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The impact of 3D printing on the humanitarian supply chain
No full textAdditive Manufacturing or 3 D printing is radically changing the way products are designed and manufactured. The humanitarian sector has started exploring how 3 D printing can help match supply with the global rise in humanitarian needs. However, there has been very little academic research in the field. This study aims to bridge this gap by reviewing twelve case studies of 3 D printed products to examine the effects of 3 D printing on the humanitarian supply chain. The findings reveal four supply chain archetypes, which demonstrate that 3 D printing is impacting the humanitarian supply chain with respects to networks, governance, processes and products. We compare the benefits and challenges of these archetypes to contest that 3 D printing will not necessarily simplify and shorten the supply chain. Instead, we suggest the need for a holistic supply chain approach that includes the local production of 3 D printers and filament, alongside local design and manufacture. This much-needed study provides the foundations for future academic research and offers relevant guidance for practitioners using 3 D printing in the humanitarian sector
Open-loop control of a global instability in a swirling jet by harmonic forcing: A weakly nonlinear analysis
No full textHighly swirling flows are often prone to precessing instabilities, with an azimuthal wave number of m=-1. We carry out a weakly nonlinear analysis to determine the response behavior of this instability to harmonic forcing. An incompressible flow is considered, where an annular inlet provides a swirling flow into a cylindrical region. For high swirl a vortex breakdown is induced, which is found to support an m=-1 instability. By expanding about the Reynolds number where this instability first occurs, a Stuart-Landau equation for the critical mode amplitude can be found and the effect of forcing can be assessed. Two types of forcing are considered. First, a Gaussian forcing confined to the inlet nozzle is used to study m=0 and m=-1 forcings. Second, optimal forcings (measured by the two-norm) with azimuthal wave numbers in the range -3≤m≤3 are considered. It is found that modal stabilization is highly dependent on the azimuthal wave number m, which governs whether the forcing is counter- or corotating with the direction of swirl. Counterrotating forcings are able to stabilize the mode for a wide range of forcing frequencies, while corotating forcings fail to yield a stable flow. In all cases, it is the base-flow modification induced by the forced response that is the dominant underlying feature responsible for the observed stabilization. This base-flow modification seeks to reduce axial momentum near the recirculation region for corotating forcings and increase it for counterrotating forcings, thus changing the size of the recirculation bubble and producing the two distinct response behaviors
Comparing energy and material efficiency rebound effects: an exploration of scenarios in the GEM-E3 macroeconomic model
No full textThis paper uses the GEM-E3 macroeconomic computable general equilibrium model to calculate the magnitude of greenhouse gas (GhG) emission rebound effects across a range of efficiency scenarios in the automotive sector supply chain. The scenarios are technically feasible as they are designed using bottom up information from the iron and steel industry. Rebound effects occur when efficiency improvements reduce prices, stimulating demand and offsetting some of the environmental benefits that would otherwise be had. This paper allows energy, material and product-service efficiency rebound effects to be compared for the first time. The results suggest that there is a greater risk of rebound effects for downstream emissions abatement strategies that save embodied emissions: 85% of the emissions savings in the product-service efficiency scenario and 77% of emissions in the material efficiency scenario are offset by economy-wide rebound effects. This compares to 7% in the energy efficiency scenario. These findings show that, in the current policy environment in which GhG emissions remain relative unconstrained, improvements in material efficiency that are particularly good at spurring growth are also likely to carry the greatest rebound effects. The conclusions of this paper are not purely dependent on the chosen macroeconomic model, but are a function of the underlying value structure along supply chains: downstream efficiency improvements that save embodied emissions involve greater potential monetary savings per unit GhG avoided, spurring rebound effects
Impact of Stabilizer Layers on the Thermal-Electromagnetic Characteristics of Direct Current Carrying HTS Coated Conductors under Perpendicular AC Magnetic Fields
No full textWhen a type-II high Tc superconductor carrying a direct current is subjected to a perpendicular AC magnetic field, a direct current voltage will appear. This phenomenon is called dynamic resistance effect. In general, the high temperature superconducting (HTS) coated conductor (CC) has two stabilizer layers. However, the impacts of two stabilizer layers on the dynamic resistance, DC electrical field, losses, and temperature rise haven't been studied yet. This paper presents the impacts of the stabilizer layers and their resistivity on the dynamic resistance effect and HTS CC tape's thermal-electromagnetic behaviors by using a temperature dependent FEM model. This work reveals that the stabilizer impacts significantly on the dynamic resistance, dc voltage, power loss, and temperature rise. It is will help design high-performance AC magnetic field-controlled PCS and switches based HTS devices
Hexagonal Boron Nitride–Enhanced Optically Transparent Polymer Dielectric Inks for Printable Electronics
No full textSolution-processable thin-film dielectrics represent an important material family for large-area, fully-printed electronics. Yet, in recent years, it has seen only limited development, and has mostly remained confined to pure polymers. Although it is possible to achieve excellent printability, these polymers have low (≈2–5) dielectric constants (εr). There have been recent attempts to use solution-processed 2D hexagonal boron nitride (h-BN) as an alternative. However, the deposited h-BN flakes create porous thin-films, compromising their mechanical integrity, substrate adhesion, and susceptibility to moisture. These challenges are addressed by developing a “one-pot” formulation of polyurethane (PU)-based inks with h-BN nano-fillers. The approach enables coating of pinhole-free, flexible PU+h-BN dielectric thin-films. The h-BN dispersion concentration is optimized with respect to exfoliation yield, optical transparency, and thin-film uniformity. A maximum εr ≈ 7.57 is achieved, a two-fold increase over pure PU, with only 0.7 vol% h-BN in the dielectric thin-film. A high optical transparency of ≈78.0% (≈0.65% variation) is measured across a 25 cm2 area for a 10 μm thick dielectric. The dielectric property of the composite is also consistent, with a measured areal capacitance variation of <8% across 64 printed capacitors. The formulation represents an optically transparent, flexible thin-film, with enhanced dielectric constant for printed electronics
Multi-objective, multi-physics optimization of 3D mixed-oxide LWR fuel assembly designs using the MOJADE algorithm
No full textOptimization problems in the research literature are typically simplified and/or heavily constrained and focus on a single set of physical processes. Real-world nuclear engineering problems feature competing multi-physics phenomena and require equally complex analysis. To prove its usefulness in this area, optimization must demonstrate an ability to handle many competing objectives whilst accurately simulating the reactor environment. This paper applies the MOJADE optimization algorithm to two design problems, a 3D PWR Supercell and a 3D BWR fuel assembly, evaluating performance objectives related to neutronics and thermal hydraulics simultaneously, using the concept of Pareto dominance. In both cases, MOJADE was able to find competitive or non-dominated designs compared to baseline solutions generated from the literature and required no control parameter tuning or training time. Analysis revealed that MOJADE can identify key variables which impact objective performance, demonstrating the algorithm's ability to provide new insight to complex 3D problems featuring multi-physics analysis
A system for generating non-uniform random variates using graphene field-effect transistors
No full textWe introduce a new method for hardware nonuniform random number generation based on the transfer characteristics of graphene field-effect transistors (GFETs) which requires as few as two transistors and a resistor. We implement the method by fabricating multiple GFETs and experimentally validating that their transfer characteristics exhibit the nonlinearity on which our method depends. We use characterisation data in simulations of a proposed architecture for generating samples from dynamically selectable non-uniform probability distributions. The method we present has the potential for Gb/s sample rates, is reconfigurable for arbitrary target distributions, and has a wide range of possible applications. Using a combination of experimental measurements of GFETs under a range of biasing conditions and simulation of the GFET-based non-uniform random variate generator, we demonstrate a speedup of Monte Carlo integration by up to 2 times. This speedup assumes the analog-to-digital converters reading the outputs from the circuit can produce samples in the same amount of time that it takes to perform memory accesses
Effect of elevated temperatures and humidity on glass/steel adhesive joints
No full textGlass/steel adhesive joints are being used increasingly in the construction industry as they offer significant structural advantages. While humidity and elevated temperatures are known to lead to the degradation of both the bulk adhesive materials and the bonded interfaces, quantification and prediction of the degradation effects are currently lacking. In this paper, the effects of elevated temperatures and humidity were determined and predicted by employing a combined experimental and numerical methodology. Bulk material and interface characterisation tests were performed to quantify the degradation of the bulk material properties and the glass/steel interfaces. Two numerical methodologies were devised and compared based on their ability to predict failure of glass/steel adhesive joints following environmental exposure, namely a continuum mechanics approach based on the bulk properties of the adhesive, and a cohesive zone modelling approach that assesses damage and failure based on the glass/steel interface properties. The results highlight the significantly different relative contributions of bulk property and interface degradation depending on the type of adhesive used
Pulsed-field magnetisation of Y-Ba-Cu-O bulk superconductors fabricated by the infiltration growth technique
No full textBulk high temperature superconductors based on the rare-earth copper oxides can be used effectively as trapped field magnets capable of generating large magnetic fields. The top-seeded infiltration growth (TSIG) processing technique can provide a more homogeneous microstructure and therefore more uniform superconducting properties than samples grown using conventional melt growth processes. In the present investigation, the properties of bulk, single grain superconductors processed by TSIG and magnetised by the pulsed-field magnetisation technique using a copper-wound solenoid have been studied. A trapped field of ∼3 T has been achieved in a 2-step buffer-assisted TSIG-processed Y-Ba-Cu-O (YBCO) sample at 40 K by magnetising the bulk superconductor completely via a single-pulse magnetisation process. Samples were also subjected to pulsed-field magnetisation at 65 K and by conventional field-cooled magnetisation at 77 K for comparison. Good correlation was observed between the microstructures, critical current densities and trapped field performance of bulk samples fabricated by TSIG and magnetised by pulsed-field and field-cooled magnetisation. The homogeneous distribution of Y2BaCuO5 inclusions within the microstructure of bulk YBCO samples fabricated by the 2-step buffer-assisted TSIG process reduces inhomogeneous flux penetration into the interior of the sample. This, in turn, results in a lower temperature rise of the bulk superconductor during the pulsed-field magnetisation process and a more effective and reliable magnetisation process
Organic neuromorphic devices: Past, present, and future challenges
No full textThe main goal of the field of neuromorphic computing is to build machines that emulate aspects of the brain in its ability to perform complex tasks in parallel and with great energy efficiency. Thanks to new computing architectures, these machines could revolutionize high-performance computing and find applications to perform local, low-energy computing for sensors and robots. The use of organic and soft materials in neuromorphic computing is appealing in many respects, for instance, because it allows better integration with living matter to seamlessly meld sensing with signal processing, and ultimately, stimulation in a closed-feedback loop. Indeed, not only can the mechanical properties of organic materials match those of tissue, but also, the working mechanisms of these devices involving ions, in addition to electrons, are compatible with human physiology. Another advantage of organic materials is the potential to introduce novel fabrication techniques relying on additive manufacturing amenable to one-of-a-kind form factors. This field is still nascent, therefore many concepts are still being proposed, without a clear winner. Furthermore, the field of application of organic neuromorphics, where bioinspiration and biointegration are extremely appealing, calls for a co-design approach from materials to systems