On the Throughput of Channels that Wear Out

This work investigates the fundamental limits of communication over a noisy discrete memoryless channel that wears out, in the sense of signal-dependent catastrophic failure. In particular, we consider a channel that starts as a memoryless binary-input channel and when the number of transmitted ones causes a sufficient amount of damage, the channel ceases to convey signals. Constant composition codes are adopted to obtain an achievability bound and the left-concave right-convex inequality is then refined to obtain a converse bound on the log-volume throughput for channels that wear out. Since infinite blocklength codes will always wear out the channel for any finite threshold of failure and therefore cannot convey information at positive rates, we analyze the performance of finite blocklength codes to determine the maximum expected transmission volume at a given level of average error probability. We show that this maximization problem has a recursive form and can be solved by dynamic programming. Numerical results demonstrate that a sequence of block codes is preferred to a single block code for streaming sources.Comment: 23 pages, 1 table, 11 figures, submitted to IEEE Transactions on Communication

A heterotic sigma model with novel target geometry

We construct a (1,2) heterotic sigma model whose target space geometry consists of a transitive Lie algebroid with complex structure on a Kaehler manifold. We show that, under certain geometrical and topological conditions, there are two distinguished topological half--twists of the heterotic sigma model leading to A and B type half--topological models. Each of these models is characterized by the usual topological BRST operator, stemming from the heterotic (0,2) supersymmetry, and a second BRST operator anticommuting with the former, originating from the (1,0) supersymmetry. These BRST operators combined in a certain way provide each half--topological model with two inequivalent BRST structures and, correspondingly, two distinct perturbative chiral algebras and chiral rings. The latter are studied in detail and characterized geometrically in terms of Lie algebroid cohomology in the quasiclassical limit.Comment: 83 pages, no figures, 2 references adde

Aligning business and information systems thinking: a cognitive approach

Business-information systems (IS) alignment has become an important strategic imperative for organizations competing in the global economy. Recent research (Reich and Benbasat [56]) indicates that building a shared understanding between business and IS executives is one way of strengthening this alignment. This paper describes a study that examines the cognitive basis of shared understanding between business and IS executives. Using Personal Construct Theory (Kelly [36]), this study uses cognitive mapping techniques to explore the commonal-ities and individualities in the cognition between these executives. Eighty business and IS executives in six companies participated in this study. The results indicate that a higher level of cognitive commonality is positively related to a higher level of business-IS alignment. This is supported by findings that greater diversity in cognitive structure and cognitive content of business and IS executives coincide with a lower level of alignment. Implications for practitioners and researchers are discussed

Centrifuge scaling considerations for fluid-particle systems

Two simulations are involved when a centrifuge is used to test models. First, the behaviour of the model in a uniform ng field is assumed to be similar to that of the prototype. Then the centrifuge is assumed to produce an equivalent ng gravitational field. For most static problems, the centrifuge does produce an equivalent ng gravitational field, but for some dynamic problems involving saturated soil these assumptions can break down. When the soil particles and fluid are moving relative to one another, the behaviour in the ng field is not similar to that in the 1g field unless the Reynolds number in both conditions is less than unity. Since this is a special circumstance, the centrifugal behaviour is not similar to that of the prototype in most cases. To illustrate this, the similarity requirements are examined for a single particle moving in a fluid. If different fluids are used in the model and prototype, then the difference in densities must also be accounted for

Unified modeling and measurement of current-programmed converters

A unified model is established for a current-programmed converter, which is both a modification and an extension of familiar models. Inclusion of the sampling effect allows the presence of an additional pole in the current-loop gain to be inferred. The resulting final double-slope asymptote is fixed in position, and the crossover frequency cannot exceed half the switching frequency. A new “stability parameter” Q_s determines the additional pole and describes the degree of peaking in the closed-loop transfer functions. Experimental verification employs an analog signal injection technique

A Unified Model for Current-Programmed Converters

A unified model is established for a current-programmed power converter, which is both a modification and an extension of familiar models. Inclusion of the sampling effect allows the presence of an additional pole ω_p in the current-loop gain to be derived. The resulting final double-slope asymptote is fixed in position, and the crossover frequency cannot exceed half the switching frequency. A stability parameter, Q_s, determines the additional pole and describes the degree of peaking in the closed-loop transfer function. Experimental verification employs an analog signal injection techniqu