Sökning: "Quaternary"

Visar resultat 11 - 15 av 229 avhandlingar innehållade ordet Quaternary.

  1. 11. Mountain centered icefields in northern Scandinavia

    Författare :Ola Fredin; Clas Hättestrand; Arjen Stroeven; Peter Jansson; Johan Kleman; Jon Landvik; Stockholms universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Scandinavia; Quaternary; Weichselian; mountain; icefield; ice sheet; Physical geography; Naturgeografi;

    Sammanfattning : Mountain centered glaciers have played a major role throughout the last three million years in the Scandinavian mountains. The climatic extremes, like the present warm interglacial or cold glacial maxima, are very short-lived compared to the periods of intermediate climate conditions, characterized by the persistence of mountain based glaciers and ice fields of regional size. LÄS MER

  3. 12. Holocene climate and environmental dynamics on the Tristan da Cunha island group, South Atlantic

    Författare :Karl Ljung; Kvartärgeologi; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; palynologi; Geology; climate change; pollen analysis; Palaeobotany; phylogeny; palynology; Paleobotanik; fylogeni; vegetation change; gyttja; peat; Holocene; Quaternary; South Atlantic; Tristan da Cunha; physical geography; Geologi; fysisk geografi;

    Sammanfattning : It has been shown that the present interglacial has been climatically dynamic with both rapid and severe climatic fluctuations. The spatial and temporal differences of these changes are however not fully resolved. The aim of this thesis is to present a detail high resolution record of past climate changes from the central South Atlantic. LÄS MER

  4. 13. Quaternary structure and interaction approaches to allosteric regulation of class I ribonucleotide reductases

    Författare :Mikael Crona; Britt-Marie Sjöberg; Mark Meuth; Stockholms universitet; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Ribonucleotide reductase; allosteric regulation; quaternary structure; subunit interactions; enzyme activity; SPR; GEMMA; Molecular biology; Molekylärbiologi; Molecular Biology; molekylärbiologi;

    Sammanfattning : Deoxyribonucleic acid (DNA) chains in which our genetic blueprint is stored are built from four DNA precursors by DNA polymerases. The enzyme ribonucleotide reductase (RNR) provides the only de novo synthesis pathway of deoxyribonucleotides from ribonucleotides and is essential for nearly all organisms. LÄS MER

  5. 14. Synthesis of Indole Alkaloids and Development of New Methodology

    Författare :Anita Hoang; Centrum för analys och syntes; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; total synthesis; indole alkaloids; Domino reactions; vicinal quaternary stereocenters; quaternary stereocenter; indoline synthesis; communesin alkaloid; perophoramidine; dehaloperophoramidine; akuammiline alkaloids; strictamine; intramolecular Heck reaction; domino carbopalladation carbonylation; indoline alkaloids;

    Sammanfattning : This thesis describes our efforts towards the total synthesis of natural products and the development of a newmethodology to afford a synthetically important scaffold.Chapter 2 outlines our efforts towards the total synthesis of a marine natural product, perophoramidine as wellas our completed synthesis of dehaloperophoramidine. LÄS MER

  7. 15. Cellulose in Quaternary Ammonium-based Solvents: Dissolution, Modification and Coagulation

    Författare :Shirin Naserifar; Chalmers tekniska högskola; []
    Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; NATURVETENSKAP; NATURAL SCIENCES; gelation; etherification; quaternary ammonium hydroxides; cellulose; dissolution;

    Sammanfattning : Processing cellulose through dissolution and regeneration is essential for many applications, yet challenges are posed because it does not readily melt or dissolve in commonly used aqueous and organic solvents. Consequently, extensive efforts have been devoted to developing novel and efficient solvents for cellulose, as well as exploring new functionalization routes. LÄS MER