Alexander Lau

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The benefits of monitoring the internal health of complex systems are recognized in mature engineering disciplines. Such monitoring helps maintain the operational reliability and availability of the system. Recently, research has begun to address the notion of health of complex software systems and its monitoring. This paper outlines a three-layer software(More)
Software systems have grown in size and complexity. It is not possible to exhaustively test them to a fault free condition before they are deployed. As a result, their execution may be marked by failures. Often, these failures are preceded by a deterioration of internal state of the program (errors) before an externally observable failure occurs.(More)
The hallmark of Weyl semimetals is the existence of open constant-energy contours on their surface-the so-called Fermi arcs-connecting Weyl points. Here, we show that, for time-reversal symmetric realizations of Weyl semimetals, these Fermi arcs, in many cases, coexist with closed Fermi pockets originating from surface Dirac cones pinned to time-reversal(More)
The Hofstadter model is a simple yet powerful Hamiltonian to study quantum Hall physics in a lattice system, manifesting its essential topological states. Lattice dimerization in the Hofstadter model opens an energy gap at half filling. Here we show that even if the ensuing insulator has a Chern number equal to zero, concomitantly a doublet of edge states(More)
Experience shows that external failures of software systems are often preceded by deterioration in their internal state (i.e. an error). An error is defined as the difference between a computed, observed, or measured value or condition and the true, specified, or theoretically correct value or condition [1]. For software systems that are designed to degrade(More)
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