PRISM: a tool for automatic verification of probabilistic systems

Probabilistic model checking is an automatic formal verification technique for analysing quantitative properties of systems which exhibit stochastic behaviour. PRISM is a probabilistic model checking tool which has already been successfully deployed in a wide range of application domains, from real-time communication protocols to biological signalling pathways. The tool has recently undergone a significant amount of development. Major additions include facilities to manually explore models, Monte-Carlo discrete-event simulation techniques for approximate model analysis (including support for distributed simulation) and the ability to compute cost- and reward-based measures, e.g. "the expected energy consumption of the system before the first failure occurs". This paper presents an overview of all the main features of PRISM. More information can be found on the website: www.cs.bham.ac.uk/~dxp/prism

Laminate comprising fibers embedded in cured amine terminated bis-imide

Amine terminated bisaspartimides are prepared by a Michael type reaction of an aromatic bismaleimide and an aromatic diamine in an aprotic solvent. These bisaspartimides are thermally polymerized to yield tough, resinous polymers crosslinked through -NH- groups. Such polymers are useful in applications requiring materials with resistance to change at elevated temperatures

Effect of doping and pressure on magnetism and lattice structure of Fe-based superconductors

Using first principles calculations, we analyze structural and magnetic trends as a function of charge doping and pressure in BaFe$_2$As$_2$, and compare to experimentally established facts. We find that density functional theory, while accurately reproducing the structural and magnetic ordering at ambient pressure, fails to reproduce some structural trends as pressure is increased. Most notably, the Fe-As bondlength which is a gauge of the magnitude of the magnetic moment, $\mu$, is rigid in experiment, but soft in calculation, indicating residual local Coulomb interactions. By calculating the magnitude of the magnetic ordering energy, we show that the disruption of magnetic order as a function of pressure or doping can be qualitatively reproduced, but that in calculation, it is achieved through diminishment of $|\mu|$, and therefore likely does not reflect the same physics as detected in experiment. We also find that the strength of the stripe order as a function of doping is strongly site-dependent: magnetism decreases monotonically with the number of electrons doped at the Fe site, but increases monotonically with the number of electrons doped at the Ba site. Intra-planar magnetic ordering energy (the difference between checkerboard and stripe orderings) and interplanar coupling both follow a similar trend. We also investigate the evolution of the orthorhombic distortion, $e=(a-b)/(a+b),$ as a function of $\mu$, and find that in the regime where experiment finds a linear relationship, our calculations are impossible to converge, indicating that in density functional theory, the transition is first order, signalling anomalously large higher order terms in the Landau functional

New Structure In The Shapley Supercluster

We present new radial velocities for 189 galaxies in a 91 sq. deg region of the Shapley supercluster measured with the FLAIR-II spectrograph on the UK Schmidt Telescope. The data reveal two sheets of galaxies linking the major concentrations of the supercluster. The supercluster is not flattened in Declination as was suggested previously and it may be at least 30 percent larger than previously thought with a correspondingly larger contribution to the motion of the Local Group.Comment: LaTex: 2 pages, 1 figure, includes conf_iap.sty style file. To appear in proceedings of The 14th IAP Colloquium: Wide Field Surveys in Cosmology, held in Paris, 1998 May 26--30, eds. S.Colombi, Y.Mellie

Electrophysiological and behavioural studies of vision in the pigeon

The literature concerning the eye and the visual pathways in the pigeon is reviewed (Chapter l).An electrophysiological investigation of the forebrain of the pigeon using the method of evoked potentials revealed four main areas within this structure in which large amplitude responses were found. These areas were the hyperstriatum, neostriatum caudale, paleostriatum augmentatum and an area of tissue surrounding the ectostriatum. Comparison of the latencies of these potentials with the latencies of potentials found within the mesencephalon and diencephalon excludes the nucleus rotundus as being involved in the relay of these potentials to the forebrain. Previous work by other authors has suggested that this nucleus is a major source of telencephalic visual afferents. Only one area within the forebrain produced potentials which are compatible as regards latency with being relayed by the nucleus rotundus. This area is the dorsolateral corticoid area. These results are discussed and compared to, previous work (Chapter 2).An investigation of the effects of destruction of the centrifugal pathway to the retina, by lesioning the isthmo-optic nucleus or sectioning the optic tract, on the pigeodb electroretinogram has revealed no evidence of this pathway being involved in the control of this potential. Evidence from two birds suggests that previous reports of centrifugal effects on the electroretinogram of the pigeon can be attributed to metabolic abnormalities occurring within the retina as a consequence of optic tract section (Chapter 5). Destruction of the hyperstriatum of the pigeon revealed no evidence of profound effects on visual discrimination tasks. Birds lesioned in this area show increased choice times on a compound colour-brightness discrimination but no increase in trials to criterion. No effects were apparent on pattern discrimination contrary to previous reports of such effects in the literature (Chapter 4). Destruction of the hyperstriatum or the neostriatum caudale revealed no profound disturbance of the animals ability to analyse visual stimuli in terms of orientation, brightness or size, when the performance of these animals was compared to controls using the method of stimulus generalisation. The gradients of the generalisation slopes to size, but not those to orientation or brightness, were significantly flatter in the experimental groups than in the control group (Chapter 5). The implication of the findings concerning the visual projections to the hyperstriatum and neostriatum caudale and the effects of lesions to these areas on our understanding of the function of the pigeons forebrain are discussed (Chapter 6)

On the formation of current sheets in response to the compression or expansion of a potential magnetic field

The compression or expansion of a magnetic field that is initially potential is considered. It was recently suggested by Janse & Low [2009, ApJ, 690, 1089] that, following the volumetric deformation, the relevant lowest energy state for the magnetic field is another potential magnetic field that in general contains tangential discontinuities (current sheets). Here we examine this scenario directly using a numerical relaxation method that exactly preserves the topology of the magnetic field. It is found that of the magnetic fields discussed by Janse & Low, only those containing magnetic null points develop current singularities during an ideal relaxation, while the magnetic fields without null points relax toward smooth force-free equilibria with finite non-zero current.Comment: Accepted for publication in Ap

Structure formation during the collapse of a dipolar atomic Bose-Einstein condensate

We investigate the collapse of a trapped dipolar Bose-Einstein condensate. This is performed by numerical simulations of the Gross-Pitaevskii equation and the novel application of the Thomas-Fermi hydrodynamic equations to collapse. We observe regimes of both global collapse, where the system evolves to a highly elongated or flattened state depending on the sign of the dipolar interaction, and local collapse, which arises due to dynamically unstable phonon modes and leads to a periodic arrangement of density shells, disks or stripes. In the adiabatic regime, where ground states are followed, collapse can occur globally or locally, while in the non-adiabatic regime, where collapse is initiated suddenly, local collapse commonly occurs. We analyse the dependence on the dipolar interactions and trap geometry, the length and time scales for collapse, and relate our findings to recent experiments.Comment: In this version (the published version) we have slightly rewritten the manuscript in places and have corrected some typos. 15 pages and 13 figure