70 research outputs found
Strong accessibility of Coxeter groups over minimal splittings
AbstractGiven a class of groups C, a group G is strongly accessible over C if there is a bound on the number of terms in a sequence Λ1,Λ2,…,Λn of graph of groups decompositions of G with edge groups in C such that Λ1 is the trivial decomposition (with 1-vertex) and for i>1, Λi is obtained from Λi−1 by non-trivially and compatibly splitting a vertex group of Λi−1 over a group in C, replacing this vertex group by the splitting and then reducing. If H and K are subgroups of a group G then H is smaller than K if H∩K has finite index in H and infinite index in K. The minimal splitting subgroups of G, are the subgroups H of G, such that G splits non-trivially (as an amalgamated product or HNN-extension) over H and for any other splitting subgroup K of W, K is not smaller than H. When G is a finitely generated Coxeter group, minimal splitting subgroups are always finitely generated. Minimal splittings are explicitly or implicitly important aspects of Dunwoody’s work on accessibility and the JSJ results of Rips–Sela, Dunwoody–Sageev and Mihalik. Our main results are that Coxeter groups are strongly accessible over minimal splittings and if Λ is an irreducible graph of groups decomposition of a Coxeter group with minimal splitting edge groups, then the vertex and edge groups of Λ are Coxeter
Adding reference immutability to Java
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2006.Includes bibliographical references (leaves 129-133).This paper describes a programming language, Javari, that is capable of expressing and enforcing immutability constraints. The specific constraint expressed is that the abstract state of the object to which an immutable reference refers cannot be modified using that reference. The abstract state is (part of) the transitively reachable state: that is, the state of the object and all state reachable from it by following references. The type system permits explicitly excluding fields from the abstract state of an object. For a statically type-safe language, the type system guarantees reference immutability. The type system is distinguishes the notions of assignability and mutability; integrates with Java's generic types and with multi-dimensional arrays; provides a mutability polymorphism approach to avoiding code duplication; and has type-safe support for reflection and serialization. This paper describes a core calculus including formal type rules for the language. Additionally, this paper describes a type inference algorithm that can be used convert existing Java programs to Javari. Experimental results from a prototype implementation of the algorithm are presented.by Matthew S. Tschantz.M.Eng
Javari: Adding Reference Immutability to Java
MEng thesisThis paper describes a programming language, Javari, that is capable of expressing and enforcing immutability constraints. The specific constraint expressed is that the abstract state of the object to which an immutable reference refers cannot be modified using that reference. The abstract state is (part of) the transitively reachable state: that is, the state of the object and all state reachable from it by following references. The type system permits explicitly excluding fields from the abstract state of an object. For a statically type-safe language, the type system guarantees reference immutability.The type system is distinguishes the notions of assignability and mutability; integrates with Java's generic types and with multi-dimensional arrays; provides a mutability polymorphism approach to avoiding code duplication; and has type-safe support for reflection and serialization. This paper describes a core calculus including formal type rules for the language.Additionally, this paper describes a type inference algorithm that can be used convert existing Java programs to Javari. Experimental results from a prototype implementation of the algorithm are presented
Privacy Architectures: Reasoning About Data Minimisation and Integrity
Privacy by design will become a legal obligation in the European Community if
the Data Protection Regulation eventually gets adopted. However, taking into
account privacy requirements in the design of a system is a challenging task.
We propose an approach based on the specification of privacy architectures and
focus on a key aspect of privacy, data minimisation, and its tension with
integrity requirements. We illustrate our formal framework through a smart
metering case study.Comment: appears in STM - 10th International Workshop on Security and Trust
Management 8743 (2014
Peaks in the Hartle-Hawking Wave Function from Sums over Topologies
Recent developments in ``Einstein Dehn filling'' allow the construction of
infinitely many Einstein manifolds that have different topologies but are
geometrically close to each other. Using these results, we show that for many
spatial topologies, the Hartle-Hawking wave function for a spacetime with a
negative cosmological constant develops sharp peaks at certain calculable
geometries. The peaks we find are all centered on spatial metrics of constant
negative curvature, suggesting a new mechanism for obtaining local homogeneity
in quantum cosmology.Comment: 16 pages,LaTeX, no figures; v2: some changes coming from revision of
a math reference: wave function peaks sharp but not infinite; v3: added
paragraph in intro on interpretation of wave functio
Privacy by Design: From Technologies to Architectures (Position Paper)
Existing work on privacy by design mostly focus on technologies rather than
methodologies and on components rather than architectures. In this paper, we
advocate the idea that privacy by design should also be addressed at the
architectural level and be associated with suitable methodologies. Among other
benefits, architectural descriptions enable a more systematic exploration of
the design space. In addition, because privacy is intrinsically a complex
notion that can be in tension with other requirements, we believe that formal
methods should play a key role in this area. After presenting our position, we
provide some hints on how our approach can turn into practice based on ongoing
work on a privacy by design environment
Trust Driven Strategies for Privacy by Design
Part 2: Full PapersInternational audienceIn this paper, we describe a multi-step approach to privacy by design. The main design step is the choice of the types of trust that can be accepted by the stakeholders, which is a key driver for the construction of an acceptable architecture. Architectures can be initially defined in a purely informal way and then mapped into a formal dedicated model. A tool integrating the approach can be used by designers to build and verify architectures. We apply the approach to a case study, an electronic toll pricing system, and show how different solutions can be suggested to the designer depending on different trust assumptions
Identification of a Novel Class of Farnesylation Targets by Structure-Based Modeling of Binding Specificity
Farnesylation is an important post-translational modification catalyzed by farnesyltransferase (FTase). Until recently it was believed that a C-terminal CaaX motif is required for farnesylation, but recent experiments have revealed larger substrate diversity. In this study, we propose a general structural modeling scheme to account for peptide binding specificity and recapitulate the experimentally derived selectivity profile of FTase in vitro. In addition to highly accurate recovery of known FTase targets, we also identify a range of novel potential targets in the human genome, including a new substrate class with an acidic C-terminal residue (CxxD/E). In vitro experiments verified farnesylation of 26/29 tested peptides, including both novel human targets, as well as peptides predicted to tightly bind FTase. This study extends the putative range of biological farnesylation substrates. Moreover, it suggests that the ability of a peptide to bind FTase is a main determinant for the farnesylation reaction. Finally, simple adaptation of our approach can contribute to more accurate and complete elucidation of peptide-mediated interactions and modifications in the cell
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