4,558 research outputs found
Photoemission electron microscopy of localized surface plasmons in silver nanostructures at telecommunication wavelengths
We image the field enhancement at Ag nanostructures using femtosecond laser
pulses with a center wavelength of 1.55 micrometer. Imaging is based on
non-linear photoemission observed in a photoemission electron microscope
(PEEM). The images are directly compared to ultra violet PEEM and scanning
electron microscopy (SEM) imaging of the same structures. Further, we have
carried out atomic scale scanning tunneling microscopy (STM) on the same type
of Ag nanostructures and on the Au substrate. Measuring the photoelectron
spectrum from individual Ag particles shows a larger contribution from higher
order photoemission process above the work function threshold than would be
predicted by a fully perturbative model, consistent with recent results using
shorter wavelengths. Investigating a wide selection of both Ag nanoparticles
and nanowires, field enhancement is observed from 30% of the Ag nanoparticles
and from none of the nanowires. No laser-induced damage is observed of the
nanostructures neither during the PEEM experiments nor in subsequent SEM
analysis. By direct comparison of SEM and PEEM images of the same
nanostructures, we can conclude that the field enhancement is independent of
the average nanostructure size and shape. Instead, we propose that the
variations in observed field enhancement could originate from the wedge
interface between the substrate and particles electrically connected to the
substrate
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
One Work Analysis, Two Domains: A Display Information Requirements Case Study
d observations, among other techniques. Given the time and resources required, we examine how to generalize a work domain analysis technique, namely the hybrid Cognitive Task Analysis (hCTA) method across two domains in order to generate a common set of display information requirements. The two domains of interest are field workers troubleshooting low voltage distribution networks and telecommunication problems. Results show that there is a high degree of similarity between the two domains due to their service call nature, particularly in tasking and decision-making. While the primary differences were due to communication protocols and equipment requirements, the basic overall mission goals, functions, phases of operation, decision processes, and situation requirements were very similar. A final design for both domains is proposed based on the joint requirements
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
Partnership between authorities and NGO”S in developing healthy eating at school - the Danish experience.:Poster to the European forum on eating at school- making healthy choices.
Addressing inequality in healthy eating among young people at vocational schools:assessing stakeholder engagement in a Whole Health & Whole School Intervention
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