A Unifying View of Loosely Time-Triggered Architectures

Cyber-Physical Systems require distributed architectures to support safety critical real-time control. Hermann Kopetz' Time-Triggered Architecture (TTA) has been proposed as both an architecture and a comprehensive paradigm for systems architecture, for such systems. TTA offers the programmer a logical discrete time compliant with synchronous programming, together with timing bounds. A clock synchronization protocol is required, unless the local clocks used themselves provide the recquired accuracy. To relax the strict requirements on synchronization imposed by TTA, Loosely Time-Triggered Architectures (LTTA) have been proposed. In LTTA, computation and communication units are all triggered by autonomous, unsynchronized, clocks. Communication media act as shared memories between writers and readers and communication is non blocking. This is at the price of communication artifacts (such as duplication or loss of data), which must be compensated for by using some "LTTA protocol". In this paper we pursue our previous work by providing a unified presentation of the two variants of LTTA (token- and time-based), with simplified analyses. We compare these two variants regarding performance and robustness and we provide ways to combine them. This report was prepared for a lecture in Gérard Berry's seminar series at the Collège de France, March 5, 2014; it is a corrected version of a paper, which appeared at Emsoft'2010. It is dedicated to our close friend Paul Caspi who died in April 2012.Les infrastructures de calcul distribuées pour le contrôle des systèmes embarqués critiques requièrent des propriétés particulières destinées à préserver les caractéristiques attendues du contrôleur. Les architectures TTA (Time-Triggered Architectures) ont été proposées par Hermann Kopetz, à la fois comme une architecture de calcul et comme une méthodologie de conception des systèmes. TTA offre au programmeur un temps logique conforme à celui de la programmation synchrone, avec en outre un contrôle strict du temps. Il requiert un protocole de synchronisation entre les horloges du système réparti. Pour affaiblir ces hypothèses, les architectures LTTA (Loosely Time-Triggered Architectures) ont été proposées récemment. Dans LTTA, les calculs et les communications sont rythmées par des horloges locales, non synchronisées. Les supports de communication se comportent comme des mémoires partagées. La communication est donc non-bloquante. Ce type de communiccation crée évidemment des artefacts à combattre par un protocole dit "LTTA". Dans cet article nous présentons une approche unifiée des deux techniques connues pour ce type de protocole, reposant sur l'usage, soit de jetons, soit du temps. On compare ces deux variantes et on étudie leur performance. Le présent rapport est une version corrigée d'un article paru à Emsoft'2010. Il est dédié à notre très cher ami Paul Caspi, décédé en Avril 2012

First NuSTAR Limits on Quiet Sun Hard X-Ray Transient Events

We present the first results of a search for transient hard X-ray (HXR) emission in the quiet solar corona with the \textit{Nuclear Spectroscopic Telescope Array} (\textit{NuSTAR}) satellite. While \textit{NuSTAR} was designed as an astrophysics mission, it can observe the Sun above 2~keV with unprecedented sensitivity due to its pioneering use of focusing optics. \textit{NuSTAR} first observed quiet Sun regions on 2014 November 1, although out-of-view active regions contributed a notable amount of background in the form of single-bounce (unfocused) X-rays. We conducted a search for quiet Sun transient brightenings on time scales of 100 s and set upper limits on emission in two energy bands. We set 2.5--4~keV limits on brightenings with time scales of 100 s, expressed as the temperature T and emission measure EM of a thermal plasma. We also set 10--20~keV limits on brightenings with time scales of 30, 60, and 100 s, expressed as model-independent photon fluxes. The limits in both bands are well below previous HXR microflare detections, though not low enough to detect events of equivalent T and EM as quiet Sun brightenings seen in soft X-ray observations. We expect future observations during solar minimum to increase the \textit{NuSTAR} sensitivity by over two orders of magnitude due to higher instrument livetime and reduced solar background.Comment: 11 pages, 7 figures; accepted for publication in The Astrophysical Journa

Some Issues In Model-Based Development for Embedded Control Systems

Abstract This presentation aims to discuss the needs for better and more solid foundations of model-based development in embedded control systems. Three particular points are discussed: a comparison between modelbased development in control and in computer sciences, the need for a sampling theory of discrete event systems and the need for precise implementation methods based on preemptive scheduling

Signatures of arithmetic simplicity in metabolic network architecture

Metabolic networks perform some of the most fundamental functions in living cells, including energy transduction and building block biosynthesis. While these are the best characterized networks in living systems, understanding their evolutionary history and complex wiring constitutes one of the most fascinating open questions in biology, intimately related to the enigma of life's origin itself. Is the evolution of metabolism subject to general principles, beyond the unpredictable accumulation of multiple historical accidents? Here we search for such principles by applying to an artificial chemical universe some of the methodologies developed for the study of genome scale models of cellular metabolism. In particular, we use metabolic flux constraint-based models to exhaustively search for artificial chemistry pathways that can optimally perform an array of elementary metabolic functions. Despite the simplicity of the model employed, we find that the ensuing pathways display a surprisingly rich set of properties, including the existence of autocatalytic cycles and hierarchical modules, the appearance of universally preferable metabolites and reactions, and a logarithmic trend of pathway length as a function of input/output molecule size. Some of these properties can be derived analytically, borrowing methods previously used in cryptography. In addition, by mapping biochemical networks onto a simplified carbon atom reaction backbone, we find that several of the properties predicted by the artificial chemistry model hold for real metabolic networks. These findings suggest that optimality principles and arithmetic simplicity might lie beneath some aspects of biochemical complexity

Status of Muon Collider Research and Development and Future Plans

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides continued work on the parameters of a 3-4 and 0.5 TeV center-of-mass (CoM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (CoM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay ($\pi \to \mu \nu_{\mu}$) channel, muon cooling, acceleration, storage in a collider ring and the collider detector. We also present theoretical and experimental R & D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the R & D since the Feasibility Study of Muon Colliders presented at the Snowmass'96 Workshop [R. B. Palmer, A. Sessler and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].Comment: 95 pages, 75 figures. Submitted to Physical Review Special Topics, Accelerators and Beam

The role of diet in the aetiopathogenesis of inflammatory bowel disease

Crohn’s disease and ulcerative colitis, collectively known as IBD, are chronic inflammatory disorders of the gastrointestinal tract. Although the aetiopathogenesis of IBD is largely unknown, it is widely thought that diet has a crucial role in the development and progression of IBD. Indeed, epidemiological and genetic association studies have identified a number of promising dietary and genetic risk factors for IBD. These preliminary studies have led to major interest in investigating the complex interaction between diet, host genetics, the gut microbiota and immune function in the pathogenesis of IBD. In this Review, we discuss the recent epidemiological, gene–environment interaction, microbiome and animal studies that have explored the relationship between diet and the risk of IBD. In addition, we highlight the limitations of these prior studies, in part by explaining their contradictory findings, and review future directions

A Unifying View of Loosely Time-Triggered Architectures

Cyber-Physical Systems require distributed architectures to support safety critical real-time control. Hermann Kopetz' Time-Triggered Architecture (TTA) has been proposed as both an architecture and a comprehensive paradigm for systems architecture, for such systems. TTA offers the programmer a logical discrete time compliant with synchronous programming, together with timing bounds. A clock synchronization protocol is required, unless the local clocks used themselves provide the recquired accuracy. To relax the strict requirements on synchronization imposed by TTA, Loosely Time-Triggered Architectures (LTTA) have been proposed. In LTTA, computation and communication units are all triggered by autonomous, unsynchronized, clocks. Communication media act as shared memories between writers and readers and communication is non blocking. This is at the price of communication artifacts (such as duplication or loss of data), which must be compensated for by using some "LTTA protocol". In this paper we pursue our previous work by providing a unified presentation of the two variants of LTTA (token- and time-based), with simplified analyses. We compare these two variants regarding performance and robustness and we provide ways to combine them. This report was prepared for a lecture in Gérard Berry's seminar series at the Collège de France, March 5, 2014; it is a corrected version of a paper, which appeared at Emsoft'2010. It is dedicated to our close friend Paul Caspi who died in April 2012.Les infrastructures de calcul distribuées pour le contrôle des systèmes embarqués critiques requièrent des propriétés particulières destinées à préserver les caractéristiques attendues du contrôleur. Les architectures TTA (Time-Triggered Architectures) ont été proposées par Hermann Kopetz, à la fois comme une architecture de calcul et comme une méthodologie de conception des systèmes. TTA offre au programmeur un temps logique conforme à celui de la programmation synchrone, avec en outre un contrôle strict du temps. Il requiert un protocole de synchronisation entre les horloges du système réparti. Pour affaiblir ces hypothèses, les architectures LTTA (Loosely Time-Triggered Architectures) ont été proposées récemment. Dans LTTA, les calculs et les communications sont rythmées par des horloges locales, non synchronisées. Les supports de communication se comportent comme des mémoires partagées. La communication est donc non-bloquante. Ce type de communiccation crée évidemment des artefacts à combattre par un protocole dit "LTTA". Dans cet article nous présentons une approche unifiée des deux techniques connues pour ce type de protocole, reposant sur l'usage, soit de jetons, soit du temps. On compare ces deux variantes et on étudie leur performance. Le présent rapport est une version corrigée d'un article paru à Emsoft'2010. Il est dédié à notre très cher ami Paul Caspi, décédé en Avril 2012