Disorder in a quantum spin liquid: flux binding and local moment formation

We study the consequences of disorder in the Kitaev honeycomb model, considering both site dilution and exchange randomness. We show that a single vacancy binds a flux and induces a local moment. This moment is polarised by an applied field $h$: in the gapless phase, for small $h$ the local susceptibility diverges as $\chi(h)\sim\ln(1/h)$; for a pair of nearby vacancies on the same sublattice, this even increases to $\chi(h)\sim1/(h[\ln(1/h)]^{3/2})$. By contrast, weak exchange randomness does not qualitatively alter the susceptibility but has its signature in the heat capacity, which in the gapless phase is power law in temperature with an exponent dependent on disorder strength.Comment: 4 pages, 2 figure

Superlanguages: developing languages and applications with XMF.

Superlanguages offer a wide range of technologies that support application development. In particular Superlanguages support Language Oriented Programming and Domain Specific Languages through syntax extensions and meta-programming. XMF has been designed as a Superlanguage and can be downloaded from this web site. This book describes Superlanguage features and shows how XMF can be used to develop new languages and applications

Applied metamodelling: a foundation for language driven development.

The motivation behind XMF was to develop a technology that would support a language driven approach to modelling and system development. Our starting point was that UML was not sufficiently flexible and in order to address this we designed an executable meta-language. This book describes the approach and provides an introduction to the key technologies: meta-models, language definition and mappings. The book concludes with a number of worked examples

Beyond annotations: a proposal for extensible java (XJ).

The XMF system is based on a bespoke language that includes some features that are key to Language Oriented Programming: grammars; syntax classes; parsers; quasi-quotes. This paper discusses various technologies and approaches for LOP and concludes that standardization is one of the key features that will bring LOP and Domain Specific Languages to the mainstream. The paper proposes an extension to Java that incorporates the key LOP and DSL features of XMF. The essential Java extensions are discussed and the paper concludes with a couple of examples

Defining OCL expressions using templates.

OCL expressions are an essential part of UML. The current versions of OCL fail to have a meta-model which means that the integration of OCL with the UML meta-model cannot be formally defined [1]. This can result in ambiguous descriptions of systems which may compromise designs. The need to redesign the OCL has been addressed by a number of proposals submitted to the OMG. In this paper we demonstrate how a definition for OCL can be stamped out from a small number of templates. Such an approach enables a high level of reuse and an increased confidence that the definition is correct. This work forms part of the 2U consortium’s efforts for the definition of UML 2.0

Site dilution in Kitaev's honeycomb model

We study the physical consequences of site dilution in Kitaev's honeycomb model, in both its gapped and gapless phases. We show that a vacancy binds a flux of the emergent $Z_2$ gauge field and induces a local moment. In the gapped phase this moment is free while in the gapless phase the susceptibility has the dependence $\chi(h)\sim\ln(1/h)$ on field strength $h$. Vacancy moments have interactions that depend on their separation, their relative sublattice, and the phase of the model. Strikingly, in the gapless phase, two nearby vacancies on the same sublattice have a parametrically larger $\chi(h)\sim(h[\ln(1/h)]^{3/2})^{-1}$. In the gapped phase, even a finite density of randomly distributed vacancies remains tractable, via a mapping to a bipartite random hopping problem. This leads to a strong disorder form of the low-energy thermodynamics, with a Dyson-type singularity in the density of states for excitations.Comment: 18 pages, 12 figure

MDA-driven development of standard-compliant OSS components: the OSS/J inventory case-study.

The telecommunications-oriented Operational Support Systems (OSS) industry have recognised the value of technology independent modelling of OSS solutions as a way to reduce cost, add agility, validate and verify solution designs against architectural guidelines of an enterprise and most importantly provide traceability in the design methodology process. The challenges faced by the OSS community is how MDA tools can deliver the promise of advanced meta-modelling, model definition and validation and model transformation for both OSS software components and integration logic in the larger OSS landscape. This paper describes how an advanced extensible meta-modelling tool is used to build an OSS component following best practice industry guidelines. Extended MOF, extended executable OCL and a powerful transformation language are used to capture the constraints in the meta-models as well as models followed by complete, 100% code generation from models. Furthermore, meta-models are also developed to capture graphical user interface elements in conjunction with the inventory data models, which are then automatically translated into code. This work is the precursor for defining extensive meta-models for a component-based OSS infrastructure based on industry best practice, for adding high degree of formality to model specifications and for enabling the verification of domain requirements by executing the models through model snapshot creation, way before system implementation takes place

A pattern based approach to defining translations between languages.

The 2U Consortium have recently submitted a proposal for the definition of the UML 2.0 infrastructure. This uses a innovative technique of rapidly “stamping out” the definition using a small number of patterns commonly found in software architecture. The contribution of this paper is to introduce the idea of reusability of mappings between languages and defining some of the reusable mapping templates. This paper also illustrates how these templates can be used to stamp out mapping between languages by stamping out a mapping between UML and Java

Unambiguous UML submission to UML 2 infrastructure RFP (ad/00-09-01).

This is a response to the UML 2.0 Request for Proposals on Infrastructure (ad/00-09-01). We propose an architecture for the definition of UML 2.0 which supports the layered and extensible definition of UML as a family of languages, and depends on the use of package extension (composition) and package template mechanisms in the metamodelling language. This submission defines that architecture and populates it with the definition of a core foundation for the definition of structural and behavioural modelling constructs for UML. Chapter 3 (“Language Architecture”) identifies all those parts of the architecture defined in any given version of this document