Efficient structural symmetry breaking for constraint satisfaction problems

Symmetry breaking for constraint satisfaction problems (CSPs) has attracted considerable attention in recent years. Various general schemes have been proposed to eliminate symmetries. In general, these schemes may take exponential space or time to eliminate all the symmetries. We identify several classes of CSPs that encompass many practical problems and for which symmetry breaking for various forms of value and variable interchangeability is tractable using dedicated search procedures or symmetry-breaking constraints that allow nogoods and their symmetrically equivalent solutions to be stored and checked efficiently

An interactive semantics of logic programming

We apply to logic programming some recently emerging ideas from the field of reduction-based communicating systems, with the aim of giving evidence of the hidden interactions and the coordination mechanisms that rule the operational machinery of such a programming paradigm. The semantic framework we have chosen for presenting our results is tile logic, which has the advantage of allowing a uniform treatment of goals and observations and of applying abstract categorical tools for proving the results. As main contributions, we mention the finitary presentation of abstract unification, and a concurrent and coordinated abstract semantics consistent with the most common semantics of logic programming. Moreover, the compositionality of the tile semantics is guaranteed by standard results, as it reduces to check that the tile systems associated to logic programs enjoy the tile decomposition property. An extension of the approach for handling constraint systems is also discussed.Comment: 42 pages, 24 figure, 3 tables, to appear in the CUP journal of Theory and Practice of Logic Programmin

Adjunct extraposition: base-generation or movement?

It has been argued that extraposition from DP is derived differently according to whether a complement or an adjunct is extraposed, with complement extraposition being derived by movement and adjunct extraposition being derived via covert QR of the host DP plus Late Merge of the adjunct (Fox & Nissenbaum 1999). We argue that adjunct extraposition is itself derivationally ambiguous, and may be derived either by movement of the adjunct or by base-generation of the adjunct in extraposed position. Accordingly, we argue for a relaxation of the strictly compositional view that nominal modification is always mediated by syntactic sisterhood. We argue that while base-generated extraposition is possible with quantificational host DPs, adjunct extraposition from definites must be derived by movement. This accounts for a number of asymmetries between extraposition from definites and from other types of DP, concerning reconstruction for Condition C, scope reconstruction, and information-structural restrictions on extraposition

Stochastic models for quality of service of component connectors

The intensifying need for scalable software has motivated modular development and using systems distributed over networks to implement large-scale applications. In Service-oriented Computing, distributed services are composed to provide large-scale services with a specific functionality. In this way, reusability of existing services can be increased. However, due to the heterogeneity of distributed software systems, software composition is not easy and requires additional mechanisms to impose some form of a coordination on a distributed software system. Besides functional correctness, a composed service must satisfy various quantitative requirements for its clients, which are generically called its quality of service (QoS). Particularly, it is tricky to obtain the overall QoS of a composed service even if the QoS information of its constituent distributed services is given. In this thesis, we propose Stochastic Reo to specify software composition with QoS aspects and its compositional semantic models. They are also used as intermediate models to generate their corresponding stochastic models for practical analysis. Based on this, we have implemented the tool Reo2MC. Using Reo2MC, we have modeled and analyzed an industrial software, the ASK system. Its analysis results provided the best cost-effective resource utilization and some suggestions to improve the performance of the system.UBL - phd migration 201

Equatorial Magnetic Waves in the Stratified Ocean of Earth's Core

Earth’s global magnetic field envelops us all, protecting us from cosmic rays, aiding our navigation, and shielding our oxygen-rich atmosphere. Yet details about its origin, operation, and future remain unknown. Recent space-based magnetic observatories let us observe the field more precisely than ever before, and we can use these measurements to study the deep interior of the Earth and illuminate a region of our planet previously observed mainly by listening to the echoes of earthquakes. In this thesis, I use observations of changes in Earth’s magnetic field to study the structure and processes occurring near the top of Earth’s core. In particular, I examine the long-debated question of whether a stratified layer of fluid, termed by some as the stratified ocean of the core or SOC (Braginsky, 1998), lies at the top of Earth’s outer core. I first implement a model to simulate fluid motions in the SOC, which I describe in chapter two. Then, I derive the properties of a class of eastward-propagating equatorially trapped magnetic waves I term eMAC waves in chapter three and develop a statistical threshold to detect these waves in chapter four. In chapter five, I apply my statistical test to observations of Earth’s geomagnetic field and find evidence for these waves in Earth’s core. Finally, in chapter six, I propose a 20-40 km thick SOC with buoyancy strength of N ≥ 10 Ω to support the observed eMAC wave modes. I then discuss the implications of this layer, propose a double-layer SOC as a way to reconcile eMAC signals with previous observations, and enumerate possible future avenues of investigation