Screened perturbation theory at four loops

We study the thermodynamics of massless phi-fourth theory using screened perturbation theory, which is a way to systematically reorganise the perturbative series. The free energy and pressure are calculated through four loops in a double expansion in powers of g^2 and m/T, where m is a thermal mass of order gT. The result is truncated at order g^7. We find that the convergence properties are significantly improved compared to the weak-coupling expansion.Comment: Talk given at Strong and Electroweak Matter 2008, Amsterdam, Aug. 25-29 2008. 4 pages, 1 figur

The chiral phase transition and the role of vacuum fluctuations

We investigate the chiral phase transition in the quark-meson effective model using optimised perturbation theory to one loop. Certain terms in the free energy are frequently omitted in calculations, on the assumption that their contribution is negligible. We show that this is not necessarily the case, and that the order of the phase transition, as well as the critical temperature, depends heavily on which contributions are included.Comment: Talk given at the IX International Conference on Quark Confinement and the Hadron Spectrum (QCHS9), Madrid, 2010. 3 pages, 4 figure

Pressure to order g8∗log(g)g^8*log(g) in ϕ4\phi^4-theory at weak coupling

We calculate the pressure of massless $\phi^4$-theory to order $g^8\log(g)$ at weak coupling. The contributions to the pressure arise from the hard momentum scale of order $T$ and the soft momentum scale of order $gT$. Effective field theory methods and dimensional reduction are used to separate the contributions from the two momentum scales: The hard contribution can be calculated as a power series in $g^2$ using naive perturbation theory with bare propagators. The soft contribution can be calculated using an effective theory in three dimensions, whose coefficients are power series in $g^2$. This contribution is a power series in $g$ starting at order $g^3$. The calculation of the hard part to order $g^6$ involves a complicated four-loop sum-integral that was recently calculated by Gynther, Laine, Schr\"oder, Torrero, and Vuorinen. The calculation of the soft part requires calculating the mass parameter in the effective theory to order $g^6$ and the evaluation of five-loop vacuum diagrams in three dimensions. This gives the free energy correct up to order $g^7$. The coefficients of the effective theory satisfy a set of renormalization group equations that can be used to sum up leading and subleading logarithms of $T/gT$. We use the solutions to these equations to obtain a result for the free energy which is correct to order $g^8\log(g)$. Finally, we investigate the convergence of the perturbative series.Comment: 29 pages and 12 figs. New version: we have pushed the calculations to g^8*log(g) using the renormalization group to sum up log(g) from higher orders. Published in JHE

The role of firm-level actors and system-level actors in processes of new regional industrial path development

Paper I, II, and III are not available as a part of the dissertation due to the copyright.This doctoral thesis departs from the understanding that regional industrial restructuring is important for handling challenges, such as globalisation, sustainability and digitalisation. Regional industrial restructuring can include changes in the existing industry as well as the development of completely new industries. The combination of the regional innovation system (RIS) approach and the theory on new path development, emerging from evolutionary economic geography (EEG) literature, leads to an understanding that industrial development happens within (open) regional systems. RISs consist of actors and networks that are embedded in an institutional framework. While one of the critiques of the RIS approach has been that it focuses too much on the system and not enough on its actors and their agency, the primary critique of the EEG approach is that it has an aggregated firm focus. This thesis addresses these criticisms by focusing more in-depth on the different actors within the regional innovation system and the interaction between them. One way this is done is by differentiating between firm-level actors and systemlevel actors. This research also focuses on the various ways these two groups of actors contribute, such as by building cross-industry innovation capability and through an entrepreneurial discovery process, to change the RIS and influence new industrial path development. These different paths lead to different forms of regional economic restructuring.publishedVersio

Strength and Ductility in two Ultra High Strength Al-Alloys AA2196 and AA7090

I denne masteroppgaven blir de mekaniske egenskapene, kornstrukturen og anisotropien i tredjegenerasjons Al-Li legeringen AA2196 undersøkt etter en foreslått varmebehandlingsprosess. Hensikten med rapporten er å undersøke om legeringen er egnet som materiale i fremdriftssystemer for romfartsapplikasjoner. Oppgaven innbefatter både strekkprøving og Charpy testing for prøver kaldbearbeidet 0-56.3%. Prøvene har blitt sammenlignet med AA7090, en annen romfartslegering, for å ha sammenligningsgrunnlag. Strekkprøving av AA2196-T8511, tilstanden som levert, ga gjennomsnittlig flytespenning på 656 MPa, strekkfasthet på 663 MPa og forlengelse på 5,68%. Størst styrke etter varmebehandling av AA2196 ble funnet etter cirka 10% kaldvalsing. De gjennomsnittlige verdiene var 435 MPa i flytespenning, 525 MPa i strekkfasthet og 7,84% forlengelse. AA7090 utviste høyere styrke, men lavere forlengelse enn AA2196. Høyest styrke ble funnet for AA7090 ved 9.2 %CW, og de respektive gjennomsnittsverdiene var på 691 MPa i flytespenning, 707 MPa i strekkfasthet and en forlengelse på 3,37%. Under Charpy testing viste AA2196 seg å ha en bruddseighet på 7,50 til 23,59 J, mens AA7090 hadde verdier i området 1,34 til 2,86 J. Økt kaldbearbeiding av AA2196 resulterte i en lavere absorbert bruddenergi. Overflaten av en Charpy test ble hardhetstestet, fikk mikrostrukturen undersøkt og ble sammenlignet med kjernen av prøven. Kjernen viste seg å ha en marginalt høyere hardhet og en finere kornstruktur enn overflaten, noe som tyder på inhomogene prøver. Bruddflatene til AA2196 var mer fiberaktive, mens bruddflatene til AA7090 var mer granulære. Grunnet høyere duktilitet i AA2196, vil noe av energien i Charpy testingen gå med til å forplante bruddet, og dermed føre til en høyere målt bruddenergi. AA2196, både før og etter varmebehandling, ble undersøkt i EBSD for å se etter tekstur. I begge tilfeller ble det observert en ekstruderingstekstur. Økt kaldbearbeiding resulterte i en mindre definert tekstur, og dermed også mindre anisotropi. Ved 55,5% kaldpressing i ekstruderingsretning ble det observert enakset kompresjonstekstur. Kaldpressing av materialet 40,1% og 58,7% i den tverrgående retningen resulterte i tendenser til rekrystalliseringstekstur, noe som er antatt å skyldes subkorn dannelse. Kornstørrelsen ble funnet ved hjelp av EBSD og viste seg å synke med økende grad av kaldbearbeiding. Den initielle kornstørrelsen ble funnet til å være 10,8 µm i ekstruderingsretningen og 3,1 µm i tverrgående retning. Etter 55,5 % kaldpressing i ekstruderingsretningen og 58,7% i tverrgående retningen ble kornstørrelsen respektivt 7,8 µm og 7,6 µm. Lysoptiske bilder ble studert og indikerte ingen rekrystallisasjon, noe som tyder på at reduksjonen i målt kornstørrelse skyldes kimdanning av subkorn. Oppvarmingstiden og holdetiden ved mykgløding, innherding og utherding ble undersøkt ved hjelp av en data logger. Det ble oppdaget at holdetiden for innherding ikke var 60 minutter på 530°C, men at materialet bare opplevde 5 minutter over 500°C, hvor det er antatt det eksisterer en grense for et enfaseområde. Dermed var det betydelig mindre Cu og Li i fast løsning, noe som kan ha ført til at mindre presipitater ble utfellet under utherdingen. Det ble også oppdaget et avvik opp mot 30°C mellom temperaturen på displayet i en varmluftsovn og på den faktiske temperaturen inne i ovnen. Utherdingskurver er blitt laget for AA2196 ved 150°C, 160°C og 180°C og for AA7090 ved 120°C. Grunnet temperaturavviket mellom display og faktisk ovnstemperatur, anbefales det at utherdingskurvene bare brukes som en indikasjon på trender. Til slutt ble ulike forbedringsforslag for varmebehandlingsprosessen lagt frem. Disse var blant annet å forvarme materialet før mykgløding, å ha lengre holdetid ved innherding for å få mer legeringselementer i fast løsning og å bruke en ovn med lavere volum luft relativt til areal, og på den måten få en ovn med lavere temperaturgradient i luften. Et deformasjonssteg ble også foreslått for å få dannet flere T1-presipitater og på den måten øke styrken og seigheten til materialet.An initial evaluation of the mechanical properties, anisotropy and grain structure of AA2196 has been conducted for a proposed heat treatment process in order to determine the applicability of the process and to determine whether the third-generation Al-Li alloy AA2196 is a suitable material for aerospace applications, particularly for propulsion systems. Tensile testing and Charpy testing have been conducted for cold rolled samples to determine the mechanical properties following cold work ranging from 0-56.3%. Additionally, these results have been compared with another aerospace alloy, AA7090, to establish a baseline for comparison. Initial tensile testing of AA2196-T8511 as delivered showed an average of yield strength of 656MPa, an average tensile strength of 663 MPa and an average elongation of approximately 5.68%. After heat treatment, the highest strength obtained for AA2196 was at approximately 10%CW, with an average yield strength of 435 MPa, an average tensile strength of 525 MPa and an average elongation of 7.84%. AA7090 exhibited higher strength and a lower elongation than AA2196. The highest strength for AA7090 was found after 9.2% cold work with averaged values for yield strength, tensile strength and %elongation at 691 MPa, 707 MPa and 3.37%, respectively. Charpy testing revealed that the fracture energies for AA2196 were in the range of 7.5-23.59J, while the fracture energy for AA7090 ranged from 1.34-2.86J. Generally, the fracture energies decreased as a result of cold work. A minor hardness increase and a finer grain structure were found when comparing the core of a Charpy sample with hardness values and grain structure close to the surface of the sample, thus implying inhomogeneous samples. Generally, the fractures of AA2196 were fibrous, while the fracture surfaces of AA7090 were more granular. It is likely that a reason for the higher fracture energy of AA2196 is due to some energy being absorbed in order to propagate the fracture, thus giving higher fracture energy. The anisotropy both prior to and following heat treatment has been investigated. In both cases, there were observed an extrusion texture. Cold pressing generally resulted in a decrease in texture, but an extensive cold pressing of 55.5% in the extrusion direction resulted in a compression texture. Both 40.1% and 58.7% cold pressing in the transverse direction resulted in a recrystallisation texture that is thought to be due to the presence of sub-grains. The grain size was found using EBSD, Electron Backscatter Diffraction. Increased amounts of cold work resulted in a decrease in grain size. The initial grain size was found to be 10.8 µm in the extrusion direction and 3.1 µm in the transverse direction. The finest grains obtained after cold working were found at 55.5%CW in the extrusion direction and 58.7%CW in the transverse direction and were 7.8 µm and 7.6 µm respectively. Investigation of OM, optical microscope, images indicated no recrystallisation, and hence the reduction in grain size was most likely due to the nucleation of sub-grains. The heating and holding time for various stages were investigated using a data logger. Heat treatment steps included were annealing, solid solution heat treatment and aging. It was found that the alloy was not solid solution heat treated for 60 minutes at 530°C, but rather experienced a holding time of only 5 minutes above 500°C, in which there is thought to exist a single-phase area. Consequently, there were less Cu and Li in solid solution than previously anticipated, which may have been detrimental to the precipitation hardening. Additionally, the temperature discrepancy between the furnace display temperature of N11/R and the air temperature were logged and found to be almost 30°C during aging at 160°C. Aging curves were created for AA2196 at 150°C, 160°C and 180°C and for AA7090 at 120°C, but due to the temperature deviation between the display and actual temperature experienced, the curves should be used as an indication only. Lastly, several improvements for the heat treatment process has been proposed, including the usage of a lower volume of air to area furnace, causing a more uniform temperature gradient within the furnace, pre-heating prior to annealing and an increased solutionising holding time. Furthermore, it has been suggested to introduce a deformation step to increase the strength and toughness of AA2196 due to the formation of T1 particles

The Secret of the Bristle-Thighed Curlew

Account of an expedition on Seward Peninsula, Alaska in June 1948, sponsored by the Arctic Institute of North America and Cornell University, during which the author discovered the bird's nesting place, sought by scientists since 1785. Includes notes on the nest and description of the bird's appearance

Analysis of the new Market Simulator ProdMarket in the future Norwegian Power System

The main objective of this thesis has been to verify ProdMarket as a software tool. Three simulation cases is created to perform a future scenario analysis assessing ProdMarket s robustness and future potential. Overall, ProdMarket shows unsatisfactory economic results for systems with high penetration of intermittent power generation. Simulations are performed on a small-scale model of the Norwegian power system. A simplified implementation of continental transfer capacity is used to explore the impacts of increased cross-county interconnectivity. Balancing of intermittent power is of particular interest. Results have been compared to a second scheduling software, EMPS. Facing increased integration and complexity, system operators and market participants are continually in need of better decision support tools to aid them in their search for effective operation and planning. ProdMarket is a state-of-the-art SINTEF-developed prototype in this search for efficiency. It uses stochastic dual-dynamic programming (SDDP) to simulate hydropower systems in great detail. For the most part, results seem reasonable. ProdMarket shows superior utilization of the balancing capacity of conventional and pumped hydro power plants, leading to smaller short-term price oscillations. Results for the simulation case representing the present Norwegian system is very good. But ProdMarket shows unacceptably poor economic results relative to EMPS as parameters are changed in the two future scenarios. Previous work with ProdMarket has shown good results when intermittent power is placed on the local level; poor results are now seen as intermittency is increased on the global level. The price model handles interaction between the local and global simulation modules in ProdMarket it is suggested as a contributor to the poor economic results. The most obvious flaw in the results is that ProdMarket stores excessive amounts of water in hydropower magazines towards the end of the simulation period. This is attributed to weaknesses in using EOPS for internal end-of-period water valuation. End valuation is considered a second contributing factor to weak economic results in the future simulation cases. Assessing the economic loss suffered as a results of each of the two problem factors presented is challenging. As a consequence, there is a great deal of uncertainty related to ProdMarket s future potential. Considerable improvements will have to be made on the model s robustness in order for ProdMarket to become a serious alternative to models such as the EMPS

Aspects of QCD thermodynamics through scalar field theory and NJL models

PhD i fysikkPhD in Physic