| 1. |
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| 2. |
- de Jong, R. S., et al.
(författare)
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4MOST : Project overview and information for the First Call for Proposals
- 2019
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Ingår i: The Messenger. - : European Southern Observatory. - 0722-6691. ; 175, s. 3-11
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We introduce the 4-metre Multi-Object Spectroscopic Telescope (4MOST), a new high-multiplex, wide-field spectroscopic survey facility under development for the four-metre-class Visible and Infrared Survey Telescope for Astronomy (VISTA) at Paranal. Its key specifications are: a large field of view (FoV) of 4.2 square degrees and a high multiplex capability, with 1624 fibres feeding two low-resolution spectrographs (R = λ/Δλ ~ 6500), and 812 fibres transferring light to the high-resolution spectrograph (R ~ 20 000). After a description of the instrument and its expected performance, a short overview is given of its operational scheme and planned 4MOST Consortium science; these aspects are covered in more detail in other articles in this edition of The Messenger. Finally, the processes, schedules, and policies concerning the selection of ESO Community Surveys are presented, commencing with a singular opportunity to submit Letters of Intent for Public Surveys during the first five years of 4MOST operations.
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| 3. |
- Hreinsdottir, S., et al.
(författare)
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Volcanic plume height correlated with magma-pressure change at Grimsvotn Volcano, Iceland
- 2014
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 7:3, s. 214-218
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Tidskriftsartikel (refereegranskat)abstract
- Magma flow during volcanic eruptions causes surface deformation that can be used to constrain the location, geometry and internal pressure evolution of the underlying magmatic source(1). The height of the volcanic plumes during explosive eruptions also varies with magma flow rate, in a nonlinear way(2,3). In May 2011, an explosive eruption at Grimsvotn Volcano, Iceland, erupted about 0.27 km(3) dense-rock equivalent of basaltic magma in an eruption plume that was about 20 km high. Here we use Global Positioning System (GPS) and tilt data, measured before and during the eruption at Grimsvotn Volcano, to show that the rate of pressure change in an underlying magma chamber correlates with the height of the volcanic plume over the course of the eruption. We interpret ground deformation of the volcano, measured by geodesy, to result from a pressure drop within a magma chamber at about 1.7 km depth. We estimate the rate of magma discharge and the associated evolution of the plume height by differentiating the co-eruptive pressure drop with time. The time from the initiation of the pressure drop to the onset of the eruption was about 60 min, with about 25% of the total pressure change preceding the eruption. Near-real-time geodetic observations can thus be useful for both timely eruption warnings and for constraining the evolution of volcanic plumes.
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| 4. |
- Sigmundsson, F., et al.
(författare)
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Segmented lateral dyke growth in a rifting event at Bardarbunga volcanic system, Iceland
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 517:7533
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Tidskriftsartikel (refereegranskat)abstract
- Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long(1). Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens(2-4), or magma flowing vertically into dykes from an underlying source(5,6), with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bardarbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System(GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bardarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bardarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.
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| 5. |
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| 7. |
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| 8. |
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| 9. |
- Árnadóttir, Thóra, et al.
(författare)
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Glacial rebound and plate spreading : results from the first countrywide GPS observations in Iceland
- 2009
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Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 177:2, s. 691-716
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Forskningsöversikt (refereegranskat)abstract
- Iceland is one of the few places on Earth where a divergent plate boundary can be observed on land. Direct observations of crustal deformation for the whole country are available for the first time from nationwide Global Positioning System (GPS) campaigns in 1993 and 2004. The plate spreading across the island is imaged by the horizontal velocity field and high uplift rates (>= 10 mm yr(-1)) are observed over a large part of central and southeastern Iceland. Several earthquakes, volcanic intrusions and eruptions occurred during the time spanned by the measurements, causing local disturbances of the deformation field. After correcting for the largest earthquakes during the observation period, we calculate the strain rate field and find that the main feature of the field is the extension across the rift zones, subparallel to the direction of plate motion. Kinematic models of the horizontal plate spreading signal indicate a slightly elevated rate of spreading in the Northern Volcanic Zone (NVZ) (23 +/- 2 mm yr(-1)), while the rates at the other plate boundary segments agree fairly well with the predicted rate of plate spreading (similar to 20 mm yr(-1)) across Iceland. The horizontal ISNET velocities across north Iceland therefore indicate that the excessive spreading rate (>30 mm yr(-1)) observed by GPS in 1987-1992 following the 1975-1984 Krafla rifting episode was significantly slower during 1993-2004. We model the vertical velocities using glacial isostatic adjustment (GIA) due to the recent thinning of the largest glaciers in Iceland. A layered earth model with a 10-km thick elastic layer, underlain by a 30-km thick viscoelastic layer with viscosity 1 x 10(20) Pa s, over a half-space with viscosity similar to 1 x 10(19) Pa s can explain the broad area of uplift in central and southeastern Iceland. A wide area of significant residual uplift ( up to 8 mm yr(-1)) is evident in north Iceland after we subtract the rebound signal from the observed rates, whereas the Reykjanes Peninsula and the Western Volcanic Zone (WVZ) appear to be subsiding at a rate of 4-8 mm yr(-1). We observe a coherent pattern of small but significant residual horizontal motion (up to 3 mm yr(-1)) away from Vatnajokull and the smaller glaciers that is most likely caused by glacial rebound. Our study demonstrates that the velocity field over a large part of Iceland is affected by deglaciation and that this effect needs to be considered when interpreting deformation data to monitor subglacial volcanoes in Iceland.
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| 10. |
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| 11. |
- Geirsson, H., et al.
(författare)
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Overview of results from continuous GPS observations in Iceland from 1995 to 2010
- 2010
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Ingår i: Jökull. - 0449-0576. ; 60:1, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- Iceland is a natural laboratory for a variety of processes associated with crustal deformation, such as earthquakes, magmatic events, tectonic plate motions, and glacial load changes. Continuous GPS (CGPS) measurements started in Iceland in 1995, and since then data from the network have helped to shed light on many different active deformation processes. The number of CGPS sites in Iceland tripled during 2006–2008, as a result of an international collaborative effort coordinated by Icelandic scientists. By early 2010 the number of CGPS stations in Iceland had reached 64, located primarily around and within the North- American–Eurasian plate boundary zone. Since its initiation, the CGPS network has played an important role in monitoring volcanoes and seismogenic areas, most notably during the 2009–2010 Eyjafjallajökull volcano unrest. Plate spreading of up to 2 cm per year usually dominates the horizontal motion observed at the CGPS sites, while uplift is observed at many of the stations due to recent retreat of the Icelandic ice caps. Co-seismic and post-seismic deformation of the largest earthquakes in 2000 and 2008 in the South Iceland Seismic Zone were captured by the network, and high-rate (1 Hz) CGPS observations helped to identify two magnitude 6 mainshocks in 2008 that were separated in time by only 2–3 seconds. The CGPS network has thus enabled us to monitor deformation occurring over days to months caused by migration of magma or fluids, post-seismic transients, rapid deformation caused by earthquakes and eruptions, as well as the long term plate spreading signal.
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| 12. |
- Gustafsdottir, Sonja Stelly, et al.
(författare)
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Translation and cross-cultural adaptation of the European Health Literacy Survey Questionnaire, HLS-EU-Q16: the Icelandic version
- 2020
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Ingår i: BMC public health. - : Springer Science and Business Media LLC. - 1471-2458. ; 20:1
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Health literacy (HL) is defined as the knowledge and competences of people to meet the complex demands of health in modern society. It is an important factor in ensuring positive health outcomes, yet Iceland is one of many countries with limited knowledge of HL and no valid HL measurement. The aim of this study was to translate the European Health Literacy Survey Questionnaire- short version (HLS-EU-Q16) into Icelandic, adapt the version, explore its psychometric properties and establish preliminary norms. METHODS: The HLS-EU-Q16 translation model included three steps: 1) translation-back-translation of HLS-EU-Q16 including specialists' review (n=6); 2) cognitive interviewing of lay people (n=17); and 3) psychometric analysis with survey participants. The HLS-EU-Q16 includes 16 items, with scores ranges from zero (low/no HL) to 16 (high HL). Statistics included were descriptive, internal consistency measured by Cronbach's α, exploratory factor analysis, and multivariate linear regression. RESULTS: After the translation and cognitive interviewing, 11 of the HLS-EU-Q16 items were reworded to adapt the instrument to Icelandic culture while maintaining their conceptual objectives. Survey participants were 251. Internal consistency of the translated and adapted instrument was α=.88. Four factors with eigenvalues >1.0 explained 62.6% of variance. Principal component analysis with Oblimin rotation presented four latent constructs, "Processing and Using Information from the Doctor" (4 items, α=.77), "Processing and Using Information from the Family and Media" (4 items, α=.85), "Processing Information in Connection to Healthy Lifestyle" (5 items, α=.76), and "Finding Information about Health Problems/Illnesses" (3 items, α=.73). Lower self-rated health was an independent predictor of lower HL (β=-.484, p=.008). Preliminary norms for HL ranged from five to 16 (M 13.7, SD±2.6) with 72.5% with sufficient HL (score 13-16), 22% with problematic HL (score 9-12) and 5.5% with inadequate HL (score 0-8). CONCLUSIONS: The Icelandic version of HLS-EU-Q16 is psychometrically sound, with reasonably clear factor structure, and comparable to the original model. This opens possibilities to study HL in Iceland and compare the results internationally. The translation model introduced might be helpful for other countries where information on HL is missing based on lack of validated tools.
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| 13. |
- Hreinsdottir, S, et al.
(författare)
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A complex earthquake sequence captured by the continuous GPS network in SW Iceland
- 2009
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36:12, s. L12309-
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Tidskriftsartikel (refereegranskat)abstract
- A complex sequence of earthquakes struck the western part of the South Iceland Seismic Zone (SISZ) on 29 May 2008. The sequence initiated with a M(w)6.3 (NEIC) earthquake in the western part of the SISZ. Aftershocks from the earthquake delineate two parallel N-S trending structures 4 km apart, in addition to activity along an E-W zone further westward. Continuous GPS measurements can best be explained by right-lateral strike-slip motion on two parallel N-S trending faults, with little slip occurring on other structures illuminated by earthquake activity. We estimate a total moment release of M(w)6.2, with M(w)6.1 on the first rupture and M(w)6.0 on the second rupture. High rate (1 Hz) CGPS data from a near-field station suggest that the main asperity on the Kross fault ruptured within 3 s of the initial mainshock on the Ingolfsfjall fault. Citation: Hreinsdottir, S., T. Amadottir, J. Decriem, H. Geirsson, A. Tryggvason, R. A. Bennett, and P. LaFemina (2009), A complex earthquake sequence captured by the continuous GPS network in SW Iceland, Geophys. Res. Lett., 36, L12309, doi: 10.1029/2009GL038391.
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| 14. |
- Jakobsson, P, et al.
(författare)
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A mean redshift of 2.8 for Swift gamma-ray bursts
- 2006
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 447:3, s. 897-903
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Tidskriftsartikel (refereegranskat)abstract
- The exceptionally high luminosities of gamma-ray bursts (GRBs), gradually emerging as extremely useful probes of star formation, make them promising tools for exploration of the high-redshift Universe. Here we present a carefully selected sample of Swift GRBs, intended to estimate in an unbiased way the GRB mean redshift (z(mean)), constraints on the fraction of high-redshift bursts and an upper limit on the fraction of heavily obscured afterglows. We find that z(mean) = 2.8 and that at least 7% of GRBs originate at z > 5. In addition, consistent with pre-Swift observations, at most 20% of afterglows can be heavily obscured. The redshift distribution of the sample is qualitatively consistent with models where the GRB rate is proportional to the star formation rate in the Universe. We also report optical, near-infrared and X-ray observations of the afterglow of GRB 050814, which was seen to exhibit very red optical colours. By modelling its spectral energy distribution we find that z = 5.3 +/- 0.3. The high mean redshift of GRBs and their wide redshift range clearly demonstrates their suitability as efficient probes of galaxies and the intergalactic medium over a significant fraction of the history of the Universe.
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| 15. |
- Keiding, M, et al.
(författare)
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Earthquakes, stress, and strain along an obliquely divergent plate boundary : Reykjanes Peninsula, southwest Iceland
- 2009
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202 .- 2169-9313 .- 2169-9356. ; 114, s. B09306-
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the seismicity and the state of stress along the obliquely divergent Reykjanes Peninsula plate boundary and compare the directions of stress from inversion of earthquake focal mechanisms with the directions of strain rate from GPS data. The seismicity on the peninsula since early instrumental recordings in 1926 shows a systematic change from primarily earthquake swarms in the west to main shock-aftershock sequences in the east. The largest earthquakes on the Reykjanes Peninsula typically occur by right-lateral slip on N-S faults and reach magnitude 6 on the eastern part of the peninsula. During 1997-2006 most earthquakes on the Reykjanes Peninsula were located in two areas, Fagradalsfjall and Krisuvik on the central part of the peninsula, as recorded by the South Iceland Lowland (SIL) seismic network. The state of stress estimated by inversion of microearthquake focal mechanisms from the SIL catalogue is mainly oblique strike slip, with a tendency toward a normal stress state. Mapping the directions of the least compressive horizontal stress (S-hmin) shows an average Shmin direction of N(120 +/- 6)degrees E and a remarkable agreement with the directions of greatest extensional strain rate ((epsilon) over dot(Hmax)) derived from GPS velocities during 2000-2006. The agreement between the directions of stress at depth and strain rate observed at the surface indicate that the earthquakes are primarily driven by plate motion.
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| 16. |
- Keiding, M., et al.
(författare)
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Strain accumulation along an oblique plate boundary : the Reykjanes Peninsula, southwest Iceland
- 2008
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Ingår i: Geophysical Journal International. - 0956-540X .- 1365-246X. ; 172:2, s. 861-872
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Tidskriftsartikel (refereegranskat)abstract
- We use annual GPS observations on the Reykjanes Peninsula (RP) from 2000 to 2006 to generate maps of surface velocities and strain rates across the active plate boundary. We find that the surface deformation on the RP is consistent with oblique plate boundary motion on a regional scale, although considerable temporal and spatial strain rate variations are observed within the plate boundary zone. A small, but consistent increase in eastward velocity is observed at several stations on the southern part of the peninsula, compared to the 1993-1998 time period. The 2000-2006 velocities can be modelled by approximating the plate boundary as a series of vertical dislocations with left-lateral motion and opening. For the RP plate boundary we estimate left-lateral motion 18(-3)(+4) mm yr(-1) and opening of 7(-2)(+3) mm yr(-1) below a locking depth of 7(-2)(+1) km. The resulting deep motion of 20(-3)(+4) mm yr(-1) in the direction of N(100(-6)(+8))degrees E agrees well with the predicted relative North America-Eurasia rate. We calculate the areal and shear strain rates using velocities from two periods: 1993-1998 and 2000-2006. The deep motion along the plate boundary results in left-lateral shear strain rates, which are perturbed by shallow deformation due to the 1994-1998 inflation and elevated seismicity in the Hengill-Hromundartindur volcanic system, geothermal fluid extraction at the Svartsengi power plant, and possibly earthquake activity on the central part of the peninsula.
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| 17. |
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| 18. |
- Kristjansson, S., et al.
(författare)
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Respiratory syncytial virus and other respiratory viruses during the first 3 months of life promote a local TH2-like response
- 2005
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Ingår i: J Allergy Clin Immunol. - : Elsevier BV. - 0091-6749. ; 116:4, s. 805-11
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Respiratory syncytial virus (RSV) infections during infancy are considered to be a risk factor for developing asthma and possibly allergic sensitization. OBJECTIVE: The aim of this study was to investigate the cytokines, chemokines, and eosinophil cationic protein in the nasopharyngeal secretions of infants < or = 7 months of age with RSV infections or other respiratory viral infections and healthy infants as controls. Groups were also analyzed according to age, < or = 3 months and >3 months, and the levels were compared within and between groups. RESULTS: Thirty-nine infants with RSV, 9 with influenza or parainfluenza virus infections and 50 controls with no history of infections, were enrolled in the study. The RSV-infected infants had significantly higher levels of IL-4; macrophage inflammatory protein 1beta, a chemoattractant for T cells; and eosinophil cationic protein in nasopharyngeal secretions compared with the control group. The levels of the TH2 cytokine IL-4 were significantly higher in RSV-infected infants < or = months of age compared with RSV-infected infants >3 months of age. In infants < or = 3 months of age, infections with influenza or parainfluenza virus caused TH2-like responses similar to those produced by RSV. CONCLUSION: Infections with RSV as well as with influenza and parainfluenza virus during early infancy preferentially promote a TH2-like response in the nose with local production of IL-4, IL-5, and macrophage inflammatory protein 1beta and infiltration and activation of eosinophils.
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| 19. |
- Oddsson, Asmundur, et al.
(författare)
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Deficit of homozygosity among 1.52 million individuals and genetic causes of recessive lethality
- 2023
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Genotypes causing pregnancy loss and perinatal mortality are depleted among living individuals and are therefore difficult to find. To explore genetic causes of recessive lethality, we searched for sequence variants with deficit of homozygosity among 1.52 million individuals from six European populations. In this study, we identified 25 genes harboring protein-altering sequence variants with a strong deficit of homozygosity (10% or less of predicted homozygotes). Sequence variants in 12 of the genes cause Mendelian disease under a recessive mode of inheritance, two under a dominant mode, but variants in the remaining 11 have not been reported to cause disease. Sequence variants with a strong deficit of homozygosity are over-represented among genes essential for growth of human cell lines and genes orthologous to mouse genes known to affect viability. The function of these genes gives insight into the genetics of intrauterine lethality. We also identified 1077 genes with homozygous predicted loss-of-function genotypes not previously described, bringing the total set of genes completely knocked out in humans to 4785.
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