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The aim of this thesis is finding a geometric configuration that allows electron insertion into a Gabor plasma lens in order to increase the density of the confined electrons and provide ignition conditions at parameters where ignition is not possible. First, simulations using CST and bender were conducted to investigate several geometric configurations in terms of their performance of inserting electrons manually. One particular design has been chosen as a basis for an experiment. In order to prepare the experiment, further simulations using the code bender have been conducted to investigate the density distribution that is formed inside the Gabor lens when inserting electrons transversally in compliance with the chosen design. Additionally, bender was used to investigate the impact of the initial electron energy on the distribution inside the lens. Simulations with and without space charge effects have shown a significant impact of the space charge effects on the resulting density dstribution. Therefore, space charge effects have proven to be the major electron redistribution process. A given electron source was characterised in order to find the performance under the conditions inside a Gabor lens. In particular, a transversal magnetic field that will be present in the experiment has to be compensated by shielding the inner regions of the source by a μ-metal layer. Using a μ-metal shield, transversal magnetic fields are sufficiently tolerable to perform measurements in a Gabor lens. Additionally, operating close to 100 eV electron energy yields a maximum in the emitted current. Adding a Wehnelt cylinder to the electron source furthermore improves the extracted current to roughly 1 mA. A test stand consisting of a newly designed anode for the Gabor lens, as well as a terminal for the electron source, was constructed. The electron source was thoroughly characterised in the environment of the Gabor lens and the ignition properties of the new system were evaluated. In further experiments, electron beam assisted ignition by increasing the residual gas pressure was observed and the impact of the position of the electron source on the ignition properties was investigated. In addition, ignition of a sub-critical state, that is a state consisting of potential, magnetic field and pressure that did not yet perform ignition by itself, was performed by increasing the extracted current from the electron source. Finally, the electron source was used to influence a pre-ignited plasma. The density was measured, which was increased by the use of the electron source in most cases. This project is part of the EDEN collaboration (Electron DENsity boosting) of the NNP Group at IAP Frankfurt with INFN institutes in Bologna and Catania.
Electron identification with a likelihood method and measurements of di-electrons for the CBM-TRD
(2017)
In this work a likelihood method has been implemented and investigated as particle identification algorithm for the CBM-TRD.
The creation of the probability distributions for the likelihood method via V0-topologies seems to be feasible and the purity of the obtained samples is sufficient for the usage in the likelihood method.
The comparison between the ANN and the likelihood method shows no differences in the identification performance. The pion suppression factor reaches the same values for the same electron identification efficiencies and the yields of the resulting di-lepton signals are comparable. The signal-to-background ratios for both methods have the same values and show a value of about 10−2 in the invariant mass range of minv = 1.5 - 2.5 GeV/c2, which is expected to be sufficient to provide access to the thermal in-medium and QGP radiation.
The investigation of a detector system without a TRD shows no pion suppression for a momentum above p = 6 GeV/c. Therefore, the background contributions increase drastically and the signal-to-background ratio decreases at all invariant masses, but especially in the invariant mass range of minv = 1.5 - 2.5 GeV/c2.
The background contributions in the invariant mass range of minv = 1.5 - 2.5 GeV/c 2 are also influenced by the selected electron identification efficiency of the TRD, which significantly shifts the fraction of the eπ contributions relative to the total number of pairs.
Since 2014 the ECB has implemented a massive expansion of monetary policy including large-scale asset purchases and negative policy rates. As the euro area economy has improved and inflation has risen, questions concerning the future normalization of monetary policy are starting to dominate the public debate.
The study argues that the ECB should develop a strategy for policy normalization and communicate it very soon to prepare the ground for subsequent steps towards tightening. It provides analysis and makes proposals concerning key aspects of this strategy. The aim is to facilitate the emergence of expectations among market participants that are consistent with a smooth process of policy normalization.
Gestern Abend lief die sehenswerte TV-Dokumentation "Nervöse Republik – Ein Jahr Deutschland" von Stephan Lamby in der ARD. Der Journalist hat bekannte Politiker wie Sarah Wagenknecht, Peter Tauber, Heiko Maas, Frauke Petry und Katarina Barley ein Jahr lang begleitet und sie zu der veränderten politischen und gesellschaftlichen Stimmung interviewt. ...
Innerhalb der historischen Kinder- und Jugendliteraturforschung gilt Karin Richter als ausgewiesene Kennerin der ostdeutschen Kinderund Jugendliteratur von 1949 bis 1990. Noch in der ehemaligen DDR habilitierte sich Richter zur Wirkungsästhetik und Poetik in der Kinder- und Jugendliteratur (1987) an der Universität Halle/ Wittenberg, von 1993–2008 war sie Professorin für Literarische Erziehung/Kinder- und Jugendliteratur an der Erziehungswissenschaftlichen Fakultät der Pädagogischen Hochschule/Universität Erfurt. In den vergangenen Jahren konzentrierten sich Richters Aktivitäten nur noch vereinzelt auf die kinder- und jugendliterarischen Texte der DDR (vgl. III). Auch dieser Band präsentiert keine neue Forschung, sondern eine persönliche Aufsatzsammlung von Beiträgen, deren Erstveröffentlichungen z. T. bis in die DDR zurückreichen. ...
Comics sind nicht linear, es gibt keine Vorgabe, ob wir zuerst die Bilder betrachten oder den Text lesen. So lassen die Brüche zwischen den Paneln, zwischen den Zeichen, zwischen den einzelnen Heften auch immer einen Raum entstehen. Einen Grenzraum, der verschiedene Lesarten und Fragen ermöglicht. Die dem Comic spezifische Ästhetik der Brüche und Wiederholungen wird im Comic 'Hure h' explizit benutzt, um Fragen nach Identität, Geschlechterrollen und Begehren aufzuwerfen und gesellschaftliche Zuschreibungen zu hinterfragen. Identität wird im Comic 'Hure h' nicht als feststehende Einheit dargestellt, sondern in ihrer fragmentierten Struktur gezeigt. Die Brüche in der Darstellung von Identität und die parodistische Bezugnahme auf gesellschaftliche Akte machen den Raum für eine Grenzüberschreitung der Geschlechternormen auf. Die Differenz zwischen den dargestellten Zeichen und deren imaginierten gesellschaftlichen Konnotationen lässt die Möglichkeit entstehen, dass Normvorstellungen und Konstruktionen von 'gender' und 'sex' als solche aufgezeigt und dadurch aufgebrochen werden.
Hatte Heidegger noch davon gesprochen, dass der Stein "weltlos" sei und auch "Pflanzen und Tiere […] gleichfalls keine Welt haben" und als "Zeug" und "Verlässlichkeit" zu einer Welt gehören, die sich dem Bewusstsein öffnet, verstehen Deleuze und Guattari das 'faire monde' gerade als eine dezentrierende Relationalität, ein Werden hin zur Welt in ihrer Vielfältigkeit und Unbestimmtheit, ja eine Bewegung des abstrakt und nichtwahrnehmbar Werdens. Julia Bee greift in ihrem Beitrag diese Idee auf und versteht Spiel als einen Modus der Praktiken des 'worlding', als ein "Anders-Werden". In Anlehnung an Brian Massumi wird das als ob des Spiels nicht als nachahmender Bezug auf eine bestehende Realität, sondern als Abstraktion und ein Mehr verstanden, das eine Ebene der Virtualität eröffnet. Am Beispiel von "Begone Dull Care", einem Animationsfilm von Norman McLaren und Evelyn Lamberts, beschreibt Bee ein solches "vibrierendes, pulsierendes und ständig transformierendes Feld der tanzenden Wahrnehmung".
Echolocation allows bats to orientate in darkness without using visual information. Bats emit spatially directed high frequency calls and infer spatial information from echoes coming from call reflections in objects (Simmons 2012; Moss and Surlykke 2001, 2010). The echoes provide momentary snapshots, which have to be integrated to create an acoustic image of the surroundings. The spatial resolution of the computed image increases with the quantity of received echoes. Thus, a high call rate is required for a detailed representation of the surroundings.
One important parameter that the bats extract from the echoes is an object’s distance. The distance is inferred from the echo delay, which represents the duration between call emission and echo arrival (Kössl et al. 2014). The echo delay decreases with decreasing distance and delay-tuned neurons have been characterized in the ascending auditory pathway, which runs from the inferior colliculus (Wenstrup et al. 2012; Macías et al. 2016; Wenstrup and Portfors 2011; Dear and Suga 1995) to the auditory cortex (Hagemann et al. 2010; Suga and O'Neill 1979; O'Neill and Suga 1982).
Electrophysiological studies usually characterize neuronal processing by using artificial and simplified versions of the echolocation signals as stimuli (Hagemann et al. 2010; Hagemann et al. 2011; Hechavarría and Kössl 2014; Hechavarría et al. 2013). The high controllability of artificial stimuli simplifies the inference of the neuronal mechanisms underlying distance processing. But, it remains largely unexplored how the neurons process delay information from echolocation sequences. The main purpose of the thesis is to investigate how natural echolocation sequences are processed in the brain of the bat Carollia perspicillata. Bats actively control the sensory information that it gathers during echolocation. This allows experimenters to easily identify and record the acoustic stimuli that are behaviorally relevant for orientation. For recording echolocation sequences, a bat was placed in the mass of a swinging pendulum (Kobler et al. 1985; Beetz et al. 2016b). During the swing the bat emitted echolocation calls that were reflected in surrounding objects. An ultrasound sensitive microphone traveling with the bat and positioned above the bat’s head recorded the echolocation sequence. The echolocation sequence carried delay information of an approach flight and was used as stimulus for neuronal recordings from the auditory cortex and inferior colliculus of the bats.
Presentation of high stimulus rates to other species, such as rats, guinea pigs, suppresses cortical neuron activity (Wehr and Zador 2005; Creutzfeldt et al. 1980). Therefore, I tested if neurons of bats are suppressed when they are stimulated with high acoustic rates represented in echolocation sequences (sequence situation). Additionally, the bats were stimulated with randomized call echo elements of the sequence and an interstimulus time interval of 400 ms (element situation). To quantify neuronal suppression induced by the sequence, I compared the response pattern to the sequence situation with the concatenated response patterns to the element situation. Surprisingly, although the bats should be adapted for processing high acoustic rates, their cortical neurons are vastly suppressed in the sequence situation (Beetz et al. 2016b). However, instead of being completely suppressed during the sequence situation, the neurons partially recover from suppression at a unit specific call echo element. Multi-electrode recordings from the cortex allow assessment of the representation of echo delays along the cortical surface. At the cortical level, delay-tuned neurons are topographically organized. Cortical suppression improves sharpness of neuronal tuning and decreases the blurriness of the topographic map. With neuronal recordings from the inferior colliculus, I tested whether the echolocation sequence also induced neuronal suppression at subcortical level. The sequence induced suppression was weaker in the inferior colliculus than in the cortex. The collicular response makes the neurons able to track the acoustic events in the echolocation sequence. Collicular suppression mainly improves the signal-to-noise ratio. In conclusion, the results demonstrate that cortical suppression is not necessarily a shortcoming for temporal processing of rapidly occurring stimuli as it has previously been interpreted.
Natural environments are usually composed of multiple objects. Thus, each echolocation call reflects off multiple objects resulting in multiple echoes following the calls. At present, it is largely unexplored how neurons process echolocation sequences containing echo information from more than one object (multi-object sequences). Therefore, I stimulated bats with a multi-object sequence which contained echo information from three objects. The objects were different distances away from each other. I tested the influence of each object on the neuronal tuning by stimulating the bats with different sequences created from filtering object specific echoes from the multi-object sequence. The cortex most reliably processes echo information from the nearest object whereas echo information from distant objects is not processed due to neuronal suppression. Collicular neurons process less selectively echo information from certain objects and respond to each echo.
For proper echolocation, bats have to distinguish between own biosonar signals and the signals coming from conspecifics. This can be quite challenging when many bats echolocate adjacent to each other. In behavioral experiments, the echolocation performance of C. perspicillata was tested in the presence of potentially interfering sounds. In the presence of acoustic noise, the bats increase the sensory acquisition rate which may increase the update rate of sensory processing. Neuronal recordings from the auditory cortex and inferior colliculus could strengthen the hypothesis. Although there were signs of acoustic interference or jamming at neuronal level, the neurons were not completely suppressed and responded to the rest of the echolocation sequence.