In the Maze of Data Languages

In data languages the positions of strings and trees carry a label from a finite alphabet and a data value from an infinite alphabet. Extensions of automata and logics over finite alphabets have been defined to recognize data languages, both in the string and tree cases. In this paper we describe and compare the complexity and expressiveness of such models to understand which ones are better candidates as regular models

Nuclearity, Local Quasiequivalence and Split Property for Dirac Quantum Fields in Curved Spacetime

We show that a free Dirac quantum field on a globally hyperbolic spacetime has the following structural properties: (a) any two quasifree Hadamard states on the algebra of free Dirac fields are locally quasiequivalent; (b) the split-property holds in the representation of any quasifree Hadamard state; (c) if the underlying spacetime is static, then the nuclearity condition is satisfied, that is, the free energy associated with a finitely extended subsystem (``box'') has a linear dependence on the volume of the box and goes like $\propto T^{s+1}$ for large temperatures $T$, where $s+1$ is the number of dimensions of the spacetime.Comment: Latex, 33 pages, no figures. v3: Corrections to the proofs of thm. 4.1 and thm. 3.1 and more reference

Phase space properties of charged fields in theories of local observables

Within the setting of algebraic quantum field theory a relation between phase-space properties of observables and charged fields is established. These properties are expressed in terms of compactness and nuclearity conditions which are the basis for the characterization of theories with physically reasonable causal and thermal features. Relevant concepts and results of phase space analysis in algebraic quantum field theory are reviewed and the underlying ideas are outlined.Comment: 33 pages, no figures, AMSTEX, DESY 94-18

Open educational resources : conversations in cyberspace

172 p. : ill. ; 25 cm.Libro ElectrónicoEducation systems today face two major challenges: expanding the reach of education and improving its quality. Traditional solutions will not suffice, especially in the context of today's knowledge-intensive societies. The Open Educational Resources movement offers one solution for extending the reach of education and expanding learning opportunities. The goal of the movement is to equalize access to knowledge worldwide through openly and freely available online high-quality content. Over the course of two years, the international community came together in a series of online discussion forums to discuss the concept of Open Educational Resources and its potential. This publication makes the background papers and reports from those discussions available in print.--Publisher's description.A first forum : presenting the open educational resources (OER) movement. Open educational resources : an introductory note / Sally Johnstone -- Providing OER and related issues : an introductory note / Anne Margulies, ... [et al.] -- Using OER and related issues : in introductory note / Mohammed-Nabil Sabry, ... [et al.] -- Discussion highlights / Paul Albright -- Ongoing discussion. A research agenda for OER : discussion highlights / Kim Tucker and Peter Bateman -- A 'do-it-yourself' resource for OER : discussion highlights / Boris Vukovic -- Free and open source software (FOSS) and OER -- A second forum : discussing the OECD study of OER. Mapping procedures and users / Jan Hylén -- Why individuals and institutions share and use OER / Jan Hylén -- Discussion highlights / Alexa Joyce -- Priorities for action. Open educational resources : the way forward / Susan D'Antoni

Scaling algebras for charged fields and short-distance analysis for localizable and topological charges

The method of scaling algebras, which has been introduced earlier as a means for analyzing the short-distance behaviour of quantum field theories in the setting of the model-independent, operator-algebraic approach, is extended to the case of fields carrying superselection charges. In doing so, consideration will be given to strictly localizable charges ("DHR-type" superselection charges) as well as to charges which can only be localized in regions extending to spacelike infinity ("BF-type" superselection charges). A criterion for the preservance of superselection charges in the short-distance scaling limit is proposed. Consequences of this preservance of superselection charges are studied. The conjugate charge of a preserved charge is also preserved, and for charges of DHR-type, the preservance of all charges of a quantum field theory in the scaling limit leads to equivalence of local and global intertwiners between superselection sectors.Comment: Latex 2e, 57 pages. Supersedes hep-th/030114

Pensions and Intergenerational Risk-Sharing When Relative Consumption Matters

Concern for relative consumption introduces an additional source of risk for future pensioners. We study its implications, in terms of optimal risk diversification, for the choice of the mix between a pay-as-you-go and a funded pension systems. We identify a necessary and sufficient condition for the optimal share of pay-as-you-go to be larger when relative consumption matters. We argue that when model parameters assume reasonable values such condition is satisfiedpay-as-you-go pensions, fully funded pensions, relative consumption, inter-generational risk-sharing

Implementation of conformal covariance by diffeomorphism symmetry

Every locally normal representation of a local chiral conformal quantum theory is covariant with respect to global conformal transformations, if this theory is diffeomorphism covariant in its vacuum representation. The unitary, strongly continuous representation implementing conformal symmetry is constructed; it consists of operators which are inner in a global sense for the representation of the quantum theory. The construction is independent of positivity of energy and applies to all locally normal representations irrespective of their statistical dimensions (index).Comment: 11 pages,no figure