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Search Results: 1 - 10 of 672238 matches for " Jón S ólafsson "
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Life cycles of Eukiefferiella claripennis (Lundbeck 1898) and Eukiefferiella minor (Edwards 1929) (Diptera: Chironomidae) in spring-fed streams of different temperatures with reference to climate change
Elísabet Ragna Hannesdóttir,Gísli Már Gíslason,Jón S ólafsson
Fauna Norvegica , 2012, DOI: 10.5324/fn.v31i0.1367
Abstract: The effect of temperature on the life cycles of two chironomid species, Eukiefferiella claripennis and Eukiefferiella minor, was studied by comparing populations from seven spring-fed streams, ranging in annual average temperatures between 5.4°C and 21.3°C. Dependent on stream, both species showed differences in their life cycles: E. claripennis was regarded univoltine in the two coldest streams, IS7 (annual average 5.4°C) and IS11 (5.3°C), and bivoltine or multivoltine in the warmer streams (ranging from 9.7°C to 21.3°C). E. claripennis developed and grew slower in the colder streams compared to the warmer ones. The winter generation in the warmer streams took longer time to complete compared to the summer generation. E. minor was bivoltine in all the streams, with no emergence during the winter in the colder streams, but in one of the warmer streams (IS6, 13.3°C) emergence was continuous throughout the year. In four streams (IS7, cold; IS6, IS5 and IS1, warm) E. minor may even have been multivoltine. There was no trend between the number of generations completed in one year and stream temperature for E. minor. The summer generation of E. minor in the cold stream IS7 produced smaller larvae compared to the winter generation. Following global warming the life cycle of E. claripennis is expected to change from univoltine to bivoltine, and could show changes in emergence pattern. E. minor on the other hand, will likely show less change in its life cycle. Changes in emergence pattern of E. minor could though be possible. doi: 10.5324/fn.v31i0.1367. Published online: 17 October 2012.
Stream hydraulics and temperature determine the metabolism of geothermal Icelandic streams L’hydraulique fluviale et la température déterminent le métabolisme de ruisseaux géothermiques islandais
Demars B. O.L.,Manson J. R.,ólafsson J. S.,Gíslason G. M.
Knowledge and Management of Aquatic Ecosystems , 2011, DOI: 10.1051/kmae/2011046
Abstract: Stream ecosystem metabolism plays a critical role in planetary biogeochemical cycling. Stream benthic habitat complexity and the available surface area for microbes relative to the free-flowing water volume are thought to be important determinants of ecosystem metabolism. Unfortunately, the engineered deepening and straightening of streams for drainage purposes could compromise stream natural services. Stream channel complexity may be quantitatively expressed with hydraulic parameters such as water transient storage, storage residence time, and water spiralling length. The temperature dependence of whole stream ecosystem respiration (ER), gross primary productivity (GPP) and net ecosystem production (NEP = GPP ER) has recently been evaluated with a “natural experiment” in Icelandic geothermal streams along a 5–25 °C temperature gradient. There remained, however, a substantial amount of unexplained variability in the statistical models, which may be explained by hydraulic parameters found to be unrelated to temperature. We also specifically tested the additional and predicted synergistic effects of water transient storage and temperature on ER, using novel, more accurate, methods. Both ER and GPP were highly related to water transient storage (or water spiralling length) but not to the storage residence time. While there was an additional effect of water transient storage and temperature on ER (r2 = 0.57; P = 0.015), GPP was more related to water transient storage than temperature. The predicted synergistic effect could not be confirmed, most likely due to data limitation. Our interpretation, based on causal statistical modelling, is that the metabolic balance of streams (NEP) was primarily determined by the temperature dependence of respiration. Further field and experimental work is required to test the predicted synergistic effect on ER. Meanwhile, since higher metabolic activities allow for higher pollutant degradation or uptake, river restoration and management should promote habitat diversity and complexity (hyporheic zone, macrophyte patches, substrate heterogeneity), especially for microbial activity. Le métabolisme des écosystèmes aquatiques fluviaux joue un r le critique dans les cycles biogéochimiques planétaires. La complexité des habitats benthiques et l’aire disponible pour les microbes par rapport au volume d’eau qui s’écoule sont considérées comme des facteurs importants pour le métabolisme de l’écosystème. Malheureusement, le creusement et l’alignement des cours d’eau pour le drainage des terres pourraient compromettre les services natu
Examples of Coorbit Spaces for Dual Pairs
J. G. Christensen,G. ólafsson
Mathematics , 2007,
Abstract: In this paper we summarize and give examples of a generalization of the coorbit space theory initiated in the 1980's by H.G. Feichtinger and K.H. Gr\"ochenig. Coorbit theory has been a powerful tool in characterizing Banach spaces of distributions with the use of integrable representations of locally compact groups. Examples are a wavelet characterization of the Besov spaces and a characterization of some Bergman spaces by the discrete series representation of $\mathrm{SL}_2(\mathbb{R})$. We present examples of Banach spaces which could not be covered by the previous theory, and we also provide atomic decompositions for an example related to a non-integrable representation.
Coorbit Spaces for Dual Pairs
J. G. Christensen,G. ólafsson
Mathematics , 2009,
Abstract: In this paper we present an abstract framework for construction of Banach spaces of distributions from group representations. This generalizes the theory of coorbit spaces initiated by H.G. Feichtinger and K. Gr\"ochenig in the 1980's. Spaces that can be described by this new technique include the whole Banach-scale of Bergman spaces on the unit disc. For these Bergman spaces we show that atomic decompositions can be constructed through sampling. We further present a wavelet characterization of Besov spaces on the forward light cone.
The circulation of Icelandic waters – a modelling study
K. Logemann,J. ólafsson,á. Snorrason,H. Valdimarsson
Ocean Science Discussions (OSD) , 2013, DOI: 10.5194/osd-10-763-2013
Abstract: The three-dimensional flow, temperature and salinity fields of the North Atlantic including the Arctic Ocean covering the time period 1992 to 2006 are simulated with the numerical ocean model CODE. The model reveals several new insights and previously unknown structures which help us to clarify open questions on the regional oceanography of Icelandic waters. These relate to the structure and geographical distribution of the coastal current, the primary forcing of the North Icelandic Irminger Current (NIIC), the path of the Atlantic Water south-east of Iceland and the structure of the North Icelandic Jet (NIJ). The model's adaptively refined computational mesh has a maximum resolution of 1 km horizontal and 2.5 m vertical in Icelandic waters. CTD profiles from this region and the river discharge of 46 Icelandic watersheds, computed by the hydrological model WaSiM, are assimilated into the simulation. The model realistically reproduces the established elements of the circulation around Iceland. However, analysis of the simulated mean flow field also provides further insights. It suggests a distinct freshwater-induced coastal current that only exists along the south-west and west coasts which is accompanied by a counter-directed undercurrent. The simulated transport of Atlantic Water over the Icelandic shelf takes place in a symmetrical system of two currents, with the established NIIC over the north-western and northern shelf, and a current over the southern and south-eastern shelf herein called the South Icelandic Current (SIC). Both currents are driven by topographically induced distortions of the Arctic Front's barotropic pressure field. The SIC is simulated to be an upstream precursor of the Faroe Current (FC). The recently discovered North Icelandic Jet (NIJ) also features in the model predictions and is found to be forced by the baroclinic pressure field of the Arctic Front, to originate east of the Kolbeinsey Ridge and to have a volume transport of around 1.5 Sv within northern Denmark Strait. The simulated multi-annual mean Atlantic Water transport of the NIIC increased by 85% during 1992 to 2006, whereas the corresponding NIJ transport decreased by 27%. Based on our model results we propose a new and further differentiated circulation scheme of Icelandic waters whose details may inspire future observational oceanography studies.
Tectonic Control of the Theistareykir Geothermal Field by Rift and Transform Zones in North Iceland: A Multidisciplinary Approach  [PDF]
Maryam Khodayar, Sveinbj?rn Bj?rnsson, Sigureur Garear Kristinsson, Ragna Karlsdóttir, Magnús ólafsson, Skúli Víkingsson
Open Journal of Geology (OJG) , 2018, DOI: 10.4236/ojg.2018.86033
Abstract: This paper presents a multidisciplinary structural analysis of a 165 km2 area in the Northern Rift Zone and the Tjörnes Fracture Zone of Iceland, and unravels the tectonic control of the Theistareykir geothermal field and its surroundings. About 10729 fracture segments (faults, open fractures, joints) are identified in the upper Tertiary to Holocene igneous series. The segments were extracted from aerial images and hillshade, and then analyzed in terms of number of sets, geometry, motions, frequency, and relative age. The correlation with surface geothermal manifestations, resistivity, earthquakes, and occasional well data reveals the critical regional and local fractures at the surface, reservoir level and greater depth. The main conclusions of this study are: 1) The structural pattern consists of N-S rift-parallel extensional fractures and the Riedel shears of the transform zone striking NNE, ENE, E-W, WNW and NW, which compartmentalize together the blocks at any scale. 2) The en échelon segmentation shows strike and oblique slips on the Riedel shears, with a dextral component on the WNW and NW planes and a sinistral component on the NNE to ENE faults. 3) Fractures form under the influence of the transform mechanism and the effect of rifting becomes significant only with time. 4) The WNW dextral oblique-slip Stórihver Fault of the transform zone has a horsetail splay that extends eastwards into the geothermal field. There, this structure, along with few NW, ENE, NNE and N-S fractures, controls the alteration, alignment of fumaroles, emanating deep gases. These fractures also rupture during natural or induced earthquakes. 5) The resistivity anomalies present en échelon geometries controlled by the six fracture sets. These anomalies display clockwise and anticlockwise rotations within the upper 8 km crustal depth, but at 8 km depth, only three sets (the N-S rift structures, and the E-W and the NW Riedel shears) are present at the rift and transform plate boundaries. Results of this study are relevant to resource exploration in other complex extensional contexts where rift and transform interact.
Downslope windstorm in Iceland – WRF/MM5 model comparison
ó. R?gnvaldsson,J.–W. Bao,H. ágústsson,H. ólafsson
Atmospheric Chemistry and Physics Discussions , 2008,
Abstract: A severe windstorm downstream of Mnt. r faj kull in Southeast Iceland is simulated on a grid of 1 km horizontal resolution by using the PSU/NCAR MM5 model and the Advanced Research WRF model. Both models are run with a new, two equation planetary boundary layer (PBL) scheme as well as the ETA/MYJ PBL schemes. The storm is also simulated using six different micro-physics schemes in combination with the MYJ PBL scheme in WRF. Output from a 3 km MM5 domain simulation is used to initialise and drive both the 1 km MM5 and WRF simulations. Both models capture gravity-wave breaking over Mnt. r faj kull, while the vertical structure of the lee wave differs between the two models and the PBL schemes. The WRF simulated downslope winds, using the MYJ PBL scheme, are in good agreement with the strength of the observed downslope windstorm, whilst using the new two equation scheme surface winds are considerably less than observed winds. The MM5 simulated surface winds, with the new two equation model, are in better agreement with observations than when using the ETA scheme. Micro-physics processes are shown to play an important role in the formation of downslope windstorms and lifting of the upslope isotherm layer from mountain height to about 1.3 times the mountain height leads to a significant increase in the downslope windstorm.
Ove Torgny, Hundra procent Roma: en njutbar k lla f r sk na dagar i Rom ( ngelholm: Sk neF rlaget, 2006)
Kjartan ólafsson
Nordicum-Mediterraneum , 2012,
Abstract: Guide books are in many ways a curious type of books. All of them promise to some extent the same promise - to introduce the reader to some place (a town, a country or even a whole continent). In doing so the guide book aims to draw out the essence of that place its true core and presents the reader with the highlights, the ‘best of’. It is somewhat unusual for guide books to spell this out as clearly as is the case with Hundra procent Roma by Ove Torgny. If the title in itself is not clear enough, this promise is also taken up on the back cover which declares that the book picks up the thread where other guide books end.
Downslope windstorm in Iceland – WRF/MM5 model comparison
ó. R gnvaldsson, J.-W. Bao, H. ágústsson,H. ólafsson
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2011,
Abstract: A severe windstorm downstream of Mt. r faj kull in Southeast Iceland is simulated on a grid of 1 km horizontal resolution by using the PSU/NCAR MM5 model and the Advanced Research WRF model. Both models are run with a new, two equation planetary boundary layer (PBL) scheme as well as the ETA/MYJ PBL schemes. The storm is also simulated using six different micro-physics schemes in combination with the MYJ PBL scheme in WRF, as well as one "dry" run. Output from a 3 km MM5 domain simulation is used to initialise and drive both the 1 km MM5 and WRF simulations. Both models capture gravity-wave breaking over Mt. r faj kull, while the vertical structure of the lee wave differs between the two models and the PBL schemes. The WRF simulated downslope winds, using both the MYJ and 2EQ PBL schemes, are in good agreement with the strength of the observed downslope windstorm. The MM5 simulated surface winds, with the new two equation model, are in better agreement to observations than when using the ETA scheme. Micro-physics processes are shown to play an important role in the formation of downslope windstorms and a correctly simulated moisture distribution is decisive for a successful windstorm prediction. Of the micro-physics schemes tested, only the Thompson scheme captures the downslope windstorm.
Nonlinear Waves in Solid Continua with Finite Deformation  [PDF]
K. S. Surana, J. Knight, J. N. Reddy
American Journal of Computational Mathematics (AJCM) , 2015, DOI: 10.4236/ajcm.2015.53032
Abstract: This work considers initiation of nonlinear waves, their propagation, reflection, and their interactions in thermoelastic solids and thermoviscoelastic solids with and without memory. The conservation and balance laws constituting the mathematical models as well as the constitutive theories are derived for finite deformation and finite strain using second Piola-Kirchoff stress tensor and Green’s strain tensor and their material derivatives [1]. Fourier heat conduction law with constant conductivity is used as the constitutive theory for heat vector. Numerical studies are performed using space-time variationally consistent finite element formulations derived using space-time residual functionals and the non-linear equations resulting from the first variation of the residual functional are solved using Newton’s Linear Method with line search. Space-time local approximations are considered in higher order scalar product spaces that permit desired order of global differentiability in space and time. Computed results for non-linear wave propagation, reflection, and interaction are compared with linear wave propagation to demonstrate significant differences between the two, the importance of the nonlinear wave propagation over linear wave propagation as well as to illustrate the meritorious features of the mathematical models and the space-time variationally consistent space-time finite element process with time marching in obtaining the numerical solutions of the evolutions.
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