375 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
A Forward Reachability Algorithm for Bounded Timed-Arc Petri Nets
Timed-arc Petri nets (TAPN) are a well-known time extension of the Petri net
model and several translations to networks of timed automata have been proposed
for this model. We present a direct, DBM-based algorithm for forward
reachability analysis of bounded TAPNs extended with transport arcs, inhibitor
arcs and age invariants. We also give a complete proof of its correctness,
including reduction techniques based on symmetries and extrapolation. Finally,
we augment the algorithm with a novel state-space reduction technique
introducing a monotonic ordering on markings and prove its soundness even in
the presence of monotonicity-breaking features like age invariants and
inhibitor arcs. We implement the algorithm within the model-checker TAPAAL and
the experimental results document an encouraging performance compared to
verification approaches that translate TAPN models to UPPAAL timed automata.Comment: In Proceedings SSV 2012, arXiv:1211.587
On Counting the Number of Consistent Genotype Assignments for Pedigrees
Consistency checking of genotype information in pedigrees plays an important role in genetic analysis and for complex pedigrees the computational complexity is critical. We present here a detailed complexity analysis for the problem of counting the number of complete consistent genotype assignments. Our main result is a polynomial time algorithm for counting the number of complete consistent assignments for non-looping pedigrees. We further classify pedigrees according to a number of natural parameters like the number of generations, the number of children per individual and the cardinality of the set of alleles. We show that even if we assume all these parameters as bounded by reasonably small constants, the counting problem becomes computationally hard (#P-complete) for looping pedigrees. The border line for counting problems computable in polynomial time (i.e. belonging to the class FP) and #P-hard problems is completed by showing that even for general pedigrees with unlimited number of generations and alleles but with at most one child per individual and for pedigrees with at most two generations and two children per individual the counting problem is in FP
Identifying Unclear Questions in Community Question Answering Websites
Thousands of complex natural language questions are submitted to community
question answering websites on a daily basis, rendering them as one of the most
important information sources these days. However, oftentimes submitted
questions are unclear and cannot be answered without further clarification
questions by expert community members. This study is the first to investigate
the complex task of classifying a question as clear or unclear, i.e., if it
requires further clarification. We construct a novel dataset and propose a
classification approach that is based on the notion of similar questions. This
approach is compared to state-of-the-art text classification baselines. Our
main finding is that the similar questions approach is a viable alternative
that can be used as a stepping stone towards the development of supportive user
interfaces for question formulation.Comment: Proceedings of the 41th European Conference on Information Retrieval
(ECIR '19), 201
Live Virtual Constructive (LVC): Interface Control Document (ICD) for the LVC Gateway
This Interface Control Document (ICD) documents and tracks the necessary information required for the Live Virtual and Constructive (LVC) systems components as well as protocols for communicating with them in order to achieve all research objectives captured by the experiment requirements. The purpose of this ICD is to clearly communicate all inputs and outputs from the subsystem components
An Experimental Study of a Separated/Reattached Flow Behind a Backward-Facing Step. Re(sub h) = 37,000
An experimental study was carried out to investigate turbulent structure of a two-dimensional incompressible separating/reattaching boundary layer behind a backward-facing step. Hot-wire measurement technique was used to measure three Reynolds stresses and higher-order mean products of velocity fluctuations. The Reynolds number, Re(sub h), based on the step height, h, and the reference velocity, U(sub 0), was 37,000. The upstream oncoming flow was fully developed turbulent boundary layer with the Re(sub theta) = 3600. All turbulent properties, such as Reynolds stresses, increase dramatically downstream of the step within an internally developing mixing layer. Distributions of dimensionless mean velocity, turbulent quantities and antisymmetric distribution of triple velocity products in the separated free shear layer suggest that the shear layer above the recirculating region strongly resembles free-shear mixing layer structure. In the reattachment region close to the wall, turbulent diffusion term balances the rate of dissipation since advection and production terms appear to be negligibly small. Further downstream, production and dissipation begin to dominate other transport processes near the wall indicating the growth of an internal turbulent boundary layer. In the outer region, however, the flow still has a memory of the upstream disturbance even at the last measuring station of 51 step-heights. The data show that the structure of the inner layer recovers at a much faster rate than the outer layer structure. The inner layer structure resembles the near-wall structure of a plane zero pressure-gradient turbulent boundary layer (plane TBL) by 25h to 30h, while the outer layer structure takes presumably over 100h
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
Monotonic Set-Extended Prefix Rewriting and Verification of Recursive Ping-Pong Protocols
Ping-pong protocols with recursive definitions of agents, but without any active intruder, are a Turing powerful model. We show that under the environment sensitive semantics (i.e. by adding an active intruder capable of storing all exchanged messages including full analysis and synthesis of messages) some verification problems become decidable. In particular we give an algorithm to decide control state reachability, a problem related to security properties like secrecy and authenticity. The proof is via a reduction to a new prefix rewriting model called Monotonic Set-extended Prefix rewriting (MSP). We demonstrate further applicability of the introduced model by encoding a fragment of the ccp (concurrent constraint programming) language into MSP
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