10,843 research outputs found
UMSL Bulletin 2023-2024
The 2023-2024 Bulletin and Course Catalog for the University of Missouri St. Louis.https://irl.umsl.edu/bulletin/1088/thumbnail.jp
The terminator region of tidally locked M-dwarf exoplanets in 3-d general circulation models
The impressive sensitivity of the James Webb Space Telescope has made it possible to
study the atmospheres of planets beyond the solar system. It will soon be followed by space
missions aiming specifically at this goal, such as the Ariel mission, Twinkle, and the Habitable
Worlds Observatory. One category of exoplanet has drawn interest because of its potential
to harbour temperate climates with liquid surface waterâand therefore potentially life. These
are rocky planets orbiting cool M-class stars, or "M-Earths." Stellar population trends and
observing biases lead to a high proportion of potentially habitable, terrestrial planets falling
into this category. Because of the low temperatures of their host stars, however, habitable
worlds of this type are found in close orbits where they are likely to be tidally locked. As the
solar system has no tidally locked planets, our knowledge of their atmospheric circulation is
currently limited to theoretical modelling.
Past modelling work has shown that the asymmetrical irradiation of tidally locked planets
results in characteristic circulation regimes which have profound consequences for observations. Atmospheric retrievals, which use statistical methods to fit 1-D atmospheric models
to observational data and quantify the confidence of the fit, are not yet able to account for
the 3-D nature of this circulation. For planets with large spatial variation in environmental
conditions caused by tidal locking, 1-D models are not able to capture the differences and
interconnections between planetary regions such as the dayside, nightside, and planetary
limb or terminator. In addition, planetary atmospheres exhibit variation over time, potentially
resulting in differences in retrieved properties between observing visits or even between
different phases of a planetâs orbit. Accounting for 4-D circulation effects in atmospheric
retrievals first requires a theoretical understanding of the impact of global-scale phenomena
such as atmospheric waves and horizontal transport on conditions at the planetary limb, and
then requires incorporation of this knowledge into the retrieval pipeline in the form of, for
example, parameterisations.
In this thesis, I address the first requirement: the theoretical understanding of the effects
of fully modelled 4-D atmospheric circulation on the planetary limb, the region probed by
transmission spectroscopy, on tidally locked planets. I focus in particular on effects caused by
the global propagation of atmospheric waves and by horizontal transport of clouds and hazes.
In Chapter 2, I show that that the atmospheric dynamics on the tidally locked Proxima Centauri
b support a longitudinally asymmetric stratospheric wind oscillation (LASO), analogous to
Earthâs quasi-biennial oscillation (QBO). The LASO has a vertical extent of 35â55 km, a
period of 5â6.5 months, and a peak-to-peak wind speed amplitude of -70 to +130 msâ1
with a maximum at an altitude of 41 km. Unlike the QBO, the LASO displays longitudinal
asymmetries related to the asymmetric thermal forcing of the planet and to interactions with
the resulting stationary Rossby waves. The equatorial gravity wave sources driving the LASO
are localised in the deep convection region at the substellar point and in a jet exit region
near the western terminator, unlike the QBO, for which these sources are distributed uniformly
around the planet. Longitudinally, the western terminator experiences the highest wind speeds
and undergoes reversals earlier than other longitudes. The antistellar point only experiences a
weak oscillation with a very brief, low-speed westward phase. The QBO on Earth is associated
with fluctuations in the abundances of water vapour and trace gases such as ozone which
are also likely to occur on exoplanets if these gases are present. Strong fluctuations in
temperature and the abundance of atmospheric species at the terminators will need to be
considered when interpreting atmospheric observations of tidally locked exoplanets.
In Chapter 3, I investigate the presence of cloud cover at the planetary limb of water-rich Earth-like planets, which is likely to weaken chemical signatures in transmission spectra and impede
attempts to characterise these atmospheres. Based on observations of Earth and solar system worlds, exoplanets with atmospheres should have both short-term weather and long-term
climate variability, implying that cloud cover may be less during some observing periods. I
identify and describe a mechanism driving periodic clear sky events at the terminators in
simulations of tidally locked Earth-like planets. A feedback between dayside cloud radiative
effects, incoming stellar radiation and heating, and the dynamical state of the atmosphere,
especially the zonal wavenumber-1 Rossby wave identified in past work on tidally locked
planets, leads to oscillations in Rossby wave phase speeds and in the position of Rossby
gyres and results in advection of clouds to or away from the planetâs eastern terminator. I
study this oscillation in simulations of Proxima Centauri b, TRAPPIST 1-e, and rapidly rotating
versions of these worlds located at the inner edge of their starsâ habitable zones. I simulate
time series of the transit depths of the 1.4 ”m water feature and 2.7 ”m carbon dioxide
feature. The impact of atmospheric variability on the transmission spectra is sensitive to the
structure of the dayside cloud cover and the location of the Rossby gyres, but none of my
simulations have variability significant enough to be detectable with current methods.
In Chapter 4, I study the interaction between the atmospheric circulation and photochemical
hazes and describe the resulting haze abundances at the terminator. Transmission spectroscopy supports the presence of unknown, light-scattering aerosols in the atmospheres
of many exoplanets. The complexity of factors influencing the formation, 3-D transport, radiative impact, and removal of aerosols makes it challenging to match theoretical models
to the existing data. My study simplifies these factors to focus on the interaction between
planetary general circulation and haze distribution at the planetary limb. I use an intermediate
complexity general circulation model, ExoPlaSim, to simulate idealised organic haze particles
as radiatively active tracers in the atmospheres of tidally locked terrestrial planets for a range
of rotation rates. I find three distinct 3-D spatial haze distributions, corresponding to three
circulation regimes, each with a different haze profile at the limb. All regimes display significant
terminator asymmetry. In my parameter space, super-Earth-sized planets with rotation periods
greater than 13 days have the lowest haze optical depths at the terminator, supporting the
choice of slower rotators as observing targets.
My thesis supports the existence of characteristic forms of temporal and spatial variability on
tidally locked planets which will undoubtedly impact observations and inform our understanding of climate conditions on the surface. Overall, the effects of purely dynamical variability may
be too small to be detected for Earth-like planets (but potentially detectable for larger ones).
The impact of the atmospheric circulation on the distribution of clouds and hazes, on the other
hand, is likely to affect even observations of terrestrial planets due to the highly scattering
nature of these aerosols and will need to be accounted for in atmospheric retrievals
UMSL Bulletin 2022-2023
The 2022-2023 Bulletin and Course Catalog for the University of Missouri St. Louis.https://irl.umsl.edu/bulletin/1087/thumbnail.jp
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The impact of enterprise social networking on knowledge sharing between academic staff in higher education
This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonHigher education institutions have always considered knowledge sharing critical for research excellence and finding proper methods for sharing knowledge across academic staff has therefore been a major issue for universities and knowledge management research. Recent evidence shows that many universities have embraced enterprise social networking tools to improve communication, relationships, partnerships, and knowledge sharing. To date, there is little understanding of the critical factors for online knowledge sharing behaviour between academic staff, and the impact of these factors on work benefits for academic staff which differ between consumptive users and contributive users in higher education. This study employed the extended unified theory of acceptance and use of technology (UTAUT) to examine factors affecting knowledge sharing about the consumptive use and contributive use of enterprise social network (ESN) behaviour. The study adopts a critical realism philosophical approach and employed a grounded theory mixed methods. The conceptual model was validated through structural equation modelling based on an online survey of 254 academic staff using enterprise social networking as a part of their work in the United Kingdom. The findings have significant theoretical and practical implications for researchers and policy makers. The research has developed a cohesive ESN use model by extending and modifying the unified theory of acceptance and use of technology. The findings indicate significant differences around factors affecting consumptive and contributive usage patterns within ESNs. Due to advances in communication technologies, this research argues that a previous model suggested by Venkatesh et al. (2003) is no longer fit for purpose and the new communication tools can lead to improved knowledge in higher education. This research also makes valuable contributions to universities from a managerial viewpoint, suggesting that universities could help their scholars find a more comprehensive range of funding sources matching scholars' ideas
TOWARD AUTOMATED THREAT MODELING BY ADVERSARY NETWORK INFRASTRUCTURE DISCOVERY
Threat modeling can help defenders ascertain potential attacker capabilities and resources, allowing better protection of critical networks and systems from sophisticated cyber-attacks. One aspect of the adversary profile that is of interest to defenders is the means to conduct a cyber-attack, including malware capabilities and network infrastructure. Even though most defenders collect data on cyber incidents, extracting knowledge about adversaries to build and improve the threat model can be time-consuming. This thesis applies machine learning methods to historical cyber incident data to enable automated threat modeling of adversary network infrastructure. Using network data of attacker command and control servers based on real-world cyber incidents, specific adversary datasets can be created and enriched using the capabilities of internet-scanning search engines. Mixing these datasets with data from benign or non-associated hosts with similar port-service mappings allows for building an interpretable machine learning model of attackers. Additionally, creating internet-scanning search engine queries based on machine learning model predictions allows for automating threat modeling of adversary infrastructure. Automated threat modeling of adversary network infrastructure allows searching for unknown or emerging threat actor network infrastructure on the Internet.Major, Ukrainian Ground ForcesApproved for public release. Distribution is unlimited
Computational reproducibility of Jupyter notebooks from biomedical publications
Jupyter notebooks facilitate the bundling of executable code with its
documentation and output in one interactive environment, and they represent a
popular mechanism to document and share computational workflows. The
reproducibility of computational aspects of research is a key component of
scientific reproducibility but has not yet been assessed at scale for Jupyter
notebooks associated with biomedical publications. We address computational
reproducibility at two levels: First, using fully automated workflows, we
analyzed the computational reproducibility of Jupyter notebooks related to
publications indexed in PubMed Central. We identified such notebooks by mining
the articles full text, locating them on GitHub and re-running them in an
environment as close to the original as possible. We documented reproduction
success and exceptions and explored relationships between notebook
reproducibility and variables related to the notebooks or publications. Second,
this study represents a reproducibility attempt in and of itself, using
essentially the same methodology twice on PubMed Central over two years. Out of
27271 notebooks from 2660 GitHub repositories associated with 3467 articles,
22578 notebooks were written in Python, including 15817 that had their
dependencies declared in standard requirement files and that we attempted to
re-run automatically. For 10388 of these, all declared dependencies could be
installed successfully, and we re-ran them to assess reproducibility. Of these,
1203 notebooks ran through without any errors, including 879 that produced
results identical to those reported in the original notebook and 324 for which
our results differed from the originally reported ones. Running the other
notebooks resulted in exceptions. We zoom in on common problems, highlight
trends and discuss potential improvements to Jupyter-related workflows
associated with biomedical publications.Comment: arXiv admin note: substantial text overlap with arXiv:2209.0430
La traduzione specializzata allâopera per una piccola impresa in espansione: la mia esperienza di internazionalizzazione in cinese di Bioretics© S.r.l.
Global markets are currently immersed in two all-encompassing and unstoppable processes: internationalization and globalization. While the former pushes companies to look beyond the borders of their country of origin to forge relationships with foreign trading partners, the latter fosters the standardization in all countries, by reducing spatiotemporal distances and breaking down geographical, political, economic and socio-cultural barriers. In recent decades, another domain has appeared to propel these unifying drives: Artificial Intelligence, together with its high technologies aiming to implement human cognitive abilities in machinery. The âLanguage Toolkit â Le lingue straniere al servizio dellâinternazionalizzazione dellâimpresaâ project, promoted by the Department of Interpreting and Translation (ForlĂŹ Campus) in collaboration with the Romagna Chamber of Commerce (ForlĂŹ-Cesena and Rimini), seeks to help Italian SMEs make their way into the global market. It is precisely within this project that this dissertation has been conceived. Indeed, its purpose is to present the translation and localization project from English into Chinese of a series of texts produced by Bioretics© S.r.l.: an investor deck, the company website and part of the installation and use manual of the Aliquis© framework software, its flagship product. This dissertation is structured as follows: Chapter 1 presents the project and the company in detail; Chapter 2 outlines the internationalization and globalization processes and the Artificial Intelligence market both in Italy and in China; Chapter 3 provides the theoretical foundations for every aspect related to Specialized Translation, including website localization; Chapter 4 describes the resources and tools used to perform the translations; Chapter 5 proposes an analysis of the source texts; Chapter 6 is a commentary on translation strategies and choices
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