7,597 research outputs found
A formal support to business and architectural design for service-oriented systems
Architectural Design Rewriting (ADR) is an approach for the design of software architectures developed within Sensoria by reconciling graph transformation and process calculi techniques. The key feature that makes ADR a suitable and expressive framework is the algebraic handling of structured graphs, which improves the support for specification, analysis and verification of service-oriented architectures and applications. We show how ADR is used as a formal ground for high-level modelling languages and approaches developed within Sensoria
Evaluating the performance of model transformation styles in Maude
Rule-based programming has been shown to be very successful in many application areas. Two prominent examples are the specification of model transformations in model driven development approaches and the definition of structured operational semantics of formal languages. General rewriting frameworks such as Maude are flexible enough to allow the programmer to adopt and mix various rule styles. The choice between styles can be biased by the programmer’s background. For instance, experts in visual formalisms might prefer graph-rewriting styles, while experts in semantics might prefer structurally inductive rules. This paper evaluates the performance of different rule styles on a significant benchmark taken from the literature on model transformation. Depending on the actual transformation being carried out, our results show that different rule styles can offer drastically different performances. We point out the situations from which each rule style benefits to offer a valuable set of hints for choosing one style over the other
Functorial Semantics for Petri Nets under the Individual Token Philosophy
Although the algebraic semantics of place/transition Petri nets under the collective token philosophy has been fully explained in terms of (strictly) symmetric (strict) monoidal categories, the analogous construction under the individual token philosophy is not completely satisfactory because it lacks universality and also functoriality. We introduce the notion of pre-net to recover these aspects, obtaining a fully satisfactory categorical treatment centered on the notion of adjunction. This allows us to present a purely logical description of net behaviours under the individual token philosophy in terms of theories and theory morphisms in partial membership equational logic, yielding a complete match with the theory developed by the authors for the collective token view of net
General formulation of general-relativistic higher-order gauge-invariant perturbation theory
Gauge-invariant treatments of general-relativistic higher-order perturbations
on generic background spacetime is proposed. After reviewing the general
framework of the second-order gauge-invariant perturbation theory, we show the
fact that the linear-order metric perturbation is decomposed into
gauge-invariant and gauge-variant parts, which was the important premis of this
general framework. This means that the development the higher-order
gauge-invariant perturbation theory on generic background spacetime is
possible. A remaining issue to be resolve is also disscussed.Comment: 4 pages, no figure. (v3) some explanations are added and a reference
is adde
Reclaiming Virtue Ethics for Economics
Virtue ethics is an important strand of moral philosophy which normative economists have largely neglected. It underpins influential critiques of the market (as a domain in which instrumental motivation corrodes virtue) and of economics (as justifying such motivation). We explain and respond to this critique. Using the methods of virtue ethics and with reference to the writings of major economists, we propose an understanding of the ‘telos’ (purpose) of markets as cooperation for mutual benefit, and identify traits that thereby count as virtues for market participants. We conclude that the market need not be seen as a virtue-free zone
Affine parameterization of the dark sector: costraints from WMAP5 and SDSS
We study a set of universe models where the dark sector is described by a
perfect fluid with an affine equation of state , focusing
specifically on cosmological perturbations in a flat universe. We perform a
Monte Carlo Markov Chain analysis spanning the full parameter space of the
model using the WMAP 5 years data and the SDSS LRG4 survey. The affine fluid
can either play the role of a unified dark matter (UDM), accounting for both
dark matter and a cosmological constant, or work alongside cold dark matter
(CDM), as a form of dark energy. A key ingredient is the sound speed, that
depends on the nature of the fluid and that, for any given background model,
adds a degree of freedom to the perturbations: in the barotropic case the
square of the sound speed is simply equal to the affine parameter ; if
entropic perturbations are present the effective sound speed has to be
specified as an additional parameter. In addition to the barotropic case, we
consider the two limiting cases of effective sound speed equal to 0 or 1. For
our UDM model is equivalent to the standard CDM with
adiabatic perturbations. Apart of a trivial subcase, all models considered
satisfy the data constraints, with quite standard values for the usual
cosmological parameters. In general our analysis confirms that cosmological
datasets require both a collisionless massive and cold component to form the
potential wells that lead to structure formation, and an effective cosmological
constant that drives the late accelerated expansion.Comment: 10 pages, 9 figure
Two-parameter non-linear spacetime perturbations: gauge transformations and gauge invariance
An implicit fundamental assumption in relativistic perturbation theory is
that there exists a parametric family of spacetimes that can be Taylor expanded
around a background. The choice of the latter is crucial to obtain a manageable
theory, so that it is sometime convenient to construct a perturbative formalism
based on two (or more) parameters. The study of perturbations of rotating stars
is a good example: in this case one can treat the stationary axisymmetric star
using a slow rotation approximation (expansion in the angular velocity Omega),
so that the background is spherical. Generic perturbations of the rotating star
(say parametrized by lambda) are then built on top of the axisymmetric
perturbations in Omega. Clearly, any interesting physics requires non-linear
perturbations, as at least terms lambda Omega need to be considered. In this
paper we analyse the gauge dependence of non-linear perturbations depending on
two parameters, derive explicit higher order gauge transformation rules, and
define gauge invariance. The formalism is completely general and can be used in
different applications of general relativity or any other spacetime theory.Comment: 22 pages, 3 figures. Minor changes to match the version appeared in
Classical and Quantum Gravit
The central structure of Broad Absorption Line QSOs: observational characteristics in the cm-mm wavelength domain
Accounting for ~20% of the total QSO population, Broad Absorption Line QSOs
are still an unsolved problem in the AGN context. They present wide troughs in
the UV spectrum, due to material with velocities up to 0.2 c toward the
observer. The two models proposed in literature try to explain them as a
particular phase of the evolution of QSOs or as normal QSOs, but seen from a
particular line of sight.
We built a statistically complete sample of Radio-Loud BAL QSOs, and carried
out an observing campaign to piece together the whole spectrum in the cm
wavelength domain, and highlight all the possible differences with respect to a
comparison sample of Radio-Loud non-BAL QSOs. VLBI observations at high angular
resolution have been performed, to study the pc-scale morphology of these
objects. Finally, we tried to detect a possible dust component with
observations at mm-wavelengths.
Results do not seem to indicate a young age for all BAL QSOs. Instead a
variety of orientations and morphologies have been found, constraining the
outflows foreseen by the orientation model to have different possible angles
with respect to the jet axis
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