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Popular Abstract in Swedish Den här avhandlingen beskriver elektrontransport i nanometerstora halvledarstrukturer vid mycket låga temperaturer (1 nanometer = 1 miljondels millimeter). De här strukturerna har helt andra elektriska egenskaper än vanliga ledare. Man ser effekter av enskilda elektroners transport, och av kvantmekaniska fenomen som kvantiserad energi och våginterferens. Området är föreIn this thesis, electron transport in mesoscopic semiconductor nanostructures, in particular so-called electron billiards or quantum dots, is studied. The thesis can be divided into two areas: the linear response regime of transport, and the nonlinear response regime of transport. The classical and quantum mechanical electron dynamics are studied for triangular and square-shaped electron billiard

We study the stability and structure of vortices emerging in two-dimensional quantum dots in high magnetic fields. Our results obtained with exact diagonalization and density-functional calculations show that vortex structures can be found in various confining potentials. In nonsymmetric external potentials we find off-electron vortices that are localized giving rise to charge deficiency or holes

Language has to be conceived wholistically. Fragmented views, provoked by attempts at describing language, turn out essentially distortive on the general phenomenon which language is, with species like genetic language, programming language, formal language, observation language, inner cerebral language, external communication language. At the center of this wholism is a linguistic complementarity

We theoretically investigate a thermoelectric heat engine based on a single-level quantum dot, calculating average quantities such as current, heat current, output power, and efficiency, as well as fluctuations (noise). Our theory is based on a diagrammatic expansion of the memory kernel together with counting statistics, and we investigate the effects of strong interactions and next-to-leading or

Quantum cascade lasers (QCLs) are periodic semiconductor heterostructures, capable of producing laser gain. They have become an important source of coherent radiation in the mid infrared, and THz frequency regions. QCLs are non-linear electric devices, and often have bias regions of negative differential resistivity (NDR). These regions are inherently unstable, and electric field domains (EFDs) fo

Quantum dots are model systems for quantum thermoelectric behavior because of their ability to control and measure the effects of electron-energy filtering and quantum confinement on thermoelectric properties. Interestingly, nonlinear thermoelectric properties of such small systems can modify the efficiency of thermoelectric power conversion. Using quantum dots embedded in semiconductor nanowires,

Transport through nanosystems is treated within the second-order von Neumann approach. This approach bridges the gap between rate equations which neglect level broadening and cotunneling, and the transmission formalism, which is essentially based on the single-particle picture thereby treating many-particle interactions oil an approximate level. Here we provide an alternative presentation of the m

The gain profile of a quantum cascade laser is strongly influenced by the lifetime of the carriers in the upper and lower laser state. The quantitative description of gain within the concept of nonequilibrium Green's functions allows for a detailed understanding of various features affecting the gain spectrum: Compensation effects between scattering processes in the upper and lower laser level, re

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In small systems with large fluctuations, the classical description of thermodynamics is no longer sufficient which has led to the development of stochastic thermodynamics. One important result from stochastic thermodynamics is that with measurement and feedback it is possible to use those fluctuations to extract work from a single heat bath coupled to the system. This is thanks to the connection

In this thesis we employ the non-equilibrium Green’s function (NEGF) method to study both finite and infinite systems. We develop a codebase capable of computing the steady state interacting NEGF in open systems, i.e. tight-binding leads contacting a central region, in both Hartree-Fock (HF) and second Born (2B) approximations of particle-particle interactions. Furthermore, we use the exact intera

Nonlinear harmonic generation has been described theoretically, and observed, in free-electron laser (FEL) amplifiers. The mechanism relies on the nonlinear, higher-order bunching when the fundamental reaches high intensities, and can also be expected in high-power FEL oscillators. We use the 3D polychromatic simulation code MEDUSA to study the nonlinear harmonic generation in FEL oscillators. Str

After a historic introduction, today's wind power technology is reviewed on a systems level, with some details, and with some brave suggestions for wind technology 2030 when power electronics (PE) will be some 2000 GW. Eternal themes like "electricity storage" are avoided. Aspects of drive-trains in towers and collection grids in parks are concisely described in the paper's core, including: 1) a p

Sepsis causes severe derangements of the coagulation system. However, the signaling mechanisms regulating sepsis-induced thrombin generation remain elusive. Herein, we hypothesized that Rho-kinase might be an important regulator of thrombin generation in abdominal sepsis. Abdominal sepsis was induced by cecal ligation and puncture (CLP) in C57Bl/6 mice. Thrombin generation, coagulation factors, lu