| 1. |
- Kanoni, Stavroula, et al.
(författare)
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Implicating genes, pleiotropy, and sexual dimorphism at blood lipid loci through multi-ancestry meta-analysis.
- 2022
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Ingår i: Genome biology. - : Springer Science and Business Media LLC. - 1474-760X .- 1465-6906 .- 1474-7596. ; 23:1
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Tidskriftsartikel (refereegranskat)abstract
- Genetic variants within nearly 1000 loci are known to contribute to modulation of blood lipid levels. However, the biological pathways underlying these associations are frequently unknown, limiting understanding of these findings and hindering downstream translational efforts such as drug target discovery.To expand our understanding of the underlying biological pathways and mechanisms controlling blood lipid levels, we leverage a large multi-ancestry meta-analysis (N=1,654,960) of blood lipids to prioritize putative causal genes for 2286 lipid associations using six gene prediction approaches. Using phenome-wide association (PheWAS) scans, we identify relationships of genetically predicted lipid levels to other diseases and conditions. We confirm known pleiotropic associations with cardiovascular phenotypes and determine novel associations, notably with cholelithiasis risk. We perform sex-stratified GWAS meta-analysis of lipid levels and show that 3-5% of autosomal lipid-associated loci demonstrate sex-biased effects. Finally, we report 21 novel lipid loci identified on the X chromosome. Many of the sex-biased autosomal and X chromosome lipid loci show pleiotropic associations with sex hormones, emphasizing the role of hormone regulation in lipid metabolism.Taken together, our findings provide insights into the biological mechanisms through which associated variants lead to altered lipid levels and potentially cardiovascular disease risk.
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| 2. |
- Abay, Simon, 1980, et al.
(författare)
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Charge transport in InAs nanowire Josephson junctions
- 2014
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - 2469-9950 .- 2469-9969 .- 1098-0121. ; 89:21, s. 214508-
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Tidskriftsartikel (refereegranskat)abstract
- We present an extensive experimental and theoretical study of the proximity effect in InAs nanowires connected to superconducting electrodes. We fabricate and investigate devices with suspended gate-controlled nanowires and nonsuspended nanowires, with a broad range of lengths and normal-state resistances. We analyze the main features of the current-voltage characteristics: the Josephson current, excess current, and subgap current as functions of length, temperature, magnetic field, and gate voltage, and compare them with theory. The Josephson critical current for a short-length device, L = 30 nm, exhibits a record high magnitude of 800 nA at low temperature that comes close to the theoretically expected value. The critical current in all other devices is typically reduced compared to the theoretical values. The excess current is consistent with the normal resistance data and agrees well with the theory. The subgap current shows a large number of structures; some of them are identified as subharmonic gap structures generated by multiple Andreev reflection. The other structures, detected in both suspended and nonsuspended devices, have the form of voltage steps at voltages that are independent of either the superconducting gap or length of the wire. By varying the gate voltage in suspended devices, we are able to observe a crossover from typical tunneling transport at large negative gate voltage, with suppressed subgap current and negative excess current, to pronounced proximity junction behavior at large positive gate voltage, with enhanced Josephson current and subgap conductance as well as a large positive excess current.
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| 3. |
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| 4. |
- Abay, Simon, 1980, et al.
(författare)
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Quantized Conductance and Its Correlation to the Supercurrent in a Nanowire Connected to Superconductors
- 2013
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 13:8, s. 3614-3617
-
Tidskriftsartikel (refereegranskat)abstract
- We report conductance and supercurrent of InAs nano wires coupled to Al-superconducting electrodes with short channel lengths and good Ohmic contacts. The nanowires are suspended 15 nm above a local gate electrode. The charge density in the nanowires can be controlled by a small change in the gate voltage. For large negative gate voltages, the number of conducting channels is reduced gradually, and we observe a stepwise decrease of both conductance and critical current before the conductance vanishes completely.
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| 5. |
- Abulaiti, Yiming, et al.
(författare)
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Luminosity determination in pp collisions at root s=8 TeV using the ATLAS detector at the LHC
- 2016
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 76:12
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Tidskriftsartikel (refereegranskat)abstract
- The luminosity determination for the ATLAS detector at the LHC during pp collisions at root s = 8 TeV in 2012 is presented. The evaluation of the luminosity scale is performed using several luminometers, and comparisons between these luminosity detectors are made to assess the accuracy, consistency and long-term stability of the results. A luminosity uncertainty of delta L/L = +/- 1.9% is obtained for the 22.7 fb(-1) of pp collision data delivered to ATLAS at root s = 8 TeV in 2012.
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| 6. |
- Abulaiti, Yiming, et al.
(författare)
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Measurements of the Higgs boson production and decay rates and constraints on its couplings from a combined ATLAS and CMS analysis of the LHC pp collision data at root s=7 and 8 TeV
- 2016
-
Ingår i: Journal of High Energy Physics (JHEP). - : SPRINGER. - 1126-6708 .- 1029-8479. ; :8
-
Tidskriftsartikel (refereegranskat)abstract
- Combined ATLAS and CMS measurements of the Higgs boson production and decay rates, as well as constraints on its couplings to vector bosons and fermions, are presented. The combination is based on the analysis of five production processes, namely gluon fusion, vector boson fusion, and associated production with a W or a Z boson or a pair of top quarks, and of the six decay modes H -> ZZ; WW, gamma gamma; tau tau; bb, and mu mu. All results are reported assuming a value of 125: 09 GeV for the Higgs boson mass, the result of the combined measurement by the ATLAS and CMS experiments. The analysis uses the CERN LHC proton-proton collision data recorded by the ATLAS and CMS experiments in 2011 and 2012, corresponding to integrated luminosities per experiment of approximately 5 fb(-1) at root s = 7TeV and 20 fb(-1) at root s = 8TeV. The Higgs boson production and decay rates measured by the two experiments are combined within the context of three generic parameterisations: two based on cross sections and branching fractions, and one on ratios of coupling modifiers. Several interpretations of the measurements with more model-dependent parameterisations are also given. The combined signal yield relative to the Standard Model prediction is measured to be 1.09 +/- 0.11. The combined measurements lead to observed significances for the vector boson fusion production process and for the H -> tau tau decay of 5.4 and 5.5 standard deviations, respectively. The data are consistent with the Standard Model predictions for all parameterisations considered.
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| 7. |
- Abulaiti, Yiming, et al.
(författare)
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Search for dark matter in association with a Higgs boson decaying to b-quarks in pp collisions at root s=13 TeV with the ATLAS detector
- 2017
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 765, s. 11-31
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Tidskriftsartikel (refereegranskat)abstract
- A search for dark matter pair production in association with a Higgs boson decaying to a pair of bottom quarks is presented, using 3.2 fb(-1) of pp collisions at a centre-of-mass energy of 13 TeV collected by the ATLAS detector at the LHC. The decay of the Higgs boson is reconstructed as a high-momentum b (b) over bar system with either a pair of small-radius jets, or a single large-radius jet with substructure. The observed data are found to be consistent with the expected backgrounds. Results are interpreted using a simplified model with a gauge boson mediating the interaction between dark matter and the Standard Model as well as a two-Higgs-doublet model containing an additional Z' boson which decays to a Standard Model Higgs boson and a new pseudoscalar Higgs boson, the latter decaying into a pair of dark matter particles.
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| 8. |
- Abulaiti, Yiming, et al.
(författare)
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Search for single production of a vector-like quark via a heavy gluon in the 4b final state with the ATLAS detector in pp collisions at root s=8 TeV
- 2016
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Ingår i: Physics Letters B. - : Elsevier BV. - 0370-2693 .- 1873-2445. ; 758, s. 249-268
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Tidskriftsartikel (refereegranskat)abstract
- A search is performed for the process pp -> G* -> B-H(b) over bar/(B) over bar (H)b -> Hb (b) over bar -> b (b) over barb (b) over bar, predicted in composite Higgs scenarios, where G* is a heavy colour octet vector resonance and B-H a vector-like quark of charge -1/3. The data were obtained from pp collisions at a centre-of-mass energy of 8 TeV corresponding to an integrated luminosity of 19.5 fb(-1), recorded by the ATLAS detector at the LHC. The largest background, multijet production, is estimated using a data-driven method. No significant excess of events with respect to Standard Model predictions is observed, and upper limits on the production cross section times branching ratio are set. Comparisons to the predictions from a specific benchmark model are made, resulting in lower mass limits in the two-dimensional mass plane of m(G*) vs. m(BH).
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| 9. |
- Abulaiti, Yiming, et al.
(författare)
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Search for the production of single vector-like and excited quarks in the Wt final state in pp collisions at root s=8 TeV with the ATLAS detector
- 2016
-
Ingår i: Journal of High Energy Physics (JHEP). - : Springer. - 1126-6708 .- 1029-8479. ; :2
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Tidskriftsartikel (refereegranskat)abstract
- A search for vector-like quarks and excited quarks in events containing a top quark and a W boson in the final state is reported here. The search is based on 20.3 fb(-1) of proton-proton collision data taken at the LHC at a centre-of-mass energy of 8 TeV recorded by the ATLAS detector. Events with one or two leptons, and one, two or three jets are selected with the additional requirement that at least one jet contains a b-quark. Single-lepton events are also required to contain at least one large-radius jet from the hadronic decay of a high-PT W boson or a top quark. No significant excess over the expected background is observed and upper limits on the cross-section times branching ratio for different vector-like quark and excited-quark model masses are derived. For the excited-quark production and decay to Wt with unit couplings, quarks with masses below 1500 GeV are excluded and coupling-dependent limits are set.
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| 10. |
- Ahlgren, Erik, 1962, et al.
(författare)
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Biokombi Rya - slutrapporter från ingående delprojekt
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Inom projektet Biokombi Rya har ett flertal olika forskargrupper samarbetat för att studera system¬effekterna av förgasning av biobränsle ur olika aspekter. Syftet med projektet är att öka kunskapen om biobränsleförgasning i Sverige samt att utreda förutsättningar för att sådana anläggningar ska vara ekonomiskt och miljömässigt intressanta. En referensgrupp har varit kopplad till projektet där förutsättningar, resultat och slutsatser har behandlats.I denna underlagsrapport har slutrapporterna från projektets delprojekt samlats. De beskriver förutsättningar, metodansatser, använda data och resultat utförligt och utgör på så sätt ett viktigt komplement till den mer övergripande beskrivningen i projektets syntesrapport. De delrapporter som ingår har valts för att täcka in samtliga delar av projektet som är av allmänt intresse. Projektresultat som publicerats på annat sätt berörs dock mer kortfattat.Projektet Biokombi Rya har pågått under två år (2005-2006) och drivits av Chalmers EnergiCentrum. Förutom de omfattande analysinsatser som författarna till denna rapport står för, har Avdelningen för kemisk teknologi vid KTH, Siemens Industrial Turbines AB och Göteborg Energi AB bidragit med expertstöd. CIT Industriell Energianalys, med undertecknad som projektledare, har stått för projektledning och koordination.Projektet har finansierats av Energimyndigheten, Göteborg Energis forsknings¬stiftelse samt Göteborg Energi AB.
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| 11. |
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| 12. |
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| 13. |
- Ben-Avraham, Dan, et al.
(författare)
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The complex genetics of gait speed : Genome-wide meta-analysis approach
- 2017
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Ingår i: Aging. - : Impact Journals, LLC. - 1945-4589. ; 9:1, s. 209-246
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Tidskriftsartikel (refereegranskat)abstract
- Emerging evidence suggests that the basis for variation in late-life mobility is attributable, in part, to genetic factors, which may become increasingly important with age. Our objective was to systematically assess the contribution of genetic variation to gait speed in older individuals. We conducted a meta-analysis of gait speed GWASs in 31,478 older adults from 17 cohorts of the CHARGE consortium, and validated our results in 2,588 older adults from 4 independent studies. We followed our initial discoveries with network and eQTL analysis of candidate signals in tissues. The meta-analysis resulted in a list of 536 suggestive genome wide significant SNPs in or near 69 genes. Further interrogation with Pathway Analysis placed gait speed as a polygenic complex trait in five major networks. Subsequent eQTL analysis revealed several SNPs significantly associated with the expression of PRSS16, WDSUB1 and PTPRT, which in addition to the meta-analysis and pathway suggested that genetic effects on gait speed may occur through synaptic function and neuronal development pathways. No genome-wide significant signals for gait speed were identified from this moderately large sample of older adults, suggesting that more refined physical function phenotypes will be needed to identify the genetic basis of gait speed in aging.
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| 14. |
- Fong, Jason, et al.
(författare)
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Speech Audio Corrector : using speech from non-target speakers for one-off correction of mispronunciations in grapheme-input text-to-speech
- 2022
-
Ingår i: INTERSPEECH 2022. - : International Speech Communication Association. ; , s. 1213-1217
-
Konferensbidrag (refereegranskat)abstract
- Correct pronunciation is essential for text-to-speech (TTS) systems in production. Most production systems rely on pronouncing dictionaries to perform grapheme-to-phoneme conversion. Unlike end-to-end TTS, this enables pronunciation correction by manually altering the phoneme sequence, but the necessary dictionaries are labour-intensive to create and only exist in a few high-resourced languages. This work demonstrates that accurate TTS pronunciation control can be achieved without a dictionary. Moreover, we show that such control can be performed without requiring any model retraining or fine-tuning, merely by supplying a single correctly-pronounced reading of a word in a different voice and accent at synthesis time. Experimental results show that our proposed system successfully enables one-off correction of mispronunciations in grapheme based TTS with maintained synthesis quality. This opens the door to production-level TTS in languages and applications where pronunciation dictionaries are unavailable.
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| 15. |
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Nyberg, Daniel, 1980, et al.
(författare)
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Effects of intrinsic radiation Q on mismatch factor of three types of small antennas: single-resonance, gradual-transition and cascaded-resonance types
- 2010
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Ingår i: IET Microwaves, Antennas and Propagation. - : Institution of Engineering and Technology (IET). - 1751-8725 .- 1751-8733. ; 4:1, s. 83-90
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Tidskriftsartikel (refereegranskat)abstract
- Resonators are traditionally characterised by their quality factor Q, which is inversely proportional to the relative bandwidth. Small antennas are often resonant, so they can be characterised by a Q, except for the fact that the correct quality measure of an antenna is the inverse Q, that is the relative bandwidth, rather than Q. Still, it has become common to study fundamental size limitations of small antennas in terms of a so-called radiation Q (or antenna Q). This study explains how this intrinsic radiation Q relates to: (i) the bandwidth-efficiency product of small single-resonance-type antennas, (ii) the gradual cut-off of spherical waves for wideband gradual-transition-type small antennas and (iii) the number of resonances needed to cover a certain frequency band for wideband cascaded-resonance-type small antennas. The study also introduces one intrinsic radiation Q for basic single TE and TM spherical mode sources, and another for combined TE and TM sources.
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| 20. |
- Nyberg, Daniel, 1980, et al.
(författare)
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Radiation Q and radiation efficiency of wideband small antennas and their relation to bandwidth and cut-off of spherical modes
- 2007
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Ingår i: 2nd European Conference on Antennas and Propagation, EuCAP 2007; Edinburgh; United Kingdom; 11 November 2007 through 16 November 2007. - : Institution of Engineering and Technology. - 9780863418426
-
Konferensbidrag (refereegranskat)abstract
- Resonators are traditionally characterized by their quality factor Q, which is inversely proportional to the relative bandwidth. Small antennas are often resonant, so they can be characterized by a Q, except for the fact that the correct quality measure of an antenna is rather the inverse Q. i.e. the relative bandwidth. Still, it has become common to study fundamental size limitations of small antennas in terms of a so-called radiation Q (or antenna Q). The paper explains how this intrinsic radiation Q relates to: i) the bandwidth- efficiency product of small single-resonance-type antennas, ii) the gradual cut-off of spherical waves for wideband gradual-transition-type small antennas, and iii) the number of resonances needed to cover a certain frequency band for wideband multiple-resonances-type small antennas. The paper also introduces one intrinsic radiation Q for basic single TE and TM spherical mode sources, and another for combined TE and TM sources.
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| 21. |
- Nyström, Ingrid, 1965, et al.
(författare)
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Biokombi Rya - Biobränsleförgasning satt i system
- 2007
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Inom projekt Biokombi Rya har ett flertal olika forskargrupper gemensamt studerat systemeffekterna av att introducera förgasning av biobränsle i Göteborgs fjärrvärmesystem, i Västsverige som region och ur ett mer generellt och långsiktigt systemperspektiv. Syftet med projektet är att öka kunskapen inför eventuell framtida utbyggnad av biobränsleförgasning i Sverige samt att utreda vilka förutsättningar som är nödvändiga för att sådana anläggningar ska bli ekonomiskt och miljömässigt intressanta inom en relativt kort tidsrymd (ca 10 år). Fokus ligger på integration av anläggningar för förgasning av biobränsle med befintliga kraftvärmeverk med kombicykel samt med fjärrvärme. Projektet vänder sig till beslutsfattare inom området på nationell, regional och lokal nivå.Övergripande systemanalys inom projektet har särskilt fokuserat på biobränslemarknaden och framtida prisbildning för biobränsle samt på den långsiktiga konkurrenskraften för biodrivmedel via förgasning. Projektet i övrigt utgår från en tillämpad fallstudie av delvis konvertering av Rya Kraftvärmeverk (Rya KVV) i Göteborg till förgasat biobränsle, vilket alltså innebär integration mellan förgasningsanläggning och ett naturgaseldat gaskombikraftvärmeverk knutet till ett fjärrvärmesystem. I denna del ingår även en konceptuell studie över olika tekniska processalternativ för produktion av värme, el och drivmedel, inklusive ett mer långsiktigt alternativ för vätgasproduktion. Inom projektet används gemensamma scenarier för energimarknaderna ca år 2020.Några av projektets viktigaste slutsatser är:• Förgasning av biobränsle kan bli intressant för både el- och drivmedelsproduktion och bidra till reducerade CO2-utsläpp, förutsatt att nivån på priset på biobränsle inte är alltför hög relativt fossilbränslepriserna. I de flesta fall är också riktade styrmedel för att premiera förnybar el- och/eller drivmedelsproduktion (t ex certifikat) en förutsättning. Vid gynnsamma förutsättningar för både ”grön” el- och drivmedelsproduktion kan en konkurrenssituation om biobränsle uppstå.• Den långsiktiga konkurrenskraften för biodrivmedel från förgasning är i hög grad beroende av teknik- och kostnadsutveckling inom både transportsektorn och andra sektorer, t ex för lagring av el och väte, bränsleceller och uthållig CO2-fri elproduktion. Tillgängligheten för insamling och lagring av CO2 från fossila anläggningar ökar konkurrenskraften betydligt, men denna effekt neutraliseras om CO2 samlas in även från biobaserade anläggningar. Vilken typ av biodrivmedel som får bäst konkurrenskraft beror till stor del på distributions- och fordonskostnader.• Göteborgs fjärrvärmesystem, med en stor andel spillvärme, och Rya Kraftvärmeverk, med relativt andra kombicykler låg elverkningsgrad, har egentligen inte de optimala förutsättningarna för att förgasning av biobränsle ska vara ekonomiskt intressant.• I flera fall kan det trots detta vara ekonomiskt intressant att bygga en anläggning för förgasning av biobränsle i Göteborg. Av de förgasningsbaserade alternativ som studerats, visar sig produktion av syntetisk naturgas från flis för användning som fordonsbränsle var den ekonomiskt mest robusta lösningen, förutsatt att det finns riktade styrmedel för ”grön” drivmedelsproduktion, t ex drivmedelscertifikat. Ombyggnad av Rya Kraftvärmeverk till delvis biobränslebaserad kraftvärme via förgasning är även detta ekonomiskt intressant i flera fall. Kraftvärme baserad på biobränsleförgasning med högre elverkningsgrad än vad som är möjligt i Rya Kraftvärmeverk skulle dock kunna vara än mer intressant.• För att en förgasningsanläggning ska vara ekonomiskt intressant är det viktigt att uppnå så hög el- respektive drivmedelsverkningsgrad som möjligt samt att anläggningen får längsta möjliga drifttid. För drivmedelsproduktion finns det betydande fördelar med att kunna utnyttja värmeöverskottet från anläggningen i ett fjärrvärmesystem eller liknande.• För fjärrvärmesystemen i regionen som helhet finns det, enligt modellresultaten och för de scenarier som använts, starka drivkrafter att öka elproduktionen i kraftvärmeverk. Med gynnsamma förutsättningar för biobränslebaserad elproduktion har konventionell biobränslebaserad kraftvärme bäst ekonomi. Med drivmedelscertifikat eller liknande kan förgasningsanläggningar istället få en betydande roll för produktion av biodrivmedel, även knutet till medelstora fjärrvärmenät.• Produktion av biodrivmedel, som DME och vätgas, kan ske till kostnader som är konkurrenskraftiga gentemot dagens bensinpris, särskilt om produktionen blir möjlig att integrera med svartlutsförgasning (här studerat för vätgas). För vätgasproduktion är i samtliga fall ekonomin och den totala effekten på CO2-utsläppen dock starkt beroende av möjligheterna att samla in och lagra CO2.• För samtliga studerade tekniker och delsystem påverkar scenarieantaganden om utvecklingen av energimarknaderna och omvärldens energisystem i hög grad resultaten. För att utvärdera robustheten och de totala klimateffekterna för en enskild investering krävs därför systemanalys, som tar hänsyn till denna omvärld.
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| 22. |
- Simon, Daniel, 1980-, et al.
(författare)
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Angle of Attack and Load Factor Limiting in Fighter Aircraft using Command Governors
- 2017
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Konferensbidrag (refereegranskat)abstract
- Modern fighter aircraft require maximum control performance in order to have the upper hand in a dogfight or when they have to outmaneuver an enemy missile. Therefore pilots must be able to maneuver the aircraft very close to the limit of what it is capable of while at the same time focus on the tactical tasks of the mission. To enable this, modern flight control systems have automatic systems for angle of attack and load factor limiting.One such design technique is reference or command governors. In this paper we investigate different ways of designing command governors for angle of attack and load factor limiting in in fighter aircraft flight control systems. We discuss different design approaches and their properties and implement one selected design in Saab's JAS 39 Gripen fighter aircraft simulation environment.
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| 23. |
- Simon, Daniel, 1980-
(författare)
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Fighter Aircraft Maneuver Limiting Using MPC : Theory and Application
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Flight control design for modern fighter aircraft is a challenging task. Aircraft are dynamical systems, which naturally contain a variety of constraints and nonlinearities such as, e.g., maximum permissible load factor, angle of attack and control surface deflections. Taking these limitations into account in the design of control systems is becoming increasingly important as the performance and complexity of the aircraft is constantly increasing.The aeronautical industry has traditionally applied feedforward, anti-windup or similar techniques and different ad hoc engineering solutions to handle constraints on the aircraft. However these approaches often rely on engineering experience and insight rather than a theoretical foundation, and can often require a tremendous amount of time to tune.In this thesis we investigate model predictive control as an alternative design tool to handle the constraints that arises in the flight control design.We derive a simple reference tracking MPC algorithm for linear systems that build on the dual mode formulation with guaranteed stability and low complexity suitable for implementation in real time safety critical systems.To reduce the computational burden of nonlinear model predictive control we propose a method to handle the nonlinear constraints, using a set of dynamically generated local inner polytopic approximations. The main benefit of the proposed method is that while computationally cheap it still can guarantee recursive feasibility and convergence.An alternative to deriving MPC algorithms with guaranteed stability properties is to analyze the closed loop stability, post design. Here we focus on deriving a tool based on Mixed Integer Linear Programming for analysis of the closed loop stability and robust stability of linear systems controlled with MPC controllers.To test the performance of model predictive control for a real world example we design and implement a standard MPC controller in the development simulator for the JAS 39 Gripen aircraft at Saab Aeronautics. This part of the thesis focuses on practical and tuning aspects of designing MPC controllers for fighter aircraft. Finally we have compared the MPC design with an alternative approach to maneuver limiting using a command governor.
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| 24. |
- Simon, Daniel, 1980-
(författare)
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Model Predictive Control in Flight Control Design : Stability and Reference Tracking
- 2014
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aircraft are dynamic systems that naturally contain a variety of constraints and nonlinearities such as, e.g., maximum permissible load factor, angle of attack and control surface deflections. Taking these limitations into account in the design of control systems are becoming increasingly important as the performance and complexity of the controlled systems is constantly increasing. It is especially important in the design of control systems for fighter aircraft. These require maximum control performance in order to have the upper hand in a dogfight or when they have to outmaneuver an enemy missile. Therefore pilots often maneuver the aircraft very close to the limit of what it is capable of, and an automatic system (called flight envelope protection system) against violating the restrictions is a necessity.In other application areas, nonlinear optimal control methods have been successfully used to solve this but in the aeronautical industry, these methods have not yet been established. One of the more popular methods that are well suited to handle constraints is Model Predictive Control (MPC) and it is used extensively in areas such as the process industry and the refinery industry. Model predictive control means in practice that the control system iteratively solves an advanced optimization problem based on a prediction of the aircraft's future movements in order to calculate the optimal control signal. The aircraft's operating limitations will then be constraints in the optimization problem.In this thesis, we explore model predictive control and derive two fast, low complexity algorithms, one for guaranteed stability and feasibility of nonlinear systems and one for reference tracking for linear systems. In reference tracking model predictive control for linear systems we build on the dual mode formulation of MPC and our goal is to make minimal changes to this framework, in order to develop a reference tracking algorithm with guaranteed stability and low complexity suitable for implementation in real time safety critical systems.To reduce the computational burden of nonlinear model predictive control several methods to approximate the nonlinear constraints have been proposed in the literature, many working in an ad hoc fashion, resulting in conservatism, or worse, inability to guarantee recursive feasibility. Also several methods work in an iterative manner which can be quit time consuming making them inappropriate for fast real time applications. In this thesis we propose a method to handle the nonlinear constraints, using a set of dynamically generated local inner polytopic approximations. The main benefits of the proposed method is that while computationally cheap it still can guarantee recursive feasibility and convergence.
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| 25. |
- Simon, Daniel, 1980-, et al.
(författare)
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Nonlinear Model Predictive Control using Feedback Linearization and Local Inner Convex Constraint Approximations
- 2013
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Ingår i: Proceedings of the 2013 European Control Conference. - 9783952417348 ; , s. 2056-2061
-
Konferensbidrag (refereegranskat)abstract
- Model predictive control (MPC) is one of the most popular advanced control techniques and is used widely in industry. The main drawback with MPC is that it is fairly computationally expensive and this has so far limited its practical use for nonlinear systems.To reduce the computational burden of nonlinear MPC, Feedback Linearization together with linear MPC has been used successfully to control nonlinear systems. The main drawback is that this results in an optimization problem with nonlinear constraints on the control signal.In this paper we propose a method to handle the nonlinear constraints that arises using a set of dynamically generated local inner polytopic approximations. The main benefits of the proposed method is guaranteed recursive feasibility and convergence.
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| 26. |
- Simon, Daniel, 1980-
(författare)
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Robust MRAC augmentation of fiight control laws for center of gravity adaptation
- 2016
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Konferensbidrag (refereegranskat)abstract
- When an aircraft is flying and burning fuel the center of gravity (c.g.) of the aircraft shifts slowly. The c.g. can also be shifted abruptly when e.g. a ghter aircraft releases a weapon. The shift in c.g. is difficult to measure or estimate so the flight control systems need to be robustly designed to cope with this variation. However for fighter aircrafts with high manoeuvrability there is room for improvements. In this paper we investigate if the use of adaptive control law augmentation can be used to better cope with the change in c.g. We augment a baseline controller with a robust Model Reference Adaptive Control (MRAC) design and analyse its benets and possible issues.
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| 27. |
- Simon, Daniel, 1980-, et al.
(författare)
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Stability analysis of Model Predictive Controllers using Mixed Integer Linear Programming
- 2016
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Ingår i: Proceedings of the 55th IEEE Conference on Decision and Control. - 9781509018376
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Konferensbidrag (refereegranskat)abstract
- It is a well known fact that finite time optimal controllers, such as MPC do not necessarily result in closed loop stable systems. Within the MPC community it is common practice to add a final state constraint and/or a final state penalty in order to obtain guaranteed stability. However, for more advanced controller structures it can be difficult to show stability using these techniques. Additionally in some cases the final state constraint set consists of so many inequalities that the complexity of the MPC problem is too big for use in certain fast and time critical applications. In this paper we instead focus on deriving a tool for a-postiori analysis of the closed loop stability for linear systems controlled with MPC controllers. We formulate an optimisation problem that gives a sufficient condition for stability of the closed loop system and we show that the problem can be written as a Mixed Integer Linear Programming Problem (MILP).
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| 28. |
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