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- Bender, P., et al.
(författare)
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Dipolar-coupled moment correlations in clusters of magnetic nanoparticles
- 2018
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Ingår i: Physical Review B. - 2469-9950 .- 2469-9969. ; 98:22
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Tidskriftsartikel (refereegranskat)abstract
- Here, we resolve the nature of the moment coupling between 10-nm dimercaptosuccinic acid-coated magnetic nanoparticles. The individual iron oxide cores were composed of >95% maghemite and agglomerated to clusters. At room temperature the ensemble behaved as a superparamagnet according to Mössbauer and magnetization measurements, however, with clear signs of dipolar interactions. Analysis of temperature-dependent ac susceptibility data in the superparamagnetic regime indicates a tendency for dipolar-coupled anticorrelations of the core moments within the clusters. To resolve the directional correlations between the particle moments we performed polarized small-angle neutron scattering and determined the magnetic spin-flip cross section of the powder in low magnetic field at 300 K. We extract the underlying magnetic correlation function of the magnetization vector field by an indirect Fourier transform of the cross section. The correlation function suggests nonstochastic preferential alignment between neighboring moments despite thermal fluctuations, with anticorrelations clearly dominating for next-nearest moments. These tendencies are confirmed by Monte Carlo simulations of such core clusters.
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- Maldanis, L., et al.
(författare)
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Heart fossilization is possible and informs the evolution of cardiac outflow tract in vertebrates
- 2016
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Ingår i: eLIFE. - : eLife Sciences Publications Ltd. - 2050-084X. ; 5:APRIL2016
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Tidskriftsartikel (refereegranskat)abstract
- Elucidating cardiac evolution has been frustrated by lack of fossils. One celebrated enigma in cardiac evolution involves the transition from a cardiac outflow tract dominated by a Multi-Valved conus arteriosus in basal actinopterygians, to an outflow tract commanded by the Non- Valved, elastic, bulbus arteriosus in higher actinopterygians. We demonstrate that cardiac preservation is possible in the extinct fish Rhacolepis buccalis from the Brazilian Cretaceous. Using X-Ray synchrotron microtomography, we show that Rhacolepis fossils display hearts with a conus arteriosus containing at least five valve rows. This represents a transitional morphology between the primitive, multivalvar, conal condition and the derived, monovalvar, bulbar state of the outflow tract in modern actinopterygians. Our data rescue a Long-Lost cardiac phenotype (119-113 Ma) and suggest that outflow tract simplification in actinopterygians is compatible with a gradual, rather than a drastic saltation event. Overall, our results demonstrate the feasibility of studying cardiac evolution in fossils.
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- Fjellgaard Mikalsen, Ragni
(författare)
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Fighting flameless fires : Initiating and extinguishing self-sustainedsmoldering fires in wood pellets
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Smoldering fires represent domestic, environmental and industrial hazards. This flameless form of combustion is more easily initiated than flaming, and is also more persistent and difficult to extinguish. The growing demand for non-fossil fuels has increased the use of solid biofuels such as biomass. This represents a safety challenge, as biomass self-ignition can cause smoldering fires, flaming fires or explosions.Smoldering and extinguishment in granular biomass was studied experimentally. The set-up consisted of a cylindrical fuel container of steel with thermally insulated side walls. The container was closed at the bottom, open at the top and heated from below by a hot surface. Two types of wood pellets were used as fuel, with 0.75-1.5 kg samples.Logistic regression was used to determine the transition region between non-smoldering and self-sustained smoldering experiments, and to determine the influence of parameters. Duration of external heating was most important for initiation of smoldering. Sample height was also significant, while the type of wood pellet was near-significant and fuel container height was not.The susceptibility of smoldering to changes in air supply was studied. With a small gap at the bottom of the fuel bed, the increased air flow in the same direction as the initial smoldering front (forward air flow) caused a significantly more intense combustion compared to the normal set-up with opposed air flow.Heat extraction from the combustion was studied using a water-cooled copper pipe. Challenges with direct fuel-water contact (fuel swelling, water channeling and runoff) were thus avoided. Smoldering was extinguished in 7 of 15 cases where heat extraction was in the same range as the heat production from combustion. This is the first experimental proof-of-concept of cooling as an extinguishment method for smoldering fires.Marginal differences in heating and cooling separated smoldering from extinguished cases; the fuel bed was at a heating-cooling balance point. Lower cooling levels did not lead to extinguishment, but cooling caused more predictable smoldering, possibly delaying the most intense combustion. Also observed at the balance point were pulsating temperatures; a form of long-lived (hours), macroscopic synchronization not previously observed in smoldering fires.For practical applications, cooling could be feasible for prevention of temperature escalation from self-heating in industrial storage units. This study provides a first step towards improved fuel storage safety for biomass.
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