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Search Results: 1 - 10 of 223888 matches for " R. Lundin "
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Rotation of the magnetic field in Earth's magnetosheath by bulk magnetosheath plasma flow
M. Yamauchi ,R. Lundin
Annales Geophysicae (ANGEO) , 2006,
Abstract: The dynamics of the energy-latitude dispersed sub-keV trapped ions inside the ring current region, the so-called wedge-like dispersions structure, were statistically studied using Viking satellite data. Probabilities with/without these signatures at various local times in the dayside are obtained in terms of different time-lags from the substorm activity monitored by the AE index. The structure appears in the early morning sector within a few hours after the substorm, and it slowly propagates eastward while decaying with a time scale of several hours. The result qualitatively confirmed the previous model that the wedge-like dispersions are originated from past substorm-related plasma injections into the nightside ring current region, and that the dispersion is formed when these injected plasma slowly moves eastward to the dayside by the drift motion (E×B (eastward), grad-<|B| (westward), and curvature (westward) drifts). However, the appearance of the structure is twice or three times faster than the model prediction, and some structure reaches even to the evening sector. The results indicate that the start location of the drift is not as far as midnight and that the drift speed is slightly faster than the model prediction. The former means that the substorm-related increase of hot plasma in the ring current region shifts or extends to the early morning sector for large substorms, and the latter means that the substantial electric field driving the sub-keV ion drift is slightly different from the model field. We also detected the evacuating effect starting right after the substorm (or storm) onset. The electric field imposed in the dayside magnetosphere seems to remove the remainder of trapped ions.
Solar activity explored with new wavelet methods
H. Lundstedt, L. Liszka,R. Lundin
Annales Geophysicae (ANGEO) , 2005,
Abstract: In order to improve the forecasts of the impact of solar activity on the terrestrial environment on time scales longer than days, improved understanding and forecasts of the solar activity are needed. The first results of a new approach of modelling and forecasting solar activity are presented. Time series of solar activity indicators, such as sunspot number, group sunspot number, F10.7, E10.7, solar magnetic mean field, Mount Wilson plage and sunspot index, have been studied with new wavelet methods; ampligrams and time-scale spectra. Wavelet power spectra of the sunspot number for the period 1610 up to the present show not only that a dramatic increase in the solar activity took place after 1940 but also that an interesting change occurred in 1990. The main 11-year solar cycle was further studied with ampligrams for the period after 1850. time-scale spectra were used to examine the processes behind the variability of the solar activity. Several interesting deterministic and more stochastic features were detected in the time series of the solar activity indicators. The solar nature of these features will be further studied. Keywords. Solar physics, astrophysics and astronomy (Magnetic fields; Stellar interiors and dynamo theory) – Space plasma physics (nonlinear phenomena) Full Article (PDF, 2245 KB) Citation: Lundstedt, H., Liszka, L., and Lundin, R.: Solar activity explored with new wavelet methods, Ann. Geophys., 23, 1505-1511, doi:10.5194/angeo-23-1505-2005, 2005. Bibtex EndNote Reference Manager XML
Demonstration of a Dynamic Braking System for Reduced Runaway Speed of Hydraulic Turbines  [PDF]
Urban Lundin, Johan Bladh
Journal of Power and Energy Engineering (JPEE) , 2017, DOI: 10.4236/jpee.2017.512007
Abstract: Reducing the overspeed during load rejection would benefit the mechanical and hydraulic systems in a hydropower station. This paper presents some selected results of a pilot installation of a dynamic braking system. The 4 MW dump load was installed and tested on a 10 MW Francis turbine unit. The results show that the overspeed reduction is obtained and compares well with simulation results. Further, a reduction in vibration levels is positive as well as the reduced time for stopping and possible resynchronization. It is argued that a similar system with continuous cooling could be used as an attractive alternative to spillway capacity.
Long-term solar activity explored with wavelet methods
H. Lundstedt, L. Liszka, R. Lundin,R. Muscheler
Annales Geophysicae (ANGEO) , 2006,
Abstract: Long-term solar activity has been studied with a set of wavelet methods. The following indicators of long-term solar activity were used; the group sunspot number, the sunspot number, and the 14C production rate. Scalograms showed the very long-term scales of 2300 years (Hallstat cycle), 900-1000 years, 400-500 years, and 200 years (de Vries cycle). Scalograms of a newly-constructed 14C production rate showed interesting solar modulation during the Maunder minimum. Multi-Resolution Analysis (MRA) revealed the modulation in detail, as well as peaks of solar activity not seen in the sunspot number. In both the group sunspot number scalogram and the 14C production rate scalogram, a process appeared, starting or ending in late 1700. This process has not been discussed before. Its solar origin is unclear. The group sunspot number ampligram and the sunspot number ampligram showed the Maunder and the Dalton minima, and the period of high solar activity, which already started about 1900 and then decreased again after mid 1990. The decrease starts earlier for weaker components. Also, weak semiperiodic activity was found. Time Scale Spectra (TSS) showed both deterministic and stochastic processes behind the variability of the long-term solar activity. TSS of the 14C production rate, group sunspot number and Mt. Wilson sunspot index and plage index were compared in an attempt to interpret the features and processes behind the long-term variability. Full Article (PDF, 1826 KB) Citation: Lundstedt, H., Liszka, L., Lundin, R., and Muscheler, R.: Long-term solar activity explored with wavelet methods, Ann. Geophys., 24, 769-778, doi:10.5194/angeo-24-769-2006, 2006. Bibtex EndNote Reference Manager XML
Penetration of the electric and magnetic field components of Schumann resonances into the ionosphere
R. Lundin, M. Yamauchi, J.-A. Sauvaud,A. Balogh
Annales Geophysicae (ANGEO) , 2005,
Abstract: The notion of frozen-in magnetic field originates from H. Alfvén, the result of a work on electromagnetic-hydrodynamic waves published in 1942. After that, the notion of frozen-in magnetic field, or ideal MHD, has become widely used in space plasma physics. The controversy on the applicability of ideal MHD started in the late 1950s and has continued ever since. The applicability of ideal MHD is particularly interesting in regions where solar wind plasma may cross the magnetopause and access the magnetosphere. It is generally assumed that a macroscopic system can be described by ideal MHD provided that the violations of ideal MHD are sufficiently small-sized near magnetic x-points (magnetic reconnection). On the other hand, localized departure from ideal MHD also enables other processes to take place, such that plasma may cross the separatrix and access neighbouring magnetic flux tubes. It is therefore important to be able to quantify from direct measurements ideal MHD, a task that has turned out to be a major challenge. An obvious test is to compare the perpendicular electric field with the plasma drift, i.e. to test if E=–v×B. Yet another aspect is to rule out the existence of parallel (to B) electric fields. These two tests have been subject to extensive research for decades. However, the ultimate test of the "frozen-in" condition, based on measurement data, is yet to be identified. We combine Cluster CIS-data and FGM-data, estimating the change in magnetic flux (δB/δt) and the curl of plasma –v×B( ×(v×B)), the terms in the "frozen-in equation". Our test suggests that ideal MHD applies in a macroscopic sense in major parts of the outer magnetosphere, for instance, in the external cusp and in the high-latitude magnetosheath. However, we also find significant departures from ideal MHD, as expected on smaller scales, but also on larger scales, near the cusp and in the magnetosphere-boundary layer. We discuss the importance of these findings. Keywords. Magnetospheric physics (Magnetopause, cusp and boundary layers; Solar wind-magnetosphere interactions) – Space plasma physics Full Article (PDF, 1856 KB) Citation: Lundin, R., Yamauchi, M., Sauvaud, J.-A., and Balogh, A.: Magnetospheric plasma boundaries: a test of the frozen-in magnetic field theorem, Ann. Geophys., 23, 2565-2578, doi:10.5194/angeo-23-2565-2005, 2005. Bibtex EndNote Reference Manager XML
Unusual heavy ion injection events observed by Freja
M. Yamauchi, L. Eliasson, R. Lundin,O. Norberg
Annales Geophysicae (ANGEO) , 2005,
Abstract: Heavy ion injection events (registered in the C+/N+/O+ mass channel) into the ionosphere at 1700km height are surveyed using the Swedish-German Freja satellite data. Heavy ion injections from the inner magnetosphere are mostly found in the nightside sector with a few exceptions that occur on the dayside. We report on these exceptional cases, particularly two specific events which seem to have a different generation/transport mechanism of heavy ions from the majority of cases: 1) mono-energetic heavy ion injection near local noon with oxygen first and protons later; and 2) a multiple heavy ion dispersion event at 9 MLT. Both events are unique without any similar events in terms of dispersion pattern during the more than 2 years of the entire Freja operation, and these events are found during the main phase of major magnetic storms (peak Dst is -144nT and -105nT). The first event is probably of dayside origin but the exact mechanism to make both energy filter and mass filter is unknown. The second event can be traced back to one localized energization of dense oxygen with strong pitch-angle anisotropy within 1000km distance from the spacecraft.
Availability, accessibility, quality and comparability of monitoring data for European forests for use in air pollution and climate change science
Clarke N,Fischer R,de Vries W,Lundin L
iForest : Biogeosciences and Forestry , 2011, DOI: 10.3832/ifor0582-004
Abstract: Data from existing monitoring programmes such as ICP Forests, ICP Integrated Monitoring and EMEP, as well as from large-scale international projects such as CarboEurope IP and NitroEurope, can be used to answer questions about the impacts of air pollution and climate change on forest ecosystems and the feedbacks of forest to climate. However, for full use to be made of the available data, a number of questions need to be answered related to the availability, accessibility, quality and comparability of the data. For example, how can these databases be accessed, e.g., freely, over the internet, on request, by authorisation? How should intellectual property rights be protected, while improving access to data? What possibilities exist for harmonisation? Which quality assurance/quality control (QA/QC) procedures have been used and for how long? These and other relevant questions are discussed.
Sequence complementarity of U2 snRNA and U2A' intron predicts intron function
Maria Lundin
Genome Biology , 2005, DOI: 10.1186/gb-2005-6-4-p6
Abstract: The U2A'i5e6i6 contains conserved sequence cassettes that are complementary to cassettes of the U2 snRNA. A possible RNA-RNA structure, based on RNA helices that may form by these complementary sequences, is presented. The structure, which is conserved in vertebrates, suggests a role of U2A'i5e6i6 in the 3'end processing of U2 snRNA primary transcript.I predict a function of the U2A' i5e6i6 RNA in the 3’end processing of the U2 snRNA primary transcripts, a process that most probably occur during the RNU colocalization to Cajal Bodies. The production of U2 snRNPs would, thus be autoregulated by coupling of splicing efficiency of one of its components (U2A') to transcription of another (U2 snRNA). Such autoregulatory function may well be a common feature of introns.
G H Mead och de sociala strukturernas betydelse f r individen
Elin Lundin
Utbildning & Demokrati : Tidsskrift f?r Didaktik och Utbildningspolitik , 2001,
Abstract: This article draws attention to unnoticed aspects of Mead’s social pragmatism. I argue that in his social pragmatism, put in modern social scientific terms, there is a tendency to transcend the dualism between agency and structure. Modern social scientists as Bourdieu, Giddens and Habermas all approach this dualism. Mead’s social pragmatism can be interpreted as an attempt to transcend the dualism by stressing the reciprocity between agency and structure. The article shows that his view is best described in the following way: social structures are both enabling and constraining in relation to the individual. In Mead’s description of taking the role of the other, especially the generalized other, and the relationship between ”I” and ”me” it clearly appears how the internalization of social structures is a necessary condition for agency. It also becomes evident how agency or creativity have a vital importance in relation to social structures, particularly for structural change.
Hydrology, element budgets, acidification, nutrient N in a climate change perspective for the northern forest region
Lundin L
iForest : Biogeosciences and Forestry , 2009, DOI: 10.3832/ifor0479-002
Abstract: The aim of this paper is to discuss the potential impact of climate change on element budgets and acidity in northern forest ecosystems. A catchment approach should provide the most appropriate unit and to be investigated in several spatial scales. Future monitoring has also to address tree composition, forestry activities, follow the soil organic matter storage and include changes in hydrology with episodic extremes.
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