| 20671. |
- Rios, Felix Leopoldo, 1985-
(författare)
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Bayesian structure learning in graphical models
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of two papers studying structure learning in probabilistic graphical models for both undirected graphs anddirected acyclic graphs (DAGs).Paper A, presents a novel family of graph theoretical algorithms, called the junction tree expanders, that incrementally construct junction trees for decomposable graphs. Due to its Markovian property, the junction tree expanders are shown to be suitable for proposal kernels in a sequential Monte Carlo (SMC) sampling scheme for approximating a graph posterior distribution. A simulation study is performed for the case of Gaussian decomposable graphical models showing efficiency of the suggested unified approach for both structural and parametric Bayesian inference.Paper B, develops a novel prior distribution over DAGs with the ability to express prior knowledge in terms of graph layerings. In conjunction with the prior, a search and score algorithm based on the layering property of DAGs, is developed for performing structure learning in Bayesian networks. A simulation study shows that the search and score algorithm along with the prior has superior performance for learning graph with a clearly layered structure compared with other priors.
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| 20672. |
- Ripellino, Giulia, 1989-
(författare)
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A search for Supersymmetry in final states with two same-flavor opposite-sign leptons, jets and missing transverse momentum with the ATLAS detector
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a search for Supersymmetry in final states containing two same-flavor opposite-sign leptons, jets and large missing transverse momentum. The search makes use of 36.1 fb−1 of proton-proton collision data collected at a center-of-mass energy of √s = 13 TeV by the ATLAS detector at the Large Hadron Collider. Two signal scenarios, which both involve the pair-production of squarks or gluinos decaying into final states with two leptons and the lightest supersymmetric particle, are targeted by the analysis. The first scenario considers decay chains with a leptonically decaying Z boson and is characterized by a peak in the dilepton invariant mass distribution. In the second scenario, decays through intermediate sleptons or an off-shell Z boson are considered. Such processes lead to a kinematic endpoint in the dilepton invariant mass distribution. The main Standard Model backgrounds include the pair-production of top quarks and direct production of Z bosons. These backgrounds are estimated with two data-driven methods. The observed data is found to be consistent with the Standard Model expectation and the results are interpreted in simplified Supersymmetry models for gluino and squark pair-production. Sensitivity is provided for gluino and squark masses up to 1.85 TeV and 1.3 TeV respectively.
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| 20673. |
- Ripellino, Giulia, 1989-
(författare)
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Haystacks and Needles : Measuring the number of proton collisions in ATLAS and probing them for the production of new exotic particles
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes my work on the ATLAS luminosity measurement and on two searches for physics beyond the Standard Model, performed using √s = 13 TeV proton-proton (pp) collision data recorded by the ATLAS detector at CERN during Run 2 of the LHC in the years 2015-2018ATLAS employs several detectors and methods to measure the relative luminosity and the absolute scale is determined using van der Meer scans during dedicated low-luminosity running periods in each year. The thesis presents the details of the track-counting method which is used to extrapolate the calibration to the high-luminosity physics data-taking regime. After data-quality selections, the full Run 2 pp data sample corresponds to an integrated luminosity of 139 fb-1, with an uncertainty of 1.7%.The first analysis presented is a search for Supersymmetry in final states with two same-flavour opposite-charge leptons, jets, and large missing transverse momentum. The search uses 36.1 fb-1 of pp collision data collected in 2015 and 2016. Signal scenarios involving pair-production of squarks or gluinos decaying into final states with two leptons and the lightest supersymmetric particle are targeted by the analysis. The main Standard Model backgrounds are estimated with data-driven methods and the observed data is found to be consistent with the expectation. Results are interpreted in simplified Supersymmetry models and exclude gluinos and squarks with masses up to 1.85 TeV and 1.3 TeV at 95% confidence level, respectively.The second analysis is a search for long-lived particles decaying into hadrons. The analysis selects events that contain multiple energetic jets and a displaced vertex and uses the full Run 2 pp collision dataset. Background estimates for Standard Model processes and instrumental effects are extracted from data. The observed yields are one event in the first signal region where 0.49±0.28 are expected and zero events in the second signal region where 0.7±0.4 are expected. The results are used to set limits at 95% confidence level on Supersymmetry scenarios with long-lived electroweakinos that decay via a small R-parity-violating coupling into triplets of quarks. Electroweakly produced neutralinos with masses up to 1.3 TeV are excluded for lifetimes between 0.01 ns and 10 ns.
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| 20674. |
- Rippner Blomqvist, Brita
(författare)
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Non-ionic block copolymers and proteins at the air-water interface
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The behavior of block copolymer and protein films at interfaces is of central importance to their function in many application areas. Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers function e.g. as emulsifiers and in coatings in oral, parenteral, and topical pharmaceutical formulations and are also widely used for cleaning purposes. The globular protein β-lactoglobulin is the most abundant whey protein and it is used within the food industry as a component of many common foods. To understand the interfacial behavior of block copolymers and proteins in such applications one has to study molecular processes like adsorption, the responses to shear and dilatational deformation of the interface (i.e. surface rheology), conformational changes of the molecules, and forces that are generated between interfacial layers. Such investigations form the focus of the work presented in this thesis. Thin film measurements with a series of block copolymers composed of poly(ethylene oxide) and poly(butylene oxide) revealed that the thickness of foam films (air-aqueous solution-air) is determined by electrostatic and steric repulsion. The range of the steric repulsion is directly dependent on the size of the polymer, in particular the length of the poly(ethylene oxide) chains. Block copolymers attached to the air-water interface change their conformation with increasing surface concentration. The study of the dilatational modulus as a function of the surface pressure of spread and adsorbed block copolymer layers showed that the block copolymers pass from a two-dimensional conformation to a three-dimensional extended structure as the available area per molecule decreases. Relaxation processes occur mainly by a redistribution of segments within the surface layer. Mixing of the hydrophobic poly(propylene oxide) segments in a sublayer of poly(ethylene oxide) and water was proposed to occur at high surface concentration of the polymer. Conformational changes (partial denaturation) of globular proteins upon adsorption at the air-water interface leads to the formation of highly viscoelastic networks, which play an important role for the stabilization of foams and emulsions. Mixed layers, formed by competitive adsorption of β-lactoglobulin and block copolymers, were also investigated. On increasing the concentration of block copolymer, the viscoelasticity of the mixed protein/block copolymer layer gradually decreased. The polymer was able to displace the protein from the interface. The drainage rate of thin liquid films was also enhanced by the presence of block copolymer. Whether or not the incorporation of the polymer in the β-lactoglobulin layer has a detrimental effect on foam stability depends on the ability of the polymer to generate long-range steric repulsion across the foam films. For pure block copolymer systems, correlations between foam stability and the thickness of interfacial layers, in the steric regime, were found. The results obtained can be utilized for increasing the understanding of the mechanisms for foam stabilization in both model and industrial systems.
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| 20675. |
- Risberg, Erik
(författare)
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Lewis Acid Mediated Alkylation and Diels-Alder Reactions of 2H-Azirines
- 2002
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes the use of 2H-azirines as reactivesubstrates in Lewis acid catalysed nucleophilic additions andin the Diels-Alder reaction.A number of carbon nucleophiles have been added to aseries of 2H-azirines in the presence and absence ofBF3·Et2O. 3-(2-Naphthyl)-2H-azirine has been used as amodel substrate in the enantioselective addition oforganolithium reagents to an 2H-azirine.A selection of Lewis acids has been screened for theirpossible use in the normal electron demand Diels-Alder reactionbetween 3-alkyl-, 3-aryl-, and 3- carboxyl-2H-azirines and avariety of dienes. Lewis acid activation was found to shortenreaction times and facilitate lower reaction temperatures.These cycloadditions proceeded with endo selectivity providinga single diastereoisomeric product.DFT calculations of Lewis acid activated 2H-azirineshave been carried out.Keywords:2H-azirines, Lewis acid activation, chiralligands, organolithium reagents, Diels-Alder reactions,DFT-calculations
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| 20676. |
- Risberg, Erik, 1975-
(författare)
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Lewis acid Mediated Aza-Diels-Alder Reactions and Asymmetric Alkylations of 2H-azirines
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes the use of 2H-azirines, three-membered unsaturatednitrogen-containing heterocycles, as reactive intermediates ina number of Lewis acid promoted alkylations and Diels-Alderreactions providing synthetically useful aziridines. In order to carry out this investigation a new generalprocedure for the ring closure of vinyl azides, forming theresultant 3-substituted-2H-azirines, was developed applying low boiling solventsin closed reaction vessels at elevated temperatures. The addition of organolithium reagents in the presence ofcommercially available chiral ligands, to the 3-(2-naphthyl)-2H-azirine was studied, which gave the correspondingaziridines. Several Lewis acids were shown to catalyze the normalelectron-demand Diels-Alder reaction between 3-alkyl-,3-aromatic-, and 3-ester-substituted 2H-azirines and various dienes. These reactions gave theexpected cycloadducts in moderate yields. Using a chiral auxiliary high diastereoselectivity wasobtained in the addition of alkyl radicals to a8-phenylmenthyl-substituted 2H-azirine-3-carboxylate. The alkyl radicals weregenerated from the corresponding trialkyl borane and molecularoxygen. Hydroborations and transmetallations were used toprepare these trialkylboranes. Catalytic amounts of CuClincreased the diastereoselectivity in the radical additionreactions. Attempts were made to explain how the coordination of aLewis acid to the azirine nitrogen atom affects thereactivity/stability of the azirine. DFT calculations and NMRexperiments involving Lewis acid-azirine complexes wereperformed. Keywords:Enantioselective, diastereoselective, vinylazide, 2H-azirines, aziridines, Lewis acid, chiral ligand,chiral auxiliary, organolithiums, Diels-Alder reaction, alkylradicals, triethylborane.
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| 20677. |
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| 20678. |
- Risberg, Per, 1975-
(författare)
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Discribing the Auto-Ignition Quality of Fuels in HCCI Engines
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Homogeneous Charge Compression Ignition (HCCI) engine is a promising engine concept that emits low concentrations of NOx and particulates and still has a high efficiency. Since the charge is auto-ignited, the auto-ignition quality of the fuel is of major importance. It has been shown in several studies that neither of the classical measures of auto-ignition quality of gasoline-like fuels, RON and MON, can alone describe this in all conditions in HCCI combustion. However, even in such cases it is possible to combine RON and MON into an octane index, OI, that describes the auto-ignition quality well in most conditions. The octane numbers are combined into the OI with the variable K according to the following equation: OI = (1-K)RON + K MON = RON – K S The OI of a sensitive fuel is the equivalent of the octane number of a primary reference fuel with the same resistance to auto-ignition in the tested condition. The K-value is dependent on the temperature and pressure history. A generic parameter Tcomp15, the temperature at 15 bar during the compression, was introduced to describe the temperature and pressure history. It was found that the K-value increases with increasing Tcomp15 and two linear equations have been suggested to describe this relationship. At high or low Tcomp15 it has been found that the sensitivity of the fuel octane quality on combustion phasing is small and the auto-ignition quality defined by the OI scale does no longer play a big role. NO affects the combustion phasing of gasoline-like fuels. This effect is most significant at low concentration where it advances the combustion phasing considerably. At higher conditions its influence is different for different fuels. A sensitive fuel is considered a good HCCI fuel since its OI changes in the same direction as the octane requirement of the engine, which would make the engine management easier. It is also likely that a sensitive fuel will enable a wider operating range. The auto-ignition quality of diesel-like fuels was studied in tests with three different strategies of mixture formation. In these tests it was found that the ignition delay increased with lower cetane number and that the cetane number described the auto-ignition quality well, even for fuels of significantly different physical properties. The experiments were, however, made at a limited range of operating conditions and low load. A good diesel-like HCCI fuel should be easy to vaporize to facilitate homogeneity. It should have a high resistance to auto-ignition, not necessarily the highest, one that allows both high and low loads at a given compression ratio. Finally, it should also function well with the injection system without a significant decrease in injection system life length.
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| 20679. |
- Risén, Emma, et al.
(författare)
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Natural Resource Potential of Macroalgae Harvesting in the Baltic Sea-Case Study Trelleborg, Sweden
- 2013
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Ingår i: Global Challenges in Integrated Coastal Zone Management. - Oxford, UK : John Wiley & Sons. - 9780470657560 ; , s. 69-84
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The interest in harvesting biomass from the Baltic Sea has increased in recent years. However, there is a lack of available data on macroalgae biomass and of cost-effective methods for site-specific quantification of macroalgae. In this study, macroalgae biomass has been quantified in Trelleborg and thus the nutrient reduction that could be achieved by harvesting on a regional scale. The biomass was estimated on the basis of existing inventories of macroalgae, photic zone distribution and bottom substrata. An independent model for estimating the potential of macroalgae growth was applied where factors affecting the growth of macroalgae, for example nutrients, light and temperature, were considered. The estimated summer stock of macroalgae biomass along the 58 km coastal stretch in Trelleborg amounts to 19 000 tonnes dry weight (dwt) red filamentous algae. If 10-30% of this summer stock were to be harvested, a nutrient reduction of 50-150 t of nitrogen could be achieved. The model for estimating biomass proved promising and worthy of further investigation.
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| 20680. |
- Risén, Emma, 1985-
(författare)
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Sustainability Aspects of Bioenergy and Nutrient Recovery from Marine Biomass : Baltic Sea case studies
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Coastal areas around the world are experiencing environmental problems such as climate change and eutrophication. These, in turn, lead to emerging challenges with excessive amounts of biomass that impact coastal communities. Developing utilisation strategies for marine biomass is therefore highly relevant and forms part of the blue growth research field. In response to environmental concerns, as a waste management strategy and as part of blue growth research initiatives, several Baltic Sea coastal projects have been initiated in recent years to study utilisation of maritime biomass. However, the sustainability of these utilisation strategies has not been critically appraised. Therefore, the work presented in this thesis explored some key sustainability aspects of two Baltic Sea case studies utilising common reed (Kalmar, Sweden) and mass-occurring filamentous macroalgae (Trelleborg, Sweden) for biogas and biofertiliser recovery. Energy analyses suggested that both case studies could provide a positive energy balance and have the potential to achieve nutrient recovery. Moreover, a contingent valuation study in Trelleborg demonstrated considerable welfare benefits of biomass utilisation. These findings indicate that marine biomass utilisation strategies highlight potential to contribute to environmental and welfare benefits of these coastal communities.
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