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- Kvist, Anders, 1961
(författare)
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Atom Probe Field Ion Microscopy of Surface Zones, Coatings and Interfaces
- 1995
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is focused on developingmethods for high resolution microanalysis of coatings on a substrate, andsurface zones of a bulk sample using atom probe field ion microscopy,APFIM. The APFIM technique is described and some examples of its applications to semiconductors,cemented carbides and intermetallic compounds are given. The main part of the thesis is concerned with the formation of Schottky andohmic contacts on highly-doped GaAs. Three different metal coatings wereanalysed, gold, silver and gold-germanium, all of them formed on an APFIMspecimen of the semiconductor. The gold and silver coatings were studied on atomically clean as well asair exposed GaAs surfaces. Intermixing occurred for Au on a clean surfacewhereas Ag showed an atomically abrupt interface. Oxygen seemed to stopintermixing between Au and GaAs, but promoted diffusion of Ag into the semiconductor. Deposition of thegold-germanium alloy was only made on oxidised GaAs surfaces and the effectof heat treatment on this contact was studied. After heat treatment a thinlayer containing a few at.% of Ge in the GaAs was observed beneath an almost pure layer of Au. A technique for preparing APFIM specimens of the near surface zone of acemented carbide sample was developed, using a combination of dimplegrinding, electropolishing and ion milling. The first results obtained froma specimen prepared with this methodare presented. The possible applicability of this technique to metal/GaAsinterfaces and CVD-coated cemented carbides is discussed. APFIM analysis for the determination of the platinum distribution in anordered Cu3Au(4 at.% Pt) alloy is presented with a particularinterest in problems related to quantitative analysis near and at grainboundaries.
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- Pennycuick, C. J., et al.
(författare)
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Wingbeat frequency and the body drag anomaly: wind-tunnel observations on a thrush nightingale (Luscinia luscinia) and a teal (Anas crecca)
- 1996
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Ingår i: Journal of Experimental Biology. - 1477-9145. ; 199:12, s. 2757-2765
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Tidskriftsartikel (refereegranskat)abstract
- A teal (Anas crecca) and a thrush nightingale (Luscinia luscinia) were trained to fly in the Lund wind tunnel for periods of up to 3 and 16 h respectively. Both birds flew in steady flapping flight, with such regularity that their wingbeat frequencies could be determined by viewing them through a shutter stroboscope. When flying at a constant air speed, the teal's wingbeat frequency varied with the 0.364 power of the body mass and the thrush nightingale's varied with the 0.430 power. Both exponents differed from zero, but neither differed from the predicted value (0.5) at the 1 % level of significance. The teal continued to flap steadily as the tunnel tilt angle was varied from -1 ° (climb) to +6 ° (descent), while the wingbeat frequency declined progressively by about 11 %. In both birds, the plot of wingbeat frequency against air speed in level flight was U-shaped, with small but statistically significant curvature. We identified the minima of these curves with the minimum power speed (Vmp) and found that the values predicted for Vmp, using previously published default values for the required variables, were only about two-thirds of the observed minimum-frequency speeds. The discrepancy could be resolved if the body drag coefficients (CDb) of both birds were near 0.08, rather than near 0.40 as previously assumed. The previously published high values for body drag coefficients were derived from wind-tunnel measurements on frozen bird bodies, from which the wings had been removed, and had long been regarded as anomalous, as values below 0.01 are given in the engineering literature for streamlined bodies. We suggest that birds of any size that have well-streamlined bodies can achieve minimum body drag coefficients of around 0.05 if the feet can be fully retracted under the flank feathers. In such birds, field observations of flight speeds may need to be reinterpreted in the light of higher estimates of Vmp. Estimates of the effective lift:drag ratio and range can also be revised upwards. Birds that have large feet or trailing legs may have higher body drag coefficients. The original estimates of around CDb=0.4 could be correct for species, such as pelicans and large herons, that also have prominent heads. We see no evidence for any progressive reduction of body drag coefficient in the Reynolds number range covered by our experiments, that is 21 600215 000 on the basis of body cross-sectional diameter.
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