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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.
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Showing 381 to 390 of 414 (0.022 seconds)Spelling suggestions: "subject:"optik"" "subject:"aptik""
| 381 |
Faseroptische Gemischbildungsanalyse in Otto-Motoren bei direkteinspritzenden Brennverfahren / Fiberoptical analysis of the mixture formation process in gasoline direct injection combustion enginesThiele, Olaf 26 October 2004 (has links)
No description available.
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| 382 |
Optische Eigenschaften von verdünnten magnetischen Halbleitern auf GaN-Basis / Optical properties of GaN-based diluted magnetic semiconductorsZenneck, Jan 18 July 2007 (has links)
No description available.
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| 383 |
Cavitation and shock wave effects on biological systems / Kavitation und Stoßwelleneffekte in biologischen SystemenWolfrum, Bernhard 10 February 2004 (has links)
No description available.
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| 384 |
High-bandwidth microrheology of cytoskeletal networks / Mikrorheologie mit hoher Bandbreite in Zytoskelett-NetzwerkenBremerich, Marcel 18 January 2012 (has links)
No description available.
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| 385 |
Quantitation Strategies in Optically Sectioning Fluorescence Microscopy / Quantifizierungsstrategien in der optisch schnittbildenden FluoreszenzmikroskopieWeigel, Arwed 15 January 2009 (has links)
No description available.
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| 386 |
Rolled-Up Vertical Microcavities Studied by Evanescent Wave Coupling and Photoluminescence SpectroscopyBöttner, Stefan 20 May 2015 (has links) (PDF)
Vertically rolled-up microcavities are fabricated using differentially strained nanomembranes by employing rate and temperature gradients during electron beam evaporation of SiO2. The geometry of the rolled-up tubes is defined by a photo-lithographically patterned polymer sacrificial layer beneath the SiO2 layers that is dissolved to start the rolling. Rolled-up tubes support resonances formed by constructive interference of light propagating along the circumference. Optical studies are performed in the visible spectral range using a micro-photoluminescence (µPL) setup to excite and detect optical modes. Record high quality factors (Q factors) of 5400 for rolled-up resonators probed in PL-emission mode are found and their limits are theoretically investigated. Axial modes can also be supported when an increased winding number in the center is realized by appropriate pattern designs. In addition, higher order radial modes can be confined when atomic layer deposition (ALD) coatings are applied. Both types of modes are identified using polarization and spatially resolved µPL maps.
Evanescent-wave coupling by tapered fibers and tubes on substrates is the second method used to study light confinement and to demonstrate frequency filtering in ALD coated rolled-up microcavities. Scans are performed by monitoring light from a tunable laser in the range of 1520-1570 nm after transmission through the tapered fiber. Dips in the spectrum are found and attributed to fundamental and axial resonant modes. Moreover, by coupling two tapered fibers to a lifted rolled-up microcavity, a four-port add-drop filter is demonstrated as a future component for vertical resonant light transfer in on-chip optical networks.
Simulations show that the subwavelength tube wall thickness limits the Q factor at infrared wavelengths and ALD coatings are necessary to enhance the light confinement. After coating, two linear polarization states are found in experiment and fundamental and axial modes can be selectively excited by coupling the fiber to different positions along the tube axis. Spatially and polarization resolved transmission maps reveal a polarization dependent axial mode distribution which is verified theoretically.
The results of this thesis are important for lab-on-chip applications where rolled-up microcavities are employed as high resolution optofluidic sensors as well as for future uses as waveguide coupled components in three-dimensional multi-level optical data processing units to provide resonant interlayer signal transfer.
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| 387 |
Synthese und Funktion nanoskaliger Oxide auf Basis der Elemente Bismut und NiobWollmann, Philipp 29 March 2012 (has links) (PDF)
Am Beispiel von ferroelektrischen Systemen auf Bismut-Basis (Bismutmolybdat, Bismutwolframat und Bismuttitanat) und von Strontiumbariumniobat werden neue Möglichkeiten zur Synthese solcher Nanopartikel aufgezeigt. Die Integration der Nanopartikel in
transparente Nanokompositmaterialien und die Entwicklung neuer Precursoren für die Herstellung von Dünnschichtproben gehen den Untersuchungen zur Anwendung als elektrooptische aktive Materialien voraus.
Durch weitere Anwendungsmöglichkeiten in der Photokatalyse, dem Test dampfadsorptiver Eigenschaften mit Hilfe eines neuartigen Adsorptionstesters (Infrasorb) und auch mit Hilfe der Ergebnisse der ferroelektrischen Charakterisierung von gesinterten Probenkörpern aus einem Spark-Plasma-Prozess wird ein gesamtheitlicher Überblick über die vielfältigen Aspekte in der Arbeit mit nanoskaligen, ferroelektrischen Materialien gegeben.
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| 388 |
Self-assembled rolled-up devices: towards on-chip sensor technologiesSmith, Elliot John 13 September 2011 (has links) (PDF)
By implementing the rolled-up microfabrication method based on strain engineering, several systems are investigated within the contents of this thesis. The structural morphing of planar geometries into three-dimensional structures opens up many doors for the creation of unique material configurations and devices. An exploration into several novel microsystems, encompassing various scientific subjects, is made and methods for on-chip integration of these devices are presented.
The roll-up of a metal and oxide allows for a cylindrical hollow-core structure with a cladding layer composed of a multilayer stack, plasmonic metamaterial. This structure can be used as a platform for a number of optical metamaterial devices. By guiding light radially through this structure, a theoretical investigation into the system makeup of a rolled-up hyperlens, is given. Using the same design, but rather propagating light parallel to the cylinder, a novel device known as a metamaterial optical fiber is defined. This fiber allows light to be guided classically and plasmonically within a single device. These fibers are developed experimentally and are integrated into preexisting on-chip structures and characterized.
A system known as lab-in-a-tube is introduced. The idea of lab-in-a-tube combines various rolled-up components into a single all-encompassing biosensor that can be used to detect and monitor single bio-organisms. The first device specifically tailored to this system is developed, flexible split-wall microtube resonator sensors. A method for the capturing of embryonic mouse cells into on-chip optical resonators is introduced. The sensor can optically detect, via photoluminescence, living cells confined within the resonator through the compression and expansion of a nanogap built within its walls.
The rolled-up fabrication method is not limited to the well-investigated systems based on the roll-up from semiconductor material or from a photoresist layer. A new approach, relying on the delamination of polymers, is presented. This offers never-before-realized microscale structures and configurations. This includes novel magnetic configurations and flexible fluidic sensors which can be designed for on-chip and roving detector applications.
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| 389 |
Implementing the circularly polarized light method for determining wall thickness of cellulosic fibresEdvinsson, Marcus January 2012 (has links)
The wall thickness of pulp fibers plays a major role in the paper industry, but it is currently not possible to measure this property without manual laboratory work. In 2007, researcher Ho Fan Jang patented a technique to automatically measure fiber wall thickness, combining the unique optical properties of pulp fibers with image analysis. In short, the method creates images through the use of an optical system resulting in color values which demonstrate the retardation of a particular wave length instead of the intensity. A device based on this patent has since been developed by Eurocon Analyzer. This thesis investigates the software aspects of this technique, using sample images generated by the Eurocon Analyzer prototype. The software developed in this thesis has been subdivided into three groups for independent consideration. First being the problem of solving wall thickness for colors in the images. Secondly, the image analysis process of identifying fibers and good points for measuring them. Lastly, it is investigated how statistical analysis can be applied to improve results and derive other useful properties such as fiber coarseness. With the use of this technique there are several problems which need to be overcome. One such problem is that it may be difficult to disambiguate the colors produced by fibers of different thickness. This complication may be reduced by using image analysis and statistical analysis. Another challenge can be that theoretical values often differ greatly from the observed values which makes the computational aspect of the method problematic. The results of this thesis show that the effects of these problems can be greatly reduced and that the method offers promising results. The results clearly distinguish between and show the expected characteristics of different pulp samples, but more qualitative reference measurements are needed in order to draw conclusions on the correctness of the results.
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| 390 |
Development of Next-Generation Optical Tweezers : The New Swiss Army Knife of Biophysical and Biomechanical ResearchNilsson, Daniel January 2020 (has links)
In a time when microorganisms are controlling the world, research in biology is more relevant than ever and this requires some powerful instruments. Optical tweezers use a focused laser beam to manipulate and probe objects on the nano- and microscale. This allows for the exploration of a miniature world at the border between biology, chemistry and physics. New methods for biophysical and physicochemical measurements are continuously being developed and at Umeå University there is a need for a new system that combines several of these methods. This would truly be the new Swiss army knife of biophysical and biomechanical research, extending their reach in the world of optical tweezing. My ambition with this project is to design and construct a robust system that incorporates optical trapping with high-precision force measurements and Raman spectroscopy, as well as introducing the possibility of generating multiple traps by using a spatial light modulator (SLM). The proposed design incorporates four different lasers and a novel combination of signal detection techniques. To allow for precise control of the systems components and laser beams, I designed and constructed motorized opto-mechanical components. These are controlled by an in-house developed software that handles data processing and signal analysis, while also providing a user interface for the system. The components include, motorized beam blockers and optical attenuators, which were developed using commonly available 3D printing techniques and electronic controllers. By designing the system from scratch, I could eliminate the known weaknesses of conventional systems and allow for a modular design where components can be added easily. The system is divided into two parts, a laser breadboard and a main breadboard. The former contains all the equipment needed to generate and control the laser beams, which are then coupled through optical fibers to the latter. This contains the components needed to move the optical trap inside the sample chamber, while performing measurements and providing user feedback. Construction and testing was done for one sub-system at a time, while the lack of time required a postponement for the implementation of Raman and SLM. The system performance was verified through Allan variance stability tests and the results were compared with other optical tweezers setups. The results show that the system follows the thermal limit for averaging times (τ) up to ~1 s when disturbances had been eliminated, which is similar to other systems. However, we could also show a decrease in variance all the way to τ = 2000 s, which is exceptionally good and not found in conventional systems. The force-resolution was determined to be on the order of femtonewtons, which is also exceptionally good. Thus, I conclude that this optical tweezers setup could lie as a solid foundation for future development and research in biological science at Umeå University for years to come.
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