2,654 research outputs found
Icing flight research: Aerodynamic effects of ice and ice shape documentation with stereo photography
Aircraft icing flight research was performed in natural icing conditions. A data base consisting of icing cloud measurements, ice shapes, and aerodynamic measurements is being developed. During research icing encounters the icing cloud was continuously measured. After the encounter, the ice accretion shapes on the wing were documented with a stereo camera system. The increase in wing section drag was measured with a wake survey probe. The overall aircraft performance loss in terms of lift and drag coefficient changes was obtained by steady level speed/power measurements. Selective deicing of the airframe components was performed to determine their contributions to the total drag increase. Engine out capability in terms of power available was analyzed for the iced aircraft. It was shown that the stereo photography system can be used to document ice shapes in flight and that the wake survey probe can measure increases in wing section drag caused by ice. On one flight, the wing section drag coefficient (c sub d) increased approximately 120 percent over the uniced baseline at an aircraft angle of attack of 6 deg. On another flight, the aircraft darg coefficient (c sub d) increased by 75 percent over the uniced baseline at an aircraft lift coefficient (C sub d) of 0.5
Quantum noise limited interferometric measurement of atomic noise: towards spin squeezing on the Cs clock transition
We investigate theoretically and experimentally a nondestructive
interferometric measurement of the state population of an ensemble of laser
cooled and trapped atoms. This study is a step towards generation of (pseudo-)
spin squeezing of cold atoms targeted at the improvement of the Caesium clock
performance beyond the limit set by the quantum projection noise of atoms. We
calculate the phase shift and the quantum noise of a near resonant optical
probe pulse propagating through a cloud of cold 133Cs atoms. We analyze the
figure of merit for a quantum non-demolition (QND) measurement of the
collective pseudo-spin and show that it can be expressed simply as a product of
the ensemble optical density and the pulse integrated rate of the spontaneous
emission caused by the off-resonant probe light. Based on this, we propose a
protocol for the sequence of operations required to generate and utilize spin
squeezing for the improved atomic clock performance via a QND measurement on
the probe light. In the experimental part we demonstrate that the
interferometric measurement of the atomic population can reach the sensitivity
of the order of N_at^1/2 in a cloud of N_at cold atoms, which is an important
benchmark towards the experimental realisation of the theoretically analyzed
protocol.Comment: 12 pages and 9 figures, accepted to Physical Review
Experimental investigation of the Landau-Pomeranchuk-Migdal effect in low-Z targets
In the CERN NA63 collaboration we have addressed the question of the
potential inadequacy of the commonly used Migdal formulation of the
Landau-Pomeranchuk-Migdal (LPM) effect by measuring the photon emission by 20
and 178 GeV electrons in the range 100 MeV - 4 GeV, in targets of
LowDensityPolyEthylene (LDPE), C, Al, Ti, Fe, Cu, Mo and, as a reference
target, Ta. For each target and energy, a comparison between simulated values
based on the LPM suppression of incoherent bremsstrahlung is shown, taking
multi-photon effects into account. For these targets and energies, we find that
Migdal's theoretical formulation is adequate to a precision of better than
about 5%, irrespective of the target substance.Comment: 8 pages, 13 figure
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