5719579
DIRAC: A Community Grid Solution
The DIRAC system was developed in order to provide a complete solution for using the distributed computing resources of the LHCb experiment at CERN for data production and analysis. It allows a concurrent use of over 10K CPUs and 10M file replicas distributed over many tens of sites. The sites can be part of a Computing Grid such as WLCG or standalone computing clusters all integrated in a single management structure. DIRAC is a generic system with the LHCb specific functionality incorporated through a number of plug-in modules. It can be easily adapted to the needs of other communities. Special attention is paid to the resilience of the DIRAC components to allow an efficient use of non-reliable resources. The DIRAC production management components provide a framework for building highly automated data production systems including data distribution and data driven workload scheduling. In this paper we give an overview of the DIRAC system architecture and design choices. We show how different components are put together to compose an integrated data processing system including all the aspects of the LHCb experiment - from the MC production and raw data reconstruction to the final user analysis.
178787319
Determining the Arrival Directions of Extensive Air Showers from Fast Timing Measurements
121598426
High-energy muons in extensive air showers
SummaryA study has been made of the density of high-energy muons (10<Eμ<300 GeV) as a function of the distance from the axis of extensive air showers in the size range 2·105<Ne<3·106,i.e. showers produced by primary cosmic rays in a decade of energy centered on 5·1015 eV. The results for muons above 50 GeV agree with those from the Lodz-Moscow group, but those for muons above 200 GeV are a little different from the only other experimental results: those of Acharyaet al. Comparison with predictions favours a CKP-type model with a «normal» comparison. The simple scaling model with any composition does not give a good fit to the data, but no doubt modifications could be made, principally an increase in the mean transverse momentum, which would restore agreement.RiassuntoSi è effettuato uno studio della densità dei muoni (10<Eμ<300 GeV) in funzione della distanza dall’asse di sciami d’aria estesi nell’intervallo di grandezza 2·105<Ne<<3·106, cioè sciami prodotti da raggi cosmici del primario in un decadimento di energia centrato su 5 · 1015 eV. I risultati per muoni al di sopra di 50 GeV sono in accordo con quelli del gruppo di Lodz-Moscow, ma quelle per muoni al di sopra di 200 GeV sono un po’ differenti dagli unici altri risultati sperimentali: quelli di Acharyaet al. Confronti con produzioni sono a favore del modello del tipo CKP con una composizione « normale ». Il modello a variazione di scala semplice con qualsiasi composizione non dà un buon adattamento ai dati, ma, senza dubbio, modificazioni potrebbero essere fatte, principalmente un aumento nell’impulso trasversale medio, che ripristinerebbero l’accordo.
122529613
A Measurement of Single Electrons, electron Pairs, and Associated Phenomena, in Proton Proton Collisions at the CERN ISR
Abstract Measurements of single-electron production in proton-proton collisions at the CERN ISR are presented for five centre-of-mass energies √s = 23.5, 30.6, 44.8, 52.7, and 62.4 GeV. The invariant cross sections for single electrons with transverse momenta of 0.60 to 4.7 GeV/c are given. Measurements of electron-positron pairs and measurements of charged hadrons produced in association with the single electrons, are also reported.
3689707
Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes
We explore the properties of dust and associated molecular gas in 352 nearby (0.01 < z < 0.07) early-type galaxies (ETGs) with prominent dust lanes, drawn from the Sloan Digital Sky Survey (SDSS). Two-thirds of these ‘dusty ETGs’ (D-ETGs) are morphologically disturbed, which suggests a merger origin, making these galaxies ideal test beds for studying the merger process at low redshift. The D-ETGs preferentially reside in lower density environments, compared to a control sample drawn from the general ETG population. Around 80 per cent of D-ETGs inhabit the field (compared to 60 per cent of the control ETGs) and less than 2 per cent inhabit clusters (compared to 10 per cent of the control ETGs). Compared to their control-sample counterparts, D-ETGs exhibit bluer ultraviolet–optical colours (indicating enhanced levels of star formation) and an active galactic nucleus fraction that is more than an order of magnitude greater (indicating a strikingly higher incidence of nuclear activity). The mass of clumpy dust residing in large-scale dust features is estimated, using the SDSS r-band images, to be in the range 104.5–106.5 M⊙. A comparison to the total (clumpy + diffuse) dust masses – calculated using the far-infrared fluxes of 15 per cent of the D-ETGs that are detected by the Infrared Astronomical Satellite (IRAS) – indicates that only 20 per cent of the dust is typically contained in these large-scale dust features. The dust masses are several times larger than the maximum value expected from stellar mass loss, ruling out an internal origin. The dust content shows no correlation with the blue luminosity, indicating that it is not related to a galactic scale cooling flow. Furthermore, no correlation is found with the age of the recent starburst, suggesting that the dust is accreted directly in the merger rather than being produced in situ by the triggered star formation. Using molecular gas-to-dust ratios of ETGs in the literature, we estimate that the median current molecular gas fraction in the IRAS-detected ETGs is ∼1.3 per cent. Adopting reasonable values for gas depletion time-scales and starburst ages, the median initial gas fraction in these D-ETGs is ∼4 per cent. Recent work has suggested that the merger activity in nearby ETGs largely involves minor mergers (dry ETG + gas-rich dwarf), with mass ratios between 1:10 and 1:4. If the IRAS-detected D-ETGs have formed via this channel, then the original gas fractions of the accreted satellites are between 20 and 44 per cent.
2572177
Citizen Science: Contributions to Astronomy Research
The contributions of everyday individuals to significant research has grown dramatically beyond the early days of classical birdwatching and endeavors of amateurs of the 19th century. Now people who are casually interested in science can participate directly in research covering diverse scientific fields. Regarding astronomy, volunteers, either as individuals or as networks of people, are involved in a variety of types of studies. Citizen Science is intuitive, engaging, yet necessarily robust in its adoption of sci-entific principles and methods. Herein, we discuss Citizen Science, focusing on fully participatory projects such as Zooniverse (by several of the au-thors CL, AS, LF, SB), with mention of other programs. In particular, we make the case that citizen science (CS) can be an important aspect of the scientific data analysis pipelines provided to scientists by observatories.
18148287
Dynamic Bayesian Combination of Multiple Imperfect Classifiers
Classifier combination methods need to make best use of the outputs of multiple, imperfect classifiers to enable higher accuracy classifications. In many situations, such as when human decisions need to be combined, the base decisions can vary enormously in reliability. A Bayesian approach to such uncertain combination allows us to infer the differences in performance between individuals and to incorporate any available prior knowledge about their abilities when training data is sparse. In this chapter we explore Bayesian classifier combination, using the computationally efficient framework of variational Bayesian inference. We apply the approach to real data from a large citizen science project, Galaxy Zoo Supernovae, and show that our method far outperforms other established approaches to imperfect decision combination.We go on to analyse the putative community structure of the decision makers, based on their inferred decision making strategies, and show that natural groupings are formed. Finally we present a dynamic Bayesian classifier combination approach and investigate the changes in base classifier performance over time.
120272757
A System of Cylindrical Drift Chambers in a Superconducting Solenoid
Abstract A superconducting solenoid at the CERN ISR has been equipped with a system of high accuracy cylindrical drift chambers. This detector consists of eight layers of field shaped drift cells with a delay line opposite each sense wire to provide coupled two dimensional readout. The design, construction, and operation of this system are discussed. The resolution and performance of the delay lines and sense wires under ISR running conditions are shown.