| 1. |
- Ahlberg, Erik, et al.
(författare)
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"Vi klimatforskare stödjer Greta och skolungdomarna"
- 2019
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Ingår i: Dagens nyheter (DN debatt). - 1101-2447.
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
- DN DEBATT 15/3. Sedan industrialiseringens början har vi använt omkring fyra femtedelar av den mängd fossilt kol som får förbrännas för att vi ska klara Parisavtalet. Vi har bara en femtedel kvar och det är bråttom att kraftigt reducera utsläppen. Det har Greta Thunberg och de strejkande ungdomarna förstått. Därför stödjer vi deras krav, skriver 270 klimatforskare.
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| 2. |
- Anderson, Ian, et al.
(författare)
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Shakra: tracking and sharing daily activity levels with unaugmented mobile phones
- 2007
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Ingår i: Mobile Networks and Applications. - : Springer Science and Business Media LLC. - 1383-469X .- 1572-8153. ; 12:2-3, s. 185-199
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Tidskriftsartikel (refereegranskat)abstract
- This paper explores the potential for use of an unaugmented commodity technology—the mobile phone— as a health promotion tool. We describe a prototype application that tracks the daily exercise activities of people, using an Artificial Neural Network (ANN) to analyse GSM cell signal strength and visibility to estimate a user’s movement. In a short-term study of the prototype that shared activity information amongst groups of friends, we found that awareness encouraged reflection on, and increased motivation for, daily activity. The study raised concerns regarding the reliability of ANN-facilitated activity detection in the ‘real world’. We describe some of the details of the pilot study and introduce a promising new approach to activity detection that has been developed in response to some of the issues raised by the pilot study, involving Hidden Markov Models (HMM), task modelling and unsupervised calibration. We conclude with our intended plans to develop the system further in order to carry out a longer-term clinical trial.
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| 3. |
- Anderson, Louise, 1989, et al.
(författare)
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ABJM theory with mass and FI deformations and quantum phase transitions
- 2015
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479 .- 1126-6708. ; 2015:5
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Tidskriftsartikel (refereegranskat)abstract
- The phase structure of ABJM theory with mass m deformation and non-vanishing Fayet-Iliopoulos (FI) parameter, zeta, is studied through the use of localisation on S-3. The partition function of the theory then reduces to a matrix integral, which, in the large N limit and at large sphere radius, is exactly computed by a saddle-point approximation. When the couplings are analytically continued to real values, the phase diagram of the model becomes immensely rich, with an infinite series of third-order phase transitions at vanishing FI-parameter [1]. As the FI term is introduced, new effects appear. For any given 0
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| 4. |
- Anderson, Lloyd B., et al.
(författare)
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Atmospheric CO2 Estimates for the Late Oligocene and Early Miocene Using Multi-Species Cross-Calibrations of Boron Isotopes
- 2024
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Ingår i: Paleoceanography and Paleoclimatology. - 2572-4517 .- 2572-4525. ; 39:1
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Tidskriftsartikel (refereegranskat)abstract
- The boron isotope (δ11B) proxy for seawater pH is a tried and tested means to reconstruct atmospheric CO2 in the geologic past, but uncertainty remains over how to treat species-specific calibrations that link foraminiferal δ11B to pH estimates prior to 22 My. In addition, no δ11B-based reconstructions of atmospheric CO2 exist for wide swaths of the Oligocene (33–23 Ma), and large variability in CO2 reconstructions during this epoch based on other proxy evidence leaves climate evolution during this period relatively unconstrained. To add to our understanding of Oligocene and early Miocene climate, we generated new atmospheric CO2 estimates from new δ11B data from fossil shells of surface-dwelling planktic foraminifera from the mid-Oligocene to early Miocene (∼28–18 Ma). We estimate atmospheric CO2 of ∼680 ppm for the mid-Oligocene, which then evolves to fluctuate between ∼500–570 ppm during the late Oligocene and between ∼420–700 ppm in the early Miocene. These estimates tend to trend higher than Oligo-Miocene CO2 estimates from other proxies, although we observe good proxy agreement in the late Oligocene. Reconstructions of CO2 fall lower than estimates from paleoclimate model simulations in the early Miocene and mid Oligocene, which indicates that more proxy and/or model refinement is needed for these periods. Our species cross-calibrations, assessing δ11B, Mg/Ca, δ18O, and δ13C, are able to pinpoint and evaluate small differences in the geochemistry of surface-dwelling planktic foraminifera, lending confidence to paleoceanographers applying this approach even further back in time.
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| 5. |
- Anderson, Louise, 1989
(författare)
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Field Theories with a Twist
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with topological field theories derived from maximally supersymmetric gauge theories. The main part of this work is the three appended research papers, each of which investigates some different aspect of these theories. Leading up to these is the first part of the thesis which aims at introducing the above-mentioned concepts in such a fashion that the papers become legible to even those readers who are less familiar with notions such as topological field theory and N=4 Yang-Mills theory from the start. This introduction begins with the concept of symmetry, and both gauge- and supersymmetry are explained. This leads on to the introduction of maximally supersymmetric gauge theories, and then finally to outlining the possible ways to create topological field theories from these. The two last chapters of this thesis are dedicated to the theories featured in the appended papers. Papers I and II both deals with the geometric Langlands-twist of N=4 Yang-Mills theory and the five-dimensional analog of this. In paper I, spherically symmetric solutions to the localisation equations of both the four- and five-dimensional topological field theories are investigated, whereas paper II presents an explicit expression for the action of the five-dimensional theory. The final paper deals with a topological twisting of (2,0) theory, which was conjectured to be relevant in the understanding of the AGT-correspondence. However, this suggested twist is shown to not result in a topological field theory on a general background by showing that the stress-tensor of the theory cannot in general be both $Q$-exact and conserved.
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| 6. |
- Anderson, Louise, 1989
(författare)
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Five-dimensional topologically twisted maximally supersymmetric Yang-Mills theory
- 2013
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Ingår i: Journal of High Energy Physics. - : Springer Science and Business Media LLC. - 1029-8479 .- 1126-6708. ; 2013:2, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- Herein, we consider a topologically twisted version of maximally supersymmetric Yang-Mills theory in five dimensions which was introduced by Witten in 2011. We consider this theory on a five manifold of the form M-4 x I for M-4 an oriented Riemannian four manifold. The complete and unique action of the theory in bulk is written down and is shown to be invariant under two scalar supersymmetries.
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| 7. |
- Anderson, Louise, 1989
(författare)
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LOST IN LOCALISATION searching for exact results in supersymmetric gauge theories
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with one of the very basics of theoretical physics: computing observable quantities. In the language commonly used to describe the subatomic world, gauge theories, this problem is far from trivial as the observables are expressed in terms of infinite-dimensional integrals. This holds true even in supersymmetric gauge theories, but in some cases, this additional symmetry may be used to reduce the infinite-dimensional integrals to finite-dimensional ones - which naturally simplifies the expressions significantly. This thesis revolves around one of these techniques: Localisation.In general, this poses strict requirements on the theory as well as the manifold on which the theory is placed. However, by first twisting the theory so as to obtain a topological field theory, localisation can be carried out on any background, whereas one otherwise is confined to manifolds with a large amount of symmetry such as for example d-dimensional spheres. The explicit calculation of the path integral is nonetheless in general still complicated even after localisation, and it is only in certain limits that it may be computed exactly. For example, simplifications often occur in the limit of infinitely many colours (the large N limit).Of the five papers appended to this thesis, the first three deal with topological twists of maximally supersymmetric Yang-Mills theory and (2,0) theory, whereas the last two revolve around the behaviour of the free energy of massive ABJM theory in the large N limit.
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| 8. |
- Anderson, Louise, 1989, et al.
(författare)
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Quantum Phase Transitions in Mass-Deformed ABJM Matrix Model
- 2014
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Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 1409:9, s. Art. no. 021-20
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Tidskriftsartikel (refereegranskat)abstract
- When mass-deformed ABJM theory is considered on S(3), the partition function of the theory localises and is given by a matrix model. We solve this model at large-N in the decompactification limit, where the radius of the three-sphere is taken to infinity. In this limit, the theory exhibits a rich phase structure with an infinite number of third-order quantum phase transitions accumulating at strong coupling.
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| 9. |
- Anderson, Louise, 1989, et al.
(författare)
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The trouble with twisting (2,0) theory
- 2014
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Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2014:3, s. Art. no. 062-
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Tidskriftsartikel (refereegranskat)abstract
- We consider a twisted version of the abelian (2,0) theory placed upon a Lorenzian six-manifold with a product structure, M_6=C×M_4. This is done by an investigation of the free tensor multiplet on the level of equations of motion, where the problem of its formulation in Euclidean signature is circumvented by letting the time-like direction lie in the two-manifold C and performing a topological twist along M_4 alone. A compactification on C is shown to be necessary to enable the possibility of finding a topological field theory. The hypothetical twist along a Euclidean C is argued to amount to the correct choice of linear combination of the two supercharges scalar on M_4. It may be slightly surprising that this is not the same linear combination as in the well known Donaldson-Witten twist. A more surprising fact however, is that this twisted theory contains no Q-exact and covariantly conserved stress tensor unless M_4 has vanishing curvature. This is to our knowledge a phenomenon which has not been observed before in topological field theories. In the literature, the setup of the twisting used here has been suggested as the origin of the conjectured AGT-correspondence, and our hope is that this work may somehow contribute to the understanding of it.
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| 10. |
- Anderson, Louise, 1989, et al.
(författare)
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Tunneling solutions in topological field theory on R x S-3 x I
- 2012
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Ingår i: Journal of High Energy Physics. - 1029-8479 .- 1126-6708. ; 2012:2, s. Article Number: 063-
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Tidskriftsartikel (refereegranskat)abstract
- We consider a topologically twisted version, recently introduced by Witten, of five-dimensional maximally supersymmetric Yang-Mills theory on a five-manifold of the form M-5 = RxW(3)xI. If the length of the interval I is sufficiently large, the supersymmetric localization equations admit pairs of static solutions (with the factor R interpreted as Euclidean time). However, these solutions disappear for a sufficiently short I, so by the topological invariance of the theory, they must be connected by an interpolating dynamic instanton solution. We study this for the case that W-3 is a three-sphere S-3 with the standard metric by making a spherically symmetric Ansatz for all fields. The solution is given as a power series in a parameter related to the length of I, and we give explicit expressions for the first non-trivial terms.
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