Symplectic integration and physical interpretation of time-dependent coupled-cluster theory

The formulation of the time-dependent Schrodinger equation in terms of coupled-cluster theory is outlined, with emphasis on the bivariational framework and its classical Hamiltonian structure. An indefinite inner product is introduced, inducing physical interpretation of coupled-cluster states in the form of transition probabilities, autocorrelation functions, and explicitly real values for observables, solving interpretation issues which are present in time-dependent coupled-cluster theory and in ground-state calculations of molecular systems under influence of external magnetic fields. The problem of the numerical integration of the equations of motion is considered, and a critial evaluation of the standard fourth-order Runge--Kutta scheme and the symplectic Gauss integrator of variable order is given, including several illustrative numerical experiments. While the Gauss integrator is stable even for laser pulses well above the perturbation limit, our experiments indicate that a system-dependent upper limit exists for the external field strengths. Above this limit, time-dependent coupled-cluster calculations become very challenging numerically, even in the full configuration interaction limit. The source of these numerical instabilities is shown to be rapid increases of the amplitudes as ultrashort high-intensity laser pulses pump the system out of the ground state into states that are virtually orthogonal to the static Hartree-Fock reference determinant.Comment: 14 pages, 13 figure

Exploitative Competition between Mountain Hare and Moose—Qualitative Effects on Hare Winter Forage?

Mountain hares (Lepus timidus) in Scandinavia are classified as Near Threatened in the Norwegian and Swedish Redlists. This is due to a possible population decline witnessed during the last decades in Scandinavia. Competition between large herbivores and mountain hares is one of several hypotheses that has been put forward to explain this decline. In a cafeteria trial we investigate the effects of previous moose (Alces alces) winter browsing on the food selection (i.e., biomass consumed, bites per minute and bitediameter) of downy birch (Betula pubescens) and goat willow (Salix caprea) by captive mountain hares. We find that mountain hares do not differentiate among previous browsing levels of downy birch, but have larger bite diameters of goat willow earlier browsed by moose, compared to non-browsed plants. Thus, effects of moose on mountain hare winter food quality seem to be limited. We highlight the need for studies focusing on (1) qualitative effects of moose browsing using wild mountain hares in a natural experimental design, and (2) quantitative effects of moose browsing on available mountain hare forage at a landscape scale during winterpublishedVersio

Elgbeiting påvirker kvaliteten på musematen

Artikkelen er publisert i Hjorteviltet 2011Elgbeiting forandrer kvaliteten på blåbærlyng som mus eter. Fjellmarkmus foretrekker tidligere beitet blåbærlyng i næringsrike områder og unngår tidligere beitet blåbærlyng fra områder med liten næringstilgang

Design optimisation of a funnel-shaped floating dock for installation of offshore wind turbines

Master's thesis in Civil and structural engineering (BYG508)Offshore wind power is a rapidly growing renewable energy industry and has a tremendous potentialof further expansion. Installation of offshore wind turbines is a challenging task. Floating windturbines are believed to be cost-effective solutions for deep water installation. This technologyis extremely sensitive to wave excitation during the installation process. As deep-water windfarms often are located in areas exposed to rough weather, innovative methods of installation areinvestigated. The floating dock concept has been proposed in recent studies in order to expand theweather window for installing spar floating wind turbines. The idea is for the dock to shield the sparfrom wave excitation. Previous studies show that a funnel-shaped dock potentially has a betterhydrodynamic performance compared to cylindrical and bottle-shaped docks. This master’s thesistakes the previous studies into consideration and investigates how a parametric design optimisationcan be carried out for a funnel-shaped dock intended for installation of floating wind turbines. Theoptimisation objective is defined as reduction of steel weight. While investigating how to bestpredict the operational constraint of piston-mode periods, the Gaussian process regression modelappeared to be the best predictor. The study revealed that the heights;T1,T2andT3, in additionto the diameters,Di1andDi2, are design parameters which significantly affect the piston-modeperiod. The optima found in this study deviate from the predictions from the GPR based model asthe geometry is outside the trained model-area. This can be solved with a new model which alsoincludes bottle-shaped and cylindrical docks

Håndtverket øl - Et kvalitativt studie på merkevarebygging av håndtverksøl i Norge

Denne oppgaven baserer seg på det norske ølmarkedet og hvordan de driver sin merkevarebygging i forhold til forbudet mot alkoholreklame. Ved å se på markedet for håndtverksøl har vi rettet oss inn mot en smalere del av markedet, men som i de siste årene har hatt en økning i omsetning og antall bryggerier. Oppgaven har blitt gjennomført ved å først undersøke markedet og litteratur rundt relevante aspekter ved markedet -internasjonalt og nasjonalt –forbudet mot alkoholreklame og merkevarebygging. Vår egen forskning har så blitt gjort i form av en kvalitativ undersøkelse basert på semistrukturerte dybdeintervjuer. Utvalget besto av fem intervjuobjekter innenfor det norske markedet for håndverksøl. Disse fem består av fire bryggerier og Bryggeriforeningen, alle med ulike posisjoner i det norske ølmarkedet. Hovedoppgaven var å få informasjon om deres syn på forbudet mot alkoholreklame og få kunnskap om deres metoder for merkevarebygging av sine ølmerker og dermed komme opp med en løsning for å markedsføre håndtverksøl i Norge. Markedet viste seg å være lite med stor konkurranse. Alle våre respondenter så på distribusjon og eksponering som svært viktig. De ulike bryggeriene benyttet seg av ulike metoder i deres merkevarebygging, noen utfordret lovverket mens andre mente at det var viktig for alles beste å holde seg innenfor. Resultatet av de ulike intervjuene endte med en rekke muligheter vi så som gode for merkevarebygging av håndtverksøl. Vi så også at det manglet et tilbud på markedet som kunne ta i bruk alle de ulike mulighetene som ble kartlagt gjennom analysen av intervjuene. Konklusjonen baserer seg på et bestemte tiltak og en kreativ løsning. Skisser, kreative metoder, pressemelding og en kommunikasjonsstrategi er vedlagt som en del av løsningen. Vi anser løsningen som høyst relevant og at det er store muligheter for suksess ved å etablere noe slikt i Norge

Climate change induced molting mismatch? Mountain hare abundance reduced by duration of snowcover and predator abundance

In northern latitudes, species that have adapted to snow cover by molting and changing pelage color will be particularly vulnerable to climate change, as predation levels may increase due to a mismatch with background coloration. Here, we investigated the synergistic effect of mammalian generalist predators (red fox Vulpes vulpes and pine marten Martes martes) and the duration of snow cover on the abundance of a winter-adapted species, the mountain hare (Lepus timidus). We analyzed 12 yr of data from 622 snow tracking lines in southeast Norway along a gradient in annual duration of snow-covered ground. The mountain hare abundance index was positively related to the generalist predator abundance index, probably due to a combined numerical and functional response of the predators. The mountain hare abundance index was negatively associated with a short duration of snow cover, and this effect was stronger in areas with a high predator abundance index. Hence, we demonstrated a causal link between the mountain hare abundance index, predators, and the duration of snow cover. We expect declining mountain hare densities in the future caused by interactive effects of reduced duration of snow-covered ground, potentially increasing generalist predator densities and the limited ability of mountain hares to adapt to the climate change-induced molting mismatch

Hvordan elgens aktiviteter rundt fôringsplasser påvirker vegetasjon, småfugler og mus

Vi har studert hvordan elgbeiting og fôringsplasser for elg påvirker vegetasjon, småfugler og mus i Stor-Elvdal i perioden 2004-2011. Det viser seg at fôringsplasser påvirker elgens fordeling i landskapet om vinteren og elgens beiting påvirker vegetasjonen, noe som igjen påvirker tilgang av mat og strukturen på leveområdet for andre dyr i skogen. Høy elgbeiting kan for eksempel føre til mindre tilgang på insektlarver for kjøttmeisunger. I tillegg fører fôringsplasser til lokale effekter gjennom gjødsling og endring av vegetasjonen på bakken. I denne artikkelen oppsummerer vi noen av resultatene med vekt på eksempler fra Stor-Elvdal

Economic Gain vs. Ecological Pain—Environmental Sustainability in Economies Based on Renewable Biological Resources

There are two main international strategies concerning how to ensure a sustainable environment: one is to develop a globally bio-based economy, or bioeconomy, to meet the increased demand of goods and products to maintain our well-being and to reduce climate change. On the other hand, there is an aim to decrease the negative impacts on nature and natural habitats to conserve and maintain ecosystems and control the loss of biodiversity. There is a trade-off between these two strategies; as we increase the commitment to the bioeconomy by intensifying biomass production, we will simultaneously challenge biodiversity through the increased pressure on, and the utilization of, biological raw materials. Here, we first review and discuss the challenges and opportunities in terrestrial and marine ecosystems for the production of biomass for the bioeconomy. We focus on the trade-offs between economic sustainability on one hand, and environmental sustainability and resilience on the other hand. We conclude with a discussion of the various bioeconomy strategies. Finally, we present a conceptual model on how to sustainably develop the bioeconomies (by introducing the concept of optimizing the economic gain/ecological pain ratio) to be able to manage the biodiversity in a sustainable way.publishedVersio

Numerical stability of time-dependent coupled-cluster methods for many-electron dynamics in intense laser pulses

We investigate the numerical stability of time-dependent coupled-cluster theory for many-electron dynamics in intense laser pulses, comparing two coupled-cluster formulations with full configuration interaction theory. Our numerical experiments show that orbital-adaptive time-dependent coupled-cluster doubles (OATDCCD) theory offers significantly improved stability compared with the conventional Hartree-Fock-based time-dependent coupled-cluster singles-and-doubles (TDCCSD) formulation. The improved stability stems from greatly reduced oscillations in the doubles amplitudes, which, in turn, can be traced to the dynamic biorthonormal reference determinants of OATDCCD theory. As long as these are good approximations to the Brueckner determinant, OATDCCD theory is numerically stable. We propose the reference weight as a diagnostic quantity to identify situations where the TDCCSD and OATDCCD theories become unstable.Comment: 5 pages, 6 figures (supplemental material, 7 pages, 11 figures