Fine-grained Simulation in the Design of Automotive Communication Systems

International audienceEarly in the design cycle, the two main approaches for verifying timing constraints and di- mensioning automotive embedded networks are worst-case schedulability analysis and simulation. The first aim of the paper is to demonstrate that both provide complementary results and that, most often, none of them alone is sufficient. In this paper, we present a simulation approach accounting for the clock drifts that occur on the network nodes at run- time and evaluate the extent to which the results ob- tained with this approach are relevant for the design- ers in order to validate the performances of a CAN- based communication system. One of the practical outcome of this study is to show that initial phasings between nodes, as well as the values of the clock drifts, do not significantly impact the frame response time distributions that can be observed on the long run

Precision luminosity measurements at LHCb

Measuring cross-sections at the LHC requires the luminosity to be determined accurately at each centre-of-mass energy √s. In this paper results are reported from the luminosity calibrations carried out at the LHC interaction point 8 with the LHCb detector for √s = 2.76, 7 and 8 TeV (proton-proton collisions) and for √sNN = 5 TeV (proton-lead collisions). Both the "van der Meer scan" and "beam-gas imaging" luminosity calibration methods were employed. It is observed that the beam density profile cannot always be described by a function that is factorizable in the two transverse coordinates. The introduction of a two-dimensional description of the beams improves significantly the consistency of the results. For proton-proton interactions at √s = 8 TeV a relative precision of the luminosity calibration of 1.47% is obtained using van der Meer scans and 1.43% using beam-gas imaging, resulting in a combined precision of 1.12%. Applying the calibration to the full data set determines the luminosity with a precision of 1.16%. This represents the most precise luminosity measurement achieved so far at a bunched-beam hadron collider

Performance of 18-Story Steel Momentframe Buildings during a large San Andreas Earthquake - A Southern California-Wide End-to-End Simulation

The mitigation of seismic risk in urban areas in the United States and abroad is of major concern for all governments. Unfortunately no comprehensive studies have attempted to address this issue in a rigorous, quantitative manner. This study tackles this problem head-on for one typical class of tall buildings in southern California. The approach adopted here can be used as a template to study earthquake risk in other seismically sensitive regions of the world, such as Taiwan, Japan, Indonesia, China, South American countries (Chile, Bolivia, etc.), and the west coast of the United States (in particular, Seattle). In 1857 a large earthquake of magnitude 7.9 [1] occurred on the San Andreas fault with rupture initiating at Parkeld in Central California and propagating in a southeasterly direction over a distance of more than 360 km. Such a unilateral rupture produces signicant directivity toward the San Fernando and Los Angeles basins. Indeed, newspaper reports (Los Angeles Star [2, 3]) of sloshing observed in the Los Angeles river point to long-duration (1-2 min) and long-period (2-8 s) shaking, which could have a severe impact on present-day tall buildings, especially in the mid-height range. To assess the risk posing tall steel moment-frame buildings from an 1857-like earthquake on the San Andreas fault, a nite source model of the magnitude 7.9 November 3, 2002 Denali fault earthquake is mapped on to the San Andreas fault with rupture initiating at Parkeld in Central California and propagating a distance of about 290 km in a south-easterly direction. As the rupture proceeds down south from Parkeld and hits the big bend on the San Andreas fault, it sheds off a signicant amount of energy into the San Fernando valley, generating large amplitude ground motion there. A good portion of this energy spills over into the Los Angeles basin with many cities along the coast such as Santa Monica and Seal Beach and more inland areas going east from Seal beach towards Anaheim experiencing long-duration shaking. In addition, the tail-end of the rupture sheds energy from SH/Love waves into the Baldwin Park-La Puente region, which is bounded by a line of mountains that creates a mini-basin, further amplifying the ground motion. The peak velocity is of the order of 1 m.s in the Los Angeles basin, including downtown Los Angeles, and 2 m.s in the San Fernando valley. Signicant displacements occur in the basins but not in the mountains. The peak displacements are in the neighborhood of 1 m in the Los Angeles basin and 2 m in the San Fernando valley. The ground motion simulation is performed using the spectral element method based seismic wave propagation program, SPECFEM3D. To study the effects of the ground motion simulated at 636 sites (spread across southern California, spaced at about 3.5 km each way), computer models of an existing 18-story steel moment-frame building and a redesigned building with the same conguration (redesigned to current standards using the 1997 Uniform Building Code) are analyzed using the nonlinear structural analysis program, FRAME3D. For these analyses, the building Y direction is aligned with the geographical north direction. As expected, the existing building model fares much worse than the redesigned building model. Fracture occurs in at least 25% of the connections in this building when located in the San Fernando valley. About 10% of connections fracture in the building when located in downtown Los Angeles and the mid-Wilshire district (Beverly Hills), while the numbers are about 20% when it is located in Santa Monica, west Los Angeles, Inglewood , Alhambra, Baldwin Park, La Puente, Downey, Norwalk, Brea, Fullerton, Anaheim and Seal Beach. The peak interstory drifts in the middle-third and bottom-third of the existing building are far greater than the top-third pointing to damage being localized to the lower oors. The localization of damage in the lower oors rather than the upper oors could potentially be worse because of the risk of more oors pancaking on top of each other if a single story gives way. Consistent with the extent of fracture observed, the peak drifts in the existing building exceed 0.10 when located in the San Fernando valley, Baldwin Park and neighboring cities, Santa Monica, west Los Angeles and neighboring cities, Norwalk and neighboring cities, and Seal Beach and neighboring cities, which is well into the postulated collapse regime. When located in downtown Los Angeles and the mid-Wilshire district, the building would barely satisfy the collapse prevention criteria set by FEMA [4] with peak drifts of about 0.05. The performance of the newly designed 18-story steel building is signicantly better than the existing building for the entire region. However, the new building still has signicant drifts indicative of serious damage when located in the San Fernando valley or the Baldwin Park area. When located in coastal cities (such as Santa Monica, Seal Beach etc.), the Wilshire-corridor (west Los Angeles, Beverly Hills, etc.), the mid-city region (Downey, Norwalk, etc.) or the booming Orange County cities of Anaheim and Santa Ana, it has peak drifts of about 0.05, once again barely satisfying the FEMA collapse prevention criteria [5]. In downtown Los Angeles it does not undergo much damage in this scenario. Thus, even though this building has been designed according to the latest code, it suffers damage that would necessitate closure for some time following the earthquake in most areas, but this should be expected since this is a large earthquake and building codes are written to limit the loss of life and ensure "collapse prevention" for such large earthquakes, but not necessarily limit damage. Unfortunately, widespread closures such as this could cripple the regional economy in the event of such an earthquake. A second scenario considered in the study involves the same Denali earthquake source mapped to the San Andreas fault but with rupture initiating in the south and propagating to the north (with the largest amount of slip occurring to the north in Central California) instead of the other way around. The results of such a scenario indicate that ground shaking would be far less severe demonstrating the effects of directivity and slip distribution in dictating the level of ground shaking and the associated damage in buildings. The peak drifts in existing and redesigned building models are in the range of 0.02-0.04 indicating that there is no signicant danger of collapse. However, damage would still be signicant enough to warrant building closures and compromise life safety in some instances. The ground motion simulation and the structural damage modeling procedures are validated using data from the January 17, 1994, Northridge earthquake while the band-limited nature of the ground motion simulation (limited to a shortest period of 2 s by the current state of knowledge of the 3-D Earth structure) is shown to have no signicant effect on the response of the two tall buildings considered here with the use of observed records from the 1999 Chi Chi earthquake in Taiwan and the 2001 Tokachi-Oki earthquake in Japan

The Longitudinal Polarimeter at HERA

The design, construction and operation of a Compton back-scattering laser polarimeter at the HERA storage ring at DESY are described. The device measures the longitudinal polarization of the electron beam between the spin rotators at the HERMES experiment with a fractional systematic uncertainty of 1.6%. A measurement of the beam polarization to an absolute statistical precision of 0.01 requires typically one minute when the device is operated in the multi-photon mode. The polarimeter also measures the polarization of each individual electron bunch to an absolute statistical precision of 0.06 in approximately five minutes. It was found that colliding and non-colliding bunches can have substantially different polarizations. This information is important to the collider experiments H1 and ZEUS for their future longitudinally polarized electron program because those experiments use the colliding bunches only.Comment: 21 pages (Latex), 14 figures (EPS

Timing verification of real­time automotive Ethernet networks: what can we expect from simulation?

Switched Ethernet is a technology that is profoundly reshaping automotive communication architectures as it did in other application domains such as avionics with the use of AFDX backbones. Early stage timing verification of critical embedded networks typically relies on simulation and worst-case schedulability analysis. When the modeling power of schedulability analysis is not sufficient, there are typically two options: either make pessimistic assumptions or ignore what cannot be modeled. Both options are unsatisfactory because they are either inefficient in terms of resource usage or potentially unsafe. To overcome those issues, we believe it is a good practice to use simulation models, which can be more realistic, along with schedulability analysis. The two basic questions that we aim to study here is what can we expect from simulation, and how to use it properly? This empirical study explores these questions on realistic case-studies and provides methodological guidelines for the use of simulation in the design of switched Ethernet networks. A broader objective of the study is to compare the outcomes of schedulability analyses and simulation, and conclude about the scope of usability of simulation in the design of critical Ethernet networks

Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer for the Radiation Belt Storm Probes Mission

The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the in situ plasma ion and electron fluxes over 4π sr at each RBSP spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution ΔE FWHM/E≈15 %. The dominant ion species (H+, He+, and O+) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance

A new list of thorium and argon spectral lines in the visible

Aims. We present a new list of thorium and argon emission lines in the visible obtained by analyzing high-resolution (R=110,000) spectra of a ThAr hollow cathode lamp. The aim of this new line list is to allow significant improvements in the quality of wavelength calibration for medium- to high-resolution astronomical spectrographs. Methods. We use a series of ThAr lamp exposures obtained with the HARPS instrument (High Accuracy Radial-velocity Planet Searcher) to detect previously unknown lines, perform a systematic search for blended lines and correct individual wavelengths by determining the systematic offset of each line relative to the average wavelength solution. Results. We give updated wavelengths for more than 8400 lines over the spectral range 3785-6915 A. The typical internal uncertainty on the line positions is estimated to be ~10 m/s (3.3 parts in 10^8 or 0.18 mA), which is a factor of 2-10 better than the widely used Los Alamos Atlas of the Thorium Spectrum (Palmer & Engleman 1983). The absolute accuracy of the global wavelength scale is the same as in the Los Alamos Atlas. Using this new line list on HARPS ThAr spectra, we are able to obtain a global wavelength calibration which is precise at the 20 cm/s level (6.7 parts in 10^10 or 0.0037 mA). Conclusions. Several research fields in astronomy requiring high-precision wavelength calibration in the visible (e.g. radial velocity planet searches, variability of fundamental constants) should benefit from using the new line list.Comment: 7 pages, 6 figures, accepted for publication in A&

Beam instrumentation for the Tevatron Collider

The Tevatron in Collider Run II (2001-present) is operating with six times more bunches and many times higher beam intensities and luminosities than in Run I (1992-1995). Beam diagnostics were crucial for the machine start-up and the never-ending luminosity upgrade campaign. We present the overall picture of the Tevatron diagnostics development for Run II, outline machine needs for new instrumentation, present several notable examples that led to Tevatron performance improvements, and discuss the lessons for future colliders