384 research outputs found
What's Decidable About Sequences?
We present a first-order theory of sequences with integer elements,
Presburger arithmetic, and regular constraints, which can model significant
properties of data structures such as arrays and lists. We give a decision
procedure for the quantifier-free fragment, based on an encoding into the
first-order theory of concatenation; the procedure has PSPACE complexity. The
quantifier-free fragment of the theory of sequences can express properties such
as sortedness and injectivity, as well as Boolean combinations of periodic and
arithmetic facts relating the elements of the sequence and their positions
(e.g., "for all even i's, the element at position i has value i+3 or 2i"). The
resulting expressive power is orthogonal to that of the most expressive
decidable logics for arrays. Some examples demonstrate that the fragment is
also suitable to reason about sequence-manipulating programs within the
standard framework of axiomatic semantics.Comment: Fixed a few lapses in the Mergesort exampl
An approach to computing downward closures
The downward closure of a word language is the set of all (not necessarily
contiguous) subwords of its members. It is well-known that the downward closure
of any language is regular. While the downward closure appears to be a powerful
abstraction, algorithms for computing a finite automaton for the downward
closure of a given language have been established only for few language
classes.
This work presents a simple general method for computing downward closures.
For language classes that are closed under rational transductions, it is shown
that the computation of downward closures can be reduced to checking a certain
unboundedness property.
This result is used to prove that downward closures are computable for (i)
every language class with effectively semilinear Parikh images that are closed
under rational transductions, (ii) matrix languages, and (iii) indexed
languages (equivalently, languages accepted by higher-order pushdown automata
of order 2).Comment: Full version of contribution to ICALP 2015. Comments welcom
Finite Automata for the Sub- and Superword Closure of CFLs: Descriptional and Computational Complexity
We answer two open questions by (Gruber, Holzer, Kutrib, 2009) on the
state-complexity of representing sub- or superword closures of context-free
grammars (CFGs): (1) We prove a (tight) upper bound of on
the size of nondeterministic finite automata (NFAs) representing the subword
closure of a CFG of size . (2) We present a family of CFGs for which the
minimal deterministic finite automata representing their subword closure
matches the upper-bound of following from (1).
Furthermore, we prove that the inequivalence problem for NFAs representing sub-
or superword-closed languages is only NP-complete as opposed to PSPACE-complete
for general NFAs. Finally, we extend our results into an approximation method
to attack inequivalence problems for CFGs
Regulation of platelet-leukocyte interaction in simulated ECC: attenuation with heparin surface modification
Algorithmic Analysis of Array-Accessing Programs
For programs whose data variables range over Boolean or finite domains, program verification is decidable, and this forms the basis of recent tools for software model checking. In this paper, we consider algorithmic verification of programs that use Boolean variables, and in addition, access a single array whose length is potentially unbounded, and whose elements range over pairs from Σ × D, where Σ is a finite alphabet and D is a potentially unbounded data domain. We show that the reachability problem, while undecidable in general, is (1) Pspace-complete for programs in which the array-accessing for-loops are not nested, (2) solvable in Ex-pspace for programs with arbitrarily nested loops if array elements range over a finite data domain, and (3) decidable for a restricted class of programs with doubly-nested loops. The third result establishes connections to automata and logics defining languages over data words
Recovery in Mind: A Recovery College's journey through the Covid-19 pandemic.
INTRODUCTION: The Covid-19 restrictions of 2020-2021 are known to have undermined the UK population's mental health. Working alongside staff, peer trainers and students at Recovery in Mind (RiM), a Recovery College (RC) in West Berkshire, England, this mixed-methods study is amongst the first to investigate how an RC has responded to the pandemic. METHODS: Working in co-production with RiM staff and peer-trainers, this study employed a mixed-methods design, gathering Warwick-Edinburgh Mental Wellbeing Scale (WEMWBS) well-being outcome measures by questionnaire and student experience, learning and co-production by interviews. FINDINGS: This research found that RiM continued to produce demonstrable improvements in student mental health. Students welcomed the way that RiM adapted to offering online and socially distanced provisions. Students valued the skills that RiM taught and the way that RiM courses reinforced prior learning; above this, however, they valued the mutual support and sense of community that participation provided. CONCLUSION: This study underlines the value of RCs maintaining 'hidden curriculums' of peer support and community involvement. This research emphasizes co-production as not only a tool for empowerment or service improvement but as a valuable skill for personal mental health recovery. Even when operating under the most unforeseen or challenging of conditions, RCs should always endeavour to prioritize and maintain co-production. PATIENT OR PUBLIC CONTRIBUTION: In accordance with the RC ethos, this was an entirely co-produced study, with academic researchers and RiM staff and peer trainers working democratically in partnership with one another to design and manage the study and to write up and disseminate findings. To ensure the independence and rigour of findings, data analysis was undertaken by external academic researchers
Languages ordered by the subword order
We consider a language together with the subword relation, the cover
relation, and regular predicates. For such structures, we consider the
extension of first-order logic by threshold- and modulo-counting quantifiers.
Depending on the language, the used predicates, and the fragment of the logic,
we determine four new combinations that yield decidable theories. These results
extend earlier ones where only the language of all words without the cover
relation and fragments of first-order logic were considered
Heating rate and electrode charging measurements in a scalable, microfabricated, surface-electrode ion trap
We characterise the performance of a surface-electrode ion "chip" trap
fabricated using established semiconductor integrated circuit and
micro-electro-mechanical-system (MEMS) microfabrication processes which are in
principle scalable to much larger ion trap arrays, as proposed for implementing
ion trap quantum information processing. We measure rf ion micromotion parallel
and perpendicular to the plane of the trap electrodes, and find that on-package
capacitors reduce this to <~ 10 nm in amplitude. We also measure ion trapping
lifetime, charging effects due to laser light incident on the trap electrodes,
and the heating rate for a single trapped ion. The performance of this trap is
found to be comparable with others of the same size scale.Comment: 6 pages, 10 figure
High-Resolution Optical Functional Mapping of the Human Somatosensory Cortex
Non-invasive optical imaging of brain function has been promoted in a number of fields in which functional magnetic resonance imaging (fMRI) is limited due to constraints induced by the scanning environment. Beyond physiological and psychological research, bedside monitoring and neurorehabilitation may be relevant clinical applications that are yet little explored. A major obstacle to advocate the tool in clinical research is insufficient spatial resolution. Based on a multi-distance high-density optical imaging setup, we here demonstrate a dramatic increase in sensitivity of the method. We show that optical imaging allows for the differentiation between activations of single finger representations in the primary somatosensory cortex (SI). Methodologically our findings confirm results in a pioneering study by Zeff et al. (2007) and extend them to the homuncular organization of SI. After performing a motor task, eight subjects underwent vibrotactile stimulation of the little finger and the thumb. We used a high-density diffuse-optical sensing array in conjunction with optical tomographic reconstruction. Optical imaging disclosed three discrete activation foci one for motor and two discrete foci for vibrotactile stimulation of the first and fifth finger, respectively. The results were co-registered to the individual anatomical brain anatomy (MRI) which confirmed the localization in the expected cortical gyri in four subjects. This advance in spatial resolution opens new perspectives to apply optical imaging in the research on plasticity notably in patients undergoing neurorehabilitation
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