| 1. |
- Ekström, Andreas, et al.
(author)
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Effects of Three-Nucleon Forces and Two-Body Currents on Gamow-Teller Strengths
- 2014
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In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 113:26, s. 262504-
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Journal article (peer-reviewed)abstract
- We optimize chiral interactions at next-to-next-to leading order to observables in two- and three-nucleon systems and compute Gamow-Teller transitions in C14 and O22,24 using consistent two-body currents. We compute spectra of the daughter nuclei N14 and F22,24 via an isospin-breaking coupled-cluster technique, with several predictions. The two-body currents reduce the Ikeda sum rule, corresponding to a quenching factor q2≈0.84–0.92 of the axial-vector coupling. The half-life of C14 depends on the energy of the first excited 1+ state, the three-nucleon force, and the two-body current.
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| 2. |
- Ekström, Andreas, 1980, et al.
(author)
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Global Sensitivity Analysis of Bulk Properties of an Atomic Nucleus
- 2019
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In: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 123:25
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Journal article (peer-reviewed)abstract
- We perform a global sensitivity analysis of the binding energy and the charge radius of the nucleus O-16 to identify the most influential low-energy constants in the next-to-next-to-leading order chiral Hamiltonian with two- and three-nucleon forces. For this purpose, we develop a subspace-projected coupled-cluster method using eigenvector continuation [Frame D. et al., Phys. Rev. Lett. 121, 032501 (2018)]. With this method, we compute the binding energy and charge radius of O-16 at more than 10(6) different values of the 16 low-energy constants in one hour on a standard laptop computer. For relatively small subspace projections, the root-mean-square error is about 1% compared to full-space coupled-cluster results. We find that 58(1)% of the variance in energy can be apportioned to a single contact term in the S-3(1) wave, whereas the radius depends sensitively on several low-energy constants and their higher-order correlations. The results identify the most important parameters for describing nuclear saturation and help prioritize efforts for uncertainty reduction of theoretical predictions. The achieved acceleration opens up an array of computational statistics analyses of the underlying description of the strong nuclear interaction in nuclei across the Segre chart.
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| 3. |
- Hagen, Espen, et al.
(author)
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Hybrid Scheme for Modeling Local Field Potentials from Point-Neuron Networks
- 2016
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In: Cerebral Cortex. - : OXFORD UNIV PRESS INC. - 1047-3211 .- 1460-2199. ; 26:12, s. 4461-4496
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Journal article (peer-reviewed)abstract
- With rapidly advancing multi-electrode recording technology, the local field potential (LFP) has again become a popular measure of neuronal activity in both research and clinical applications. Proper understanding of the LFP requires detailed mathematical modeling incorporating the anatomical and electrophysiological features of neurons near the recording electrode, as well as synaptic inputs from the entire network. Here we propose a hybrid modeling scheme combining efficient point-neuron network models with biophysical principles underlying LFP generation by real neurons. The LFP predictions rely on populations of network-equivalent multicompartment neuron models with layer-specific synaptic connectivity, can be used with an arbitrary number of point-neuron network populations, and allows for a full separation of simulated network dynamics and LFPs. We apply the scheme to a full-scale cortical network model for a similar to 1 mm(2) patch of primary visual cortex, predict laminar LFPs for different network states, assess the relative LFP contribution from different laminar populations, and investigate effects of input correlations and neuron density on the LFP. The generic nature of the hybrid scheme and its public implementation in hybridLFPy form the basis for LFP predictions from other and larger point-neuron network models, as well as extensions of the current application with additional biological detail.
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| 4. |
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| 5. |
- Hagen, Gaute, 1958-
(author)
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3D Rotational Angiography of Transplanted Renal Arteries : A Clinical and Experimental Study
- 2004
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Doctoral thesis (other academic/artistic)abstract
- Three-dimensional rotational angiography (3D-RA) is an established method within the field of interventional neuroradiology. The method has also a great potential in other areas with a complicated arterial anatomy. The purpose of this study was firstly to develop an investigative protocol for 3D-RA in renal transplanted patients with threatening allograft failure in diagnosing stenosis in the transplanted renal artery; secondly the protocol was evaluated and compared with a modified protocol including reduced contrast medium load. Furthermore, the advantages of the 3D reconstructions compared to the angiographic images were evaluated, likewise if an extended angle of rotation reduced the artifacts in the 3D reconstructions. The two protocols were compared with regard to image quality and acute nephrotoxicity. The accuracy of Doppler ultrasonography and the result of percutaneous transluminal angioplasty (PTA) were also assessed.3D-RA was consecutively performed in 57 renal transplanted patients with suspicion of renal artery stenosis. A significant stenosis was found in 49% of the patients. The 3D reconstructions profiled 43% of the transplant renal artery stenoses better than the angiographic images. An extended angle of rotation reduced the artifacts. There was no statistical difference regarding image quality between the two protocols, and the renal function was equally affected in both protocols. Doppler ultrasonography sensitivity was 100%; specificity was 48% and positive predictive value 67%. PTA had a technical success rate of 92% and a clinical success rate of 75% after 3 months.3D-RA is a helpful supplement in cases with complicated vascular anatomy, especially when PTA may be indicated. The 3D reconstructions profile the course of the artery more frequently than the angiographic images and support PTA. The 3D reconstructions are degraded of artifacts. Sampling artifacts can be diminished by increased C-arm rotation and increased number of projections. The distortions caused by beam hardening remain to be solved.
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| 6. |
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| 7. |
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| 8. |
- Hagen, Gaute, et al.
(author)
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Outcome after percutaneous transluminal angioplasty of arterial stenosis in renal transplant patients
- 2009
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In: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 50:3, s. 270-275
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Journal article (peer-reviewed)abstract
- BACKGROUND: Ensuring graft survival in renal transplant patients is of paramount importance. Early detection and treatment of complications such as transplant renal artery stenosis (TRAS) are essential. PURPOSE: To evaluate the technical and clinical success rate of renal transplant patients with stenosis in the transplant renal artery or in the iliac artery after percutaneous transluminal angioplasty (PTA). MATERIAL AND METHODS: PTA was carried out on 24 patients with TRAS or iliac artery stenosis. Altogether, 28 stenoses were treated with PTA. The immediate technical result and the clinical outcomes after 1 and 3 months were assessed as well as clinical adverse events. A reduction in serum creatinine and/or a reduction in the number of antihypertensive drugs were criteria for clinical success. RESULTS: The immediate technical success rate after PTA was 93%. The clinical success rate after 1 month was 58%, increasing to 75% after 3 months. CONCLUSION: The technical success rate is not equivalent to the clinical success rate when treating TRAS with PTA. Furthermore, there is a delay in clinical response, sometimes of 3 months, after a technically successful PTA.
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| 9. |
- Hagen, Gaute, et al.
(author)
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Three-dimensional rotational angiography of transplanted renal arteries : influence of an extended angle of rotation on beam-hardening artifacts
- 2005
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In: Acta Radiologica. - : SAGE Publications. - 0284-1851 .- 1600-0455. ; 46:2, s. 170-176
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Journal article (peer-reviewed)abstract
- PURPOSE:To investigate whether three-dimensional rotational angiography (3D-RA) of the transplant renal artery performed with an extended angle of rotation can reduce beam-hardening artifacts in 3D reconstructed images without image quality being lost or side effects to the transplanted kidney being increased.MATERIAL AND METHODS:3D-RA with a C-arm rotation of 180 degrees was performed consecutively in 12 renal transplanted patients with suspicion of renal artery stenosis. A 1.7-mm balloon occlusion catheter was placed using the crossover technique and this was compared to a protocol with 160 degrees rotation and a traditional 1.4-mm catheter in 10 patients. The occurrence of beam-hardening artifacts was registered and the effects of the reduced contrast load on image quality and of arterial occlusion on renal function were assessed.RESULTS:The extended angle of rotation, from 160 degrees to 180 degrees, reduced the beam-hardening artifacts. Artifacts were observed in 4/11 patients (36%) in the study group and in all 10 (100%) of the controls. There was no statistical difference regarding image quality between the two protocols. Renal function was equally affected in both protocols.CONCLUSION:3D-RA with an extended C-arm rotation reduced the beam-hardening artifacts. Image quality was not reduced despite the reduced contrast medium load. The different protocols had no effect on patient outcome.
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| 10. |
- Hu, Baishan, et al.
(author)
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Ab initio predictions link the neutron skin of Pb-208 to nuclear forces
- 2022
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In: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2481 .- 1745-2473. ; 18:10, s. 1196-1200
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Journal article (peer-reviewed)abstract
- Heavy atomic nuclei have an excess of neutrons over protons, which leads to the formation of a neutron skin whose thickness is sensitive to details of the nuclear force. This links atomic nuclei to properties of neutron stars, thereby relating objects that differ in size by orders of magnitude. The nucleus Pb-208 is of particular interest because it exhibits a simple structure and is experimentally accessible. However, computing such a heavy nucleus has been out of reach for ab initio theory. By combining advances in quantum many-body methods, statistical tools and emulator technology, we make quantitative predictions for the properties of Pb-208 starting from nuclear forces that are consistent with symmetries of low-energy quantum chromodynamics. We explore 10(9) different nuclear force parameterizations via history matching, confront them with data in select light nuclei and arrive at an importance-weighted ensemble of interactions. We accurately reproduce bulk properties of Pb-208 and determine the neutron skin thickness, which is smaller and more precise than a recent extraction from parity-violating electron scattering but in agreement with other experimental probes. This work demonstrates how realistic two- and three-nucleon forces act in a heavy nucleus and allows us to make quantitative predictions across the nuclear landscape. Predictions of the properties of Pb-208 from first principles augmented by statistical learning techniques reproduce those seen in experiments but rule out very thick neutron skins.
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