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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.
21

Aktive Regionen der Sonnenoberfläche und ihre zeitliche Variation in zweidimensionaler Spektro-Polarimetrie

Nickelt-Czycykowski, Iliya Peter. Unknown Date (has links) (PDF)
Potsdam, Universiẗat, Diss., 2008.
22

Construção de um interferômetro de Bath para análise do comportamento da superfície de vidros usados na confecção de espelhos côncavos /

Bacha, Marcelo Gomes. January 2012 (has links)
Orientador: Rosa Maria Fernandes Scalvi / Banca: José Humberto Dias da Silva / Banca: Eduardo Bellini Ferreira / O Programa de Pós-Graduação em Ciência e Tecnologia de Materiais, POSMAT, tem carater institucional e integra as atividades de pesquisa em materiais de diversos campi / Resumo: Neste trabalho foi comparado o desempenho dos dois vidros mais utilizados na fabricação de espelhos côncavos de médio porte (até 25 cmde diâmetro). Os materiais analisados foram vidros nos sistema soda-cálcio e boro-silicato. Os espelhos foram comparados em relação a dilatação térmica e a sua rigidez elástica, tendo como principal objetivo avaliar qual vidro deformaria menos sua superfície mantendo sua qualidade óptica em relação a variação da tmmperatura e do seu próprio peso. Para tanto, a análise foi realizada através dos resultados captados pelo interferômetro de Bath, montado no Observatório Didático de Astronomia "Lionel José Andriatto", da Faculdade de Ciências, UNESP, Bauru. Como amostras para o trabalho, foram utilizados espelhos primários côncavos de telescópios Newtonianos construídos com os vidros analisados. As medidas foram inspiradas nas condições que os espelhos sofrem durante o seu uso, ambientes com temperatura variável e efeitos causados pela gravidade quando os espelhos estão na posição vertical. Ainda para testar a rigidez elástica dos vidros, os espelhos foram apoiados apenas pelas bordas. Os parâmetros utilizados para verificar o desempenho da superfície dos espelhos, foram deformados na curvatura, somatória das deformações na frente de onda e fator Strehl. Utilizando as franjas de interforometrias que foram associadas aos polinômios de Zernike por análise computacional, foi possível realizar o levantamento dos defeitos na superfície com precisão de nanômetros. Através dos dados obtidos no trabalho foi possível confirmar o desempenho superior do espelho feito com vidro de boro-silicato, esse material se apresentou mais estável em todas as medidas realizadas, sofrendo deformações na superfície menores que o vidro soda-cálcico / Abstract: This work aims to compare the performance of two types of glasses, which are the most used in the manufacture of medium sized concave mirrors (up to 25 cm of diameter). The investigated materials were soda-lime and borosilicate glasses. The mirrors were compared concerning their thermal expansion and their elastic rigidity, and the main goal was to find out which glass would have a less deformed surface, main goal was to find out which glass would have a less deformed surface, maintaining the optical quality, under temperature variation and the mirror weight itself. In order to accomplish that, an analysis was carried out based on data collected by the Bath interferometer, built in the Didactic Astronomy Observatory "Lionel José Andriatto". As samples for this work, it was used concave primary mirrors of Newtonian telescopes built with these glasses. The measurements were based on conditions that mirrors are exposed during their regular use, such as variable temperature environments and gravity effects when the mirrors are kept upright. Besides, to test the rigidity, the glass mirrors were held only by the edges. To check the performance, the used parameters were deformation in curvature, the sum of the wavefront deformations and Strehl factor. Interometer fringes were associated with Zernikes polynomials by computational analyses, making possible a survey of defects on the surface with nanometer accuracy. Using data obtained in this study, it was possible to confirm the superior performance of the mirror built with borosilicate glass, which was the most stable sample in all the measurements, presenting less surface deformations when compared with the sodalime glass / Mestre
23

Neutral hydrogen intensity mapping on small scales using MeerKAT

Townsend, Mogamad-Junaid January 2021 (has links)
>Magister Scientiae - MSc / In the post-reionisation universe, intensity mapping (IM) with the 21 cm line of neutral hydrogen (HI) provides a potential means of probing the large-scale structure of the universe. With such a probe, a wide variety of interesting phenomena such as the Baryon Acoustic Oscillations (BAO) and Redshift Space Distortions (RSD) can be studied. The MeerKAT telescope has the potential to make full use of this technique, especially in the single-dish mode, which will probe the scales relevant to BAO and RSD. A useful complementary of this is HI IM with MeerKAT in interferometer-mode, which will enable the extraction of cosmological information on semi-linear and small scales. In this study, full end-to-end simulations of interferometric observations with MeerKAT for HI IM were developed. With this, the power spectrum extraction was analysed using the foreground avoidance technique. This took into account the foreground wedge from point source contamination extracted from real MIGHTEE COSMOS data, as well as RFI flagging. The errors on the power spectrum estimator were then calculated through a Monte Carlo process using 1000s of realisations of both the thermal noise and HI signal. In doing so, precision constraints on the HI power spectrum are found at z = 0:27 on scales 0:4 < k < 10 Mpc-1 for mock visibility data sets which contain the HI signal contaminated by noise, mimicking the MIGHTEE COSMOS field for total observation times & 20 hours. These results illustrate the potential of doing precision cosmology with MeerKAT’s MIGHTEE survey and interferometer-mode HI IM.
24

Neutral hydrogen intensity mapping on small scales using MeerKAT

Townsend, Mogamad-Junaid January 2021 (has links)
>Magister Scientiae - MSc / In the post-reionisation universe, intensity mapping (IM) with the 21 cm line of neutral hydrogen (HI) provides a potential means of probing the large-scale structure of the universe. With such a probe, a wide variety of interesting phenomena such as the Baryon Acoustic Oscillations (BAO) and Redshift Space Distortions (RSD) can be studied. The MeerKAT telescope has the potential to make full use of this technique, especially in the single-dish mode, which will probe the scales relevant to BAO and RSD. A useful complementary of this is HI IM with MeerKAT in interferometer-mode, which will enable the extraction of cosmological information on semi-linear and small scales. In this study, full end-to-end simulations of interferometric observations with MeerKAT for HI IM were developed. With this, the power spectrum extraction was analysed using the foreground avoidance technique. This took into account the foreground wedge from point source contamination extracted from real MIGHTEE COSMOS data, as well as RFI flagging. The errors on the power spectrum estimator were then calculated through a Monte Carlo process using 1000s of realisations of both the thermal noise and HI signal. In doing so, precision constraints on the HI power spectrum are found at z = 0:27 on scales 0:4 < k < 10 Mpc-1 for mock visibility data sets which contain the HI signal contaminated by noise, mimicking the MIGHTEE COSMOS field for total observation times & 20 hours. These results illustrate the potential of doing precision cosmology with MeerKAT’s MIGHTEE survey and interferometer-mode HI IM.
25

Theoretical Study of Bose-Einstein Condensate-Based Atom Michelson Interferometers

Kafle, Rudra Prasad 26 April 2012 (has links)
Atom interferometers and gyroscopes are highly sensitive atom-optical devices which are capable to measure inertial, gravitational, electric, and magnetic fields and to sense rotations. Theoretically, the signal-to-noise ratio of atomic gyroscopes is about a hundred billion times more than that of their optical counterparts for the same particle flux and the enclosed area. Ultra cold atoms from a Bose-Einstein condensate (BEC) can easily be controlled and coherently manipulated on small chips by laser pulses. Atom-optical devices will therefore play a significant role in fundamental research, precision measurements, and navigation systems. In BEC-based atom interferometers, a BEC in a trap is split by using laser pulses, the split clouds are allowed to evolve, they are reflected, and then recombined by laser pulses to observe interference. The split clouds accumulate spatial phase because of the trap and the nonlinearity caused by atom-atom interactions. A velocity mismatch due to reflection laser pulses also introduces a phase gradient across each cloud. These factors contribute to spatial relative phase between the clouds at recombination, causing the loss of contrast of the interference fringes. The main objective of this dissertation is to study the dynamics of a split condensate in atom Michelson interferometers, investigate the effect of trap frequencies, nonlinearity, and the velocity mismatch on the contrast, and to obtain the best theoretical limit of performance in terms of the experimental parameters: trap frequencies, number of atoms, and the velocity imparted to the clouds by the splitting laser pulses.
26

Plasma diagnostics for particle confinement studies in magnetic fusion devices

Hägg, Linus January 2018 (has links)
This thesis investigates the performance and improves a double color interferometer setup, absolutely calibrates a line radiation Balmer H-alpha measurement setup, and uses measurements from both setups to estimate the particle confinement time of a plasma. The double colour interferometer at the magnetic confinement plasma device EXTRAP T2R measures the line integrated electron density of the plasma. Electron density is an important parameter in fusion plasma diagnostics but the interferometer at EXTRAP T2R have had several problems. The interferometer setup was changed as follows: A piezo phase shifter was added, the beam expander was adjusted with the help of thermal image plates, and the electronics setup was rewired to remove interferences. The setup for Balmer H-alpha line radiation measurements was calibrated and characterized. The particle confinement time was estimated using Abel inversion to produce radial profiles of electron density, electron temperature and H-alpha irradiance. The interferometer upgrades did not solve all the problems, but the electron density measurements are now reliable up to around 10 – 20 ms. Since the interferometer only has one channel the electron density profile could not be determined reliably. However, the particle confinement time was estimated for two possible electron density profiles and the results agree with previous studies. / Fusionsvetenskap strävar efter att producera en ny, effektiv energikälla. I och med den ökande energikonsumtionen får fusionsvetenskap en allt viktigare roll i samhället. Kärnfusion har stor potential som energikälla, men att utvinna dess energi kommer med lika stora tekniska utmaningar. I det här projektet tacklas en av dessa utmaningar; att mäta elektrontätheten och joniseringshastigheten i ett plasma. Detta utfördes på EXTRAP T2R, ett magnetiskt inneslutningssystem för plasma på Alfvén laboratoriet, Kungliga Tekniska högskolan, Stockholm. Projektet behandlar två olika mätinstrument: En interferometer som mäter elektrontätheten i plasmat och en H-alphaexperimentuppställning som mäter joniseringshastigheten i plasmat. Interferometern har uppgraderats och justerats för att ge mer tillförlitliga mätningar. Den behöver förbättras ytterligare men kan ger nu tillförlitliga täthetsmätningar i början av plasma-skott. H$\alpha$-experimentuppställningen har karakteriserats och kalibrerats. Genom att mäta elektrontätheten och joniseringshastigheten kan partikelinneslutningstiden uppskattas. Partikelinneslutningstiden är den genomsnittliga tiden innan en partikel lämnar plasmat via en av många processer. Denna uppskattning baserades på två möjliga täthetsprofiler i plasmat eftersom en fullständig mätning skulle kräva flera interferometrar. Trots detta så stämmer uppskattningen väl överens med tidigare studier.
27

Quantum interference spectroscopy with rubidium

Schultz, Eric M. January 1900 (has links)
Master of Science / Department of Physics / Brett D. DePaola / A recent powerful spectroscopic technique that has been implemented using femtosecond lasers excites atoms or molecules through quantum interference effects. The results are oscillations in excited state populations that represent the optical frequencies used in the excitation pathway, these frequencies can be found by Fourier analysis. The technique uses a Mach-Zender interferometer wherein one femtosecond pulse is split into two pulses that are phase coherent. These pulses are the pump and probe pulses which are delayed with respect to one another by a variable time. During the delay between pulses the state excited by the first (pump) pulse evolves in time before the probe pulse is used to excite the atom into its final state. The observed final state population exhibits interference between the several possible pathways to the final state. The information gained from this method will allow for advances in other processes such as the dynamics of photo-association.
28

A study of the variability of dynamics and temperatures near the mesopause from observations of the hydroxyl (OH) Meinel band emissions

Choi, Gi-Hyuk January 1996 (has links)
No description available.
29

Drag-free control and technological risk assessment for the LISA gravitational wave space antenna

Roberts, Peter January 2000 (has links)
The quest for the direct detection and observation of gravitational waves remains one of the lasting scientific challenges of the 20th century, and one that will continue on into the 21 st. Concepts and technologies are being developed that will, early in the new millennium, allow their direct observation for the first time. This will be the beginning of the gravitational wave astronomy revolution. The LISA (Laser Interferometer Space Antenna) mISSIOn is one of the cornerstones of this revolution. Observing in the low-frequency band, it will provide information about our universe that cannot be gathered from the ground. This band contains sources fundamental to our understanding of how the universe began and operates. In turn, fundamental to the LISA mission is the concept of drag-free control. This provides the relatively undisturbed environment for the test-masses which form the references for the measurement of the gravitational waves. Without it the effect of gravitational waves would be but a whisper amongst a cacophony of disturbances. It is drag-free control for the LISA mission which forms the basis for the majority of this thesis. The research and development work carried out by the author has involved the development of a control model of the LISA dragfree control system to assess its feasibility. The author proposes a different approach to the problems involved from that suggested by other authors. It is shown that this approach, unlike those suggested in the mission baseline studies, fulfills the control requirements for the LISA mission. Technological risk assessment in general, as well as that associated with the LISA mission, is also considered.
30

Wetting properties of stainless steel surfaces

Chimezie, Ugochi, Srinivas Gurram, Akhila January 2016 (has links)
Systematic pre cleaning, disinfection and sterilization of medical equipment used in examination and treatment of patients are very important for safe care of the patients and the staff handling these instruments. Due to the technical properties of stainless steel, its hygienic experience and the sophisticated look of the stainless steel, it has dominated the medical health care environments for decades. The wetting properties of stainless steel surfaces are presumed to be essential for the process of clean ability and for a wide variety of bio compatibility.In collaboration with the topical company for this thesis, the idea is to find the correlation between the surface properties of various stainless steel in relation to their wetting and spreading ability to enable efficient cleaning of the surface. For a substrate surface to be thoroughly cleaned of any debris or soil, it should be able to allow proper adherence of the liquid across its surface to a certain degree good enough to ensure good wettability of the surface and conversely easy and proper removal of any attached soil on the surface. Higher demand on cleaning, disinfection and sterilization processes became more and more pressing due the development of complex medical equipment.Different stainless steel (316L) surface finishes and some surgical equipment are investigated using the state of the equipment at Halmstad University. Using the imaging interferometer and mapping software, Mountain Map, the results obtained is controlled readings and classification of the various surface parameters. Contact angle measurements were carried out on each surface with three polar (Distilled water, Glycerol and Ethylene glycol) and one non polar (Olive Oil) probe liquids with a drop volume of 3μm using Theta Optical Tensiometer and One Attention Software for the analysis. The impact and correlations of the surface parameters on wettability was later compared from the measurements obtained.

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