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Computational Studies of Oxygen Reduction Catalysts
Get PDFDissertation submitted in partial fulfillment of a Philosophiae Doctor degree in ChemistryThe oxygen reduction reaction (ORR) is of central importance in the development
of more efficient and durable fuel cells and computer simulations can be used to
help explain and predict properties of ORR catalysts. In this thesis, various simulation
methods are used, their accuracy tested, and some new tools developed for simulations of different types of ORR catalysts. The first part of the thesis presents a ReaxFF reactive
force field study of the oxidation of platinum nanoparticles, the catalyst currently
used in most fuel cells. The simulations make use of a grand-canonical Monte Carlo
simulation approach to study the mechanism of oxidative nanoparticle degradation.
Electrochemical oxidation phase diagrams are constructed and they show that stable
surface oxides can form under fuel cell operating conditions. Furthermore, clusters of
Pt6O8 stoichiometry are identified as the primary oxidation product and this provides a
detailed, atomic scale mechanism for the degradation of platinum nanoparticle ORR
catalysts.
In the second part of the thesis, metal-free ORR catalysts are studied, namely
nitrogen-doped graphene (NG). There, electron density functional theory calculations
are used to estimate the thermodynamics of possible reaction paths and provide an
estimate of the overpotential. Various density functional approximations are tested
against high level diffusion Monte Carlo calculations on the binding and migration
of an *O adatom on graphene, an important intermediate in the ORR. It is found
that generalized-gradient approximation (GGA) functionals have low accuracy while
some hybrid functionals and a self-interaction corrected GGA functional give good
agreement with the reference calculation. A hybrid functional is then used to calculate
the free energy of ORR intermediates to estimate the overpotential for various catalyst
structures and compositions. While overpotentials are initially found to be unfavorable,
the presence of water molecules at the catalyst surface is estimated to reduce the
calculated overpotentials significantly. This shows that proper inclusion of the aqueous
electrolyte is important. From this conclusion, a significant challenge arises as inclusion
of many solvent molecules makes the simulated system too large for electronic structure
calculations.
In the third part of the thesis, a new methodology is developed to make it possible
to include the aqueous electrolyte in simulations by using a hybrid simulation approach
where part of the system — the catalyst as well as the reacting species and nearby
water molecules — are included in the electronic structure calculation, while the rest of
the aqueous electrolyte is described using a potential energy function. The separation
between the two regions is made to lie through the aqueous phase in order to make
it easier to describe the interaction between atoms on opposite sides of the boundary.
Therein, the challenge is to enforce the boundary in such a way that atoms and molecules do not wander from one region to another. A new method referred to as scattering-adapted flexible inner region ensemble separator (SAFIRES) is developed for this purpose. It represents an improvement on a previous algorithm called FIRES. With
SAFIRES, the boundary between the two regions is flexible and adjusts automatically
but particles cannot move between the regions. It is demonstrated that using SAFIRES,
the energy, atomic forces, and probability distribution for the location of atoms are
reproduced accurately compared to results of simulations where where no boundary is
present. The SAFIRES algorithm dynamically changes the time step in the iterative
algorithm for time evolution to identify and enforce elastic collisions of atoms with
the boundary separating the two regions. A new propagator is introduced to simulate
the time evolution of the system with or without a connection to a heat bath. Tests
are carried out by simulating a Lennard-Jones liquid, a Lennard-Jones liquid/solid
interface, and water described using a potential energy function. With the SAFIRES
method, along with the recently developed, self-consistent polarizable hybrid simulation
methodology, the stage is set for proper inclusion of the aqueous phase at the electrode
surface in future electrochemistry simulations.Supported by a PhD fellowship from the University of Iceland research fun
Ecosystem services of whales in the Arctic: co-production, valuation and governance
Get PDFThe thesis examines the dynamics of Arctic social-ecological systems (SES) that enable
human wellbeing benefits through whale ecosystem services (ES). It does so through a
review of relevant literature, construction of conceptual models, two primary economic
and socio-cultural whale ES valuation studies, and an assessment of whale ES governability.
The results indicate multiple human wellbeing benefits and associated economic, socio-
cultural and biophysical values derived from marine ecosystems through whale ES in
selected case study communities in Greenland, Iceland and Norway. These benefits include
but are not limited to tourism, education, cultural identity, community cohesiveness, commercial and indigenous whaling, biodiversity enhancement, ecosystem regulation, inspiration for arts, and existence values. The case studies demonstrate that they are obtained by communities through human-nature co-production of whale ES and governed by a multilayered web of formal and informal governance interactions. The social-ecological complexity revealed in the analysis of whale ES underlines the importance of context and plural ES values in Arctic marine resource governance. It also implies a necessity to study
social and ecological phenomena together as one co-evolving Earth system. Following
these observations, conceptual models were developed integrating elements of ES, their
co-production, and interactive governance and governability theories. The results of the
governability assessment reveal high complexity and dynamics related to whale ES, ability
of actors to self-govern, and a need for reflective and adaptive governance regimes. The
relevance of the methodology and conceptual models applied in this research extends beyond the Arctic and can be applied in other natural resource contexts.Í þessari doktorsritgerð er gangverk félagslegra vistkerfa á norðurslóðum sem gera
mönnum kleift að njóta góðs af vistkerfisþjónustu hvala skoðað. Þetta var gert með því að
rýna núverandi stöðu þekkingar á tengdum fræðum, smíði á hugmyndalíkönum, tveimur
frumrannsóknum á efnahagslegu og félags-menningarlegu gildi vistkerfisþjónustu hvala og
mati á stjórnhæfni vistkerfisþjónustu hvala. Niðurstöðurnar benda til margvíslegs
ávinnings fyrir velferð manna og tengdra efnahags-, félags-menningar- og lífeðlislegra
gilda frá vistkerfum í hafi, sem tengd eru vistkerfisþjónustu hvala í þeim samfélögum á
Grænlandi, Íslandi og Noregi sem valin voru sem tilvik rannsóknarinnar. Ávinning frá
vistkerfisþjónustu hvala má meðal annars sjá hvað varðar ferðaþjónustu, fræðslu,
menningarlega sjálfsmynd, samfélagslega samheldni, hvalveiðar í bæði atvinnuskyni og
fyrir frumbyggja, eflingu líffræðilegs fjölbreytileika, regluverk tengt vistkerfinu, innblástur
fyrir listsköpun og tilvistargildi. Tilviksrannsóknirnar sýna að samfélagið í heild sinni
nýtur ávinningsins með því að lifa í sátt og samlyndi við náttúruna og með góðri, marglaga
stjórnun í gegnum formleg og óformleg samskipti. Greining á vistkerfisþjónustu hvala
varpaði ljósi á félags-vistfræðilegt flækjustig sem undirstrikar mikilvægi þess að íhuga
samhengið og margvísleg gildi vistkerfisþjónustu í stjórnun auðlinda hafsins á
norðurslóðum. Þessi greining gaf einnig til kynna nauðsyn þess að rannsaka félags- og vistfræðileg fyrirbæri saman sem hluta af þróunarkerfi jarðarinnar. Í kjölfar þessara athugana
voru hugmyndalíkön þróuð þar sem þættir úr vistkerfisþjónustu, samframleiðsla þeirra og
gagnvirkar stjórnunar- og stjórnhæfnikenningar voru samþættar. Niðurstöður á mati á
stjórnhæfni sýndu fram á hátt flækjustig og gangverk tengd vistkerfisþjónustu hvala, hæfni
aðila til að stjórna sér sjálfir og þörf fyrir sveigjanleg stjórnkerfi. Gildi aðferðafræðinnar og
þeirra hugmyndalíkana sem þróuð voru í þessari rannsókn nær út fyrir norðurslóðir og er
hægt að beita á aðrar náttúruauðlindir.NordForsk (grant number 76654) - ARCPATH project
University of Iceland Doctoral FundPrinted versio
Low-Cost Unattended Design of Miniaturized 4 × 4 Butler Matrices with Nonstandard Phase Differences
Get PDFPublisher's version (útgefin grein)Design of Butler matrices dedicated to Internet of Things and 5th generation (5G) mobile systems-where small size and high performance are of primary concern-is a challenging task that often exceeds capabilities of conventional techniques. Lack of appropriate, unified design approaches is a serious bottleneck for the development of Butler structures for contemporary applications. In this work, a low-cost bottom-up procedure for rigorous and unattended design of miniaturized 4 x 4 Butler matrices is proposed. The presented approach exploits numerical algorithms (governed by a set of suitable objective functions) to control synthesis, implementation, optimization, and fine-tuning of the structure and its individual building blocks. The framework is demonstrated using two miniaturized matrices with nonstandard output-port phase differences. Numerical results indicate that the computational cost of the design process using the presented framework is over 80% lower compared to the conventional approach. The footprints of optimized matrices are only 696 and 767 mm(2), respectively. Small size and operation frequency of around 2.6 GHz make the circuits of potential use for mobile devices dedicated to work within a sub-6 GHz 5G spectrum. Both structures have been benchmarked against the state-of-the-art designs from the literature in terms of performance and size. Measurements of the fabricated Butler matrix prototype are also provided.This work was supported in part by the National Science Centre of Poland Grant 2017/27/B/ST7/00563 and by the National Centre for Research and Development Grant NOR/POLNOR/HAPADS/0049/2019-00.Peer reviewe
Dark Acoustic Oscillations in Structure Formation: The High Redshift Universe
Get PDFThe nature of dark matter (DM) as a particle is still an unresolved mystery in Physics. Therefore, a vast amount of competing particle models have been proposed. A promising category among these models are those that include relevant collisional damping in the primordial power spectrum due to the interactions with relativistic particles in the early Universe. This damping is reflected in the DM distribution as dark acoustic oscillations (DAOs) before the onset of structure formation (analogous to the baryonic acoustic oscillations in the photon-baryon plasma, but at smaller, galactic scales) which are potentially observable.
In this Thesis, two effective parameters are proposed that fully describe DAO models based on their key features in the linear power spectrum: the amplitude/height (relative to the Cold Dark Matter expectations) and scale of their primary DAO peak (effectively setting the cut-off scale for structure formation). In the limit of a peak height of zero, this parametrization also includes warm dark matter (WDM), which has a very different particle origin with a collisionless damping and a featureless cut-off in the power spectrum. A large suite of tailored N-body zoom-in simulations is used to cover the DAO parameter space that is still unconstrained, but relevant for galaxy formation. A novel (scale-dependent) way to compare different structure formation is introduced that makes it possible to identify the regions of distinct non-linear structure formation at high redshifts z≳5 based on statistical measures such as the non-linear power spectrum and the halo mass function. It is found that for a large part of the DAO parameter space, the non-linear power spectrum is actually indistinguishable from WDM models and only a small region of the models with the strongest DAOs has a distinct power spectrum (this region shrinks as the redshift becomes lower). However, the halo mass function breaks this WDM-DAO degeneracy and even the weakest DAO models show a distinct slope in the halo mass function for low-mass haloes, as long as the DAO scale is large enough. With these results, the proposed parametrization offers a quick way to connect a specific DM particle model to its linear power spectrum and from there (using the suite of simulations performed in this Thesis) to the non-linear power spectrum and halo mass function. It is also shown that the properties of DAO haloes can be well described by the extended Press-Schechter (EPS) formalism using a smooth-k filter. On the other hand, the structure of haloes within the DAO cosmology is well described by the well-known Navarro-Frenk-White profile (widely used in Cold Dark Matter, CDM). Relative to CDM, low-mass haloes in DAO models have a a lower concentration, which is also well approximated by the concentration-mass relation predicted by the EPS model and a simple mass assembly model based on hierarchical structure formation.
These results can be used to perform inexpensive calculations of the (high-redshift) halo mass function and concentration-mass relation instead of computationally expensive N-body simulations for virtually all the DAO parameter space explored in this Thesis. Finally, we show that truly distinct strong DAO features can potentially survive in the 1D Flux power spectrum down to redshifts probed by the Lyman-α forest (z=3-5.4) and upcoming 21-cm observations at the cosmic dawn (z=10-25). Future dedicated simulations including baryonic physics within the template provided in this Thesis should be able to give a detailed prediction for these possible observational signatures, to be searched for in future observations.Eðli hulduefnis er enn óleyst ráðgáta innan eðlisfræðinnar og því hefur verið stungið
upp á ógrynni líkana til að lýsa því. Eitt þeirra sem lofar góðu, inniheldur hulduefni sem
víxlverkar við afstæðilegar eindir í hinum unga alheimi. Þessi víxlverkun endurspeglast
í dreifingu hulduefnis sem þrýstingssveiflur (e. DAO) áður en uppbygging alheimsins
hefst og er hugsanlega mælanleg.
Í þessari ritgerð eru kynntar tvær breytur sem lýsa að fullu DAO líkönum út frá
sérkennum þeirra í aflrófinu: útslagi og hæð megintopps DAO. Sérsniðin hermilíkön
eru síðan nýtt til að rannsaka breyturými DAO sem tengist myndun vetrarbrauta. Kynnt
er ný aðferð til að bera saman mismunandi formgerðir alheimsins. Hún gerir það
mögulegt að bera kennsl á svæði með ólínulegri uppbyggingu formgerðar við há rauðvik
(z & 5); er þetta byggt á tölfræðilegum mælikvörðum eins og ólínulega aflrófinu og
massadreifingarreglu hjúpsins.
Ein af niðurstöðunum er sú að fyrir stóran hluta breyturýmis DAO er ólínulega
aflrófið í raun óaðgreinanlegt frá líkönum sem innihalda svokallað volgt hulduefni. Auk
þess hefur aðeins lítill hluti af þeim líkönum með kröftugustu DAO, auðgreinanlegt
aflróf. Hins vegar brýtur massadreifingregla hjúpsins margfeldnina á milli DAO og
volgs hulduefnis. Þessar niðurstöður sýna að hægt er að nota áðurnefndar breytur á
skjótan hátt til að tengja ákveðið hulduefnislíkan við línulega aflrófið og þaðan (með
því að nota hermilíkönin í þessri ritgerð) við ólínulega aflrófið og massadreifingarreglu
hjúpsins.
Einnig er sýnt fram á hægt er að lýsa eiginleikum DAO hjúpa með útvíkkaðri
aðferðarfræði Press-Schechter með því að nota slétta k síu. Aftur á móti er formgerð
hjúpa innan DAO-heimsfræði lýst vel með hinu þekkta Navarro-Frenk-White sniði
(mikið notað í köldu hulduefni). Miðað við kalt hulduefni, er samansöfnun hjúpa
með lágan massa minni en í DAO líkönum. Þessar niðurstöður er hægt að nýta til að
framkvæma hagkvæma útreikninga, við hátt rauðvik, á massadreifingarreglu hjúpsins
og massa-samansöfnunar sambandinu, í stað keyrslu hermilíkana sem kosta mikinn
reiknitíma í tölvum. Þetta á við um nánast allt DAO breyturýmið sem kannað er í þessari
ritgerð.
Að lokum sýnum við að ákveðnir eiginleikar DAO geta hugsanlega lifað af í 1D
aflrófinu, niður í rauðvik sem kannað er með Lyman-α skóginum (z = 3 − 5.4) og
komandi 21-cm athugunum (z = 10−25). Væntanleg hermilíkön sem taka eðlisfræði
þungeinda með í reikninginn, innan þess ramma sem settur er fram í þessari ritgerð,
ættu að geta spáð ítarlega fyrir um væntanlegar mæliniðurstöður sem leitað verður í
náinni framtíð
Essays on International Fisheries Management
Get PDFThis thesis consists of three chapters on the economics of international fisheries management.
The first chapter explores the economic and biological effects of exploiter and
species interactions in a multinational and multispecies fishery. The Northeast Atlantic
pelagic complex fishery (Norwegian spring-spawning herring, mackerel, and blue whiting) is harvested by several countries, and the species are ecologically interdependent
through, for example, predation and competition for food. I develop a stylized bioeconomic model of the pelagic complex fishery, and estimate the outcomes of different
types of fishery management. Specifically, I consider (1) whether exploiters ignore or
take into account species interactions, and (2) whether countries cooperate or compete
in the fishery. I consider three major exploiters: Norway, the European Union, and Iceland, which differ in terms of harvesting costs and ex-vessel prices. In the cooperative
case, applying multispecies management increases the net present value of the fishery by over 20 percent compared to single-species management. The global optimum
(i.e., cooperation and multispecies management) increases net present value by over
91 percent compared to the situation where both the common property and biological
externality are uninternalized. Non-cooperative management leads to poor biological
outcomes, such as depletion of the mackerel stock, irrespective of the type of biological
management adopted.
The second chapter examines empirically the effectiveness of Regional Fisheries
Management Organizations (RFMOs). The fraction of overexploited and collapsed international fish stocks has grown over the past decades, but has international management improved sustainability of managed stocks? The purpose of RFMOs is to promote sustainable use and conservation of international fisheries within their purview.
To elicit whether RFMOs have a conservation effect, I examine if RFMO management has reduced the probability of stock collapse. I exploit global fisheries data bases, and
construct a large panel data set on stock status of 87 RFMO-managed species during
1950–2014. I use a differences-in-differences strategy that compares probability of collapse in managed fisheries before and after RFMO establishment to collapse of other
international stocks. I find some tentative evidence to suggest that RFMOs may have
improved the sustainability of managed stocks, but the effect differs across individual
RFMOs.
The third chapter studies to what extent the number of exploiters in international
fisheries contributes to overexploitation. The number of harvesting countries may be a
key determinant of biological and economic outcomes in international fisheries. Theory
predicts that an increase in the number of independent harvesting countries increases
the probability of poor resource management. I combine information on the number
of harvesting countries and stock status in almost 1,300 internationally shared ocean
fish stocks. I use global fisheries catch data to construct indicators of stock status,
and estimate an ordered dependent variable model, controlling for key economic and
ecological variables. I complement the catch data analysis by studying a smaller set
of international fish stocks using biomass data. When using the catch data, the results
suggest that more harvesting countries is associated with a higher probability that stocks
are overexploited or collapsed. When using the biomass data, the results suggest that
an increase in the number of harvesting countries leads to (1) an increase in the odds of
overexploitation, and (2) a reduction in total biomass.Þessi ritgerð samanstendur af þremur sjálfstæðum köflum um hagfræði alþjóðlegrar
fiskveiðistjórnunar.
Fyrsti kaflinn fjallar um hagrænar og lifræðilegar afleiðingar af samspili fiskveiðiþjóða
og fiskistofna í uppsjávarfiskikerfinu (norsku vorgotssíldarinnar, makríls og kolmunna)
í Norður-Atlantshafi. Nokkur þjóðríki nýta þessa uppsjávarfiskikerfi til fiskveiða og
fiskistofnarnir hafa áhrif hver á annan m.a. með afráni og fæðusamkeppni. Ég byggi
upp lífhagfræðilegt líkan af þessum fiskveiðum og nota líkanið til að meta árangur af
mismunandi stjórnun fiskveiðanna. Nánar tiltekið kanna ég (1) hvort veiðiþjóðirnar
taka tillit til líffræðilegs samspils stofnanna og (2) hvort þjóðirnar samhæfi veiðar sínar
eða keppi hver við aðrar. Líkanið tekur til þriggja veiðiþjóða: Noregs, Evrópusambandsins og Íslands, sem eru mismunandi hvað snertir veiðikostnað og aflaverð. Sé
gert ráð fyrir því að þessar þjóðir samhæfi veiðar sínar gefur líkanið til kynna að virði
fiskveiðanna hækki um meira en 20% ef beitt er margstofnafiskveiðistjórnun fremur
en einsstofnastjórnun sem ekki tekur tillit til líffræðilegs samspil stofnanna. Hagkvæmasta nýting (þ.e. samhæfðar veiðar og margstofnafiskveiðistjórnun) hækkar núvirði
veiðanna um meira en 91% miðað við það núvirði sem fengist úr samkeppnisveiðum án
tillits til líffræðilegs samspils stofnanna.
Í öðrum kaflanum eru raungögn notuð til þess að kanna skilvirkni þess fyrirkomulags við stjórnun alþjóðlegra fiskveiða sem nefnt má Svæðisbundin Samtök um
Fiskveiðistjórnun (SSF; enska Regional Fisheries Management Organizations eða RFMOs). Hlutfall alþjóðlegra fiskistofna sem taldir eru hafa hrunið hefur vaxið jafnt
og þétt undanfarna áratugi. Hlutverk SSF er að tryggja sjálfbæra nýtingu og verndun
fiskistofna á sínum svæðum. Samkvæmt hagfræðikenningum er hins vegar erfitt fyrir
SSF að koma á aðhaldssamri fiskveiðistjórnun vegna fríþegahvatanna í alþjóðlegum
fiskveiðum. Til að varpa ljósi á hvort SSF hafi áhrif í fiskverndunarátt skoðum við hvort tilvera þeirra dragi úr líkunum á stofnhruni. Í þessu skyni hagnýtum við okkur
fyrirliggjandi gagnasöfn um alþjóðlegar fiskveiðar og setjum saman stórt tímaraðaþverksurðar gagnamengi um stofnstærðir yfir 150 alþjóðlegrar fiskitegunda á tímabilinu 1950–2014. Annar hluti gagnamengisins, viðfangshópurinn, eru stofnar þessara
tegunda sem hafa komist í umsjón SSF einhvern tíma á tímabilinu. Hinn hlutinn,
samanburðarhópurinn, eru stofnar sem aldrei hafa verið undir stjórn SSF. Tölfræðileg
kennsl eru borin á samhengið með hjálp aðferðar aðstoðarbreyta, þar sem alþjóðlegar skuldbindingar viðkomandi þjóðríkja eru notaðar sem aðstoðarbreyta fyrir tilveru
SSF. Niðurstaðan er að ekki séu neinar vísbendingar um að tilvist SSF minnki líkur á
stofnhruni. Þessi niðurstaða helst óbreytt þótt viðfangsshópnum og samanburðarhópnum sé breytt.
Í þriðja kaflanum er grafist fyrir um að hvaða marki fjöldi veiðiþjóða í alþjóðlegum
fiskveiðum stuðli af ofnýtingu fiskistofna. Vera kann að fjöldi nýtingarþjóða ráði miklu
um líffræðilegar og efnahagslegar afleiðingar alþjóðlegra fiskveiða. Forspá fræðikenninga er að líkur á slæmri fiskveiðistjórnun vaxi með fjölda nýtingarþjóða. Ég leiði
saman gögn um fjölda nýtingarþjóða og stofnstærðir meira en 1300 alþjóðlegra fiskistofna.
Ég nota alþjóðleg gögn um fiskafla til að útbúa mælikvarða á stofnstærð og met líkan
fyrir raðaða háða breytu (e. ordered dependent variable model) þar sem fallsamhengið
tekur einnig tillit til hagrænna og lífríkis- lykilbreyta. þessari athugun til viðbótar bæti
ég annarri þar sem háða breytan er mælingar á raunverulegum stofnstærðum en fjöldi
athugana hins vegar miklu færri. Þegar aflagögn eru notuð til að meta stofnstærðir
benda niðurstöður til þess að fleiri veiðiþjóðir auki líkur á ofnýtingu og stofnhruni. Þegar beint stofnmat er notað benda niðurstöður til þess að fleiri veiðiþjóðir leiði til (1)
meiri líkinda á ofnýtingu og (2) minnkunar í stofnstærð
Topology and symmetry-breaking in the strong light-matter coupling regime
Get PDFThe physics of light-matter interactions is a rapidly developing research area at the junction between condensed matter physics and quantum optics. Depending on the strength of the light-matter interaction the systems behave very differently. In the current thesis, we mainly (but not exclusively), focus on the regime of (ultra)strong light-matter interaction. Typically, the strong coupling regime implies the employment of various low-dimensional semiconductor structures embedded into a microcavity, or irradiation by a strong laser field, or considering cold atoms, trapped in the vicinity of a waveguide. In the current thesis, we investigate various quantum systems and phenomena in the (ultra)strong coupling regime, including:
1)topological insulator based on a two-dimensional array of dressed quantum rings;
2)the new type of a polariton Z topological insulator;
3)Bose-Einstein condensate in a tilted polariton ring;
4)chiral waveguide quantum optomechanics;
5)the new type of a Hall effect for composite particles (excitons), that we refer to as the anomalous exciton Hall effect;
6)transition metal dichalcogenide polaritons in the presence of free carriers; and other related phenomena.Eðlisfræði víxlverkunar ljóss og efnis þróast hratt sem rannsóknarsvið á mörkum þéttefnisfræði og skammtaljósfræði. Hegðun eðlisfræðikerfa þar sem þessi víxlverkun á
við er mjög mismunandi og fer eftir styrkleika þess. Í þessari ritgerð, skoðum við aðallega svið ofursterkrar víxlverkunar ljóss og efnis án þess að einskorða okkur við það.
Svið ofursterkrar víxlverkunar ljóss og efnis gefur almennt til kynna notkun á ýmsum lágvídda hálfleiðarakerfum, ágeislun með sterku leysissviði, eða kaldar frumeindir
í gildru nálægt bylgjuleiðurum. Ritgerð þessi fjallar um rannsóknir okkar á mismunandi skammtakerfum og fyrirbærum í sviði ofursterkrar kúplunar, svo sem:
1) grenndareinangrara byggða á tvívíðri grind af ágeisluðum skammtahringjum;
2) nýja tegund Z grenndareinangrara byggða á ljósskauteindum;
3) Bose-Einstein þéttingu í hallandi hring ljósskauteindahring;
4) skammtaljósaflfræði með hendnum bylgjuleiðara;
5) nýja tegund Hallhrifa fyrir samsettar eindir (örveindir), sem við köllum afbrigðileg
Hallhrif örveinda;
6) hliðarmálms díkalkogeníða (TMD) ljósskauteindir í nærveru frjálsra rafbera;
og fleiri tengd fyrirbæri
Erfðir kransæðasjúkdóms með áherslu á þátt blóðfitu
No full textKransæðasjúkdómur dregur fleiri til dauða á hverju ári en nokkur annar sjúkdómur á
heimsvísu. Sjúkdómurinn einkennist af framvindu æðakölkunar, sem er flókið og
margþætt ferli. Á undanförnum 14 árum hafa rannsóknir með víðtækri erfðamengisleit
leitt til stórstígra framfara í skilningi manna á hlutverki erfðaþátta í framgangi
æðakölkunar. Sem dæmi hafa nýlegar erfðarannsóknir undirstrikað orsakasamband
milli lípóprótína sem innihalda apólípóprótín B og aukinnar áhættu á
kransæðasjúkdómi.
Doktorsritgerð þessi byggir á fjórum birtum rannsóknum. Rannsóknirnar voru unnar
við Íslenska erfðagreiningu og byggja á yfirgripsmiklum gagnagrunni sem geymir
arfgerðar- og svipgerðarupplýsingar yfir 160.000 Íslendinga. Hver einstaklingur var
arfgerðargreindur með DNA-örflögum en auk þess voru erfðamengi allt að 50.000
einstaklinga heilraðgreind. Arfgerðarupplýsingar sem fengust með heilraðgreiningu
voru síðan notaðar til að áætla arfðgerðir í heildarúrtakinu með líkindafræðilegum
hætti.
Fyrsta rannsóknin skoðaði áhrif 50 algengra erfðaþátta kransæðasjúkdóms á
útbreiðslu sjúkdómsins við kransæðaþræðingu hjá yfir 8.600 einstaklingum.
Erfðafræðilegt áhættuskor sem tekur saman áhrif þessara breytileika hafði fylgni við
aukna útbreiðslu kransæðasjúkdóms. Niðurstöðurnar sýndu að samanlögð áhrif
algengra erfðaþátta kransæðasjúkdóms spáðu ekki aðeins fyrir um áhættu, heldur
einnig útbreiðslu sjúkdómsins við kransæðaþræðingu.
Önnur rannsóknin skoðaði hvort erfðaþættir sem hafa þekkt tengsl við blóðfitu hafi
áhrif á útbreiðslu kransæðasjúkdóms meðal yfir 17.000 einstaklinga sem höfðu gengist
undir kransæðaþræðingu eða mat á kalki í kransæðum með tölvusneiðmyndun.
Erfðaskor fyrir mismunandi blóðfitutegundir voru notuð til þess að kanna fylgni við
útbreiðslu kransæðasjúkdóms og meta hvort orsakasamhengi sé til staðar, með aðferð
sem nefnist á ensku Mendelian randomization. Þessi rannsókn undirstrikaði
orsakaáhrif kólesteróls sem bundið er í lípóprótínum sem innihalda apólípóprótín B
(þ.e. ekki-HDL kólesteról) á þróun æðakölkunar í kransæðum.
Þriðja rannsóknin miðaði að því að skoða algengi og afleiðingar arfbundinnar
kólesterólhækkunar meðal 160.000 einstaklinga. Bornar voru saman tvenns konar
skilgreiningar sem byggja annars vegar á arfgerð (þ.e. að sjúkdómsvaldandi
stökkbreyting sé til staðar) og hins vegar á klínískri svipgerð sem samræmist
sjúkdóminum (samkvæmt Dutch Lipid Clinic Network skilmerkjunum). Tuttugu
meinvaldandi stökkbreytingar fundust, en tólf þeirra voru áður óþekktar í íslensku þýði.
Samanlagt algengi stökkbreytinganna var u.þ.b. 1 af 800 í heildarúrtakinu. Arfbundin kólesterólhækkun sem skilgreind er út frá klínískri svipgerð var hins vegar mun
algengari (2,2% meðal fullorðinna einstaklinga með kólesterólmælingar) og í minnihluta
tilfella mátti rekja hana til undirliggjandi stökkbreytingar. Báðir hópar með arfbundna
kólesterólhækkun voru mjög vanmeðhöndlaðir með kólesteróllækkandi lyfjum.
Fjórða rannsóknin segir frá uppgötvun afar sjaldgæfrar stökkbreytingar í geni
lágþéttni-lípóprótína (LDL) viðtakans (LDLR), sem veldur aukinni virkni prótínsins.
Stökkbreytingin er 2,5 kílóbasa brottfelling á 3’ stýrisvæði (e. 3’ untranslated region)
sem fannst í sjö einstaklingum innan sömu fjölskyldunnar. Arfberar höfðu yfir 70%
lægra gildi lágþéttni-LDL kólesteróls í blóði og yfirborðstjáning LDL viðtakans í
eitilfrumum þeirra var nærri tvöföld á við þá sem ekki bera stökkbreytinguna. Þetta er
fyrsta stökkbreytingin í LDLR sem vitað er að auki verulega tjáningu viðtakans og
veldur þar með mikilli lækkun LDL kólesteróls í blóði. Greining á áhrifum
stökkbreytingarinnar varpar ljósi á þátt 3’ stýrisvæðisins í tjáningu LDL viðtakans og
sýnir að stytting þess getur aukið tjáningu viðtakans verulega.
Saman varpa þessar rannsóknir ljósi á áhrif algengra og sjaldgæfra arfbreytileika á
meingerð kransæðasjúkdóms, með sérstaka áherslu á þátt blóðfitu.Coronary artery disease (CAD) is a common disease that remains the leading cause of
death worldwide. CAD is characterized by the development of coronary
atherosclerosis, a complex and multifaceted process. Over the last 14 years, genomewide association studies have greatly improved our understanding of the contribution of
DNA sequence variants to the development of coronary atherosclerosis. For example,
genetic studies have underscored that circulating apolipoprotein B (apoB)-containing
lipoproteins such as low-density lipoproteins (LDL) are causally related to the
development of CAD.
This thesis is based on four genetic studies. The studies were carried out at
deCODE genetics, Reykjavík, Iceland, and are based on an extensive database that
holds the genotypes and phenotypes of over 160,000 Icelandic participants. Each
participant was chip-genotyped and up to 50,000 participants additionally underwent
whole-genome sequencing (WGS); the sequence variants identified using WGS were
then imputed into the entire genotyped sample.
The first study examined the effects of 50 common risk variants for CAD on the
extent of coronary atherosclerosis using angiographic data from over 8,600 genotyped
participants. A genetic risk score that combines the effects of these variants was
associated with increased extent of angiographic CAD, thus demonstrating that the
cumulative burden of these variants is not only associated with increased risk of CAD,
but also its angiographic extent.
The second study assessed the contribution of many established lipid-associated
variants with the extent of coronary atherosclerosis in a total of over 17,000
participants who had undergone coronary angiography or coronary artery calcium
scanning. Genetic scores for different lipid traits were used in a Mendelian
randomization analysis to evaluate the causal effects of different lipid traits on the
extent of coronary atherosclerosis. This study highlighted the causal role of non-HDL
cholesterol in the development of coronary atherosclerosis.
The third study sought to characterize monogenic familial hypercholesterolemia
(FH) and clinically defined FH (using the Dutch Lipid Clinic Network criteria) in over
160,000 genotyped Icelanders. Twenty FH mutations were identified in about 50,000
individuals in a WGS subsample, 12 of which had not been described in Iceland
previously. The prevalence of these mutations was approximately 1 in 800 in the
overall sample. Clinical FH was much more common than monogenic FH (prevalence
2.2% in adults with available cholesterol measurements) and rarely explained by monogenic FH. Both monogenic FH and clinical FH were severely undertreated, as
guideline-directed goals for lipid-lowering treatment were rarely achieved.
The fourth study describes the discovery of an extremely rare gain-of-function
mutation in the LDL receptor gene (LDLR). This mutation is a 2.5 kilobase deletion
involving the 3’ untranslated region (UTR) of the gene, found in seven individuals within
a single four generation family in Iceland. The mutation was associated with over 70%
reduction in blood levels of LDL cholesterol and almost two-fold higher surface
expression of the LDL receptor in lymphoblast cell lines derived from the carriers. This
mutation is the first known high-impact gain-of-function mutation in LDLR. The
functional consequences of this mutation highlight the role of negative regulation by the
3’ UTR on LDLR mRNA expression and demonstrate the 3’ UTR shortening via
alternative polyadenylation is a powerful modulator of LDL receptor expression.
In summary, these studies demonstrate the influence of common and rare
sequence variants on the development of coronary atherosclerosis with a particular
emphasis on the role of blood lipids
‘I am the black duck’ affective aspects of working-class mothers’ involvement in parental communities
Get PDFPost-printThe aim of this study is to analyse working-class mothers’ narratives of social interactions among parents at their children’s schools. A special focus is paid to the emotions that arise in such interactions and their role in the reproduction of class. A narrative analysis of six stories of white, working-class mothers of compulsory school aged children was carried out. The study is set in Iceland, which gives a unique opportunity for classed and gendered analysis of parental communities as the country is at the forefront of gender equality in the world. Additionally, the compulsory school system is still relatively unsegregated. Findings show that the parental communities reproduce the symbolic violence endured by the working-class mothers within the field of education. Accounts of resistance and anger are present in some of the accounts but affective responses such as inferiority and shame are all-encompassing and contribute to the reproduction of class.Icelandic Gender Equality FundPeer Reviewe
Transition Pathways for the Farmed Salmon Value Chain: Industry Perspectives and Sustainability Implications
Get PDFPublisher´s version / Útgefin greinSalmon is the most consumed farmed seafood in the EU and there is no indication that demand will abate. Yet salmon aquaculture’s environmental impacts are significant, and its future is likely to be shaped by demands of increased but at the same time more sustainable production. This study developed an integrated theoretical framework based on the multi-level perspective (MLP) and a global value chain (GVC) governance framework and applied it to the global farmed salmon value chain. The objective was to provide insights on the most likely transition pathway towards sustainability based on industry and expert perspectives. The perceptions on challenges and drivers of change, were gathered through focus groups and in-depth interviews, and fitted to the integrated framework to facilitate the transition pathway analysis. Viewing the qualitative findings in the context of the MLP framework provided information about the current workings of the system, the drivers of change in the socio-technical landscape and niche-innovations and their potential to challenge or enhance the current system and thus indicated possible system transitions. To emphasize the role of industry actors in shaping the future of the salmon value chain, the analysis was strengthened using the GVC model which added information about power relations, signaling the ability of system actors to motivate or resist change. The findings indicate that, due to resistance in the regime and the fact that niche-innovations are not yet sufficiently developed, the farmed salmon value chain will continue to be predominated by traditional sea-based aquaculture but that there will be a gradual shift towards more diversity in terms of production methods in response to landscape pressures. The discussion addresses sustainability challenges and policy implications for the farmed salmon value chain and highlights the need for a food system perspective.Peer Reviewe
The timing and mechanisms of sulfur release by Icelandic flood lava eruptions: Holuhraun 2014–15 CE and Laki 1783–84 CE a case study.
Get PDFThis dissertation is submitted in partial fulfilment of a degree of
Doctor of Philosophy in Earth Sciences
Department of Earth Sciences, Durham University and Institute of
Earth Sciences, University of IcelandFlood lavas (FL), or high magnitude (1–100 km3) basaltic fissure eruptions have a recurrence interval of 250–500 years in Iceland. These events can produce atmospheric volcanic pollution at tropospheric–stratospheric levels via their sulfur (S) emissions. Current knowledge of the modulating role of shallow conduit processes on the vent activity, as well as the mechanisms and timing of peak S release into the atmosphere, is limited.
This project has two key aims: first, to evaluate the influence of shallow conduit processes on eruption style and dynamics during peak intensities of explosive phases; second, to produce a novel chalcophile stable isotope proxy for the speciation of released S and the redox state of the system upon eruption. Two selected case studies for this project are: (i) the recent low intensity and magnitude end-member, 2014–15 CE Holuhraun, and (ii) a high intensity and magnitude end-member, 1783–84 CE Laki which is well-documented in detailed contemporary accounts.
Micro-textural analysis of the ‘frozen’ outer rinds of pyroclasts from both eruptions, which record the state of the magma prior to fragmentation, identified relative shifts in vesicle number density associated with changes in eruptive intensity. Whole pyroclast textural mapping and in-situ geochemical analysis constrain the modification of the interior of the clasts via post-fragmentation expansion. This process enhanced the contrasts between discrete pre-existing melt domains which mingled prior to eruption. These domains record different shallow conduit histories, in particular contrasting ascent rates, and therefore preserve evidence of equilibrium and disequilibrium vesiculation within the same clast. Zinc and copper stable isotope compositions of lava and tephra from distinct phases of eruptive activity were utilised to fingerprint the mechanisms of S loss. Changes in the efficiency of volatile loss of S can be linked to known changes in vent dynamics, as well as changes in S loss associated with both the evolving transport system, redox conditions at the vent and in the flow field.
The textural and geochemical findings from these two eruptions will help further our understanding of shallow conduit, eruptive and emplacement processes during the many ill-constrained basaltic fissure eruptions of different intensities and magnitudes worldwide.NERC Iapetus DTP
HI Doctoral Student Teaching Grant
Watanabe Trust Fund
Vísinda- og rannsóknarsjóður Suðurland