| 1. |
- Anderson, Siwan, et al.
(författare)
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Political Selection in Local Elections: Evidence from Rural Uganda
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Political selection is crucial to the quality of governance. Yet our general knowledge of the individual characteristics that correlate with the political selection process is scant. Our paper contributes to this knowledge gap by collecting detailed data on the quality, perceptions, attitudes, and promises of all candidates involved in a recent local election in rural Uganda. Our context is unique - with two separate governing bodies for males and females. The paper demonstrates, that male and female political selection into these two parallel institutions share important similarities but also differ along several dimensions.
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| 2. |
- Björkman, Andrea, et al.
(författare)
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Aberrant recombination and repair during immunoglobulin class switching in BRCA1-deficient human B cells.
- 2015
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Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 112:7, s. 2157-2162
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Tidskriftsartikel (refereegranskat)abstract
- Breast cancer type 1 susceptibility protein (BRCA1) has a multitude of functions that contribute to genome integrity and tumor suppression. Its participation in the repair of DNA double-strand breaks (DSBs) during homologous recombination (HR) is well recognized, whereas its involvement in the second major DSB repair pathway, nonhomologous end-joining (NHEJ), remains controversial. Here we have studied the role of BRCA1 in the repair of DSBs in switch (S) regions during immunoglobulin class switch recombination, a physiological, deletion/recombination process that relies on the classical NHEJ machinery. A shift to the use of microhomology-based, alternative end-joining (A-EJ) and increased frequencies of intra-S region deletions as well as insertions of inverted S sequences were observed at the recombination junctions amplified from BRCA1-deficient human B cells. Furthermore, increased use of long microhomologies was found at recombination junctions derived from E3 ubiquitin-protein ligase RNF168-deficient, Fanconi anemia group J protein (FACJ, BRIP1)-deficient, or DNA endonuclease RBBP8 (CtIP)-compromised cells, whereas an increased frequency of S-region inversions was observed in breast cancer type 2 susceptibility protein (BRCA2)-deficient cells. Thus, BRCA1, together with its interaction partners, seems to play an important role in repairing DSBs generated during class switch recombination by promoting the classical NHEJ pathway. This may not only provide a general mechanism underlying BRCA1's function in maintaining genome stability and tumor suppression but may also point to a previously unrecognized role of BRCA1 in B-cell lymphomagenesis.
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| 3. |
- Björkman, Andrea
(författare)
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Molecular mechanisms of antibody diversification in human B-cells
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- B-cells undergo several somatic rearrangement/mutational processes during development to diversify their immunoglobulin (Ig) receptors. First, the antigen binding Ig variable (V) region is assembled through V(D)J recombination. Later, B-cells undergo class switch recombination (CSR), which exchanges the constant region and thus Ig isotype and immune effector function. In addition, point mutations are introduced into the Ig V regions, to increase the affinity between the Ig and antigen, by somatic hypermutation (SHM). These processes rely on numerous DNA damage response (DDR) and DNA repair proteins, such as those from the classical non-homologous end-joining (c-NHEJ) pathway. The aim of this thesis was to elucidate the functions of some of these proteins during antibody diversification in human cells. In Paper I, cells from patients with Cornelia de Lange syndrome (CdLS), with mutations in the gene encoding the cohesin loader NIPBL, were studied. The analysis of CSR junctions from these patients revealed an altered repair pattern. It was characterized by reduced direct end-joining and increased microhomology (MH) usage, indicating a shift from c-NHEJ to alternative end-joining (A-EJ). A role for NIPBL in promoting NHEJ was shown to be conserved in yeast. Furthermore, the early recruitment of the DDR factor 53BP1 to DSBs was impaired in the NIPBL-deficient cells, suggesting a mechanism for the involvement of NIPBL/cohesin in NHEJ. In Paper II, the Ig heavy (H) chain and T cell receptor (TCR) β chain V region repertoires were analyzed in CdLS patients by high through-put sequencing methods. The cells from the CdLS patients showed reduced lymphocyte receptor diversity and a skewed V gene usage, which seemed dependent on the location of the genes at the IgH and TCRβ loci. Furthermore, the frequency of SHMs in the IgH V regions was reduced. These results might imply a role for cohesin in the regulation of SHM, as well as in processes ensuring that V genes throughout the Ig locus are used during V(D)J recombination. In Paper III, the CSR junctions were analyzed in individuals deficient in the tumor suppressor BRCA1. The CSR junctions showed several aberrations, including increased MH usage, elevated frequency of intra-switch deletions and unusual insertions containing inversions. Alterations were also observed at the CSR-junctions from patients with defects in the BRCA1-associated proteins BRIP1, BRCA2, CtIP and RNF168. Thus, it seems as BRCA1 together with its interaction partners play an important role in promoting the c-NHEJ pathway during CSR. In Paper IV, CSR junctions were examined in the two only patients described with DNAPKcs-deficiency to date. Furthermore, CSR-junctions from DNA-PKcs-deficient mice and the Ramos B-cell line, transfected with a switch plasmid and treated with DNA-PKcs inhibitor, were studied. The role of DNA-PKcs in CSR has been unclear, but the analysis of CSR junctions from all DNA-PKcs-deficient models revealed a shift to A-EJ, suggesting that CSR, indeed, is affected in DNA-PKcs-deficient cells.
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| 4. |
- Björkman, Frida, et al.
(författare)
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Sex and maturity status affected the validity of a submaximal cycle test in adolescents.
- 2018
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Ingår i: Acta Paediatrica. - : Wiley. - 0803-5253 .- 1651-2227. ; 107:1, s. 126-133
-
Tidskriftsartikel (refereegranskat)abstract
- AIM: This study assessed the validity and reliability of the Ekblom-Bak (EB) submaximal cycle test in adolescents and identified any sex- or maturity-related factors for prediction errors.METHODS: We recruited 50 healthy subjects through a public announcement in Stockholm, Sweden, in 2016. The 27 boys and 23 girls were aged 10-15 years and in Tanner stages I-IV. They performed an EB test and incremental treadmill running test for direct measurement of maximal oxygen uptake (VO2 max).RESULTS: The estimation error of VO2 max was 0.09 L/min. The correlation (r) was 0.86, and the standard error of the estimate (SEE) was 0.29 L/min. The largest overestimation was seen in prepubertal boys (0.49 L/min). The best precision of the EB test was achieved when boys in Tanner stages I and II were re-calculated using the prediction equation developed for adult women. This yielded a mean difference of -0.05 L/min, r = 0.92 and SEE 0.23 L/min, in the entire sample. The prediction error was lowered in boys, but not girls, with increasing pubertal maturity.CONCLUSION: The EB test was reasonably valid in adolescents, seemed to be related to sex and maturity status, and our findings support its use.
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| 5. |
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| 6. |
- Björkman Nyqvist, Martina, et al.
(författare)
-
Political Selection in Local Elections: Evidence from Rural Uganda
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Political selection is crucial to the quality of governance. Yet our general knowledge of the individual characteristics that correlate with the political selection process is scant. Our paper contributes to this knowledge gap by collecting detailed data on the quality, perceptions, attitudes, and promises of all candidates involved in a recent local election in rural Uganda. Our context is unique - with two separate governing bodies for males and females. The paper demonstrates, that male and female political selection into these two parallel institutions share important similarities but also differ along several dimensions.
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| 7. |
- Björkman Nyqvist, Martina, et al.
(författare)
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Reducing Child Mortality in the Last Mile : Experimental Evidence on Community Health Promoters in Uganda
- 2019
-
Ingår i: American Economic Journal. - : American Economic Association. - 1945-7782 .- 1945-7790. ; 11:3, s. 155-192
-
Tidskriftsartikel (refereegranskat)abstract
- The delivery of basic health products and services remains abysmal in many parts of the world where child mortality is high. This paper shows the results from a large-scale randomized evaluation of a novel approach to health care delivery In randomly selected villages, a sales agent was locally recruited and incentivized to conduct home visits, educate households on essential health behaviors, provide medical advice and referrals, and sell preventive and curative health products. Results after 3 years show substantial health impact: under 5-years child mortality was reduced by 27 percent at an estimated average cost of $68 per life-year saved.
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| 8. |
- Björkman Nyqvist, Martina, et al.
(författare)
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Reducing Child Mortality in the Last Mile: A Randomized Social Entrepreneurship Intervention in Uganda
- 2017
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The delivery of basic health products and services remains abysmal in many parts of the world where child mortality is high. This paper shows the results from a largescale randomized evaluation of a novel “social entrepreneurship” approach to health care delivery. In randomly selected villages a sales agent was locally recruited and incentivized to conduct home visits, educate households on essential health behaviors, provide medical advice and referrals, and sell preventive and curative health products. Results after three years show substantial health impact: under-5 child mortality was reduced by 27% at an estimated cost of $71 per life-year saved.
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| 9. |
- Björkman Nyqvist, Martina, et al.
(författare)
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Replication data for: Reducing Child Mortality in the Last Mile: Experimental Evidence on Community Health Promoters in Uganda
- 2019
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The delivery of basic health products and services remains abysmal in many parts of the world where child mortality is high. This paper shows the results from a large-scale randomized evaluation of a novel approach to health care delivery. In randomly selected villages, a sales agent was locally recruited and incentivized to conduct home visits, educate households on essential health behaviors, provide medical advice and referrals, and sell preventive and curative health products. Results after 3 years show substantial health impact: under 5-years child mortality was reduced by 27 percent at an estimated average cost of $68 per life-year saved.
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| 10. |
- Björkman Nyqvist, Martina, et al.
(författare)
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The impact of the COVID-19 pandemic on children’s learning and wellbeing : Evidence from India
- 2023
-
Ingår i: Journal of Development Economics. - : Elsevier Ltd. - 1872-6089 .- 0304-3878. ; 164
-
Tidskriftsartikel (refereegranskat)abstract
- We study the impact of the COVID-19 pandemic and associated school closure on primary school children’s learning and mental wellbeing in Assam, India. Using a comprehensive dataset that tracked and repeatedly surveyed approximately 5000 children across 200 schools between 2018 and 2022, we find that children lost the equivalent of nine months of learning in mathematics and eleven months in language, during the pandemic. Children lacking resources and parental support experienced the largest losses. Regular practice, teacher interaction, and technology were associated with less learning loss. Over the same period, children’s psychological wellbeing improved. Our research provides valuable insights for designing post-emergency programs. • During the pandemic primary school children in Assam lost 9–11 months of learning.• Children with fewer resources and support at home lost the most.• Teachers’ calls, regular practice, and technology were associated with smaller losses.• Children’s psychological well-being improved during the pandemic.
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| 11. |
- Björkman Nyqvist, Martina, et al.
(författare)
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Weather Shocks, Child Mortality, and Adaptation: Experimental Evidence from Uganda
- 2023
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Background Human-caused climate change is already increasing the intensity and frequency of extreme weather events, such as droughts. The health and economic consequences of these events are expected to be particularly severe for populations in low-income settings whose livelihoods rely on rain-fed agriculture. Within these populations, children are an especially vulnerable group, as undernutrition is linked to 45% of all child deaths across the globe. Despite progress, adaptation gaps exist. We still lack strong evidence on policies to effectively mitigate climate change's most severe consequences for children. In this paper we ask whether adaptation investments in the form of improved community healthcare can build climate resilience in a low-income country setting.
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| 12. |
- Callen, Michael, et al.
(författare)
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COVID-19 vaccine acceptance and hesitancy in low- and middle-income countries
- 2021
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Ingår i: Nature Medicine. - : Springer Nature. - 1546-170X .- 1078-8956. ; 27:8, s. 1385-1394
-
Tidskriftsartikel (refereegranskat)abstract
- Widespread acceptance of COVID-19 vaccines is crucial for achieving sufficient immunization coverage to end the global pandemic, yet few studies have investigated COVID-19 vaccination attitudes in lower-income countries, where large-scale vaccination is just beginning. We analyze COVID-19 vaccine acceptance across 15 survey samples covering 10 low- and middle-income countries (LMICs) in Asia, Africa and South America, Russia (an upper-middle-income country) and the United States, including a total of 44,260 individuals. We find considerably higher willingness to take a COVID-19 vaccine in our LMIC samples (mean 80.3%; median 78%; range 30.1 percentage points) compared with the United States (mean 64.6%) and Russia (mean 30.4%). Vaccine acceptance in LMICs is primarily explained by an interest in personal protection against COVID-19, while concern about side effects is the most common reason for hesitancy. Health workers are the most trusted sources of guidance about COVID-19 vaccines. Evidence from this sample of LMICs suggests that prioritizing vaccine distribution to the Global South should yield high returns in advancing global immunization coverage. Vaccination campaigns should focus on translating the high levels of stated acceptance into actual uptake. Messages highlighting vaccine efficacy and safety, delivered by healthcare workers, could be effective for addressing any remaining hesitancy in the analyzed LMICs. © 2021, The Author(s).
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| 13. |
- Du, Likun, et al.
(författare)
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Cernunnos influences human immunoglobulin class switch recombination and may be associated with B cell lymphomagenesis
- 2012
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Ingår i: Journal of Experimental Medicine. - : Rockefeller University Press. - 0022-1007 .- 1540-9538. ; 209:2, s. 291-305
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Tidskriftsartikel (refereegranskat)abstract
- Cernunnos is involved in the nonhomologous end-joining (NHEJ) process during DNA double-strand break (DSB) repair. Here, we studied immunoglobulin (Ig) class switch recombination (CSR), a physiological process which relies on proper repair of the DSBs, in B cells from Cernunnos-deficient patients. The pattern of in vivo generated CSR junctions is altered in these cells, with unusually long microhomologies and a lack of direct end-joining. The CSR junctions from Cernunnos-deficient patients largely resemble those from patients lacking DNA ligase IV, Artemis, or ATM, suggesting that these factors are involved in the same end-joining pathway during CSR. By screening 269 mature B cell lymphoma biopsies, we also identified a somatic missense Cernunnos mutation in a diffuse large B cell lymphoma sample. This mutation has a dominant-negative effect on joining of a subset of DNA ends in an in vitro NHEJ assay. Translocations involving both Ig heavy chain loci and clonal-like, dynamic IgA switching activities were observed in this tumor. Collectively, our results suggest a link between defects in the Cernunnos-dependent NHEJ pathway and aberrant CSR or switch translocations during the development of B cell malignancies.
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| 14. |
- Guariso, Andrea, et al.
(författare)
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The Impact of the COVID-19 pandemic on children's learning and wellbeing : Evidence from India
- 2023
-
Ingår i: SSRN Electronic Journal. - Stockholm : Mistra Center for Sustainable Markets (Misum). - 1556-5068.
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- We study the impact of the COVID-19 pandemic and associated school closure on primary school children’s learning and mental well-being in Assam, India. Using a comprehensive dataset that tracked and repeatedly surveyed approximately 5,000 children across 200 schools between 2018 and 2022, we find that children lost the equivalent of nine months of learning in mathematics and eleven months in language, during the pandemic. Children lacking resources and parental support experienced the largest losses. Regular practice, teacher interaction, and technology helped sustain learning. Over the same period, children’s psychological well-being improved. Our research provides valuable insights for designing post-emergency programs.
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| 15. |
- Kattge, Jens, et al.
(författare)
-
TRY plant trait database - enhanced coverage and open access
- 2020
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Ingår i: Global Change Biology. - : Wiley-Blackwell. - 1354-1013 .- 1365-2486. ; 26:1, s. 119-188
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Tidskriftsartikel (refereegranskat)abstract
- Plant traits-the morphological, anatomical, physiological, biochemical and phenological characteristics of plants-determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of trait-based plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits-almost complete coverage for 'plant growth form'. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and trait-environmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives.
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| 16. |
- Keuschnig, Christoph, et al.
(författare)
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Selection processes of Arctic seasonal glacier snowpack bacterial communities
- 2023
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Ingår i: Microbiome. - : BioMed Central (BMC). - 2049-2618. ; 11:1
-
Tidskriftsartikel (refereegranskat)abstract
- BackgroundArctic snowpack microbial communities are continually subject to dynamic chemical and microbial input from the atmosphere. As such, the factors that contribute to structuring their microbial communities are complex and have yet to be completely resolved. These snowpack communities can be used to evaluate whether they fit niche-based or neutral assembly theories.MethodsWe sampled snow from 22 glacier sites on 7 glaciers across Svalbard in April during the maximum snow accumulation period and prior to the melt period to evaluate the factors that drive snowpack metataxonomy. These snowpacks were seasonal, accumulating in early winter on bare ice and firn and completely melting out in autumn. Using a Bayesian fitting strategy to evaluate Hubbell’s Unified Neutral Theory of Biodiversity at multiple sites, we tested for neutrality and defined immigration rates at different taxonomic levels. Bacterial abundance and diversity were measured and the amount of potential ice-nucleating bacteria was calculated. The chemical composition (anions, cations, organic acids) and particulate impurity load (elemental and organic carbon) of the winter and spring snowpack were also characterized. We used these data in addition to geographical information to assess possible niche-based effects on snow microbial communities using multivariate and variable partitioning analysis.ResultsWhile certain taxonomic signals were found to fit the neutral assembly model, clear evidence of niche-based selection was observed at most sites. Inorganic chemistry was not linked directly to diversity, but helped to identify predominant colonization sources and predict microbial abundance, which was tightly linked to sea spray. Organic acids were the most significant predictors of microbial diversity. At low organic acid concentrations, the snow microbial structure represented the seeding community closely, and evolved away from it at higher organic acid concentrations, with concomitant increases in bacterial numbers.ConclusionsThese results indicate that environmental selection plays a significant role in structuring snow microbial communities and that future studies should focus on activity and growth.
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| 17. |
- Lehmann, Philipp, et al.
(författare)
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Complex responses of global insect pests to climate warming
- 2020
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Ingår i: Frontiers in Ecology and the Environment. - : Wiley. - 1540-9295 .- 1540-9309. ; 18:3, s. 141-150
-
Forskningsöversikt (refereegranskat)abstract
- Although it is well known that insects are sensitive to temperature, how they will be affected by ongoing global warming remains uncertain because these responses are multifaceted and ecologically complex. We reviewed the effects of climate warming on 31 globally important phytophagous (plant-eating) insect pests to determine whether general trends in their responses to warming were detectable. We included four response categories (range expansion, life history, population dynamics, and trophic interactions) in this assessment. For the majority of these species, we identified at least one response to warming that affects the severity of the threat they pose as pests. Among these insect species, 41% showed responses expected to lead to increased pest damage, whereas only 4% exhibited responses consistent with reduced effects; notably, most of these species (55%) demonstrated mixed responses. This means that the severity of a given insect pest may both increase and decrease with ongoing climate warming. Overall, our analysis indicated that anticipating the effects of climate warming on phytophagous insect pests is far from straightforward. Rather, efforts to mitigate the undesirable effects of warming on insect pests must include a better understanding of how individual species will respond, and the complex ecological mechanisms underlying their responses.
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| 18. |
- Lejaeghere, Kurt, et al.
(författare)
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Reproducibility in density functional theory calculations of solids.
- 2016
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 351:6280, s. 1415-1422
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Tidskriftsartikel (refereegranskat)abstract
- The widespread popularity of density functional theory has given rise to an extensive range of dedicated codes for predicting molecular and crystalline properties. However, each code implements the formalism in a different way, raising questions about the reproducibility of such predictions. We report the results of a community-wide effort that compared 15 solid-state codes, using 40 different potentials or basis set types, to assess the quality of the Perdew-Burke-Ernzerhof equations of state for 71 elemental crystals. We conclude that predictions from recent codes and pseudopotentials agree very well, with pairwise differences that are comparable to those between different high-precision experiments. Older methods, however, have less precise agreement. Our benchmark provides a framework for users and developers to document the precision of new applications and methodological improvements.
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| 19. |
- Lembrechts, Jonas J., et al.
(författare)
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SoilTemp : A global database of near-surface temperature
- 2020
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 26:11, s. 6616-6629
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Tidskriftsartikel (refereegranskat)abstract
- Current analyses and predictions of spatially explicit patterns and processes in ecology most often rely on climate data interpolated from standardized weather stations. This interpolated climate data represents long-term average thermal conditions at coarse spatial resolutions only. Hence, many climate-forcing factors that operate at fine spatiotemporal resolutions are overlooked. This is particularly important in relation to effects of observation height (e.g. vegetation, snow and soil characteristics) and in habitats varying in their exposure to radiation, moisture and wind (e.g. topography, radiative forcing or cold-air pooling). Since organisms living close to the ground relate more strongly to these microclimatic conditions than to free-air temperatures, microclimatic ground and near-surface data are needed to provide realistic forecasts of the fate of such organisms under anthropogenic climate change, as well as of the functioning of the ecosystems they live in. To fill this critical gap, we highlight a call for temperature time series submissions to SoilTemp, a geospatial database initiative compiling soil and near-surface temperature data from all over the world. Currently, this database contains time series from 7,538 temperature sensors from 51 countries across all key biomes. The database will pave the way toward an improved global understanding of microclimate and bridge the gap between the available climate data and the climate at fine spatiotemporal resolutions relevant to most organisms and ecosystem processes.
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| 20. |
- Orlandini, Andrea, et al.
(författare)
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ExCITE Project : A Review of Forty-Two Months of Robotic Telepresence Technology
- 2016
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Ingår i: Presence - Teleoperators and Virtual Environments. - Cambridge, USA : MIT Press. - 1054-7460 .- 1531-3263. ; 25:3, s. 204-221
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Tidskriftsartikel (refereegranskat)abstract
- This article reports on the EU project ExCITE with specific focus on the technical development of the telepresence platform over a period of 42 months. The aim of the project was to assess the robustness and validity of the mobile robotic telepresence (MRP) system Giraff as a means to support elderly people and to foster their social interaction and participation. Embracing the idea of user-centered product refinement, the robot was tested over long periods of time in real homes. As such, the system development was driven by a strong involvement of elderly people and their caregivers but also by technical challenges associated with deploying the robot in real-world contexts. The results of the 42-months’ long evaluation is a system suitable for use in homes rather than a generic system suitable, for example, in office environments.
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| 21. |
- Platzer-Björkman, Charlotte, et al.
(författare)
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Deposition of magnesium hydride thin films using radio frequency reactive sputtering
- 2011
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:18, s. 5949-5954
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Tidskriftsartikel (refereegranskat)abstract
- Reactive sputter deposition of MgHx thin films was performed using mixed hydrogen–argon plasma. This technique allows in-situ deposition of metal hydride films in contrast to the commonly applied ex-situ hydrogenation of metallic films. Partly transparent films were obtained and the formation of crystalline MgH2 could be observed for thicknesses above about 200 nm. The formation of some metallic Mg in the films could not be avoided. Increased hydrogen loading by increased pressure, H2:Ar ratio or reduced power produced films of porous structure that easily oxidise. More densely packed films remain stable for several months of air exposure. Post-deposition treatments in H-plasma showed evidence of hydrogenation of deposited films without the use of a catalysing capping film. Film properties are studied by X-ray diffraction, scanning electron microscopy and by optical and resistivity measurements.
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| 22. |
- Saini, Nishant, et al.
(författare)
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Bandgap engineered Cu 2 ZnGe x Sn 1−x S 4 solar cells using an adhesive TiN back contact layer
- 2021
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388. ; 880
-
Tidskriftsartikel (refereegranskat)abstract
- Kesterite-based solar cells are mainly restricted by their lower than expected open-circuit voltage (V ) due to non-radiative recombination. Therefore, an approach to reduce bulk and interface recombination through band gap grading to induce a back surface field is attempted. This contribution presents the challenges in the formation of compositional grading of the wide bandgap material Cu ZnGe Sn S (CZGTS) and successful fabrication of solar cells with an additional adhesive TiN interlayer. It is observed that the TiN interlayer improves adhesion between CZGTS and the back contact. The microstructure of the Cu ZnSnS (CZTS) film is significantly affected by the concentration of Ge, and the existence of a Ge concentration gradient is strongly correlated to the formation of smaller Ge-rich and larger Sn-rich grains. The bandgap grading is exploited with a moderate Ge concentration of up to (Ge/(Ge+Sn) = 0.25) in CZTS. As the Ge profile stretched all the way to the front interface, the cliff-like band alignment at the front interface of the absorber could negate the beneficial effect of Ge inclusion in the bulk and back interface of the absorber. Ordering the absorber can introduce an additional downward shift in the valence band. In one of the samples, the increased ordering and high concentration of Ge in CZTS are suggested to enhance the hole barrier at the back interface. It is concluded that the effect of the bandgap grading with Ge can only be realized with optimization of interface band alignment and back contact formation. oc 2 x 1−x 4 2 4
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| 23. |
- Saini, Nishant, et al.
(författare)
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Bandgap engineered Cu2ZnGexSn1−xS4 solar cells using an adhesive TiN back contact layer
- 2021
-
Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 880
-
Tidskriftsartikel (refereegranskat)abstract
- Kesterite-based solar cells are mainly restricted by their lower than expected open-circuit voltage (Voc) due to non-radiative recombination. Therefore, an approach to reduce bulk and interface recombination through band gap grading to induce a back surface field is attempted. This contribution presents the challenges in the formation of compositional grading of the wide bandgap material Cu2ZnGexSn1−xS4 (CZGTS) and successful fabrication of solar cells with an additional adhesive TiN interlayer. It is observed that the TiN interlayer improves adhesion between CZGTS and the back contact. The microstructure of the Cu2ZnSnS4 (CZTS) film is significantly affected by the concentration of Ge, and the existence of a Ge concentration gradient is strongly correlated to the formation of smaller Ge-rich and larger Sn-rich grains. The bandgap grading is exploited with a moderate Ge concentration of up to (Ge/(Ge+Sn) = 0.25) in CZTS. As the Ge profile stretched all the way to the front interface, the cliff-like band alignment at the front interface of the absorber could negate the beneficial effect of Ge inclusion in the bulk and back interface of the absorber. Ordering the absorber can introduce an additional downward shift in the valence band. In one of the samples, the increased ordering and high concentration of Ge in CZTS are suggested to enhance the hole barrier at the back interface. It is concluded that the effect of the bandgap grading with Ge can only be realized with optimization of interface band alignment and back contact formation.
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| 24. |
- Spolaor, Andrea, et al.
(författare)
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Climate change is rapidly deteriorating the climatic signal in Svalbard glaciers
- 2024
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Ingår i: CRYOSPHERE. - 1994-0416 .- 1994-0424. ; 18:1, s. 307-320
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Tidskriftsartikel (refereegranskat)abstract
- The Svalbard archipelago is particularly sensitive to climate change due to the relatively low altitude of its main ice fields and its geographical location in the higher North Atlantic, where the effect of Arctic amplification is more significant. The largest temperature increases have been observed during winter, but increasing summer temperatures, above the melting point, have led to increased glacier melt. Here, we evaluate the impact of this increased melt on the preservation of the oxygen isotope ( delta 18 O) signal in firn records. delta 18 O is commonly used as a proxy for past atmospheric temperature reconstructions, and, when preserved, it is a crucial parameter to date and align ice cores. By comparing four different firn cores collected in 2012, 2015, 2017 and 2019 at the top of the Holtedahlfonna ice field (1100 m a.s.l.), we show a progressive deterioration of the isotope signal, and we link its degradation to the increased occurrence and intensity of melt events. Our findings indicate that, starting from 2015, there has been an escalation in melting and percolation resulting from changes in the overall atmospheric conditions. This has led to the deterioration of the climate signal preserved within the firn or ice. Our observations correspond with the model's calculations, demonstrating an increase in water percolation since 2014, potentially reaching deeper layers of the firn. Although the delta 18 O signal still reflects the interannual temperature trend, more frequent melting events may in the future affect the interpretation of the isotopic signal, compromising the use of Svalbard ice cores. Our findings highlight the impact and the speed at which Arctic amplification is affecting Svalbard's cryosphere.
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- Zdanowicz, Christian, 1966-, et al.
(författare)
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Strategies and Best Practices for Monitoring Seasonal Snow Cover Composition
- 2019
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Seasonal snow covers up to 45 million km^2 every winter. As such, it represents a major interface between the Earth's surface and atmosphere. It also offers a convenient sampling medium to monitor water isotopes in solid precipitation and the net deposition of a wide variety of atmospheric species, including nutrients, organic compounds (OCs), trace metals, dust, black carbon (BC), and many others. Impurities such as dust and BC are light-absorbing and as such can modify the radiative properties of snow, while other atmospheric species such as OCs or certain metals can adversely affect the aquatic environment and drinking water quality in meltwater-fed basins. Systematic monitoring of seasonal snowpack composition may therefore offer a way of supplementing direct observations of air and precipitation chemistry. It may also lend itself well to certain "citizen science" activities, provided a set of standardized protocols can be adopted, and an adequate platform for data collection and sharing be established. In recent years, some recommendations to this effect were made by the snow science community through the IASC Cryosphere Working Group, the WMO Global Cryosphere Watch and EU Harmosnow initiative. The purpose of this presentation is to stimulate a continued discussion of the merits, challenges and caveats of establishing a network of coordinated snowpack composition observations. Examples of existing or recently-developed monitoring protocols for snowpacks in Arctic and montane regions will be presented and discussed.
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