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- PostComputational analysis of a combined heat and power steam turbine for a small modular reactor(2024) Räisänen, Sylvi; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Retegan Vollmer, Teodora; Lahdelma, Risto
- PostAnalysis of GNSS signal measurement accuracy(2024) Rachman Harfian, Alif; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Haas, Rüdiger; Bergstrand , Steneceiver-related errors significantly influence the accuracy of GNSS signal measure ments. One of these errors pertains to the antenna phase center correction. Several antenna calibration techniques, such as robot calibration, can mitigate the impact of such errors. However, there is a possibility that calibration corrections may not completely eliminate the errors in the antenna phase center. To address this issue, calibrated antenna phase center corrections were investigated by measuring GNSS signal observations at four different stations, each tilted to various angles in specific directions, involving up to six baseline length formations. This experiment was dis tinct from previous studies, which only involved one baseline length between two different stations with antennas physically tilted towards each other. Observation data from the four different stations were retrieved and processed using GipsyX with the Precise Point Positioning (PPP) method, and Bernese with the single dif ference technique (DGNSS). Additionally, a laser tracker was utilized to measure the station positions and baseline lengths, providing more precise measurements. The phase residual error models were derived from L1, L2 and L3 frequency observations. The error models indicate that all three frequency observations are influenced by er rors corresponding to antenna phase center corrections, with an error of -0.8867 mm for L1, -1.5728 mm for L2, and -0.3901 mm for L3.
- PostDesign, fabrication and characterization of wideband waveguide terminations(2023) Flosason, Karl Birkir; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Belitsky, Victor; Desmaris, VincentThis thesis reports on two novel designs for high performance, wideband waveguide terminations for terahertz frequencies, demonstrated here in the range 210-370 GHz corresponding to ALMA bands 6-7. With advancing technology in the design and fabrication of high sensitivity radioastronomy receivers, each component and aspect of the system needs to be pushed to the limits when it comes to performance and bandwidth. The highest sensitivity and state-of-the-art receivers today for radioastronomy use 2SB mixer topologies, which require terminations to terminate the fourth port of a waveguide RF hybrid coupler. Reflections from that termination will both increase the level of noise generally but also risk introducing spectral line images or ghosts from the heterodyne downmixing process, which may cause confusion of spectral lines when the tools are used for spectroscopy. Minimizing the reflections from that waveguide termination is a step in improving over-all performance, and taking full advantage of increased performance of the 2SB topology. The goal of the project was to design, fabricate and measure two distinct and novel termination designs, fabricated with well established methods, and materials with known and reliable behaviours in cryogenic operation, and achieve the best possible performance over the widest possible bandwidth. One design based on an E-probe on quartz substrate, showing in simulations S11 < -26 dB over 270-370 GHz, and another design based on a tapered finline structure showing in simulations S11 < -37.5 dB over 220-390 GHz. Both designs use TiN resistive thin-film to dissipate the RF energy in ohmic losses. To validate and verify the design and fabrication process, the performance was then measured using a VNA and the required frequency extensions. Measuring reflection accurately at such low levels and at these frequencies is challenging, and the measurements are likely to underestimate the real performance. Uncertainties in the measurements are described and their scale evaluated both by measurements and simulation.
- PostThe potential for bio-CCS in Europe: Marginal abatement costs and transport logistics(2024) Hidesjö, Sanna; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Johnsson, Filip; Beiron, Johanna
- PostWill solvents present challenges for carbon capture?(2024) Humpage, Samuel; Chanal-Bertaud, Vincent; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Hedenus, Fredrik; Millinger, Markus