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- Cordiner, M. A., et al.
(författare)
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On the ubiquity of molecular anions in the dense interstellar medium
- 2013
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 770:1
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Tidskriftsartikel (refereegranskat)abstract
- Results are presented from a survey for molecular anions in seven nearby Galactic star-forming cores and molecular clouds. The hydrocarbon anion C6H- is detected in all seven target sources, including four sources where no anions have been previously detected: L1172, L1389, L1495B, and TMC-1C. The C6H-/C6H column density ratio is greater than or similar to 1.0% in every source, with a mean value of 3.0% (and standard deviation 0.92%). Combined with previous detections, our results show that anions are ubiquitous in dense clouds wherever C6H is present. The C6H-/C6H ratio is found to show a positive correlation with molecular hydrogen number density, and with the apparent age of the cloud. We also report the first detection of C4H- in TMC-1 (at 4.8 sigma confidence), and derive an anion-to-neutral ratio C4H-/C4H = (1.2 +/- 0.4) x 10(-5)(= 0.0012% +/- 0.0004%). Such a low value compared with C6H- highlights the need for a revised radiative electron attachment rate for C4H. Chemical model calculations show that the observed C4H- could be produced as a result of reactions of oxygen atoms with C5H- and C6H-.
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- Hanczyc, Piotr, 1985, et al.
(författare)
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Spontaneous formation of liquid crystalline phases and phase transitions in highly concentrated plasmid DNA
- 2011
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Ingår i: Liquid Crystals. - : Informa UK Limited. - 1366-5855 .- 0267-8292. ; 38:4, s. 461-468
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Tidskriftsartikel (refereegranskat)abstract
- The liquid crystalline (LC) properties of two supercoiled plasmid DNA samples, pBSK (2958 bp) and pGEM (3000 bp), have been studied using polarised light microscopy (PLM), circular dichroism (CD) and UV-Vis spectroscopy. The influence of methods of isolation on plasmid LC behaviour is described, and using PLM we have demonstrated the spontaneous formation of cholesteric fingerprint-like textures. Preliminary studies of LC phase transitions in pGEM show the irreversibility of LC phase formation, as a consequence of changes in the tertiary structure of supercoiled plasmids. Using UV-Vis spectroscopy a hyperchromic effect was observed with increasing temperature. The CD spectra clearly showed structural changes, and probably mismatching of DNA bases, during cooling. Finally, we have observed an irreversible phase transition in plasmid DNA which is very different from that previously reported in linear DNA.
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- Wirström, Eva, 1977, et al.
(författare)
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COLD WATER VAPOR IN THE BARNARD 5 MOLECULAR CLOUD
- 2014
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8213 .- 2041-8205. ; 788:2
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Tidskriftsartikel (refereegranskat)abstract
- After more than 30 yr of investigations, the nature of gas-grain interactions at low temperatures remains an unresolved issue in astrochemistry. Water ice is the dominant ice found in cold molecular clouds; however, there is only one region where cold (similar to 10 K) water vapor has been detected-L1544. This study aims to shed light on ice desorption mechanisms under cold cloud conditions by expanding the sample. The clumpy distribution of methanol in dark clouds testifies to transient desorption processes at work-likely to also disrupt water ice mantles. Therefore, the Herschel HIFI instrument was used to search for cold water in a small sample of prominent methanol emission peaks. We report detections of the ground-state transition of o-H2O (J = 1(10)-1(01)) at 556.9360 GHz toward two positions in the cold molecular cloud, Barnard 5. The relative abundances of methanol and water gas support a desorption mechanism which disrupts the outer ice mantle layers, rather than causing complete mantle removal.
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- Wirström, Eva, 1977, et al.
(författare)
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Using Methanol Beacons to Find Water in the Dark
- 2013
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Ingår i: The Universe Explored by Herschel, 15 – 18 October 2013, Noordwijk, The Netherlands.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Interstellar methanol is only formed efficiently from hydrogenation of COmolecules accreted onto grains, and icy grain mantles are observed to consist of 1-30% methanol relative to water. In regions of both low and high mass star formation gas-phase methanol abundances are consistent with partial or complete removal of the ices, either by thermal evaporation or by shock-induced sputtering in outflows. However, the widespread presence of gas-phase methanol in molecular clouds attests to some non-thermal desorption process at work. In particular, distinct peaks of methanol emission at positions significantly offset from protostellar activity implies a transient desorption process, such as clump-clump collisions, rather than a continuous one like photodesorption. Such processes are likely to disrupt a major part of the ice mantles and lead to high gas-phase water abundances clearly distinguishable from what is expected from photodesorption or steady-state gas-phase chemistry.We will report on the first detection of gas-phase water in a cold dark cloud - well offset from protostellar activity - resulting from a small scale survey with Herschel HIFI towards methanol peaks. Physical properties of the sources as well as implications for mantle desorption mechanisms and chemistry in dark clouds will be discussed and compared to those of active star formation.
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