| 1911. |
- Syed, J., et al.
(författare)
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The "Maggie" filament: Physical properties of a giant atomic cloud
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 657
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Tidskriftsartikel (refereegranskat)abstract
- Context. The atomic phase of the interstellar medium plays a key role in the formation process of molecular clouds. Due to the line-of-sight confusion in the Galactic plane that is associated with its ubiquity, atomic hydrogen emission has been challenging to study. Aims. We investigate the physical properties of the "Maggie" filament, a large-scale filament identified in H I emission at line-of-sight velocities, upsilon(LSR) similar to -54 km s(-1). Methods. Employing the high-angular resolution data from The H I/OH Recombination line survey of the inner Milky Way (THOR), we have been able to study H I emission features at negative upsilon(LSR) velocities without any line-of-sight confusion due to the kinematic distance ambiguity in the first Galactic quadrant. In order to investigate the kinematic structure, we decomposed the emission spectra using the automated Gaussian fitting algorithm GAUSSPY+. Results. We identify one of the largest, coherent, mostly atomic H I filaments in the Milky Way. The giant atomic filament Maggie, with a total length of 1.2 +/- 0.1 kpc, is not detected in most other tracers, and it does not show signs of active star formation. At a kinematic distance of 17 kpc, Maggie is situated below (by approximate to 500 pc), but parallel to, the Galactic H I disk and is trailing the predicted location of the Outer Arm by 5-10 km s(-1) in longitude-velocity space. The centroid velocity exhibits a smooth gradient of less than +/- 3 km s(-1) (10 pc)(-1) and a coherent structure to within +/- 6 km s(-1). The line widths of similar to 10 km s(-1) along the spine of the filament are dominated by nonthermal effects. After correcting for optical depth effects, the mass of Maggie's dense spine is estimated to be 7.2(-1.9)(+2.5) x 10(5) M-circle dot. The mean number density of the filament is similar to 4 cm(-3), which is best explained by the filament being a mix of cold and warm neutral gas. In contrast to molecular filaments, the turbulent Mach number and velocity structure function suggest that Maggie is driven by transonic to moderately supersonic velocities that are likely associated with the Galactic potential rather than being subject to the effects of self-gravity or stellar feedback. The probability density function of the column density displays a log-normal shape around a mean of < N-HI > = 4.8 x 10(20) cm(-2), thus reflecting the absence of dominating effects of gravitational contraction. Conclusions. While Maggie's origin remains unclear, we hypothesize that Maggie could be the first in a class of atomic clouds that are the precursors of giant molecular filaments.
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| 1912. |
- Thiel, V., et al.
(författare)
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Time-of-flight secondary ion mass spectrometry (TOF-SIMS) : Principles and practice in the biogeosciences
- 2014
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Ingår i: Principles and practice of analytical techniques in Geosciences. - : Royal Society of Chemistry. - 9781849736497 ; , s. 122-170
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Bokkapitel (refereegranskat)abstract
- Time-of-flight secondary ion mass spectrometry (TOF-SIMS) provides chemical information on the outermost molecular layers of sample surfaces without solvent extraction. In TOF-SIMS, a pulsed beam of high-energy ions (primary ions) is scanned over a selected analysis area on the sample. During the primary ion bombardment, neutral and charged particles (secondary ions) are released from the outermost molecular layers of the sample surface. Analysis of the secondary ions in a TOF analyser yields a mass spectral data set that allows the retrospective production of(1) ion images showing the spatial signal intensity distribution from selected ions over the analysis area; (2) mass spectra from the total analysis area; or (3) mass spectra from user-defined regions of interest inside the analysis area. In the so-called static SIMS regime, the primary ions are provided in very short pulses and the analysis is completed before the incoming primary ions damage a significant fraction of the surface. Static TOF-SIMS is therefore capable of providing molecularly specific secondary ions, and thus mass spectra with detailed organic information, which is not possible with other (‘dynamic’) SIMS techniques. In this chapter, we describe the principles of static TOF-SIMS instrumentation and data evaluation, review a number of relevant applications, and discuss the potential of this technique in the biogeosciences, with a focus on organic biomarker applications.
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| 1913. |
- Wallstrom, S. H. J., et al.
(författare)
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Chlorine-bearing molecules in molecular absorbers at intermediate redshifts
- 2019
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 629
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Tidskriftsartikel (refereegranskat)abstract
- We use observations of chlorine-bearing species in molecular absorbers at intermediate redshifts to investigate chemical properties and Cl-35/Cl-37 isotopic ratios in the absorbing sightlines. Chloronium (H2Cl+) is detected along three independent lines of sight in the z = 0.89 and z = 0.68 molecular absorbers located in front of the lensed quasars PKS 1830-211 and B 0218+357, respectively. Hydrogen chloride (HCl) was observed only toward PKS 1830-211, and is found to behave differently from H2Cl+. It is detected in one line of sight with an abundance ratio [H2Cl+]/[HCl] similar to 1, but remains undetected in the other, more diffuse, line of sight, with a ratio [H2Cl+] / [HCl] > 17. The absorption profiles of these two chlorine-bearing species are compared to other species and discussed in terms of the physical properties of the absorbing gas. Our findings are consistent with the picture emerging from chemical models where different species trace gas with different molecular hydrogen fraction. The Cl-35/Cl-37 isotopic ratios are measured in the different lines of sight and are discussed in terms of stellar nucleosynthesis.
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| 1914. |
- Lengyel, Tamas, 1986, et al.
(författare)
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Pre-emphasis enabled 50 Gbit/s transmission over 1000 m SMF using a 1060 nm single-mode VCSEL
- 2018
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Ingår i: Electronics Letters. - : Institution of Engineering and Technology (IET). - 1350-911X .- 0013-5194. ; 54:20, s. 1186-1187
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Tidskriftsartikel (refereegranskat)abstract
- A single-mode 1060 nm vertical-cavity surface-emitting laser (VCSEL) and single-mode fibre (SMF) based link with two-tap active pre-emphasis enabling error-free transmission of 50 Gbit/s NRZ-OOK over 1000 m is presented.
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| 1915. |
- Hylén, Astrid, 1991, et al.
(författare)
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FOSFOR - ett djupgående problem
- 2022
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Ingår i: Havsutsikt. ; :2, s. 17-19
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Trots att utsläppen av fosfor och kväve minskat i Östersjön så fortsätter effekterna av övergödningen. Ofta har konstgjord syresättning föreslagits som åtgärd, eftersom stora mängder fosfor i havet hänger ihop med syrefria bottnar. Men kommer det att hjälpa? Enligt den sammanställda forskningen är det mycket tveksamt.
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| 1916. |
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| 1917. |
- Carlsson, Christel
(författare)
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Limitations and possibilities for microbial degradation of organic contaminants in aquifers
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many factors can influence the rate of microbial degradation of organic contaminants in aquifers. Some of these factors, e.g. sorption, the presence of dissolved organic matter (DOM), biomass, redox conditions, cometabolism, microbial community composition, and activity of degrading microorganisms, are addressed in the thesis, with the ambition to gain insights for bioremediation in aquifers, and to prevent contaminants from spreading to drinking water supplies. The influence of sorption of organic contaminants and bacteria on biodegradation was investigated under both diffusion limited and advective flow conditions. The results demonstrated that degradation by suspended bacteria of dissolved aniline and 2,4-dichlorophenol (2,4-DCP) was faster than the degradation of the same compounds sorbed to the solids. Nevertheless, sorption to the solids was not sufficient to exclude trace contaminants from degradation. In another investigation, the main effect of DOM on microbial phenanthrene degradation in groundwater was stimulation of microbial growth and activity of degrading populations, with hydrophilic DOM having a better effect than hydrophobic. In another study, glyphosate degradation was different in a mixture of sediment and groundwater from two aquifers (Vejen, Denmark and Vomb, Sweden). Laboratory experiments excluded sorption and organic carbon limitation as major sources of the observed differences. Glyphosate degradation was positively correlated to the density of bacteria, but the difference in density between the two sites was too small to account for the degradation difference. Instead, it was found that the differences in metabolic activity of the degrading strains and the microbial community composition of the aquifers were large and coincided with differences in rates of biodegradation. Glyphosate sorption was lower and biodegradation was slower under anaerobic conditions compared with aerobic, and most of the degraded glyphosate was not mineralized but cometabolized to AMPA. The thesis pin-points to the possibilities to increase contaminant biodegradation in aquifers by the addition of i) oxygen to stimulate aerobic degradation, ii) a primary growth substrate, e.g. DOM, to increase biomass and thereby stimulate metabolic or cometabolic degradation, and iii) microorganisms to increase the degrading population and/or genetic capacity.
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| 1918. |
- Dorrepaal, E, et al.
(författare)
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Are growth forms consistent predictors of leaf litter quality and decomposability across peatlands along a latitudinal gradient?
- 2005
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Ingår i: Journal of Ecology. - : Wiley. - 1365-2745 .- 0022-0477. ; 93:4, s. 817-828
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Tidskriftsartikel (refereegranskat)abstract
- Plant growth forms are widely used to predict the effects of environmental changes, such as climate warming and increased nitrogen deposition, on plant communities, and the consequences of species shifts for carbon and nutrient cycling. We investigated whether the relationship between growth forms and patterns in litter quality and decomposition are independent of environmental conditions and whether growth forms are as good as litter chemistry at predicting decomposability. We used a natural, latitudinal gradient in NW Europe as a spatial analogue for future increases in temperature and nitrogen availability. Our screening of 70 species typical of Sphagnum-dominated peatlands showed that leaf litters of Sphagnum mosses, evergreen and deciduous shrubs, graminoids and forbs differed significantly in litter chemistry and that the ranking of the growth forms was independent of the region for all litter chemistry variables. Differences among growth forms were usually larger than differences related to the environmental gradient. After 8 and 20 months incubation in outdoor, Sphagnum-based decomposition beds, growth forms generally differed in decomposability, but these patterns varied with latitude. Sphagnum litters decomposed slower than other litters in all regions, again explaining its high representation in organic deposits of peatlands. Forb litters generally decomposed fastest, while the differences among the other growth forms were small, particularly at higher latitudes. Multiple regression analyses showed that growth forms were better at predicting leaf litter decomposition than chemical variables in warm-temperate peatlands with a high N-load, but less so in the subarctic, low-N region. Our results indicate that environmental changes may be less important in determining ecosystem leaf litter chemistry directly than are their indirect effects through changes in the relative abundance of growth forms. However, climatic and nutritional constraints in high-latitude peatlands promote convergence towards nutrient-efficient plant traits, resulting in similar decomposition rates of vascular growth forms despite differences in litter chemistry. The usefulness of the growth-form concept in predicting plant community controls on ecosystem functioning is therefore somewhat limited.
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| 1919. |
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| 1920. |
- Gonzalez Rodriguez, Adrian, 1988, et al.
(författare)
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Melting transition of oriented Li-DNA fibers submerged in ethanol solutions
- 2021
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Ingår i: Biopolymers. - : Wiley. - 0006-3525 .- 1097-0282. ; 112:3
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Tidskriftsartikel (refereegranskat)abstract
- The melting transition of Li-DNA fibers immersed in ethanol-water solutions has been studied using calorimetry and neutron diffraction techniques. The data have been analyzed using the Peyrard-Bishop-Dauxois model to determine the strengths of the intra- and inter-base pair potentials. The data and analysis show that the potentials are weaker than those for DNA in water. They become weaker still and the DNA less stable as the ethanol concentration increases but, conversely, the fibers become more compact and the distances between base pairs become more regular. The results show that the melting transition is relatively insensitive to local confinement and depends more on the interaction between the DNA and its aqueous environment.
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