Sökning: "polar"

Visar resultat 16 - 20 av 523 avhandlingar innehållade ordet polar.

1. 16. Sulfur in polar ice and snow : Interpretations of past atmosphere and climate through glacial archives

   Författare :Ulf Jonsell; Margareta Hansson; Mark Curran; Stockholms universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; ice cores; aerosols; sulfate; methanesulfonate; sulfur isotopes; climate; glacial cycles; Antarctica; Greenland; Physical geography; Naturgeografi;

   Sammanfattning : Snow contains information on the atmosphere it is deposited from. This information is stored in polar ice sheets (Antarctica and Greenland), which are unique geochronological archives of past climate and atmospheric composition. On time scales from annual to glacial cycles, this thesis deals with the signals of sulfur compounds in these archives. LÄS MER

3. 17. Mesoscale processes in the polar atmosphere : radar remote sensing, balloon-borne in situ measurements and modelling

   Författare :Maria Mihalikova; Suzanne Gray; Luleå tekniska universitet; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Rymdteknik; Space Technology;

   Sammanfattning : Mesoscale processes (atmospheric phenomena with horizontal scales ranging from a few tens to several hundred kilometres and lasting from a few tens of minutes to a few days) have the potential to influence the chemical composition of the troposphere. Tropopause folds and mountain waves are two important types of mesoscale processes. LÄS MER

4. 18. Hot-wall MOCVD of N-polar group-III nitride materials and high electron mobility transistor structures

   Författare :Hengfang Zhang; Vanya Darakchieva; Jr-Tai Chen; Ingemar Persson; Fatemeh (Shadi) Shahedipour-Sandvik; Linköpings universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Nitrogen-polar; MOCVD; III-nitride; GaN; AlN; C-face SiC; HEMTs;

   Sammanfattning : Group III-Nitride semiconductors: indium nitride (InN), gallium nitride (GaN), aluminum nitride (AlN) and their alloys continue to attract significant scientific interest due to their unique properties and diverse applications in photonic and electronic applications. Group-III nitrides have direct bandgaps which cover the entire spectral range from the infrared (InN) to the ultraviolet (GaN) and to the deep ultraviolet (AlN). LÄS MER

5. 19. All Digital Polar Transmitter Design for Software Defined Radio : Architecture and Low Power Circuit Implementation

   Författare :Liang Rong; Li-Rong Zheng; Henrik Sjöland; KTH; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Switching Power Amplifier; All Digital Polar Transmitter; Lowpass Sigma Delta Modulation; Software Defined Radio; RFID; H-Bridge Architecture; Resonating; Filter Matching Network.; SRA - ICT; SRA - Informations- och kommunikationsteknik;

   Sammanfattning : The evolving wireless communication technology is aiming highdata rate, high mobility, long distance and at the meantime, co-existwith various different standards. This developing trend requires ahighly linear transceiver system and it causes the problem of lowefficiency due to the large crest factor of signals. LÄS MER

7. 20. Investigation of Polar Mesosphere Summer Echoes in Northern Scandinavia

   Författare :Victoria Barabash; Umeå universitet; []
   Nyckelord :NATURVETENSKAP; NATURAL SCIENCES; Physics; Polar Mesosphere Summer Echoes; middle atmospheric dynamics; ionospheric disturbances; solar radiation; aerosol; MST radar; planetary waves; noctilucent clouds; Fysik; Physics; Fysik; rymdfysik; Space Physics;

   Sammanfattning : This PhD thesis deals with phenomena which are closely related to the unique thermal structure of the polar summer mesosphere, namely Polar Mesosphere Summer Echoes (PMSE). PMSE are strong radar echoes commonly observed by VHF MST radars from thin layers in the 80-90 km altitude interval at high latitudes during summer. LÄS MER