23 research outputs found
Characterisation and calibration of a scintillating fibre detector with > 4000 multi-anode photomultiplier channels
In the Kaos spectrometer at the Mainz Microtron a high-resolution coordinate
detector for high-energy particles is operated. It consists of scintillating
fibres with diameters of 4000 multi-anode
photomultiplier channels. It is one of the most modern focal-plane detectors
for magnetic spectrometers world-wide. To correct variations in the detection
efficiency, caused by the different gains and the different optical
transmittances, a fully automated off-line calibration procedure has been
developed. The process includes the positioning of a radioisotope source
alongside the detector plane and the automated acquisition and analysis of the
detector signals. It was possible to characterise and calibrate each individual
fibre channel with a low degree of human interaction.Comment: Nucl. Instrum. Meth. A (2012
Remote surface damage detection on rotor blades of operating wind turbines by means of infrared thermography
Wind turbines are constantly exposed to wind gusts, dirt
particles and precipitation. Depending on the site, surface defects on rotor
blades emerge from the first day of operation on. While erosion increases
quickly with time, even small surface defects can affect the performance of
the wind turbine. Consequently, there is demand for an easily
applicable remote monitoring method for rotor blades that is capable of
detecting surface defects at an early stage. In this work it is investigated if
infrared thermography (IRT) can meet these requirements by visualizing
differences in the thermal transport and the corresponding surface
temperature of the wall-bounded flow.Firstly, a validation of the IRT method compared to stereoscopic particle image velocimetry measurements is
performed comparing both types of experimental results for the boundary layer of a flat plate.
Then, the main characteristics of the flow in the wake of generic surface defects on different types
of lifting surfaces are studied both experimentally and numerically: temperature gradients behind protruding
surface defects on a flat plate and a DU 91-W2-250 profile are studied by means of IRT.
The same is done with the wall shear stress from Reynolds-averaged Navier–Stokes simulations of a wind turbine blade.
It is consistently observed, both in the experiments and the simulations, that turbulent wedges are formed
on the flow downstream of generic surface defects. These wedges provide valuable information about the
kind of defects that generate them. At last, experimental and numerical performance measures are taken into
account for evaluating the aerodynamic impact of surface defects on rotor blades. We conclude that the IRT method
is a suitable remote monitoring technique for detecting surface defects on wind turbines at an early stage.</p
Measurement of polarization transfer in the quasi-elastic process
Polarization transfer to a bound proton in polarized electron knock-out
reactions, , is a powerful tool to look
for in-medium modification of the bound proton. It requires comparison to
calculations which consider the many-body effects accompanying the quasi-free
process. We report here measured components , , and
their ratio , of polarization transfer to protons
bound in , which is described well by the shell model and for
which reliable calculations are available. While the calculations capture the
essence of the data, our statistical precision allows us to observe deviations
which cannot be explained by simple scaling, including by varying the proton
electromagnetic form factor ratio . We further explore the deviations
of the ratio of the polarization transfer components from that of a free
proton, , and its dependence on the bound-proton virtuality