Sökning: "Chemical abundances"

Visar resultat 1 - 5 av 51 avhandlingar innehållade orden Chemical abundances.

1. 1. 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

3. 2. Recovery of Scandium using Antisolvent Crystallization in the Valorization of Scandium-containing Waste Streams

   Författare :Edward Peters; Kerstin Forsberg; Michael Svärd; Jens-Petter Andreassen; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Antisolvent crystallization; ammonium scandium hexafluoride; ammonium metal fluorides; phase equilibria; solubility; supersaturation; seeding; agitation mechanism; crystal size distribution; morphology; Chemical Engineering; Kemiteknik;

   Sammanfattning : Scandium is widely dispersed in the earth’s crust and is rarely concentrated in ores, and a viable option to guarantee a secure supply of scandium is to recover the metal from waste streams of other mining and metallurgical facilities. The valorization of such streams to recover metals of value is a prerequisite to alleviate the global shortages of scandium and other rare earth elements. LÄS MER

4. 3. Clues to galaxy evolution from spectroscopic observations of Galactic centre stars

   Författare :Brian Thorsbro; Astronomi - Genomgår omorganisation; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Chemical abundances; Late-type stars; Star clusters; Galactic center; Galaxy chemical evolution; Chemical enrichment;

   Sammanfattning : In this work we present results from spectroscopic observations of Galactic centre stars. High resolution stellar spectroscopy can be used to determine accurate stellar metallicities and abundances. Observing stars in the Galactic centre is challenging due to extreme extinction. LÄS MER

5. 4. Optical lifetime studies using time-resolved spectroscopy with applications to the solar chemical composition

   Författare :Bertel Engman; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES;

   Sammanfattning : This survey presents six previously published papers dealing with time-resolved atomic and molecular spectroscopy with applications to the chemical composition of the solar atmosphere. Three methods of measuring mean lives of excited states have been used:Beam-foil spectroscopy Beam-laser spectroscopy High-frequency deflectionThe methods used to estimate the abundances of the chemical elements in the sun will also be outlined. LÄS MER

7. 5. NMR studies of metabolites and xenobiotics : From time-points to long-term metabolic regulation

   Författare :Ina Ehlers; Jürgen Schleucher; Farquhar Graham; Umeå universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; NMR spectroscopy; isotopomer; phospholipid; persistent organic pollutant; CO2 fertilization; photorespiration;

   Sammanfattning : Chemical species carry information in two dimensions, in their concentrations and their isotopic signatures. The concentrations of metabolites or synthetic compounds describe the composition of a chemical or biological system, while isotopic signatures describe processes in the system by their reaction pathways, regulation, and responses to external stimuli. LÄS MER