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Sökning: LAR1:lu > Naturvetenskap

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1.
  • Omstedt, Anders, et al. (författare)
  • Biogeochemical control of the coupled CO2-O2 system of the Baltic Sea: A review of the results of Baltic-C
  • 2014
  • Ingår i: Ambio. - Springer. - 0044-7447. ; 43:1, s. 49-59
  • Tidskriftsartikel (refereegranskat)abstract
    • Past, present, and possible future changes in the Baltic Sea acid-base and oxygen balances were studied using different numerical experiments and a catchment-sea model system in several scenarios including business as usual, medium scenario, and the Baltic Sea Action Plan. New CO2 partial pressure data provided guidance for improving the marine biogeochemical model. Continuous CO2 and nutrient measurements with high temporal resolution helped disentangle the biogeochemical processes. These data and modeling indicate that traditional understandings of the nutrient availability-organic matter production relationship do not necessarily apply to the Baltic Sea. Modeling indicates that increased nutrient loads will not inhibit future Baltic Sea acidification; instead, increased mineralization and biological production will amplify the seasonal surface pH cycle. The direction and magnitude of future pH changes are mainly controlled by atmospheric CO2 concentration. Apart from decreasing pH, we project a decreasing calcium carbonate saturation state and increasing hypoxic area.
2.
  • Callaghan, Terry V., et al. (författare)
  • Multi-Decadal Changes in Tundra Environments and Ecosystems Synthesis of the International Polar Year-Back to the FutureProject (IPY-BTF)
  • 2011
  • Ingår i: Ambio. - Springer. - 0044-7447. ; 40:6, s. 705-716
  • Tidskriftsartikel (refereegranskat)abstract
    • Understanding the responses of tundra systemsto global change has global implications. Most tundraregions lack sustained environmental monitoring and oneof the only ways to document multi-decadal change is toresample historic research sites. The International PolarYear (IPY) provided a unique opportunity for such researchthrough the Back to the Future (BTF) project (IPY project#512). This article synthesizes the results from 13 paperswithin this Ambio Special Issue. Abiotic changes includeglacial recession in the Altai Mountains, Russia; increasedsnow depth and hardness, permafrost warming, andincreased growing season length in sub-arctic Sweden;drying of ponds in Greenland; increased nutrient availabilityin Alaskan tundra ponds, and warming at mostlocations studied. Biotic changes ranged from relativelyminor plant community change at two sites in Greenland tomoderate change in the Yukon, and to dramatic increasesin shrub and tree density on Herschel Island, and in subarcticSweden. The population of geese tripled at one sitein northeast Greenland where biomass in non-grazed plotsdoubled. A model parameterized using results from a BTFstudy forecasts substantial declines in all snowbeds andincreases in shrub tundra on Niwot Ridge, Colorado overthe next century. In general, results support and provideimproved capacities for validating experimental manipulation,remote sensing, and modeling studies.
3.
  • Werner, Josephina, et al. (författare)
  • Succinic acid in aqueous solution connecting microscopic surface composition and macroscopic surface tension
  • 2014
  • Ingår i: Physical Chemistry, Chemical Physics - PCCP. - 1463-9076. ; 16:39, s. 21486-21495
  • Tidskriftsartikel (refereegranskat)abstract
    • The water vapor interface of aqueous solutions of succinic acid, where pH values and bulk concentrations were varied, has been studied using surface sensitive X-ray photoelectron spectroscopy (XPS) and molecular dynamics (MD) simulations. It was found that succinic acid has a considerably higher propensity to reside in the aqueous surface region than its deprotonated form, which is effectively depleted from the surface due to the two strongly hydrated carboxylate groups. From both XPS experiments and MD simulations a strongly increased concentration of the acid form in the surface region compared to the bulk concentration was found and quantified. Detailed analysis of the surface of succinic acid solutions at different bulk concentrations led to the conclusion that succinic acid saturates the aqueous surface at high bulk concentrations. With the aid of MD simulations the thickness of the surface layer could be estimated, which enabled the quantification of surface concentration of succinic acid as a multiple of the known bulk concentration. The obtained enrichment factors were successfully used to model the surface tension of these binary aqueous solutions using two different models that account for the surface enrichment. This underlines the close correlation of increased concentration at the surface relative to the bulk and reduced surface tension of aqueous solutions of succinic acid. The results of this study shed light on the microscopic origin of surface tension, a macroscopic property. Furthermore, the impact of the results from this study on atmospheric modeling is discussed.
4.
  • Pendrill, Ann-Marie (författare)
  • Students compete in European Union Science Olympiad 2010
  • 2010
  • Ingår i: Physics Education. - 0031-9120. ; 45:4, s. 318-320
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • In April 2010, young students from 21 countries competed in EUSO - the European Union Science Olympiad. Each country sent two teams of three students to an experimental science competition. The first day, the teams helped an alien find water on Earth, and the second day, the solved a criminal case.
5.
  • Muneer, Faraz, et al. (författare)
  • Nanostructural Morphology of Plasticized Wheat Gluten and Modified Potato Starch Composites: Relationship to Mechanical and Barrier Properties
  • 2015
  • Ingår i: Biomacromolecules. - 1525-7797 .- 1526-4602. ; 16:3, s. 695-705
  • Tidskriftsartikel (refereegranskat)abstract
    • In the present study, we were able to produce composites of wheat gluten (WG) protein and a novel genetically modified potato starch (MPS) with attractive mechanical and gas barrier properties using extrusion. Characterization of the MPS revealed an altered chain length distribution of the amylopectin fraction and slightly increased amylose content compared to wild type potato starch. WG and MPS of different ratios plasticized with either glycerol or glycerol and water were extruded at 110 and 130 degrees C. The nanomorphology of the composites showed the MPS having semicrystalline structure of a characteristic lamellar arrangement with an approximately 100 A period observed by small-angle X-ray scattering and a B-type crystal Structure observed by wide-angle X-ray scattering analysis. WG has a structure resembling the hexagonal macromolecular arrangement as reported previously in WG films. A larger amount of beta-sheets was observed in the samples 70/30 and 30/70 WG-MPS processed at 130 degrees C with 45% glycerol. Highly polymerized WG protein was found in the samples processed at 130 degrees C versus 110 degrees C. Also, greater amounts of WG protein in the blend resulted in greater extensibility (110 degrees C) and a decrease in both E-modulus and maximum stress at 110 and 130 degrees C, respectively. Under ambient conditions the WG-MPS composite (70/30) with 45% glycerol showed excellent gas barrier properties to be further explored in multilayer film packaging applications.
6.
  • Ohrwall, Gunnar, et al. (författare)
  • Acid-Base Speciation of Carboxylate Ions in the Surface Region of Aqueous Solutions in the Presence of Ammonium and Aminium Ions
  • 2015
  • Ingår i: The Journal of Physical Chemistry Part B. - The American Chemical Society. - 1520-5207. ; 119:10, s. 4033-4040
  • Tidskriftsartikel (refereegranskat)abstract
    • The acid base speciation of surface-active carboxylate ions in the surface region of aqueous solutions was studied with synchrotron-radiation-based photoelectron spectroscopy. The protonated form was found at an extraordinarily large fraction compared to that expected from the bulk pH. When adding salts containing the weak acid NH4+ to the solution, the fraction of the acidic form at the surface increases, and to a Much greatet extent than expected from the bulk pH of the solution. We show that ammonium ions also are overrepresented in the surface region, and propose that the interaction between the surface-active anionic carboxylates and cationic ammonium ions creates a carboxylateammonium bilayer close to the surface, which increases the probability of the protonation of the carboxylae ions. By comparing the situation when a salt of the less volatile amine diethanolatnine is used, We also show that the observed evaporation of ammonia that occurs after such an event only affects the equilibrium marginally.
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7.
  • Schmidt, Henning T., et al. (författare)
  • First storage of ion beams in the Double Electrostatic Ion-Ring Experiment DESIREE
  • 2013
  • Ingår i: Review of Scientific Instruments. - 0034-6748. ; 84:5, s. 055115
  • Tidskriftsartikel (refereegranskat)abstract
    • We report on the first storage of ion beams in the Double ElectroStatic Ion Ring ExpEriment, DESIREE, at Stockholm University. We have produced beams of atomic carbon anions and small carbon anion molecules (C-n(-), n = 1, 2, 3, 4) in a sputter ion source. The ion beams were accelerated to 10 keV kinetic energy and stored in an electrostatic ion storage ring enclosed in a vacuum chamber at 13 K. For 10 keV C-2(-) molecular anions we measure the residual-gas limited beam storage lifetime to be 448 s +/- 18 s with two independent detector systems. Using the measured storage lifetimes we estimate that the residual gas pressure is in the 10(-14) mbar range. When high current ion beams are injected, the number of stored particles does not follow a single exponential decay law as would be expected for stored particles lost solely due to electron detachment in collision with the residual-gas. Instead, we observe a faster initial decay rate, which we ascribe to the effect of the space charge of the ion beam on the storage capacity.
8.
  • Shannigrahi, Ardhendu Sekhar, et al. (författare)
  • n-Alkanoic monocarboxylic acid concentrations in urban and rural aerosols: Seasonal dependence and major sources
  • 2014
  • Ingår i: Atmospheric research. - 0169-8095. ; 143, s. 228-237
  • Tidskriftsartikel (refereegranskat)abstract
    • We report new data on the abundance and distribution of n-monocarboxylic acids (n-MCAs) in fine- and coarse-mode aerosols in rural and urban areas of Sweden, and determine their possible sources. Overall, C6–C16n-MCAs accounted for ~ 0.5–1.2% of the total PM10 (particulate matter ≤ 10 μm) mass. In general, the C12–C16 fraction was the most abundant (> 75%), with the exception of wintertime samples from a rural site, where C6–C11 acids accounted for 65% of the total C6–C16n-MCA mass. Positive matrix factorization analysis revealed four major sources of n-MCAs: traffic emissions, wood combustion, microbial activity, and a fourth factor that was dominated by semi-volatile n-MCAs.Traffic emissions were important in the urban environment in both seasons and at the rural site during winters, and were a major source of C9–C11 acids. Wood combustion was a significant source at urban sites during the winter and also to some extent at the rural site in both seasons. This is consistent with the use of wood for domestic heating but may also be related to meat cooking. Thus, during the winter, traffic, wood combustion and microbial activity were all important sources in the urban environment, while traffic was the dominant source at the rural site. During the summer, there was considerable day-to-day variation in n-MCA concentrations but microbial activity was the dominant source. The semi-volatile low molecular weight C6–C8 acids accounted for a small (~ 5–10%) fraction of the total mass of n-MCAs. This factor is unlikely to be linked to a single source and its influence instead reflects the partitioning of these compounds between the gas and particle phases. This would explain their greater contribution during the winter.
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9.
  • Sjövall, Peter, et al. (författare)
  • Molecular preservation of the pigment melanin in fossil melanosomes.
  • 2012
  • Ingår i: Nature Communications. - Nature Publishing Group. - 2041-1723. ; 3:Online 08 May 2012
  • Tidskriftsartikel (refereegranskat)abstract
    • Fossil feathers, hairs and eyes are regularly preserved as carbonized traces comprised of masses of micrometre-sized bodies that are spherical, oblate or elongate in shape. For a long time, these minute structures were regarded as the remains of biofilms of keratinophilic bacteria, but recently they have been reinterpreted as melanosomes; that is, colour-bearing organelles. Resolving this fundamental difference in interpretation is crucial: if endogenous then the fossil microbodies would represent a significant advancement in the fields of palaeontology and evolutionary biology given, for example, the possibility to reconstruct integumentary colours and plumage colour patterns. It has previously been shown that certain trace elements occur in fossils as organometallic compounds, and hence may be used as biomarkers for melanin pigments. Here we expand this knowledge by demonstrating the presence of molecularly preserved melanin in intimate association with melanosome-like microbodies isolated from an argentinoid fish eye from the early Eocene of Denmark.
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10.
  • Zhang, Chu, et al. (författare)
  • An in situ sample environment reaction cell for spatially resolved x-ray absorption spectroscopy studies of powders and small structured reactors.
  • 2015
  • Ingår i: Review of Scientific Instruments. - American Institute of Physics. - 1089-7623. ; 86:3
  • Tidskriftsartikel (refereegranskat)abstract
    • An easy-to-use sample environment reaction cell for X-ray based in situ studies of powders and small structured samples, e.g., powder, pellet, and monolith catalysts, is described. The design of the cell allows for flexible use of appropriate X-ray transparent windows, shielding the sample from ambient conditions, such that incident X-ray energies as low as 3 keV can be used. Thus, in situ X-ray absorption spectroscopy (XAS) measurements in either transmission or fluorescence mode are facilitated. Total gas flows up to about 500 mln/min can be fed while the sample temperature is accurately controlled (at least) in the range of 25-500 °C. The gas feed is composed by a versatile gas-mixing system and the effluent gas flow composition is monitored with mass spectrometry (MS). These systems are described briefly. Results from simultaneous XAS/MS measurements during oxidation of carbon monoxide over a 4% Pt/Al2O3 powder catalyst are used to illustrate the system performance in terms of transmission XAS. Also, 2.2% Pd/Al2O3 and 2% Ag - Al2O3 powder catalysts have been used to demonstrate X-ray absorption near-edge structure (XANES) spectroscopy in fluorescence mode. Further, a 2% Pt/Al2O3 monolith catalyst was used ex situ for transmission XANES. The reaction cell opens for facile studies of structure-function relationships for model as well as realistic catalysts both in the form of powders, small pellets, and coated or extruded monoliths at near realistic conditions. The applicability of the cell for X-ray diffraction measurements is discussed.
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