Advancing spaceborne tools for the characterization of planetary ionospheres and circumstellar environments

This work explores remote sensing of planetary atmospheres and their circumstellar surroundings. The terrestrial ionosphere is a highly variable space plasma embedded in the thermosphere. Generated by solar radiation and predominantly composed of oxygen ions at high altitudes, the ionosphere is dynamically and chemically coupled to the neutral atmosphere. Variations in ionospheric plasma density impact radio astronomy and communications. Inverting observations of 83.4 nm photons resonantly scattered by singly ionized oxygen holds promise for remotely sensing the ionospheric plasma density. This hypothesis was tested by comparing 83.4 nm limb profiles recorded by the Remote Atmospheric and Ionospheric Detection System aboard the International Space Station to a forward model driven by coincident plasma densities measured independently via ground-based incoherent scatter radar. A comparison study of two separate radar overflights with different limb profile morphologies found agreement between the forward model and measured limb profiles. A new implementation of Chapman parameter retrieval via Markov chain Monte Carlo techniques quantifies the precision of the plasma densities inferred from 83.4 nm emission profiles. This first study demonstrates the utility of 83.4 nm emission for ionospheric remote sensing. Future visible and ultraviolet spectroscopy will characterize the composition of exoplanet atmospheres; therefore, the second study advances technologies for the direct imaging and spectroscopy of exoplanets. Such spectroscopy requires the development of new technologies to separate relatively dim exoplanet light from parent star light. High-contrast observations at short wavelengths require spaceborne telescopes to circumvent atmospheric aberrations. The Planet Imaging Concept Testbed Using a Rocket Experiment (PICTURE) team designed a suborbital sounding rocket payload to demonstrate visible light high-contrast imaging with a visible nulling coronagraph. Laboratory operations of the PICTURE coronagraph achieved the high-contrast imaging sensitivity necessary to test for the predicted warm circumstellar belt around Epsilon Eridani. Interferometric wavefront measurements of calibration target Beta Orionis recorded during the second test flight in November 2015 demonstrate the first active wavefront sensing with a piezoelectric mirror stage and activation of a micromachine deformable mirror in space. These two studies advance our ``close-to-home'' knowledge of atmospheres and move exoplanetary studies closer to detailed measurements of atmospheres outside our solar system

Valence losses at interfaces in aluminium alloys

The aim of this project was to investigate EELS from two-layer systems and relate the results to the existing theory. Two systems were investigated, magnesium silicide platelets within an aluminium matrix and silicon precipitates within an aluminium matrix. Both systems were prepared through thermal treatment of a 6061 A1 alloy. The majority of the data presented in this thesis was acquired using EELS. However, energy dispersive x-ray spectroscopy (EDX) and electron microscopy were also used. EELS was performed on two different electron microscopes, the VG HB5 STEM and the FEI Tecnai TF20 (S)TEM. The bulk of the results were acquired on the HB5. To facilitate the comparison of theoretical and experimental results, the data was separated into bulk and interface components. The component amounts were then plotted against distance from the interface. Bessel functions were then fitted to this plot to give characteristic values. These values represented how well the optimal interface position had been chosen, the comparative decay of the interface plasmon on each side of the interface and the relative thickness of the bulk material. The experimental data from most of the interfaces examined indicated significant variations in the thickness of the sample. Despite this, the experimental results were found to follow the trend suggested by the theoretical equations. Analysis of the characteristic values indicated that the data from the HB5 and Tecnai for an interface showed a strong correlation. However, comparison of the experimental values with the theoretical reference showed a deviation of ~20%. Though the source of this deviation was not clear, a number of possible causes were investigated. Theoretical models were generated of systems with a variety of thickness profiles. In addition, systems containing steps, wide and narrow bulk plasmons and a thin interfacial layer of a third material were all considered. The deviation between the results from experiment and the simple theoretical model was believed to be consistent with the factors affecting EELS from a real interface. In particular, thickness variations and imperfections at the interface were found to be the most likely cause of the discrepancy between theory and experiment

An Open-Source Gaussian Beamlet Decomposition Tool for Modeling Astronomical Telescopes

In the pursuit of directly imaging exoplanets, the high-contrast imaging community has developed a multitude of tools to simulate the performance of coronagraphs on segmented-aperture telescopes. As the scale of the telescope increases and science cases move toward shorter wavelengths, the required physical optics propagation to optimize high-contrast imaging instruments becomes computationally prohibitive. Gaussian Beamlet Decomposition (GBD) is an alternative method of physical optics propagation that decomposes an arbitrary wavefront into paraxial rays. These rays can be propagated expeditiously using ABCD matrices, and converted into their corresponding Gaussian beamlets to accurately model physical optics phenomena without the need of diffraction integrals. The GBD technique has seen recent development and implementation in commercial software (e.g. FRED, CODE V, ASAP) but appears to lack an open-source platform. We present a new GBD tool developed in Python to model physical optics phenomena, with the goal of alleviating the computational burden for modeling complex apertures, many-element systems, and introducing the capacity to model misalignment errors. This study demonstrates the synergy of the geometrical and physical regimes of optics utilized by the GBD technique, and is motivated by the need for advancing open-source physical optics propagators for segmented-aperture telescope coronagraph design and analysis. This work illustrates GBD with Poisson's spot calculations and show significant runtime advantage of GBD over Fresnel propagators for many-element systems.Comment: 13 pages, 9 figures, submitted to SPIE Astronomical Telescopes & Instrumentation 202

Hazard Perception and Reporting

Reporting of hazards is a key aspect of safety management in industry, but relatively little empirical investigation of reporting has been undertaken. This research reports on an investigation that was carried out in the Science gallery at Trinity College Dublin to explore the detection and reporting of hazards by members of the public. Three simulated hazards were developed and placed around the risk lab. The experiment was designed to assess the capacity to recall recognise and report hazards of the participants by means of an exit survey. Participants performed better at recognition than recollection with no actual reporting of hazards recorded. The results validated some of the findings suggested by the literature and can assist in the development of a new experimental methodology as training within organizations to improve awareness of hazards and reporting practices

Compact Three Mirror Anastigmat Space Telescope Design using 6.5m Monolithic Primary Mirror

The utilization of a 6.5m monolithic primary mirror in a compact three-mirror anastigmat (TMA) telescope design offers unprecedented capabilities to accommodate various next generation science instruments. This design enables the rapid and efficient development of a large aperture telescope without segmented mirrors while maintaining a compact overall form factor. With its exceptional photon collection area and diffraction-limited resolving power, the TMA design is ideally suited for both the ground and space active/adaptive optics concepts, which require the capture of natural guide stars within the field of view for wavefront measurement to correct for misalignments and shape deformation caused by thermal gradients. The wide field of view requirement is based on a statistical analysis of bright natural guide stars available during observation. The primary mirror clear aperture, compactness requirement, and detector pixel sizes led to the choice of TMA over simpler two-mirror solutions like Ritchey-Chretien (RC) telescopes, and the TMA design offers superior diffraction-limited performance across the entire field of view. The standard conic surfaces applied to all three mirrors (M1, M2, and M3) simplify the optical fabrication, testing, and alignment process. Additionally, the TMA design is more tolerant than RC telescopes. Stray light control is critical for UV science instrumentation, and the field stop and Lyot stop are conveniently located in the TMA design for this purpose.Comment: Presented at SPIE, Optics+Photonics 2023, Astronomical Optics: Design, Manufacture, and Test of Space and Ground Systems IV in San Diego, CA, US

WFIRST Coronagraph Technology Requirements: Status Update and Systems Engineering Approach

The coronagraphic instrument (CGI) on the Wide-Field Infrared Survey Telescope (WFIRST) will demonstrate technologies and methods for high-contrast direct imaging and spectroscopy of exoplanet systems in reflected light, including polarimetry of circumstellar disks. The WFIRST management and CGI engineering and science investigation teams have developed requirements for the instrument, motivated by the objectives and technology development needs of potential future flagship exoplanet characterization missions such as the NASA Habitable Exoplanet Imaging Mission (HabEx) and the Large UV/Optical/IR Surveyor (LUVOIR). The requirements have been refined to support recommendations from the WFIRST Independent External Technical/Management/Cost Review (WIETR) that the WFIRST CGI be classified as a technology demonstration instrument instead of a science instrument. This paper provides a description of how the CGI requirements flow from the top of the overall WFIRST mission structure through the Level 2 requirements, where the focus here is on capturing the detailed context and rationales for the CGI Level 2 requirements. The WFIRST requirements flow starts with the top Program Level Requirements Appendix (PLRA), which contains both high-level mission objectives as well as the CGI-specific baseline technical and data requirements (BTR and BDR, respectively)... We also present the process and collaborative tools used in the L2 requirements development and management, including the collection and organization of science inputs, an open-source approach to managing the requirements database, and automating documentation. The tools created for the CGI L2 requirements have the potential to improve the design and planning of other projects, streamlining requirement management and maintenance. [Abstract Abbreviated]Comment: 16 pages, 4 figure

Molecular Analysis of the shaking-b Locus of Drosophila melanogaster

One strategy for the isolation of molecules required for the establishment of specific synapses is to screen for mutations which disrupt identified neuronal connections and subsequently to clone and characterise the genes involved. The giant fibre system of Drosophila melanogaster is an ideal focus for such investigations. This system mediates the fly's jump-escape response, allowing neuronal connectivity mutants to be isolated as a subset of those flies which fail to jump in response to a light-off stimulus. The Passover mutation was isolated in this way, and was subsequently shown to be an allele of the shaking-B (shak-B) locus, thus implicating shaking-B in the establishment of neuronal connectivity, and inspiring the molecular analysis which is reported here. Genetic analysis reveals two distinct functions at the shaking-B locus, one (termed shak-B(neural)) is required for the normal development of the imaginal nervous system, while the other, shak-B(lethal) is an essential function, without which the animals die as embryos or first instar larvae. Most shaking-B alleles disrupt both of these genetic functions, although some (like shak-B passover) are specifically neural, while others (such as shak-B L41) affect only the essential function. The 19E3 polytene region in which shaking-B resides was cloned by chromosome walking from microcloned entry points and the breakpoints of deficiency chromosomes which encroach upon the shak-B region were used to define a 15 kb stretch of walk in which at least some of the gene must lie. Unique DNA fragments from this area were used to probe cDNA libraries and the embryonic cDNA KE2(1.8) was isolated. The KE2(1.8) cDNA was sequenced and found to contain no extensive regions of reading frame, though an internal 122 codon open reading frame (ORF) was implicated by computer algorithms as a likely coding region, and was found be highly homologous to the N terminus of the Drosophila Ogre protein and to part of the C. elegans Unc-7 protein, both of which are implicated in nervous system development. An asymmetric PCR strategy was used to sequence this small ORF from shak-B mutant chromosomes, and a 17 bp deletion which is predicted to abolish translation of the ORF was found to underlie the shak-BL41 allele. Due to the rarity of shak-B cDNAs, a library screening strategy based upon inverse PCR was devised. This technique enabled the isolation of cDNAs representing a further four shak-B transcript forms, while yet another two cDNAs were isolated by conventional means. Sequence analysis of these clones and of the genomic regions from which they were derived has provided a wealth of data regarding the putative products and genomic organisations of these transcripts. The SIPC8 cDNA contains an ORF of 372 residues, implying a protein of 44.4 kDa with extended homology to Ogre and Unc-7. In the neural and lethal shak-B alleles shak-B allelels and shak-B r-9-29 this reading frame was found to be disrupted by a mutation which introduces a stop codon in a downstream exon. This finding, together with the identification of the shak-BEC201 allele suggested that Shak-B(neural) and Shak'B(lethal) proteins have unique N terminal regions but converge upon common C terminal sequences. While the SIPC8 cDNA is disrupted by lesions causing lethal alleles, the P2.4 cDNA isolated by Krishnan and colleagues was found to contain an ORF with a unique N terminus, and a C terminus common to that of the SIPC8 reading frame. The unique N terminus of P2.4 was found (BCrishnan et aL, 1993) to be disrupted by lesions underlying shak-B(neural) mutations including shak-B passover go fulfilling the criteria demanded of a shak-B(neural) transcript. Shak-B proteins contain hydrophobic segments suggestive of transmembrane domains, and assessment of the likely transmembrane dispositions of all putative Shak-B proteins was carried out using optimal computer algorithms. Based on these structural predictions and on the phenotypes and expression patterns of shaking-B and its homologues, the possible functions of Shaking-B proteins are considered

β1-adrenoceptor blockade treatment of right ventricular dysfunction caused by pulmonary hypertension

Failure of the right ventricle (or ventricular) (RV) is the leading cause of death in patients with pulmonary arterial hypertension (PAH), however no treatments specifically target the failing RV. β1-adrenoceptor blockers (β-blockers, BB) reduce mortality in left heart failure but current clinical guidelines caution against their use in PAH. Recent studies suggest β-blockers may be beneficial in PAH however the mechanisms remain unknown. The present study sought to establish whether the β1- blocker metoprolol (10 mg/kg/day) improved survival and function in a rat model of PAH induced by monocrotaline (60 mg/kg, MCT), and to elucidate the mechanisms responsible. Daily metoprolol or placebo was administered 15 days post-monocrotaline injection. PAH resulted in severe RV hypertrophy, dysfunction and heart failure by median day 23 in placebo treated rats (FAIL), whereas metoprolol extended the median survival to day 31 (MCT+BB). RV function measured by echocardiography and catheterisation was severely impaired in FAIL, but was partially restored in MCT+BB on day 23±1. Metoprolol appeared to act primarily on the myocardium and not the vasculature. Contractile abnormalities in isolated FAIL RV cardiomyocytes included increased cell volume, negative force and Ca2+ transient response to faster pacing, increased stiffness to stretch and shorter resting sarcomere length. Reduced creatine kinase activity was found in FAIL; creatine kinase inhibition reproduced characteristics of FAIL in healthy cells, whereas exogeneous creatine kinase reversed the shorter sarcomere length in FAIL cells. Contractile and Ca2+ handling properties of MCT+BB cells were partially or fully restored relative to healthy cells. Capillary density was reduced in FAIL and partially restored in MCT+BB; computer modelling indicated fewer areas of hypoxia in MCT+BB RV. Assessment of FAIL RV mitochondria revealed reduced creatine-coupled respiration but no other detectable defects. Metoprolol improved survival, Ca2+-handling, contractility, oxygen delivery and diastolic properties of PAH rats. β-blockers represent a novel myocardium-specific therapy to target the failing RV in PAH

Simulating the efficacy of the implicit-electric-field-conjugation algorithm for the Roman Coronagraph with noise

The Roman Coronagraph is expected to perform its high-order wavefront sensing and control (HOWFSC) with a ground-in-the-loop scheme due to the computational complexity of the Electric-Field-Conjugation (EFC) algorithm. This scheme provides the flexibility to alter the HOWFSC algorithm for given science objectives. A new alternative implicit-EFC algorithm is of particular interest as it requires no optical model to create a dark-hole, making the final contrast independent of the model accuracy. The intended HOWFSC scheme involves running EFC while observing a bright star such as $\zeta$ Puppis to create the initial dark-hole, then slew to the science target while maintaining the contrast with low-order WFSC over the given observation. Given a similar scheme, the efficacy of iEFC is simulated for two coronagraph modes, namely the Hybrid Lyot Coronagraph (HLC) and the wide-field-of-view Shaped-Pupil-Coronagraph (SPC-WFOV). End-to-end physical optics models for each mode serve as the tool for the simulations. Initial monochromatic simulations are presented and compared with monochromatic EFC results obtained with the FALCO software. Various sets of calibration modes are tested to understand the optimal modes to use when generating an iEFC response matrix. Further iEFC simulations are performed using broadband images with the assumption that $\zeta$ Puppis is the stellar object being observed. Shot noise, read noise, and dark current are included in the broadband simulations to determine if iEFC could be a suitable alternative to EFC for the Roman Coronagraph.Comment: 15 pages, 16 figure

Laser Guide Star for Large Segmented-Aperture Space Telescopes, Part I: Implications for Terrestrial Exoplanet Detection and Observatory Stability

Precision wavefront control on future segmented-aperture space telescopes presents significant challenges, particularly in the context of high-contrast exoplanet direct imaging. We present a new wavefront control architecture that translates the ground-based artificial guide star concept to space with a laser source aboard a second spacecraft, formation flying within the telescope field-of-view. We describe the motivating problem of mirror segment motion and develop wavefront sensing requirements as a function of guide star magnitude and segment motion power spectrum. Several sample cases with different values for transmitter power, pointing jitter, and wavelength are presented to illustrate the advantages and challenges of having a non-stellar-magnitude noise limited wavefront sensor for space telescopes. These notional designs allow increased control authority, potentially relaxing spacecraft stability requirements by two orders of magnitude, and increasing terrestrial exoplanet discovery space by allowing high-contrast observations of stars of arbitrary brightness.Comment: Submitted to A