In this thesis, "culture" refers to the collection of subjective human traits, such as preferences an opinions, that a given, geographically bounded population has at a given moment in time.... Show moreIn this thesis, "culture" refers to the collection of subjective human traits, such as preferences an opinions, that a given, geographically bounded population has at a given moment in time. Representative samples of individuals from such populations are studied, focusing on individual opinions expressed on various topics, present in multivariate empirical data that had been previously collected, mainly via social surveys. We propose and exploit new methods for analyzing such data, relying on mathematical notions specific to statistical mechanics and information theory, but also on agent-based models/simulations of opinion/cultural dynamics driven by social influence. These methods provide new insights about how human culture is organized. They provide indications that cultural structure has universal properties, independent of the geographical region and of the set of survey questions. Furthermore, these properties suggest that culture is shaped around a small number of "rationalities", while also having a certain hierarchical organization that is robust to social influence dynamics. Finally, we propose a method of filtering the noise in the data, which seems to allow for the identification of cultural modules that are not visible otherwise. However, we also show that visible modules may well be just artifacts of survey design. Show less
Electrons in a crystal lattice have properties that may differ from those of a free electron in vacuum. The effective mass can be different from the bare electron mass, and it may even vanish, ... Show moreElectrons in a crystal lattice have properties that may differ from those of a free electron in vacuum. The effective mass can be different from the bare electron mass, and it may even vanish, so that the electron behaves in some respects as a relativistic massless particle such as a photon. The magnetic moment of the intrinsic angular momentum, the electron spin, may be also different from that of an elementary particle. Spin-like degrees of freedom, referred to as "pseudospin" or "valley isospin", can also arise in the effective low-energy description of electrons in the lattice fields. These various degrees of freedom are of interest as ways to store and transport information: one speaks of "spintronics" and "valleytronics" as alternatives to "electronics". For these purposes it is of interest to study the interplay between the orbital motion of electrons and their spin (spin-like) degrees of freedom, the so-called "spin-orbit coupling". In some systems where this interaction is strong, it causes the electron spin to be tied to the direction of motion. This thesis contains results about the effects of this "spin-momentum locking" on two classes of materials, oxide interfaces and Weyl semimetals, with a focus on their electrical transport properties. Show less
In the first part of this thesis we study the geometry of folding patterns. Specifically, we focus on crease patterns consisting entirely of four-vertices; these are points where four fold... Show moreIn the first part of this thesis we study the geometry of folding patterns. Specifically, we focus on crease patterns consisting entirely of four-vertices; these are points where four fold lines come together. A single four-vertex is the simplest example of a foldable crease pattern that can be folded without bending the material in between the folds, and has a remarkable property: despite its single degree of freedom, it has two distinct folding motions. We make use of this property, and show how to design arbitrarily large four-vertex crease patterns, which can fold into two or more shapes. This is in contrast to other design methods, which produce patterns that can only fold into one specific shape. In the second part of this thesis, we study single four-vertices, and show a robust method to obtain four-vertices with three energy minima, which correspond to three different stable folded configurations. This too is in contrast to other experimental methods, which can only generate bistable vertices or patterns. Show less
Mechanical metamaterials are man-made materials which derive their unusual properties from their structure rather than their composition. Their structure, or architecture, often consists of... Show moreMechanical metamaterials are man-made materials which derive their unusual properties from their structure rather than their composition. Their structure, or architecture, often consists of periodically arranged building blocks whose mutual interactions realize unusual properties. In this thesis, we investigate the role of two aspects of mechanical metamaterials: The beam ligaments and the microstructures of hinging squares. Both aspects play an important role in mechanical metamaterials, but give rise simultaneously to several open problems. First, although the mechanical behaviour of slender beam ligaments is well understood, the finite-width ligaments that often occur in mechanical metamaterials lead to new physics; wide beams exhibit a negative post-buckling stiffness, characterized by a decreasing force after buckling, which is not well understood. Second, fully filled microstructures of hinging squares constitute an auxetic mechanism, but possible new zero modes derived from (diluted) microstructures with missing squares remain largely unexplored. How does the number of zero modes increases in such diluted systems, can we count these additional modes, and what is their spatial structure? Here we address these open problems, thereby providing the necessary understanding to fully leverage the characteristics of wide beam ligaments and diluted collections of hinging squares for the design of novel mechanical functionalities. Show less
This thesis is devoted to an in-depth examination of the various effects of disorder in the cuprate high-temperature superconductors. Disorder is ubiquitous in these materials and is central to... Show moreThis thesis is devoted to an in-depth examination of the various effects of disorder in the cuprate high-temperature superconductors. Disorder is ubiquitous in these materials and is central to a number of phenomena observed in various phases. We revisit several phenomena in the cuprates in light of what is now known about the nature of disorder present in these materials. First, the phenomenon of quasiparticle scattering interference is revisited using a number of different realistic models of distributed disorder which go beyond the single-impurity paradigms used in much of the literature. Next, we study the manner in which a finite DOS at the Fermi energy, seen in a large number of experiments, is generated by various models of disorder, and consider the possibility that smooth disorder from off-plane dopants explains this phenomenon. In addition the localization properties of the superconducting quasiparticles in the presence of various types of disorder are studied. Finally, we show how a number of nontrivial interaction effects in the superconducting and normal states of the cuprates could be visualized by scanning tunneling spectroscopy experiments. Show less
This thesis describes a study from both a theoreticaL and an experimental point of view. I deveLop a new ru•deL for electron transport through networks of interconnected narnzparticLes In the... Show moreThis thesis describes a study from both a theoreticaL and an experimental point of view. I deveLop a new ru•deL for electron transport through networks of interconnected narnzparticLes In the Coulomb blockade regime and compare this ru•del tc experimental data. The main conclusion from this study is that cotunneLing does not give any significant contribution tc electron transport. Instead, transport is governed by perccIatLng paths thrcugh the netwcrk. Here, disorder In the array (in the form of variation of the Coulomb chargLng energy of the nanzparticLes) is the domLnating factor. Morecver, usLng Low—energy electron potentiometry, I visualise the f Low cf electrcns through the network. We find here that the contact resistance is negligibLe, and Chat the electi•zn flow 13 not impeded by small irregularities such as small and grain boundaries . Show less
In this thesis we study quantum transport phenomena on the nanometer scale, in two classes of materials: topological insulators with induced superconductivity and graphene superlattices. Both... Show moreIn this thesis we study quantum transport phenomena on the nanometer scale, in two classes of materials: topological insulators with induced superconductivity and graphene superlattices. Both topics are motivated by recent experimental developments: the first topic arose from the search for Majorana fermions in a quantum spin Hall insulator, the second topic arose from the search for massive Dirac fermions in the Kekulé band structure of graphene on a copper substrate. We focus on lattice models, solving them both numerically and analytically. Show less
This thesis is a collection of experimental attempts to enhance photoluminescence of fluorescent molecules and quantum dots with single gold nanorods (GNRs) and relevant applications. Special... Show moreThis thesis is a collection of experimental attempts to enhance photoluminescence of fluorescent molecules and quantum dots with single gold nanorods (GNRs) and relevant applications. Special attention is focused on the interactions between single emitters and GNRs. The idea is to increase the emission of weak emitters by the excellent optical properties of GNRs so that weak light emitters will then be bright enough to be detected and studied individually. We can thus generalize single-molecule fluorescence spectroscopy to weakly emitting species which are currently undetectable by conventional single-molecule spectroscopy. The research is important for extending the scope of single-molecule spectroscopy, which is a powerful technique for understanding the dynamic behaviors at the nanometer scale in biological systems and other materials. Show less
Electron microscopy has become an extremely important techniquein a wide variety of elds. The resolving power is vastly superiorto light microscopes and electron microscopy has proven tobe valuable... Show moreElectron microscopy has become an extremely important techniquein a wide variety of elds. The resolving power is vastly superiorto light microscopes and electron microscopy has proven tobe valuable in elds ranging from archaeology and geology to biology andcondensed-matter physics.A major disadvantage is that the electron energy used in conventional ElectronMicroscopy (EM) ranges from 10’s to 100’s of keV. Such energetic electronscan signicantly damage the specimen. This is especially relevant in thestudy of biological samples and organic materials in general. Major eorts arebeing made to avoid this radiation damage from interfering with the studyof such materials. There are several approaches to minimize damage in EM.These include developing better detectors such that lower electron doses aresucient to form an image, and lowering the electron energies to several keV.In this dissertation I present the development of, and measurements with, atransmission electron microscope that uses electron energies ve orders ofmagnitude lower than in conventional Transmission Electron Microscopes(TEMs). The energies we use are in the order of a few eV. Hence, we call ourtechnique ’eV-TEM’. Show less
Single-molecule fluorescence was invented in the 1990s and has quickly developed into an indispensable technique in the biomedical sciences and condensed-matter research. It has revolutionized... Show moreSingle-molecule fluorescence was invented in the 1990s and has quickly developed into an indispensable technique in the biomedical sciences and condensed-matter research. It has revolutionized the fields of molecular biology, imaging (super-resolution), and catalysis, to name a few. In this thesis, we will apply fluorescence enhancement by single gold nanorods to extend single-molecule studies to chromophores with low fluorescence quantum yields and to high concentrations of probe molecules. Following single-molecule trajectories, we will explore variations in the electron-transfer rates of the metalloprotein azurin both from molecule to molecule and for the same molecule as a function of time. Evidence for conformational substates will be discussed based on dynamic heterogeneity. Show less
Scattering of light in the presence of nano-structured materials, i.e. with features in the order of the wavelength of the light or smaller, reveals details of how light interacts with matter at... Show moreScattering of light in the presence of nano-structured materials, i.e. with features in the order of the wavelength of the light or smaller, reveals details of how light interacts with matter at the nanoscale. In this dissertation we present four cases of light scattering on nano-structures. First we describe how light confined in 2D structures, namely a dielectric membrane and a metal layer, interacts with either a single nano-hole or a hole-array. Then, we study two cases of light propagating in random scattering media: we show how phase modulation can be used to measure scattering properties in a volume scatterer (e.g. white paint), and we investigate light transport in a rough thin-film silicon solar cell. Show less
There are many interpretations of quantum mechanics, and ultimately experiments are needed to verify or falsify these interpretations. In this thesis we work towards an experiment that should make... Show moreThere are many interpretations of quantum mechanics, and ultimately experiments are needed to verify or falsify these interpretations. In this thesis we work towards an experiment that should make the study of the existence of gravitational-induced collapse of the wave function feasible. We propose to use a Magnetic Resonance Force Microscope where we let the magnetic tip interact with a controlled Nitrogen-Vacancy center to study the superposition of the tip’s position (Ch.1 and Ch. 5). We have shown theoretically (Ch. 2) and experimentally (Ch.3) how spins on the surface and in the bulk can change the resonance frequency of the resonator and increase the dissipation. Using this theory we have measured the bulk impurity and surface spin density of diamond and performed local spin resonance on the bulk spins (Ch. 4). An important part of this thesis forms the partly new techniques and instrumentation that this experiment needs (Ch. 6). One of these techniques led to the study of the tip-sample capacitance in general SPM-applications which can be used to do fast pre-approaches and in-situ tip characterizations (Ch. 7). Show less
We investigate how radiation pressure can be used to influence the mechanical motion of a micro-mirror suspended from springs. This trampoline resonator is part of an optical Fabry-Perot cavity. By... Show moreWe investigate how radiation pressure can be used to influence the mechanical motion of a micro-mirror suspended from springs. This trampoline resonator is part of an optical Fabry-Perot cavity. By tuning the laser frequency with respect to the optical resonance, we are able to optically cool the mechanical motion of the resonator. When combining this optical cooling with cryogenic cooling techniques, we are able to bring the mechanical resonator close to the quantum mechanical ground state. This is a requirement for future experiments to investigate the fundamentals of quantum mechanics. Show less
In this work the reconstruction of a tau neutrino signal in the KM3NeT detector is discussed. Tau neutrinos leave a two shower signature in the detector, which is a unique signature among all... Show moreIn this work the reconstruction of a tau neutrino signal in the KM3NeT detector is discussed. Tau neutrinos leave a two shower signature in the detector, which is a unique signature among all neutrino interactions. By identifying and reconstructing these tau signatures the KM3NeT detector will be able to distinguish all three neutrino flavors. In addition, cosmic tau neutrinos suffer significantly less from atmospheric backgrounds, makign them ideal messengers for cosmic events. The presented reconstruction is the first tau reconstruction for the KM3NeT detector and resulted in a total expected observation rate of half a tau event per year for one unit of the KM3NeT detector. Show less
We investigate the buildup of galaxies from various vantage points. The first two chapters focus on the stellar content of galaxies, especially the distribution of stellar masses at birth and... Show moreWe investigate the buildup of galaxies from various vantage points. The first two chapters focus on the stellar content of galaxies, especially the distribution of stellar masses at birth and potential variations therein in various galactic environments. We find that in some cases these inferred variations can be due to an underestimation of model and measurement errors. Furthermore, we infer the consequences of these proposed variations on the interpretation of galaxy properties and galaxy formation processes. Chapters 3 and 4 focus on the buildup of galaxies in time through mergers and in-situ star formation. We test and improve observational models that aim to trace galaxies though cosmic time, by applying them to cosmological hydrodynamical simulations, for which we have access to the full history and evolution of galaxies since the beginning of time. The fifth chapter focusses on the buildup of galaxy morphology. We follow the buildup of morphological components in a cosmological simulation, which leads us to conclude that galaxy formation is a three-phase process, consisting of an early, rather disorganised, phase, followed by a phase in which stars are formed primarily in an organised rotating disk, and ending in a late phase of merger-driven spheroid formation. Show less
Shape and biological function are tightly connected. Physical descriptions are used to connect the shape of a biological system with its function. One system investigated here is the dendritic... Show moreShape and biological function are tightly connected. Physical descriptions are used to connect the shape of a biological system with its function. One system investigated here is the dendritic spine, which is the connection between neurons. The dendritic spine is mimicked in an artificial system. In this way, I was able to show that the shape of the dendritic spine is important in memory and learning. The shape of a cell itself is governed by its actin cytoskeleton. I showed that a simple model can be used to describe the shape of adherent cells. An adherent cell attaches itself at discrete points to the substrate. The edge of the cell in between these points can be described as a part of an ellipse. I show that all edges of a single cell can all be described with a single ellipse. On a small scale, the shape of the membrane of a cell changes with changing lipid content. I used light to change the lipid content, triggering phase unmixing in an artificial lipid membrane. I show that various important parameters change significantly. Show less
In this thesis, classes of strongly interacting quantum field theories, have been studied. A non-perturbative method applied to these theories are gauge/gravity duality or holographic duality,... Show moreIn this thesis, classes of strongly interacting quantum field theories, have been studied. A non-perturbative method applied to these theories are gauge/gravity duality or holographic duality, which map a system of quantum field theory to a theory of gravity in higher dimensions. This thesis focused on the transport coefficients which govern the low energy excitations of these systems. Show less
The thesis describes experimental steps towards reduction of friction on the macroscopic scale by scenarios of thermo- and superlubricity well-known on the nanoscale. The friction study involves... Show moreThe thesis describes experimental steps towards reduction of friction on the macroscopic scale by scenarios of thermo- and superlubricity well-known on the nanoscale. The friction study involves experiments on tailored Si nanopillar arrays, micropatterned Diamond-Like Carbon coating and high-quality graphene. Show less
In mechanical metamaterials, large deformations can occur in systems which are topological from the point of view of linear waves. The interplay between such nonlinearities and topology affects... Show moreIn mechanical metamaterials, large deformations can occur in systems which are topological from the point of view of linear waves. The interplay between such nonlinearities and topology affects wave propagation. Beyond perfectly periodic systems, defects provide a way to modify and control the properties of metamaterials, and can also interact with both nonlinearities and the bulk topology. To investigate these, we explore the wave propagation in three mechanical models, i.e.~solitary waves in topological rotor chains, lattice waves in twisted kagome networks, and transverse shock waves in flexible strings. Show less
The four possible segments A, T, C and G that link together to form DNA molecules, and with their ordering encode genetic information, are not only different in name, but also in their physical and... Show moreThe four possible segments A, T, C and G that link together to form DNA molecules, and with their ordering encode genetic information, are not only different in name, but also in their physical and chemical properties. The result is that DNA molecules with different sequences have different physical behavior. For instance, one sequence may lead to a very flexible DNA molecule, another to a very stiff one. A DNA molecule with a given sequence may be straight, or intrinsically curved. This leads to an interplay between the information stored in a DNA molecule on one hand, and the physical properties of that molecule on the other. This is of great importance in our cells, where lengths of DNA far longer than the size of the cells that contain them need to be significantly folded up. The research presented in this thesis looks at how we can model this interplay, what its effects can be, and whether nature has made use of it to encode mechanical signals into real genomes. Show less
