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.

Fractionated phytoplankton primary production, exudate release and bacterial production in a Baltic eutrophication gradient

Abstract: The distribution of phytoplankton primary production into four size fractions (>10 μm, 10-3 μm, 3-0.2 μm and <0.2 μm), the utilization of algal exudates by bacteria and the bacterial production were studied in a eutrophication gradient in the northern Baltic proper. The polluted area exhibits substantially increased nutrient, especially nitrogen, levels while only minor differences occur in salinity and temperature regimes. Total primary production was 160 g C · m-2 · yr-1 at the control station and about 275 g C · m-2 · yr-1 at the eutrophicated stations. The estimated total exudate release was 16% of the totally fixed 14CO2 in the control area and 12% in the eutrophicated area (including the estimated bacterial uptake of exudates). The difference in14CO2 uptake rates between incubation of previously filtered water (<3, <2, <1 μm) and unfiltered water was used to estimate bacterial uptake of phytoplankton exudates which were found to contribute about half of the estimated bacterial carbon requirement in both areas. Bacterial production was estimated by the frequency of dividing cells (FDC) method as being 38 g C · m-2 · yr-1 at the control station and 50 g C · m-2 · yr-1 at the eutrophicated stations. To estimate the mean in situ bacterial cell volume a correlation between FDC and cell volume was used. The increased annual primary production in the eutrophicated area was due mainly to higher production during spring and autumn, largely by phytoplankton cells (mainly diatoms) retained by a 10 μm filter. Primary production duringsummer was similarin the two areas, as was the distribution on different size fractions. This could possibly explain the similar bacterial production in the trophic layers at all stations since the bulk of bacterial production occurs during summer. It was demonstrated that selective filtration does not quantitatively separate photoautotrophs and bacteria. A substantial fraction of the primary production occurs in the size fraction <3 μm. The primary production encountered in the 3-0.2 μm fraction was due to abundant picoplankton (0.5 to 8 · 107 ind · l-1), easily passing a 3 μm filter. The picoplankton was estimated to constitute up to 25% of the total phytoplankton biomass in the control area and up to 10% in the eutrophicated area.

Herschel Detects a Massive Dust Reservoir in Supernova 1987A

Abstract: We report far-infrared and submillimeter observations of supernova 1987A, the star whose explosion was observed on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160,000 light years away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of about 17 to 23 kelvin at a rate of about 220 times the luminosity of the Sun. The intensity and spectral energy distribution of the emission suggest a dust mass of about 0.4 to 0.7 times the mass of the Sun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts.

Oxygen Production in Nature: A Light-Driven Metalloradical Enzyme Process

Abstract: Dioxygen is thermodynamically hot but kinetically cool, which makes it an ideal reagent for maximizing biological free energy production and for carrying out difficult chemical transformations in enzyme active sites.1 The widespread use of dioxygen in biological catalysis has led to an enzyme classification scheme s monooxygenases, dioxygenases, oxidases s that is based on the specifics of the chemistry in which O2 participates. Examples of the remarkable utility of dioxygen in biology abound and include its use in maximizing ATP production in aerobic respiration, in C-H bond activation in the P450 enzymes and methane monoxygenases, and in the degradation of important biomaterials such as lignin. Although nature has devised a multitude of mechanisms by which to activate dioxygen for useful chemistry, only one system, Photosystem II (PSII) in plants and algae, has evolved that has the capacity to lift water out of its thermodynamic well to generate dioxygen. This singular development provided photosynthetic organisms with an abundant and ubiquitous substrate for growth and diversification. The molecular mechanism by which PSII is able to strip hydrogen atoms from water and release O2 as waste is coming into view. In this article, we review the physical structure and energetics of PSII. We then discuss and analyze a metalloradical enzyme mechanism for the water-oxidation process it catalyzes.

Employability and Employees’ Well‐Being: Mediation by Job Insecurity

Abstract: The current study's aims are twofold: first, we investigate the relationship between employability and both work-related (engagement) and general (life satisfaction) well-being. Second, we study ho ...