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Erratum: Design, development, testing at ISO standards and: In vivo feasibility study of a novel polymeric heart valve prosthesis (Biomater. Sci. (2020) DOI: 10.1039/d0bm00412j)
No full textThe authors of this article would like to clarify that while they have been in contact with Kraton for informal discussions around their work, there is no formal collaboration or business arrangement with the company. The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers
Nonasymptotic Gaussian Approximation for Inference with Stable Noise
No full textThe results of a series of theoretical studies are reported, examining the convergence rate for different approximate representations of alpha -stable distributions. Although they play a key role in modelling random processes with jumps and discontinuities, the use of alpha -stable distributions in inference often leads to analytically intractable problems. The LePage series, which is a probabilistic representation employed in this work, is used to transform an intractable, infinite-dimensional inference problem into a finite-dimensional (conditionally Gaussian) parametric problem. A major component of our approach is the approximation of the tail of this series by a Gaussian random variable. Standard statistical techniques, such as Expectation-Maximization (EM), Markov chain Monte Carlo, and Particle Filtering, can then be readily applied. In addition to the asymptotic normality of the tail of this series, we establish explicit, nonasymptotic bounds on the approximation error. Their proofs follow classical Fourier-analytic arguments, using Esséen's smoothing lemma. Specifically, we consider the distance between the distributions of: (i) the tail of the series and an appropriate Gaussian; (ii) the full series and the truncated series; and (iii) the full series and the truncated series with an added Gaussian term. In all three cases, sharp bounds are established, and the theoretical results are compared with the actual distances (computed numerically) in specific examples of symmetric alpha -stable distributions. This analysis facilitates the selection of appropriate truncations in practice and offers theoretical guarantees for the accuracy of resulting estimates. One of the main conclusions obtained is that, for the purposes of inference, the use of a truncated series together with an approximately Gaussian error term has superior statistical properties and is likely a preferable choice in practice
A stochastic approach to model chemical looping combustion
No full textA stochastic model is presented of two coupled fluidised-bed reactors with a steady circulation of particles between them. The particles undergo reaction in each fluidised bed. The model uniquely accounts for the full conversion history of particles as they are circulated. Chemical looping combustion (CLC) is an example of such a process. We have previously used the model, in a general form, to understand the sensitivity of a CLC process to factors such as the nature of the gas-solid reactions or the residence time distribution of the particles in the reactors. To demonstrate that the stochastic model is also valuable for simulating and optimising specific configurations of CLC, it is applied in this paper to simulate CLC with methane as the fuel gas, conducted in a laboratory-scale circulating fluidised bed. Under the operating conditions of the circulating fluidised bed, it was found that the oxidation and reduction reactions were limited by the intrinsic chemical kinetics of the oxygen carrier particles. It was possible to conduct experiments in a packed bed reactor for reduction and a thermogravimetric analyser for oxidation where the reaction was also limited by the intrinsic chemical kinetics. This enabled a single particle model, for inclusion in the stochastic model, to be developed independently of the experiments in the circulating fluidised bed. The resulting stochastic model was able to simulate the performance of the circulating fluidised bed with reasonable accuracy
A field-tested robotic harvesting system for iceberg lettuce
No full textAgriculture provides an unique opportunity for the development of robotic systems; robots must be developed which can operate in harsh conditions and in highly uncertain and unknown environments. One particular challenge is performing manipulation for autonomous robotic harvesting. This paper describes recent and current work to automate the harvesting of iceberg lettuce. Unlike many other produce, iceberg is challenging to harvest as the crop is easily damaged by handling and is very hard to detect visually. A platform called Vegebot has been developed to enable the iterative development and field testing of the solution, which comprises of a vision system, custom end effector and software. To address the harvesting challenges posed by iceberg lettuce a bespoke vision and learning system has been developed which uses two integrated convolutional neural networks to achieve classification and localization. A custom end effector has been developed to allow damage free harvesting. To allow this end effector to achieve repeatable and consistent harvesting, a control method using force feedback allows detection of the ground. The system has been tested in the field, with experimental evidence gained which demonstrates the success of the vision system to localize and classify the lettuce, and the full integrated system to harvest lettuce. This study demonstrates how existing state-of-the art vision approaches can be applied to agricultural robotics, and mechanical systems can be developed which leverage the environmental constraints imposed in such environments
Firms' intellectual property ownership aggressiveness in university–industry collaboration projects: Choosing the right governance mode
No full textIntellectual property (IP) ownership aggressiveness constitutes an organization's strategic stance that prioritizes its IP protection. An organization thus pursues a rigid approach to protect its background IP and strives for exclusive ownership of the foreground IP that results from collaborative projects. This paper investigates how firms' IP ownership aggressiveness influences university–industry collaboration (UIC) project success and examines if the relationship is contingent on the governance modes that firms employ in UICs, especially the intensity of contract formality and shared governance. Analysing survey data from UIC projects of medium-sized to large firms covering four industries, we find that the levels of contract formality and shared governance moderate the effect of firms' IP ownership aggressiveness on project success. Strong contract formality leads to a negative relationship between firms' IP ownership aggressiveness and UIC project success. Conversely, if firms apply strong shared governance, the relationship between IP ownership aggressiveness and UIC project success is positive. Given firms' strategic approach to protect background IP and claim ownership of foreground IP, these results have implications for UIC managers when selecting governance modes to best support UIC project success
Ordered graphitic microfoams via shrinkage and catalytic conversion of polymer scaffolds
No full textCarbon foams are a highly attractive class of low-density materials whose structural, electrical, thermal, and chemical properties are strongly linked to the level of graphitization and 3D structure. Pyrolytic graphitization requires very high temperatures (>2000 °C), and most current graphitic foams are stochastically arranged with restricted control over pore size and architecture. We report on the shrinkage and catalytic conversion of commercial polymer foams and 3D printed templates as a facile, cost-effective method to scalably reach and control sub-200 μm unit cell sizes and a high level of graphitization at temperatures below 1100 °C. We demonstrate the conversion of 3D printed cubic polymer lattices to an identically shaped carbonaceous network with shrinkage controlled via an atomic layer deposited oxide coating up to a maximum 125 fold decrease in volume and over 95% mass loss through slow carbonization. This is accompanied by a reduction in the unit cell size from 1000 μm to 170 μm and strut widths from 550 μm to 65 μm. The structures are subsequently coated with a sacrificial metal catalyst by electroless deposition to achieve efficient graphitization while maintaining structural order. We discuss the underlying mechanisms and opportunities to tailor the processes and structure to manifold application needs
A small-strain niobium nitride anode with ordered mesopores for ultra-stable potassium-ion batteries
No full textLithium-ion batteries (LIBs) are considered as fascinating energy storage devices. However, scarcity and high cost of lithium resources lead to increasing research interest in next-generation batteries, such as potassium-ion batteries (KIBs), due to their similar electrochemical characteristics to LIBs and abundant potassium resources. However, significant problems in the search for suitable anode materials for KIBs continue to exist due to the hazards of potassium metal and unstable cycling performance of carbonaceous materials and metal oxides due to the large ionic size of potassium. Herein, we report on a well-ordered mesoporous niobium nitride/N-doped carbon hybrid (m-NbN/NC), verifying the potential of the transition metal nitride as the new K+ insertion host. The electrode delivers reversible capacities of 143 mA h g-1 at 0.01 A g-1 and 49 mA h g-1 at 1 A g-1. More impressively, a capacity retention of 100% at 0.5 A g-1 after 2000 cycles was achieved. In situ X-ray diffraction and ex situ scanning electron microscopy (SEM) analysis indicated that the m-NbN/NC electrode retains its structural integrity during potassiation that was accompanied by small strain, which was ascribed to the high proportion of surface-controlled reaction. This work points at a feasible new class of anode materials for ultra-stable KIBs
Measuring the bipolar charge distribution of nanoparticles: Review of methodologies and development using the Aerodynamic Aerosol Classifier
No full textA review of methodologies to measure the bipolar charge distribution of nanoparticles is completed, including their advantages/disadvantages and sequential development. This summary also provides context for a new development, which uses an Aerodynamic Aerosol Classifier (AAC) and Differential Mobility Analyzer (DMA) in tandem for a similar purpose. It is demonstrated that the tandem AAC-DMA system overcomes some significant limitations of the previous methodologies, such as multiply-charged particle artefacts and low measurement signals. The tandem AAC-DMA methodology also has the sensitivity to detect other charging phenomena, such as the effects of different sample flow rates through the charger, free-ions downstream of the charger, the inlet insert on the 85Kr charger and different particle chargers (x-ray, old 85Kr and new 85Kr). The charge fractions of the particles at low-flow (0.6 L/min) through the new 85Kr charger agreed well (average absolute difference of 0.007) with widely-used charging theory. However, significant deviations from theory (up to a 0.044 difference in charge fractions) were found with a higher sample flow rate (1.2 L/min), with different exposure times to free-ions downstream of the charger, or with the inlet insert on the new 85Kr charger. It was found that regardless of flow rate, a soft x-ray charger resulted in charge fractions which deviated significantly from theory (up to a 0.084 difference in charge fractions), producing higher fractions of positively charged particles and lower fractions of negatively charged particles relative to theory. All of these deviations are likely due to the simplifying assumptions made by the charging theory. Therefore, rigorous measurement of particle charge distributions are necessary for accurate aerosol characterization, such as standard SMPS measurements
Carrierless amplitude and phase modulation in wireless visible light communication systems
No full textVisible light communications (VLCs) have attracted considerable interest in recent years owing to the potential to simultaneously achieve data transmission and illumination using low-cost light-emitting diodes (LEDs). However, the high-speed capability of such links is typically limited by the low bandwidth of LEDs. As a result, spectrally efficient advanced modulation formats have been considered for use in VLC links in order to mitigate this issue and enable higher data rates. Carrierless amplitude and phase (CAP) modulation is one such spectrally efficient scheme that has attracted significant interest in recent years owing to its good potential and practical implementation. In this paper, we introduce the basic features of CAP modulation and review its use in the context of indoor VLC systems. We describe some of its attributes and inherent limitations, present related advances aiming to improve its performance and potential and report on recent experimental demonstrations of LED-based VLC links employing CAP modulation
Broad bandwidth dual-wavelength fiber laser simultaneously delivering stretched pulse and dissipative soliton
No full textWe numerically and experimentally demonstrate the generation of broad bandwidth mode-locked dual-wavelength pulses with diverse-pattern from a dispersion managed erbiumdoped (Er-doped) fiber laser. The two-peak gain profile of the Er-doped fiber is shown to have advantages in achieving broadband dual-wavelength pulses compared to a comb filter in our cavity. Our obtained bandwidths of 24 nm and 11.5 nm represent the broadest achieved in an Er-doped dual-wavelength fiber laser to date. In addition, the weak third-order dispersion (TOD) of the fibers facilitates two dispersion-pattern pulses (one stretched pulse and one dissipative soliton) generated in the near zero dispersion regime. Our results provide a convenient, effective way to obtain such sources for potential applications, such as in dual-comb metrology and multicolor pulses in nonlinear microscopy