Comparison of different sources for laboratory X-ray microscopy

This paper describes the setup of two different solutions for laboratory X-ray microscopy working with geometric magnification. One setup uses thin-film transmission targets with an optimized tungsten-layer thickness and the electron gun and optics of an electron probe micro analyzer to generate a very small X-ray source. The other setup is based on a scanning electron microscope and uses microstructured reflection targets. We also describe the structuring process for these targets. In both cases we show that resolutions of 100 nm can be achieved. Also the possibilities of computed tomography for 3D imaging are explored and we show first imaging examples of high-absorption as well as low-absorption specimens to demonstrate the capabilities of the setups.Comment: 6 pages, 4 figures, proceedings of the 14th International Workshop on Radiation Imaging Detector

Laser microscopy of tunneling magnetoresistance in manganite grain-boundary junctions

Using low-temperature scanning laser microscopy we directly image electric transport in a magnetoresistive element, a manganite thin film intersected by a grain boundary (GB). Imaging at variable temperature allows reconstruction and comparison of the local resistance vs temperature for both, the manganite film and the GB. Imaging at low temperature also shows that the GB switches between different resistive states due to the formation and growth of magnetic domains along the GB. We observe different types of domain wall growth; in most cases a domain wall nucleates at one edge of the bridge and then proceeds towards the other edge.Comment: 5 pages, 4 figures; submitted to Phys. Rev. Let

Intrinsic Josephson Effects in the Magnetic Superconductor RuSr2GdCu2O8

We have measured interlayer current transport in small sized RuSr2GdCu2O8 single crystals. We find a clear intrinsic Josephson effect showing that the material acts as a natural superconductor-insulator-ferromagnet-insulator-superconductor superlattice. So far, we detected no unconventional behavior due to the magnetism of the RuO2 layers.Comment: 4 pages, 5 figures, to appear in Phys. Rev. Let

Intrinsic Tunneling in Cuprates and Manganites

The most anisotropic high temperature superconductors like Bi2Sr2CaCu2O8, as well as the recently discovered layered manganite La1.4Sr1.6Mn2O7 are layered metallic systems where the interlayer current transport occurs via sequential tunneling of charge carriers. As a consequence, in Bi2Sr2CaCu2O8 adjacent CuO2 double layers form an intrinsic Josephson tunnel junction while in in La1.4Sr1.6Mn2O7 tunneling of spin polarized charge carriers between adjacent MnO2 layers leads to an intrinsic spin valve effect. We present and discuss interlayer transport experiments for both systems. To perform the experiments small sized mesa structures were patterned on top of single crystals of the above materials defining stacks of a small number of intrinsic Josephson junctions and intrinsic spin valves, respectively.Comment: 6 pages, 8 figure

Utilization of Multiple Modalities for Imaging and Analyzing Kinematics of the Lower Extremities

The hip joint is a complex structure made up of many different muscles, ligaments, and bones. Mathematically modeling such a joint has become more and more popular due to the non-invasive nature of mathematical modeling compared to in-vivo testing. Previous versions of such a model set a great foundation, but further development and analyses were necessary to further the understanding of the hip joint. Several features were added such as the ability to detect neck impingement and tracking of the foot version angle throughout an activity. With most of the development done, it was time to start utilizing the hip model in larger analyses. One area that was focused on in these analyses using the hip model was 2D vs 3D planning and how differences in the bone morphology could affect the outcomes depending on if they were considered. Another study that utilized the hip model focused on changes in foot version angle and how they affected a patient’s postoperative kinematics. Outside of the hip model, the studies focused on comparing different segmentation methods for bone model creation as well as gathering femoral morphology for a comparison between the internal and external features to further understanding of the femoral canal. In this dissertation, the primary objective was to perform several hip analysis studies utilizing the hip analysis software. These studies included comparisons across several hip implants, as well as comparing different preoperative planning techniques and how they affected postoperative outcomes. The secondary objective was further development of the fully functional hip analysis software to take a closer look at the femoral morphology, as well as include new features to be able to fully analyze out-of-plane information not found in 2D planning

A Nation is a Machine for Capital

The 21st century has been fraught with deeply impactful inflection points in the trajectory of our nation. These pivotal moments affect varying and at times overlapping aspects of our lives, whether they be cultural, economic, spatial, or otherwise. The timeline of this thesis kicks off with one of these inflection points; the 2010 Supreme Court case Citizens United v. FEC. Effectively opening the door for corporate financial involvement (read: meddling and black-mailing) in the political sphere, the paradigm shift this case brought sets the stage for extrapolation and speculation of an alternate reality; a reality where corporations are the “powers that be”. This thesis is a story with two sets of “actors”. On one side there are the corporations, with their present day interests rendered with the implementation of megaprojects, the goals of which vary widely from corporation to corporation. The other side is composed of the dissidents, the Davids of this Goliath-ruled future. What effect do these megastructures have on the physical landscape? On the flora and fauna? On the socioeconomic stratification of its constituent inhabitants? What is architecture\u27s role in all of this? What architectures are used to supplement corporate rule, and how do these very same architectures become their own undoing? Can the human spirit overcome the indomitable will of the corporate machine

On the dc Magnetization, Spontaneous Vortex State and Specific Heat in the superconducting state of the weakly ferromagnetic superconductor RuSr2_{2}GdCu2_{2}O8_{8}

Magnetic-field changes $<$ 0.2 Oe over the scan length in magnetometers that necessitate sample movement are enough to create artifacts in the dc magnetization measurements of the weakly ferromagnetic superconductor RuSr$_{2}$GdCu$_{2}$O$_{8}$ (Ru1212) below the superconducting transition temperature $T_{c} \approx$ 30 K. The observed features depend on the specific magnetic-field profile in the sample chamber and this explains the variety of reported behaviors for this compound below $T_{c}$. An experimental procedure that combines improvement of the magnetic-field homogeneity with very small scan lengths and leads to artifact-free measurements similar to those on a stationary sample has been developed. This procedure was used to measure the mass magnetization of Ru1212 as a function of the applied magnetic field H (-20 Oe $\le$ H $\le$ 20 Oe) at $T < T_{c}$ and discuss, in conjunction with resistance and ac susceptibility measurements, the possibility of a spontaneous vortex state (SVS) for this compound. Although the existence of a SVS can not be excluded, an alternative interpretation of the results based on the granular nature of the investigated sample is also possible. Specific-heat measurements of Sr$_{2}$GdRuO$_{6}$ (Sr2116), the precursor for the preparation of Ru1212 and thus a possible impurity phase, show that it is unlikely that Sr2116 is responsible for the specific-heat features observed for Ru1212 at $T_{c}$.Comment: 17 pages, 6 figure

Perkolation und Elastizität von Netzwerken - Von Zellulären Strukturen zu Faserbündeln

A material’s microstructure is a principal determinant of its effective physical properties. Structure-property relationships that provide a functional form for the dependence of a physical property (e.g. elasticity) on the microstucture’s morphology are essential for the physical understanding and also the practical application in material design. This work focuses on materials with spatial mesoscopic network structure. A new model with adjustable network topology is introduced and its percolation properties and effective elastic properties are examined. In an initially four-coordinated network, ordered or disordered, each vertex is separated with probability p to form two two-coordinated vertices, yielding network geometries that change continuously from network structures to bundles of unbranched, interwoven fibres. The percolation properties of this so-called vertex model are studied for a two-dimensional square lattice and a three-dimensional diamond network, revealing a percolation transition at p = 1 in both cases. The analysis of the pair-connectedness function and finite size scaling exhibits critical behaviour with critical exponents β = 0.32 ± 0.02, ν = 1.29 ± 0.04 in two dimensions and β = 0.0021 ± 0.0004, ν = 0.54 ± 0.01 in three dimensions. The values of the exponents differ from those of conventional site and bond percolation, indicating that this vertex model belongs to a different universality class. In addition, in three dimensions the critical exponents do not obey the hyperscaling relations of bond percolation, but a heuristic new hyperscaling relation is found. After inflating the network edges to circular cylinders of finite radius, the resulting structure is interpreted as solid material in network shape, henceforth called network solid. Changes of probability p strongly affect the mechanical properties of such network solids. This is demonstrated by calculating the effective linear-elastic bulk and shear moduli using a finite element method based on voxel representations of the structures. Separating a fraction of the network nodes leads to a strong decay of the effective moduli whose functional dependence can be approximated, for p < 0.5, by an exponential decay for both, fixed and periodic boundary conditions. This is verified for ordered (diamond and nbo) as well as for irregular (foam) initial structures. Compression experiments on laser-sintered models based on diamond network solids confirm these results. In case of periodic boundary conditions, a cross-over from an exponential to a power-law decay in (1 − p) close to the critical point at p = 1 is observed. From this, the elastic critical exponent fc can be estimated as fc = 3.0 ± 0.1, which also differs from the site and bond percolation exponent. The morphological analysis of this work has several applications. For linear-elastic solids, it suggests that the network connectivity can be used as design parameter, for example for open-cell metal foams or bone scaffolds, as the elastic properties can be adjusted to a given value while keeping the pore space geometry and thus transport properties almost constant. The results of the percolation analysis are especially relevant for network models of biological or synthetic polymers with varying degree of cross-linking.Die Mikrostruktur eines Materials hat großen Einfluß auf seine effektiven physikalischen Eigenschaften. Funktionale Abhängigkeiten physikalischer Größen (z.B. der Elastizität) von der Morphologie der Mikrostruktur sind essentiell für das physikalische Verständnis und die praktische Anwendung im Materialdesign. Der Fokus dieser Arbeit liegt auf Materialien, deren Mikrostruktur durch ein Netzwerk dargestellt werden kann. Ein neues Modell mit einstellbarer Netzwerktopologie wird vorgestellt, dessen Perkolationseigenschaften und effektive elastische Eigenschaften untersucht werden. Ausgehend von einem ursprünglich vier-verbundenen, geordneten oder ungeordneten Netzwerk wird jeder Vertex mit Wahrscheinlichkeit p in zwei zwei-verbundene Vertizes getrennt. Netzwerkgeometrien werden dadurch kontinuierlich zu Bündeln verschlungener Fasern. Somit wird über den Parameter p die mittlere Verbundenheit der Vertizes von vier im ursprünglichen Netzwerk auf zwei bei p = 1 herabgesetzt. Die Perkolationseigenschaften dieses sogenannten Vertex-Modells werden auf dem zweidimensionalen Quadratgitter und dem dreidimensionalen Diamantnetz untersucht. Beide Modelle zeigen einen Perkolationsübergang bei p = 1. Die Analyse der Paar-Verbundenheitsfunktion und das Finite-Size-Scaling offenbaren kritisches Verhalten mit kritischen Exponenten β = 0.32 ± 0.02, ν = 1.29 ± 0.04 in zwei Dimensionen und β = 0.0021 ± 0.0004, ν = 0.54 ± 0.01 in drei Dimensionen. Die Werte der Exponenten unterscheiden sich von konventioneller Site- und Bond-Perkolation, was darauf hindeutet, dass das Vertex-Modell zu einer neuen Universalitätsklasse gehört. In drei Dimensionen werden außerdem neue Hyperskalen-Beziehungen für das Vertex-Modell vorgeschlagen. Werden die Kanten der Netzwerkstrukturen durch Kreiszylindern mit endlichem Radius ersetzt, können sie als Festkörper in Form eines Netzwerkes interpretiert werden. Nachfolgend werden diese Strukturen Netzwerkkörper genannt. Mithilfe einer Finite-Elemente-Methode, die auf voxelierten Repräsentationen der Strukturen basiert, werden die effektiven, linear-elastischen Eigenschaften berechnet, wobei eine Veränderung von p großen Einfluß auf die mechanischen Eigenschaften solcher Netzwerkkörper hat. Die Trennung von Netzwerkknoten führt für p < 0.5 zu einem starken Abfall der effektiven linear-elastischen Moduln, deren funktionale Abhängigkeit von p sowohl für periodische als auch nicht-periodische Randbedingungen durch einen exponentiellen Abfall approximiert werden kann. Dies kann für geordnete (Diamant und nbo) und für ungeordnete (Schaum) Ausgangsstrukturen gezeigt werden. Kompressionsexperimente an Laser-gesinterten, auf der Diamantstruktur basierenden Modellen bestätigen dieses Ergebnis. Im Falle periodischer Randbedingungen kann ein Cross-over Verhalten von einem exponentiellen zu einem algebraischen Abfall in (1 − p) nah am kritischen Punkt p = 1 beobachtet werden. Daraus kann der elastische kritische Exponent fc zu fc = 3.0 ± 0.1 abgeschätzt werden, der sich ebenfalls von dem elastischen kritischen Exponenten der Site- und Bondperkolation unterscheidet. Für die morphologische Analyse dieser Arbeit gibt es verschiedene Anwendungen. Für linear-elastische Festkörper legt sie nahe, die Netzwerkverbundenheit als Designparameter, z.B. für offenzellige Metallschäume oder Knochengerüste, zu verwenden, da die elastischen Eigenschaften auf einen bestimmten Wert eingestellt werden können, während die Porenraumgeometrie und somit die Transporteigenschaften kaum verändert werden. Die Ergebnisse der Perkolationsanalyse sind im Speziellen für Netzwerkmodelle biologischer und synthetischer Polymere mit variablem Vernetzungsgrad relevant