3,889 research outputs found

    Investigation of micro gas turbine system configurations for compact lightweight applications based on reversible bladeless Tesla machinery

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    Globally, the demand for low-emission, cost-effective, low-noise, lightweight and compact devices is rapidly increasing. In order to meet such market demands on a small scale, microgas turbines (MGTs) could play a crucial role. However, there are many challenges with MGT compatibility with internal combustion engines (e.g., low efficiency, fuel flexibility, light weight-compactness). As part of this study, the focus is on the component basis, where the study examines the Tesla or bladeless turbomachinery in both a compressor and expander configuration. Since little data is available on Tesla compressors/pumps, this study focuses primarily on the bladeless compressor, which is also analyzed as an expander due to its reversibility. The activity started from a 3-kW air Tesla expander prototype available at the University of Genoa. It is examined in compressor mode using a 3D CFD approach and its results are compared to experimental results. The CFD and experiments show good agreement for the pressure, with an error of less than 3% at zero flow condition. Despite the CFD analysis predicting a static efficiency of around 42% (without losses), the experiment did not meet that prediction due to significant leakage flows and other losses. Moreover, using LMS Test Lab software, the acoustic behavior of the Tesla compressor has been analyzed at different speeds and distances, and several aspects are compared with conventional or bladed technologies (same tip speed, same mass flow rate, and same pressure). It has been demonstrated that Tesla technologies are substantially quieter than bladed technologies. To improve Tesla compressor performance, a 3D numerical analysis has been carried out for the rotor only and coupled rotor-stator and volute configurations. The disk gap is optimized by relying on Ekman and Reynolds numbers. Based on the numerical analysis, the disk gap should be 3 times the thickness of the boundary layer with the best Reynolds number 9-11 and Ekman number 1.5-1.65. Moreover, numerical analysis has been performed for 2, 2.5, 3 and 4 diameter ratios in order to optimize the rotor diameter ratio. Higher diameter ratios indicate better performance than lower diameter ratios. Based on a CFD analysis, it has been predicted that at low mass flow rates, greater than 95 % efficiency can be achieved with the optimal disk gap and diameter ratio. In this case, the outlet flow angle would be around 89.9 degree, however, in practice, maintaining almost a tangential flow angle is difficult. In order to improve the performance of Tesla compressors, several stators have been studied. The stator outlet and inlet ratio between 2 and 4 is optimal for stator/diffuser performance. With an optimal rotor and eight stators, CFD analysis predicts a total stator efficiency of >53%; however, with a low number of stators, this efficiency will be somewhat improved. As part of an effort to enhance the performance of the Tesla compressor, a (stator-less) volute design has also been numerically analyzed, which shows better performance in terms of pressure ratio and efficiency than the stator configuration. Compared to a stator configuration, the total to static efficiency is estimated to increase by 3 to 5%. A new reversible Tesla prototype model has been developed using an optimized rotor (optimal disk gap and diameter ratio) and volute configuration for 22 krpm. CFD predicted total to static efficiency of 58% in compressor mode and 66% in expander mode without consideration of system losses. For this new reversible machine, leakage and end wall losses are also analyzed under a variety of conditions, including different end wall gaps and different exit radial clearances (with and without sealing systems). The implementation of the sealing system has resulted in a reduction in leakage, but the amount varies in accordance with the clearance of the radial exit. The end wall power loss varies with end wall gap, but usually ranges between 50 W-60 W for 22 krpm design speed, while power is around 600 W. During this dissertation writing, experimental work on a reversible bladeless machine is in progress. Preliminary results show the pressure ratio is 1.24 and the isentropic efficiency is 31%. Comparing these results with CFD simulations at closed valve conditions shows good agreement in terms of pressure ratio with < 3% error. It is observed that leakage occurs during the first test which passes through the narrow radial clearance of 0.3 mm. As a result of this preliminary investigation, some modifications have been made to the test-rig in order to ensure that good results are achieved with the least amount of leakage. An in-depth study of the reversible Tesla machine (compressor and expander) has shown that such technologies possess several attractive features (reversibility, low noise level, cost effective and operate with any kind of fluid), but are difficult to implement as Tesla envisioned (higher efficiency). Under ideal design conditions, however, such technologies could potentially achieve > 50% efficiency. The use of such technologies can be beneficial in areas where conventional technologies are not practical or less efficient

    Anti-Pseudomonas aeruginosa activity of natural antimicrobial peptides when used alone or in combination with antibiotics

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    The World Health Organization has recently published a list of 12 drug-resistant bacteria that posed a significant threat to human health, and Pseudomonas aeruginosa (P. aeruginosa) was among them. In China, P. aeruginosa is a common pathogen in hospital acquired pneumonia, accounting for 16.9–22.0%. It is a ubiquitous opportunistic pathogen that can infect individuals with weakened immune systems, leading to hospital-acquired acute and systemic infections. The excessive use of antibiotics has led to the development of various mechanisms in P. aeruginosa to resist conventional drugs. Thus, there is an emergence of multidrug-resistant strains, posing a major challenge to conventional antibiotics and therapeutic approaches. Antimicrobial peptides are an integral component of host defense and have been found in many living organisms. Most antimicrobial peptides are characterized by negligible host toxicity and low resistance rates, making them become promising for use as antimicrobial products. This review particularly focuses on summarizing the inhibitory activity of natural antimicrobial peptides against P. aeruginosa planktonic cells and biofilms, as well as the drug interactions when these peptides used in combination with conventional antibiotics. Moreover, the underlying mechanism of these antimicrobial peptides against P. aeruginosa strains was mainly related to destroy the membrane structure through interacting with LPS or increasing ROS levels, or targeting cellular components, leaded to cell lysis. Hopefully, this analysis will provide valuable experimental data on developing novel compounds to combat P. aeruginosa

    A numerical study of the hadronic gamma ray emission from cosmic ray protons in radio jets

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    This thesis is a numerical study of the gamma ray emission from clusters and it is aimed at constraining the cosmic ray content of jets from radio galaxies. It involves the simulation and numerical analysis of Lagrangian tracers injected by the jets from radio galaxies into the Intracluster Medium evolving in a cosmological simulation. I have analyzed different sets of radio jet simulations, in which the cosmic rays are transported into the ICM. The jet simulations encompasses a single radio galaxy (Vazza et al (2021) A&A), a single radio galaxy with varying powers (Vazza et al (2023) A&A) and multiple radio galaxies (Vazza et al (2023) Galaxies). I have utilized Lagrangian tracers within the simulations to monitor the transport of cosmic rays originating from the radio jets into the ICM. I have calculated the gamma-ray flux under various radio jet conditions and compared it with the observational data from FERMI LAT. This comparative analysis has enabled me to establish constraints on the allowed cosmic ray energy content in the radio jets. I concluded that if radio galaxies have multiple bursts, then they violate the FERMI limit. In my simulations, for N_burst = 4, the gamma-ray flux surpasses the FERMI limit. Therefore, this can be used to limit the cosmic ray energy budget to be ≀ 25% of magnetic field energy in radio jet. This is due to the fact that the initial conditions have an equality between cosmic ray energy and the magnetic field energy. In my thesis I also proved that such limits hold for even variations of the initial jet power. Since neutrino and gamma ray flux are linked by the same process, in my thesis as an additional task I also focus on the injection of neutrinos diffused into the clusters of galaxy by hadronic collision and comparing the neutrino flux with the observational results of IceCube. Overall my thesis has shown that gamma-ray and neutrino data can be used to refine existing physical models of radio jets in clusters of galaxies

    X-ray View of Hyper-Luminous Quasars at z = 2 ~ 4: the WISSH project

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    At the cosmic noon (z≈2-4), hyper-luminous quasars (HyLQSOs) shine at L_bol>10^47 erg/s and the most energetic multiphase winds are predicted to be ejected. These are the most efficient feedback governing AGN-galaxy co-evolution. The WISSH project aims at investigating the multi-wavelength properties of 85 WISE/SDSS selected type 1 (i.e. unobscured) HyLQSOs at the cosmic noon, to study their spectral and wind properties. We focuse on the X-ray emission of this sample, processing Chandra/XMM-Newton data. The slope of the primary power-law (Γ) and possible intrinsic column density (N_H ) are measured. Γ is broadly consistent with the expected range ~1.8-2. About 24% of the sources for which N_H can be estimated exhibits N_H≄10^22 cm^(-2). The observed quasars have an intrinsic 2-10 keV luminosity L_X≈10^(43-46) erg/s. Knowing the bolometric and monochromatic 2500 Å (L_2500 ) luminosities, we derive the bolometric correction (k_bol ) and X-ray - to - optical index (α_OX ). In the L_bol-k_bol and L_2500-α_OX, WISSH QSOs arrange anomalously with respect to literature relations, i.e. covering a wide range of k_bol and α_OX for a given bolometric or monochromatic luminosity. This evidence highlights a possible different coupling in the accretion disk - corona. The offset of the observed α_OX from the expected one (from literature relations) defines ∆(α_OX). Having ∆(α_OX )0.15)

    Prospects of Detecting Non-thermal Protons in Solar Flares via Lyman Line Spectroscopy: Revisiting the Orrall-Zirker Effect

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    Solar flares are efficient particle accelerators, with a substantial fraction of the energy released manifesting as non-thermal particles. While the role that non-thermal electrons play in transporting flare energy is well studied, the properties and importance of non-thermal protons is rather less well understood. This is in large part due to the paucity of diagnostics, particularly at the lower-energy (deka-keV) range of non-thermal proton distributions in flares. One means to identify the presence of deka-keV protons is by an effect originally described by \cite{1976ApJ...208..618O}. In the Orrall-Zirker effect, non-thermal protons interact with ambient neutral hydrogen, and via charge exchange produce a population of energetic neutral atoms (ENAs) in the chromosphere. These ENAs subsequently produce an extremely redshifted photon in the red wings of hydrogen spectral lines. We revisit predictions of the strength of this effect using modern interaction cross-sections, and numerical models capable of self-consistently simulating the flaring non-equilibrium ionization stratification, and the non-thermal proton distribution (and, crucially, their feedback on each other). We synthesize both the thermal and non-thermal emission from \lya\ and \lyb, the most promising lines that may exhibit a detectable signal. These new predictions are are weaker and more transient than prior estimates, but the effects should be detectable in fortuitous circumstances. We degrade the \lyb\ emission to the resolution of the Spectral Imaging of the Coronal Environment (SPICE) instrument on board Solar Orbiter, demonstrating that though likely difficult, it should be possible to detect the presence of non-thermal protons in flares observed by SPICE.Comment: Accepted for publication in The Astrophysical Journa

    Sorption direct air capture with CO2 utilization

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    Direct air capture (DAC) is gathering momentum since it has vast potential and high flexibility to collect CO2 from discrete sources as “synthetic tree” when compared with current CO2 capture technologies, e.g., amine based post-combustion capture. It is considered as one of the emerging carbon capture technologies in recent decades and remains in a prototype investigation stage with many technical challenges to be overcome. The objective of this paper is to comprehensively discuss the state-of-the-art of DAC and CO2 utilization, note unresolved technology bottlenecks, and give investigation perspectives for commercial large-scale applications. Firstly, characteristics of physical and chemical sorbents are evaluated. Then, the representative capture processes, e.g., pressure swing adsorption, temperature swing adsorption and other ongoing absorption chemical loops, are described and compared. Methods of CO2 conversion including synthesis of fuels and chemicals as well as biological utilization are reviewed. Finally, techno-economic analysis and life cycle assessment for DAC application are summarized. Based on research achievements, future challenges of DAC and CO2 conversion are presented, which include providing synthesis guidelines for obtaining sorbents with the desired characteristics, uncovering the mechanisms for different working processes and establishing evaluation criteria in terms of technical and economic aspects

    Probing particle acceleration in stellar binary systems using gamma-ray observations

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    Only a few gamma-ray sources have been established as proton accelerators over the last decades, among them two extraordinary binary systems, the massive colliding wind binary Eta Carinae (eta Car) and the recurrent nova RS Ophiuchi (RS Oph). In this thesis, the nature of acceleration processes up to TeV energies are probed in these systems using very-high energy (VHE; ≄ 100 GeV) gamma-ray data from the High Energy Stereoscopic System (H.E.S.S.) in conjunction with data from the Fermi Large Area Telescope (LAT). To obtain reliable results from Imaging Atmospheric Cherenkov Telescopes like H.E.S.S., an accurate match between simulations and actual observations is crucial. Thus, in the first part of this thesis the successful validation of the simulations of the full 5-telescope H.E.S.S. array is presented. Based on this, the scientific verification of the monoscopic analysis was achieved using data from the large 28 m-telescope recently upgraded with a FlashCam prototype. The resulting spectrum of the Crab Nebula, the standard candle in the VHE regime, is found to be in good agreement with previous measurements by H.E.S.S. and other instruments. Using this verified analysis configuration, the nova RS Oph was successfully detected during its 2021 outburst, making it the first nova with confirmed VHE emission. A detailed light curve was derived from the highly statistically significant gamma-ray signal observed with the full H.E.S.S. array. The combined properties of the H.E.S.S. measurements with simultaneous Fermi-LAT data clearly favor a common origin of the whole gamma-ray emission, implying efficient acceleration of hadrons at the external shock caused by the eruption. eta Car has been firmly established as a source of gamma-rays by Fermi-LAT and H.E.S.S. over the last decade. With its highly eccentric orbit lasting 5.5 years, the periastron passage of the two stars is extremely close, making it a particularly interesting phase range. The 2020 periastron passage was the first such event to be extensively monitored by H.E.S.S. In this thesis, the detection of a VHE signal from eta Car during the 2020 periastron is presented, making use of a novel time-based image cleaning technique for the monoscopic analysis. In combination with simultaneous Fermi-LAT data, its spectral properties are characterized and together with previous and follow-up observations, for the first time, a VHE light curve spanning a full orbit is derived. At least some fraction of the accelerated particles traced by the gamma-ray emission likely escape from eta Car, potentially interacting with target material on different spatial scales. With the detection of Fermi-LAT excess emission associated to molecular clouds in the Carina Nebula, this hypothesis is tested. Whereas the cosmic ray density profile is indicative of an origin of the interacting cosmic rays from eta Car, a larger escaping flux than predicted by models or a contribution from other cosmic ray sources is needed to match the measured flux

    Cold gas disks in main-sequence galaxies at cosmic noon: Low turbulence, flat rotation curves, and disk-halo degeneracy

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    We study the dynamics of cold molecular gas in two main-sequence galaxies at cosmic noon (zC-488879 at z≃1.47z\simeq1.47 and zC-400569 at z≃2.24z\simeq2.24) using new high-resolution ALMA observations of multiple 12^{12}CO transitions. For zC-400569 we also re-analyze high-quality Hα\alpha data from the SINS/zC-SINF survey. We find that (1) Both galaxies have regularly rotating CO disks and their rotation curves are flat out to ∌\sim8 kpc contrary to previous results pointing to outer declines in the rotation speed VrotV_{\rm rot}; (2) The intrinsic velocity dispersions are low (σCOâ‰Č15\sigma_{\rm CO}\lesssim15 km/s for CO and σHαâ‰Č37\sigma_{\rm H\alpha}\lesssim37 km/s for Hα\alpha) and imply Vrot/σCO≳17−22V_{\rm rot}/\sigma_{\rm CO}\gtrsim17-22 yielding no significant pressure support; (3) Mass models using HST images display a severe disk-halo degeneracy: models with inner baryon dominance and models with "cuspy" dark matter halos can fit the rotation curves equally well due to the uncertainties on stellar and gas masses; (4) Milgromian dynamics (MOND) can successfully fit the rotation curves with the same acceleration scale a0a_0 measured at z≃0z\simeq0. The question of the amount and distribution of dark matter in high-zz galaxies remains unsettled due to the limited spatial extent of the available kinematic data; we discuss the suitability of various emission lines to trace extended rotation curves at high zz. Nevertheless, the properties of these two high-zz galaxies (high Vrot/σVV_{\rm rot}/\sigma_{\rm V} ratios, inner rotation curve shapes, bulge-to-total mass ratios) are remarkably similar to those of massive spirals at z≃0z\simeq0, suggesting weak dynamical evolution over more than 10 Gyr of the Universe's lifetime.Comment: 18 pages, 11 figures, 4 tables, 2 appendices. Accepted for publication in Astronomy and Astrophysic

    Ethohydraulische Modellierung

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    Die Ethohydraulik hat als vergleichsweise junge Transdisziplin zum Ziel, einen reproduzierbaren, kausalen Zusammenhang zwischen dem Verhalten aquatischer Lebewesen (Ethologie) und der Strömungscharakteristik (Hydraulik) zu finden. Diese Grundlagen werden dazu eingesetzt, die anthropogen beeinflussten und querverbauten GewĂ€sser fĂŒr die Fischfauna wieder durchgĂ€ngig zu gestalten und deren BiodiversitĂ€t zu erhalten. Unter ethohydraulischer Modellierung wird in dieser Arbeit die VerknĂŒpfung genannter Disziplinen in sowohl physikalischen als auch hydrodynamisch-numerischen Modellen verstanden, bei denen auch vielfĂ€ltige Methoden angrenzender Fachgebiete mit einfließen. Die Modelle selbst decken verschiedene Skalen von neuroethologischen Untersuchungen ĂŒber kleinrĂ€umige schwimmkinematische Betrachtungen der Körperbewegung bis hin zu langen Wanderrouten entlang unserer BinnengewĂ€sser ab. Um Fische gezielt zu leiten, ist ein VerstĂ€ndnis ihrer Sinneswelt ebenso wichtig wie ein VerstĂ€ndnis fĂŒr den verhaltensauslösenden Strömungsreiz. Daher wird in dieser Arbeit zunĂ€chst ein tiefgehender Einblick in die Biologie von Fischen mit ihren sensorischen Systemen, in ihr vielfĂ€ltiges Verhalten sowie in mögliche Beobachtungsmethoden zur Verhaltensanalyse gegeben. Anschließend wird detailliert auf die kinematischen und dynamischen Grundlagen der Strömung sowie deren messtechnische und numerische Analyse eingegangen. Diese umfangreiche Zusammenstellung ethohydraulischer Grundlagen bildet ein KernstĂŒck der Arbeit. Damit sollen neue DenkanstĂ¶ĂŸe gegeben und Analysemöglichkeiten dargelegt werden. Außerdem werden die ethohydraulischen Untersuchungen an einem SchrĂ€grechensetup (55° und 30° zur Anströmung) im wasserbaulichen Forschungslabor der TU Darmstadt dargelegt. Dort wurden zum einen die hydromechanischen Signaturen mithilfe einer neuartigen fischförmigen Druckmesssonde (FSS; Fischsinnessonde) und einem Acoustic Doppler Velocimeter (ADV) aufgezeichnet. Zum anderen wurde das Verhalten potamodromer Fischarten beobachtet. Basierend auf den durchgefĂŒhrten Tests werden zunĂ€chst die Messungen mit der FSS auf unterschiedlichste Weise ausgewertet. Dabei wird deutlich herausgearbeitet, dass der Fischkörper als eine Art Geschwindigkeits-Druck-Wandler wirkt. Nicht nur der frontal auftreffende Geschwindigkeitsanteil ist in Form des Staudrucks detektierbar, sondern auch der auf die Flanken auftreffende, senkrecht zur OberflĂ€che wirkende Geschwindigkeitsanteil korreliert mit dem dort vorhandenen Druck sowie dessen bilateralem Gradienten. Dies gilt sowohl fĂŒr die konvektiv transportieren Wirbelstrukturen als auch fĂŒr den mittleren, lokal wirkenden Druckwert. Neben neuen, auf den FSS-Messungen basierenden Hypothesen bezĂŒglich der hydrodynamischen Bildgebung des betrachteten Setups mit dem Seitenlinienorgan, dem Strömungssinn der Fische, werden außerdem Empfehlungen fĂŒr die weitere Optimierung der Sonde gegeben. Weiterhin werden in bisherigen fischökologischen Untersuchungen analysierte und fĂŒr die Ethohydraulik relevante Verhaltensweisen zusammengestellt. Diese sollen einen ersten Ansatz zur Vereinheitlichung der Terminologie darstellen. Zudem wird auf die mögliche Quantifizierung und Operationalisierung des Fischverhaltens und abschließend auf einige, fĂŒr ethohydraulische Untersuchungen relevante, hydrodynamische Parameter eingegangen sowie deren Relevanz diskutiert. Die Erkenntnisse aus diesen Analysen werden in abschließenden Empfehlungen zur gezielten Weiterentwicklung von Methoden zur ethohydraulischen Modellierung zusammengefasst, wobei Strömungs- und Verhaltensgradienten eine bedeutende Rolle einnehmen

    Probing the Multiphase Interstellar Medium in an Extreme Starburst at High Redshift

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    In this thesis we present a range of observations and results relating to the lensed hyperluminous sub-mm galaxy ‘9io9’ at z = 2.6, where we have used sub-mm/mm spectroscopy targeting the dense and cold interstellar medium to better undertstand the conditions underlying extreme star formation (1000× that of the Milky Way) in galaxies the early Universe. In Chapter 2 we present new observations with the Atacama Large Millimeter/sub-millimeter Array (ALMA) of the 122- and 205-ÎŒm fine-structure line emission of singly-ionised nitrogen in 9io9. The 122-/205-ÎŒm [N II] line ratio is sensitive to electron density, ne, in the ionised interstellar medium, and we use this to measure ne ≈ 300cm−3 averaged across the galaxy. This is over an order of magnitude higher than the Milky Way average, but comparable to localised Galactic star-forming regions. Combined with observations of the atomic carbon (C I(1–0)) and carbon monoxide (CO J = 4–3) in the same system, we reveal the conditions in this intensely star-forming system. The majority of the molecular interstellar medium has been driven to high density, and the resultant conflagration of star formation produces a correspondingly dense ionised phase, presumably co-located with myriad H II regions that litter the gas-rich disk. In Chapter 3 we present the detection of the ground state rotational emission of ammonia, ortho- NH3 (JK = 10 → 00) in 9io9. The integrated line profile is consistent with other molecular and atomic emission lines which have resolved kinematics well-modelled by a 5 kpc-diameter rotating disc. This implies that the gas responsible for NH3 emission is broadly tracing the global molecular reservoir, but likely distributed in pockets of high density (n ≳ 5×104 cm−3). With a luminosity of 2.8×106 L⊙, the NH3 emission represents 2.5×10−7 of the total infrared luminosity of the galaxy, comparable to the ratio observed in the Kleinmann-Low nebula in Orion and consistent with sites of massive star formation in the Milky Way. If LNH3/LIR serves as a proxy for the ‘mode’ of star formation, this hints that the nature of star formation in extreme starbursts in the early Universe is similar to that of Galactic star-forming regions, with a large fraction of the cold interstellar medium in this state, plausibly driven by a storm of violent disc instabilities in the gas-dominated disc. This supports the ‘full of Orions’ picture of star formation in the most extreme galaxies seen close to the peak epoch of stellar mass assembly. In Chapter 4 we present new ALMA observations of 9io9 detecting COJ=5→4 and its isotopologues 13COJ=5→4 and C18OJ=5→4. Since 13C is mainly produced by intermediatemass stars and 18O is produced by massive stars, 13CO/C18O is sensitive to the shape of the stellar initial mass function (IMF), where the IMF of the Milky Way has a power law slope α2 ≈ 2.3–2.6 for stars of masses above 0.5M⊙. We measure a galaxy-integrated luminosity ratio 13CO/C18O = 1.6±0.1, consistent with the ratio observed in local ultraluminous infrared galaxies and submillimetre-selected galaxies at high redshift, and significantly lower than the 13CO/C18O of the Milky Way. It has been argued that the low 13CO/C18O observed in extreme star-forming galaxies in the early Universe is evidence for a top-heavy IMF in these systems. In this work we use state-of-the-art chemical evolution models to conclude that irrespective of stellar rotation, the observed 13CO/C18O is consistent with a Kroupa IMF with high-mass slope of α2 = 2.3 (as in our Milky Way models) and also the steeper ‘top-heavy’ α2 = 2.1 slope. In Chapter 5 we present a discussion of ongoing work on an ALMA spectral scan of 9io9, alongside some potential future avenues of research, in particular pushing to higher resolution with ALMA, and MIRI observations with JWST probing the mid infrared PAH emission as a AGN diagnostic
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