| 1. |
- Abele, H., et al.
(författare)
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Particle physics at the European Spallation Source
- 2023
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Ingår i: Physics reports. - : Elsevier. - 0370-1573 .- 1873-6270. ; 1023, s. 1-84
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Forskningsöversikt (refereegranskat)abstract
- Presently under construction in Lund, Sweden, the European Spallation Source (ESS) will be the world’s brightest neutron source. As such, it has the potential for a particle physics program with a unique reach and which is complementary to that available at other facilities. This paper describes proposed particle physics activities for the ESS. These encompass the exploitation of both the neutrons and neutrinos produced at the ESS for high precision (sensitivity) measurements (searches).
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| 2. |
- Engström, Hans, et al.
(författare)
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Laser hybrid welding of high strength steels
- 2001
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Ingår i: Congress proceedings. - Orlando, Fla. : Laser institute of America. - 0912035730 ; , s. 125-134
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Konferensbidrag (refereegranskat)abstract
- This paper presents results from an ongoing investigation into laser-arc-hybrid welding of thick, high strength steels used in the heavy mechanical and heavy automotive industries. The results include welding parameters for a 6 and 12 kW laser combined with conventional MIG/MAG equipment. In this work, the laser-arc-hybrid welding technique has been further developed and applied to thick steel plate welding, giving high quality welds at high speeds. Successful welds were obtained on 6-12 mm plate thickness with laser, plasma or sheared edges as received from the blanking process. Thereby any costly, additional joint preparation is avoided, giving the hybrid welding technique an enhanced potential for use in the heavy automotive and mechanical industries
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| 3. |
- Behar, Etienne, et al.
(författare)
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Dawn-dusk asymmetry induced by the Parker spiral angle in the plasma dynamics around comet 67P/Churyumov-Gerasimenko
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 478:2, s. 1570-1575
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Tidskriftsartikel (refereegranskat)abstract
- When interacting, the solar wind and the ionised atmosphere of a comet exchange energy and momentum. Our aim is to understand the influence of the average Parker spiral configuration of the solar wind magnetic field on this interaction. We compare the theoretical expectations of an analytical generalised gyromotion with Rosetta observations at comet 67P/Churyumov-Gerasimenko. A statistical approach allows one to overcome the lack of upstream solar wind measurement. We find that additionally to their acceleration along (for cometary pick-up ions) or against (for solar wind ions) the upstream electric field orientation and sense, the cometary pick-up ions are drifting towards the dawn side of the coma, while the solar wind ions are drifting towards the dusk side of the coma, independent of the heliocentric distance. The dynamics of the interaction is not taking place in a plane, as often assumed in previous works.
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| 4. |
- Behar, Etienne, et al.
(författare)
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Solar wind dynamics around a comet : A 2D semi-analytical kinetic model
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
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Tidskriftsartikel (refereegranskat)abstract
- Aims.We aim at analytically modelling the solar wind proton trajectories during their interaction with a partially ionised cometaryatmosphere, not in terms of bulk properties of the flow but in terms of single particle dynamics.Methods.We first derive a generalised gyromotion, in which the electric field is reduced to its motional component. Steady-stateis assumed, and simplified models of the cometary density and of the electron fluid are used to express the force experienced byindividual solar wind protons during the interaction.Results.A three-dimensional (3D) analytical expression of the gyration of two interacting plasma beams is obtained. Applying it to acomet case, the force on protons is always perpendicular to their velocity and has an amplitude proportional to 1/r2. The solar winddeflection is obtained at any point in space. The resulting picture presents a caustic of intersecting trajectories, and a circular regionis found that is completely free of particles. The particles do not lose any kinetic energy and this absence of deceleration, togetherwith the solar wind deflection pattern and the presence of a solar wind ion cavity, is in good agreement with the general results of theRosettamission.Conclusions.The qualitative match between the model and thein situdata highlights how dominant the motional electric field isthroughout most of the interaction region for the solar wind proton dynamics. The model provides a simple general kinetic descriptionof how momentum is transferred between these two collisionless plasmas. It also shows the potential of this semi-analytical modelfor a systematic quantitative comparison to the data.
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| 5. |
- Behar, Etienne, et al.
(författare)
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The birth and growth of a solar wind cavity around a comet : Rosetta observations
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 469:Suppl. 2, s. S369-S403
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Tidskriftsartikel (refereegranskat)abstract
- The Rosetta mission provided detailed observations of the growth of a cavity in the solar wind around comet 67P/Churyumov–Gerasimenko. As the comet approached the Sun, the plasma of cometary origin grew enough in density and size to present an obstacle to the solar wind. Our results demonstrate how the initial slight perturbations of the solar wind prefigure the formation of a solar wind cavity, with a particular interest placed on the discontinuity (solar wind cavity boundary) passing over the spacecraft. The slowing down and heating of the solar wind can be followed and understood in terms of single particle motion. We propose a simple geometric illustration that accounts for the observations, and shows how a cometary magnetosphere is seeded from the gradual steepening of an initially slight solar wind perturbation. A perspective is given concerning the difference between the diamagnetic cavity and the solar wind cavity.
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| 6. |
- Behar, Etienne, et al.
(författare)
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The root of a comet tail : Rosetta ion observations at comet 67P/Churyumov–Gerasimenko
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
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Tidskriftsartikel (refereegranskat)abstract
- Context.The first 1000 km of the ion tail of comet 67P/Churyumov–Gerasimenko were explored by the EuropeanRosettaspacecraft,2.7 au away from the Sun.Aims.We characterised the dynamics of both the solar wind and the cometary ions on the night-side of the comet’s atmosphere.Methods.We analysed in situ ion and magnetic field measurements and compared the data to a semi-analytical model.Results.The cometary ions are observed flowing close to radially away from the nucleus during the entire excursion. The solar windis deflected by its interaction with the new-born cometary ions. Two concentric regions appear, an inner region dominated by theexpanding cometary ions and an outer region dominated by the solar wind particles.Conclusions.The single night-side excursion operated byRosettarevealed that the near radial flow of the cometary ions can beexplained by the combined action of three different electric field components, resulting from the ion motion, the electron pressuregradients, and the magnetic field draping. The observed solar wind deflection is governed mostly by the motional electric field−uion×B.
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| 7. |
- Carlsson, Ella, et al.
(författare)
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Mass composition of the escaping plasma at Mars
- 2006
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 182:2, s. 320-328
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Tidskriftsartikel (refereegranskat)abstract
- Data from the Ion Mass Analyzer (IMA) sensor of the ASPERA-3 instrument suite on Mars Express have been analyzed to determine the mass composition of the escaping ion species at Mars. We have examined 77 different ion-beam events and we present the results in terms of flux ratios between the following ion species: CO2+/O+ and O-2(+)/O+. The following ratios averaged over all events and energies were identified: CO2+/O+ = 0.2 and O-2(+)/O+ = 0.9. The values measured are significantly higher, by a factor of 10 for O-2(+)/O+, than a contemporary modeled ratio for the maximum fluxes which the martian ionosphere can supply. The most abundant ion species was found to be O+, followed by O-2(+) and CO2+. We estimate the loss of CO2+ to be 4.0 x 10(24) s(-1) (0.29 kg s(-1)) by using the previous measurements of Phobos-2 in our calculations. The dependence of the ion ratios in relation to their energy ranges we studied, 0.3-3.0 keV, indicated that no clear correlation was found.
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| 8. |
- Carlsson, Svante, et al.
(författare)
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Computing vision points in polygons
- 1999
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Ingår i: Algorithmica. - 0178-4617 .- 1432-0541. ; 24:1, s. 50-75
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Tidskriftsartikel (refereegranskat)abstract
- We consider a restricted version of the art gallery problem within simple polygons in which the guards are required to lie on a given one-dimensional object, a watchman route. We call this problem the vision point problem . We prove the following: • The original art gallery problem is NP-hard for the very restricted class of street polygons. • The vision point problem can be solved efficiently for the class of street polygons. • A linear time algorithm for the vision point problem exists for the subclass of street polygons called straight walkable polygons
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| 9. |
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| 10. |
- Gupta, R.B., et al.
(författare)
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Elastic impact between a finite conical rod and a long cylindrical rod
- 1978
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Ingår i: Journal of Sound and Vibration. - 0022-460X .- 1095-8568. ; 60:4, s. 555-563
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Tidskriftsartikel (refereegranskat)abstract
- Elastic impact between a truncated finite conical rod and a long cylindrical rod is studied (i) experimentally, (ii) analytically, by using one-dimensional wave theory to obtain a closed-form solution, and (iii) numerically, by using a three-dimensional axisymmetric finite element model. The results are compared for cones of different lengths but with the same end diameters. The agreement between the results from studies (i) and (iii) is very good in general. As expected, the deviation of the results of study (ii) from those of studies (i) and (iii) becomes increasingly apparent as the slenderness of the cones decreases.
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