Numerical homogenization of time-dependent Maxwell\u27s equations with dispersion effects

This thesis studies the propagation of electromagnetic waves in heterogeneous structures such as metamaterials. The governing equations for this problem are Maxwell\u27s equations with highly oscillatory parameters. We use an analytic homogenization result which yields an effective Maxwell system that involves a convolution integral. This convolution represents dispersive effects that result from the interaction of the wave with the (locally) periodic microscopic structure. We discretize in space using the Finite Element Heterogeneous Multiscale Method (FE-HMM) and provide a semi-discrete error estimate. The rigorous error analysis in space is supplemented by a rather standard time discretization at the end of which an efficient, fully discrete method is proposed. This method uses a recursive approximation of the convolution that relies on the assumption that the convolution kernel is an exponential function. Eventually, we present numerical experiments both for the microscopic and the macroscopic scale

Observational Tests of Open Strings in Braneworld Scenarios

We consider some consequences of describing the gauge and matter degrees of freedom in our universe by open strings, as suggested by the braneworld scenario. We focus on the geometric effects described by the open string metric and investigate their observational implications. The causal structure of spacetime on the brane is altered; it is described not by the usual metric $g_{\mu\nu}$, but instead by the open string metric, that incorporates the electromagnetic background, $G_{\mu\nu} = g_{\mu\nu} - (2\pi \alpha^\prime)^2 (F^2)_{\mu\nu}$. The speed of light is now slower when propagating along directions transverse to electromagnetic fields or an NS-NS two form, so that Lorentz invariance is explicitly broken. A generalized equivalence principle guarantees that the propagation of {\it all} particles, not just photons, (with the exception of gravitons) is slower in these transverse directions. We describe a variety of astrophysical and laboratory-based experiments designed to detect the predicted variations in the causal structure. We show that current technology cannot probe beyond open string lengths of $10^{-13}$ cm, corresponding to MeV string scales. We also point out that in a braneworld scenario, constraints on large scale electromagnetic fields together with a modest phenomenological bound on the NS-NS two-form naturally lead to a bound on the scale of canonical noncommutativity that is two orders of magnitude below the string length. By invoking theoretical constraints on the NS-NS two-form this bound can be improved to give an extremely strong bound on the noncommutative scale well below the Planck length, $\sqrt{|\theta|_{max}} < 10^{-35} {\rm cm} \times ({{\rm TeV} \over {\rm string} {\rm scale}}Comment: Minor grammatical corrections and two reference added. 27 pages, 1 eps figure. Submitted to JHE

Determining Dark Matter properties with a XENONnT/LZ signal and LHC-Run3 mono-jet searches

We develop a method to forecast the outcome of the LHC Run 3 based on the hypothetical detection of $\mathcal{O}(100)$ signal events at XENONnT. Our method relies on a systematic classification of renormalisable single-mediator models for dark matter-quark interactions, and is valid for dark matter candidates of spin less than or equal to one. Applying our method to simulated data, we find that at the end of the LHC Run 3 only two mutually exclusive scenarios would be compatible with the detection of $\mathcal{O}(100)$ signal events at XENONnT. In a first scenario, the energy distribution of the signal events is featureless, as for canonical spin-independent interactions. In this case, if a mono-jet signal is detected at the LHC, dark matter must have spin 1/2 and interact with nucleons through a unique velocity-dependent operator. If a mono-jet signal is not detected, dark matter interacts with nucleons through canonical spin-independent interactions. In a second scenario, the spectral distribution of the signal events exhibits a bump at non zero recoil energies. In this second case, a mono-jet signal can be detected at the LHC Run 3, dark matter must have spin 1/2 and interact with nucleons through a unique momentum-dependent operator. We therefore conclude that the observation of $\mathcal{O}(100)$ signal events at XENONnT combined with the detection, or the lack of detection, of a mono-jet signal at the LHC Run 3 would significantly narrow the range of possible dark matter-nucleon interactions. As we argued above, it can also provide key information on the dark matter particle spin.Comment: 17 pages, 8 figures, updated operator coefficients and figures, version accepted by PR

Sulfur, mercury, and boron adducts of sydnone imine derived anionic N-heterocyclic carbenes

The sydnone imines (5-benzoylimino)-3-(2-methoxyphenyl)-sydnone imine and molsidomine were deprotonated at C4 to give sydnone imine anions which can be represented as anionic N-heterocyclic carbenes, respectively. Trapping reactions with sulfur gave unstable sydnone imine sulfides which were stabilized by the formation of methyl thioethers, methyl sulfoxides, gold complexes [(PPh3) Au-S-sydnone imine] and a bis(ligand) mercury(II) complex. The latter possesses a tetrahedral coordination of the mercury central atom to the sulfur atoms with the N6 nitrogen atoms coordinating as neutral ligands. Water converted the molsidomine anion into ethyl(2-morpholino-2-thioxoacetyl) carbamate. Mercury(II) chloride and triphenylborane were employed to trap the sydnone imine carbenes as mercury complexes as well as BPh3 adducts.Peer reviewe

Digitale Kompetenz beim Modellieren und Experimentieren im Physikunterricht

Im Physikunterricht ist das Arbeiten mit Modellen ein wesentlicher Bestandteil der Erkenntnisgewinnung, doch Schüler*innen bereitet das abstrakte Modellieren häufig Schwierigkeiten [1]. Mithilfe des Ansatzes der Augmented Reality (AR) können diese Schwierigkeiten durch die Kombination aus realem Experimentieren und gleichzeitigem, digitalen Modellieren möglicherweise überwunden werden. Da Lehrkräfte ihre eigenen digitalen Kompetenzen häufig als unzureichend einschätzen [2], wird im Rahmen des Projektes „diMEx“ ein Aus- bzw. Fortbildungskonzept für (angehende) Lehrkräfte entwickelt, in welchem die Nutzung von AR im experimentierbasierten Physikunterricht vermittelt werden soll. Das Konzept soll langfristig in die universitäre Ausbildung eingebunden werden und dient der Vernetzung der drei Phasen der Lehrkräfteausbildung.Das Projekt geht den Fragen nach, inwiefern sich Digitalisierungs- und Modellkompetenzen von (angehenden) Lehrkräften in einer Fort- und Ausbildung fördern lassen und wie die beschriebene Nutzung von AR den Umgang mit Modellen im Physikunterricht verbessern kann. Weiterhin wird erforscht, inwiefern sich die Einstellungen der Lehrkräfte hinsichtlich der Implementierung digitaler Modellierungen in ihrem Unterricht verändern. Die anhand einer quantitativen Bedarfsanalyse entwickelte Fortbildung erstreckt sich über mehrere Veranstaltungen und orientiert sich am DOIT-Modell [3]. Die geplante summative Evaluation wird nach dem Mixed-Methods-Ansatz erfolgen und sowohl quantitative als auch qualitative Elemente umfassen

Digitale Kompetenz beim Modellieren und Experimentieren im Physikunterricht

Im Physikunterricht ist das Arbeiten mit Modellen ein wesentlicher Bestandteil der Erkenntnisgewinnung, doch Schüler*innen bereitet das abstrakte Modellieren häufig Schwierigkeiten [1]. Mithilfe des Ansatzes der Augmented Reality (AR) können diese Schwierigkeiten durch die Kombination aus realem Experimentieren und gleichzeitigem, digitalen Modellieren möglicherweise überwunden werden. Da Lehrkräfte ihre eigenen digitalen Kompetenzen häufig als unzureichend einschätzen [2], wird im Rahmen des Projektes „diMEx“ ein Aus- bzw. Fortbildungskonzept für (angehende) Lehrkräfte entwickelt, in welchem die Nutzung von AR im experimentierbasierten Physikunterricht vermittelt werden soll. Das Konzept soll langfristig in die universitäre Ausbildung eingebunden werden und dient der Vernetzung der drei Phasen der Lehrkräfteausbildung.Das Projekt geht den Fragen nach, inwiefern sich Digitalisierungs- und Modellkompetenzen von (angehenden) Lehrkräften in einer Fort- und Ausbildung fördern lassen und wie die beschriebene Nutzung von AR den Umgang mit Modellen im Physikunterricht verbessern kann. Weiterhin wird erforscht, inwiefern sich die Einstellungen der Lehrkräfte hinsichtlich der Implementierung digitaler Modellierungen in ihrem Unterricht verändern. Die anhand einer quantitativen Bedarfsanalyse entwickelte Fortbildung erstreckt sich über mehrere Veranstaltungen und orientiert sich am DOIT-Modell [3]. Die geplante summative Evaluation wird nach dem Mixed-Methods-Ansatz erfolgen und sowohl quantitative als auch qualitative Elemente umfassen

Anionic N-heterocyclic carbenes derived from sydnone imines such as molsidomine. Trapping reactions with selenium, palladium, and gold

The sydnone imines Molsidomine and 5-(benzoylimino)-3-(2-methoxyphenyl)-1,2,3-oxadiazolium-2-ide gave anionic N-heterocyclic carbenes on deprotonation at C4 which were trapped as methylated selenium adducts, gold complexes (X-ray analysis) as well as palladium complexes (X-ray analysis). The C-13 NMR resonance frequencies of the carbene carbon atom are extremely shifted upfield and appear at delta = 142.1 ppm (Molsidomine carbene) and delta = 159.8 ppm (sydnone imine carbene). The Pd complexes were applied as catalysts in Suzuki-Miyaura and Sonogashira-Hagihara cross-coupling reactions. (C) 2017 Elsevier Ltd. All rights reserved.Peer reviewe

Sydnone anions and abnormal N-heterocyclic carbenes of O-ethylsydnones : Characterizations, calculations and catalyses

Peer reviewe

Trajectories and Drivers of Genome Evolution in Surface-Associated Marine Phaeobacter

The extent of genome divergence and the evolutionary events leading to speciation of marine bacteria have mostly been studied for (locally) abundant, free-living groups. The genus Phaeobacter is found on different marine surfaces, seems to occupy geographically disjunct habitats, and is involved in different biotic interactions, and was therefore targeted in the present study. The analysis of the chromosomes of 32 closely related but geographically spread Phaeobacter strains revealed an exceptionally large, highly syntenic core genome. The flexible gene pool is constantly but slightly expanding across all Phaeobacter lineages. The horizontally transferred genes mostly originated from bacteria of the Roseobacter group and horizontal transfer most likely was mediated by gene transfer agents. No evidence for geographic isolation and habitat specificity of the different phylogenomic Phaeobacter clades was detected based on the sources of isolation. In contrast, the functional gene repertoire and physiological traits of different phylogenomic Phaeobacter clades were sufficiently distinct to suggest an adaptation to an associated lifestyle with algae, to additional nutrient sources, or toxic heavy metals. Our study reveals that the evolutionary trajectories of surface-associated marine bacteria can differ significantly from free-living marine bacteria or marine generalists

Borane adducts of punicine and of its dehydroxy derivatives (pyridinium-1-yl)-2-and 3-phenolates

The natural product punicine (Punica granatum) exists in two tautomeric forms, the cross-conjugated mesomeric betaine 1-(pyridinium-1-yl)-2-hydroxy-phenyl-5-olate and the conjugated mesomeric betaine 1-(pyridinium-1-yl)-5-hydroxy-phenyl-2-olate. Punicine as well as its picoline derivatives reacted with tris(pentafluorophenyl)borane exclusively at the 2'-olate group to form zwitterionic borates. Correspondingly, the 5'-dehydroxy derivate of punicine, the conjugated heterocyclic mesomeric betaine 1-(pyridinium-1-yl)-phenyl-2-olate and its picoline derivatives also gave borates, whereas analogous reactions of the cross-conjugated isomer 2'-dehydroxypunicine [1-(pyridinium-1-yl)-phenyl-3-olatel did not result in the formation of stable adducts. (C) 2020 Elsevier Ltd. All rights reserved.Peer reviewe