MRC Laboratory of Molecular Biology
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High energy density anodes using hybrid Li intercalation and plating mechanisms on natural graphite
No full textLithium plating on conventional graphite anodes in lithium-ion batteries is typically considered an undesirable side reaction, a safety hazard or a degradation mechanism. However, lithium plating and stripping allow for efficient energy storage, and therefore various new porous anode designs with tailored surface coatings and electrolyte systems have been proposed to achieve reversible Li plating and stripping. Unfortunately, these material designs often rely on highly porous plating scaffolds with an overall lower volumetric energy and power density than conventional graphite anodes. Herein, a novel anode design is presented which leverages the good volumetric performance of industrial graphite anodes and further enhances their capacity by allowing for a reversible Li plating on their surface. The latter is achieve by conformally coating them with a nanoscale lithiophilic Si coating. As a result, excellent volumetric energy densities of 656 mA h cm-3 and gravimetric capacities of 551 mA h g-1 are achieved, which are a clear improvement compared to the commercial graphite anode (app. 570 mA h cm-3 and 360 mA h g-1 respectively). Moreover, by carefully balancing the thickness of the Si layer and the plating capacity, a capacity retention close to 100% is achieved after 200 cycles in half cells. Overall, this approach leverages the advances in industrial graphite anode manufacturing while at the same time embracing the additional capacity offered by reversible plating and stripping of Li metal, resulting in full cells energy densities of 474 W h kg-1 and 912 W h L-1, which is a step forward compared to previous Li metal and graphite anodes
Unified geometrical framework for the plastic design of reinforced concrete structures
No full text© 2020 The Authors. Structural Concrete published by John Wiley & Sons Ltd on behalf of International Federation for Structural Concrete. Although the analysis and design of structures in static equilibrium can be intuitively carried out using simple equilibrium-based methods such as graphic statics, the application of these methods to engineering problems that take into consideration specific material properties is generally limited. Within the domain of reinforced concrete, existing geometric approaches for developing stress fields and yield lines based on the theory of plasticity are especially useful. However, these approaches usually rely on iterative constructions and are generally limited to two-dimensional cases. By taking advantage of graphic statics, this article introduces the theoretical basis for an entirely geometrical method to generate discrete stress fields and yield line patterns in two- and three-dimensional reinforced concrete structures. The proposed approach is based on the use of reciprocal stress functions and the relationship between form and force diagrams
Hybrid 3D/Inkjet-Printed Organic Neuromorphic Transistors
No full textOrganic electrochemical transistors (OECTs) are proving essential in bioelectronics and printed electronics applications, with their simple structure, ease of tunability, biocompatibility, and suitability for different routes to fabrication. OECTs are also being explored as neuromorphic devices, where they emulate characteristics of biological neural networks through co-location of information storage and processing on the same unit, overcoming the von Neumann performance bottleneck. To achieve the long-term vision of translating to inexpensive, low-power computational devices, fabrication needs to be feasible with adaptable, scalable digital techniques. Here, a hybrid direct-write additive manufacturing approach to fabricating OECTs is shown. 3D printing of commercially available printing filament is combined to deliver conducting and insulating layers, with inkjet printing of semiconducting thin films to create OECTs. These printed OECTs show depletion mode operation paired-pulse depression behavior and evidence of adaptation to support their translation to neuromorphic devices. These results show that a hybrid of accessible and design-flexible AM techniques can be used to rapidly fabricate devices that exhibit good OECT and neuromorphic performances
Bayesian pseudocoresets
No full textStandard Bayesian inference algorithms are prohibitively expensive in the regime of modern large-scale data. Recent work has found that a small, weighted subset of data (a coreset) may be used in place of the full dataset during inference, taking advantage of data redundancy to reduce computational cost. However, this approach has limitations in the increasingly common setting of sensitive, high-dimensional data. Indeed, we prove that there are situations in which the Kullback-Leibler (KL) divergence between the optimal coreset and the true posterior grows with data dimension; and as coresets include a subset of the original data, they cannot be constructed in a manner that preserves individual privacy. We address both of these issues with a single unified solution, Bayesian pseudocoresets—a small weighted collection of synthetic “pseudodata”—along with a variational optimization method to select both pseudodata and weights. The use of pseudodata (as opposed to the original datapoints) enables both the summarization of high-dimensional data and the differentially private summarization of sensitive data. Real and synthetic experiments on high-dimensional data demonstrate that Bayesian pseudocoresets achieve significant improvements in posterior approximation error compared to traditional coresets, and that pseudocoresets provide privacy without a significant loss in approximation quality
Negating gust effects by actively pitching a wing
No full textAir vehicle gust encounters can result in extreme loads that are detrimental for stability. This is a particular problem for micro-air vehicles which generally fly at speeds on the same order as atmospheric gust velocities. In order to improve controllability in these situations, this paper studies the potential of using active pitch motions to mitigate gust effects. Experiments, performed at a Reynolds number of 30 000, expose a flat plate wing to a high-amplitude gust (gust ratio = 1). The responses of three different pitch profiles are compared in order to determine their potential for load mitigation. The first profile maintains a zero mean effective angle of attack throughout the gust encounter. The second profile is calculated using a vortex method which captures effects due to shed vorticity and added mass. These two profiles achieve a 75% reduction of the gust lift response. The final profile is a combination of the previous two pitch profiles after completing additional corrections, and achieves a 95% mitigation of the uncontrolled lift response. This demonstrates that a high-amplitude gust can be alleviated using only a single degree-of-freedom pitch motion. The importance of shed vorticity behaviour is highlighted by an analysis of the three pitch profiles, which displays different trends when the wing enters and exits the gust, despite the symmetry of the gust profile
A-Priori Validation of Scalar Dissipation Rate Models for Turbulent Non-Premixed Flames
No full text© 2020, The Author(s). The modelling of scalar dissipation rate in conditional methods for large-eddy simulations is investigated based on a priori direct numerical simulation analysis using a dataset representing an igniting non-premixed planar jet flame. The main objective is to provide a comprehensive assessment of models typically used for large-eddy simulations of non-premixed turbulent flames with the Conditional Moment Closure combustion model. The linear relaxation model gives a good estimate of the Favre-filtered scalar dissipation rate throughout the ignition with a value of the related constant close to the one deduced from theoretical arguments. Such value of the constant is one order of magnitude higher than typical values used in Reynolds-averaged approaches. The amplitude mapping closure model provides a satisfactory estimate of the conditionally filtered scalar dissipation rate even in flows characterised by shear driven turbulence and strong density variation
Thermal History-Dependent Current Relaxation in hBN/MoS<inf>2</inf> van der Waals Dimers
No full textCombining atomically thin layers of van der Waals (vdW) materials in a chosen vertical sequence is an emerging route to create devices with desired functionalities. While this method aims to exploit the individual properties of partnering layers, strong interlayer coupling can significantly alter their electronic and optical properties. Here we explored the impact of the vdW epitaxy on electrical transport in atomically thin molybdenum disulfide (MoS2) when it forms a vdW dimer with crystalline films of hexagonal boron nitride (hBN). We observe a thermal history-dependent long-term (over âˆ40 h) current relaxation in the overlap region of MoS2/hBN heterostructures, which is absent in bare MoS2 layers (or homoepitaxial MoS2/MoS2 dimers) on the same substrate. Concurrent relaxation in the low-frequency Raman modes in MoS2 in the heterostructure region suggests a slow structural relaxation between trigonal and octahedral polymorphs of MoS2 as a likely driving mechanism that also results in inhomogeneous charge distribution in the MoS2 layer. Our experiment yields an aspect of vdW heteroepitaxy that can be generic to electrical devices with atomically thin transition-metal dichalcogenides
Phase flicker in liquid crystal on silicon devices
No full textThis paper reviews the phase flicker associated with the phase-only liquid crystal on silicon (LCOS) technology. The phase response of the LCOS device often fluctuates with the driving waveforms. Such phase flicker can cause detrimental effect in applications operating on either holographic or non-holographic principles. The origin of the phase flicker and its impact on the performances of various LCOS-based optical systems are explained. Methods to characterise the temporal response of the LCOS device will also be presented. The efforts to reduce the phase flicker in LCOS devices were reviewed. Perspectives on the future directions are also given
Full bandwidth coarse integral holographic video displays with spatial tiling for scalability
No full textThis paper introduces full bandwidth Coarse Integral Holographic Display architecture with spatial tiling for scalability. The new method uses a large resonant scanner in conjunction with spatial tiling of spatial light modulators (SLMs) to create doubling the hologram's horizontal size and utilize the full bandwidth of the SLMs
On how the generation of lift can be explained in a closed form based on the fundamental conservation equations
No full textThe generation of lift is a fundamental problem in aerodynamics and in general in fluid mechanics. The explanations on how lift is generated are often very incomplete or even not correct. Perhaps the most popular explanation of lift is the one with the Bernoulli equation and with the longer path over an airfoil as compared to the path below the airfoil, assuming the flow arrives at the same time at the trailing edge on both paths. This is an intuitive assumption, but no equation is derived from this assumption. In some explanations the Bernoulli equation is also complemented with Newton´s laws of motion. In other explanations Newton´s law is said to be the only explanation. Other explanations mention the Venturi suction effect to explain the generation of lift. In books of aerodynamics and on the homepage of well-known research institutes the explanations are, although better and partially correct, still very often incomplete. In this contribution the generation of lift is explained in a scientific way based on the conservation principles of mass, momentum and energy and how they have to be applied to close the system of equations in order to explain the generation of lift. The most common incomplete or incorrect explanations of lift are also analysed and it is explained why they are incomplete or wrong. In this work the generation of lift is explained based on the conservation equations. It is shown how and when they apply to the problem of lift generation and how the system of equations has to be closed