| 1. |
- Hobiger, Thomas, 1978, et al.
(författare)
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Combining VLBI and GPS for inter-continental frequency transfer
- 2015
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Ingår i: 22nd European VLBI for Geodesy and Astrometry (EVGA) Working Meeting.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- For decades the Global Positioning System (GPS) has been the only space geodetic technique routinely used for inter-continental frequency transfer applications. In the past VLB) has also been considered for this purpose and the method's capabilities were studied several times. However, compared to GPS current VLBI technology only provides few observations per hour, thus limiting its potential to improve frequency comparisons. We therefore investigate the effect of combining VLBI and GPS on the observation level in order to draw the maximum benefit from the strength of each individual technique. As a test-bed for our study we use the CONT11 campaign observed in 2011. First we review the frequency transfer performance that can be achieved with independent technique-specific analyses. With this analysis approach both techniques, GPS and VLBI, show similar frequency link instabilities at the level of 1e-14 to 1e-15 (MDEV) on inter-continental baselines for averaging times of one day. We also perform a combined analysis of VLBI and GPS data on the observation level and demonstrate that our combination approach leads to small but consistent improvements for frequency transfer of up to 10%, in particular for averaging periods longer than 3000 s. We discuss the implications of these findings and present our ideas about how VLBI can contribute to international frequency transfer tasks.
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| 2. |
- Billnert, Robert, 1981, et al.
(författare)
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Novel Scintillation Detectors for Prompt Fission γ-Ray Measurements
- 2012
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Ingår i: Physics Procedia. - : Elsevier BV. - 1875-3884 .- 1875-3892. ; 31, s. 29-34
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Konferensbidrag (refereegranskat)abstract
- In this work we present first results from measurements of prompt fission γ-rays from the spontaneous fission in 252Cf. New and accurate data on corresponding γ-rays from the reactions 235U(nth,f) and 239Pu(nth,f) are highly demanded for the modeling of new Generation-IV nuclear reactor systems. For these experiments we employed scintillation detectors made out of new materials (LaBr3, LaCl3 and CeBr3), whose properties were necessary to know in order to obtain reliable results. Hence, we have characterized these detectors. In all the important properties these detectors outshine sodium-iodine detectors that where used in the 1970s, when the existing data had been acquired. Our finding is that the new generation of scintillation detectors is indeed promising, as far as an improved precision of the demanded data is concerned.
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| 3. |
- Gustafsson, Magnus
(författare)
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Diatom-diatom interactions with light : Applications and line shape theoretical aspects
- 2008
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Ingår i: Spectral line shapes, volume 15. - Melville, NY : American Institute of Physics (AIP). - 9780735405882 ; 15, s. 297-301
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Konferensbidrag (refereegranskat)abstract
- Recent advances in calculations of collision-induced absorption- and Raman-spectra in pure diatomic gases are presented. An extensive calculation of H2-H2 absorption from 40 K to 400 K has provided improved understanding of the atmosphere of Uranus. A highly advanced close-coupling calculation of H2-H2 light scattering has verified that the line shapes are affected by interference between the permanent H2 and the H2-H2 interaction-induced polarizabilities. A few directions that the research in astrophysical applications of collision-induced absorption is taking are also described. For instance, H2-H 2 dipole and potential surfaces for vibrations higher than v = 1 are currently being developed to enable simulations of collision-induced absorption at temperatures relevant for white dwarf atmospheres. For low temperature N 2-N2 absorption there is unresolved discrepancy between measurement and simulation. A possible solution to this puzzle is suggested
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| 4. |
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| 5. |
- Micheva, Genoveva, et al.
(författare)
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A Super-Deep Study of the Outskirts of Haro 11
- 2010
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Ingår i: Hunting for the dark: The hidden side of galaxy formation. - New York : American Institute of Physics. - 9780735407862 ; , s. 295-296
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The low surface brightness host of Haro 11 has been observed to have anomalously red optical/NIR colors of V-K = 4.2+/-0.8 [1]. Predictions from current stellar evolutionary models for any normal stellar population over a wide range of metallicities are inconsistent with this color. We present the deepest V and K band observations to date of Haro 11 and derive a new V-K color for the host galaxy. Our new data suggest a far less extreme colour of V-K = 2.3+/-0.2, which is perfectly consistent with the expectations for an old host galaxy with the same metallicity as that derived from nebular emission lines in the star-forming center.
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| 6. |
- Väisänen, Petri, et al.
(författare)
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Star Formation Properties and Dynamics of Luminous Infrared Galaxies with Adaptive Optics
- 2010
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Ingår i: Galaxy Wars: Stellar Populations and Star Formation in Interacting Galaxies : proceedings of a conference held 19-22 July 2009 at East Tennessee State University, Johnson City, Tennessee, USA.. - San Francisco : Astronomical Society of the Pacific. ; , s. 323-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Near infrared adaptive optics observations are crucial to be able to interpret kinematic and dynamical data and study star formation properties within the often extremely dusty interacting luminous IR galaxies (LIRGs). NIR AO data are also needed to find supernovae in their bright and dusty central regions and to fully characterize the young stellar clusters found in these kinds of systems. We have used AO in the K-band to survey a sample of LIRGs at 0.1 arcsec (30 to 100 pc) resolution. The data are merged with SALT and AAT spectroscopic follow-up and HST and Spitzer archival imaging. The first AO detected SNe are reported as well as details of the first studied LIRGs. One LIRG showed an unexpected third component in the interaction, which moreover turned out to host the most active star formation. Another target showed evidence in the NIR of a very rare case of leading spiral arms, rotating in the same direction as the arms open.
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| 7. |
- Desmaris, Vincent, 1977, et al.
(författare)
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Microfabrication Technology for All-Metal Sub-mm and THz Waveguide Receiver Components
- 2008
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Ingår i: In Proceedings of The 19th International Symposium on Space Terahertz Technology, Groningen, 28-30 April, 2008, ed. W. Wild, Space Research Organization of the Netherlands (SRON). ; part I, s. 342-345
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Konferensbidrag (refereegranskat)abstract
- A novel technology for manufacturing of micromachined all-metal waveguide circuits and structures for the frequency band from 200 up to 7000 GHz (Sub-Millimeter and THz) is presented. The waveguide circuits are formed using metal electroplating with preceding sputtering of a thin metal film seed layer over a photo-lithographically patterned thick SU-8 photo-resist. The process provides possibility of making 3-dimensional structures via facilitating of multi-level (layered) designs. Surface roughness of the THz waveguide structure was demonstrated to be below 0.1 µm. This technology was used to build a state-of-the art waveguide balanced 1.3 THz Hot Electron Bolometer mixer and other application for radio astronomy instrumentation.
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| 8. |
- Whale, Mark, et al.
(författare)
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Physical Optics Analysis of the ALMA BANd 5 Front End Optics
- 2008
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Ingår i: In Proceedings of The 19th International Symposium on Space Terahertz Technology, Groningen, 28-30 April, 2008, ed. W. Wild, Space Research Organization of the Netherlands (SRON). ; part I, s. 368-372
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Konferensbidrag (refereegranskat)
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| 9. |
- Meledin, Denis, 1974, et al.
(författare)
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APEX Band T2: A 1.25 – 1.39 THz Waveguide Balanced HEB Receiver
- 2008
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Ingår i: Proceedings of The 19th International Symposium on Space Terahertz Technology, Groningen, 28-30 April, 2008, ed. W. Wild, Space Research Organization of the Netherlands (SRON). ; part I, s. 162-166
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Konferensbidrag (refereegranskat)abstract
- A waveguide 1.25 - 1.39 THz Hot Electron Bolometer (HEB) balanced receiver was successfully developed, characterized and installed at the Atacama Pathfinder EXperiment (APEX) telescope. The receiver employs a quadrature balanced scheme using a waveguide 90-degree 3 dB RF hybrid, HEB mixers and a 180-degree IF hybrid. The HEB mixers are based on ultrathin NbN film deposited on crystalline quartz with a MgO buffer layer. Integrated into the multi-channel APEX facility receiver (SHeFI), the results presented here demonstrate exceptional performance; a receiver noise temperature of 1000 K measured at the telescope at the center of the receiver IF band 2-4 GHz, and at an LO frequency of 1294 GHz. Stability of the receiver is in line with the SIS mixer bands of the SHeFI, and gives a spectroscopic Allan time of more than 200 s at 1382 GHz with a noise bandwidth of 1 MHz.
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| 10. |
- Sundin, Maria, 1965, et al.
(författare)
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Mars - a target for teachers and science students
- 2020
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Ingår i: Contribution to IAU 367S, Education and Heritage in the Era of Big Data in Astronomy, 8-12 December 2020..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A case study is here presented of an interdisciplinary course about Mars for teachers and science students. We aim to share the experience of creating an interdisciplinary approach with lecturers spanning physics, geology, radiation physics and philosophy. Issues in ethics, morality, rights and obligations, conflict management and human psychology as well as rocket orbits, fuel economy, radiation hazards and knowledge of the solar system have proven to be a valued and successful initiative for the further training of teachers and science students. The focus of the course is on planning for a journey with humans to the planet Mars. This provides a great opportunity to package complex societal problems in a physics context. The course is offered with a special sustainability content mark. Mankind has always had a strong and dependent relationship with the physical landscape. The land has given us food and shelter but also imposed challenges and disasters. Understanding the physical environment has been crucial for our survival and development. The same will be equally, or more important for Mars where life conditions are much more extreme. We highlight similarities and differences in the geologic processes that have shaped Earth and Mars. What conditions do the future explorers on Mars have to manage? We then enter the modern era and explore the dynamic Martian landscape of today. Also, by learning to read the landscape we may find locations of shelter such as vast systems of lava tubes, or locations of essential resources such as preserved glacial ice etc. A journey to Mars will cause substantially higher personal irradiation than obtained on Earth. The radiation part of the course lectures starts with defining the different radiation types and the biological effects these different types of radiation will cause. Then, the difference between the irradiation on Earth to the elevated irradiation in space and on Mars is described. Thereafter, it is discussed if this elevated radiation burden can cause acute biological effects, e.g. fatigue, vomiting and death, and late biological effects as cancer induction. Last, possible radiation protection strategies are described and discussed. The philosophy of space exploration consists of philosophical approaches to ethics, presently applied to the topic of Mars exploration and colonization, with environmental ethics (anthropocentric vs ecocentric) and value theory at its core. Four main uses of philosophy are distinguished: ethics, aesthetics, cognition and existentialism. Research has shown that visual representation is an important part for students to be able to create a deeper understanding of concepts as well as context about the material that is taught. Interdisciplinary and complex societal problems have also been shown to be important in science teaching. One way for the teacher to develop his/her teaching is to take further education courses in universities whose focus is to seek and discuss the complex societal problems as well as its solutions from a physics and teacher perspective. Future research could be done on the impact of this course on the education in different levels.
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