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Université de Fribourg

Thermal energy transport across the interface between phase change material n-heneicosane in solid and liquid phases and few-layer graphene

Chilukoti, Hari Krishna ; Zhou, Tianhang ; Ardham, Vikram Reddy ; Böhm, Michael C. ; Müller-Plathe, Florian

In: The Journal of Physical Chemistry C, 2019, vol. 123, no. 48, p. 29192–29202

Molecular dynamics simulations have been performed to investigate the mechanism of thermal energy transport at the interface between n-heneicosane in solid and liquid phases and few-layer graphene at different temperatures under two heating modes (in the “heat-matrix” mode, heat is flowing from the heated heneicosane molecules to the cooled ones through the graphene layers and in the...

Université de Fribourg

Quantum simulation meets nonequilibrium dynamical mean-field theory: exploring the periodically driven, strongly correlated fermi-hubbard model

Sandholzer, Kilian ; Murakami, Yuta ; Görg, Frederik ; Minguzzi, Joaquín ; Messer, Michael ; Desbuquois, Rémi ; Eckstein, Martin ; Werner, Philipp ; Esslinger, Tilman

In: Physical Review Letters, 2019, vol. 123, no. 19, p. 193602

We perform an ab initio comparison between nonequilibrium dynamical mean-field theory and optical lattice experiments by studying the time evolution of double occupations in the periodically driven Fermi-Hubbard model. For off-resonant driving, the range of validity of a description in terms of an effective static Hamiltonian is determined and its breakdown due to energy absorption close to...

Université de Fribourg

The influence of substituents on gelation and stacking order of oligoaramid – based supramolecular networks

Drechsler, Susanne ; Balog, Sandor ; Kilbinger, Andreas F. M. ; Casalini, Tommaso

In: Soft Matter, 2019, vol. 15, no. 36, p. 7250–7261

Self-assembly has proven to be a powerful tool for functional, smart materials such as hydrogels derived from low molecular weight compounds. However, the targeted design of functional gelators remains difficult. Here, we present a set of four Y-shaped aromatic amide tetramers with varying functionalities able to undergo different non- covalent interactions. These compounds were explored...

Université de Fribourg

Coupling of electronic and nuclear motion in a negative ion resonance: Experimental and theoretical study of benzene

Allan, Michael ; Čurík, Roman ; Čársky, Petr

In: The Journal of Chemical Physics, 2019, vol. 151, no. 6, p. 064119

We present calculated and measured elastic and vibrational excitation cross sections in benzene with the objective to assess the reliability of the theoretical method and to shed more light on how the electronic motion of the incoming electron is coupled with the nuclear motion of the vibrations. The calculation employed the discrete momentum representation method which involves solving the...

Université de Neuchâtel

Ecosystem engineers’ contribution to soil structure formation in floodplains

Schomburg, Andreas ; Le Bayon, Claire (Dir.) ; Guenat, Claire (Codir.) ; Brunner, Philip (Codir.)

Thèse de doctorat : Université de Neuchâtel, 2019.

Soil structure formation constitutes an extremely important process in near-natural and restored floodplains. A stable soil structure protects riverbanks from erosion and contributes to the preservation of ecosystem services. However, developing a soil structure in alluvial soils is difficult for several reasons. Extensive alluvial dynamics cause periodic waterlogging and continuously rejuvenate...

Université de Fribourg

A DuMond-type crystal spectrometer for synchrotron-based X-ray emission studies in the energy range of 15–26 keV

Jagodziński, Paweł ; Szlachetko, Jakub ; Dousse, Jean-Claude ; Hoszowska, Joanna ; Szlachetko, Monika ; Vogelsang, U. ; Banaś, Dariusz ; Pakendorf, T. ; Meents, A. ; Bokhoven, Jeroen A. van ; Kubala-Kukuś, Aldona ; Pajek, Marek ; Nachtegaal, Maarten

In: Review of Scientific Instruments, 2019, vol. 90, no. 6, p. 063106

The design and performance of a high-resolution transmission-type X-ray spectrometer for use in the 15–26 keV energy range at synchrotron light sources is reported. Monte Carlo X-ray-tracing simulations were performed to optimize the performance of the transmission-type spectrometer, based on the DuMond geometry, for use at the Super X-ray absorption beamline of the Swiss Light Source at...

Université de Fribourg

Last phase of the Little Ice Age forced by volcanic eruptions

Brönnimann, Stefan ; Franke, Jörg ; Nussbaumer, Samuel U. ; Zumbühl, Heinz J. ; Steiner, Daniel ; Trachsel, Mathias ; Hegerl, Gabriele C. ; Schurer, Andrew ; Worni, Matthias ; Malik, Abdul ; Flückiger, Julian ; Raible, Christoph C.

In: Nature Geoscience, 2019, vol. 12, no. 8, p. 650–656

During the first half of the nineteenth century, several large tropical volcanic eruptions occurred within less than three decades. The global climate effects of the 1815 Tambora eruption have been investigated, but those of an eruption in 1808 or 1809 whose source is unknown and the eruptions in the 1820s and 1830s have received less attention. Here we analyse the effect of the sequence of...

Université de Fribourg

Anomalous fluxes in overdamped Brownian dynamics with Lorentz force

Vuijk, Hidde Derk ; Brader, Joseph M. ; Sharma, Abhinav

In: Journal of Statistical Mechanics: Theory and Experiment, 2019, vol. 2019, no. 6, p. 063203

We study the stochastic motion of a particle subject to spatially varying Lorentz force in the small-mass limit. The limiting procedure yields an additional drift term in the overdamped equation that cannot be obtained by simply setting mass to zero in the velocity Langevin equation. We show that whereas the overdamped equation of motion accurately captures the position statistics of the...

Université de Neuchâtel

Rubidium vapour-cell frequency standards : metrology of optical and microwave frequency references

Moreno, William ; Mileti, Gaetano (Dir.)

Thèse de doctorat : Université de Neuchâtel, 2019.

This thesis concerns the development, study, and optimisation of compact and high-performance frequency references based on rubidium (Rb) vapour cells1. More specially, two Rb vapour-cell frequency references are studied: an optical-frequency reference at 1.5 μm and a double-resonance pulsed optically pumped (POP) atomic clock. The use of vapour cells allows compact frequency...

Haute Ecole d'Ingénierie

Transformateur MHz pour plasma atmosphérique

Udressy, Julien ; Ellert, Christoph (Dir.)

Mémoire de bachelor : Haute Ecole d'Ingénierie, 2018.

Le but de ce travail de diplôme est de concevoir un transformateur dans la gamme des radiofréquences afin d’élever la tension de sortie de la « Match Box » de 300V à 1kV. A ce niveau de tension, un signal sinusoïdal dans les MHz doit permettre d’enclencher et d’entretenir un plasma atmosphérique entre deux électrodes distantes de 1mm. Les sources de plasma ponctuelles peuvent...