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.

Noise Reduction in Hyperspectral Imagery: Overview and Application

Abstract: Hyperspectral remote sensing is based on measuring the scattered and reflected electromagnetic signals from the Earth’s surface emitted by the Sun. The received radiance at the sensor is usually degraded by atmospheric effects and instrumental (sensor) noises which include thermal (Johnson) noise, quantization noise, and shot (photon) noise. Noise reduction is often considered as a preprocessing step for hyperspectral imagery. In the past decade, hyperspectral noise reduction techniques have evolved substantially from two dimensional bandwise techniques to three dimensional ones, and varieties of low-rank methods have been forwarded to improve the signal to noise ratio of the observed data. Despite all the developments and advances, there is a lack of a comprehensive overview of these techniques and their impact on hyperspectral imagery applications. In this paper, we address the following two main issues; (1) Providing an overview of the techniques developed in the past decade for hyperspectral image noise reduction; (2) Discussing the performance of these techniques by applying them as a preprocessing step to improve a hyperspectral image analysis task, i.e., classification. Additionally, this paper discusses about the hyperspectral image modeling and denoising challenges. Furthermore, different noise types that exist in hyperspectral images have been described. The denoising experiments have confirmed the advantages of the use of low-rank denoising techniques compared to the other denoising techniques in terms of signal to noise ratio and spectral angle distance. In the classification experiments, classification accuracies have improved when denoising techniques have been applied as a preprocessing step.

Obesity in psoriasis: leptin and resistin as mediators of cutaneous inflammation.

Abstract: Summary Background Obesity is a significant risk factor for psoriasis and body mass index (BMI) correlates with disease severity. Objectives To investigate the relationship between obesity and psoriasis, focusing on the role of adipokines such as leptin and resistin. Patients/methods Patients with psoriasis (n = 30) were recruited and their BMI, waist circumference and disease severity [Psoriasis Area and Severity Index (PASI)] were recorded. Fasting serum samples were obtained on enrolment and after a course of ultraviolet (UV) B treatment. Age-, sex- and BMI-matched healthy controls were also recruited. Results On enrolment, serum leptin and soluble leptin receptor levels were not raised compared with the controls. However, resistin, interleukin (IL)-1β, IL-6, and chemokines CCL2, CXCL8 and CXCL9 were all significantly elevated in the patient group and serum resistin correlated with disease severity (r = 0·372, P = 0·043). Improvement after UVB treatment was accompanied by decreased serum CXCL8. In vitro, both leptin and resistin could induce CXCL8 and tumour necrosis factor-α production by blood monocytes, and leptin could additionally induce IL-1β and IL-1 receptor antagonist production. Leptin also dose dependently increased secretion of the growth factor amphiregulin by ex vivo-cultured lesional psoriasis skin. Conclusions These data support the view that leptin and resistin may be involved in the pathogenesis of psoriasis in overweight individuals, possibly by augmenting the cytokine expression by the inflammatory infiltrate.

The optically unbiased gamma-ray burst host (tough) survey. I. Survey design and catalogs

Abstract: Long-duration gamma-ray bursts (GRBs) are powerful tracers of star-forming galaxies. We have defined a homogeneous subsample of 69 Swift GRB-selected galaxies spanning a very wide redshift range. Special attention has been devoted to making the sample optically unbiased through simple and well-defined selection criteria based on the high-energy properties of the bursts and their positions on the sky. Thanks to our extensive follow-up observations, this sample has now achieved a comparatively high degree of redshift completeness, and thus provides a legacy sample, useful for statistical studies of GRBs and their host galaxies. In this paper, we present the survey design and summarize the results of our observing program conducted at the ESO Very Large Telescope (VLT) aimed at obtaining the most basic properties of galaxies in this sample, including a catalog of R and Ks magnitudes and redshifts. We detect the host galaxies for 80% of the GRBs in the sample, although only 42% have Ks-band detections, which confirms that GRB-selected host galaxies are generally blue. The sample is not uniformly blue, however, with two extremely red objects detected. Moreover, galaxies hosting GRBs with no optical/NIR afterglows, whose identification therefore relies on X-ray localizations, are significantly brighter and redder than those with an optical/NIR afterglow. This supports a scenario where GRBs occurring in more massive and dusty galaxies frequently suffer high optical obscuration. Our spectroscopic campaign has resulted in 77% now having redshift measurements, with a median redshift of 2.14 ± 0.18. TOUGH alone includes 17 detected z> 2 Swift GRB host galaxies suitable for individual and statistical studies—a substantial increase over previous samples. Seven hosts have detections of the Lyα emission line and we can exclude an early indication that Lyα emission is ubiquitous among GRB hosts, but confirm that Lyα is stronger in GRB-selected galaxies than in flux-limited samples of Lyman break galaxies.

The Light Curve of the Macronova Associated with the Long-Short Burst GRB 060614

Abstract: The Swift-detected GRB 060614 was a unique burst that straddles an imaginary divide between long- and short-duration gamma-ray bursts (GRBs), and its physical origin has been heavily debated over the years. Recently, a distinct, very soft F814W-band excess at t similar to 13.6 days after the burst was identified in a joint-analysis of VLT and Hubble Space Telescope optical afterglow data of GRB 060614, which has been interpreted as evidence for an accompanying macronova (also called a kilonova). Under the assumption that the afterglow data in the time interval of 1.7-3.0 days after the burst are due to external FS emission, when this assumption is extrapolated to later times it is found that there is an excess of flux in several multi-band photometric observations. This component emerges at similar to 4 days after the burst, and it may represent the first time that a multi-epoch/band light curve of a macronova has been obtained. The macronova associated with GRB 060614 peaked at t less than or similar to 4 days after the burst, which is significantly earlier than that observed for a supernova associated with a long-duration GRB. Due to the limited data, no strong evidence for a temperature evolution is found. We derive a conservative estimate of the macronova rate of similar to 16.3(8.2)(+16.3) Gpc(-3) yr(-1), implying a promising prospect for detecting the gravitational wave radiation from compact-object mergers by upcoming Advanced LIGO/VIRGO/KAGRA detectors (i.e., the rate is R-GW similar to 0.5(-0.25)(+0.5)(D/200 Mpc)3 yr(-1)).