IMEX evolution of scalar fields on curved backgrounds

Inspiral of binary black holes occurs over a time-scale of many orbits, far longer than the dynamical time-scale of the individual black holes. Explicit evolutions of a binary system therefore require excessively many time steps to capture interesting dynamics. We present a strategy to overcome the Courant-Friedrichs-Lewy condition in such evolutions, one relying on modern implicit-explicit ODE solvers and multidomain spectral methods for elliptic equations. Our analysis considers the model problem of a forced scalar field propagating on a generic curved background. Nevertheless, we encounter and address a number of issues pertinent to the binary black hole problem in full general relativity. Specializing to the Schwarzschild geometry in Kerr-Schild coordinates, we document the results of several numerical experiments testing our strategy.Comment: 28 pages, uses revtex4. Revised in response to referee's report. One numerical experiment added which incorporates perturbed initial data and adaptive time-steppin

Black.(Selected cases of phenomena in visual arts, culture and their possibilities in education)

Univerzita Karlova Pedagogická fakulta DISERTAČNÍ PRÁCE Černá. (Vybrané případy fenoménu ve výtvarném umění, kultuře a jejich možnosti v edukaci) MgA. Jan Pfeiffer 2023 Charles University, Faculty of Education DISSERTATION Black. (Selected cases of phenomena in visual arts, culture and their possibilities in education) MgA. Jan Pfeiffer 2023 Abstract The subject of this work is black, or the designation for color. But it is also an artistic concept and means of expression. The subject of my interest are selected cases of the black phenomenon in visual arts, culture, and their possibilities in education. I understand black as a phenomenon that I explore through my own creative work. In the course of it, I ask myself questions, such as: what stimuli, for example, black gives us and how it is connected with our socio-cultural background and its perception. I also ask contemporary artists working consciously or unconsciously with black, what black enables them in their work, and how it supports them, whether it is crucial for them. My intention is to open new perspectives on the subject of black and its connection with daily life, the ability to treat this phenomenon as a conscious gesture, an opinion - distinguishing different uses of black context. I also examine the possibilities of reasoning verified in...Univerzita Karlova Pedagogická fakulta DISERTAČNÍ PRÁCE Černá. (Vybrané případy fenoménu ve výtvarném umění, kultuře a jejich možnosti v edukaci) MgA. Jan Pfeiffer 2023 Abstrakt Předmětem této práce je černá neboli označení pro barvu. Je to ale také výtvarný koncept a výrazový prostředek. Předmětem mého zájmu jsou tedy vybrané případy fenoménu černá ve výtvarném umění, kultuře a jejich možnosti v edukaci. Černou chápu jako fenomén, který zkoumám prostřednictvím vlastní výtvarné tvorby. V jejím průběhu si kladu otázky, jako např.: jaké podněty nám černá dává a jak je provázána s naším sociokulturním pozadím a jeho vnímáním. Ptám se také současných umělců, pracujících vědomě či nevědomě s černou, co jim v práci černá umožňuje a jak je pro ně nosná, zda je pro ně klíčová. Mým záměrem je otevření nových pohledů na téma černé a jejího propojení s denním životem, schopnost zacházet s tímto fenoménem jako s vědomým gestem, názorem - odlišení rozdílného užití černé v různých kontextech. Zkoumám rovněž možnosti uvažování ověřené v rozdílných kontextech, které by byly inspirativní pro pedagogickou práci. Výzkumný model využívá kombinaci několika metod, a to metodologií kvalitativního výzkumu vztaženého k praxi umělecké tvorby, respektive kombinace jejich přístupů. Výraznou inspirací pro mě jsou zejména...Oddělení pro vědeckou činnostFaculty of EducationPedagogická fakult

Imaginary Versus Virtual Loci: Evaluating the Memorization Accuracy in a Virtual Memory Palace

The Method of Loci (MOL) is a mnemonic strategy to memorize declarative knowledge. In the late 90s researchers started to experimentally analyze the MOL by providing their participants a virtual world. This digital environment was meant to serve the users as a template for their personal memory palace. Past studies differed in central aspects of their experimental design. One difference is that earlier studies integrated the learning content in multiple and different ways. The design of the learning content is an essential aspect and should make a difference based on cognitive theories. This study analyzes if participants perform better with virtually presented learning content or if the MOL works better when users have to imagine the content. Results encourage future concepts of the virtual MOL to implement the learning content in the environment

Textile based dye-sensitized solar cells with natural dyes

Natural dyes extracted from hibiscus petals, elderberries and mallow flowers were investigated in dye-sensitized solar cells. Two approaches were followed: 1. Hybrid glass/fabric cells with titanium dioxide on glass as working electrode and a textile counter electrode; 2. hybrid fabric/glass cells with zinc oxide as working electrode on textile and a glass counter electrode. The zinc oxide layer on cotton was prepared by electroless deposition whereas the titanium dioxide coated glass electrodes were obtained directly from the manufacturer. In both cases the redox couple consisted of iodine / triiodide and the counter electrode was based on an electrically conductive fabric

Onset of Bloch oscillations in the almost-strong-field regime

In the field of high-order harmonic generation from solids, the electron motion typically exceeds the edge of the first Brillouin zone. In conventional nonlinear optics, on the other hand, the excursion of band electrons is negligible. Here, we investigate the transition from conventional nonlinear optics to the regime where the crystal electrons begin to explore the first Brillouin zone. It is found that the nonlinear optical response changes abruptly already before intraband currents due to ionization become dominant. This is observed by an interference structure in the third-order harmonic generation of few-cycle pulses in a non-collinear geometry. Although approaching Keldysh parameter γ = 1, this is not a strong-field effect in the original sense, because the iterative series still converges and reproduces the interference structure. The change of the nonlinear interband response is attributed to Bloch motion of the reversible (or transient or virtual) population, similar to the Bloch motion of the irreversible (or real) population which affects the intraband currents that have been observed in high-order harmonic generation