644,784 research outputs found
The composition of Event-B models
The transition from classical B [2] to the Event-B language and method [3] has seen the removal of some forms of model structuring and composition, with the intention of reinventing them in future. This work contributes to thatreinvention. Inspired by a proposed method for state-based decomposition and refinement [5] of an Event-B model, we propose a familiar parallel event composition (over disjoint state variable lists), and the less familiar event fusion (over intersecting state variable lists). A brief motivation is provided for these and other forms of composition of models, in terms of feature-based modelling. We show that model consistency is preserved under such compositions. More significantly we show that model composition preserves refinement
First results of the air shower experiment KASCADE
The main goals of the KASCADE (KArlsruhe Shower Core and Array DEtector)
experiment are the determination of the energy spectrum and elemental
composition of the charged cosmic rays in the energy range around the knee at
ca. 5 PeV. Due to the large number of measured observables per single shower a
variety of different approaches are applied to the data, preferably on an
event-by-event basis. First results are presented and the influence of the
high-energy interaction models underlying the analyses is discussed.Comment: 3 pages, 3 figures included, to appear in the TAUP 99 Proceedings,
Nucl. Phys. B (Proc. Suppl.), ed. by M. Froissart, J. Dumarchez and D.
Vignau
A seismic approach to testing different formation channels of subdwarf B stars
There are many unknowns in the formation of subdwarf B stars. Different
formation channels are considered to be possible and to lead to a variety of
helium-burning subdwarfs. All seismic models to date, however, assume that a
subdwarf B star is a post-helium-flash-core surrounded by a thin inert layer of
hydrogen. We examine an alternative formation channel, in which the subdwarf B
star originates from a massive (>~2 Msun) red giant with a non-degenerate
helium-core. Although these subdwarfs may evolve through the same region of the
log g-Teff diagram as the canonical post-flash subdwarfs, their interior
structure is rather different. We examine how this difference affects their
pulsation modes and whether it can be observed.
Using detailed stellar evolution calculations we construct subdwarf B models
from both formation channels. The iron accumulation in the driving region due
to diffusion, which causes the excitation of the modes, is approximated by a
Gaussian function. The pulsation modes and frequencies are calculated with a
non-adiabatic pulsation code. A detailed comparison of two subdwarf B models
from different channels, but with the same log g and Teff, shows that their
mode excitation is different. The excited frequencies are lower for the
post-flash than for the post-non-degenerate subdwarf B star. This is mainly due
to the differing chemical composition of the stellar envelope. A more general
comparison between two grids of models shows that the excited frequencies of
most post-non-degenerate subdwarfs cannot be well-matched with the frequencies
of post-flash subdwarfs. In the rare event that an acceptable seismic match is
found, additional information, such as mode identification and log g and Teff
determinations, allows us to distinguish between the two formation channels.Comment: 10 pages, 8 figures, 2 tables, accepted for publication in A&
The Fermi Bubbles: Gamma-ray, Microwave, and Polarization Signatures of Leptonic AGN Jets
The origin of the Fermi bubbles and the microwave haze is yet to be
determined. To disentangle different models requires detailed comparisons
between theoretical predictions and multi-wavelength observations. Our previous
simulations have demonstrated that the primary features of the Fermi bubbles
could be successfully reproduced by recent jet activity from the central active
galactic nucleus (AGN). In this work, we generate gamma-ray and microwave maps
and spectra based on the simulated properties of cosmic rays (CRs) and magnetic
fields in order to examine whether the observed bubble and haze emission could
be explained by leptons contained in the AGN jets. We also investigate the
model predictions of the polarization properties of the Fermi bubbles. We find
that: (1) The same population of leptons can simultaneously explain the bubble
and haze emission given that the magnetic fields within the bubbles are very
close to the exponentially distributed ambient field, which can be explained by
mixing in of the ambient field followed by turbulent field amplification; (2)
The centrally peaked microwave profile suggests CR replenishment, which is
consistent with the presence of a more recent second jet event; (3) The bubble
interior exhibits a high degree of polarization because of ordered radial
magnetic field lines stretched by elongated vortices behind the shocks;
highly-polarized signals could also be observed inside the draping layer; (4)
Enhancement of rotation measures could exist within the shock-compressed layer
because of increased gas density and more amplified and ordered magnetic
fields. We discuss the possibility that the deficient haze emission at b<-35
degrees is due to the suppression of magnetic fields, which is consistent with
the existence of lower-energy CRs causing the polarized emission at 2.3 GHz.
Possible AGN jet composition in the leptonic scenario is also discussed.Comment: 15 pages, 9 figures, matched with MNRAS published versio
The automated translation of integrated formal specifications into concurrent programs
The PROB model checker [LB03] provides tool support for an integrated formal specification approach, which combines the state-based B specification language [Abr96] with the event-based process algebra CSP [Hoa78]. The JCSP package [WM00b] presents a concurrent Java implementation for CSP/occam. In this thesis, we present a developing strategy for implementing such a combined specification as a concurrent Java program. The combined semantics in PROB is flexible and ideal for model checking, but is too abstract to be implemented in programming languages. Also, although the JCSP package gave us significant inspiration for implementing formal specifications in Java, we argue that it is not suitable for directly implementing the combined semantics in PROB. Therefore, we started with defining a restricted semantics from the original one in PROB. Then we developed a new Java package, JCSProB, for implementing the restricted semantics in Java. The JCSProB package implements multi-way synchronization with choice for the combined B and CSP event, as well as a new multi-threading mechanism at process level. Also, a GUI sub-package is designed for constructing GUI programs for JCSProB to allow user interaction and runtime assertion checking. A set of translation rules relates the integrated formal models to Java and JCSProB, and we also implement these rules in an automated translation tool for automatically generating Java programs from these models. To demonstrate and exercise the tool, several B/CSP models, varying both in syntactic structure and behavioural properties, are translated by the tool. The models manifest the presence and absence of various safety, deadlock, and fairness properties; the generated Java code is shown to faithfully reproduce them. Run-time safety and fairness assertion checking is also demonstrated. We also experimented with composition and decomposition on several combined models, as well as the Java programs generated from them. Composition techniques can help the user to develop large distributed systems, and can significantly improve the scalability of the development of the combined models of PROB.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Probing the Color Structure of the Perfect QCD Fluids via Soft-Hard-Event-by-Event Azimuthal Correlations
We develop a comprehensive dynamical framework, CIBJET, to calculate on an
event-by-event basis the dependence of correlations between soft ( Gev)
and hard ( Gev) azimuthal flow angle harmonics on the color
composition of near-perfect QCD fluids produced in high energy nuclear
collisions at RHIC and LHC. CIBJET combines consistently predictions of
event-by-event VISHNU2+1 viscous hydrodynamic fluid fields with CUJET3.1
predictions of event-by-event jet quenching. We find that recent correlation
data favor a temperature dependent color composition including bleached
chromo-electric components and an emergent chromo-magnetic degrees
of freedom consistent with non-perturbative lattice QCD information in
the confinement/deconfinement temperature range.Comment: 6 pages, 6 figures; Accepted version to appear in Chinese Physics
A Study of Cosmic Ray Composition in the Knee Region using Multiple Muon Events in the Soudan 2 Detector
Deep underground muon events recorded by the Soudan 2 detector, located at a
depth of 2100 meters of water equivalent, have been used to infer the nuclear
composition of cosmic rays in the "knee" region of the cosmic ray energy
spectrum. The observed muon multiplicity distribution favors a composition
model with a substantial proton content in the energy region 800,000 -
13,000,000 GeV/nucleus.Comment: 38 pages including 11 figures, Latex, submitted to Physical Review
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