This thesis describes efforts to improve the realism of numerical models of giant planet formation and migration in an attempt to better understand these processes. A new approach has been taken to the modelling of accretion, designed to mimic reality by allowing gas to accumulate upon a protoplanetary surface. Implementing this treatment in three-dimensional self-gravity radiation hydrodynamics calculations provides an excellent model for planet growth, allowing an exploration of the factors that affect accretion. Moreover, these calculations have also been extended to investigate the migration of protoplanets through their parent discs as they grow. When focusing on the growth of non-migrating protoplanets, the models are performed using small sections of disc, enabling excellent resolution right down to the core; gas structures and flow can be resolved on scales from ~ 10^4 to 10^11 metres. Using radiative transfer, these models reveal the importance of opacity in determining the accretion rates. For the low mass protoplanets, equivalent in mass to a giant planet core (~ 10 M⊕), the accretion rates were found to increase by up to an order of magnitude for a factor of 100 reduction in the grain opacity of the parent circumstellar disc. However, even these low opacities lead to growth rates that are an order of magnitude slower than those obtained in locally-isothermal conditions. For high mass protoplanets (>~ 100M⊕), the accretion rates show very little dependence upon opacity. Nevertheless, the rates obtained using radiative transfer are still lower than those obtained in locally-isothermal models by a factor of ~2, due to the release of accretion energy as heat. Only high mass protoplanets are found to be capable of developing circumplanetary discs, and this ability is dependent upon the opacity, as are the scaleheights of such discs. However, their radial extents were found to be independent of the opacity and the protoplanet mass, all reaching ≈ RH/3, inline with analytic predictions. Migration is investigated using global models, ensuring a self-consistently evolved disc. Using locally-isothermal calculations, it was found that the capture radius of an accreting sink particle, used to model a protoplanet without a surface, must be small (<< RH) to yield migration timescales consistent with linear theory of Type I migration. In the low mass regime of Type I migration, accreting sinks with such small radii yield timescales consistent with those models in which a protoplanetary surface is used. However, for high mass protoplanets, undergoing Type II migration, the surface treatment leads to faster rates of migration, indicating the importance of a realistic accretion model. Using radiative transfer, with high opacities, leads to a factor of ~ 3 increase in the migration timescale of the lowest mass protoplanets, improving their chances of survival. As suitable gas giant progenitors, their survival is key to understanding the growth of giant planets. An unexpected result of the radiative transfer was a reduction in the migration timescale of high mass planets. This appears to be a result of the less thoroughly evacuated gaps created by planets in non-locally-isothermal discs, which affects the corotation torque.

Supersonic deceleration has been identified as a critical deficiency in extending heritage technologies to the high-mass systems required to achieve long-term exploration goals at Mars. Supersonic retropropulsion (SRP), or the use of retropropulsive thrust while an entry vehicle is traveling at supersonic conditions, is an approach addressing this deficiency. The focus of this dissertation is aerodynamic and performance evaluation of SRP as a decelerator technology for high-mass Mars entry systems. This evaluation was completed through a detailed SRP performance analysis, establishment of the relationship between vehicle performance and the aerodynamic-propulsive interaction, and an assessment of the required fidelity and computational cost in simulating SRP flowfields, with emphasis on the effort required in conceptual design. Trajectory optimization, high-fidelity computational aerodynamic analysis, and analytical modeling of the SRP aerodynamic-propulsive interaction were used to define the fidelity and effort required to evaluate individual SRP concepts across multiple mission scales.

Hållbarhet är ett viktigt koncept i dagens samhälle där TBL teorin blivit allt mer använd av företag. TBL teorin är uppdelad i tre perspektiv, people, planet och profit. Digitaliseringen av revisionsbranschen har på senare tid genomgått stora förändringar. Informations och kommunikationsteknologier (IKT) är ett område inom digitalisering som används flitigt inom revision. Frågan om IKT påverkar revisorns hållbara arbete utifrån TBL teorin har vi inte funnit någon forskning om. För att undersöka syftet med studien har en kvantitativ ansats applicerats och data har samlats in via en webbaserad enkätundersökning vilket revisorer och revisorsassistenter på olika revisionsbyråer deltagit i. Enkätens frågor formulerades utifrån den beroende variabeln revisorns hållbara arbete och den oberoende variabeln IKT. Enkäten undersökte även fyra kontrollvariabler. Resultatet från studien visar på att IKT har en positiv påverkan på revisorns hållbara arbete. Inga kontrollvariabler påverkar sambandet mellan IKT och revisorns hållbara arbete. Dessutom anser revisorer att people, planet och profit är viktiga begrepp och arbetar mycket med samtliga. Profit anses dock vara viktigast och planet anses vara minst viktig. Tidsramen för att slutföra studien och revisorernas högsäsong har begränsat enkätens svarsfrekvens. Detta är något som framtida forskning bör ha i åtanke för att kunna undersöka ämnet ytterligare. / Sustainability is an important concept within today’s society whereas the TBL theory has become increasingly useful by companies. The TBL theory is divided into three perspectives which are people, planet and profit. Lately digitalization of the accounting profession has been through some big changes. Information and communication technologies (ICT) is a field within digitalization that is used diligently within audit. The question if ICT effects the auditors sustainable work using the TBL theory is something that we have not found any research about. To examine the purpose of the study a quantitative approach has been applicated and data has been collected using an online survey that auditors and auditor assistants on different firms has been a part of. The surveys questions were formulated from the dependent variable, the audits sustainable work and the independent variable, ICT. The survey also examined four control variables. The result from the study showed that ICT has a positive effect on the auditors´ sustainable work. Where no control variables effected the correlation between ICT and the auditors´ sustainable work. The auditors also consider people, planet and profit to be important concepts and works a lot with all of them. Profit, however, is considered the most important and planet is considered the least important. The time frame to finish the study and the peak season for auditors has limited the surveys response rate. This is something that future research should consider to be able to investigate the subject further.

This master thesis investigates the integration of stakeholder analysis into the Double Materiality Assessment (DMA) for green industries, with a particular focus on its relevance within the framework of the Corporate Sustainability Reporting Directive (CSRD). With a deadline for compliance by large companies operating in the European Union by 2025, urgency surrounds the need to comprehensively understand the Impacts, Risks and Opportunities (IROs). The study centers on H2 Green Steel (H2GS), a pioneering green industry in Sweden, to examine two of its key stakeholders, the society and the planet. As a silent stakeholder, the planet requires a unique approach within the DMA process. By utilizing action research methodology, stakeholders representing society and the planet are studied, offering insights that can be applied as a model for other companies undertaking similar assessments. Through a combination of data collection methods including mapping H2GS’s value chain, conducting semi-structured interviews, and utilising stakeholder analysis tools, such a power-interest grid, the study identifies key stakeholders and assesses their relationships with the company. Additionally, the study evaluates IROs related to the planet through a comparative analysis of methods outlined by the DMA guideline, ensuring comprehensivecoverage of the silent stakeholder’s perspective. The findings underscore the critical role ofcivil society stakeholders, particularly in the context of large industries within small communities. Continuous dialogue is essential for integrating societal perspectives into corporate strategies. Moreover, for planetary stakeholders, a multifaceted approach combining global research, local assessments, engagement with proxy organizations, and validation by expert groups is recommended to ensure a comprehensive understanding of related IROs. Engagement with indigenous communities, such as the Sámi in Sweden, is emphasized to address social implications effectively. In conclusion, this study underscores the importance of stakeholder engagement in the DMA process, offering insights and methodologies that can aidcompanies in assessing their impacts comprehensively, thereby contributing to corporatesustainability and regulatory compliance. / Denna masteruppsats undersöker integrationen av intressentanalys i Double Materiality Assessment (DMA) för gröna industrier, med särskilt fokus på dess relevans inom ramen för Corporate Sustainability Reporting Directive (CSRD). Med en deadline för efterlevnad av stora företag som är verksamma i Europeiska unionen senast 2025, är det ett brådskande behov av att på ett heltäckande sätt förstå Impacts, Risks and Opportunities (IROs). Studien fokuserar på H2 Green Steel (H2GS), en banbrytande grön industri i Sverige, för att undersöka två av dess viktigaste intressenter, samhälle och planet. Som en tyst intressent kräver planeten ett unikt tillvägagångssätt inom DMA-processen. Genom att använda aktionsforskningsmetodik studeras intressenter som representerar samhället och planeten, vilket ger insikter som kan användas som modell för andra företag som gör liknande bedömningar. Genom en kombination av datainsamlingsmetoder inklusive kartläggning av H2GS värdekedja, genomförande av semistrukturerade intervjuer och utnyttjande av analysverktyg för intressenter, såsom ett kraftnät, identifierar studien nyckelintressenter och bedömer deras relationer med företaget. Dessutom utvärderar studien IROs relaterade till planeten genom en jämförande analys av metoder som beskrivs i DMA-riktlinjen, vilket säkerställer en omfattande täckning av den tysta intressentens perspektiv. Resultaten understryker den avgörande roll som det civila samhällets intressenter spelar, särskilt i samband med stora industrier inom små samhällen. En kontinuerlig dialog är väsentlig för att integrera samhällsperspektiv i företagsstrategier. Dessutom, för planetära intressenter, rekommenderas ett mångfacetterat tillvägagångssätt som kombinerar global forskning, lokala bedömningar, engagemang med proxyorganisationer och validering av expertgrupper för att säkerställa en heltäckande förståelse av relaterade IROs. Engagemang med ursprungsbefolkningar, såsom samerna i Sverige, betonas för att effektivt kunna hantera sociala konsekvenser. Sammanfattningsvis understryker denna studie vikten av intressenternas engagemang i DMA-processen, och erbjuder insikter och metoder som kan hjälpa företag att bedöma deras effekter på ett heltäckande sätt, och därmed bidra till företagens hållbarhet och regelefterlevnad.

No description available.

I have carried out three-dimensional numerical simulations of self-gravitating discs to determine under what circumstances they fragment to form bound clumps that may grow into giant planets. Through radiation hydrodynamical simulations using a Smoothed Particle Hydrodynamics code, I find that the disc opacity plays a vital role in determining whether a disc fragments. Specifically, opacities that are smaller than interstellar Rosseland mean values promote fragmentation (even at small radii, R &lt; 25AU) since low opacities allow a disc to cool quickly. This may occur if a disc has a low metallicity or if grain growth has occurred. Given that the standard core accretion model is less likely to form planets in a low metallicity environment, I predict that gravitational instability is the dominant planet formation mechanism in a low metallicity environment. In addition, I find that the presence of stellar irradiation generally acts to inhibit fragmentation (since the discs can only cool to the temperature defined by stellar irradiation). However, fragmentation may occur if the irradiation is sufficiently weak that it allows the disc to attain a low Toomre stability parameter. With specific reference to the HR 8799 planetary system, I find that it is only possible for fragments to form in the radial range where the HR 8799 planets are located (approximately 24-68 AU) if the disc is massive. In such a high mass regime, mass transport occurs in the disc causing the surface mass density to alter. Therefore, fragmentation is not only affected by the disc temperature and cooling, but also by any restructuring due to the gravitational torques. The high mass discs also pose a problem for the formation of this system because the protoplanets accrete from the disc and end up with masses greater than those inferred from observation and thus, the growth of planets would need to be inhibited. In addition, I find that further subsequent fragmentation at small radii also takes place. By way of analytical arguments in combination with hydrodynamical simulations using a parameterised cooling method, I explore the fragmentation criteria which in the past, has placed emphasis on the cooling timescale in units of the orbital timescale, beta. I find that at a given radius the surface mass density (i.e. disc mass and profile) and star mass also play a crucial role in determining whether a disc fragments or not as well as where in the disc fragments form. I find that for shallow surface mass density profiles (p&lt;2, where the surface mass density is proportional to R^{-p}), fragments form in the outer regions of the disc. However for steep surface mass density profiles (p is greater than or similar to 2), fragments form in the inner regions of a disc. In addition, I find that the critical value of the cooling timescale in units of the orbital timescale, beta_crit, found in previous simulations is only applicable to certain disc surface mass density profiles and for particular disc radii and is not a general rule for all discs. I obtain an empirical fragmentation criteria between the cooling timescale in units of the orbital timescale, beta, the surface mass density, the star mass and the radius. Finally, I carry out crucial resolution testing by performing the highest resolution disc simulations to date. My results cast some serious doubts on previous conclusions concerning fragmentation of self-gravitating discs.

The Planet Formation Imager (PFI) project aims to provide a strong scientific vision for ground-based optical astronomy beyond the upcoming generation of Extremely Large Telescopes. We make the case that a breakthrough in angular resolution imaging capabilities is required in order to unravel the processes involved in planet formation. PFI will be optimised to provide a complete census of the protoplanet population at all stellocentric radii and over the age range from 0.1 to similar to 100 Myr. Within this age period, planetary systems undergo dramatic changes and the final architecture of planetary systems is determined. Our goal is to study the planetary birth on the natural spatial scale where the material is assembled, which is the "Hill Sphere" of the forming planet, and to characterise the protoplanetary cores by measuring their masses and physical properties. Our science working group has investigated the observational characteristics of these young protoplanets as well as the migration mechanisms that might alter the system architecture. We simulated the imprints that the planets leave in the disk and study how PFI could revolutionise areas ranging from exoplanet to extragalactic science. In this contribution we outline the key science drivers of PFI and discuss the requirements that will guide the technology choices, the site selection, and potential science/technology tradeoffs.

Context. HR4796A is surrounded by a debris disc, observed in scattered light as an inclined ring with a high surface brightness. Past observations have raised several questions. First, a strong brightness asymmetry detected in polarised reflected light has recently challenged our understanding of scattering by the dust particles in this system. Secondly, the morphology of the ring strongly suggests the presence of planets, although no planets have been detected to date. Aims. We aim here at measuring with high accuracy the morphology and photometry of the ring in scattered light, in order to derive the phase function of the dust and constrain its near-infrared spectral properties. We also want to constrain the presence of planets and set improved constraints on the origin of the observed ring morphology. Methods. We obtained high-angular resolution coronagraphic images of the circumstellar environment around HR4796A with VLT/SPHERE during the commissioning of the instrument in May 2014 and during guaranteed-time observations in February 2015. The observations reveal for the first time the entire ring of dust, including the semi-minor axis that was previously hidden either behind the coronagraphic spot or in the speckle noise. Results. We determine empirically the scattering phase function of the dust in the H band from 13.6 degrees to 166.6 degrees. It shows a prominent peak of forward scattering, never detected before, for scattering angles below 30 degrees. We analyse the reflectance spectra of the disc from the 0.95 mu m to 1.6 mu m, confirming the red colour of the dust, and derive detection limits on the presence of planetary mass objects. Conclusions. We confirm which side of the disc is inclined towards the Earth. The analysis of the phase function, especially below 45 degrees, suggests that the dust population is dominated by particles much larger than the observation wavelength, of about 20 mu m. Compact Mie grains of this size are incompatible with the spectral energy distribution of the disc, however the observed rise in scattering efficiency beyond 50 degrees points towards aggregates which could reconcile both observables. We do not detect companions orbiting the star, but our high-contrast observations provide the most stringent constraints yet on the presence of planets responsible for the morphology of the dust.

No description available.

In the coming years, high-contrast imaging surveys are expected to reveal the characteristics of the population of wide-orbit, massive, exoplanets. To date, a handful of wide planetary mass companions are known, but only one such multi-planet system has been discovered: HR 8799. For low mass planetary systems, multi-planet interactions play an important role in setting system architecture. In this paper, we explore the stability of these high mass, multi-planet systems. While empirical relationships exist that predict how system stability scales with planet spacing at low masses, we show that extrapolating to super-Jupiter masses can lead to up to an order of magnitude overestimate of stability for massive, tightly packed systems. We show that at both low and high planet masses, overlapping mean-motion resonances trigger chaotic orbital evolution, which leads to system instability. We attribute some of the difference in behavior as a function of mass to the increasing importance of second order resonances at high planet-star mass ratios. We use our tailored high mass planet results to estimate the maximum number of planets that might reside in double component debris disk systems, whose gaps may indicate the presence of massive bodies.