1,721,386 research outputs found
Control of airborne nanoparticles
No full textSingle-particle diffractive imaging at x-ray free-electron lasers is a promising technique for reconstructing the three dimensional structure of biomolecules such as proteins or viruses, avoiding drawbacks of conventional diffractive imaging methods, such as the need of crystalline sample. In order to achieve atomic resolution a huge amount of diffraction patterns of identical particles, ideally in gas phase are needed. Currently such experiments are limited, amongst other things, by the sample delivery set-up, typically aerosol injectors, not providing the densities necessary, to have on average a single particle in the x-ray focus. Within this dissertation, several improvements either of the delivery set-up itself, or of the characterization scheme used to optimize aerosol injectors are presented. A new simulation framework for the computation of particle trajectories through aerosol injection set-ups was developed to not only be limited by empirically derived values for specific conditions, e. g., room temperature, but to be general applicable to particles in rarefied gases. These simulations are able to reliably describe density measurements of a current aerodynamic lens stack injector. Also they are able to reproduce data measured for injection devices, developed and build within the scope of this work. These new injectors are an aerodynamic lens stack tailor made for the needs of single- particle diffractive imaging experiments with a quick release mount allowing for fast adoption of the geometry and a buffer gas cell using helium at a temperature of 4 K and providing shock frozen sample. In addition a method to measure pressure maps at the tip of an aerosol injector within a vacuum chamber was developed and demonstrated.Die Nutzung der Röntgenstrahlung von freien-elektronen Lasern verspricht die drei dimensionalen Struktur von einzelnen Biomolekülen, wie Proteinen oder Viren zu bestimmen. Um dabei atomare Auflösung erreichen zu können sind sehr viele Beugungsbildern identischer Teilchen notwendig. Durch experimente an einzelnen Teilchen können dabei die üblichen Nachteile, wie die Notwendigkeit von kristallinen Strukturen umgangen werden. Aktuell limitiert dabei noch Probenufbau, typischerweise ein Aerosolinjektors der verantwortlich dafür ist die Probe in Form eines Molekühlstrahls bereit zu stellen, die Effizienz dieser Experimente. Der Molekühlstrahl weßt nicht die ausreichende Teilchendichte auf, die notwendig wäre um im Schnitt ein einzelnes Teilchen im Fokus des Röntgenstrahles zu haben. Im Zuge dieser Dissertation werden mehrere Verbesserungen, entweder an dem Probenaufbau selbst, oder an dem Characterisierungsschema, das genutzt wird um diesen Aufbau zu Optimieren, vorgestellt. Ein neues Simulationskonzept für die Berechnung von Teilchentrajektorien durch Aerosolinjektoren wurde aufgesetzt. Dabei sind die Simulationen nicht mehr auf empirisch bestimmte Werte angewiesen und somit auch nicht mehr in der Anwendbarkeit auf bestimmte Konditionen, wie zum Beispiel Raumtemperatur, beschränkt. Diese Simulation sind in der Lage Messungen von einem aktuellen Aerodynamischen Linsen System zu beschreiben. Zudem können sie Messdaten reproduzieren, die für Injektoren aufgenommen wurden, die im Rahmen dieser Arbeit entwickelt und gebaut wurden. Einer dieser neuen Injektoren is ein Aerodynamisches Linsen System angepasst an die Bedürfnisse von Röntgenbeugungsexperimenten. Es verfuugt über einen Schnellverschluss und erlaubt schnell die Geometrie zu welchseln. Der zweite Injektor is eine Puffergaszelle die mit Helium bei Temperaturen von 4 K arbeitet und schockgefrorene Probem bereitstellt. Zudem wurde eine Methode konzipiert und demonstriert um Drücke an unterschiedlichen Positionen an der Spitze eines Aerosolinjektors zu messen
Toward cryogenic beams of nanoparticles and proteins
No full textTo determine the structure of (bio-)nanoparticles, and possibly, the dynamics and function of it, the ultrashort and bright pulses generated from x-ray free-electron lasers can be used. X-ray free-electron lasers provide x-ray pulses with pulse durations of a few tens of femtoseconds and high photon numbers, sufficiently high to record scattering off a single macromolecule. This method of imaging is called single-particle diffractive imaging. The ultrashort pulses outrun radiation damage and an intact particle is imaged. This promising technique has one bottleneck: sample injection. Currently, the output of the experiments is limited by a low number of collected diffraction patterns and a low hit rate. The (bio-)nanoparticles are injected into the x-ray beam with aerosol injectors consisting of an aerosolization source and an aerodynamic lens stack to generate a continuous stream of nanoparticles. One concern despite the low hit rate in these experiments is the purity of the particle beam, that is consisting of clusters of nanoparticles, different charge states and spatial conformers. Within this thesis, sample delivery methods are improved toward the overall goal of imaging single proteins. To study the injector properties, a novel particle-beam characterization method to image the transverse particle beam profile is presented, capable of characterizing the particle flux and the particles’ velocity from an aerodynamic lens stack injector. Improvements on the aerosol sample delivery are made based on existing aerosol injectors to improve the hit rate through better particle focusing. Using simulations, the optimization of the geometry is performed efficiently. The optimized injector geometry is implemented in the setup and used for generating a particle beam of gold nanoparticles. Toward the aim of imaging single proteins, important steps are taken in understanding the particle-beam formation for smaller nanoparticles using particle trajectory calculations and extending the particle-beam detection towards smaller nanoparticles using optical scattering. Another crucial step in sample delivery is taken by generating a particle beam consisting of shock-frozen sub-100 nm particles, opening up the path toward a sample delivery setup that is capable of providing a pure particle beam for single-particle imaging experiments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Control of Bionanoparticles with Electric Fields
No full textSingle-particle imaging (SPI) is a method that promises high-resolution structure determination of artificial or biological nanoparticles, including proteins. In a thin stream, these particles are guided into the brilliant flashes of free-electron lasers. Upon interception, incoming photons diffract off randomly-oriented individual nanoparticles in the gas phase. The low-signal snapshots are then classified and combined to retrieve the real-space structure of the investigated molecules. Since this is the result from averaging over hundreds of thousands of individual images, in order to achieve atomic resolution with SPI, the nanoparticles need to be identical on the same length scales. For various reasons, biological molecules, like proteins, have structural variability. Different oligomeric or conformational states may co-exist already in solution and multiple charges, for example acquired in the process of aerosolization, deform soft proteins due to Coulomb stretching. When not accounted for, these and other morphologic deviations introduce positional ambiguity and effectively reduce the overall achievable experimental resolution. In light of these challenges, methods to characterize and control the particles to deliver high-purity particle beams in SPI experiments need to be developed. Here I present experimental results on the production of beams of aerosolized nanoparticles with well-characterized charge- and oligomeric states and ways to modulate their charge-state distributions. Furthermore, based on computational modeling, an electrostatic deflection setup to enable the spatial separation of conformers is proposed, in which charge-neutral biological macromolecules can be separated according to their conformational states. These findings are crucial steps toward atomic-resolution imaging of identical macromolecules in the gas phase, which can be directly applied in SPI experiments.Single-Particle Imaging (SPI) ist eine Methode, die hochauflösende Strukturbildgebung von künstlichen oder biologischen Nanopartikeln wie Proteinen verspricht. Diese Teilchen werden in einem dünnen Strahl in die brillanten Pulse von Freie-Elektronen-Lasern gelenkt. Bei einem Treffer werden wenige Photonen an zufällig orientierten einzelnen Nanopartikeln in der Gasphase gestreut. Die signalschwachen Schnappschüsse werden klassifiziert und kombiniert, um die Raumstruktur der untersuchten Moleküle zu bestimmen. Da dies das Ergebnis der Mittelung hunderttausender einzelner Bilder ist, müssen die Nanopartikel strikt identisch sein, um mit SPI atomare Auflösung zu realisieren. Biologische Moleküle, wie zum Beispiel Proteine, weisen jedoch aus verschiedenen Gründen strukturelle Variabilität auf.Verschiedene Oligomere oder Konformationszustände können bereits in Lösung koexistieren, und Mehrfachladungen, die beispielsweise bei der Aerosolisierung entstehen, verformen flexible Proteine aufgrund Coulomb’scher Streckung. Wenn nicht berücksichtigt, führen diese und andere morphologische Abweichungen zu Positionsambiguität und verringern die experimentell erreichbare Strukturauflösung. Angesichts dieser Herausforderungen müssen Methoden zur Charakterisierung und Kontrolle der Partikel entwickelt werden, um hochreine Partikelstrahlen für SPI-Experimente zu generieren. In dieser Arbeit werden experimentelle Ergebnisse zur Erzeugung von Strahlen aerosolisierter Nanopartikel mit eingehend charakterisierten Ladungs- und Oligomerzuständen sowie Möglichkeiten zur Modulation ihrer Ladungszustandsverteilungen vorgestellt. Darüber hinaus wird auf Grundlage von Simulationen ein elektrostatischer Deflektor beschrieben, mit dem ladungsneutrale biologische Makromoleküle entsprechend ihrer Konformationszustände getrennt werden können. Diese Erkenntnisse sind entscheidende Schritte auf dem Weg zu atomar aufgelöster Bildgebung identischer Moleküle in der Gasphase, die unmittelbar in SPI-Experimenten angewendet werden können
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Charakterisierung von Aerosolstrahlen mittels Laserionisationsmassenspektrometrie
No full textEines der interessantesten heutigen Projekte in der Biochemie und der Molekülphysik ist die Beobachtung von biologischen oder chemischen Reaktionen in Molekülen mit atomarer räumlicher Präzision. Eine vielversprechende Methode hierfür basiert auf dem Einsatz einer aerodynamischen Linse zur Fokussierung der Teilchen und der Untersuchung dieser Moleküle mit FreieElektronen-Lasern, um die Struktur der Moleküle, also die Positionen der Elektronen und Atomkerne, festzustellen. In dieser Arbeit wurde zuerst anhand der Proteinase K gezeigt, dass bei der Aerosolbildung und der Injektion ins Vakuum die Struktur der Probenmoleküle weitesgehend intakt bleibt. Desweiteren wurde gezeigt, dass es möglich ist, bevor man zum eigentlichen Ex-periment an den Freie-Elektronen-Laser geht, bereits im Labor die aerodynamische Linse oder jegliches anderes Fokussiersystem mit Hilfe eines Femtosekundenlasers zu kalibrierenund mit dieser Methode das Strahlprofil des Aerosols zu vermessen
Preparatory studies on diiodo-molecules for use in gas phase electron diffraction
No full textIn the framework of this thesis several candidate molecules were tested with regard to their feasibility for benchmark electron diffraction experiments on controlled gaseous samples. Electron diffraction serves as a tool for structure determination of molecules in the gas phase without the need for crystalline samples. This is especially important for a variety of biomolecules which are difficult to crystallize and cannot be examined using conventional x-ray diffraction techniques. The diffraction signal, and therefore informational content of structure, can be increased when the molecules are prepared in a controlled fashion. During this work 2,5-Diiodobenzonitrile, 1,2-Diiodoethane and 4,4’-Diiodoazobenzene were chosen as candidate molecules and their suitability for electron diffraction was verified with the help of simulations and experimental studies. The simulated diffraction patterns were created using the program CMIdiffract and served as a first aid for deciding on which molecule would provide the most analysable data. Two candidates, 2,5-Diiodobenzonitrile and 1,2-Diiodoethane, were selected and introduced into an experimental set-up that combined a molecular beam creating apparatus with an electron gun. Firstly, attempts were made to create stable molecular beams of the samples and determine their molecular composition by recording time-of-flight spectra. Subsequently, control of molecules was tested by deflecting the beams with inhomogeneous electrostatic fields which leads to a separation of the target molecules from seeding gas. Successful deflection served as a first preparatory step towards the actual electron diffraction experiment. Mandatory properties of molecules for use in electron diffraction are discussed and the examined candidate molecules are assessed regarding their experimental feasibility. Encountered difficulties with the selected candidate molecules and possible solutions are proposed in the outlook of this thesis
Untersuchung der Photoelektronen-Winkelverteilungen von ausgerichteten Molekülen in der Gasphase
No full textThis work investigates if and how photoelectron diffraction might become a suitable tool to measure structural changes of small molecules in the gas-phase with femtosecond temporal and angstrom spatial resolution. Molecular-frame photoelectron angular distributions (MFPAD) of O(1)-, S(2)- and F(1)-electrons from carbonyl sulfide and fluoromethane molecules have been measured in photoelectron-photoion coincidence experiments at the synchrotron radiation sources DORIS and PETRA III (kinetic energy of photoelectrons: 16 eV < E < 283 eV). It has been investigated which degree of molecular orientation is necessary to observe a rich structure in the MFPADs, which influence linearly and circularly polarized photons have on MFPADs, and if MFPADs of photoelectrons with a few 100 eV kinetic energy can be described by a simple scattering model.The relation of the measured MFPADs to the molecular structure was examined by MSX calculations. At the free-electron laser FLASH, S(2)-photoelectron angular distributions of adiabatically laser-aligned OCS molecules have been measured (E=44 eV). In an IR-pump-XUV-probe experiment at FLASH, molecular dynamics have been observed in the photoelectron angular distributions with femtosecond temporal resolution. The influence of the alignment and the pump laser on molecules and on photoelectrons has been discussed. This work indicates avenues how to reach the goal of observing ultrafast molecular structural changes by photoelectron diffraction
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