Fak. 2 Mathematik und Naturwissenschaften

1790 Items

Recent Submissions
Jitter-correction for IR/UV-XUV pump-probe experiments at the FLASH free-electron laser

Savelyev, Evgeny ; Boll, Rebecca ; Bomme, Cédric ; Schirmel, Nora ; Redlin, Harald ; Erk, Benjamin ; Düsterer, Stefan ; Müller, Erland ; Höppner, Hauke ; Toleikis, Sven ; Müller, Jost ; Kristin Czwalinna, Marie ; Treusch, Rolf ; Kierspel, Thomas ; Mullins, Terence ; Trippel, Sebastian ; Wiese, Joss ; Küpper, Jochen ; Brauβe, Felix ; Krecinic, Faruk ; Rouzée, Arnaud ; Rudawski, Piotr ; Johnsson, Per ; Amini, Kasra ; Lauer, Alexandra ; Burt, Michael ; Brouard, Mark ; Christensen, Lauge ; Thøgersen, Jan ; Stapelfeldt, Henrik ; Berrah, Nora ; Müller, Maria ; Ulmer, Anatoli ; Techert, Simone ; Rudenko, Artem ; Rolles, Daniel (2017)

In pump-probe experiments employing a free-electron laser (FEL) in combination with a synchronized optical femtosecond laser, the arrival-time jitter between the FEL pulse and the optical laser pulse often severely limits the temporal resolution that can be achieved. Here, we present a pump-probe experiment on the UV-induced dissociation of 2,6-difluoroiodobenzene (C6H3F2I) molecules performed ...

Multimode optical feedback dynamics of InAs/GaAs quantum-dot lasers emitting on different lasing states

Huang, H. ; Arsenijević, D. ; Schires, K. ; Sadeev, T. ; Bimberg, D. ; Grillot, F. (2016)

Quantum dot lasers are envisioned to be the next generation of optical transmitters used for short-reach communication links, owing to their low threshold current and high temperature operation. However, in a context of steady increase in both speed and reach, quantum dot lasers emitting on their upper energy levels have been recently of greater interest as they are touted for their faster modu...

Efficiency of four-wave mixing in injection-locked InAs/GaAs quantum-dot lasers

Huang, H. ; Arsenijević, D. ; Schires, K. ; Sadeev, T. ; Erasme, D. ; Bimberg, D. ; Grillot, F. (2016)

Frequency conversion using highly non-degenerate four-wave mixing is investigated in optically injection-locked InAs/GaAs quantum-dot Fabry-Perot lasers with different ridge waveguide dimensions. Conversion efficiencies up to -16 dB with a large optical signal-to-noise ratios of 36 dB are unveiled. The conversion bandwidth is extended to 4 THz with a quasi-symmetrical response between up- and d...

The fate of the 2√3 × 2√3R(30°) silicene phase on Ag(111)

Liu, Zhi-Long ; Wang, Mei-Xiao ; Liu, Canhua ; Jia, Jin-Feng ; Vogt, Patrick ; Quaresima, Claudio ; Ottaviani, Carlo ; Olivieri, Bruno ; Padova, Paola de ; Lay, Guy Le (2014)

Silicon atoms deposited on Ag(111) produce various single layer silicene sheets with different buckling patterns and periodicities. Low temperature scanning tunneling microscopy reveals that one of the silicene sheets, the hypothetical √7 × √7 silicene structure, on 2√3 × 2√3 Ag(111), is inherently highly defective and displays no long-range order. Moreover, Auger and photoelectron spectroscopy...

Response to “Comment on ‘Indications of energetic consequences of decoherence at short times for scattering from open quantum systems’” [AIP Advances 1, 049101 (2011)]

Chatzidimitriou-Dreismann, Chariton Aris ; Gray, E. MacA. ; Blach, T. P. (2011)

The Comment by Mayers and Reiter criticizes our work on two counts. Firstly, it is claimed that the quantum decoherence effects that we report in consequence of our experimental analysis of neutron Compton scattering from H in gaseous H2 are not, as we maintain, outside the framework of conventional neutron scattering theory. Secondly, it is claimed that we did not really observe such effects, ...

Synthesis of an electronically modified carbon nitride from a processable semiconductor, 3-amino-1,2,4-triazole oligomer, via a topotactic-like phase transition

Savateev, Aleksandr ; Pronkin, Sergey ; Epping, Jan Dirk ; Willinger, Marc Georg ; Antonietti, Markus ; Dontsova, Dariya (2017)

A thermally induced topotactic transformation of organic polymeric semiconductors is achieved using similarity of the chemical structures of two C,N,H-containing materials. Namely, the oligomer of 3-amino-1,2,4-triazole (OATA) is transformed into an electronically modified graphitic carbon nitride (OATA-CN) upon heating at 550 °C. During the transition, the flat band potential of the organic se...

Cyclohexa-1,4-dienes in transition-metal-free ionic transfer processes

Keess, Sebastian ; Oestreich, Martin (2017)

Safe- and convenient-to-handle surrogates of hazardous chemicals are always in demand. Recently introduced cyclohexa-1,4-dienes with adequate substitution fulfil this role as El+/H− equivalents in B(C6F5)3-catalysed transfer reactions of El–H to π- and σ-donors (C[double bond, length as m-dash]C/C[triple bond, length as m-dash]C and C[double bond, length as m-dash]O/C[double bond, length as m-d...

Synthesis of a cyclopentadienyl(imino)stannylene and its direct conversion into halo(imino)stannylenes

Ochiai, Tatsumi ; Inoue, Shigeyoshi (2017)

The reaction of stannocene Cp2Sn with iminolithium LiNIPr (NIPr = bis(2,6-diisopropylphenyl)imidazolin-2-iminato) afforded the dimeric cyclopentadienyl(imino)stannylene [(η1-Cp)SnNIPr]2 (1). Compound 1 exhibits unexpected reactivity towards haloalkanes. The high-yield conversion of 1 into chlorostannylene [ClSnNIPr]2 (2) and bromostannylene [BrSnNIPr]2 (3) were accomplished by treatment with di...

Construction of a polyproline structure with hydrophobic exterior using octahydroindole-2-carboxylic acid

Kubyshkin, Vladimir ; Budisa, Nediljko (2016)

The proline analogue (2S,3aS,7aS)-octahydroindole-2-carboxylic acid (Oic) has been previously applied as a proline substitute in pharmocologically active peptides and as a structural component of the antihypertensive drug Perindopril. Herein, we describe the formation of an oligoproline structure by an Oic oligomer. A series of Oic oligomers were investigated to show the structural and energeti...

Multi-chimera States in the Leaky Integrate-and-Fire Model

Tsigkri-DeSmedt, N.D. ; Hizanidis, J. ; Hövel, Philipp ; Provata, A. (2015)

We study the dynamics of identical leaky integrate-and-fire neurons with symmetric non-local coupling. Upon varying control parameters (coupling strength, coupling range, refractory period) we investigate the system's behaviour and highlight the formation of chimera states. We show that the introduction of a refractory period enlarges the parameter region where chimera states appear and affects...

PNIPAM microgels in external fields

Backes, Sebastian (2018)

Poly(N-isopropylacrylamide) (PNIPAM) microgels respond to changes in temperature by shrinking in aqueous solution above their volume phase transition temperature (VPTT). Additionally, they shrink in mixtures of water and ethanol, although both individual liquids are good solvents. This is termed cononsolvency. Combined DLS experiments and MD simulations show that microgels in aqueous alcohol bu...

Rhodium-catalysed hydroformylation of long-chain alkenes in aqueous multiphase systems: Kinetic studies and systematic process development

Pogrzeba, Tobias (2018)

In the course of the development of new sustainable industrial chemical processes the exploitation of switchable solvent systems is increasingly investigated in various fields. The application of highly efficient catalysts and safer solvents is mandatory to make a step towards a greener chemistry, as well as to find innovative ways to reduce waste from chemical reactions. Consequently, the use ...

Structural examination of hydrophobic tunnels in proteins

Kalms, Jacqueline (2018)

Enzymes are the biological macromolecular catalysts of life, which work with high substrate specificity, under fine-tuned conditions compared to chemical catalysts. The majority of the catalytic centres of enzymes are located deeply within the protein matrix. To provide efficient substrate accessibility to the active site most proteins offer permanent or transient tunnels as transport pathways....

Epitaxial growth of GaN quantum dots on smooth AlN

Bellmann, Konrad (2018)

A fundamental limitation of current quantum dot based monolithic quantum-devices emitting single or entangled photons is the operation at cryogenic temperatures. A straightforward solution is the use of group-III nitrides. In particular, the large bandgap difference between the two binary compounds GaN and AlN of 2.6 eV can provide superior exciton confinement for an energy separation between d...

Protein adsorption on nanostructured silica surfaces

Meißner, Jens (2018)

This Ph.D. thesis presents a study of the interaction of globular proteins with nanostructured silica surfaces. It aims to gain a better understanding of the consequences of a high surface curvature and confinement on the adsorption behavior and morphology of the adsorbed protein. The adsorption behavior of lysozyme and 𝛽-lactoglobulin on silica nanoparticles was studied from pH 2 to 11 and ...

Bioinspired solid catalysts for the hydroxylation of methane

Le, Ha Vu (2018)

Abundant and cheap resources including natural gas, methane hydrates, and biogas, whose major component is methane, have been considered as promising alternatives to decline the dependence of chemical and energy industries on crude oil. However, there is currently an underutilization of these resources, especially due to the costly transportation and storage, and high chemical inertness of meth...

Synchronization and waves in confined complex active media

Totz, Jan Frederik (2018)

The aim of this thesis is the study and characterization of a number of self-organized patterns with potential relevance to biological systems and beyond. To this end we utilize the well-established oscillating Belousov-Zhabotinsky (BZ) reaction in chemical experiments as well as numerical simulations of the underlying model equations on graphics cards. The first part of this thesis features e...

Supported liquid phase catalysts

Ahi, Hamideh (2018)

This thesis deals with the investigation of silica-supported vanadia-based Supported Liquid Phase (SLP) catalysts in Oxidative Dehydrogenation of Propane (ODP). The aim is a better understanding of the structural requirements of oxidation catalysts. The approach is based on the observation that high-performance catalysts in selective oxidation exhibit a thin surface layer, which is chemically a...

Gas-phase activation of CO2 and CH4 by selected transition-metal complexes: ligand effects and the role of the metal

Firouzbakht, Marjan (2018)

Die vorliegende Arbeit behandelt die Übergangsmetall-vermittelten Aktivierungen von CO2 und CH4, die mittels massenspektrometrischer Methoden und quantenchemischer Rechnungen untersucht wurden. Die Kationen der jeweiligen Übergangsmetalle wurden durch Elektrosprayionisation (ESI) erzeugt und anschließend mit der Tandem-Massenspektrometrie unter Quadrupol-Hexapol-Quadrupol Anordnung charakterisi...

Gravity-induced dynamics of a squirmer microswimmer in wall proximity

Rühle, Felix ; Blaschke, Johannes ; Kuhr, Jan-Timm ; Stark, Holger (2018-02-07)

We perform hydrodynamic simulations using the method of multi-particle collision dynamics and a theoretical analysis to study a single squirmer microswimmer at high Péclet number, which moves in a low Reynolds number fluid and under gravity. The relevant parameters are the ratio α of swimming to bulk sedimentation velocity and the squirmer type β. The combination of self-propulsion, gravitation...