189,227 research outputs found

    Path Puzzles: Discrete Tomography with a Path Constraint is Hard

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    We prove that path puzzles with complete row and column information--or equivalently, 2D orthogonal discrete tomography with Hamiltonicity constraint--are strongly NP-complete, ASP-complete, and #P-complete. Along the way, we newly establish ASP-completeness and #P-completeness for 3-Dimensional Matching and Numerical 3-Dimensional Matching.Comment: 16 pages, 8 figures. Revised proof of Theorem 2.4. 2-page abstract appeared in Abstracts from the 20th Japan Conference on Discrete and Computational Geometry, Graphs, and Games (JCDCGGG 2017

    Study on Flow Dynamics of Carbon Dioxide/Natural Gas in a Nanoporous Adsorbent-based Adsorption Column

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    This study will investigate the flow dynamics of the carbon dioxide-natural gas flow in a nanoporous adsorbent-based adsorption column through computational approach. The process is simulated through the use of computational fluid dynamics (CFD) software by varying the process parameters such as particle diameter sizes, column geometry and column dimension. The proposed dimensional characteristic of the column to be studied is in a demo sized version, which is predicted to be about 50 times larger than the current studied lab-scale version. In this study, the actual adsorption rate of CO2 by the nanoporous adsorbent is not considered, whereby the simulation is merely based upon the ‘non-reactive’ flow of the gases through a porous domain. It is expected that the analysis of the flow dynamics for the process would provide a viable information on the possible operating conditions for the demo scale adsorption column that would be used in the design of the actual version for the purification of CO2 from natural gas

    Lengths of divisible codes with restricted column multiplicities

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    We determine the minimum possible column multiplicity of even, doubly-, and triply-even codes given their length. This refines a classification result for the possible lengths of qrq^r-divisible codes over Fq\mathbb{F}_q. We also give a few computational results for field sizes q>2q>2. Non-existence results of divisible codes with restricted column multiplicities for a given length have applications e.g. in Galois geometry and can be used for upper bounds on the maximum cardinality of subspace codes.Comment: 26 pages, 7 table

    Modeling the extra-column volume in a small column setup for bulk gas adsorption

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    This study aims at highlighting the importance of an accurate characterization of the extra-column volume (ECV) and presents an experimental and computational protocol based on the characterization of the extra-column volume in terms of step-response experiments performed under various flow rates and pressures of 1bar, 5bar and 10bar. The experiments are interpreted by describing the extra-column volume with a compartment model that reflects the geometry of the physical setup and that involves a stagnant zone to account for the non-ideal flow behavior through the piping system. The use of a mathematical model combining the description of the adsorption column and of the ECV can successfully predict experimental CO2-H2 breakthrough profiles performed at different pressures on an activated carbon adsorbent. This work shows how the presence of non-negligible extra-column effects can be accounted for, for the determination of adsorption transport parameter

    Investigation of flow through a computationally generated packed column using CFD and additive layer manufacturing

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    Preprint submitted to Computers and Chemical Engineering 18 March 2014. © The AuthorsThe version of record is available from the publisher via doi:10.1016/j.compchemeng.2014.04.005.When analysing packed beds using CFD approaches, producing an accurate geometry is often challenging. Often a computational model is produced from non-invasive imaging of the packed bed using 3d MRI or μ-CT. This work pioneers the exact reverse of this, by creating a physical bed from the computational model using Additive Layer Manufacturing (ALM). The paper focuses on both experimental analysis and computational analysis of packed columns of spheres. A STL file is generated of a packed column formed using a Monte-Carlo packing algorithm, and this is meshed and analysed using Computational Fluid Dynamics. In addition to this, a physical model is created using ALM on a 3d printer. This allows us to analyse the identical bed geometry both computationally and experimentally and compare the two. Pressure drop and flow patterns are analysed within the bed in detail. © 2014 Elsevier Ltd

    GMAW shielding gas flow optimisation by refinement of nozzle geometry

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    With an ongoing demand to improve the efficiency of the gas metal arc welding process, steps are being taken to reduce the shielding gas consumption. However, sufficient shielding gas coverage of the weld region is essential for the generation of high quality welds, and drafts can be detrimental to its efficiency. In industry, the general practise to ensure coverage is to increase the shielding gas flow rate, however, too high a flow rate can induce undesirable turbulence in the shielding gas column, whilst adding unnecessary cost to the process. A simplified computational fluid dynamics model has been generated, and validated through extensive experimental trials, to accurately model the shielding gas flow when subjected to the adverse effects of cross drafts. Several nozzle geometry changes have been investigated with the aim of improving the shielding gas column’s resistance to drafts, eliminating the requirement to increase the shielding gas flow rate

    Correlation of Automorphism Group Size and Topological Properties with Program-size Complexity Evaluations of Graphs and Complex Networks

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    We show that numerical approximations of Kolmogorov complexity (K) applied to graph adjacency matrices capture some group-theoretic and topological properties of graphs and empirical networks ranging from metabolic to social networks. That K and the size of the group of automorphisms of a graph are correlated opens up interesting connections to problems in computational geometry, and thus connects several measures and concepts from complexity science. We show that approximations of K characterise synthetic and natural networks by their generating mechanisms, assigning lower algorithmic randomness to complex network models (Watts-Strogatz and Barabasi-Albert networks) and high Kolmogorov complexity to (random) Erdos-Renyi graphs. We derive these results via two different Kolmogorov complexity approximation methods applied to the adjacency matrices of the graphs and networks. The methods used are the traditional lossless compression approach to Kolmogorov complexity, and a normalised version of a Block Decomposition Method (BDM) measure, based on algorithmic probability theory.Comment: 15 2-column pages, 20 figures. Forthcoming in Physica A: Statistical Mechanics and its Application
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