| 1. |
- Amiri, M., et al.
(författare)
-
Periodic activity from a fast radio burst source
- 2020
-
Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 582:7812, s. 351-355
-
Tidskriftsartikel (refereegranskat)abstract
- Fast radio bursts (FRBs) are bright, millisecond-duration radio transients originating from sources at extragalactic distances1, the origin of which is unknown. Some FRB sources emit repeat bursts, ruling out cataclysmic origins for those events2–4. Despite searches for periodicity in repeat burst arrival times on timescales from milliseconds to many days2,5–7, these bursts have hitherto been observed to appear sporadically and—although clustered8—without a regular pattern. Here we report observations of a 16.35 ± 0.15 day periodicity (or possibly a higher-frequency alias of that periodicity) from the repeating FRB 180916.J0158+65 detected by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project4,9. In 38 bursts recorded from 16 September 2018 to 4 February 2020 utc, we find that all bursts arrive in a five-day phase window, and 50 per cent of the bursts arrive in a 0.6-day phase window. Our results suggest a mechanism for periodic modulation either of the burst emission itself or through external amplification or absorption, and disfavour models invoking purely sporadic processes.
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
- Engelkamp, B., et al.
(författare)
-
Spin-polarized surface electronic structure of Ta(110) : Similarities and differences to W(110)
- 2015
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:8
-
Tidskriftsartikel (refereegranskat)abstract
- Tantalum and tungsten, direct neighbors in the periodic table, exhibit a very similar electronic structure. Compared with tungsten, however, the bands of tantalum are less occupied due to the lack of one electron. As a consequence, an exceptional Dirac-cone-like surface state, observed below the Fermi level for W(110), may appear above the Fermi level for Ta(110). To prove this conjecture, we investigate the unoccupied surface electronic structure of Ta(110) by spin- and angle-resolved inverse photoemission and electronic-structure calculations. Surprisingly, our results do not show the expected Dirac-cone-like surface state. Instead, spin-polarized unoccupied surface bands are identified, which have no equivalent in W(110). These findings are explained by the difference in the energetic positions of the surface states relative to the bulk states for Ta(110) and W(110) caused by the different lattice constants.
|
|
| 6. |
- Ghadimi, P., et al.
(författare)
-
Rooster tail depression by originating a modified transom stern form using a Reynolds averaged Navier Stokes solver
- 2015
-
Ingår i: Scientia Iranica. International Journal of Science and Technology. - : Sharif University of Technology. - 1026-3098 .- 2345-3605. ; 22:3, s. 765-777
-
Tidskriftsartikel (refereegranskat)abstract
- The present article relates to a new transom stern form for high speed planing hulls. To depress the intensive transom wave known as a "rooster tail", an innovative form of transom stern is originated. The new form of the transom stern is introduced by cutting the bottom of the hull near the transom stern. To verify the capability of the modified transom stern, a three dimensional RANS solver is used. It is demonstrated that by using the new transom stern shape, the intensive wave behind the transom will be substantially reduced in the range of the parameters under investigation. In the meantime, it is expected that the radar signature will also be decreased. To study the effect of the modified transom at various Froude numbers and different trim angles, a set of numerical experiments are conducted. Three Froude numbers and four trim angles are considered and it is observed that the cutted transom stern has a significant effect on the reduction of height and length (height reduction up to 61% and length reduction up to 63%) of the rooster tail. Additionally, the accuracy of the numerical solutions is validated by comparing them against the results of empirical formula existing in the literature.
|
|
| 7. |
- Ghadimi, P., et al.
(författare)
-
Three-dimensional simulation of transom stern flow at various Froude numbers and trim angles
- 2018
-
Ingår i: Progress in Computational Fluid Dynamics, An International Journal. - : Inderscience Publishers. - 1468-4349 .- 1741-5233. ; 18:4, s. 232-240
-
Tidskriftsartikel (refereegranskat)abstract
- Numerical simulation of transom stern flow has proven to be an interesting topic, but a complicated task in the hydrodynamic field of research. In this paper, a three-dimensional numerical simulation is presented using Ansys-CFX to survey the free surface flow, downstream of the transom stern. To this end, finite volume method coupled with volume of fluid is utilised and k-ϵ turbulent model is applied. The numerical solutions are validated by comparing the findings against the results of empirical formula available in the literature. In order to conduct a parametric study, four different Froude numbers, four trim angles, and two deadrise angles are considered and the effect of each of these parameters is studied.
|
|
| 8. |
|
|
| 9. |
- Wortelen, H., et al.
(författare)
-
Spin-orbit influence on dz2 -type surface state at Ta(110)
- 2015
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 92:16
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of spin-orbit interaction on an occupied surface state at Ta(110) is investigated with spin- and angle-resolved photoemission and electronic structure calculations. The surface state appears in a symmetry gap at a binding energy of 0.45 eV at Γ¯ and exhibits a free-electron-like E(k) dispersion with an effective mass m∗/me of about -1.35 along Γ¯H¯. Photoemission results for excitation with s- and p-polarized light confirm the predicted dz2-type symmetry of the state close to Γ¯. Spin-resolved data for finite k reveal a pure Rashba-type spin texture with a Rashba parameter of 0.063±0.007eVÅ. These findings clearly prove a sizable impact of spin-orbit coupling on the dz2 surface state and resolve a longstanding disagreement on this issue.
|
|
