Warwick Research Archives Portal Repository

    To support adaptivity in agent-based learning systems - the use of learning objects and learning style

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    Few intelligent learning systems exist which are dynamic and able to provide personalized learning materials to satisfy individual students' requirements. We have developed an agent-based learning system that incorporates learning objects to facilitate personalization, and is based on a learning style theory as the pedagogic foundation for adaptivity. In this paper, we present our novel approach to the incorporation of learning style theory and learning objects, and evaluation indicates that the approach is able to provide personalized learning materials and improve the adaptivity in learning systems

    Fermions without fermion fields

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    It is shown that an arbitrary fermion hopping Hamiltonian can be mapped into a system with no fermion fields, generalizing an earlier model of Levin and Wen. All operators in the Hamiltonian of the resulting description commute (rather than anticommute) when acting at different sites, despite the system having excitations obeying Fermi statistics. While extra conserved degrees of freedom are introduced, they are all locally identified in the representation obtained. The same methods apply to Majorana (half) fermions, which for Cartesian lattices mitigate the fermion doubling problem. The generality of these results suggests that the observation of Fermion excitations in nature does not demand that anticommuting Fermion fields be fundamental

    SOA services in higher education

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    Service Oriented Architecture (SOA) is a recent architectural framework for distributed software system development in which software components are packaged as Services. It has become increasingly popular in academia and in industry, but has been principally used in the business domain. However, in higher education, SOA has rarely been applied or investigated. In this paper, we propose the idea of applying SOA technologies in the education domain, to increase both interoperability and flexibility within the e-learning environment. We expect that both students and teachers in higher educational institutions can benefit from this approach. We also describe a number of possible SOA services, along with a high level service roadmap to support a university's learning and teaching activities

    Newly discovered cataclysmic variables from the INT/WFC photometric Hα survey of the northern Galactic plane

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    We report the discovery of 11 new cataclysmic variable (CV) candidates by the Isaac Newton Telescope (INT) Photometric H alpha Survey of the northern Galactic plane (IPHAS). Three of the systems have been the subject of further follow-up observations. For the CV candidates IPHAS J013031.90+622132.4 and J051814.34+294113.2, time-resolved optical spectroscopy has been obtained and radial-velocity measurements of the H alpha emission line have been used to estimate their orbital periods. A third CV candidate (IPHAS J062746.41+014811.3) was observed photometrically and found to be eclipsing. All three systems have orbital periods above the CV period gap of 2-3 h. We also highlight an other system, IPHAS J025827.88+635234.9, whose spectrum distinguishes it as a likely high-luminosity object with unusual C and N abundances

    Instability of condensation in the zero-range process with random interaction

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    The zero-range process is a stochastic interacting particle system that is known to exhibit a condensation transition. We present a detailed analysis of this transition in the presence of quenched disorder in the particle interactions. Using rigorous probabilistic arguments, we show that disorder changes the critical exponent in the interaction strength below which a condensation transition may occur. The local critical densities may exhibit large fluctuations, and their distribution shows an interesting crossover from exponential to algebraic behavior

    Correction : perfect simulation for a class of positive recurrent Markov chains

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    In [1] we introduced a class of positive recurrent Markov chains, named tame chains. A perfect simulation algorithm, based on the method of dominated CFTP, was then shown to exist in principle for such chains. The construction of a suitable dominating process was flawed, in that it relied on an incorrectly stated lemma ([1], Lemma 6). This claimed that a geometrically ergodic chain, subsampled at a stopping time σ , satisfies a geometric Foster–Lyapunov drift condition with coefficients not depending on σ. This is true if σ is a stopping time independent of the chain, but not if this independence does not hold. Reference [1], Lemma 6 is therefore false as stated

    On the orbital periods of the AM CVn stars HP Librae and V803 Centauri

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    We analyse high time resolution spectroscopy of the AM CVn stars HP Librae and V803 Centauri, taken with the New Technology Telescope (NTT) and the Very Large Telescope (VLT) of the European Southern Observatory, Chile. We present evidence that the literature value for V803 Cen's orbital period is incorrect, based on an observed 'S-wave' in the binary's spectrogram. We measure a spectroscopic period P-V803 (Cen) = 1596.4 +/- 1.2 s of the S-wave feature, which is significantly shorter than the 1611 -s periods found in previous photometric studies. We conclude that the latter period likely represents a 'superhump'. If one assumes that our S-wave period is the orbital period, V803 Cen's mass ratio can be expected to be much less extreme than previously thought, at q similar to 0.07 rather than q similar to 0.016. This relaxes the constraints on the masses of the components considerably: the donor star then does not need to be fully degenerate, and the mass of the accreting white dwarf no longer has to be very close to the Chandrasekhar limit. For HP Lib, we similarly measure a spectroscopic period P-HP (Lib) = 1102. +/- 8 0.2 s. This supports the identification of HP Lib's photometric periods found in the literature, and the constraints upon the masses derived from them

    Phase-resolved spectroscopy of the helium dwarf nova 'SN 2003aw' in quiescence

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    High time resolution spectroscopic observations of the ultracompact helium dwarf nova 'SN 2003aw' in its quiescent state at V similar to 20.5 reveal its orbital period at 2027.8 +/- 0.5 s or 33.80 min. Together with the photometric 'superhump' period of 2041.5 +/- 0.5 s, this implies a mass ratio q approximate to 0.036. We compare both the average and time-resolved spectra of 'SN 2003aw' and Sloan Digital Sky Survey (SDSS) J124058.03-015919.2. Both show a DB white dwarf spectrum plus an optically thin, helium-dominated accretion disc. 'SN 2003aw' distinguishes itself from the SDSS source by its strong calcium H & K emission lines, suggesting higher abundances of heavy metals than the SDSS source. The silicon and iron emission lines observed in the SDSS source are about twice as strong in 'SN 2003aw'. The peculiar 'double bright spot' accretion disc feature seen in the SDSS source is also present in time-resolved spectra of 'SN 2003aw', albeit much weaker

    Pore-blockade times for field-driven polymer translocation

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    We study pore-blockade times for a translocating polymer of length N, driven by a field E across the pore in three dimensions. The polymer performs Rouse dynamics, i.e., we consider polymer dynamics in the absence of hydrodynamical interactions. We find that the typical time for which the pore remains blocked during a translocation event scales as similar to N(1+ 2 nu)/(1+nu)/E, where nu similar or equal to 0.588 is the Flory exponent for the polymer. We show, in line with our previous work, that this scaling behavior stems from polymer dynamics in the immediate vicinity of the pore - in particular, the memory effects in the polymer chain tension imbalance across the pore. This result, like numerical results from several other groups, violates the lower bound similar to N1+nu/E suggested earlier in the literature. We discuss why this lower bound is incorrect and show, on the basis of the conservation of energy, that the correct lower bound for the pore-blockade time for field-driven translocation is given by eta N-2 nu/E, where eta is the viscosity of the medium surrounding the polymer

    Dynamical origin of spontaneous symmetry breaking in a field-driven nonequilibrium system

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    A one-dimensional driven two-species model with parallel sublattice update and open boundaries is considered. Although the microscopic many-body dynamics is symmetric with respect to the two species and interactions are short-ranged, there is a region in parameter space with broken symmetry in the steady state. The sublattice update is deterministic in the bulk and allows for a detailed analysis of the relaxation dynamics, so that symmetry breaking can be shown to be the result of an amplification mechanism of fluctuations. In contrast to previously considered models, this leads to a proof for spontaneous symmetry breaking which is valid throughout the whole region in parameter space with a symmetry broken steady state
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