52 research outputs found
Properties of Distributed Time Arc Petri Nets
In recent work we started a research on a distributed-timed extension of Petri nets where time parameters are associated with tokens and arcs carry constraints that qualify the age of tokens required for enabling. This formalism enables to model e.g. hardware architectures like GALS. We give a formal definition of process semantics for our model and investigate several properties of local versus global timing: expressiveness, reachability and coverability
Performance evaluation of an emergency call center: tropical polynomial systems applied to timed Petri nets
We analyze a timed Petri net model of an emergency call center which
processes calls with different levels of priority. The counter variables of the
Petri net represent the cumulated number of events as a function of time. We
show that these variables are determined by a piecewise linear dynamical
system. We also prove that computing the stationary regimes of the associated
fluid dynamics reduces to solving a polynomial system over a tropical
(min-plus) semifield of germs. This leads to explicit formul{\ae} expressing
the throughput of the fluid system as a piecewise linear function of the
resources, revealing the existence of different congestion phases. Numerical
experiments show that the analysis of the fluid dynamics yields a good
approximation of the real throughput.Comment: 21 pages, 4 figures. A shorter version can be found in the
proceedings of the conference FORMATS 201
A First Look at Rotation in Inactive Late-Type M Dwarfs
We have examined the relationship between rotation and activity in 14
late-type (M6-M7) M dwarfs, using high resolution spectra taken at the W.M.
Keck Observatory and flux-calibrated spectra from the Sloan Digital Sky Survey.
Most were selected to be inactive at a spectral type where strong H-alpha
emission is quite common. We used the cross-correlation technique to quantify
the rotational broadening; six of the stars in our sample have vsini > 3.5
km/s. Our most significant and perplexing result is that three of these stars
do not exhibit H-alpha emission, despite rotating at velocities where previous
work has observed strong levels of magnetic field and stellar activity. Our
results suggest that rotation and activity in late-type M dwarfs may not always
be linked, and open several additional possibilities including a
rotationally-dependent activity threshold, or a possible dependence on stellar
parameters of the Rossby number at which magnetic/activity "saturation" takes
place in fully convective stars.Comment: 8 pages, 4 figures, accepted for publication in Ap
Weak Bisimulation Approximants
Bisimilarity ⌠and weak bisimilarity â are canonical notions of equivalence between processes, which are defined co-inductively, but may be approached â and even reached â by their (transfinite) inductively-defined approximants âŒÎ± and âα. For arbitrary processes this approximation may need to climb arbitrarily high through the infinite ordinals before stabilising. In this paper we consider a simple yet well-studied process algebra, the Basic Parallel Processes (BPP), and investigate for this class of processes the minimal ordinal α such that â = âα. The main tool in our investigation is a novel proof of Dicksonâs Lemma. Unlike classical proofs, the proof we provide gives rise to a tight ordinal bound, of Ï n, on the order type of non-increasing sequences of n-tuples of natural numbers. With this we are able to reduce a long-standing bound on the approximation hierarchy for weak bisimilarity â over BPP, and show that â = âÏ Ï
Formal Model Engineering for Embedded Systems Using Real-Time Maude
This paper motivates why Real-Time Maude should be well suited to provide a
formal semantics and formal analysis capabilities to modeling languages for
embedded systems. One can then use the code generation facilities of the tools
for the modeling languages to automatically synthesize Real-Time Maude
verification models from design models, enabling a formal model engineering
process that combines the convenience of modeling using an informal but
intuitive modeling language with formal verification. We give a brief overview
six fairly different modeling formalisms for which Real-Time Maude has provided
the formal semantics and (possibly) formal analysis. These models include
behavioral subsets of the avionics modeling standard AADL, Ptolemy II
discrete-event models, two EMF-based timed model transformation systems, and a
modeling language for handset software.Comment: In Proceedings AMMSE 2011, arXiv:1106.596
Pediatric and adult-onset HCM mutations in the myosin motor domain have similar properties
Hypertrophic Cardiomyopathy (HCM) is a common genetic disorder that typically involves left ventricular hypertrophy and abnormal cardiac contractility. Mutations in ÎČ-MyHC are a major cause of HCM and are typically characterized with cardiac hypercontractility, but the specific mechanistic changes to myosin function that lead to the disease remain incompletely understood. Predicting the severity of any single ÎČ-MyHC mutation is hindered by a lack of detailed evaluation at the molecular level. In addition, since the cardiomyopathy can take 20 - 40 years to develop, the severity of the mutations must be somewhat subtle. We hypothesized that mutations which result in childhood cardiomyopathies may show a more severe indication of molecular changes in myosin and be therefore easier to identify. In this work, we performed steady-state and transient kinetics analysis of the myosin carrying one of eight miss sense mutations in the motor domain. Five of these have been identified in childhood cardiomyopathies. The derived parameters were used to model the ATP driven cross bridge. Contrary to our hypothesis, the results show no clear differences between early and late onset HCM mutations. Despite the lack of distinction between early and late onset HCM, the predicted A·M·D occupancy for [A] = 3 Kapp along with the closely related Duty Ratio (DR) and the measured ATPases all change in parallel (in both sign and degree of change) compared to the WT values. Six of the eight HCM mutations are clearly distinct from a set of DCM mutations previously characterized
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