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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Vibrationsdämpning av svarvbom / Dampening vibrations of a boring bar

Ekström, Camilla January 2014 (has links)
Rapporten består utav en teoretisk undersökning kring hur vibrationer i en svarvbom vid resonans kan dämpas på ett enkelt sätt. CS Produktion, för vilka undersökningen gjorts, har velat öka sin invändiga bearbetning från 1,5 m till 2,5 m. Med så långa överhäng på en bom är det risk för resonansvibrationer som ger dålig ytfinhet och kan i värsta fall skada maskin och personal. Bom och infästning har arbetats fram i ett tidigare arbete, efter arbetet kvarstod utvecklandet av en lösning för dämpningen av bommen. Problemet har undersökts teoretiskt avseende två möjligheter, utifrån om störfrekvensen träffar en eller flera egenfrekvenser för bommen. Störfrekvensen uppstår från den skärande bearbetningen och måste mätas upp för att senare kunna avgöra vilket av de två fallen som är lämpligt att utgå ifrån. Den första modellen för en träff av egenfrekvensen är en inre stång med en vikt i den fria änden av stången, med den andra änden inskruvad i bommens ändplatta. Anordningen beräknas så att egenfrekvensen sammanfaller med bommens egenfrekvens som är i riskområdet för resonans. Den inre anordningen fungerar som massdämpare. Den andra modellen för flera träffar av egenfrekvenserna har två lösningar som beror på hur bommen beter sig vid ingrepp. Grunden är ett inre rör som kan liknas vid en mindre version av bommen för att den ska få liknande egenskaper. Röret beräknas så att det får likvärdiga egenfrekvenser som bommen och kommer då följa modellen för ett system med två frihetsgrader vid resonans. För varje egenfrekvens på bommen ger röret en vibrationsdämpande effekt vid resonansområdena. Projektet visar att empiriska mätningar behöver göras för att med säkerhet kunna avgöra hur problemet ska avhjälpas. Med mätningar kan också koncepten vidareutvecklas, alternativt ligga till grund för att ta fram mer avancerade lösningar. / The report consists of a theoretical study of how vibrations in a boring bar at resonance can be minimized in a simple way. CS Produktion, the commissioning company, wanted to increase their capacity for internal turning from 1.5 m to 2.5 m. With a long overhang there is a risk of dangerous resonant vibrations that can give a bad surface, or may even damage the equipment and injury employees. The bar and the attachment has been developed in another project, but the project lacked a solution for the resonant vibrations. The problem has been studied from two theoretical possible scenarios, based on whether the interference frequency matches one or more natural frequencies of the bar. Interference frequency arises from the cutting work and must be measured in order determine which of the two cases that is appropriate to start from. The first model for one hit of the natural frequency is a single rod with a weight at the free end of the rod, with the other end screwed into the end plate of the bar. The device is calculated so that the natural frequency coincides with the natural frequency of the bar that is in the danger zone for resonance and function as mass damper. The second model for multiple hits of the natural frequencies have two solutions that depend on how the bar behaves when machining. The design is an inner pipe that resembles a smaller version of the bar for it to have similar properties. The pipe has been calculated to have equal natural frequencies as the bar, and will then follow the system of two degrees of freedom at resonance. The pipe provides a vibration dampening effect on the resonance regions. To be able to reliably determine how the problem should be solved, this project shows that empirical measurements are needed. These measurements could serve as a basis for further concept development or more advanced concepts.
2

Advanced MRI data processing /

Rydell, Joakim, January 2007 (has links)
Diss. (sammanfattning) Linköping : Univ., 2007. / Härtill 4 uppsatser.
3

Application of high-resolution NMR spectroscopy in metabolic studies of the eye

Risa, Øystein January 2004 (has links)
<p>High-resolution NMR spectroscopy has, during the last two decades, had an increasing impact in biological and biochemical research. Rapid advances have led to improvements in sensitivity and dispersion of the spectra and have allowed more detailed assignment and monitoring of endogenous biochemical molecules. One of the latest implementations has been a technique known as high-resolution magic angle spinning (HR-MAS) NMR spectroscopy which has made it possible to obtain high-resolution proton spectra of intact tissue and cells. Simultaneous detection of a large number of metabolites by NMR spectroscopy has been successfully applied to investigate disordered metabolism for a numerous of diseases and toxic processes.</p><p>The objectives in the present work have been to evaluate different <sup>1</sup>H NMR spectroscopy protocols as analytical tools in eye research, and further use these protocols to extract and interpret information on metabolic changes in the eye induced by external pathological stimuli. Special focus has been paid to changes in the lens and the development of cataracts.</p><p>The <sup>1</sup>H NMR spectra of intact lenses and eye tissue extracts in present thesis showed an extensive picture of NMR detectable metabolites. In addition to the detailed analysis of extracts from cornea, lens and aqueous humour, this work has created a basis for implementation and interpretation of HR-MAS <sup>1</sup>H NMR spectroscopy on intact lens tissue. Several significant changes in the metabolic content in cornea, aqueous humour, and lens after alkali-burns to the eye were detected and showed how careful <sup>1</sup>H NMR spectroscopy analysis of tissue extracts provided new information (quantitative and qualitative) on the metabolic reaction pattern in the anterior eye segment in relation to eye alkali-burn injuries.</p><p>HR-MAS studies on lenses exposed <i>in vivo </i>to different ultraviolet-B doses did not reveal any dose-response relationship for the metabolic changes. However, significant concentration changes for most of the observed metabolites seven days post exposure demonstrated that closeto- threshold UVB radiation had great impact on the metabolites in the lens. Further time dependency studies of metabolic changes in rat lens after UVB radiation showed that significant changes in metabolite concentrations were subsequent to lens opacity development. Long-term steroid treatment (36 days) seemed to have greater impact on the metabolic changes compared to the UVB-induced changes 24 hours after UVB radiation. Even though no obvious cataract was detected after the combined treatment of steroids and UVB radiation, significant changes were observed for several metabolites.</p> / Paper III is reprinted with kind permission from Elsevier, sciencedirect.com
4

Application of high-resolution NMR spectroscopy in metabolic studies of the eye

Risa, Øystein January 2004 (has links)
High-resolution NMR spectroscopy has, during the last two decades, had an increasing impact in biological and biochemical research. Rapid advances have led to improvements in sensitivity and dispersion of the spectra and have allowed more detailed assignment and monitoring of endogenous biochemical molecules. One of the latest implementations has been a technique known as high-resolution magic angle spinning (HR-MAS) NMR spectroscopy which has made it possible to obtain high-resolution proton spectra of intact tissue and cells. Simultaneous detection of a large number of metabolites by NMR spectroscopy has been successfully applied to investigate disordered metabolism for a numerous of diseases and toxic processes. The objectives in the present work have been to evaluate different 1H NMR spectroscopy protocols as analytical tools in eye research, and further use these protocols to extract and interpret information on metabolic changes in the eye induced by external pathological stimuli. Special focus has been paid to changes in the lens and the development of cataracts. The 1H NMR spectra of intact lenses and eye tissue extracts in present thesis showed an extensive picture of NMR detectable metabolites. In addition to the detailed analysis of extracts from cornea, lens and aqueous humour, this work has created a basis for implementation and interpretation of HR-MAS 1H NMR spectroscopy on intact lens tissue. Several significant changes in the metabolic content in cornea, aqueous humour, and lens after alkali-burns to the eye were detected and showed how careful 1H NMR spectroscopy analysis of tissue extracts provided new information (quantitative and qualitative) on the metabolic reaction pattern in the anterior eye segment in relation to eye alkali-burn injuries. HR-MAS studies on lenses exposed in vivo to different ultraviolet-B doses did not reveal any dose-response relationship for the metabolic changes. However, significant concentration changes for most of the observed metabolites seven days post exposure demonstrated that closeto- threshold UVB radiation had great impact on the metabolites in the lens. Further time dependency studies of metabolic changes in rat lens after UVB radiation showed that significant changes in metabolite concentrations were subsequent to lens opacity development. Long-term steroid treatment (36 days) seemed to have greater impact on the metabolic changes compared to the UVB-induced changes 24 hours after UVB radiation. Even though no obvious cataract was detected after the combined treatment of steroids and UVB radiation, significant changes were observed for several metabolites. / Paper III is reprinted with kind permission from Elsevier, sciencedirect.com
5

Musikens avtryck : Reflektioner över musikundervisning och dess inflytande / Musical footprints : Reflections over the perceived impact of music education

Salomonsson, Natanael, Persson, Emil January 2023 (has links)
Den här studien har utforskat vuxna människors minnen och erfarenheter av den musikundervisning de fick under mellan- och högstadiet. Studien genomfördes genom kvalitativa intervjuer där deltagarna fick svara på frågor kopplade till meningsfullhet och vilken, om någon, påverkan undervisningen har haft på livet efter skolgången. De sex deltagarna i studien är alla i åldrarna 35-50 år och arbetar inte professionellt med musik idag. Resultaten visar på behovet av en motiverande, engagerande och meningsfull undervisning i musik och att den upplevda meningsfullheten är sammankopplad med en känsla av delaktighet i undervisningen och deltagarnas egna musikaliska identitet. Tidigare forskning visar på ämnets potential, men studien visar att undervisningen i flera fall misslyckats med att uppnå den potentialen. Känslan av att kunna något och att lära tillsammans är återkommande i resultatet. Vikten av en positiv och resonant upplevelse av undervisningen där läraren är inkluderande och kompetent efterfrågas av deltagarna. Studien belyser hur undervisningen kan upplevas av den elev som inte har ett aktivt intresse för musik och hur en lärare kan agera för att göra undervisningen meningsfull.
6

Resonans / Kandidatexamensarbete

Partovi, Arezo, Svärd, Jenny January 2014 (has links)
This report describes how the system may be exposed to oscillations and how this can lead to resonance. Resonance is a phenomenon that occurs when a system is affected by external periodic oscillations with frequencies close to the system's natural frequencies. Structures subjected to resonance can risk great damage and destruction, why resonance is something that is important to take into account when designing structures. Alternative ways to counteract resonance is to supply damping in the system. Damping means that the resonance decreases instead of letting the amplitude increase.The report discusses some examples on constructions that have experienced the effect of resonance. The control tower in Stockholm's Arlanda Airport was swaying so much that water tanks had to be installed as resonance dampers, where the water swung in opposite phase compared to the tower. The oscillations probably started due to the fact that the tower was too lightweight in relation to its height. Tacoma Narrows Bridge in Washington, USA, oscillated in the amount that the bridge collapsed. The reason was that the bridge weighed too little to withstand the strong wind forces. The stadium Ullevi in Gothenburg had to be strengthened due to the fact that a jumping crowd during a concert caused resonance oscillations which endangered parts of the construction. After the concert, beams with decent damping attributes were installed against the rooftops to reduce the risk of damage to these. Broughtons Suspension Bridge in Britain fell apart when soldiers marched in step and in this way contributed to the oscillations of the bridge. The bridge also had structural parts whose strength was not sufficient.
7

Jämförelse av antenners beteende under vibration

Dickman Ekvall, Matilda January 2022 (has links)
Vibrationer i underlaget kan försämra prestandan hos kommunikationsantenner. Detta har undersökts i denna rapport.  Tre sändarantenner med olika utseende och egenskaper genomgick flera vibrationstester för att identifiera resonansfrekvenser i strukturen. Signalstyrkan mellan sändar- och mottagarantenn registrerades under alla tester för att identifiera resonansfrekvenser.  Vid försöken monterades antennerna på en sändarbox. När kretskortet i sändarboxen inte fixerades ordentligt orsakade det komplexa vibrationer i hela antennstrukturen. Detta kan vara en fråga som kräver separat omfattande forskning. I denna rapport studerades själva antennernas beteende och därför behövde sändarboxen gjutas för att garantera kretskortets fasta position. De tre antennerna visade alla olika beteende under testerna
8

Jämförelse av antenners beteende under vibration

Dickman Ekvall, Matilda January 2022 (has links)
Vibrationer i underlaget kan försämra prestandan hos kommunikationsantenner. Detta har undersökts i denna rapport.  Tre sändarantenner med olika utseende och egenskaper genomgick flera vibrationstester för att identifiera resonansfrekvenser i strukturen. Signalstyrkan mellan sändar- och mottagarantenn registrerades under alla tester för att identifiera resonansfrekvenser.  Vid försöken monterades antennerna på en sändarbox. När kretskortet i sändarboxen inte fixerades ordentligt orsakade det komplexa vibrationer i hela antennstrukturen. Detta kan vara en fråga som kräver separat omfattande forskning. I denna rapport studerades själva antennernas beteende och därför behövde sändarboxen gjutas för att garantera kretskortets fasta position. De tre antennerna visade alla olika beteende under testerna. Inga slutsatser om antennernas strukturella beteende kunde dras eftersom det var för få tester på för få antenner.
9

Konstruktion av testrigg för utmattningsprovning : Från definiering av testmetod till konstruktionsunderlag / Design of a testrig for fatigue testing

Müllback, Rasmus January 2018 (has links)
On behalf of and in collaboration with Valmet AB this thesis has been fulfilled and executed at their development department in Sundsvall. Valmet AB design, develop and manufacture machines and equipment for the pulp, paper and energy industry. One of their key products is the TwinRoll press. The TwinRoll press consist, among others, of a part called mantle section which in terms of manufacturing is rather complex. This part itself consists of frame ribs, which during operation endure high loads in a high amount of cycles during its life-span. Due to this, fatigue failure sometimes occurs, which in consequence causes mantle section failure. Theoretical determination of the fatigue strength has been proven difficult, which has created needs for experimental fatigue testing. The goal with the thesis was to define a method for fatigue testing and to design and develop a rig which could perform the testing according to the defined method. The initial part of the project consisted of a literature study about fatigue testing and how it normally is performed. Then the work with the test method started and the loads during normal operation was specified, as well as parameters that might affect the test results. This part was important as the parameters could be transformed into requirements which the test rig needed to satisfy. When the method for testing and the measurable requirements were done, concepts were generated via individual sketching and brainstorming. A final concept was chosen for detailed design in SolidWorks after using methods like voting and Pugh’s concept selection matrix. The rig was modelled and drawings for manufacturing was produced, and then dimensioned through both simulations with FEM and calculations by hand. The final construction was then inspected with VR-technology. The conclusion of the thesis was that the frame ribs should, as a suggestion, be fatigue tested with constant stress amplitudes until failure, and then repeated for other stress values until the amount of generated data is enough for evaluation in a stress-number-diagram. A Wöhler-curve should then be generated for desired probability of failure and finally be evaluated in a Haigh-diagram. The developed test rig will perform testing on one frame rib at a time with a high frequency hydraulic cylinder, were the sample used is a piece of the mantle section. Furthermore, the sample is fixed in both directions to correspond to stress generated by shrinkage which an entire frame rib normally withstands.
10

Gryningen nalkas : En komparativ studie av Johannes av Korsets och Hartmut Rosas förståelse av vägen mot ett gott förhållande till världen

Wanemark, Joel January 2022 (has links)
This study presents a comparative analysis of Hartmut Rosa and St John of the Cross and their respective view of the way towards a good relationship to the world. Using Rosa’s theory of acceleration, alienation and resonance as a frame of reference, a discursive analysis of modern texts on the thoughts of St John is performed to explore how the thoughts of St John can be enriched by Rosa. Thereby the aim is to widen the conversation on how Christians and the church might speak of a good relationship to the world in the present day. The analysis shows that several key elements from Rosa’s theory of resonance can be found in the thoughts of St John of the Cross, thus highlighting both the potential of reading John of the Cross in a modern setting and Rosa’s enriching contributions. They also agree in their emphasis on giving up the desire to control as a necessity in establishing a good relationship to the world. However, the transcendent, mystical reality of St John enables him to go furthert han Rosa with regards to for example the length to which a person should give up control or on how suffering is an essential part of the transformation. The study nevertheless shows that Rosa’s description of modern society can aid putting the thoughts of St John into the present, and that Rosa’s theories of structural change based on a new relationship to the world can widen the conversation on how the church might apply the mystical thoughts of St John today.

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