374 research outputs found

    Application of the quick scan audit methodology in an industrial filter production process

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    The quick scan audit methodology (QSAM) is an established investigative tool to assess the health of business processes and supply chains within short schedules. This study extends the standard QSAM procedure to include the simulation step. It also extends the QSAM to a wider industry platform by applying it into the precision mechanical engineering industry, where managers have been under competitive pressure to reduce an industrial filter production lead time. Following a review of the relevant literature, this paper presents the research design adopted in the study. The QSAM has been conducted using various data collection techniques (such as observations, process activity mapping, interviews, questionnaires, brainstorming and access to company documents) and data analysis methods (including cause and effect analysis, Pareto analysis and time series plot). This is followed by the development of a set of improvement strategies, namely, direct information sharing, priority planning, and additional data recording and analysis. In addition to testing the potential benefits of changing scheduling approaches for the paint plant, simulation has been utilized in this study as a communication means to increase employee participation in the QSAM process and enhance the audit accuracy. It has also provided the case company with a better understanding of the behaviour and characteristics of the system under study, thus facilitating more thoughtful decisions to improve the system. The paper concludes with further research opportunities derived from this study

    Homogeneous nucleation of quark-gluon plasma, finite size effects and long-lived metastable objects

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    The general formalism of homogeneous nucleation theory is applied to study the hadronization pattern of the ultra-relativistic quark-gluon plasma (QGP) undergoing a first order phase transition. A coalescence model is proposed to describe the evolution dynamics of hadronic clusters produced in the nucleation process. The size distribution of the nucleated clusters is important for the description of the plasma conversion. The model is most sensitive to the initial conditions of the QGP thermalization, time evolution of the energy density, and the interfacial energy of the plasma-hadronic matter interface. The rapidly expanding QGP is first supercooled by about ΔT=TTc=46\Delta T = T - T_c = 4-6 %. Then it reheats again up to the critical temperature T_c. Finally it breaks up into hadronic clusters and small droplets of plasma. This fast dynamics occurs within the first 510fm/c5-10 fm/c. The finite size effects and fluctuations near the critical temperature are studied. It is shown that a drop of longitudinally expanding QGP of the transverse radius below 4.5 fm can display a long-lived metastability. However, both in the rapid and in the delayed hadronization scenario, the bulk pion yield is emitted by sources as large as 3-4.5 fm. This may be detected experimentally both by a HBT interferometry signal and by the analysis of the rapidity distributions of particles in narrow p_T-intervals at small p_T on an event-by-event basis.Comment: 29 pages, incl. 12 figures and 1 table; to be published in Phys. Rev.

    Homogeneous Bubble Nucleation driven by local hot spots: a Molecular Dynamics Study

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    We report a Molecular Dynamics study of homogenous bubble nucleation in a Lennard-Jones fluid. The rate of bubble nucleation is estimated using forward-flux sampling (FFS). We find that cavitation starts with compact bubbles rather than with ramified structures as had been suggested by Shen and Debenedetti (J. Chem. Phys. 111:3581, 1999). Our estimate of the bubble-nucleation rate is higher than predicted on the basis of Classical Nucleation Theory (CNT). Our simulations show that local temperature fluctuations correlate strongly with subsequent bubble formation - this mechanism is not taken into account in CNT

    Structure and Stability of an Amorphous Metal

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    Using molecular dynamics simulations, with a realistic many-body embedded-atom potential, and a novel method to characterize local order, we study the structure of pure nickel during the rapid quench of the liquid and in the resulting glass. In contrast with previous simulations with pair potentials, we find more crystalline order and fewer icosahedra for slower quenching rates, resulting in a glass less stable against crystallization. It is shown that there is not a specific amorphous structure, only the arrest of the transition from liquid to crystal, resulting in small crystalline clusters immersed in an amorphous matrix with the same structure of the liquid.Comment: 4 pages, 4 ps figs., to appear in Phys. Rev. Let

    Nucleation and Bulk Crystallization in Binary Phase Field Theory

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    We present a phase field theory for binary crystal nucleation. In the one-component limit, quantitative agreement is achieved with computer simulations (Lennard-Jones system) and experiments (ice-water system) using model parameters evaluated from the free energy and thickness of the interface. The critical undercoolings predicted for Cu-Ni alloys accord with the measurements, and indicate homogeneous nucleation. The Kolmogorov exponents deduced for dendritic solidification and for "soft-impingement" of particles via diffusion fields are consistent with experiment.Comment: 4 pages, 4 figures, accepted to PR

    The financial fragility and the crisis of the Greek government sector

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    The purpose of this paper is to develop Minskyan financial fragility indices for the government sector and to examine the financial structure of the Greek government before and after the onset of the sovereign debt crisis in 2009. We provide empirical evidence that clearly shows the growing financial fragility of the Greek public sector in the 2000s. We also assess the effectiveness of the implemented bailout adjustment programmes in Greece and claim that the conducted austerity measures and fiscal consolidation have not significantly improved the financial posture of the Greek government sector. We argue that the implementation of fiscal and wage austerity in an economy that lacks structural competitiveness produces prolonged recession and unemployment with adverse feedback effects on the financial fragility of the government
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