The Anatomy and Facets of Dynamic Policies

Information flow policies are often dynamic; the security concerns of a program will typically change during execution to reflect security-relevant events. A key challenge is how to best specify, and give proper meaning to, such dynamic policies. A large number of approaches exist that tackle that challenge, each yielding some important, but unconnected, insight. In this work we synthesise existing knowledge on dynamic policies, with an aim to establish a common terminology, best practices, and frameworks for reasoning about them. We introduce the concept of facets to illuminate subtleties in the semantics of policies, and closely examine the anatomy of policies and the expressiveness of policy specification mechanisms. We further explore the relation between dynamic policies and the concept of declassification.Comment: Technical Report of publication under the same name in Computer Security Foundations (CSF) 201

Computing With Contexts A simple approach

AbstractThis article describes how the use of a higher-order syntax representation of contexts [due to A. Pitts] combines smoothly with higher-order syntax for evaluation rules, so that definitions can be extended to work over contexts. This provides “for free” — without the development of any new language-specific context calculi - evaluation rules for contexts which commute with hole-filling. We have found this to be a useful technique for directly reasoning about operational equivalence. A small illustration is given based on a unique fixed-point induction principle for a notion of guarded context in a functional language

First year mechanics taught through modelling in VPython

This paper describes a development project carried out in 2008/9 aimed at developing model-based learning in mechanics for a first year physics module. Based on the work in the literature, VPython, the visual extension to the Python programming language, was chosen as the vehicle for developing the models. VPython is ideally suited to modelling mechanics for various reasons, including a class of variables called vectors which have all the properties of vectors in mathematics, the ease with which basic models in VPython can be constructed, and the instant feedback on the operation of the models afforded by their visual nature. Thus the emphasis is much more on the physics and the modelling rather than computation. It is shown how an analysis of students‟ understanding has revealed that Newton‟s third law of motion causes difficulties, leading to a greater emphasis on this concept in the modelling for 2009/10. In addition, a greater attention was given to the methods and techniques of modelling, especially spatial reasoning. The evidence for student reasoning in this way is presented

Ausubel’s principle of prior knowledge in first year mechanics

The Force Concept Inventory, a 30-question multiple choice test, has been used to test the baseline knowledge in mechanics prior to a course of instruction at Hull over the three years corresponding to entry in 2008, 2009 and 2010. Students whose pre-university education occurred outside the UK or who were repeating the year have been excluded from the analysis in order to focus attention on first-time UK students. These constitute the great majority of the entrants and the results essentially characterise the entry-level knowledge of a typical cohort. Two interesting findings have emerged. First, there is a wide range of abilities within each cohort, as judged by the test scores, and secondly, analysis of the scores question by question reveals a remarkable consistency between the different cohorts. This consistency extends even to the distribution of choices within individual questions. Five such questions are analysed in detailed to reveal which aspects of mechanics a typical class finds difficult. Ausubel‟s principle of first finding out what students know in order to teach accordingly can therefore be applied not to the individual students but to the class as a whole and suggestions as to how instruction might be tailored to address the weaknesses revealed by the Force Concept Inventory are discussed

Additive decompositions for rings of modular forms

We study rings of integral modular forms for congruence subgroups as modules over the ring of integral modular forms for the full modular group. In many cases these modules are free or decompose at least into well-understood pieces. We apply this to characterize which rings of modular forms are Cohen--Macaulay and to prove finite generation results. These theorems are based on decomposition results about vector bundles on the compactified moduli stack of elliptic curves.Comment: Complete revision. Comments welcome. arXiv admin note: text overlap with arXiv:1609.0926

Civil Procedure—Availability of Class Actions to Consumers for Fraudulent Misrepresentation by Seller

Vasquez v. Superior Court of San Joaquin County, 4 Cal. 3d 800, 484 P.2d 964, 94 Cal. Rptr. 796 (1971)