University of Iceland

About: University of Iceland is a education organization based out in Reykjavik, Suðurnes, Iceland. It is known for research contribution in the topics: Population & Genome-wide association study. The organization has 5423 authors who have published 16199 publications receiving 694762 citations. The organization is also known as: Háskóli Íslands.

Where perception meets memory: A review of repetition priming in visual search tasks

Abstract: What we have recently seen and attended to strongly influences how we subsequently allocate visual attention. A clear example is how repeated presentation of an object’s features or location in visual search tasks facilitates subsequent detection or identification of that item, a phenomenon known as priming. Here, we review a large body of results from priming studies that suggest that a short-term implicit memory system guides our attention to recently viewed items. The nature of this memory system and the processing level at which visual priming occurs are still debated. Priming might be due to activity modulations of low-level areas coding simple stimulus characteristics or to higher level episodic memory representations of whole objects or visual scenes. Indeed, recent evidence indicates that only minor changes to the stimuli used in priming studies may alter the processing level at which priming occurs. We also review recent behavioral, neuropsychological, and neurophysiological evidence that indicates that the priming patterns are reflected in activity modulations at multiple sites along the visual pathways. We furthermore suggest that studies of priming in visual search may potentially shed important light on the nature of cortical visual representations. Our conclusion is that priming occurs at many different levels of the perceptual hierarchy, reflecting activity modulations ranging from lower to higher levels, depending on the stimulus, task, and context—in fact, the neural loci that are involved in the analysis of the stimuli for which priming effects are seen.

The First FERMI-LAT Gamma-Ray Burst Catalog

Abstract: In three years of observations since the beginning of nominal science operations in August 2008, the Large Area Telescope (LAT) on board the Fermi Gamma Ray Space Telescope has observed high-energy (>20 MeV) \gamma-ray emission from 35 gamma-ray bursts (GRBs). Among these, 28 GRBs have been detected above 100 MeV and 7 GRBs above ~ 20 MeV. The first Fermi-LAT catalog of GRBs is a compilation of these detections and provides a systematic study of high-energy emission from GRBs for the first time. To generate the catalog, we examined 733 GRBs detected by the Gamma-Ray Burst Monitor (GBM) on Fermi and processed each of them using the same analysis sequence. Details of the methodology followed by the LAT collaboration for GRB analysis are provided. We summarize the temporal and spectral properties of the LAT-detected GRBs. We also discuss characteristics of LAT-detected emission such as its delayed onset and longer duration compared to emission detected by the GBM, its power-law temporal decay at late times, and the fact that it is dominated by a power-law spectral component that appears in addition to the usual Band model.

Ash generation and distribution from the April-May 2010 eruption of Eyjafjallajökull, Iceland

Abstract: The 39-day long eruption at the summit of Eyjafjallajokull volcano in April–May 2010 was of modest size but ash was widely dispersed. By combining data from ground surveys and remote sensing we show that the erupted material was 4.8±1.2·1011 kg (benmoreite and trachyte, dense rock equivalent volume 0.18±0.05 km3). About 20% was lava and water-transported tephra, 80% was airborne tephra (bulk volume 0.27 km3) transported by 3–10 km high plumes. The airborne tephra was mostly fine ash (diameter <1000 µm). At least 7·1010 kg (70 Tg) was very fine ash (<28 µm), several times more than previously estimated via satellite retrievals. About 50% of the tephra fell in Iceland with the remainder carried towards south and east, detected over ~7 million km2 in Europe and the North Atlantic. Of order 1010 kg (2%) are considered to have been transported longer than 600–700 km with <108 kg (<0.02%) reaching mainland Europe.

Universal transition state scaling relations for (de)hydrogenation over transition metals

Abstract: We analyse the transition state energies for 249 hydrogenation/dehydrogenation reactions of atoms and simple molecules over close-packed and stepped surfaces and nanoparticles of transition metals using Density Functional Theory. Linear energy scaling relations are observed for the transition state structures leading to transition state scaling relations for all the investigated reactions. With a suitable choice of reference systems the transition state scaling relations form a universality class that can be approximated with one single linear relation describing the entire range of reactions over all types of surfaces and nanoclusters.