Opin visindi
Not a member yet
2982 research outputs found
Sort by
Anticipated food scarcity and food preferences
Get PDFIn the recent decade, marketing literature has acknowledged the advantages of applying an evolutionary lens to understand consumer behavior in different domains. Food choice context is one such domain, having implications for societal well-being, especially for public health and addressing environmental issues. In this thesis, I investigate how mechanisms that have emerged as adaptations to food scarcity—frequent throughout human history—affect modern consumers’ food preferences, potentially leading to maladaptive outcomes. In Paper I, we highlight that selection pressures adjusted humans to forage in ancestral, hostile environments when they were wandering between periods of food scarcity and food sufficiency. Consequently, consumers often fail to choose foods appropriate to their current needs in contemporary retail contexts. Rather than attempting to override these hardwired and evolutionarily outdated food preferences, we recommend policymakers leverage them in such a way that facilitates healthier food choices. A series of studies reported in Paper II show that exposing people to climate change-induced food scarcity distant in time and space shifts their current food preferences. Specifically, people exposed to such video content exhibit a stronger preference toward energy-dense (vs. low-calorie) foods than their peers exposed to a control video. In Paper III, we aimed to account for potential confounds stemming from the control video used in studies reported in Paper II. Additionally, we strived to conceptually replicate these earlier findings by exposing participants to subtle cues to food scarcity—a winter forest walk. Although not all studies yielded significant results at conventional levels, this empirical package—when taken together—corroborated the earlier findings. Despite that studies described in Papers II–III provided a shred of empirical evidence showing a potency of food scarcity cues in increasing preferences toward energy-dense (vs. low-calorie) products, it was still unclear what drove such a shift in food liking. Thus, in Paper IV, we have developed and psychometrically validated the Anticipated Food Scarcity Scale (AFSS), measuring the degree to which people perceive food resources as becoming less available in the future. Aside from being a candidate mechanism partially explaining findings reported in Papers II–III, anticipated food scarcity (AFS) is also related to some aspects of prosociality. Studies presented in this thesis suggest that when environmental cues to food scarcity are present, people show a stronger preference toward energy-dense (vs. low-calorie) foods than their peers unexposed to such cues. Policymakers should consider these results when designing climate change and other similar campaigns, as such communication often depicts food scarcity. Additional research may explore the possibility that exposure to food scarcity cues affects food choices. Considering that we found AFS correlated with certain prosocial attitudes, it is a new psychological construct that warrants future investigation through multidisciplinary research.The research associated with the Four Academic Papers reported in this Thesis was funded by the Icelandic Research Fund (Doctoral Student Grant toMichał Folwarczny number 206880-051).Accepte
A Practical Approach for Estimating the Optimum Tilt Angle of a Photovoltaic Panel for a Long Period—Experimental Recorded Data
Get PDFIn this study, recorded empirical data were applied with a practical approach to investigate the optimal tilt angle of the flat plate collectors facing south for a long period in Tehran, Iran. The data included 20 years of recorded average total radiation on the horizontal plane in Tehran’s meteorological station. Based on the previous studies, the annual optimum tilt angle for Tehran was estimated at 33 degrees annually; however, this estimation does not focus on the energy absorption and effectiveness of changing the tilt angle monthly, seasonally, and bi-annually via measured data. This paper aims to explain this distinction between various radiation receptions with different tilt angle adjustments. This study shows that annual solar cumulative radiation energy gained via a monthly tilt angle can be approximately 7% higher than that achieved with an annual tilt angle setup. Additionally, the seasonal and bi-annual tilt angles have about 6% more annual cumulative radiation absorption than the annual tilt angle setup. Moreover, with consideration of similar monthly received radiation, the results illustrate that the radiation gained with a monthly tilt angle set up was 20% greater in the summer months than an annual tilt angle adjustment.Peer Reviewe
The Value of Normal Body Weight: Evidence from Iceland
Get PDFCalculations of societal costs of underweight, overweight and obesity have generally failed to include the value of the utility reductions, associated with deviations from normal weight. To remedy this, the monetary compensation needed to offset the welfare loss associated with being underweight, overweight, or obese, according to World Health Organizations standards, is estimated. For this purpose, the compensating income variation (CIV) method is applied to individual-level data from an Icelandic health and lifestyle survey carried out in 2007, 2009, 2012, and 2017. The results show that both males and females would on average be willing to pay a positive amount to move from obesity to normal weight, albeit a varying amount by income group. The CIV for moving from obesity to normal weight among males for the low-, medium-, and high-income groups are 25,768, and 9,191, 95,494. However, only females show a positive willingness to pay for not being overweight. The CIV for overweight females for the three income groups is 6,375, and $37,488 per year.The authors gratefully acknowledge financial support from The Icelandic Research Fund [grant number 184975] and the University of Iceland Research Fund.Pre-print (óritrýnt handrit
Tectonic position, structure, and Holocene activity of the Hofsjökull volcanic system, central Iceland
Get PDFThe Hofsjökull volcanic system is located at the northern border of the Hreppar microplate on the Mid-Atlantic plate boundary in Iceland, between the more active Western and Eastern volcanic zones. In this study, fractures, and faults within the fissure swarms of the volcanic system were mapped and the throw and orientation of faults measured. This was done using both aerial photographs and ArcticDEM digital elevation models, as well as during fieldwork. The Hofsjökull volcanic system contains 3–4 fissure swarms extending northwards or southwards from the glacially covered Hofsjökull central volcano. Although these fissure swarms have been active during the Holocene, no clear sink holes were found along the faults, suggesting that they have been filled by sediments. This indicates that the fissure swarms have been less active than fissure swarms in other branches of the plate boundary in Iceland where GPS geodetic measurements show current spreading. Unbroken hyaloclastite covering a fault in the northern Hofsjökull fissure swarm suggests that this part of the northern Hofsjökull fissure swarm has not been active since the earliest part of Holocene, or during the latest stage of glaciation in the area. Still, the fault scarps in the northern Hofsjökull fissure swarm are rather sharp, indicating little erosion by glaciers. This may suggest increased activity in the Hofsjökull fissure swarm during the end of the last glaciation or at the beginning of the Holocene, which is in line with other studies showing increased magmatic activity in Iceland during that period. Fractured Holocene lava flows in the southern and western Hofsjökull fissure swarms indicate that they have been active during the Holocene. The Kerlingarfjöll rhyolitic massif is located south of the Hofsjökull central volcano. The southern fissure swarms are located both east and west of Kerlingarfjöll, but no clear indications are found of the fissure swarm in the rhyolitic massif itself. This may occur as dike intrusions (which likely form the faults) are prevented from penetrating the rhyolite due to density differences, and/or due to the topographic high of Kerlingarfjöll.Rannis, rannsóknasjóður, styrknúmer 196226-052.Peer reviewe
Valumics - Understanding Food Value Chains and Network Dynamics
No full textEuropean Commission H2020 VALUMICS - Understanding food value chains and network dynamics.
https://cordis.europa.eu/project/id/727243
Complex food value chains present a significant challenge. In recognition of the intricate and diverse nature of food value chains, the EU-funded VALUMICS project aims to equip decision-makers throughout European food value chains with a comprehensive suite of tools and approaches, enhancing their ability to evaluate strategic and operational policies. With a consortium of 19 European partners from 14 countries and two Asian partners, VALUMICS aims to bolster the resilience, integrity and sustainability of these crucial chains. By going beyond current research boundaries, VALUMICS introduces novel modelling approaches, consumer research and foresight analysis. This groundbreaking project provides policymakers with new perspectives, bridging economic, environmental and social dimensions to secure a sustainable and nutritious future for Europe.The functioning of food value chains entails a complex organisation from farm to fork which is characterised by various governance forms and externalities which have shaped the overall food system. VALUMICS food value chain case studies: wheat to bread, dairy cows to milk, beef cattle to steak, farmed salmon to fillets and tomato to processed tomato were selected to enable explorative and empirical analysis to better understand the functioning of the food system and, to identify the main challenges that need to be addressed to improve sustainability, integrity, resilience, and fairness of European food chains. The VALUMICS system analysis was executed through four operational phases starting with Groundwork & analysis including mapping specific attributes and impacts of food value chains and their externalities. This was followed by Case study baseline analysis, which provided input to the third phase on Modelling and exploration of future scenarios and finally Policy and synthesis of the overall work.
This report is an overall synthesis of the VALUMICS results as follows:
• Key findings from the VALUMICS project on the functioning of European food value chains and their impacts on more sustainable, resilient, fairer, and transparent food system are summarised through a compilation of 25 Research Findings and Policy Briefs.
• By highlighting the major contributions from the research activities throughout the four phases of the VALUMICS project, this report delivers an assessment of various factors influencing sustainability, resilience, efficiency and fairness and effective chain relationships of different food value chains, and their determinants.
• The synthesis of the outcome allows the identification of opportunities and challenges characterising the functioning of food supply chains, and thus, the prospects and potentials for strengthening the EU food sector
Gasification of Woody Biomasses and Forestry Residues: Simulation, Performance Analysis, and Environmental Impact
Get PDFWood and forestry residues are usually processed as wastes, but they can be recovered to produce electrical and thermal energy through processes of thermochemical conversion of gasification. This study proposes an equilibrium simulation model developed by ASPEN Plus to investigate the performance of 28 woody biomass and forestry residues’ (WB&FR) gasification in a downdraft gasifier linked with a power generation unit. The case study assesses power generation in Iceland from one ton of each feedstock. The results for the WB&FR alternatives show that the net power generated from one ton of input feedstock to the system is in intervals of 0 to 400 kW/ton, that more that 50% of the systems are located in the range of 100 to 200 kW/ton, and that, among them, the gasification system derived by tamarack bark significantly outranks all other systems by producing 363 kW/ton. Moreover, the environmental impact of these systems is assessed based on the impact categories of global warming (GWP), acidification (AP), and eutrophication (EP) potentials and normalizes the environmental impact. The results show that electricity generation from WB&FR gasification is environmentally friendly for 75% of the studied systems (confirmed by a normalized environmental impact [NEI] less than 10) and that the systems fed by tamarack bark and birch bark, with an NEI lower than 5, significantly outrank all other systems owing to the favorable results obtained in the environmental sector.This paper was a part of the project funded by Icelandic Research Fund (IRF), (in Icelandic: Rannsoknasjodur) and the grant number is 196458-051Peer Reviewe
Calculations of Ground and Excited Electronic States Using Self-Interaction Corrected Density Functionals
Get PDFDirect optimization methods for the calculation of ground and excited electronic states are presented for both total density and orbital-density-dependent functionals. The methods have been developed for various types of basis sets including localized atomic orbitals, plane waves and real space grid. The algorithms have been implemented in combination with the projector-augmented-wave method to represent inner electrons of the atoms. The direct optimization method is shown to be more robust and faster than the conventional self-consistent field approach in calculations of both ground and excited states. An assessment of the Perdew-Zunger self-interaction correction (PZ-SIC) to the energy functional has also been made and its performance compared to the commonly used generalized gradient approximation (GGA). PZ-SIC is found to systematically improve the description of the atomization and ionization energy as well as the band gaps of insulators, but needs to be scaled by a half. PZ-SIC can be especially important for the accurate description of systems containing transition metals as is illustrated by the excellent results obtained for the Mn dimer, a system where results of GGA calculations are qualitatively incorrect. However, PZ-SIC does not substantially improve the excitation energy of small organic molecules as the correction there tends to cancel out when the energy of ground and excited states is compared. The efficient and practical implementation of PZ-SIC presented here paves the way for the development of more accurate orbital-density-dependent functionals.Aðferðir til að reikna út grunn og örvuð rafeindaástönd með beinni bestun hafa verið
þróaðar, bæði fyrir felli háð heildarrafeindaþéttni sem og almennari felli háð þéttni
svigrúmanna. Aðferðirnar hafa verið þróaðar fyrir ýmsar gerðir grunna svo sem staðbundin atómsvigrúm, planbylgjur og grind í raunrúminu. Þær hafa verið innleiddar
með ’projector-augmented-wave’ aðferðinni til að lýsa áhrifum innri rafeinda atómanna.
Beina bestunin reynist vera áreiðanlegri og hraðvirkari en þær aðferðir sem áður hafa
verið notaðar bæði hvað varðar reikninga á grunnástöndum sem og örvuðum ástöndum.
Áhrif sjálfsvíxverkunarleiðréttingar Perdew og Zunger (PZ-SIC) á útkomu reikninganna
hefur einnig verið könnuð og niðurstöðurnar bornar saman við almennu stigulnálgunina (GGA). PZ-SIC leiðréttingin reynist bæta kerfisbundið útreiknaða sundrunarorku
sameinda sem og jónunarorku og einnig orkugeil einangrara, en þarf að skalast niður
í helming. Reikningar á eiginleikum kerfa með hliðarmálmatóm geta batnað sérlega
mikið með PZ-SIC leiðréttingunni og þar er Mn tvennan sérlega afgerandi tilfelli þar
sem reikningar með PZ-SIC gefa mjög góða niðurstöðu á sama tíma og GGA gefur
verulega rangar niðurstöður. Hins vegar hefur PZ-SIC ekki mikil áhrif á útreiknaða
örvunarorku lítilla lífrænna sameinda þar eð leiðréttingin á grunn og örvaða ástandinu
styttist þar að miklu leiti út. Sú skilvirka innsetning á PZ-SIC sem er framsett hér opnar
leiðina fyrir þróun á nákvæmari fellum háðum svigrúmaþéttni.Fellowship from the University of Iceland, the University of Iceland Research Fund and the Icelandic Research Fund
Development and evaluation of computational methods for studies of chemical reactions
Get PDFMethods for identifying the mechanism and estimating the rate of chemical reactions are presented and evaluated for a wide range of systems, using both classical and quantum mechanical description of the atomic nuclei. In the classical case, the minimum energy path (MEP) connecting two minima, that represent states of the system, is found. Energy maxima on the path correspond to first order saddle points on the energy surface and give an estimate for the activation energy of the transition. For quantum mechanical description of the atoms, the optimal tunneling path (OTP) is found. This path is equivalent to a first order saddle point on the action surface, referred to as an instanton, and can be used to calculate the rate of thermally assisted tunneling. In order to navigate on these surfaces, the energy and force acting on the atoms needs to be evaluated. Such calculations are typically carried out using computationally intensive electronic structure methods. It is, therefore, important to develop both reliable and efficient algorithms to navigate on these surfaces in an efficient way with as few evaluations of the energy and atomic forces as possible.
The various methods presented in this work are extensions of the widely used nudged elastic band (NEB) method. In NEB, a trial path represented by a set of points is iteratively displaced towards a target path, an MEP or OTP. The path is displaced downhill on the surface along the directions perpendicular to the path and spring forces are used to keep discretization points evenly distributed along the path. To achieve this, an accurate estimate of the tangent to the path is needed in order to decompose the forces into perpendicular and parallel components. In the first part of this work, the computational efficiency of NEB calculations of MEPs for molecular reactions is addressed. There, excessive computational effort is often needed because the MEPs often include long segments with little or no change in the energy. Computational resources are therefore wasted on resolving irrelevant segments of the path. Moreover, a sparse distribution of points along the path may also yield an inaccurate estimate of the tangent. This can affect the efficiency of an NEB calculation and can even lead to non-convergence. Two NEB variants are presented to automatically focus the computational effort on the most important part of the MEP, i.e. the region around the highest energy maximum. In one of these methods, a loose convergence on the MEP is first obtained and then a new set of points is automatically distributed in the region of the energy barrier to improve the resolution around the energy maximum and hence improve the tangent estimate there. In the second method, an increased density of points is obtained in the critical region of the MEP by adaptively scaling the strength of the spring interaction according to the energy, making the springs stiffer in regions of higher energy. Experience will show which one of these two approaches will turn out to be optimal, or perhaps a combination of both. The computational effort when searching for saddle points can be reduced further by using a combination of NEB and an eigenvector-following (EF) method. In this approach, the points along the path are first converged loosely to the MEP. Then, information obtained from the NEB path and the point of maximum energy are used to automatically start an EF search to swiftly target the saddle point. These methods are applied to various chemical reactions and to a database of 121 molecular reactions. The methods have been implemented in the ORCA quantum chemistry software which is rapidly becoming the most widely used tool for electronic structure calculations in computational chemistry.
In the second part of this work, the focus is on the quantum mechanical description of the atomic nuclei and identification of OTPs. An OTP traces out the same path on the action surface as an instanton and can therefore be used to estimate the tunneling rate. Calculations of OTPs are found to be more efficient than the typical search method used for instanton calculations. The main reason is that the distribution of system images along the OTP are controllable while the points accumulate near the endpoints in instanton calculations. Therefore, fewer images can be used to represent the path in OTP calculations compared to instanton calculations.
In the first two parts, the electronic structure computations are carried out using density functional theory (DFT) as is now commonly done in computational chemistry. However, the selection of an appropriate level of theory for calculations of molecules and chemical reactions can be difficult. In this regard, a particularly interesting and challenging diamine cation is studied in the third part of this work. In this case, the existence of both a localized and delocalized electronic state has been inferred from experimental measurements. While, standard electronic structure methods, e.g. commonly used density functionals and the coupled cluster singles-doubles-(triples), method are unable to predict the existence of a localized electronic state. To shed light on this issue, which has turned into a controversy in the literature, and determine whether the localized state truly exists, high-level multireference wavefunction calculations of the energy surface are carried out and found to establish the existence of the localized state.Aðferðir til þess að finna hvarfgang og meta hraða efnahvarfa eru þróaðar og prófaðar
á fjölbreytilegum kerfum, þar sem bæði klassísk og skammtafræðileg lýsing á atómkjörnum er notuð. Fyrir klassíska lýsingu á atómunum eru fundnir lágmarksorkuferlar
sem tengja tvö orkulágmörk og samsvara stöðugum ástöndum kerfisins. Á slíkum
ferli samsvarar orkuhámark fyrsta stigs söðulpunkti á orkuyfirborðinu og gefur mat á
virkjunarorkunni fyrir hvarfið. En, fyrir skammtafræðilega lýsingu á atómunum er besti
smugferillinn fundinn. Þessi ferill samsvarar fyrsta stigs söðulpunkti á verkunaryfirborðinu og er oft kenndur við snareindir. Út frá slíkum punkti er hægt að reikna hraða
á varmaörvuðu smugi. Til þess að hægt sé að kanna slík yfirborð og finna þessa ferla
þarf að reikna orku og kraftinn sem verkar á atómin. Slíkir reikningar fela yfirleitt í sér
þunga tölvuútreikninga. Því er afar mikilvægt að þróa aðferðir sem eru bæði nákvæmar
og hagkvæmar að því leiti að sem fæsta orku og kraftareikninga þurfi til.
Hinar ýmsu aferðir sem eru þróaðar hér eru útvíkkanir á hinni vel þekktu teygjubandsaðferð, NEB. Í þessari aðferð er ferill, sem er lýst sem safni af hnitum atómanna,
færður í átt að lausnarferlinum, annað hvort lágmarksorkuferli eða besta smugferli, með
ítrun. Hver punktur í þessari strjálu lýsingu á ferlinum er þá færður niður eftir yfirborðinu í stefnu hornétt á ferilinn og gormkraftar notaðir til þess að viðhalda jafndreifingu
á punktunum eftir ferlinum. Þetta krefst þess að hafa nógu gott mat á snertlinum eftir
ferlinum til þess að framkvæma vörpun á kröftunum í þverstæða og samsíða þætti. Í
fyrsta hluta verksins er hagkvæmni teygjubandsaðferðarinnar fyrir reikninga á lágmarksorkuferlum fyrir sameindahvörf metin og betrumbætt. Raunin er að oft er þörf á að
nota óþarflega mikla reiknigetu fyrir teygjubandsreikninga á slíkum hvörfum, þar sem
orkan á lágmarksorkuferlinum breytist oft lítið sem ekkert á köflum. Þar af leiðandi er
reikniafli sóað í að lýsa lítilvægum hluta ferilsins á sama tíma og upplausn ferilsins er
ekki nægjanlega góð til að fá mat á snertilnum á mikilvægum hluta hans. Þetta getur haft
mikil áhrif á kostnað teygjubandsreikninga og getur jafnvel orsakað það að samleitni
náist ekki. Tvær breytingar á teygjubandsaðferðinni eru settar fram þar sem áhersla er
lögð á mikilvægasta hluta lágmarksorkuferilsins, þ.e. þann hluta sem inniheldur hæsta
orkuhámarkið. Í annarri aðferðinni er veikri samleitni á lágmarksorkuferlinum fyrst
náð og síðan er nýju punktasafni sjálfvirkt dreift á svæði orkuhólsins til þess að bæta
upplausnina á ferlinum í grennd við hámarkið. Í hinni aðferðinni er auknum þéttleika
punkta náð á þessu mikilvæga svæði lágmarksorkuferilsins með skölun á styrkleika
gormkraftsins samkvæmt orku kerfinsins á hverjum stað, þar sem gormarnir eru gerðir
stífari á háorkusvæðum á meðan ítranirnar eru framkvæmdar. Reynslan mun sýna hvor
aðferðin, eða mögulega samsetning beggja, er hagkvæmari. Með því að setja saman
teygjubandsaðferðina og eiginvigrarakningu er dregið enn frekar úr reiknikostnaði þegar
leitað er að söðulpunktum. Í þeirri aðferð er grófri samleitni á lágmarksorkuferlinum náð.
Upplýsingum er síðan safnað af ferlinum, þ.m.t. punktinum með hæstu orkuna. Þessar
upplýsingar eru sjálfvirkt notaðar til þess að byrja eiginvigrarakningu sem auðveldlega nær samleitni á söðulpunktinn sem svarar til viðkomandi efnahvarfs. Aðferðirnar eru
notaðar á ýmis efnahvörf og á gagnasafn sem inniheldur 121 sameindahvörf. Aðferðirnar hafa verið innleiddar í ORCA skammtaefnafræði hugbúnaðinum sem nýtur ört
vaxandi vinsælda og er á góðri leið með að verða útbreiddasti hugbúnaður í heimi fyrir
rafeindastrúkturreikninga í efnafræði.
Í öðrum hluta verksins er lögð áhersla á skammtafræðilega lýsingu atómanna og
leit að bestu smugferlum. Besti smugferill fylgir sömu leið og snareind á verkunaryfirborðinu og því er hægt að hann til þess að reikna út skammtafræðilegan smughraða
efnahvarfa. Reikningar á bestu smugferlum eru hagkvæmari en hefðbundna leitaraðferðin sem notuð hefur verið til þess að finna snareindir. Aðal ástæðan fyrir þessari auknu
hagkvæmi er sú að það er hægt að stjórna dreifingu punktanna á ferlinum í leitinni
að besta smugferlinum, á meðan flestir punktarnir enda í grennd við endapunktana
í snareindareikningum. Því er hægt að nota færri punkta til að ná góðri upplausn á
ferlinum í reikningum á bestu smugferlum í samanburði við snareindareikninga.
Í fyrstu tveimur hlutum verksins er notast við þéttnifellafræði til að reikna rafeindastrúkturinn eins og almennt tíðkast nú í reikniefnafræði. Aftur á móti getur val á
viðeigandi orkuyfirborði fyrir reikninga á sameindum og efnahvörfum oft reynst erfitt.
Með þetta í huga er sérstaklega áhugaverð og erfið díamínkatjón skoðuð í þriðja hluta
verksins. Tilraunamælingar á þessari sameind hafa verið túlkaðar þannig að bæði sé
tilstaðar staðbundið og óstaðbundið rafeindaástand. Hefðbundnar rafeindastrúktúraðferðir sýna hins vegar ekki tilvist staðbundna rafeindnaástandsins, svo sem vinsæl
rafeindaþéttleikafelli og jafnvel CCSD(T) aðferðin. Nákvæmir og flóknir fjölástands
bylgjufallsreikningar (e. multireference wavefunction calculations) eru notaðir til að
varpa ljósi á þetta misræmi á milli rafeindareikninga og tilrauna og skera úr um tilvist staðbundna rafeindaástandsins. Í samræmi við niðurstöður tilraunanna, spá þessir
nákvæmari reikningar fyrir um tilvist staðbundna ástandsins.Doctoral grant of the University of Iceland Research Fund,
Icelandic Research Fun
Stellar orbits in adiabatically and impulsively evolving dark matter dominated potentials
Get PDFIn the ΛCDM concordance model cold and collision-less dark matter (CDM) accounts
for about four fifths of the Universe’s total matter content, while visible baryonic matter
makes up the final fifth. The ΛCDM model successfully describes how large scale
structure forms from tiny density fluctuations in the early Universe, explaining the
growth of dark matter (DM) overdensities and their eventual collapse into gravitation-
ally self-bound objects called haloes which host the visible galaxies. The most enduring
challenges to the ΛCDM paradigm arise on the scale of dwarf galaxies whose internal
kinematics are seemingly at odds with the radial density profiles of the corresponding
DM haloes predicted by CDM N-body simulations. While the evidence for such mis-
matches remains controversial, several mechanisms have been proposed to reconcile
the success of ΛCDM on large scales with these observations on smaller scales. Typ-
ically, such mechanisms rely on non-gravitational effects to redistribute mass within,
and thus alter the gravitational potential of, DM haloes. Depending on the specific
mechanism, this mass redistribution occurs on timescales which are either longer or
shorter than the typical dynamical timescales of stars in dwarf galaxies. In this thesis, I
show that stars can be used as kinematic tracers to differentiate between adiabatically,
i.e., slowly evolving, and impulsively, i.e., fast evolving potentials. In adiabatically
evolving potentials, the actions of kinematic tracers are conserved. For moderately fast
evolving spherical potentials, I show that the evolution of radial actions is perturbative
and oscillatory. In this regime, the evolution of radial action distributions of tracers is
well described by a diffusion equation. The evolution of a tracer’s radial action becomes
non-perturbative as the rate at which the potential changes becomes large compared
to the tracer’s radial period. An impulsive change in the gravitational potential, under
which actions are not conserved, changes the energy of kinematic tracers by an amount
that depends on their orbital phase. Using controlled N-body simulations, I demon-
strate that as a consequence of the latter, shell-like signatures related to phase mixing
emerge in the phase space of kinematic tracers whose orbits where characterized by
similar integrals of motion prior to the change in the potential. Such orbital families are
reasonably approximated by sets of stars with similar ages and metallicites. Ongoing
phase mixing in orbital families within dwarf galaxies with slow-rising rotation curves
would indicate the presence of strong and impulsive supernova feedback which may
have converted the central cusps of the dwarfs’ host haloes into cores. Using a suite of
hydrodynamic simulations of an isolated dwarf, I find that the kinematic properties of
stars and gas differ in many ways between galaxies whose host haloes have an impulsive
or an adiabatic core formation history. The complete absence of shell-like signatures
of phase mixing in orbital families would be a strong indication that cores are likely
formed adiabatically, for example through self-interactions between the DM particles.Í hinu samræmda ΛCDM líkani er um fimmtungur alls efnis sýnilegar þungeindir og fjórir fimmtu hlutar hulduefni. Líkanið gefur góða lýsingu á því hvernig stórgerð alheimsins
er til komin vegna lítilla þéttleikasveiflna í árdaga og hvernig yfirþéttleiki hulduefnis
þróast yfir í þyngdarbundna hjúpa sem hýsa sýnilegar vetrarbrautir. Sterkasta áskorun
líkansins kemur fram á skala dvergvetrarbrauta en gangfræði þeirra virðist stangast á
við þéttleikaprófíl hulduefnishjúpanna sem spáð er í fjölagna hermireikningum. Þó
vísbendingarnar um þetta misræmi séu umdeildar eru nokkrar mögulegar skýringar á því
hvernig á þessu getur staðið. Oft byggjast þessar skýringar á þyngdarverkunarlausum
hrifum sem breyta massadreifingu hulduefnishjúpsins og þar með einnig þyngdarmætti
hans. Það fer svo eftir eðli hrifanna hvort massadreifingin breytist á tímaskala sem er
styttri eða lengri en dæmigerður hreyfifræðilegur tími stjarna í dvergvetrarbrautum.
Í þessari ritgerð sýni ég að nota má stjörnur sem hreyfifræðilega spora (tracer)
til að greina á milli annars vegar óverminna (hægfara) breytinga á mættinu og hins
vegar snöggra breytinga á því. Í óvermnum breytingum er verkun hreyfifræðilegu
sporanna varðveitt. Þá sýni ég að í kúlusamhverfu mætti sem þróast miðlungi hratt er
radíalverkunin bæði truflin (perturbative) og sveiflukennd og að lýsa má þróun dreifingar radíalverkunarinnar með sveimjöfnu. Tímaþróun radíalverkunar sporanna verður
ótruflin þegar tímaþróun mættisbreytinganna verður hraðari en sem nemur útþáttarlotu
(radial period) sporanna. Við snögga breytingu í þyngdarmættinu, þar sem verkunin
er ekki varðveitt, breytist orka sporanna um stærð sem er háð brautarfasa þeirra. Með
stýrðri hermun fjölagnakerfa sýni ég að afleiðing hins síðarnefnda er að í fasarúmi
sporanna koma fram merki um hvelamyndun í brautum þeirra. Þeim má lýsa allvel
með fjölskyldum stjarna af svipuðum aldri og málminnihaldi. Fasablöndun fjölskyldna
brauta stjarna í dvergvetrarbrautum með hægt vaxandi snúningshraðarit er vísbending
um sterka og snögga sprengistjörnusvörun sem gæti hafa breytt þéttleikaprófíl hjúps
dvergvetrarbrautarinnar. Með hermun einangraðrar dvergvetrarbrautar sýni ég að hreyfifræði gass og stjarna er ólík eftir því hvort kjarni hjúpsins hefur þróast óvermið eða
snögglega. Ef engin merki er að finna um fasablöndnun brautarfjölskyldna er það sterk
vísbending um að hjúpurinn hafi þróast á óverminn hátt, t.d. með eiginvíxlverkun á
milli einda hulduefnisins.This work was supported by a Grant of Excellence from the Icelandic Research
Fund (grant number 173929
The effects of losartan and diazepam on emotional processing
Get PDFGiven the prevalence and substantial economic costs of anxiety disorders, and the
shortcomings of current treatments, there is dire need for research that helps inform the
development of new treatments and medications. The aim of this thesis was to further our
understanding of the effects of two medications relevant to anxiety, losartan and diazepam, to help inform the use of existing treatments and lead to more effective ones.
Research has indicated that the angiotensin receptor antagonist losartan may potentially be a promising candidate to enhance the efficacy of exposure-based therapies. It however remains to be fully clarified how losartan affects some of the mechanisms relevant to exposure success. In the first study, a single dose of losartan was shown to increase activation in the paracingulate gyrus, insular cortex, lingual gyrus, and fusiform gyrus in healthy, high trait anxious volunteers, which possibly reflects modulation of higher-order visual processing. There was however no evidence found for an effect of losartan on neural responses in the hippocampus during non-emotional memory encoding. Losartan was also shown to increase positive attentional bias, which was reflected in attention being more firmly held by positive stimuli compared to neutral stimuli. Given that both greater reactivity in higher-order visual regions and positive valence training have been shown to be relevant for therapy success, these results may provide further support that losartan might potentially have synergistic effects with exposure therapy, but this remains to be tested directly. The most common pharmacological treatments for anxiety disorders include selective serotonin reuptake inhibitors and benzodiazepines, but both groups of medications have limitations. A better understanding of how existing medications exert their anxiolytic effects may help guide development of new medications. As benzodiazepines are not effective in treating depression, researching their effects provide a means of teasing apart antidepressant and anxiolytic effects. A comprehensive understanding of the cognitive neuropsychological mechanisms behind their anxiolytic effects is still lacking. In the second study, a 7-day treatment of diazepam was shown to lower connectivity between the amygdala and the pre- and post-central gyrus during cognitive reappraisal, and between limbic regions and the precuneous cortex in response to aversive pictures in healthy volunteers. The treatment also led to a decrease in activation in the right vlPFC during reappraisal, and to an increase in activation in the left vlPFC and right ACC in response to positive stimuli, without any subjective changes in mood and state anxiety. Diazepam may thus potentially be exerting its short-term anxiolytic effects by modulating activity within these brain areas. Taken together, these findings provide valuable insights into potential mechanisms through which diazepam and losartan may exert their therapeutic effects. A better understanding of these mechanisms can hopefully help inform the development of future anxiolytics and combination treatments