Sökning: "Astronomi och astrofysik"

Visar resultat 16 - 20 av 469 avhandlingar innehållade orden Astronomi och astrofysik.

1. 16. Dispersive and polarimetric properties of waves in space plasma

   Författare :Jan Bergman; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Astronomy; Astronomi; Astronomy and astrophysics; Astronomi och astrofysik; Space Physics; rymdfysik;

   Sammanfattning : Various aspects regarding dispersive and polarimetric properties of waves in space plasma are discussed from a theoretical viewpoint, which is extended to include numerical as well as experimental studies. From a more technical viewpoint, two scientific instruments are described. LÄS MER

3. 17. Radio waves in the ionosphere : Propagation, generation and detection

   Författare :Tobia Carozzi; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Astronomy; Astronomi; Astronomy and astrophysics; Astronomi och astrofysik; Space Physics; rymdfysik;

   Sammanfattning : We discuss various topics concerning the propagation, generation, and detec-tionof high-frequency (HF) radio waves in the Earth's ionosphere. With re-gardsto propagation, we derive a full wave Hamiltonian and a polarization evo-lutionequation for electromagnetic waves in a cold, stratified magnetoplasma. LÄS MER

4. 18. Chemical Abundance Analysis of Population II Stars : The Summary Includes a Background in General Astronomy

   Författare :Karin Jonsell; Bengt Gustafsson; Bengt Edvardsson; Paul Barklem; Christopher Sneden; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Astronomy; Astronomy; Galactic evolution; Halo; Milky Way; Oxygen; r-element; s-element; Stellar abundances; Astronomi; Astronomy and astrophysics; Astronomi och astrofysik;

   Sammanfattning : We are made of stardust in the sense that most atomic nuclei around us have been formed by stars. Stars synthesise new elements and expel them to the interstellar medium, from which later new generations of stars are born. We can map this chemical evolution by analysing the atmospheric contents of old Galactic halo stars. LÄS MER

5. 19. Stochastic Chemical Evolution : A Study of Scatter in Relative Elemental Abundances in Extremely Metal-poor Stars

   Författare :Torgny Karlsson; Bengt Gustafsson; Mike Edmunds; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Astronomy; nucleosynthesis; chemical evolution; Galactic evolution; supernovae; chemical abundances; Population II stars; Astronomi; Astronomy and astrophysics; Astronomi och astrofysik;

   Sammanfattning : Chemical evolution addresses the problem of the formation of the chemical elements and their evolution throughout the history of the universe. This thesis discusses in particular the chemical evolution in the young universe and what we may learn from the observations of the oldest stars. LÄS MER

7. 20. An Observational Study of Accretion Processes in T Tauri Stars

   Författare :Henricus Cornelis Stempels; Nikolai Piskunov; Gibor Basri; Uppsala universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Astronomy; Star formation; T Tauri stars; Emission lines; Accretion; NLTE radiative transfer; Astronomi; Astronomy and astrophysics; Astronomi och astrofysik; Astronomy; Astronomi;

   Sammanfattning : This thesis is a detailed observational study of the accretion processes in T Tauri stars (TTS). The interaction between the central star, the circumstellar disk and the magnetic field gives rise to a wide range of features in the spectra of TTS. LÄS MER