Visualization of space-time-structure of electromagnetic fields

In the course of this work are techniques for visualization of time-dependant electromagnetic fields in space-time representation introduced. This happens on the basis of wave propagation, as this phenomenon is still not adequately researched. Therefore in this work are usually scalar fields used. The methods which are developed in this work could also be used for visualization of other typical wave propagation phenomena. In the case of vector field data, such as electromagnetic fields, they must be used on their magnitude. This methods also set a foundation for further developments in combination with analysis based on vector topology of electromagnetic fields, for further more detailed visualizations. The in the course of this work introduced methods base on the extraction of height ridge and valley surfaces. To avoid occlusions in space-time representation and further reduce the complexity of the representation, so-called virtual sources are introduced in the visualisation of wave phenomena. For this are two approaches on extracting these virtual sources explored and different approaches on processing them to space-time curves. By using these space-time-curves for a reconstruction of the original field, they deliver a compact representation of the field. This allows an effective visualisation and interpretation of the space-time structures in the field and their relations.Im Rahmen dieser Arbeit werden Techniken zur Visualisierung zeitabhängiger, zweidimensionaler elektromagnetischer Felder in einer Raum-Zeit-Darstellung vorgestellt. Dies geschieht auf Basis der Wellenausbreitung, da dieses Phänomen noch nicht angemessen erforscht wurde. In dieser Arbeit wird daher vorwiegend mit Skalarfeldern gearbeitet. Die hier entwickelten Methoden können allgemein zur Visualisierung der Wellenausbreitung verwendet werden und müssen im Fall von Vektorfeldern auf deren Magnitude angewendet werden, wie dies bei elektromagnetischen Feldern der Fall ist. Die entwickelten Methoden bieten auch eine Basis für Weiterentwicklungen im Zusammenspiel mit Analysen auf der Vektortopologie der elektromagnetischen Felder, für weitere, detailliertere Visualisierungen. Die in dieser Arbeit vorgestellten Methoden basieren auf der Extraktion von Grad- und Talflächen. Um Verdeckungen in der Raum-Zeit-Darstellung zu vermeiden und die Komplexität der Darstellung weiter zu reduzieren, werden so genannte virtuelle Quellen in die Visualisierung der Wellenausbreitung eingeführt. Dabei werden zwei Ansätze zur Extraktion dieser virtuellen Quellen vorgestellt und verschiedene Ansätze um diese zu Raum-Zeit-Kurven zu verarbeiten. In dem diese Raum-Zeit-Kurven als Basis einer Rekonstruktion des ursprünglichen Feldes verwendet werden, liefern sie eine kompakte Repräsentation des Feldes, was eine effektive Visualisierung

Neogenin-mediated hemojuvelin shedding occurs after hemojuvelin traffics to the plamsa membrane

Hemochromatosis type 2 gene (HFE2) is highly expressed in skeletal muscle and liver hepatocytes. Its encoded protein, hemojuvelin (HJV), is a co-receptor for the bone morphogenetic proteins 2 and 4 (BMP2 and BMP4) and enhances the BMP-induced hepcidin expression. Hepcidin is a central iron regulatory hormone predominantly secreted from hepatocytes. HJV also binds neogenin, a membrane protein widely expressed in many tissues. Neogenin is required for the processing and release of HJV from cells. The role that neogenin plays in HJV trafficking was investigated, using HepG2 cells, a human hepatoma cell line. Knockdown of endogenous neogenin markedly suppresses HJV release, but has no evident effect on HJV trafficking to the plasma membrane. Addition of a soluble neogenin ectodomain to cells markedly inhibits HJV release, indicating that the HJV shedding is not processed before trafficking to the cell surface. At the plasma membrane it undergoes endocytosis in a dynamin-independent but cholesterol-dependent manner. The additional findings that HJV release is coupled to lysosomal degradation of neogenin, that HJV undergoes endocytosis, and that cholesterol depletion by filipin blocks both HJV endocytosis and HJV release, suggest that neogenin-mediated HJV release occurs after the HJV-neogenin complex is internalized from the cell surface

Novel roles of the chemorepellent axon guidance molecule RGMa in cell migration and adhesion

The repulsive guidance molecule A (RGMa) is a contact-mediated axon guidance molecule that has significant roles in central nervous system (CNS) development. Here we have examined whether RGMa has novel roles in cell migration and cell adhesion outside the nervous system. RGMa was found to stimulate cell migration from Xenopus animal cap explants in a neogenin-dependent and BMP-independent manner. RGMa also stimulated the adhesion of Xenopus animal cap cells, and this adhesion was dependent on neogenin and independent of calcium. To begin to functionally characterize the role of specific domains in RGMa, we assessed the migratory and adhesive activities of deletion mutants. RGMa lacking the partial von Willebrand factor type D (vWF) domain preferentially perturbed cell adhesion, while mutants lacking the RGD motif affected cell migration. We also revealed that manipulating the levels of RGMa in vivo caused major migration defects during Xenopus gastrulation. We have revealed here novel roles of RGMa in cell migration and adhesion and demonstrated that perturbations to the homeostasis of RGMa expression can severely disrupt major morphogenetic events. These results have implications for understanding the role of RGMa in both health and disease

Identification of the Neogenin-Binding Site on the Repulsive Guidance Molecule A

Repulsive guidance molecule (RGM) is a membrane-bound protein that was originally identified as an axon guidance molecule in the chick retinotectal system. RGMa, one of the 3 isoforms found in mammals, is involved in laminar patterning, cephalic neural tube closure, axon guidance, and inhibition of axonal regeneration. In addition to its roles in the nervous system, RGMa plays a role in enhancing helper T-cell activation. Binding of RGM to its receptor, neogenin, is considered necessary to transduce these signals; however, information on the binding of RGM to neogenin is limited. Using co-immunoprecipitation studies, we have identified that the RGMa region required for binding to neogenin contains amino acids (aa) 259–295. Synthesized peptide consisting of aa 284–293 directly binds to the extracellular domain (ECD) of recombinant neogenin, and addition of this peptide inhibits RGMa-induced growth cone collapse in mouse cortical neurons. Thus, we propose that this peptide is a promising lead in finding reagents capable of inhibiting RGMa signaling

BMP Signaling Modulates Hepcidin Expression in Zebrafish Embryos Independent of Hemojuvelin

Hemojuvelin (Hjv), a member of the repulsive-guidance molecule (RGM) family, upregulates transcription of the iron regulatory hormone hepcidin by activating the bone morphogenetic protein (BMP) signaling pathway in mammalian cells. Mammalian models have identified furin, neogenin, and matriptase-2 as modifiers of Hjv's function. Using the zebrafish model, we evaluated the effects of hjv and its interacting proteins on hepcidin expression during embryonic development. We found that hjv is strongly expressed in the notochord and somites of the zebrafish embryo and that morpholino knockdown of hjv impaired the development of these structures. Knockdown of hjv or other hjv-related genes, including zebrafish orthologs of furin or neogenin, however, failed to decrease hepcidin expression relative to liver size. In contrast, overexpression of bmp2b or knockdown of matriptase-2 enhanced the intensity and extent of hepcidin expression in zebrafish embryos, but this occurred in an hjv-independent manner. Furthermore, we demonstrated that zebrafish hjv can activate the human hepcidin promoter and enhance BMP responsive gene expression in vitro, but is expressed at low levels in the zebrafish embryonic liver. Taken together, these data support an alternative mechanism for hepcidin regulation during zebrafish embryonic development, which is independent of hjv

Simulation frameworks for cognitive processes II

Diese Fachstudie beschäftigt sich mit der Untersuchung und dem Vergleich der kognitiven Frameworks ACT-R, Apex und Soar. Dazu wird eine Einführung in die Grundlagen der Kognitionswissenschaft und der KI gegeben. Sowohl der Gehirnaufbau als auch verschiedene Modelle der Wissensrepräsentation und der Informationsverarbeitung werden aufgezeigt. Im Anschluss legen die Autoren Architektur, Einsatzgebiete, Ergebnisvisualisierung und Grenzen der untersuchten Frameworks dar. Abschließend werden die Frameworks bewertet und ein Ausblick in die weitere Entwicklung gegeben.This paper presents the research and comparison of the cognitive architectures ACT-R, Apex and Soar. This includes an introduction in the basics of cognitive science and AI. Authors show the structure of brain as well as several models of knowledge representation and information processing. Afterwards the authors point out the structure, applications, result visualization and the limits of cognitive architectures. Finally this paper evaluates the frameworks and gives an outlook for the development in the future