394,534 research outputs found
Automata Tutor v3
Computer science class enrollments have rapidly risen in the past decade.
With current class sizes, standard approaches to grading and providing
personalized feedback are no longer possible and new techniques become both
feasible and necessary. In this paper, we present the third version of Automata
Tutor, a tool for helping teachers and students in large courses on automata
and formal languages. The second version of Automata Tutor supported automatic
grading and feedback for finite-automata constructions and has already been
used by thousands of users in dozens of countries. This new version of Automata
Tutor supports automated grading and feedback generation for a greatly extended
variety of new problems, including problems that ask students to create regular
expressions, context-free grammars, pushdown automata and Turing machines
corresponding to a given description, and problems about converting between
equivalent models - e.g., from regular expressions to nondeterministic finite
automata. Moreover, for several problems, this new version also enables
teachers and students to automatically generate new problem instances. We also
present the results of a survey run on a class of 950 students, which shows
very positive results about the usability and usefulness of the tool
Computability and analysis: the legacy of Alan Turing
We discuss the legacy of Alan Turing and his impact on computability and
analysis.Comment: 49 page
Crystal nucleation mechanism in melts of short polymer chains under quiescent conditions and under shear flow
We present a molecular dynamics simulation study of crystal nucleation from
undercooled melts of n-alkanes, and we identify the molecular mechanism of
homogeneous crystal nucleation under quiescent conditions and under shear flow.
We compare results for n-eicosane(C20) and n-pentacontahectane(C150), i.e. one
system below the entanglement length and one above. Under quiescent conditions,
we observe that entanglement does not have an effect on the nucleation
mechanism. For both chain lengths, the chains first align and then straighten
locally. Then the local density increases and finally positional ordering sets
in. At low shear rates the nucleation mechanism is the same as under quiescent
conditions, while at high shear rates the chains align and straighten at the
same time. We report on the effects of shear rate and temperature on the
nucleation rates and estimate the critical shear rates, beyond which the
nucleation rates increase with the shear rate. We show that the viscosity of
the system is not affected by the crystalline nuclei.Comment: 9 page
Different Approaches to Proof Systems
The classical approach to proof complexity perceives proof systems as deterministic, uniform, surjective, polynomial-time computable functions that map strings to (propositional) tautologies. This approach has been intensively studied since the late 70’s and a lot of progress has been made. During the last years research was started investigating alternative notions of proof systems. There are interesting results stemming from dropping the uniformity requirement, allowing oracle access, using quantum computations, or employing probabilism. These lead to different notions of proof systems for which we survey recent results in this paper
Quadtrees as an Abstract Domain
Quadtrees have proved popular in computer graphics and spatial databases as a way of representing regions in two dimensional space. This hierarchical data-structure is flexible enough to support non-convex and even disconnected regions, therefore it is natural to ask whether this datastructure can form the basis of an abstract domain. This paper explores this question and suggests that quadtrees offer a new approach to weakly relational domains whilst their hierarchical structure naturally lends itself to representation with boolean functions
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