Fakultät 2 Mathematik und Naturwissenschaften

1693 Items

Recent Submissions
High throughput modules for performance and mechanism assessment of flame retardants in polymeric materials

Rabe, Sebastian (2017)

Due to the ever-increasing number of additives, adjuvants, synergists, and fillers, together with variations in concentration, particle size distribution and other modifications, methods for accelerated assessment of flame retarded polymeric materials are strongly needed. This work presents two novel approaches to assess the rapid screening of flame retardants in polymeric materials. Furthermor...

Multimethod metrology of multilayer mirrors using EUV and X-Ray radiation

Haase, Anton (2017)

Multilayer mirrors for the extreme ultraviolet (EUV) spectral range are essential optical elements of next-generation lithography systems and in scientific applications, e.g. water window microscopes. Their failure so far to reach theoretically predicted peak reflectivity values significantly hinders their applicability and raises the question of the reasons behind that limited performance. Thi...

Photolumineszenz- und Raman-Spektroskopie von zweidimensionalem MoS2

Scheuschner, Nils (2017)

In this work the electronic and vibrational properties of two-dimensional molybdenum disulfide (MoS2) are examined using Raman- and photoluminescencespectroscopy (PL). Spatially resolved measurements of suspended MoS2 and Si/SiO2 supported MoS2 show an increase of the charge carrier concentration of the MoS2 in the supported areas. Furthermore the indirect band gap energy of bilayer MoS2 is dec...

Unconventional magnetic properties of low-dimensional antiferromagnets BaNi2V2O8 and BaCu2V2O8

Klyushina, Ekaterina (2017)

This work explores the magnetic properties of two novel compounds BaCu2V2O8 and BaNi2V2O8 which both provide rare physical realizations of model magnetic systems that are characterized by unconventional magnetic behaviour at finite temperatures. BaNi2V2O8 has an ideal honeycomb crystal structure where S=1 nickel magnetic ions are arranged on well isolated honeycomb layers. The nearest neighbour...

Magnetic properties of rare earth zirconate pyrochlores

Xu, Jianhui (2017)

Diese Dissertation behandelt experimentelle Untersuchungen an drei magnetischen Pyrochloren, Nd2Zr2O7, Sm2Zr2O7 and Gd2Zr2O7. Es wurden einkristalline und pulverförmige Proben hergestellt wobei die zwei erstgenannten Substanzen in der Pyrochlor Struktur kristallisieren, während Gd2Zr2O7 einige Platzwechsel-Defekte von Gd/Zr aufweist. Alle Verbindungen zeigen in den makroskopischen Eigenschaften...

Synthese von fluoreszierenden 7-Azatryptophan-Derivaten und deren Einbau in Modellpeptide

Noichl, Benjamin Philipp (2017)

In nature, proteins evolve to ensure the survival of living organisms in their natural environments. To equip them with new features and functions, classical protein engineering, based on canonical twenty amino acids, could lead to the improvement of these proteins by mutagenesis. Proteins sequences containing exclusively naturally occurring amino acids (i.e. canonical 20) are often unsuitable ...

Sharp-interface formation during lithium intercalation into silicon

Meca, Esteban ; Münch, Andreas ; Wagner, Barbara (2017)

In this study, we present a phase-field model that describes the process of intercalation of Li ions into a layer of an amorphous solid such as amorphous silicon (a-Si). The governing equations couple a viscous Cahn–Hilliard-Reaction model with elasticity in the framework of the Cahn–Larché system. We discuss the parameter settings and flux conditions at the free boundary that lead to the forma...

Pinning of interfaces in a random elastic medium and logarithmic lattice embeddings in percolation

Dondl, Patrick W. ; Scheutzow, Michael ; Throm, Sebastian (2015)

For a model of a driven interface in an elastic medium with random obstacles we prove the existence of a stationary positive supersolution at non-vanishing driving force. This shows the emergence of a rate-independent hysteresis through the interaction of the interface with the obstacles despite a linear (force = velocity) microscopic kinetic relation. We also prove a percolation result, namely...

Topological and symbolic dynamics for hyperbolic systems with holes

Bundfuss, Stefan ; Krüger, Tyll ; Troubetzkoy, Serge (2010)

We consider an axiom A diffeomorphism or a Markov map of an interval and the invariant set Ω* of orbits which never falls into a fixed hole. We study various aspects of the symbolic representation of Ω* and of its non-wandering set Ωnw. Our results are on the cardinality of the set of topologically transitive components of Ωnw and their structure. We also prove that Ω* is generically a subshif...

Motion and structure of atmospheric mesoscale baroclinic vortices: dry air and weak environmental shear

Päschke, Eileen ; Marschalik, Patrik ; Owinoh, Antony Z. ; Klein, Rupert (2012)

A strongly tilted, nearly axisymmetric vortex in dry air with asymmetric diabatic heating is analysed here by matched asymptotic expansions. The vortex is in gradient wind balance, with vortex Rossby numbers of order unity, and embedded in a quasigeostrophic (QG) background wind with weak vertical shear. With wind speeds of 60–120 km h-1, such vortices correspond to tropical storms or nascent h...

On the random dynamics of Volterra quadratic operators

Jamilov, U. U. ; Scheutzow, M. ; Wilke-Berenguer, M. (2015)

We consider random dynamical systems generated by a special class of Volterra quadratic stochastic operators on the simplex Sm-1. We prove that in contrast to the deterministic set-up the trajectories of the random dynamical system almost surely converge to one of the vertices of the simplex Sm-1, implying the survival of only one species. We also show that the minimal random point attractor o...

Manipulating shear-induced non-equilibrium transitions in colloidal films by feedback control

Vezirov, Tarlan A. ; Gerloff, Sascha ; Klapp, Sabine H. L. (2015)

Using Brownian Dynamics (BD) simulations we investigate non-equilibrium transitions of sheared colloidal films under controlled shear stress sigma(xz). In our approach the shear rate (gamma) over dot is a dynamical variable, which relaxes on a time scale tau(c) such that the instantaneous, configuration-dependent stress sigma(xz)(t) approaches a pre-imposed value. Investigating the dynamics und...

Record activity and stability of dealloyed bimetallic catalysts for proton exchange membrane fuel cells

Han, Binghong ; Carlton, Christopher E. ; Kongkanand, Anusorn ; Kukreja, Ratandeep S. ; Theobald, Brian R. ; Gan, Lin ; O'Malley, Rachel ; Strasser, Peter ; Wagner, Frederick T. ; Shao-Horn, Yang (2015)

We demonstrate the unprecedented proton exchange membrane fuel cell (PEMFC) performance durability of a family of dealloyed Pt-Ni nanoparticle catalysts for the oxygen reduction reaction (ORR), exceeding scientific and technological state-of-art activity and stability targets. We provide atomic-scale insight into key factors controlling the stability of the cathode catalyst by studying the infl...

Unprecedented silicon(II)-> calcium complexes with N-heterocyclic silylenes

Blom, Burgert ; Klatt, Günter ; Gallego, Daniel ; Tan, Gengwen ; Drieß, Matthias (2015)

The first N-heterocyclic silylene (NHSi) complexes of any s-block element to date are reported for calcium: [(eta(5)-C5Me5)(2)Ca<--:Si(O-C6H4-2-Bu-t){((NBu)-Bu-t)(2)CPh}] (6) and [(eta(5)-C5Me5)(2)Ca<--:Si((NBuCH)-Bu-t)(2)] (7). Complexes 6 and 7 are isolable in a facile way upon reaction of the corresponding free N-heterocyclic silylenes (NHSis) with [(eta(5)-C5Me5)(2)Ca] (2). Complexes 6 and ...

Nuclear resonance vibrational spectroscopy reveals the FeS cluster composition and active site vibrational properties of an O-2-tolerant NAD(+)-reducing [NiFe] hydrogenase

Lauterbach, Lars ; Wang, Hongxin ; Horch, Marius ; Gee, Leland B. ; Yoda, Yoshitaka ; Tanaka, Yoshihito ; Zebger, Ingo ; Lenz, Oliver ; Cramer, Stephen P. (2015)

Hydrogenases are complex metalloenzymes that catalyze the reversible splitting of molecular hydrogen into protons and electrons essentially without overpotential. The NAD(+)-reducing soluble hydrogenase (SH) from Ralstonia eutropha is capable of H-2 conversion even in the presence of usually toxic dioxygen. The molecular details of the underlying reactions are largely unknown, mainly because of...

Laser-induced fluorescence of free diamondoid molecules

Richter, Robert ; Röhr, Merle I. S. ; Zimmermann, Tobias ; Petersen, Jens ; Heidrich, Christoph ; Rahner, Ramon ; Möller, Thomas ; Dahl, Jeremy E. ; Carlson, Robert M. K. ; Mitric, Roland ; Rander, Torbjörn ; Merli, Andrea (2015)

We observe the fluorescence of pristine diamondoids in the gas phase, excited using narrow band ultraviolet laser light. The emission spectra show well- defined features, which can be attributed to transitions from the excited electronic state into different vibrational modes of the electronic ground state. We assign the normal modes responsible for the vibrational bands, and determine the geom...

Reliable palladium nanoparticle syntheses in aqueous solution: the importance of understanding precursor chemistry and growth mechanism

Kettemann, Frieder ; Wuithschick, Maria ; Caputo, Gianvito ; Krähnert, Ralph ; Pinna, Nicola ; Rademann, Klaus ; Polte, Jörg (2015)

Reliable protocols for the synthesis of palladium nanoparticles (Pd-NPs) in aqueous solution are rarely found and the corresponding growth mechanisms often remain unknown. Furthermore, syntheses of Pd-NPs always demand the use of stabilizing agents which are often unfavorable for catalytic applications. In this contribution, the importance of the palladium precursor chemistry as a prerequisite ...

Surface enhanced vibrational spectroscopic evidence for an alternative DNA-independent redox activation of endonuclease III

Moe, Elin ; Sezer, Murat ; Hildebrandt, Peter ; Todorovic, Smilja (2015)

Surface enhanced vibrational spectro-electrochemistry of endonuclease III provides direct evidence that the [4Fe-4S] cluster is responsible for the enzyme redox activity, and that this process is not exclusively DNA-mediated, as currently proposed. We report the first surface enhanced resonance Raman spectrum of a [4Fe-4S](2+) cluster containing enzyme.

From molecular copper complexes to composite electrocatalytic materials for selective reduction of CO2 to formic acid

Tran Ngoc Huan ; Andreiadis, Eugen S. ; Heidkamp, Jonathan ; Simon, Philippe ; Derat, Etienne ; Cobo, Saioa ; Royal, Guy ; Bergmann, Arno ; Strasser, Peter ; Dau, Holger ; Artero, Vincent ; Fontecave, Marc (2015)

The development of new energy storage technologies is central to solving the challenges facing the widespread use of renewable energies. An option is the reduction of carbon dioxide (CO2) into carbon-based products which can be achieved within an electrochemical cell. Future developments of such processes depend on the availability of cheap and selective catalysts at the electrode. Here we show...

Photoresponsive self-assemblies based on fatty acids

Fameau, Anne-Laure ; Arnould, Audrey ; Lehmann, Maren ; von Klitzing, Regine (2015)

Photoresponsive surfactant system based on fatty acids has been developed by the introduction in aqueous solution of a photoacid generator (PAG). Self-assembly transitions are triggered by UV irradiation due to a pH change induced by the presence of PAG.