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Visar resultat 1 - 5 av 170 avhandlingar som matchar ovanstående sökkriterier.

1. 1. Radiofrequency fields : exposure, dose and health

   Författare :Jonna Wilén; Umeå universitet; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; electromagnetic fields; SAR; Specific Absorption; subjective symptoms;

   Sammanfattning : The overall aim of this thesis is to increase our knowledge of relevant exposure parameters when discussing possible health implication from exposure to radiofrequency electromagnetic fields (RF), especially effects that might occur at non-thermal levels.In this thesis an effort is made to broaden the exposure assessment and to take the exposure time into account and combine it with the Specific Absorption Rate (SAR) and the field parameters (electric and magnetic field strength) to approach a dose concept. LÄS MER

3. 2. ELF electromagnetic field exposure and biological experimentation

   Författare :Martin Lindgren; Chalmers tekniska högskola; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; cell experiments; v´biological effects; control-normalized evaluations; magnetic fields; overestimation; electromagnetic fields; replication; calcium wave; extremely low frequency; stray currents;

   Sammanfattning : .... LÄS MER

4. 3. Characterization of the MRI patient exposure environment and exposure assessment methods for magnetic fields in MRI scanners

   Författare :Jennifer Frankel; Jonna Wilén; Anders Garpebring; Johan Olsrud; Peter Lundberg; Umeå universitet; []
   Nyckelord :MEDICIN OCH HÄLSOVETENSKAP; MEDICAL AND HEALTH SCIENCES; electromagnetic fields; exposure assessment; magnetic resonance imaging; switched gradient fields; radiofrequency fields; exposure metrics; radiofysik; radiation physics;

   Sammanfattning : Magnetic resonance imaging (MRI) has become one of the most common imaging modalities available in modern medicine, and it is an indispensable diagnostic tool thanks to the unparalleled soft-tissue contrast and high image resolution. It is also a unique exposure environment consisting of a complex mix of magnetic fields. LÄS MER

5. 4. Features and Origin of Electromagnetic Fields Generated by Lightning Flashes

   Författare :Mohd Muzafar Ismail; Vernon Cooray; Farhad Rachidi; Uppsala universitet; []
   Nyckelord :negative cloud-to-ground lightning flashes; HF and VHF radiation; chaotic pulse trains; lightning initiation; zero-crossing time; electromagnetic fields; Engineering Science with specialization in Atmospheric Discharges; Teknisk fysik med inriktning mot atmosfäriska urladdningar;

   Sammanfattning : Negative cloud-to-ground (CG) lightning flashes transport negative charge from cloud to ground. Negative ground flashes typically involve various processes identified as preliminary breakdown, stepped leader, return stroke, dart leader, dart-stepped leader, subsequent return stroke, and cloud activity between strokes, such as regular pulse trains and chaotic pulse trains. LÄS MER

7. 5. Electromagnetic Interference in Distributed Outdoor Electrical Systems, with an Emphasis on Lightning Interaction with Electrified Railway Network

   Författare :Nelson Theethayi; Rajeev Thottappillil; Farhad Rachidi; Uppsala universitet; []
   Nyckelord :TEKNIK OCH TEKNOLOGIER; ENGINEERING AND TECHNOLOGY; Electrical engineering; Electromagnetic Compatibility EMC ; Lightning; Lightning Protection; Transmission Lines; Electromagnetic Wave Propagation; Underground Cables; Grounding; Electromagnetic Transients; Electromagnetic Interference; Shielding Effectiveness; Railway Systems; Elektroteknik; elektronik och fotonik; Electrical engineering; electronics and photonics; Elektroteknik; elektronik och fotonik;

   Sammanfattning : This thesis deals with the electromagnetic compatibility (EMC) problems of distributed electrical networks, especially that caused by lightning to electrified railway. Lightning transients were found to damage important devices that control train movements, causing traffic stoppage and delays. LÄS MER