Turku Centre for Computer Science

About: Turku Centre for Computer Science is a facility organization based out in Turku, Finland. It is known for research contribution in the topics: Decidability & Word (group theory). The organization has 382 authors who have published 1027 publications receiving 19560 citations.

Computational power of intramolecular gene assembly

Abstract: The process of gene assembly in ciliates, an ancient group of organisms, is one of the most complex instances of DNA manipulation known in any organism. Three molecular operations Id, hi, and dlad have been postulated for the gene assembly process. We propose in this paper a mathematical model for contextual variants of Id and dlad on strings: recombinations can be done only if certain contexts are present. We prove that the proposed model is Turing-universal.

Grouping PCBs with Minimum Feeder Changes

Abstract: In printed circuit board (PCB) assembly, the majority of electronic components are inserted by high-speed placement machines. Although the efficient utilization of the machinery is important for a manufacturer, it is hard to fully realize in high-mix low-volume production environments. On the machine level, the component setup strategy adopted by the manufacturer has a significant impact on the overall production efficiency. Usually, the setup strategy is formulated as a part type grouping problem or a minimum setup problem. In this article, we consider a hybridization of these two problems for the single machine case: The object function to be minimized includes a weighted sum of the number of part type groups (giving the number of setup occasions) and the number of feeder changeovers. We present algorithms for the problem and compare their efficiency.

On one-pass term rewriting

Abstract: Reducing a term with a term rewriting system (TRS) is a highly nondeterministic process and usually no bound for the lengths of the possible reduction sequences can be given in advance. Here we consider two very restrictive strategies of term rewriting, one-pass root-started rewriting and one-pass leaf-started rewriting. If the former strategy is followed, rewriting starts at the root of the given term t and proceeds continuously towards the leaves without ever rewriting any part of the current term which has been produced in a previous rewrite step. When no more rewriting is possible, a one-pass root-started normal form of the term t has been reached. The leaf-started version is similar, but the rewriting is initiated at the leaves and proceeds towards the root. The requirement that rewriting should always concern positions immediately adjacent to parts of the term rewritten in previous steps distinguishes our rewriting strategies from the IO and OI rewriting schemes considered in [5] or [2]. It also implies that the top-down and bottom-up cases are different even for a linear TRS. Let ~ = (E, R) be a TRS over a ranked alphabet E. For any E-tree language T, we denote the sets of one-pass root-started sententiM forms, one-pass root-started normal forms, one-pass leaf-started sentential forms and one-pass leaf-started normal forms of trees in T by lrSn(T), lrNT~(T), I~Sn(T) and I~Nn(T), respectively. We show that the following inclusion problems, where T~ = (E, R) is a left-linear TRS and T1 and T2 are two regular E-tree languages, are decidable. The one-pass root-started sentential form inclusion problem: lrSn(T1) c T2? The one-pass root-started normal form inclusion problem: lrNn(T1) c T2? The one-pass leaf-started sentential form inclusion problem: 1~ Sn(T1) c_ T2? The one-pass leaf-started normal form inclusion problem: 1iNn(T1) c T2? In [9] the inclusion problem for ordinary sentential forms is called the secondorder reachability problem and the problem is shown to be decidable for a TRS T~ which preserves recognizability, i.e. if the set of sentential forms of the trees of

Refinement-Based modeling of 3d nocs

Abstract: Three-dimensional Networks-on-Chip (3D NoC) have recently emerged essentially via the stacking of multiple layers of two-dimensional NoCs. The resulting structures can support a very high level of parallelism for both communication and computation as well as higher speeds, at the cost of increased complexity. To address the potential problems due to the highly complex NoCs, we study them with formal methods. In particular, we base our study on the refinement relation between models of the same system. We propose three abstract models of 3D NoCs, M0, M1, and M2 so that M0 ⊑ M1 ⊑ M2, where ''' denotes the refinement relation. Each of these models provides templates for communication constraints and guarantees the communication correctness. We then show how to employ one of these models for reasoning about the communication correctness of the XYZ-routing algorithm.