3,388 research outputs found
Citizen participation in news
No full textThe process of producing news has changed significantly due to the advent of the Web, which has enabled the increasing involvement of citizens in news production. This trend has been given many names, including participatory journalism, produsage, and crowd-sourced journalism, but these terms are ambiguous and have been applied inconsistently, making comparison of news systems difficult. In particular, it is problematic to distinguish the levels of citizen involvement, and therefore the extent to which news production has genuinely been opened up. In this paper we perform an analysis of 32 online news systems, comparing them in terms of how much power they give to citizens at each stage of the news production process. Our analysis reveals a diverse landscape of news systems and shows that they defy simplistic categorisation, but it also provides the means to compare different approaches in a systematic and meaningful way. We combine this with four case studies of individual stories to explore the ways that news stories can move and evolve across this landscape. Our conclusions are that online news systems are complex and interdependent, and that most do not involve citizens to the extent that the terms used to describe them imply
Book Review: Jesus in an age of enlightenment: Radical gospels from Thomas Hobbes to Thomas Jefferson. By Jonathan C.P Birch
No full textThis is a pre-copyedited, author-produced PDF of an article accepted for publication in [Literature and Theology] following peer review. The version of record [Greenaway, J. (2021). Jesus in an Age of Enlightenment: Radical gospels from Thomas Hobbes to Thomas Jefferson. By Jonathan C.P Birch. Literature and Theology, 35(1), 100–102] is available online at: [https://academic.oup.com/litthe/article/35/1/100/6130117?guestAccessKey=0523008b-46e6-4ed2-ab5d-001d93207bed].A review of Jesus in an Age of Enlightenment: Radical Gospels from Thomas Hobbes to Thomas Jefferson by Jonathan C.P Birc
‘Decolonisation’ in China, 1949-1959
No full textIn this chapter Jonathan Howlett adopts perspectives and models from wider literatures on decolonisation to explore the Chinese Communist Party’s elimination of the British semi-colonial presence from China after the revolution of 1949 and to place it within its global context. He focuses in particular on the CCP’s attempts to address the economic, cultural and human legacies of semi-colonialism within a comparative context. In so doing, the author seeks to complicate our understanding of the Sino-British relationship by exploring one of its most dramatic phases and to further illuminate this neglected period in Chinese history
THE FLAT TRANSMISSION SPECTRUM OF THE SUPER-EARTH GJ1214b FROM WIDE FIELD CAMERA 3 ON THE HUBBLE SPACE TELESCOPE
No full textCapitalizing on the observational advantage offered by its tiny M dwarf host, we present Hubble Space Telescope/Wide Field Camera 3 (WFC3) grism measurements of the transmission spectrum of the super-Earth exoplanet GJ1214b. These are the first published WFC3 observations of a transiting exoplanet atmosphere. After correcting for a ramp-like instrumental systematic, we achieve nearly photon-limited precision in these observations, finding the transmission spectrum of GJ1214b to be flat between 1.1 and 1.7 mu m. Inconsistent with a cloud-free solar composition atmosphere at 8.2 sigma, the measured achromatic transit depth most likely implies a large mean molecular weight for GJ1214b's outer envelope. A dense atmosphere rules out bulk compositions for GJ1214b that explain its large radius by the presence of a very low density gas layer surrounding the planet. High-altitude clouds can alternatively explain the flat transmission spectrum, but they would need to be optically thick up to 10 mbar or consist of particles with a range of sizes approaching 1 mu m in diameter
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Understanding Kepler's Super-Earths and Sub-Neptunes: Insights from Thermal Evolution and Photo-Evaporation
No full textExtrasolar planet surveys have identified an abundant new population of highly irradiated planets with sizes that are in between that of the Earth and Neptune. Such planets are unlike anything found in our own Solar System, and many of their basic properties are not understood. As such, these planets provide a fundamental test for models of planets formation and evolution with important implications for the formation of the Earth and planet habitability. In order to understand these new classes of planets, we have developed planetary structure and evolution models that can be used both to answer questions about individual planetary systems and to study populations of planets as a whole. In brief, these models allow usto follow a planet's mass, size, internal structure, and composition as it ages; from the time it finishes formation until it is detected billions of years later.These evolution models are critical because a planet's composition can change substantially over its lifetime. Close-in planets, like most of those found so far, are bombarded by large amounts of ionizing radiation, which over time can completely strip away a planet's atmosphere; even turning a gas-rich Neptune sized planet into a barren rocky super-Earth.Using these models, we explore the structure, composition, and evolution of sub- Neptune sized extrasolar planets found by NASA's Kepler mission. We examine the relationships between planetary masses, radii, and compositions. We show how these compositionshave been sculpted by photo-evaporation, and we examine the interplay between thermal and evaporative evolution
Topsy Turvy - Jonathan Swift on Human Nature, Reason, and Morality
No full textThis is the author accepted manuscript. The final version of the book is available from the publisher via the link in this record.No abstrac
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Bayesian Statistical Inference of Giant Planet Physics
No full textThe many exoplanet discoveries of recent years have opened new avenues for studying giant planets and their formation. The giant planets of our solar system have been studied up close and in great detail, and exoplanets can complement this with a rich population to examine statistically. More than just studying their occurrence rates, it is possible to combine physical and statistical models to uncover aspects of their physical processes. I apply this strategy here on a series of related topics. First, I study a set of cool giant exoplanets, infer their bulk compositions, and demonstrate that there is a relationship between a planet's mass and its composition. I further discuss the implications to their formation, and how a planet's bulk composition can usefully complement its observed atmospheric abundances. I also consider hot Jupiters, inferring the amount of internal heating required to explain their anomalously large radii, the cause of which is one of the longest standing open questions in exoplanet science. I show through a careful examination of their radii and parent star evolution that these objects appear to reinflate quickly when their equilibrium temperature is increased. This strongly constrains the physical mechanisms that are causing their inflation. Finally, I outline several immediately relevant areas for future work to better understand these objects
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Understanding Atmospheres of Exoplanets and Brown Dwarfs with JWST
No full textWe have entered a new era of detailed exoplanet and brown dwarf atmospheric characterization with the James Webb Space Telescope (JWST), enabling very high signal-to-noise spectroscopic observations. This has allowed us to probe their atmospheres and interiors with unprecedented detail. This thesis introduces new constraints on previously uncertain processes such as atmospheric dynamics, cloud physics, and interior heat flux of transiting and self-luminous giant exoplanets, exo-Neptunes, and brown dwarfs, using newly developed advanced theoretical models and JWST observations.Constraints on Aerosols– Using 3D general circulation models, we examine whether the unknown 3D cloud distribution in exoplanets and brown dwarfs can be probed by their disk-integrated polarized thermal radiation. Our findings show that the clouds predicted in 3D GCMs can replicate the observed thermal polarization of brown dwarfs Luhman 16 A and B. However, we also show that small-scale vortices and cloud particle radii can sufficiently alter the disk-integrated polarized signals from such objects. To probe the 3D distribution pattern of aerosols in giant transiting exoplanet atmospheres, we present limb-resolved transmission spectra of the morning and evening limbs of hot Jupiter WASP-94A b, obtained using JWST. We find the colder morning limb of WASP-94A b is completely enshrouded in aerosols whereas the hotter evening limb is clear, showing prominent gas absorption features. We leverage these observations to show that aerosols in hot Jupiters can be primarily composed of condensate clouds instead of photochemical hazes. We also show that ignoring such aerosol-driven limb-to-limb differences can lead to severe (∼5σ) bias in their inferred composition, not only for hot Jupiters, but for the broader class of transiting exoplanets including smaller planets like sub-Neptunes.Constraints on Atmospheric Dynamics– Atmospheric dynamics is one of the least understood and most poorly constrained aspects of substellar atmospheres. Atmospheric dynamics along the radial direction, or vertical mixing, is often represented by the Kzz diffusion parameter. Theoretical and empirical uncertainty on Kzz spans several orders of magnitude. To constrain Kzz, we introduce PICASO 3.0, an opensource Python-based 1D radiative-convective equilibrium model that self-consistently treats disequilibrium chemistry from vertical mixing. Using PICASO 3.0, we demonstrate that JWST data can precisely constrain Kzz in both radiative and convective atmospheric regions. Our models predict brown dwarfs with higher gravities and temperatures of 500-900 K should have a second “detached” radiative region, which makes them ideal targets for constraining the very uncertain Kzz in their radiative atmospheres. To explore how metallicity, C/O ratio, and Kzz together shape the spectra of directly imaged planets and brown dwarfs, we present the Sonora Elf Owl model grid, which has been calculated with the PICASO model. We show that metallicity and Kzz driven vertical mixing can have degenerate effects on their spectra at various wavelength ranges. We use this model grid along with AKARI and Spitzer observations to show that free-floating brown dwarfs with temperatures between 500-900 K indeed have very low Kzz values, which agrees with our theoretical predictions of detached radiative regions in their deep atmospheres.Constraints on Interior and Atmospheric Properties– To assess whether JWST can constrain vertical mixing and interior properties of transiting planets, including warm-to-hot sub-Neptunes and gas giants, we integrate photochemistry into PICASO using the Photochem model. We show that CH4 is an ideal probe of Kzz in warm giants, while CO is better for warm sub-Neptunes. We also find that SO2 is no longer the main S- bearing gas in planets with Teq≤700 K or Teq ≥1100 K, with CS and CS2 becoming dominant. Using this model and JWST data, we constrain the atmospheric and interior properties of Neptune-class exoplanet GJ 436 b. We present the panchromatic JWST eclipse spectrum of GJ 436 b, showing it differs significantly from previously published Spitzer photometry in the 3.6 µm band. We find weak evidence of CO2 absorption in its spectrum. Using PICASO modeling, we find the planet’s day-side is either covered with a thick layer of aerosols with a metallicity ≥300×solar, or its interior is colder (Tint ∼ 60 K) with a metallicity ≥80×solar. Future observations of the planet, preferably in transmission, are required to distinguish between these scenarios and constrain its interior properties more precisely
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Clouds and Hazes in Exoplanets and Brown Dwarfs
No full textThe formation of clouds significantly alters the spectra of cool substellar atmospheres from terrestrial planets to brown dwarfs. In cool planets like Earth and Jupiter, volatile species like water and ammonia condense to form ice clouds. In hot planets and brown dwarfs, iron and silicates instead condense, forming dusty clouds. Irradiated methane-rich planets may have substantial hydrocarbon hazes. During my dissertation, I have studied the impact of clouds and hazes in a variety of substellar objects. First, I present results for cool brown dwarfs in- cluding clouds previously neglected in model atmospheres. Model spectra that include sulfide and salt clouds can match the spectra of T dwarf atmospheres; water ice clouds will alter the spectra of the newest and coldest brown dwarfs, the Y dwarfs. These sulfide/salt and ice clouds potentially drive spectroscopic variability in these cool objects, and this variability should be distinguishable from variability caused by hot spots.Next, I present results for small, cool exoplanets between the size of Earth and Neptune. They likely have sulfide and salt clouds and also have photochemical hazes caused by stellar irradiation. Vast resources have been dedicated to characterizing the handful of super Earths and Neptunes accessible to current telescopes, yet of the planets smaller than Neptune studied to date, all have radii in the near-infrared consistent with being constant in wavelength, likely showing that these small planets are consistently enshrouded in thick hazes and clouds. For the super Earth GJ 1214b, very thick, lofted clouds of salts or sulfides in high metallicity (1000× solar) atmospheres create featureless transmission spectra in the near-infrared. Photochemical hazes also create featureless transmission spectra at lower metallicities. For the Neptune-sized GJ 436b, its thermal emission and transmission spectra combine indicate a high metallicity atmosphere, potentially heated by tides and affected by disequilibrium chemistry. I show that despite the challenges, there are promising avenues for understanding small planets: by observing thermal emission and reflected light, we can break the degeneracies and con- strain the atmospheric compositions. These future observations will provide rich diagnostics of molecules and clouds in small planets
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Terrestrial Exoplanet Atmospheres: From Primordial Compositions to Likely Observable Biosignatures
No full textExoplanet science is now focusing on characterizing the physics and chemistry of exoplanet atmospheres, including those of terrestrial-class, potentially habitable planets. In this thesis, I use a combination of laboratory experiments and theoretical modeling to understand two themes related to these atmospheres: (1) their primordial outgassing compositions from an experimental cosmochemistry approach, and (2) the planetary context for observable biosignature gases using modeling tools. There is no first-principles understanding of how to connect a planet’s bulk composition to its initial atmospheric properties. Since terrestrial exoplanets likely form their atmospheres through outgassing, an important step towards establishing this connection is to assay meteorites, remnants of planetary building blocks, by heating and measuring their outgassed volatiles. In the first theme, I use multiple experimental techniques to determine meteorites’ outgassing compositions over a range of temperatures and pressures. I describe the results of heating carbonaceous chondrite samples and measuring their abundances of released volatiles as a function of temperature in a high-vacuum environment. I find that these meteorites outgas significant amounts of H2O, CO, CO2 and smaller quantities of H2 and H2S. I also discuss a complementary bulk element analysis to monitor outgassing of heavier elements (e.g., sulfur, iron, zinc). I compare these experimental results to thermochemical equilibrium models of chondrite outgassing and determine how these experiments can improve atmospheric models and inform the connection between bulk composition and early atmospheres.For the second theme, I perform a comprehensive analysis of the necessary planetary conditions for atmospheric methane to be a compelling biosignature gas. Methane is one of the only biosignatures that JWST can readily detect in terrestrial atmospheres. Therefore, it is essential to understand methane biosignatures to contextualize these imminent observations. Using a combination of multiphase thermodynamic and atmospheric chemistry models, I investigate abiotic sources of methane and determine the planetary conditions for which these sources could be enhanced on terrestrial planets so as to result in false positives. I determine that known abiotic processes cannot easily generate atmospheres rich in CH4 and CO2 with limited CO due to the strong redox disequilibrium between CH4 and CO2, providing the first tentative framework for assessing methane biosignatures
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