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- Li, Shunyi, et al.
(författare)
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Intrinsic energy band alignment of functional oxides
- 2014
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Ingår i: Physica Status Solidi - Rapid Research Letetrs. - : Wiley. - 1862-6254 .- 1862-6270. ; 8:6, s. 571-576
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Tidskriftsartikel (refereegranskat)abstract
- The energy band alignment at interfaces between different materials is a key factor, which determines the function of electronic devices. While the energy band alignment of conventional semiconductors is quite well understood, systematic experimental studies on oxides are still missing. This work presents an extensive study on the intrinsic energy band alignment of a wide range of functional oxides using photoelectron spectroscopy with in-situ sample preparation. The studied materials have particular technological importance in diverse fields as solar cells, piezotronics, multiferroics, photoelectrochemistry and oxide electronics. Particular efforts have been made to verify the validity of transitivity, in order to confirm the intrinsic nature of the obtained band alignment and to understand the underlying principles. Valence band offsets up to 1.6 eV are observed. The large variation of valence band maximum energy can be explained by the different orbital contributions to the density of states in the valence band. The framework provided by this work enables the general understanding and prediction of energy band alignment at oxide interfaces, and furthermore the tailoring of energy level matching for charge transfer in functional oxides. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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- Hartley, Philippa, et al.
(författare)
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SKA Science Data Challenge 2: analysis and results
- 2023
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Ingår i: Monthly Notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 523:2, s. 1967-1993
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Tidskriftsartikel (refereegranskat)abstract
- The Square Kilometre Array Observatory (SKAO) will explore the radio sky to new depths in order to conduct transformational science. SKAO data products made available to astronomers will be correspondingly large and complex, requiring the application of advanced analysis techniques to extract key science findings. To this end, SKAO is conducting a series of Science Data Challenges, each designed to familiarize the scientific community with SKAO data and to drive the development of new analysis techniques. We present the results from Science Data Challenge 2 (SDC2), which invited participants to find and characterize 233 245 neutral hydrogen (H i) sources in a simulated data product representing a 2000 h SKA-Mid spectral line observation from redshifts 0.25-0.5. Through the generous support of eight international supercomputing facilities, participants were able to undertake the Challenge using dedicated computational resources. Alongside the main challenge, 'reproducibility awards' were made in recognition of those pipelines which demonstrated Open Science best practice. The Challenge saw over 100 participants develop a range of new and existing techniques, with results that highlight the strengths of multidisciplinary and collaborative effort. The winning strategy - which combined predictions from two independent machine learning techniques to yield a 20 per cent improvement in overall performance - underscores one of the main Challenge outcomes: that of method complementarity. It is likely that the combination of methods in a so-called ensemble approach will be key to exploiting very large astronomical data sets.
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- Ahuja, SK, et al.
(författare)
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A plea for justice for jailed medical workers
- 2006
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Ingår i: Science (New York, N.Y.). - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 314:5801, s. 924-925
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 8. |
- Lieleg, C, et al.
(författare)
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Nucleosome Remodeling at the Yeast PHO8 and PHO84 Promoters without the Putatively Essential SWI/SNF Remodeler
- 2023
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Ingår i: International journal of molecular sciences. - : MDPI AG. - 1422-0067. ; 24:5
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Tidskriftsartikel (refereegranskat)abstract
- Chromatin remodeling by ATP-dependent remodeling enzymes is crucial for all genomic processes, like transcription or replication. Eukaryotes harbor many remodeler types, and it is unclear why a given chromatin transition requires more or less stringently one or several remodelers. As a classical example, removal of budding yeast PHO8 and PHO84 promoter nucleosomes upon physiological gene induction by phosphate starvation essentially requires the SWI/SNF remodeling complex. This dependency on SWI/SNF may indicate specificity in remodeler recruitment, in recognition of nucleosomes as remodeling substrate or in remodeling outcome. By in vivo chromatin analyses of wild type and mutant yeast under various PHO regulon induction conditions, we found that overexpression of the remodeler-recruiting transactivator Pho4 allowed removal of PHO8 promoter nucleosomes without SWI/SNF. For PHO84 promoter nucleosome removal in the absence of SWI/SNF, an intranucleosomal Pho4 site, which likely altered the remodeling outcome via factor binding competition, was required in addition to such overexpression. Therefore, an essential remodeler requirement under physiological conditions need not reflect substrate specificity, but may reflect specific recruitment and/or remodeling outcomes.
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- Marques-Chaves, R., et al.
(författare)
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Extreme N-emitters at high redshift : Possible signatures of supermassive stars and globular cluster or black hole formation in action
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 681
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Tidskriftsartikel (refereegranskat)abstract
- Context. Recent James Webb Space Telescope (JWST) spectroscopic observations of the z = 10.6 galaxy GN-z11 have revealed a very peculiar UV spectrum exhibiting intense emission lines of nitrogen, which are not typically detected in galaxy spectra. This observation indicates a super-solar N/O abundance ratio at low metallicity, which only resembles the abundances seen in globular cluster (GC) stars. This discovery suggests that we might be seeing proto-GCs in formation or possibly even signatures of supermassive stars.Aims. To examine whether other objects with strong N IV and/or N III emission lines (N-emitters, hereafter) exist and to better understand their origin and nature, we have examined the available JWST spectra and data from the literature.Methods. Using the NIRSpec/JWST observations from CEERS, we found an extreme N-emitter, CEERS-1019 at z = 8.6782, showing intense N IV] λ1486 and N III] λ1750 emission. From the observed rest-UV and optical lines, we conclude that it is compatible with photoionization from stars and we have determined accurate abundances for C, N, O, and Ne, relative to H. We also (re-)analyzed other N-emitters from the literature, including three lensed objects at z = 2.3 − 3.5 (Sunburst cluster, SMACS2031, and Lynx arc) and a low-redshift compact galaxy, Mrk 996. We carried out a comparison among the observed abundance ratios to observations from normal star-forming galaxies, predicted wind yields from massive stars, and predictions from supermassive stars (SMS with ∼104 − 105M⊙).Results. For CEERS-1019, we find a highly supersolar ratio log(N/O)= − 0.18 ± 0.11, and abundances of log(C/O)= − 0.75 ± 0.11 and log(Ne/O)= − 0.63 ± 0.07, which are normal compared to other galaxies at the low metallicity (12 + log(O/H) = 7.70 ± 0.18) of this galaxy. The three lensed N-emitters also show strongly enhanced N/O ratios and two of them normal C/O. The high N/O abundances can be reproduced by massive star winds assuming a special timing and essentially no dilution with the ambient interstellar medium (ISM). Alternatively, these N/O ratios can be explained by mixing the ejecta of SMS with comparable amounts of unenriched ISM. Massive star ejecta (from WR stars) are needed to explain the galaxies with enhanced C/O (Lynx arc, Mrk 996). On the other hand, a SMS in the “conveyer-belt model” (put forward to explain globular clusters) would predict a high N/O and small changes in C/O, compatible with CEERS-1019, the Sunburst cluster, SMACS2031, and GN-z11. Based on the chemical abundances, possible enrichment scenarios, and other properties (e.g., their compactness and high ISM density), we discuss which objects could contain proto-GCs. We suggest that this is the case for CEERS-1019, SMACS2031, and the Sunburst cluster. Enrichment in the Lynx arc and Mrk 996 is likely due to normal massive stars (WR), which implies that the star-forming regions in these objects cannot become GCs. Finally, we propose that some N-emitters enriched by SMS could also have formed intermediate mass black holes and we suggest that this might be the case for GN-z11.Conclusions. Our observations and analysis reinforce the suggested link between some N-emitters and proto-GC formation, which is supported both by empirical evidence and quantitative models. Furthermore, the observations provide possible evidence for the presence of supermassive stars in the early Universe (z > 8) and at z ∼ 2 − 3. Our analysis also suggests that the origin and nature of the N-emitters is diverse, including objects such as GN-z11, which may possibly host an active galactic nucleus (AGN).
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