1,147 research outputs found
Achieving international consensus for the prevention of orthopaedic wound blistering: results of a Delphi survey
No full textThis article presents the results of an international 2 stage Delphi survey carried out via e-mail to achieve consensus as to the most effective postoperative wound management to prevent blistering and other complications. Seventeen prospective participants were invited to be members of the Delphi Panel of which 13 agreed to be involved. The panel suggested that an ideal wound dressing would conform easily to the wound, be easy to apply and remove, allow for swelling and minimise pain on removal. Participants were in agreement that the primary wound dressing should be left in situ for as long as possible, providing there was no excessive oozing or signs of infection. The authors recognise that the Delphi Panel was relatively compact; however, the study arguably provides some useful data that can be used to identify the consequences of wound blistering and important factors that need to be considered when choosing a wound dressing to prevent blistering
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Decoding Exoplanetary System Architectures: Characterizing Multi-Planet Systems and their Host Stars
No full textIn this thesis, I investigate the architectures of exoplanetary systems, from detecting and characterizing individual planets to studying population-level trends and evaluating model predictiveness and accuracy. I particularly focus on complex multi-planet systems, leveraging the common formation and evolutionary environments of planets orbiting the same star to investigate system histories. I make use of space- and ground-based observations at both optical and near-infrared wavelengths to precisely and accurately determine both planet and stellar host parameters. I also investigate the accuracy of global models of planetary system architectures, revealing for the first time that empirical models of planetary systems based on the Kepler sample are not appropriately predictive for all planetary systems. These results highlight the need for both nuanced empirical models and analytical approaches that combine the statistical power of the observed sample of exoplanets and the physics encoded in planet formation models
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Detecting and Characterizing Small Planets in Diverse Environments
No full textOur ability to detect and characterize small planets in diverse environments is expanding rapidly with the development and continued improvement of the transit and radial velocity methods. Better models, instruments, and telescopes are producing greater planet yields and tighter planetary radius and mass constraints, which in turn provide new targets for atmospheric characterization and produce new insights on planet composition, formation, and evolution. In this thesis, I present work on the characterization and mass determination of small planets with the radial velocity method, the detection of new planets via the transit method, and the study of a planet’s atmosphere through transmission spectroscopy and its implications for planet formation and planet population features.First, I report on mass estimation and characterization of the long-period exoplanet Kepler- 538b. This sub-Neptune with a period of P = 81.7 days is the only planet known to be orbiting its Sun-like star (0.892 M⊙). Simultaneously modeling Kepler photometry and radial velocities (RVs) yields a semi-amplitude of 1.68 ± 0.39 m s−1 and a planet mass of 10.6 ± 2.5 M⊕, which made Kepler-538b the smallest planet beyond P = 50 days with an RV mass measurement at the time of publication. Precise mass measurements on long-period planets will not only directly address questions about the long-period planet population, but also draw comparisons and shed light on aspects of the short-period planet population like the planetary radius occurrence gap and the impact of high stellar irradiation on exoplanet compositions and atmospheres.Next, I discuss K2-136c, a sub-Neptune with a period of P = 17.3 days and the largest of three transiting planets orbiting a late-K dwarf (0.742 M⊙) in the young Hyades open cluster (650 ± 70 Myr). Collecting and analyzing RV data from the HARPS-N and ESPRESSO spectrographs jointly with photometry from the K2 and TESS space telescopes yielded an RV semi-amplitude of 5.46 ± 0.45 m s−1 for K2-136c, corresponding to a mass of 18.0 ± 1.7 M⊕. K2-136c is now the smallest planet to have a measured mass in an open cluster and one of the youngest planets ever with a mass measurement. As a result, this system adds an important new window into young small planet compositions, atmospheric mass loss constraints around young active stars, and planetary evolution at relatively unexplored ages.I then present the TATER planet detection pipeline and apply it to high-cadence photometry of 914 known planet systems observed during TESS Cycle 3. This work has led to the new validation of 4 short-period planets. This study provides independent modeling and vetting of hundreds of planet candidates while also expanding the known planet population and providing updated transit ephemerides and planet radii.Finally, I report on the atmospheric characterization of WASP-166b, a short-period super- Neptune (P = 5.44 d, Mp = 32.1 ± 1.6 M⊕, Rp = 7.1 ± 0.3 R⊕). WASP-166b is located near the edge of the Hot Neptune Desert, a sparse region of exoplanet parameter space at high stellar irradiation and intermediate planet radii. Using transmission spectroscopy of WASP-166b (two transit observations with the James Webb Space Telescope), initial analyses show evidence of H2O and CO2; no evidence of SO2, NH3, or a cloud deck; constraints on planetary metallicity and the C/O ratio; and a plausible formation pathway that includes planetesimal accretion followed by core erosion or photoevaporation. This in turn points to mechanisms that can create substellar or stellar C/O ratios and superstellar metallicities, like photoevaporation and core erosion, as feasible components of the formation of the Hot Neptune Desert
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Discovery and Demographics of Hot Planets Orbiting Hot Stars
No full textSurveys dedicated to detecting exoplanets via the transit and radial velocity methods have revolutionized our understanding of planet formation and evolution by revealing the the prevalence of planets orbiting close to their stars. Transit surveys have been especially groundbreaking due to their abilities to discover large quantities of planets with small orbital separations, which can they be further characterized via transmission spectroscopy, emission spectroscopy, and thermal phase curve observations to reveal details about their atmospheres and surfaces. In recent years, the Transiting Exoplanet Survey Satellite (TESS) has provided the opportunity to expand these techniques into entirely new regimes, due to its ability to search for transiting planets around a greater variety of stars and around brighter stars that are more amendable to follow-up observations. This thesis focuses on the utilization of TESS data to search for and study the demographics of these planets.First, I present TRICERATOPS, a tool designed to statistically validate transiting exoplanets and identify likely astrophysical false positives in TESS data. To statistically validate a transiting exoplanet is to confirm its planetary nature by ruling out plausible false positive scenarios, such as those that arise when multiple stars are blended together in the data. This is a particularly pertinent problem for TESS, which is equipped with relatively low-resolution cameras that often cannot distinguish light originating from individual stars, especially in crowded fields. I discuss the design and efficacy of TRICERATOPS, demonstrating that it is an effective tool for identifying the most promising planet candidates detected by TESS and prioritizing follow-up observations with both ground-based and space-based telescopes.Next, I use TRICERATOPS and an array of ground-based follow-up observations to validate 13 hot and potentially terrestrial planets detected by TESS. These planets are unlike any rocky bodies in the Solar System; they orbit their stars at distances of only a few stellar radii and are so highly irradiated that many are expected to have molten surfaces. Their high temperatures also mean that they emit infrared light at levels detectable by JWST. Emission spectroscopy and thermal phase curve observations of these worlds can reveal the presence and composition of an atmosphere, measure Bond albedo, and calculate heat redistribution properties. Prior to TESS, very few of these types of planets were known around bright stars amenable to JWST observations. This sample therefore facilitates the investigation of hot Earth-size worlds at a population level.Finally, I conduct a search for planets smaller than Saturn orbiting A-type stars. A-type stars, which are roughly twice as massive and nearly twice as hot as Sun-like stars, have historically been avoided by transit and radial velocity surveys due to their large radii and rapid rotation rates, which hinder our ability to detect planets around them. As a consequence, early transit surveys like the Kepler mission acquired very little data of these stars, limiting our understanding of planet demographics to stars like the Sun and cooler. By observing all bright stars across nearly the entire sky, TESS has provided the best opportunity yet to search for small planets orbiting relatively hot stars. Through this search, I discover and validate a single planet: HD 56414 b, a Neptune-size planet orbiting one of the hottest planet-hosting stars known to date on a 29-day orbital period. The orbital period of this planet is long compared to the typical planet detected by TESS, suggesting that Neptune-size planets with smaller orbital separations may not exist around A-type stars. I display that atmospheric photoevaporation due to high levels of near-ultraviolet radiation offers one possible explanation for this phenomenon. To test this hypothesis more robustly, I calculate the occurrence rate of small planets with orbital periods under 10 days around A-type stars. I demonstrate, for the first time, that sub-Saturns and sub-Neptunes are rarer around A-type stars than they are around their cooler counterparts. I also find evidence that super-Earths are as common or less common around A-type stars than cooler stars. These results suggest that small planets are unable to form at, migrate to, or survive at the small orbital separations probed by TESS around these hot stars. Overall, these findings significantly advance our understanding of how planets form and evolve around stars hotter than the Sun, providing a more holistic picture of planetary populations throughout the galaxy
A framework for optimizing exoplanet targets for the James Webb Space Telescope
No full textThe James Webb Space Telescope (JWST) will devote a significant amount of observing time to the study of exoplanets. It will not be serviceable as was the Hubble Space Telescope, and therefore the spacecraft/instruments will have a relatively limited life. It is important to get as much science as possible out of this limited observing time. We provide an analysis framework (including a suite of computer tools) that can be used to optimize the list of exoplanet targets for atmospheric characterization. The tools take survey data from K2, TESS, or other sources; estimate planet masses as required; generate model spectra based on potential atmospheric characteristics; and then, given the capabilities of the various JWST instruments, determine an optimal target set. For a simulated survey data set of 1984 targets we categorize and rank the targets by observation time required to detect an atmosphere
A dressing method for soliton solutions of the Camassa-Holm equation
No full textThe soliton solutions of the Camassa-Holm equation are derived by the implementation of the dressing method. The form of the one and two soliton solutions coincides with the form obtained by other methods.18 pages, 2 figure
Effect of TIG-dressing on fatigue strength and weld toe geometry of butt welded connections in high strength steel
No full textWhen high strength steels are applicated in dynamically loaded structures, fatigue problems can arise. In most current design codes, the fatigue strength of high strength steels is either not discussed or determined as similar to mild steels. This assumption can be related to the dominance of the crack propagation life during in the total fatigue life when considering welded connections. Weld improvements can increase the length of the crack initiation life and thus increase the total fatigue life and may lead to a difference in fatigue strength between high strength steel and mild steels. This study focuses on the the effects of TIG-dressing on the weld toe geometry and the fatigue strength of TIG-dressed specimens. First a literature study is presented which summarizes earlier researches into the effect of TIG-dressing on fatigue strength and the behaviour of high strength steel in fatigue conditions, both in an as welded situation as after TIG-dressing. The weld toe geometry before and after TIG-dressing is determined. This leads to a extensive data set containing the geometry of the complete weld. The weld toe is then described with the aid of four parameters: weld toe radius, weld toe angle, weld height and undercut. Any influence of the static strength of the material, or any differences between rolled and cast steel are investigated. A comparison is made between the as welded specimens and TIG-dressed specimens. This changed geometry has been coupled to a changed fatigue strength with the aid of the notch stress approach. FEM analyses of the weld toe, based on measured geometries, have been carried out to determine stress concentration factors. Adjustments of the fatigue strength to account for loading mode, thickness, residual stress and mean stress have been derived from literature. A small reduction in residual stress, caused by the TIG-dressing procedure, has also been derived from literature. Fatigue tests have been carried out on 24 specimens ranging from S460 to S1100, made from both cast and rolled steels. The specimens are also adjusted for loading mode, thickness, residual stress and mean stress and compared with the developed model and a larger dataset of comparable as welded specimens. Due to the relatively small number of specimens per steel grade, a reliable quantitative fatigue strength improvement cannot be specified. A extensive qualitative analysis gives insight in the overall trends. From all used plates, hardness measurements are available, which have not been thoroughly analyzed. During the fatigue tests, crack dimensions have been determined during the crack propagation life. These measurements also have not been analyzed. Both data sets are added in annexes and are digitally available at the author or one of the members of the graduation committee.Steel StructuresStructural EngineeringCivil Engineering and Geoscience
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