattices indicate that the nucleon screening mass decreases linearly as $\mu$ increases predicting a critical chemical potential of one third the nucleon mass, $m_N/3$, by extrapolation. The meson spectrum does not change as $\mu$ increases over the same range, from zero to $m_\pi/2$. Past studies of quenched lattice QCD have suggested that there is phase transition at $\mu = m_\pi/2$. We provide alternative explanations for these results, and find a number of technical reasons why standard lattice simulation techniques suffer from greatly enhanced fluctuations and finite size effects for $\mu$ ranging from $m_\pi/2$ to $m_N/3$. We find evidence for such problems in our simulations, and suggest that they can be surmounted by improved measurement techniques.Comment: 23 pages, Revte

Flux-tubes in three-dimensional lattice gauge theories

Flux-tubes in different representations of SU(2) and U(1) lattice gauge theories in three dimensions are measured. Wilson loops generate heavy ``quark-antiquark'' pairs in fundamental ($j=1/2$), adjoint ($j=1$), and quartet ($j=3/2$) representations of SU(2). The first direct lattice measurements of the flux-tube cross-section ${\cal A}_j$ as a function of representation are made. It is found that ${\cal A}_j \approx {\rm constant}$, to about 10\%. Results are consistent with a connection between the string tension $\sigma_j$ and ${\cal A}_j$ suggested by a simplified flux-tube model, $\sigma_j = g^2 j(j+1) / (2 {\cal A}_j)$ [$g$ is the gauge coupling], given that $\sigma_j$ scales like the Casimir $j(j+1)$, as observed in previous lattice studies in both three and four dimensions. The results can discriminate among phenomenological models of the physics underlying confinement. Flux-tubes for singly- and doubly-charged Wilson loops in compact QED$_3$ are also measured. It is found that the string tension scales as the squared-charge and the flux-tube cross-section is independent of charge to good approximation. These SU(2) and U(1) simulations lend some support, albeit indirectly, to a conjecture that the dual superconductor mechanism underlies confinement in compact gauge theories in both three and four dimensions.Comment: 15 pages (REVTEX 2.1). Figures: 11, not included (available by request from [email protected] by regular mail, postscript files, or one self-unpacking uuencoded file

Effective Lagrangian Approach to Weak Radiative Decays of Heavy Hadrons

Motivated by the observation of the decay $\bar{B}\to \bar{K}^*\gamma$ by CLEO, we have systematically analyzed the two-body weak radiative decays of bottom and charmed hadrons. There exist two types of weak radiative decays: One proceeds through the short-distance $b\to s\gamma$ transition and the other occurs through $W$-exchange accompanied by a photon emission. Effective Lagrangians are derived for the $W$-exchange bremsstrahlung processes at the quark level and then applied to various weak electromagnetic decays of heavy hadrons. Predictions for the branching ratios of $\bar{B}^0\to D^{*0} \gamma,~\Lambda_b^0\to\Sigma_c^0\gamma,~\Xi_b^0\to \Xi_c^0\gamma$ and \Xi_b^0\to\xip_c^0\gamma are given. In particular, we found ${\cal B}(\bar{B}^0 \to D^{*0}\gamma)\approx 0.9\times 10^{-6}$. Order of magnitude estimates for the weak radiative decays of charmed hadrons: $~D^0\to \bar{K}^{*0}\gamma,~\Lambda_c^+\to\Sigma^+\gamma$ and $\Xi_c^0\to\Xi^0\gamma$ are also presented. Within this approach, the decay asymmetry for antitriplet to antitriplet heavy baryon weak radiative transitions is uniquely predicted by heavy quark symmetry. The electromagnetic penguin contribution to $\Lambda_b^0\to\Lambda\gamma$ is estimated by two different methods and its branching ratio is found to be of order $1\times 10^{-5}$. We conclude that weak radiative decays of bottom hadrons are dominated by the short-distance $b\to s\gamma$ mechanism.Comment: 28 pages + 3 figures (not included), CLNS 94/1278, IP-ASTP-04-94. [Main changes in this revised version: (i) Sect 2 and subsection 4.1 are revised, (ii) A MIT bag method for calculating the decay rate of $Lambda_b \to\Lambda+gamma$ is presented, (iii) All predictions are updated using the newly available 1994 Particle Data Group, and (iv) Appendix and subsections 3.3 and 4.4 are deleted.