278 research outputs found
An Automata-Theoretic Approach to the Verification of Distributed Algorithms
We introduce an automata-theoretic method for the verification of distributed
algorithms running on ring networks. In a distributed algorithm, an arbitrary
number of processes cooperate to achieve a common goal (e.g., elect a leader).
Processes have unique identifiers (pids) from an infinite, totally ordered
domain. An algorithm proceeds in synchronous rounds, each round allowing a
process to perform a bounded sequence of actions such as send or receive a pid,
store it in some register, and compare register contents wrt. the associated
total order. An algorithm is supposed to be correct independently of the number
of processes. To specify correctness properties, we introduce a logic that can
reason about processes and pids. Referring to leader election, it may say that,
at the end of an execution, each process stores the maximum pid in some
dedicated register. Since the verification of distributed algorithms is
undecidable, we propose an underapproximation technique, which bounds the
number of rounds. This is an appealing approach, as the number of rounds needed
by a distributed algorithm to conclude is often exponentially smaller than the
number of processes. We provide an automata-theoretic solution, reducing model
checking to emptiness for alternating two-way automata on words. Overall, we
show that round-bounded verification of distributed algorithms over rings is
PSPACE-complete.Comment: 26 pages, 6 figure
Modelling end-pumped solid state lasers
The operation dynamics of end-pumped solid-state lasers are investigated by means of a spatially resolved numerical rate-equation model and a time-dependent analytical thermal model. The rate-equation model allows the optimization of parameters such as the output coupler transmission and gain medium length, with the aim of improving the laser output performance. The time-dependent analytical thermal model is able to predict the temperature and the corresponding induced thermal stresses on the pump face of quasi-continuous wave (qcw) end-pumped laser rods. Both models are found to be in very good agreement with experimental results
Stable high repetition rate single frequency Q-switched Nd:YAG ring laser
Reliable single-frequency operation of a diode-pumped, Q-switched, Nd:YAG ring laser at high repetition frequencies up to 25kHz has been achieved by active stabilisation of the prelase power. Average powers of 250mW have been obtained for a 1.2 watt diode pump
Weighted Automata and Logics for Infinite Nested Words
Nested words introduced by Alur and Madhusudan are used to capture structures
with both linear and hierarchical order, e.g. XML documents, without losing
valuable closure properties. Furthermore, Alur and Madhusudan introduced
automata and equivalent logics for both finite and infinite nested words, thus
extending B\"uchi's theorem to nested words. Recently, average and discounted
computations of weights in quantitative systems found much interest. Here, we
will introduce and investigate weighted automata models and weighted MSO logics
for infinite nested words. As weight structures we consider valuation monoids
which incorporate average and discounted computations of weights as well as the
classical semirings. We show that under suitable assumptions, two resp. three
fragments of our weighted logics can be transformed into each other. Moreover,
we show that the logic fragments have the same expressive power as weighted
nested word automata.Comment: LATA 2014, 12 page
Propositional Dynamic Logic with Converse and Repeat for Message-Passing Systems
The model checking problem for propositional dynamic logic (PDL) over message
sequence charts (MSCs) and communicating finite state machines (CFMs) asks,
given a channel bound , a PDL formula and a CFM ,
whether every existentially -bounded MSC accepted by
satisfies . Recently, it was shown that this problem is
PSPACE-complete.
In the present work, we consider CRPDL over MSCs which is PDL equipped with
the operators converse and repeat. The former enables one to walk back and
forth within an MSC using a single path expression whereas the latter allows to
express that a path expression can be repeated infinitely often. To solve the
model checking problem for this logic, we define message sequence chart
automata (MSCAs) which are multi-way alternating parity automata walking on
MSCs. By exploiting a new concept called concatenation states, we are able to
inductively construct, for every CRPDL formula , an MSCA precisely
accepting the set of models of . As a result, we obtain that the model
checking problem for CRPDL and CFMs is still in PSPACE
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