15,637 research outputs found

    What is an ANZAC? An American Response to Australian Warriors

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    Rarely, in the annals of historical memory does one find a story as compelling and depressing as the narrative of the ANZACs. Never have men fought so bravely and ultimately so futilely to protect a land they only knew from history and geography books. With a deep sense of responsibility and youthful nationalism, these Australians and New Zealanders volunteered for service to the British Crown. Few knew their actions and the actions of their comrades and enemies would result in the war to end all wars, World War I. Few Australians knew their engagements would be covered in many of the major newspapers of the day. The New York Times was one of these papers. Through their coverage of Australian maneuvers, American’s were, for the first time, exposed to Australia and its people

    Cross-sectional river shapes: A variational discharge-resistance formulation

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    Cross-sectional river shapes were obtained from a variational principle: minimizing the bed friction for a given discharge and a given maximum lateral bed slope (angle of repose). The optimal shape is found to be independent of both the exponent in the friction law adopted and the value of the discharge, but it does depend on the angle of repose. The optimal profile is a single stream; for braided rivers the solution is suboptimal

    Linear evolution of sandwave packets

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    We investigate how a local topographic disturbance of a flat seabed may become morphodynamically active, according to the linear instability mechanism which gives rise to sandwave formation. The seabed evolution follows from a Fourier integral, which can generally not be evaluated in closed form. As numerical integration is rather cumbersome and not transparent, we propose an analytical way to approximate the solution. This method, using properties of the fastest growing mode only, turns out to be quick, insightful, and to perform well. It shows how a local disturbance develops gradually into a sandwave packet, the area of which increases roughly linearly with time. The elevation at the packetÂżs center ultimately tends to increase, but this may be preceded by an initial stage of decrease, depending on the spatial extent of the initial disturbance. In the case of tidal asymmetry, the individual sandwaves in the packet migrate at the migration speed of the fastest growing mode, whereas the envelope moves at the group speed. Finally, we apply the theory to trenches and pits and show where results differ from an earlier study in which sandwave dynamics have been ignored

    Numerical equilibrium analysis for structured consumer resource models

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    In this paper, we present methods for a numerical equilibrium and stability analysis for models of a size structured population competing for an unstructured resource. We concentrate on cases where two model parameters are free, and thus existence boundaries for equilibria and stability boundaries can be defined in the (two-parameter) plane. We numerically trace these implicitly defined curves using alternatingly tangent prediction and Newton correction. Evaluation of the maps defining the curves involves integration over individual size and individual survival probability (and their derivatives) as functions of individual age. Such ingredients are often defined as solutions of ODE, i.e., in general only implicitly. In our case, the right-hand sides of these ODE feature discontinuities that are caused by an abrupt change of behavior at the size where juveniles are assumed to turn adult. So, we combine the numerical solution of these ODE with curve tracing methods. We have implemented the algorithms for “Daphnia consuming algae” models in C-code. The results obtained by way of this implementation are shown in the form of graphs
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