Fast Magnetic Flux Line Allocation Algorithm for Interactive Visualization Using Magnetic Flux Line Existence Probability

The visualization of magnetic flux lines is one of the most effective ways to intuitively grasp a magnetic field. The depiction of continuous and smooth magnetic flux lines according to the magnetic field is of paramount importance. Thus, it is important to adequately allocate the distribution of magnetic flux lines in the analyzed space. The authors have already proposed two methods of determining the allocation of magnetic flux lines in 3-D space. However, both methods exhibited a long computation time to determine the allocation of magnetic flux lines. For solving this problem, in this paper, we propose a new improved method for correct allocation of magnetic flux lines in 3-D space with modest computational cost. The main advantages of this method are shorter computation time, correct allocation of the magnetic flux lines, and especially short computation time for visualization of magnetic flux lines when changes in the number of depicted flux lines is requested

Dynamics in the Magnetospheres of Compact Objects

Esta tesis doctoral explora el modelado de la dinámica en las magnetosferas alrededor de objetos compactos (agujeros negros y estrellas de neutrones), y sus implicaciones en la formación de fenómenos de alta energía como las llamaradas en magnetares y la emisión de alta variabilidad en el rango de los teraelectronvoltios (TeV) de algunos núcleos galácticos activos, por medio de simulaciones numéricas. Las sorprendentes imágenes de las sombras de los agujeros negros (BH) del centro galáctico y la galaxia M87 proporcionan una primera visión directa de la física de los flujos de acreción en los entornos más extremos del universo. La extracción eficiente de energía en forma de flujos de plasma colimados o chorros de un BH en rotación está directamente relacionada con la topología del campo magnético circundante. La electrodinámica relativista libre de fuerza en relatividad general (GRFFE, por sus siglas en inglés) es una de las aproximaciones posibles para estudiar ciertos plasmas empleado para analizar la energía de los flujos colimados salientes en las que los campos magnéticos fuertes dominan sobre todos los fenómenos relacionados con la inercia del plams. En dicha aproximación se pueden modelizar numéricamente flujos de energía en escenarios astrofísicos diversos empleando simulaciones globales, ventaja que hemos explotado para varias aplicaciones. En este trabajo, presentamos estrategias numéricas capaces de modelizar magnetosferas tanto estacionarias como totalmente dinámicas y libres de fuerza de objetos compactos. Mientras resolvemos el equilibrio de las magnetosferas de BH con un resolvedor recientemente desarrollado de la llamada ecuación Grad-Shafranov, la evolución dinámica es proporcionada por una implementación de GRFFE en la infraestructura del Einstein Toolkit. Esta tesis doctoral revisa de forma detallada la metodología detrás de este paquete de código recientemente desarrollado y su aplicación a magnetares y BH que giran rápidamente. Combinamos una serie de pruebas numéricas y astrofísicas para corroborar los hallazgos astrofísicos obtenidos mediante simulaciones numéricas a gran escala. Ponemos especial énfasis en el modelado correcto de las ondas de plasma e identificamos las limitaciones del método empleado con gran cuidado. Proporcionamos una descripción detallada de las técnicas empleadas para preservar el carácter libre de fuerza del plasma simulado y mantener, en la medida de lo posible, las propiedades conservativas (especialemente de la carga) en la solución numérica. Los resultados científicos de este proyecto han sido presentados en una serie de publicaciones en revistas especializadas. Entre los avances realizados, destaca la mejora de las técnicas numéricas utilizadas para resolver las magnetosferas de equilibrio de Kerr BHs a través de sus superficies singulares aplicando discretización de las derivadas parciales de tipo sesgado. Como aplicación directa, reprodujimos una serie de magnetosferas de BH con distintas topologías, todas ellas previamente consideradas en la literatura y proporcionamos una primera revisión detallada de las propiedades de convergencia. Además, identificamos inestabilidades en las ramas de alta energía de las magnetosferas “retorcidas” de magnetares. Después de la aparición de las antedichas inestabiliades, se libera una fracción sustancial de la energía magnetosférica, la cual puede actuar como el mecanismo desencadenante de los repetidores de gamma blandos (SGR) más potentes. Proporcionamos una argumentación consistente para conectar los resultados de nuestras simulaciones con la huella bolométrica esperada de la observación de las llamaradas gigantes de magnetares. Finalmente, confirmamos la posibilidad de extracción de energía por el mecanismo de Blandford / Znajek a partir de BH que giran rápidamente en magnetosferas dinámicas tridimensionales inducidas por la acumulación de estructuras magnéticas a pequeña escala. Presentamos un extenso estudio de parámetros en el que analizamos la influencia de la geometría de los bucles magnéticos en la eficiencia de producción de chorros, lo cuales presentan una polaridad magnetica que va alternándo con el tiempo. Asociamos directamente episodios eficientes de extracción de energía con el establecimiento de condiciones que son favorables para el proceso de Blandford / Znajek, las cuales surgen de forma bastante natural en el curso de nuestras simulaciones.This Ph.D. thesis explores the modeling of dynamics in magnetospheres around compact objects (black holes and neutron stars), and their implications in the formation of high energy phenomena such as magnetar flares and the highly variable teraelectron Volt (TeV) emission of some active galactic nuclei, by means of numerical simulations. The amazing images of black hole (BH) shadows from the galactic center and the M87 galaxy provide a first direct glimpse into the physics of accretion flows in the most extreme environments of the universe. The efficient extraction of energy in the form of collimated outflows or jets from a rotating BH is directly linked to the topology of the surrounding magnetic field. General Relativistic force-free electrodynamics (GRFFE) is one possible plasma limit employed to analyze energetic outflows in which strong magnetic fields are dominant over all inertial phenomena. It is capable to model energy flows in astrophysical scenarios in global simulations and we have exploited this for several applications. In this work, we present numerical strategies capable of modeling both, stationary, and fully dynamic force-free magnetospheres of compact objects. While we solve for equilibrium BH magnetospheres with a newly developed solver of the so-called Grad-Shafranov equation, the dynamical evolution is provided by an implementation of GRFFE on the infrastructure of the Einstein Toolkit. This Ph.D. thesis reviews the methodology behind this newly developed code package and its application to magnetars and rapidly spinning BHs in detail. It combines a series of numerical and astrophysical tests to substantiate the astrophysical findings obtained by large scale numerical simulations. We put special emphasis on the correct modeling of plasma waves and identify the limitations of the employed method with great care. We give a detailed account of the techniques employed to conservation the force-free character of the simulated plasma. Scientific results of this project are presented by a series of publications. We improved the numerical techniques used to solve for equilibrium magnetospheres of Kerr BHs across their singular surfaces by biased discretization stencils. As a direct application, we reproduced an array of BH magnetoshperes found throughout the literature and provided a first detailed review of convergence properties. Furthermore, we identified instabilities in the high energy branches of twisted magnetar magnetospheres. After their onset, a substantial fraction of the magnetospheric energy is released and may act as the triggering mechanism of the most powerful soft-gamma repeaters (SGRs). We provide a consistent argumentation for the connection of these simulations to the bolometric fingerprint expected from the observation of giant magnetar flares. Finally, we confirmed the possibility of energy extraction by the Blandford/Znajek mechanism from rapidly spinning BHs in 3D dynamical magnetospheres induced by the accretion of small scale magnetic structures. We presented an extensive parameter study in which we analyzed the influence of magnetic loop geometry on the efficiency of the striped jet like outflow. We directly associated efficient episodes of energy extraction with the establishment of conditions which are favorable to the Blandford/Znajek process, arising quite naturally in the course of our simulations

Cosmic ray feedback in galaxies and galaxy clusters -- A pedagogical introduction and a topical review of the acceleration, transport, observables, and dynamical impact of cosmic rays

Understanding the physical mechanisms that control galaxy formation is a fundamental challenge in contemporary astrophysics. Recent advances in the field of astrophysical feedback strongly suggest that cosmic rays (CRs) may be crucially important for our understanding of cosmological galaxy formation and evolution. The appealing features of CRs are their relatively long cooling times and relatively strong dynamical coupling to the gas. In galaxies, CRs can be close to equipartition with the thermal, magnetic, and turbulent energy density in the interstellar medium, and can be dynamically very important in driving large-scale galactic winds. Similarly, CRs may provide a significant contribution to the pressure in the circumgalactic medium. In galaxy clusters, CRs may play a key role in addressing the classic cooling flow problem by facilitating efficient heating of the intracluster medium and preventing excessive star formation. Overall, the underlying physics of CR interactions with plasmas exhibit broad parallels across the entire range of scales characteristic of the interstellar, circumgalactic, and intracluster media. Here we present a review of the state-of-the-art of this field and provide a pedagogical introduction to cosmic ray plasma physics, including the physics of wave-particle interactions, acceleration processes, CR spatial and spectral transport, and important cooling processes. The field is ripe for discovery and will remain the subject of intense theoretical, computational, and observational research over the next decade with profound implications for the interpretation of the observations of stellar and supermassive black hole feedback spanning the entire width of the electromagnetic spectrum and multi-messenger data.Comment: invited A&ARv review; revised version; accepted for publication; 238 page

NASA's Microgravity Science Research Program

The ongoing challenge faced by NASA's Microgravity Science Research Program is to work with the scientific and engineering communities to secure the maximum return from our Nation's investments by: assuring that the best possible science emerges from the science community for microgravity investigations; ensuring the maximum scientific return from each investigation in the most timely and cost-effective manner; and enhancing the distribution of data and applications of results acquired through completed investigations to maximize their benefits

Power Generation by Resonant Self-Actuation

Die Forschung im Bereich der Mikro-Energiegewinnung wurde durch den Bedarf an au-tarken sowie stabilen Energiequellen für vernetzte und drahtlose Sensoren vorangetrieben. Abwärme, insbesondere bei Temperaturen unter 200 °C, stellt eine vielversprechende, aber mit den derzeitigen Umwandlungstechnologien schwer zu gewinnende Energiequelle dar. Der Fortschritt von thermomagnetischen Generatoren (TMGs) mit hoher Leistung wurde durch den Mangel an Weiterentwicklungen von thermomagnetischen Materialien behindert. Diese Arbeit stützt sich auf frühere Forschungsarbeiten zu TMGs im kleinen Maßstab. Die Hauptziele sind: • Entwicklung eines LEM-Modells (Lumped Element Model) zur Simulation des TMG, um die Leistung zu analysieren und zu optimieren. • Nutzung von LEM und Experimenten, um die Auswirkungen verschiedener De-signparameter zu verstehen. • Die Hochskalierung des Volumens des aktiven Materials eines TMG, um die absolute Ausgangsleistung eines einzelnen Generators zu erhöhen. • Die Hochskalierung des TMG durch Parallelbetrieb mehrerer TMGs zur Vergrößerung der lateralen Größe. • Erweiterung des Betriebsbereichs der Wärmequelle auf Temperaturen nahe der Raumtemperatur, ohne die resonante Selbstaktivierung zu verlieren. Zunächst werden mittels experimenteller Messungen und LEM-Simulationen TMGs, die auf verschiedenen Materialien wie dem Ni-Mn-Ga Heusler-Legierungsfilm, Gadolinium und La-Fe-Si-H basieren, grundsätzlich erforscht. Die Auswirkung verschiedener Designparameter auf die Leistung des TMGs wird untersucht. Dabei beschreiben LEM-Simulationen die gekoppelten dynamischen Eigenschaften von TMGs, die Filme aus magnetischen Formgedächtnislegierungen (MSMA) verwenden. Die TMG nutzen Selbstaktivierung, indem ein temperaturabhängige Magnetisierungsänderungen und einen schnellen Wärmetransfer durch thermomagnetische Dünnschichten ausgenutzt wird. Detaillierte LEM-Simulationen zeigen die Temperaturänderung, die Magnetfeldänderung und die daraus resultierende Magnetisierung der TM-Filme über Zeit und Position. Opti-male Bedingungen für eine resonante Selbstaktivierung werden durch sorgfältiges Design der TMG-Parameter erreicht, was zu einer kontinuierlichen, ungedämpften Oszillation des TMG-Ausleger führt. In dieser Arbeit werden verschiedene Design-Parameter erörtert, die sich auf die resonante Selbstaktivierung im Falle von Ni-Mn-Ga-Dünnschichten auswirken, wobei die Bedeutung der Feinabstimmung jedes Parameters für eine maximale Ausgangsleistung hervorgehoben wird. Die Auswirkungen von Faktoren wie Magnet, Spulenwindungen, Auslegersteifigkeit, Lastwiderstand (RL), Curie-Temperatur (Tc), Wärmeübergangskoeffizient (hf) und Wärmewiderstand (Rb) werden untersucht, um ihren Einfluss auf die TMG-Leistung zu verstehen. LEM-Simulationen zeigen kritische Werte für hf und Rb, die eine stabile Energieerzeugung mit signifikantem Hub und Frequenz ermöglichen, was zu einer deutlichen Steigerung der elektrischen Leistung führt. Die Hochskalierung des TMG mit Ni-Mn-Ga-Dünnschicht zeigt gegensätzliche Auswir-kungen auf die Leistungsabgabe und die Grundfläche, wobei eine verbesserte elektrische Leistung pro Grundfläche durch eine Erhöhung der Schichtdicke von 5 auf 40 µm erreicht wird. Bei einer Temperaturänderung von nur 3 °C und einer Frequenz von 146 Hz wer-den Werte von 50 µW/cm2 erreicht. Die parallelen Architekturen sind entscheidend für die Erzeugung ausreichender Energie für die direkte Anwendung. Die thermische Kreuz-kopplung beeinträchtigt die dynamische Leistung und die Leistungsabgabe von parallel betriebenen TMGs. Thermische Effekte machen sich vor allem bei geringen Abständen zwischen den Bauelementen und hohen Temperaturen der Wärmequelle bemerkbar, wobei jedoch keine magnetischen oder mechanischen Wechselwirkungen zwischen den parallel arbeitenden TMGs beobachtet werden. Bei Verwendung von Gadolinium als aktiver TM-Schicht ist ein Betrieb bei einer niedrigen Wärmequellentemperatur (Tsource) von 40 °C möglich. Der TMG kann bei dieser Tsource eine Leistung von 1,3 µW bei einer Frequenz von 54 Hz erzeugen, was einer Ausgangs-leistung von 10 µW/cm2 pro Fläche entspricht. Bei einer Tsource von 65 °C steigt dieser Wert sprunghaft auf 24 µW/cm2 bei einer Frequenz von 117 Hz an. Obwohl für eine opti-male Leistung eine Tamb von 11 °C erforderlich ist, kann das Bauelement die resonante Selbstaktivierung bis zu einer Umgebungstemperatur (Tamb) von 19 °C aufrechterhalten und dabei immer noch 8,7 µW/cm2 Leistung bei einer Tsource von 50 °C erzeugen. Außer-dem werden die scharfen Grenzen der Betriebstemperaturen in Bezug auf Tsource und Tamb untersucht und vorgestellt. Ein TMG, bei den hydrierten La-Fe-Si-Legierungen als aktiven TM-Film verwendet, kann 38 µW/cm2 aus einer Tsource von 90°C erzeugen, während es mit einer Frequenz von 137 Hz arbeitet

Microgravity Science and Applications: Program Tasks and Bibliography for Fiscal Year 1996

NASA's Microgravity Science and Applications Division (MSAD) sponsors a program that expands the use of space as a laboratory for the study of important physical, chemical, and biochemical processes. The primary objective of the program is to broaden the value and capabilities of human presence in space by exploiting the unique characteristics of the space environment for research. However, since flight opportunities are rare and flight research development is expensive, a vigorous ground-based research program, from which only the best experiments evolve, is critical to the continuing strength of the program. The microgravity environment affords unique characteristics that allow the investigation of phenomena and processes that are difficult or impossible to study an Earth. The ability to control gravitational effects such as buoyancy driven convection, sedimentation, and hydrostatic pressures make it possible to isolate phenomena and make measurements that have significantly greater accuracy than can be achieved in normal gravity. Space flight gives scientists the opportunity to study the fundamental states of physical matter-solids, liquids and gasses-and the forces that affect those states. Because the orbital environment allows the treatment of gravity as a variable, research in microgravity leads to a greater fundamental understanding of the influence of gravity on the world around us. With appropriate emphasis, the results of space experiments lead to both knowledge and technological advances that have direct applications on Earth. Microgravity research also provides the practical knowledge essential to the development of future space systems. The Office of Life and Microgravity Sciences and Applications (OLMSA) is responsible for planning and executing research stimulated by the Agency's broad scientific goals. OLMSA's Microgravity Science and Applications Division (MSAD) is responsible for guiding and focusing a comprehensive program, and currently manages its research and development tasks through five major scientific areas: biotechnology, combustion science, fluid physics, fundamental physics, and materials science. FY 1996 was an important year for MSAD. NASA continued to build a solid research community for the coming space station era. During FY 1996, the NASA Microgravity Research Program continued investigations selected from the 1994 combustion science, fluid physics, and materials science NRAS. MSAD also released a NASA Research Announcement in microgravity biotechnology, with more than 130 proposals received in response. Selection of research for funding is expected in early 1997. The principal investigators chosen from these NRAs will form the core of the MSAD research program at the beginning of the space station era. The third United States Microgravity Payload (USMP-3) and the Life and Microgravity Spacelab (LMS) missions yielded a wealth of microgravity data in FY 1996. The USMP-3 mission included a fluids facility and three solidification furnaces, each designed to examine a different type of crystal growth

Electrocaloric coolers and pyroelectric energy harvesters based on multilayer capacitors of Pb(Sc0.5Ta0.5)O3

The following work investigates the development of heat pumps that exploit electrocaloric effects in Pb(Sc,Ta)03 (PST) multilayer capacitors (MLCs). The electrocaloric effect refers to reversible thermal changes in a material upon application (and removal) of an electric field. Electrocaloric cooling is interesting because 1) it has the potential to be more efficient than competing technologies, such as vapour-compression systems, and 2) it does not compel the use of greenhouse gases, which is crucial in order to slow down global warming and mitigate the effects of climate change. The continuous progress in the field of electrocalorics has promoted the creation of several electrocaloric based heat pump prototypes. Despite the different designs and working principles utilized, these prototypes have struggled to maintain temperature variations as large as 10 K, discouraging their industrial development. In this work, bespoke PST-MLCs exhibiting large electrocaloric effects near room temperature were embodied in a novel heat pump with the motivation to surpass the 10 K-barrier. The experimental design of the heat pump was based on the outcome of a numerical model. After implementing some of the modifications suggested by the latter, consistent temperature spans of 13 K at 30 °C were reported, with cooling powers of 12 W / kg. Additional simulations predicted temperature spans as large as 50 K and cooling powers in the order of 1000 W / kg, if a new set of plausible modifications were to be put in place. Similarly, these very same PST-MLCs samples were implemented into pyroelectric harvesters revisiting Olsen's pioneering work from 1980. The harvested energies were found to be as large as 11.2 J, with energy densities reaching up to 4.4 J / cm3 of active material, when undergoing temperature oscillations of 100 K under electric fields applied of 140-200 kV / cm. These findings are two and four times, respectively, larger than the best reported values in the literature. The results obtained in this dissertation are beyond the state-of-the-art and show that 1) electrocaloric heat pumps can indeed achieve temperature spans larger than 10 K, and 2) pyroelectric harvesters can generate electrical energy in the Joule-range. Moreover, numerical models indicated that there is still room for improvement, especially when it comes to the power of these devices. This should encourage the development of these kinds of electrocaloric- and pyroelectric-based applications in the near future