| 1. |
- Donadini, Fabio, et al.
(författare)
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Holocene geomagnetic paleointensities: A blind test of absolute paleointensity techniques and materials
- 2007
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Ingår i: Physics of the Earth and Planetary Interiors. - : Elsevier BV. - 0031-9201. ; 161:1-2, s. 19-35
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Tidskriftsartikel (refereegranskat)abstract
- Through several decades of research, absolute paleointensity estimates have been obtained from a wide range of rocks with varying ages, covering the last 3.45 Ga years. These paleointensity data are crucial to study the past geodynamo and the geological evolution of the Earth's deep interior. However, paleointensity data are often difficult to interpret, and on-going discussions concerning the past geomagnetic field invariably focus on data reliability, and which kind of material, and method, is best suited for absolute paleointensity experiments. In this paper we blind test paleointensity methods and materials using the new GEOMAGIA50 database that contains all available experimental information about published paleointensity estimates covering the last 50,000 years. Our analysis is built on simple comparisons of results obtained from different materials, and methodologies, to investigate their possible influence on the paleointensity estimate. We also study the effect of various numbers of samples, and dating accuracies. We focus on paleointensity estimates from the last 12,000 years, which includes the Holocene epoch. The advantage of this period is that data have been obtained from a wide array of methodological techniques as well as a wide selection of materials, including both natural ones (e.g. lava flows) and various archaeological artifacts. Our main observations are (i) that well-fired archaeological materials (bricks, potteries, clays, and ceramics) show the best correlation with the rest of the dataset, which we interpret to suggest that these data are the most reliable, and (ii) although paleointensity data obtained from lava flows are slightly more scattered, there is no evidence for paleointensity data from lavas to be significantly lower or higher than other data, irrespective of the methodology. (c) 2007 Elsevier B.V. All rights reserved.
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| 2. |
- Brown, Maxwell C., et al.
(författare)
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GEOMAGIA50.v3: 1. general structure and modifications to the archeological and volcanic database Recent advances in environmental magnetism and paleomagnetism
- 2015
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Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1343-8832 .- 1880-5981. ; 67:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: GEOMAGIA50.v3 is a comprehensive online database providing access to published paleomagnetic, rock magnetic, and chronological data from a variety of materials that record Earth's magnetic field over the past 50 ka. Findings: Since its original release in 2006, the structure and function of the database have been updated and a significant number of data have been added. Notable modifications are the following: (1) the inclusion of additional intensity, directional and metadata from archeological and volcanic materials and an improved documentation of radiocarbon dates; (2) a new data model to accommodate paleomagnetic, rock magnetic, and chronological data from lake and marine sediments; (3) a refinement of the geographic constraints in the archeomagnetic/volcanic query allowing selection of particular locations; (4) more flexible methodological and statistical constraints in the archeomagnetic/volcanic query; (5) the calculation of predictions of the Holocene geomagnetic field from a series of time varying global field models; (6) searchable reference lists; and (7) an updated web interface. This paper describes general modifications to the database and specific aspects of the archeomagnetic and volcanic database. The reader is referred to a companion publication for a description of the sediment database. Conclusions: The archeomagnetic and volcanic part of GEOMAGIA50.v3 currently contains 14,645 data (declination, inclination, and paleointensity) from 461 studies published between 1959 and 2014. We review the paleomagnetic methods used to obtain these data and discuss applications of the data within the database. The database continues to expand as legacy data are added and new studies published. The web-based interface can be found at http://geomagia.gfz-potsdam.de.
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| 3. |
- Brown, Maxwell C., et al.
(författare)
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GEOMAGIA50.v3: 2. A new paleomagnetic database for lake and marine sediments
- 2015
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Ingår i: Earth, Planets and Space. - : Springer Science and Business Media LLC. - 1343-8832 .- 1880-5981. ; 67:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: GEOMAGIA50.v3 for sediments is a comprehensive online database providing access to published paleomagnetic, rock magnetic, and chronological data obtained from lake and marine sediments deposited over the past 50 ka. Its objective is to catalogue data that will improve our understanding of changes in the geomagnetic field, physical environments, and climate. Findings: GEOMAGIA50.v3 for sediments builds upon the structure of the pre-existing GEOMAGIA50 database for magnetic data from archeological and volcanic materials. A strong emphasis has been placed on the storage of geochronological data, and it is the first magnetic archive that includes comprehensive radiocarbon age data from sediments. The database will be updated as new sediment data become available. Conclusions: The web-based interface for the sediment database is located at http://geomagia.gfz-potsdam.de/geomagiav3/SDquery.php. This paper is a companion to Brown et al. (Earth Planets Space doi:10.1186/s40623-015-0232-0, 2015) and describes the data types, structure, and functionality of the sediment database.
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| 4. |
- Falk, John, et al.
(författare)
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Immersion freezing ability of freshly emitted soot with various physico-chemical characteristics
- 2021
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Ingår i: Atmosphere. - : MDPI AG. - 2073-4433. ; 12:9
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Tidskriftsartikel (refereegranskat)abstract
- The immersion freezing ability of soot particles has in previous studies been reported in the range of low/insignificant to very high. The aims of this study were to: (i) perform detailed physico-chemical characterisation of freshly produced soot particles with very different properties, (ii) investigate the immersion freezing ability of the same particles, and (iii) investigate the potential links between physico-chemical particle properties and ice-activity. A miniCAST soot generator was used to produce eight different soot samples representing a wide range of physico-chemical properties. A continuous flow diffusion chamber was used to study each sample online in immersion mode over the temperature (T) range from −41 to −32◦C, at a supersaturation of about 10% with respect to liquid water. All samples exhibited low to no heterogeneous immersion freezing. The most active sample reached ice-activated fractions (AF) of 10−3 and 10−4 at temperatures of 1.7 and 1.9 K, respectively, above the homogeneous freezing temperature. The samples were characterized online with respect to a wide range of physico-chemical properties including effective particle density, optical properties, particle surface oxidation and soot maturity. We did observe indications of increasing immersion freezing ice-activity with increasing effective particle density and increasing particulate PAH fraction . Hence, those properties, or other properties co-varying with those, could potentially enhance the immersion freezing ice-activity of the studied soot particle types. However, we found no significant correlation between the physico-chemical properties and the observed ice-nucleating ability when the particle ensemble was extended to include previously published results including more ice-active biomass combustion soot particles. We conclude that it does not appear possible in general and in any straightforward way to link observed soot particle physico-chemical properties to the ice-nucleating ability using the online instrumentation included in this study. Furthermore, our observations support that freshly produced soot particles with a wide range of physico-chemical properties have low to insignificant immersion freezing ice-nucleating ability.
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| 5. |
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| 6. |
- Kaartinen, Tanja, et al.
(författare)
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Low interleukin-2 concentration favors generation of early memory T cells over effector phenotypes during chimeric antigen receptor T-cell expansion
- 2017
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Ingår i: Cytotherapy. - : ELSEVIER SCI LTD. - 1465-3249 .- 1477-2566. ; 19:6, s. 689-702
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Tidskriftsartikel (refereegranskat)abstract
- Background. Adoptive T-cell therapy offers new options for cancer treatment. Clinical results suggest that T-cell persistence, depending on T-cell memory, improves efficacy. The use of interleukin (IL)-2 for in vitro T-cell expansion is not straightforward because it drives effector T-cell differentiation but does not promote the formation of T-cell memory. We have developed a cost-effective expansion protocol for chimeric antigen receptor (CAR) T cells with an early memory phenotype.Methods. Lymphocytes were transduced with third-generation lentiviral vectors and expanded using CD3/CD28 microbeads. The effects of altering the IL-2 supplementation (0-300 IU/mL) and length of expansion (10-20 days) on the phenotype of the T-cell products were analyzed.Results. High IL-2 levels led to a decrease in overall generation of early memory T cells by both decreasing central memory T cells and augmenting effectors. T memory stem cells (T-SCM, CD95(+)CD45RO(-)CD45RA(+)CD27(+)) were present variably during T-cell expansion. However, their presence was not IL-2 dependent but was linked to expansion kinetics. CD19-CART cells generated in these conditions displayed in vitro antileukemic activity. In summary, production of CART cells without any cytokine supplementation yielded the highest proportion of early memory T cells, provided a 10 fold cell expansion and the cells were functionally potent.Discussion. The number of early memory T cells in a T-cell preparation can be increased by simply reducing the amount of IL-2 and limiting the length of T-cell expansion, providing cells with potentially higher in vivo performance. These findings are significant for robust and cost:effective T-cell manufacturing.
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| 7. |
- Knudsen, Mads Faurschou, et al.
(författare)
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Variations in the geomagnetic dipole moment during the Holocene and the past 50 kyr
- 2008
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 1385-013X .- 0012-821X. ; 272:1-2, s. 319-329
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Tidskriftsartikel (refereegranskat)abstract
- All absolute paleointensity data published in peer-reviewed journals were recently compiled in the GEOMACIA50 database. Based on the information in GEOMAGIA50, we reconstruct variations in the geomagnetic dipole moment over the past 50 kyr, with a focus on the Holocene period. A running-window approach is used to determine the axial dipole moment that provides the optimal least-squares fit to the paleointensity data, whereas associated error estimates are constrained using a bootstrap procedure. We Subsequently compare the reconstruction from this study with previous reconstructions of the geomagnetic dipole moment, including those based on cosmogenic radionuclides (Be-10 and C-14). This comparison generally lends Support to the axial dipole moments obtained in this study. Our reconstruction shows that the evolution of the dipole moment was highly dynamic, and the recently observed rates of change (5% per century) do not appear unique. We observe no apparent link between the occurrence of archeomagnetic jerks and changes in the geomagnetic dipole moment, Suggesting that archeomagnetic jerks most likely represent drastic changes in the orientation of the geomagnetic dipole axis or periods characterized by large secular variation of the non-dipole field. This Study also shows that the Holocene geomagnetic dipole moment was high compared to that of the preceding similar to 40 kyr, and that similar to 4.10(22) Am-2 appears to represent a critical threshold below which geomagnetic excursions and reversals occur. (C) 2008 Elsevier B.V. All rights reserved.
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| 8. |
- Korhonen, Kimmo, et al.
(författare)
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Ice-nucleating ability of particulate emissions from solid-biomass-fired cookstoves : An experimental study
- 2020
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:8, s. 4951-4968
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Tidskriftsartikel (refereegranskat)abstract
- This research was part of the Salutary Umeå Study of Aerosols in Biomass Cookstove Emissions (SUSTAINE) laboratory experiment campaign. We studied ice-nucleating abilities of particulate emissions from solid-fuel-burning cookstoves, using a portable ice nuclei counter, Spectrometer Ice Nuclei (SPIN). These emissions were generated from two traditional cookstove types commonly used for household cooking in sub-Saharan Africa and two advanced gasifier stoves under research to promote sustainable development alternatives. The solid fuels studied included biomass from two different African tree species, Swedish softwood and agricultural residue products relevant to the region. Measurements were performed with a modified version of the standard water boiling test on polydisperse samples from flue gas during burning and size-selected accumulation mode soot particles from a 15 m3 aerosol-storage chamber. The studied soot particle sizes in nanometers were 250, 260, 300, 350, 400, 450 and 500. From this chamber, the particles were introduced to water-supersaturated freezing conditions (-32 to-43 °C) in the SPIN. Accumulation mode soot particles generally produced an ice-activated fraction of 10-3 in temperatures 1-1.5 °C higher than that required for homogeneous freezing at fixed RHw D 115 %. In five special experiments, the combustion performance of one cookstove was intentionally modified. Two of these exhibited a significant increase in the icenucleating ability of the particles, resulting in a 10-3 ice activation at temperatures up to 5.9 °C higher than homogeneous freezing and the observed increased ice-nucleating ability. We investigated six different physico-chemical properties of the emission particles but found no clear correlation between them and increasing ice-nucleating ability. We conclude that the freshly emitted combustion aerosols form ice via immersion and condensation freezing at temperatures only moderately above homogeneous freezing conditions.
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| 9. |
- Korhonen, Kimmo, et al.
(författare)
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Particle emissions from a modern heavy-duty diesel engine as ice nuclei in immersion freezing mode: a laboratory study on fossil and renewable fuels
- 2022
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7324. ; 22:23, s. 1615-1631
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Tidskriftsartikel (refereegranskat)abstract
- We studied ice-nucleating abilities of particulate emissions from a modern heavy-duty diesel engine using three different types of fuel. The polydisperse particle emissions were sampled during engine operation and introduced to a continuous-flow diffusion chamber (CFDC) instrument at a constant relative humidity RHwater=110 %, while the temperature was ramped between −43 and −32 ∘C (T scan). The tested fuels were EN 590 compliant low-sulfur fossil diesel, hydrotreated vegetable oil (HVO), and rapeseed methyl ester (RME); all were tested without blending. Sampling was carried out at different stages in the engine exhaust aftertreatment system, with and without simulated atmospheric processing using an oxidation flow reactor. In addition to ice nucleation experiments, we used supportive instrumentation to characterize the emitted particles for their physicochemical properties and presented six parameters. We found that the studied emissions contained no significant concentrations of ice-nucleating particles likely to be of atmospheric relevance. The substitution of fossil diesel with renewable fuels, using different emission aftertreatment systems such as a diesel oxidation catalyst, and photochemical aging of total exhaust had only minor effect on their ice-nucleating abilities.
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| 10. |
- Kristensen, Thomas Bjerring, et al.
(författare)
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Properties and emission factors of cloud condensation nuclei from biomass cookstoves - Observations of a strong dependency on potassium content in the fuel
- 2021
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Ingår i: Atmospheric Chemistry And Physics. - : Nicolaus Copernicus University Press. - 1680-7316 .- 1680-7324. ; 21:10, s. 8023-8044
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Tidskriftsartikel (refereegranskat)abstract
- Residential biomass combustion is a significant source of aerosol particles on regional and global scales influencing climate and human health. The main objective of the current study was to investigate the properties of cloud condensation nuclei (CCN) emitted from biomass burning of solid fuels in different cookstoves mostly of relevance to sub- Saharan east Africa.The traditional three-stone fire and a rocket stove were used for combustion of wood logs of Sesbania and Casuarina with birch used as a reference. A natural draft and a forced-draft pellet stove were used for combustion of pelletised Sesbania and pelletised Swedish softwood alone or in mixtures with pelletised coffee husk, rice husk or water hyacinth. The CCN activity and the effective density were measured for particles with mobility diameters of v65, v100 and v200 nm, respectively, and occasionally for 350 nm particles. Particle number size distributions were measured online with a fast particle analyser. The chemical composition of the fuel ash was measured by application of standard protocols.The average particle number size distributions were by number typically dominated by an ultrafine mode, and in most cases a soot mode was centred around a mobility diameter of v150 nm. The CCN activities decreased with increasing particle size for all experiments and ranged in terms of the hygroscopicity parameter, from v0:1 to v0:8 for the ultrafine mode and from v0:001 to v0:15 for the soot mode. The CCN activity of the ultrafine mode increased (i) with increasing combustion temperature for a given fuel, and (ii) it typically increased with increasing potassium concentration in the investigated fuels. The primary CCN and the estimated particulate matter (PM) emission factors were typically found to increase significantly with increasing potassium concentration in the fuel for a given stove. In order to link CCN emission factors to PM emission factors, knowledge about stove technology, stove operation and the inorganic fuel ash composition is needed. This complicates the use of ambient PM levels alone for estimation of CCN concentrations in regions dominated by biomass combustion aerosol, with the relation turning even more complex when accounting for atmospheric ageing of the aerosol.
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