| 1. |
- Kehoe, Laura, et al.
(författare)
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Make EU trade with Brazil sustainable
- 2019
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 364:6438, s. 341-
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 2. |
- Wiedorn, Max O., et al.
(författare)
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Megahertz serial crystallography
- 2018
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- The new European X-ray Free-Electron Laser is the first X-ray free-electron laser capable of delivering X-ray pulses with a megahertz inter-pulse spacing, more than four orders of magnitude higher than previously possible. However, to date, it has been unclear whether it would indeed be possible to measure high-quality diffraction data at megahertz pulse repetition rates. Here, we show that high-quality structures can indeed be obtained using currently available operating conditions at the European XFEL. We present two complete data sets, one from the well-known model system lysozyme and the other from a so far unknown complex of a beta-lactamase from K. pneumoniae involved in antibiotic resistance. This result opens up megahertz serial femtosecond crystallography (SFX) as a tool for reliable structure determination, substrate screening and the efficient measurement of the evolution and dynamics of molecular structures using megahertz repetition rate pulses available at this new class of X-ray laser source.
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| 3. |
- Brette, Romain, et al.
(författare)
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Simulation of networks of spiking neurons : A review of tools and strategies
- 2007
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Ingår i: Journal of Computational Neuroscience. - : Springer Science and Business Media LLC. - 0929-5313 .- 1573-6873. ; 23:3, s. 349-398
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Forskningsöversikt (refereegranskat)abstract
- We review different aspects of the simulation of spiking neural networks. We start by reviewing the different types of simulation strategies and algorithms that are currently implemented. We next review the precision of those simulation strategies, in particular in cases where plasticity depends on the exact timing of the spikes. We overview different simulators and simulation environments presently available (restricted to those freely available, open source and documented). For each simulation tool, its advantages and pitfalls are reviewed, with an aim to allow the reader to identify which simulator is appropriate for a given task. Finally, we provide a series of benchmark simulations of different types of networks of spiking neurons, including Hodgkin-Huxley type, integrate-and-fire models, interacting with current-based or conductance-based synapses, using clock-driven or event-driven integration strategies. The same set of models are implemented on the different simulators, and the codes are made available. The ultimate goal of this review is to provide a resource to facilitate identifying the appropriate integration strategy and simulation tool to use for a given modeling problem related to spiking neural networks.
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| 4. |
- Esteve, Romain, et al.
(författare)
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Electrical properties of MOS structures based on 3C-SiC(111) epilayers grown by Vapor-Liquid-Solid Transport and Chemical-Vapor Deposition on 6H-SiC(0001)
- 2010
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Ingår i: AIP Conference Proceedings. - : AIP Publishing. - 9780735408470 ; , s. 55-58
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Konferensbidrag (refereegranskat)abstract
- The electrical properties of post-oxidized PECVD oxides in wet oxygen based on 3C-SiC(111) epilayers grown by Vapor-Liquid-Solid and Chemical-Vapor-Deposition mechanisms on 6H-SiC(0001) have been studied. Different 6H-SiC(0001) samples exhibiting diverse crystal orientations (on-axis, 2 degrees off-axis) and growth conditions were regarded. A comparative study of oxide qualities has been carried out via capacitance and conductance measurements (C-G-V). Achieved interface traps densities and effective oxide charges were compared for the different samples. Reliability issues have been considered via current measurements (I-V and TZDB) and statistical data treatment techniques (Weibull plots). Oxides based on 3C-SiC layer grown by a process combining VLS and CVD methods demonstrated low interface states densities D-it of 1.2 x 10(10) eV(-1)cm(-2) at 0.63 eV below the conduction band and fixed oxide charges Q(eff)/(g) estimated to -0.1 x 10(11) cm(-2)
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| 5. |
- Futrzynski, Romain, 1988-
(författare)
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Drag reduction using plasma actuators
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is motivated by the application of active flow control on the cabin of trucks, thereby providing a new means of drag reduction. Particularly, the work presented strives to identify how plasma actuators can be used to reduce the drag caused by the detachment of the flow around the A-pillars. This is achieved by conducting numerical simulations, and is part of a larger project that also includes experimental.The effect of plasma actuators is modeled through a body force, which adds very little computational cost and is suitable for implementation in most CFD solvers. The spatial distribution of this force is described by coefficients which have been optimized against experimental data, and the model was shown to be able to accurately reproduce the wall jet created by a single plasma actuator in a no-flow condition.A half cylinder geometry - a simplified geometry for the A-pillar of a truck - was used in a preliminary Large Eddy Simulation (LES) study that showed that the actuator alone, operated continuously, was not sufficient to achieve a significant reduction of the drag. Nevertheless, a significant drag reduction was obtained by simply increasing the strength of the body force to a higher value, showing that this type of actuation remains relevant for the reduction of drag.In the course of finding ways to improve the efficiency of the actuator, dynamic mode decomposition was investigated as a post-processing tool to extract structures in the flow. Such structures are identified by their spatial location and frequency, and might help to understand how the actuator should be used to maximize drag reduction. Thus a parallel code for dynamic mode decomposition was developed in order to facilitate the treatment of the large amounts of data obtained by LES. This code and LES itself were thereafter evaluated in the case of a pulsating channel flow. By using the dynamic mode decomposition it was possible to accurately extract oscillating profiles at the forcing frequency, although harmonics with lower amplitude compared to the turbulence intensity could not be obtained.
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| 6. |
- Futrzynski, Romain, 1988-
(författare)
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Effect of drag reducing plasma actuators using LES
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The work performed in this thesis explores new ways of reducing the drag of ground vehicles. Specifically, the effect of plasma actuators are investigated numerically with the intention to delay separation around a half-cylinder, a geometry chosen to represent a simplified A-pillar of a truck.The plasma actuators have to be included in turbulent flow simulations. Therefore, emphasis is first put on finding a numerical model that can reproduce the effect of the plasma without increasing the computational cost. This effect is modeled through a body force term added to the Navier-Stokes equations. To determine the strength and spatial extent of this body force, optimization was performed to minimize the difference between experimental and simulated profiles of plasma induced velocity. The plasma actuator model is thereafter used in Large Eddy Simulations (LES) of the flow around a half-cylinder at Reynolds number Re=65*10^3 and Re=32*10^3. Two types of actuation cases are performed. In the first case, a single actuator is used. In the second case, a pair of consecutive actuators are used, and their position on the half-cylinder is changed. It is found that a drag reduction of up to 10% is achievable. Moreover, the ideal location for actuation is determined to be near the separation point of the non-actuated flow. Finally, dynamic mode decomposition (DMD) is investigated as a tool to extract coherent dynamic structures from a turbulent flow field. The DMD is first used to analyze a channel flow where pulsations are imposed at a known frequency. It is found that DMD gives similar results to phase averaging done at the oscillation frequency. However, the presence of turbulence noise hinders the ability to identify modes at higher harmonics. The DMD is also used to post-process the half-cylinder flow case. There, it is found that the spectrum of the wake is broadband. Nevertheless, modes within distinct frequency ranges are found to be located in distinct spatial regions.
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| 7. |
- Futrzynski, Romain, 1988-, et al.
(författare)
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Numerical simulation of a plasma actuator on a half-submerged cylinder
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In this paper Large Eddy Simulations are used to study the reduction of drag that can be achieved on a half-submerged cylinder by using a type of plasma actuator: the single dielectric barrier discharge. Two body force models, one based on an exponential decrease of the force away from the plasma, the other based on a simplified electric field between the electrodes, are compared to experimental values when the actuator is positioned at the apex of the cylinder in an otherwise quiescent environment. The cylinder is then put in a crossflow, and the exponential-based model, which gives the velocity profiles the closest to the experimental data, is used to simulate the effect of the plasma actuator on such a flow. The reduction in drag is changed as the position of the actuator is varied.
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| 8. |
- Sobolev, Egor, et al.
(författare)
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Megahertz single-particle imaging at the European XFEL
- 2020
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Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 3:1
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Tidskriftsartikel (refereegranskat)abstract
- The emergence of high repetition-rate X-ray free-electron lasers (XFELs) powered by superconducting accelerator technology enables the measurement of significantly more experimental data per day than was previously possible. The European XFEL is expected to provide 27,000 pulses per second, over two orders of magnitude more than any other XFEL. The increased pulse rate is a key enabling factor for single-particle X-ray diffractive imaging, which relies on averaging the weak diffraction signal from single biological particles. Taking full advantage of this new capability requires that all experimental steps, from sample preparation and delivery to the acquisition of diffraction patterns, are compatible with the increased pulse repetition rate. Here, we show that single-particle imaging can be performed using X-ray pulses at megahertz repetition rates. The results obtained pave the way towards exploiting high repetition-rate X-ray free-electron lasers for single-particle imaging at their full repetition rate.
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