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- Engwall, Erik, 1977-
(författare)
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Low-Energy Ion Escape from the Terrestrial Polar Regions
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The contemporary terrestrial atmosphere loses matter at a rate of around 100,000 tons per year. A major fraction of the net mass loss is constituted by ions, mainly H+ and O+, which escape from the Earth’s ionosphere in the polar regions. Previously, the outflow has only been measured at low altitudes, but to understand what fraction actually escapes and does not return, the measurements should be conducted far from the Earth. However, at large geocentric distances the outflowing ions are difficult to detect with conventional ion instruments on spacecraft, since the spacecraft electrostatic potential normally exceeds the equivalent energy of the ions. This also means that little is known about the ion outflow properties and distribution in space far from the Earth. In this thesis, we present a new method to measure the outflowing low-energy ions in those regions where they previously have been invisible. The method is based on the detection by electric field instruments of the large wake created behind a spacecraft in a flowing, low-energy plasma. Since ions with low energy will create a larger wake, the method is more sensitive to light ions, and our measured outflow is essentially the proton outflow. Applying this new method on data from the Cluster spacecraft, we have been able to make an extensive statistical study of ion outflows from 5 to 19 Earth radii in the magnetotail lobes. We show that cold proton outflows dominate in these large regions of the magnetosphere in both flux and density. Our outflow values of low-energy protons are close to those measured at low altitudes, which confirms that the ionospheric outflows continue far back in the tail and contribute significantly to the magnetospheric content. We also conclude that most of the ions are escaping and not returning, which improves previous estimates of the global outflow. The total loss of protons due to high-latitude escape is found to be on the order of 1026 protons/s.
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| 2. |
- Thomas, Kavita Elisheba, 1974-
(författare)
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But What Do They Mean? : Modelling Contrast Between Speakers in Dialogue Signalled by “But”
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Understanding what is being communicated in a dialogue involves determining how it is coherent, that is, how the successive turns in the dialogue are related, what the speakers’ intentions, goals, beliefs, and expectations are and how they relate to each other’s responses. This thesis aims to address how turns in dialogue are related when one speaker indicates contrast with something in the preceding discourse signalled by “but”. Different relations cued by “but” will be distinguished and characterised when they relate material spanning speaker turns and an implementation in a working dialogue system is specified with the aim of enabling a better model of dialogue understanding and achieving more precise response generation.A large amount of research in discourse addresses coherence in monologue, and much of it focuses on cases in which the coherence relation is explicitly signalled via a cue-phrase or discourse marker (e.g., “on the other hand”, “but”, et cetera) which provides an explicit cue about the nature of the underlying relation linking the two clauses. However despite research on Speech Acts, planning research into speakers’ intentions, and semantic approaches to question-answering dialogues, very little work has focused on coherence relations across turns in dialogue even given the presence of a cue-phrase.This thesis will explore what sorts of relations the speaker of the “but” perceives between elements in the dialogue, and in particular, it will focus on “but”s communicating Denial of Expectation, Concession, and Correction by determining what underlying cross-turn expectations are denied in the former two, and what is being corrected in the latter case. We will extend work by Lagerwerf (1998) in monologue which presents a treatment for Denial of Expectation and Concession arguing that “but” implicates a defeasible expectation which is then denied (in Denial of Expectation) or argued against (in Concession). We also follow Knott’s approach (Knott, 1999a) of describing the semantics of a cue-phrase algorithmically from the agent’s mental model of the related utterances.Task-oriented and nontask-oriented spoken dialogues involving turn-initial “but” are examined, motivating a logical scheme whereby Denial of Expectation, Concession and Correction can be distinguished. These relations are then modelled in the PTT (Poesio and Traum, 1998) Information State (Matheson, Poesio and Traum, 2000) model of dialogue, enabling more relevant response generation in dialogue systems. A systematic response deliberation scheme based on the speakers’ underlying beliefs is proposed based on the analysis and modelling of relations presented in this thesis.
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| 3. |
- Anand, K J S, et al.
(författare)
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Effects of morphine analgesia in ventilated preterm neonates : primary outcomes from the NEOPAIN randomised trial
- 2004
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Ingår i: The Lancet. - 0140-6736 .- 1474-547X. ; 363:9422, s. 1673-82
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Opioid analgesia is commonly used during neonatal intensive care. We undertook the Neurologic Outcomes and Pre-emptive Analgesia in Neonates (NEOPAIN) trial to investigate whether pre-emptive morphine analgesia decreases the rate of a composite primary outcome of neonatal death, severe intraventricular haemorrhage (IVH), and periventricular leucomalacia (PVL) in preterm neonates.METHODS: Ventilated preterm neonates (n=898) from 16 centres were randomly assigned masked placebo (n=449) or morphine (n=449) infusions. After a loading dose (100 microg/kg), morphine infusions (23-26 weeks of gestation 10 microg kg(-1) h(-1); 27-29 weeks 20 microg kg(-1) h(-1); 30-32 weeks 30 microg kg(-1) h(-1)) were continued as long as clinically justified (maximum 14 days). Open-label morphine could be given on clinical judgment (placebo group 242/443 [54.6%], morphine group 202/446 [45.3%]). Analyses were by intention to treat.FINDINGS: Baseline variables were similar in the randomised groups. The placebo and morphine groups had similar rates of the composite outcome (105/408 [26%] vs 115/419 [27%]), neonatal death (47/449 [11%] vs 58/449 [13%]), severe IVH (46/429 [11%] vs 55/411 [13%]), and PVL (34/367 [9%] vs 27/367 [7%]). For neonates who were not given open-label morphine, rates of the composite outcome (53/225 [24%] vs 27/179 [15%], p=0.0338) and severe IVH (19/219 [9%] vs 6/189 [3%], p=0.0209) were higher in the morphine group than the placebo group. Placebo-group neonates receiving open-label morphine had worse rates of the composite outcome than those not receiving open-label morphine (78/228 [34%] vs 27/179 [15%], p<0.0001). Morphine-group neonates receiving open-label morphine were more likely to develop severe IVH (36/190 [19%] vs 19/219 [9%], p=0.0024).INTERPRETATION: Pre-emptive morphine infusions did not reduce the frequency of severe IVH, PVL, or death in ventilated preterm neonates, but intermittent boluses of open-label morphine were associated with an increased rate of the composite outcome. The morphine doses used in this study decrease clinical signs of pain but can cause significant adverse effects in ventilated preterm neonates.
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| 5. |
- Serk, Henrik, 1980-, et al.
(författare)
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Global CO2 fertilization of Sphagnum peat mosses via suppression of photorespiration during the twentieth century
- 2021
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Natural peatlands contribute significantly to global carbon sequestration and storage of biomass, most of which derives from Sphagnum peat mosses. Atmospheric CO2 levels have increased dramatically during the twentieth century, from 280 to > 400 ppm, which has affected plant carbon dynamics. Net carbon assimilation is strongly reduced by photorespiration, a process that depends on the CO2 to O2 ratio. Here we investigate the response of the photorespiration to photosynthesis ratio in Sphagnum mosses to recent CO2 increases by comparing deuterium isotopomers of historical and contemporary Sphagnum tissues collected from 36 peat cores from five continents. Rising CO2 levels generally suppressed photorespiration relative to photosynthesis but the magnitude of suppression depended on the current water table depth. By estimating the changes in water table depth, temperature, and precipitation during the twentieth century, we excluded potential effects of these climate parameters on the observed isotopomer responses. Further, we showed that the photorespiration to photosynthesis ratio varied between Sphagnum subgenera, indicating differences in their photosynthetic capacity. The global suppression of photorespiration in Sphagnum suggests an increased net primary production potential in response to the ongoing rise in atmospheric CO2, in particular for mire structures with intermediate water table depths.
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| 6. |
- Tyburski, Robin, 1991-
(författare)
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Deciphering the Mechanistic Diversity of Proton-Coupled Electron Transfer Reactions
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proton coupled electron transfer is ubiquitous in biological and artificial reaction systems. Much has been done in order to describe the occurrence of such reactions. However, PCET reactivity is often very complex. For instance, there are multiple (stepwise and concerted) mechanistic pathways through which PCET may occur. The aim of this thesis is to further describe factors and underlying principles governing PCET reactivity. The contents of this thesis can be summarized in three parts:In the first part (chapter 4), the competition between different PCET mechanisms is discussed. Considering all mathematical expressions for the dependence of the rate constants on The Gibbs free energy changes (driving forces) associated with electron and proton transfer, mechanistic Zone-Diagrams are constructed. These show which of the mechanistic pathways is dominant, given a certain electron and proton transfer driving force. It is shown, how these diagrams simplify discussion of PCET reactivity. Strategies for modifying the mechanistic landscape, suppressing or favoring a CEPT mechanism, are demonstrated in the PCET oxidation of 4-methoxyphenol by photogenerated Ru(III) oxidants in the presence of pyridine bases. These are discussed utilizing the zone-diagram methodology. Implications for catalytic applications are discussed.The second part (chapter 5) introduces pressure dependence as a tool for mechanistic characterization of the PCET reactions. The PCET oxidation of tungsten hydrides covalently linked to pyridine bases by photogenerated Ru(III) oxidants was studied, and contributions from multiple mechanistic pathways were uncovered. It is shown, how each pathway has a characteristic pressure dependence. These can be related to changes in electrostriction of the solvent modifying the volume profile of the reaction.Finally, the third part (Chapter 6) deals with the concerted pathway. The possibility of photo-EPT, where electronic excitation directly yields the PCET product state, in Phenol/N-Methyl-4,4’-bipyridine complexes is discussed. It is shown that the optical charge-transfer absorption in these complexes is not coupled to proton transfer, in spite of previous claims. Further, the pressure dependence of the CEPT quenching of excited state fac-Re(CO)3(2,2’-bpy)(4,4’-bpy)+ by substituted Phenols is monitored. It is shown that the observed pressure dependence cannot be rationalized using the electrostriction arguments outlined in chapter 5. Instead, a model relating the observations to pressure induced changes of contributing proton tunneling distances is constructed.
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