Atoms and molecules are the basic units of matter. If we keep dividing a bar of gold or a glass of water into smaller parts, at the end we are left with a single gold atom or a water molecule. We... Show moreAtoms and molecules are the basic units of matter. If we keep dividing a bar of gold or a glass of water into smaller parts, at the end we are left with a single gold atom or a water molecule. We could not divide them further without them losing their identity. Molecular electronics is the study of how electrons, which are fundamental particles in nature, flow through these basic units of the matter once connected between two electrical leads. At such small dimensions matter starts to lose its macroscopic properties and its behaviour is governed by the rules of quantum mechanics. A molecule can have various electronic and mechanical degrees of freedom (or eigenstates) with discrete energies. The electrons flowing through the molecule can interact with these degrees of freedom making single molecule devices. Better control and understanding of these interactions and study of how the atomic structure of the macroscopic electrical leads affect the electronic-transport forms the main focus of this thesis. Controlled manipulation of single atoms and molecules using a low-temperature scanning tunnelling microscope, probing charge transport using high-frequency shot-noise measurement and the use of graphene as possible electrodes are the three directions which are investigated here. Show less
Polymers are the main building blocks of many biological systems, and thus polymer models are important tools for our understanding. One such biological system is the large scale organisation of... Show morePolymers are the main building blocks of many biological systems, and thus polymer models are important tools for our understanding. One such biological system is the large scale organisation of chromatin. A key question here, is how during cell division the chromosomes can separate without entanglement and knotting. One proposal is that this achieved by a specific spatial organisation of the chromosomes, known as the "fractal globule". Using Monte Carlo simulations, we found that fractal globules are unstable and thus cannot represent the biological system without further ingredients. Another proposal is that topological effects cause spatial separation of the chromosomes. These topological effects can be studied using simulations of nonconcatenated ring polymers. Using a compute device called the Graphics Processing Unit, very detailed and long simulations were carried out. From these a picture emerged in which ring polymers behave much slower than was found in previous studies. A second biological system studied here is the folded state of the protein. This is modeled by the Hamiltonian walk. Here, instead of simulations, we exactly enumerated all Hamiltonian walks of the 4x4x4 cube. Interestingly, simulations show that for larger systems many more walks exist than previously estimated. Show less
