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Fault tolerance and ultimate physical limits of nanocomputation
Published in David Crawley, Konstantin Nikolić, Michael Forshaw, 3D Nanoelectronic Computer Architecture and Implementation, 2020
A S Sadek, K Nikolić, M Forshaw
As the limits of CMOS technology are approached, and as Moore’s law starts to be challenged, attempts have been made to set technology-independent bounds on computation [23, 27, 28] and nanocomputation in particular [77]. Physics itself is the ultimate computer and so the limits to computation must be decisively derived from its underlying laws. Many of the limits derived may seem irrelevant to our current engineering capabilities but the underlying principles of what physics tells us about the bounds to information processing are just as relevant under more practical conditions. Frank has shown through the consideration of physical limits that the optimum nanocomputational architecture for classical computing is a reversible, highly parallel 3D mesh of processors that removes entropy from the system ballistically [77]. More generally, limits on computational speed, communication and memory have been derived from relativity, thermodynamics, statistical mechanics and quantum field theory. With a few exceptions, one notable theme that has been overlooked by researchers is the effect of errors on computation and its fundamental basis in the physical limits of computing. Sadek et al have shown how noise effects and fault tolerance are essential considerations and delineated their basis in thermodynamics [3]. We now review this body of work and consider the suggestions it makes as to the direction we should take for the future development of 3D nanoscale information systems.
Evaluation of the PAR Mitigation System in Swiss PWR Containment Using the GOTHIC Code
Published in Nuclear Technology, 2019
Davide Papini, Michele Andreani, Pascal Steiner, Bojan Ničeno, Jens-Uwe Klügel, Horst-Michael Prasser
The GOTHIC thermal-hydraulic program18 is based on a two-phase, multifluid formulation, and it solves the conservation of mass, energy, and momentum for three fields: a multicomponent gas mixture, a continuous liquid, and droplets. A full treatment of the momentum transport terms is considered, with inclusion of turbulent shear and turbulent mass and energy diffusion. GOTHIC has the necessary capabilities for simulating the 3-D distribution of hydrogen from the time point of release to the time point of possible slow deflagration (flame acceleration cannot be simulated). These capabilities include fundamental models for transport phenomena (turbulent and molecular diffusion, natural convection, multiple gases, and steam condensation); capability to handle complex geometry; operation of engineering devices (valves, doors, hatches, PARs, etc.); possibility of easy transfer of initial and boundary conditions from severe accident codes; and, compared to CFD codes, capability to obtain accurate results with relatively coarse mesh.19 The GOTHIC code is based on built-in correlations for heat transfer, pressure drops, etc., that do not require modeling boundary layers like in most CFD codes but, indeed, rely on bulk values and hence take advantage of not too fine nodalizations at the wall. As a consequence, the coarse-mesh approach of GOTHIC limits its computation costs and makes it suitable to simulate the large time and spatial scales involved during a severe accident.
Evaluating the Visibility of Architectural Features for People with Low Vision – A Quantitative Approach
Published in LEUKOS, 2022
William B. Thompson, Robert A. Shakespeare, Siyun Liu, Sarah H. Creem-Regehr, Daniel J. Kersten, Gordon E. Legge
Since knowing the likelihood of being able to see one point on a potential hazard is of limited value, we average the hazard value over all such points in each analyzed image, producing the HVS. Since this equally weights each geometry point in the image, this is most often combined with a region of interest (ROI) specification that limits the computation to the specific areas with mobility hazards of questionable visibility.