| 1. |
- Schael, S., et al.
(författare)
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Electroweak measurements in electron positron collisions at W-boson-pair energies at LEP
- 2013
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 532:4, s. 119-244
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Forskningsöversikt (refereegranskat)abstract
- Electroweak measurements performed with data taken at the electron positron collider LEP at CERN from 1995 to 2000 are reported. The combined data set considered in this report corresponds to a total luminosity of about 3 fb(-1) collected by the four LEP experiments ALEPH, DELPHI, 13 and OPAL, at centre-of-mass energies ranging from 130 GeV to 209 GeV. Combining the published results of the four LEP experiments, the measurements include total and differential cross-sections in photon-pair, fermion-pair and four-fermion production, the latter resulting from both double-resonant WW and ZZ production as well as singly resonant production. Total and differential cross-sections are measured precisely, providing a stringent test of the Standard Model at centre-of-mass energies never explored before in electron positron collisions. Final-state interaction effects in four-fermion production, such as those arising from colour reconnection and Bose Einstein correlations between the two W decay systems arising in WW production, are searched for and upper limits on the strength of possible effects are obtained. The data are used to determine fundamental properties of the W boson and the electroweak theory. Among others, the mass and width of the W boson, m(w) and Gamma(w), the branching fraction of W decays to hadrons, B(W -> had), and the trilinear gauge-boson self-couplings g(1)(Z), K-gamma and lambda(gamma), are determined to be: m(w) = 80.376 +/- 0.033 GeV Gamma(w) = 2.195 +/- 0.083 GeV B(W -> had) = 67.41 +/- 0.27% g(1)(Z) = 0.984(-0.020)(+0.018) K-gamma - 0.982 +/- 0.042 lambda(gamma) = 0.022 +/- 0.019. (C) 2013 Elsevier B.V. All rights reserved.
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| 2. |
- Brändström, U., et al.
(författare)
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Results from the intercalibration of optical low light calibration sources 2011
- 2012
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Ingår i: Geoscientific Instrumentation, Methods and Data Systems. - : Copernicus GmbH. - 2193-0856 .- 2193-0864. ; 1:1, s. 43-51
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Tidskriftsartikel (refereegranskat)abstract
- Following the 38th Annual European Meeting onAtmospheric Studies by Optical Methods in Siuntio in Finland,an intercalibration workshop for optical low light calibrationsources was held in Sodankyl¨a, Finland. The mainpurpose of this workshop was to provide a comparable scalefor absolute measurements of aurora and airglow. All sourcesbrought to the intercalibration workshop were compared tothe Fritz Peak reference source using the Lindau CalibrationPhotometer built by Wilhelm Barke and Hans Lauche in1984. The results were compared to several earlier intercalibrationworkshops. It was found that most sources were fairlystable over time, with errors in the range of 5–25 %. To furthervalidate the results, two sources were also intercalibratedat UNIS, Longyearbyen, Svalbard. Preliminary analysis indicatesagreement with the intercalibration in Sodankyl¨a withinabout 15–25 %.
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| 3. |
- Hysell, D. L., et al.
(författare)
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Heater-induced ionization inferred from spectrometric airglow measurements
- 2014
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Ingår i: Journal of Geophysical Research A: Space Physics. - 2169-9380. ; 119:3, s. 2038-2045
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Tidskriftsartikel (refereegranskat)abstract
- Spectrographic airglow measurements were made during an ionospheric modification experiment at High Frequency Active Auroral Research Program on 12 March 2013. Artificial airglow enhancements at 427.8, 557.7, 630.0, 777.4, and 844.6 nm were observed. On the basis of these emissions and using a methodology based on the method of Backus and Gilbert (1968, 1970), we estimate the suprathermal electron population and the subsequent equilibrium electron density profile, including contributions from electron impact ionization. We find that the airglow is consistent with heater-induced ionization in view of the spatial intermittency of the airglow.
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| 4. |
- Malm, Johan, 1982-, et al.
(författare)
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A vorticity stretching diagnostic for turbulent and transitional flows
- 2012
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Ingår i: Theoretical and Computational Fluid Dynamics. - : Springer Science and Business Media LLC. - 0935-4964 .- 1432-2250. ; 26:6, s. 485-499
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Tidskriftsartikel (refereegranskat)abstract
- Vorticity stretching in wall-bounded turbulent and transitional flows has been investigated by means of a new diagnostic measure, denoted by , designed to pick up regions with large amounts of vorticity stretching. It is based on the maximum vorticity stretching component in every spatial point, thus yielding athree-dimensional scalar field. The measure was applied in four different flows with increasing complexity: (a) the near-wall cycle in an asymptotic suction boundary layer (ASBL), (b) K-type transition in a plane channelflow, (c) fully turbulent channel flow at Reτ = 180 and (d) a complex turbulent three-dimensional separated flow. Instantaneous data show that the coherent structures associated with intense vorticity stretching in all four cases have the shape of flat ‘pancake’ structures in the vicinity of high-speed streaks, here denoted ‘h-type’events. The other event found is of ‘l-type’, present on top of an unstable low-speed streak. These events (l-type) are further thought to be associated with the exponential growth of streamwise vorticity in the turbulent near-wall cycle. It was found that the largest occurrence of vorticity stretching in the fully turbulent wall-bounded flows is present at a wall-normal distance of y + = 6.5, i.e. in the transition between the viscous sublayer and buffer layer. The associated structures have a streamwise length of ∼200–300 wall units. In K-type transition, the -measure accurately locates the regions of interest, in particular the formation of high-speed streaks nearthe wall (h-type) and the appearance of the hairpin vortex (l-type). In the turbulent separated flow, the structures containing large amounts of vorticity stretching increase in size and magnitude in the shear layer upstreamof the separation bubble but vanish in the backflow region itself. Overall, the measure proved to be useful inshowing growing instabilities before they develop into structures, highlighting the mechanisms creating high shear region on a wall and showing turbulence creation associated with instantaneous separations.
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| 5. |
- Malm, Johan, et al.
(författare)
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A vorticity stretching diagnostic for turbulent flows
- 2011
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Ingår i: 7th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2011. - : International Symposium on Turbulence and Shear Flow Phenomena, TSFP.
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Konferensbidrag (refereegranskat)abstract
- Vorticity stretching in wall-bounded turbulent and transitional flows has been investigated by means of a new diagnostic, designed to pick up regions with large amounts of vorticity stretching. It was found that the largest occurrence of vorticity stretching in fully turbulent channel flows is present at a wall-normal distance of y+ = 6.5, i.e. in the transition between the viscous sublayer and the buffer region. Instantaneous data showed that the coherent structures associated with these stretching events have the shape of flat ‘pancake structures’ in the vicinity of high-speed streaks, here denoted ‘h-type’ events. The other event found, also studied in an asymptotic suction boundary layer, is the ‘l-type’ event present on top of an unstable low-speed streak. These events are further thought to be associated with the exponential growth of streamwise vorticity in the turbulent near-wall cycle.
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| 6. |
- Rehill, B., et al.
(författare)
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Identifying turbulent spots in transitional boundary layers
- 2011
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Ingår i: Proc. ASME Turbo Expo. - 9780791854655 ; , s. 1859-1868
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Konferensbidrag (refereegranskat)abstract
- An artificial turbulent spot is simulated in a zero free-stream turbulence base flow and a base flow with organised streaks. Six identification methods are used in order to isolate the turbulent spot from the surrounding non-turbulent fluid. These are (i) instantaneous wall-normal velocity, v′, (ii) instantaneous spanwise velocity, w′, (iii) instantaneous turbulent dissipation, (iv) λ2 - criterion, (v) Q - criterion and (vi) gradient of the Finite Time Lyapunov Exponent. All methods are effective in isolating the turbulent spot from the streaks. The robustness of each technique is determined from the sensitivity of the maximum spot dimensions to changes in threshold level. The Q-criterion shows the least sensitivity for the zero free-stream turbulence case and the instantaneous turbulent dissipation technique is least sensitive in the organised streaks case. For both cases the v′ technique was the most sensitive to changes in threshold level.
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| 7. |
- Rehill, B., et al.
(författare)
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Identifying Turbulent Spots in Transitional Boundary Layers
- 2012
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Ingår i: Journal of turbomachinery. - : ASME International. - 0889-504X .- 1528-8900. ; 135:1, s. 011019-
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Tidskriftsartikel (refereegranskat)abstract
- An artificial turbulent spot is simulated in a zero free-stream turbulence base flow and a base flow with organized streaks. Six identification methods are used in order to isolate the turbulent spot from the surrounding nonturbulent fluid. These are (i) instantaneous wall-normal velocity v, (ii) instantaneous spanwise velocity w, (iii) instantaneous turbulent dissipation, (iv) lambda(2) criterion, (v) Q criterion, and (vi) gradient of the finite time Lyapunov exponent. All methods are effective in isolating the turbulent spot from the streaks. The robustness of each technique is determined from the sensitivity of the maximum spot dimensions to changes in threshold level. The Q criterion shows the least sensitivity for the zero free-stream turbulence case and the instantaneous turbulent dissipation technique is least sensitive in the organized streaks case. For both cases the v technique was the most sensitive to changes in threshold level.
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| 8. |
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