Superbursts (SBs) are large, seemingly spontaneous activity fluctuations often encountered in high density neural networks in vitro. Little effort has been put forth to define and analyze SBs which are paroxysmal bursting discharges. Through qualitative and quantitative means, I have described specific occurrences of superbursting activity. A complex of paroxysmal bursting has been termed a "superburst episode," and each individual SB is a "superburst event" which is comprises a fine burst structure. Quantitative calculations (employing overall spike summations and coefficient of variation (CV) calculations), reveal three distinct phases. Phase 1 is a "build up" phase of increasingly strong, coordinated bursting with an average of a 17.6% ± 13.7 increase in activity from reference. Phase 2, the "paroxysmal" phase, is comprised of massive coordinated bursting with high frequency spike content. Individual spike activity increases by 52.9% ± 14.6. Phase 3 is a "recovery phase" of lower coordination and an average of a 50.1% ± 35.6 decrease in spike production from reference. SBs can be induced and terminated by physical manipulation of the medium. Using a peristaltic pump with a flow rate of 0.4ml/min, superbursting activity ceases approximately 28.3 min after the introduction of flow. Alternatively, upon cessation of medium flow superbursting activity reemerges after approximately 8.5 min. Additionally, this study explored other methods capable of inducing superbursting activity using osmotic shocks. The induction and termination of SBs demonstrates that the cell culture environment plays a major role in generating this phenomenon. The observations that high density multi-layer neuronal networks in culture are more likely to enter paroxysmal bursting also supports the hypothesis that enrichment and depletion layers of metabolites and ionic species are involved in such unusual activity. The dynamic similarity of the SB phenomenon with epileptiform discharges make further quantification on the spike pattern level pertinent and important.

No description available.

No description available.

No description available.

Multi-metallic aerogels have recently emerged as a novel and promising class of unsupported electrocatalyst materials due to their high catalytic activity and improved durability for various electrochemical reactions. Aerogels can be prepared by a spontaneous one-step gelation process, where the chemical co-reduction of metal precursors and the prompt formation of nanochain-containing hydrogels, as a preliminary stage for the preparation of aerogels, take place. However, detailed knowledge about the homogeneity and chemical distribution of these three-dimensional Pd–Pt aerogels at the nano-scale as well as at the macro-scale is still unclear. Therefore, we used a combination of spectroscopic and microscopic techniques to obtain a better insight into the structure and elemental distribution of the various Pd-rich Pd–Pt aerogels prepared by the spontaneous one-step gelation process. Synchrotron-based extended X-ray absorption fine structure (EXAFS) spectroscopy and high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) in combination with energy-dispersive X-ray spectroscopy (EDX) were employed in this work to uncover the structural architecture and chemical composition of the various Pd-rich Pd–Pt aerogels over a broad length range. The Pd80Pt20, Pd60Pt40 and Pd50Pt50 aerogels showed heterogeneity in the chemical distribution of the Pt and Pd atoms inside the macroscopic nanochain-network. The features of mono-metallic clusters were not detected by EXAFS or STEM-EDX, indicating alloyed nanoparticles. However, the local chemical composition of the Pd–Pt alloys strongly varied along the nanochains and thus within a single aerogel. To determine the electrochemically active surface area (ECSA) of the Pd–Pt aerogels for application in electrocatalysis, we used the electrochemical CO stripping method. Due to their high porosity and extended network structure, the resulting values of the ECSA for the Pd–Pt aerogels were higher than that for a commercially available unsupported Pt black catalyst. We show that the Pd–Pt aerogels possess a high utilization of catalytically active centers for electrocatalytic applications based on the nanostructured bimetallic framework. Knowledge about the homogeneity and chemical distribution of the bimetallic aerogels can help to further optimize their preparation by the spontaneous one-step gelation process and to tune their electrocatalytic reactivity.

Die Morphologie der Buchlungen von Arachniden (Arachnida Lamarck, 1801 – Arthropoda, Chelicerata) wurde in der vorliegenden Dissertation einer streng vergleichenden Analyse unterzogen, welche mit Hilfe moderner Methoden eine neue Sicht auf die Phylogenie der Arachniden eröffnet. Aus dem Vergleich mit den potentiellen Schwestergruppen (Xiphosura, Eurypterida) und mit Skorpionsfossilien erweist sich der einmalige Landgang eines gemeinsamen Vorfahrens aller rezent terrestrischen Arachniden. Buchlungen-Daten von 200 rezenten + 2 fossilen Skorpionen, 16 Geißelspinnen (Amblypygi), 17 Geißelskorpionen (Thelyphonida), einem Schizomiden (Schizomida), einem ausgestorbenen Trigonotarbiden (Trigonotarbida) und der Außengruppe, den rezenten Pfeilschwanzkrebsen (Xiphosura), wurden zu einem illustrierten Katalog zusammengestellt. Die unüberschaubare Vielfalt der oft graduell variierenden Strukturen macht die eindeutige Definition der Merkmale und auftretenden Merkmalszustände notwendig. Es wurden folgende 5 Merkmale definiert: (1) die Oberflächen der Atemlamellen, (2) der Lamellenrand, (3) der posteriore Stigmenrand, (4) der anteriore Stigmenrand und (5) die Wand des Atriums. Hierbei tragen die Merkmale 1-3 mit ihrer unerwarteten Fülle innerhalb der Skorpione maßgeblich zur Aufklärung ihrer Verwandtschaftsverhältnisse bei. Ähnliches wird von den Merkmalen 4 und 5 bezogen auf die Uropygi s. lat. vermutet. Ein sechstes Merkmal (Sensillen/Poren) wurde definiert, doch nur vereinzelt erfasst. Raster-Elektronenmikroskopie diente der Erfassung der cuticulären Feinstruktur der Buchlungen. Die Struktur der Buchlungen im Gesamten wurde mittels histologischer Schnittserien und mit auf µCT basierenden 3D-Rekonstruktionen untersucht. Für die Untersuchung von Trigonotarbiden-Fossilien wurde eine Methode entwickelt, die 3D-Rekonstruktion aus Sequenzen von Mikrofotos in unterschiedlichen Fokusebenen generiert. / Strict comparative analyses of the morphology of arachnid book lungs (Arachnida Lamarck, 1801 - Arthropoda: Chelicerata) were carried out in the present doctoral thesis using modern methods, resulting in a new perspective on arachnid phylogeny. Comparisons with potential aquatic sistergroups (Xiphosura and/or Eurypterida) and fossil scorpions give rise to the hypothesis of the unique terrestrialization of ancestors, which is common for all arachnids. Data from 200 Recent + 2 extinct scorpions, 16 whip spiders (Amblypygi), 17 whip scorpions (Thely-phonida), 1 schizomid (Schizomida), 1 extinct trigonotarbid (Trigonotarbida) and 1 outgroup - horseshoe crab (Xiphosura) are assembled into an illustrated catalogue of arachnid book lungs. Following the observations of these gradually differing cuticular structures the vast variation of book-lung fine structure across Arachnida requires unequivocal definition of characters and character states. Five characters are defined, which are assigned to distinct homologous book-lung structures: (1) the surface structure of the respiratory lamellae, (2) structure of the distal edges of the lamellae, (3) the posterior edge of the spiracle, (4) the anterior edge of the spiracle and (5) the structure of the wall lining the atrial chamber. Especially the book-lung characters 1-3 contain unexpected information, which helps resolve relationships within Scorpiones to a high degree, and characters 4 and 5 are of considerable importance for Uropygi s. lat. One sixth character (sensilla/pores) is mentioned, but sporadically examined. However, cuticular book-lung fine structure is studied using SEM, the gross morphology is reassessed using histological sectioning and 3D-reconstructions based on µCT. For investigations on trigonotabid fossils a new method yielding 3D-reconstructions from stacks of subsequent focal layers was developed.

In dieser Arbeit werden lambda-Strukturen und s-Strukturen eingeführt, und Funktionen S und Lambda entwickelt, die lambda-Strukturen auf s-Strukturen abbilden und umgekehrt. lambda-Strukturen sind eng verwandt mit den in von Jensen untersuchten Prämäusen (iterierbare Prämäuse dieser Art sind lambda-Strukturen), und s-Strukturen wurden in Anlehnung an die von Mitchell und Steel betrachteten Prämäuse definiert. Wieder sind iterierbare Prämäuse dieser Art auch s-Strukturen. Für die Definition dieser Strukturen wurde eine neue, schwache Form der initial segment condition entwickelt (die s'-ISC), die stark genug für die Anwendungen ist. Um zu zeigen, dass die hier entwickelten Funktionen die gewünschte Korrespondenz realisieren, wurden Methoden zur Übersetzung von Formeln entwickelt, die teilweise sehr allgemein gehalten sind. So ist die Übersetzung von Sigma-1-Formeln, die in einer Nachfolgerstufe der Jensen-Hierarchie gelten, in entsprechende Sigma-omega-Formeln in der Vorgängerstufe, anwendbar auf beliebige J-Strukturen. Es werden normale s-Iterationen eingeführt, die den normalen Iterationen von Prämäusen im Sinne von Mitchell-Steel nachgebildet sind, aber auf lambda-Strukturen angewandt werden, und es wird gezeigt, dass die entwickelten Funktionen komponentenweise auf Iterationen angewandt werden können, um normale s-Iterationen von lambda-Strukturen in normale Iterationen von s-Strukturen zu übersetzen, und umgekehrt. Mit diesen Methoden lassen sich auch Iterationsstrategien übersetzen, und man erhält, dass die entwickelten Funktionen normal s-iterierbare lambda-Strukturen auf normal iterierbare s-Strukturen abbilden, und umgekehrt. Auch bleiben die wesentlichen feinstrukturellen Größen, wie bspw. Projekta, und unter gewissen Voraussetzungen (soundness und 1-solidity) auch die Standard-Parameter, erhalten. / In this work we introduce lambda-structures and s-structures, and develop functions S and Lambda, which map lambda-structures to s-structures and vice versa. lambda-structures are closely related to the premice studied in recent work of Jensen (iterable premice of this kind are lambda-structures), and s-structures were defined with the premice developed by Mitchell and Steel in mind. Again, iterable premice of this kind are s-structures. For the definition of these structures, a new form of the initial segment condition condition, called s'-ISC, was developed, which is a common weakening of the versions used in by Steel and Jensen. It still suffices for the applications. In order to show that the functions introduced establish the desired correspondence, we developed methods for translating formulae, which in part are very generally applicable. For instance, the translation of Sigma-1-formulae which hold in a successor level of the Jensen-hierarchy into corresponding Sigma-omega-formulae in the predecessor level, can be applied to arbitrary J-structures. We introduce normal s-iterations, which have been designed so as to rebuild the iterations of premice in the sense of Mitchell-Steel but are applied to lambda-structures. It is shown that the translation functions can be applied component-wise to normal iterations, in order to translate normal s-iterations of lambda-structures into normal iterations of s-structures, and vice versa. Using these methods, we can also translate iteration strategies and the result is that the functions introduced in this work map normally s-iterable lambda-structures to normally iterable s-structures, and vice versa. Also,the fundamental fine structural notions, such as projecta, and under additional hypotheses (soundness and 1-solidity) standard-parameters, are preserved.

Le milieu interstellaire (MIS) joue un rôle important dans l'évolution des galaxies. Les radiations et vents stellaires, ainsi que les supernovae par exemple, sont à l'origine de nombreux processus ayant un impact sur les propriétés globales des galaxies. Cependant, l'efficacité des ces processus est liée aux propriétés et à la structure des différentes phases du MIS, et est souvent incertaine. Grace à la sensibilité et résolution accrues des nouveaux télescopes observant dans l'infrarouge lointain (FIR) et le submillimetrique (comme par exemple le Herschel Space Observatory, SOFIA et ALMA), il est désormais possible d'étudier en détail les interactions réciproques entre la formation stellaire et les différentes phases du MIS environnant. Ce travail est axé sur les propriétés physiques du gaz dans les Nuages de Magellan. Le Grand Nuage de Magellan et le Petit Nuage de Magellan, nos plus proches voisins, tout deux à métallicité sub-solaire, sont de bons laboratoires pour étudier les interactions entre la formation stellaire et l'environnement. La région 30 Doradus, dans le Grand Nuage de Magellan, l'une des plus massives et des plus actives régions de formation stellaire connues dans notre voisinage, est étudiée en détail. Les observations des télescopes spatiaux Herschel et Spitzer sont utilisées pour contraindre la pression, le champ de radiation ainsi que la structure tri-dimensionnelle des régions de photo-dissociation (PDR), en combinaison avec le code PDR de Meudon. Cette modélisation permet également d'estimer la fraction de gaz moléculaire qui n'est pas détectée par le traceur généralement utilisé CO. Cette méthode est ensuite appliquée à d'autres régions de formation stellaire dans les Nuages de Magellan, présentant différents environnements. Cette étude permet d'évaluer les diagnostiques clés du chauffage et du refroidissement du gaz à faible métallicité dans des régions actives de formation stellaire, avec une bonne résolution spatiale. Ceci constitue une première étape pour mieux comprendre les observations non résolues de telles régions dans des galaxies lointaines. / The interstellar medium (ISM) plays a major role in galaxy evolution. Feedback from stars, in particular, drives several processes responsible for the global properties of a galaxy. However, the efficiency of these processes is related to the properties and structure of the different gas and dust ISM phases and remains uncertain. Due to the increased sensitivity and resolution of the new far-infrared (FIR) and submillimeter facilities (such as the Herschel Space Observatory, SOFIA and ALMA, in particular), it now becomes possible to study in detail the interplay between star formation and the surrounding ISM phases. This work focuses on the physical properties of the gas in the Magellanic Clouds. The Large Magellanic Cloud and the Small Magellanic Cloud, our closest neighbors, both at subsolar metallicity, are good laboratories to study the interaction between star formation and environment.The 30 Doradus region, in the Large Magellanic Cloud, one of the most massive and active star forming region known in our neighborhood, is first studied in detail. We use the FIR and mid-infrared tracers, provided by the space telescopes Herschel and Spitzer, to bring constrains on the pressure, radiation field and 3D structure of the photo-dissociation regions (PDR) in this extreme region, using the Meudon PDR code. This modeling allows us to estimate the fraction of molecular gas not traced by CO, also known as the "CO-dark" molecular gas.We apply this method to other star forming regions of the Magellanic Clouds, which are characterized by different environmental conditions. This study allows us to evaluate key diagnostics of the gas heating and cooling of low metallicity resolved starburst regions. This is a first step toward understanding similar but unresolved regions, in high-redshift galaxies.

Les applications émergentes des nanocristaux de CdSe nécessitent une compréhension approfondie des propriétés d’émission et de relaxation des sous-niveaux de structure fine de l’exciton de bord de bande. Cette thèse porte sur l’étude spectroscopique de nanocristaux individuels de CdSe présentant une photostabilité remarquable aux températures cryogéniques. La distribution spectrale de leur photoluminescence en fonction de la température et d’un champ magnétique appliqué fournit une signature précise des niveaux de plus basse énergie, révélatrice de leur morphologie et leur structure cristalline. Une méthode d’excitation de la luminescence de haute résolution spectrale a été développée pour sonder la totalité des niveaux de structure fine. Les raies de recombinaison des huit états ont ainsi été résolues pour la première fois dans une situation de levée totale de dégénérescence produite par l’anisotropie des nanocristaux et l’application d’un champ magnétique. L’excitation sélective des nanocristaux dans les niveaux supérieurs de la structure fine permet aussi d’étudier les mécanismes de relaxation de spin entre les branches excitoniques à trou lourd et à trou léger. Des canaux de relaxation sélectifs peuvent notamment être mis à profit pour préparer un nanocristal dans un niveau quantique unique.Des nanocristaux à double coque ont été conçus pour être efficacement photo-chargés, produisant une émission stable à partir de l’exciton chargé (trion) à la température de l’hélium liquide. La recombinaison du trion est purement radiative, avec une signature spectrale caractérisée par une raie d’émission sans phonon unique et intense. Sous champ magnétique, son éclatement en quatre composantes Zeeman livre les facteurs de Landé de l’électron et du trou. L’analyse des poids de ces composantes permet aussi de trouver le taux de relaxation de spin du trion et le signe de sa charge. Une inhibition remarquable de la relaxation de spin se produit lorsque l’éclatement Zeeman est inférieur à l’énergie du premier mode de phonons acoustiques du nanocristal. / The development of emerging applications of CdSe nanocrystals requires a detailed understanding of the band-edge exciton fine structure and relaxation pathways. This thesis is focused on cryogenic spectroscopy of single nanocrystal with a remarkable photostability. Photoluminescence spectra as a function of temperature and under external magnetic fields provide a spectral fingerprint of the low energy sub-levels, revealing the morphology and the crystal structure of individual nanocrystals. In order to probe the entire band-edge exciton fine structure, a high resolution luminescence excitation technique has been developed. Zeeman and anisotropy-induced splittings are used to reveal the entire 8-state band-edge fine structure, enabling complete comparison with band-edge exciton models. State selective excitation allows the preparation of single quantum states. It is also used to map the hole spin relaxation pathways between the fine structure sub-levels.Charged quantum dots provide an important platform for a range of emerging quantum technologies. Double shell CdSe nanocrystals are engineered to efficiently ionize at cryogenic temperatures, resulting in trion emission with a single sharp zero-phonon line and a near-unity quantum yield. Zeeman splitting of this line enables direct determination of electron and hole g-factors. Spin relaxation is observed in high fields, enabling identification of the trion charge. Importantly, we show that spin flips are completely inhibited for Zeeman splittings below the low-energy bound for confined acoustic phonons. This charac- teristic unique to colloidal quantum dots has potential applications in single spin coherent manipulation.

In the growing field of spintronics there is a strong need for development of flexible lightweight semi-conducting magnets. Molecular organic-based magnets are attractive candidates since it is possible to tune their properties by organic chemistry, making them so-called “designer magnets”. Vanadium tetracyanoethylene, V(TCNE)x, is particularly interesting since it is a semiconductor with Curie temperature above room temperature (TC~400 K). The main problem with these organic-based magnets is that they are extremely air sensitive. This thesis reports on the frontier electronic structure of the V(TCNE)x by characterization with photoelectron spectroscopy (PES) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy. It also presents a new and more flexible preparation method of this class of organic-based thin film magnets. The result shows improved air stability of the V(TCNE)x prepared with this method as compared to V(TCNE)x prepared by hitherto used methods.