MRC Laboratory of Molecular Biology
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Direct laser grain writing in steels
No full textLaser melting the surface of 304 stainless steel allows controlled grain growth in the direction of the laser scan [1]. We demonstrate the application of laser surface melting with a Yb fibre laser as a technique for single crystal grain refinement and security marking in polycrystalline metals via localized grain nucleation. Single crystals were achieved after three consecutive passes with constant laser parameters throughout the length of the laser raster at 19.17 kJ/cm2 average energy at 300K, 0.1% O2 environment. The depth of localized grain nucleation was measured to be approximately 20 mm for a single pass, making hidden messages in the bulk of the material possible after mechanically removing the immediate surface melt. The patterns are undetectable by conventional optical microscopy but can be viewed with interferometric microscopy due to fine height differences between untreated and laser treated surface regions, this way establishing a metal security marking technique
The Emergence, Evolution and Frequent Failure of the Industrial Symbiosis: The Evidence from the Sugar Refinery Industry, Chongzuo City, China
No full textIndustrial symbiosis (hereafter IS) has been hailed as a win-win solution to our industrial pollution problems, but such projects have frequently failed. The present research set out to explore the dynamics and causal mechanism of IS development and to discover the causes of its failure. It studied forty-nine IS-based projects and the IS development history of seventeen firms in the sugar refinery Industry, Chongzuo City, China. The main research question was: Why did many IS-based projects in the sugar refineries often fail? It followed a qualitative research strategy and employing the research design of “multiple (embedded) case studies.” Empirical data were collected through semi-structured interviews and archival research. They were analysed to identify the answers to the research questions. From the data analysis have emerged six key findings: the implicit project process model for carrying out waste utilisation and IS development, the critical success factors for the success of IS-based waste utilisation projects, the historical trajectory of IS evolution at the firm and network levels, the conditions for the successful evolution and expansion of IS ecosystems, the underlying dynamics generating IS ecosystems, as well as the root causes of frequent failure in IS development. Based on the research findings and the theorisation thereof, the present research has come to the conclusion that the emergence, evolution and development of IS in the sugar refinery industry in Chongzuo City were initiated and shaped by the focal firms’ diversification strategy to utilise their waste resources. The root causes of the IS failure lay in the collapse of the firms’ waste utilization businesses and the unresolved conflict between the internal rigidity in the IS networks due to the tightly coupled manufacturing processes and the incoming external uncertainties through various interfaces of the businesses with their environment, particularly the changing by-product markets
Effect of Anode Slippage on Cathode Cutoff Potential and Degradation Mechanisms in Ni-Rich Li-Ion Batteries
No full textLi-ion batteries based on Ni-rich layered cathodes are the state-of-the-art technology for electric vehicles; however, batteries using these advanced materials suffer from rapid performance fading. In this work, we report a critical turning point during the aging of graphite/LiNi0.8Mn0.1Co0.1O2 (NMC811) full cells, after which the degradation is significantly accelerated. This turning point was identified using differential voltage analysis (DVA) applied to standard two-electrode data, which shows that graphite becomes progressively less lithiated, as confirmed by operando long-duration X-ray diffraction, and therefore has a higher electrochemical potential at the end of charge. This increase leads to a proportional increase in the cathode potential, and an accelerated impedance increase is observed from this point. This mechanism is expected to be universal for the vast majority of Li-ion battery chemistries, particularly for Ni-rich cathodes, whose degradation is extremely sensitive to the upper cutoff voltage, and our work provides fundamental guidelines for developing effective countermeasures
Feedback identification of conductance-based models
No full text© 2020 Elsevier Ltd This paper applies the classical prediction error method (PEM) to the estimation of nonlinear discrete-time models of neuronal systems subject to input-additive noise. While the nonlinear system exhibits excitability, bifurcations, and limit-cycle oscillations, we prove consistency of the parameter estimation procedure under output feedback. Hence, this paper provides a rigorous framework for the application of conventional nonlinear system identification methods to discrete-time stochastic neuronal systems. The main result exploits the elementary property that conductance-based models of neurons have an exponentially contracting inverse dynamics. This property is implied by the voltage-clamp experiment, which has been the fundamental modeling experiment of neurons ever since the pioneering work of Hodgkin and Huxley
A bacterial size law revealed by a coarse-grained model of cell physiology.
No full textUniversal observations in Biology are sometimes described as "laws". In E. coli, experimental studies performed over the past six decades have revealed major growth laws relating ribosomal mass fraction and cell size to the growth rate. Because they formalize complex emerging principles in biology, growth laws have been instrumental in shaping our understanding of bacterial physiology. Here, we discovered a novel size law that connects cell size to the inverse of the metabolic proteome mass fraction and the active fraction of ribosomes. We used a simple whole-cell coarse-grained model of cell physiology that combines the proteome allocation theory and the structural model of cell division. This integrated model captures all available experimental data connecting the cell proteome composition, ribosome activity, division size and growth rate in response to nutrient quality, antibiotic treatment and increased protein burden. Finally, a stochastic extension of the model explains non-trivial correlations observed in single cell experiments including the adder principle. This work provides a simple and robust theoretical framework for studying the fundamental principles of cell size determination in unicellular organisms
An empirical model to evaluate the effects of environmental humidity on the formation of wrinkled, creased and porous fibre morphology from electrospinning
No full textAbstract Controlling environmental humidity level and thus moisture interaction with an electrospinning solution jet has led to a fascinating range of polymer fibre morphological features; these include surface wrinkles, creases and surface/internal porosity at the individual fibre level. Here, by cross-correlating literature data of far-field electrospinning (FFES), together with our experimental data from near-field electrospinning (NFES), we propose a theoretical model, which can account, phenomenologically, for the onset of fibre microstructures formation from electrospinning solutions made of a hydrophobic polymer dissolved in a water-miscible or polar solvent. This empirical model provides a quantitative evaluation on how the evaporating solvent vapour could prevent or disrupt water vapor condensation onto the electrospinning jet; thus, on the condition where vapor condensation does occur, morphological features will form on the surface, or bulk of the fibre. A wide range of polymer systems, including polystyrene, poly(methyl methacrylate), poly-l-lactic acid, polycaprolactone were tested and validated. Our analysis points to the different operation regimes associated FFES versus NFES, when it comes to the system’s sensitivity towards environmental moisture. Our proposed model may further be used to guide the process in creating desirable fibre microstructure.</jats:p
Wide field of view crystal orientation mapping of layered materials
No full textLayered materials (LMs) are at the centre of an ever increasing research effort due to their potential use in a variety of applications. The presence of imperfections, such as bi- or multilayer areas, holes, grain boundaries, isotropic and anisotropic deformations, etc. are detrimental for most (opto)electronic applications. Here, we present a set-up able to transform a conventional scanning electron microscope into a tool for structural analysis of a wide range of LMs. An hybrid pixel electron detector below the sample makes it possible to record two dimensional (2d) diffraction patterns for every probe position on the sample surface (2d), in transmission mode, thus performing a 2d+2d=4d STEM (scanning transmission electron microscopy) analysis. This offers a field of view up to 2 mm2, while providing spatial resolution in the nm range, enabling the collection of statistical data on grain size, relative orientation angle, bilayer stacking, strain, etc. which can be mined through automated open-source data analysis software. We demonstrate this approach by analyzing a variety of LMs, such as mono- and multi-layer graphene, graphene oxide and MoS2, showing the ability of this method to characterize them in the tens of nm to mm scale. This wide field of view range and the resulting statistical information are key for large scale applications of LMs
Advances in Latent Variable and Causal Models
No full textThis thesis considers three different areas of machine learning concerned with the modelling of data, extending theoretical understanding in each of them. First, the estimation of f- divergences is considered in a setting that is naturally satisfied in the context of autoencoders. By exploiting structural assumptions on the distributions of concern, the proposed estimator is shown to exhibit fast rates of concentration and bias-decay. In contrast, in much of the existing f-divergence estimation literature, fast rates are only obtainable under strong conditions that are difficult to verify in practice. Next, novel identifiability results are presented for nonlinear Independent Component Analysis (ICA) in a multi-view setting, extending the scarce literature of known identifiability results for nonlinear ICA. A result of particular note is that if one noiseless view of the sources is supplemented by a second view that is appropriately corrupted by source-level noise, the sources can be fully reconstructed from the observations up to tolerable ambiguities. This setting is applicable to areas such as neuroimaging, where multiple data modalities may be available. Finally, a framework is introduced to evaluate when two causal models are consistent with one another, meaning that a correspondence can be established between them such that reasoning about the effects of interventions in both models agree. This can be used to understand when two models of the same system at different levels of detail are consistent, and has application to the problem of causal variable definition. This work has broad implications to the causal modelling process in general, as there is often a mismatch between the level at which measurements are made and the level at which the underlying ‘true’ causal structure exists, yet causal inference algorithms generally seek to discover causal structure at the level of measurements
The sponge effect and carbon emission mitigation potentials of the global cement cycle
No full textCement plays a dual role in the global carbon cycle like a sponge: its massive production contributes significantly to present-day global anthropogenic CO2 emissions, yet its hydrated products gradually reabsorb substantial amounts of atmospheric CO2 (carbonation) in the future. The role of this sponge effect along the cement cycle (including production, use, and demolition) in carbon emissions mitigation, however, remains hitherto unexplored. Here, we quantify the effects of demand- and supply-side mitigation measures considering this material-energy-emissions-uptake nexus, finding that climate goals would be imperiled if the growth of cement stocks continues. Future reabsorption of CO2 will be significant (~30% of cumulative CO2 emissions from 2015 to 2100), but climate goal compliant net CO2 emissions reduction along the global cement cycle will require both radical technology advancements (e.g., carbon capture and storage) and widespread deployment of material efficiency measures, which go beyond those envisaged in current technology roadmaps
High-Resolution Integral Imaging of Micron-Sized Objects
No full textWe present computational reconstruction of 3D images from a micron-sized object using a nanophotonic lens array made of hybrid combination of multiwall carbon nanotubes and liquid Crystals