| 1. |
- Maksimovic, M., et al.
(författare)
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The Solar Orbiter Radio and Plasma Waves (RPW) instrument
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 642
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Tidskriftsartikel (refereegranskat)abstract
- The Radio and Plasma Waves (RPW) instrument on the ESA Solar Orbiter mission is described in this paper. This instrument is designed to measure in-situ magnetic and electric fields and waves from the continuous to a few hundreds of kHz. RPW will also observe solar radio emissions up to 16 MHz. The RPW instrument is of primary importance to the Solar Orbiter mission and science requirements since it is essential to answer three of the four mission overarching science objectives. In addition RPW will exchange on-board data with the other in-situ instruments in order to process algorithms for interplanetary shocks and type III langmuir waves detections.
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| 2. |
- Andersson, Malin, et al.
(författare)
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A Continuous-time LPV model for battery state-of-health estimation using real vehicle data
- 2020
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Ingår i: CCTA 2020 - 4th IEEE Conference on Control Technology and Applications. - : Institute of Electrical and Electronics Engineers Inc.. ; , s. 692-698
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Konferensbidrag (refereegranskat)abstract
- One approach for State-of-health estimation onboard electric vehicles is to train a data-driven virtual battery on operational data and use this model, rather than the actual battery, for performance tests. A temperature-dependent continuous-time output-error (OE) model is proposed as virtual battery and identified and validated on real operational data from electric buses. The proposed model is compared to discrete-time and parameter-invariant models and shows better performance on all data sets. In addition, the OE model structure is shown to be superior to a conventional Auto Regressive eXogenous (ARX) model for the purpose of modeling the battery voltage response. Finally, challenges regarding vehicle log data are identified and improvements to the model are suggested in order to capture observed un-modeled phenomena.
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| 3. |
- Brethouwer, Gert, et al.
(författare)
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Turbulence and cyclic bursts in rotating channel flow
- 2020
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Ingår i: ETC 2013 - 14th European Turbulence Conference. - : Zakon Group LLC.
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Konferensbidrag (refereegranskat)abstract
- DNS have been performed of turbulent channel flow with spanwise rotation and bulk Reynolds number Re up to 30000. At moderate rotation rates Ro the flow on one side of the channel is approximately laminar, or has turbulent patches or oblique turbulent-laminar patterns. Intense cyclic bursts of turbulence with long time intervals are in some cases observed at sufficiently high Re and Ro. A linear analysis indicates that the turbulence bursts are initiated by a linear instability of plane waves aligned with the rotation axis. This linear instability can develop even if parts of the flow are strongly turbulent.
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| 4. |
- Brett, Calvin
(författare)
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Neutron and X-ray Surface Scattering Reveals the Morphology of Soft Matter Thin Films
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The last decades have been overshadowed by reports about the seemingly endless increase use of fossil-based resources. With the development of new products, our mindset is changing so that we more and more need to consider sustainability in our daily lives. Furthermore, smarter devices are indispensable in our world and daily life, and these are expected to be smaller and smaller in size.To support the transition from fossil-based to sustainable materials, we need to develop knowledge of new materials. Within this thesis project, the aim has been to understand the thin-film properties of sustainable materials and to develop methodologies to measure these. As sustainable template material wood-based nanocellulose was chosen as a bio-degradable representative with favourable favourable physical properties, such as lightweight, transparency, and flexibility. These properties make nanocellulose a perfect candidate for future advanced applications in thin-film organic solar cells, supercapacitors, or sensors. Nanocellulose comprises only a part of such a device, and hence the relevant functional materials and their combinations have to be studied to reveal the interaction between multiple material components on the final device performance. As the nanoscale, or even Ångstrom scale, governs the macroscopic physical properties, it is crucial to understand the materials in detail. Ergo, neutron and X-ray surface-sensitive scattering methods were applied to study nanoparticle deposition layering kinetics and the effects of environmental changes, which revealed the morphology of the resulting nanoporous nanocellulose thin films. The knowledge was used to infiltrate water-soluble intrinsic conductive polymers into these nanopores, which serves as a model for transparent but conductive templates for organic electronics. By changing the environment of the films through humidity cycling, the impact of the environment during a real-life application could be illustrated. Neutron scattering experiments also showed that the cellulose-conductive polymer composite (or hybridmaterial) changes irreversibly during humidity cycling while the pure nanocellulose films show fully reversible properties.Furthermore, the thermal decomposition of silver nitrate deposited on nanocellulose was studied to understand the nanofibrils' impact on the synthesis of nanoparticles. The transparency allowed in situ studies of the synthesis process, the spectroscopic properties as well as the plasmonic effect, which demonstrated routes for minimal material usage concepts for surface synthesis processes. It was also discovered that the process allows for band-gap tuning, which can be directly be applied in organic solar cells to tailor the band-gap to be adapted and hence increasing the efficiency.The morphological properties, as studied using X-rays and neutrons, were correlated to macroscopic properties by measuring wettability, surface topography, spectroscopy, or conductivity to examine the full materials application possibilities. Neutron and X-ray scattering methods are complementary and wisely combined, thus allowed pioneering studies of bio-based sustainable nanocomposites leading to advanced functional material concepts that support the development of devices using less fossil-based materials.
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| 5. |
- Dobrota, Ana S., et al.
(författare)
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Altering the reactivity of pristine, N- and P-doped graphene by strain engineering : A DFT view on energy related aspects
- 2020
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Ingår i: Applied Surface Science. - : ELSEVIER. - 0169-4332 .- 1873-5584. ; 514
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Tidskriftsartikel (refereegranskat)abstract
- For carbon-based materials, in contrast to metal surfaces, a general relationship between strain and reactivity is not yet established, even though there are literature reports on strained graphene. Knowledge of such relationships would be extremely beneficial for understanding the reactivity of graphene-based surfaces and finding optimisation strategies which would make these materials more suitable for targeted applications. Here we investigate the effects of compressive and tensile strain (up to +/- 5%) on the structure, electronic properties and reactivity of pure, N-doped and P-doped graphene, using DFT calculations. We demonstrate the possibility of tuning the topology of the graphene surface by strain, as well as by the choice of the dopant atom. The reactivity of (doped) strained graphene is probed using H and Na as simple adsorbates of great practical importance. Strain can both enhance and weaken H and Na adsorption on (doped) graphene. In case of Na adsorption, a linear relationship is observed between the Na adsorption energy on P-doped graphene and the phosphorus charge. A linear relationship between the Na adsorption energy on flat graphene surfaces and strain is found. Based on the adsorption energies and electrical conductivity, potentially good candidates for hydrogen storage and sodiumion battery electrodes are discussed.
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| 6. |
- El Khoury, George K., et al.
(författare)
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Turbulent pipe flow : New DNS data and large-scale structures
- 2020
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Ingår i: ETC 2013 - 14th European Turbulence Conference. - : Zakon Group LLC.
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Konferensbidrag (refereegranskat)abstract
- Large-scale fully resolved direct numerical simulations (DNSs) have been performed with a high-order spectral element method to study the flow of an incompressible viscous fluid in a smooth circular pipe of radius R and axial length 25R in the turbulent flow regime at four different friction Reynolds numbers Reτ = 180, 360, 550 and 1000. The new data is compared to other simulation data sets, obtained in pipe, channel and boundary-layer geometry. The pressure is the variable that differs the most between the cases; a significantly higher mean and fluctuating pressure are observed in boundary layers that is linked to a stronger wake region. Critical assessment of the available DNS data is conducted in order to determine which difference or correspondence between the data sets are real and caused by physics, and which discrepancies are likely due to statistical or numerical inaccuracies. Furthermore, two-dimensional spectra of axial/streamwise velocity show an imprint of the large-scale motions from the outer layer in all canonical flows, however with different amplitude.
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| 7. |
- Jawerth, Marcus, et al.
(författare)
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Mechanical and Morphological Properties of Lignin-Based Thermosets
- 2020
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Ingår i: ACS APPLIED POLYMER MATERIALS. - : AMER CHEMICAL SOC. - 2637-6105. ; 2:2, s. 668-676
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Tidskriftsartikel (refereegranskat)abstract
- The need for renewable alternatives for fossil-based aromatic material constituents is evident for a more sustainable society. Lignin is the largest source of naturally occurring aromatic compounds but has mainly been considered as waste material or energy source in the pulp and paper industry. Developments in extracting lignin from these processes provide a large source for renewable aromatic structures to be used in various applications. Producing thermosets out of lignin is a very promising route to utilize this raw material toward, for example, composite application. The buildup of the molecular network based on oligomeric lignin segments will be different from traditional thermoset analogues, where the constituents often are smaller molecules, and will have an effect on the material properties. In this work LignoBoost Kraft lignin is refined, chemically modified, and used to produce freestanding thermosets with different architectures and properties. These different thermosets are evaluated, and the possibilities to tailor the material properties through work-up and modification are demonstrated. Morphological studies on the formed thermosets using X-ray scattering show systematic differences in molecular stacking and aggregate sizes.
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| 8. |
- Lamas, L., et al.
(författare)
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Revision of the Eurocodes – aspects of geotechnical and rock engineering design
- 2020
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Ingår i: ISRM International Symposium - EUROCK 2020. - : International Society for Rock Mechanics.
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Konferensbidrag (refereegranskat)abstract
- The Structural Eurocodes (EN 199x) are a suite of European standards for the design of buildings and civil engineering works, published in 2006 by the European Committee for Standardization (CEN) and with implementation starting in 2010. EN 1990 sets the basis of structural design, with the other Eurocodes dealing with different materials and specific aspects of the design; Eurocode 7 (EN 1997) deals with geotechnical aspects. In 2010, CEN began a process of evolving the Eurocodes in order to incorporate improvements that reflect the state-of-the-art in engineering design and the needs of the civil engineering market; to improve the ease-of-use of the standards; and to harmonize practice between countries. The existing EN 1990 is founded on limit state concepts, and reliability of design is provided mainly by a semi-probabilistic method based on partial factors. Applying the same method to geotechnical design has proved to be difficult, and the revised EN 1990 will present improvements concerning geotechnical design. Reflecting these changes, the title of EN 1990 was changed to “Basis of structural and geotechnical design”. Although initially developed for structures involving soils, Eurocode 7 is also applicable to rock engineering design. A major target of the current revision is that the code should treat soil and rock on an equal basis. The evolution of the Eurocode 7 has been accompanied by a group of rock engineering experts working under CEN, who started their activity in 2011. The paper is authored by the current members of this group and presents the situation of the revision of Eurocode 7 in October 2019, namely: the main objectives of the revision; the new structure adopted for the code, with three parts, and the implementation schedule of the revised Eurocodes; the main changes implemented so far in geotechnical design and rock engineering; the main rock engineering aspects still needing to be addressed.
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| 9. |
- Lazeroms, Werner, et al.
(författare)
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Explicit algebraic models for turbulent flows with buoyancy effects
- 2020
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Ingår i: ETC 2013 - 14th European Turbulence Conference. - : Zakon Group LLC.
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Konferensbidrag (refereegranskat)abstract
- For turbulent flows that are influenced by an active scalar, the Reynolds stresses and scalar flux are coupled in a complicated way, which makes it difficult to model these flows. A framework has been derived for obtaining explicit algebraic Reynolds-stress and scalar-flux models for two-dimensional mean flows with stratification. For the specific case of stably stratified parallel shear flows, the derived model was shown to give good results. As an extension of these results, two more cases are considered: unstable stratification in a horizontal channel and natural convection in a vertical channel.
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| 10. |
- Mai, Vien V., et al.
(författare)
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Convergence of a stochastic gradient method with momentum for non-smooth non-convex optimization
- 2020
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Ingår i: 37th International Conference on Machine Learning, ICML 2020. - : International Machine Learning Society (IMLS). ; , s. 6576-6585
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Konferensbidrag (refereegranskat)abstract
- Stochastic gradient methods with momentum are widely used in applications and at the core of optimization subroutines in many popular machine learning libraries. However, their sample complexities have not been obtained for problems beyond those that are convex or smooth. This paper establishes the convergence rate of a stochastic subgradient method with a momentum term of Polyak type for a broad class of non-smooth, non-convex, and constrained optimization problems. Our key innovation is the construction of a special Lyapunov function for which the proven complexity can be achieved without any tuning of the momentum parameter. For smooth problems, we extend the known complexity bound to the constrained case and demonstrate how the unconstrained case can be analyzed under weaker assumptions than the state-of-The-Art. Numerical results confirm our theoretical developments.
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