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- Lutzenkirchen, J., et al.
(författare)
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The surface chemistry of sapphire-c: A literature review and a study on various factors influencing its IEP
- 2018
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686 .- 1873-3727. ; 251, s. 1-25
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Forskningsöversikt (refereegranskat)abstract
- A wide range of isoelectric points (IEPs) has been reported in the literature for sapphire-c (alpha-alumina), also referred to as basal plane, (001) or (0001), single crystals. Interestingly, the available data suggest that the variation of IEPs is comparable to the range of IEPs encountered for particles, although single crystals should be much better defined in terms of surface structure. One explanation for the range of IEPs might be the obvious danger of contaminating the small surface areas of single crystal samples while exposing them to comparatively large solution reservoirs. Literature suggests that factors like origin of the sample, sample treatment or the method of investigation all have an influence on the surfaces and it is difficult to clearly separate the respective, individual effects. In the present study, we investigate cause-effect relationships to better understand the individual effects. The reference IEP of our samples is between 4 and 4.5. High temperature treatment tends to decrease the IEP of sapphire-c as does UV treatment. Increasing the initial miscut (i.e. the divergence from the expected orientation of the crystal) tends to increase the IEP as does plasma cleaning, which can be understood assuming that the surfaces have become less hydrophobic due to the presence of more and/or larger steps with increasing miscut or due to amorphisation of the surface caused by plasma cleaning. Pre-treatment at very high pH caused an increase in the IEP. Surface treatments that led to IEPs different from the stable value of reference samples typically resulted in surfaces that were strongly affected by subsequent exposure to water. The streaming potential data appear to relax to the reference sample behavior after a period of time of water exposure. Combination of the zeta potential measurements with AFM investigations support the idea that atomically smooth surfaces exhibit lower IEPs, while rougher surfaces (roughness on the order of nanometers) result in higher IEPs compared to reference samples. Two supplementary investigations resulted in either surprising or ambiguous results. On very rough surfaces (roughness on the order of micrometers) the IEP lowered compared to the reference sample with nanometer-scale roughness and transient behavior of the rough surfaces was observed. Furthermore, differences in the IEP as obtained from streaming potential and static colloid adhesion measurements may suggest that hydrodynamics play a role in streaming potential experiments. We finally relate surface diffraction data from previous studies to possible interpretations of our electroldnetic data to corroborate the presence of a water film that can explain the low IEP. Calculations show that the surface diffraction data are in line with the presence of a water film, however, they do not allow to unambiguously resolve critical features of this film which might explain the observed surface chemical characteristics like the dangling OH-bond reported in sum frequency generation studies. A broad literature review on properties of related surfaces shows that the presence of such water films could in many cases affect the interfacial properties. Persistence or not of the water film can be crucial. The presence of the water film can in principle affect important processes like ice-nucleation, wetting behavior, electric charging, etc. (C) 2017 Elsevier B.V. All rights reserved.
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- Wallentin, Lars, et al.
(författare)
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Efficacy and safety of apixaban compared with warfarin at different levels of predicted international normalized ratio control for stroke prevention in atrial fibrillation
- 2013
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Ingår i: Circulation. - 0009-7322 .- 1524-4539. ; 127:22, s. 2166-2176
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundIn the Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation (ARISTOTLE) trial, apixaban compared with warfarin reduced stroke and systemic embolism, major bleeding, and mortality. We evaluated treatment effects in relation to 2 predictions of time in therapeutic range (TTR).Methods and ResultsThe trial randomized 18 201 patients with atrial fibrillation to apixaban 5 mg twice daily or warfarin for at least 12 months. For each patient, a center average TTR was estimated with the use of a linear mixed model on the basis of the real TTRs in its warfarin-treated patients, with a fixed effect for country and random effect for center. For each patient, an individual TTR was also predicted with the use of a linear mixed effects model including patient characteristics as well. Median center average TTR was 66% (interquartile limits, 61% and 71%). Rates of stroke or systemic embolism, major bleeding, and mortality were consistently lower with apixaban than with warfarin across center average TTR and individual TTR quartiles. In the lowest and highest center average TTR quartiles, hazard ratios for stroke or systemic embolism were 0.73 (95% confidence interval [CI], 0.53–1.00) and 0.88 (95% CI, 0.57–1.35) (Pinteraction=0.078), for mortality were 0.91 (95% CI, 0.74–1.13) and 0.91 (95% CI, 0.71–1.16) (Pinteraction=0.34), and for major bleeding were 0.50 (95% CI, 0.36–0.70) and 0.75 (95% CI, 0.58–0.97) (Pinteraction=0.095), respectively. Similar results were seen for quartiles of individual TTR.ConclusionsThe benefits of apixaban compared with warfarin for stroke or systemic embolism, bleeding, and mortality appear similar across the range of centers’ and patients’ predicted quality of international normalized ratio control.Clinical Trial RegistrationURL: http://www.clinicaltrials.gov. Unique identifier: NCT00412984.
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- Welling, D. T., et al.
(författare)
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Recommendations for Next-Generation Ground Magnetic Perturbation Validation
- 2018
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Ingår i: Space Weather. - 1542-7390. ; 16:12, s. 1912-1920
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Tidskriftsartikel (refereegranskat)abstract
- Data-model validation of ground magnetic perturbation forecasts, specifically of the time rate of change of surface magnetic field, dB/dt, is a critical task for model development and for mitigation of geomagnetically induced current effects. While a current, community-accepted standard for dB/dt validation exists (Pulkkinen et al., 2013), it has several limitations that prevent more complete understanding of model capability. This work presents recommendations from the International Forum for Space Weather Capabilities Assessment Ground Magnetic Perturbation Working Team for creating a next-generation validation suite. Four recommendations are made to address the existing suite: greatly expand the number of ground observatories used, expand the number of events included in the suite from six to eight, generate metrics as a function of magnetic local time, and generate metrics as a function of activity type. For each of these, implementation details are explored. Limitations and future considerations are also discussed.
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- Ågren, Karin, et al.
(författare)
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Detection of currents and associated electric fields in Titan's ionosphere from Cassini data
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 116:4, s. A04313-
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Tidskriftsartikel (refereegranskat)abstract
- We present observations from three Cassini flybys of Titan using data from the radio and plasma wave science, magnetometer and plasma spectrometer instruments. We combine magnetic field and cold plasma measurements with calculated conductivities and conclude that there are currents of the order of 10 to 100 nA m (2) flowing in the ionosphere of Titan. The currents below the exobase (similar to 1400 km) are principally field parallel and Hall in nature, while the Pedersen current is negligible in comparison. Associated with the currents are perpendicular electric fields ranging from 0.5 to 3 mu V m (1).
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