Software integration testing based on communication coverage criteria and partial model generation

This paper considers the problem of integration testing the components of a timed distributed software system. We assume that communication between the components is specified using timed interface automata and use computational tree logic (CTL) to define communication-based coverage criteria that refer to send- and receive-statements and communication paths. The proposed method enables testers to focus during component integration on such parts of the specification, e.g. behaviour specifications or Markovian usage models, that are involved in the communication between components to be integrated. A more specific application area of this approach is the integration of test-models, e.g. a transmission gear can be tested based on separated models for the driver behaviour, the engine condition, and the mechanical and hydraulical transmission states. Given such a state-based specification of a distributed system and a concrete coverage goal, a model checker is used in order to determine the coverage or generate test sequences that achieve the goal. Given the generated test sequences we derive a partial test-model of the components from which the test sequences are derived. The partial model can be used to drive further testing and can also be used as the basis for producing additional partial models in incremental integration testing. While the process of deriving the test sequences could suffer from a combinatorial explosion, the effort required to generate the partial model is polynomial in the number of test sequences and their length. Thus, where it is not feasible to produce test sequences that achieve a given type of coverage it is still possible to produce a partial model on the basis of test sequences generated to achieve some other criterion. As a result, the process of generating a partial model has the potential to scale to large industrial software systems. While a particular model checker, UPPAAL, was used, it should be relatively straightforward to adapt the approach for use with other CTL based model checkers. A potential additional benefit of the approach is that it provides a visual description of the state-based testing of distributed systems, which may be beneficial in other contexts such as education and comprehension

Ion-size effects on cuprate High Temperature Superconductors

There are two general ways to compress the cuprates, by external pressure or by internal pressure as induced by isovalent-ion substitution. Paradoxically, they have the opposite effect on the superconducting transition temperature. This thesis seeks to understand the salient difference between these two pressures. We study three families of cuprates where the ion size can be systematically altered; Bi$_2$(Sr$_{1.6-x}$A$_x$)Ln$_{0.4}$CuO$_{6+ \delta}$, ACuO$_2$ and LnBa$_{2-x}$Sr$_x$Cu$_3$O$_{7-\delta}$ where Ln is a Lanthenide or Y and A=\{Mg,Ca,Sr,Ba\}. We use a variety of techniques to explore our paradox, for example; Raman spectroscopy to measure the antiferromagnetic exchange energy and energy gaps, Density Functional Theory to calculate the density of states, Muon Spin Relaxation to measure the superfluid density as well as a variety of more conventional techniques to synthesize and characterise our samples. Our Raman studies show that an energy scale for spin fluctuations cannot resolve the different effects of the two pressures. Similarly the density of states, while an important property, does not clearly resolve the paradox. Our superfluid density measurements show that the disorder resulting from isovalent-ion substitution is secondary in importance for the superconducting transition temperature. Instead, we find that the polarisability is a key property of the cuprates with regard to superconductivity. This understanding resolves the paradox! It implies that electron pairing results from either (i) a short-range interaction where the polarisability screens repulsive longer-range interactions and/or (ii) the relatively unexplored idea of the exchange of quantized, coherent polarisation waves. More generally, we have also demonstrated the utility of studying ion-size effects to further our collective understanding of the cuprates.Comment: PhD thesis. 238 pages, 79 figure

Muon-spin-rotation study of the magnetic structure in the tetragonal antiferromagnetic state of weakly underdoped Ba1−x _{1-x} Kx _{x} Fe2 _{2} As2 _{2}

With muon spin rotation ($\mu$SR) we studied the transition between the orthorhombic antiferromagnetic (o-AF) and the tetragonal antiferromagnetic (t-AF) states of a weakly underdoped Ba$_{1-x}$K$_{x}$Fe$_{2}$As$_{2}$ single crystal. We observed some characteristic changes of the magnitude and the orientation of the magnetic field at the muon site which, due to the fairly high point symmetry of the latter, allow us to identify the magnetic structure of the t-AF state. It is the so-called, inhomogeneous double-$\mathbf{Q}$ magnetic structure with $c$-axis oriented moments which has a vanishing magnetic moment on half of the Fe sites.Comment: 5 pages, 4 figures. Supplementary Material: 8 figure

Dark matter as a Cosmic Bose-Einstein Condensate and possible Superfluid [pre-print]

Dark matter arising from spontaneous symmetry breaking of a neutral scalar field coupled to gravity comprises ultra low mass bosons with a Bose-Einstein condensation temperature far above the present background temperature. Assuming galactic halos to consist of a Bose-Einstein condensate of astronomical extent, we calculate the condensate coherence length, transition temperatures, mass distribution, and orbital velocity curves, and deduce the particle mass and number density from the observed rotation curves for the Andromeda and Triangulum galaxies. We also consider the possibility of superfluid behaviour in the halos of rotating galaxies, and estimate the critical angular frequency and line density for formation of quantised vortices

Maine Crusades and Crusaders, 1830-1850 and Addenda

The article reviews the proliferation of agencies and movements for advancing Christian piety and morals in 19th century Maine. The Addenda reviews a number of publications regarding Maine Indigenous Peoples

Coherent Degenerate Dark Matter: A Galactic Superfluid? [pre-print]

Dark matter comprising a Bose-Einstein condensate (BEC) forms structures of the size of its coherence length, as determined by equilibrium between quantum pressure and gravitational attraction. This is also the core size of quantum vortices in a BEC superfluid. From the density and rotation curve of the Andromeda Galaxy (M31) we estimate the particle mass, particle density, coherence length, critical temperature, critical angular frequency, and vortex line density of the dark matter condensate composing the halo

Quantum Stabilization of General-Relativistic Variable-Density Degenerate Stars

Research by one of the authors suggested that the critical mass of constant-density neutron stars will be greater than eight solar masses when the majority of their neutrons group into bosons that form a Bose-Einstein condensate, provided the bosons interact with each other and have scattering lengths on the order of a picometer. That analysis was able to use Newtonian theory for the condensate with scattering lengths on this order, but general relativity provides a more fundamental analysis. In this paper, we determine the equilibrium states of a static, spherically-symmetric variable-density mixture of a degenerate gas of noninteracting neutrons and a Bose-Einstein condensate using general relativity. We use a Klein-Gordan Lagrangian density with a Gross-Pitaevskii term for the condensate and an effective field for the neutrons. We show that a new class of compact stars can exist with masses above the Oppenheimer-Volkoff limit, provided the scattering length of the bosons is large enough. These stars have no internal singularities, obey causality, and demonstrate a quantum mechanism consistent with general relativity that could prevent collapsed stars from becoming black holes