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- Osborn, H. P., et al.
(författare)
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The PDS 110 observing campaign - photometric and spectroscopic observations reveal eclipses are aperiodic
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 485:2, s. 1614-1625
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Tidskriftsartikel (refereegranskat)abstract
- PDS 110 is a young disc-hosting star in the Orion OB1A association. Two dimming events of similar depth and duration were seen in 2008 (WASP) and 2011 (KELT), consistent with an object in a closed periodic orbit. In this paper, we present data from a ground-based observing campaign designed to measure the star both photometrically and spectroscopically during the time of predicted eclipse in 2017 September. Despite high-quality photometry, the predicted eclipse did not occur, although coherent structure is present suggesting variable amounts of stellar flux or dust obscuration. We also searched for radial velocity (RV) oscillations caused by any hypothetical companion and can rule out close binaries to 0.1Ms. Asearch of Sonneberg plate archive data also enabled us to extend the photometric baseline of this star back more than 50 yr, and similarly does not re-detect any deep eclipses. Taken together, they suggest that the eclipses seen in WASP and KELT photometry were due to aperiodic events. It would seem that PDS 110 undergoes stochastic dimmings that are shallower and of shorter duration than those of UX Ori variables, but may have a similar mechanism.
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- Ho, Joshua W. K., et al.
(författare)
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Comparative analysis of metazoan chromatin organization
- 2014
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 512:7515, s. 449-U507
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Tidskriftsartikel (refereegranskat)abstract
- Genome function is dynamically regulated in part by chromatin, which consists of the histones, non-histone proteins and RNA molecules that package DNA. Studies in Caenorhabditis elegans and Drosophila melanogaster have contributed substantially to our understanding of molecular mechanisms of genome function in humans, and have revealed conservation of chromatin components and mechanisms(1-3). Nevertheless, the three organisms have markedly different genome sizes, chromosome architecture and gene organization. On human and fly chromosomes, for example, pericentric heterochromatin flanks single centromeres, whereas worm chromosomes have dispersed heterochromatin-like regions enriched in the distal chromosomal 'arms', and centromeres distributed along their lengths(4,5). To systematically investigate chromatin organization and associated gene regulation across species, we generated and analysed a large collection of genome-wide chromatin data sets from cell lines and developmental stages in worm, fly and human. Here we present over 800 new data sets from our ENCODE and modENCODE consortia, bringing the total to over 1,400. Comparison of combinatorial patterns of histone modifications, nuclear lamina-associated domains, organization of large-scale topological domains, chromatin environment at promoters and enhancers, nucleosome positioning, and DNA replication patterns reveals many conserved features of chromatin organization among the three organisms. We also find notable differences in the composition and locations of repressive chromatin. These data sets and analyses provide a rich resource for comparative and species-specific investigations of chromatin composition, organization and function.
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- Latham, Kenneth G., et al.
(författare)
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Influence of counter ions of ammonium for nitrogen doping and carbon properties in hydrothermal carbonization : characterization and supercapacitor performance
- 2021
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Ingår i: Materials Advances. - : Royal Society of Chemistry. - 2633-5409. ; 2:1, s. 384-397
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Tidskriftsartikel (refereegranskat)abstract
- Ammonium has been successfully utilized to nitrogen dope carbon structures via hydrothermal carbonization, although the influence of different attached counter ions (anions) on the resultant carbon physicochemical properties and electrochemical performance has not been examined before. Four different counter ions (SO42-, PO43-, Cl-, and Fe(SO4)(2)) attached to ammonium were seen to influence the hydrothermal reaction, nitrogen incorporation levels, physicochemical properties, activation ability and supercapacitor performance. For instance, nitrogen K-edge NEXAFS found differences in the levels of pyridinic and pyrrolic groups with PO43- incorporating predominately pyridinic nitrogen groups. PO43- also achieved the highest surface area (2132.6 m(2) g(-1)), however this material was unstable as a supercapacitor, losing almost 50% of its performance over 500 cycles. SO42- resulted in the highest level of nitrogen incorporation (5.53 at%) and hydrothermal yield (45.5%), while Fe(SO4)(2)(2-) resulted in the lowest (2.92 at%). However, Fe(SO4)(2)(2-) produced unique flower like structures not seen in any of the other anions. Cl- produced the highest performing material, achieving 190 F g(-1) at 10 mV s(-1) in 1 M KOH and had moderate nitrogen incorporation (3.42 at%). Overall, this study indicates that the anion has substantial influence on the physicochemical properties of the material, allowing an additional level of tailoring.
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| 8. |
- Latham, Kenneth G., et al.
(författare)
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Nitrogen doped heat treated and activated hydrothermal carbon : NEXAFS examination of the carbon surface at different temperatures
- 2018
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Ingår i: Carbon. - : Elsevier. - 0008-6223 .- 1873-3891. ; 128, s. 179-190
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Tidskriftsartikel (refereegranskat)abstract
- Hydrothermal carbons have been shown to have controllable surface functionalization through various post-treatment techniques, which indicates these materials may be tuned for specific applications. For this reason, Near Edge X-ray Absorption Fine Structure (NEXAFS) studies have been conducted on a series of nitrogen doped and non-doped heat treated and activated hydrothermal carbons to further understand the changes in surface functionality with treatment. The NEXAFS carbon K-edge spectrum of the non-doped samples displayed a loss of oxygen functionalities (C=O and C-OH) as well as the furan ring structure with increasing temperature, while C=C bonds from graphitic groups increased. This effect was amplified further upon the addition of phosphoric acid (H3PO4) during activation. The doped hydrothermal carbons displayed similar functionality to the non-doped, although the effect of both heat treatment and activation was diminished. The nitrogen K-edge displayed characteristic peaks for pyridine and imines/amides, with pyrroles located under the broad ionization step. This work represents the first time a series of heat treated and activated hydrothermal carbons have been examined via NEXAFS spectroscopy. Additionally, difference analysis has been applied to the NEXAFS spectra to obtain a deeper understanding in the changes in surface functionality, a previously unused technique for these materials.
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