Modeling of stick-slip phenomena using molecular dynamics

Molecular dynamics simulations are performed to investigate the atomic-scale stick-slip phenomenon of a pyramidal diamond tip inserted into the Ag(010) surface. The mechanisms behind the stick-slip events are investigated by considering sliding speeds between 1.0 and 5.0 ms-1 and vertical support displacements of 5 and 15 Å. The analysis of the dynamic features of the substrate shows that dislocations are extrinsically linked to the stick events, with the emission of a dislocation in the substrate region near the tip, when slip occurs after stick. For small vertical displacements, the scratch in the substrate is not continuous because the tip can jump over the surface when slipping, whereas at 15 Å, a continuous scratch is formed. The dynamic friction coefficient increases from ∼0.13 to ∼0.46 with increasing depth, but the static friction coefficient increases only from ∼0.32 to ∼0.54. At the larger depths the tip does not come to a halt during stick as it does for shallow indents. Instead the tip motion is more continuous with stick and slip manifested by periods of faster and slower motion. Although the exact points of stick and slip depend on the sliding speed, the damage to the substrate, the atomistic stick-slip mechanisms, and the friction coefficients are relatively independent of speed over the range of values considered

Diffusion dynamics of defects in Fe and Fe-P systems

The dimer method with the Ackland EAM potential has been used to determine the diffusion mechanisms of isolated defects in the bulk of α-Fe. Three defect systems were studied, an isolated vacancy, a P-vacancy complex and a P interstitial defect. Using an event table consisting of the transitions found using the dimer method, the kinetic Monte Carlo method has been used to simulate the diffusion of these defects. Periodic boundary conditions were used to simulate Fe crystals with finite concentrations of P atoms between 0.006 at. % and 0.038 at. %. At lower temperatures of around 350 K, substitutional P atoms in Fe act as centers of attraction for vacancy defects, such that the defect moves as a P-vacancy complex for most of the time. However, as the temperature is increased, the phosphorus atom and the vacancy spend greater amounts of time dissociated. We found that P interstitial defects can also diffuse through the lattice. Diffusion constants have been calculated for these systems at various temperatures and P concentrations. These showed that an Fe-P dumbbell is the most mobile of these defect systems and a P-vacancy complex the least mobile. For the isolated vacancy and P interstitial defect systems, the diffusion constant was found to satisfy the Arrhenius relation; the P-vacancy complex, however, showed a deviation from this relation

Risk modelling of fires and explosions in open-sided offshore platform modules

Incidents involving fires and explosions present a major hazard to the workforce on offshore oil and gas platforms. Following the Piper Alpha Disaster in 1988, platform operators for the UK sector are required to submit safety cases for approval by the Health and Safety Executive. A key requirement of these safety cases is that hazards associated with an accidental release of hydrocarbons have been demonstrated to be as low as reasonably practicable. This paper aims to describe a process for estimating the expected number of fatalities on offshore platforms with open-sided modules using a Monte Carlo simulation method implemented within the safety and reliability of offshore structures (SAROS) software. The process involves estimation of the frequency and magnitude of jet fires, pool fires, and explosions. This is combined with the distribution of the workforce over the platform at the time of the incident to predict the risk of fatality

Simulating radiation damage in a bcc Fe system with embedded yttria nanoparticles

We present a molecular dynamics study of radiation damage arising from nuclear collisions close to embedded yttria nanoparticles in a bcc Fe matrix. The model assumes a perfect body-centred cubic (bcc) iron matrix in which yttria nano-particles are embedded as a simplified model of an Oxide Dispersion Strengthened steel. It is shown how the nano-particles interact with nearby initiated collision cascades, through cascade blocking and absorbing energy. Fe defects accumulate at the interface both directly from the ballistic collisions and also by attraction of defects generated close by. The nano-particles generally remain intact during a radiation event and release absorbed energy over times longer than the ballistic phase of the collision cascade

Mesoscopic structure features in synthetic graphite

The mesocopic structure features in the coke fillers and binding carbon regions of a synthetic graphite grade have been examined by high resolution transmission electron microscopy (TEM) and Raman spectroscopy. Within the fillers, the three-dimensional structure is composed of crystal laminae with the basal plane dimensions (La) of hundreds nanometres, and thicknesses (Lc) of tens of nanometres. These laminae have a nearly perfect graphite structure with almost parallel c-axes, but their a-b planes are orientated randomly to form a “crazy paving” structure. A similar structure exists in the binding carbon regions, with a smaller La. Significantly bent laminae are widely seen in quinoline insoluble inclusions and the graphite regions developed around them. The La values measured by TEM are consistent with estimates from the intensity ratios of the D to G Raman peak in these regions. Atomistic modelling finds that the lowest energy interfaces in the crazy paving structure comprise 5, 6 and 7 member carbon rings. The bent laminae tend to maintain the 6 member rings, but are strained elastically. We suggest that a 7 member carbon ring leaves a cavity representing an arm-chair graphite edge contributing to the Raman spectra D peak

Analysis of socio-economic impacts of wind and solar photovoltaic energies in Europe

Los impactos socioeconómicos asociados a las energías renovables son objeto de un intenso debate internacional. Esta investigación pretende cuantificar cuatro de los principales impactos socioeconómicos asociados a las tecnologías eólica y solar fotovoltaica en los Estados miembros de la Unión Europea en el período 2008-2013. Se analizan los costes del apoyo público y los principales beneficios de estas tecnologías. Los beneficios debidos a la reducción de emisiones y al ahorro de combustibles fósiles se calculan con una robusta metodología, basada en una herramienta internacionalmente validada. Asimismo, se ha diseñado una innovadora metodología para el cálculo de los empleos brutos que aplica factores dinámicos de empleo y considera la capacidad productora de cada país y las curvas de aprendizaje. La principal aportación de esta tesis es el diseño de ambas metodologías, de sencilla aplicación, basadas en datos públicos y fácilmente replicables. Los resultados son similares a los de otros autores, validando ambas metodologías y pueden servir como instrumento para analizar inversiones y diseñar políticas energéticas.Many articles in the specialised economic press have debated about the socio-economic impacts related to renewable energies. The aim of this paper is to quantify some of the main socio-economic impacts attributed to the deployment of wind and photovoltaic technologies in the European Member States during a six-year period (2008-2013). This research considers the costs of supporting electricity from both technologies and some benefits of so doing. The economic benefits in terms of CO2 emissions reductions and fossil fuels substitution are calculated with a robust methodology, based on an internationally validated tool. The effects on employment have been calculated by means of an innovative methodology, which considers the existing industry structure of each Member State and the learning curves. The main contribution of this PhD is the design of both methodologies which are simple, based on public data and easily replicable. The results obtained are similar to the conclusions from the existing literature, validating both methodologies. They can provide a useful input for future policies

The life course of delinquency: reflections on the meaning of trajectories, transitions and turning points in youth justice

This article challenges contemporary analyses of the nature of youth justice in England and Wales as partial and restricted in theoretical and conceptual terms. A life course perspective is adopted to examine the trajectory of youth justice as a dynamic artefact, constantly shaped by recurring, reconstructed and r/evolving contextual, thematic and stakeholder influences. A critical and thematic review of academic, government, policy and media literature using social construction as its analytical frame of reference in turn opens up the theoretical space to articulate an internally-coherent and nuanced framework for understanding the nature and development of youth justice past, present and future

Child First and the end of ‘bifurcation’ in youth justice?

Purpose: This study aims to critically evaluate the trajectory of the “Child First” guiding principle for youth justice in England and Wales, which challenges adult-centric constructions of children (when they offend) as “threatening” and asserts a range of theoretical and principled assumptions about the nature of childhood and children’s evolving capacity. Design/methodology/approach: Focussing on how Child First seeks to transcend the socio-historically bifurcated (polarised/dichotomised) thinking and models/strategies/frameworks of youth justice, this study examines the extent and nature of this binary thinking and its historical and contemporary influence on responses to children’s offending, latterly manifested as more hybridised (yet still discernibly bifurcated) approaches. Findings: Analyses identified an historical and contemporary influence on bifurcated responses to offending by children in the United Kingdom/England and Wales, subsequently manifested as more hybridised (yet still discernibly bifurcated) approaches. Analyses also identified a contemporary, progressive challenge to bifurcated youth justice thinking, policy and practice through the “Child First” guiding principle. Originality/value: By tracing the trajectory of Child First as an explicit, progressive challenge to previous youth justice thinking and formal “approaches”, to the best of the authors’ knowledge, they are the first to question whether, in taking this approach, Child First represents a clean break with the past, or is just the latest in a series of strategic realignments in youth justice seeking to resolve inherent tensions between competing constructions of children and their behaviour.</p

Additional file 2: of Cryopreservation of equine mesenchymal stem cells in 95 % autologous serum and 5 % DMSO does not alter post-thaw growth or morphology in vitro compared to fetal bovine serum or allogeneic serum at 20 or 95 % and DMSO at 10 or 5 %

Is a figure showing flow histograms of CellTrace™ dye in MSCs cryopreserved in six different freezing solutions, 24 hours post thaw and monolayer expansion. (JPEG 285 kb

Biophysical characteristics of KCNQ1 current.

<p>Properties of <i>I</i>_KCNQ1 were developed using experimental data from human KCNQ1 clones expressed in <i>Xenopus laevis</i> oocytes (<i>black</i>) and Chinese hamster cell (<i>gray</i>) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-TristaniFirouzi1" target="_blank">[23]</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-Larsen2" target="_blank">[35]</a>, as well as KCNQ-like currents in mouse smooth muscle cells <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-Yeung1" target="_blank">[10]</a>. <i>A</i>, <i>V</i>-dependent activation steady state (<i>n</i>_Q1∞). <i>B</i>, <i>V</i>-dependent steady states for fast inactivation (<i>w</i>_Q1∞) and slow inactivation (<i>s</i>_Q1∞). <i>C</i>, <i>V</i>-dependent activation time constants (<i>τ_n</i>_Q1f and <i>τ_n</i>_Q1s). <i>D</i>, fast (<i>τ_w</i>_Q1) and slow (<i>τ_s</i>_Q1) inactivation time constants. <i>τ_w</i>_Q1 is <i>V</i>-dependent and fitted to experimental data <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-TristaniFirouzi1" target="_blank">[23]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-Pusch1" target="_blank">[26]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-Seebohm1" target="_blank">[27]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-Seebohm2" target="_blank">[30]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-Gao1" target="_blank">[33]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-Larsen2" target="_blank">[35]</a>. <i>τ_s</i>_Q1 is set as a constant at 50 s. This value is chosen to best reproduce the published time tracings from Jensen et al. (2007) <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-Jensen1" target="_blank">[32]</a>. <i>E</i> and <i>F</i>, simulated time tracings of <i>I</i>_KCNQ1 with two different voltage-clamp protocols from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0114034#pone.0114034-Jensen1" target="_blank">[32]</a> (<i>insets</i>) and the experimental time tracings are shown for comparison. (Experimental tracing adapted with permission from Jensen et al. (2007); copyright 2007, Biophysical Society.) <i>G</i>, simulated <i>I-V</i> relationship of <i>I</i>_KCNQ1 using the same voltage-clamp protocol as in <i>E</i>. All <i>I-V</i> data are normalized to the maximal current value at <i>V</i> = 40 mV.</p