University of Iceland
  • Reykjavík, Iceland
Recent publications
Background Mechanical ventilation is a life-saving therapy for critically ill patients, providing rest to the respiratory muscles and facilitating gas exchange in the lungs. Ventilator-induced lung injury (VILI) is an unfortunate side effect of mechanical ventilation that may lead to serious consequences for the patient and increase mortality. The four main injury mechanisms associated with VILI are: baro/volutrauma caused by overstretching the lung tissues; atelectrauma, caused by repeated opening and closing of the alveoli resulting in shear stress; oxygen toxicity due to use of high ratio of oxygen in inspired air, causing formation of free radicals; and biotrauma, the resulting biological response to tissue injury, that leads to a cascade of events due to excessive inflammatory reactions and may cause multi-organ failure. An often-overlooked part of the inflammatory reaction is oxidative stress. In this research, a mouse model of VILI was set up with three tidal volume settings (10, 20 and 30 mL/kg) at atmospheric oxygen level. Airway pressures and heart rate were monitored and bronchoalveolar lavage fluid (BALF) and lung tissue samples were taken. Results We show a correlation between increased inflammation and barrier failure, and higher tidal volumes, evidenced by increased IL-6 expression, high concentration of proteins in BALF along with changes in expression of adhesion molecules. Furthermore, swelling of mitochondria in alveolar type II cells was seen indicating their dysfunction and senescence-like state. RNA sequencing data present clear increases in inflammation, mitochondrial biogenesis and oxidative stress as tidal volume is increased, supported by degradation of Keap1, a redox-regulated substrate adaptor protein. Conclusions Oxidative stress seems to be a more prominent mechanism of VILI than previously considered, indicating that possible treatment methods against VILI might be identified by impeding oxidative pathways.
The aim of and inspiration behind this paper was to explain the reasons, also observed by other researchers, of the discrepancy in the results of experimental free convection, which for small Rayleigh and Nusselt numbers in the initial phase of research can sometimes reach several hundred percent. These discrepancies decrease with increasing heating power and plate surface temperature, in proportion to the increase in Ra and Nu, reaching typical values for this type of research. To explain this phenomenon, a comprehensive theoretical and experimental analysis of the influence of the physical properties of a fluid (air and water) as well as primary (tw and t∞) and secondary (tav and Δt) temperatures on the Rayleigh number was carried out. The impact was found to be unequal. The plate temperature tw is of greater importance, which is much higher than the much lower and almost constant temperature t∞ of the undisturbed area, especially since it causes convective movement, generating differences in fluid density and thus driving the phenomenon. Similarly, the direct contribution of the temperature difference Δt to Ra suggests that it has a greater influence on convective heat transfer than the average temperature of the medium tav. By analysing the effect of each of these temperatures separately, it was possible to show that their mutual, compatible or opposite interaction (tw/t∞) causes a different scattering of results, or may even lead to unusual Rayleigh numbers (Ra temperature dualism). This study led not only to a better understanding of the phenomenon, but even to a prediction of its unusual behaviour, unheard of in typical experimental studies of free convection. For example, if we consider the theoretical convective heat transfer from a plate l = 0.15 m in air in the context of the interaction of tav and Δt, it turns out that for the same Δt = 40 K, the Rayleigh number may assume, depending on tav = (tw + t∞)/2, different values. So, for tw = 50 °C, t∞ = 10 °C and tav = 30 °C, Ra = 1.213.10⁷, whereas for tw = 90 °C, t∞ = 50 °C and tav = 70 °C it is ≈ 1.7 times smaller (Ra = 0.687.10⁷). This hypothetical phenomenon, unheard of in typical experimental studies, which could occur, and maybe even does occur in smelting, thermal energy, etc., forces us to think about the values of Nusselt numbers, heat transfer coefficients and heat fluxes for these two cases. This lies beyond the scope of the present paper, but it is a topic for possible future research.
While supercritical geothermal resources receive increasing attention, it has so far remained unclear if and how they could be utilized. In order to provide a tool that can simulate both the natural transient evolution of a supercritical resource near a magma intrusion and its response to possible operation schemes, we augmented the CSMP++ simulation platform with a Peaceman-type well model. For the purpose of generic porous medium simulations of the supercritical resource’s response to direct production, injection or other operation schemes, only a single in-/outflow interval per well is considered and flow in the wellbore is not simulated. The model’s semi-analytical source/sink function accounts for the rapid change in pressure near the wells in the reservoir simulation. As the implementation is based on the 3D Control Volume Finite Element Method it allows the use of unstructured computational grids in order to be able to include geologically realistic geometries. We validate that the well model provides robust solutions of well pressures and rates. Such robust solutions are also obtained for supercritical conditions where water is highly compressible and, therefore, does not strictly fulfil the assumptions used in the derivation of the Peaceman model. To illustrate how a magma-related supercritical resource responds to well operation, we first simulate the evolution of a geothermal system around and above a 2 km deep, explicitly represented magma body. During the system’s hottest phase, ca. 2700 years after its initiation and during progressive inward cooling of the magma body, a well completion interval is activated at 2.1 to 2.2 km depth where temperatures then reach 420 to 490 °C. For the relatively low host rock permeability used in the model (10−15 m2), injection and production rates remain quite limited at several kg/s. Yet, the evolving patterns of temperature, enthalpy, density and flow rates provide some first insights into supercritical resource response to operation.
We consider electronic and optical properties of group III-Nitride monolayers using first-principle calculations. The group III-Nitride monolayers have flat hexagonal structures with almost zero planar buckling, Δ. By tuning the Δ, the strong σ-σ bond through sp2 hybridization of a flat form of these monolayers can be changed to a stronger σ-π bond through sp3 hybridization. Consequently, the band gaps of the monolayers are tuned due to a dislocation of the s- and p-orbitals towards the Fermi energy. The band gaps decrease with increasing Δ for those flat monolayers, which have a band gap greater than 1.0eV, while no noticeable change or a flat dispersion of the band gap is seen for the flat monolayers, that have a band gap less than 1.0eV. The decreased band gap causes a decrease in the excitation energy, and thus the static dielectric function, refractive index, and the optical conductivity are increased. In contrast, the flat band gap dispersion of few monolayers in the group III-Nitride induces a reduction in the static dielectric function, the refractive index, and the optical conductivity. We therefore confirm that tuning of the planar buckling can be used to control the physical properties of these monolayers, both for an enhancement and a reduction of the optical properties. These results are of interest for the design of optoelectric devices in nanoscale systems.
Humans can rapidly estimate the statistical properties of groups of stimuli, including their average and variability. But recent studies of so-called Feature Distribution Learning (FDL) have shown that observers can quickly learn even more complex aspects of feature distributions. In FDL, observers learn the full shape of a distribution of features in a set of distractor stimuli and use this information to improve visual search: response times (RT) are slowed if the target feature lies inside the previous distractor distribution, and the RT patterns closely reflect the distribution shape. FDL requires only a few trials and is markedly sensitive to different distribution types. It is unknown, however, whether our perceptual system encodes feature distributions automatically and by passive exposure, or whether this learning requires active engagement with the stimuli. In two experiments, we sought to answer this question. During an initial exposure stage, participants passively viewed a display of 36 lines that included one orientation singleton or no singletons. In the following search display, they had to find an oddly oriented target. The orientations of the lines were determined either by a Gaussian or a uniform distribution. We found evidence for FDL only when the passive trials contained an orientation singleton. Under these conditions, RT's decreased as a function of the orientation distance between the target and the mean of the exposed distractor distribution. These results suggest that passive exposure to a distribution of visual features can affect subsequent search performance, but only if a singleton appears during exposure to the distribution.
Accurate secular trend estimates and their uncertainties of GNSS coordinate time series is imperative for its geophysical applications. However, trend estimates would be severely biased by complex periodicities, outliers and undetected offsets. We propose a modified robust trend estimator for GNSS time series named Median Inter-Periodic Difference Adjusted for Skewness (MIPDAS) to obtain reliable trend estimates. MIPDAS derives multiple trend sample sets with adaptive data windows to reduce the effects of periodicities and evaluates trend uncertainties with Variance in Rate (VR). Our simulation results indicate that MIPDAS estimates present better robustness than those of MIDAS. Besides the trend estimates, the MIPDAS-derived uncertainties could also effectively reflect noise types, noise amplitudes, and the impacts of unsettled periodicities. Moreover, the experiments with real IGMAS- and IGS-derived coordinate time series prove that the MIPDAS estimates are consistent with the ones by maximum likelihood estimation. Finally, through further combining trend sample sets from multi-source series and down-weighting noisier data, MIPDAS enhances its reliability and the trend uncertainties are reduced by around 64% to 89%.
The effect of transverse magnetic field on the band structure, magnetization and inter-miniband magnetoabsorption of a one-dimensional superlattice of planar quantum rings is discussed. The band structure calculations are made in the framework of diagonalization procedure. A complete set of basis functions, reflecting the structure periodicity in superlattice direction and the effect of magnetic field is constructed, considering the Landau gauge of the vector potential in the Hamiltonian. It is shown that the energy minibands reveal repeating nodes that correspond to a degeneration of quantum states. The magnetization of the system mimics the main peculiarities of the same quantity for a single QR, however considerable differences are observed as well. The examination of the magnetoabsorption indicates on the possibility to extract an information about the existence of nodes in the band structure and the arrangement of quantum states in the neighboring minibands.
High-resolution magnetotelluric and gravity data have been collected over the Kiejo-Mbaka geothermal field, located along the NW–SE trending Mabka fault, in the Karonga Rift basin (East Africa Rift System). Such resolution allowed to reconstruct the field structure with unprecedented detail. Resistivity modelling has been obtained by three-dimensional finite-differences inversion of MT data, while density modelling has been accomplished by surface-oriented inversion of gravity data. Geophysical modelling has identified two sedimentary sub-basins separated by the Mbaka fault ridge, exposing the basement; these previously unknown sedimentary fills have a maximum thickness of ca. 1.5 km. The estimation of the clay cation exchange capacity (CEC) from magnetotellurics identifies a layer of low-temperature smectite alteration in the south-western sub-basin sediments, interpreted as a clay cap. The resulting updated conceptual model of the Kiejo-Mbaka geothermal system is therefore a fault-controlled system with lateral leakage into the sediments, expectably implying a larger reservoir volume than previously estimated. Article highlights Geophysical survey of the Kiejo-Mbaka geothermal field (East Africa Rift System). Geophysical modelling depicted a secondary sedimentary reservoir. Outcomes deeply revised the resource assessment.
Humans are surprisingly good at learning the statistical characteristics of their visual environment. Recent studies have revealed that not only can the visual system learn repeated features of visual search distractors, but also their actual probability distributions. Search times were determined by the frequency of distractor features over consecutive search trials. The search displays applied in these studies involved many exemplars of distractors on each trial and while there is clear evidence that feature distributions can be learned from large distractor sets, it is less clear if distributions are well learned for single targets presented on each trial. Here, we investigated potential learning of probability distributions of single targets during visual search. Over blocks of trials, observers searched for an oddly colored target that was drawn from either a Gaussian or a uniform distribution. Search times for the different target colors were clearly influenced by the probability of that feature within trial blocks. The same search targets, coming from the extremes of the two distributions were found significantly slower during the blocks where the targets were drawn from a Gaussian distribution than from a uniform distribution indicating that observers were sensitive to the target probability determined by the distribution shape. In Experiment 2, we replicated the effect using binned distributions and revealed the limitations of encoding complex target distributions. Our results demonstrate detailed internal representations of target feature distributions and that the visual system integrates probability distributions of target colors over surprisingly long trial sequences.
Background Immigration is rapidly increasing in Iceland with 13.6% of the population holding foreign citizenship in 2020. Earlier findings identified inequities in childbirth care for some women in Iceland. To gain insight into the quality of intrapartum midwifery care, migrant women's use of pain management methods during birth in Iceland was explored. Methods A population‐based cohort study including all women with a singleton birth in Iceland between 2007 and 2018, in total 48 173 births. Logistic regression analyses with odds ratios (ORs) and 95% confidence intervals (CIs) were used to investigate the relationship between migrant backgrounds defined as holding foreign citizenship and the use of pain management during birth. The main outcome measures were use of nonpharmacological and pharmacological pain management methods. Results Data from 6097 migrant women were included. Migrant women had higher adjusted OR (aORs) for no use of pain management (aOR = 1.23 95% CI [1.12, 1.34]), when compared to Icelandic women. Migrant women also had lower aORs for the use of acupuncture (0.73 [0.64, 0.83]), transcutaneous electrical nerve stimulation (TENS) (0.92 [0.01, 0.67]), shower/bath (0.73 [0.66, 0.82]), aromatherapy (0.59 [0.44, 0.78]), and nitrous oxide inhalation (0.89 [0.83, 0.96]). Human Development Index (HDI) scores of countries of citizenship <0.900 were associated with lower aORs for the use of various pain management methods. Conclusions Our results suggest that being a migrant in Iceland is an important factor that limits the use of nonpharmacological pain management, especially for migrant women with citizenship from countries with HDI score <0.900.
Past findings concerning whether and how feedback from external evaluations benefit the improvement of schools are inconsistent and sometimes even conflicting, which highlights the contextual nature of such evaluations and underscores the importance of exploring them in diverse contexts. Considering that broad international debate, we investigated the use and impact of feedback from external evaluations in compulsory schools in Iceland, particularly as perceived by principals and teachers in six such schools. A qualitative research design was adopted to examine changes in the schools made during a 4–6-year period following external evaluations by conducting interviews with principals and teachers, along with a document analysis of evaluation reports, improvement plans and progress reports. The findings reveal that feedback from external evaluations has been used for instrumental, conceptual, persuasive and reinforcement-oriented purposes in the schools, albeit to varying degrees. According to the principals and teachers, the improvement actions presented in the schools’ improvement plans were generally implemented or continue to be implemented in some way, and the changes made have mostly been sustained.
Icelandic basalts have low oxygen isotope (δ18O) values compared to other ocean island localities. While this observation is often ascribed to the assimilation of low-δ18O crust, a low-δ18O mantle beneath Iceland has also been suggested. To discern crustal from mantle-derived signals, high-quality in-situ and bulk crystal δ18O measurements have been obtained from olivine crystals covering 16 Ma of activity at the Iceland hotspot. The results are combined with olivine (ol) major, minor and trace element chemistry. Relationships between δ18Ool and indicators of melt evolution do not support a singular process responsible for lowering of δ18O values. However, correlations are observed between δ18Ool values and indicators of crustal processes. Such patterns are used to filter out data that are likely to reflect effects from crustal assimilation to highlight δ18Ool values indicative of source-derived variability only. Although filtered, the dataset reveals, that δ18Ool values, significantly lower than the canonical depleted upper mantle value, are derived from the Iceland mantle. Coupled δ18Ool and ³He/⁴Heol measurements done on olivine crystals from the same samples demonstrate that low-δ18O components (down to δ18Oolivine = 4.2‰) are a trait of the modern Iceland plume and that low-δ18O and low-³He/⁴He components have become more apparent in the hotspot products since 60 Ma. Olivine chemistry characteristics suggest that this low-δ18O component is best sampled in melts that reflect contributions from pyroxenitic mantle lithologies, likely related to the recycling of oceanic lithosphere within the plume. An increase in plume flux, as traced by increasing plume temperatures and plume buoyancy after 35 Ma, led to enhanced entrainment of lower mantle material carrying recycled low-δ18O oceanic lithosphere. Such material has become more apparent with time as is reflected in source-derived low-δ18O and high ³He/⁴He values in olivine from the modern Iceland plume. Moreover, the coincidence of the Iceland plume-head and the North Atlantic Rift at from ∼25 Ma likely assisted and further promoted enhanced plume-melting. Thus, the combination of changes in mantle upwelling and tectonic reorganisation of the North Atlantic led to the introduction of recycled oceanic lithosphere into the Iceland plume and the formation of the Iceland Plateau ∼25 Ma.
Waste management in Iceland has developed considerably in recent years. Before 1990, most of the waste was either burnt in open pits or landfilled. In the past, information about waste management in Iceland used to be almost exclusively published in reports and was primarily based on rough estimates. Currently, incinerators and landfilling sites are highly regulated and follow EU legislation. Additionally, reporting has gradually improved and is approaching EU standards, although improvement is still needed. In an international context, Iceland is far behind the other Nordic countries as well as the EU-27 countries in reducing landfill rates and enhancing energy recovery and recycling rates. According to the EU landfill directive, the total amount of municipal solid waste (MSW) landfilled must be below 10% by 2035; however, it is currently over 60%. Other targets are similarly far off, and it is unlikely that Iceland will meet those in time without immediate and significant changes in waste management. This article aims to evaluate MSW management in Iceland at the national and regional levels, its compliance with the EU’s targets for waste management and the associated costs inflicted on municipalities. Hence, annual accounts data were used when comparing regions and municipalities. It was found that there are significant differences in per capita waste management expenditure between municipalities with less than 1,000 inhabitants (€379) and ones with more than 10,000 inhabitants (€106). Without changes in proposed future waste management strategies, this gap will inevitably increase in the upcoming years.
The EEG is suggested as a potential diagnostic and prognostic biomarker for seasonal affective disorder (SAD). As a pre-clinical form of SAD, seasonality is operationalized as seasonal variation in mood, appetite, weight, sleep, energy, and socializing. Importantly, both EEG biomarkers and seasonality interact with age. Inducing sad mood to assess cognitive vulnerability was suggested to improve the predictive value of summer assessments for winter depression. However, no EEG studies have been conducted on induced sad mood in relation to seasonality, and no studies so far have controlled for age. We recorded EEG and calculated bandpower in 114 participants during rest and during induced sad mood in summer. Participants were grouped by age and based on a seasonality score as obtained with the seasonal pattern assessment questionnaire (SPAQ). Participants with high seasonality scores showed significantly larger changes in EEG power from rest to sad mood induction, specifically in the alpha frequency range (p = 0.027), compared to participants with low seasonality scores. Furthermore, seasonality interacted significantly with age (p < 0.001), with lower activity in individuals with high seasonality scores that were older than 50 years but the opposite pattern in individuals up to 50 years. Effects of sad mood induction on brain activity are related to seasonality and can therefore be consider as potential predicting biomarkers for SAD. Future studies should control for age as a confounding factor, and more studies are needed to elaborate on the characteristics of EEG biomarkers in participants above 50 years.
Photosymbiodemes are a special case of lichen symbiosis where one lichenized fungus engages in symbiosis with two different photosynthetic partners, a cyanobacterium and a green alga, to develop two distinctly looking photomorphs. We investigated differential gene expression in photosymbiodemes of the lichen Peltigera britannica at different temperatures representing mild and putatively stressful conditions and compared gene expression of thallus sectors containing cyanobacterial photobionts with thallus sectors with both green algal and cyanobacterial photobionts. Firstly, because of known ecological differences between photomorphs, we investigated symbiont-specific responses in gene expression to temperature increases. Secondly, we quantified photobiont-mediated differences in fungal gene expression. High temperatures expectedly led to an upregulation of genes involved in heat shock responses in all organisms in whole transcriptome data. As expected, the expression of genes involved in photosynthesis was increased in both photobiont types at 15 and 25 °C. The green algae exhibited thermal stress responses mainly at 25 °C, the fungus and the cyanobacteria already at 15 °C, demonstrating symbiont-specific responses to environmental cues and symbiont-specific ecological optima. Furthermore, photobiont-mediated differences in fungal gene expression could be identified, with upregulation of distinct biological processes in the different morphs, showing that interaction with specific symbiosis partners profoundly impacts fungal gene expression.
Background In recent years a variety of eHealth solutions has been introduced to enhance efficiency and to empower patients, leading to a more accessible and equitable health care system. Within pediatric care eHealth has been advocated to reduce emergency and hospital outpatient visits, with many parents preferring eHealth to physical visits following the transition from hospital to home. Still, not many studies have focused on access from the parental perspective. Therefore, the aim of the study was to analyze access to health care as perceived by parents when caring for their child at home, with conventional care supported by eHealth following pediatric surgery or preterm birth. Methods Twenty-five parents who went home with their child following hospitalization and received conventional care supported by eHealth (a tablet) were interviewed in this qualitative study. Directed content analysis was used, guided by a framework for dimensions of access previously described as: approachability, acceptability, affordability, appropriateness, and availability. Results All dimensions of access were present in the material with the dimensions of approachability, appropriateness and acceptability most frequently emphasized. The dimensions highlighted a strong acceptance of eHealth, which was perceived by the parents as beneficial, particularly access to communication with health care personnel familiar to them. The chat function of the tablet was often mentioned as positive. A new dimension was also identified: “aperture.” It is defined by the pathways by which communication is transmitted in cyberspace, and these pathways are not easily visualized for parents submitting information, therefore generating concerns. Conclusions Parents generally experienced good access to the eHealth-supported health care. Describing access through its dimensions complemented previous descriptions of eHealth in pediatric care and gave new insights. As such, the new dimension of “aperture”, the indeterminate opening of pathways of communication reflecting the uncertainty of not comprehending cyberspace, could be further evaluated. The dimensional framework of access is recommended when evaluating eHealth in the future. Trial registration identifier: NCT04150120.
A complete Lyapunov function describes the qualitative behaviour of a dynamical system: the areas where the orbital derivative vanishes and where it is strictly negative characterise the chain recurrent set and the gradient-like flow, respectively. Moreover, its local maxima and minima show the stability properties of the connected components of the chain recurrent set. In this study, we use collocation with radial basis functions to numerically compute approximations to complete Lyapunov functions and then localise and analyse the stability properties of the connected components of the chain recurrent set using its gradient and Hessian. In particular, we improve the estimation of the chain recurrent set, and we determine the dimension and the stability properties of its connected components.
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7,073 members
Solveig Asa Arnadottir
  • Department of Physiotherapy
Jakob Kristinsson
  • Department of Pharmacology and Toxicology
Jón Grétar Stefánsson
  • Biomedical Center
Matthias Eydal
  • Institute for Experimental Pathology at Keldur
Brynja Ingadottir
  • Faculty of Nursing
Sturlugata 8, 101, Reykjavík, Iceland