| 1. |
- Ferri, Julien, 1990, et al.
(författare)
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Enhancement of laser-driven ion acceleration in non-periodic nanostructured targets
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:1
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Tidskriftsartikel (refereegranskat)abstract
- Using particle-in-cell simulations, we demonstrate an improvement of the target-normal-sheath acceleration (TNSA) of protons in non-periodically nanostructured targets with micron-scale thickness. Compared to standard flat foils, an increase in the proton cutoff energy by up to a factor of two is observed in foils coated with nanocones or perforated with nanoholes. The latter nano-perforated foils yield the highest enhancement, which we show to be robust over a broad range of foil thicknesses and hole diameters. The improvement of TNSA performance results from more efficient hot-electron generation, caused by a more complex laser-electron interaction geometry and increased effective interaction area and duration. We show that TNSA is optimized for a nanohole distribution of relatively low areal density and that is not required to be periodic, thus relaxing the manufacturing constraints.
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| 2. |
- Andersson, Joakim, 1964, et al.
(författare)
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Spare Parts Demand Prediction by Using a Random Forest Approach
- 2023
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Ingår i: IFIP Advances in Information and Communication Technology. - 1868-4238 .- 1868-422X. ; 691 AICT, s. 793-804
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Konferensbidrag (refereegranskat)abstract
- Spare parts forecasting, in general, is a complex task, due to its intermittent and erratic demand patterns. Furthermore, the underlying reason for the demand is usually not considered since most forecasting methods are based on demand history, merely. Spare parts demand is dependent on the need for replacement of components due to repair or maintenance reasons, which varies due to, e.g., life cycle, utilization of the finished product, and the number of finished products. Although machine learning methods have been more prevalent for spare parts forecasting in recent years, the prediction of initial demand, i.e., what to be stocked before the breakdowns and maintenance needs occur is understudied. So, the purpose of this paper is to investigate if the spare part need can be predicted before the demand occurs and, by that, increase the availability to the customers and decrease the cost of unavailability, e.g., expediting costs and lost sales. By adopting a machine learning model based on decision trees, called Random Forest, we predicted the probability of initial sales based on the installed base, and categorical variables such as product group, vital code, function, and weight, for spare parts at an automotive company. The analysis was made for three different markets in the Asia-pacific region and predictions were made for three different time horizons, 1, 3, and 6 months and the model performance shows potentially good results with an accuracy of around 70%. We also analyzed the business impact concerning availability and supply chain-related costs where, for example, we obtained a substantially lower total supply chain cost.
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| 3. |
- Bello-Benitez, E., et al.
(författare)
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Structure and evolution of magnetohydrodynamic solitary waves with Hall and finite Larmor radius effects
- 2019
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Ingår i: Physical Review E. - 2470-0045. ; 99:2
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Tidskriftsartikel (refereegranskat)abstract
- Nonlinear and low-frequency solitary waves are investigated in the framework of the one-dimensional Hall-magnetohydrodynamic model with finite Larmor effects and two different closure models for the pressures. For a double adiabatic pressure model, the organization of these localized structures in terms of the propagation angle with respect to the ambient magnetic field theta and the propagation velocity C is discussed. There are three types of regions in the theta-C plane that correspond to domains where either solitary waves cannot exist, are organized in branches, or have a continuous spectrum. A numerical method valid for the two latter cases, which rigorously proves the existence of the waves, is presented and used to locate many waves, including bright and dark structures. Some of them belong to parametric domains where solitary waves were not found in previous works. The stability of the structures has been investigated by performing a linear analysis of the background plasma state and by means of numerical simulations. They show that the cores of some waves can be robust, but, for the parameters considered in the analysis, the tails are unstable. The substitution of the double adiabatic model by evolution equations for the plasma pressures appears to suppress the instability in some cases and to allow the propagation of the solitary waves during long times.
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| 4. |
- Ferri, Julien, 1990, et al.
(författare)
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Effects of oblique incidence and colliding pulses on laser-driven proton acceleration from relativistically transparent ultrathin targets
- 2020
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Ingår i: Journal of Plasma Physics. - 0022-3778 .- 1469-7807. ; 86:5
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Tidskriftsartikel (refereegranskat)abstract
- The use of ultrathin solid foils offers optimal conditions for accelerating protons to high energies from laser-matter interactions. When the target is thin enough that relativistic self-induced transparency sets in, all of the target electrons get heated to high energies by the laser, which maximizes the accelerating electric field and therefore the final ion energy. In this work, we first investigate how ion acceleration by ultraintense femtosecond laser pulses in transparent CH2 solid foils is modified when turning from normal to oblique (45 degrees) incidence. Due to stronger electron heating, we find that higher proton energies can be obtained at oblique incidence but in thinner optimum targets. We then show that proton acceleration can be further improved by splitting the laser pulse into two half-pulses focused at opposite incidence angles. An increase by similar to 30% in the maximum proton energy and by a factor of similar to 4 in the high-energy proton charge is reported compared to the reference case of a single normally incident pulse.
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| 5. |
- Siminos, E., et al.
(författare)
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Generation of intense isolated CEP-tunable sub-cycle pulses in laser-driven wakes
- 2020
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Ingår i: Optics InfoBase Conference Papers. - 2162-2701.
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Konferensbidrag (refereegranskat)abstract
- We present a scheme which leverages laser-driven wakes in plasmas to produce carrier-envelope-phase tunable sub-cycle pulses with central wavelength ranging from the midinfrared to the ultraviolet and up to few tens of mJ energy.
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| 6. |
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