174 research outputs found
Semantics of multi-mode DAE systems
Deliverable D.4.1.1 of the ITEA2 Modrio collaborative projectHybrid systems modelers exhibit a number of difficulties related to the mix of continuous and discrete dynamics and sensitivity to the discretization scheme. Modular modeling, where subsystems models can be simply assembled with no rework, calls for using Differential Algebraic Equations (DAE). In turn, DAE are strictly more difficult than ODE. They require sophisticated pre-processing using various notions of index before they can be submitted to a solver. In this report we study some fundamental issues raised by the modeling and simulation of hybrid systems involving DAEs. The objective of this work is to serve for the evolution and the design of future releases of the Modelica language for such systems. We focus on the following questions: * What is the proper notion of index for a hybrid DAE system? * What are the primitive statements needed for a DAE hybrid systems modeler? The differentiation index for DAE explicitly relies on everything being differentiable. Therefore, generalizations to hybrid systems must be done with caution. We propose relying on non-standard analysis for this. Non-standard analysis formalizes differential equations as discrete step transition systems with infinitesimal time basis. We can thus bring hybrid DAE systems to their nonstandard form, where the notion of difference index can be firmly used. From this study, general hints for future releases of Modelica can be drawn
Loosely Time-Triggered Architectures: Improvements and Comparisons
International audienceLoosely Time-Triggered Architectures (LTTAs) are a proposal for constructing distributed embedded control systems. They build on the quasi-periodic architecture, where computing units execute 'almost periodically', by adding a thin layer of middleware that facilitates the implementation of synchronous applications.In this paper, we show how the deployment of a synchronous application on a quasi-periodic architecture can be modeled using a synchronous formalism. Then we detail two protocols, Back-Pressure LTTA, reminiscent of elastic circuits, and Time-Based LTTA, based on waiting. Compared to previous work, we present controller models that can be compiled for execution and a simplified version of the Time-Based protocol. We also compare the LTTA approach with architectures based on clock synchronization
Collection and processing of shipboard ADCP velocities from the Barents Sea Polar Front Experiment
The Barents Sea Polar Front Experiment was a combined physical oceanography and acoustic tomography field study
which took place from 6-26 August 1992. Both shipboard and moored data were collected in a 80 x 70 km experimental
region on the south flank of Sptisbergen Bank about 60 km east of Bear Island. Of principal interest in this report are the
data from an Acoustic Doppler Current Profier (ADCP) which was operated continuously during the experimental period as
a part of the shipboard instrumentation aboard the USNS Barlett. The data from eight current meters deployed on three
moorings in the experimental region are used to supplement the ADCP analysis. Preliminary results showed that velocities
in the experimental region were dominated by semi-diurnal tides. The strong tidal oscilations dictated the use of a tide
removal scheme to extract a steady flow component from the space-time grid of ADCP velocities. This report describes the
configuration and operation of the ADCP, the space-time sampling grid on which the data were collected, the determination
of absolute velocity from the ADCP measurements, and the application and results of a tide removal technique which
allowed estimation of the sub-tidal flow.Funding was provided by the Office of Naval Research under
Grant No. NOOOI4-90-J-1359
Myocardial perfusion imaging with a novel selective A2a adenosine receptor agonist (CVT-3146): Important differences in radiotracer behavior
A colimit decomposition for homotopy algebras in Cat
Badzioch showed that in the category of simplicial sets each homotopy algebra
of a Lawvere theory is weakly equivalent to a strict algebra. In seeking to
extend this result to other contexts Rosicky observed a key point to be that
each homotopy colimit in simplicial sets admits a decomposition into a homotopy
sifted colimit of finite coproducts, and asked the author whether a similar
decomposition holds in the 2-category of categories Cat. Our purpose in the
present paper is to show that this is the case.Comment: Some notation changed; small amount of exposition added in intr
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