Seminář se koná každé úterý v 10:40 v posluchárně ÚTF MFF UK
v 10. patře katedrové budovy v Tróji, V Holešovičkách 2, Praha 8
Internal and external processes such as mantle convection, deglaciation, and atmospheric circulation force planetary bodies to move as a whole relative to their rotation axis. The rotation poles of planets and moons thus wander on their surfaces, as shown by paleomagnetic, astrometric, or geological observations (true polar wander). Due to the extremely slow rotation of Venus and its near absence of a rotational bulge, true polar wander on Venus was thought to be anomalous - the rotation pole was considered to follow a circular path on the planet's surface (wobble). Here, we argue instead that true polar wander on Venus proceeds similarly to that of fast rotating planets such as Earth or Mars, and derive a scaling law for the offset between the rotation and figure poles during true polar wander.
Professor Werner Espe (1899 Elbing, Prussia – 1970 Bratislava), a nearly forgotten figure of German and Czechoslovak history, was a student of physics in Berlin around 1920, who then played a key role in advancing vacuum technologies, electrovacuum technology, and electronics in the Czechoslovak Republic after 1945. Let us reconstruct his personal life story throughout the turbulent 20th century, as well as the network of his teachers, colleagues, and students, and his own substantial scientific research.
(seminář v češtině)
Přednáška představí inženýrský proces transformace ideového návrhu technického experimentu do jeho fyzické realizace. Budou zmíněny obvyklé tolerance výrobních metod a jejich faktické limity. Budou naznačeny postupy, zaručující minimalizaci nebo statickou a dynamickou kompenzaci vybraných veličin. Závěrem bude prezentován postup konstrukce a realizace konkrétního měřicího zařízení od formulace požadavků na jeho funkci až po jeho fyzickou realizaci.
I will introduce and discuss various entropies in quantum theory and their meaning. I will specifically focus on the classical thermodynamic entropy and then generalize this notion to quantum physics to arrive at the notion called observational entropy.
In the first part we discuss earlier work by Exner and Lipovský, in which they consider quantum graphs consisting of a compact part and semi-infinite leads. Such a system may contain embedded eigenvalues in the continuous spectrum, which, under perturbation, move into the second sheet of the complex energy surface and produce resonances. We also show how the scattering and resolvent resonances in quantum graphs coincide and how ”nothing is lost at the perturbation” in the sense of the number of poles. In the second part we then introduce a cut-off technique known since the eighties to our quantum graph framework. Using it, one can identify resonances through the eigenvalue behavior of the system ”closed in a box”. We prove its validity, which was before done only in the case of one-dimensional potential scattering, and illustrate it with examples.
Feynman diagrams are a terrible way to calculate scattering amplitudes. They are woefully inefficient, and manifestly introduce an infinite amount of redundancy which obscures any structure which the scattering amplitudes have. In this talk I will highlight certain modern approaches to scattering amplitudes. In particular, there are geometric ideas, such as the Amplituhedron, which directly capture scattering amplitudes without any auxiliary constructions such as Lagrangians, virtual particles, or even spacetime itself. This gives a radically new way to think about the physics of scattering in QFT.
Cellular phenomena at the microscopic level are usually modeled via molecular simulations. These simulations have the advantage of giving an accurate description of the molecular interactions that give rise to biological phenomena. However, they are computationally expensive and hard to interpret. In particular, they are not capable of giving a satisfactory view of slow processes, such as organelle morphogenesis or cell division. For this purpose, continuum models are preferable. These models can be validated by structural data (e.g. electron microscopy). However, they can also be directly parametrized by molecular simulations. I present such a "data-driven" model for large membrane deformations, e.g., those induced by cell penetrating peptides as well as a more reductive morphoelastic model for bacterial division.
Over the last ten years, a population of so-called "Ultra Diffuse Galaxies" has been uncovered which was not predicted by cosmological models. These systems are the same size as the Milky Way but a thousand times fainter, with their total mass still a matter of contention. I will present the results from Arecibo surveys regarding the detection of several UDGs in neutral hydrogen emission, allowing estimates of their dynamical mass. I will also examine how these compare to other, similar objects of extremely low luminosity dubbed `blue blobs', which have been proposed to result from gas stripping in galaxy clusters, reviewing whether clusters are likely to be responsible for the creation or destruction of such objects, or whether both processes might be in effect.
Jiří Horáček David Heyrovský