Welcome to my website!
My name is Jakub Cehula, and I am a master's student of Theoretical Physics at Charles University in Prague. I am also a member of Time-domain astronomy group of Ondřej Pejcha. I recently (Aug 2020 - Jun 2021) spent two semesters as an exchange student at Stockholm University, where I studied astronomy. Before working in the field of astronomy, I worked in the field of continuum mechanics under my supervisor Vít Průša.
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Stability of stars undergoing rapid mass loss
Binary mass transfer is a common phenomenon in stellar astrophysics. If the mass transfer proceeds on dynamical timescale, the binary can undergo a catastrophic interaction accompanied by tremendous loss of mass, angular momentum, and energy. This so-called common envelope evolution phase is a crucial step in the formation of close binaries composed of compact objects (white dwarfs, neutron stars, black holes), which includes progenitors of gravitational wave sources detected by LIGO. By improving existing models of binary mass transfer we can correct the predictions of common envelope evolution and constraint the rates of close binaries composed of compact objects.
Together with my current supervisor, Ondřej Pejcha, we have recently developed new model of binary mass transfer, see my master thesis (2021). We have treated the mass transfer as a special case of stellar wind. We have relied on the assumption that the Roche potential sets up a de Laval nozzle around the first Lagrange point. The mass is then transferred through the nozzle. Our binary mass transfer model predicts mass transfer rates in the same order of magnitude as the standard models which use the Bernoulli's law. But the advantage of our model is that it is extendable to account for radiation.
Origami-like structures made of light activated shape memory polymers
Light activated shape memory polymers (LASMPs) are smart materials with the ability of remembering a deformed state (temporary shape) due to exposure to UV light and returning to the permanent (original) shape by the exposure to UV light with a different wavelength. Regarding the shape of smart materials frequent inspiration is taken from the art of origami, the Japanese art of folding paper into various shapes.
I have developed a code for computer modelling of such origami-like structures made of LASMPs, see Cehula & Průša (2020, Int. J. Eng. Sci. 150, 103235). The code is a modification to the state-of-the-art code for simulations of elastic origami-like structures developed by Liu & Paulino (2018, Origami, 7, 1167-1182). The original code is called MERLIN2, my modification is called MERLIN2.LUX.