604 research outputs found
Calculating Colimits Compositionally
We show how finite limits and colimits can be calculated compositionally
using the algebras of spans and cospans, and give as an application a proof of
the Kleene Theorem on regular languages
Studies on aphid transmission of potato virus Y
Imperial Users onl
Motion Descriptions in English and Greek: A Cross-Typological Developmental Study of Conversations and Narratives
Theoretical claims about typologically constrained differences in how speakers habitually describe physical motion are tested through three cross-linguistic developmental studies. Three types of data are analyzed in Greek and English, languages here characterized respectively as Verb- and Satellite-framed in the coding of motion: spontaneous conversations between adults and children aged 1;8–4;6 as well as two types of narratives elicited through pictures and a film from 4-, 7-, 10-year olds and adults. Results show, on the one hand, largely predictable cross-linguistic differences, with overall greater attention paid to manner in English than in Greek and different patterns for coding path. On the other hand, the very appearance as well as intensity of typological effects also depend upon various interacting factors: the precise ways of measuring them, the age of speakers, type, content and communicative exigencies of the discourse as well as the detailed structural characteristics of a language
Towards Realizability Checking of Contracts using Theories
Virtual integration techniques focus on building architectural models of
systems that can be analyzed early in the design cycle to try to lower cost,
reduce risk, and improve quality of complex embedded systems. Given appropriate
architectural descriptions and compositional reasoning rules, these techniques
can be used to prove important safety properties about the architecture prior
to system construction. Such proofs build from "leaf-level" assume/guarantee
component contracts through architectural layers towards top-level safety
properties. The proofs are built upon the premise that each leaf-level
component contract is realizable; i.e., it is possible to construct a component
such that for any input allowed by the contract assumptions, there is some
output value that the component can produce that satisfies the contract
guarantees. Without engineering support it is all too easy to write leaf-level
components that can't be realized. Realizability checking for propositional
contracts has been well-studied for many years, both for component synthesis
and checking correctness of temporal logic requirements. However, checking
realizability for contracts involving infinite theories is still an open
problem. In this paper, we describe a new approach for checking realizability
of contracts involving theories and demonstrate its usefulness on several
examples.Comment: 15 pages, to appear in NASA Formal Methods (NFM) 201
Staphylococcus aureus DivIB is a peptidoglycan-binding protein that is required for a morphological checkpoint in cell division
Bacterial cell division is a fundamental process that requires the coordinated actions of a number of proteins which form a complex macromolecular machine known as the divisome. The membrane-spanning proteins DivIB and its orthologue FtsQ are crucial divisome components in Gram-positive and Gram-negative bacteria respectively. However, the role of almost all of the integral division proteins, including DivIB, still remains largely unknown. Here we show that the extracellular domain of DivIB is able to bind peptidoglycan and have mapped the binding to its β subdomain. Conditional mutational studies show that divIB is essential for Staphylococcus aureus growth, while phenotypic analyses following depletion of DivIB results in a block in the completion, but not initiation, of septum formation. Localisation studies suggest that DivIB only transiently localises to the division site and may mark previous sites of septation. We propose that DivIB is required for a molecular checkpoint during division to ensure the correct assembly of the divisome at midcell and to prevent hydrolytic growth of the cell in the absence of a completed septum
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