From space to ground: planetary atmospheres revealed through a machine learning approach

In recent years, the study of exoplanetary atmospheres has flourished well beyond expectations. Current data are unveiling the key properties of hot massive planets orbiting very close to their stars, but sometimes results are not easy to interpret due to systematics affecting the data and degeneracies across the parameter space. The focus of my thesis is the study of exoplanetary atmospheres through spectroscopic observations using space and ground-based observatories. The first part of the thesis describes the development of a new pipeline to analyse the low-resolution exoplanet data recorded with the WFC3 (Wide Field Camera 3) on-board the Hubble Space Telescope (HST). The focus is on a particular dataset: HAT-P-32b which is one of the most inflated Hot-Jupiters to date. Two different approaches are presented: a more standard parametric method and the use of a machine learning technique such as independent component analysis (ICA) applied for the first time on HST dataset. Water vapour and possibly more exotic metaloxides such as VO and TiO are found in the atmosphere of HAT-P-32b. Further observations at longer wavelengths are needed to confirm these and other chemical compounds. The second part describes the development of a new pipeline to analyse high resolution datasets recorded with ground based instruments (VLT/CRIRES, TNG/GIANO-B). High-resolution spectroscopy (HRS) allows to resolve molecular bands into individual lines. Using radial velocity measurements and techniques such as Cross-Correlation Function, it is possible to separate three physically different sources: telluric absorption, stellar absorption and planetary transmission spectrum, which are normally entangled. The standard method used in the literature to analyse HRS data consists on applying corrections for the airmass and for the stellar signal and the use of ad-hoc masks to eliminate residual, strong features. The analysis method that I have developed is based on a novel use of Principal Component Analysis (PCA) that aims to maximise the planetary signal without any manual corrections. The two approaches are highly complementary and may be used to constrain the thermal structure and the composition of the planetary atmosphere

Revisiting Size-Based Scheduling with Estimated Job Sizes

We study size-based schedulers, and focus on the impact of inaccurate job size information on response time and fairness. Our intent is to revisit previous results, which allude to performance degradation for even small errors on job size estimates, thus limiting the applicability of size-based schedulers. We show that scheduling performance is tightly connected to workload characteristics: in the absence of large skew in the job size distribution, even extremely imprecise estimates suffice to outperform size-oblivious disciplines. Instead, when job sizes are heavily skewed, known size-based disciplines suffer. In this context, we show -- for the first time -- the dichotomy of over-estimation versus under-estimation. The former is, in general, less problematic than the latter, as its effects are localized to individual jobs. Instead, under-estimation leads to severe problems that may affect a large number of jobs. We present an approach to mitigate these problems: our technique requires no complex modifications to original scheduling policies and performs very well. To support our claim, we proceed with a simulation-based evaluation that covers an unprecedented large parameter space, which takes into account a variety of synthetic and real workloads. As a consequence, we show that size-based scheduling is practical and outperforms alternatives in a wide array of use-cases, even in presence of inaccurate size information.Comment: To be published in the proceedings of IEEE MASCOTS 201

Examination of the seepage face boundary condition in subsurface and coupled surface/subsurface hydrological models

A seepage face is a nonlinear dynamic boundary that strongly affects pressure head distributions, water table fluctuations, and flow patterns. Its handling in hydrological models, especially under complex conditions such as heterogeneity and coupled surface/subsurface flow, has not been extensively studied. In this paper, we compare the treatment of the seepage face as a static (Dirichlet) versus dynamic boundary condition, we assess its resolution under conditions of layered heterogeneity, we examine its interaction with a catchment outlet boundary, and we investigate the effects of surface/subsurface exchanges on seepage faces forming at the land surface. The analyses are carried out with an integrated catchment hydrological model. Numerical simulations are performed for a synthetic rectangular sloping aquifer and for an experimental hillslope from the Landscape Evolution Observatory. The results show that the static boundary condition is not always an adequate stand-in for a dynamic seepage face boundary condition, especially under conditions of high rainfall, steep slope, or heterogeneity; that hillslopes with layered heterogeneity give rise to multiple seepage faces that can be highly dynamic; that seepage face and outlet boundaries can coexist in an integrated hydrological model and both play an important role; and that seepage faces at the land surface are not always controlled by subsurface flow. The paper also presents a generalized algorithm for resolving seepage face outflow that handles heterogeneity in a simple way, is applicable to unstructured grids, and is shown experimentally to be equivalent to the treatment of atmospheric boundary conditions in subsurface flow models

ExoReL^R: A Bayesian Inverse Retrieval Framework for Exoplanetary Reflected Light Spectra

The high-contrast imaging technique is meant to provide insight into those planets orbiting several astronomical units from their host star. Space missions such as Wide-Field InfraRed Survey Telescope, Habitable Exoplanet Imaging Mission, and Large Ultra-Violet/Optical/InfraRed Surveyor will measure reflected light spectra of cold gaseous and rocky planets. To interpret these observations, we introduce EXOREL^R (Exoplanetary Reflected Light Retrieval), a novel Bayesian retrieval framework to retrieve cloud properties and atmospheric structures from exoplanetary reflected light spectra. As a unique feature, it assumes a vertically nonuniform volume mixing ratio (VMR) profile of water and ammonia, and uses it to construct cloud densities. In this way, clouds and molecular mixture ratios are consistent. We apply EXOREL^R on three test cases: two exoplanets (υ And e and 47 Uma b) and Jupiter. We show that we are able to retrieve the concentration of methane in the atmosphere, and estimate the position of clouds when the signal-to-noise ratio of the spectrum is higher than 15, in line with previous works. Moreover, we described the ability of our model to give a chemical identity to clouds, and we discussed whether or not we can observe this difference in the planetary reflection spectrum. Finally, we demonstrate how it could be possible to retrieve molecular concentrations (water and ammonia in this work) below the clouds by linking the nonuniform VMR profile to the cloud presence. This will help to constrain the concentration of water and ammonia unseen in direct measurements

A Novel Highly Integrated Hybrid Energy Storage System for Electric Propulsion and Smart Grid Applications

This chapter addresses potentialities and advantages of a highly integrated hybrid energy storage system (HESS) for electric propulsion and smart grids. This configuration consists of a highly integrated battery-ultracapacitor system (HIBUC) and aims to benefit from the advantages of both passive and active HESS configurations. Particularly, the integration of the ultracapacitor module (UM) within the DC-link of the DC/AC multilevel converter enables the decoupling between DC-link voltage and energy content without the need for any additional DC/DC converter. As a result, HIBUC benefits from simplicity and energy flow management capabilities very similar to those achieved by passive and active HESS configurations, respectively. This is highlighted properly by a theoretical analysis, which also accounts for a comparison between HIBUC and both passive and active HESS configurations. Some HIBUC application examples are also reported, which highlight the flexibility and potentialities of HIBUC for both electric propulsion systems and smart grids

A Statistical Approach for Modeling the Aging Effects in Li-Ion Energy Storage Systems

This paper presents a novel approach for the technical and economic assessment of Li-ion battery energy storage systems (BESS) in smart grids supported by renewable energy sources. The approach is based on the definition of a statistical battery degradation cost model (SBDCM), able to estimate the expected costs related to BESS aging, according to the statistical properties of its expected cycling patterns. This new approach can improve the assessment of the economical sustainability of BESSs in this kind of applications, helping in this way the planning processes in electricity infrastructures in presence of high penetration of intermittent renewable energy sources. The SBDCM proposed in this paper is a statistical generalization of a battery degradation model presented in the literature. The proposed approach has been validated numerically comparing the results with those of the deterministic model considering for the BESS a stochastic dataset of input signals. In order to test the usefulness of the proposed model in a real world application, the proposed SBDCM has been applied to the evaluation of the economic benefit associated to the development of distributed energy storage system scenarios in the Italian power system, aimed to provide ancillary services for supporting electricity market

Reflected spectroscopy of small exoplanets III: probing the UV band to measure biosignature gasses

Direct-imaging observations of terrestrial exoplanets will enable their atmospheric characterization and habitability assessment. Considering the Earth, the key atmospheric signatures for the biosphere is O$_2$ and the photochemical product O$_3$. However, this O$_2$-O$_3$ biosignature is not detectable in the visible wavelengths for most of the time after the emergence of oxygenic photosynthesis life (i.e., the Proterozoic Earth). Here we demonstrate spectroscopic observations in the ultraviolet wavelengths for detecting and characterizing O$_2$ and O$_3$ in Proterozoic Earth-like planets, using ExoReL$^\Re$. For an O$_2$ mixing ratio 2 to 3 orders of magnitude less than the present-day Earth, and an O$_3$ mixing ratio of $10^{-7}-10^{-6}$, we find that O$_3$ can be detected and its mixing ratio can be measured precisely (within $~1$ order of magnitude) in the ultraviolet ($0.25-0.4\ \mu$m) in addition to visible-wavelength spectroscopy. With modest spectral resolution ($R=7$) and S/N ($\sim10$) in the ultraviolet, the O$_3$ detection is robust against other potential gases absorbing in the ultraviolet (e.g., H$_2$S and SO$_2$), as well as the short-wavelength cutoff between 0.2 and 0.25 $\mu$m. While the O$_3$ detection does not rely on the near-infrared spectra, extending the wavelength coverage to the near-infrared ($1-1.8\ \mu$m) would provide essential information to interpret the O$_3$ biosignature, including the mixing ratio of H$_2$O, the cloud pressure, as well as the determination of the dominant gas of the atmosphere. The ultraviolet and near-infrared capabilities should thus be evaluated as critical components for future missions aiming at imaging and characterizing terrestrial exoplanets, such as the Habitable Worlds Observatory.Comment: 13 pages, 8 figures, 3 tables, accepted for publication in A

Construcciones discursivas en torno al prejuicio, racismo y discriminación en el marco de la inmigración latinoamericana contemporánea a Uruguay

En el siguiente estudio se busca conocer construcciones discursivas en torno a prejuicio, racismo y discriminación relacionados con la movilidad reciente de personas de origen latinocaribeño hacia Uruguay. Para ello se realiza una aproximación teórico-metodológica desde el Socioconstruccionismo y la Psicología Discursiva. Entendemos discurso (habla y textos) como una práctica social constituida, situada y constructiva de relaciones y versiones de realidades en contextos argumentativos configurados por los grupos involucrados en el proceso migratorio. Se espera obtener repertorios interpretativos y construcciones de versiones de mundo emergentes de tres espacios de producción discursiva. En primer lugar, las construcciones sobre prejuicio, racismo y discriminación desplegadas por las propias personas en movilidad que actualmente residen en Uruguay. A continuación, aquellas producciones resultado del encuentro en espacios sociales e institucionales (trabajo, en servicio de salud, educación). Por último, interesa las producciones discursivas que se inscriben en el espacio de apoyo y acompañamiento al Migrante. (ONGS, Grupos de inmigrantes, Oficinas de apoyo al migrante) Se utiliza habla transcrita producto de conversaciones obtenidas de entrevistas en profundidad, que abarcan informantes claves tanto de nacionales uruguayos como personas de origen latinocaribeño en el proceso migratorio actual. Los resultados obtenidos esperan contribuir con el conocimiento de cómo los discursos como prácticas sociales operan construyendo versiones de mundo y modos de subjetivación. Asimismo, se espera que la producción de dicho conocimiento pueda ser útil para definir políticas públicas pertinentes que garanticen el cumplimiento de derechos y para diseñar estrategias que permitan una comprensión actualizada del fenómeno psicosocial estudiado.The following study seeks to know discursive constructions around prejudice, racism and discrimination related to the recent mobility of people of Latin American origin to Uruguay. To do this, a theoretical-methodological approach is made from Socioconstructionism and Discursive Psychology. We understand discourse (speech and texts) as a constituted, situated and constructive social practice of relationships and versions of realities in argumentative contexts configured by the groups involved in the migratory process. It is expected to obtain interpretative repertoires and constructions of emerging world versions of three spaces of discursive production. In the first place, the constructions on prejudice, racism and discrimination deployed by the very people in mobility that currently reside in Uruguay. Then those productions resulting from the meeting in social and institutional spaces (work, health service providers, education). Finally, it is interesting the discursive constructions of actors that work directly on the issue of migration (NGOs, Groups of immigrants, Offices of support to the migrant) Transcribed speech is used as a result of conversations obtained from in-depth interviews, which include key informants from both Uruguayan nationals and people of Latin American origin in the current migratory process. The results obtained hope to contribute with the knowledge of how discourses as social practices operate by building world versions and modes of subjectivation. It is also expected that the production of such knowledge can be useful to define relevant public policies that guarantee the fulfillment of rights and to design strategies that allow an updated understanding of the psychosocial phenomenon studied