Fak. 2 Mathematik und Naturwissenschaften

2104 Items

Recent Submissions
Laboratory based GIXRF and GEXRF spectrometers for multilayer structure investigations

Szwedowski-Rammert, Veronika ; Baumann, Jonas ; Schlesiger, Christopher ; Waldschläger, Ulrich ; Gross, Armin ; Kanngießer, Birgit ; Mantouvalou, Ioanna (2019-02-11)

This work reports laboratory angle resolved measurements with the goal of establishing laboratory techniques to obtain a more complete idea of the intralayer composition of multilayer samples. While X-ray reflectometry is a widely available technique for the characterization of multilayer samples, angle resolved XRF measurements (grazing emission/incidence X-ray fluorescence) are usually perfor...

XPS studies on dispersed and immobilised carbon nitrides used for dye degradation

Rieß, Julian ; Lublow, Michael ; Anders, Steven ; Tasbihi, Minoo ; Acharjya, Amitava ; Kailasam, Kamalakannan ; Thomas, Arne ; Schwarze, Michael ; Schomäcker, Reinhard (2019-06-05)

Liquid phase adsorption is a common technique in waste water purification. However, this process has some downsides. The removal of environmentally harmful contaminants from organic liquids by adsorption produces secondary waste which has to be treated afterwards. The treatment can be e.g. high temperatures or a landfill. Photocatalysts such as CN6 can remove the dye under light irradiation but...

Real-time imaging of activation and degradation of carbon supported octahedral Pt–Ni alloy fuel cell catalysts at the nanoscale using in situ electrochemical liquid cell STEM

Beermann, Vera ; Holtz, Megan E. ; Padgett, Elliot ; de Araujo, Jorge Ferreira ; Muller, David A. ; Strasser, Peter (2019-05-20)

Octahedrally shaped Pt–Ni alloy nanoparticles on carbon supports have demonstrated unprecedented electrocatalytic activity for the oxygen reduction reaction (ORR), sparking interest as catalysts for low-temperature fuel cell cathodes. However, deterioration of the octahedral shape that gives the catalyst its superior activity currently prohibits the use of shaped catalysts in fuel cell devices,...

Effect of alkali ions on optical properties of flavins: vibronic spectra of cryogenic M+lumiflavin complexes (M = Li–Cs)

Müller, David ; Nieto, Pablo ; Miyazaki, Mitsuhiko ; Dopfer, Otto (2019-01-07)

Flavin compounds are frequently used by nature in photochemical processes because of their unique optical properties which can be strongly modulated by the surrounding environment such as solvation or coordination with metal ions. Herein, we employ vibronic photodissociation spectroscopy of cryogenic M+LF complexes composed of lumiflavin (LF, C13H12N4O2), the parent molecule of the flavin famil...

Broadband ultrafast spectroscopy on mixed–dimensional InAs/GaAs systems

Kolarczik, Mirco (2019)

This thesis deals with light matter interaction and electron dynamics in coupled systems of nanostructured III-V semiconductors, particularly with quantum dots embedded in quantum wells. Its focus is on the role of dimensionality and the characterization of quantum dot states with respect to their two- and many-level nature. The sample under investigation is a semiconductor optical amplifier un...

Kooperative Bindungsaktivierung von Al–H- und Sn–H-Bindungen in Hydroalanen bzw. -stannanen für die Katalyse

Forster, Francis (2019)

Die vorliegende Dissertation widmet sich der kooperativen Bindungsaktivierung von E–H-Bindungen (E = R2Al, R3Sn, R3Ge) an den polaren Ru–S-Bindungen von Ohki–Tatsumi-Komplexen sowie dem Einsatz der somit erzeugten schwefelstabilisierten Hauptgruppenelektrophile in der Katalyse. Die Aktivierung der Al–H-Bindung in DIBAL–H an den Ruthenium(II)-Thiolaten lieferte die entsprechenden Hydroalanaddu...

Homogen-universelle metrische Räume

Rothacker, Edgar (1976)

Homogeneous universal metric spaces are constructed in the Jónsson class of metric spaces starting from finite metric spaces over the rationals and then completing the construction over the reals; the main theorem deals with the finite homgeneity property established by Urysohn for his famous universal metric space: we show that this can be extended to totally bounded metric spaces, thereby ext...

Homogen-universelle verallgemeinerte metrische Räume unter besonderer Berücksichtigung nicht-archimedischer Metriken

Rothacker, Edgar (1978)

Homogeneous universal metric spaces are constructed over generalized distance sets such as totally ordered abelian groups or linear orderings without any further structure; the latter yields the basis for the study of hom.-univ. ultrametric spaces in the third part of this work; finally the fourth part studies the Cauchy completeness in connection with the construction of the appropriately ge...

Synthesis, characterization, and crystal structure of aqua­bis­­(4,4′-dimeth­­oxy-2,2′-bi­pyridine)[μ-(2R,3R)-tartrato(4−)]dicopper(II) octa­hydrate

Wiedemann, Dennis ; Kulko, Roman-David ; Grohmann, Andreas (2019-06-11)

Typical electroless copper baths (ECBs), which are used to chemically deposit copper on printed circuit boards, consist of an aqueous alkali hydroxide solution, a copper(II) salt, formaldehyde as reducing agent, an L-(+)-tartrate as complexing agent, and a 2,2′-bi­pyridine derivative as stabilizer. Actual speciation and reactivity are, however, largely unknown. Herein, we report on the synthesi...

New approaches in angle resolved X-ray analysis of stratified materials in the laboratory

Szwedowski-Rammert, Veronika (2019)

Providing access to angular resolved X-ray fluorescence methods in laboratories can enhance the dissemination of these methods for the depth-resolved elemental analysis of samples with layers in the nanometer range. The measurements are so far mainly performed at synchrotron radiation facilities and thus the number of users is limited. Especially in the hard X-ray range, where the production of...

Spectroscopic investigation of phytochromes and NIR fluorescent variants

Buhrke, David (2019)

In this work, vibrational spectroscopic methods (resonance Raman [RR] and infrared absorption [IR]) were used for the investigation of phytochromes. Phytochromes are bistable photoreceptor proteins that bind bilins (BV, PCB, PΦB) as chromophores. Various plant, cyanobacterial, and bacterial variants regulate biological processes through the light dependent switching between metastable states th...

Megaelectron volt secondary-ion mass spectrometry – yield dependence on experimental parameters and new capabilities of the technique

Stoytschew, Valentin (2019)

Time of flight Mega-electron Secondary Ion Mass Spectroscopy (TOF MeV SIMS) is a mass spectrometry technique using swift heavy ions (𝑚>16 𝑢, 𝐸𝑘𝑖𝑛>1 𝑀𝑒𝑉) to induce desorption of secondary ions from a sample. While swift heavy ions have been used for several decades to achieve high molecular secondary ion yields in mass spectrometry, there has been no systematic investigation into the ex...

Non-linear x-ray diffraction from ferromagnetic thin-films

Schneider, Michael (2019)

In this thesis, fluence-dependent absorption and diffraction from solid-state samples in the extreme ultra-violet (XUV) regime is investigated. At these wavelengths, fluence dependent effects occur predominantly in experiments at free-electron laser (FEL) sources and attract considerable interest as they have important implications for the conclusiveness of studies performed at these light sour...

Untersuchungen zur Züchtung von CuAlO2-Einkristallen

Wolff, Nora (2019)

Die vorliegende Arbeit entstand während meiner Tätigkeit als wissenschaftliche Mitarbeiterin am Leibniz-Institut für Kristallzüchtung in Berlin. Das Ziel der Arbeit war Bedingungen zu definieren, unter denen CuAlO2-Einkristalle aus dem Eigenfluss gezüchtet werden können. Zusätzlich wurden Untersuchungen zum Mischkristallsystem CuAlO2-CuFeO2 gemacht. Mithilfe thermodynamischer Messungen (DTA-TG)...

Studying protein-cofactor complexes: a combined experimental and theoretical approach

Salewski, Johannes (2019)

The majority of enzymes contains one or more organic or inorganic cofactor molecule(s) attached to the protein matrix which enable their respective functions. The interaction between these cofactor molecules and the protein environment is highly specific and determines the structure–function relationship of many enzymes. The work in this thesis utilizes a combination of experimental and theoret...

Computational Aminoacyl-tRNA Synthetase Library Design for Photocaged Tyrosine

Baumann, Tobias ; Hauf, Matthias ; Richter, Florian ; Albers, Suki ; Möglich, Andreas ; Ignatova, Zoya ; Budisa, Nediljko (2019-05-11)

Engineering aminoacyl-tRNA synthetases (aaRSs) provides access to the ribosomal incorporation of noncanonical amino acids via genetic code expansion. Conventional targeted mutagenesis libraries with 5–7 positions randomized cover only marginal fractions of the vast sequence space formed by up to 30 active site residues. This frequently results in selection of weakly active enzymes. To overcome ...

In-Cell Synthesis of Bioorthogonal Alkene Tag S-Allyl-Homocysteine and Its Coupling with Reprogrammed Translation

Nojoumi, Saba ; Ma, Ying ; Schwagerus, Sergej ; Hackenberger, Christian P. R. ; Budisa, Nediljko (2019-05-09)

In this study, we report our initial results on in situ biosynthesis of S-allyl-l-homocysteine (Sahc) by simple metabolic conversion of allyl mercaptan in Escherichia coli, which served as the host organism endowed with a direct sulfhydration pathway. The intracellular synthesis we describe in this study is coupled with the direct incorporation of Sahc into proteins in response to methionine co...

The Mismatch Principle and L1-analysis compressed sensing

Genzel, Martin (2019)

This thesis contributes to several mathematical aspects and problems at the interface of statistical learning theory and signal processing. Although based on a common theoretical foundation, the main results of this thesis can be divided into two major topics of independent interest. The first one deals with the estimation capacity of the generalized Lasso, i.e., least squares minimization comb...

Message routeing and percolation in interference limited multihop networks

Tóbiás, András József (2019)

This thesis consists of two main parts. In the first part, we investigate a probabilistic model for routeing of messages in relay-augmented multihop ad-hoc networks, where each transmitter sends one message to the origin. Given the (random) transmitter locations, we weight the family of random, uniformly distributed message trajectories by an exponential probability weight, favouring trajectori...

Precious metal-free bifunctional catalysts for reversible seawater electrolyzers

Dresp, Sören (2019)

Regenerative hydrogen, which is produced by renewable electricity used in water electrolyzers, is considered as ideal energy carrier of the future. The selective splitting of seawater into oxygen and hydrogen seem to be a promising alternative compared to established water electrolysis technologies, which typically use highly purified water and electrolytes only. In addition, the back transform...