2,256 research outputs found

    On event-by-event fluctuations in nuclear collisions

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    We demonstrate that a new type of analysis in heavy-ion collisions, based on an event-by-event analysis of the transverse momentum distribution, allows us to obtain information on secondary interactions and collective behaviour that is not available from the inclusive spectra. Using a random walk model as a simple phenomenological description of initial state scattering in collisions with heavy nuclei, we show that the event-by-event measurement allows a quantitative determination of this effect, well within the resolution achievable with the new generation of large acceptance hadron spectrometers. The preliminary data of the NA49 collaboration on transverse momentum fluctuations indicate qualitatively different behaviour than that obtained within the random walk model. The results are discussed in relation to the thermodynamic and hydrodynamic description of nuclear collisions

    The PROOF Distributed Parallel Analysis Framework based on ROOT

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    The development of the Parallel ROOT Facility, PROOF, enables a physicist to analyze and understand much larger data sets on a shorter time scale. It makes use of the inherent parallelism in event data and implements an architecture that optimizes I/O and CPU utilization in heterogeneous clusters with distributed storage. The system provides transparent and interactive access to gigabytes today. Being part of the ROOT framework PROOF inherits the benefits of a performant object storage system and a wealth of statistical and visualization tools. This paper describes the key principles of the PROOF architecture and the implementation of the system. We will illustrate its features using a simple example and present measurements of the scalability of the system. Finally we will discuss how PROOF can be interfaced and make use of the different Grid solutions.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, CA, USA, March 2003, 5 pages, LaTeX, 4 eps figures. PSN TULT00

    Hard Probe Capabilities of CMS in Heavy Ion Collisions at the LHC

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    Heavy ion collisions at the Large Hadron Collider (LHC) will produce strongly interacting matter at unprecedented energy densities. At LHC collision energies, new hard probes of the dense initial collision system will become readily available. We present an overview of the capabilities of the Compact Muon Solenoid (CMS) detector to use these probes for a detailed study of QCD phenomenology at the highest energy densities.Comment: Proceedings for Hard Probes 2006, Asilomar; CMS Conference Report 2006/06

    On Event-by-Event Fluctuations in Nuclear Collisions

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    We demonstrate that a new type of analysis in heavy-ion collisions, based on an event-by-event analysis of the transverse momentum distribution, allows us to obtain information on secondary interactions and collective behaviour that is not available from the inclusive spectra. Using a random walk model as a simple phenomenological description of initial state scattering in collisions with heavy nuclei, we show that the event-by-event measurement allows a quantitative determination of this effect, well within the resolution achievable with the new generation of large acceptance hadron spectrometers. The preliminary data of the NA49 collaboration on transverse momentum fluctuations indicate qualitatively different behaviour than that obtained within the random walk model. The results are discussed in relation to the thermodynamic and hydrodynamic description of nuclear collisions.Comment: 9 page

    Rational Strain Engineering in Delafossite Oxides for Highly Efficient Hydrogen Evolution Catalysis in Acidic Media

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    The rational design of hydrogen evolution reaction (HER) electrocatalysts which are competitive with platinum is an outstanding challenge to make power-to-gas technologies economically viable. Here, we introduce the delafossites PdCrO2_2, PdCoO2_2 and PtCoO2_2 as a new family of electrocatalysts for the HER in acidic media. We show that in PdCoO2_2 the inherently strained Pd metal sublattice acts as a pseudomorphic template for the growth of a strained (by +2.3%) Pd rich capping layer under reductive conditions. The surface modification continuously improves the electrocatalytic activity by simultaneously increasing the exchange current density j0_0 from 2 to 5 mA/cmgeo2^2_{geo} and by reducing the Tafel slope down to 38 mV/decade, leading to overpotentials η10\eta_{10} < 15 mV for 10 mA/cmgeo2^2_{geo}, superior to bulk platinum. The greatly improved activity is attributed to the in-situ stabilization of a β\beta-palladium hydride phase with drastically enhanced surface catalytic properties with respect to pure or nanostructured palladium. These findings illustrate how operando induced electrodissolution can be used as a top-down design concept for rational surface and property engineering through the strain-stabilized formation of catalytically active phases

    The Hot QCD White Paper: Exploring the Phases of QCD at RHIC and the LHC

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    The past decade has seen huge advances in experimental measurements made in heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) and more recently at the Large Hadron Collider (LHC). These new data, in combination with theoretical advances from calculations made in a variety of frameworks, have led to a broad and deep knowledge of the properties of thermal QCD matter. Increasingly quantitative descriptions of the quark-gluon plasma (QGP) created in these collisions have established that the QGP is a strongly coupled liquid with the lowest value of specific viscosity ever measured. However, much remains to be learned about the precise nature of the initial state from which this liquid forms, how its properties vary across its phase diagram and how, at a microscopic level, the collective properties of this liquid emerge from the interactions among the individual quarks and gluons that must be visible if the liquid is probed with sufficiently high resolution. This white paper, prepared by the Hot QCD Writing Group as part of the U.S. Long Range Plan for Nuclear Physics, reviews the recent progress in the field of hot QCD and outlines the scientific opportunities in the next decade for resolving the outstanding issues in the field.Comment: 110 pages, 33 figures, 429 references. Prepared as part of the U.S. Long-Range Plan for Nuclear Physic

    Mobile 3D sensor for documenting maintenance processes of large complex structures

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    With the new handheld goSCOUT3D sensor system, the entire surface of complex industrial machinery spanning several meters can be captured three-dimensionally within a matter of minutes. In addition, a comprehensive photo collection is registered and precisely assigned to the corresponding 3D object points in one hybrid 2D/3D model. At the basis of the robust 3D digitization are the measuring principles of photogrammetric reconstruction using a high-resolution color camera and simultaneous localization and imaging using a tracking unit. Following image acquisition, the process leading to generation of the complete hybrid model is fully automated. Under continuous movement of the sensor head, up to six images per second and a total of up to several thousand images can be recorded. Those images are then aligned in 3D space and used to reconstruct the 3D model. Results regarding accuracy measurements are presented as well as application examples of digitized technical machinery under maintenance and inspection
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