Recent large-scale mapping of dust continuum emission from star-forming clouds has revealed their hierarchical nature, which includes web-like filamentary structures that often harbor clumpy over-densities where new stars form. Understanding the motions of these structures and how they interact to form stars, however, can only be learned through observations of emission from their molecular gas. Observations of tracers such as ammonia (NH3), in particular, reveal the stability of dense gas structures against forces such as the inward pull of gravity and the outward push of their internal pressure, thus providing insights into whether or not those structures are likely to form stars in the future. Due to recent large-scale ammonia surveys that have mapped both nearby and distant clouds in the Galaxy, it is finally possible to investigate and compare the stability of star-forming structures in different environments. In this dissertation, we utilize ammonia survey data to provide one of the largest investigations to date into the stability of structures in star-forming regions. Dense gas structures have been identified in a self-consistent manner across a variety of star-forming regions and the environmental factors (e.g., the presence or lack of local filaments and heating by local massive stars) most influential to their stability were investigated. The analysis has revealed that dense gas structures identified by ammonia observations in nearby star-forming clouds tend to be gravitationally bound. In high-mass star-forming clouds, however, bound and unbound ammonia structures are equally likely. This result suggests that either gravity is more important to structure stability at the small scales probed in nearby clouds or ammonia is more widespread in high-mass star-forming regions. In addition, a new method to detect and measure emission with multiple velocity components along the line of sight has been developed. Based on convolutional neural networks and named Convnet Line-fitting Of Emission-line Regions (CLOVER), the method is markedly faster than traditional analysis techniques, requires no input assumptions about the emission, and has demonstrated high classification accuracy. Since high-mass star-forming regions are often plagued by multiple velocity components along the line of sight, CLOVER will improve the accuracy of stability measurements for many clouds of interest to the star formation community. / Graduate

Osteoporosis is a common bone disease that increases risk of low-trauma fractures associated with substantial morbidity, mortality, and financial costs. Clinically, osteoporosis is defined by low bone mineral density (BMD). BMD explains approximately 60-70% of the variance in bone strength. The remainder is due to the cumulative and synergistic effects of other factors, including trabecular and cortical bone micro-architecture. In vivo quantitative characterization of trabecular bone (TB) micro-architecture with high accuracy, reproducibility, and sensitivity to bone strength will improve our understanding of bone loss mechanisms and etiologies benefitting osteoporotic diagnostics and treatment monitoring processes. The overall aim of the Ph.D. research is to design, develop and evaluate new 3-D imaging processing algorithms to characterize the quality of TB micro-architectural in terms of topology, orientation, thickness and spacing, and to move the new technology from investigational research into the clinical arena. Two algorithms regarding to this purpose were developed and validated in detail - (1) star-line-based TB thickness and marrow spacing computation algorithm, and (2) tensor scale (t-scale) based TB topology and orientation computation algorithm. The TB thickness and marrow spacing algorithm utilizes a star-line tracing technique that effectively accounts for partial voluming effects of in vivo imaging with voxel size comparable to TB thickness and also avoids the problem of digitization associated with conventional algorithms. Accuracy of the method was examined on computer-generated phantom images while the robustness of the method was evaluated on human ankle specimens in terms of stability across a wide range of resolutions, repeat scan reproducibility under in vivo condition, and correlation between thickness values computed at ex vivo and in vivo resolutions. Also, the sensitivity of the method was examined by its ability to predict bone strength of cadaveric specimens. Finally, the method was evaluated in an in vivo human study involving forty healthy young-adult volunteers and ten athletes. The t-scale based TB topology and orientation computation algorithm provides measures characterizing individual trabeculae on the continuum between perfect plate and perfect rod as well as individual trabecular orientation. Similar to the TB thickness and marrow spacing computation algorithm, accuracy was examined on computer-generated phantoms while robustness of the algorithm across ex vivo and in vivo resolution, repeat scan reproducibility, and the sensitivity to experimental mechanical bone strength were evaluated in a cadaveric ankle study. And the application of the algorithm was evaluated in a human study involving forty healthy young-adult volunteers and ten patients with SSRI treatment. Beside these two algorithms, an image thresholding algorithm based on the class uncertainty theory is developed to segment TB structure in CT images. Although the algorithm was developed for this specific application, it also works effectively for general 2-D and 3-D images. Moreover, the class uncertainty theory can be utilized as adaptive information in more sophisticated image processing algorithms such as Snakes, ASMs and graph search.

Evidence-based practice (EBP) is used worldwide to improve the quality of patient care to provide cost-effective care. EBP is a mandate for nursing practice combining individual clinical judgment with available expertise to generate a positive outcome for the patient. Investigators have documented that nurses have varying degrees of confidence and knowledge about EBP. The purpose of this project was to improve knowledge of EBP among registered nurses (RNs). The ACE Star Model of Knowledge transformation was used as the conceptual model. The key project question was to assess the level of knowledge and confidence about EBP among RNs in a cardio-thoracic (CT) intensive care unit (ICU) before and after viewing a computer-based EBP educational module. The quasi-experimental project used a 1 group pretest-posttest design. In the pretest, a convenience sample (n = 29) completed ACE-ERI competencies to self-assess confidence in EBP and an EBP Knowledge Test. The participants then viewed an EBP educational module based on major steps in EBP practice. Afterward, they repeated both tests. As a group, the paired t test showed a significant increase in scores for the ACE-ERI competencies between pretest and posttest scores. Using the Wilcoxon Signed Rank Test, knowledge scores increased but were not statistically significant. These findings suggested that there was improvement in both confidence and knowledge supporting the use of the educational module. In order to effectively implement EBP, nurses require knowledge to assess the quality and evidence for improved patient outcome. These results can guide administrators and educators to enhance RN EBP by the use of educational modules to improve the quality of patient care creating positive social change.

Les études Galactiques nécessitent de grands échantillons d'étoiles dont la masse, l'âge, les abondances, la vitesse et la distance sont connues. Les observations spectroscopiques permettent de mesurer certains de ces paramètres et les autres sont soit déterminés par d'autres moyens, ou dérivés par le calcul. Le besoin d'échantillons statistiquement représentatifs a motivé la construction d'instruments, et la réalisation de grands relevés comme le SDSS, LAMOST et GAIA... Ces projets génèrent une énorme quantité de données que les méthodes d'analyse interactives traditionnelles ne peuvent pas gérer. Cela a motivé des efforts pour concevoir des méthodes automatiques. Mon travail a commencé dans ce contexte, et les objectifs étaient de développer et tester une méthode automatique, puis de l'appliquer à des spectres stellaires à moyenne résolution. La thèse comporte quatre sections : 1. Je présente le package informatique ULySS, et en particulier son application à la détermination des paramètres atmosphériques des étoiles. 2. Nous avons utilisé ULySS pour déterminer les paramètres atmosphériques des 1273 étoiles de la bibliothèque CFLIB. 3. Nous avons appliqué la même méthode sur des observations obtenus pendant la mise en service de LAMOST et nous avons préparé une base de données de spectres de références pour les relevés futurs avec cet instrument. 4. Nous avons cherché des étoiles présumées pauvres en métaux (MP) en se servant des données de vérification scientifique de LAMOST. Cette étude contribue à l'étude des étoiles MP dans la Voie Lactée et montre la faisabilité de ces recherches avec LAMOST et ULySS / Galactic studies require large samples of stars with known mass, age, abundance, spatial velocity and distance etc. Spectroscopic observations allow ones to measure some of these parameters and to derive the others. The need for statistically representative samples motivated the construction of instruments and the realization of large surveys like SDSS, LAMOST and GAIA... These projects bring an enormous quantity of data that the traditional interactive spectral analysis methods cannot handle. This triggered efforts to design automatic methods. My work started in this context, and the goals were to develop and test an automatic method and to apply it to medium resolution stellar spectra. The thesis contains four sections: 1. The ULySS package, and in particular its application to the determination of the atmospheric parameters of stars is presented. 2. We used ULySS to determine the atmospheric parameters of the 1273 stars of the CFLIB library. 3. We applied the same method on LAMOST commissioning observations and we prepared stellar spectral templates for the future surveys. 4. We searched new metal-poor (hearafter MP) stellar candidates from LAMOST commissioning observations. The result of these MP star candidates is a prelude to the feasibility of LAMOST's capability on searching and enlarging the sample of MP stars in the Milky Way

Supernovae (SNe) and more specifically Core-Collapsed SNe (CC SNe) are signatures of on-going star formation (SF), and higher star formation rates. In this project, we perform a study of all SNe ever discovered inside a specific type of galaxy: a type-1 Active Galactic Nucleus (AGN1). We calculate the SN detection fraction for CC SNe and thermonuclear SNe in AGN1. In AGN1, inclination of the host galaxy and the radial distance of the SN to the center of the galaxy are displayed. As a second goal, we gather all SNe from the OpenSN catalogue found close to an AGN1, classify them and compare them with the full sample of OpenSN catalogue host galaxies. Results:We found and calculated the SN detection fraction of AGN1s. We found 16 SNe exploding in 13 different AGN1 host galaxies. The CC/Ia SN ratio is ~ 0.78. Comparing by similar morphology, the AGN1-host galaxies with all the host galaxies from OpenSN, we see that the detection fractions are higher in spiral AGN1 hosts than in normal spiral galaxies, but the difference is not significant (~ 0.4\sigma) to be considered.

<p>This thesis is a detailed observational study of the accretion processes in T Tauri stars (TTS). The interaction between the central star, the circumstellar disk and the magnetic field gives rise to a wide range of features in the spectra of TTS. The current picture of TTS is based on rather simple models assuming that accretion is a homogeneous and axisymmetric process. Although these models have been successful in explaining some observational signatures of TTS such as the shape of emission lines, the static nature of these models makes them unsuitable for describing the strong variability of the veiling spectrum and emission lines of TTS. An improved understanding of this variability is of key importance to study the dynamic processes related to the accretion flow and the winds.</p><p>This study is based on a set of high-quality spectroscopic observations with the UVES spectrograph at the 8-m VLT in 2000 and 2002. These spectra, with exposure times as short as 10-15 minutes, have high spectral resolution and high signal-to-noise ratios and cover a large part of the optical wavelength range. From this dataset we determine the basic physical parameters of several TTS and model their photospheres. These models then serve as a basis for a detailed investigation of variations of the veiling continuum and line emission. We confirm that the level of veiling correlates with some of the strongest emission lines and that coherent changes in accretion occur on a timescale of a few hours, comparable to the free-fall time from the disk to the star. From the properties of the emission lines formed close to the central star and in the stellar wind we derive restrictions on the geometry of the observed systems.</p><p>Because the intrinsic axial symmetry of a single star makes it almost impossible to disentangle rotational modulation from inhomogeneity and axial asymmetry of the accretion flow, we study a series of spectra of a close spectroscopic binary at different orbital phases and derive the 3D structure of flows between the disk and the star. Finally, we calculate the profiles of hydrogen emission lines by iteratively solving 3D NLTE radiative transfer in a state-of-the-art magnetospheric model.</p>

<p>This thesis describes some aspects of noncommutative geometry and conformal field theory. The motivation for the investigations made comes to a large extent from string theory. This theory is today considered to be the most promising way to find a solution to the problem of unifying the four fundamental interactions in one single theory. The thesis gives a short background presentation of string theory and points out how noncommutative geometry and conformal field theory are of relevance within the string theoretical framework. There is also given some further information on noncommutative geometry and conformal field theory. The results from the three papers on which the thesis is based are presented in the text. It is shown in Paper 1 that, for a gauge theory in a flat noncommutative background only the gauge groups <i>U(N)</i> can be used in a straightforward way. These theories can arise as low energy limits of string theory. Paper 2 concerns boundary conformal field theory, which can be used to describe open strings in various backgrounds. Here different orbifold theories which are described using simple currents of the chiral algebra are investigated. The formalism is applied to ``branes´´ in <b>Z</b>₂<b> </b>orbifolds of the <i>SU(2)</i> WZW-model and to the <i>D</i>-series of unitary minimal models. In Paper 3 two different descriptions of an invariant star-product on <i>S²</i> are compared and the characteristic class that classifies the star-product is calculated. The Fedosov-Nest-Tsygan index theorem is used to compute the characteristic class.</p>

Laura Linney has an extensive education and experience in performance, which has influenced her to create a well-defined methodology when she approaches new roles. She uses a dialectical approach to performance. This approach has two parts as she outlined in a personal interview: phase one is her research, education, understanding of the script, and previous experiences working together to create a character, while phase two is her release of control over the character and the opportunity for the text (film or otherwise) and role to take on their own distinct personalities. This means that Linney eventually gives up agency over her characters in order for them to be effective and successful in the whole of a film. In effect, her characters are created by numerous influences within and outside her range of control. My intentions in this article are to prove that this dialectical methodology is prominent within all aspects of Laura Linney?s performances. In fact, I suggest that her utilization of this technique is what makes her a dynamic, effective, and unique actress. The dialectical nature of her performance techniques can be observed most effectively in specific breakthrough moments within her films. These moments exist most prominently in Linney?s films that are rooted in close character analysis like You Can Count On Me, The Savages, and the HBO mini-series John Adams. Close textual analyses of these scenes show a dramatic hiatus from the standard performance that she has used to help build a character. They show distinct differences between characters, which reinforces my point that each role is not only mandated by Linney?s creative power over her acting, but also a complete release of this control. They highlight how Linney allows herself to be directed and molded to develop deep, complex characters that work organically within the greater text of the film.

This dissertation describes the current version of GenASiS and reports recent progress in its development. GenASiS is a new computational astrophysics code built for large-scale and multi-dimensional computer simulations of astrophysical phenomena, with primary emphasis on the simulations of neutron star mergers and core-collapse supernovae. Neutron star mergers are of high interest to the astrophysics community because they should be the prodigious source of gravitation waves and the most promising candidates for gravitational wave detection. Neutron star mergers are also thought to be associated with the production of short-duration, hard-spectral gamma-ray bursts, though the mechanism is not well understood. In contrast, core-collapse supernovae with massive progenitors are associated with long-duration, soft-spectral gamma-ray bursts, with the `collapsar' hypothesis as the favored mechanism. Of equal interest is the mechanism of core-collapse supernovae themselves, which has been in the forefront of many research efforts for the better half of a century but remains a partially-solved mystery. In addition supernovae, and possibly neutron star mergers, are thought to be sites for the emph{r}-process nucleosynthesis responsible for producing many of the heavy elements. Until we have a proper understanding of these events, we will have only a limited understanding of the origin of the elements. These questions provide some of the scientific motivations and guidelines for the development of GenASiS. In this document the equations and numerical scheme for Newtonian and relativistic magnetohydrodynamics are presented. A new FFT-based parallel solver for Poisson's equation in GenASiS are described. Adaptive mesh refinement in GenASiS, and a novel way to solve Poisson's equation on a mesh with refinement based on a multigrid algorithm, are also presented. Following these descriptions, results of simulations of neutron star mergers with GenASiS such as their evolution and the gravitational wave signals and spectra that they generate are shown. In the context of core-collapse supernovae, we explore the capacity of the stationary shock instability to generate magnetic fields starting from a weak, stationary, and radial magnetic field in an initially spherically symmetric fluid configuration that models the stalled shock in the post-bounce supernova environment. Our results show that the magnetic energy can be amplified by almost 4 orders of magnitude. The amplification mechanisms for the magnetic fields are then explained.

We investigate the rotational and thermal properties of star-forming molecular clouds using hydrodynamic simulations. Stars form from molecular cloud cores by gravoturbulent fragmentation. Understanding the angular momentum and the thermal evolution of cloud cores thus plays a fundamental role in completing the theoretical picture of star formation. This is true not only for current star formation as observed in regions like the Orion nebula or the ρ-Ophiuchi molecular cloud but also for the formation of stars of the first or second generation in the universe. <br><br> In this thesis we show how the angular momentum of prestellar and protostellar cores evolves and compare our results with observed quantities. The specific angular momentum of prestellar cores in our models agree remarkably well with observations of cloud cores. Some prestellar cores go into collapse to build up stars and stellar systems. The resulting protostellar objects have specific angular momenta that fall into the range of observed binaries. We find that collapse induced by gravoturbulent fragmentation is accompanied by a substantial loss of specific angular momentum. This eases the "angular momentum problem" in star formation even in the absence of magnetic fields. <br><br> The distribution of stellar masses at birth (the initial mass function, IMF) is another aspect that any theory of star formation must explain. We focus on the influence of the thermodynamic properties of star-forming gas and address this issue by studying the effects of a piecewise polytropic equation of state on the formation of stellar clusters. We increase the polytropic exponent γ from a value below unity to a value above unity at a certain critical density. The change of the thermodynamic state at the critical density selects a characteristic mass scale for fragmentation, which we relate to the peak of the IMF observed in the solar neighborhood. Our investigation generally supports the idea that the distribution of stellar masses depends mainly on the thermodynamic state of the gas. <br><br> A common assumption is that the chemical evolution of the star-forming gas can be decoupled from its dynamical evolution, with the former never affecting the latter. Although justified in some circumstances, this assumption is not true in every case. In particular, in low-metallicity gas the timescales for reaching the chemical equilibrium are comparable or larger than the dynamical timescales. <br><br> In this thesis we take a first approach to combine a chemical network with a hydrodynamical code in order to study the influence of low levels of metal enrichment on the cooling and collapse of ionized gas in small protogalactic halos. Our initial conditions represent protogalaxies forming within a fossil HII region -- a previously ionized HII region which has not yet had time to cool and recombine. We show that in these regions, H₂ is the dominant and most effective coolant, and that it is the amount of H₂ formed that controls whether or not the gas can collapse and form stars. For metallicities Z <= 10^-3 Z_sun, metal line cooling alters the density and temperature evolution of the gas by less than 1% compared to the metal-free case at densities below 1 cm^-3 and temperatures above 2000 K. We also find that an external ultraviolet background delays or suppresses the cooling and collapse of the gas regardless of whether it is metal-enriched or not. Finally, we study the dependence of this process on redshift and mass of the dark matter halo. / Sterne sind fundamentale Bestandteile des Kosmos. Sie entstehen im Inneren von turbulenten Molekülwolken, die aus molekularem Wasserstoffgas und Staub bestehen. Durch konvergente Strömungen in der turbulenten Wolke bilden sich lokale Dichtemaxima, die kollabieren, falls die zum Zentrum der Wolke gerichtete Schwerkraft über die nach außen gerichteten Druckkräfte dominiert. Dies ist der Fall, wenn die Masse des Gases einen kritischen Wert überschreitet, der Jeansmasse genannt wird. Die Jeansmasse hängt von der Dichte und der Temperatur des Gases ab und fällt im isothermen Fall mit steigender Dichte stetig ab, so dass während des Kontraktionsprozesses immer kleinere Teilmassen instabil werden. Es kommt zur Fragmentierung der Molekülwolke zu protostellaren Kernen, den direkten Vorläufern der Sterne. <br><br> In der vorliegenden Arbeit werden die zeitliche Entwicklung des Drehimpulses der protostellaren Kerne und der Einfluss der thermischen Eigenschaften des Gases mit Hilfe von dreidimensionalen hydrodynamischen Simulationen untersucht. Hierbei konzentrieren wir uns auf zwei fundamentale Probleme, die jede Theorie der Sternentstehung lösen muss: das "Drehimpulsproblem" und die Massenverteilung der Sterne (IMF). Die thermischen Eigenschaften des Gases sind nicht nur von Bedeutung für die derzeitige Sternentstehung in beobachtbaren Regionen wie z.B. der Orionnebel oder die ρ-Ophiuchi Molekülwolke, sondern auch für die Entstehung von Sternen der ersten und zweiten Generation im frühen Universum. <br><br> Wir betrachten die Entwicklung des spezifischen Drehimpulses von protostellaren Kernen und vergleichen unsere Resultate mit beobachteten Werten. Wir finden eine gute Übereinstimmung zwischen den spezifischen Drehimpulsen der protostellaren Kerne in unserem Model und denen der beobachteten Kerne in Molekülwolken. In unseren Simulationen geht der gravitative Kollaps mit einem Verlust an spezifischem Drehimpuls einher. Somit kann das Drehimpulsproblem der Sternentstehung auch ohne Betrachtung der Magnetfelder entschärft werden. <br><br> Ein weiterer Schwerpunkt der Arbeit ist die Untersuchung des Einflusses der thermodynamischen Eigenschaften des Gases auf die Massenverteilung der Sterne, die aus diesem Gas entstehen. Wir verwenden eine stückweise polytrope Zustandgleichung, die die Temperatur-Dichte-Beziehung genauer beschreibt. Wir zeigen, dass Veränderungen in der Zustandgleichung bei einer bestimmten Dichte einen direkten Einfluss auf die charakteristische Massenskala der Fragmentierung haben und somit den Scheitelpunkt der Sternmassenverteilung in der solaren Umgebung bestimmen. <br><br> Des Weiteren sind die thermodynamischen Eigenschaften des Gases auch für die Sternentstehung im frühen Universum von Bedeutung. Das primordiale Gas, aus dem die ersten Sterne gebildet wurden, enthält keine Metalle (Elemente schwerer als H oder He), da diese erst durch Kernreaktionen in Sternen gebildet werden. In dieser Arbeit untersuchen wir den Einfluss einer geringen Metallizität auf das Kühlungs- und Kollapsverhalten von Gas, aus welchem die zweite Generation von Sternen entstanden ist. Dieses Gas ist anfänglich heiß und ionisiert und befindet sich in kleinen protogalaktischen Halos aus dunkler Materie. Unsere hydrodynamischen Simulationen, die auch ein adäquates chemisches Netzwerk beinhalten, zeigen, dass die Temperatur- und Dichteentwicklung des Gases während der Anfangsphase des Kollapses durch eine geringe Metallizität im Gas kaum beeinflusst wird. Wir stellen weiterhin fest, dass externe ultraviolette Strahlung den Kühlprozess des Gases ohne Metallizität und des Gases mit geringer Metallizität gleichermaßen verzögert oder sogar verhindert. Außerdem untersuchen wir den Einfluss der Rotverschiebung und der Masse des Halos aus dunkler Materie auf die Kühlung und den Kollaps des Gases.