Empirically Constrained Color-Temperature Relations. II. uvby

(Abriged) A new grid of theoretical color indices for the Stromgren uvby photometric system has been derived from MARCS model atmospheres and SSG synthetic spectra for cool dwarf and giant stars. At warmer temperatures this grid has been supplemented with the synthetic uvby colors from recent Kurucz atmospheric models without overshooting. Our transformations appear to reproduce the observed colors of extremely metal-poor turnoff and giant stars (i.e., [Fe/H]<-2). Due to a number of assumptions made in the synthetic color calculations, however, our color-temperature relations for cool stars fail to provide a suitable match to the uvby photometry of both cluster and field stars having [Fe/H]>-2. To overcome this problem, the theoretical indices at intermediate and high metallicities have been corrected using a set of color calibrations based on field stars having accurate IRFM temperature estimates and spectroscopic [Fe/H] values. Encouragingly, isochrones that employ the transformations derived in this study are able to reproduce the observed CMDs (involving u-v, v-b, and b-y colors) for a number of open and globular clusters (including M92, M67, the Hyades, and 47Tuc) rather well. Moreover, our interpretations of such data are very similar, if not identical, with those given by VandenBerg & Clem (2003, AJ, 126, 778) from a consideration of BV(RI)c observations for the same clusters. In the present investigation, we have also analyzed the observed Stromgren photometry for the classic Population II subdwarfs, compared our "final" (b-y)-Teff relationship with those derived empirically in a number of recent studies, and examined in some detail the dependence of the m1 index on [Fe/H].Comment: 70 pages, 26 figures. Accepted for publication in AJ (Feb 2004). Postscript version with high resolution figures and complete Table 3 available at http://astrowww.phys.uvic.ca/~jclem/uvb

Formal timing analysis of CAN-to-Ethernet gateway strategies in automotive networks

International audienceDue to increased bandwidth and scalability demands, Ethernet technology is finding its way into recent in-vehicle networks. Tomorrow's heterogeneous networks will feature legacy buses [e.g. controller area network (CAN) or FlexRay] as well as high-speed Ethernet devices, connected by switches and gateways. As Ethernet offers significantly larger frame sizes than CAN, the efficient transmission of CAN data over an Ethernet backbone depends heavily on the way this data is multiplexed into Ethernet frames. This article focuses on the timing impact introduced by various CAN/Ethernet multiplexing strategies at the gateways. We present a formal analysis method to derive upper bounds on end-to-end latencies for complex multiplexing strategies, which is key for the design of safety-critical real-time systems. We capture complex inter-domain signal paths spanning multiple buses, gateways, and switches and show the applicability in a realistic automotive setu

Building Timing Predictable Embedded Systems

A large class of embedded systems is distinguished from general purpose computing systems by the need to satisfy strict requirements on timing, often under constraints on available resources. Predictable system design is concerned with the challenge of building systems for which timing requirements can be guaranteed a priori. Perhaps paradoxically, this problem has become more difficult by the introduction of performance-enhancing architectural elements, such as caches, pipelines, and multithreading, which introduce a large degree of nondeterminism and make guarantees harder to provide. The intention of this paper is to summarize current state-of-the-art in research concerning how to build predictable yet performant systems. We suggest precise definitions for the concept of “predictability”, and present predictability concerns at different abstractions levels in embedded software design. First, we consider timing predictability of processor instruction sets. Thereafter, We consider how programming languages can be equipped with predictable timing semantics, covering both a language-based approach based on the synchronous paradigm, as well as an environment that provides timing semantics for a mainstream programming language (in this case C). We present techniques for achieving timing predictability on multicores. Finally we discuss how to handle predictability at the level of networked embedded systems, where randomly occurring errors must be considered

Building Timing Predictable Embedded Systems

International audienceA large class of embedded systems is distinguished from general purpose computing systems by the need to satisfy strict requirements on timing, often under constraints on available resources. Predictable system design is concerned with the challenge of building systems for which timing requirements can be guaranteed a priori. Perhaps paradoxically, this problem has become more difficult by the introduction of performance-enhancing architectural elements, such as caches, pipelines, and multithreading, which introduce a large degree of uncertainty and make guarantees harder to provide. The intention of this paper is to summarize current state-of-the-art in research concerning how to build predictable yet performant systems. We sug- gest precise definitions for the concept of “predictability”, and present predictability concerns at different abstraction levels in embedded system design. First, we consider timing predictability of processor instruction sets. Thereafter, we consider how programming languages can be equipped with predictable timing semantics, covering both a language-based approach based on the synchronous programming paradigm, as well as an environment that provides timing semantics for a mainstream programming language (in this case C). We present techniques for achieving timing predictability on multicores. Finally we discuss how to handle predictability at the level of networked embedded systems, where randomly occurring errors must be considered