On the tuning of a wave-energy driven oscillating-water-column seawater pump to polychromatic waves

Performance of wave-energy devices of the oscillating water column (OWC) type is greatly enhanced when a resonant condition with the forcing waves is maintained. The natural frequency of such systems can in general be tuned to resonate with a given wave forcing frequency. In this paper we address the tuning of an OWC sea-water pump to polychromatic waves. We report results of wave tank experiments, which were conducted with a scale model of the pump. Also, a numerical solution for the pump equations, which were proven in previous work to successfully describe its behavior when driven by monochromatic waves, is tested with various polychromatic wave spectra. Results of the numerical model forced by the wave trains measured in the wave tank experiments are used to develop a tuning criterion for the sea-water pump.Comment: 21 pages, 14 figure

Characteristics of turbulent flames in a confined and pressurised jet-in-hot-coflow combustor

Available online 16 August 2022Combustion in hot and low oxygen environments—such as those encountered in practical devices including inter-turbine burners and sequential gas turbines—is not yet fully understood at a fundamental level, particularly in terms of the effects of pressure. To meet this gap in understanding, a confined-and-pressurised jet-in-hotcoflow (CP-JHC) combustor has been developed to facilitate optical diagnostics of turbulent flames in hot and vitiated coflows for the studies of flame stabilisation, structure and soot formation at elevated pressures. The CPJHC burner has been designed for steady operation at 10 bar with internal temperatures of up to 1975 K, with a water-cooled central jet issuing into a hot oxidant stream of combustion products from a non-premixed natural gas/H2 burner. This work describes the key features and operational capabilities of the CP-JHC burner and presents a selection of experimental results showing characteristics not previously available. Specifically, temperature measurements of the hot coflow are used to estimate the enthalpy deficit of the stream, revealing an increase in thermal efficiency with increasing heat input, and a decrease with increasing pressure. Chemiluminescence imaging of OH* and CH* is performed for turbulent jet flames to study the flame structure under various operating conditions, and true-colour imaging results are also included to highlight the change in soot formation under elevated pressures. The mean images indicate a change in stabilisation behaviour with changes in pressure and jet Reynolds number (Rejet), which is further investigated by a statistical analysis of the shortexposure CH* images. This analysis reveals that an increase in Rejet from 10,000 to 15,000 leads to an increase in the mean lift-off height (from the jet exit plane) from approximately 1.5 to 6 jet diameters at atmospheric pressure, while the flames at elevated pressures show significantly less variation and tend to stabilise at the jet exit for P > 3.5 bar(a). The experimental findings are complemented by numerical simulations of laminar opposed flow flames, providing additional insights into the fundamental chemical kinetics effects which influence these flames. In particular, a monotonic reduction in both the maximum and integrated OH* and CH* mass fractions is observed with increasing pressure. This reduction is particularly pronounced at lower pressures, with a reduction to 10% of the atmospheric-pressure value at 3 bar(a) for the integrated OH* mass fraction. Additionally, this behaviour is shown to be related to the combined effects of a shift in the formation pathways and the increased impact of collisional quenching.D.B. Proud, M.J. Evans, Q.N. Chan, P.R. Medwel

A new species of the lenticel fungal genus Claviradulomyces (Ostropales) from the Brazilian Atlantic forest tree Xylopia sericea (Annonaceae)

Claviradulomyces xylopiae sp. nov. is introduced for a fungus occurring in association with abnormal (enlarged, spongy) lenticels of Xylopia sericea (Annonaceae), a common tree of the Atlantic forest and Cerrado ecosystems in Brazil. This is the second species described in the genus and, although it is morphologically distinct from the type species, C. dabeicola from West Africa, it possesses the same characteristics. Apothecial ascomata have periphysoids and paraphyses that are inflated apically (clavate), and ornamented with denticles (raduliform). Furthermore, similar to the type species, it also has long-cylindric or acerose, aseptate ascospores and conidia. An additional asexual morph was produced in culture and is described. Molecular studies of C. dabeicola and the new species confirmed a placement in Ostropales, although a relationship to Odontotremataceae was not supported. Both species were consistently in association with abnormal lenticular development on their woody hosts. It remains to be ascertained, however, if these are the causal agents of the bark disorders, or, simply, opportunistic colonisers. The finding of the second species in the genus Claviradulomyces on a plant from a distantly related family to that of the host of C. dabeicola (Erythroxylaceae) for the genus on a different continent suggests that fungi in this genus may be common on lenticels of other woody plants, and could even have a pantropical distribution. It is possible that fungi in the genus have remained unreported until now because lenticels have remained neglected as a habitat surveyed by mycologists

Generalisation of the eddy-dissipation concept for jet flames with low turbulence and low Damkohler number

Moderate or intense low oxygen dilution (MILD) combustion has been the focus of a range of fundamental experimental and numerical studies. Reasonable agreement between experimental and numerical investigations, however, requires finite-rate chemistry models and, often, ad hoc model adjustment. To remedy this, an adaptive eddy dissipation concept (EDC) combustion model has previously been developed to target conditions encountered in MILD combustion; however, this model relies on a simplified, pre-defined assumption about the combustion chemistry. The present paper reports a generalised version of the modified EDC model without the need for an assumed, single-step chemical reaction or ad hoc coefficient tuning. The results show good agreement with experimental measurements of two CH4/H2 flames in hot coflows, showing improvements over the standard EDC model as well as the previously published modified EDC model. The updated version of the EDC model also demonstrates the capacity to reproduce the downstream transition in flame structure of a MILD jet flame seen experimentally, but which has previously proven challenging to capture computationally. Analyses of the previously identified dominant heat-release reactions provide insight into the structural differences between a conventional autoignitive flame and a flame in the MILD combustion regime, whilst highlighting the requirement for a generalised EDC combustion model.M.J.Evans, C.Petre, P.R.Medwell, A.Parent

Spatio-temporal structure of cell distribution in cortical Bone Multicellular Units: a mathematical model

Bone remodelling maintains the functionality of skeletal tissue by locally coordinating bone-resorbing cells (osteoclasts) and bone-forming cells (osteoblasts) in the form of Bone Multicellular Units (BMUs). Understanding the emergence of such structured units out of the complex network of biochemical interactions between bone cells is essential to extend our fundamental knowledge of normal bone physiology and its disorders. To this end, we propose a spatio-temporal continuum model that integrates some of the most important interaction pathways currently known to exist between cells of the osteoblastic and osteoclastic lineage. This mathematical model allows us to test the significance and completeness of these pathways based on their ability to reproduce the spatio-temporal dynamics of individual BMUs. We show that under suitable conditions, the experimentally-observed structured cell distribution of cortical BMUs is retrieved. The proposed model admits travelling-wave-like solutions for the cell densities with tightly organised profiles, corresponding to the progression of a single remodelling BMU. The shapes of these spatial profiles within the travelling structure can be linked to the intrinsic parameters of the model such as differentiation and apoptosis rates for bone cells. In addition to the cell distribution, the spatial distribution of regulatory factors can also be calculated. This provides new insights on how different regulatory factors exert their action on bone cells leading to cellular spatial and temporal segregation, and functional coordination.Comment: 14 pages, 5 figures; v2: Completed model description after Eq. (16), clarified discussion/description after Eq. (23), between Eqs. (29)-(31), and in 2nd bullet point in conclusion

The Dimensional-Reduction Anomaly in Spherically Symmetric Spacetimes

In D-dimensional spacetimes which can be foliated by n-dimensional homogeneous subspaces, a quantum field can be decomposed in terms of modes on the subspaces, reducing the system to a collection of (D-n)-dimensional fields. This allows one to write bare D-dimensional field quantities like the Green function and the effective action as sums of their (D-n)-dimensional counterparts in the dimensionally reduced theory. It has been shown, however, that renormalization breaks this relationship between the original and dimensionally reduced theories, an effect called the dimensional-reduction anomaly. We examine the dimensional-reduction anomaly for the important case of spherically symmetric spaces.Comment: LaTeX, 19 pages, 2 figures. v2: calculations simplified, references adde

New Critical Behavior in Einstein-Yang-Mills Collapse

We extend the investigation of the gravitational collapse of a spherically symmetric Yang-Mills field in Einstein gravity and show that, within the black hole regime, a new kind of critical behavior arises which separates black holes formed via Type I collapse from black holes formed through Type II collapse. Further, we provide evidence that these new attracting critical solutions are in fact the previously discovered colored black holes with a single unstable mode.Comment: 13 pages, 4 figure

Kink Stability of Self-Similar Solutions of Scalar Field in 2+1 Gravity

The kink stability of self-similar solutions of a massless scalar field with circular symmetry in 2+1 gravity is studied, and found that such solutions are unstable against the kink perturbations along the sonic line (self-similar horizon). However, when perturbations outside the sonic line are considered, and taking the ones along the sonic line as their boundary conditions, we find that non-trivial perturbations do not exist. In other words, the consideration of perturbations outside the sonic line limits the unstable mode of the perturbations found along the sonic line. As a result, the critical solution for the scalar collapse remains critical even after the kink perturbations are taken into account.Comment: latex, one figur

Genomic and transcriptomic characterization of Pseudomonas aeruginosa small colony variants derived from a chronic infection model

Phenotypic change is a hallmark of bacterial adaptation during chronic infection. In the case of chronic Pseudomonas aeruginosa lung infection in patients with cystic fibrosis, well-characterized phenotypic variants include mucoid and small colony variants (SCVs). It has previously been shown that SCVs can be reproducibly isolated from the murine lung following the establishment of chronic infection with mucoid P. aeruginosa strain NH57388A. Using a combination of single-molecule real-time (PacBio) and Illumina sequencing we identify a large genomic inversion in the SCV through recombination between homologous regions of two rRNA operons and an associated truncation of one of the 16S rRNA genes and suggest this may be the genetic switch for conversion to the SCV phenotype. This phenotypic conversion is associated with large-scale transcriptional changes distributed throughout the genome. This global rewiring of the cellular transcriptomic output results in changes to normally differentially regulated genes that modulate resistance to oxidative stress, central metabolism and virulence. These changes are of clinical relevance because the appearance of SCVs during chronic infection is associated with declining lung function

Structural differences of ethanol and DME jet flames in a hot diluted coflow

This study compares the flame structure of ethanol and dimethyl ether (DME) in a hot and diluted ox- idiser experimentally and computationally. Experiments were conducted on a Jet in Hot Coflow (JHC) burner, with the fuel jet issuing into a 1250-K coflow at three oxygen levels. Planar measurements using OH-LIF, CH 2 O-LIF, and Rayleigh scattering images reveal that the overall spatial distribution and evolution of OH, CH 2 O, and temperature were quite similar for the two fuels. For both the ethanol and the DME flames, a transitional flame structure occurred as the coflow oxygen level increased from 3% to 9%. This indicates that the flames shift away from the MILD combustion regime. Reaction flux analyses of ethanol and DME were performed with the OPPDIF code, and ethane (C 2 H 6 ) was also included in the analyses for comparison. These analyses reveal that the H 2 /O 2 pathways are very important for both ethanol and DME in the 3% O 2 cases. In contrast, the importance of fuel-specific reactions overtakes that of H 2 /O 2 reactions when fuels are burnt in the cold air or in the vitiated oxidant stream with 9% O 2 . Unsteady laminar flamelet analyses were also performed to investigate the ignition processes and help interpret experimental results. Flamelet equations were solved in time and mixture fraction field, which was pro- vided by non-reactive Large-Eddy Simulation (LES).Jingjing Ye, Paul R. Medwell, Konstantin Kleinheinz, Michael J. Evans, Bassam B. Dally, Heinz G. Pitsc