8,630 research outputs found

    Null Strings in Kerr Spacetime

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    The null string's equations of motion and constraints in the Kerr spacetime are given. We assume a generic ansatz for the null strings in the Kerr spacetime and we present the resulting solutions in quadratures. Some specific string configurations, that follow from the generic one, are considered separately. In each case we also extract the corresponding solutions in the Schwarzschild spacetime.Comment: 11 pages, LaTex, no figures, final version to be published in Phys.Lett.B, references adde

    Nuclear emulsion readout techniques developed for the CHORUS experiment

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    The CHORUS experiment is pursuing the study of the production and decay of short lived particles from neutrino interactions in a nuclear emulsion target. The extraction of the full information from the emulsion sheets has been possible only thanks to the development of fully automatic microscopes. The technique of automatic scanning, pioneered in Nagoya, involves precision mechanics, high quality optics and a readout scheme allowing for fast decisions. From the R&D efforts within the various institutes of the CHORUS collaboration, the complementary approaches adopted by the Nagoya and CERN/NIKHEF groups are described here. Both are based on the principle that all information from the emulsion sheets should be extracted at the highest possible rate, limited only by the camera readout and the mechanical stability of the microscope stage. (12 refs)

    The POOL Data Storage, Cache and Conversion Mechanism

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    The POOL data storage mechanism is intended to satisfy the needs of the LHC experiments to store and analyze the data from the detector response of particle collisions at the LHC proton-proton collider. Both the data rate and the data volumes will largely differ from the past experience. The POOL data storage mechanism is intended to be able to cope with the experiment's requirements applying a flexible multi technology data persistency mechanism. The developed technology independent approach is flexible enough to adopt new technologies, take advantage of existing schema evolution mechanisms and allows users to access data in a technology independent way. The framework consists of several components, which can be individually adopted and integrated into existing experiment frameworks.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics (CHEP03), La Jolla, Ca, USA, March 2003, 5 pages, PDF, 6 figures. PSN MOKT00

    On cost-effective reuse of components in the design of complex reconfigurable systems

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    Design strategies that benefit from the reuse of system components can reduce costs while maintaining or increasing dependability—we use the term dependability to tie together reliability and availability. D3H2 (aDaptive Dependable Design for systems with Homogeneous and Heterogeneous redundancies) is a methodology that supports the design of complex systems with a focus on reconfiguration and component reuse. D3H2 systematizes the identification of heterogeneous redundancies and optimizes the design of fault detection and reconfiguration mechanisms, by enabling the analysis of design alternatives with respect to dependability and cost. In this paper, we extend D3H2 for application to repairable systems. The method is extended with analysis capabilities allowing dependability assessment of complex reconfigurable systems. Analysed scenarios include time-dependencies between failure events and the corresponding reconfiguration actions. We demonstrate how D3H2 can support decisions about fault detection and reconfiguration that seek to improve dependability while reducing costs via application to a realistic railway case study

    Giant central lumbar disc herniations: a case for the transdural approach.

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    Giant central lumbar disc protrusions can pose a significant operative challenge. Clinically, these patients are at risk of permanent disability, due not only to preoperative neural compromise caused by the protrusion itself but also to the potential iatrogenic risks associated with the standard extradural microdiscectomy technique. This is the first report to date of a giant central L3/4 disc protrusion being successfully treated through a transdural microdiscectomy approach. Prior to this report, there have been just two cases describing its application in the lumbar spine. However, neither of these reports has described its use below the level of L2/3. We compare our surgical technique with these authors and discuss the pros and cons of this surgical approach relative to the standard extradural microdiscectomy technique. Overall, we have observed encouraging results from this approach and this report would support a role for further investigation into this rarely used technique

    Supporting group maintenance through prognostics-enhanced dynamic dependability prediction

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    Condition-based maintenance strategies adapt maintenance planning through the integration of online condition monitoring of assets. The accuracy and cost-effectiveness of these strategies can be improved by integrating prognostics predictions and grouping maintenance actions respectively. In complex industrial systems, however, effective condition-based maintenance is intricate. Such systems are comprised of repairable assets which can fail in different ways, with various effects, and typically governed by dynamics which include time-dependent and conditional events. In this context, system reliability prediction is complex and effective maintenance planning is virtually impossible prior to system deployment and hard even in the case of condition-based maintenance. Addressing these issues, this paper presents an online system maintenance method that takes into account the system dynamics. The method employs an online predictive diagnosis algorithm to distinguish between critical and non-critical assets. A prognostics-updated method for predicting the system health is then employed to yield well-informed, more accurate, condition-based suggestions for the maintenance of critical assets and for the group-based reactive repair of non-critical assets. The cost-effectiveness of the approach is discussed in a case study from the power industry

    Qualitative precursory pattern before several strong earthquakes in Greece.

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    Μελετήθηκε η χρονική μεταβολή τριών σεισμικών παραμέτρων, δηλαδή, του αριθμού των σεισμών Ν, της παραμέτρου b-value και της εκλυόμενης σεισμικής ενέργειας, πριν από την εκδήλωση ισχυρών σεισμών στην Ελλάδα, για το χρονικό διάστημα 2000- 2008. Η ανάλυση έγινε με τη χρήση δεδομένων του καταλόγου σεισμών του Γεωδυναμικού Ινστιτούτου του Εθνικού Αστεροσκοπείου Αθηνών. Συγκεκριμένες φάσεις της χρονικής διακύμανσης των σεισμικών παραμέτρων, γύρω από σχετικές μέσες τιμές τους, σε δεδομένο χρονικό διάστημα, μπορούν να συσχετιστούν με τις φάσεις προετοιμασίας και εκδήλωσης ενός ισχυρού σεισμού. Η επαναλαμβανόμενηκανονικότητα της αυτής της συσχέτισης μπορεί να θεωρηθεί ως ποιοτικό μοτίβο (pattern) πρόδρομης συμπεριφοράς. H συνεχής παρακολούθηση της μεταβολής της σεισμικότητας και η αναγνώριση των φάσεων του παραπάνω μοτίβου, μπορεί να συμβάλει στην αξιολόγηση του σεισμικού κινδύνου και της πρόγνωσης μιας επικείμενης ισχυρής σεισμικής δραστηριότητας, σε μια δεδομένη περιοχή.The temporal variation of the seismicity, based on the analysis of three seismic parameters i.e., number of earthquakes, b-value and energy released, were investigated before several strong earthquakes occurrence in Greece the time period 2000-2008. The seismic parameters estimates were obtained by the means of new tool, suited to analyze earthquake catalogue, and visualize their spatio-temporalvariation behaviour. The seismic data used were taken from the earthquake catalogue of the Geodynamic Institute of National Observatory of Athens, Greece. The obtained temporal variation series shows significant changes around their relative mean values, which specific phases can be related to the strong earthquakes preparation stages. This relation shows remarkable temporal regularity so that itcan be establish considered as a precursor seismicity pattern. These results suggest that identification of this behaviour, by the continuous monitoring of the temporal variation of the seismic parameters, can contribute to the assessment of the current seismic hazard and to the impending strong earthquake parameters evaluation, in a given area