The Potential of Restarts for ProbSAT

This work analyses the potential of restarts for probSAT, a quite successful algorithm for k-SAT, by estimating its runtime distributions on random 3-SAT instances that are close to the phase transition. We estimate an optimal restart time from empirical data, reaching a potential speedup factor of 1.39. Calculating restart times from fitted probability distributions reduces this factor to a maximum of 1.30. A spin-off result is that the Weibull distribution approximates the runtime distribution for over 93% of the used instances well. A machine learning pipeline is presented to compute a restart time for a fixed-cutoff strategy to exploit this potential. The main components of the pipeline are a random forest for determining the distribution type and a neural network for the distribution's parameters. ProbSAT performs statistically significantly better than Luby's restart strategy and the policy without restarts when using the presented approach. The structure is particularly advantageous on hard problems.Comment: Eurocast 201

Managing Work Within a Virtual Enterprise - Revising Project Planning Practice

This paper presents the findings of an empirical study into the management of projects within a virtual environment. In a virtual project, co-workers can be both geographically and temporally dispersed. The control and co-ordination of the work output of the virtual project team is a key process for business success. Traditional project management techniques have been found wanting when applied to virtual projects. New techniques need to be developed. This paper identifies key factors in the control and co-ordination of virtual projects and proposes a project management process for virtual projects

An overview of microclimate tools for predicting the thermal comfort, meteorological parameters and design strategies in outdoor spaces

Abstract There are several outdoor microclimatic simulation software tools in use. The current research aims to identify some of the most prominent computer-based tools based on their capacity of predicting a significant number of variables and compare them in order to establish their differences. This article provides an overview of the applications of computational fluid dynamics in outdoor performance simulation, focused on three topics: general criteria, specific outputs, strategies, and elements can be investigated by the tool. The results have shown that ENVI-met tool is capable of predicting and simulating the set microclimate variables

Towards a simplified description of thermoelectric materials: Accuracy of approximate density functional theory for phonon dispersions

We calculate the phonon-dispersion relations of several two-dimensional materials and diamond using the density-functional based tight-binding approach (DFTB). Our goal is to verify if this numerically efficient method provides sufficiently accurate phonon frequencies and group velocities to compute reliable thermoelectric properties. To this end, the results are compared to available DFT results and experimental data. To quantify the accuracy for a given band, a descriptor is introduced that summarizes contributions to the lattice conductivity that are available already in the harmonic approximation. We find that the DFTB predictions depend strongly on the employed repulsive pair-potentials, which are an important prerequisite of this method. For carbon-based materials, accurate pair-potentials are identified and lead to errors of the descriptor that are of the same order as differences between different local and semi-local DFT approaches

Solution heat treatment, forming and in-die quenching of a commercial sheet magnesium alloy into a complex-shaped component: experimentation and FE analysis

Interest in lightweight materials, particularly magnesium alloys, has increased significantly with rising efficiency requirements in the automotive sector. Magnesium is the lightest available structural metal, with a density approximately 35% lower than that of aluminium. The potential is great for magnesium to become a primary material used in future low carbon vehicle structures; however, there are significant obstacles, namely low ductility and formability, particularly at room temperature. The aim of this work is to present the feasibility of using the solution Heat treatment, Forming, and in-die Quenching (HFQ) process to produce complex shapes from a sheet magnesium alloy, and to use the results to verify a simulation of the process developed using commercial FE software. Uniaxial tensile tests were initially conducted to establish the optimum parameters for forming the part. Stamping trials were then carried out using these parameters, and a simulation set up modelling the forming operation. It was shown that the HFQ process could be used to form a successful component from this alloy, and that a good match was achieved between the results of the forming experiments and the simulation.The authors gratefully acknowledge the support from the EPSRC (Grant Ref: EP/I038616/1) for TARF-LCV: Towards Affordable, Closed-Loop Recyclable Future Low Carbon Vehicle Structures

A virtual crystal plasticity simulation tool for micro-forming

AbstractThe trend of increasing miniaturization of varied products and devices with a wide range of applications necessitates the forming of metallic parts with dimensions at the micron scale. In micro-forming, the stress and deformation are highly anisotropic. Hence, conventional macro-mechanics models fail to capture the important features, such as necking and bending resulting from strain localization. In this paper, a virtual integrated micro-mechanics simulation tool is presented, that was developed within the framework of Crystal Plasticity (CP) theory. With this tool, a polycrystalline Finite Element (FE) model was produced by introducing grain size, orientations and distribution patterns using VGRAIN software. ABAQUS software was used and the CP constitutive equations were implemented through a user-defined material subroutine, VUMAT. Typical micro-forming processes simulated include tension, extrusion and hydro-forming to demonstrate the effectiveness of the integrated simulation system. Finally, a map is proposed that establishes bounds of appropriate usage for different modeling techniques, namely a macromechanics plasticity model and a micro-mechanics crystal plasticity model, which will be useful to engineers in the metal forming industry in choosing suitable simulation tools

Scattering solutions of the spinless Salpeter equation

A method to compute the scattering solutions of a spinless Salpeter equation (or a Schrodinger equation) with a central interaction is presented. This method relies on the 3-dimensional Fourier grid Hamiltonian method used to compute bound states. It requires only the evaluation of the potential at equally spaced grid points and yields the radial part of the scattering solution at the same grid points. It can be easily extended to the case of coupled channel equations and to the case of non-local interactions.Comment: 7 page

On the origin of plasticity-induced microstructure change under sliding contacts

Discrete dislocation plasticity (DDP) calculations are carried out to investigate the response of a single crystal contacted by a rigid sinusoidal asperity under sliding loading conditions to look for causes of microstructure change in the dislocation structure. The mechanistic driver is identified as the development of lattice rotations and stored energy in the subsurface, which can be quantitatively correlated to recent tribological experimental observations. Maps of surface slip initiation and substrate permanent deformation obtained from DDP calculations for varying contact size and normal load suggest ways of optimally tailoring the interface and microstructural material properties for various frictional loads