7,219 research outputs found
Causality and replication in concurrent processes
The replication operator was introduced by Milner for obtaining a simplified description of recursive processes. The standard interleaving semantics denotes the replication of a process P, written !P, a shorthand for its unbound parallel composition, operationally equivalent to the process P | P | âŠ, with P repeated as many times as needed. Albeit the replication mechanism has become increasingly popular, investigations on its causal semantics has been scarce. In fact, the correspondence between replication and unbound parallelism makes it difficult to recover basic properties usually associated with these semantics, such as the so-called concurrency diamond. In this paper we consider the interleaving semantics for the operator proposed by Sangiorgi and Walker, and we show how to refine it in order to capture causality. Furthermore, we prove it coincident with the standard causal semantics for recursive process studied in the literature, for processes defined by means of constant invocations
Health effects of home energy efficiency interventions in England: a modelling study
Objective: To assess potential public health impacts of changes to indoor air quality and temperature due to energy efficiency retrofits in English dwellings to meet 2030 carbon reduction targets. Design: Health impact modelling study. Setting: England. Participants: English household population. Intervention: Three retrofit scenarios were modelled: (1) fabric and ventilation retrofits installed assuming building regulations are met. (2) As with scenario (1) but with additional ventilation for homes at risk of poor ventilation. (3) As with scenario (1) but with no additional ventilation to illustrate the potential risk of weak regulations and non-compliance. Main Outcome: Primary outcomes were changes in quality adjusted life years (QALYs) over 50 years from cardiorespiratory diseases, lung cancer, asthma and common mental disorders due to changes in indoor air pollutants, including: second-hand tobacco smoke, PM2.5 from indoor and outdoor sources, radon, mould, and indoor winter temperatures. Results: The modelling study estimates showed that scenario (1) resulted in positive effects on net mortality and morbidity of 2,241 (95% credible intervals (CI) 2,085 to 2,397) QALYs per 10,000 persons over 50 years due to improved temperatures and reduced exposure to indoor pollutants, despite an increase in exposure to outdoorâgenerated PM2.5. Scenario (2) resulted in a negative impact of -728 (95% CI -864 to -592) QALYs per 10,000 persons over 50 years due to an overall increase in indoor pollutant exposures. Scenario (3) resulted in -539 (95% CI -678 to -399) QALYs per 10,000 persons over 50 years due to an increase in indoor exposures despite targeting. Conclusions: If properly implemented alongside ventilation, energy efficiency retrofits in housing can improve health by reducing exposure to cold and air pollutants. Maximising the health benefits requires careful understanding of the balance of changes in pollutant exposures, highlighting the importance of ventilation to mitigate the risk of poor indoor air quality
Structure of bottle-brush brushes under good solvent conditions. A molecular dynamics study
We report a simulation study for bottle-brush polymers grafted on a rigid
backbone. Using a standard coarse-grained bead-spring model extensive molecular
dynamics simulations for such macromolecules under good solvent conditions are
performed. We consider a broad range of parameters and present numerical
results for the monomer density profile, density of the untethered ends of the
grafted flexible backbones and the correlation function describing the range
that neighboring grafted bottle-brushes are affected by the presence of the
others due to the excluded volume interactions. The end beads of the flexible
backbones of the grafted bottle-brushes do not access the region close to the
rigid backbone due to the presence of the side chains of the grafted
bottle-brush polymers, which stretch further the chains in the radial
directions. Although a number of different correlation lengths exist as a
result of the complex structure of these macromolecules, their properties can
be tuned with high accuracy in good solvents. Moreover, qualitative differences
with "typical" bottle-brushes are discussed. Our results provide a first
approach to characterizing such complex macromolecules with a standard bead
spring model.Comment: To appear in Journal of Physics Condensed Matter (2011
Choreographies in Practice
Choreographic Programming is a development methodology for concurrent
software that guarantees correctness by construction. The key to this paradigm
is to disallow mismatched I/O operations in programs, called choreographies,
and then mechanically synthesise distributed implementations in terms of
standard process models via a mechanism known as EndPoint Projection (EPP).
Despite the promise of choreographic programming, there is still a lack of
practical evaluations that illustrate the applicability of choreographies to
concrete computational problems with standard concurrent solutions. In this
work, we explore the potential of choreographies by using Procedural
Choreographies (PC), a model that we recently proposed, to write distributed
algorithms for sorting (Quicksort), solving linear equations (Gaussian
elimination), and computing Fast Fourier Transform. We discuss the lessons
learned from this experiment, giving possible directions for the usage and
future improvements of choreography languages
Compositional Performance Modelling with the TIPPtool
Stochastic process algebras have been proposed as compositional specification formalisms for performance models. In this paper, we describe a tool which aims at realising all beneficial aspects of compositional performance modelling, the TIPPtool. It incorporates methods for compositional specification as well as solution, based on state-of-the-art techniques, and wrapped in a user-friendly graphical front end. Apart from highlighting the general benefits of the tool, we also discuss some lessons learned during development and application of the TIPPtool. A non-trivial model of a real life communication system serves as a case study to illustrate benefits and limitations
Full abstraction for fair testing in CCS
In previous work with Pous, we defined a semantics for CCS which may both be
viewed as an innocent presheaf semantics and as a concurrent game semantics. It
is here proved that a behavioural equivalence induced by this semantics on CCS
processes is fully abstract for fair testing equivalence. The proof relies on a
new algebraic notion called playground, which represents the 'rule of the
game'. From any playground, two languages, equipped with labelled transition
systems, are derived, as well as a strong, functional bisimulation between
them.Comment: 15 pages, to appear in CALCO '13. To appear Lecture notes in computer
science (2013
Process algebra modelling styles for biomolecular processes
We investigate how biomolecular processes are modelled in process algebras, focussing on chemical reactions. We consider various modelling styles and how design decisions made in the definition of the process algebra have an impact on how a modelling style can be applied. Our goal is to highlight the often implicit choices that modellers make in choosing a formalism, and illustrate, through the use of examples, how this can affect expressability as well as the type and complexity of the analysis that can be performed
The OLYMPUS Internal Hydrogen Target
An internal hydrogen target system was developed for the OLYMPUS experiment
at DESY, in Hamburg, Germany. The target consisted of a long, thin-walled,
tubular cell within an aluminum scattering chamber. Hydrogen entered at the
center of the cell and exited through the ends, where it was removed from the
beamline by a multistage pumping system. A cryogenic coldhead cooled the target
cell to counteract heating from the beam and increase the density of hydrogen
in the target. A fixed collimator protected the cell from synchrotron radiation
and the beam halo. A series of wakefield suppressors reduced heating from beam
wakefields. The target system was installed within the DORIS storage ring and
was successfully operated during the course of the OLYMPUS experiment in 2012.
Information on the design, fabrication, and performance of the target system is
reported.Comment: 9 pages, 13 figure
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