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Magnetic Dynamos: How Do They Even Work?Jackel, Benjamin 11 1900 (has links)
The origin of cosmic magnetic fields is a important area of astrophysics. The process by which they are created falls under the heading of dynamo theory, and is the topic of this thesis. Our focus for the location of where these magnetic fields operate is one the most ubiquitous objects in the universe, the accretion disk. By studying the accretion disk and the dynamo process that occurs there we wish to better understand both the accretion process and the dynamo process in stars and galaxies as well.
We analyse the output from a stratified zero net flux shearing box simulation performed using the ATHENA MHD code in collaboration with Shane Davis. The simulation has turbulence which is naturally forced by the presence of a linear instability called the magnetorotational instability (MRI). We utilise Fourier filtering and the tools of mean field dynamo theory to establish a connection between the calculated EMF and the model predictions of the dynamically quenched alpha model. We find a positive correlation for both components parallel to the large scale magnetic field and the azimuthal components.
We have explored many aspects of the theory including additional contributions from magnetic buoyancy and an effect arising from the large scale shear and the current density. We also directly measure the turbulent correlation time for the velocity and magnetic fields both large scale and small. We can also observe the effects of the dynamo cycle, with the azimuthal component of the large scale magnetic field flipping sign in this analysis.
We find a positive correlation between the divergence of the eddy scale magnetic helicity flux and the component of the electromotive force parallel to the large scale magnetic field. This correlation directly links the transfer of magnetic helicity to the dynamo process in a system with naturally driven turbulence. This highlights the importance of magnetic helicity and its conservation even in a system with triply periodic boundary conditions. / Thesis / Doctor of Philosophy (PhD)
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Effekten av stavlängd på ländryggens rörelseomfång vid stakning inom längdskidåkning : En pilotstudie / The effects of pole length on lumbar range of motion during double poling in cross-country skiing : A pilot studyGustafsson, Maja, Mäki, Fredrik January 2024 (has links)
Introduktion: Ryggproblematik inom längdskidåkning har blivit ett omdiskuterat ämne inom idrottssektorn, detta i samband med att deltekniken stakning tagit allt större plats inom den klassiska skidåkningen. En regel om maximal stavlängd på 83% av åkarens kroppslängd har införts, samtidigt som studier visar att en längre stav än 83% visat fördelar för prestation. Förutom de prestationsrelaterade effekterna har forskning visat på att längre stavar ger mindre ledvinklar. En ökad grad flexion av ländryggen antas öka risken för att drabbas av diskbråck. Om stavlängden har betydelse för denna skulle optimering av stavlängd kunna bidra till att förebygga skador. Syfte: Syftet med denna experimentella pilotstudie var att jämföra rörelseomfång i ländryggen vid stakning med stavar i olika längder, samt hur stavlängder påverkar ledvinklar i knä, fot, höft, bäcken och thorakalrygg. Metod: En försöksperson rekryterades. Mätningen utfördes i en snöhall på uppmätt sträcka om 50m, vid stakning med stavlängderna 83%, 86% och 89% av kroppslängden. För mätning av rörelseomfång användes ett IMU-system. Insamlad data extraherades via Noraxon MR3 och bearbetades i Matlab för att få fram medelvärden av ledvinklar. Resultat: Lumbalflexionen var som störst vid 89% stavlängd (41,5°) och lägst vid 86% (36,3°). Minst ledvinklar i fot, knä, höft och bäcken uppmättes samtliga vid stavlängd 89%, där även thorakalflexionen var som minst. Konklusion: Resultaten indikerar att stavlängder inom 83-86% av kroppslängden minskar rörelseomfånget och flexionsgraden av ländryggen vid stakning. Ytterligare forskning behövs för att bekräfta sambandet mellan ländryggsflexion och stavlängd och om en optimal stavlängd skulle kunna verka skadeförebyggande.
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Empirical analysis of disk sector prefixes for digital forensicsNecaise, Nathan Joseph 05 May 2007 (has links)
Forensic analysis on a media with fragmented and deleted files is a difficult task. There is a lack of tools and techniques that can accurately and quickly detect fragmented suspect files. Fragmented file data that resides in slack space is often overlooked by digital forensic tools. This thesis proposes to use a prefix signature of 4, 8, 16, or 32 bytes instead of either a complete sector comparison or a hash of the complete sector. The experiments show that the 32 byte has as much discrimination as an MD5 or SHA hash in uniquely identifying a sector. It is shown that the false positive rate does not exceed 10% for prefix signature sizes of 32, 16, and 8 bytes. Also the difference in false positive rates for the 32 and 16 byte prefixes does not exceed 25% as compared to MD5 and SHA hashes.
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Improving Hard Disk Drive Write IO Performance with Phase Change Memory as a Buffer CacheBalasubramanian, Sanchayeni January 2017 (has links)
No description available.
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AUTOMATED VERTEBRA SEGMENTATION AND QUANTIFICATION ALGORITHM OF WHOLE SPINE MR IMAGESZHONG, JIA 07 October 2004 (has links)
No description available.
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Dust Grain Growth and Disk Evolution of a Set of Young Stellar ObjectsCARPENTER, WILLIAM JOSEPH 22 April 2008 (has links)
No description available.
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An Experimental Investigation on Friction and Scuffing Failure of Lubricated Point ContactsSoma, Sai Goutham 22 December 2015 (has links)
No description available.
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A methodology for determining relationships between jet engine disk part geometry and feature dimensionsGallaher, Shawn M. January 2002 (has links)
No description available.
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Dynamic simulation of convective mixing in a disk-ring reactorRussell, Nicholas Frantz January 1991 (has links)
No description available.
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Sharpening The Tools of Gravitational MicrolensingPoindexter, Shawn David January 2009 (has links)
No description available.
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