It has been a long-standing mystery how complex biological structures emerge from such seemingly uncoordinated building blocks as cells and tissues, in the presence of only minimal environmental... Show moreIt has been a long-standing mystery how complex biological structures emerge from such seemingly uncoordinated building blocks as cells and tissues, in the presence of only minimal environmental guidance. In particular, unifying descriptions independent of microscopic details of a specific organism are rare. In recent years, hydrodynamics has successfully been applied to describe certain types living systems. The thesis is concerned with understanding different aspects of structure formation in active liquids and biological systems. In the first chapter we investigate the coarsening dynamics in the Toner-Tu theory and compare it with an experimental colloidal system. Afterwards, we investigate the effect of chirality in active nematics, with applications to biological tissues. In the last part we derive and study a model to explain geometric deformations due to the presence of activity. The resulting dynamics might be able to explain morphogenetic processes. Show less
Geometric frustration occurs when local order cannot propagate through space. A common example is the surface of a soccer ball, which cannot be tiled with hexaganons only. Geometric frustration can... Show moreGeometric frustration occurs when local order cannot propagate through space. A common example is the surface of a soccer ball, which cannot be tiled with hexaganons only. Geometric frustration can also be present in materials. In fact, geometry can act as an instrument to design the mechanical, optical or physical properties of fluids and solids. The first two parts of this thesis discuss frustrated liquid crystals confined to droplets of various shapes and sizes. The droplet shape determines the orientation of the liquid crystal molecules and in turn its response to light. In the final part we study the fracture mechanics of curved elastic plates. By tuning the curvature of the plate, the critical length at which the crack starts growing can be controlled. Finally, we find that the path that the crack takes depends on the curvature. Show less
The central topic in this thesis is the effect of topological defects in two distinct types of condensed matter systems. The first type consists of graphene and topological insulators. By... Show moreThe central topic in this thesis is the effect of topological defects in two distinct types of condensed matter systems. The first type consists of graphene and topological insulators. By studying the long-range effect of lattice defects (dislocations and disclinations) we find that the graphene electrons mimic fundamental Dirac electrons in spaces with curvature and torsion. We show that these long-range effects influence interferometric transport measurements: (i) Emphasizing the importance of electron dephasing in graphene; (ii) Enabling a characterization of neutral Majorana states, which are important for quantum computation applications, and conjectured to exist in topological insulators. Considering also the microscopic structure of graphene dislocations, we interpret local tunneling experiments on graphite grain boundaries. The second type of systems we study are the high temperature cuprate superconductors, where the strongly interacting electrons lead to coexisting symmetry breaking orders in the pseudogap phase. We observe and describe the interplay of nematic (orientational) and stripe (translational) orderings in local tunneling experiments, with stripe dislocations playing the key role. We also describe the observed phonon anomaly in cuprates through the effect of metallic stripes. Show less
