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A novel method for performing exponentiation modulo 2 k is described. The algorithm has a critical path consisting of k dependent shift-and-add modulo 2 k operations. Although 3 is the preferred exponent base, the algorithm can be extended easily in order to perform the general binary powering operation. Introduction and background: The basic integer(More)
We present an empirical investigation into the prevalence and impact of distributed denial-of-service (DDoS) attacks on operators in the Bitcoin economy. To that end, we gather and analyze posts mentioning " DDoS " on the popular Bitcoin forum bitcointalk.org. Starting from around 3 000 different posts made between May 2011 and October 2013, we document 142(More)
Two geometrically identical models of the leaflets of a bicuspid bioprosthetic heart valve have been constructed using finite elements. The boundary conditions applied to the models were also identical but a linear material model has been used in one and a nonlinear elastic model in the other. The models were fullscale and contained 2600 Belytschko-Lin-Tsai(More)
The effect of changing the modulus and thickness of the material in the leaflets of an artificial heart valve has been investigated. This has been achieved with a finite element model of the valve having approximately 2300 thin shell elements. The valve motion and the resulting stresses are modelled dynamically during closure, and subsequent pressurisation.(More)
A novel algorithm for computing the discrete logarithm modulo 2 k that is suitable for fast software or hardware implementation is described. The chosen preferred implementation is based on a linear-time multiplier-less method and has a critical path of less than k modulo 2 k shift-and-add operations. Introduction and summary: Hardware capabilities for(More)