Key aerodynamic technologies for aircraft engine nacelles

Customer requirements and vision in aerospace dictate that the next generation of civil transport aircraft should have a strong emphasis on increased safety, reduced environmental impact and reduced cost without sacrificing performance. In this context, the School of Mechanical and Aerospace Engineering at the Queen's University of Belfast and Bombardier have, in recent years, been conducting research into some of the key aerodynamic technologies for the next generation of aircraft engine nacelles. Investigations have been performed into anti-icing technology, efficient thrust reversal, engine fire zone safety, life cycle cost and integration of the foregoing with other considerations in engine and aircraft design. A unique correlation for heat transfer in an anti-icing system has been developed. The effect of normal vibration on heat transfer in such systems has been found to be negligible. It has been shown that carefully designed natural blockage thrust reversers without a cascade can reduce aircraft weight with only a small sacrifice in the reversed thrust. A good understanding of the pressure relief doors and techniques to improve the performance of such doors have been developed. Trade off studies between aerodynamics, manufacturing and assembly of engine nacelles have shown the potential for a significant reduction in life cycle cost

Evidence of a recent decline in UK emissions of hydrofluorocarbons determined by the InTEM inverse model and atmospheric measurements

National greenhouse gas inventories (GHGIs) are submitted annually to the United Nations Framework Convention on Climate Change (UNFCCC). They are estimated in compliance with Intergovernmental Panel on Climate Change (IPCC) methodological guidance using activity data, emission factors and facility-level measurements. For some sources, the outputs from these calculations are very uncertain. Inverse modelling techniques that use high-quality, long-term measurements of atmospheric gases have been developed to provide independent verification of national GHGIs. This is considered good practice by the IPCC as it helps national inventory compilers to verify reported emissions and to reduce emission uncertainty. Emission estimates from the InTEM (Inversion Technique for Emission Modelling) model are presented for the UK for the hydrofluorocarbons (HFCs) reported to the UNFCCC (HFC-125, HFC-134a, HFC-143a, HFC-152a, HFC-23, HFC-32, HFC-227ea, HFC-245fa, HFC-43-10mee and HFC-365mfc). These HFCs have high global warming potentials (GWPs), and the global background mole fractions of all but two are increasing, thus highlighting their relevance to the climate and a need for increasing the accuracy of emission estimation for regulatory purposes. This study presents evidence that the long-term annual increase in growth of HFC-134a has stopped and is now decreasing. For HFC-32 there is an early indication, its rapid global growth period has ended, and there is evidence that the annual increase in global growth for HFC-125 has slowed from 2018. The inverse modelling results indicate that the UK implementation of European Union regulation of HFC emissions has been successful in initiating a decline in UK emissions from 2018. Comparison of the total InTEM UK HFC emissions in 2020 with the average from 2009-2012 shows a drop of 35ĝ€¯%, indicating progress toward the target of a 79ĝ€¯% decrease in sales by 2030. The total InTEM HFC emission estimates (2008-2018) are on average 73 (62-83)ĝ€¯% of, or 4.3 (2.7-5.9)ĝ€¯Tgĝ€¯CO2-eqĝ€¯yr-1 lower than, the total HFC emission estimates from the UK GHGI. There are also significant discrepancies between the two estimates for the individual HFCs.</p

Quantifying Adaptive Evolution in the Drosophila Immune System

It is estimated that a large proportion of amino acid substitutions in Drosophila have been fixed by natural selection, and as organisms are faced with an ever-changing array of pathogens and parasites to which they must adapt, we have investigated the role of parasite-mediated selection as a likely cause. To quantify the effect, and to identify which genes and pathways are most likely to be involved in the host–parasite arms race, we have re-sequenced population samples of 136 immunity and 287 position-matched non-immunity genes in two species of Drosophila. Using these data, and a new extension of the McDonald-Kreitman approach, we estimate that natural selection fixes advantageous amino acid changes in immunity genes at nearly double the rate of other genes. We find the rate of adaptive evolution in immunity genes is also more variable than other genes, with a small subset of immune genes evolving under intense selection. These genes, which are likely to represent hotspots of host–parasite coevolution, tend to share similar functions or belong to the same pathways, such as the antiviral RNAi pathway and the IMD signalling pathway. These patterns appear to be general features of immune system evolution in both species, as rates of adaptive evolution are correlated between the D. melanogaster and D. simulans lineages. In summary, our data provide quantitative estimates of the elevated rate of adaptive evolution in immune system genes relative to the rest of the genome, and they suggest that adaptation to parasites is an important force driving molecular evolution

Patterns of Polymorphism and Demographic History in Natural Populations of Arabidopsis lyrata

Many of the processes affecting genetic diversity act on local populations. However, studies of plant nucleotide diversity have largely ignored local sampling, making it difficult to infer the demographic history of populations and to assess the importance of local adaptation. Arabidopsis lyrata, a self-incompatible, perennial species with a circumpolar distribution, is an excellent model system in which to study the roles of demographic history and local adaptation in patterning genetic variation.We studied nucleotide diversity in six natural populations of Arabidopsis lyrata, using 77 loci sampled from 140 chromosomes. The six populations were highly differentiated, with a median FST of 0.52, and structure analysis revealed no evidence of admixed individuals. Average within-population diversity varied among populations, with the highest diversity found in a German population; this population harbors 3-fold higher levels of silent diversity than worldwide samples of A. thaliana. All A. lyrata populations also yielded positive values of Tajima's D. We estimated a demographic model for these populations, finding evidence of population divergence over the past 19,000 to 47,000 years involving non-equilibrium demographic events that reduced the effective size of most populations. Finally, we used the inferred demographic model to perform an initial test for local adaptation and identified several genes, including the flowering time gene FCA and a disease resistance locus, as candidates for local adaptation events.Our results underscore the importance of population-specific, non-equilibrium demographic processes in patterning diversity within A. lyrata. Moreover, our extensive dataset provides an important resource for future molecular population genetic studies of local adaptation in A. lyrata

Population genomics of the Wolbachia endosymbiont in Drosophila melanogaster

Wolbachia are maternally-inherited symbiotic bacteria commonly found in arthropods, which are able to manipulate the reproduction of their host in order to maximise their transmission. Here we use whole genome resequencing data from 290 lines of Drosophila melanogaster from North America, Europe and Africa to predict Wolbachia infection status, estimate cytoplasmic genome copy number, and reconstruct Wolbachia and mtDNA genome sequences. Complete Wolbachia and mitochondrial genomes show congruent phylogenies, consistent with strict vertical transmission through the maternal cytoplasm and imperfect transmission of Wolbachia. Bayesian phylogenetic analysis reveals that the most recent common ancestor of all Wolbachia and mitochondrial genomes in D. melanogaster dates to around 8,000 years ago. We find evidence for a recent incomplete global replacement of ancestral Wolbachia and mtDNA lineages, which is likely to be one of several similar incomplete replacement events that have occurred since the out-of-Africa migration that allowed D. melanogaster to colonize worldwide habitats.Comment: 41 pages, 5 figure

Molecular Evolution of Regulatory Genes in Spruces from Different Species and Continents: Heterogeneous Patterns of Linkage Disequilibrium and Selection but Correlated Recent Demographic Changes

Genes involved in transcription regulation may represent valuable targets in association genetics studies because of their key roles in plant development and potential selection at the molecular level. Selection and demographic signatures at the sequence level were investigated for five regulatory genes belonging to the knox-I family (KN1, KN2, KN3, KN4) and the HD-Zip III family (HB-3) in three Picea species affected by post-glacial recolonization in North America and Europe. To disentangle neutral and selective forces and estimate linkage disequilibrium (LD) on a gene basis, complete or nearly complete gene sequences were analysed. Nucleotide variation within species, haplotype structure, LD, and neutrality tests, in addition to coalescent simulations based on Tajima’s D and Fay and Wu’s H, were estimated. Nucleotide diversity was generally low in all species (average π = 0.002–0.003) and much heterogeneity was seen in LD and selection signatures among genes and species. Most of the genes harboured an excess of both rare and frequent alleles in the three species. Simulations showed that this excess was significantly higher than that expected under neutrality and a bottleneck during the Last Glacial Maximum followed by population expansion at the Pleistocene/Holocene boundary or shortly after best explains the correlated sequence patterns. These results indicate that despite recent large demographic changes in the three boreal species from two continents, species-specific selection signatures could still be detected from the analysis of nearly complete regulatory gene sequences. Such different signatures indicate differential subfunctionalization of gene family members in the three congeneric species

Stable Recombination Hotspots in Birds

The DNA-binding protein PRDM9 has a critical role in specifying meiotic recombination hotspots in mice and apes, but it appears to be absent from other vertebrate species, including birds. To study the evolution and determinants of recombination in species lacking the gene that encodes PRDM9, we inferred fine-scale genetic maps from population resequencing data for two bird species: the zebra finch, Taeniopygia guttata, and the long-tailed finch, Poephila acuticauda. We found that both species have recombination hotspots, which are enriched near functional genomic elements. Unlike in mice and apes, most hotspots are shared between the two species, and their conservation seems to extend over tens of millions of years. These observations suggest that in the absence of PRDM9, recombination targets functional features that both enable access to the genome and constrain its evolution.5 page(s

Medial longitudinal arch development of school children : The College of Podiatry Annual Conference 2015: meeting abstracts

Background Foot structure is often classified into flat foot, neutral and high arch type based on the variability of the Medial Longitudinal Arch (MLA). To date, the literature provided contrasting evidence on the age when MLA development stabilises in children. The influence of footwear on MLA development is also unknown. Aim This study aims to (i) clarify whether the MLA is still changing in children from age 7 to 9 years old and (ii) explore the relationship between footwear usage and MLA development, using a longitudinal approach. Methods We evaluated the MLA of 111 healthy school children [age = 6.9 (0.3) years] using three parameters [arch index (AI), midfoot peak pressure (PP) and maximum force (MF: % of body weight)] extracted from dynamic foot loading measurements at baseline, 10-month and 22-month follow-up. Information on the type of footwear worn was collected using survey question. Linear mixed modelling was used to test for differences in the MLA over time. Results Insignificant changes in all MLA parameters were observed over time [AI: P = .15; PP: P = .84; MF: P = .91]. When gender was considered, the AI of boys decreased with age [P = .02]. Boys also displayed a flatter MLA than girls at age 6.9 years [AI: mean difference = 0.02 (0.01, 0.04); P = .02]. At baseline, subjects who wore close-toe shoes displayed the lowest MLA overall [AI/PP/MF: P < .05]. Subjects who used slippers when commencing footwear use experienced higher PP than those who wore sandals [mean difference = 31.60 (1.44, 61.75) kPa; post-hoc P = .04]. Discussion and conclusion Our findings suggested that the MLA of children remained stable from 7 to 9 years old, while gender and the type of footwear worn during childhood may influence MLA development. Clinicians may choose to commence therapy when a child presents with painful flexible flat foot at age 7 years, and may discourage younger children from wearing slippers when they commence using footwear