No description available.

The discovery of carbon nanotubes by Iijima in 1991 has created a torrent of new research activities. Research on carbon nanotubes ranges from studying their fundamental properties, such as their electron band structure and plasma frequencies, to developing new applications, such as self-assembled nano-circuits and field emission displays. Robust models are now needed to enable a better understanding of the electronic response of carbon nanotubes. We use time-dependent density functional theory to derive a two-fluid two-dimensional (2D) hydrodynamic model describing the collective response of a multiwalled carbon nanotube with dielectric media embedded inside or surrounding the nanotube. We study plasmon hybridization of the nanotube system in the UV range, the stopping force for ion channelling, the dynamical image potential for fast ions, channelled diclusters and point dipoles, and the energy loss for ions with oblique trajectories. Comparisons are made of results obtained from the 2D hydrodynamic model with those obtained from an extension of the 3D Kitagawa model to cylindrical geometries.

The discovery of carbon nanotubes by Iijima in 1991 has created a torrent of new research activities. Research on carbon nanotubes ranges from studying their fundamental properties, such as their electron band structure and plasma frequencies, to developing new applications, such as self-assembled nano-circuits and field emission displays. Robust models are now needed to enable a better understanding of the electronic response of carbon nanotubes. We use time-dependent density functional theory to derive a two-fluid two-dimensional (2D) hydrodynamic model describing the collective response of a multiwalled carbon nanotube with dielectric media embedded inside or surrounding the nanotube. We study plasmon hybridization of the nanotube system in the UV range, the stopping force for ion channelling, the dynamical image potential for fast ions, channelled diclusters and point dipoles, and the energy loss for ions with oblique trajectories. Comparisons are made of results obtained from the 2D hydrodynamic model with those obtained from an extension of the 3D Kitagawa model to cylindrical geometries.

Title: Radiation corrections to atomic spectra. Author: Vojtěch Patkóš Department: Department of chemical physics and optics Supervisor: doc. Mgr. Jaroslav Zamastil, Ph.D., KCHFO Abstract: In present time accuracy of spectroscopic measurements achieved fan- tastic accuracy 1 part in 10 to the power 14. If these measures are followed by theoretical calculations of similar accuracy we can test quantum electrodynamics and part of the standard model responsible for parity violating weak forces by comparing theory and experiment and set some of the basic physical constants like Rydberg constant, mass and radius of nucleus, constant of fine structure and it's variation in time etc. For achieving this kind of accuracy of calculations one must take into account so called radiation corrections. This thesis focus is on accurate calculation of the most important of them, the self-energy of electron in one-loop aproximation. Keywords: Quantum electrodynamics, radiation corrections, self-energy of elec- tron.

No description available.

No description available.

The imaginary part of the retarded self energy is of particular interest as it contains a lot of physical information about particle interactions. In higher order loop diagrams the calculation become extremely tedious and if we have to do the same at finite temperature, it includes an extra dimension to the difficulty. In such a condition we require to switch between bases and select the best basis for a particular diagram. We have shown in our calculation that in higher order loop diagrams, at finite temperature, the R/A basis is most convenient on summing over the internal vertices and very efficient on calculating some particular diagrams while the result is most easily interpretable in the Keldysh basis for most other complex diagrams. / February 2010

Apresentamos dois modelos para o elétron na eletrodinâmica clássica que incorporam alguns efeitos da eletrodinâmica quântica. No primeiro modelo, o elétron é tratado como uma partícula extensa como conseqüência das oscilações de alta-freqüência (Zitterbewegung) que sua carga elétrica realiza. Mostramos que este modelo prevê corretamente a magnitude do spin do elétron e lhe atribui o mesmo fator giromagnético previsto pela equação de Dirac sem correções radiativas. Neste modelo, a auto-energia do elétron diverge logaritmicamente como resultado da distribuição extensa de sua carga elétrica. No segundo modelo, a criação de pares virtuais em torno do elétron é levada em conta por uma generalização da lagrangeana do campo eletromagnético que respeita as simetrias da eletrodinâmica clássica. Esta generalização altera a interação entre o elétron e o campo eletromagnético em pequenas distâncias e permite que a auto-força de uma partícula puntiforme seja determinada de modo consistente. Mostramos que as soluções da equação de movimento resultante não apresentam auto-aceleração nem pré-aceleração, sendo consistentes com a causalidade. / We present two models for the electron in classical electrodynamics, which include some effects from quantum electrodynamics. In the first model, the electron is treated as an extended particle owing to the high-frequency oscillations (Zitterbewegung) of its electrical charge. We show that this model predicts correctly the magnitude of the electron spin and it gives the electron the same gyromagnetic factor as predicted by Dirac equation without radiative corrections. In this model, the electron self-energy has a logarithmic divergence due to the extended distribution of its electric charge. In the second model, virtual pair creation around the electron is taken into account by a generalization of the lagrangian for the electromagnetic field that preserves the symmetries of classical electrodynamics. This generalization changes the interaction of the electron with the electromagnetic field at small distances and allows us to evaluate the self-force of a point particle in a consistent way. We show that the solutions of the derived equation of motion do not exhibit self-acceleration nor pre-acceleration, being consistent with causality.

The imaginary part of the retarded self energy is of particular interest as it contains a lot of physical information about particle interactions. In higher order loop diagrams the calculation become extremely tedious and if we have to do the same at finite temperature, it includes an extra dimension to the difficulty. In such a condition we require to switch between bases and select the best basis for a particular diagram. We have shown in our calculation that in higher order loop diagrams, at #12;finite temperature, the R/A basis is most convenient on summing over the internal vertices and very efficient on calculating some particular diagrams while the result is most easily interpretable in the Keldysh basis for most other complex diagrams.

Apresentamos dois modelos para o elétron na eletrodinâmica clássica que incorporam alguns efeitos da eletrodinâmica quântica. No primeiro modelo, o elétron é tratado como uma partícula extensa como conseqüência das oscilações de alta-freqüência (Zitterbewegung) que sua carga elétrica realiza. Mostramos que este modelo prevê corretamente a magnitude do spin do elétron e lhe atribui o mesmo fator giromagnético previsto pela equação de Dirac sem correções radiativas. Neste modelo, a auto-energia do elétron diverge logaritmicamente como resultado da distribuição extensa de sua carga elétrica. No segundo modelo, a criação de pares virtuais em torno do elétron é levada em conta por uma generalização da lagrangeana do campo eletromagnético que respeita as simetrias da eletrodinâmica clássica. Esta generalização altera a interação entre o elétron e o campo eletromagnético em pequenas distâncias e permite que a auto-força de uma partícula puntiforme seja determinada de modo consistente. Mostramos que as soluções da equação de movimento resultante não apresentam auto-aceleração nem pré-aceleração, sendo consistentes com a causalidade. / We present two models for the electron in classical electrodynamics, which include some effects from quantum electrodynamics. In the first model, the electron is treated as an extended particle owing to the high-frequency oscillations (Zitterbewegung) of its electrical charge. We show that this model predicts correctly the magnitude of the electron spin and it gives the electron the same gyromagnetic factor as predicted by Dirac equation without radiative corrections. In this model, the electron self-energy has a logarithmic divergence due to the extended distribution of its electric charge. In the second model, virtual pair creation around the electron is taken into account by a generalization of the lagrangian for the electromagnetic field that preserves the symmetries of classical electrodynamics. This generalization changes the interaction of the electron with the electromagnetic field at small distances and allows us to evaluate the self-force of a point particle in a consistent way. We show that the solutions of the derived equation of motion do not exhibit self-acceleration nor pre-acceleration, being consistent with causality.