Global properties of an exact string theory solution in two and four dimensions

This paper discusses global properties of exact (in alpha prime) string theory solutions: A deformed black hole solution in two dimensions and a Taub-NUT type solution in four dimensions. These models are exact by virtue of having CFT descriptions in terms of heterotic coset models. The analysis includes analytic continuations of the metric, motion of test particles, and the T-duality which acts as a map between different regions of the extended solutions, rendering the physical spacetimes non-singular.Comment: 16 pages, 3 figures; v2: minor corrections, as printed in journa

Aspects of plane waves and Taub-NUT as exact string theory solutions

This thesis is a study of some aspects of string theory solutions that are exact in the inverse string tension ɑ', and thus are valid beyond the low-energy limit. I investigate D-brane interactions in the maximally supersymmetric plane wave solution of type IIb string theory, and study the fate of the stringy halo surrounding D-branes. I find that the halo is like in flat space for Lorentzian D-branes, while it receives a non-trivial modification for Euclidean D-branes. I also comment on the connection between Hagedorn temperature and T-duality, which motivates a more general study of T-duality in null directions. I consider such transformations in a spinning D-brane solution of supergravity, and find that divergences in the field components associated with null T-dualities are invisible to string and brane probes. I also observe that there are closed timelike curves in all the T-dual solutions, but that none of them are geodesies. The second half of the theses is an investigation of the fate of closed tirnelike curves and of cosmological singularities in an exact stringy Taub-NUT solution of heterotic string theory, and in a rotating generalisation of it. I compute the exact spacetime fields, using a description in terms of a gauged Wess-Zumino-Novikov-Witten model and find that the ɑ' corrections are mild. The key features of the Taub-NUT geometry persist, together with the emergence of a new region of space with Euclidean signature. Closed timelike curves are still present, which is inter-preted as a sign that they might be a natural ingredient in string theory, for instance in pre-Big-Bang cosmological scenarios

A pedestrian approach to the high energy limits of branes and other gravitational systems

In this article we study limits of models that contain a dimensionful parameter such as the mass of the relativistic point-particle. The limits are analogous to the massless limit of the particle and may be thought of as high energy limits. We present the ideas and work through several examples in a (hopefully) pedagogical manner. Along the way we derive several new results.Comment: 19 pages, 1 figur

Quantifying the Market Value of Wave Power compared to Wind&Solar - a case study

This study discusses the market value of electricity production by different sustainable sources, and shows how it is influenced by the correlation between electricity market price and energy production. The generic discussion is accompanied by a case study comparing the value of wave, wind and solar power using time series data for production and prices generated by grid and market simulations. The study has shown that simplified common-practise approaches (which do not consider correlation) fail to correctly reveal the market value of electricity production. It has also been shown that wave power can achieve a market value that is significantly higher than wind and slightly higher than solar. These differences in market value have been explained through correlation between electricity production and price, which is different for different energy sources. The study has identified competitive advantages of wave power towards the dominant sustainable energy sources, that need to be taken into account when competitiveness and profitability are to be assessed.acceptedVersio

The Low Emission Oil and Gas Open reference platform—An off-grid energy system for renewable integration studies

The data that support the findings of this study are openly available in Zenodo at https://doi.org/10.5281/zenodo (7373223)This article introduces and describes the integrated energy system of the Low Emission Oil and Gas Open reference platform. It is a hypothetical case meant to represent a typical oil and gas installation in the North Sea. The aim of this detailed specification is to serve as an open reference case where all the information about it can be publicly shared, facilitating benchmarking and collaboration. The relevance of this reference case of an off-grid energy system is not limited to the oil and gas industry, since it can also be seen as a special kind of electrical micro grid. The remote offshore location makes it especially relevant for studying offshore wind power and ocean energy sources like wave power. The specification has an emphasis on the energy system and electrical configuration, but also includes a basic description of the oil field and processing system. The intention is that it will serve as a basis for energy system studies and relating power system stability analyses regarding the integration of renewable energy sources. This allows for comparisons of a base case with different design modifications, new operational planning methods, power management strategies and control concepts. Examples of possible modifications are the replacement of gas turbines by wind turbines, addition of energy storage systems, a more variable operation of loads etc. The last part of the article demonstrates the behaviour of the reference platform implemented in two software tools: one for operational planning and one for dynamic power system analyses.publishedVersio

The N=8 Supergravity Hamiltonian as a Quadratic Form

We conjecture that the light-cone Hamiltonian of N=8 Supergravity can be expressed as a quadratic form. We explain why this rewriting is unique to maximally supersymmetric theories. The N=8 quartic interaction vertex is constructed and used to verify that this conjecture holds to second order in the coupling constant.Comment: 23 pages, minor corrections in appendix

The Exact Geometry of a Kerr-Taub-NUT Solution of String Theory

In this paper we study a solution of heterotic string theory corresponding to a rotating Kerr-Taub-NUT spacetime. It has an exact CFT description as a heterotic coset model, and a Lagrangian formulation as a gauged WZNW model. It is a generalisation of a recently discussed stringy Taub-NUT solution, and is interesting as another laboratory for studying the fate of closed timelike curves and cosmological singularities in string theory. We extend the computation of the exact metric and dilaton to this rotating case, and then discuss some properties of the metric, with particular emphasis on the curvature singularities.Comment: 14 pages, 3 figure

Water mass modification in an Arctic fjord through cross-shelf exchange: The seasonal hydrography of Kongsfjorden, Svalbard

Kongsfjorden and the West Spitsbergen Shelf is a region whose seasonal hydrography is dominated by the balance of Atlantic Water, Arctic waters, and glacial melt. Regional seasonality and the cross-shelf exchange processes have been investigated using conductivity-temperature-depth (CTD) observations from 2000–2003 and a 5-month mooring deployment through the spring and summer of 2002. Modeling of shelf-fjord dynamics was performed with the Bergen Ocean Model. Observations show a rapid and overwhelming intrusion of Atlantic Water across the shelf and into the fjord during midsummer giving rise to intense seasonality. Pockets of Atlantic Water, from the West Spitsbergen Current, form through barotropic instabilities at the shelf front. These leak onto the shelf and propagate as topographically steered features toward the fjord. Model results indicate that such cross-front exchange is enhanced by north winds. Normally, Atlantic Water penetration into the fjord is inhibited by a density front at the fjord mouth. This geostrophic control mechanism is found to be more important than the hydraulic control common to many fjords. Slow modification of the fjord water during spring reduces the effectiveness of geostrophic control, and by midsummer, Atlantic Water intrudes into the fjord, switching from being Arctic dominant to Atlantic dominant. Atlantic Water continues to intrude throughout the summer and by September reaches some quasi steady state condition. The fjord adopts a ‘‘cold’’ or ‘‘warm’’ mode according to the degree of Atlantic Water occupation. Horizontal exchange across the shelf may be an important process causing seasonal variability in the northward heat transport to the Arctic

Operational Planning and Power Management System for Offshore Platform With Wind Energy Supply – Impacts on CO2 Reduction and Power Quality

publishedVersio