| 1. |
- Wagner, J., et al.
(författare)
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First 230? : GHz VLBI fringes on 3C 279 using the APEX Telescope (Research Note)
- 2015
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 581
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Tidskriftsartikel (refereegranskat)abstract
- Aims. We report about a 230? GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). Methods. We installed VLBI equipment and measured the APEX station position to 1? cm accuracy (1σ). We then observed 3C 279 on 2012 May 7 in a 5? h 230? GHz VLBI track with baseline lengths of 2800? Mλ to 7200? Mλ and a finest fringe spacing of 28.6? μas. Results. Fringes were detected on all baselines with signal-to-noise ratios of 12 to 55 in 420? s. The correlated flux density on the longest baseline was ∼0.3? Jy beam-1, out of a total flux density of 19.8? Jy. Visibility data suggest an emission region ≤ 38? μas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 1010? K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ∼ 38? μas. Conclusions. With APEX the angular resolution of 230? GHz VLBI improves to 28.6? μas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40? μas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.
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| 2. |
- Mohaupt, P., et al.
(författare)
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Extension and optimization of the load range of DRT test systems for testing extra long HV and UHV cables
- 2012
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Ingår i: 44th International Conference on Large High Voltage Electric Systems 2012.
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Konferensbidrag (refereegranskat)abstract
- In the last few years, the demand for testing extra-long cables, such as submarine cables has grown rapidly. The existing testing methods have been complemented by a new testing technology called DRT (Differential Resonance Technology). This testing method enables testing of extra-long cables by comparably small and light-weight equipment using a low frequency for the test voltage, e.g. 0.1Hz up to 5Hz. This leads to a significant decrease of the required power of the test source [1]. In a resonant circuit only the losses of the generator's individual components, specifically the high voltage reactor, have to be covered by the mains. The testing power itself remains fully compensated. Typical ratios between the testing power and the input power of resonant test systems start at 50 and go up to 100, depending on the load. Unfortunately, voltage generation based on inductive generation principles such as resonant circuits cannot economically be used for frequencies below 10Hz due to the massive iron cores needed for such a low frequency. The DRT method for the generation of low frequency high voltage is based on a high frequency voltage whose amplitude is modulated by the desired low frequency. Using a resonator, which is tuned to the high frequency, and a demodulator, the desired low frequency high voltage can be generated [1,2]. The input power required - and in direct relation to this the size and weight of the equipment - is significantly smaller than for other existing methods. In order to optimize the operation performance of the DRT system, this paper describes mathematical methods and algorithms, which have already been implemented and tested in a DRT test set. The basis for these algorithms is a mathematical description of the system based on an envelope model. Using this mathematical description of the nonlinear system behavior, a systematic analysis of the performance and the limits of the system can be given. The theoretical approach was experimentally proven by measuring the output voltage and the input power of a prototype unit ultimately designed to produce 200 kV rms. A first test was performed at SP Technical Research Institute of Sweden, using their reference measurement system for very low frequency (VLF) [3, 4] to measure the high VLF voltage. The reference measurement system provides a traceable uncertainty of down to 0.04 % over a voltage range up to 200 kV rms. The frequency range of the reference system is from 0.1 Hz up to 50 Hz. This system permits acquisition of complete waveforms that can be analysed for harmonic content and/or THD (Total Harmonic Distortion). Further tests are planned, where the connected load will be increased to the specified maximum 1 μF at 200 kV, and the characteristics will be explored both as regards to output voltage quality, input power requirements and distortion on the input current.
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| 3. |
- Mohaupt, P., et al.
(författare)
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Extension and optimization of the load range of DRT test systems for testing extra-long HV and UHV cables
- 2013
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Ingår i: Elektrotechnik und Informationstechnik. - : Springer Science and Business Media LLC. - 0932-383X.
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Tidskriftsartikel (refereegranskat)abstract
- In the last few years, the demand for testing extra-long cables, such as submarine cables has grown rapidly. The existing testing methods have been complemented by a new testing technology called DRT (Differential Resonance Technology). This testing method enables testing of extra-long cables by comparably small and light-weight equipment using a low frequency for the test voltage, e.g. 0.1 Hz up to 5 Hz. This leads to a significant decrease of the required power of the test source (P. Mohaupt and A. Bergman in CIGRE 2010). In a resonant circuit only the losses of the generator's individual components, specifically the high voltage reactor, have to be covered by the mains. The testing power itself remains fully compensated. Typical ratios between the testing power and the input power of resonant test systems start at 50 and go up to 100, depending on the load. Unfortunately, voltage generation based on inductive generation principles such as resonant circuits cannot economically be used for frequencies below 10 Hz due to the massive iron cores needed for such a low frequency. The DRT method for the generation of low frequency high voltage is based on a high frequency voltage whose amplitude is modulated by the desired low frequency. Using a resonator, which is tuned to the high frequency, and a demodulator, the desired low frequency high voltage can be generated (P. Mohaupt and A. Bergman in CIGRE 2010; P. Mohaupt and T. Mehl in Jicable 2011). The input power required-and in direct relation to this the size and weight of the equipment-is significantly smaller than for other existing methods. In order to optimize the operation performance of the DRT system, this paper describes mathematical methods and algorithms, which have already been implemented and tested in a DRT test set. The basis for these algorithms is a mathematical description of the system based on an envelope model. Using this mathematical description of the nonlinear system behavior, a systematic analysis of the performance and the limits of the system can be given. The theoretical approach was experimentally proven by measuring the output voltage and the input power of a prototype unit ultimately designed to produce 200 kV rms. A first test was performed at SP Technical Research Institute of Sweden, using their reference measurement system for very low frequency (VLF) S. Bergman and A. Bergman (Proc. CPEM Conf. Dig., pp. 682-683, 2010; IEEE Trans. Instrum. Meas. 60:2422-2426, 2011) to measure the high VLF voltage. The reference measurement system provides a traceable uncertainty of down to 0.04 % over a voltage range up to 200 kV rms. The frequency range of the reference system is from 0.1 Hz up to 50 Hz. This system permits acquisition of complete wave-forms that can be analysed for harmonic content and/or THD (Total Harmonic Distortion). Further tests are planned, where the connected load will be increased to the specified maximum 1 μF at 200 kV, and the characteristics will be explored both as regards to output voltage quality, input power requirements and distortion on the input current. © 2013 CIGRE -- Reprint from www.cigre.org with kind permission.
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| 4. |
- Bergman, Åke, et al.
(författare)
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Science and policy on endocrine disrupters must not be mixed : a reply to a "common sense" intervention by toxicology journal editors
- 2013
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Ingår i: Environmental Health. - : BioMed Central (BMC). - 1476-069X. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- The "common sense" intervention by toxicology journal editors regarding proposed European Union endocrine disrupter regulations ignores scientific evidence and well-established principles of chemical risk assessment. In this commentary, endocrine disrupter experts express their concerns about a recently published, and is in our considered opinion inaccurate and factually incorrect, editorial that has appeared in several journals in toxicology. Some of the shortcomings of the editorial are discussed in detail. We call for a better founded scientific debate which may help to overcome a polarisation of views detrimental to reaching a consensus about scientific foundations for endocrine disrupter regulation in the EU.
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| 5. |
- Draxler, K., et al.
(författare)
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International comparison of current transformer calibration systems up to 10 kA at 50 Hz frequency
- 2016
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Ingår i: 2016 Conference on Precision Electromagnetic Measurements (CPEM 2016). - 9781467391344
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Konferensbidrag (refereegranskat)abstract
- Current transformers (CTs) are precision devices that scale high currents down to values that can be easily handled by measurement equipment. To support CT applications in revenue metering, a comparison on AC current transformer calibration systems was performed among 15 European national metrology institutes using a precision CT as the travelling device. The first comparison results for the transformation ratios (4, 5, 6, 8, 10) kA/5 A of the travelling CT at nominal burden of 5 VA and 15 VA indicate good agreement between the participating laboratories. The main differences are found for phase displacement, at least partly caused by the instability of the traveling standard.
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| 6. |
- Rutgersson, A., et al.
(författare)
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Optimization of temperature, time, and lactic acid concentration to inactivate lipoxygenase and lipase and preserve phytase activity in barley (cv. Blenheim) during soaking
- 1997
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Ingår i: Cereal Chemistry. - 0009-0352 .- 1943-3638. ; 74:6, s. 727-732
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Tidskriftsartikel (refereegranskat)abstract
- A barley-soaking process was studied to find conditions that inactivate the prooxidative enzyme lipoxygenase and the lipolytic enzyme lipase but preserve phytase activity to develop possible procedures for production of barley products with potentially high mineral bioavailability and good oxidative stability. Lactic acid concentration, temperature, and soaking time were studied. The study was done using a multivariate experimental design. Lactic acid concentration varied between 0 and 1%, temperature varied between 45 and 70°C, and soaking time varied between 30 and 120 min. Although conditions under which lipoxygenase was inactivated were found, total inactivation of lipase was not obtained. Total lipoxygenase inactivation with <20% remaining lipase activity and >60% remaining phytase activity was reached after soaking in 1% lactic acid at suitable time-temperature combinations of 70-110 min and 53-58°C.
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| 7. |
- Schon, K., et al.
(författare)
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Intercomparison on PD calibrators and PD instruments
- 1999
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Ingår i: IEE Conference Publication. - : Institute of Electrical and Electronics Engineers (IEEE). - 0852967195 ; , s. 1.5.S1-1.8.S1
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Konferensbidrag (refereegranskat)abstract
- Within the framework of a European project, two partial discharge calibrators were circulated to thirteen laboratories for an intercomparison of impulse charge measurements in the range between 1 pC and 500 pC. The deviations of the charge values q reported by the laboratories were, with a very few exceptions, within ±(0.1 pC+0.03·q). Furthermore, the characteristics of several partial discharge measuring instruments were investigated. The indication of some of the instruments showed deviations of more than ten percent from the correct values.
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| 8. |
- Bergman, Anders, et al.
(författare)
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Design of a wideband HVDC reference divider
- 2012
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Ingår i: Conference on Precision Electromagnetic Measurements, CPEM 2012. - : IEEE. ; , s. 207-208
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Konferensbidrag (refereegranskat)
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| 9. |
- Bergman, Anders, et al.
(författare)
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Metrology for high voltage direct current
- 2010
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Ingår i: CPEM Digest (Conference on Precision Electromagnetic Measurements). - 9781424467952 ; , s. 669-670
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Konferensbidrag (refereegranskat)abstract
- HVDC energy transmission is crucial for a successful uptake of renewable energy sources in the grid. A research program is described, intended to provide metrology support for the needs of HVDC energy transmission. This program will provide improvements for the present HVDC metrology infrastructure: accurate measurement of HVDC, determination of losses in HVDC systems, on-site power quality measurements at HVDC substations, and DC metering. It is a combined effort of 7 European national metrology institutes, one university and one industrial partner. © 2010 IEEE.
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| 10. |
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