Multiprocessor Global Scheduling on Frame-Based DVFS Systems

In this ongoing work, we are interested in multiprocessor energy efficient systems, where task durations are not known in advance, but are know stochastically. More precisely, we consider global scheduling algorithms for frame-based multiprocessor stochastic DVFS (Dynamic Voltage and Frequency Scaling) systems. Moreover, we consider processors with a discrete set of available frequencies

Gang FTP scheduling of periodic and parallel rigid real-time tasks

In this paper we consider the scheduling of periodic and parallel rigid tasks. We provide (and prove correct) an exact schedulability test for Fixed Task Priority (FTP) Gang scheduler sub-classes: Parallelism Monotonic, Idling, Limited Gang, and Limited Slack Reclaiming. Additionally, we study the predictability of our schedulers: we show that Gang FJP schedulers are not predictable and we identify several sub-classes which are actually predictable. Moreover, we extend the definition of rigid, moldable and malleable jobs to recurrent tasks

Sexual activity and school deviant behaviour among adolescents: peer influence and homophily interactions with sex and ethnicity

Criminologist and sociologists have since long recognized the importance of peer influence in adolescence, but only rarely are peer influence interactions studied with regard to important salient status characteristics. This study examines whether homophily status characteristics condition the influence between best friends and the individual´s behaviour. The focus of the study is on school deviant behaviour as well as sexual activity. More specifically, we address the question to what extent peer influence differs for friends of the same sex or ethnicity (i.e. homophilic relationships), compared to friends who differ on sex and ethnicity (i.e. heterophilic relationships). Data from the Flemish Educational Assessment Study are used, which collected complete network data, from a representative sample of Flemish adolescents in secondary schools (N=11,837), clustered in 160 networks. Results indicate that peers best friend relationships are indeed strongly homophilic on both of these status dimensions and that homophilic friendships are significantly more influential than heterophilic ones. Further results show that native Belgian adolescents (majority teens) are significantly more influenced by homophilic relationships than adolescents belonging to a ethno-cultural minority group (minority teens). For sexual activity, girls are influenced stronger by homophilic relationships than boys, while for school deviant behavior the opposite is true. Cross-ethnic influence of majority teens on minority teens is substantially smaller than for minority teens on majority teens, especially for sexual activity. Implications of these findings for theory development and prevention programs are discussed

Applied knowledge management : a set of well-tried tools

For almost 20 years, Knowledge Management projects hit various domains. This paper focuses on selected tools now of general practice and becoming popular among the practitioners. Originally out of the Information Science labs, the tools introduced here have been proved tested efficient and reliable after hundreds of real projects, no matter what type of industry and domain use them. This paper aims to briefly describe a set of four well-tried Knowledge Management tools allowing practitioners to analyse and structure, describe and represent, share and store, teach and transmit knowledge. This now common practice should open the path to new models for the Knowledge Economy. Dealing with complexity becomes easier as well as putting the Information system at the crossing of the interactive information flows instead of keeping it out of reach of a majority of knowledge workers. Due to the massive retirement of the baby boomers, a large loss of workforce challenges the companies for the first time in history. How to evaluate and pass to the next generation its core business of knowledge is thus of critical importance. This paper reminds that Knowledge Management is no longer a solely academic issue since tools of the next generation are now available, beefing up the growing domain of the knowledge economy.E-learning, Intranets, Knowledge economy, Knowledge management

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ATLAS Commander: an ATLAS production tool

This paper describes the ATLAS production tool AtCom (for ATLAS Commander). The purpose of the tool is to automate as much as possible the task of a production manager: defining and submitting jobs in large quantities, following up upon their execution, scanning log files for known and unknown errors, updating the various ATLAS bookkeeping databases on successful completion of a job whilst cleaning up and resubmitting otherwise. The design of AtCom is modular, separating the generic basic job management functionality from the interactions with the various databases on the one hand, and the computing systems on the other hand. Given the near future reality of different flavors of computing systems (legacy and GRID) deployed concurrently at the various, or even a single ATLAS site, AtCom allows several of them to be used at the same time transparently.Comment: Talk from the 2003 Computing in High Energy and Nuclear Physics Conference (CHEP03), La Jolla, Ca, USA, March 2003, 7 pages, PDF, PSN : MONT00

Hydrodynamics of High Specific Power Pumps for Off-Design Operating Conditions

Part load operation of high energy centrifugal pumps is associated with increased vibration levels which may adversely affect the machines operational safety. The main sources of vibrations in centrifugal pumps are of hydrodynamic nature. The interaction between rotating and stationary flow fields yields spatially distributed pressure fluctuation patterns, which excites mechanical vibrations of the rotating and stationary pump components. As virtually all modern, high-energy machines are operated using variable speed drives, an operation, where the excitation by rotor-stator interaction pressure fluctuations matches one of the natural frequencies of the impeller or the pumps stationary components, appears to be unavoidable during the impeller life span. This may yield, provided these vibrations are not sufficiently damped, structural damage to the centrifugal pump components. Moreover, at off-design operation of centrifugal pumps, further phenomena are superposed to the Rotor-Stator interaction effects. Local flow separations affect the flow structure in the hydraulic components, modifying existing and creating supplementary hydraulic forces as excitations for deformations and vibrations at additional frequencies. In the present work, experimental investigations of part-load hydrodynamic phenomena as sources of mechanical excitations in a conventional, high-energy centrifugal pump stage are presented. These investigations include unsteady pressure fluctuation measurements in the rotating and stationary elements of the investigated pump stage, performed at different rotational speeds and operating points. The unsteady pressure measurements were accompanied by measurements of impeller deformations using strain gauges embedded in the impeller shroud wall. The acquired data have been completed by measurements of shaft and bearing housing vibrations. The measurements at part-load operation unveiled the existence of stationary and rotating instabilities in the diffuser of the pump stage, referred as stall. Stationary stall, which expresses itself as a non-rotating high pressure zone in the Rotor-Stator interface, yields additional pressure fluctuations at the rotational frequency and its harmonics. At specific relative flow rates, this high pressure pattern begins to rotate around the impeller circumference. This slowly rotating high pressure zone has a dramatic impact on the mechanical behavior of the pump stage. On the one hand, it forms the highest contribution to the impeller shroud strain, generating deformations several times higher than the ones generated by rotor-stator interaction pressure fluctuations. The perturbations in the circumferential pressure distribution yield further a radial net force, slowly rotating around the impeller circumference. This effect has been identified using the shaft vibration measurements, where it can be shown, that the shaft centerline displacement directly follows the radial force direction. This can negatively affect the rotor system dynamic stability but can also be used to detect rotating stall during the operation of the pump, as external pressure fluctuation measurements not always allow the detection of rotating stall. The impeller blade passage through the stall zone strongly affects the flow in the impeller side rooms. The entrainment of fluid with low circumferential velocity reduces strongly the rotation of the flow in the side rooms and thus affects the steady pressure distribution and the axial net force. The blade passage through the detachment zone adds periodic variations of the axial force acting on the impeller, which can be identified in the axial shaft vibration signature, allowing a detection of stationary stall by a thorough analysis of the axial shaft vibrations

Discrete Frequency Selection of Frame-Based Stochastic Real-Time Tasks

Energy-efficient real-time task scheduling has been actively explored in the past decade. Different from the past work, this paper considers schedulability conditions for stochastic real-time tasks. A schedulability condition is first presented for frame-based stochastic real-time tasks, and several algorithms are also examined to check the schedulability of a given strategy. An approach is then proposed based on the schedulability condition to adapt a continuous-speed-based method to a discrete-speed system. The approach is able to stay as close as possible to the continuous-speed-based method, but still guaranteeing the schedulability. It is shown by simulations that the energy saving can be more than 20% for some system configurationsComment: 10 page