Search

Background The long-term outcomes of COVID-19 hospitalisation in individuals with pre-existing airway diseases are unknown. Methods Adult participants hospitalised for confirmed or clinically suspected COVID-19 and discharged between 5 March 2020 and 31 March 2021 were recruited to the Post-hospitalisation COVID-19 (PHOSP-COVID) study. Participants attended research visits at 5 months and 1 year post discharge. Clinical characteristics, perceived recovery, burden of symptoms and health-related quality of life (HRQoL) of individuals with pre-existing airway disease (i.e., asthma, COPD or bronchiectasis) were compared to the non-airways group. Results A total of 615 out of 2697 (22.8%) participants had a history of pre-existing airway diseases (72.0% diagnosed with asthma, 22.9% COPD and 5.1% bronchiectasis). At 1 year, the airways group participants were less likely to feel fully recovered (20.4% versus 33.2%, p

Background Pre-existing cardiovascular disease (CVD) or cardiovascular risk factors have been associated with an increased risk of complications following hospitalisation with COVID-19, but their impact on the rate of recovery following discharge is not known.Objectives To determine whether the rate of patient-perceived recovery following hospitalisation with COVID-19 was affected by the presence of CVD or cardiovascular risk factors.Methods In a multicentre prospective cohort study, patients were recruited following discharge from the hospital with COVID-19 undertaking two comprehensive assessments at 5 months and 12 months. Patients were stratified by the presence of either CVD or cardiovascular risk factors prior to hospitalisation with COVID-19 and compared with controls with neither. Full recovery was determined by the response to a patient-perceived evaluation of full recovery from COVID-19 in the context of physical, physiological and cognitive determinants of health.Results From a total population of 2545 patients (38.8% women), 472 (18.5%) and 1355 (53.2%) had CVD or cardiovascular risk factors, respectively. Compared with controls (n=718), patients with CVD and cardiovascular risk factors were older and more likely to have had severe COVID-19. Full recovery was significantly lower at 12 months in patients with CVD (adjusted OR (aOR) 0.62, 95% CI 0.43 to 0.89) and cardiovascular risk factors (aOR 0.66, 95% CI 0.50 to 0.86).Conclusion Patients with CVD or cardiovascular risk factors had a delayed recovery at 12 months following hospitalisation with COVID-19. Targeted interventions to reduce the impact of COVID-19 in patients with cardiovascular disease remain an unmet need.Trail registration number ISRCTN10980107.

Introduction: One of the important elements influencing the well-being of society is a highly educated, professional staff of the entire therapeutic team. Physiotherapists play a significant role in this team, which is why the higher education system is expected to make efforts to develop optimal education programs, including the development of practical skills. The purpose of this article is to present the Healint4All project, whose mission is to facilitate international internships for students of physiotherapy and other medical professions, which will allow high-class professionals in the healthcare sector to enter the job market. Material and methods: A step-by-step process of creating a protocol for auditing places of clinical practice was prepared. Virtual, interactive teaching resources were developed to prepare auditors. A literature analysis, focus interviews in groups of academic teachers, practitioners, and students. A pilot study of the protocol in live environments was conducted. Results: Both potential auditees (medical institutions) and auditors (universities) positively assessed the newly created tool. The recommendations included paying attention to transparency, simplicity, and linguistic correctness in all language versions of the protocol. It was suggested that the protocol, containing everything useful, should not be too long and would not burden the user with time. Conclusions: In the opinion of students and experts who evaluated the Healint4All protocol, it will contribute to increasing the supply and quality of international placements offered by healthcare organizations throughout Europe, as well as simplifying the processes involved in organizing these for students, educational institutions, and healthcare organizations.

Abstract COVID-19 has stimulated the rapid development of new antibody and small molecule therapeutics to inhibit SARS-CoV-2 infection. Here we describe a third antiviral modality that combines the drug-like advantages of both. Bicycles are entropically constrained peptides stabilized by a central chemical scaffold into a bi-cyclic structure. Rapid screening of diverse bacteriophage libraries against SARS-CoV-2 Spike yielded unique Bicycle binders across the entire protein. Exploiting Bicycles’ inherent chemical combinability, we converted early micromolar hits into nanomolar viral inhibitors through simple multimerization. We also show how combining Bicycles against different epitopes into a single biparatopic agent allows Spike from diverse variants of concern (VoC) to be targeted (Alpha, Beta, Delta and Omicron). Finally, we demonstrate in both male hACE2-transgenic mice and Syrian golden hamsters that both multimerized and biparatopic Bicycles reduce viraemia and prevent host inflammation. These results introduce Bicycles as a potential antiviral modality to tackle new and rapidly evolving viruses.

Custom proteases find applications as therapeutics, in research and in biotechnological applications. Here, the authors establish a protease selection system based on bacterial alpha-2-macroglobulin protease inhibitors and evolve staphylococcal proteases for increased activity and altered specificity.

In the opportunistic human pathogen Pseudomonas aeruginosa (Pae), carbon catabolite repression (CCR) orchestrates the hierarchical utilization of N and C sources, and impacts virulence, antibiotic resistance and biofilm development. During CCR, the RNA chaperone Hfq and the catabolite repression control protein Crc form assemblies on target mRNAs that impede translation of proteins involved in uptake and catabolism of less preferred C sources. After exhaustion of the preferred C-source, translational repression of target genes is relieved by the regulatory RNA CrcZ, which binds to and acts as a decoy for Hfq. Here, we asked whether Crc action can be modulated to relieve CCR after exhaustion of a preferred carbon source. As Crc does not bind to RNA per se, we endeavored to identify an interacting protein. In vivo co-purification studies, co-immunoprecipitation and biophysical assays revealed that Crc binds to Pae strain O1 protein PA1677. Our structural studies support bioinformatics analyzes showing that PA1677 belongs to the isochorismatase-like superfamily. Ectopic expression of PA1677 resulted in de-repression of Hfq/Crc controlled target genes, while in the absence of the protein, an extended lag phase is observed during diauxic growth on a preferred and a non-preferred carbon source. This observations indicate that PA1677 acts as an antagonist of Crc that favors synthesis of proteins required to metabolize non-preferred carbon sources. We present a working model wherein PA1677 diminishes the formation of productive Hfq/Crc repressive complexes on target mRNAs by titrating Crc. Accordingly, we propose the name CrcA (catabolite repression control protein antagonist) for PA1677.

Summary: Background: The scale of COVID-19 and its well documented long-term sequelae support a need to understand long-term outcomes including frailty. Methods: This prospective cohort study recruited adults who had survived hospitalisation with clinically diagnosed COVID-19 across 35 sites in the UK (PHOSP-COVID). The burden of frailty was objectively measured using Fried's Frailty Phenotype (FFP). The primary outcome was the prevalence of each FFP group—robust (no FFP criteria), pre-frail (one or two FFP criteria) and frail (three or more FFP criteria)—at 5 months and 1 year after discharge from hospital. For inclusion in the primary analysis, participants required complete outcome data for three of the five FFP criteria. Longitudinal changes across frailty domains are reported at 5 months and 1 year post-hospitalisation, along with risk factors for frailty status. Patient-perceived recovery and health-related quality of life (HRQoL) were retrospectively rated for pre-COVID-19 and prospectively rated at the 5 month and 1 year visits. This study is registered with ISRCTN, number ISRCTN10980107. Findings: Between March 5, 2020, and March 31, 2021, 2419 participants were enrolled with FFP data. Mean age was 57.9 (SD 12.6) years, 933 (38.6%) were female, and 429 (17.7%) had received invasive mechanical ventilation. 1785 had measures at both timepoints, of which 240 (13.4%), 1138 (63.8%) and 407 (22.8%) were frail, pre-frail and robust, respectively, at 5 months compared with 123 (6.9%), 1046 (58.6%) and 616 (34.5%) at 1 year. Factors associated with pre-frailty or frailty were invasive mechanical ventilation, older age, female sex, and greater social deprivation. Frail participants had a larger reduction in HRQoL compared with before their COVID-19 illness and were less likely to describe themselves as recovered. Interpretation: Physical frailty and pre-frailty are common following hospitalisation with COVID-19. Improvement in frailty was seen between 5 and 12 months although two-thirds of the population remained pre-frail or frail. This suggests comprehensive assessment and interventions targeting pre-frailty and frailty beyond the initial illness are required. Funding: UK Research and Innovation and National Institute for Health Research.

ABSTRACT The human pathogen Pseudomonas aeruginosa (Pa) is one of the most frequent and severe causes of nosocomial infection. This organism is also a major cause of airway infections in people with cystic fibrosis (CF). Pa is known to have a remarkable metabolic plasticity, allowing it to thrive under diverse environmental conditions and ecological niches; yet, little is known about the central metabolic pathways that sustain its growth during infection or precisely how these pathways operate. In this work, we used a combination of ‘omics approaches (transcriptomics, proteomics, metabolomics, and 13C-fluxomics) and reverse genetics to provide systems-level insight into how the infection-relevant organic acids succinate and propionate are metabolized by Pa. Moreover, through structural and kinetic analysis of the 2-methylcitrate synthase (2-MCS; PrpC) and its paralogue citrate (CIT) synthase (GltA), we show how these two crucial enzymatic steps are interconnected in Pa organic acid assimilation. We found that Pa can rapidly adapt to the loss of GltA function by acquiring mutations in a transcriptional repressor, which then derepresses prpC expression. Our findings provide a clear example of how “underground metabolism,” facilitated by enzyme substrate promiscuity, “rewires” Pa metabolism, allowing it to overcome the loss of a crucial enzyme. This pathogen-specific knowledge is critical for the advancement of a model-driven framework to target bacterial central metabolism. IMPORTANCE Pseudomonas aeruginosa is an opportunistic human pathogen that, due to its unrivalled resistance to antibiotics, ubiquity in the built environment, and aggressiveness in infection scenarios, has acquired the somewhat dubious accolade of being designated a “critical priority pathogen” by the WHO. In this work, we uncover the pathways and mechanisms used by P. aeruginosa to grow on a substrate that is abundant at many infection sites: propionate. We found that if the organism is prevented from metabolizing propionate, the substrate turns from being a convenient nutrient source into a potent poison, preventing bacterial growth. We further show that one of the enzymes involved in these reactions, 2-methylcitrate synthase (PrpC), is promiscuous and can moonlight for another essential enzyme in the cell (citrate synthase). Indeed, mutations that abolish citrate synthase activity (which would normally prevent the cell from growing) can be readily overcome if the cell acquires additional mutations that increase the expression of PrpC. This is a nice example of the evolutionary utility of so-called “underground metabolism.”

Background: With aging, many people develop Alzheimer’s disease or related dementias (ADRD) as well as chronic physical health problems. The consequent care needs can be complicated, with heavy demands on families, households and communities, especially in resource-constrained settings with limited formal care services. However, research on ADRD caregiving is largely limited to primary caregivers and high-income countries. Our objectives are to analyse in a rural setting in South Africa: (1) how extended households provide care to people with ADRD; and (2) how the health and wellbeing of all caregivers are affected by care roles. Methods: The study will take place at the Agincourt health and socio-demographic surveillance system site of the MRC/Wits Rural Public Health and Health Transitions Research Unit in Mpumalanga Province, northeast South Africa. We will recruit 100 index individuals predicted to currently have ADRD or cognitive impairment using data from a recent dementia survey. Quantitative surveys will be conducted with each index person’s nominated primary caregiver, all other household members aged over 12, and caregiving non-resident kin and non-kin to determine how care and health are patterned across household networks. Qualitative data will be generated through participant observation and in-depth interviews with caregivers, select community health workers and key informants. Combining epidemiological, demographic and anthropological methods, we will build a rich picture of households of people with ADRD, focused on caregiving demands and capacity, and of caregiving’s effects on health. Discussion: Our goal is to identify ways to mitigate the negative impacts of long-term informal caregiving for ADRD when formal supports are largely absent. We expect our findings to inform the development of locally relevant and community-oriented interventions to improve the health of caregivers and recipients, with implications for other resource-constrained settings in both higher- and lower-income countries.

Pseudomonas aeruginosa (PA) depends on the Entner-Doudoroff pathway (EDP) for glycolysis. The main enzymatic regulator in the lower half of the EDP is pyruvate kinase. PA contains genes that encode two isoforms of pyruvate kinase, denoted PykAPA and PykFPA. In other well-characterized organisms containing two pyruvate kinase isoforms (such as Escherichia coli) each isozyme is differentially regulated. The structure, function and regulation of PykAPA has been previously characterized in detail, so in this work, we set out to assess the biochemical and structural properties of the PykFPA isozyme. We show that pykFPA expression is induced in the presence of the diureide, allantoin. In spite of their relatively low amino acid sequence identity, PykAPA and PykFPA display broadly comparable kinetic parameters, and are allosterically regulated by a very similar set of metabolites. However, the x-ray crystal structure of PykFPA revealed significant differences compared with PykAPA. Notably, although the main allosteric regulator binding-site of PykFPA was empty, the “ring loop” covering the site adopted a partially closed conformation. Site-directed mutation of the proline residues flanking the ring loop yielded apparent “locked on” and “locked off” allosteric activation phenotypes, depending on the residue mutated. Analysis of PykFPA inter-protomer interactions supports a model in which the conformational transition(s) accompanying allosteric activation involve re-orientation of the A and B domains of the enzyme and subsequent closure of the active site.

Protein kinases are a large class of enzymes with numerous biological roles and many have been implicated in a vast array of diseases, including cancer and the novel coronavirus infection COVID-19. Thus, the development of chemical probes to selectively target each kinase is of great interest. Inhibition of protein kinases with ATP-competitive inhibitors has historically been the most widely used method. However, due to the highly conserved structures of ATP-sites, the identification of truly selective chemical probes is challenging. In this review, we use the Ser/Thr kinase CK2 as an example to highlight the historical challenges in effective and selective chemical probe development, alongside recent advances in the field and alternative strategies aiming to overcome these problems. The methods utilised for CK2 can be applied to an array of protein kinases to aid in the discovery of chemical probes to further understand each kinase’s biology, with wide-reaching implications for drug development.

For several centuries, microorganisms and enzymes have been used for many different applications. Although many enzymes with industrial applications have already been reported, different screening technologies, methods and approaches are constantly being developed in order to allow the identification of enzymes with even more interesting applications. In our work, we have performed data mining on the Chitinophaga sp. genome, a gram-negative bacterium isolated from a bacterial consortium of sugarcane bagasse isolated from an ethanol plant. The analysis of 8 Mb allowed the identification of the chtcp gene, previously annotated as putative Cht4039. The corresponding codified enzyme, denominated as ChtCP, showed the HEXXH conserved motif of family M32 from thermostable carboxypeptidases. After expression in E. coli, the recombinant enzyme was characterized biochemically. ChtCP showed the highest activity versus benziloxicarbonil Ala-Trp at pH 7.5, suggesting a preference for hydrophobic substrates. Surprisingly, the highest activity of ChtCP observed was between 55 °C and 75 °C, and 62% activity was still displayed at 100 °C. We observed that Ca2+, Ba2+, Mn2+ and Mg2+ ions had a positive effect on the activity of ChtCP, and an increase of 30 °C in the melting temperature was observed in the presence of Co2+. These features together with the structure of ChtCP at 1.2 Å highlight the relevance of ChtCP for further biotechnological applications.

Surface sediments from sites across the Indian margin of the Arabian Sea were analysed for their elemental and stable isotopic organic carbon (Corg) and total nitrogen compositions, grain size distributions and biochemical indices of organic matter (OM) source and/or degradation state. Site locations ranged from the estuaries of the Mandovi and Zuari rivers to depths of ~ 2000 m on the continental slope, thus spanning nearshore muds and sands on the shelf and both the oxygen minimum zone (OMZ) on the upper slope (~ 200–1300 m) and the seasonal hypoxic zone that appears on the shelf. Source indices showed mixed marine and terrigenous OM within the estuaries, but consistent predominance (80–100%) of marine OM on the shelf and slope. Thus, riverine terrigenous OM is diluted or replaced by autochthonous marine OM and/or is efficiently re-mineralised, within or immediately offshore of the estuaries. Organic C contents of surface shelf sediments varied from < 0.5 wt% in relict shelf sands to up to ~ 4 wt% for nearshore muds, while upper slope sites within the OMZ showed a wide range (~ 2 to 7 + wt%), progressively decreasing below the OMZ to ≤ 1 wt% at 2000 m. Thus, major variability (~ 5 wt%) was found at slope sites within the OMZ of similar depth and near-identical bottom-water O2 concentrations. A strong relationship between %Corg and sediment grain size was seen for sediments within the OMZ, but lower relative Corg contents were found for sites on the shelf and below the OMZ. Further, Corg loadings, when related to estimated sediment surface area, indicated distinct enrichment of Corg in the OMZ sediments relative to sites above and below the OMZ and to sediments from normoxic margins. Diagenetic indices confirmed that lower Corg content below the OMZ is associated with more extensive OM degradation, but that shelf sediment OM is not consistently more degraded than that found within the OMZ. Together, the results indicate that OM distribution across the margin is controlled by interplay between hydrodynamic processes and varying preservation associated with O2 availability. This inference is supported by multiple regression analysis. Hydrodynamic processes (expressed as %Silt) followed by O2 availability, can explain the large majority of %Corg variability when the shelf and slope are considered as a whole. However, while O2 becomes the primary influence on %Corg for sediments below the OMZ, %Silt is the primary influence across the OMZ and, apparently, the shelf. Thus, reduced O2 exposure is responsible for OM enrichment within the OMZ, but hydrodynamic processes are the overriding control on sediment OM distributions across both the shelf and the OMZ.

The majority of cilia are formed and maintained by the highly conserved process of intraflagellar transport (IFT). Mutations in IFT genes lead to ciliary structural defects and systemic disorders termed ciliopathies. Here we show that the severely truncated sensory cilia of hypomorphic IFT mutants in C. elegans transiently elongate during a discrete period of adult aging leading to markedly improved sensory behaviors. Age-dependent restoration of cilia morphology occurs in structurally diverse cilia types and requires IFT. We demonstrate that while DAF-16/FOXO is dispensable, the age-dependent suppression of cilia phenotypes in IFT mutants requires cell-autonomous functions of the HSF1 heat shock factor and the Hsp90 chaperone. Our results describe an unexpected role of early aging and protein quality control mechanisms in suppressing ciliary phenotypes of IFT mutants, and suggest possible strategies for targeting subsets of ciliopathies.

This Australian national study was undertaken to profile the unsuitable counselling student, and to achieve greater operational specificity to guide counselling educators who must make critical decisions that impact admittance to the counselling profession. Findings suggest that in every 25 students as many as three will have questionable suitability for counselling, evidenced primarily by problems associated with self awareness and interpersonal issues, areas of functioning that are rarely systematically or objectively assessed. Such students are likely to be identified via skills-based classes and, of concern, at least half of these students "slip through the gate" and go on to graduate. Discussion addresses implications for educators.

The future role of natural gas systems in a deeply decarbonised world is very uncertain. This work seeks to characterise the changes that the clean energy transition is likely to induce in the natural gas chain, across extraction and transmission, distribution networks and gas consumption/use trends, for various scenarios with different demand and supply drivers. First, the results of a least-cost macro-scale energy system planning optimisation are explored to identify future natural gas demand and supply requirements. Second, those findings are used as inputs to a detailed analysis of the full gas supply chain, from extraction to final use, to examine the evolution of i) stored resource levels; ii) transmission and distribution networks operation and financing; and iii) required capacity and siting of gas generation; all, with a realistic account of the related infrastructure. Australia is investigated as a case study that relies on natural gas for both domestic and export purposes. Results project a shift towards a more localised gas consumption to be largely supplied by fewer basins, with associated potential transmission and extraction bottlenecks. They anticipate an overall less utilised, ageing distribution network with potential challenges to asset reliability and financing. Finally, they demonstrate both the scheduled and early retirement of fossil generation assets can allow the siting of considerable amounts of new gas power firming capacity on brownfield sites, thus offering an opportunity to reduce total system costs. [Display omitted] • Integrated macro-scale and geospatial analysis of future natural gas supply chain. • Natural gas user and exporter Australia selected as case study up to 2060. • 50–90% lower and more localised domestic natural gas energy demand. • Up to 3-fold usage downturn calls for novel financing of gas distribution networks. • Brownfields to host 26–60% of new firming gas power for 0.1–0.5% lower system costs. [ABSTRACT FROM AUTHOR]

Legumes, which develop a symbiosis with nitrogen fixing bacteria, have an increased demand for iron. Iron is required for the synthesis of iron-containing proteins in the host, including the highly abundant leghemoglobin, and in bacteroids for nitrogenase and cytochromes of the electron transport chain. Deficiencies in iron can affect initiation and development of the nodule. Within root cells, iron is chelated with organic acids such as citrate and nicotianamine and distributed to other parts of the plant. Transport to the nitrogen-fixing bacteroids in infected cells of nodules is more complicated.Formation of the symbiosis results in bacteroids internalized within root cortical cells of the legume where they are surrounded by a plant derived membrane termed the symbiosome membrane (SM). This membrane forms an interface that regulates nutrient supply to the bacteroid. Consequently, iron must cross this membrane before being supplied to the bacteroid. Iron is transported across the symbiosome membrane as both ferric and ferrous iron. However uptake of Fe(II) by both the symbiosome and bacteroid is faster than Fe(III) uptake. Members of more than one protein family may be responsible for Fe(II) transport across the SM. The only Fe(II) transporter in nodules characterized to date is GmDMT1, which is located on the symbiosome membrane in soybean. Like the root plasma membrane, the symbiosome membrane has ferric iron reductase activity. The protein responsible has not been identified but is predicted to reduce ferric iron accumulated in the symbiosome space prior to uptake by the bacteroid. With the recent publication of a number of legume genomes including Medicago truncatula and Glycine max, a large number of additional candidate transport proteins have been identified. Members of the NRAMP, YSL, VIT and ZIP transport families show enhanced expression in nodules and are expected to play a role in the transport of iron and other metals across symbiotic membranes.

Sound generation by planar flame annihilation for methane/hydrogen/air premixed flames is investigated using one-dimensional (1D) fully-resolved simulations. The Foundational Fuel Chemistry Model (FFCM) is used to undertake the simulations for different initial pressures and temperatures, for volumetric mixtures of 0 to 100% hydrogen in the fuel mixture. For cases with 25% to 80% of hydrogen in the fuel mixture three stages of annihilation are observed. The first stage exhibits a gradual flame extinction coupled with the generation of a pressure wave with a long wavelength. The second stage features a more rapid extinction as the flame accelerates towards the symmetry axis, producing a sharp pressure drop. The final stage exhibits a gradual decrease in pressure due to slow reactions such as CO oxidation. The contribution of the first stage increases as more hydrogen is added to the fuel. These stages are not distinctive when the fuel is pure hydrogen. The time derivative of the heat release rate is verified to be the dominant source of sound for annihilation events. A correlation linking the sound amplitude from planar annihilation events to key flame parameters is demonstrated to work for the studied fuel blends. The FFCM is then reduced using a modified Directed Relation Graph with Error Propagation and Sensitivity Analysis (DRGEPSA) method with error bounds based on the laminar flame speed, s L. A good agreement between the s L predictions for the reduced and the detailed mechanisms are found. Furthermore, the developed reduced mechanisms in this work are shown to predict the generated sound by flame annihilation accurately. [ABSTRACT FROM AUTHOR]

This work investigates the oxidation of hydrogen near its second explosion limit in a turbulent flow reactor at pressures of 1 to 8 bar, temperatures of 950 K and an equivalence ratio of 0.035. The concentrations of H 2 , O 2 and H 2 O are measured along the reactor and simulated using several kinetic models from the literature. These experiments demonstrate evident negative pressure dependence from roughly 1 to 4 bar, with further increases in pressure resuming its positive impact on reaction rates. The simulated and measured species concentrations along the reactor generally agree within a factor of 2. Further investigation is then conducted to measure the rate coefficient of reaction H + O 2 (+ M) = HO 2 (+M) (R2), which is one of the most sensitive reactions in hydrogen's oxidation chemistry at these conditions. This investigation is conducted by using nitric oxide (NO) as a dopant and measuring the resulting, quasi-steady-state concentrations of NO 2. The rate coefficients are obtained at 950 – 1010 K. Combined with literature results, an Arrhenius expression is proposed, k 2 , 0 N 2 = 4.50 × 1020 (T/K)−1.73 [cm6 mole−2 s−1], for the reaction rate at the low-pressure limit over 500 K – 2000 K with N 2 as the bath gas. Simulations using the models from the literature with the proposed Arrhenius expression for this reaction then demonstrate improved agreement with the experiments. [ABSTRACT FROM AUTHOR]

Abstract This paper studies the oxidation of n-heptane, iso-octane, ethanol and their mixtures in a pressurized flow reactor, with a focus on the potential relation between the fuels oxidation reactivity and their octane ratings. The flow reactor experiments are conducted at 550–900 K, 10 bar and an equivalence ratio of 0.058. Carbon monoxide is measured as an indicator of the global reactivity. Evident low temperature oxidation and negative temperature coefficient (NTC) behaviors are observed for n-heptane and iso-octane over a similar temperature window (600–800 K). Ethanol, on the other hand, shows negligible reactivity up to 800 K but produces a substantial amount of CO above 850 K indicating significantly higher reactivity than iso-octane. Oxidation of these fuels is then classified into low temperature oxidation (LTO), NTC, intermediate temperature oxidation (ITO), and high temperature oxidation (HTO) regimes. A systematic study is then conducted on primary reference fuels (PRFs) and ethanol/iso-octane mixtures. PRFs show approximately linear blending in terms of CO formation in the LTO, NTC, and ITO regimes, which is consistent with the definition of the octane number scale. In contrast, adding ethanol into iso-octane disproportionally inhibits the CO formation over the same temperature range, with 20 vol% of ethanol completely suppressing the reactivity of iso-octane. Such behavior is also consistent with the synergistic octane blending of the two compounds recently reported [Foong et al. Fuel 115 (2014) 727–739]. These results suggest a potential connection between the oxidation reactivity of these fuels and their octane blending behaviors. Kinetic modeling is conducted using the latest combustion mechanisms for neat compounds and gasoline surrogate. Good agreement in CO formation is observed between the model and experiment for both neat fuels and their mixtures. [ABSTRACT FROM AUTHOR]

This study explores the autoignition characteristics of three C5 isomers, namely n -pentane, 2-methylbutane ( iso -pentane) and 2,2-dimethylpropane ( neo -pentane). These measurements are intended to enhance understanding of C5 autoignition chemistry, and provide experimental data to guide improvements to a general hydrocarbon oxidation mechanism. To that end, the autoignition behavior of these three C5 isomers was investigated in a modified CFR engine at an intake temperature of 120 °C and a fixed engine speed of 600 rpm to determine the critical compression ratio (CCR) at which hot ignition occurs. To find the critical compression ratio, the engine compression ratio (CR) was gradually increased to the point where CO in the engine exhaust rapidly decreased and significant high temperature heat release was observed, while holding equivalence ratio constant. Fundamental ignition behaviors such as the CCR and the calculated percentage of low temperature heat release (%LTHR) demonstrate the impact of chain length and methyl substitutions on ignition reactivity. The %LTHR shows a stronger two stage heat release for n- pentane than for neo- pentane observed at critical ignition conditions. In contrast, single stage heat release is observed for iso- pentane, leading to the weakest overall oxidation reactivity of the three isomers. Key reaction paths forming conjugate alkenes and C 5 oxygenated species control the autoignition reactivity of n- pentane and iso- pentane within the low temperature and NTC regimes. However, neo- pentane forms no conjugate alkene due to its unique molecular structure, and instead produces iso -butene to retard its oxidation. [ABSTRACT FROM AUTHOR]

This paper describes a study on the autoignition of three pentane isomers ( n-, neo- and iso- pentane) in a Cooperative Fuel Research (CFR) engine operating at standard, ASTM knocking conditions. The Research Octane Numbers (RONs) of these three fuels are first measured and compared to historical data. Autoignition of pentane/air mixtures in the CFR engine are then simulated using a two-zone model with detailed chemical kinetics. Initial and boundary conditions for these kinetic simulations are systematically calibrated using engine simulation software. Two published, detailed kinetic mechanisms for these fuels are tested with a published NO sub-mechanism incorporated into them. Simulations using both of these mechanisms demonstrate autoignition in the engine for all three pentanes, and that residual NO promotes autoignition, as found in previous studies. Differences between these two mechanisms and the engine experiments are nonetheless observed, and these differences are consistent with those observed in simulations of published rapid compression machine (RCM) data. Comparison of the RCM and the CFR engine modelling also suggests the need for high accuracy experiments and high-fidelity models due to the significant impact that small differences in autoignition timing can potentially produce in real engines. [ABSTRACT FROM AUTHOR]

This paper investigates the autoignition of C 3 /C 4 hydrocarbon mixtures in a CFR octane rating engine. The four species examined – propane, propylene (propene), n -butane and iso -butane – are the primary constituents of Liquefied Petroleum Gas (LPG), and are also important intermediates in the oxidation of larger hydrocarbons. In-cylinder pressure data was acquired for both autoigniting and non-autoigniting engine operation at the same test conditions. The latter was used to calibrate a two-zone model of the CFR engine in a prior work, thus enabling the inclusion of the unburned charge chemical kinetics for further examination in this paper. The in-cylinder heat transfer and residual gas composition are both shown to affect autoignition significantly. In particular, physically reasonable concentrations of nitric oxide (NO) are found to be a strong promoter of autoignition in almost all cases, in keeping with several, more fundamental studies. The inclusion of NO in the residual gas is also required to obtain good agreement between the measured and modelled autoignition timing. This in turn suggests that kinetic interaction between hydrocarbon fuels and NO plays a vital role in octane rating, and its inclusion is important when modelling the autoignition of hydrocarbons in spark-ignition engines more generally. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a numerical investigation of sound generation by two-dimensional laminar premixed flames. Direct numerical simulation (DNS) is used to study low Mach number flames with different Lewis numbers, namely Le =0.5, 1 and 2, excited by velocity perturbations at the inflow boundary for a range of frequencies. At intermediate forcing frequencies, ‘flame pinch-off’ and ‘flame island burn-out’ are observed as strong, monopolar sound sources for Le =1 and 2. However, these events produce almost no sound for Le =0.5. Dowling’s reformulation of Lighthill’s acoustic analogy is used to investigate the contribution of heat release rate fluctuations to the radiated sound. A comparison of direct calculation of heat release rate fluctuations and estimated values using a flamelet theory suggested by Clavin and Siggia [7], which assumes that heat release fluctuations are due to flame surface area fluctuations, shows good agreement for unity Lewis number when the forcing period is larger than the flame time. For forcing periods smaller than the flame time, flamelet theory does not succeed in describing the effects of heat release fluctuations, as expected. However, even for forcing periods greater than the flame time, the flamelet theory does not capture the observed trend with Lewis number. The pressure fluctuations due to heat release are always over-predicted by flamelet theory for Le =0.5 and under-predicted for Le =2. The flamelet model, intended for application to turbulent flames, assumes a constant consumption speed along the flame surface. The failure of this model in the case of non-unity Lewis number in the present unsteady laminar flames can be therefore due to the large modification of the consumption speed where large surface area fluctuation is present. [Copyright &y& Elsevier]

An experimental and numerical study of the spray from an air-assisted fuel injector in a direct-injection spark ignition (DISI) engine is presented. The experiments are performed using ultraviolet laser diagnostics in a motoring optical engine that is a DISI variant of a production port-fuel-injected engine. Non-optical single-cylinder firing engine results of experiments and simulations are also presented. Recent related work by the present authors has shown that, under design conditions, the air-assisted injector exhibits strong coupling between the liquid and gas phases. It results in a filled-in conical spray of relatively fine atomization and low penetration, with liquid and vapour fuel concentrations close to the centrally located injector and spark plug, as required for lean stratified operation. This paper shows the strong effect of increasing the chamber temperature on spray evaporation and penetration. This observed temperature effect shows that spray evaporation should vary significantly during cold start. Exhaust gas recirculation (EGR) may also have a beneficial effect on DISI engine performance through enhanced spray evaporation, although this is difficult to verify experimentally. If true, this effect of EGR is a separate mechanism to the known beneficial effects of EGR in air-assisted DISI engines. [ABSTRACT FROM AUTHOR]

The present paper addresses the effects of creep cavitation damage on other mechanical properties – chiefly those that affect behaviour outside the creep range. Such effects seem not to have been systematically studied, yet they are significant for the understanding and prediction of component integrity and life. The paper presents results obtained mainly as byproducts of research programmes on low alloy steels for both fossil and nuclear power plant and seeks to rationalise the findings to generate an overall picture of the effect. It is seen that a simple loss of effective section model is adequate to describe many of the phenomena observed, but that other factors may also need consideration. [ABSTRACT FROM AUTHOR]

This paper discusses the requirements for the propulsion system of supersonic cruise aircraft that are quiet enough to fly over land and operate from civil airports, have trans-pacific range in the order of 11,112 km (6000 nmi), and payload in the order of 4545 kg (10,000 lb.). It is concluded that the resulting requirements for both the fuel consumption and engine thrust/weight ratio for such aircraft will require high compressor exit and turbine inlet temperatures, together with bypass ratios that are significantly higher than typical supersonic-capable engines. Several technologies for improving both the fuel consumption and weight of the propulsion system are suggested. Some of these directly reduce engine weight while others, by improving individual component performance, will enable higher bypass ratios. The latter should therefore also indirectly reduce the bare engine weight. It is emphasized, however, that these specific technologies require considerable further development. While the use of higher bypass ratio is a significant departure from more usual engines designed for supersonic cruise, it is nonetheless considered to be a practical option for an aircraft of this kind. [ABSTRACT FROM AUTHOR]

This paper discusses the structure of the flow within the engine inlet of an uninhabited combat air vehicle (UCAV). The UCAV features a top-mounted, serpentine inlet leading to an engine buried within the fuselage. The performance of the inlet is found to depend strongly on a flow separation that occurs within the inlet. Both the time-averaged and the unsteady structure of this separation is studied, and an argument relating the inlet performance to the behavior of this separation is suggested. The results presented in this paper also suggest that there are considerable aerodynamic limitations to further shortening or narrowing of the inlet. Since there are substantial, system level benefits from using a smaller inlet, the case for separated flow control therefore appears clear. [ABSTRACT FROM AUTHOR]

This paper describes an investigation into the effect that passing wakes have on a separation bubble that exists on the pressure surface and near the leading edge of a low-pressure turbine blade. Previous experimental studies have shown that the behavior of this separation is strongly incidence dependent and that it responds to its disturbance environment. The results presented in this paper examine the effect of wake passing in greater detail. Two-dimensional, Reynolds averaged, numerical predictions are first used to examine qualitatively the unsteady interaction between the wakes and the separation bubble. The separation is predicted to consist of spanwise vortices whose development is in phase with the wake passing. However, comparison with experiments shows that the numerical predictions exaggerate the coherence of these vortices and also overpredict the time-averaged length of the separation. Nonetheless, experiments strongly suggest that the predicted phase locking of the vortices in the separation onto the wake passing is physical. [ABSTRACT FROM AUTHOR]