| 1. |
- Birch, C. E., et al.
(författare)
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Modelling atmospheric structure, cloud and their response to CCN in the central Arctic : ASCOS case studies
- 2012
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:7, s. 3419-3435
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Tidskriftsartikel (refereegranskat)abstract
- Observations made during late summer in the central Arctic Ocean, as part of the Arctic Summer Cloud Ocean Study (ASCOS), are used to evaluate cloud and vertical temperature structure in the Met Office Unified Model (MetUM). The observation period can be split into 5 regimes; the first two regimes had a large number of frontal systems, which were associated with deep cloud. During the remainder of the campaign a layer of low-level cloud occurred, typical of central Arctic summer conditions, along with two periods of greatly reduced cloud cover. The short-range operational NWP forecasts could not accurately reproduce the observed variations in near-surface temperature. A major source of this error was found to be the temperature-dependant surface albedo parameterisation scheme. The model reproduced the low-level cloud layer, though it was too thin, too shallow, and in a boundary-layer that was too frequently well-mixed. The model was also unable to reproduce the observed periods of reduced cloud cover, which were associated with very low cloud condensation nuclei (CCN) concentrations (< 1 cm(-3)). As with most global NWP models, the MetUM does not have a prognostic aerosol/cloud scheme but uses a constant CCN concentration of 100 cm(-3) over all marine environments. It is therefore unable to represent the low CCN number concentrations and the rapid variations in concentration frequently observed in the central Arctic during late summer. Experiments with a single-column model configuration of the MetUM show that reducing model CCN number concentrations to observed values reduces the amount of cloud, increases the near-surface stability, and improves the representation of both the surface radiation fluxes and the surface temperature. The model is shown to be sensitive to CCN only when number concentrations are less than 10-20 cm(-3).
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| 2. |
- Birch, Cathryn, et al.
(författare)
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The performance of a global and mesoscale model over the central Arctic Ocean during the summer melt season
- 2009
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Ingår i: Journal of Geophysical Research : Atmospheres. ; 114, s. D13104-
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Tidskriftsartikel (refereegranskat)abstract
- Measurements of turbulent fluxes, clouds, radiation, and profiles of meanmeteorological parameters, obtained over an ice floe in the central Arctic Ocean during theArctic Ocean Experiment 2001, are used to evaluate the performance of U.K. Met OfficeUnified Model (MetUM) and Coupled Ocean/Atmosphere Mesoscale Prediction System(COAMPS) in the lower atmosphere during late summer. Both the latest version of theMetUM and the version operational in 2001 are used in the comparison to gain aninsight as to whether updates to the model have improved its performance over the Arcticregion. As with previous model evaluations over the Arctic, the pressure, humidity,and wind fields are satisfactorily represented in all three models. The older version of theMetUM underpredicts the occurrence of low-level Arctic clouds, and the liquid and icecloud water partitioning is inaccurate compared to observations made during SHEBA.In the newer version, simulated ice and liquid water paths are improved, but theoccurrence of low-level clouds are overpredicted. Both versions overestimate the amountof radiative heat absorbed at the surface, leading to a significant feedback of errorsinvolving the surface albedo, which causes a large positive bias the surface temperature.Cloud forcing in COAMPS produces similar biases in the downwelling shortwave andlongwave radiation fluxes to those produced by UM(G25). The surface albedoparameterization is, however, more realistic, and thus, the total heat flux and surfacetemperature are more accurate for the majority of the observation period.
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| 3. |
- Bostrom, Mathias, et al.
(författare)
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Lifshitz interaction can promote ice growth at water-silica interfaces
- 2017
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 95:15
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Tidskriftsartikel (refereegranskat)abstract
- At air-water interfaces, the Lifshitz interaction by itself does not promote ice growth. On the contrary, we find that the Lifshitz force promotes the growth of an ice film, up to 1-8 nm thickness, near silica-water interfaces at the triple point of water. This is achieved in a system where the combined effect of the retardation and the zero frequency mode influences the short-range interactions at low temperatures, contrary to common understanding. Cancellation between the positive and negative contributions in the Lifshitz spectral function is reversed in silica with high porosity. Our results provide a model for how water freezes on glass and other surfaces.
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| 4. |
- Diaz de Grenu, Borja, et al.
(författare)
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Fluorescent Discrimination between Traces of Chemical Warfare Agents and Their Mimics
- 2014
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 136:11, s. 4125-4128
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Tidskriftsartikel (refereegranskat)abstract
- An array of fluorogenic probes is able to discriminate between nerve agents, sarin, soman, tabun, VX and their mimics, in water or organic solvent, by qualitative fluorescence patterns and quantitative multivariate analysis, thus making the system suitable for the in-the-field detection of traces of chemical warfare agents as well as to differentiate between the real nerve agents and other related compounds.
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| 5. |
- Erlöv, Tobias, et al.
(författare)
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Automatic Measurements of Diameter, Distension and Intima Media Thickness of the Aorta in Premature Rabbit Pups Using B-Mode Images.
- 2014
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Ingår i: Ultrasound in Medicine and Biology. - : Elsevier BV. - 0301-5629. ; 40:2, s. 371-377
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Tidskriftsartikel (refereegranskat)abstract
- To improve cardiovascular research, there is a growing need for arterial characterization in small animals. We developed a method, ARTIC (arterial characterization) for measuring lumen diameter, distension and intima media thickness (IMT). In this study ARTIC was used to automatically characterize the aorta of premature rabbit pups. Automatic measurements were compared with manual measurements, both performed by three observers. Diameter was 769 ± 140 μm (manual) and 766 ± 142 μm (automatic), distension was 35 ± 15 μm (manual) and 40 ± 12 μm (automatic) and IMT was 84 ± 11 μm (manual) and 88 ± 8 μm (automatic) (mean ± standard deviation). The variation in the measured diameter, distension and IMT ranged from 1.1% to 26.0% (manual) and from 1.0% to 9.0% (automatic). The intra-class correlation coefficient ranged from 33.0% to 99.3% (manual) and from 76.9% to 99.6% (automatic). The evaluation revealed that it is feasible to use ARTIC on B-mode images of arteries with small dimensions, which makes it a useful tool for arterial characterization in small animals.
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| 6. |
- Holmgren, Erik, et al.
(författare)
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Effects of asymmetry in strongly coupled spin vortex pairs
- 2019
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Ingår i: Journal of Physics D. - : IOP PUBLISHING LTD. - 0022-3727 .- 1361-6463. ; 52:10
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Tidskriftsartikel (refereegranskat)abstract
- Effects of magnetic asymmetry on strongly coupled spin-vortex pairs with parallel core polarization and antiparallel chirality in synthetic nanomagnets are investigated. This includes vortex-core length asymmetry, biasing field asymmetry, and pinning of one of the two vortex cores. Our experimental observations as well as analytical and micromagnetic modeling show how magnetic asymmetry can be used to differentiate magneto-resistively otherwise degenerate multiple stable states of a vortex pair. These results expand the knowledge base for spin vortex arrays in nanostructures and should be useful in light of the recent proposals on coding information into multiple topological spin states, such as single and multiple vortex core/chirality states.
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| 7. |
- Holmgren, Erik, et al.
(författare)
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Transient dynamics of strongly coupled spin vortex pairs : Effects of anharmonicity and resonant excitation on inertial switching
- 2018
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Ingår i: Applied Physics Letters. - : AMER INST PHYSICS. - 0003-6951 .- 1077-3118. ; 112:19
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Tidskriftsartikel (refereegranskat)abstract
- Spin vortices in magnetic nanopillars are used as GHz oscillators, with frequency however essentially fixed in fabrication. We demonstrate a model system of a two-vortex nanopillar, in which the resonance frequency can be changed by an order of magnitude, without using high dc magnetic fields. The effect is due to switching between the two stable states of the vortex pair, and we show that it can be done with low-amplitude fields of sub-ns duration. We detail the relevant vortex-core dynamics and explain how field anharmonicity and phase control can be used to enhance the performance.
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| 8. |
- Kulyk, Mykola, et al.
(författare)
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Magnetocaloric effect in multilayers studied by membrane-based calorimetry
- 2022
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 56:2, s. 025002-025002
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Tidskriftsartikel (refereegranskat)abstract
- We study magnetic multilayers, incorporating dilute ferromagnetic spacers between strongly-ferromagnetic layers exhibiting a proximity-enhanced magnetocaloric effect (MCE). Using magnetometry and direct measurements of the adiabatic temperature change based on a nanomembrane-calorimetry, we find that the MCE in the studied multilayer is indeed enhanced compared to that in the bulk spacer material. We develop a phenomenological numerical model of the studied trilayer and find that a long-range exchange interaction through the weakly-ferromagnetic spacer is required to adequately describe the magnetic and magnetocaloric properties of the system.
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| 9. |
- Li, Yang, et al.
(författare)
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Premelting and formation of ice due to Casimir-Lifshitz interactions : Impact of improved parameterization for materials
- 2022
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 105:1
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Tidskriftsartikel (refereegranskat)abstract
- Recently, the premelting and formation of ice due to the Casimir-Lifshitz interaction, proposed in early 1990s by Elbaum and Schick [Phys. Rev. Lett. 66, 1713 (1991)], have been generalized to diverse practical scenarios, yielding novel physical intuitions and possibilities of application for those phenomena. The properties of materials, in particular, the electrical permittivity and permeability, exert significant influence on the Casimir-Lifshitz energies and forces and hence on the corresponding premelting and formation of ice. To address these influences in detail and explore the resulting physics, here we revisit and extend the analyses of previous work with both the dielectric data utilized there and the latest dielectric functions for ice and cold water. For the four-layer cases considered by some of us, the existence of stable configurations depending on the initial conditions has been confirmed, and different types of stability corresponding to minima of the Casimir-Lifshitz free energy are demonstrated. As the new dielectric functions for ice and cold water deviate considerably from those used by Elbaum and Schick, their vital impact on three- and four-layer configurations is therefore being reconsidered.
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| 10. |
- Milton, Freja, et al.
(författare)
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Zinks spridning i miljön - En litteraturstudie
- 2018
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Zinc is one of our most common and most occurring metals. The metal is very useful and is used to prevent corrosion. Zinc is toxic for water living organisms when it occurs in concentrations over 20 μg/l. The metal affects the aquatic organism’s reproduction, survival and growth negatively. It is especially young individuals and embryos who will be affected by enhanced concentrations of zinc. The toxicity for zinc is determined by its bioavailability and is affected by its metal form, pH, redox ratio, DOC etc.The largest emissions of zinc occur to water followed by emissions to air. Within both categories diffuse emission is most dominated. The biggest zinc emission source is leakages from wooded ground followed by atmospheric deposition on the water surface. Industries is the greatest point source. The leakage from wooded ground is derived from atmospheric deposition of zinc.This report has chosen to focus and examine three types of human activities who causes zinc emissions. The activities which has been chosen for more extensive studies are artificial turfs with rubber granulates, traffic related emissions and emissions from goods. The traffic causes zinc emissions around the roads and the pollutant is usually not spread far from the road. Locally high levels of zinc along the roadside can therefore occur. Galvanized goods are believed to be a major secondary emission source even in places other than the traffic environment.Negative effects on aquatic or soil environment due to enhanced concentrations of zinc in Sweden is considered low. Generally, the chemical status in surface water in watercourses are good. Despite this, the risk of environment impact due to zinc should not be underestimated. Zinc have been accumulated in the soil for a long time. If the soil or sediments characteristics changes it could lead to devastating effects on nearby recipients.
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