1,124 Works

Traceability of the Hannover FG5X-220 to the SI units

Manuel Schilling & Ludger Timmen
The absolute measurement of g is currently realized through the laser interferometric measurement of a free falling retro-reflector. The Micro-g LaCoste FG5X is a free-fall gravimeter with a laser interferometer in Mach-Zehnder configuration which uses simultaneous time and distance measurements to calculate the absolute value of g. Because the instrument itself contains the necessary working standards for precise time and length measurements, it is considered independent of external references. The timing is kept with a...

Konzepte zur Beleuchtung von Lichtmodulatoren

Peer-Phillip Ley, Marcel Philipp Held, Alexander Wolf & Roland Lachmayer
Hochauflösende Pixellichtsysteme werden mithilfe verschiedener Modulatortechnologien in unterschiedlichen Anwendungsbereichen eingesetzt. Zur Umsetzung wirkungsgradstarker Systeme sind geeignete Beleuchtungskonzepte der Modulatorfläche erforderlich. Dieses Paper stellt anwendungsbezogene Vor- und Nachteile abbildender und nichtabbildender Beleuchtungskonzepte gegenüber.

Anforderungen an die Ausleuchtung von Lichtmodulatoren

Marcel Philipp Held, Peer-Phillip Ley, Alexander Wolf & Roland Lachmayer
Hochaufgelöste Beleuchtungssysteme erfordern für einen effizienten und lichtstarken Betrieb eine möglichst exakte Ausleuchtung der lichtmodulierenden Fläche. In diesem Paper werden relevante Technologien gegenübergestellt und hinsichtlich eines Einsatzes in der Fahrzeuglichttechnik evaluiert.

Herstellung, Charakterisierung und mikromechanische Modellierung von magneto-sensitiven Elastomeren

Sahbi Aloui
Magneto-sensitive elastomers (MSE) belong to the class of smart materials. They show a self-adjusting and adaptive behaviour in random occurrences and are also denoted as intelligent materials. They are characterised by the ability to react in a target-oriented acting to changes in operating or environmental conditions without external regulation. MSE are prepared by mixing magnetic fillers within the rubber matrix. Mechanical and magnetorheological measurements show that particle size, filler loading and coupling agent considerably influence...

Targetomics, application of in vitro screening methods for the identification of new drugs

Sona Mohammadi Ostad Kalayeh
The effect of various natural products and chemical compounds to their corresponding molecular target is often unidentified. Drugs are effective by binding to a molecule (the target) and inhibiting its function. In order to perform an efficient target-oriented drug discovery, target and related tests are needed. These tests are mostly based on a binding or catalytic function, which are usually visualized by optical methods. Subsequently, the cell- or enzyme-based drug tests can be done. In...

Bestimmung von Codephasen-Variationen bei GNSS-Empfangsantennen und deren Einfluss auf die Positionierung, Navigation und Zeitübertragung

Tobias Kersten
Die globale Positionierung, Navigation sowie Zeit- und Frequenzübertragung [positioning, navigation and timing] (PNT) ist in der heutigen Gesellschaft zu einem integralen Bestandteil des täglichen Lebens geworden, so dass die präzise und autonome Georeferenzierung in der letzten Dekade in weiten Teilen unseres Lebensbereiches rasant Einzug gehalten hat. Positionierungs- und Navigationsverfahren werden u.a. in der öffentlichen Infrastruktur, dem See-, Land- und Luftverkehr intensiv verwendet. Sicherheitskritische Anwendungen verlangen ein Integritätsmonitoring der empfangenen Signale, die robuste und zertifizierte Signale...

Ionenstrahlzerstäubte Materialmischungen zur Herstellung von spannungsfreien, optischen Schichtsystemen auf flexiblen (PMMA-) Substraten

Melanie Gauch
Durch den aktuellen Trend zu Polymeren und damit einhergehend zu flexiblen Materialien steht die optische Dünnschichttechnik vor neuen Herausforderungen. Mithilfe der physikalischen Gasphasenabscheidung (PVD), wie zum Beispiel der Ionenstrahlzerstäubung, können heutzutage qualitativ hochwertige optische Beschichtungen hergestellt werden. Diese Beschichtungen bestehen in der Regel aus Oxiden, die sich durch eine große Transparenz und eine hohe chemische Stabilität auszeichnen. Zum Beschichten von Polymeren sind Oxide jedoch nur bedingt geeignet, da oxidische Schichten meistens eine hohe Eigenspannung haben....

Investigations of boundary-layer transition and airloads on rotating blades

Armin Weiss
Measurements of surface pressure and boundary-layer transition on rotating blades is important for the validation of numerical tools, used e.g. to predict rotor efficiency in the design process. In this work, surface pressure distributions and boundary-layer transition were measured on a Mach-scaled helicopter rotor blade. Optical measurement techniques were used to obtain data at high spatial resolution and were complemented by integral thrust and local surface pressure tap measurements. Various collective pitch settings were investigated...

Tierarten im Klimawandel in Harz und Lüneburger Heide

Janine Sybertz & Michael Reich
Im Rahmen des Forschungsverbunds KLIFF („Klimafolgenforschung in Niedersachsen“, 2009 - 2013) wurde die Empfindlichkeit von insgesamt 227 nach Roter Liste gefährdeten Arten der Artengruppen Brutvögel, Amphibien, Reptilien, Tagfalter, Libellen und Heuschrecken gegenüber Auswirkungen des Klimawandels in den naturräumlichen Regionen „Harz“ und „Lüneburger Heide und Wendland“ untersucht. Neben der Empfindlichkeit gegenüber spezifisch klimawandelbedingten Auswirkungen wurde auch die Empfindlichkeit gegenüber Umweltveränderungen im Allgemeinen ermittelt, um so Rückschlüsse auf das Anpassungspotential einer Art ziehen zu können. Bis zum...

Experimental setup to characterize flow-induced anisotropy of sheet metals

F. Gutknecht, G. Gerstein, H. Traphöner, T. Clausmeyer & F. Nürnberger
For many metals, a transient variation of the yield stress can be observed when changing the orientation of a load-path. Such behavior affects the manufacturing process itself, e.g. by increasing forming forces, altered material properties or springback of the manufactured components. Hence, the aim of this work is to develop a novel experimental setup to characterize hardening effects due to flow-induced anisotropy for sheet metals. The proposed experiment consists of two subsequent forming operations. Initially,...

Design considerations for the electrical power supply of future civil aircraft with active high-lift systems

J.-K. Mueller, A. Bensmann, B. Bensmann, T. Fischer, T. Kadyk, G. Narjes, F. Kauth, B. Ponick, J.R. Seume, U. Krewer, R. Hanke-Rauschenbach & A. Mertens
Active high-lift systems of future civil aircraft allow noise reduction and the use of shorter runways. Powering high-lift systems electrically have a strong impact on the design requirements for the electrical power supply of the aircraft. The active high-lift system of the reference aircraft designconsideredinthispaperconsistsofa?exibleleading-edgedevicetogetherwithacombination of boundary-layer suction and Coanda-jet blowing. Electrically driven compressors distributed along the aircraft wings provide the required mass?ow of pressurized air. Their additional loads signi?cantly increase the electric power demand...

Contributions to sustainable invoicing processes and transportation

Kathrin Sabine Kühne
Irrespective of potential benefits of sustainability, both individuals and organizations, are faced with current challenges. This thesis is organized in two parts consisting of two research articles in Part A (Electronic Invoices) and three research articles in Part B (Transportation). In both parts, the three types of sustainability - social equity, economic efficiency, and ecological awareness - are addressed in detail. Given that XML-based invoice standards are designed for an invoice exchange, Part A of...

Skyrme–Faddeev model from 5d super-Yang–Mills

Olaf Lechtenfeld & Alexander D. Popov
We consider 5d Yang–Mills–Higgs theory with a compact ADE-type gauge group G and one adjoint scalar field on R3,1×R+, where R+=[0,∞) is the half-line. The maximally supersymmetric extension of this model, with five adjoint scalars, appears after a reduction of 6d N=(2,0) superconformal field theory on R3,1×R+×S1 along the circle S1. We show that in the low-energy limit, when momenta along R3,1 are much smaller than along R+, the 5d Yang–Mills–Higgs theory reduces to a...

Matrix heater in the gravitational wave observatory GEO 600

H. Wittel, C. Affeldt, A. Bisht, S. Doravari, H. Grote, J. Lough, H. Lück, E. Schreiber, K.A. Strain & Karsten Danzmann
Large scale laser interferometric gravitational wave detectors (GWDs), such as GEO 600 require high quality optics to reach their design sensitivity. The inevitable surface imperfections, inhomogeneities, and light-absorption induced thermal lensing in the optics, can convert laser light from the fundamental mode to unwanted higher order modes, and pose challenges to the operation and sensitivity of the GWDs. Here we demonstrate the practical implementation of a thermal projection system which reduces those unwanted effects via...

Generalized two-field α-attractor models from geometrically finite hyperbolic surfaces

C.I. Lazaroiu & C.S. Shahbazi
We consider four-dimensional gravity coupled to a non-linear sigma model whose scalar manifold is a non-compact geometrically finite surface Σ endowed with a Riemannian metric of constant negative curvature. When the space-time is an FLRW universe, such theories produce a very wide generalization of two-field α-attractor models, being parameterized by a positive constant α, by the choice of a finitely-generated surface group Γ⊂PSL(2,R) (which is isomorphic with the fundamental group of Σ) and by the...

Phase extraction for laser interferometry in space : phase readout schemes and optical testing

Thomas S. Schwarze
This thesis was carried out in the area of gravitational physics, specifically in the fields of gravitational wave astronomy and gravimetry. Both fields do or will make use of satellite missions. The planned gravitational wave observatory Laser Interferometer Space Antenna (LISA) aims to detect gravitational waves in the mHz range while missions like the Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) and the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) measured or will measure,...

Traceability of the Hannover FG5X-220 to the SI units

Manuel Schilling & Ludger Timmen
The absolute measurement of g is currently realized through the laser interferometric measurement of a free falling retro-reflector. The Micro-g LaCoste FG5X is a free-fall gravimeter with a laser interferometer in Mach-Zehnder configuration which uses simultaneous time and distance measurements to calculate the absolute value of g. Because the instrument itself contains the necessary working standards for precise time and length measurements, it is considered independent of external references. The timing is kept with a...

Type-II Zeeman Slower and design and construction of a cryogenic buffer gas beam source

Maurice Petzold
Ultrakalte Moleküle versprechen neue Einsichten in diversen Forschungsfeldern die von kontrollierter ultrakalter Chemie über Präzisionsmessungen paritätsverletzender Effekte bis hin zu stark korrelierten dipolaren Quantenvielteilchensystemen reichen. Jedoch verbieten die zusätzlichen Freiheitsgrade der Rotation und Vibration von Molekülen, den direkten Transfer atomarer Kühltechniken. Das direkte Laserkühlen von Molekülen hat dennoch eine rasante Entwicklung in den letzten Jahren erlebt und schloss die Lücke zwischen kryogenen Temperaturen und dem ultrakalten Regime. Der limitierende Faktor in derzeitigen Experimenten ist die...

Carbonate sedimentology and chemostratigraphy of Kimmeridgian shoal-water deposits in the Lower Saxony Basin of Northern Germany

Fanfan Zuo
The Late Jurassic is generally considered to be an equable greenhouse-type climate with a high global sea level. Within the Late Jurassic, the Kimmeridgian stage represents a temperature plateau, reaching peak warmth. During this period, large parts of Europe were covered by shallow epicontinental seas with widespread deposition of subtropical shoal-water carbonates. Unfortunately, the absence of open-marine marker fossils hampers a precise age assignment of these Kimmeridgian strata. In addition, the fragmentary shoal-water record with...

Research data management services at Leibniz University Hanover : A self-assessment by the RDM Service Team based on the RISE questionnaire (v1.1)

Reiko Kaps, Anke Krüger, Anneke Meyer, Janna Neumann, Jessika Rücknagel, Volker Soßna & Frauke Ziedorn
In 2018, the Research Data Management Service of Leibniz University Hanover conducted a self-evaluation using the “Research Infrastructure Self Evaluation Framework” (RISE) published by the British Digital Curation Centre. The main objective of the self-assessment was to gauge current achievements and to determine the fields in which further development is required in order to update road map documents. Another aim was to test the applicability of “RISE” in a German context. This report presents the...

Genetic diversity and morphological characterization of African nightshade entries (section Solanum L.)

Regina Chemutai Rono
African nightshade is an indigenous leafy vegetable in sub-Saharan Africa valued for its high nutrient content and therefore provide nutritional security and also potential to generate income especially to small scale farmers. Production is however below potential due to lack of superior varieties that are high yielding and tolerant to environmental stresses. Development of varieties through breeding programs has been initiated in order to supply farmers with quality seeds. The efforts to improve this crop...

Contributions to decision support for wind energy, literature research processes and towards a better world through information systems

André Koukal
Decision making is an important and complex challenge for companies, organizations and individuals. Making the right operational and strategic decisions at the right time has a big influence on a successful development and the survival in competition. To make the best possible decisions it is essential to have access to aggregated and processed information which are accurate, reliable and consistent. Decision support contributes to the decision-making process by preparing and providing relevant information. Decision support...

Predictor-corrector framework for the sequential assembly of optical systems based on wavefront sensing

Christopher Schindlbeck, Christian Pape & Eduard Reithmeier
Alignment of optical components is crucial for the assembly of optical systems to ensure their full functionality. In this paper we present a novel predictor-corrector framework for the sequential assembly of serial optical systems. Therein, we use a hybrid optical simulation model that comprises virtual and identified component positions. The hybrid model is constantly adapted throughout the assembly process with the help of nonlinear identification techniques and wavefront measurements. This enables prediction of the future...

Enhancement of the damage resistance of ultra-fast optics by novel design approaches

Thomas Willemsen, Marco Jupé, Mark Gyamfi, Sebastian Schlichting & Detlev Ristau
Dielectric components are essential for laser applications. Chirped mirrors are applied to compress the temporal pulse broadening crucial in the femtosecond regime. However, the design sensitivity and the electric field distribution of chirped mirrors is complex often resulting in low laser induced damage resistances. An approach is presented to increase the damage resistance of pulse compressing mirrors up to 190% in the NIR spectral range. Layers with critical high field intensity of a binary mirror...

High repetition rate, J-level, CPA-free ultrashort pulse multipass amplifier based on Ho:YLF

Moritz Hinkelmann, Dieter Wandt, Uwe Morgner, Jörg Neumann & Dietmar Kracht
We report on CPA-free multipass amplification of ps-pulses in Holmium-doped yttrium lithium fluoride (Ho:YLF) crystals up to µJ pulse-energy-covering repetition rates from 10 kHz up to 500 kHz. The seed pulses at a wavelength of 2.05 µm are provided by a Ho-based all-fiber system consisting of a soliton oscillator and a subsequent pre-amplifier followed by a free-space AOM as pulse-picker. Considering the achieved pulse peak power at MW-level, this system is a powerful tool for...

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