2,912 research outputs found
Verifying linearizability on TSO architectures
Linearizability is the standard correctness criterion for fine-grained, non-atomic concurrent algorithms, and a variety of methods for verifying linearizability have been developed. However, most approaches assume a sequentially consistent memory model, which is not always realised in practice. In this paper we define linearizability on a weak memory model: the TSO (Total Store Order) memory model, which is implemented in the x86 multicore architecture. We also show how a simulation-based proof method can be adapted to verify linearizability for algorithms running on TSO architectures. We demonstrate our approach on a typical concurrent algorithm, spinlock, and prove it linearizable using our simulation-based approach. Previous approaches to proving linearizabilty on TSO architectures have required a modification to the algorithm's natural abstract specification. Our proof method is the first, to our knowledge, for proving correctness without the need for such modification
Weak refinement in Z
An important aspect in the specification of distributed systems is the role of the internal (or unobservable) operation. Such operations are not part of the user interface (i.e. the user cannot invoke them), however, they are essential to our understanding and correct modelling of the system. Various conventions have been employed to model internal operations when specifying distributed systems in Z. If internal operations are distinguished in the specification notation, then refinement needs to deal with internal operations in appropriate ways. However, in the presence of internal operations, standard Z refinement leads to undesirable implementations.
In this paper we present a generalization of Z refinement, called weak refinement, which treats internal operations differently from observable operations when refining a system. We illustrate some of the properties of weak refinement through a specification of a telecommunications protocol
Admit your weakness: Verifying correctness on TSO architectures
âThe final publication is available at http://link.springer.com/chapter/10.1007%2F978-3-319-15317-9_22 â.Linearizability has become the standard correctness criterion for fine-grained non-atomic concurrent algorithms, however, most approaches assume a sequentially consistent memory model, which is not always realised in practice. In this paper we study the correctness of concurrent algorithms on a weak memory model: the TSO (Total Store Order) memory model, which is commonly implemented by multicore architectures. Here, linearizability is often too strict, and hence, we prove a weaker criterion, quiescent consistency instead. Like linearizability, quiescent consistency is compositional making it an ideal correctness criterion in a component-based context. We demonstrate how to model a typical concurrent algorithm, seqlock, and prove it quiescent consistent using a simulation-based approach. Previous approaches to proving correctness on TSO architectures have been based on linearizabilty which makes it necessary to modify the algorithmâs high-level requirements. Our approach is the first, to our knowledge, for proving correctness without the need for such a modification
Phenomenological description of the gamma* p cross section at low Q2
Low Q2 photon-proton cross sections are analysed using a simple,
QCD-motivated parametrisation ,
which gives a good description of the data. The Q2 dependence of the gamma* p
cross section is discussed in terms of the partonic transverse momenta of the
hadronic state the photon fluctuates into.Comment: 14 pages, revtex, epsfig, 2 figure
Building a refinement checker for Z
In previous work we have described how refinements can be checked using a
temporal logic based model-checker, and how we have built a model-checker for Z
by providing a translation of Z into the SAL input language. In this paper we
draw these two strands of work together and discuss how we have implemented
refinement checking in our Z2SAL toolset.
The net effect of this work is that the SAL toolset can be used to check
refinements between Z specifications supplied as input files written in the
LaTeX mark-up. Two examples are used to illustrate the approach and compare it
with a manual translation and refinement check.Comment: In Proceedings Refine 2011, arXiv:1106.348
Shafranov's virial theorem and magnetic plasma confinement
Shafranov's virial theorem implies that nontrivial magnetohydrodynamical
equilibrium configurations must be supported by externally supplied currents.
Here we extend the virial theorem to field theory, where it relates to
Derrick's scaling argument on soliton stability. We then employ virial
arguments to investigate a realistic field theory model of a two-component
plasma, and conclude that stable localized solitons can exist in the bulk of a
finite density plasma. These solitons entail a nontrivial electric field which
implies that purely magnetohydrodynamical arguments are insufficient for
describing stable, nontrivial structures within the bulk of a plasma.Comment: 9 pages no figure
Inelastic diffraction and color-singlet gluon-clusters in high-energy hadron-hadron and lepton-hadron collisions
It is proposed, that ``the colorless objects'' which manifest themselves in
large-rapidity-gap events are color-singlet gluon-clusters due to
self-organized criticality (SOC), and that optical-geometrical concepts and
methods are useful in examing the space-time properties of such objects. A
simple analytical expression for the -dependence of the inelastic single
diffractive cross section ( is the four-momentum transfer
squared) is derived. Comparison with the existing data and predictions for
future experiments are presented. The main differences and similarities between
the SOC-approach and the ``Partons in the Pomeron (Pomeron and
Reggeon)''-approach are discussed.Comment: 12 pages, 2 figure
Exclusive diffractive processes and the quark substructure of mesons
Exclusive diffractive processes on the nucleon are investigated within a
model in which the quark-nucleon interaction is mediated by Pomeron exchange
and the quark substructure of mesons is described within a framework based on
the Dyson-Schwinger equations of QCD. The model quark-nucleon interaction has
four parameters which are completely determined by high-energy and elastic scattering data. The model is then used to predict vector-meson
electroproduction observables. The obtained - and -meson
electroproduction cross sections are in excellent agreement with experimental
data. The predicted dependence of -meson electroproduction also
agrees with experimental data. It is shown that confined-quark dynamics play a
central role in determining the behavior of the diffractive, vector-meson
electroproduction cross section. In particular, the onset of the asymptotic
behavior of the cross section is determined by a momentum scale that is
set by the current-quark masses of the quark and antiquark inside the vector
meson. This is the origin of the striking differences between the
dependence of -, - and -meson electroproduction cross
sections observed in recent experiments.Comment: 53 pages, 23 figures, revtex and epsfig. Minor additions to tex
Universality of the preasymptotics in the hadron and photon diffraction
We note that it is premature to make a conclusion on the multiplicity of the
Pomerons on the basis of the available experimental data since the interactions
have a preasymptotic natureComment: 4 pages, latex, no figure
The regulation of genes of unknown function implicated in nitrosative stress tolerance in Escherichia coli K-12
This study was designed to determine the regulatory network that controls expression from two K-12 promoters, and , during anaerobic growth. These promoters were identified from transcriptomic studies as being positively regulated by NarL independently of FNR, the master regulator of anaerobic respiration. Biochemical and genetic analyses presented in this study confirmed that expression from both the and promoters is dependent upon NarL, which binds to a single site in the promoter and two sites in the promoter. The nucleoid-associated protein, Fis, repressed transcription from both promoters, especially in rich medium, by binding to sites that overlap the NarL site, excluding the essential activator. Both promoters were more active in the absence of functional FNR. However, mutational analysis revealed that FNR does not bind to the promoter region, so this effect is indirect. How the absence of functional FNR might affect NarL-dependent nitrite signalling was investigated. The Ogt protein is known function as an O-alkyguanine methyltransferase. However, the functions of the gene products of and another operon implicated in nitrosative stress management, , were unknown. Strains carrying a chromosomal deletion were not more sensitive to nitric oxide or hydroxylamine compared with the parental strain, suggesting that the products of this operon are not essential for dealing with these toxic nitrogen species. Conversely, a strain deleted in was shown to be slightly more sensitive to both nitric oxide and hydroxylamine, implicating Hcp and Hcr in nitrosative stress management.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
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