Classes of Terminating Logic Programs

Termination of logic programs depends critically on the selection rule, i.e. the rule that determines which atom is selected in each resolution step. In this article, we classify programs (and queries) according to the selection rules for which they terminate. This is a survey and unified view on different approaches in the literature. For each class, we present a sufficient, for most classes even necessary, criterion for determining that a program is in that class. We study six classes: a program strongly terminates if it terminates for all selection rules; a program input terminates if it terminates for selection rules which only select atoms that are sufficiently instantiated in their input positions, so that these arguments do not get instantiated any further by the unification; a program local delay terminates if it terminates for local selection rules which only select atoms that are bounded w.r.t. an appropriate level mapping; a program left-terminates if it terminates for the usual left-to-right selection rule; a program exists-terminates if there exists a selection rule for which it terminates; finally, a program has bounded nondeterminism if it only has finitely many refutations. We propose a semantics-preserving transformation from programs with bounded nondeterminism into strongly terminating programs. Moreover, by unifying different formalisms and making appropriate assumptions, we are able to establish a formal hierarchy between the different classes.Comment: 50 pages. The following mistake was corrected: In figure 5, the first clause for insert was insert([],X,[X]

DEMON: a Local-First Discovery Method for Overlapping Communities

Community discovery in complex networks is an interesting problem with a number of applications, especially in the knowledge extraction task in social and information networks. However, many large networks often lack a particular community organization at a global level. In these cases, traditional graph partitioning algorithms fail to let the latent knowledge embedded in modular structure emerge, because they impose a top-down global view of a network. We propose here a simple local-first approach to community discovery, able to unveil the modular organization of real complex networks. This is achieved by democratically letting each node vote for the communities it sees surrounding it in its limited view of the global system, i.e. its ego neighborhood, using a label propagation algorithm; finally, the local communities are merged into a global collection. We tested this intuition against the state-of-the-art overlapping and non-overlapping community discovery methods, and found that our new method clearly outperforms the others in the quality of the obtained communities, evaluated by using the extracted communities to predict the metadata about the nodes of several real world networks. We also show how our method is deterministic, fully incremental, and has a limited time complexity, so that it can be used on web-scale real networks.Comment: 9 pages; Proceedings of the 18th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, Beijing, China, August 12-16, 201

Optical and Magnetic Behaviour of Low Dimensional Structures

Low dimensional structures can exhibit unusual properties due to the quantum confinement of electrons. This may manifest itself in any effects that depend on electron behaviour. In this study, the optical and magnetic properties in particular of two types of low dimensional structures are examines. Quantum wires are structures that have macroscopic length scales along one dimension and nanometre length scales in the others. Two Indium induced reconstructions of Silicon surfaces were grown and examined to determine if quantum confinement, a necessary requirement for a quantum wire, did exist for their structures. A UHV compatible Reflectance Anisotropy Spectroscopy (RAS) instrument, that measures the difference in reflectivity of linearly polarised light along orthogonal surface directions, was constructed for this purpose. The Si (111) 4x1-In and Si (001)4x3-In systems were studies. Studies revealed an optical anisotropy of 1.65% for Si (111)4x1-In which, considering the result is from a layer just a monolayer in thickness is very high for a metal-semiconductor system and may be indicative of confinement. Si (111)4x3-In revealed a smaller but still considerable anisotropy of 0.5%. The wires were also studied with Scanning Tunnelling Microscopy (STM) in an effort to conclusively determine the structure. The results gave strong evidence in support of the structural model proposed by Bunk, et al. Scanning-tunnelling spectroscopy provided information on surface states which agree qualitatively with photoemission data. Metallic nanoparticles have been attracting considerable interest due to their novel optical and magnetic properties and as potential components in ‘spintronic’ devices. Iron and cobalt particles were examined by preparing films on Silicon or Graphite (HOPG) substrates. The films were characterised using Atomic Force Microscopy and STM to determine particle coverage, density and distribution. The particles internal composition was examined using Mossbauer spectroscopy and XPS. The films were then examined using a variation of the RAS technique. Magneto Optical Kerr Effect (MOKE) and its time resolved counterpart TRMOKE. Both give an indication of a materials magnetisation by responding to difference in electron spin population. These results were compared to those obtained form SQUID magnetometry. It seems that for monolayers of particles in this size regime. i.e. ~10nm, the optical techniques do not have the required sensitivity to detect a magnetic response, despite their surface specificity. Hence the results at least help to place a lower limit on the techniques’ sensitivity. Iron particles were also examined using Magnetic Force Microscopy, which demonstrated a stronger response over a single particle than a particle cluster. A computational model was generated to explain this interesting effect. This verified the hypothesis that dipolar interactions between the neighbouring particles in a cluster were sufficiently strong to prevent the tip from aligning the particles magnetic moments. In the absence of these interactions, as is the case with an isolated particle, the tip can align the moment

A study of the behaviour of post-tensioned brickwork beams.

SIGLELD:D48252/84 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

The use of fabrics as formwork for concrete structures and elements

This paper presents and describes a series of studies into the use of flexible fabrics as formwork for concrete structures as alternative to conventional rigid formwork