Investigation of rim seal exchange and coolant re-ingestion in rotor stator cavities using gas concentration techniques

Gas turbine engine performance requires effective and reliable internal cooling over the duty cycle of the engine. Understanding the effectiveness of cooling flows when making life predictions for rotating components subject to the main gas path temperatures is crucial. A test facility has been developed at the University of Sussex incorporating a two stage turbine designed to support a European funded research project with the objective of enhancing the understanding of interactions between main annulus gas paths and secondary air systems. This thesis describes the specific contribution of the author to the research conducted at the test facility. Non-invasive gas seeding and concentration measurement techniques together with hot geometry displacement measurements have been developed to meet three distinct objectives: to determine inter-stage seal flows between rotor disc cavities; to provide data to quantify rim seal exchange flows between rotor stator cavities and the main annulus gas path for both bulk ingestion and egress conditions; and, to provide data to quantify the re-ingestion of cooling air egressed into the main annulus gas path. Detailed knowledge of these flows is vital to understanding the flow structures within rotor stator cavities and to optimise coolant delivery methods. Experimental results are presented for a number of cooling flow supply geometries and flow rates. The gas concentration measurement techniques developed and the results obtained are compared to traditional measurements as well as numerical simulations carried out by research project partners. This work develops the measurement techniques of rotor stator cavity flows and provides data suitable for the validation of improved thermo-mechanical and CFD codes, beneficial to the engine design process

Recovering low molecular weight extractives from degraded straw by oyster mushroom at the farm scale for high value use

The cultivation of mushrooms on wheat straw can be considered a solid state fermentation, yet following harvest the residual, partially degraded straw is discarded. During cultivation, the degradation of lignocellulose in the straw takes place by the fungus under the action of enzymes releasing degradation products with small molecular weight, some of which are potentially valuable. These compounds may be extracted from straw after mushroom cultivation in two stages: an aqueous extraction followed by a solvent extraction. The present work is focused on the first stage of the process. The aqueous extraction releases water soluble compounds, such as sugars and phenolics with lower molecular weight, which are easily obtained. The partially degraded straw may then be treated with organic solvents to release water insoluble lignin breakdown products, such as fatty acids, phenolics and other aromatics. It is important to conduct scale-up experiments at a scale that would reflect the amount of waste straw generated by a mushroom farm. A study was performed using a vessel of 300 L capacity with mixing impeller, by observing the influence of the temperature (20oC, 25oC, 40oC, 60oC and 80oC) and water-to-dry straw ratio (from 40:1 to 90:1) on the total extracted matter and especially on sugar and phenolic compounds yields. A microbial study of the aqueous extract was also performed at 20oC and 25oC to explain the high concentration of organic carbon in the extract under certain circumstances. The optimum extraction conditions were determined by taking into account the yield and the energy consumption of the process. The conclusion was that the extraction temperature can be conducted between 20oC and 25oC with good results for obtaining liquor which can be used in a biogas installation. The extraction should be conducted at 80oC to obtain greater yields of sugars and phenolics

Statistical modelling of transcript profiles of differentially regulated genes

Background: The vast quantities of gene expression profiling data produced in microarray studies, and the more precise quantitative PCR, are often not statistically analysed to their full potential. Previous studies have summarised gene expression profiles using simple descriptive statistics, basic analysis of variance (ANOVA) and the clustering of genes based on simple models fitted to their expression profiles over time. We report the novel application of statistical non-linear regression modelling techniques to describe the shapes of expression profiles for the fungus Agaricus bisporus, quantified by PCR, and for E. coli and Rattus norvegicus, using microarray technology. The use of parametric non-linear regression models provides a more precise description of expression profiles, reducing the "noise" of the raw data to produce a clear "signal" given by the fitted curve, and describing each profile with a small number of biologically interpretable parameters. This approach then allows the direct comparison and clustering of the shapes of response patterns between genes and potentially enables a greater exploration and interpretation of the biological processes driving gene expression. Results: Quantitative reverse transcriptase PCR-derived time-course data of genes were modelled. "Splitline" or "broken-stick" regression identified the initial time of gene up-regulation, enabling the classification of genes into those with primary and secondary responses. Five-day profiles were modelled using the biologically-oriented, critical exponential curve, y(t) = A + (B + Ct)Rt + ε. This non-linear regression approach allowed the expression patterns for different genes to be compared in terms of curve shape, time of maximal transcript level and the decline and asymptotic response levels. Three distinct regulatory patterns were identified for the five genes studied. Applying the regression modelling approach to microarray-derived time course data allowed 11% of the Escherichia coli features to be fitted by an exponential function, and 25% of the Rattus norvegicus features could be described by the critical exponential model, all with statistical significance of p < 0.05. Conclusion: The statistical non-linear regression approaches presented in this study provide detailed biologically oriented descriptions of individual gene expression profiles, using biologically variable data to generate a set of defining parameters. These approaches have application to the modelling and greater interpretation of profiles obtained across a wide range of platforms, such as microarrays. Through careful choice of appropriate model forms, such statistical regression approaches allow an improved comparison of gene expression profiles, and may provide an approach for the greater understanding of common regulatory mechanisms between genes

Growth of massive seed black holes and their impact on their host galaxies

The recent discovery of an 800 million solar mass black hole powering a quasar at a redshift corresponding to 690 million years after the Big Bang is the latest in a growing list of observations of super-massive black holes (SMBHs) that were most likely seeded with masses larger than those expected from the remnants of the first generation of stars. This thesis investigates the consequences of the seeding of SMBHs by massive black holes on galaxy evolution through a combination of analytic modelling techniques. Firstly, I analytically model the growth of gravitational instabilities in an isolated proto-galaxy disc as it progresses into a fully-formed galaxy in the presence of a massive seed black hole formed directly through isothermal collapse. The model shows for the first time how the gravitational effects of a seed black hole lead to an increase in the stability of the disc and an increase in the star formation timescale in the region of the disc close to the black hole. This gravitational imprint of the black hole on the galactic disc has the effect of suppressing star formation. To investigate if this has a lasting effect on the properties of seed hosting galaxies, I evolve the disc galaxy model from the epoch of seed formation down to z ~ 6. I show how star formation in seed hosting galaxies is further regulated by a combination of gravitational stability and the accretion of gas onto the black hole, leading to a scenario where the resulting ratio of black hole to stellar mass at z = 6 is significantly higher than observed in the local universe. I also investigate how the growth of massive seed black holes is regulated by the mass and momentum transport in the disc. The inward accretion of gas towards the central massive black hole and therefore the accretion of gas onto the black hole itself is a function of the stability of the disc. The stabilising effect of the black hole therefore has the potential to regulate the inflow of gas, depending on the relative masses of the galaxy disc and black hole. I find that even in the regime where the inflow rate is not affected by the presence of the black hole, viscosity driven accretion is too inefficient for even massive seeds to grow into a SMBHs by z ~ 6. This indicates the isolated growth of SMBHs is not possible. Indeed, merger events or other processes which are efficient at dissipating angular momentum are required to provide the necessary rapid accretion of gas for SMBHs to form. Finally, I study the dynamical heating of a dark matter halo through the accretion of massive black hole systems. Modelled as both a black hole embedded in its own subhalo and as a naked black hole, the infall of the black hole system acts as a perturber to the density of the central halo, converting potential energy to heat the gas of the central halo through dynamical friction. The timescale over which this infall occurs decreases with a larger perturber mass relative to the central halo mass. The total energy released through black hole accretion during the period of infall is strongly dependent on the black hole growth model. Generally, the total energy from black hole growth exceeds the total energy from dynamical friction. However, the energy released through dynamical friction reaches a maximum when the perturber's proximity to the centre of the central halo is minimised, generally after black hole accretion has ceased. There is therefore a period of time where dynamical friction is the primary source of heating within a halo, potentially contributing to the luminosities of some distant quasars and leading to over-estimates in inferred black hole masses

New approaches to investigating the function of mycelial networks

Fungi play a key role in ecosystem nutrient cycles by scavenging, concentrating, translocating and redistributing nitrogen. To quantify and predict fungal nitrogen redistribution, and assess the importance of the integrity of fungal networks in soil for ecosystem function, we need better understanding of the structures and processes involved. Until recently nitrogen translocation has been experimentally intractable owing to the lack of a suitable radioisotope tracer for nitrogen, and the impossibility of observing nitrogen translocation in real time under realistic conditions. We have developed an imaging method for recording the magnitude and direction of amino acid flow through the whole mycelial network as it captures, assimilates and channels its carbon and nitrogen resources, while growing in realistically heterogeneous soil microcosms. Computer analysis and modeling, based on these digitized video records, can reveal patterns in transport that suggest experimentally testable hypotheses. Experimental approaches that we are developing include genomics and stable isotope NMR to investigate where in the system nitrogen compounds are being acquired and stored, and where they are mobilized for transport or broken down. The results are elucidating the interplay between environment, metabolism, and the development and function of transport networks as mycelium forages in soil. The highly adapted and selected foraging networks of fungi may illuminate fundamental principles applicable to other supply networks

Mortality Rate of Bullous Pemphigoid in a US Medical Center

All patients at the Medical College of Wisconsin Affiliated Hospitals with a new diagnosis of bullous pemphigoid (BP) between May 1, 1997 and September 1, 2002 were included in this study. The age at onset, date of death or date of last follow-up visit, mode of treatment, co-morbidities, and initial and follow-up hospitalizations were noted. Thirty-eight new patients were identified and complete follow-up data were obtained on 37 of the patients. Patients were followed a minimum of 1 y or until the time of death. The mean duration of follow-up was 20 mo. Kaplan–Meier analysis of our population indicated a 1-y survival probability of 88.96% (standard error 5.21%), with a 95% confidence interval (75.6%, 94.2%). This survival rate was considerably higher than that recently reported in several studies from Europe (29%–41% first year mortality). Although the age at onset and co-morbidities of our patients were similar to those in the European studies, the rate of hospitalization of our patients was much lower than that of patients from Europe (1.5 d per patient vs 11–25 d per patient). This study suggests that differences in practice patterns may be an important factor in the reduced mortality rate in US BP patients compared with Europe

How black holes stop their host galaxy from growing without AGN feedback

Super-massive black holes (SMBHs) with $M_{\bullet} \sim 10^9$ M$_{\odot}$ at $z>6$ likely originate from massive seed black holes (BHs). We investigate the consequences of seeding SMBHs with direct collapse BHs (DCBHs) ($M_{\bullet}=10^{4-6}\, \mathrm{M}_\odot$) on proto-galactic disc growth. We show that even in the absence of direct feedback effects, the growth of seed BHs reduces the development of gravitational instabilities in host galaxy discs, suppressing star formation and confining stars to a narrow ring in the disc and leading to galaxies at $z \sim 6$ which lie above the local BH-stellar mass relation. The relative magnitude of cosmic and BH accretion rates governs the evolution of the BH-stellar mass relation. For typical DCBH formation epochs, $z_{\rm{i}} \sim 10$, we find star formation is inhibited in haloes growing at the average rate predicted by $\Lambda$CDM which host BHs capable of reaching $M_{\bullet}\sim 10^9 \, \mathrm{M}_{\odot}$ by $z\gtrsim6$. Slower growing BHs cause a delay in the onset of star formation; a $M_{\bullet} \sim 10^6$ M$_{\odot}$ seed growing at $0.25$ times the Eddington limit will delay star formation by $\sim100$ Myr. This delay is reduced by a factor of $\sim10$ if the halo growth rate is increased by $\sim 0.6\, \sigma$. Our results suggest that SMBHs seeded by DCBHs and their host galaxies form in separate progenitor haloes. In the absence of subsequent mergers, higher than average cosmic accretion or earlier seed formation ($z_{\rm i} \sim 20$) are required to place the evolving BH on the local BH-stellar mass relation by $z=6$.Comment: 18 pages, 14 figures, 3 tables, published in mnra

Incorporating alternative interaction modes, forbidden links and trait‐based mechanisms increases the minimum trait dimensionality of ecological networks

1. Individual-level traits mediate interaction outcomes and community structure. It is important, therefore, to identify the minimum number of traits that characterise ecological networks, that is, their ‘minimum dimensionality’. Existing methods for estimating minimum dimensionality often lack three features associated with in- creased trait numbers: alternative interaction modes (e.g. feeding strategies such as active vs. sit-and-wait feeding), trait-mediated ‘forbidden links’ and a mechanistic description of interactions. Omitting these features can underestimate the trait numbers involved, and therefore, minimum dimensionality. We develop a ‘mini- mum mechanistic dimensionality’ measure, accounting for these three features.2. The only input our method requires is the network of interaction outcomes. We assume how traits are mechanistically involved in alternative interaction modes. These unidentified traits are contrasted using pairwise performance inequalities between interacting species. For example, if a predator feeds upon a prey spe- cies via a typical predation mode, in each step of the predation sequence, the predator's performance must be greater than the prey's. We construct a system of inequalities from all observed outcomes, which we attempt to solve with mixed integer linear programming. The number of traits required for a feasible system of inequalities provides our minimum dimensionality estimate.3. We applied our method to 658 published empirical ecological networks includ- ing primary consumption, predator–prey, parasitism, pollination, seed dispersal and animal dominance networks, to compare with minimum dimensionality estimates when the three focal features are missing. Minimum dimensionality was typically higher when including alternative interaction modes (54% of empirical networks), ‘forbidden interactions’ as trait-mediated interaction outcomes (92%) or a mechanistic perspective (81%), compared to estimates missing these features. Additionally, we tested minimum dimensionality estimates on simulated networks with known dimensionality. Our method typically estimated a higher minimum dimensionality, closer to the actual dimensionality, while avoiding the overestimation associated with a previous method.4. Our method can reduce the risk of omitting traits involved in different interaction modes, in failure outcomes or mechanistically. More accurate estimates will allow us to parameterise models of theoretical networks with more realistic structure at the interaction outcome level. Thus, we hope our method can improve predictions of community structure and structure-dependent dynamics

Brown dwarf disks with Herschel: linking far-infrared and (sub)-mm fluxes

AN would like to acknowledge funding from Science Foundation Ireland (Grant 13/ERC/I2907). AS acknowledges support from STFC grant ST/M001296/1. This work was partly supported by the Italian Ministero dell’Istruzione, Università e Ricerca through the grant Progetti Premiali 2012 – iALMA (CUP C52I13000140001). Our research was also supported by NSERC grants to RJ.Brown dwarf disks are excellent laboratories to test our understanding of disk physics in an extreme parameter regime. In this paper we investigate a sample of 29 well-characterized brown dwarfs and very low-mass stars, for which Herschel far-infrared fluxes and (sub)-mm fluxes are available. We measured new Herschel/PACS fluxes for 11 objects and complement these with (sub)-mm data and Herschel fluxes from the literature. We analyze their spectral energy distributions in comparison with results from radiative transfer modeling. Fluxes in the far-infrared are strongly affected by the shape and temperature of the disk (and hence stellar luminosity), whereas the (sub)-mm fluxes mostly depend on disk mass. Nevertheless, there is a clear correlation between far-infrared and (sub)-mm fluxes. We argue that the link results from the combination of the stellar mass-luminosity relation and a scaling between disk mass and stellar mass. We find strong evidence of dust settling to the disk midplane. The spectral slopes between near- and far-infrared are mostly between −0.5 and −1.2 in our sample, which is comparable to more massive T Tauri stars; this may imply that the disk shapes are similar as well, although highly flared disks are rare among brown dwarfs. We find that dust temperatures in the range of 7−15 K, calculated with T ≈ 25 (L/L⊙)0.25 K, are appropriate for deriving disk masses from (sub)-mm fluxes for these low luminosity objects. About half of our sample hosts disks with at least one Jupiter mass, confirming that many brown dwarfs harbor sufficient material for the formation of Earth-mass planets in their midst.Publisher PDFPeer reviewe