10,813 research outputs found
Abundance Tomography of Type Ia Supernovae
No full textMany uncertainties about the physics of Type Ia Supernovae have been revealed in the recent past, and numerous pieces are puzzled together to achieve a complete description of the phenomenon of thermonuclear explosions in the sky. However, very important parts are still missing. In particular, the concept lacks a proper connection between the various evolutionary steps, namely the progenitor scenario, explosion theory, nucleosynthesis from the burning, and the observations. Early time spectra of Type Ia Supernovae naturally contain information about all of these processes and are at the centre of the entire scenario. Appropriate models of that phase can provide the missing link and improve our understanding of this field enormously.
The goal of this thesis is to advance new methods to calculate synthetic spectra in order to extract the information contained in the observations more efficiently. Based on a well established radiation transfer code, a new technique called "Abundance Tomography" is developed to derive the abundance distribution of Type Ia Supernovae ejecta. While previous approaches were limited to the determination of the abundances of specific species in restricted regions of the supernova envelope, here a complete stratified distribution of all major elements is obtained. This method is applied to the very well observed normal SN 2002bo. Combining the early spectra with those of the nebular phase leads to a coverage of the entire ejecta from the centre out to the highest velocities. The abundances derived are used to compute a synthetic bolometric light curve to test the radial distribution of Fe group and intermediate-mass elements.
The sampling procedure of the incident radiation field at the lower boundary is modified to obtain a better description of the real situation in Type Ia Supernovae. This improves the overall flux distribution significantly, especially in the red part of the spectrum, where almost no real line opacity is found. Synthetic spectra with this new procedure reproduce the observations much more accurately, as is shown by models of SN 2002er.
Hydrogen lines have never been detected convincingly in Type Ia Supernovae spectra. However, using spectra that were observed more than 10 days before maximum light, it is shown that small amounts of hydrogen in the outer parts of the ejecta can explain high velocity line absorptions, seen rather frequently in various objects, e.g. SN 2002dj, SN 2003du, and SN 1999ee. The hydrogen is not claimed to be primordial to the white dwarf but it is rather the effect of the supernova ejecta interacting with circumstellar material, namely the white dwarf's accretion disk build up prior to the explosion.
Finally, UV spectra of Type Ia Supernovae are discussed. The ability of the Monte Carlo technique to deal naturally with this wavelength region is proven. Applications are presented by modelling spectra of SN 2001ep and SN 2001eh obtained with the Hubble Space Telescope.
The results are discussed in the broader context of Type Ia Supernovae physics: What causes the diversity in the nearby sample? What are the progenitors and how does the explosion work? What is the influence on cosmological models?
A detailed knowledge of the abundances, their distribution in the Supernova ejecta, and their ultimate causes delivers the key to these fundamental issues.Die Entdeckung der Dunklen Energie basiert nicht zuletzt auf der Interpretation von Beobachtungen weit entfernter bzw. hoch rotverschobener Supernovae vom Typ Ia (z>0,1). Gleichwohl steht eine vollständige und konsistente Beschreibung des physikalischen Ablaufs thermonuklearer Explosionen, die dem Phänomen der Supernovae Ia zugrunde liegen, immer noch aus.
So konnte bislang der Zusammenhang zwischen den einzelnen Entwicklungsstufen - vom Vorläuferstern über die explosive
Nukleosynthese bis hin zur Phase der homologen Expansion - und den Beobachtungen noch nicht hinreichend geklärt werden. Die Spektren aus der frühen Phase, d.h. einige Tage nach der Explosion, enthalten wichtige Informationen über diesen Ablauf; deren Interpretation steht damit im Zentrum der derzeitigen Supernova Ia Forschung. Geeignete Modelle zur Erzeugung synthetischer Spektren sind das notwendige Werkzeug, um wesentliche Details der thermonuklearen Explosion zu überprüfen und so eine Möglichkeit zur Quantifizierung der Dunklen Energie bereitzustellen.
Ziel dieser Arbeit ist es, mit Hilfe neuer Methoden zur Berechnung synthetischer Spektren die in den Beobachtungen enthaltenen Informationen zu extrahieren und zu analysieren. Den entscheidenden methodischen Schritt stellt dabei die Entwicklung der Tomographie der Elementhäufigkeiten dar. Als wesentlicher Fortschritt kann die Verteilung der Elemente in der Hülle der Supernovae detailliert untersucht werden. Bisherige Verfahren beschränkten sich hierbei lediglich auf die Bestimmung globaler Häufigkeiten spezieller Elemente, während die neue Methode eine vollständige Analyse der radialabhängigen Verteilung aller wichtigen Elemente zulässt. Die Ergebnisse einer ersten Anwendung werden für die Supernova 2002bo präsentiert. Dabei wurde die Spektralanalyse der frühen Phase mit den Ergebnissen der Nebelphase kombiniert, um so eine vollständige Bestimmung der Häufigkeiten - vom innersten Punkt der Hülle bis hin zu den höchsten Radialgeschwindigkeitswerten - zu erhalten. Im
nächsten Schritt wurden die Ergebnisse der Häufigkeitsverteilung dazu verwendet, die bolometrische Lichtkurve zu berechnen. Durch den Vergleich mit der beobachteten Lichtkurve konnte so die geschichtete Verteilung der Eisengruppen- und mittelschweren Elemente präzise bestätigt werden.
Desweiteren wurde das Samplingverfahren zur Berechnung des
Strahlungsfeldes im innersten Bereich erheblich verbessert und so modifiziert, dass es den bei Supernovae Ia vorherrschenden physikalischen Bedingungen besser entspricht. Damit konnte die Strahlungsflussverteilung signifikant verbessert werden, was insbesondere im opazitätsarmen roten Bereich des Spektrums von entscheidender Bedeutung ist. Anhand von Modellen zur Supernova 2002er wird ferner gezeigt, dass die auf der neuen Methode basierenden synthetischen Spektren die Beobachtungen in wesentlichen Punkten, wie beispielsweise die dominanten Spektrallinien von S, Si, Ca und Fe, erheblich besser repräsentieren.
Ein weiterer für das Gesamtverständnis wichtiger Punkt bezieht sich auf die Frage nach der Wasserstoffhäufigkeit.
Bislang konnten in Typ Ia Supernova Spektren keine Wasserstofflinien nachgewiesen werden. Anhand von Spektren, die mehr als 10 Tage vor dem Helligkeitsmaximum aufgenommen wurden, konnten wir jedoch zeigen, dass bislang ungeklärte
Linienabsorptionen, hauptsächlich von Ca und Si bei sehr hohen Geschwindigkeiten durch kleine Mengen Wasserstoff aus der Akkretionsscheibe erklärt werden können. Dieses Ergebnis
birgt erhebliche Implikationen für das Verständnis der
Supernova Ia Vorläufersterne.
Für die Diskussion der Ergebnisse in einem größeren astrophysikalischen Rahmen sind desweiteren folgende Fragestellungen relevant: Was verursacht bei den nahen Objekten das unterschiedliche Verhalten ihrer Lichtkurven? Woraus entstehen sie und wie läuft die Explosion im Detail ab? Welche Konsequenzen hat die präzise Parameterstudie von Supernovae Ia für die Kosmologie?
Wie in dieser Arbeit gezeigt wird, liefert die exakte Kenntnis der Häufigkeitsverteilung der Elemente in den
Supernovae Ia Hüllen den Schlüssel zur Beantwortung dieser
elementaren Fragen
Danza y Co-creatividad kinestésica Humano-IA
No full textHuman-machine interaction in dance is not a new phenomenon, however, the evolution of Artificial Intelligence (AI) in recent years allows new scenarios where novel methods of creative collaboration between human and artificial intelligence are proposed. From an interdisciplinary approach, this article provides an analysis of different software for choreographic creation and synthesises the findings from the creative collaboration between the author and an AI dancer, which were presented at the Leverhulme Centre for the Future of Intelligence at the University of Cambridge (UK). The author concludes that in order to co-create dance with an AI, it is not enough to simply use it, but it must enable an experience in which the human and machine can be exposed to a mutual influence that is not limited to logical reasoning, but is based on kinaesthetic intuition.La interacción humano-maquina en la danza no es un fenómeno nuevo, sin embargo, la evolución de la Inteligencia Artificial (IA) en los últimos años permite nuevos escenarios donde se plantean novedosos métodos de colaboración creativa entre la inteligencia humana y la artificial. Desde un enfoque interdisciplinario, este artículo provee un análisis de distintos softwares para la creación coreográfica y sintetiza los hallazgos provenientes de la colaboración creativa entre el autor y un bailarín de IA, los cuales fueron presentados en el Leverhulme Centre for the Future of Intelligence en la Universidad de Cambridge (Reino Unido). El autor concluye que para co-crear danza con una IA no basta con utilizarla, sino que es fundamental propiciar una experiencia donde el humano y la maquina puedan exponerse a una influencia mutua que no se limite al razonamiento lógico, sino que se base en la intuición kinestésica
First in the Nation in Education : Final Report,1984.
No full textThis report is one step in an ongoing process of change and is a plea for commitment for high standards in education in Iowa. Contains the final reports of the six subcommittees as adopted by the Excellence in Education Task Force, and the five recommendations made by the Task Force
Role of chain pairing for the production of functional soluble IA major histocompatibility complex class II molecules
No full textStructural studies of cellular receptor molecules involved in immune recognition require the production of large quantities of the extracellular domains of these glycoproteins. The murine major histocompatibility complex (MHC) class II-restricted response has been extensively studied by functional means, but the engineering and purification of the native, empty form of the most-studied murine MHC class II molecule, IA, has been difficult to achieve. IA molecules, which are the murine equivalent of human histocompatibility leukocyte antigen-DQ molecules, have a low efficiency of chain pairing, which results in poor transport to the cell surface and in the appearance of mixed isotype pairs. We have engineered soluble IA molecules whose pairing has been forced by the addition of leucine zipper peptide dimers at their COOH-terminus. The molecules are secreted "empty" into the extracellular medium and can be loaded with single peptide after purification. These IA molecules have been expressed in milligram quantity for crystallization as well as for activation of T cells and measurement of MHC class II-T cell receptor interactions
Application of the IS-MP-IA model to the German economy and policy implications
No full textExtending the IS-MP-IA model developed by Romer (2000) and applying the GARCH (Engle, 1982, 2001) methodology, the author finds that equilibrium GDP in Germany is positively affected by stock market performance and real exchange rate appreciation, and negatively influenced by the expected inflation rate, the government deficit/GDP ratio, and the U.S. federal funds rate. The relatively low deficit/GDP ratio of 1.83% in 2003 indicates that its fiscal condition was healthy. However, some other EU members may need to exercise fiscal discipline. Because real appreciation has a positive impact on output, a stronger euro may not be a concern for Germany but may be worried by those EU member nations which depend upon exports to stimulate their economies.
Structural basis of plasticity in T cell receptor recognition of a self peptide MHC antigen
No full textAn alpha beta T cell receptor structure at 2.5 angstrom and its orientation in the TCR-MHC complex
No full text
Monoclonal antibodies to the carboxy-terminal Ea sequence of pro-insulin-like growth factor-IA (proIGF-IA) recognize proIGF-IA secreted by IM9 B-lymphocytes
No full textInsulin-like growth factor-I (IGF-I) circulates in human serum as a 7 kDa peptide but analysis of IGF-I cDNAs predicts two pro-hormone precursors (proIGF-IA and proIGF-IB) with distinct C-terminal E domains. The function of these precursors, and the E peptides generated on cleavage to mature IGF-I, is unknown, largely because of a lack of tools for distinguishing precursors from constituent peptides. We used a synthetic Ea peptide to develop monoclonal antibodies (MAbs) which can recognize the carboxy-terminal sequence of proIGF-IA. These were characterized using proIGF-IA generated by transfected HEK293 cells. The anti-proIGF-IA MAbs immunoprecipitated two peptides (19-21 and 14 kDa) which were also recognized by MAbs to mature IGF-I. The proIGF-IA MAbs could also detect peptides of 9 and 4 kDa predicted to be Ea peptides. Treatment with N-glycosidase proved the 19-21 kDa and 9 kDa bands to be glycosylated proIGF-IA and Ea peptide respectively. Using these antibodies, we have identified proIGF-IA secreted from the IM9 B-lymphocyte cell line. This work paves the way for studies on proIGF-IA and Ea peptide regulation and function. © 2001 Harcourt Publishers Ltd
IA Generativa pode ser coautora?
No full textIn this essay, we argue that Generative Artificial Intelligence can be considered a co-author when it significantly contributes to the creative process of producing a work. We present the concept of human-AI hybrid authorship, which involves revising the concepts of work, author, and (co)authorship, moving beyond an anthropocentric perspective. To support this notion, we analyze legal, ethical, artistic, and historical aspects. We conclude that Generative AI can be recognized as a co-author from a pragmatic standpoint. The notion of hybrid authorship is then used to analyze reality, discussing emblematic cases of co-creation with generative technologies.En este ensayo, argumentamos que la Inteligencia Artificial Generativa puede ser considerada coautora cuando contribuye significativamente al proceso creativo de producción de una obra. Presentamos el concepto de autoría híbrida humano-IA, que implica revisar los conceptos de obra, autor y (co)autoría, superando una perspectiva antropocéntrica. Para fundamentar esta noción, analizamos aspectos legales, éticos, artísticos e históricos. Concluimos que la IA Generativa puede ser reconocida como coautora desde un punto de vista pragmático. La noción de autoría híbrida se moviliza entonces para analizar la realidad, discutiendo casos emblemáticos de cocreación con tecnologías generativas.No presente artigo ensaístico, defende-se que a Inteligência Artificial Generativa pode ser considerada coautora quando contribui significativamente para o processo criativo de produção de uma obra. É apresentada a noção de autoria híbrida humano-IA, que implica em revisões dos conceitos de obra, autor e (co)autoria que superem a perspectiva antropocêntrica. Para fundamentar essa noção, são analisados aspectos legais, éticos, artísticos e históricos. Conclui-se que a IA Generativa pode ser reconhecida como coautora do ponto de vista pragmático. A noção de autoria híbrida é então mobilizada para analisar a realidade, discutindo casos emblemáticos sobre a cocriação com as tecnologias generativas
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