| 1. |
- Fanourgakis, George S., et al.
(författare)
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Evaluation of global simulations of aerosol particle and cloud condensation nuclei number, with implications for cloud droplet formation
- 2019
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 19:13, s. 8591-8617
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Tidskriftsartikel (refereegranskat)abstract
- A total of 16 global chemistry transport models and general circulation models have participated in this study; 14 models have been evaluated with regard to their ability to reproduce the near-surface observed number concentration of aerosol particles and cloud condensation nuclei (CCN), as well as derived cloud droplet number concentration (CDNC). Model results for the period 2011-2015 are compared with aerosol measurements (aerosol particle number, CCN and aerosol particle composition in the submicron fraction) from nine surface stations located in Europe and Japan. The evaluation focuses on the ability of models to simulate the average across time state in diverse environments and on the seasonal and short-term variability in the aerosol properties. There is no single model that systematically performs best across all environments represented by the observations. Models tend to underestimate the observed aerosol particle and CCN number concentrations, with average normalized mean bias (NMB) of all models and for all stations, where data are available, of -24% and -35% for particles with dry diameters >50 and >120nm, as well as -36% and -34% for CCN at supersaturations of 0.2% and 1.0%, respectively. However, they seem to behave differently for particles activating at very low supersaturations (<0.1%) than at higher ones. A total of 15 models have been used to produce ensemble annual median distributions of relevant parameters. The model diversity (defined as the ratio of standard deviation to mean) is up to about 3 for simulated N3 (number concentration of particles with dry diameters larger than 3nm) and up to about 1 for simulated CCN in the extra-polar regions. A global mean reduction of a factor of about 2 is found in the model diversity for CCN at a supersaturation of 0.2% (CCN0.2) compared to that for N3, maximizing over regions where new particle formation is important. An additional model has been used to investigate potential causes of model diversity in CCN and bias compared to the observations by performing a perturbed parameter ensemble (PPE) accounting for uncertainties in 26 aerosol-related model input parameters. This PPE suggests that biogenic secondary organic aerosol formation and the hygroscopic properties of the organic material are likely to be the major sources of CCN uncertainty in summer, with dry deposition and cloud processing being dominant in winter. Models capture the relative amplitude of the seasonal variability of the aerosol particle number concentration for all studied particle sizes with available observations (dry diameters larger than 50, 80 and 120nm). The short-term persistence time (on the order of a few days) of CCN concentrations, which is a measure of aerosol dynamic behavior in the models, is underestimated on average by the models by 40% during winter and 20% in summer. In contrast to the large spread in simulated aerosol particle and CCN number concentrations, the CDNC derived from simulated CCN spectra is less diverse and in better agreement with CDNC estimates consistently derived from the observations (average NMB -13% and -22% for updraft velocities 0.3 and 0.6ms-1, respectively). In addition, simulated CDNC is in slightly better agreement with observationally derived values at lower than at higher updraft velocities (index of agreement 0.64 vs. 0.65). The reduced spread of CDNC compared to that of CCN is attributed to the sublinear response of CDNC to aerosol particle number variations and the negative correlation between the sensitivities of CDNC to aerosol particle number concentration (Nd=Na) and to updraft velocity (Nd=w). Overall, we find that while CCN is controlled by both aerosol particle number and composition, CDNC is sensitive to CCN at low and moderate CCN concentrations and to the updraft velocity when CCN levels are high. Discrepancies are found in sensitivities Nd=Na and Nd=w; models may be predisposed to be too "aerosol sensitive" or "aerosol insensitive" in aerosol-cloud-climate interaction studies, even if they may capture average droplet numbers well. This is a subtle but profound finding that only the sensitivities can clearly reveal and may explain intermodel biases on the aerosol indirect effect.
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| 2. |
- Brate, Jon, et al.
(författare)
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Unicellular Origin of the Animal MicroRNA Machinery
- 2018
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 28:20, s. 3288-
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Tidskriftsartikel (refereegranskat)abstract
- The emergence of multicellular animals was associated with an increase in phenotypic complexity and with the acquisition of spatial cell differentiation and embryonic development. Paradoxically, this phenotypic transition was not paralleled by major changes in the underlying developmental toolkit and regulatory networks. In fact, most of these systems are ancient, established already in the unicellular ancestors of animals [1-5]. In contrast, the Microprocessor protein machinery, which is essential for microRNA (miRNA) biogenesis in animals, as well as the miRNA genes themselves produced by this Microprocessor, have not been identified outside of the animal kingdom [6]. Hence, the Microprocessor, with the key proteins Pasha and Drosha, is regarded as an animal innovation [7-9]. Here, we challenge this evolutionary scenario by investigating unicellular sister lineages of animals through genomic and transcriptomic analyses. We identify in Ichthyosporea both Drosha and Pasha (DGCR8 in vertebrates), indicating that the Microprocessor complex evolved long before the last common ancestor of animals, consistent with a pre-metazoan origin of most of the animal developmental gene elements. Through small RNA sequencing, we also discovered expressed bona fide miRNA genes in several species of the ichthyosporeans harboring the Microprocessor. A deep, pre-metazoan origin of the Microprocessor and miRNAs comply with a view that the origin of multicellular animals was not directly linked to the innovation of these key regulatory components.
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| 3. |
- Butenko, Melinka A., et al.
(författare)
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Inflorescence deficient in abscission controls floral organ abscission in Arabidopsis and identifies a novel family of putative Ligands in Plants
- 2003
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Ingår i: The Plant Cell. - : American Society of Plant Biologists. - 1040-4651 .- 1532-298X. ; 15:10, s. 2296-2307
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Tidskriftsartikel (refereegranskat)abstract
- Abscission is an active process that enables plants to shed unwanted organs. Because the purpose of the flower is to facilitate pollination, it often is abscised after fertilization. We have identified an Arabidopsis ethylene-sensitive mutant, inflorescence deficient in abscission (ida), in which floral organs remain attached to the plant body after the shedding of mature seeds, even though a floral abscission zone develops. The IDA gene, positioned in the genomic DNA flanking the single T-DNA present in the ida line, was identified by complementation. The gene encodes a small protein with an N-terminal signal peptide, suggesting that the IDA protein is the ligand of an unknown receptor involved in the developmental control of floral abscission. We have identified Arabidopsis genes, and cDNAs from a variety of plant species, that encode similar proteins, which are distinct from known ligands. IDA and the IDA-like proteins may represent a new class of ligands in plants
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| 4. |
- Grini, S., et al.
(författare)
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Dynamic Impurity Redistributions in Kesterite Absorbers
- 2020
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951.
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Tidskriftsartikel (refereegranskat)abstract
- Cu2ZnSn(S,Se)4 is a promising nontoxic earth-abundant solar cell absorber. To optimize the thin films for solar cell device performance, postdeposition treatments at temperatures below the crystallization temperature are normally performed, which alter the surface and bulk properties. The polycrystalline thin films contain relatively high concentrations of impurities, such as sodium, oxygen and hydrogen. During the treatments, these impurities migrate and likely agglomerate at lattice defects or interfaces. Herein, impurity redistribution after air annealing for temperatures up to 200 °C and short heavy water treatments are studied. In addition, nonuniformities of the sodium distribution on a nanometer and micrometer scale are characterized by atom probe tomography and secondary ion mass spectrometry, respectively. Sodium and oxygen correlate to a greater extent after heat treatments, supporting strong binding between the two impurities. Redistributions of these impurities occur even at room temperature over longer time periods. Heavy water treatments confirm out-diffusion of sodium with more incorporation of oxygen and hydrogen. It is observed that the increased hydrogen content does not originate from the heavy water. The existence of an “ice-like” layer on top of the Cu2ZnSnS4 layer is proposed.
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| 5. |
- Grini, Sigbjörn, et al.
(författare)
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Strong Interplay between Sodium and Oxygen in Kesterite Absorbers : Complex Formation, Incorporation, and Tailoring Depth Distributions
- 2019
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Ingår i: Advanced Energy Materials. - : WILEY-V C H VERLAG GMBH. - 1614-6832 .- 1614-6840. ; 9:27
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Tidskriftsartikel (refereegranskat)abstract
- Sodium and oxygen are prevalent impurities in kesterite solar cells. Both elements are known to strongly impact performance of the kesterite devices and can be connected to efficiency improvements seen after heat treatments. The sodium distribution in the kesterite absorber is commonly reported, whereas the oxygen distribution has received less attention. Here, a direct relationship between sodium and oxygen in kesterite absorbers is established using secondary ion mass spectrometry and explained by defect analyses within the density functional theory. The calculations reveal a binding energy of 0.76 eV between the substitutional defects Na-Cu and O-S in the nearest neighbor configuration, indicating an abundance of Na Symbol of the Klingon Empire O complexes in kesterite absorbers at relevant temperatures. Oxygen incorporation is studied by introducing isotopic O-18 at different stages of the Cu2ZnSnS4/Mo/soda-lime glass baseline processing. It is observed that oxygen from the Mo back contact and contaminations during the sulfurization are primary contributors to the oxygen distribution. Indeed, unintentional oxygen incorporation leads to immobilization of sodium. This results in a strong correlation between sodium and oxygen, in excellent agreement with the theoretical calculations. Consequently, oxygen availability should be monitored to optimize postdeposition heat treatments to control impurities in kesterite absorbers and ultimately, the solar cell efficiency.
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| 6. |
- Pausata, Francesco S. R., et al.
(författare)
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High-latitude volcanic eruptions in the Norwegian Earth System Model : the effect of different initial conditions and of the ensemble size
- 2015
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Ingår i: Tellus. Series B, Chemical and physical meteorology. - : Stockholm University Press. - 0280-6509 .- 1600-0889. ; 67
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Tidskriftsartikel (refereegranskat)abstract
- Large volcanic eruptions have strong impacts on both atmospheric and ocean dynamics that can last for decades. Numerical models have attempted to reproduce the effects of major volcanic eruptions on climate; however, there are remarkable inter-model disagreements related to both short-term dynamical response to volcanic forcing and long-term oceanic evolution. The lack of robust simulated behaviour is related to various aspects from model formulation to simulated background internal variability to the eruption details. Here, we use the Norwegian Earth System Model version 1 to calculate interactively the volcanic aerosol loading resulting from SO2 emissions of the second largest high-latitude volcanic eruption in historical time (the Laki eruption of 1783). We use two different approaches commonly used interchangeably in the literature to generate ensembles. The ensembles start from different background initial states, and we show that the two approaches are not identical on short-time scales (<1 yr) in discerning the volcanic effects on climate, depending on the background initial state in which the simulated eruption occurred. Our results also show that volcanic eruptions alter surface climate variability (in general increasing it) when aerosols are allowed to realistically interact with circulation: Simulations with fixed volcanic aerosol show no significant change in surface climate variability. Our simulations also highlight that the change in climate variability is not a linear function of the amount of the volcanic aerosol injected. We then provide a tentative estimation of the ensemble size needed to discern a given volcanic signal on surface temperature from the natural internal variability on regional scale: At least 20-25 members are necessary to significantly detect seasonally averaged anomalies of 0.5 degrees C; however, when focusing on North America and in winter, a higher number of ensemble members (35-40) is necessary.
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| 7. |
- Ross, N., et al.
(författare)
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Cu2ZnSn(S,Se)4 Solar Cell Absorbers from Diffusion of Selenium into Annealed Cu2ZnSnS4 Absorbers
- 2016
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Ingår i: 2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC). - New York : IEEE. - 9781509027248 ; , s. 492-497
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Konferensbidrag (refereegranskat)abstract
- Small grain compound-sputtered Copper Zinc Tin Sulfide (CZTS) precursors and large grain recrystallized CZTS solar cell absorbers are annealed at sub-recrystallization temperatures in selenium atmosphere to promote selenium diffusion into the CZTS films. Grazing incidence x-ray diffraction and Raman spectroscopy show the presence of two distinct sulfide and mixed sulfide/selenide phases, with the selenide-like phase more prominent at the front surface of the absorber. Only a narrow range of sulfur-to-selenium ratios is observed in the sulfide/selenide phase. Secondary ion mass spectrometry profiles show a compositional sulfur-selenium gradient for samples annealed at 450 degrees C. Scanning electron microscopy with energy dispersive X-ray spectroscopy reveals that the compositional gradient is formed by a spatial distribution of sulfide/selenide grains, embedded in the remaining sulfide absorber. Sulfur-selenium gradients within single absorber grains are not observed, indicating that the mixed sulfide/selenide phase nucleates and grows in competition with the existing sulfide phase, rather than forming by replacement of anions within existing crystals. IV and EQE measurements of devices fabricated from the selenized absorbers support this conclusion.
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| 8. |
- Ross, N., et al.
(författare)
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Mixed sulfur and selenium annealing study of compound-sputtered bilayer Cu2ZnSnS4 / Cu2ZnSnSe4 precursors
- 2017
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Ingår i: 2017 IEEE 44Th Photovoltaic Specialist Conference (PVSC). - : IEEE. - 9781509056057 ; , s. 3269-3274
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Konferensbidrag (refereegranskat)abstract
- Copper zinc tin sulfide (CZTS) and copper zinc tin selenide (CZTSe) precursor films are compound co-sputtered from metal sulfide and selenide targets. A bilayer precursor consisting of a CZTS-only underlayer and CZTSe-only overlayer is also sputtered. These precursor films are annealed with varying ratios of elemental sulfur and selenium to promote the formation of recrystallized Cu2ZnSn(S, Se) 4 (CZTSSe) solar cell absorber layers with intermediate sulfur-to-selenium ratios Sr=[S]/([S]+[Se]). The films are characterized by scanning electron microscope (SEM) energy dispersive X-ray spectroscopy (EDX), secondary ion mass spectrometry (SIMS), and grazingincidence X-ray diffraction (GIXRD). Selenium-containing precursors produce absorber layers with rougher surfaces, leading to higher short-circuit currents Jsc for some annealing conditions. The Sr value of the crystallized absorber is independent of the ratio of sulfur to selenium in the precursor unless sulfur is deficient in the anneal. Sulfur-selenium distribution in bilayer precursors after mixed S/Se annealing is found to be uniform: neither a step nor significant sulfur-gradient remains. We relate the chalcogen distribution after annealing to the excess of chalcogen in the anneal, and discuss the consequences for back-grading of the band gap by sulfur-selenium variation. Both the thickness and Sr value of the Mo(S, Se) 2 back contact is found to be dependent on the sulfur-selenium ratio of the precursor, with CZTSe precursors producing thicker and more selenium rich back contact layers.
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| 9. |
- Ross, Nils, et al.
(författare)
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Practical limitations to selenium annealing of compound co-sputtered Cu2ZnSnS4 as a route to achieving sulfur-selenium graded solar cell absorbers
- 2017
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 623, s. 110-115
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Tidskriftsartikel (refereegranskat)abstract
- The suitability of selenium annealing as a technique to introduce energy band gap gradients via sulfur selenium substitution in Cu2ZnSnS4 (CZTS) films is evaluated. Compound co-sputtered CZTS precursors are annealed in selenium atmosphere at 425 degrees C, either as-deposited or after a short time sulfur pre-anneal. The films are investigated by Raman spectroscopy and X-ray diffractometry, and the spatial distribution of elemental species measured by secondary ion mass spectrometry and energy dispersive X-ray spectroscopy. Sulfur-selenium gradients are not achieved for the as-deposited precursor. Sulfur-selenium gradients are achieved in the early stages of annealing for pre-anneal samples, where Cu2ZnSn(S,Se)(4) (CZTSSe) formation is found to be correlated spatially with sodium distribution. These gradients are lost as the annealing progresses. Selenisation occurs by CZTSSe grain growth, rather than by direct substitution of selenium for sulfur. The spatial correlation of high sodium concentration with CZTSSe formation suggests that liquid phase sodium selenide facilitates selenium incorporation during recrystallisation, limiting the practicality of anion-grading of CZTSSe during the annealing step as a means of establishing a graded band gap.
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| 10. |
- Stangeland, Biljana, et al.
(författare)
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AtMBD8 is involved in control of flowering time in the C24 ecotype of Arabidopsis thaliana
- 2009
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Ingår i: Physiologia Plantarum. - : Blackwell Publishing. - 0031-9317 .- 1399-3054. ; 136:1, s. 110-126
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Tidskriftsartikel (refereegranskat)abstract
- The Arabidopsis thaliana accession C24 is a vernalization-responsive, moderately late flowering ecotype. We report that a mutation in AtMBD8, which encodes a protein with a putative Methyl-CpG-Binding Domain (MBD), in C24 background, results in a delay in flowering time during both long and short days. The atmbd8-1 mutant responded to vernalization as wild type (wt) plants. Consistent with a role in modulation of flowering time, an AtMBD8::GUS-reporter construct was expressed in the shoot meristem region and developing leaves. Full-genome transcriptional profiling revealed very few changes in gene expression between atmbd8-1 and wt plants. The expression level of FLC, the major repressor of transition to flowering, was unchanged in atmbd8-1, and in accordance with that, genes upstream of FLC were unaffected by the mutation. The expression level of CONSTANS, involved in photoperiodic control of flowering, was very similar in atmbd8-1 and wt plants. In contrast, the major promoters of flowering, FT, and SOC1, were both downregulated. As FT is a regulator of SOC1, we conclude that AtMBD8 is a novel promotor of flowering that acts upstream of FT in the C24 accession. In contrast to atmbd8-1, the Colombia (Col) SALK T-DNA insertion line, atmbd8-2, did not display a delayed transition to flowering. Transcriptional profiling revealed that a substantial number of genes were differentially expressed between C24 and Col wt seedlings. Several of these genes are also differentially expressed in late flowering mutants. We suggest that these differences contribute to the contrasting effect of a mutation in AtMBD8 in the two ecotypes.
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