Now showing items 21-40 of 672

• #### Aging and condensed phase chemistry affects the hygroscopicity of ambient SOA

Secondary inorganic and organic aerosol particles are ubiquitous constituents in the atmosphere. They are largely produced through the photo-oxidation of gaseous precursor molecules, such as SO2, NOx and VOCs, from both anthropogenic and natural sources. Once grown to atmospherically relevant sizes, they can act as cloud condensation nuclei (CCN) and thus affect earth’s climate (IPCC, 2013). However, their chemical composition can vary considerably over their atmospheric lifetime (up to one week) as a result of which, their physico-chemical properties may change significantly due to chemical transformation processes (Jimenez et al., 2009). One of these properties is hygroscopicity, which largely depends on the chemical composition. Linking both, measured chemical composition and hygroscopicity helps to advance our current understanding of the hygroscopicity parametrisation. In this work we investigated how photochemical aging of the organic aerosol fraction and chemical reactions between inorganic and organic compounds can affect the hygroscopicity parameter κ (Petters and Kreidenweis, 2007). The measurements were conducted at the semi-rural Taunus Observatory/ Germany during summer 2012. An extensive suite of particle phase characterizing instrumentation was applied for the detailed composition analysis of submicron aerosol: We used online atmospheric pressure chemical ionization mass spectrometry (APCI-MS) (Vogel et al., 2013), aerosol mass spectrometry (AMS), and filter sampling for laboratory based analysis using ultrahigh performance liquid chromatography coupled to electrospray ionization ultrahigh resolution (OrbitrapTM) mass spectrometry (UHPLC/ESI-UHRMS). The AMS allows quantification of total organics, sulfate and nitrate, whereas the APCI-MS can identify single organic species (organic acids, organosulfates, nitrooxy-organosulfates), both at a high measurement frequencies (< 1 minute). The UHPLC/ESI-UHRMS analysis of filter samples provides vital information helping to understand the complex online spectra of the APCI-MS by the unambiguous determination of the elemental composition of different organic compounds. Furthermore, we used a MARGA (Monitor for Aerosols and Gases in Ambient Air) to measure the concentration of purely inorganic sulfate in PM10. Finally a CCN counter coupled to a differential mobility analyser (DMA) and to a condensation particle counter (CPC) was used to measure size-resolved CCN efficiency spectra and to derive the hygroscopicity parameter κ. We determined the κ-value of the ambient aerosol from size resolved chemical composition measurements by the AMS and compared it to the measured values of the CCN efficiency spectra. The relative evolution of the aerosol aging was determined by measuring the ratio of two biogenic acids: the aging product 1,2,3-methyl-butane-tricarboxylic acid (MBTCA) and the first generation oxidation product pinic acid by the online APCI-MS. The occurrence of organosulfates and nitrooxy-organosulfates was observed by the ultrahigh resolution MS analysis and the online APCI-MS. Comparison of the total sulfate concentration measured by the AMS with the sulfate measurements by the MARGA allowed for the determination of the fraction of sulfate which is bonded to organic molecules. We observed that photochemical aging and the formation of (hydrophobic) nitrooxy-organosulfates is responsible for the observed bias between the predicted and measured κ-value.
• #### Aircraft Electrical Propulsion for High-Speed Flight: Rim Driven Fan (RDF) Technology

The aim of this programme of studies is to research and develop electrical Rim Driven Fan (RDF) technology for high-speed aircraft propulsion and to provide knowledge to support Society’s efforts to combat climate change using zero-emission technologies. The objectives were to conduct research into the state-of-the-art of aircraft electrical propulsion, to estimate the performance of single and dual stage contra-rotating fans over a range of diameters, to provide a methodology to enable the aerodynamic design and detailed Computational Fluid Dynamic (CFD) analyses of small contra-rotating fans and to create a conceptual design for an RDF device suitable to power an unmanned aircraft. In completing this work, literature reviews were carried out on electrically powered propulsion for aircraft, electrical motor technologies and rim drive technology for aircraft propulsion. Original research was undertaken in the form of aerodynamic analyses, using derived numerical and CFD techniques, to determine the optimum performance of single and dual stage (contrarotating) rim driven fans for high-speed electric aircraft applications. Original research was also undertaken in the form of electrical analyses using Motor-CAD finite element software to analyse the feasibility of novel rim-drive concepts such as slotless stator designs, aluminium windings and iron-less rotors with Halbach magnet arrays in an RDF context. The results of these studies have contributed new knowledge that has been peer-reviewed and internationally published. An original RDF design concept, suitable to power an unmanned aircraft, was devised and a UK patent application filed. The main findings of this work are that RDF technology offers a viable means of high-speed aircraft propulsion with a dual-stage contrarotating, air-cooled fan arrangement. That optimum RDF power density is achieved with slotless windings and iron-less rotors configured with Halbach magnet arrays which reduce their rotating mass. These findings have enabled a feasible novel RDF design to be created which is a significant contribution in the field of electrical aircraft propulsion. The results of this work also contribute the significant new knowledge that dual stage contra-rotating RDF configurations provide the potential for an increase in thrust per frontal area, and higher exhaust-air velocities, when compared with existing hub-driven fan technologies. This work has established a novel fan design technique, that can be used by technologists to analyse and design future electrical fan concepts, and offers a significant contribution towards Society’s efforts to combat climate change with zero-emission technologies. Opportunities for further areas of study in this field are in the analyses of large diameter high thrust versions of RDFs suitable for large manned aircraft and hovercraft applications.
• #### Airlift Bioreactor for Biological Applications with Microbubble Mediated Transport Processes

Airlift bioreactors can provide an attractive alternative to stirred tanks, particularly for bioprocesses with gaseous reactants or products. Frequently, however, they are susceptible to being limited by gas-liquid mass transfer and by poor mixing of the liquid phase, particularly when they are operating at high cell densities. In this work we use CFD modelling to show that microbubbles generated by fluidic oscillation can provide an effective, low energy means of achieving high interfacial area for mass transfer and improved liquid circulation for mixing. The results show that when the diameter of the microbubbles exceeded 200 μm, the “downcomer” region, which is equivalent to about 60 % of overall volume of the reactor, is free from gas bubbles. The results also demonstrate that the use of microbubbles not only increases surface area to volume ratio, but also increases mixing efficiency through increasing the liquid velocity circulation around the draft tube. In addition, the depth of downward penetration of the microbubbles into the downcomer increases with decreasing bubbles size due to a greater downward drag force compared to the buoyancy force. The simulated results indicate that the volume of dead zone increases as the height of diffuser location is increased. We therefore hypothesise that poor gas bubble distribution due to the improper location of the diffuser may have a markedly deleterious effect on the performance of the bioreactor used in this work.
• #### An algorithm for the numerical solution of two-sided space-fractional partial differential equations.

We introduce an algorithm for solving two-sided space-fractional partial differential equations. The space-fractional derivatives we consider here are left-handed and right-handed Riemann–Liouville fractional derivatives which are expressed by using Hadamard finite-part integrals. We approximate the Hadamard finite-part integrals by using piecewise quadratic interpolation polynomials and obtain a numerical approximation of the space-fractional derivative with convergence order
• #### An algorithm to detect small solutions in linear delay differential equations

This preprint discusses an algorithm that provides a simple reliable mechanism for the detection of small solutions in linear delay differential equations.
• #### Algorithms for the fractional calculus: A selection of numerical methods

This article discusses how numerical algorithms can help engineers work with fractional models in an efficient way.
• #### An Altered Four Circulant Construction for Self-Dual Codes from Group Rings and New Extremal Binary Self-dual Codes I

We introduce an altered version of the four circulant construction over group rings for self-dual codes. We consider this construction over the binary field, the rings F2 + uF2 and F4 + uF4; using groups of order 4 and 8. Through these constructions and their extensions, we find binary self-dual codes of lengths 16, 32, 48, 64 and 68, many of which are extremal. In particular, we find forty new extremal binary self-dual codes of length 68, including twelve new codes with \gamma=5 in W68,2, which is the first instance of such a value in the literature.
• #### Alternative Representations of 3D-Reconstructed Heritage Data

By collecting images of heritage assets from members of the public and processing them to create 3D-reconstructed models, the HeritageTogether project has accomplished the digital recording of nearly 80 sites across Wales, UK. A large amount of data has been collected and produced in the form of photographs, 3D models, maps, condition reports, and more. Here we discuss some of the different methods used to realize the potential of this data in different formats and for different purposes. The data are explored in both virtual and tangible settings, and—with the use of a touch table—a combination of both. We examine some alternative representations of this community-produced heritage data for educational, research, and public engagement applications.
• #### Alternative selection of processing additives to enhance the lifetime of OPVs

The use of processing additives is known to accelerate the degradation of Organic Photovoltaics (OPVs) and therefore, this paper studies the impact of selecting alternative processing additives for PCPDTBT:PC71BM solar cells in order to improve the stability. The use of naphthalene-based processing additives has been undertaken, which is shown to reduce the initial power conversion efficiency by 23%-42%, primarily due to a decrease in the short-circuit current density, but also fill factor. However, the stability is greatly enhanced by using such additives, with the long term stability (T50%) enhanced by a factor of four. The results show that there is a trade-off between initial performance and stability to consider when selecting the initial process additives. XPS studies have provided some insight into the decreased degradation and show that using 1-chloronaphthalene (ClN) leads to reduced morphology changes and reduced oxidation of the thiophene-ring within the PCPDTBT backbone.

• #### An analysis of the L1 scheme for stochastic subdiffusion problem driven by integrated space-time white noise

We consider the strong convergence of the numerical methods for solving stochastic subdiffusion problem driven by an integrated space-time white noise. The time fractional derivative is approximated by using the L1 scheme and the time fractional integral is approximated with the Lubich's first order convolution quadrature formula. We use the Euler method to approximate the noise in time and use the truncated series to approximate the noise in space. The spatial variable is discretized by using the linear finite element method. Applying the idea in Gunzburger \et (Math. Comp. 88(2019), pp. 1715-1741), we express the approximate solutions of the fully discrete scheme by the convolution of the piecewise constant function and the inverse Laplace transform of the resolvent related function. Based on such convolution expressions of the approximate solutions, we obtain the optimal convergence orders of the fully discrete scheme in spatial multi-dimensional cases by using the Laplace transform method and the corresponding resolvent estimates.
• #### An analysis of the modified L1 scheme for time-fractional partial differential equations with nonsmooth data

We introduce a modified L1 scheme for solving time fractional partial differential equations and obtain error estimates for smooth and nonsmooth initial data in both homogeneous and inhomogeneous cases. Jin \et (2016, An analysis of the L1 scheme for the subdiffusion equation with nonsmooth data, IMA J. of Numer. Anal., 36, 197-221) established an $O(k)$ convergence rate for the L1 scheme for smooth and nonsmooth initial data for the homogeneous problem, where $k$ denotes the time step size. We show that the modified L1 scheme has convergence rate $O(k^{2-\alpha}), 0< \alpha <1$ for smooth and nonsmooth initial data in both homogeneous and inhomogeneous cases. Numerical examples are given to show that the numerical results are consistent with the theoretical results.
• #### Analysis of transient Rivlin-Ericksen fluid and irreversibility of exothermic reactive hydromagnetic variable viscosity

The study analysed unsteady Rivlin-Ericksen fluid and irreversibility of exponentially temperature dependent variable viscosity of hydromagnetic two-step exothermic chemical reactive flow along the channel axis with walls convective cooling. The non-Newtonian Hele-Shaw flow of Rivlin-Erickson fluid is driven by bimolecular chemical kinetic and unvarying pressure gradient. The reactive fluid is induced by periodic changes in magnetic field and time. The Newtons law of cooling is satisfied by the constant heat coolant convection exchange at the wall surfaces with the neighboring regime. The dimensionless non-Newtonian reactive fluid equations are numerically solved using a convergent and consistence semi-implicit finite difference technique which are confirmed stable. The response of the reactive fluid flow to variational increase in the values of some entrenched fluid parameters in the momentum and energy balance equations are obtained. A satisfying equations for the ratio of irreversibility, entropy generation and Bejan number are solved with the results presented graphically and discussed quantitatively. From the study, it was obtained that the thermal criticality conditions with the right combination of thermo-fluid parameters, the thermal runaway can be prevented. Also, the entropy generation can minimize by at low dissipation rate and viscosity.
• #### An Analysis of Virtual Team Characteristics: A Model for Virtual Project Managers

An integrated model, created to guide project managers, is outlined for the implementation and management of virtual teams. This model is developed by means of an exploratory literature review and an empirical investigation of virtual team utilization in a multinational medical device manufacturer, which examines several factors critical to their success. A TOWS matrix is used to structure the results of the analysis and to identify future virtual team strategies for the organization. The study demonstrates that a structured approach is essential to ensure that the benefits resulting from virtual teamwork are maximized.

• #### An analytic approach to the normalized Ricci flow-like equation: Revisited

In this paper we revisit Hamilton’s normalized Ricci flow, which was thoroughly studied via a PDE approach in Kavallaris and Suzuki (2010). Here we provide an improved convergence result compared to the one presented Kavallaris and Suzuki (2010) for the critical case λ=8πλ=8π. We actually prove that the convergence towards the stationary normalized Ricci flow is realized through any time sequence.
• #### Analytical and numerical investigation of mixed-type functional differential equations

This journal article is concerned with the approximate solution of a linear non-autonomous functional differential equation, with both advanced and delayed arguments.
• #### An Analytical and Numerical Study of Magnetic Spring Suspension with Energy Recovery Capabilities

As the automotive paradigm shifts towards electric, limited range remains a key challenge. Increasing the battery size adds weight, which yields diminishing returns in range per kilowatt-hour. Therefore, energy recovery systems, such as regenerative braking and photovoltaic cells, are desirable to recharge the onboard batteries in between hub charge cycles. While some reports of regenerative suspension do exist, they all harvest energy in a parasitic manner, and the predicted power output is extremely low, since the majority of the energy is still dissipated to the environment by the suspension. This paper proposes a fundamental suspension redesign using a magnetically-levitated spring mechanism and aims to increase the recoverable energy significantly by directly coupling an electromagnetic transducer as the main damper. Furthermore, the highly nonlinear magnetic restoring force can also potentially enhance rider comfort. Analytical and numerical models have been constructed. Road roughness data from an Australian road were used to numerically simulate a representative environment response. Simulation suggests that 10’s of kW to >100 kW can theoretically be generated by a medium-sized car travelling on a typical paved road (about 2–3 orders of magnitude higher than literature reports on parasitic regenerative suspension schemes), while still maintaining well below the discomfort threshold for passengers (<0.315 m/s2 on average).
• #### Analytical and numerical treatment of oscillatory mixed differential equations with differentiable delays and advances

This article discusses the oscillatory behaviour of the differential equation of mixed type.
• #### Angus I. Kirkland and Sarah J. Haigh (Eds.): Nanocharacterization, 2nd ed.

Book review of NanoCharacterisation, second edition, Editors Angus I. Kirkland and Sarah J. Haigh. Published by Royal Society of Chemistry ISBN: 978-1-84973-805-7