Stockholm University

About: Stockholm University is a education organization based out in Stockholm, Sweden. It is known for research contribution in the topics: Population & Context (language use). The organization has 21052 authors who have published 62567 publications receiving 2725859 citations. The organization is also known as: University of Stockholm & Stockholms universitet.

A change in the optical polarization associated with a γ-ray flare in the blazar 3C 279

Abstract: It is widely accepted that strong and variable radiation detected over all accessible energy bands in a number of active galaxies arises from a relativistic, Doppler-boosted jet pointing close to our line of sight1. The size of the emitting zone and the location of this region relative to the central supermassive black hole are, however, poorly known, with estimates ranging from light-hours to a light-year or more. Here we report the coincidence of a gamma (γ)-ray flare with a dramatic change of optical polarization angle. This provides evidence for co-spatiality of optical and γ-ray emission regions and indicates a highly ordered jet magnetic field. The results also require a non-axisymmetric structure of the emission zone, implying a curved trajectory for the emitting material within the jet, with the dissipation region located at a considerable distance from the black hole, at about 105 gravitational radii.

Spitzer Observations of Massive, Red Galaxies at High Redshift*

Abstract: We study massive galaxies at z ~ 1-3.5 using HST optical imaging, ground-based near-IR imaging, and Spitzer observations at 3-24 μm. From Ks-selected galaxies in the 130 arcmin2 GOODS-S field, we identify 153 distant red galaxies (DRGs) with (J - Ks)Vega ≥ 2.3. This sample is approximately complete in stellar mass for passively evolving galaxies above 1011 M☉ and z ≤ 3. Roughly half of the DRGs are objects whose optical and near-IR rest-frame light is dominated by evolved stars combined with ongoing star formation (at zmed ~ 2.5), and the others are galaxies whose light is dominated by heavily reddened (A1600 4-6 mag) starbursts (at zmed ~ 1.7). Very few DRGs (10%) have no indication of current star formation. DRGs at z ~ 1.5-3 with stellar masses ≥1011 M☉ have specific star formation rates (SFRs per unit mass) including the reradiated far-IR emission that range from 0.2 to 10 Gyr-1. Based on the X-ray luminosities and rest-frame near-IR colors, roughly one-quarter of the DRGs contain AGNs, implying that the growth of supermassive black holes coincides with the formation of massive galaxies. At 1.5 ≤ z ≤ 3, the DRGs with M ≥ 1011 M☉ have an integrated specific SFR comparable to the global value of all galaxies. In contrast, galaxies at z ~ 0.3-0.75 with M ≥ 1011 M☉ have an integrated specific SFR less than the global value and more than an order of magnitude lower than that for massive DRGs. At z 1, lower mass galaxies dominate the overall cosmic mass assembly. This suggests that the bulk of star formation in massive galaxies occurs at early cosmic epochs and is largely complete by z ~ 1.5. Further mass assembly in these galaxies takes place with low specific SFRs.

Stable Atmospheric Boundary Layers and Diurnal Cycles: Challenges for Weather and Climate Models

Abstract: The representation of the atmospheric boundary layer is an important part of weather and climate models and impacts many applications such as air quality and wind energy. Over the years, the performance in modeling 2-m temperature and 10-m wind speed has improved but errors are still significant. This is in particular the case under clear skies and low wind speed conditions at night as well as during winter in stably stratified conditions over land and ice. In this paper, the authors review these issues and provide an overview of the current understanding and model performance. Results from weather forecast and climate models are used to illustrate the state of the art as well as findings and recommendations from three intercomparison studies held within the Global Energy and Water Exchanges (GEWEX) Atmospheric Boundary Layer Study (GABLS). Within GABLS, the focus has been on the examination of the representation of the stable boundary layer and the diurnal cycle over land in clear-sky conditions. For thi...

Cognitive factors in odor detection, odor discrimination, and odor identification tasks

Abstract: The purpose of this study was to determine cognitive correlates of olfactory performance across three different tasks. A total of 170 men and women (30-87 years of age) were assessed in olfactory sensitivity, discrimination, and identification. Also, participants were tested in a range of cognitive tests covering executive functioning, semantic memory, and episodic memory. Hierarchical regression analyses showed that proficiency in executive functioning and semantic memory contributed significantly to odor discrimination and identification performance, whereas all of the cognitive factors proved unrelated to performance in the odor threshold test. This pattern of outcome suggests that an individual's cognitive profile exerts a reliable influence on performance in higher order olfactory tasks.