7,285 research outputs found
Rich Interfaces for Dependability: Compositional Methods for Dynamic Fault Trees and Arcade models
This paper discusses two behavioural interfaces for reliability analysis: dynamic fault trees, which model the system reliability in terms of the reliability of its components and Arcade, which models the system reliability at an architectural level. For both formalisms, the reliability is analyzed by transforming the DFT or Arcade model to a set of input-output Markov Chains. By using compositional aggregation techniques based on weak bisimilarity, significant reductions in the state space can be obtained
Modeling views in the layered view model for XML using UML
In data engineering, view formalisms are used to provide flexibility to users and user applications by allowing them to extract and elaborate data from the stored data sources. Conversely, since the introduction of Extensible Markup Language (XML), it is fast emerging as the dominant standard for storing, describing, and interchanging data among various web and heterogeneous data sources. In combination with XML Schema, XML provides rich facilities for defining and constraining user-defined data semantics and properties, a feature that is unique to XML. In this context, it is interesting to investigate traditional database features, such as view models and view design techniques for XML. However, traditional view formalisms are strongly coupled to the data language and its syntax, thus it proves to be a difficult task to support views in the case of semi-structured data models. Therefore, in this paper we propose a Layered View Model (LVM) for XML with conceptual and schemata extensions. Here our work is three-fold; first we propose an approach to separate the implementation and conceptual aspects of the views that provides a clear separation of concerns, thus, allowing analysis and design of views to be separated from their implementation. Secondly, we define representations to express and construct these views at the conceptual level. Thirdly, we define a view transformation methodology for XML views in the LVM, which carries out automated transformation to a view schema and a view query expression in an appropriate query language. Also, to validate and apply the LVM concepts, methods and transformations developed, we propose a view-driven application development framework with the flexibility to develop web and database applications for XML, at varying levels of abstraction
Observer Dependent Horizon Temperatures: a Coordinate-Free Formulation of Hawking Radiation as Tunneling
We reformulate the Hamilton-Jacobi tunneling method for calculating Hawking
radiation in static, spherically-symmetric spacetimes by explicitly
incorporating a preferred family of frames. These frames correspond to a family
of observers tied to a locally static timelike Killing vector of the spacetime.
This formulation separates the role of the coordinates from the choice of
vacuum and thus provides a coordinate-independent formulation of the tunneling
method. In addition, it clarifies the nature of certain constants and their
relation to these preferred observers in the calculation of horizon
temperatures. We first use this formalism to obtain the expected temperature
for a static observer at finite radius in the Schwarzschild spacetime. We then
apply this formalism to the Schwarzschild-de Sitter spacetime, where there is
no static observer with 4-velocity equal to the static timelike Killing vector.
It is shown that a preferred static observer, one whose trajectory is geodesic,
measures the lowest temperature from each horizon. Furthermore, this observer
measures horizon temperatures corresponding to the well-known Bousso-Hawking
normalization.Comment: 11 pages, 1 2-part figure, references added, appendix added,
discussion streamline
On cost-effective reuse of components in the design of complex reconfigurable systems
Design strategies that benefit from the reuse of system components can reduce costs while maintaining or increasing dependability—we use the term dependability to tie together reliability and availability. D3H2 (aDaptive Dependable Design for systems with Homogeneous and Heterogeneous redundancies) is a methodology that supports the design of complex systems with a focus on reconfiguration and component reuse. D3H2 systematizes the identification of heterogeneous redundancies and optimizes the design of fault detection and reconfiguration mechanisms, by enabling the analysis of design alternatives with respect to dependability and cost. In this paper, we extend D3H2 for application to repairable systems. The method is extended with analysis capabilities allowing dependability assessment of complex reconfigurable systems. Analysed scenarios include time-dependencies between failure events and the corresponding reconfiguration actions. We demonstrate how D3H2 can support decisions about fault detection and reconfiguration that seek to improve dependability while reducing costs via application to a realistic railway case study
Cosmic structure sizes in generic dark energy models
The maximum allowable size of a spherical cosmic structure as a function of
its mass is determined by the maximum turn around radius , the
distance from its centre where the attraction on a radial test particle due to
the spherical mass is balanced with the repulsion due to the ambient dark
energy. In this work, we extend the existing results in several directions. (a)
We first show that for , the expression for found
earlier using the cosmological perturbation theory, can be derived using a
static geometry as well. (b) In the generic dark energy model with arbitrary
time dependent state parameter , taking into account the effect of
inhomogeneities upon the dark energy as well, where it is shown that the data
constrain , and (c) in the quintessence and the
generalized Chaplygin gas models, both of which are shown to predict structure
sizes consistent with observations.Comment: v2, 19pp; added references and discussions, improved presentation;
accepted in EPJ
When is S=A/4?
Black hole entropy and its relation to the horizon area are considered. More
precisely, the conditions and specifications that are expected to be required
for the assignment of entropy, and the consequences that these expectations
have when applied to a black hole are explored. In particular, the following
questions are addressed: When do we expect to assign an entropy?; when are
entropy and area proportional? and, what is the nature of the horizon? It is
concluded that our present understanding of black hole entropy is somewhat
incomplete, and some of the relevant issues that should be addressed in
pursuing these questions are pointed out.Comment: 14 pages, no figures. Revtex file. Manuscript edited and discussion
expanded. References added, conclusions unchanged. Version to be published in
MPL
Optimised surface-electrode ion-trap junctions for experiments with cold molecular ions
We discuss the design and optimisation of two types of junctions between
surface-electrode radiofrequency ion-trap arrays that enable the integration of
experiments with sympathetically cooled molecular ions on a monolithic chip
device. A detailed description of a multi-objective optimisation procedure
applicable to an arbitrary planar junction is presented, and the results for a
cross junction between four quadrupoles as well as a quadrupole-to-octupole
junction are discussed. Based on these optimised functional elements, we
propose a multi-functional ion-trap chip for experiments with translationally
cold molecular ions at temperatures in the millikelvin range. This study opens
the door to extending complex chip-based trapping techniques to
Coulomb-crystallised molecular ions with potential applications in mass
spectrometry, spectroscopy, controlled chemistry and quantum technology.Comment: 19 pages, 10 figure
- …